bluuebunny/crossref_metadata_2025 huggingface dataset:
Large-Amplitude Vibrations of Thin Panels
Authors: Amabili M.
Published: April 2008

Geometrically nonlinear vibrations of circular cylindrical panels with different boundary conditions and subjected to harmonic excitation are numerically investigated. The Donnell's nonlinear strain-displacement relationships are used to describe geometric nonlinearity; in-plane inertia is taken into account. Different boundary conditions are studied and the results are compared; for all of them zero normal displacements at the edges are assumed. In particular, three models are considered in order to investigate the effect of different boundary conditions: Model A for free in-plane displacement orthogonal to the edges, elastic distributed springs tangential to the edges and free rotation; Model B for classical simply supported edges; Model C for fixed edges and distributed rotational springs at the edges. Clamped edges are obtained with the Model C for very high value of the stiffness of rotational springs. The nonlinear equations of motion are obtained by the Lagrange multi-mode approach, and are studied by using the code AUTO based on pseudo-arclength continuation method. Convergence of the solution with the number of generalized coordinates is numerically verified. Complex nonlinear dynamics is also investigated by using bifurcation diagrams from direct time integration and calculation of the Lyapunov exponents and the Lyapunov dimension. Interesting phenomena such as (i) subharmonic response, (ii) period doubling bifurcations, (iii) chaotic behavior and (iv) hyper-chaos with four positive Lyapunov exponents have been observed.
A Thin-Film Piezoelectric Microactuator Optically Powered via an Integrated Micro-Solar Cell
Authors: Deshpande Mandar , Saggere Laxman
Published: April 2008

A novel optically powered microactuator is developed via the integration of a thin film piezoelectric microactuator with a micro-solar cell on the same chip. The integrated microactuator has an overall area of 2×2 mm2 and is less than 0.25 mm in thickness. The paper presents the details of fabrication and preliminary experimental results confirming the optical actuation. The solar cell is fabricated by doping a n-type dopant in a p-type silicon wafer. The thin film piezoelectric microactuator is fabricated alongside the solar cell via the solgel method. The microactuator prototypes are tested for optical actuation under low light intensities in the range 0.1-1.26 W/m2, and corresponding center point displacements of the actuators and the photovoltages output by the solar cells are measured. An unpoled microactuator prototype produced a maximum displacement of 31 nm corresponding to an input light intensity 1.26 W/m2.
Dynamics of the Interface of a Gas-Liquid Meniscus in Complex PDMS Micro-Geometries
Authors: Xu Jie , Attinger Daniel
Published: April 2008

This article describes the design and manufacturing of microfluidic chips, where an injected gas-liquid meniscus is used for actuation purpose. The dynamics of the meniscus during its controlled motion is studied. The critical pressures to move the meniscus are measured and compared to theoretical result. Three different micro-geometries are compared in term of their ability to stabilize the meniscus. Also, the meniscus response to ultrasonic excitation is studied. When the excitation is weak, traveling waves are found and their wavelength decreases with increasing excitation frequencies. When the ultrasonic excitation is stronger, subharmonic and superharmonic oscillations at the meniscus interface are observed.
Kinetics-Based Modeling of Bond-Metal Dissolution and IMC During Soldering
Authors: Faizan Mohammad , Wang Guo-X.
Published: April 2008

Soldering has become an indispensable joining process in the electronic packaging industry. The industry is aiming for the use of environment friendly lead-free solders. All the lead-free solders are high tin-containing alloys. During the soldering process, an intense interaction of metallization on PCB and tin from the solder occurs at the metallization/solder interface. Intermetallic compound (IMC) is formed at the interface and subsequently PCB bond-metal (substrate) is dissolved into the molten solder. In the present study the terms bond-metal and substrate will be used interchangeably and the term 'substrate' refers to the top layer of the PCB which comes in contact with the molten solder during soldering reaction. Thickness of the intermetallic phase formed at the joint interface and amount of substrate lost is critical in achieving reliable solder joints. During the wet phase of soldering process, the IMC does not grow as layered structure; rather it takes the shape of scallops. The growth of scalloped IMC during the solder/substrate interaction entails complicated physics. Understanding of the actual kinetics involved in the formation of IMC phase is important in controlling the process to achieve desired results. This paper presents theoretical analysis of the kinetics involved in the formation of the scalloped intermetallic phase. The intermetallic phase growth is experimentally investigated to support the underlying kinetics of the process. Numerical model has been suggested to translate the physics of the process. The model is based on the basic mass diffusion equations and can predict the substrate dissolution and IMC thickness as a function of soldering time.
Fabrication and Mechanical Characterization of Carbon Nanotube Based Nanoknives
Authors: Singh Gurpreet , Rice Paul , McIntosh Richard J. , Mahajan Roop L.
Published: April 2008

A prototype microtome knife for cutting ~100 nm thick slices of frozen-hydrated biological samples has been constructed by use of multiwalled carbon nanotubes (MWCNT). A piezoelectric-based 3-D manipulator was used inside a scanning electron microscope (SEM) to select and position individual MWCNTs, which were subsequently welded in place by electron beam-induced deposition (EBID). The device employs a pair of tungsten needles with provision to adjust the distance between the needle tips, accommodating various lengths of MWCNTs. We have performed experiments to test the breaking strength of the MWCNT in the completed device with an atomic force microscope (AFM) tip. An increasing force was applied at the midpoint of the nanotube until failure, which was observed in situ in the SEM. The initial force/deflection data appear promising, and efforts are underway to characterize and improve the strength of the device by conducting more such tests and modifying the welding process.
Numerical Simulation and Analysis for 3D Elastic-Plastic Rough Contacts
Authors: Wang Fan , Keer Leon M. , Wang Q. Jane
Published: April 2008

A 3D elastic-plastic rough contact (EPC) solution and code is developed using a modified semi-analytical method. The total surface deflection is induced by the contact pressure and plastic strain. A purely elastic contact field and a residual field arising from the plastic deformation are simulated iteratively to gain the final approximate solution for the elastic-plastic rough contact. Frictionless normal contact between a rigid ball and an elastic-plastic half space with polished, turned, and honed rough surfaces was numerically simulated using the developed EPC code. The distributions of surface pressures, real contact area, total stresses, residual stresses, residual displacements, and plastic strains are obtained through simulation. The effects of surface roughness, wavelength, and plastic hardening behavior upon the calculated results are analyzed.
A New Negative-Tone, UV Lithography Photoresist for Fabrication of Ultra-High-Aspect-Ratio Microstructures
Authors: Yang Ren , Soper Steven , Wang Wanjun
Published: April 2008

We report a new type of negative-tone photoresist in this paper. The resist is based on the composite of EPON resins 154 165 (both from Hexion Specialty Chemicals, Inc., Columbus, OH 43215). These two epoxy resins were mixed in an optimal ratio and dissolved into the gamma-butyrolactone (GBL) solvent. The mixture was then photosensitized by adding a given amount of triaryl sulfonium salt to obtain the new negative tone photoresist that can be used in for ultra high aspect ratio microstructures with UV lithography. The preliminary study has found that microstructures with height of more than 1000 μm and feature sizes of 10 μm (aspect-ratios of more than 100) can be obtained using the new resist film with ultraviolet lithography. The microstructures have excellent sidewall quality. In this paper, both the material properties and lithography properties of this new type of UV resist will be presented. The potential applications of the new resist in microfabrication and MEMS systems are also discussed.
Prediction of Effective Thermo-Mechanical Properties of Particulate Composites
Authors: Annapragada S. Ravi , Sun Dawei , Garimella Suresh V.
Published: April 2008

A micromechanics model is developed to predict the effective thermo-mechanical properties of energetic materials, which are composite materials made from agglomeration of particles of a range of sizes. A random packing algorithm is implemented to construct a representative volume element for the heterogeneous material based on the experimentally determined particle diameter distribution. The effective mechanical properties of the material are then evaluated through finite element modeling, while its thermal properties are determined through a finite volume approach. The model is first carefully validated against results from the literature and is then used to estimate the thermo-mechanical properties of particular energetic materials. Good agreement is found between experimental results and predictions. The stress-bridging phenomenon in the particulate materials is captured by the model. Thermodynamic averaging is shown to be a poor representation for the estimation of thermal properties of these heterogeneous materials. Also, the general elastic-plastic assumption is found not to be applicable for describing the mechanical behavior of energetic composites.
Surrogate Models for Predicting the Performance of a Liquid-Liquid Cylindrical Cyclone Separator
Authors: Pacheco Jorge E. , Reyes Miguel A.
Published: April 2008

Liquid-Liquid Cylindrical Cyclone (LLCC) separators are devices used in the petroleum industry to extract a portion of the water from the oil-water mixture obtained at the well. The oil-water mixture entering the separator is divided due to centrifugal and buoyancy forces in an upper (oil rich) exit and a bottom (water rich) exit. The advantages in size and cost compared with traditional vessel type static separators are significant. The use of LLCC separators has not been widespread due to the lack of proven performance prediction tools. Mechanistic models have been developed over the years as tools for predicting the behavior of these separators. These mechanistic models are highly dependent on the inlet flow pattern prediction. Thus, for each specific inlet flow pattern a sub-model has to be developed. The use of surrogate models will result in prediction tools that are accurate over a wider range of operational conditions. We propose in this study to use surrogate models based on a minimum-mean-squared-error method of spatial prediction known as Kriging. Kriging models have been used in different applications ranging from structural optimization, conceptual design, multidisciplinary design optimization to mechanical and biomedical engineering. These models have been developed for deterministic data. They are targeted for applications where the available information is limited due to the cost of the experiments or the time consumed in numerical simulations. We propose to use these models with a different framework so that they can manage information from replications. For the LLCC separator a two-stage surrogate model is built based on the Bayesian surrogate multistage approach, which allows for data to be incorporated as the model is improved. Cross validation mean squared error measurements are analyzed and the model obtained shows good predicting capabilities. These surrogate models are efficient and versatile predicting tools that do not require information about the physical phenomena that drives the separation process.
Mathematical and Experimental Investigation of Thermal Response of an Automobile Passenger With a Ventilated Seat
Authors: Shin Kwangjin , Park Hyunjae , Kim Jongsoo , Kim Kyuil
Published: April 2008

This paper presents mathematical and experimental models developed for the prediction of thermal interactions of an automobile passenger with the cabin environment and a ventilated seat. The mathematical model developed in this work employs existing and modified human-body heat balance equations along with variable thermo-physical environmental conditions. The model predicts steady-state and transient variations of passenger skin and seat-surface temperatures with time before and after activating the seat ventilation system for the given and selected cabin air conditions and heated seat temperature. In calculating the temperature changes with time after activating the ventilated-seat system, the modified heat balance equation along with the numerical analysis using the CFD package (Fluent, v.6) has been iteratively used, in which appropriate air-side average heat transfer coefficients were determined by using the Reynolds and Nusselt analogies for various system operating conditions. An experimental chamber was built to simulate the vehicle air and seat conditions attainable during a hot summer day. A selected number of individuals have participated in the experiments. Passengers' skin and seat-surface temperatures were measured with time after activating the ventilated-seat system for various chamber conditions. Investigation of the results obtained from the mathematical model and the experimental work showed that the seat ventilation system proposed in this work is able to provide the passenger thermal comfort initiation within about 2-3 minutes after activating the seat ventilation system. It was also found that the mathematical model developed in this work needs to be improved in order to include the non-uniform chamber air and seat conditions. The additional detailed experimental works are also required to quantify the passengers' thermal responses along with various chamber conditions.
Analysis and Feedback Control of Planar SOFC Systems for Fast Load Following in APU Applications
Authors: Xi Handa , Sun Jing
Published: April 2008

Solid Oxide Fuel Cell (SOFC) based Auxiliary Power Unit (APU) systems have many practical advantages given their high efficiency, low emissions and flexible fueling strategies. This paper focuses on model-based analysis and feedback control design for planar SOFC systems to achieve fast load following capability. A dynamic model is first developed for the integrated co-flow planar SOFC and CPOX (Catalytic Partial Oxidation) system aiming at APU applications. Simulation results illustrate that an open-loop system with optimal steady-state operating setpoints exhibits a slow transient power response when load increases. Feedback control is then explored to speed up the system response by controlling the flow rates of fuel and air supplies to the system. Model linearization, balanced truncation and Linear Quadratic Gaussian (LQG) approaches are used to derive the low-order observer-based controller. With the feedback controller developed, we show, through simulations, that the closed-loop system can have faster load following capability. Different feedback strategies are also considered and their impacts on closed-loop system performance are analyzed.
Experimental System Identification of Force Reflecting Hand Controller
Authors: Zumbado Fernando A. , McJunkin Samuel T. , O'Malley Marcia K.
Published: April 2008

This paper describes the combined time and frequency domain identification of the first three degrees-of-freedom (DOF) of a six degree-of-freedom force reflecting hand controller (FRHC). The FRHC is used to teleoperate Robonaut, a humanoid robotic assistant developed by NASA, via a bilateral teleoperation architecture. Three of the six DOF of the FRHC are independently identified due to the decoupled nature of the manipulator design. The frequency response for each axis is acquired by coupling a known environmental impedance to the joint axis and then applying a sinusoidal sweep torque input. Several data sets are averaged in the frequency domain to obtain an averaged frequency response. A coherence analysis is then performed and data with low coherence values are ignored for subsequent analysis and model fitting. The paper describes the use of coherence data to ensure acceptable model fits for transfer function estimation. Results of the identification experiments are presented, including implications of assumptions of decoupling and linearity. In addition, frequency and time domain validations for each axis model are performed using data sets excluded from the parameter estimation, with strong correlation.
System Level Bench Test for Trailing Arm Strength Estimation
Authors: Muthu Jaychandar , Soundrapandian Kanak , Mukherjee Jyoti
Published: April 2008

For suspension components, bench testing for strength is mostly accomplished at component level. However, replicating loading and boundary conditions at the component level in order to simulate the suspension system environment may be difficult. Because of this, the component's bench test failure mode may not be similar to its real life failure mode in vehicle environment. A suspension system level bench test eliminates most of the discrepancies between simulated component level and real life vehicle level environments resulting in higher quality bench tests yielding realistic test results. Here, a suspension level bench test to estimate the strength of its trailing arm link is presented. A suspension system level nonlinear finite element model was built and analyzed using ABAQUS software. The strength loading was applied at the wheel end. The analysis results along with the hardware test correlations are presented. The reasons why a system level test is superior to a component level one are also highlighted.
Comparison of Dynamic Planar SOFC Models With Different Assumptions of Temperature Layers in Energy Balance
Authors: Xi Handa , Sun Jing
Published: April 2008

As Solid Oxide Fuel Cell (SOFC) technology is quickly developing and continuously evolving, high-fidelity mathematical models based on physical principles become essential tools for SOFC system design and analysis. Different modeling assumptions, however, are used by different groups, while in-depth analysis of influence of these assumptions on model performance can not be found in literature. Meanwhile, to support system optimization and control design activities, a trade-off often has to be made between high fidelity and low complexity. One factor that could define this trade-off is the number of temperature layers assumed to represent the SOFC structure. In this paper, we investigate different models for co-flow planar SOFCs that are derived using the finite volume approach with different assumptions of temperature layers in energy balance. The model with four temperature layers is used as the baseline model, and the other models aimed at reducing the complexity of the baseline model are developed and compared through simulations for different steady state and transient scenarios. Simulation results show that the model with as few as two temperature layers—solid structure and air flow—is able to capture the dynamics of SOFCs, while assuming only one temperature layer results in substantially different dynamic characteristics.
Experimental Study and Numerical Modeling of the Dynamic Behaviour of Tyre/Suspension While Running Over an Obstacle
Authors: Gobbi M. , Giorgetta F. , Guarneri P. , Rocca G. , Mastinu G.
Published: April 2008

Simulation tools have been widely used to complement experimentation for suspension design in the automotive industry not only for reducing the development time, but also to allow the optimization of the vehicle performance. Both a test method and a simulation tool are presented for the analysis of Noise-Vibration-Harshness (NVH) performances of road vehicles suspension systems. A single suspension (corner) has been positioned on a rotating drum (2.6 m diameter) installed in the Laboratory for the Safety of Transport of the Politecnico di Milano. The suspension system is excited as the wheel passes over different cleats fixed to the working surface of the drum. The forces and the moments acting at the suspension-chassis joints are measured up to 250 Hz by means of five six-axis load cells. A mathematical representation that can accurately reflect tyre dynamic behaviour while passing over different cleats is fundamental for evaluating the suspension system quality (NVH) and for developing new suspension design and control strategies. Since the phenomenon is highly non-linear, it is rather difficult to predict the actual performance by using a physical model. However universal "black-box" models can be successfully used in the identification and control of non-linear systems. The paper deals with the simulation of the tyre/suspension dynamics by using Recurrent Neural Networks (RNN). RNN are derived from the Multi Layer Feed-forward Neural Networks (MLFNN), by adding feedback connections between output and input layers. The Neural Network (NN) has been trained with the experimental data obtained in the laboratory. The results obtained from the NN demonstrate very good agreement with the experimental results over a wide range of operation conditions. The NN model can be effectively applied as a part of vehicle system model to accurately predict elastic bushings and tyre dynamics behaviour.
Response Surface Methodology Models for Engine Mount Optimization in Motorcycles
Authors: Kaul Sudhir , Dhingra Anoop K. , Hunter Timothy G.
Published: April 2008

This paper presents Response Surface Methodology (RSM) modeling techniques to solve the engine mount optimization problem for motorcycle applications. A theoretical model that represents the structural dynamics of the engine mount system in motorcycles is first used to build the RSM model. The RSM model is then used to solve the engine mount optimization problem to enhance vibration isolation. This leads to a substantial reduction in computational effort and simplifies the governing model, yielding an input-output relationship between the variables of interest. Design of Experiments (DOE) techniques are used to build the RSM model from the theoretical model. Full factorial and fractional factorial formulations are used to construct the governing experiments. Normal probability plots are used to determine the statistical significance of the resulting coefficients. The statistically significant variables are then used to build the response surface. The design variables for the engine mount optimization problem include mount stiffness, position and orientation vectors. The influence of the orientation variables is highly non-linear and is difficult to model by using a response surface consisting of lower order terms only. Two separate algorithms are proposed to overcome this problem and the results from the RSM models are compared to those from the theoretical model.
Hybrid Two-Fluid DEM Simulation of Gas-Solid Fluidized Beds
Authors: Sun Jin , Battaglia Francine , Subramaniam S.
Published: April 2008

Simulations of gas-solid fluidized beds have been carried out using a hybrid simulation method, which couples the discrete element method (DEM) for particle dynamics with the ensemble-averaged two-fluid (TF) equations for the fluid phase. The coupling between the two phases is modeled using an interphase momentum transfer term. The results of the hybrid TF-DEM simulations are compared to experimental data and two-fluid model simulations. It is found that the TF-DEM simulation is capable of predicting general fluidized bed dynamics, i.e., pressure drop across the bed and bed expansion, which are in agreement with experimental measurements and two-fluid model predictions. In addition, the TF-DEM model demonstrates the capability to capture more heterogeneous structural information of the fluidized beds than the two-fluid model alone. The microstructures in fluidized beds are analyzed and the implications to kinetic theory for granular flows are discussed. However, the TF-DEM simulations depend on the form of the interphase momentum transfer model, which can be computed in terms of averaged or instantaneous particle quantities. Various forms of the interphase momentum transfer model are examined, and their suitability to the hybrid TF-DEM simulation approach is evaluated.
A Risk Based Study of Tipover and Off-Dock Accidents Involving Stand-Up Lift Trucks
Authors: Berry Thomas A.
Published: April 2008

It is known that operators of stand-up lift trucks who are involved in either tipover or off-dock accidents are at risk of injury whether they stay within the operator compartment during the accident, are ejected from the operator compartment, or try to jump clear of the falling lift truck. This paper presents the results of a study and analysis of 347 tipover accidents and 192 off-dock accidents involving stand-up lift trucks, all occurring between 1978 and 2002. Tipover accident reports were evaluated with respect to the severity of injury, the action of the operator, and the direction of the lift truck tipover. Off-dock accidents were evaluated with respect to the severity of the injury, the operator action and the direction that the lift truck went off the dock. The results for both tipover and off-dock accidents will be presented to allow comparison between operator action and the severity of tipover to provide designers of stand-up lift trucks with means to best reduce the likelihood of severe injuries or deaths.
In-Plane Thermoelectric Properties of Horizontally Aligned InAs/GaAs Quantum Dot Superlattices
Authors: Yadav A. , Pipe K. P. , Ye W. , Goldman R. S.
Published: April 2008

The thermoelectric properties of aligned quantum dot chains are calculated taking in account the change in band structure due to quantum size effects. From the calculated band structure, the Seebeck coefficient and electrical conductivity are calculated in a constant relaxation time approximation (CRTA). The power factor is plotted as a function of the size and spacing of dots and an increase is shown in the power factor for decreasing dot size. The net power factor is calculated using a parallel conductor model. The results are compared to the case of randomly spaced dots which have a power factor calculated using an effective resistance model.
Multiphysics Modeling of an Active Noise Control Device
Authors: Zahui Marcellin
Published: April 2008

Cost and availability of fast computer computers have made it affordable to solve complex engineering problems involving multiple physics using a single finite elements model. The practice is commonly referred to as multiphysics modeling. The objective in this study is to investigate the effectiveness of multiphysics modeling tools as applied to engineering design and analysis. Therefore, active noise control, which involves four different fields of sciences and engineering, has been chosen for the study. The physics involved in active noise control are: Electromagnetic, Structural vibration, Fluid, and Acoustic. The initial goal was to solve a simple noise cancellation problem using a single finite elements model and a personal computer. The task was rather difficult and inefficient. The approach presented here uses a single finite element model and combination of two modeling and analysis software. A well known active noise control methodology is used to cancel the noise radiated by a simply supported circular vibrating disk using a loudspeaker. Harmonic load is applied to the disk and the resulting displacements are fed to a controller designed using MATLAB/SIMULINK®. The output of the controller is used in the ANSYS® finite elements model to compute the acoustic field with and without control. The results show that more than one software packages running on separate personal computers are recommended for an effective multiphysics modeling.
Model Based Design of Piezoelectric Generators Utilizing Geometrical and Material Properties
Authors: Richter Bjo¨rn , Twiefel Jens , Hemsel Tobias , Wallaschek Jo¨rg
Published: April 2008

This paper presents a general model based on the electromechanical circuit theory. The model is set up as a mechanical equivalent model for base excited systems and describes the behaviour of a piezoelectric element around one resonance frequency which is sufficient for most practical applications. The model is extended to obtain the influence of geometrical and material properties. The derivated properties are used to describe the parameters of the general model which is easy to handle. Using this model either the calculation of the output power on a specific electric load or the determination of the design of the used piezoelectric element for a needed electric output power is possible. The paper focuses on the design of the ratio of length and width of a piezoelectric bimorph. The validity of the model is shown by the comparison of computed and experimental results.
Non-Intrusive Technique for Measuring Instability Wave Amplitudes at Simplex Swirl Atomizer Exit
Authors: Orekhov Viktor L. , Panchagnula Mahesh V.
Published: April 2008

An optical method for non-intrusive wave amplitude measurement is examined. An experimental setup was constructed to produce sprays of various fluids including Canola oil and glycerin-water mixtures, such that precise control of pressure up to 140 psi was possible. A spray was produced by a 20 Gallon per hour oil burner nozzle at varying pressures. Initially, a smooth laminar conical sheet was noticed which eventually was found to break up into droplets. A laser was passed through the laminar conical sheet and was projected onto a surface on the other side and resulted in a vertical linear projection. This projection is postulated to be formed due to the scanning motion of the laser beam as instability waves pass through the laser. The angle of this scan was found to be a function of pressure, cone angle, and distance of laser from nozzle. High resolution images were taken of the film profile as well as the projected image and image analysis software was used to calculate cone angles and angular scan of the laser. Tests were performed with Canola Oil as well as a mixture of glycerin and water in order to evaluate the effect of viscosity and surface tension on the measurements. The resulting data was used to illustrate a principle for determining the instability wave amplitude using this technique.
Spray Cooling of an Inverted Heated Surface
Authors: Pyrtle Frank , Sato Alberto D.
Published: April 2008

Experiments were performed to determine heat transfer characteristics of water sprays impacting a flat, inverted surface. Using a compressed gas tank to provide motive force in an open loop spray cooling system, droplet sprays were produced without the assistance of an atomizing gas stream. A range of droplet volumetric fluxes was produced for cooling the inverted heated surface using a full-cone spray nozzle. Heat transfer curves were plotted in the form of heat flux as a function of wall temperature difference, for volumetric flow rates up to 627 mL/min, dissipating up to 451 W/cm2. Heat transfer coefficients were also determined as functions of heat flux. The results were compared to prior data for standard, downward spraying onto heated surfaces.
Characterization of Biomimetic Mineral Coated 3D PLGA Scaffolds
Authors: Jayasuriya A. Champa , Shah Chiragkumar , Goel Vijay , Ebraheim Nabil A.
Published: April 2008

The bone-like carbonate apatite (BLCA) coatings can be coated biomimetically in the polymer surfaces by soaking in the simulated body fluid (SBF). This SBF contains similar ionic constituents to human blood plasma. Micro-porous 3D poly(lactic-co-glycolic acid) PLGA scaffolds were fabricated by the solvent casting/salt leaching technique using chloroform to dissolve the polymer. We accelerated the deposition of mineral on scaffolds for 1-2 days, modifying the mineralization process using surface treatments and 5x SBF. These scaffolds were analyzed by Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR) and X-ray Diffraction (XRD). The scaffolds coated with BLCA layer were placed in the 24 well plates containing 2 ml of media, such as Tris Buffered Saline-pH 7.4, cell culture media containing αMEM supplemented with 10% FBS, and 1% penicillin-streptomycin and incubated at 37°C for 21 days. The BLCA layer on surfaces of scaffold was stable even after 21 days immersed in Tris Buffered Saline and cell culture media. This study suggests that BLCA were stable for at least 3 weeks in the both media, and therefore, mineral has a potential to use as a carrier for biological molecules for localized release applications as well as bone tissue engineering applications.
Comparison of Experimental and Numerical Temperature Distributions in Tissues During Short Pulse Laser Irradiation Using Focused Beam
Authors: Dutta Ashim , Pal Gopalendu , Mitra Kunal , Grace Michael S.
Published: April 2008

The objective of this work is to perform experimental measurements validated with numerical modeling results for analyzing the temperature distributions and heat affected zone during short pulse laser irradiation of tissues using focused beam. A Q-switched laser is used as a radiation source. A threelayered tissue phantom model of skin consisting of epidermis, dermis, and fatty tissues is first considered for model validation. Tumors are simulated with inhomogeneities embedded inside the tissue phantoms. Experiments are next conducted with freshly excised skin tissue samples from mice and finally on live anaesthetized mice to consider the bulk effect of convective heat transfer due to blood flow. Experimental measurements of axial and radial temperature distributions for all the cases are compared with numerical modeling results obtained using Pennes' bio-heat transfer equation coupled with either traditional Fourier parabolic or non-Fourier hyperbolic heat conduction formulation. Experimentally measured temperature profiles in tissue phantoms, skin tissue samples, and live anaesthetized mice are found to match extremely well with the predictions from the non-Fourier model than the Fourier formulation by considering skin as a multi-layered medium. It is also observed that focused laser beam produces desired temperature rise at the target site with lesser radial spread compared to a collimated laser beam source.
A Novel Technique for Frequency and Time Optimization of Automotive Engine Mount Parameters
Authors: Arzanpour S. , Eslaminasab N. , Shubert B. , Narimani A. , Golnaraghi M. F.
Published: April 2008

In this paper, we examine a linear one degree of freedom engine mount to obtain optimum mount parameters in a passive configuration. An engine mount is a device that may be used to isolate vehicle body from the engine vibrations - forced excitation, while minimizing the effects of road-induced disturbances on the engine - base excitation. The linearity of the system allows us to analyze the frequency and time response characteristics in both excitation cases analytically. Optimal damping and stiffness values for the isolator are obtained by minimizing certain cost functions in the frequency and time domains, respectively. In the frequency domain the cost function is based on the root mean square (RMS) of the absolute acceleration and relative displacement in the frequency domain, and in the time domain it is based on the transmitted acceleration and displacement. The time and frequency responses of the isolator are optimized by varying the stiffness and damping ratios for both base and forced excitation cases. These optimal values are obtained, and the results are verified numerically. In this case, although the mathematical model is linear, it is interesting to note that the time and frequency optimal values are not the same. As a result, this exercise shows that no passive-mount is adequate to perfectly deal with all application specs and isolation criteria. In this paper, a novel approach is suggested to select the mount parameters for various passive or active configurations.
IN2TEC: A Multidisciplinary Research Project Involving Researchers, Students and Industry
Authors: Neves M. M. , Cunha J. L. , Arezes P. M. , Lea˜o C. P. , Teixeira S. F. C. F. , Lobarinhas P. , Teixeira J. C.
Published: April 2008

Bearing in mind that undergraduate students must get involved in research and that local industry must be a university partner, the School of Engineering, from University of Minho, has taken the initiative in funding some technical research projects in specifically defined areas (http://www.eng.uminho.pt). In this context, one of the projects founded concerns the development and testing of functional knitting which can be used with success in the lining of a shoe. The study of shoe comfort is of great importance to sport and leisure footwear manufactures, because in these particular situations, moisture disposal over a number of hours is a main problem. Three structures which combine different raw materials (soybean fiber, bamboo fiber, corn fiber, cotton, polypropylene and polyester) have been manufactured by a local textile factory. A group of students mainly from Mechanical and Textile Engineering classes are currently testing these knitting in terms of their water vapor and air permeability and other physical parameters at the laboratory. Tests with a thermal manikin have been used to measure its thermal insulation. A transient model for heat and mass transfer in a fabric has been implemented. From the solution, temperature and vapor density profiles in the fabric thickness can be obtained as well as, the amount of water dissolved in the fabric. This model has been integrated with an existing human thermal comfort model. Thermal comfort surveys are now being made at the Ergonomics Laboratory of the University of Minho with undergraduate Mechanical and Industrial Engineering students, wearing sport shoes manufactured by a local footwear factory, and these results can be compared using statistical analysis, with the experimental and numerical results already obtained.
Assesment of Modeling and Discretization Error in Finite-Volume Large Eddy Simulations
Authors: Adedoyin Adetokunbo A. , Walters D. Keith , Bhushan Shanti
Published: April 2008

Large eddy simulations of turbulent flows are known to suffer from two separate error sources: the subgrid stress model and the numerical discretization scheme. In general, the two sources of error cannot be separately quantified for finite-difference/finite-volume CFD simulations. The motivation of this paper lies in the desire to determine optimum combinations of currently available subgrid stress models and numerical schemes for use in large eddy simulations of complex flows. Error assessments for large eddy simulation of turbulent fluid flow are presented. These assessments were carried out using pseudospectral simulation techniques in order to isolate finite-differencing and modeling errors by explicitly adding numerical derivative error terms to the simulations and analyzing their effect. Results from several combinations of subgrid stress model and spatial discretization scheme are presented. Simulations were performed for decaying isotropic turbulence on both 323 and 643 grids. Results were compared in terms of spectral energy distributions at succeeding time intervals. For verification, the pseudo-spectral results were compared to LES solutions obtained from a commercially available finite-volume flow solver (FLUENT), and comparisons were made in terms of energy decay rates, numerical versus subgrid stress dissipation levels, and computed energy spectra. The results highlight the interaction between subgrid stress model and discretization scheme. The results also indicate that certain combinations of model and numerical scheme may be more appropriate for finite-volume LES than others.
Void Evolution via Coupled Creep and Electromigration in Confined Small Scale Interconnects
Authors: Lu Wei , Kim Dongchoul
Published: April 2008

This paper proposes a three dimensional electromigration model for void evolution in small scale interconnects. Concurrent kinetics of creep flow and surface diffusion as well as the effect of surrounding material are considered to provide better understanding of the evolution process. The multiple kinetics and energetics are incorporated into a diffusive interface model. A semi-implicit Fourier spectral method and the preconditioned biconjugate-gradient method are proposed in the computations to achieve high efficiency and numerical stability. We systematically studied kinetic processes from diffusion dominated to creep dominated. Which process dominates, as revealed by the analysis, is determined by a combination of viscosity, mobility, interconnect thickness, and void radius. Previous studies on electromigration suggest that the void shape evolution is determined by the competition between the electron wind force and the surface energy. There exists a critical initial void shape, which determines whether a void evolves into a slit or not. However, our simulations show that in the same situation a creep dominated process can lead to a quite different morphology. A spherical void can evolve into a bowl shape, and further split into two smaller voids. It is also shown that the interconnect geometry has an important effect.
A Nonlithographic Approach for Creating Unstable Hierarchical (Micro-Nano) Superhydrophobic Silicon Surfaces
Authors: Wang Ming-Fang , Nraghuna Nithin , Ziaie Babak
Published: April 2008

In this paper, we report on an inexpensive non-lithographic approach to create superhydrophobic silicon surfaces using porous silicon technology. We have used a two-step method to create an unstable hierarchical (micro-nano) superhydrophobic silicon surface. Our technique is a unique combination of a high current density (170mA/cm2) porous silicon formation step followed by a wet etching step in BOE/HNO3. Porous silicon layers, of both n- and p-type wafers were used in these experiments. The contact and rolling angles were measured for: 1) regular porous silicon, 2) porous silicon with hierarchical fractal-shape structure, and 3) hierarchical fractal-shape porous silicon after the wet etching step. For both n- and p-type wafers, the contact angles of regular porous silicon (nonhierarchical) were around 120° with a rolling angle of 90°. With hierarchical structure, the contact angle increased to 135° and after addition wet etching, the contact angle approached 160° (superhydrophobic). Besides, after wet etching step the surface became extremely unstable showing a very low rolling angle (<1°).
Dynamic Model of Electron Beam Induced Deposition (EBID) of Residual Hydrocarbons in Electron Microscopy
Authors: Rykaczewski Konrad , White Ben , Browning Jenna , Marshall Andrew D. , Fedorov Andrei G.
Published: April 2008

Adsorbed species surface diffusion Electron beam induced deposition (EBID) of residuals carbon can be either a contamination problem or can provide a basis for 3-D nanofabrication and nanoscale metrology. In this process a solid deposit is formed at the point of impact of the electron beam due to the decomposition of residual hydrocarbon species adsorbed on the solid substrate. The first observation of EBID can be traced to miscroscopists who noticed the growth of thin films of carbon while imaging using an electron microscope. The process was referred to as "contamination" because of its adverse effects on the microscope's imaging quality. Later, it has been demonstrated that with appropriate control of the electron beam this problematic contamination can be exploited to deposit three dimensional nanostructures with the spatial resolution down to 10nm. Numerous researchers have experimentally explored various factors influencing EBID growth rate and geometry of the deposit. To date, the most comprehensive theoretical model predicting the shape of the deposit in EBID is due to Silvis-Cividjian[1]. However, this model accounts for electron transport only. A few, fairly rudimentary models have also been developed for mass transport in EBID, but usually limited to rather simplistic treatment of electron transport. To this end, we have developed a comprehensive dynamic model of EBID coupling mass transport, electron transport and scattering, and species decomposition to predict deposition of carbon nano-dots. The simulations predict the local species and electron density distributions, as well as the 3-D profile and the growth rate of the deposit. Since the process occurs in a high vacuum environment surface diffusion is considered as the primary transport mode of surface-adsorbed hydrocarbon precursor. Transport, scattering, and absorption of primary electron as well as secondary electron generation are treated using the Monte Carlo methods. Low energy secondary electrons (SE) are the major contributors to hydrocarbon decomposition due to their energy range matching peak dissociation reaction cross section energies for precursor molecules. The local SE flux at the substrate and at the free surface of the growing deposit is computed using the Fast Secondary Electron (FSE) model. When combined with the total dissociation reaction corssection and the local hydrocarbon surface concentration, this allows us to compute the local deposition rate. The deposition rates are then used to predict the shape profile evolution of the deposit. Simulation results are compared with an AFM imaging of carbon EBID.
Development and Initial Validation of a Two-Equation Transition Sensitive Turbulence Model for CFD Simulations
Authors: Jones J. M. , Walters D. K.
Published: April 2008

This paper presents the initial development and validation of a modified two-equation eddy-viscosity turbulence model for computational fluid dynamics (CFD) prediction of transitional and turbulent flow. The new model is based on a k-ω model framework, making it more easily implemented into existing general-purpose CFD solvers than other recently proposed model forms. The model incorporates inviscid and viscous damping functions for the eddy viscosity, as well as a production damping term, in order to reproduce the appropriate effects of laminar, transitional, and turbulent boundary layer flow. It has been implemented into a commercially available flow solver (FLUENT) and evaluated for simple attached and separated flow conditions, including 2-D flow over a flat plate and a circular cylinder. The results presented show that the new model is able to yield reasonable predictions of transitional flow behavior using a very simple modeling framework, including an appropriate response to freestream turbulence and boundary layer separation.