bluuebunny/crossref_metadata_2025 huggingface dataset:
Microresonators Based on 1:2 Internal Resonance
Authors: Vyas Ashwin , Bajaj Anil K.
Published: April 2008

A nonlinear autoparametric resonance based microresonator concept is explored in this study. The concept is illustrated by modelling an electrostatically actuated T-beam structure, with the first two modes of the structure in 1:2 internal resonance. The response of the system to primary resonance of the first and second mode is presented. When the second mode is resonantly actuated, the second mode in turn excites the first mode due to 1:2 internal resonance and the nonlinear coupling between the two modes. The structure therefore oscillates in first mode with half the frequency of excitation voltage. This is a unique feature of this microresonator, and as a result of this feature, the resonator can serve as a filter as well as a mixer in RF MEMS devices. When the first mode is excited, the structure oscillates in both the first and the second mode and thus has an output signal with frequency twice the input signal. The response also showed Hopf-bifurcations for higher actuation voltages.
Comparison of Hydraulic Pump Faults Diagnosis Methods: Wavelet vs. Spectral Analyses
Authors: Gao Yingjie , Zhang Qin , Kong Xiangdong
Published: April 2008

This paper introduces two faults diagnosis methods, a conventional spectral analysis method and a wavelet transform method, for hydraulic pump applications. The fundamental technologies of both methods, as well as their performance in detecting a few common hydraulic pump defects, are described in this paper. The performance of both diagnoses methods were evaluated based on experimental results. In order to eliminate the effects of border distortion arising from applying wavelet transform to finite-length signals, the pump outlet pressure in this case, a preprocess on the obtained signals is carried to clean up the errors prior to faults diagnosis analysis. Validation results obtained from both methods in analyzing the same data sets indicated that the wavelet transform based method showed a more sensitive and robust detecting capability than that obtained from a spectrum analyses approach.
Thermo-Mechanical Damage Modeling for a Glass-Fiber Phenolic-Resin Composite Material
Authors: Luo Changsong , DesJardin Paul E.
Published: April 2008

The objective of this research is the development of a thermo-mechanical damage model for composite materials subject to high temperature thermal and radiative environments that are representative of large scale fires. The damage to the structure is expressed as two regions of non-charred and charred material. In the char region, the pyrolysis process of resin is complete and there are only fiber, char and gas. Homogenization methods are imposed to treat the damaged material in terms of the volume fractions associated with composite fiber, resin and char. A transport equation for the phase averaged temperature is presented using a Darcy law to account for the gas transport in the structure. Mechanical response in the composite is taken into account by solving a homogenized form of the linear elasticity equations. Required transport properties for temperature and displacement equations are based on mixture weighted properties of the fiber, gas, resin and char and are dependent on the local volume fraction of each. Numerical simulations of a two-dimensional composite clamped beam subject to radiation heat loading are presented. Overall, good agreement is obtained between the numerical predictions and experimental data for temperature and gas pressure with comparisons to the thermal experimental data of Henderson and Florio [8,9]. Results show that during early stages of heating, the decomposition of the resin results in local stress concentrations due to the increase in temperature and pressure.
Computational Simulation on Thermal Aspect of Micro-Fabrication Process for MEMS Device
Authors: Yee Raymond K. , Chan Gabriel C.
Published: April 2008

The inherent residual stresses and strains from micro fabrication process can have profound effects on the functionality and reliability of MEMS devices. Surface micromachining fabrication involves a series of sequential steps of addition and subtraction of materials through deposition and etching techniques. For instance, when a typical micro cantilever beam is fabricated, layers of silicon dioxide and polysilicon structures are deposited on top of silicon substrate. Part of the silicon dioxide layer is chemically etched out before the deposition of polysilicon layer. Due to mismatch of coefficients of thermal expansion (CTE) in layered structure, thermal cycle loading during micromachining fabrication can induce significant residual stress within a part from thermal aspect alone. Computational method is used to simulate the micromachining fabrication process for MEMS and to predict the residual stresses/strains in a selected MEMS device. The focus of the study is on the thermal aspect of deposition and etching processes during micromachining. Particular attention is placed on the effects of deposition temperature and polysilicon film thickness on resulting residual stresses.
Optimization of Spine Sensor Location in Resin Ttransfer Molding
Authors: Rodriguez A. , Minaie B. , Restrepo O. , Hsiao K.-T.
Published: April 2008

Resin Transfer Molding (RTM) is a manufacturing process to produce polymer composite parts. RTM is comprised of four stages: 1) cutting and placing of the fiber mats (preform) inside a mold, 2) resin injection, 3) curing of the part, and 4) demolding of the hardened part. Resin injection is the most critical stage in RTM and it can be affected by unpredictable parameters such as preform permeability variations. These variations can produce unrepeatable filling patterns where the Last Point to Fill (LPF) may not coincide with the exit vent location. Failure to completely wet the fibers inside the mold can cause dry spots which are major defects that usually require the part to be scrapped. In order to overcome the uncertainties in the filling stage, adaptive control can be used to monitor and regulate the flow front such that the LPF coincides with the vent location. Recently, the development of sensors has allowed continuous sensing of the flow front in a straight line. Such sensors can be placed between the injection gates and the vent. The location of these sensors can affect adaptive control and the resulting filling pattern and, therefore, the final quality of the part. The work presented in this paper uses a search algorithm to find the optimal location for the sensors. The results of this optimization study can be used to enhance future control algorithms and, therefore, can lead to a more successful RTM process.
Three-Dimensional Electrokinetic Focusing in a Planar Microstructure
Authors: Coleman Jeffrey T. , Lansdorp Bob M. , Sinton David
Published: April 2008

Hydrodynamic focusing is commonly employed to reduce the cross-sectional area of a microfluidic sample stream. Two-dimensional focusing is achieved by combining a central sample stream with a buffer sheathing flow on adjacent sides of a standard microfluidic cross chip. This method of on-chip hydrodynamic focusing is the most common, perhaps due to the relative ease and popularity of planar microfluidic chip fabrication methods. The application of two-dimensional focusing to on-chip flow cytometry is limited for two reasons: Firstly, the degree of focusing obtained is limited by the microchannel depth. Secondly, many biological analytes adhere to channel walls mitigating the optical measurements. Three-dimensional focusing can both increase the focus intensity, and minimize interaction between the analyte stream and the channel walls in the viewed region. In this work, a new method is presented for obtaining three-dimensional hydrodynamic focusing on a planar microfluidic geometry using strategically placed surface charge patches. Numerical simulations are employed to show the concentration profiles resulting from the local flow circulations induced by the surface patches in an electrokinetically-driven flow.
Mathematical Modeling of Thermal Effects in Steady State Dynamics of Microresonators Using Lorentzian Function: Part 1 — Thermal Damping
Authors: Nakhaie Jazar G. , Mahinfalah M. , Aagaah M. R. , Mahmoudian N. , Khazaei A. , Alimi M. H.
Published: April 2008

Mathematical modeling of thermal effects on steady state dynamics of microresonators, utilizing an analytical approach is studied. Thermal phenomena has two distinct effects, which in this report are called, thermal damping and temperature relaxation. In this part of a two-part report we investigate the thermal damping and its effects on microresonator dynamics. To do this, first the reduced order mathematical model of the system is introduced as a forced mass-spring-damper system, and then a linearized model of electric actuated microbeam resonator is employed. The effect of thermal damping is modeled as an increase in damping rate, utilizing a Lorentzian function of excitation frequency. The steady state frequency-amplitude dependency of the system will be derived utilizing averaging perturbation method. The developed analytic equation describing the frequency response of the system around resonance can be utilized to explain the dynamics of the system, as well as design of dynamic parameters. However, we have focused on exploration of thermal damping.
Sensitivity of Jump Avoidance Condition of Piecewise Linear Vibration Isolator to Dynamical Parameters
Authors: Deshpande Sagar , Mehta Sudhir , Nakhaie Jazar G.
Published: April 2008

An adapted averaging method is employed to obtain an implicit function for frequency response of a bilinear vibration isolator system under steady state. This function is examined for jump-avoidance and a condition is derived which when met ensures that the undesirable phenomenon of ‘Jump’ does not occur and the system response is functional and unique. The jump avoidance and sensitivity of the condition are examined and investigated as the dynamic parameters vary. The results of this investigation can be directly employed in design of effective piecewise linear vibration isolators. A linear vibration system is defined as one in which the quantities of mass (or inertia), stiffness, and damping are linear in behavior and do not vary with time [1]. Although mathematical models employing a linear ordinary differential equation with constant coefficients portray a simple and manageable system for analytical scrutiny, in most cases they are an incomplete representation simplified for the sake of study. Most real physical vibration systems are more accurately depicted by non-linear governing equations, in which the non-linearity may stem from structural constraints causing a change in stiffness and damping characteristics, or from inherent non-linear behavior of internal springs and dampers. This paper focuses on a general form of such a non-linear system. This study of piecewise-linear systems will allow hazardous system behavior over operating frequency ranges to be gauged and controlled in order to avoid premature fatigue damage, and prolong the life of the system.
An Equivalent Continuum-Atomistic Characterization Model for Nanographitic Materials
Authors: Karami G.
Published: April 2008

An equivalent continuum-atomistic algorithm is proposed for carbon-based structures such as nano-scale graphene platelets (NGPs) and carbon nanotubes (CNTs) individually or as stiffeners with polymers. This equivalent continuum-atomistic model will account for the nonlocal effect at the atomistic level and will be a highly accurate mean to determine the bulk properties of graphene-structured materials from its atomistic parameters. In the model, the equivalent continuum and atomic domains are analyzed by finite elements and molecular dynamics finite element-based where atoms stand as nodes in discretized form. Micromechanics idea of representative volume elements (RVE) will be used to determine averaged homogenized properties. In the procedure, a unit hexagonal cell will be the RVE. A minimum volume of material containing this RVE and the neighboring hexagonal cells will be chosen. The size of this volume should cover all the atoms, which have bonded, and nonbonded interaction with the atoms of the RVE unit cell. This minimum volume will be subjected to several load cases. Determination of the response of the RVE hexagonal unit cell contained within the minimum volume, and its potential energy density under the defined load cases, will lead to the determination of mechanical parameters of an equivalent, continuum geometrical shape. For a single layer NGP the thickness of the hexagonal continuum plate is assumed to be 0.34 nm, while in three-dimension and multilayered the actual thickness of layers can be implemented. Under identical loading on the minimum volumes, identical potential (strain) energies for both models will be assumed. Through this equivalence a linkage between the molecular force field constants and the structural elements stiffness properties will be established.
Multi-Level Boundary Element Methods for Steady Heat Diffusion in Three-Dimensions
Authors: Grigoriev M. M. , Dargush G. F.
Published: April 2008

We have recently developed a novel multi-level boundary element method (MLBEM) for steady heat diffusion in irregular two-dimensional domains (Numerical Heat Transfer Part B: Fundamentals, 46: 329–356, 2004). This presentation extends the MLBEM methodology to three-dimensional problems. First, we outline a 3-D MLBEM formulation for steady heat diffusion and discuss the differences between multi-level algorithms for two and three dimensions. Then, we consider an example problem that involves heat conduction in a semi-infinite three-dimensional domain. We investigate the performance of the MLBEM formulation using a single-patch approach. The MLBEM algorithms are shown facilitate fast and accurate numerical solutions with no loss of the solution accuracy. More dramatic speed-ups can be achieved provided that patch-edge corrections are also evaluated using multi-level technique.
Design Guidelines for Anisotropic Conductive Adhesive Assemblies in Microelectronics Packaging
Authors: Chin M. , Hu S. J. , Barber J. R.
Published: April 2008

The multiple parameters that are involved in the design of anisotropic conductive adhesive (ACA) assemblies, and the overlapping influences that they have on the final electrical contact resistance, represent a difficult challenge for the designers. The most conflicting parameters include initial bonding force F, number of particles N, adhesion strength GA, and modulus of elasticity E of the cured resin. It is well known that as the bonding force increases, the contact resistance decreases. However, when the bonding force reaches a certain maximum value, the contact between conductive particle and conductive track is disrupted due to delamination of the cured resin during the elastic recovery. The authors have shown in previous studies that the delamination is caused by high residual stresses and that it depends largely on the adhesion strength of the assembly and on the modulus of elasticity of the cured resin. Additionally, the authors have provided a methodology to quantify the maximum threshold value of the bonding force for different numbers of particles trapped between mating conductive tracks. In this paper, the relationships between contact resistance R and each one of these conflicting parameters are systematically combined to create design diagrams that give regions of robust design. It is found, for example, that for particles of radius 5μm, E = 0.9 GPa, GA = 50 J/m2, and 2 ≤ N ≤ 5, the required bonding force to achieve contact resistance within the range 7 < R < 40 mω, is 2.5 < F < 20mN.
Intelligent Model Predictive Control of a Flexible-Link Robotic Manipulator
Authors: Fan Tao , de Silva C. W.
Published: April 2008

This paper presents an intelligent, model-based predictive control (IMPC) strategy for motion control a flexible-link robot manipulator. The proposed IMPC is based on a two-level hierarchical control architecture. This control structure is used to combine the advantages of crisp model-based predictive control and knowledge-based soft control techniques. The top-level is a fuzzy-rule based intelligent decision-making system. The low-level consists of two modules: Real time system identification module, and the model-based predictive control (MPC) module. The top-level intelligent fuzzy-rule based tuner interacts with the low-level modules. Based on the desired system performance, the state feedbacks, and the knowledge base, the top-level fuzzy tuner automatically adjusts the tuning parameters of the MPC controller. It is also able to adjust the model structure of system identification module, if necessary, for large model errors, and will increase the robustness of the controller. A multi-stage MPC algorithm is used by MPC module to ensure the nominal stability of the controller based on Lyapunov’s theorem. Physical implementation of the IMPC in a prototype flexible link manipulator system (FLMS) is explored. The performance of the proposed IMPC scheme is evaluated using computer simulations of the prototype FLMS. The results show that the IMPC can effectively control the motion of a flexible-link robot manipulator.
Measurement of Thermophysical Properties of Thin Film Shape Memory Alloys Using the 3-Omega Method
Authors: Jain Ankur , Goodson Kenneth E.
Published: April 2008

The excellent mechanical properties of thin film shape memory alloys like Nickel-Titanium (NiTi) have led to their widespread use in MEMS-based micropumps, microactuators, microgrippers, etc. Shape memory based micropumps and actuators have superior work densities compared to other technologies. Characterization of thermophysical properties of these materials is important for modeling the behavior of NiTi-based microdevices. For example, the frequency response of shape-memory based microactuators depends on the rate of dissipation of thermal energy, which is a strong function of the thermal properties of the thin film. While bulk thermal properties of NiTi have been reported before, there exists very little work on measuring these properties for the thin film form. This paper uses the 3-ω method for measurement of thermal conductivity of NiTi thin films. NiTi is sputtered on a Silicon substrate, followed by patterning of a metal heater line. Front-to-backside alignment and Deep Reactive Ion Etching (DRIE) of the substrate results in a free standing thin film of NiTi. A sinusoidal electric current is passed through the metal heater, and the third harmonic of the voltage is measured using a lock-in amplifier. This is used to determine the temperature oscillation in the metal heater, which provides the thin film thermal conductivity using a recently developed analytical model for 3-ω measurements in a two-dimensional free standing thin film. The measured values are found to be much lower than the known bulk thermal conductivity of NiTi. This highlights the importance of thin film property measurements instead of using bulk properties. Data obtained in this work is likely to be useful for improved modeling of thin film shape memory based microdevices.
Improved Control of Open-Center Systems for Haptic Applications
Authors: Kontz M. E. , Huggins J. D. , Book W. J. , Frankel J. G.
Published: April 2008

The use of haptic interfaces to control mobile hydraulic machinery has several enhancing features over traditional human-machine-interfaces compromising of joysticks/levers. A prohibitive attribute of these systems is cost due to added complexity. One way to limit this cost is to use lower cost hydraulic components such as a constant displacement pumps and proportional directional control valves. In this type of system, a main pressure regulator is needed to supply the other closed-center valves with pressure and dump the additional flow from the pump to tank. An energy-saving solution has a load-sensing pressure regulator that maintains the system pressure a preset margin above the highest active load pressure. With the addition of pressure compensators on each proportional valve, these valves can provide steady-state flow proportional to an input voltage generated from a joystick. Using these valves for haptic applications requires closed-loop control. Applying closed-loop control to these valves can excite instabilities in the valve assembly due to complex interactions and nonlinearities in the load-sensing pressure regulator. This paper describes and analyzes these interactions. It also shows through experimental examples of how these characteristics limit closed-loop performance and destabilize the system. A possible valve modification is presented and closed-loop performance is compared using the original and modified system.
Comparison of a One-Dimensional Model of a High-Temperature Solid-Oxide Electrolysis Stack With CFD and Experimental Results
Authors: O’Brien J. E. , Stoots C. M. , Herring J. Stephen , Hawkes G. L.
Published: April 2008

A one-dimensional model has been developed to predict the thermal and electrochemical behavior of a high-temperature steam electrolysis stack. This electrolyzer model allows for the determination of the average Nernst potential, cell operating voltage, gas outlet temperatures, and electrolyzer efficiency for any specified inlet gas flow rates, current density, cell active area, and external heat loss or gain. The model includes a temperature-dependent area-specific resistance (ASR) that accounts for the significant increase in electrolyte ionic conductivity that occurs with increasing temperature. Model predictions are shown to compare favorably with results obtained from a fully 3-D computational fluid dynamics model. The one-dimensional model was also employed to demonstrate the expected trends in electrolyzer performance over a range of operating conditions including isothermal, adiabatic, constant steam utilization, constant flow rate, and the effects of operating temperature.
Enhanced Laser Cooling of Ion-Doped Nanopowders
Authors: Ruan Xiulin , Kaviany Massoud
Published: April 2008

Enhanced laser cooling performance of rare-earth ion doped nanocrystalline powders is predicted, using Yb3+:Y2O3 as the model material. This is achieved by enhancing the anti-Stokes off-resonance absorption, which is proportional to the three factors considered in this paper: dopant concentration, pumping field energy, and anti-Stokes transition rate. The concept of the optimum dopant concentration for cooling is proposed based on the fact that higher concentration increases absorption while decreases quantum efficiency. Using the concentration quenching theory of energy transfer, the optimum concentration, which gives the maximum cooling power, is found to be larger than the currently used value, suggesting noticeable enhancement effects for laser cooling. The pumping field energy is enhanced in random nanopowders compared with bulk crystals under the same irradiation, due to the multiple scattering of photons. Photons are thus localized in the medium and do not propagate through, increasing the photon absorption of the pumping beam. This also contributes significantly to laser cooling enhancement. Using molecular dynamics simulations, the phonon density of states (DOS) of the nanopowder is calculated, and found to have extended, small tails at low and high frequencies. The second-order electronic transition rate for the anti-Stokes luminescence is calculated using the Fermi golden rule, which includes the influence of this phonon DOS, and is shown to have enhancement effects on the laser cooling efficiency using nanopowders. Finally, it is concluded that these three enhancement mechanisms are exactly equivalent to increasing the number of the three participating carriers (electron, photon, and phonon) in the interacting volume.
Three Dimensional Modeling of Carbon Foams
Authors: Druma A. , Alam M. K. , Anghelescu M. , Druma C. , Maruyama B.
Published: April 2008

The relationship between the 3D structure of the open-cell carbon foams and its properties is particularly difficult to establish without a “true” representation of the foam. The complex structure of graphitized carbon foams is difficult to capture using one or even two-dimensional models. Several attempts have been made to model carbon foams as cellular materials. However, the regular models cannot account for the complex interaction between the pores in the true foam. The present paper characterizes the structure of “true” foam and links it to its thermal and mechanical properties.
Chatter Prediction in Orthogonal Cutting Based on Lambert Function
Authors: Elias Alex , Rodriguez Ciro A. , Delgadillo Eva , Martinez Alejandro , Araya Francisco , Flores Victor
Published: April 2008

This paper will illustrate the application of the Lambert Function, as originally proposed by Asl and Ulsoy, to obtain the stability lobes in orthogonal cutting operations. The Lambert function approach will be compared to the classical approach. It will be shown that the stability lobes obtained with this procedure match with those obtained with the classical approach, under certain system parameter values.
Planar Microfabricated Check Valves Utilizing Large Compliance of PDMS
Authors: Yang Bozhi , Lin Qiao
Published: April 2008

This paper presents three types of planar check valves that uniquely exploit the large compliance of simple PDMS structures. The micro check valves consist of a thin compliant flap and a rigid stopper embedded in a microchannel. The flap is perpendicular to the flow and lies near the stopper, forming a restricted fluid path inside the channel. In particular, a novel “zero flap-stopper gap” valve design was proposed and fabricated using a special technique, in which the flap and stopper are in contact naturally forming a normally-closed device with high diodicity. Testing results show that the check valves can achieve a diodicity up to 105. The check valves can be fabricated using the standard replica molding technique from PDMS, and thus are highly amenable to integration with other PDMS-based microfluidic systems.
Course and Program Outcome Assessment Process
Authors: Karimi Amir
Published: April 2008

Course and Program Outcome assessment process at the University of Texas at San Antonio (UTSA) is briefly discussed. It is explained how data were collected, analyzed, and used in the enhancement of the undergraduate programs. This paper describes the management of the assessment process. Lessons learned from assessment experience are described and how these assessment processes will be streamlined in the future are highlighted.
MEMS Testbed for Mechanical Testing of Nanowires
Authors: Desai A. A. , Haque M. A. , Eklund P. C.
Published: April 2008

In this paper, we present a MEMS test bed for electromechanical testing of nanowires and nanotubes. The MEMS device exploits the mechanics of post buckling deformation of slender columns to achieve very high force and displacement resolution. The proposed technique involves manipulating the nanowire or nanotube to the device site and hence is applicable to any type of one-dimensional solid. Initial experiments on semiconducting ZnO nanowires estimated the elastic modulus to be 1 GPa.
Integrated Pressure-Flow-Temperature Sensor for Hydraulic Systems
Authors: Groepper Charlie , Cui Tianhong , Li Perry , Stelson Kim
Published: April 2008

The design of a miniature low-cost MEMS (Micro-Electronic Mechanical Systems) based sensor for sensing pressure, flow and temperature in fluid power systems is presented. The sensor is small enough to be incorporated into hydraulic components such as pumps, motor and cylinders. Considerable literature exists on the development of MEMS-based pressure and temperature sensors; therefore the primary challenge addressed in this paper is a low cost flow sensing method that does not impose extra energy dissipation into the system. The flow sensing principle adopted for use with the sensor utilizes the small pressure differences that develop as fluid flows through any geometry. As an example to prove the validity of this principle, pressure-flow relationships are determined for an elbow geometry. Specifically, the pressure differences arising from the momentum change of the fluid as it passes through the elbow are correlated to the flow rate of the fluid through the bend. The pressure-flow correlations derived from theoretical modeling, computational fluid dynamic (CFD) simulation, and experimental measurement using the flow bend geometry are compared and a calibration scheme determined. The first generation MEMS sensor incorporates pressure, flow and temperature measurement capability on a single sensor die. Pressure sensing is accomplished with piezoresistive strain elements, and temperature sensing is done with a thermister.
A General Approach for Introducing Materials Handling Topics in a Mechanical Engineering Degree Course
Authors: Dartnall W. John
Published: April 2008

This paper outlines the development of the teaching materials for an introductory lecture/chapter in a single semester final-year materials handling course for undergraduate and postgraduate mechanical engineers. The study of materials handling equipment and processes primarily involves the application of mechanical engineering design principles emanating from the mechanics of machine elements, structures, thermo-fluids and particle mechanics. The detail topics of our course are from two main areas: • Bulk materials handling by screw, bucket and belt conveyors as well as pneumatic and hydraulic conveyors. • Unit (discrete) materials handling of artifacts and manufactured (packaged) products. For undergraduate and early postgraduate students, we utilize this course to provide an opportunity for students to amalgamate and integrate their engineering knowledge and experiences, and solve complex, real world problems of the materials handling industries. Although the students are mostly fresh from their engineering sciences and hence have skills at applying basic principles, many have little or no practical experience in the materials handling industries. For this reason we start by discussing the significance of the industry and expose them to that fact that these industries have historically expanded from simple (manual) handling to large scale mechanical handling of goods and bulk solids. The particle mechanics aspect of the bulk handling component of the course is relatively unfamiliar to the students. For this reason, after giving our brief history and socio-economic perspective of the materials handling industry, we emphasize general principles related to the handling of particulate solids. We differentiate between design approaches where designers work from basic mechanics and the common empirical design procedures often outlined by manufacturers.
Building Vertical Walls by Deposition of Molten Metal Droplets
Authors: Fang M. , Chandra S. , Park C. B.
Published: April 2008

Experiments were conducted to determine conditions under which good metallurgical bonding was achieved in vertical walls composed of multiple layers of droplets that were fabricated by depositing tin droplets layer by layer. Molten tin droplets (0.75 mm diameter) were deposited using a pneumatic droplet generator on an aluminum substrate. The primary parameters varied in experiments were those found to most affect bonding between droplets on different layers: droplet temperature (varied from 250°C to 325°C) and substrate temperature (varied from 100°C to 190°C). Considering the cooling rate of droplet is much faster than the deposition rate previous deposition layer cooled down too much that impinging droplets could only remelt a thin surface layer after impact. Assuming that remelting between impacting droplets and the previous deposition layer is a one-dimensional Stefan problem with phase change an analytical solution can be found and applied to predict the minimum droplet temperature and substrate temperature required for local remelting. It was experimentally confirmed that good bonding at the interface of two adjacent layers could be achieved when the experimental parameters were such that the model predicted remelting.
NIST Development of Reference Material Scaffolds for Tissue Engineering
Authors: Dunkers Joy P. , Leigh Stefan D. , Cicerone Marcus T. , Landis Forrest A. , Wang Francis W. , Tesk John A.
Published: April 2008

In consultation with ASTM and other stakeholders in Tissue-Engineered Medical Products (TEMPs) industry, the National Institute of Standards and Technology (NIST) initiated a project designed to produce Reference Material scaffolds for tissue engineering. The rationale for Reference Material scaffolds was developed through several NIST/Industry workshops. In brief, Reference Material scaffolds have multiple uses: facilitating the development and the validation of new test methods that measure interactions among various components of a TEMP; comparison with other scaffolds and scaffold materials in terms of cellular responses, biodegradation, and releases of growth factors; and comparisons of responses among various cell lines. The primary customers for Reference Material scaffolds are expected to be the TEMPs industry, academic researchers, regulators, and standards developing organizations. There are many properties of a TEMP that warrant development of multiple Reference Material scaffolds. Currently, NIST is defining a set of Reference Material scaffolds based on geometric descriptors such as permeability, pore volume, pore size distribution, interconnectivity, and tortuosity. In consultation with ASTM, NIST is testing three candidate scaffolds produced by: three dimensional (3-D) printing, stereolithography, and fused deposition modeling (FDM). Scaffolds made by these methods have been obtained from Mayo Clinic (Rochester, MN), Case Western Reserve University (CWRU) (Cleveland, OH), and Osteopore International (Singapore), respectively, for structural characterization. These prototype scaffolds, with well-defined architectures, have been selected to address the following items of interest: 1) establishment of useful functional definitions of porosity content, interconnectivity, and pores; 2) evaluation of testing methods listed in the Standard Guide for the Porosity of Polymeric Scaffolds for Use in Tissue-Engineered Medical Products, which is being drafted by ASTM. Currently, NIST and the Center for Devices and Radiological Health of the Food and Drug Administration, as well as other groups from US and foreign laboratories, are actively carrying out cross-validation test of these prototype scaffolds.
A Framework for Warranty Prediction During Product Development
Authors: Esterman Marcos , Gerst Philip , Stiebitz Paul H. , Ishii Kosuke
Published: April 2008

This paper describes the challenges faced by companies to manage warranty performance during product development. Understanding and reducing warranty cost often focuses exclusively on the analysis of product failures. However, warranty costs can also be incurred by events such as misaligned customer expectations that do not involve a product failure, per se. Many experts agree that effective management of system reliability and reliability validation during product development is a key to achieve superior time to market and life cycle quality. The paper first surveys the challenges faced by various organizations ranging from consumer electronics to aircraft engines to experimental high-energy physics accelerators. From the survey emerge some key and common issues that these companies face: identification of failure events; reliability modeling and prediction; prototyping and validation testing. The paper then reviews the current state of the art to identify areas for improvements as well as needed integrations in order to develop a comprehensive framework that will be useful to product developers to manage and predict warranty performance during product development. This framework extends and integrates three areas: 1) extend scenario-based FMEA to include the diagnosis and repair of failure events as part of the scenario; 2) use of Bayesian methods to integrate field data, product development data and engineering judgments; 3) generate costs models that allow tradeoff studies between product design, service model design and warranty policies. The paper concludes by presenting a future research agenda.
Modeling the Response of a Transient Thermal System Using Gaussian Processes
Authors: Emery A. F. , Bardot D.
Published: April 2008

Estimating sensitivities and the uncertainties associated with variable parameters can be prohibitively expensive for complex systems, particularly when sampling techniques, e.g., Monte Carlo, are employed. One approach is to define a response surface based on easy to compute functions using least squares fitting. However, such a surface does not pass through each of the data points and makes it difficult to determine the degree of interaction between the parameters of the system. Parameter interactions can be accurately determined using global sensitivity, but it is computationally expensive. Gaussian Processes can be used to create an inexpensive to evaluate response surface that is an accurate representation of the data. The paper describes the use of Gaussian Processes in conjunction with global sensitivity to examine the behavior of a thermal system, showing that the combination is an effective tool.
PSO: A Novel Technique to Optimize a Coal Preparation Plant
Authors: Gupta Vishal , Unjawala Hussain , Mahajan Ajay , Mohanty Manoj
Published: April 2008

A coal preparation plant typically has multiple cleaning circuits based on size of coal particles. Each circuit is operated to produce the same product quality so that the blend of clean coal meets the targeted product quality constraints. Though, this approach of producing the clean coal satisfies the product quality constraints as given by the customer, it may suffer from the loss of overall clean coal yield by 1–2%. Numerous studies conducted in the past illustrate that the optimal yield can be obtained by operating each circuit to produce the same incremental product quality. However, this approach is good enough for single product quality constraints but it fails to produce optimal yield with multiple product quality constraints. A newer optimization technique known as particle swarming is developed for the yield optimization of a coal preparation plant while satisfying multiple product quality constraints. The optimization model incorporates two product quality constraints - product ash and sulfur assay. The results indicate that an increment of 2.73% in the yield could be achieved by both equal incremental ash quality approach and particle swarm optimization. The additional yield can generate extra revenue of $5,460,000 per annum without significantly adding to the implementation/operation cost.
High-Speed Biaxial Tissue Properties of the Human Cadaver Aorta
Authors: Shah Chirag S. , Mason Matthew J. , Yang King H. , Hardy Warren N. , Van Ee Chris A. , Morgan Richard , Digges Kennerly
Published: April 2008

Traumatic rupture of the aorta (TRA) is one of the leading causes of mortality in automobile crashes. Finite element (FE) modeling, used in conjunction with laboratory experiments, has emerged as increasingly important tool to understand the mechanisms of TRA. Appropriate material modeling of the aorta is a key aspect of such efforts. The current study focuses on obtaining biaxial mechanical properties of aorta tissue at strain rates typically experienced during automotive crashes. Five descending thoracic aorta samples from human cadavers were harvested in a cruciate shape. The samples were subjected to equibiaxial stretch at a strain rate of 44 s−1 using a new biaxial tissue-testing device. Inertially compensated loads were measured. High-speed videography was used to track ink dots marked on the center of each sample to obtain strain. The aorta tissue exhibited anisotropic and nonlinear behavior. The tissue was stiffer in the circumferential direction with a modulus of 10.64 MPa compared to 7.94 MPa in longitudinal direction. The peak stresses along the circumferential and longitudinal directions were found to be 1.89 MPa and 1.76 MPa, respectively. The tissue behavior can be used to develop a better constitutive representation of the aorta, which can be incorporated into FE models of the aorta.
Principles of Steerability for Dissipative Passive Haptic Interfaces
Authors: Gao Dalong , Book Wayne J.
Published: April 2008

This research focuses on the control limitation brought by brakes, one type of dissipative passive actuators on planar passive haptic interfaces. The concept of steerability is defined based on the force generation analysis to identify the limitation. Passive steerability angle is defined to quantify steerability. Two-sided steerability is required for a planar robot to redirect motion to both left and right of the current velocity. A non-redundant 2R manipulator does not have two-sided steerability at all situations. Redundancy brought by serial or parallel structures could improve the manipulator’s steerability. The steerability theorem was developed to determine two-sided steerability for a multi-joint manipulator.
Flow and Species Transport Control in Grooved Micro-Channels
Authors: Hahm Jungyoon , Beskok Ali
Published: April 2008

We demonstrate flow control concepts in a grooved micro-channel using selectively patterned, electroosmotically active surfaces and locally applied electric fields. This framework enables formation of rather complex flow patterns in simple micro-geometries. Ability to vary the electric field magnitude and its polarity also manifests time-dependent flow alterations, which results in flow and species transport control abilities. The results obtained in a single micro-groove constitute the proof of concept for flow and species transport control in an integrated serial micro-fluidic process, where multiple species can be trapped and released in prescribed amounts in a micro-channel with multiple grooves. The groove size determines volume of the entrapped species. In addition, each groove can simultaneously contain one or two species at the same time. The proposed flow and species transport control scheme allows control over the interspecies diffusion and mixing time and length scales by simply adjusting the electric field direction and its magnitude. We envision utilization of flow and species transport in a grooved micro channel, where combinatorial chemistry experiments can be performed using multiple grooves, where each groove can be addressed (filled, emptied or mixed) independently.
Risk Analysis and Safety Evaluation of Biomass Cookstoves
Authors: Johnson Nathan G. , Bryden Mark , Xiao Angran
Published: April 2008

Combustion of biomass in open fires and ad hoc unventilated stoves is the primary form of household energy for two to three billion people worldwide. These cookstoves have significant health, social, and economic impacts on poor families in developing countries. These impacts include disease, injury, excess time spent gathering fuel, deforestation, and high fuel costs relative to income. In an attempt to address many of these problems numerous non-governmental organizations have developed several biomass cookstove designs in the past five to ten years. These designs have generally focused on increasing fuel efficiency, and to a lesser degree, reducing particulate emissions. This emphasis has been driven largely by the availability of relatively straight forward fuel efficiency tests for biomass cookstoves developed 10–20 years ago and the ability of researchers to adapt current air pollution testing methods for stoves. In contrast there are no safety standards or hazard evaluations available for biomass cookstoves. Because of this the safety of the cookstove is seldom explicitly considered as a part of the design process. This paper addresses the basic safety issues that should be considered in the design of biomass stoves used in developing countries, describes the reasoning behind these safety issues, and proposes a set of safety guidelines for testing and evaluating stove safety. These guidelines are intended for testing and evaluating in the field as well as in the design lab.
A Novel Method for Determining Pressure Sensitivity of Underwater Shear-Stress Sensor Skins
Authors: Clendenin Jason , Xu Yong , Tung Steve
Published: April 2008

This paper reports the development of a novel method for determining the pressure sensitivity of two types of surface micromachined underwater shear stress sensor skins for micro shear stress sensing applications. The two types of sensors consisted of a thin-diaphragm sensor and a thick-diaphragm sensor. The focus is on the use of a combination of metrology and numerical simulation to theoretically determine the pressure sensitivity of the sensors and compare to experimental data. Using this combination, the nitride diaphragm deflection, the intrinsic stress of the diaphragm, and the piezoresistive gauge factor of the polysilicon sensing element were successfully determined. For the thin-diaphragm sensor, the tensile intrinsic stress and gauge factor were determined to be 28 MPa and 4, respectively. For the thick diaphragm sensor, the average tensile intrinsic stress and gauge factor were 48 MPa and 12, respectively. Using these numbers, the pressure sensitivity of the shear stress sensors was successfully modeled and verified against experimental results.
Modularization of Work Tasks for Global Engineering
Authors: Leung Peter , Ishii Kosuke , Benson Jan
Published: April 2008

This paper introduces a methodology that guides the modularization of work task for global engineering. Global engineering is a new collaboration model of co-developing engineering design systems with distributed teams. We consider the decision of allocating subsystem designs to engineering teams as modularization of work tasks. Previous efforts have reviewed the different approaches to analyzing product modularization, but few studies have investigated developing a methodology that focuses on process applications. We begin this paper with an overview of current modularization methods and of the definitions of Global Engineering. Then we present the three-step modularization methodology in detail: 1.) decompose the design system and its functional specifications by a flow down technique, 2.) identify the couplings between the system parts and the functional requirements, and plot the interactions in a matrix, and 3.) modularize design work based on the identified couplings for worksharing. As a case study, we apply the method to a vehicle interior design. We conclude the paper by discussing the case study findings and the appropriate application of this analysis. We also explain the methodology’s limitations and propose future research opportunities.