Bounds for self-stabilization in unidirectional networks

Abstract: A distributed algorithm is self-stabilizing if after faults and attacks hit the system and place it in some arbitrary global state, the systems recovers from this catastrophic situation without external intervention in finite time. Unidirectional networks preclude many common techniques in self-stabilization from being used, such as preserving local predicates. In this paper, we investigate the intrinsic complexity of achieving self-stabilization in unidirectional networks, and focus on the classical vertex coloring problem. When deterministic solutions are considered, we prove a lower bound of $n$ states per process (where $n$ is the network size) and a recovery time of at least $n(n-1)/2$ actions in total. We present a deterministic algorithm with matching upper bounds that performs in arbitrary graphs. When probabilistic solutions are considered, we observe that at least $\Delta + 1$ states per process and a recovery time of $\Omega(n)$ actions in total are required (where $\Delta$ denotes the maximal degree of the underlying simple undirected graph). We present a probabilistically self-stabilizing algorithm that uses $\mathtt{k}$ states per process, where $\mathtt{k}$ is a parameter of the algorithm. When $\mathtt{k}=\Delta+1$, the algorithm recovers in expected $O(\Delta n)$ actions. When $\mathtt{k}$ may grow arbitrarily, the algorithm recovers in expected O(n) actions in total. Thus, our algorithm can be made optimal with respect to space or time complexity.


Sub-$\mu$ structured Lotus Surfaces Manufacturing

Abstract: Sub-micro structured surfaces allow modifying the behavior of polymer films or components. Especially in micro fluidics a lotus-like characteristic is requested for many applications. Structure details with a high aspect ratio are necessary to decouple the bottom and the top of the functional layer. Unlike to stochastic methods, patterning with a LIGA-mold insert it is possible to structure surfaces very uniformly or even with controlled variations (e.g. with gradients). In this paper we present the process chain to realize polymer sub-micro structures with minimum lateral feature size of 400 nm and up to 4 micrometers high.


Linear and Non Linear Behaviour of Mechanical Resonators for Optimized Inertial Electromagnetic Microgenerators

Abstract: The need for wearable or abandoned microsystems, as well as the trend to a lower power consumption of electronic devices, make miniaturized renewable energy generators a viable alternative to batteries. Among the different alternatives, an interesting option is the use of inertial microgenerators for energy scavenging from vibrations present in the environment. These devices constitute perpetual energy sources without the need for refilling, thus being well suited for abandoned sensors, wireless systems or microsystems which must be embedded within the structure, without outside physical connections. Different electromagnetic energy scavenging devices have been described in the literature [1,2,3], based on the use of a velocity damped resonator, which is well suited for harvesting of vibrational energy induced by the operation of machines. These vibrations are characterized by a well defined frequency (in the range between few Hz's and few kHz's) and low displacement amplitudes. Adjusting the resonant frequency of the system to that of the vibrations allows amplification of these low amplitude displacements. Moreover, for these applications, the use of an electromagnetic device has the potential advantages of a good level of compatibility with Si Microsystem technology, as well as the possibility of relatively high electromechanical coupling with simple designs.


Design And Fabrication of Condenser Microphone Using Wafer Transfer And Micro-electroplating Technique

Abstract: A novel fabrication process, which uses wafer transfer and micro-electroplating technique, has been proposed and tested. In this paper, the effects of the diaphragm thickness and stress, the air-gap thickness, and the area ratio of acoustic holes to backplate on the sensitivity of the condenser microphone have been demonstrated since the performance of the microphone depends on these parameters. The microphone diaphragm has been designed with a diameter and thickness of 1.9 mm and 0.6 $\mu$m, respectively, an air-gap thickness of 10 $\mu$m, and a 24% area ratio of acoustic holes to backplate. To obtain a lower initial stress, the material used for the diaphragm is polyimide. The measured sensitivities of the microphone at the bias voltages of 24 V and 12 V are -45.3 and -50.2 dB/Pa (at 1 kHz), respectively. The fabricated microphone shows a flat frequency response extending to 20 kHz.


Porous Alumina Based Capacitive MEMS RH Sensor

Abstract: The aim of a joint research and development project at the BME and HWU is to produce a cheap, reliable, low-power and CMOS-MEMS process compatible capacitive type relative humidity (RH) sensor that can be incorporated into a state-of-the-art, wireless sensor network. In this paper we discuss the preparation of our new capacitive structure based on post-CMOS MEMS processes and the methods which were used to characterize the thin film porous alumina sensing layer. The average sensitivity is approx. 15 pF/RH% which is more than a magnitude higher than the values found in the literature. The sensor is equipped with integrated resistive heating, which can be used for maintenance to reduce drift, or for keeping the sensing layer at elevated temperature, as an alternative method for temperature-dependence cancellation.


Integrated RF MEMS/CMOS Devices

Abstract: A maskless post-processing technique for CMOS chips is developed that enables the fabrication of RF MEMS parallel-plate capacitors with a high quality factor and a very compact size. Simulations and measured results are presented for several MEMS/CMOS capacitors. A 2-pole coupled line tunable bandpass filter with a center frequency of 9.5 GHz is designed, fabricated and tested. A tuning range of 17% is achieved using integrated variable MEMS/CMOS capacitors with a quality factor exceeding 20. The tunable filter occupies a chip area of 1.2 x 2.1 mm2.


Design Methodology and Manufacture of a Microinductor

Abstract: Potential core materials to supersede ferrite in the 0.5-10 MHz frequency range are investigated. The performance of electrodeposited nickel-iron, cobalt-iron-copper alloys and the commercial alloy Vitrovac 6025 have been assessed through their inclusion within a custom-made solenoid microinductor. Although the present inductor, at 500 KHz, achieves 77% power efficiency for 24.7W/cm3 power density, an optimized process predicts a power efficiency of 97% for 30.83W/cm3 power density. The principle issues regarding microinductor design and performance are discussed.


Megasonic Enhanced Electrodeposition

Abstract: A novel way of filling high aspect ratio vertical interconnection (microvias) with an aspect ratio of >2:1 is presented. High frequency acoustic streaming at megasonic frequencies enables the decrease of the Nernst-diffusion layer down to the sub-micron range, allowing thereby conformal electrodeposition in deep grooves. Higher throughput and better control over the deposition properties are possible for the manufacturing of interconnections and metal-based MEMS.


UV Direct-Writing of Metals on Polyimide

Abstract: Conductive micro-patterned copper tracks were fabricated by UV direct-writing of a nanoparticle silver seed layer followed by selective electroless copper deposition. Silver ions were first incorporated into a hydrolyzed polyimide surface layer by wet chemical treatment. A photoreactive polymer coating, methoxy poly(ethylene glycol) (MPEG) was coated on top of the substrate prior to UV irradiation. Electrons released through the interaction between the MPEG molecules and UV photons allowed the reduction of the silver ions across the MPEG/doped polyimide interface. The resultant silver seed layer has a cluster morphology which is suitable for the initiation of electroless plating. Initial results showed that the deposited copper tracks were in good agreement with the track width on the photomask and laser direct-writing can also fabricate smaller line width metal tracks with good accuracy. The facile fabrication presented here can be carried out in air, at atmospheric pressure, and on contoured surfaces.


Micro Embossing of Ceramic Green Substrates for Micro Devices

Abstract: Multilayered ceramic substrates with embedded micro patterns are becoming increasingly important, for example, in harsh environment electronics and microfluidic devices. Fabrication of these embedded micro patterns, such as micro channels, cavities and vias, is a challenge. This study focuses on the process of patterning micro features on ceramic green substrates using micro embossing. A ceramic green tape that possessed near-zero shrinkage in the x-y plane was used, six layers of which were laminated as the embossing substrate. The process parameters that impact on the pattern fidelity were investigated and optimized in this study. Micro features with line-width as small as several micrometers were formed on the ceramic green substrates. The dynamic thermo-mechanical analysis indicated that extending the holding time at certain temperature range would harden the green substrates with little effect on improving the embossing fidelity. Ceramic substrates with embossed micro patterns were obtain d after co-firing. The embedded micro channels were also obtained by laminating the green tapes on the embossed substrates.


Characterization and Modeling of an Electro-thermal MEMS Structure

Abstract: Thermal functional circuits are an interesting and perspectivic group of the MEMS elements. A practical realization is called Quadratic Transfer Characteristic (QTC) element which driving principle is the Seebeck-effect. In this paper we present the analyses of a QTC element from different perspectives. To check the real behavior of the device, we measured a few, secondary properties of the structure which correspond to special behavior because these properties can not be easily derived from the main characteristics.


Measurement of Large Forces and Deflections in Microstructures

Abstract: Properties of typical MEMS materials have been widely investigated. Mechanical properties of MEMS structures depend not only on the bulk material properties, but also structural factors. A measurement system has been made to measure force/deflection on microstructures to examine some of the structural properties. This is a stylus setup integrated with a load cell and a linear actuator. First, the requirements for the measurement system were established. Then the system was built up and characterized. We have successfully made measurements on a typical micromechanical structure, a cantilever accelerometer design. The stylus placement accuracy, the spring constant along the proof mass, analysis of the force/deflection curve shape and destructive tests on the cantilever have been investigated in our experiment and will be presented in this paper.


Contactless Thermal Characterization of High Temperature Test Chamber

Abstract: In this paper the methodology and the results of a contactless thermal characterization of a high temperature test chamber will be introduced. The test chamber is used for fatigue testing of different MEMS devices where the homogenous temperature distribution within the close proximity from the heating filaments is very important. Our aim was to characterize the evolving temperature distribution inside the test chamber. In order to achieve smaller time constant a new contactless sensor card was developed. The contactless thermal characterization method introduced in this paper enables in situ heat distribution measurement inside the test chamber during operation, with the detection of potentially uneven heat distribution.


Processing and Characterization of Precision Microparts from Nickel-based Materials

Abstract: The objective of this research was to study the influence of electroplating parameters on electrodeposit characteristics for the production of nickel (Ni) and nickel-iron (Ni-Fe) microparts by photoelectroforming. The research focused on the most relevant parameter for industry, which is the current density, because it determines the process time and the consumed energy. The results of the Ni and Ni-Fe characterisations can be divided into two aspects closely linked with each other ; the morphology and the hardness.


Manufacturing of A micro probe using supersonic aided electrolysis process

Abstract: In this paper, a practical micromachining technology was applied for the fabrication of a micro probe using a complex nontraditional machining process. A series process was combined to machine tungsten carbide rods from original dimension. The original dimension of tungsten carbide rods was 3mm ; the rods were ground to a fixed-dimension of 50 micrometers using precision grinding machine in first step. And then, the rod could be machined to a middle-dimension of 20 micrometers by electrolysis. A final desired micro dimension can be achieved using supersonic aided electrolysis. High-aspect-ratio of micro tungsten carbide rod was easily obtained by this process. Surface roughness of the sample with supersonic aided agitation was compared with that with no agitation in electrolysis. The machined surface of the sample is very smooth due to ionized particles of anode could be removed by supersonic aided agitation during electrolysis. Deep micro holes can also be achieved by the machined high-aspect-rati tungsten carbide rod using EDM process. A micro probe of a ball shape at the end was processed by proposed supersonic aided electrolysis machining process.


Large Area Roller Embossing of Multilayered Ceramic Green Composites

Abstract: In this paper, we will report our achievements in developing large area patterning of multilayered ceramic green composites using roller embossing. The aim of our research is to pattern large area ceramic green composites using a modified roller laminating apparatus, which is compatible with screen printing machines, for integration of embossing and screen printing. The instrumentation of our roller embossing apparatus, as shown in Figure1, consists of roller 1 and rollers 2. Roller 1 is heated up to the desired embossing temperature ; roller 2 is, however, kept at room temperature. The mould is a nickel template manufactured by plating nickel-based micro patterns (height : 50 $\mu$m) on a nickel film (thickness : 70 $\mu$m) ; the substrate for the roller embossing is a multilayered Heraeus Heralock HL 2000 ceramic green composite. Comparing with the conventional simultaneous embossing, the advantages of roller embossing include : (1) low embossing force ; (2) easiness of demoulding ; (3) localized area in contact with heater ; and etc. We have demonstrated the capability of large area roller embossing with a panel size of 150mmx 150mm on the mentioned substrate. We have explored and confirmed the impact of parameters (feed speed, temperature of roller and applied pressure) to the pattern quality of roller embossing. Furthermore, under the optimized process parameters, we characterized the variations of pattern dimension over the panel area, and calculated a scaling factor in order to make the panel compatible with other processes. Figure 2 shows the embossed patterns on a 150mmx 150mm green ceramic panel.


Study of mechanical response in embossing of ceramic green substrate by micro-indentation

Abstract: Micro-indentation test with a micro flat-end cone indenter was employed to simulate micro embossing process and investigate the thermo-mechanical response of ceramic green substrates. The laminated low temperature co-fired ceramic green tapes were used as the testing material ; the correlations of indentation depth versus applied force and applied stress at the temperatures of 25 degrees C and 75degrees C were studied. The results showed that permanent indentation cavities could be formed at temperatures ranging from 25 degrees C to 75 degrees C, and the depth of cavities created was applied force, temperature and dwell time dependent. Creep occurred and made a larger contribution to the plastic deformation at elevated temperatures and high peak loads. There was instantaneous recovery during the unloading and retarded recovery in the first day after indentation. There was no significant pile-up due to material flow observed under compression at the temperature up to 75 degrees C. The plastic deformation was the main cause for formation of cavity on the ceramic green substrate under compression. The results can be used as a guideline for embossing ceramic green substrates.


Top-Down Behavioral Modeling Methodology of a Piezoelectric Microgenerator For Integrated Power Harvesting Systems

Abstract: In this study, we developed a top/down methodology for behavioral and structural modeling of multi-domain microsystems. Then, we validated this methodology through a study case : a piezoelectric microgenerator. We also proved the effectiveness of VHDL-AMS language not only for modeling in behavioral and structural levels but also in writing physical models that can predict the experimental results. Finally, we validated these models by presenting and discussing simulations results.


Hybridization of Magnetism and Piezoelectricity for an Energy Scavenger based on Temporal Variation of Temperature

Abstract: Autonomous microsystems are confronted today to a major challenge : the one of energy supply. Energy scavenging, i.e. collecting energy from the ambient environment has been developed to answer this problematic. Various sources have already been successfully used (solar, vibration). This article presents temporal variations of temperature as a new source of exploitable energy. A brief review will take place at the beginning, exposing the different approaches used in the past. Then we will focus our attention on hybridization of magnetism and piezoelectricity. A new kind of thermal generator is proposed and a preliminary model is exposed. Conclusions will be drawn on the suitability of this prototype and the improvements that are needed to increase its potential.


Simulation of an Electrostatic Energy Harvester at Large Amplitude Narrow and Wide Band Vibrations

Abstract: An electrostatic in-plane overlap varying energy harvester is modeled and simulated using a circuit simulator. Both linear and nonlinear models are investigated. The nonlinear model includes mechanical stoppers at the displacement extremes. Large amplitude excitation signals, both narrow and wide band, are used to emulate environmental vibrations. Nonlinear behavior is significant at large displacement due to the impact on mechanical stoppers. For a sinusoidal excitation the mechanical stoppers cause the output power to flatten and weakly decrease. For a wide band excitation, the output power first increases linearly with the power spectral density of the input signal, then grows slower than linearly.


Optimization and AMS Modeling for Design of an Electrostatic Vibration Energy Harvester's Conditioning Circuit with an Auto-Adaptive Process to the External Vibration Changes

Abstract: Electrostatic transducers for vibration energy scavenging have been an object to numerous studies, but are still facing major issues relating to their conditioning circuit. One of the most popular ones uses a charge pump and a flyback circuit based on a Buck DC-DC converter (Fig. 1). A commutation between the energy accumulation in the charge pump and the recharge of the buffer capacitor Cres is assured by a switch which is the major bottleneck in the energy harvester circuit. The commutation timing of the switch determines the efficiency of the energy harvesting. In previous papers [1] the switch commutates periodically with some fixed duty ratio. However, this solution is not appropriate when the environment parameters, e.g. the vibration frequency, change. We found that the switching should be ordered by the internal state of the circuit, an not by some fixed timing scenario. We presents how to find the optimal operation mode of the harvester. To validate the study, the system was modeled using a mixed VHDL-AMS - ELDO model.


Fabrication of Nanostructured PLGA Scaffolds Using Anodic Aluminum Oxide Templates

Abstract: PLGA (poly(lactic-co-glycolic acid)) is one of the most used biodegradable and biocompatible materials. Nanostructured PLGA even has great application potentials in tissue engineering. In this research, a fabrication technique for nanostructured PLGA membrane was investigated and developed. In this novel fabrication approach, an anodic aluminum oxide (AAO) film was use as the template ; the PLGA solution was then cast on it ; the vacuum air-extraction process was applied to transfer the nano porous pattern from the AAO membrane to the PLGA membrane and form nanostures on it. The cell culture experiments of the bovine endothelial cells demonstrated that the nanostructured PLGA membrane can double the cell growing rate. Compared to the conventional chemical-etching process, the physical fabrication method proposed in this research not only is simpler but also does not alter the characteristics of the PLGA. The nanostructure of the PLGA membrane can be well controlled by the AAO temperate.


High Performance Microreactor for Rapid Fluid Mixing and Redox Reaction of Ascorbic Acid

Abstract: A novel micro device with a mechanism of split and recombination (SNR) for rapid fluidic mixing and reaction, named a SNR micro-reactor, was designed, fabricated and systematically analyzed. This SNR micro-reactor possessing an in-plane dividing structure requires only simple fabrication. We investigated this reactor and compared it numerically and experimentally with a slanted-groove micromixer (SGM). From the numerical results the mixing indices and mixing patterns demonstrated that the mixing ability of the SNR micro-reactor was much superior to that of the SGM. From a mixing test with phenolphthalein and sodium hydroxide solutions, the mixing lengths of the SNR micro-reactor were less than 4 mm for a Reynolds number over a wide range (Re = 0.1 - 10). From a comparison of mixing lengths, the results revealed also that the SNR micro-reactor surpassed the SGM in mixing performance by more than 200 %. As a reaction length is a suitable test of the performance of a reactor, we introduced a redox reaction between ascorbic acid and iodine solutions to assess the reaction capability of these micro devices ; the reaction lengths of the SNR micro-reactor were much shorter than those of a SGM. The SNR micro-reactor has consequently a remarkable efficiency for fluid mixing and reaction.


Cell Trapping Utilizing Insulator-based Dielectrophoresis in The Open-Top Microchannels

Abstract: The ability to manipulate or separate a biological small particle, such as a living cell and embryo, is fundamental needed to many biological and medical applications. The insulator-based dielectrophoresis (iDEP) trapping is composed of conductless tetragon structures in micro-chip. In this study, a lower conductive material of photoresist was adopted as a structure in open-top microchannel instead of a metallic wire to squeeze the electric field in a conducting solution, therefore, creating a high field gradient with a local maximum. The microchip with the open-top microchannels was designed and fabricated herein. The insulator-based DEP trapping microchip with the open-top microchannels was designed and fabricated in this work. The cells trapped by DEP force could be further treated or cultured in the open-top microchannel ; however, those trapped in the microchip with enclosed microchannels could not be proceeded easily.


Design and Analysis of a Chaotic Micromixer with Vortices Modulation

Abstract: A novel design for vortex modulation of a passive chaotic micromixer, named a circulation-disturbance micromixer (CDM), has been achieved and analyzed experimentally and numerically. The systematic numerical analyses - topological flow characteristics and particle tracking method - have been developed, that enable visualization of detailed mixing patterns. To display the cross section of mixing region of flows in our CDM, the biotin-streptavidin binding is detected through the fluorescence resonance energy transfer (FRET) pair of fluorescent proteins - R-phycoerythrin (RPE) and cross-linked allophycocyanin (clAPC). We expect the diagnosis technique using FRET will be successfully applied to biochemical analysis in microfluidic system.


Portable Valve-less Peristaltic Micro-pump Design and Fabrication

Abstract: This paper is to describe a design and fabrication method for a valve-less peristaltic micro-pump. The valve-less peristaltic micro-pump with three membrane chambers in a serial is actuated by three piezoelectric (PZT) actuators. With the fluidic flow design, liquid in the flow channel is pumped to a constant flow speed ranged from 0.4 to 0.48 mm/s. In term of the maximum flow rate of the micro-pump is about 365 mircoliters/min, when the applied voltage is 24V and frequency 50 Hz. Photolithography process was used to fabricate the micro-pump mold. PDMS molding and PDMS bonding method were used to fabricate the micro-channel and actuator chambers. A portable drive controller was designed to control three PZT actuators in a proper sequence to drive the chamber membrane. Then, all parts were integrated into the portable valve-less peristaltic micro-pump system.


Microfluidic Device for Continuous Magnetophoretic Separation of Red Blood Cells

Abstract: This paper presents a microfluidic device for magnetophoretic separation red blood cells from blood under contionous flow. The separation method consist of continous flow of a blood sample (diluted in PBS) through a microfluidic channel which presents on the bottom "dots" of feromagnetic layer. By appling a magnetic field perpendicular on the flowing direction, the feromagnetic "dots" generates a gradient of magnetic field which amplifies the magnetic force. As a result, the red blood cells are captured on the bottom of the microfluidic channel while the rest of the blood is collected at the outlet. Experimental results show that an average of 95 % of red blood cells are trapped in the device


Fabrication of Embedded Microvalve on PMMA Microfluidic Devices through Surface Functionalization

Abstract: The integration of a PDMS membrane within orthogonally placed PMMA microfluidic channels enables the pneumatic actuation of valves within bonded PMMA-PDMS-PMMA multilayer devices. Here, surface functionalization of PMMA substrates via acid catalyzed hydrolysis and air plasma corona treatment were investigated as possible techniques to permanently bond PMMA microfluidic channels to PDMS surfaces. FTIR and water contact angle analysis of functionalized PMMA substrates showed that air plasma corona treatment was most effective in inducing PMMA hydrophilicity. Subsequent fluidic tests showed that air plasma modified and bonded PMMA multilayer devices could withstand fluid pressure at an operational flow rate of 9 mircoliters/min. The pneumatic actuation of the embedded PDMS membrane was observed through optical microscopy and an electrical resistance based technique. PDMS membrane actuation occurred at pneumatic pressures of as low as 10kPa and complete valving occurred at 14kPa for 100 micrometers x 100 micrometers channel cross-sections.


Hot Roller Embossing for the Creation of Microfluidic Devices

Abstract: We report on the hot roller embossing of polymer sheets for the creation of microfluidic structures. Measurements conducted on 100 $\mu$m features showed that the lateral dimensions could be replicated to within 2% tolerance, while over 85% of mould depth was embossed. Feature sizes down to 50 $\mu$m and feature depths up to 30 $\mu$m had been achieved. At lower temperatures, asymmetric pile up of polymer material outside embossed regions was observed with higher pile up occurring on the trailing side of the embossed regions.


Geometrical Variation Analysis of an Electrothermally Driven Polysilicon Microactuator

Abstract: The analytical models that predict thermal and mechanical responses of microactuator have been developed. These models are based on electro thermal and thermo mechanical analysis of the microbeam. Also, Finite Element Analysis (FEA) is used to evaluate microactuator tip deflection. Analytical and Finite Element results are compared with experimental results in literature and show good agreement in low input voltages. A dimensional variation of beam lengths, beam lengths ratios and gap are introduced in analytical and FEA models to explore microactuator performance. An electrothermally driven polysilicon microactuator similar to Pan's actuator architecture has been studied in this paper. This microactuator generates deflection through asymmetric heating of the hot and cold polysilicon arms with different lengths. For this microactuator architecture, an optimal beam length ratio equal to 0.46 has been obtained to achieve maximum tip deflection. . As it was expected, the results show decreasing air gap increase microactuator tip deflection. It is also found that for microactuators with longer hot arms, microactuator tip deflections are more sensitive to beam length ratios and air gap.


In-Plane Bistable Nanowire For Memory Devices

Abstract: We present a nanomechanical device design to be used in a non-volatile mechanical memory point. The structure is composed of a suspended slender nanowire (width : 100nm, thickness 430nm length : 8 to 30$\mu$m) clamped at its both ends. Electrodes are placed on each sides of the nanowire and are used to actuate the structure (writing, erasing) and to measure the position through a capactive bridge (reading). The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released, the stressed material relaxes and the beam buckles in a position of lower energy. Such symmetric beams, called Euler beams, show two stable deformed positions thus form a bistable structure. This paper will present the fabrication, simulation and mechanical and electrical actuation of an in plane bistable nanowire. Final paper will include a section on FEM simulations.


RF-MEMS Switched Varactors for Medium Power Applications

Abstract: In RF (Radio Frequency) domain, one of the limitations of using MEMS (Micro Electromechanical Systems) switching devices for medium power applications is RF power. Failure phenomena appear even for 500 mW. A design of MEMS switched capacitors with an enhanced topology is presented in this paper to prevent it. This kind of device and its promising performances will serve to fabricate a MEMS based phase shifter able to work under several watts.


Low-Drift Flow Sensor with Zero-Offset Thermopile-Based Power Feedback

Abstract: A thermal flow sensor has been realised consisting of freely-suspended silicon-rich silicon-nitride microchannels with an integrated Al/poly-Si++ thermopile in combination with up- and downstream Al heater resistors. The inherently zero offset of the thermopile is exploited in a feedback loop controlling the dissipated power in the heater resistors, eliminating inevitable influences of resistance drift and mismatch of the thin-film metal resistors. The control system cancels the flow-induced temperature difference across the thermopile by controlling a power difference between both heater resistors, thereby giving a measure for the flow rate. The flow sensor was characterised for power difference versus water flow rates up to 1.5 ul/min, being in good agreement with a thermal model of the sensor, and the correct low-drift operation of the temperature-balancing control system has been verified.


Single Chip Sensing of Multiple Gas Flows

Abstract: The fabrication and experimental characterization of a thermal flow meter, capable of detecting and measuring two independent gas flows with a single chip, is described. The device is based on a 4 x 4 mm2 silicon chip, where a series of differential micro-anemometers have been integrated together with standard electronic components by means of postprocessing techniques. The innovative aspect of the sensor is the use of a plastic adapter, thermally bonded to the chip, to convey the gas flow only to the areas where the sensors are located. The use of this inexpensive packaging procedure to include different sensing structures in distinct flow channels is demonstrated.


Comparison Between Damping Coefficients of Measured Perforated Micromechanical Test Structures and Compact Models

Abstract: Measured damping coefficients of six different perforated micromechanical test structures are compared with damping coefficients given by published compact models. The motion of the perforated plates is almost translational, the surface shape is rectangular, and the perforation is uniform validating the assumptions made for compact models. In the structures, the perforation ratio varies from 24% - 59%. The study of the structure shows that the compressibility and inertia do not contribute to the damping at the frequencies used (130kHz - 220kHz). The damping coefficients given by all four compact models underestimate the measured damping coefficient by approximately 20%. The reasons for this underestimation are discussed by studying the various flow components in the models.


A piecewise-linear reduced-order model of squeeze-film damping for deformable structures including large displacement effects

Abstract: This paper presents a reduced-order model for the Reynolds equation for deformable structure and large displacements. It is based on the model established in [11] which is piece-wise linearized using two different methods. The advantages and drawbacks of each method are pointed out. The pull-in time of a microswitch is determined and compared to experimental and other simulation data.


RF-MEMS beam components : FEM modelling and experimental identification of pull-in in presence of residual stress

Abstract: In this paper an experimental validation of numerical approaches aimed to predict the coupled behaviour of microbeams for out-of-plane bending tests is performed. This work completes a previous investigation concerning in plane microbeams bending. Often out-of-plane microcantilevers and clamped-clamped microbeams suffer the presence of residual strain and stress, which affect the value of pull-in voltage. In case of microcantilever an accurate modelling includes the effect of the initial curvature due to microfabrication. In double clamped microbeams a preloading applied by tensile stress is considered. Geometrical onlinearity caused by mechanical coupling between axial and flexural behaviour is detected and modelled. Experimental results demonstrate a good agreement between FEM approaches proposed and tests. A fairly fast and accurate prediction of pull-in condition is performed, thus numerical models can be used to identify residual stress in microbridges by reverse analysis from the measured value of pull-in voltage.


Validation of compact models of microcantilever actuators for RF-MEMS application

Abstract: Microcantilever specimens for in-plane and out-ofplane bending tests are here analyzed. Experimental validation of 2D and 3D numerical models is performed. Main features of in-plane and out-of-plane layouts are then discussed. Effectiveness of plane models to predict pull-in in presence of geometric nonlinearity due to a large tip displacement and initial curvature of microbeam is investigated. The paper is aimed to discuss the capability of 2D models to be used as compact tools to substitute some model order reduction techniques, which appear unsuitable in presence of both electromechanical and geometric nonlinearities.


Numerical Investigation of Laser-Assisted Nanoimprinting on a Copper Substrate from a Perspective of Heat Transfer Analysis

Abstract: The technique of laser-assisted nanoimprinting lithography (LAN) has been proposed to utilize an excimer laser to irradiate through a quartz mold and melts a thin polymer film on the substrate for micro- to nano-scaled fabrications. In the present study, the novel concept of that copper was adopted as the substrate instead of silicon, which is conventionally used, was proposed. The micro/nano structures on the copper substrate could be fabricated by chemical/electrochemical etching or electroforming ; following by the patterns have been transferred onto the substrate using LAN process. Alternatives of the substrate materials could lead versatile applications in micro/nano-fabrication. To demonstrate the feasibility of this concept numerically, this study introduced optical multiple reflection theory to perform both analytical and numerical modeling during the process and to predict the thermal response theoretically.


Micro-electroforming metallic bipolar electrodes for mini-DMFC stacks

Abstract: This paper describes the development of metallic bipolar plate fabrication using micro-electroforming process for mini-DMFC (direct methanol fuel cell) stacks. Ultraviolet (UV) lithography was used to define micro-fluidic channels using a photomask and exposure process. Micro-fluidic channels mold with 300 micrometers thick and 500 micrometers wide were firstly fabricated in a negative photoresist onto a stainless steel plate. Copper micro-electroforming was used to replicate the micro-fluidic channels mold. Following by sputtering silver (Ag) with 1.2 micrometers thick, the metallic bipolar plates were completed. The silver layer is used for corrosive resistance. The completed mini-DMFC stack is a 2x2 cm2 fuel cell stack including a 1.5x1.5 cm2 MEA (membrane electrode assembly). Several MEAs were assembly into mini-DMFC stacks using the completed metallic bipolar plates. All test results showed the metallic bipolar plates suitable for mini-DMFC stacks. The maximum output power density is 9.3mW/cm2 and current density is 100 mA/cm2 when using 8 vol. % methanol as fuel and operated at temperature 30 degrees C. The output power result is similar to other reports by using conventional graphite bipolar plates. However, conventional graphite bipolar plates have certain difficulty to be machined to such micro-fluidic channels. The proposed micro-electroforming metallic bipolar plates are feasible to miniaturize DMFC stacks for further portable 3C applications.


On the determination of Poisson's ratio of stressed monolayer and bilayer submicron thick films

Abstract: In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (s0) and biaxial Young's modulus (E/(1-u)). Associating square and rectangular membranes with different length to width ratios, the Poisson's ratio (u) can also be determined. LPCVD Si3N4 monolayer and Si3N4/SiO2 bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si3N4, E = 212 $\pm$ 14 GPa, s0 = 420 $\pm$ 8 and u = 0.29.


New high fill-factor triangular micro-lens array fabrication method using UV proximity printing

Abstract: A simple and effective method to fabricate a high fill-factor triangular microlens array using the proximity printing in lithography process is reported. The technology utilizes the UV proximity printing by controlling a printing gap between the mask and substrate. The designed approximate triangle microlens array pattern can be fabricated the high fill-factor triangular microlens array in photoresist. It is due to the UV light diffraction to deflect away from the aperture edges and produce a certain exposure in photoresist material outside the aperture edges. This method can precisely control the geometric profile of high fill factor triangular microlens array. The experimental results showed that the triangular micro-lens array in photoresist could be formed automatically when the printing gap ranged from 240 micrometers to 840 micrometers. The gapless triangular microlens array will be used to increases of luminance for backlight module of liquid crystal displays.


Design Optimization for an Electro-Thermally Actuated Polymeric Microgripper

Abstract: Thermal micro-actuators are a promising solution to the need for large-displacement, gentle handling force, low-power MEMS actuators. Potential applications of these devices are micro-relays, assembling and miniature medical instrumentation. In this paper the development of thermal microactuators based on SU-8 polymer is described. The paper presents the development of a new microgripper which can realize a movement of the gripping arms with possibility for positioning and manipulating of the gripped object. Two models of polymeric microgripper electrothermo- mechanical actuated, using low actuation voltages, designed for SU-8 polymer fabrication were presented. The electro-thermal microgrippers were designed and optimized using finite element simulations. Electro-thermo-mechanical simulations based on finite element method were performed for each of the model in order to compare the results. Preliminary experimental tests were carried out.


Design And Fabrication of High Numerical Aperture And Low Aberration Bi-Convex Micro Lens Array

Abstract: Micro lens array is crucial in various kinds of optical and electronic applications. A micro lens array with high numerical aperture (NA) and low aberration is in particular needed. This research is aimed to design and fabricate such a micro lens array with simple structure while keeps the same NA of a same-diameter hemisphere lens. A bi-convex semispherical micro lens array, with corresponding NA 0.379, by PDMS is first designed and analyzed. Experiments are further conducted to fabricate the designed micro lens array by the thermal reflow process. The formed profile is then sputtered with copper to serve as the mold. The front and the rear micro lens array are fabricated by plating PDMS to the mold and then assembled to form the designed micro lens array.


Micromachined Inclinometer Based on Fluid Convection

Abstract: This paper presents a numerical simulation and experimental results of a one-dimensional thermal inclinometer with the cavity filled of gas and liquid. The sensor principle consists of one heating resistor placed between two detectors. When the resistor is electrically powered, it creates a symmetrical temperature profile inside a micromachined silicon cavity. By applying a tilt to the sensor, the profile shifts in the same direction of the sensible axis corresponding to the horizontal one to one. The temperature profile and the sensitivity according to the CO2 gas and mineral oil SAE50 have been studied using numerical resolution of fluid dynamics equations with the computational fluid dynamics (CFD) software package Fluent V6.2. We have shown that the sensitivity of liquid sensors is higher than the gas sensors one. By using micromachined silicon technique, a thermal inclinometer with one pair of detectors placed at 300 um from the heater has been made. Experimental measurements corroborate with the numerical simulation.


Model Based Sensor System for Temperature Measurement in R744 Air Conditioning Systems

Abstract: The goal is the development of a novel principle for the temperature acquisition of refrigerants in CO2 air conditioning systems. The new approach is based on measuring the temperature inside a pressure sensor, which is also needed in the system. On the basis of simulative investigations of different mounting conditions functional relations between measured and medium temperature will be derived.


Integrated 3D Sound Intensity Sensor with Four-Wire Particle Velocity Sensors

Abstract: A new symmetrical four-wire sensor configuration has resulted in a fully integrated sound intensity sensor with significant lower noise floor and smaller size than its predecessors. An integrated sound pressure sensor was further miniaturized by using a folded "back chamber" at both sides of the chip.


High Aspect Pattern Formation by Integration of Micro Inkjetting and Electroless Plating

Abstract: This paper reports on formation of high aspect micro patterns on low temperature co-fired ceramic (LTCC) substrates by integrating micro inkjetting with electroless plating. Micro inkjetting was realized by using an inkjetting printer that ejects ink droplets from a printhead. This printhead consists of a glass nozzle with a diameter of 50 micrometers and a piezoelectric transducer that is coated on the nozzle. The silver colloidal solution was inkjetted on a sintered CT800 ceramic substrate, followed by curing at 200 degrees C for 60 minutes. As a result, the silver trace with a thickness of 200 nm was obtained. The substrate, with the ejected silver thin film as the seed layer, was then immersed into a preinitiator solution to coat a layer of palladium for enhancing the deposition of nickel. Electroless nickel plating was successfully conducted at a rate of 0.39 micrometers /min, and the thickness of traces was plated up to 84 micrometers. This study demonstrates that the integration of inkjetting with plating is an effective method to form high aspect patterns at the demand location.


A Nanostructual Microwave Probe Used for Atomic Force Microscope

Abstract: In order to develop a new structure microwave probe, the fabrication of AFM probe on the GaAs wafer was studied. A waveguide was introduced by evaporating Au film on the top and bottom surfaces of the GaAs AFM probe. A tip having 8 micrometers high, and curvature radius about 50 nm was formed. The dimensions of the cantilever are 250x30x15 micrometers. The open structure of the waveguide at the tip of the probe was introduced by using FIB fabrication. AFM topography of a grating sample was measured by using the fabricated GaAs microwave probe. The fabricated probe was found having nanometer scale resolution, and microwave emission was detected successfully at the tip of the probe by approaching Cr-V steel and Au wire samples.


SANA - Security Analysis in Internet Traffic through Artificial Immune Systems

Abstract: The Attacks done by Viruses, Worms, Hackers, etc. are a Network Security-Problem in many Organisations. Current Intrusion Detection Systems have significant Disadvantages, e.g. the need of plenty of Computational Power or the Local Installation. Therefore, we introduce a novel Framework for Network Security which is called SANA. SANA contains an artificial Immune System with artificial Cells which perform certain Tasks in order to to support existing systems to better secure the Network against Intrusions. The Advantages of SANA are that it is efficient, adaptive, autonomous, and massively-distributed. In this Article, we describe the Architecture of the artificial Immune System and the Functionality of the Components. We explain briefly the Implementation and discuss Results.


High Density out-of-Plane Microprobe Array

Abstract: MEMS technology has been developed rapidly in the last few years. More and more special micro structures were discussed in several publications. However, all of the structures were produced by consist of the three fundamental structures, which included bridge, cantilever and membrane structures. Even the more complex structures were no exception. The cantilever with the property of simple design and easy fabrication among three kinds of fundamental structure, therefore, it was popular used in the design of MEMS device.


Simulation of Coating -Visco-Elastic liquid in the Mico-Nip of Metering Size Press

Abstract: For a set of operating conditions and coating color formulations, undesirable phenomena like color spitting and coating ribs may be triggered in the Micro-nip during the coating process. Therefore, our interest in this work focus on another parameter affect on the undesirable phenomena as the vortices in the Micro-nip. The problem deals with the flow through the Micro-nip of metering size press. The flow enters and exits at a tangential velocity of 20 m/s between two rollers with diameter 80 cm and 60 -m apart. In the upper and bottom part of the domain the angular velocity is 314 rad /s. It has one sub-domain. Previous studies focus on the Micro-nip without considering the inertia and the viscoelasticity of the material. Roll coating is a technique commonly used in the coating industry to meter a thin fluid film on a moving substrate. During the film formation, the fluid is subjected to very high shear and extensional rates over a very short period of time. The fluid domain changes as a function of the hydrodynamic pressure within the nip as a result of the deformable cover usually used on one of the rolls. The free surface also adds more complexity to the flow due to the force equilibrium in the fluid gas interface. Last of all, the rheological behavior of the coating fluid is usually non-Newtonian, so the metering flow hydrodynamics is finally very difficult to describe. It is concluded that the normal forces of micro-nip increases with increasing the inhibitors. Therefore, it affects on the smoothness and creates defects. On the other hand, it can be concluded that the creation of big vortex in the middle of micro-nip affects on the coating liquid behavior.


A Microcantilever-based Gas Flow Sensor for Flow Rate and Direction Detection

Abstract: The purpose of this paper is to apply characteristics of residual stress that causes cantilever beams to bend for manufacturing a micro-structured gas flow sensor. This study uses a silicon wafer deposited silicon nitride layers, reassembled the gas flow sensor with four cantilever beams that perpendicular to each other and manufactured piezoresistive structure on each micro-cantilever by MEMS technologies, respectively. When the cantilever beams are formed after etching the silicon wafer, it bends up a little due to the released residual stress induced in the previous fabrication process. As air flows through the sensor upstream and downstream beam deformation was made, thus the airflow direction can be determined through comparing the resistance variation between different cantilever beams. The flow rate can also be measured by calculating the total resistance variations on the four cantilevers.


Process nano scale mechanical properties measurement of thin metal films using a novel paddle cantilever test structure

Abstract: A new technique was developed for studying the mechanical behavior of nano-scale thin metal films on substrate is presented. The test structure was designed on a novel "paddle" cantilever beam specimens with dimensions as few hundred nanometers to less than 10 nanometers. This beam is in triangle shape in order to provide uniform plane strain distribution. Standard clean room processing was used to prepare the paddle sample. The experiment can be operated by using the electrostatic deflection on the paddle uniform distributed stress cantilever beam and then measure the deposited thin metal film materials on top of it. A capacitance technique was used to measurement on the other side of the deflected plate to measure its deflection with respect to the force. The measured strain was converted through the capacitance measurement for the deflection of the cantilever. System performance on the residual stress measurement of thin films are calculated with three different forces on the "paddle" cantilever beam, including the force due to the film, compliance force and electrostatic force.


High Q-factor CMOS-MEMS inductor

Abstract: This study investigates a high Q-factor spiral inductor fabricated by the CMOS (complementary metal oxide semiconductor) process and a post-process. The spiral inductor is manufactured on silicon substrate using the 0.35 micrometers CMOS process. In order to reduce the substrate loss and enhance the Q-factor of the inductor, silicon substrate under the inductor is removed using a post-process. The post-process uses RIE (reactive ion etching) to etch the sacrificial layer of silicon dioxide, and then TMAH (tetra methyl ammonium hydroxide) is employed to remove the underlying silicon substrate and obtain the suspended spiral inductor. The advantage of the post process is compatible with the CMOS process. The Agilent 8510C network analyzer and a Cascade probe station are used to measure the performances of the spiral inductor. Experiments indicate that the spiral inductor has a Q-factor of 15 at 11 GHz, an inductance of 4 nH at 25.5 GHz and a self-resonance frequency of about 27 GHz.


Copper Electrodeposition for 3D Integration

Abstract: Two dimensional (2D) integration has been the traditional approach for IC integration. Due to increasing demands for providing electronic devices with superior performance and functionality in more efficient and compact packages, has driven the semiconductor industry to develop more advanced packaging technologies. Three-dimensional (3D) approaches address both miniaturization and integration required for advanced and portable electronic products. Vertical integration proved to be essential in achieving a greater integration flexibility of disparate technologies, reason for which a general trend of transition from 2D to 3D integration is currently being observed in the industry. 3D chip integration using through silicon via (TSV) copper is considered one of the most advanced technologies among all different types of 3D packaging technologies. Copper electrodeposition is one of technologies that enable the formation of TSV structures. Because of its well-known application for copper damascene, it was believed that its transfer to filling TSV vias would be easily adopted. However, as any new technology at its beginning, there are several challenges that need to be addressed and resolved before becoming a fully mature technology. This paper will address the TSV fill processes using copper electrodeposition, the advantages as well as difficulties associated with this technology and approaches taken to overcome them. Electrochemical characterization of the organics behavior and their effect on via filling will be presented. The effect of wafer design on process performance and throughput, including necessary process optimizations that are required for achieving void-free via filling while reducing the processing time, will be discussed.


Technologies for 3D Heterogeneous Integration

Abstract: 3D-Integration is a promising technology towards higher interconnect densities and shorter wiring lengths between multiple chip stacks, thus achieving a very high performance level combined with low power consumption. This technology also offers the possibility to build up systems with high complexity just by combining devices of different technologies. For ultra thin silicon is the base of this integration technology, the fundamental processing steps will be described, as well as appropriate handling concepts. Three main concepts for 3D integration have been developed at IZM. The approach with the greatest flexibility called Inter Chip Via - Solid Liquid Interdiffusion (ICV-SLID) is introduced. This is a chip-to-wafer stacking technology which combines the advantages of the Inter Chip Via (ICV) process and the solid-liquid-interdiffusion technique (SLID) of copper and tin. The fully modular ICV-SLID concept allows the formation of multiple device stacks. A test chip was designed and the total process sequence of the ICV-SLID technology for the realization of a three-layer chip-to-wafer stack was demonstrated. The proposed wafer-level 3D integration concept has the potential for low cost fabrication of multi-layer high-performance 3D-SoCs and is well suited as a replacement for embedded technologies based on monolithic integration. To address yield issues a wafer-level chip-scale handling is presented as well, to select known-good dies and work on them with wafer-level process sequences before joining them to integrated stacks.


Through Silicon Vias as Enablers for 3D Systems

Abstract: This special session on 3D TSV's will highlight some of the fabrication processes and used technologies to create vias from the frontside of an active circuit to its backside and potential implementation solutions to form complex systems leveraging these novel possibilities. General techniques for via formation are discussed as well as advanced integration solutions leveraging the power of 3D TSV's.


Fabrication of 3D Packaging TSV using DRIE

Abstract: Emerging 3D chips stacking and MEMS/Sensors packaging technologies are using DRIE (Deep Reactive Ion Etching) to etch through-silicon via (TSV) for advanced interconnections. The interconnection step can be done prior to or post CMOS manufacturing, each requiring different etch process performances. A review of the DRIE capability in terms of etching profile, etch rate, etch depth has been carried out. Excellent tool flexibility allows a wide range of basic and complex profiles to be achieved. Unlike other techniques, DRIE has the capability to etch feature sizes ranging from sub-micron to millimeter width. The main specificity of the DRIE is that etch rate is sensitive to the total exposed area and the aspect ratio. For the TSV applications, where the total exposed area is lower than 10%, high etch rates are achievable. A study has also been done to highlight the importance of via profile for the success of the refilling step. In addition, due to the high flexibility of DRIE, we also explore the capability of using this technique for wafer thinning and plasma die separation.


Study of First-Order Thermal Sigma-Delta Architecture for Convective Accelerometers

Abstract: This paper presents the study of an original closed-loop conditioning approach for fully-integrated convective inertial sensors. The method is applied to an accelerometer manufactured on a standard CMOS technology using an auto-aligned bulk etching step. Using the thermal behavior of the sensor as a summing function, a first order sigma-delta modulator is built. This "electro-physical" modulator realizes an analog-to-digital conversion of the signal. Besides the feedback scheme should improve the sensor performance.


High Density Through Silicon Via (TSV)

Abstract: The Through Silicon Via (TSV) process developed by Silex provides down to 30 micrometers pitch for through wafer connections in up to 600 micrometers thick substrates. Integrated with MEMS designs it enables significantly reduced die size and true "Wafer Level Packaging" - features that are particularly important in consumer market applications. The TSV technology also enables integration of advanced interconnect functions in optical MEMS, sensors and microfluidic devices. In addition the Via technology opens for very interesting possibilities considering integration with CMOS processing. With several companies using the process already today, qualified volume manufacturing in place and a line-up of potential users, the process is becoming a standard in the MEMS industry. We provide a introduction to the via formation process and also present some on the novel solutions made available by the technology.


Rejection of Power Supply Noise in Wheatstone Bridges : Application to Piezoresistive MEMS

Abstract: This paper deals with the design of MEMS using piezoresistivity as transduction principle. It is demonstrated that when the sensor topology doesn't allow a perfect matching of strain gauges, the resolution is limited by the ability of the conditioning circuit (typically a Wheatstone bridge) to reject power supply noise. As this ability is strongly reduced when an offset voltage is present at the output of the bridge, the proposed architecture implements a feedback loop to control MOS transistors inserted in the Wheatstone bridge to compensate resistor mismatches. This feedback exhibits a very good offset cancellation and therefore a better resolution is achieved.


Next Generation of TCAD Environments for MEMS Design

Abstract: In this paper we present the latest version of the TCAD environment BICEP'S (Braunschweigs Integrated CAD-Environment for Product Planning and Process Simulation). By using a central process database, which allows the exchange of all relevant process data it is able to overcome many of the mentioned obstacles. The database and process planning tool can be used by process developers to document changes in process settings and the influence of such changes on the process result. This information can then be used by the designers to set-up a simulation file for a detailed analysis of the impact of such parameter changes on the requested design. This will be shown by the example of silicon etching using an atomistic etch simulator.


Noise Analysis and Noise-based Optimization for Resonant MEMS Structures

Abstract: This paper presents a detailed noise analysis and a noise-based optimization procedure for resonant MEMS structures. A design for high sensitivity of MEMS structures needs to take into account the noise shaping induced by damping phenomena at micro scale. The existing literature presents detailed models for the damping at microscale, but usually neglects them in the noise analysis process, assuming instead a white spectrum approximation for the mechano-thermal noise. The present work extends the implications of the complex gas-solid interaction into the field of noise analysis for mechanical sensors, and provides a semi-automatic procedure for behavioral macromodel extraction and sensor optimization with respect to signal-to-noise ratio.


Haptic sensing for MEMS with application for cantilever and Casimir effect

Abstract: This paper presents an implementation of the Cosserat theory into haptic sensing technologies for real-time simulation of microstructures. Cosserat theory is chosen instead of the classical theory of elasticity for a better representation of stress, especially in the nonlinear regime. The use of Cosserat theory leads to a reduction of the complexity of the modelling and thus increases its capability for real time simulation which is indispensable for haptic technologies. The incorporation of Cosserat theory into haptic sensing technology enables the designer to simulate in real-time the components in a virtual reality environment (VRE) which can enable virtual manufacturing and prototyping. The software tool created as a result of this methodology demonstrates the feasibility of the proposed model. As test demonstrators, a cantilever microbeam and microbridge undergoing bending in VRE are presented.


On-Chip Hotplate for Temperature Control of Cmos Saw Resonators

Abstract: Due to the sensitivity of the piezoelectric layer in surface acoustic wave (SAW) resonators to temperature, a method of achieving device stability as a function of temperature is required. This work presents the design, modeling and characterization of integrated dual-serpentine polysilicon resistors as a method for temperature control of CMOS SAW resonators. The design employs the oven control temperature stabilization scheme where the device's temperature is elevated to higher than Tmax to maintain constant device temperature. The efficiency of the polysilicon resistor as a heating element was verified through a 1-D partial differential equation model, 3-D CoventorWare finite element simulations and measurements using Compix thermal camera. To verify that the on-chip hotplate is effective as a temperature control method, both DC and RF measurements of the heater together with the resonator were conducted. Experimental results have indicated that the TCF of the CMOS SAW resonator of -97.2 ppm/deg C has been reduced to -23.19 ppm/deg C when heated to 56 deg C.


Modelling methodology of MEMS structures based on Cosserat theory

Abstract: Modelling MEMS involves a variety of software tools that deal with the analysis of complex geometrical structures and the assessment of various interactions among different energy domains and components. Moreover, the MEMS market is growing very fast, but surprisingly, there is a paucity of modelling and simulation methodology for precise performance verification of MEMS products in the nonlinear regime. For that reason, an efficient and rapid modelling approach is proposed that meets the linear and nonlinear dynamic behaviour of MEMS systems.


Low Voltage Totally Free Flexible RF MEMS Switch With Anti-Stiction System

Abstract: This paper concerns a new design of RF MEMS switch combined with an innovative process which enable low actuation voltage (<5V) and avoid stiction. First, the structure described with principal design issues, the corresponding anti-stiction system is presented and FEM simulations are done. Then, a short description of the process flow based on two non polymer sacrificial layers. Finally, RF measurements are presented and preliminary experimental protocol and results of anti-stiction validation is detailed. Resulting RF performances are -30dB of isolation and -0.45dB of insertion loss at 10 GHz.


High Quality Factor Silicon Cantilever Driven by PZT Actuator for Resonant Based Mass Detection

Abstract: A high quality factor (Q-factor) piezoelectric lead zirconat titanate (PZT) actuated single crystal silicon cantilever was proposed in this paper for resonant based ultra-sensitive mass detection. Energy dissipation from intrinsic mechanical loss of the PZT film was successfully compressed by separating the PZT actuator from resonant structure. Excellent Q-factor, which is several times larger than conventional PZT cantilever, was achieved under both atmospheric pressure and reduced pressures. For a 30 micrometer-wide 100 micrometer-long cantilever, Q-factor was measured as high as 1113 and 7279 under the pressure of 101.2 KPa and 35 Pa, respectively. Moreover, it was found that high-mode vibration can be realized by the cantilever for the pursuit of great Q-factor, while support loss became significant because of the increased vibration amplitude at the actuation point. An optimized structure using node-point actuation was suggested then to suppress corresponding energy dissipation.


A New Four States High Deflection Low Actuation Voltage Electrostatic Mems Switch for RF Applications

Abstract: This paper presents a new electrostatic MEMS (MicroElectroMechanical System) based on a single high reliability totally free flexible membrane. Using four electrodes, this structure enables four states which allowed large deflections (4$\mu$m) with low actuation voltage (7,5V). This design presents also a good contact force and improve the restoring force of the structure. As an example of application, a Single Pole Double Throw (SPDT) for 24GHz applications, based on this design, has been simulated.


Design and Fabrication of a Novel Micro Electromagnetic Actuator

Abstract: The present study presents a new micro electromagnetic actuator utilizing a PDMS membrane with a magnet. The actuator is integrated with micro coils to electromagnetically actuate the membrane and results in a large deflection. The micro electromagnetic actuator proposed in this study is easily fabricated and is readily integrated with existing bio-medical chips due to its planar structure.


Flexible Micro Thermoelectric Generator based on Electroplated Bi2Te3

Abstract: We present and discuss the fabrication process and the performance of a flexible micro thermoelectric generator with electroplated Bi2Te3 thermocouples in a SU-8 mold. Demonstrator devices generate 278uWcm-2 at dTmeas=40K across the experimental set up. Based on model calculations, a temperature difference of dTG=21.4K across the generator is assumed. Due to the flexible design and the chosen generator materials, the performance stays high even for curved contact surfaces. The measurement results correlate well with the model based design optimization predictions.


A Novel Piezoelectric Microtransformer for Autonmous Sensors Applications

Abstract: This work relates to a novel piezoelectric transformer to be used in an autonomous sensor unit, possibly in conjunction with a RF-MEMS retro-modulator.


Optimization of efficiency and energy density of passive micro fuel cells and galvanic hydrogen generators

Abstract: A PEM micro fuel cell system is described which is based on self-breathing PEM micro fuel cells in the power range between 1 mW and 1W. Hydrogen is supplied with on-demand hydrogen production with help of a galvanic cell, that produces hydrogen when Zn reacts with water. The system can be used as a battery replacement for low power applications and has the potential to improve the run time of autonomous systems. The efficiency has been investigated as function of fuel cell construction and tested for several load profiles.


Design and Fabrication of Acoustic Wave Actuated Microgenerator for Portable Electronic Devices

Abstract: The past few years have seen an increasing focus on energy harvesting issue, including power supply for portable electric devices. Utilize scavenging ambient energy from the environment could eliminate the need for batteries and increase portable device lifetimes indefinitely. In addition, through MEMS technology fabricated micro-generator could easy integrate with these small or portable devices. Several different ambient sources, including solar, vibration and temperature effect, have already exploited [1-3]. Each energy source should be used in suitable environment, therefore to produce maximum efficiency. In this paper, we present an acoustic wave actuated micro-generator for power system by using the energy of acoustic waves, such as the sound from human voices or speakerphone, to actuate a MEMS-type electromagnetic transducer. This provides a longer device lifetime and greater power system convenience. Moreover, it is convenient to integrate MEMS-based microgenerators with small or porta le devices


Package Hermeticity Testing with Thermal Transient Measurements

Abstract: The rapid incursion of new technologies such as MEMS and smart sensor device manufacturing requires new tailor-made packaging designs. In many applications these devices are exposed to humid environments. Since the penetration of moisture into the package may result in internal corrosion or shift of the operating parameters, the reliability testing of hermetically sealed packages has become a crucial question in the semiconductor industry.


Micro-tensile tests on micromachined metal on polymer specimens: elasticity, plasticity and rupture

Abstract: This study is focused on the mechanical characterization of materials used in microelectronic and micro- electromechanical systems (MEMS) devices. In order to determine their mechanical parameters, a new deformation bench test with suitable micromachined specimens have been developed. Uniaxial tensile tests were performed on "low cost" specimens, consisting in electroplated thin copper films and structures, deposited on a polimide type substrate. Moreover, a cyclic mechanical actuation via piezoelectric actuators was tested on the same deformation bench. These experiments validate the device for performing dynamic characterization of materials, and reliability studies of different microstructures.


Open Ended Microwave Oven for Packaging

Abstract: A novel open waveguide cavity resonator is presented for the combined variable frequency microwave curing of bumps, underfills and encapsulants, as well as the alignment of devices for fast flip-chip assembly, direct chip attach (DCA) or wafer-scale level packaging (WSLP). This technology achieves radio frequency (RF) curing of adhesives used in microelectronics, optoelectronics and medical devices with potential simultaneous micron-scale alignment accuracy and bonding of devices. In principle, the open oven cavity can be fitted directly onto a flip-chip or wafer scale bonder and, as such, will allow for the bonding of devices through localised heating thus reducing the risk to thermally sensitive devices. Variable frequency microwave (VFM) heating and curing of an idealised polymer load is numerically simulated using a multi-physics approach. Electro-magnetic fields within a novel open ended microwave oven developed for use in micro-electronics manufacturing applications are solved using a de icated Yee scheme finite-difference time-domain (FDTD) solver. Temperature distribution, degree of cure and thermal stresses are analysed using an Unstructured Finite Volume method (UFVM) multi-physics package. The polymer load was meshed for thermophysical analysis, whilst the microwave cavity - encompassing the polymer load - was meshed for microwave irradiation. The two solution domains are linked using a cross-mapping routine. The principle of heating using the evanescent fringing fields within the open-end of the cavity is demonstrated. A closed loop feedback routine is established allowing the temperature within a lossy sample to be controlled. A distribution of the temperature within the lossy sample is obtained by using a thermal imaging camera.


Mechanical Fatigue on Gold MEMS Devices: Experimental Results

Abstract: The effect of mechanical fatigue on structural performances of gold devices is investigated. The pull-in voltage of special testing micro-systems is monitored during the cyclical load application. The mechanical collapse is identified as a dramatic loss of mechanical strength of the specimen. The fatigue limit is estimated through the stair-case method by means of the pull-in voltage measurements. Measurements are performed by means of the optical interferometric technique.


Decomposition Techniques for Subgraph Matching

Abstract: In the constraint programming framework, state-of-the-art static and dynamic decomposition techniques are hard to apply to problems with complete initial constraint graphs. For such problems, we propose a hybrid approach of these techniques in the presence of global constraints. In particular, we solve the subgraph isomorphism problem. Further we design specific heuristics for this hard problem, exploiting its special structure to achieve decomposition. The underlying idea is to precompute a static heuristic on a subset of its constraint network, to follow this static ordering until a first problem decomposition is available, and to switch afterwards to a fully propagated, dynamically decomposing search. Experimental results show that, for sparse graphs, our decomposition method solves more instances than dedicated, state-of-the-art matching algorithms or standard constraint programming approaches.


Submodular approximation: sampling-based algorithms and lower bounds

Abstract: We introduce several generalizations of classical computer science problems obtained by replacing simpler objective functions with general submodular functions. The new problems include submodular load balancing, which generalizes load balancing or minimum-makespan scheduling, submodular sparsest cut and submodular balanced cut, which generalize their respective graph cut problems, as well as submodular function minimization with a cardinality lower bound. We establish upper and lower bounds for the approximability of these problems with a polynomial number of queries to a function-value oracle. The approximation guarantees for most of our algorithms are of the order of sqrt(n/ln n). We show that this is the inherent difficulty of the problems by proving matching lower bounds. We also give an improved lower bound for the problem of approximately learning a monotone submodular function. In addition, we present an algorithm for approximately learning submodular functions with special structure, whose guarantee is close to the lower bound. Although quite restrictive, the class of functions with this structure includes the ones that are used for lower bounds both by us and in previous work. This demonstrates that if there are significantly stronger lower bounds for this problem, they rely on more general submodular functions.


Adaptive Affinity Propagation Clustering

Abstract: Affinity propagation clustering (AP) has two limitations: it is hard to know what value of parameter 'preference' can yield an optimal clustering solution, and oscillations cannot be eliminated automatically if occur. The adaptive AP method is proposed to overcome these limitations, including adaptive scanning of preferences to search space of the number of clusters for finding the optimal clustering solution, adaptive adjustment of damping factors to eliminate oscillations, and adaptive escaping from oscillations when the damping adjustment technique fails. Experimental results on simulated and real data sets show that the adaptive AP is effective and can outperform AP in quality of clustering results.


On the Convergence Time of the Best Response Dynamics in Player-specific Congestion Games

Abstract: We study the convergence time of the best response dynamics in player-specific singleton congestion games. It is well known that this dynamics can cycle, although from every state a short sequence of best responses to a Nash equilibrium exists. Thus, the random best response dynamics, which selects the next player to play a best response uniformly at random, terminates in a Nash equilibrium with probability one. In this paper, we are interested in the expected number of best responses until the random best response dynamics terminates. As a first step towards this goal, we consider games in which each player can choose between only two resources. These games have a natural representation as (multi-)graphs by identifying nodes with resources and edges with players. For the class of games that can be represented as trees, we show that the best-response dynamics cannot cycle and that it terminates after O(n^2) steps where n denotes the number of resources. For the class of games represented as cycles, we show that the best response dynamics can cycle. However, we also show that the random best response dynamics terminates after O(n^2) steps in expectation. Additionally, we conjecture that in general player-specific singleton congestion games there exists no polynomial upper bound on the expected number of steps until the random best response dynamics terminates. We support our conjecture by presenting a family of games for which simulations indicate a super-polynomial convergence time.


Contact state analysis using NFIS and SOM

Abstract: This paper reports application of neuro- fuzzy inference system (NFIS) and self organizing feature map neural networks (SOM) on detection of contact state in a block system. In this manner, on a simple system, the evolution of contact states, by parallelization of DDA, has been investigated. So, a comparison between NFIS and SOM results has been presented. The results show applicability of the proposed methods, by different accuracy, on detection of contact's distribution.


Clustering of scientific citations in Wikipedia

Abstract: The instances of templates in Wikipedia form an interesting data set of structured information. Here I focus on the cite journal template that is primarily used for citation to articles in scientific journals. These citations can be extracted and analyzed: Non-negative matrix factorization is performed on a (article x journal) matrix resulting in a soft clustering of Wikipedia articles and scientific journals, each cluster more or less representing a scientific topic.


Online Ad Slotting With Cancellations

Abstract: Many advertisers buy advertisements (ads) on the Internet or on traditional media and seek simple, online mechanisms to reserve ad slots in advance. Media publishers represent a vast and varying inventory, and they too seek automatic, online mechanisms for pricing and allocating such reservations. In this paper, we present and study a simple model for auctioning such ad slots in advance. Bidders arrive sequentially and report which slots they are interested in. The seller must decide immediately whether or not to grant a reservation. Our model allows a seller to accept reservations, but possibly cancel the allocations later and pay the bidder a cancellation compensation (bump payment). Our main result is an online mechanism to derive prices and bump payments that is efficient to implement. This mechanism has many desirable properties. It is individually rational; winners have an incentive to be honest and bidding one's true value dominates any lower bid. Our mechanism's efficiency is within a constant fraction of the a posteriori optimally efficient solution. Its revenue is within a constant fraction of the a posteriori revenue of the Vickrey-Clarke-Groves mechanism. Our results make no assumptions about the order of arrival of bids or the value distribution of bidders and still hold if the items for sale are elements of a matroid, a more general setting than slot allocation.


Spectrum Allocation in Two-Tier Networks

Abstract: Two-tier networks, comprising a conventional cellular network overlaid with shorter range hotspots (e.g. femtocells, distributed antennas, or wired relays), offer an economically viable way to improve cellular system capacity. The capacity-limiting factor in such networks is interference. The cross-tier interference between macrocells and femtocells can suffocate the capacity due to the near-far problem, so in practice hotspots should use a different frequency channel than the potentially nearby high-power macrocell users. Centralized or coordinated frequency planning, which is difficult and inefficient even in conventional cellular networks, is all but impossible in a two-tier network. This paper proposes and analyzes an optimum decentralized spectrum allocation policy for two-tier networks that employ frequency division multiple access (including OFDMA). The proposed allocation is optimal in terms of Area Spectral Efficiency (ASE), and is subjected to a sensible Quality of Service (QoS) requirement, which guarantees that both macrocell and femtocell users attain at least a prescribed data rate. Results show the dependence of this allocation on the QoS requirement, hotspot density and the co-channel interference from the macrocell and surrounding femtocells. Design interpretations of this result are provided.


Randomized Work-Competitive Scheduling for Cooperative Computing on $k$-partite Task Graphs

Abstract: A fundamental problem in distributed computing is the task of cooperatively executing a given set of $t$ tasks by $p$ processors where the communication medium is dynamic and subject to failures. The dynamics of the communication medium lead to groups of processors being disconnected and possibly reconnected during the entire course of the computation furthermore tasks can have dependencies among them. In this paper, we present a randomized algorithm whose competitive ratio is dependent on the dynamics of the communication medium and also on the nature of the dependencies among the tasks.


A New Stream Cipher: Dicing

Abstract: In this paper, we will propose a new synchronous stream cipher named DICING, which can be viewed as a clock-controlled one but with a new mechanism of altering steps. It has satisfactory performance and there have not been found weakness for the known attacks, the key sizes can be 128bits and 256bits respectively.


Assessment of effective parameters on dilution using approximate reasoning methods in longwall mining method, Iran coal mines

Abstract: Approximately more than 90% of all coal production in Iranian underground mines is derived directly longwall mining method. Out of seam dilution is one of the essential problems in these mines. Therefore the dilution can impose the additional cost of mining and milling. As a result, recognition of the effective parameters on the dilution has a remarkable role in industry. In this way, this paper has analyzed the influence of 13 parameters (attributed variables) versus the decision attribute (dilution value), so that using two approximate reasoning methods, namely Rough Set Theory (RST) and Self Organizing Neuro- Fuzzy Inference System (SONFIS) the best rules on our collected data sets has been extracted. The other benefit of later methods is to predict new unknown cases. So, the reduced sets (reducts) by RST have been obtained. Therefore the emerged results by utilizing mentioned methods shows that the high sensitive variables are thickness of layer, length of stope, rate of advance, number of miners, type of advancing.


Testability of Reversible Iterative Logic Arrays

Abstract: Iterative Logic Arrays (ILAs) are ideal as VLSI sub-systems because of their regular structure and its close resemblance with FPGAs (Field Programmable Gate Arrays). Reversible circuits are of interest in the design of very low power circuits where energy loss implied by high frequency switching is not of much consideration. Reversibility is essential for Quantum Computing. This paper examines the testability of Reversible Iterative Logic Arrays (ILAs) composed of reversible k-CNOT gates. For certain ILAs it is possible to find a test set whose size remains constant irrespective of the size of the ILA, while for others it varies with array size. Former type of ILAs is known as Constant-Testable, i.e. C-Testable. It has been shown that Reversible Logic Arrays are C-Testable and size of test set is equal to number of entries in cells truth table implying that the reversible ILAs are also Optimal-Testable, i.e. O-Testable. Uniform-Testability, i.e. U-Testability has been defined and Reversible Heterogeneous ILAs have been characterized as U-Testable. The test generation problem has been shown to be related to certain properties of cycles in a set of graphs derived from cell truth table. By careful analysis of these cycles an efficient test generation technique that can be easily converted to an ATPG program has been presented for both 1-D and 2D ILAs. The same algorithms can be easily extended for n-Dimensional Reversible ILAs.


A Simple Dynamic Mind-map Framework To Discover Associative Relationships in Transactional Data Streams

Abstract: In this paper, we informally introduce dynamic mind-maps that represent a new approach on the basis of a dynamic construction of connectionist structures during the processing of a data stream. This allows the representation and processing of recursively defined structures and avoids the problem of a more traditional, fixed-size architecture with the processing of input structures of unknown size. For a data stream analysis with association discovery, the incremental analysis of data leads to results on demand. Here, we describe a framework that uses symbolic cells to calculate associations based on transactional data streams as it exists in e.g. bibliographic databases. We follow a natural paradigm of applying simple operations on cells yielding on a mind-map structure that adapts over time.


Throughput and Delay Analysis of Wireless Random Access Networks

Abstract: This paper studies the network throughput and transport delay of a multihop wireless random access network based on a Markov renewal model of packet transportation. We show that the distribution of the source-to-destination (SD) distance plays a critical role in characterizing network performance. We establish necessary and sufficient condition on the SD distance for scalable network throughput, and address the optimal rate allocation issue with fairness and the QoS requirements taken into consideration. In respect to the end-to-end performance, the transport delay is explored in this paper along with network throughput. We characterize the transport delay by relating it to nodal queueing behavior and the SD-distance distribution; the former is a local property while the latter is a global property. In addition, we apply the large deviation theory to derive the tail distribution of transport delay. To put our theory into practical network operation, several traffic scaling laws are provided to demonstrate how network scalability can be achieved by localizing the traffic pattern, and a leaky bucket scheme at the network access is proposed for traffic shaping and flow control.


Searching for Frequent Colors in Rectangles

Abstract: We study a new variant of colored orthogonal range searching problem: given a query rectangle $Q$ all colors $c$, such that at least a fraction $\tau$ of all points in $Q$ are of color $c$, must be reported. We describe several data structures for that problem that use pseudo-linear space and answer queries in poly-logarithmic time.


Binary Morphisms to Ultimately Periodic Words

Abstract: This paper classifies binary morphisms that map to ultimately periodic words. In particular, if a morphism h maps an infinite non-ultimately periodic word to an ultimately periodic word then it must be true that h(0) commutes with h(1).


Almost-natural proofs

Abstract: Razborov and Rudich have shown that so-called "natural proofs" are not useful for separating P from NP unless hard pseudorandom number generators do not exist. This famous result is widely regarded as a serious barrier to proving strong lower bounds in circuit complexity theory. By definition, a natural combinatorial property satisfies two conditions, constructivity and largeness. Our main result is that if the largeness condition is weakened slightly, then not only does the Razborov-Rudich proof break down, but such "almost-natural" (and useful) properties provably exist. Specifically, under the same pseudorandomness assumption that Razborov and Rudich make, a simple, explicit property that we call "discrimination" suffices to separate P/poly from NP; discrimination is nearly linear-time computable and almost large, having density 2^{-q(n)} where q is a quasi-polynomial function. For those who hope to separate P from NP using random function properties in some sense, discrimination is interesting, because it is constructive, yet may be thought of as a minor alteration of a property of a random function. The proof relies heavily on the self-defeating character of natural proofs. Our proof technique also yields an unconditional result, namely that there exist almost-large and useful properties that are constructive, if we are allowed to call non-uniform low-complexity classes "constructive." We note, though, that this unconditional result can also be proved by a more conventional counting argument. Finally, we give an alternative proof, communicated to us by Salil Vadhan at FOCS 2008, of one of our theorems, and we make some speculative remarks on the future prospects for proving strong circuit lower bounds.


A language for mathematical knowledge management

Abstract: We argue that the language of Zermelo Fraenkel set theory with definitions and partial functions provides the most promising bedrock semantics for communicating and sharing mathematical knowledge. We then describe a syntactic sugaring of that language that provides a way of writing remarkably readable assertions without straying far from the set-theoretic semantics. We illustrate with some examples of formalized textbook definitions from elementary set theory and point-set topology. We also present statistics concerning the complexity of these definitions, under various complexity measures.


Linear Time Algorithm for Weak Parity Games

Abstract: We consider games played on graphs with the winning conditions for the players specified as weak-parity conditions. In weak-parity conditions the winner of a play is decided by looking into the set of states appearing in the play, rather than the set of states appearing infinitely often in the play. A naive analysis of the classical algorithm for weak-parity games yields a quadratic time algorithm. We present a linear time algorithm for solving weak-parity games.


Approximation Algorithms for Shortest Descending Paths in Terrains

Abstract: A path from s to t on a polyhedral terrain is descending if the height of a point p never increases while we move p along the path from s to t. No efficient algorithm is known to find a shortest descending path (SDP) from s to t in a polyhedral terrain. We give two approximation algorithms (more precisely, FPTASs) that solve the SDP problem on general terrains. Both algorithms are simple, robust and easy to implement.


Model Checking One-clock Priced Timed Automata

Abstract: We consider the model of priced (a.k.a. weighted) timed automata, an extension of timed automata with cost information on both locations and transitions, and we study various model-checking problems for that model based on extensions of classical temporal logics with cost constraints on modalities. We prove that, under the assumption that the model has only one clock, model-checking this class of models against the logic WCTL, CTL with cost-constrained modalities, is PSPACE-complete (while it has been shown undecidable as soon as the model has three clocks). We also prove that model-checking WMTL, LTL with cost-constrained modalities, is decidable only if there is a single clock in the model and a single stopwatch cost variable (i.e., whose slopes lie in {0,1}).


Efficiently Simulating Higher-Order Arithmetic by a First-Order Theory Modulo

Abstract: In deduction modulo, a theory is not represented by a set of axioms but by a congruence on propositions modulo which the inference rules of standard deductive systems---such as for instance natural deduction---are applied. Therefore, the reasoning that is intrinsic of the theory does not appear in the length of proofs. In general, the congruence is defined through a rewrite system over terms and propositions. We define a rigorous framework to study proof lengths in deduction modulo, where the congruence must be computed in polynomial time. We show that even very simple rewrite systems lead to arbitrary proof-length speed-ups in deduction modulo, compared to using axioms. As higher-order logic can be encoded as a first-order theory in deduction modulo, we also study how to reinterpret, thanks to deduction modulo, the speed-ups between higher-order and first-order arithmetics that were stated by G\"odel. We define a first-order rewrite system with a congruence decidable in polynomial time such that proofs of higher-order arithmetic can be linearly translated into first-order arithmetic modulo that system. We also present the whole higher-order arithmetic as a first-order system without resorting to any axiom, where proofs have the same length as in the axiomatic presentation.


A Fast Algorithm and Datalog Inexpressibility for Temporal Reasoning

Abstract: We introduce a new tractable temporal constraint language, which strictly contains the Ord-Horn language of Buerkert and Nebel and the class of AND/OR precedence constraints. The algorithm we present for this language decides whether a given set of constraints is consistent in time that is quadratic in the input size. We also prove that (unlike Ord-Horn) this language cannot be solved by Datalog or by establishing local consistency.


A Time Efficient Indexing Scheme for Complex Spatiotemporal Retrieval

Abstract: The paper is concerned with the time efficient processing of spatiotemporal predicates, i.e. spatial predicates associated with an exact temporal constraint. A set of such predicates forms a buffer query or a Spatio-temporal Pattern (STP) Query with time. In the more general case of an STP query, the temporal dimension is introduced via the relative order of the spatial predicates (STP queries with order). Therefore, the efficient processing of a spatiotemporal predicate is crucial for the efficient implementation of more complex queries of practical interest. We propose an extension of a known approach, suitable for processing spatial predicates, which has been used for the efficient manipulation of STP queries with order. The extended method is supported by efficient indexing structures. We also provide experimental results that show the efficiency of the technique.


A Simple In-Place Algorithm for In-Shuffle

Abstract: The paper presents a simple, linear time, in-place algorithm for performing a 2-way in-shuffle which can be used with little modification for certain other k-way shuffles.


NAPX: A Polynomial Time Approximation Scheme for the Noah's Ark Problem

Abstract: The Noah's Ark Problem (NAP) is an NP-Hard optimization problem with relevance to ecological conservation management. It asks to maximize the phylogenetic diversity (PD) of a set of taxa given a fixed budget, where each taxon is associated with a cost of conservation and a probability of extinction. NAP has received renewed interest with the rise in availability of genetic sequence data, allowing PD to be used as a practical measure of biodiversity. However, only simplified instances of the problem, where one or more parameters are fixed as constants, have as of yet been addressed in the literature. We present NAPX, the first algorithm for the general version of NAP that returns a $1 - \epsilon$ approximation of the optimal solution. It runs in $O(\frac{n B^2 h^2 \log^2n}{\log^2(1 - \epsilon)})$ time where $n$ is the number of species, and $B$ is the total budget and $h$ is the height of the input tree. We also provide improved bounds for its expected running time.


Grammatical Evolution with Restarts for Fast Fractal Generation

Abstract: In a previous work, the authors proposed a Grammatical Evolution algorithm to automatically generate Lindenmayer Systems which represent fractal curves with a pre-determined fractal dimension. This paper gives strong statistical evidence that the probability distributions of the execution time of that algorithm exhibits a heavy tail with an hyperbolic probability decay for long executions, which explains the erratic performance of different executions of the algorithm. Three different restart strategies have been incorporated in the algorithm to mitigate the problems associated to heavy tail distributions: the first assumes full knowledge of the execution time probability distribution, the second and third assume no knowledge. These strategies exploit the fact that the probability of finding a solution in short executions is non-negligible and yield a severe reduction, both in the expected execution time (up to one order of magnitude) and in its variance, which is reduced from an infinite to a finite value.