bluuebunny/crossref_metadata_2025 huggingface dataset:
Glutamatergic calcium dynamics and deregulation of rat retinal ganglion cells
Authors: Hartwick Andrew T. E. , Hamilton Claire M. , Baldridge William H.
Published: May 2008

A rise in intracellular calcium levels ([Ca2+]i) is a key trigger for the lethal effects of the excitatory neurotransmitter glutamate in various central neurons, but a consensus has not been reached on the pathways that mediate glutamate‐dependent increases of [Ca2+]iin retinal ganglion cells (RGCs). Using Ca2+imaging techniques we demonstrated that, in the absence of external Mg2+, the Ca2+signal evoked by glutamate was predominantly mediated by NMDA‐type glutamate receptors (NMDA‐Rs) in immunopanned RGCs isolated from neonatal or adult rats. Voltage‐gated Ca2+channels and AMPA/kainate‐Rs contributed a smaller portion of the Ca2+response at saturating concentrations of glutamate. Consistent with NMDA‐R involvement, extracellular Mg2+inhibited RGC glutamate responses, while glycine had a potentiating effect. With Mg2+present externally, the effect of AMPA/kainate‐R antagonists was enhanced and both NMDA‐ and AMPA/kainate‐R antagonists greatly reduced the glutamate‐induced increases of RGC [Ca2+]i. This finding indicates that the primary contribution of AMPA/kainate‐Rs to RGC glutamatergic Ca2+dynamics is through the depolarization‐dependent relief of the Mg2+block of NMDA‐R channels. The effect of glutamate receptor antagonists on glutamatergic Ca2+signals from RGCs in adult rat retinal wholemounts yielded results similar to those obtained using immunopanned RGCs. Additional experiments on isolated RGCs revealed that during a 1 h glutamate (10–1000 μm) exposure, 18–28% of RGCs exhibited delayed Ca2+deregulation (DCD) and the RGCs that underwent DCD were positive for the death marker annexin V. RGCs with larger glutamate‐evoked Ca2+signals were more likely to undergo DCD, and NMDA‐R blockade significantly reduced the occurrence of DCD. Identifying the mechanisms underlying RGC excitotoxicity aids in our understanding of the pathophysiology of retinal ischaemia, and this work establishes a major role for NMDA‐R‐mediated increases in [Ca2+]iin glutamate‐related RGC death.
Three-Dimensional Finite Element Simulation of Nonlinear Dynamic Rotor Systems of a Turbocharger
Authors: Kozhenkov Anatoly A. , Deitch Rafail S.
Published: May 2008

This paper presents the modeling procedure for a high-velocity rotor system (RS) combined with sliding bearings. The equations for motion of the RS parts were derived based on the model of a rotating elastic medium. Lubrication layers have been calculated with the use of the Reynolds equations. The discretization of the RS model has been carried out using three-dimensional contact finite element method and two-dimensional method of finite differences. The integration with respect to time is performed by an absolutely stable step-by-step method. The paper also compares and discusses computed and experimental amplitude-frequency characteristics of the self-oscillating turbocharger’s RS. The values of dynamic loads in parts, as well as reactions, clearances, and losses in bearings, computed based on the presented modeling procedure make the RS designing more accurate and reliable.
Self-Similarity in Vibration Time Series: Application to Gear Fault Diagnostics
Authors: Loutridis S. J.
Published: May 2008

The vibration time series of gear systems exhibit self-similarity. The time-series behavior is characterized by an exponent, known as the scaling exponent. An algorithm is proposed for the estimation of both global and local exponents, thus providing a means of examining the time-series fine structure. The proposed algorithm is applied to experimental data recorded from gear pairs with localized defects in the form of bending fatigue cracks. It is shown that an examination of the exponent empirical histogram allows detection of damage at an early stage and also provides an estimate of the defect magnitude.
A Nonlinear Fracture Mechanics Approach to Modeling Fatigue Crack Growth in Solder Joints
Authors: Bhate D. , Chan D. , Subbarayan G. , Nguyen L.
Published: May 2008

Predicting the fatigue life of solder interconnections is a challenge due to the complex nonlinear behavior of solder alloys and the importance of the load history. Long experience with Sn–Pb solder alloys together with empirical fatigue life models such as the Coffin–Manson rule have helped us identify reliable choices among package design alternatives. However, for the currently popular Pb-free choice of SnAgCu solder joints, designing accelerated thermal cycling tests and estimating the fatigue life are challenged by the significantly different creep behavior relative to Sn–Pb alloys. In this paper, a hybrid fatigue modeling approach inspired by nonlinear fracture mechanics is developed to predict the crack trajectory and fatigue life of a solder interconnection. The model is shown to be similar to well accepted cohesive zone models in its theoretical development and application and is anticipated to be computationally more efficient compared to cohesive zone models in a finite element setting. The approach goes beyond empirical modeling in accurately predicting crack trajectories and is validated against experiments performed on lead-free as well as Sn–Pb solder joint containing microelectronic packages. Material parameters relevant to the model are estimated via a coupled experimental and numerical technique.
Robust Optimal Balancing of High-Speed Machinery Using Convex Optimization
Authors: Li Guoxin , Lin Zongli , Allaire Paul E.
Published: May 2008

For high-speed rotating machinery, such as turbomachinery, the vibration caused by the rotor mass imbalance is a major source of maintenance problems. Vibration reduction by balancing under practical constraints and data uncertainty is often a challenging problem. In this paper, we formulate the problem of high-speed flexible rotor balancing as a convex optimization problem. This formulation not only solves the minmax balancing problem efficiently, but also allows the inclusion of various practical constraints. This formulation can be extended in a generalized unified balancing approach, which combines the advantages of both the influence coefficient approach and the modal balancing. Furthermore, a robust balancing approach is also developed to handle uncertainties in the influence coefficient and in the vibration response. This robust balancing approach provides the safeguard for the worse case scenario under the unknown but bounded uncertainty. All the resulting optimization problems are solved by second order cone programming. A large turbine generator balancing case is used to demonstrate that the proposed balancing technique provides the flexibility and efficiency beyond those of the existing balancing methods.
Experimental and Modeling of the Stress-Strain Behavior of a BGA Interconnect Due to Thermal Load
Authors: Zhang Yan , Liu Johan , Larsson Ragnar
Published: May 2008

A plastic ball grid array component interconnect has been experimentally investigated and modeled on the basis of micropolar theory. The experimental results were analyzed, and the data also provided the verification for the micropolar interface model. Two different interconnect cross sections, namely, one near the component boundary and the other in the center region beneath the chip, have been measured. The effects of thermal cycling on the interconnect deformation have been considered. The deformation fields, due to the mismatch of the material properties of the constituents in the assembly system, have been observed by means of a multifunction macro-micro-moiré interferometer, whereby the displacement distributions have been obtained and analyzed for the different specimens. The interconnect layer is usually of smaller size as compared to the neighboring component, and there are even finer internal structures included in the interconnect. The scale difference makes conventional methods time consuming and of low efficiency. An interface model based on the micropolar theory has been developed, cf. Zhang, Y., and Larsson, R., 2007, “Interface Modelling of ACA Flip-Chip Interconnects Using Micropolar Theory and Discontinuous Approximation,” Comput. Struct., 85, pp. 1500–1513, Larsson, R., and Zhang, Y., 2007, “Homogenization of Microsystem Interconnects Based on Micropolar Theory and Discontinuous Kinematics,” J. Mech. Phys. Solids, 55, pp. 819–841, aiming at predicting the interconnect behavior under thermal load, especially when there exist internal structures in the interface and the component/structure sizes vary in a wide range. Numerical simulations, using the micropolar interface model, show a fairly good agreement between the experimental data and the numerical simulations.
On Failure Mechanisms in Flip Chip Assembly—Part 1: Short-Time Scale Wave Motion
Authors: Oh Yoonchan , Suh C. Steve , Sue Hung-Jue
Published: May 2008

The demand for higher clock speed and larger current magnitude in high-performance flip chip packaging configurations of small footprint has raised the concern over rapid thermal transients and large thermal spatial gradients that could severely compromise package performance. This paper explores coupled electrical-thermal-mechanical multiphysics to evaluate the concern and to establish the knowledge base necessary for improving flip chip reliability. It is found that within the first few hundreds of nanoseconds after power-on, there are fast-attenuating, dispersive stress waves of extremely high frequency propagating in the package. The concepts of high cycle fatigue, power density, and joint time-frequency analysis are employed to characterize the waves along with the various damage modes resulting from the propagation of these short-lived dynamical disturbances in bulk materials and along bimaterial interfaces. A qualitative measure for failure is developed to evaluate the extent of damage inflicted by short-time wave motion. Damages identified in this study are in agreement with physical failure modes commonly seen in industry, thus implying that micron scale cracks or interfacial adhesion flaws initiated at the short-time scale would be further propagated by the coefficient of thermal expansion induced thermal stresses at the long-time scale and result in eventual electrical disruptions.
Studies on Size and Lubricant Effects for Fluidic Self-Assembly of Microparts on Patterned Substrate Using Capillary Effect
Authors: Lin Cheng , Tseng Fangang , Chieng Ching-Chang
Published: May 2008

Conventional pick-and-place technology platform in handling microscale component assembly processes has technical limitations in terms of capacity, efficiency, and accuracy. The fluidic self-assembly (FSA) approach employs a lubricant fluid carrying micropart flows over a target wafer patterned with binding sites, which results in part-substrate attachment. This technique transports microparts from one location to another with orientation control and parallel sorting. The present study demonstrates a FSA approach for fast, economic, and precise handling of microscale parts with square (few are in rectangular) shapes. The microparts fabricated from silicon-oxide wafers and ranging in size from 350×350×170μm3to1000×1000×440μm3 aligned and filled to designated sites in the substrate under water. The effects of micropart sizes and lubricants on the FSA processes are compared. This study provides a fundamental analysis for achieving and optimizing the self-alignment. The polymer or solder adhesion force of the square-patterned micropart immobilized at the larger binding sites were estimated to be 117±15μN and 510±50μN, respectively, which results in higher assembly yield of up to 100% for these samples.
Determination of Discharge Coefficient for Ball Valves With Calibrated Inserts
Authors: Rouss Gino James , Janna William S.
Published: May 2008

The valve coefficient was measured for 1/2-, 3/4- and 1 nominal ball valves. It was desired to use a recently designed orifice insert with these valves to obtain smaller valve coefficients. Orifice inserts were placed into the body of a threaded ball valve just upstream of the spherical control element. The valve coefficient was measured for each insert, and an expression was determined to relate the orifice diameter to other pertinent flow parameters. Two groups were chosen to correlate the collected data, and a graph was developed. These results can be used as an aid in sizing the orifice insert needed to obtain the desired valve coefficient. The study has shown that a two parameter power law equation can be used as an aid in predicting the desired results. Knowing pipe size and schedule, the diameter of the orifice insert needed to obtain the desired valve coefficient can be approximated with minimum error. An error analysis performed on the collected data shows that the results are highly accurate, and that the experimental process is repeatable.
Numerical Modeling of a Mechanical Structure Coupled to a Fluid Line Subsystem
Authors: Catania Giuseppe , Naldi Giovanni
Published: May 2008

Mechanical system modeling and simulation of its dynamic behaviour is a commonly required task in many industrial fields. Fluid transmissions are frequently employed in some applications, and some standard techniques are known to obtain a consistent dynamic model of a fluid line, including the contribution of inertia, compressibility and friction. When fast transient phenomena are to be studied, the full mechanical system including structural and fluid components should be modeled in advance, so that the system designer can avoid a possible critical behaviour. In this work, full fluid piping modeling is first investigated by means of one- and bi-dimensional approaches. It can be shown that a secondary effect, such as laminar flow frequency dependent friction, may consistently improve the accuracy of the simulated line response. The analytical coupling between the discrete model of mechanical substructures, elastically and fluid coupled by a secondary fluid continuous subsystem, is investigated. The formulation of a non standard eigenproblem is proposed to obtain the main full dynamical system properties, such as eigenvalues and shapes. A numerical application example is reported, and results are discussed in detail.
A Novel Silicon Base Piezoresistive Pressure Sensor Using Front Side Etching Process
Authors: Peng Chih-Tang , Lin Ji-Cheng , Lin Chun-Te , Chiang Kuo-Ning , Shie Jin-Shown
Published: May 2008

By applying the etching via technology, this study proposes a novel front-side etching fabrication process for a silicon based piezoresistive pressure sensor to replace the conventional backside bulk micro-machining. The distinguishing features of this novel structure are chip size reduction and fabrication costs degradation. In order to investigate the sensor performance and the sensor packaging effect of the structure proposed in this research, the finite element method was adopted for analyzing the sensor sensitivity and stability. The sensitivity and the stability of the novel sensor after packaging were studied by applying mechanical as well as thermal loading to the sensor. Furthermore, the fabrication process and the sensor performance of the novel pressure sensor were compared with the conventional back-side etching type pressure sensor for the feasibility validation of the novel sensor. The results showed that the novel pressure sensor provides better sensitivity than the conventional one, and the sensor output signal stability can be enhanced by better packaging structure designs proposed in this study. Based on the above findings, this novel structure pressure sensor shows a high potential for membrane type micro-sensor application.
Quantifying Effects of Controlling Factors on Flow and Stress Distribution in Stenotic Arteries With Lipid Cores
Authors: Tang Dalin , Yang Chun , Kobayashi Shunichi , Ku David N.
Published: May 2008

2D and 3D multi-physics experiment-based nonlinear models with fluid-structure interactions (FSI) and structure-structure interactions (SSI) are introduced to model blood flow and stress/strain distributions in stenotic arteries with lipid pools. Material properties for the vessel and plaque are based on experimental measurements and information available in the literature (Huang et. al., 2001; Tang et. al., 2001). The Navier-Stokes equations are used as the governing equations for the fluid. Mooney-Rivlin models are used for both arteries and lipid cores. A well-tested finite element package ADINA is used to solve the models to perform flow and stress/strain analysis. Our results indicate that artery plaque stress/strain distributions are affected considerably (50%–400% or even more) by vessel material properties, stenosis severity and eccentricity, tube axial pre-stretch, pressure conditions, lipid core material property, size, position and geometry, and fluid-structure and structure-structure (vessel wall and lipid core) interactions. Differences in model assumptions and controlling factor specifications must be taken into consideration when interpreting the significance of computational results.
Development of a Magnetic Targeting Device Applied to Interlocking of Distal Intramedullary Nail Screw Holes
Authors: Szakelyhidi David C.
Published: May 2008

A magnetic targeting device was developed to assist orthopedic surgeon’s with distal interlocking of intramedullary nails, in which the novel device aligns the surgeon’s drill at the correct location for drilling. This device has significant advantages over current technology, being percutaneous, portable, and using no fluoroscopy for targeting. This device can allow shorter surgery, decreased radiation exposure, and fewer complications for the surgeon and patient.
A Planar Fabricated 1-3 Composite Ultrasonic Transducer to Determine the Dynamic Response of Microstructures
Authors: Lai Wen Pin , Fang Weileun
Published: May 2008

A novel excitation device using pulsed 1–3 composite ultrasonic transducer is presented. This composite transducer generates a bulk acoustic wave (BAW) to impact the microstructures like a hammer. Thus, a broad bandwidth and constant power spectrum for the vibration test of microstructures are available. The characteristics of a BAW hammer produced with the 1–3 composite transducer were simulated by commercial software PIEZOCAD. According to the proposed wafer level fabrication process of the 1–3 composite BAW hammer, it is possible to design the 1–3 composite BAW hammer to generate an impulse with a specific waveform. Thus the natural behavior of the microstructure within a specific frequency range can be determined. The experimental results of a BAW hammer with composite structure agree well with the simulation predictions. Moreover, the dynamic response of microstructures including the resonant frequency, mode shape and the modal damping can be measured in a single impulse excitation. Since the measurement apparatus is readily to be built, this approach has the potential to do the on-line test for batch production.
Design, Analysis, and Testing of Electrostatically Actuated Micromembranes
Authors: Yeary Lucas , Cunningham Glenn , Panduga Nagesh , Darvennes Corinne , Walsh Kevin , Crain Mark , Cohn Robert W. , Harfenist Steven A. , Frolik Jeff
Published: May 2008

This paper reports a numerical design analysis of electrostatically actuated micromembranes. We systematically compare membrane performance in terms of natural frequencies, pull-in voltage (the bias voltage at which the membrane contacts the base electrode) and the effects of variable leg lengths for a given membrane size. Some experimental data on membrane deflection profiles versus bias voltage is included along with some experimentally determined pull-in voltages. Polysilicon micromembranes were successfully fabricated using the low cost MUMPs process that limits the user to three structural layers. The devices are designed with an emphasis on the response of the membrane to applied DC bias voltage to allow for variable stiffening. Circular membranes with diameters ranging from 60 to 160 μm, suspended 2 μm over square back plates of side lengths varying from 60 to 140 μm are investigated for voltages up to 90 volts. Three-dimensional electromechanical finite element simulations have been performed. Pull-in voltage values from simulations compare favorably with the measured results. It was observed that, for maximum deflection of the membrane upon application of DC bias voltage, the optimal dimensions for back plate and top membrane should fall within the ranges 80–120 μm and 80–140 μm, respectively.
Global Stress-Strain Relationship of a Beating Heart
Authors: Zhao Fuzhang , Chen Jim S. J. , Blagg Andrew G. , Margulies Kenneth B.
Published: May 2008

An integrated computational-experimental method was developed to characterize the global nonlinear elastic stress-strain behavior of a beating rat heart. This method combines finite element (FE) simulation with the experimental end-diastolic cavity pressure- balloon volume relationship of left ventricle (LV) to characterize the deformation resistance of a beating heart. In the FE simulations, the hyperelastic Ogden strain energy potential was used and geometric nonlinearity was also considered. The elastic moduli for the ex-vivo rat heart obtained through the study vary from 0.003 to 0.577 MPa.
An Investigation of Damping Mechanisms in Translational Euler-Bernoulli Beams Using a Lyapunov-Based Stability Approach
Authors: Dadfarnia Mohsen , Jalili Nader , Dawson Darren M.
Published: May 2008

A translational cantilevered Euler-Bernoulli beam with tip mass dynamics at its free end is used to study the effect of several damping mechanisms on the stabilization of the beam displacement. Specifically, a Lyapunov-based controller utilizing a partial differential equation model of the translational beam is developed to exponentially stabilize the beam displacement while the beam support is regulated to a desired set-point position. Depending on the composition of the tip mass dynamics assumption (i.e. body-mass, point-mass, or massless), it is shown that proper combination of different damping mechanisms (i.e., strain-rate, structural, or viscous damping) guarantees exponential stability of the beam displacement. This novel Lyapunov-based approach, which is based on the energy dissipation mechanism in the beam, brings new dimensions to the stabilization problem of translational beams with tip mass dynamics. The stability analysis utilizes relatively simple mathematical tools to illustrate the exponential and asymptotic stability results. The numerical results are presented to show the effectiveness of the controller.
Reciprocating Battery Cooling for Hybrid and Fuel Cell Vehicles
Authors: Park Chanwoo , Jaura Arun K.
Published: May 2008

Traction batteries for hybrid and fuel cell vehicles must maintain temperatures within operational limits for longer battery lifetime and better performance. The uneven battery temperature due to improper heat transfer during discharging/charging could accumulate battery degradation on hot cells resulting in early failure of the battery pack. Current battery systems use a unidirectional coolant flow for battery thermal management. However, due to the nature of the cooling method, the unidirectional cooling systems are prone to show a largest temperature differential ΔTs between the battery cells at fixed flow boundaries, although sophisticated thermal/fluid designs are implemented to make the battery temperature uniform. Here, an innovative battery cooling method ([1]) using a reciprocating cooling flow is proposed. The reciprocating cooling system switches the coolant flow direction periodically by a valve-fan mechanism. By switching the flow direction periodically and thus the cold and hot boundaries of the battery cooling system, the battery cell temperatures are regulated with a very small fluctuation and the temperature differential ΔTs is drastically reduced. In hybrid electric vehicle and fuel cell vehicle applications, the cooling improvement using the new concept would set battery cooling system free of auxiliary air-conditioning system. Parametric study shows that using the reciprocating cooling system for a Li-Ion battery system, an optimum reciprocating period to minimize temperature differential ΔTs and maximum battery temperature Ts,max exists.
Advances in Actuation Systems to Improve Vehicle Performance and Safety
Authors: Brader John S. , Trevett Nathan R. , Rocheleau David N.
Published: May 2008

Actuation and modeling for drive-by-wire applications are discussed. Previous work in advanced actuation for two automotive systems, active suspension and camless engines, is surveyed, outlining the major advancements throughout the previous decade. More recent research in these areas is discussed and focuses on recent improvements to system modeling and design. Specifically, a four-corner suspension model and a piezoelectric piloted hydraulic actuator for engine valve actuation are introduced. The four-corner suspension model addresses the three-dimensional parameters associated with active suspension design and improves upon the accepted quarter-car model. The piezoelectric based camless engine actuator is introduced as the next generation of camless engine actuation systems and addresses control issues through the relationship between input voltage and piezoelectric displacement.
Systematic State Equation Derivation for Linear Systems Using the Normal Tree Method
Authors: Altun Kerem , Platin Bu¨lent E. , Balkan Tuna
Published: May 2008

A systematic method to derive the state equations of a linear system starting from its linear graph is proposed. The normal tree is used in the analysis, which is a method to determine the dependencies between energy storage elements in the system. An algorithm to list all normal trees of a system graph is developed, which enables the determination of energy-based state variable sets and corresponding state equations. A computer program is developed to realize these algorithms, which derives the state equations of a system, given its linear graph.
On the Expansion of Nonlinear Models Using Bell-Shaped Basis Functions
Authors: Kiriakidis Kiriakos
Published: May 2008

We propose a method that approximates any nonlinear model, without regard to complexity, by minimizing its distance from a rich model set. The method produces, potentially through an automated procedure, the approximation of the nonlinear dynamics in the form of a finite expansion associated with certain basis functions and provides an upper bound on the approximation error.
Reduction of NOx Emission of Heavy Duty Gas Turbines by Improving Mixing Quality Using CFD Tools
Authors: Geng Weiqun , Pennell Douglas , Bernero Stefano , Flohr Peter
Published: May 2008

Jets in cross flow are one of the fundamental issues for mixing studies. As a first step in this paper, a generic geometry of a jet in cross flow was simulated to validate the CFD (Computational Fluid Dynamics) tool. Instead of resolving the whole injection system, the effective cross-sectional area of the injection hole was modeled as an inlet surface directly. This significantly improved the agreement between the CFD and experimental results. In a second step, the calculated mixing in an ALSTOM EV burner is shown for varying injection hole patterns and momentum flux ratios of the jet. Evaluation of the mixing quality was facilitated by defining unmixedness as a global non-dimensional parameter. A comparison of ten cases was made at the burner exit and on the flame front. Measures increasing jet penetration improved the mixing. In the water tunnel the fuel mass fraction within the burner and in the combustor was measured across five axial planes using LIF (Laser Induced Fluorescence). The promising hole patterns chosen from the CFD computations also showed a better mixing in the water tunnel than the other. Distribution of fuel mass fraction and unmixedness were compared between the CFD and LIF results. A good agreement was achieved. In a final step the best configuration in terms of mixing was checked with combustion. In an atmospheric test rig measured NOx emissions confirmed the CFD prediction as well. The most promising case has about 40% less NOx emission than the base case.
A Numerical Simulation of Oxide Formation During the Melting of Aluminum in Aluminum Furnace
Authors: De Anindya Kanti , Mukhopadhyay Achintya , Sen Swarnendu , Puri Ishwar K.
Published: May 2008

A significant amount of aluminum is processed by melting secondary aluminum that contains small amounts of magnesium. A major drawback of aluminum production in secondary melt furnaces is the formation of dross or aluminum oxide by the oxidation of the molten metal. Since aluminum scrap forms a major source of the metal in secondary aluminum processing, the presence of alloying elements plays a key role in the oxidation process. Here, we consider the early stage of oxidation of Al-Mg alloy, during which primarily oxidation of magnesium to magnesium oxide occurs. We have simulated the processes in an aluminum melting furnace and considered the metal oxidation to be limited by one-dimensional diffusion. Our results predict the temporal variation of the oxygen distribution and the rate of metal evaporation and formation of the metal oxide. The effects of melt composition, gas temperature and oxygen concentration in the gas are discussed.
Electrocapillary Piston Motion and a Prototype of Phase-Manipulating Micromirror
Authors: Wan Zhiliang , Feinerman Alan , Friedman Gary , Zeng Hongjun
Published: May 2008

In this paper we study the piston motion of a mercury droplet that is confined in a metal-plated micro-hole. This droplet is actuated by the electrocapillary effect and large displacements of up to 250μm are achieved with very low voltages (2V). We use a high-speed camera (10,000frames/s) to capture the piston motion and we find the resonance frequency is ~45Hz. The mercury droplet geometry in equilibrium state is analyzed based on Laplace equation and volume conservation. A mathematical model is developed and predicts a resonant frequency of mercury droplet and the value is found to be 119Hz. A prototype of piston-motion micromirror is also demonstrated in the experiment, with frequency of 400Hz and amplitude of ~8μm at 2V.
Effect of Tip Gap and Squealer Geometry on Measured Heat Transfer Over a HPT Rotor Blade Tip
Authors: Nasir Hasan , Ekkad Srinath V. , Kontrovitz David M. , Bunker Ronald S. , Prakash Chander
Published: May 2008

The present study explores the effects of gap height and tip geometry on heat transfer distribution over the tip surface of a HPT first stage rotor blade. The pressure ratio (inlet total pressure to exit static pressure for the cascade) used was 1.2, and the experiments were run in a blow-down test rig with a four-blade linear cascade. A transient liquid crystal technique was used to obtain the tip heat transfer distributions. Pressure measurements were made on the blade surface and on the shroud for different tip geometries and tip gaps to characterize the leakage flow and understand the heat transfer distributions. Two different tip gap-to-blade span ratio of 1% and 2.6% are investigated for a plane tip and a deep squealer with depth-to-blade span ratio of 0.0416. For a shallow squealer with depth-to-blade span ratio of 0.0104, only 1% gap-to-span ratio is considered. The presence of the squealer alters the tip gap flow field significantly and produces lower overall heat transfer coefficients. The effects of different partial squealer arrangements are also investigated for the shallow squealer depth. These simulate partial burning off of the squealer in real turbine blades. Results show that in some cases, partial burning of squealers along the pressure surface may be beneficial in terms of overall reduction in heat transfer coefficients over the tip surface compared to the plain tip.
Adaptive Mechatronic Suspension of Railway Vehicles: Focus on Lateral Dynamics
Authors: Choroman´ski Włodzimierz , Kisilowski Jerzy
Published: May 2008

The subject of research in this work are models of railway bogies with so-called mechatronic suspension. The author presents concepts of the railway bogies construction in which the suspension parameters are controlled electronically by a computer control unit. The main purpose of the control is to stabilise the motion of the railway vehicle on the straight track and to ensure good guiding features on curved track. In the case of the classic solution for railway bogies a simultaneous fulfilment of both requirements imposes a contradictory requirement on the suspension parameters. It seems that a mechatronic suspension which has adaptively changeable parameters can overcome these difficulties. The authors propose fuzzy controllers to the synthesis of the control unit.
Model of Multiscale Transport in Carbon Foams
Authors: Druma C. , Alam M. K. , Druma A. M.
Published: May 2008

A number of carbon foam products are being developed for use as insulation, heat spreaders, and compact heat exchanger cores. Such foams have voids that are typically of the order 100 microns, and pore walls are about 10 microns. Within the walls of the pores, the graphene planes are arranged anisotropically so that the thermal transport is highly dependent on the orientation of the bulk foam. This results in bulk conductivities that range from 1 W/mK to 200 W/mK. The bulk properties of such a porous medium are difficult to determine analytically, particularly for the case of high concentration of non-spherical pores, or when the porous material is anisotropic or non-homogeneous. A finite element analysis has been developed to calculate the bulk thermal conductivity of carbon foams containing micropores of different shapes. The effective thermal conductivity is then evaluated by comparing the results of the analytical and numerical models.
CFD Modeling of Cross Corrugated Microturbine Recuperator
Authors: Hejcˇi´k Jirˇi´ , Ji´cha Miroslav
Published: May 2008

The CFD code STAR CD was used to assess the thermal and hydraulic performance of a primary surface type gas turbine recuperator, with Cross Corrugated (CC) surface. The main goal of CFD modeling was to evaluate heat transfer and pressure drops predicted by the 1D methodology and thus to verify the recuperator efficiency. Two computational domains were made. The first for heat transfer and pressure drops simulation in the recuperator core and the latter for pressure drops predicted at the inlet and outlet ports. Details of the recuperator core, computational domains and the boundary conditions for CFD simulation as well as relevant results are presented.
Pyrolysis Characteristics of Biomass Resources
Authors: Yamamiya Takashi , Ota Masahiro , Mozammel Hoque Md. , Murakami Kazuhiko
Published: May 2008

This study deals with understanding pyrolysis mechanism of various biomass resources, such as wood chip, dead leaves, coffee grounds and paper. At the same time, the pyrolysis gases at various temperatures were analyzed, such as 773K, 1023K and 1273K. Thermogravimetric technique is used to investigate the thermal decomposition mechanism. The pyrolysis gases of all samples were analyzed by gaschromatograph every temperature for 150min. The gas pressure increasing by pyrolysis was measured, and compared with all samples for understanding gas generation.
Advanced Design of Worm Wheels Made of Dissimilar Materials
Authors: Vorel Michal , Leidich Erhard
Published: May 2008

In order to provide the necessary wear and friction features in a worm gear, the worm wheels are often made of specific material, mainly bronze. Considerable material cost reduction is achieved by substituting the inner part of the wheel by a steel hub, which is joined with the bronze toothed rim by various means. In this paper, results of research to the optimum design and production of the wheel welded by the electron beam technology are presented. Namely, the crack distribution in the weld and residual stresses in the whole wheel were invetigated and an improved welding technology along with a modified weld geometry were proposed to eliminate the cracks considerably. The new welding technology is also applicable to gear wheels made of similarly related material combinations.
Approach to Meet an Overall Transient Performance Criterion of a PEM Fuel Cell System
Authors: Pedersen Peder , Korsgaard Anders R. , Christensen Morten O.
Published: May 2008

Fuel Cells have been intensely researched and developed in the recent decade, where especially the fuel cell MEA (Membrane Electrode Assembly) and stack have been the main focus. Now the system control components surrounding the fuel cell have been given more attention. This paper gives a novel system approach of setting up the demands for control components such as valve actuators for a PEM (Proton Exchange Membrane) fuel cell system in order to meet an overall transient system performance criterion. Overall control considerations are treated, and the major time constants of the sub-systems are analyzed. The result is a method for specifying dynamic performance criteria for the individual control components. By proper selection of the components it can be shown that the electric load buffer may be omitted due to the internal capacitance of the fuel cell. Test results from a 2.5 kW PEM fuel cell test facility show close agreement with simulation results from the novel system approach.
The Measurement and Prediction of Boundary Layer Entropy Generation Rate
Authors: Walsh E. J. , Davies M. R. D.
Published: May 2008

In this paper hot wire measurements of the boundary layer velocity profiles at discrete locations along the suction surface of a turbine blade profile are presented. The measured aerodynamic data is transformed into thermodynamic data by way of the entropy function for the investigated Reynolds numbers of 76,000, 120,000 and 185,000 based on inlet velocity and chord length. The measurements are compared with predictions obtained from a commercially available computational fluid dynamics code and a prediction technique based on semi-empirical correlations. Interestingly the accuracy of the relatively simple semi-empirical technique, in respect to entropy production, is found to be comparable to that of the time consuming CFD code over the range of Reynolds numbers tested.
A Batch Fabricated Linear Synchronous Motor
Authors: Fo¨hse Martin , Sto¨lting Hans-D. , Edler Jens , Gatzen Hans H.
Published: May 2008

Micro electro-mechanical systems (MEMS) technology opens up new ways of miniaturizing electromagnetic motors. A very promising approach for building miniature linear actuators is to fabricate the stator as well as the traveler separately and merging the motor components in a microassembly process [1]. This paper describes design, fabrication, and evaluation results of a linear synchronous actuator following this basic approach.
An Actively Controlled Harmonic Force Generator
Authors: Mikus Oldrich , Olgac Nejat , Sipahi Rifat
Published: May 2008

The electromagnetic shakers (also known as voice coil actuators) are commonly utilized for computer controlled force applications. When the force trace becomes harmonic, however, the devices which use rotating eccentric masses are more feasible to operate. If, on the other hand, one wishes to vary three descriptors, the amplitude, frequency and the phase angle of these harmonics the design and the operation of the structure become more challenging. A novel design and control are presented in this paper to achieve this objective with a very favorable ratio between the peak force and the weight. The variation in the force amplitude is taken from zero to Fmax, while the frequency range varies about ±10% around the nominal operating frequency. Indefinite variations of relative phase angle (i.e., zero to 2π) with respect to a given harmonic signal can be achieved using this new device. The transition from a set of the tree descriptors to another set is achieved under an open loop control of the device. On a prototype experimental setting we demonstrate a successful deployment of the control. Such a structure can be used in some cases for generating desired harmonic force excitations, and in some mission critical application, for canceling vibration caused by quasi static harmonic forcing.
Thermal Characterization and Optimization of Active System IPEM
Authors: Pang Ying-Feng , Scott Elaine P.
Published: May 2008

An in depth parametric study was conducted to optimize the thermal performance of an active system integrated power electronic module (IPEM). Commercial finite element software was utilized in these analyses. Design parameters included material selection, geometry, and placement. Model-based optimization software tool were investigated for use in this procedure and demonstrated promise in automating the design process.
Simulation and Design of E. Coli-Based Rotary Micropump for Use in Microfluidic Systems: Integration of Micro-Nano-Bio
Authors: Al-Fandi Mohamed G. , Malshe Ajay P. , Sundaram Shankar , Jenkins Jerry , Tung Steve , Kim Jin-Woo
Published: May 2008

This paper presents the results of the computational fluid dynamic (CFD) modeling of viscous fluid flow in a novel cell motor actuated micropump. A cell motor is a bacterial flagellar cell tethered to a surface by a single flagellum, this flagellum acts as a pivot around which the cell body rotates. As a test case for investigation, the micropump consisted of two Escherichia coli cell motors tethered to the bottom of a microchannel with fixed dimensions. The CFD modeling of the micropump was performed using CFD-ACE+ simulation software (CFD Research Corporation). The biological cell motor was modeled as an ellipse with constant rotational speed of 10 Hz clockwise. The results of this model demonstrated the effect of the biological cell motor placement within the microchannel, as well as the rotational phase between the two biological cell motors, on the volumetric flowrate. Pumping action was observed as the cell motor location was moved adjacent to the sidewall of the microchannel. The rates of fluid pumping were of the order of 11 pL/hr when the cell motors were rotating in phase and their placement was close to the sidewall of the microchannel.
Evolutionary Based Optimal Synthesis of Four-Bar Mechanisms
Authors: Koladiya D. , Shiakolas P. S. , Kebrle J.
Published: May 2008

Graphical and analytical syntheses have been well applied to path, motion and function generation of planar mechanisms. Optimization techniques in common, require “good initial guesses” and do not necessarily converge to a solution. This paper presents a methodology to synthesize mechanisms employing an evolutionary optimization approach technique known as Differential Evolution. The initial bounds for the design variables are defined automatically using a newly developed and novel technique called the Geometric Centroid of Precision Points. Optimum synthesis of four-bar linkages for path generation with user defined accuracy level at required precision points is discussed.
Bistable Nature of the Hydrophobic Contact Angle on Rough Surfaces
Authors: He Bo , Patankar Neelesh A. , Lee Junghoon
Published: May 2008

This paper studies the bistable nature of the hydrophobic contact angle on the rough surfaces. It was experimentally shown that a droplet of liquid can liquid can form two different contact angles on a surface that has roughness patterns. External disturbances can cause a transition between the two different energy states. This paper verifies the theoretical prediction by matching experiments and establishes a design criterion for a robust hydrophobic rough surface on which the contact angle will not change due to external disturbances. This fact is critical in microfluidic applications, where a rough surface is used for applications based on wettability amplification.
CNT Extracted Lithography
Authors: Chung Jaehyun , Lee Kyong-Hoon , Lee Junghoon
Published: May 2008

High quality nanoscale gaps were fabricated using carbon nanotubes (CNTs) as shadow masks for metal deposition. We used electric-field guided assembly to deposit and individual multi-walled CNT (MWCNT) across a pair of electrodes. Metal was deposited by electron-beam evaporation on the substrate where MWCNT was assembled. Then, the MWCNT was removed by sonication, leaving a pattern that replicates the shape of the MWCNT. This approach enables a mass fabrication of well-defined nanoscale features aligned and positioned with high accuracy.
The Mechanical Behavior of a Micromachined PZT Membrane
Authors: Demir I. , Richards R. F. , Bahr D. F. , Richards C. D.
Published: May 2008

The mechanical behavior of a micromachined PZT membrane for power applications is investigated. The membrane is a bulk-micromachined silicon membrane that supports a thin film of piezoelectric ceramic (PZT) sandwiched between platinum and gold electrodes. The membrane undergoes large periodic deflections to convert mechanical power to electrical power in a micro heat engine. An analysis using a variational approach is developed to find an approximate closed from solution based on energy minimization. Experiments were conducted to obtain material properties, residual stresses, and pressure deflection relationships. The modeled results compare well to the experimental results.
A Hybrid Adaptive and Robust Control Strategy for a Class of Linear Systems
Authors: Zhang Yisheng , Alleyne Andrew G.
Published: May 2008

This paper presents a hybrid control strategy to avoid the basic trade-off between performance and robustness for individual controllers. The hybrid control strategy utilizes a robust controller for guaranteed robustness and adequate performance when the plant model is not well known and/or in the presence of significant disturbances, and employs an adaptive controller for high performance after sufficient system information has been collected. Based on traditional dwell-time approaches, a coordinated dwell-time approach is developed and incorporated into the hybrid control strategy, which guarantees the global stability of the hybrid system for a class of linear systems, as well as combine the benefits of robust control and adaptive control.
Rapid Diagnosis of Inhomogeneity in Turbid Media
Authors: Wan Siew Kan , Guo Zhixiong , Kumar Sunil
Published: May 2008

In this work, a novel approach is proposed that would be able to rapidly diagnose the presence and location of inhomogeneity in turbid media. In this approach, ultrafast pulse laser is used as a detecting source and the time-resolved backscattered light signals are collected around the boundary of the target. The log slopes in the decaying log tail of the detected signals will be analyzed and used for the detection and image of embedded inhomogeneity. The relatively high absorption in the foreign object will result in a steeper log slope when the detector is located close to the object. A slim graphite of 1.6 mm in diameter embedded in a tissue phantom has been successfully detected in a preliminary experiment and the location of the graphite is determined from the v-groove profile of log slopes. A Monte Carlo program has been developed to further simulate and investigate the feasibility and quality of this method to diagnose the presence of a tumor-like material embedded inside a highly scattering media. A 2D reconstructed image confirms the potential of this novel method to detect and image accurately and rapidly the presence of tumors in biological tissues.