bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Particulate Filtration of Alumina Nano-Particles in VARTM Processing of Hybrid Composites
Authors: Akinyede Oladapo , Sankar Jag , Mohan Ram , Kelkar Ajit
Published: May 2009

Hybrid composites composed of particulate inclusion in the resin for fiber reinforced plastics are manufactured using the low-cost vacuum assisted resin transfer molding (VARTM) composite technology. Particulate inclusions are known to influence to some degree, the thermo-mechanical properties of resin systems and are dispersed in the resin before fabrication by this low cost processing technique. Particulates are dispersed in resin systems via ultrasonic agitation to obtain exfoliated/ intercalated particle dispersion morphology. Highly dispersible grade particulate boehmite nano-alumina with 110nm mean particle size was pre-dispersed in a low viscosity epoxy resin prior to VARTM processing. Fiber lay-up with high tow density (10K) S-glass fabric was impregnated. The flow regime of the infused modified resin and the mold setup configuration influence the percolation and filtration of the particulates in the mold lay-up. The occurrence of filtration depends on the mold lay-up configuration and flow regime. The flow pattern is varied to induce filtration by transverse percolation through the distribution media and through-fabric longitudinal flow schemes (without distribution media). Resin samples from the flow front were collected and are studied via thermo-gravimetric analysis (TGA). The dynamics of particulate flow and the potential filtration effects due to the fiber lay-up during the infusion of low viscosity resin are studied. These are based on analyzing the residual mass of the 110nm alumina particles in epoxy resin that is collected after infusion through the fiber lay-up during the manufacture of advanced hybrid composite.
Design and Development of a Safety Vacuum Release System
Authors: Levin Alan R.
Published: May 2009

The U.S. Consumer Product Safety Commission collects data on entrapments from suction in suction outlets in swimming pools and Spas. There are currently two national specifications for the testing and marking of manufactured safety vacuum release systems for swimming pools, spas and hot tubs: ASTM designation F2387-04 Standard Specification for Manufactured Safety Vacuum Release Systems (SVRS) for Swimming Pools, Spas and Hot Tubs, and ASME A112.19.17-2002 Manufactured Safety Vacuum Release Systems (SVRS) for Residential and Commercial Swimming Pool, Spa, Hot Tub, and Wading Pool Suction Systems. Over the last two years an electronically controlled system, containing several safety functions, in addition to those specified in the standards, has been developed, tested by an outside laboratory and certified to meet both the applicable standards. This paper includes the results of the testing and changes to the system to meet both the specifications and internal worse case failure analysis. This paper compares and contrasts the two applicable standards, as well as detailing the results of testing both in the laboratory and in the field.
An Investigation on Effect of Workpiece Reinforcement Percentage on Tool Wear in Cutting Al-SiC Metal Matrix Composites
Authors: Avinash C. , Ramaswamy S. , Raguraman S. , Muthukrishnan N.
Published: May 2009

The tool wear mechanism in machining of metal matrix composites (MMC) and its dependence on the percentage of reinforcements with MMC was investigated. Silicon carbide metal matrix composites of two samples were prepared by using stir casting method. Samples having 10 percentage & 20 percentage of silicon carbide particles (grain size ranging from 55 to 85 micron meter) by weight were fabricated in the form of cylindrical bars. Experiments were conducted in medium duty lathe by using poly crystalline diamond (PCD) insert of 1500 grade as cutting insert and the experiment was performed by using design of experiments (L27 orthogonal array) on two different samples and the parameters obtained were optimized by analyzing the power consumed by main spindle and surface finish of machined component. The results from machining of this fabricated Aluminum Alloy A356, reinforced with SiC particles MMC is highlighted in this paper. All trails were carried out with time duration of one minute. By setting these optimum parameters, tool wear study was carried out till the flank wear reached 0.4mm. The results showed that tool life was minimum while machining 20 percentage of SiC reinforcement MMC as compared with 10 percentage of SiC reinforcement. The tool wear images were captured by Cam scope with a magnification of 100X which supports the results.
The Structure Micro-Vibration Response Analysis of Large Scale Precision Mirror Mount
Authors: Zhou Hai , Zhang Jun-Wei , Lin Dong-Hui , Zhou Yi
Published: May 2009

The stability of Laser beams in the high power solid laser facility is the guarantee of target practice successfully, so the laser beams have a strict request to the stability of all kind of optical elements and their mounts structure in the facility. Broadband Ambient Vibration, local vibration, transient temperature change and so on are all the factors that cause the instability of mirror mount. Among these factors, broadband ambient vibration takes a large percentage. Aiming at the problem of a large scale precision mirror mount’s structure stability under the excitation of ambient vibration, this paper discusses the way of ambient vibration measuring by digital seismograph and data process method, gets the velocity spectrum from transforming the ground moving signal collected by digital seismograph, which can be used to the vibration response analysis of precision mirror mount. And then builds the finite element model of the switchyard mirror mount, uses the measured velocity spectrum as the loads, analyzes the response of mirror mount by the spectrum analysis module of ANSYS. The result indicates that the displacement of the choose points on the mirror mount are less than 1.0×10−6m when under exciting of measured velocity spectrum, which is inside the permitted limit. The analysis indicates that using the result measured by digital seismograph to analyze the mirror mount is reasonable and the ambient can satisfy the requirements of the mirror’s mount.
High Bandwidth Motion Control for Multi-Axis Servohydraulic Mechanisms
Authors: Plummer A. R.
Published: May 2009

A practical motion control method is presented for multiaxis parallel servohydraulic mechanisms in which the payload behaves as a rigid mass. The ability of this method to decouple the control axes is demonstrated. A modal control approach is used – i.e. the modes of vibration of the system are controlled individually. These modes are dependent on the inertial properties of the payload and the compliance of the actuators due to oil compressibility. For each mode, a partial non-linear dynamic inversion is performed in the control loop. To avoid the need to differentiate the position feedback signals, accelerometers are also used, and three-element motion state vectors are estimated using composite filtering. Command feedforward is used to increase the tracking bandwidth, and the closed-loop part of the controller can be conceived as a model-based disturbance observer. Simulation results are presented based on a detailed validated model of a large vibration table used for earthquake simulation. Just three of the six degrees-of-freedom of the table are considered, and the results for horizontal acceleration tracking response are presented, along with the ability of the controller to reject the ‘overturning moment’.
Mechanical Behavior and Toughness of Electrospun Polycaprolactone Nanofibers
Authors: Baji Avinash , Wong Shing-Chung , Blackledge Todd , Reneker Darrell , Tripatanasuwan Sureeporn
Published: May 2009

This study examines the toughness and mechanical properties of biodegradable poly(ε-caprolactone) (PCL) with varying hydroxyapatite (HAP) content (0 – 30 wt%). Fracture toughness of HAP-filled PCL was also examined for the electrospun fibers using the essential work of fracture (EWF) concept. The electrospun fibers exhibited a diameter ranging from 200–500 nm and a combination of HAP particle sizes ranging from (50–100 nm) under the SEM. The tensile stress-strain behavior and fracture toughness of electrospun nanofibers were assessed using a nanoforce tensile tester. The electrospun system showed a substantial increase in plane-stress essential work of fracture in comparison to bulk specimens processed from pellets. Toughness decreased as HAP loading increased. The effect of simulated body fluid (SBF) on the mechanical properties was also studied. Mechanical properties including tensile strength and modulus were found to increase with HAP concentration in general. Compression molded electrospun nanofibers were spatially confined such that the tensile strength and stiffness of molded and spun fibers are remarkably higher than those from molded specimen of pellets.
Performance Identification of a New Type of Speed Governor for Kaplan Turbines
Authors: Vasiliu N. , Manea I. , Calinoiu C. , Vasiliu D.
Published: May 2009

The paper contains a summary of the experimental results of a long-term research program aiming to design, manufacture, setup and full industrial test a new type of electro hydraulic digital speed governor for Kaplan water turbines. Computational methods, control software, design problems, and mainly performance validation are shortly presented. The work represents the second part of a final research report on the modern electro hydraulic speed control of the power units.
Flow Field Analysis of Dielectrophoretically-Suspended Particles
Authors: Williams Stuart J. , Wereley Steven T.
Published: May 2009

Understanding the fluid dynamics around a particle in suspension is important for a complete investigation of many hydrodynamic phenomena, including microfluidic models. A novel tool that has been used to analyze fluid velocity fields in microfluidics is micro-resolution particle image velocimetry (μPIV) [1]. Dielectrophoresis (DEP) is a technique that can translate and trap particles by induced polarization in the presence of nonuniform electric fields. In this paper, DEP has been used to capture and suspend a single 10.1μm diameter spherical particle in a microfluidic channel. μPIV is then used with smaller tracer particles (0.5μm) to investigate the hydrodynamics of fluid flow past the trapped particle.
Integrated Hierarchical Durability Design Tool for Electronic Packaging
Authors: Lee Jung-Chuan , Twigg David W. , Rassaian Mostafa
Published: May 2009

Durability and reliability of solder joint interconnections between electronic parts and printed wiring assemblies (PWA) in a vibration environment is increasingly important since the introduction of lead-free solder, which is known to be an order of magnitude more susceptible to fatigue failure than its tin-lead counterpart. In this paper, an integrated hierarchical durability design tool is introduced to analyze the Line Replaceable Units (LRU) as a whole under a vibration environment. The results will be used for solder joint fatigue analysis. This paper describes the automation of box-, board-, and part-level analyses. The box-level analysis combines PWA’s and the mounting chassis in an automated fashion. The construction of PWA’s is also through this automated tool. NIKE3D-based acoustic analysis tool is conducted on the assembled model for vibration analysis. The results are exported to the automated part-level analysis for final solder joint fatigue analysis and to subsequent visualization display. This paper illustrates this detailed processes and presents a simple example will be presented.
A State-Space Representation Model and Learning Algorithm for Real-Time Decision-Making Under Uncertainty
Authors: Malikopoulos Andreas A. , Papalambros Panos Y. , Assanis Dennis N.
Published: May 2009

Modeling dynamic systems incurring stochastic disturbances for deriving a control policy is a ubiquitous task in engineering. However, in some instances obtaining a model of a system may be impractical or impossible. Alternative approaches have been developed using a simulation-based stochastic framework, in which the system interacts with its environment in real time and obtains information that can be processed to produce an optimal control policy. In this context, the problem of developing a policy for controlling the system’s behavior is formulated as a sequential decision-making problem under uncertainty. This paper considers real-time sequential decision-making under uncertainty modeled as a Markov Decision Process (MDP). A state-space representation model is constructed through a learning mechanism and is used to improve system performance over time. The model allows decision making based on gradually enhanced knowledge of system response as it transitions from one state to another, in conjunction with actions taken at each state. A learning algorithm is implemented realizing in real time the optimal control policy associated with the state transitions. The proposed method is demonstrated on the single cart-pole balancing problem and a vehicle cruise control problem.
Safety Analysis of Sling and Strap Failures
Authors: Brickman Dennis B. , Smith Kenneth M.
Published: May 2009

This paper addresses the safe use of lifting slings and tie down straps in the field. From time to time, web straps used as lift slings or tie down devices fail in service. The appearance of the failed portion of the web provides insight into the cause of the strap failure and provides physical evidence of the pre-failure condition of the strap. The safety analysis consists of a technical literature review, research of applicable safety standards and guidelines, results of testing of slings and straps to failure in a variety of initial conditions, and evaluation of the appearance of the straps after testing. The paper presents an evaluation of the effect on breaking strength of the web or sling of various intentionally-applied cuts to the material, and an appraisal of the post-test appearance as it relates to the pre-test condition. Furthermore, comparisons using macroscopic and microscopic techniques are made of the failed surfaces of the tested slings and straps to products that are known to have failed during field applications. The results presented in this paper make a significant contribution to the technical literature concerning the safety and failure prevention of industrial sling and strap products.
Novel Packaging Method for Miniature High Temperature Piezoelectric Actuators
Authors: Seeley Charles E. , Knobloch Aaron J. , Kapusta Christopher J.
Published: May 2009

There is a need for miniature actuators that operate at high temperature, high frequency and lend themselves to integration with other small devices such as relays, valves and micro electromechanical systems (MEMS). Actuators based on piezoelectric materials have the potential to develop high forces at high frequency, but operation at elevated temperature may be problematic and obtaining useful stroke as the actuator is scaled down in size is a significant challenge. This paper presents the design and fabrication steps for a novel piezoelectric actuator that addresses these challenges and is capable of operating at temperatures in excess of 200°C with a stroke greater than 10μm and a length of less than 25mm. Several packaging adhesives and two piezoelectric materials were evaluated for the miniature actuator design. Results indicate that although this first generation device did not meet the stroke requirement of 10μm, the high temperature package design will enable new capabilities for next generation devices.
Geometric Modeling and Optimization of Multi-Material Compliant Mechanisms Using Multi-Layer Wide Curves
Authors: Zhou Hong , Ting Kwun-Lon
Published: May 2009

Multi-material compliant mechanisms enhance the performance of regular single-material compliant mechanisms by adding a new design option, material type variation. This paper introduces a geometric modeling method for multimaterial compliant mechanisms by using multi-layer wide curves. Based on the introduced modeling method, a geometric optimization approach for multi-material compliant mechanisms is proposed. A multi-layer wide curve is a curve with variable cross-sections and multiple materials. In this paper, every connection in the multi-material compliant mechanism is represented by a multi-layer wide curve and the whole mechanism is modeled as a set of connected multi-layer wide curves. The geometric modeling and optimization of a multi-material compliant mechanism are considered as the generation and optimal selection of the control parameters of the corresponding multi-layer wide curves. The deformation and performance of multi-material compliant mechanisms is evaluated by the isoparametric degenerate-continuum nonlinear finite element procedure. The problem-dependent objectives are optimized and the practical constraints are imposed during the optimization process. The effectiveness of the proposed geometric modeling and optimization procedures is verified by the demonstrated examples.
Infrared Radiative Properties of Heavily Doped Silicon at Room Temperature
Authors: Basu S. , Lee B. J. , Zhang Z. M.
Published: May 2009

This paper describes an experimental investigation on the infrared radiative properties of heavily-doped silicon (Si) at room temperature. Lightly-doped Si wafers were ion implanted with boron and phosphorus atoms to doping concentrations of 1×1020 and 1×1021 cm−3. Rapid thermal annealing was performed to activate the implanted dopants. A Fourier-transform infrared spectrometer was employed to measure the normal transmittance as well as reflectance of the samples in the spectral region from 2 to 20 μm. Accurate carrier mobility and ionization models were identified after carefully reviewing the available literature, and then incorporated into Drude model to predict the dielectric function of doped Si. The radiative properties of doped Si samples were calculated by treating the doped region as multilayer thin films of different doping concentrations on a thick Si substrate. The measured spectral transmittance and reflectance agree well with the model predictions. The results obtained from this study will facilitate the future applications of heavily-doped Si in semiconductor as well as MEMS devices.
Dynamics of Temperatures in Thermally-Coupled, Heated Rooms With PI Control
Authors: Thwaites Frederick W. , Sen Mihir
Published: May 2009

The purpose of this study is to analyze the behavior of a set of thermally-controlled rooms arranged in the form of a ring. Each room is heated and can exchange heat with its neighbors as well as with the environment. The heater in each room is PI controlled. A lumped capacitance approximation is used for the rooms leading to a system of first-order differential equations. Numerical methods are used to determine the time-dependent behavior of the coupled system. The linear stability of the system is analyzed for various parameters. The stability is found to be independent of the strength of the thermal coupling between rooms.
Theoretical Investigation of On-Chip Multi-Species Transport in Micro-Channels for Analysis Applications
Authors: Shao Zhanjie , Schneider Gerry E. , Ren Carolyn L.
Published: May 2009

A complete mathematical model is developed for application to simulate the unsteady two-step on-chip sample injection and separation processes in microfluidic devices. The origin and applicability of the slip-wall velocity boundary condition is discussed. Due to electrophoresis effect, migration influence of every species is considered in the model and then solved for separation analysis. The model is non-dimensionalized in a unique manner to reveal effects of some key fundamental parameters: the Reynolds-Schmidt number, electrophoretic mobility of sample species, applied potentials, etc. In particular, the influence of ReSci is examined over the commonly encountered range and the effect of electrophoretic mobilities on separation is investigated for three different types of samples. Results include center-line concentration profiles as well as concentration contour plots over a range of nondimensional time (less than 400). Resolution is defined and employed to evaluate the separation results. The magnitude of calculated separation resolution (around 2.0) is comparable to experimental results. Through parametric studies, the characteristics of both injection and separation are revealed numerically and well understood for future effective control and innovative chip design.
Full Sheet Control Through the Use of Steer-Able Nips
Authors: Ergueta Edgar I. , Sanchez Rene E. , Horowitz Roberto , Tomizuka Masayoshi
Published: May 2009

State of the art high speed color printers require sheets being accurately positioned as they arrive to the image transfer station (ITS). This goal has been achieved by constructing and building a steerable nips mechanism, which is located upstream from the ITS. This mechanism consists of two rollers which not only rotate to advance the paper along the track, but also steer the paper in the yaw direction. This paper presents the design, experimental setup, system model, and the control law necessary to precisely correct for the lateral and angular positions of the sheet as well as to deliver it on time to the ITS. The system model is nonlinear and subject to four nonholonomic constraints. The control strategy used is based on linearization by state feedback with the addition of internal loops for the control of the process direction velocity and steering position of the rollers. This paper also provides a formal convergence analysis for the controller designed as well as the methodology required to tune it. The success of this mechatronic approach is corroborated through simulation and experimental results, which show that the controller is able to correct sheet errors under the condition that the page has nonzero initial and final longitudinal velocities.
Biomechanical Evaluation of In-Stenting Restenosis
Authors: Gu Linxia , Muttyam Aswini K.
Published: May 2009

Coronary heart disease is the single leading cause of death in America today. Annually, an estimated 1.2 million Americans suffer from a new or recurrent coronary attack. Coronary heart disease is caused by atherosclerosis, the narrowing of the coronary arteries due to fatty build ups of plaque. It’s likely to produce angina pectoris (chest pain), heart attack or both. The placement of a stent in the artery is used to prevent the collapse of the balloon treated artery. However the struts can introduce the excessive stresses on the artery wall and cause the artery to be re-blocked after weeks or months (in-stent restenosis). This study will quantify how key parameters of a stent such as mesh design, strut thickness, and plaque geometry affect the restenosis conditions. Results will identify the desirable properties necessary for the development of effective therapeutic strategy for reducing in-stent restenosis.
A Lagrangian Uniform-Mesh Finite Element Method Applied to Problems Governed by Poisson’s Equation
Authors: Gu Linxia , Kumar Ashok V.
Published: May 2009

A method is presented for the solution of Poisson’s Equations using a Lagrangian formulation. The interpolation functions are the Lagrangian operation of those used in the classical finite element method, which automatically satisfy boundary conditions exactly even though there are no nodes on the boundaries of the domain. The integration is introduced in an implicit way by using approximated step functions. Classical surface integration terms used in the weak form are unnecessary due to the interpolation function in the Lagrangian formulation. Furthermore, the Lagrangian formulation simplified the connection between the mesh and the solid structures, thus providing a very easy way to solve the problems without a conforming mesh.
Using Copulas to Model Dependence in Simulation Risk Assessment
Authors: Kelly Dana L.
Published: May 2009

Typical engineering systems in applications with high failure consequences such as nuclear reactor plants often employ redundancy and diversity of equipment in an effort to lower the probability of failure and therefore risk. However, it has long been recognized that dependencies exist in these redundant and diverse systems. Some dependencies, such as common sources of electrical power, are typically captured in the logic structure of the risk model. Others, usually referred to as intercomponent dependencies, are treated implicitly by introducing one or more statistical parameters into the model. Such common-cause failure models have limitations in a simulation environment. In addition, substantial subjectivity is associated with parameter estimation for these models. This paper describes an approach in which system performance is simulated by drawing samples from the joint distributions of dependent variables. The approach relies on the notion of a copula distribution, a notion which has been employed by the actuarial community for ten years or more, but which has seen only limited application in technological risk assessment. The paper also illustrates how equipment failure data can be used in a Bayesian framework to estimate the parameter values in the copula model. This approach avoids much of the subjectivity required to estimate parameters in traditional common-cause failure models. Simulation examples are presented for failures in time. The open-source software package R is used to perform the simulations. The open-source software package WinBUGS is used to perform the Bayesian inference via Markov chain Monte Carlo sampling.
Multiple Time-Scale Molecular Simulations: Modeling Realistic Loading Rates
Authors: Medyanik S. N. , Guleryuz E.
Published: May 2009

The vast gap between the molecular dynamics (MD) and experimental time scales poses serious problems to direct comparison between the MD simulation and experimental results. The inability of the traditional MD simulation methods to model long enough time scales also results in modeling unrealistically high loading rates and strain rates that are usually at least six or seven orders of magnitude higher than the corresponding experimental values. This may have a tremendous effect on the realism and quality of the simulation results.
Nanomechanical Microcantilevers for In-Vitro Biomolecular Detection
Authors: Eom Kilho , Kwon Tae Yun , Park Jinsung , Na Sungsoo , Yoon Dae Sung , Kim Tae Song
Published: May 2009

Nanomechanical microcantilevers have enabled the sensitive label-free detection of chemical and/or biological molecules. In recent years, resonating microcantilevers have achieved the unprecedented sensitivity in detecting molecules. In this article, we review our current works on the label-free detection of biomolecules based on resonating microcantilevers. Our piezoelectric thick film microcantilevers exhibit the relatively high quality factor in a viscous liquid, indicating the potential of our cantilever to in situ biosensor applications for real-time detection of biomolecular interactions. It is shown that our microcantilevers allow the noise-free real-time monitoring of biomolecular recognitions, providing the insight into kinetics of biomolecular recognitions.
Three-Dimensional Finite Element Analysis of Mixed-Mode Interfacial Delamination for the Pull-Off Test
Authors: Sun Zuo , Dillard David A.
Published: May 2009

A three-dimensional nonlinear finite element analysis model is presented to study mixed-mode interfacial delamination for a pull-off test consisting of a thin film strip debonded from a glass substrate. Since the strain energy release rates of all three modes (Mode I, Mode II, and Mode III) and the mode mixities vary along the width of the debond front, prediction of the in-situ shape of the debond front remains an interesting and challenging topic. A cohesive zone model is incorporated into the three-dimensional finite element model to predict the interfacial crack propagation profile for the film deformation regime ranging from bending plate to stretching membrane. This three-dimensional finite element model is found to provide additional insights for interfacial delamination for the pull-off test.
Experimental Measurements and Numerical Modeling Validation of Temperature Distribution in Tissue Medium During Short Pulse Laser Irradiation
Authors: Dutta Ashim , Kim Kyunghan , Mitra Kunal , Guo Zhixiong
Published: May 2009

The objective of this paper is to analyze the temperature distributions and heat affected zone in skin tissue medium when irradiated with either a collimated or a focused laser beam from a short pulse laser source. Single-layer and three-layer tissue phantoms containing embedded inhomogeneities are used as a model of human skin tissue having subsurface tumor. Q-switched Nd:YAG laser is used in this study. Experimental measurements of axial and radial temperature distribution in the tissue phantom are compared with the numerical modeling results. For numerical modeling, the transient radiative transport equation is first solved using discrete ordinates method for obtaining the intensity distribution and radiative heat flux inside the tissue medium. Then the temperature distribution is obtained by coupling the bio-heat transfer equation with either hyperbolic non-Fourier or parabolic Fourier heat conduction model. The hyperbolic heat conduction equation is solved using MacCormack’s scheme with error terms correction. It is observed that experimentally measured temperature distribution is in good agreement with that predicted by hyperbolic heat conduction model. The experimental measurements also demonstrate that converging laser beam focused directly at the subsurface location can produce desired high temperature at that location as compared to that produced by collimated laser beam for the same laser parameters.
Molecular Dynamics Simulation Studies of Pore Formation in Lipid Bilayers in the Presence of Dimethylsulfoxide
Authors: Pinisetty Dinesh , Alapati Raghava , Moldovan Dorel , Devireddy Ram V.
Published: May 2009

We report in this work our observations from detailed atomistic investigations of the interactions between solutions containing 11.3 mol% of dimethylsulfoxide (DMSO) and three fully hydrated bilayers of lipid molecules, (BLMs). The BLMs considered were: dipalmitoyl-phosphatidylcholine (DPPC), palmitoyloleoyl-phosphatidylcholine (POPC) and dimyristoylphosphatidylcholine (DMPC); all in the fluid phase and under equilibrium conditions at 323K and 298K, respectively. All of our simulations were performed over 100 ns total simulation time and in the absence of any externally applied stress to the membranes. In all three systems investigated, in the presence of DMSO, we observed that small hydrophobic pores start to open across the membranes at various times during the simulations ranging from 10 ns for the DMPC, 45ns for POPC to 50ns for DPPC membrane. By carefully analyzing the membranes structures we concluded that hydrophobic pores open and close continuously during the simulation beyond the above mentioned time marks. Interestingly, as there is no external stress applied to the membranes these hydrophobic pores are presumably nucleated by thermal fluctuations. In all three systems we also observe that after some time after the first hydrophobic pore nucleation the pore starts to grow and transforms into a hydrophilic pore which continue to grow at an even higher rate. Our MD simulation studies of various BLMs indicate that the presence of DMSO may lower the pore edge line tension leading to pore nucleation and growth due to only thermal fluctuations.
Modeling Support Loss in SOI-Based Micromechanical Resonators
Authors: Xu Yang , Hao Zhili
Published: May 2009

In light of recent efforts to quantitatively evaluate the quality factor (Q) of micromechanical resonators, this paper presents an analytical-numerical model for calculating support loss in micromechanical resonators made from Silicon-On-Insulator (SOI) wafers. The time-harmonic stress due to the vibrations in a micromechanical resonator is obtained through numerical simulation, while the vibration displacement on substrate due to the stress from micromechanical resonators is analytically derived, with the assumption that the substrate is a semi-infinite medium. The combination of the time-harmonic stress from the resonator and the vibration displacement on substrate gives rise to a quantitative evaluation of support loss, which is further verified with the experimental data in the literature. This analytical-numerical combined model is general and applicable to SOI-based micromechanical resonators with different structural geometries.
Steady “Attractors” for Forced Flow of Vapor Condensing Over a Horizontal Plate (Problem in Cess and Koh) and Their Unsteady Responses to Initial Disturbances and Noise
Authors: Kulkarni S. , Narain A. , Mitra S.
Published: May 2009

Accurate steady and unsteady numerical solutions of the full 2-D governing equations – that model the film condensation of saturated vapor flowing over a horizontal plate (the problem of Cess [1] and Koh [2]) – are obtained and new results on the solutions’ unsteady response to disturbances are presented. The computations reveal important features of this classical condensing flow problem. The results highlight the scope and limitations of the well-known similarity solution given by Koh [2]. For the steady problem formulation, the paper discusses the similarities and differences between the solution obtained by solving the full 2-D governing equations and the one obtained semi-analytically by the similarity solution approach of Koh [2]. It is shown that the pressure variations in the vapor domain near the leading edge, though small, are important in deciding condensation dynamics (steady and unsteady) and cannot, in general, be neglected, as is the case with the similarity solution. For this shear driven flow, by considering the unsteady solutions, the paper finds that any initial guess leads to an unsteady solution which is attracted to a long-term steady solution (which is same as the solution as the steady problem). However, the attraction rates gradually diminish with increasing distance from the leading edge and decreasing inlet speed. The steady solutions for this external flow problem are generally found to be stable to initial disturbances at the interface or in the interior of the flow domain. However, since these flows can only be physically realized on suitable finite length portions of the plate, the issue of their stability and sensitivity to exit pressure disturbances and ever-present noise (through exit pressure or bottom plate) is also considered. For example, for the finite domain realization of this problem, it is found that the flows are stable to small initial disturbances to the nearly uniform value of exit pressure. These finite domain realizations of the flow are unique in the sense that they allow different non-uniform steady pressure prescriptions leading to different steady solutions – particularly near the exit zone. As a result, near the exit of a long plate, large unsteadiness is expected due to sensitivity to small exit pressure noise/fluctuations. The exit pressure noise for finite domain realization of these flows is expected because of practical difficulties in maintaining constant uniform pressures at downstream locations of the top and exit boundaries. It is shown that the transverse component of gravity does not affect the solution or its dynamic response except for the expected changes in the nature of hydrostatic pressure variations.
Haptic Interface for an AFM for Nanomanipulation
Authors: Ellingwood Brian , Gurocak Hakan
Published: May 2009

This paper presents research on a nanomanipulator developed using an atomic force microscope (AFM) and an inexpensive off-the-shelf force feedback joystick for haptic interface. The system allows a user to manually position the AFM tip over a sample and provides force feedback to him based on the sample-tip interactions. The haptic interface adds a new channel of information to the user during the blind manipulation stage with the AFM. The paper describes the system configuration, design details of the haptic interface and control software. Results of a particle string splitting experiment and a particle identification experiment are presented.
Testing the Commonality of Student Conceptual Explanations Across Institutions
Authors: Newcomer J. L. , Steif P. S.
Published: May 2009

To gain insight into the cognitive activities of students during an assessment task, students in Statics courses at three universities were asked to explain their answer to a multiple choice question about the equilibrium of bodies under given loads. Explanations were compared for similarity of terminology using Latent Semantic Analysis and then coded to determine if and when students invoked concepts of force and moment equilibrium. Both terminology and thinking was shown to be consistent across universities. Ideas related to equilibrium were invoked by nearly all students. Students differed principally on whether they applied both force and moment equilibrium consistently and correctly, and if they clearly differentiated between forces and moments. Different codings were sufficiently correlated with the different answer choices, so that one could make a reasonable guess as to a student’s thinking based on the answer choice alone.
Modeling of Multiphase Flow Boiling in Meso-Channels
Authors: Schwarzkopf John D. , Crowe Clayton T. , Dutta Prashanta
Published: May 2009

Modeling two-phase heat transfer coefficients and corresponding surface temperatures can be difficult. In macro flows, the Chen and Bennett model showed good agreement with experimental data from various researchers. This model was derived from the original Chen model and is primarily based on physical properties with some empiricism. The purpose of this paper is to present a method of modifying a macro-boiling model to predict surface temperatures and heat transfer coefficients associated with meso-channel flow boiling and augmented boiling associated with spray cooling in mesochannels. In order to validate the model, experimental data was gathered. The spray module consisted of 17 sloped channels each having an inlet and exit hydraulic diameter of 1.55 mm and 1.17 mm respectively and a plan length of 33 mm. The heat flux was in the range of 11 – 61kW/m2 and the mass flux was 80 kg/m2-s. The quality of fluid (PF5050) ranged from 0 – 75%. The fluid inlet temperature was 29°C and the saturation temperature was 34°C. The modified model shows good agreement with the experimental data with deviations on the order of 10%.
An Automated Valve for Dispersion Control in On-Chip Electrophoresis
Authors: Cui Huanchun , Dutta Prashanta , Ivory Cornelius F.
Published: May 2009

Band dispersion and sample loss into a side channel is a major problem when an electrokinetically-mobilized concentration zone passes a T-junction in a networked microfluidic chip. The band dispersion can be minimized in linear electrophoretic systems such as zone electrophoresis and moving boundary electrophoresis by applying a constant additional electric field in the side channel. However, constant valve voltages have shown to provide unsatisfactory valve performance during nonlinear electrophoresis (isotachophoresis). In this study, an automated valve system was developed to reduce the band dispersion at the intersection during non-linear electrophoresis. The automated valve consists of two integrated microelectrodes and a control system. With the automated control system, two integrated microelectrodes provide an effective way to manipulate current streamlines, thus acting as a non-mechanical valve for charged species in electrokinetic separations. Experimental results with this non-mechanical valve show decreased dispersion and increased reproducibility as protein zones isotachophoretically passed the T-junction.
A Novel Bayesian Framework for Uncertainty Management in Physics-Based Reliability Models
Authors: Azarkhail M. , Modarres M.
Published: May 2009

The physics-of-failure (POF) modeling approach is a proven and powerful method to predict the reliability of mechanical components and systems. Most of POF models have been originally developed based upon empirical data from a wide range of applications (e.g. fracture mechanics approach to the fatigue life). Available curve fitting methods such as least square for example, calculate the best estimate of parameters by minimizing the distance function. Such point estimate approaches, basically overlook the other possibilities for the parameters and fail to incorporate the real uncertainty of empirical data into the process. The other important issue with traditional methods is when new data points become available. In such conditions, the best estimate methods need to be recalculated using the new and old data sets all together. But the original data sets, used to develop POF models may be no longer available to be combined with new data in a point estimate framework. In this research, for efficient uncertainty management in POF models, a powerful Bayesian framework is proposed. Bayesian approach provides many practical features such as a fair coverage of uncertainty and the updating concept that provide a powerful means for knowledge management, meaning that the Bayesian models allow the available information to be stored in a probability density format over the model parameters. These distributions may be considered as prior to be updated in the light of new data when they become available. At the first part of this article a brief review of classical and probabilistic approach to regression is presented. In this part the accuracy of traditional normal distribution assumption for error is examined and a new flexible likelihood function is proposed. The Bayesian approach to regression and its bonds with classical and probabilistic methods are explained next. In Bayesian section we shall discuss how the likelihood functions introduced in probabilistic approach, can be combined with prior information using the conditional probability concept. In order to highlight the advantages, the Bayesian approach is further clarified with case studies in which the result of calculation is compared with other traditional methods such as least square and maximum likelihood estimation (MLE) method. In this research, the mathematical complexity of Bayesian inference equations was overcome utilizing Markov Chain Monte Carlo simulation technique.
Dynamic Modeling of an Absorption Refrigeration System Using Ionic Liquids
Authors: Cai Weihua , Sen Mihir , Paolucci Samuel
Published: May 2009

Ionic liquids are generally non-volatile, non-toxic, and nonflammable with high heat capacity, high density, and high thermal and chemical stability. This paper considers their use as absorbents in an absorption refrigeration cycle. A dynamic model of a single-effect absorption refrigeration cycle using ionic liquids as absorbent is developed. Modeling of the cycle performance requires thermodynamic properties which are obtained from an equation of state for the refrigerant-absorbent mixture (solution). The transient response of the cycle is investigated. Some design and operating parameters that affect the cycle performance are identified.
Investigation of Particle Swarm Optimization Dynamics
Authors: Chen Cheng-Hung , Bosworth Ken W. , Schoen Marco P.
Published: May 2009

In this work, a set of operators for a Particle Swarm (PS) based optimization algorithm is investigated for the purpose of finding optimal values for some of the classical benchmark problems. Particle swarm algorithms are implemented as mathematical operators inspired by the social behaviors of bird flocks and fish schools. In addition, particle swarm algorithms utilize a small number of relatively uncomplicated rules in response to complex behaviors, such that they are computationally inexpensive in terms of memory requirements and processing time. In particle swarm algorithms, particles in a continuous variable space are linked with neighbors, therefore the updated velocity means of particles influences the simulation results. The paper presents a statistical investigation on the velocity update rule for continuous variable PS algorithm. In particular, the probability density function influencing the particle velocity update is investigated along with the components used to construct the updated velocity vector of each particle within a flock. The simulation results of several numerical benchmark examples indicate that small amount of negative velocity is necessary to obtain good optimal values near global optimality.
The Design Space of Superalloy-Based Actively Cooled Combustor Walls for H2-Powered Hypersonic Vehicles
Authors: Valdevit Lorenzo , Vermaak Natasha , Zok Frank W. , Evans A. G.
Published: May 2009

The walls of combustion chambers used for air-breathing hypersonic vehicles are subject to substantial thermo-mechanical loads, and require active cooling by the fuel in conjunction with advanced material systems. Solutions based on metallics are preferable to ceramic matrix composites due to their lower cost and greater structural robustness. Previous work suggested that a number of metallic materials (e.g. Nickel, Copper and Niobium alloys) could be used to fabricate actively cooled sandwich structures that withstand the thermo-mechanical loads for a Mach 7, hydrocarbon-powered vehicle (albeit with different weight efficiencies). However, this conclusion changes when the Mach number is increased. This work explores the feasibility of the Nickel superalloy MARM246 for a wide range of Mach numbers (7–12). Since hydrocarbon fuels are limited to Mach 7–8, Hydrogen is used as the coolant of choice. A previously derived analytical model (appropriately modified for gaseous coolant) is used to explore the design space. The relative importance of each design constraint is assessed, resulting in the distillation of essential guidelines for optimal design.
Bond Pad Effects on Steady State Thermal Conductivity Measurement Using Suspended Micromachined Test Structures
Authors: Phinney Leslie M. , Piekos Edward S. , Kuppers Jaron D.
Published: May 2009

This study examines the effects of bond pads on the measurement of thermal conductivity for micromachined polycrystalline silicon using suspended test structures and a steady state resistance method. Bond pad heating can invalidate the assumption of constant temperature boundary conditions used for data analysis. Bond pad temperatures above the heat sink temperature arise from conduction out of the bridge test element and Joule heating in the bond pad. Simulations results determined correction factors for the electrical resistance offset, Joule heating effects in the beam, and Joule heating in the bond pads. Fillets at the base of the beam reduce the effect of bond pad heating until they become too large.