bluuebunny/crossref_metadata_2025 huggingface dataset:
The Strain Distribution and Force Transmission Path Through Pubic Rami During Lateral Pelvic Impacts
Authors: Untaroiu Costin D. , Salzar Robert S. , Guillemot Herve´ , Crandall Jeff R.
Published: August 2009

The pubic rami fracture is a common pelvic injury for vehicle occupants as well as for pedestrians struck during side impacts. While many studies have investigated the structural properties of the pelvis in lateral loading, relatively few investigations have compared the applied loads with local response of the pubic rami. The aims of this study are to investigate the force transmission paths and strain distribution for the anterior (i.e., rami) and posterior (i.e., sacrum) regions of the pelvis under acetabular impact loading. Eight male postmortem human surrogate pelves were tested to failure in quasi-static (n = 2) and dynamic (n = 6) conditions using an Instron test machine and a drop-tower, respectively. The denuded pelves were potted and then cut along a line connecting the greater sciatic notch and the middle of anterior iliac spine. Lateral loading was applied at the site of the acetabulum using a custom-fit femoral head surrogate made of steel. An acoustic emission (AE) sensor and uniaxial strain gages were affixed to the four rami (anterior and posterior) to assess the time of fracture as well as the regional strain distribution. In addition to measuring the impacting force, the loads transmitted through the pelvis were recorded on the non-struck side using load cells at the inferior and superior potting attachment points. To better understand the load path and strain distribution through the rami a finite element model of a human pelvis was developed from computer tomography data and validated based on available published test data. Then, the lateral impact test was numerically simulated and the model responses were mostly within the min-max ranges of the test data. The test data and FE simulations showed that prior to the fracture the pubic symphysis joint transmitted the higher percentage of load (about 66% in dynamic tests). The strain distribution analysis of the impact pelvic tests showed that the pubic rami are subjected predominantly to compressive stress on the anterior side and tensile stress on the posterior side. While the anterior pubic side of the non-impact part of the pelvis was always subjected to compressive stress, some test variability was observed on other regions of the non-impact sides. In addition to providing validation data for computational models, the results highlight the vulnerability of pubic rami structure in carrying lateral load in acetabular impacts and may lend insight into the development of injury countermeasures.
Particle-Particle Interactions on the Surface of a Drop Subjected to a Uniform Electric Field
Authors: Nudurupati S. , Janjua M. , Singh P. , Aubry N.
Published: August 2009

We recently proposed a technique in which an externally applied uniform electric field was used to alter the distribution of particles on the surface of a drop immersed in another immiscible liquid. Particles move along the drop surface to form a ring near the drop equator or collect at the poles depending on their dielectric constant relative to that of the two liquid involved. This motion is due to the dielectrophoretic force that acts upon particles because the electric field on the surface of the drop is non-uniform, despite the fact that the applied electric field is uniform. This technique could be useful to concentrate particles at a drop surface within well-defined regions (poles and equator), and separate two types of particles at the surface of a drop. In this paper we show that in addition to the dielectrophoretic force the particles also interact with each other via the dipole-dipole interactions to form chains or move away from each other depending the local direction of the electric field. The regions in which the local electric field is normal to the drop surface, i.e., the poles, the particles move away from each other. On the other hand, near the equator, where the local direction of electric field is tangential to the drops surface, they form chains that are aligned parallel to the electric field direction.
Calculation of Dynamic Coefficients for a Magnetically Levitated Artificial Heart Pump Using a CFD Approach
Authors: Untaroiu Alexandrina , Wood Houston G. , Allaire Paul E. , Dimond Timothy W.
Published: August 2009

The artificial heart community acknowledges the 3rd generation Ventricular Assist Devices (VADs) as the leading technology in mechanical blood pump development. This category consists of rotary pumps with no mechanical or fluid bearings in contact with the fluid medium, usually magnetic or noncontacting hydrodynamic bearings. A magnetic suspension prevents the rotating impeller from contacting the pump’s internal surfaces and reduces regions of stagnant and high shear flow that normally surround a fluid or mechanical bearing. Magnetic bearings have no moving parts in contact and thus do not wear over time; this generally lengthens the operational life of the pumps as compared to those supported by conventional bearings. Employing this 3rd generation technology, the University of Virginia has been developing a ventricular assist device (LifeFlow) with a rotor that is suspended entirely by magnetic bearings. In order to perform the stability analysis, the hydrodynamic effects of the rotating impeller should be included in the calculation. This study describes the method to calculate the stiffness, damping, and mass coefficients, based on the CFD prediction of radial fluid forces exerted on the impeller due to its eccentric position inside the pump housing over a range of operating conditions. In consideration of the suspension design, the fluid forces exerted on the levitated axial impeller were estimated using CFD such that any fluid perturbations would be accounted for and counterbalanced during the suspension and motor design phase.
Changes in the Dynamic Stability of Walking in Active Healthy Older Adults Independent of Changes in Walking Speed
Authors: Kang Hyun Gu , Dingwell Jonathan B.
Published: August 2009

Older adults commonly walk slower, which many believe helps improve their walking stability. However, they remain at increased risk of falls. We investigated how differences in age and walking speed independently affect dynamic stability during walking, and how age-related changes in leg strength and ROM affected this relationship. Eighteen active healthy older and 17 younger adults walked on a treadmill for 5 minutes each at each of 5 speeds (80–120% of preferred). Local divergence exponents and maximum Floquet multipliers (FM) were calculated to quantify each subject’s responses to small inherent perturbations during walking. These older adults exhibited the same preferred walking speeds as the younger subjects (p = 0.860). However, these older adults still exhibited greater local divergence exponents (p<0.0001) and higher maximum FM (p<0.007) than young adults at all walking speeds. These older adults remained more unstable (p<0.04) even after adjusting for declines in both strength and ROM. In both age groups, local divergence exponents decreased at slower speeds and increased at faster speeds (p<0.0001). Maximum FM showed similar changes with speed (p<0.02). The older adults in this study were healthy enough to walk at normal speeds. However, these adults were still more unstable than the young adults, independent of walking speed. This greater instability was not explained by loss of leg strength and ROM. Slower speeds led to decreased instability in both groups.
A Hybrid Heat Flux Distribution Model for Jet Impingment on a Flat Plate
Authors: Carbajal Gerardo , Peterson G. P. , Sobhan C. B. , Queheillalt D. T.
Published: August 2009

A hybrid numerical-experimental technique has been developed to determine the unknown non-uniform heat flux distribution produced by the impingement of a jet on one side of a vertical flat aluminum plate. The method involves coupling of the unknown heat flux distribution as a boundary condition to the heat diffusion equation, which is solved by the finite volume method utilizing a computer code developed for the purpose. The heat flux distribution has been modeled using both a deterministic parabolic function and a probabilistic function. The resulting transient inverse problem was solved by comparing the numerical solution with the experimental data on the back side of the plate. In the experimental method, the aluminum plate was heated for 40 seconds, and an infrared camera located at the back side was used to record the transient temperature data at intervals of one second. A propane torch was the source of the impinging jet, with the flux intensity assumed to be constant with respect to time. The solid plate was cooled by natural convection and radiation heat transfer at the back side. It was found that use of the probabilistic function for the heat flux distribution produced numerical results where the temperature difference between the numerical and experimental data was within an error limit of 0.4 °C. Conversely, the parabolic function produced temperature results that did not match well with the experimental data.
Dynamic Analysis of High-Contact-Ratio Spur Gears With Asymmetric Teeth
Authors: Karpat F. , Ekwaro-Osire S.
Published: August 2009

In this research, a numerical technique is used to study the performance of high-contact-ratio (HCR) spur gears with asymmetric teeth. Asymmetric teeth have been shown to minimize dynamic loads and to increase the load carrying capacity. This is due to the fact that these teeth have a larger pressure angle on the drive side compared to the coast side. In literature, symmetric gear teeth with HCR have been shown to also yield low dynamic loads and high load capacities. HCR gears have these positive attributes because for gears in a mesh, the number of tooth pairs sharing the transmitted load alternates between two and three. In this study, the separate benefits of an HCR gear and asymmetric teeth are unified into a spur gear with asymmetric teeth. In this case, the effect of the gear contact ratio, addendum factor, mesh stiffness, pressure angles, and operation speeds on dynamic tooth loads are considered. The influences of these parameters on dynamic response are presented and discussed. A comparison between standard and non standard gear pairs in literature is also presented, with respect to dynamic tooth loads. Sample simulation results, which were obtained by using an in-house computer program, are discussed. The results obtained are shown to match well with some related analytical and experimental results in literature. It is further demonstrated that HCR spur gears with asymmetric teeth do provide a marked advantage compared to the conventional spur gears with symmetric teeth.
Characterization of Compressive Behavior of Developing Human Talus
Authors: Mahmoodian Roza , Leasure Jeremi , Siegler Sorin , Capaldi Franco
Published: August 2009

Mechanical characterization of human cartilage anlagen is required in order to effectively model congenital musculoskeletal deformities. Such modeling can effectively explore the effect of treatment procedures and potentially suggest enhanced treatment methods. We therefore determined the stress relaxation behavior of cartilage plugs obtained from third-trimester still-born fetuses in unconfined and confined compression geometries. The material parameters determined were the aggregate modulus HA = 0.15 ± 0.07 MPa, permeability coefficients k0 = 2.01 ± 0.8 × 10−14m4N−1s−1 and M = 4.6 ± 1.0, Young’s modulus Es = 0.06 ± 0.03 MPa, and Poisson’s ratio ν = 0.4 ± 0.06. As compared to adult articular cartilage, stiffness was an order of magnitude lower than the values reported in the literature, inferring the relative softness of the tissue; and the permeability was an order of magnitude higher indicating relative ease of flow in the tissue. Poisson’s ratio also was close to the higher end of the range found in previous studies. Such material is expected to deform and relax to larger extents.
Computational and Experimental Investigation of Arterial Hemodynamics
Authors: Rose William C. , Johnson David , Spaeth Justin , Edwards Jonathan , Beris Antony
Published: August 2009

Dynamic arterial blood pressure and blood flow are key determinants of normal or pathological functioning of the cardiovascular system. The measurement of these variables at multiple locations in the body is clinically and physiologically valuable, but difficult to achieve except with invasive methods which carry significant risk to the patient. We have developed and here present a computational model of systemic arterial hemodynamics. The model predicts dynamic pressures and flows throughout the systemic arterial vascular bed. The inputs to the model are pressure or flow measured at a single site, and a description of the architectural and mechanical properties of the blood and blood vessels. We have also measured dynamic pressure and flow noninvasively in healthy women and men. We use these measurements to test and refine the model. The arterial model includes over 24 million blood vessels. The dimensions and branching patterns of 45 large arteries are derived from population averages. Approximately half of these vessels terminate in self-similar branching networks of arteries which extend to capillary-sized vessels. Womersley’s linearization of the Navier-Stokes equations is used to describe the relationship between pressure and flow in each vessel. The inviscid wave velocity in each vessel is estimated based on the combined effects of Young’s modulus, vessel thickness and diameter, and the rheological properties of blood. The blood is modeled as a non-Newtonian fluid whose hematocrit and viscosity vary with vessel size. Wave reflections are computed at all junctions between vessels. The nonlinear pressure drop occurring at the bifurcation of each vessel into daughter vessels is estimated and taken into account when computing the pressures and flows throughout the network. Dynamic pressure is measured noninvasively by applanation tonometry. Dynamic blood velocity is measured with Doppler ultrasonography, and vessel diameter is measured using ultrasound. Custom software uses the electrocardiogram to average data from multiple beats to create ensemble average waveforms for pressure, velocity, and diameter. Data has been collected from the radial and carotid arteries. The experimentally measured pressure from one site is used as input to the model. The model predictions are compared to the other experimental measurements. Blood vessel mechanical properties are estimated by adjusting the model parameters to get good agreement between measured and predicted quantities. This capability can be used to understand effects of pathological changes in vascular properties on local pressure and flow behavior throughout the vasculature.
Characterization and Modeling of Capacitive Micromachined Ultrasonic Transducers for Diagnostic Ultrasound
Authors: Doody Christopher B. , White Robert D. , Wadhwa Jaspreet S. , Lemmerhirt David F.
Published: August 2009

This paper describes the characterization and modeling of capacitive micromachined ultrasonic transducers (cMUTs). Computational models of the transducers were produced through the combined use of finite element analysis (FEA) and lumped element modeling. Frequency response plots were generated for both transducers in air and water environments. Through the use of laser Doppler velocimetry, transient step response and frequency sweep tests were performed on single array elements. These measurements are compared to the predicted results represented in the models. The computational results for both coupled and uncoupled arrays are compared, and show a significant increase in the array bandwidth due to coupling. Frequency sweep tests were also performed on column array elements, and results were compared between driven and adjacent, non-driven columns.
Fourier Transform Infrared Spectroscopic Assessment of Changes in Composition of Proteoglycans and Collagen in Developing Human Fetal Tarsal Bones
Authors: Leasure Jeremi , Mahmoodian Roza , Siegler Sorin , Capaldi Franco , Pleshko Nancy
Published: August 2009

The proteoglycan and collagen composition of cartilage is known to change during fetal and postnatal development. The current report represents the first attempt to semi-quantitatively determine the changes in the composition of developing human fetal cartilage. Human fetal talus bones were obtained from late 2nd and 3rd trimester specimen. Fetal bones are comprised of an intramembranous tissue commonly referred to as cartilage anlagen. During maturation the anlagen develops an ossific nucleus. Fourier Transform Infrared Spectroscopy (FT-IRS) and Fourier Transform Infrared Imaging Spectroscopy (FT-IRIS) were used to assess the changes in composition relating to tissues main constituents, collagen (COL) and proteoglycan (PG). FT-IRS was used to obtain average values of composition across the entire anterior-posterior length of each bone. Relative percent composition values of COL and PG were calculated by multivariate least-squares analysis of model compound spectral features associated with COL (Amide I spectral absorbance) and PG (C-O-C sugar absorbance). It was shown that PG/Amide I values decreases from 4.9 +/−3.4 to 2.9 +/−3.2 over development. These values were translated to a relative percent compositional drop of PG from 49.9% +/−16.2% to 36.4% +/−8.1%. FT-IRIS was used to observe the spatial changes in composition from the subchondral region to the articulating surfaces. Collagen was observed to be distributed away from the articulating surfaces with increase in development. Proteoglycans were observed to have uniform concentrations with a marked decrease in PG across developmental stages. A noticeable benchmark in development is the ossific nucleus which was absent in the 2nd trimester. The findings of the current study demonstrate that cartilage anlage contains approximately triple the amount of proteoglycan in the 2nd trimester as compared to that previously reported in hyaline articular cartilage. The proteoglycan decreases over development, resulting in double the proteoglycan in the 3rd trimester as compared to previously reported adult values. No site-specific, macroscopic (FT-IRS), differences in PG content were found while microscopic assessment (FT-IRIS) observed heterogeneity with marked changes in PG content.
Modeling of Relative Damping in Defining the Equilibrium Point Trajectory for the Human Arm Movement Control
Authors: Chen Kai , Foulds Richard A. , Adamovich Sergei , Qiu Qinyin , Swift Katharine
Published: August 2009

Existing research suggests that limb motion can be represented as an Equilibrium Point (EP) trajectory in combination with a trajectory that reflects specified damping and stiffness at each joint. This model utilizes the concept of relative damping, an integral factor in defining the Equilibrium Point trajectory, to help maintain stability during the arm movement. By using commercialized Flock of Bird® (FOB) sensor, we can obtain experimental trajectories and angular information for human elbow and shoulder joints, as well as forearm and upper arm position during reaching in slow and fast movements. We replaced the complicated inverse kinematics computation of brain with our simple relative damping model, and then calculated the EP trajectories of the elbow and shoulder to use as inputs to our following forward kinematics model. The model generated trajectories which closely match the experimental data. The novel features of this model include the EP trajectory input generated by relative damping. Therefore, we conclude that multi-joint manipulations can be modeled by an appropriate EP trajectory along with relative damping.
A Root Locus Method for Stability Analysis of Heat Conduction in Multilayer Composite Solids
Authors: Yang Bingen , Shi Hang
Published: August 2009

Excessive heat generation within a body can cause unbounded temperature or thermal instability. In this work, a stability criterion is established for one-dimensional composite solids with internal heat generation at a rate proportional to their temperature. In the development, a spatial state formulation is used to derive a characteristic equation for system eigenvalues. A root locus analysis of the characteristic equation yields a stability criterion, by which an upper bound of heat source for thermal stability is obtained, and the gain of heat source is related to the number of unstable (positive) eigenvalues. The proposed stability test requires minimum numerical effort, does not require the information about system eigenvalues, and is applicable to various spatial distributions of heat source.
Comparative Study of Different Weave Architectures of Woven Textile Composites Under Low Velocity Impact Loading
Authors: Chandekar Gautam S. , Kelkar Ajit D. , Mohan Ram V. , Thatte Bhushan S.
Published: August 2009

Fiberglass epoxy laminates are strong in out-of-plane loading such as low velocity impact. Woven textile composites have better properties in mutually orthogonal and out of plane directions than the unidirectional laminates. Along with the improvement in properties, they have low manufacturing cost since much of the fabrication can be automated. In the present study, different weave architectures such as basket weave, twill weave, 4 harness satin and 8 harness satin were studied numerically for response under low velocity impact loading. Main consideration was given to the maximum load carrying capacity and maximum energy absorbed by the laminates. All numerical investigations were performed using LS-DYNA® software. The laminates were modeled in VPG using 3D solid elements in a mosaic fashion to represent different weave patterns. Mechanical properties were calculated by classical micro-mechanical theory and assigned to the elements.
SnAP: A Comprehensive Software Package for the Simulation of Serial Manipulators
Authors: Gonza´lez-Barbosa E. A. , Gonza´lez-Palacios M. A. , Aguilera-Corte´s L. A.
Published: August 2009

The solution of kinematics problem for serial manipulators is fundamental for their analysis, simulation and computer control, for this reason, this paper introduces the software package called SnAP (Serial n-Axes Manipulators), which is developed under the ADEFID framework [1], where the manipulator is conceptualized as a derived class from CRobokin, CMachine and CIpiSModel, which are fundamental ADEFID classes. SnAP has been developed with efficient algorithms in a closed-loop solution to solve direct kinematics, whereas for the case of inverse kinematics, matrix formulation, elimination and numerical methods are implemented. Furthermore, for the architecture definition, the user is able to display a dialog box in which the design parameters are set while the solid model is updated simultaneously showing the actual configuration. Since ADEFID provides tools to graphical interface with embedded control components, SnAP adopted them to not only simulate virtually, but also with a parametric prototype designed for this purpose.
Exploring Microscale Phenomena With the µPIVOT (µPIV and Optical Tweezers)
Authors: Tretheway Derek C. , Ne`ve Nathalie , Kohles Sean S.
Published: August 2009

The hydrodynamic interaction between particles contributes significantly to the rheological properties of many suspensions [1] regardless if the suspending fluid is Newtonian or non-Newtonian. While the theoretical framework for particle-particle interactions in Newtonian fluids is well established, theoretical analysis of particle-fluid and particle-particle interactions in non-Newtonian fluids is limited due to difficulties in establishing a proper constitutive equation for non-Newtonian fluids. The direct study of particle-particle interactions will resolve the hydrodynamic forces between suspended particles, aid the development of Newtonian and non-Newtonian fluid suspension models, and provide experimental validation of existing models.
Numerical Optimization of a Cogenerating Parabolic Solar Collector Receiver
Authors: Gonzalez Catalina , Rhee Jinny
Published: August 2009

The motivation for this study comes from the need for a clean, renewable energy source, which is greater now more than ever to reduce the country’s dependence on fossil fuels. Cogenerating solar systems can provide heat and electricity for many industrial applications such as power generation and absorption refrigeration systems. For example, data centers that run on conventional refrigeration systems are one of the largest electricity consumers in the nation, accounting for 1.2% of the total electricity consumption in 2005. This electricity consumption, almost half of which is used to run the data center’s air conditioning units, translates to $2.7 billion in electricity costs for that year. Using cogenerating solar systems for these types of applications could represent a significant amount of savings in electricity costs. The objective of this paper is to numerically optimize a receiver for a cogenerating photovoltaic and thermal parabolic solar collector that will produce both heat and electricity. The solar cogeneration system studied will convert solar energy into both heat and electricity by using a combination of photovoltaic cells, a parabolic trough thermal collector, and water as the liquid heat exchanger on the photovoltaic cells. The peak electrical efficiency of the multi-junction gallium arsenide Spectrolab photovoltaic cells used in this study is about 32%, with the rest of the solar energy being absorbed as heat. These temperature gains in the cells can lead to a decrease in efficiency. However, in cogenerating systems, water is used as a working fluid to remove heat from the photovoltaic cells, thus aiding in increasing the electrical efficiency of the photovoltaic system as well as increasing the thermal energy gained from the solar thermal collector. The numerical analysis for this project will use Flotherm, a CFD tool used to solve fluid and thermal problems. A single-phase water cooled square duct receiver subjected to non-uniform heating will be analyzed in Flotherm to determine the optimal parameters for the best convection heat transfer between the working fluid and the photovoltaic cells. To enhance the heat transfer between photovoltaic cells and working fluid, the inner surface of the receiver tube receiving the heat flux will be improved by adding fins to increase heat transfer and induce turbulent flow. The initial receiver design will be compared with other receivers to determine the optimal design. Results will be presented parametrically for a range of flow rates and receiver geometry.
Femtosecond Laser-Induced Silicon Surface Morphology in Water
Authors: Han Yukun , Lin Cheng-Hsiang , Tsai Hai-Lung
Published: August 2009

This article investigates the use of femtosecond laser induced surface morphology on silicon wafer surface in water confinement. Unlike irradiation of silicon surfaces in the air, there are no laser induced periodic structures, but irregular roughness is formed when the silicon wafer is ablated under water. The unique discovery of a smoothly processed silicon surface in water confinement under certain laser parameter combinations may help improve laser direct micromachining surface quality in industrial applications.
Experimental Study of Fluid Flow in Microchannel
Authors: Lu Xi , Nnanna A. G. Agwu
Published: August 2009

This paper presents a study of fluid flow through microchannel. Based on the work of Senta and Nnanna, [23], a trapezoidal-shaped manifold is used to ensure uniform flow distribution in the microchannel. Analysis further shows that flow uniformity among the channels largely depends on shape of the manifolds, length and location of inlet and outlets, and the inlet flow rate. The test setup consists of one hundred twenty-six 14.5μm-width channels, flow loop, heat source, thermal sensors and pressure transducers. Flow of fluid through the channels is regulated using a peristaltic pump. Experiments were conducted from various flow rates and heat loads. According to experimental data, microchannel has significant impact in the heat transfer rate for all the flow rates considered. This enhancement could be attributed to laminar flow in the microchannels, conduction heat transfer through the walls of the channel, fluid-channel wall interaction, and microconvection within the channel. Results show raises some concerns on the use of empirical correlations for flow between two parallel plates to predict heat transfer behavior in microchannels. In the absence of experimental data, f ≈ −2(dp/dx)dh/ρum2 provides a reasonable estimate of friction factor in microchannel.
Dye Doped Clad Modified Evanescent Optical Fiber (CMEOF) Sensor Array for the Detection of Aqueous-Ammonia
Authors: Abdi Abdeq M. , Shastry Sistla S. , Nnanna A. G. Agwu
Published: August 2009

We are currently developing pH sensitive dye doped clad modified evanescent optical fiber (CMEOF) sensor array for the detection of aqueous-ammonia. The quasi-distribution of CMEOF ammonia sensors allows efficient measurement of aqueous-ammonia at several locations using a single fiber optic line. CMEOF sensors are fabricated by immobilized pH sensitive dyes in sol-gel and applying the dye doped sol-gel as a thin film around a bare core optical fiber. The CMEOF sensors are then sealed from water using a gas permeable membrane, PDMS-vinyl. The dyes in each CMEOF sensor are tailored to operate at slightly different wavelengths by appropriate choice of dyes. Wavelength-division-multiplexing (WDM) and linear system of equations (LSE) are used to interrogate each CMEOF sensor and determine the concentration of aqueous-ammonia at each sensor location.
Polymeric Micro/Nanofiber Manufacturing and Mechanical Characterization
Authors: Nain Amrinder S. , Sitti Metin , Amon Cristina
Published: August 2009

Polymeric nanofibers are finding increasing number of applications and hold the potential to revolutionize diverse fields such as tissue engineering, smart textiles, sensors, and actuators. Aligning and producing long smooth, uniform and defect-free fibers with control on fiber dimensions at the submicron and nanoscale has been challenging due to fragility of polymeric materials. Besides fabrication, the other challenge lies in the ability to characterize these fibers for mechanical properties, as they are widely believed to have improved properties than bulk due to minimization of defects. In this study we present an overall strategy for fabrication and mechanical characterization of polymeric fibers with diameters ranging from sub-50 nm to sub-microns. In the proposed fabrication strategy, polymeric solution is continuously pumped through a glass micropipette which is collected in the form of aligned fiber arrays on a rotating substrate. Polymer molecular weight and polymer solution concentration play dominant roles in controlling the fiber dimensions, which can be used to deposit fibers of different diameters in the same layer or successively built up multi-layer structures. Using this approach, we demonstrate single and multi-layer architectures of several polymeric systems such as Polystyrene (PS), Poly(methyl methacrylate) (PMMA), Poly lactic acid (PLA), and poly(lactic-co-glycolic acid) (PLGA). Further, we demonstrate the ability to manufacture PMMA fixed-free boundary condition cantilevers by breaking the fixed-fixed boundary condition PMMA fibers using Atomic Force Microscope (AFM) in the lateral mode. An integrated approach for mechanical characterization of polymeric fibers is developed. In this approach, the fibers are first deposited on commercially available Transmission Electron Microscopy (TEM) grids in aligned configurations and are mapped for accurate locations under the TEM. Subsequently, the fibers are carefully placed under the AFM and mechanically characterized for flexural modulus using lateral force microscopy (LFM). Finally, accurate fiber dimensions are determined under the Scanning Electron Microscope (SEM). The unique advantage of this approach lies in the ability to deposit a large number of fibers with tunable diameters in aligned configurations with fixed-fixed boundary conditions and requires no external manipulation. Finally, we present a novel methodology to study the resonance characteristics of fixed-fixed boundary condition suspended fibers using a commercially available Laser Doppler Vibrometer (LDV) for sensor applications. The methods developed in this study will greatly aid in increasing our fundamental knowledge of polymeric materials at reduced lengthscales and allow integration of these one-dimensional building blocks in bottom-up assembly environments.
Numerical Investigation of Oxide Layer Growth of Stainless Steel LBE at a Mesoscopic Level
Authors: Tan Taide , Chen Yitung
Published: August 2009

The corrosiveness of LBE, as an ideal coolant candidate in reactors and accelerator driven systems (ADS), presents a critical challenge for safe applications. One of the effective ways to protect the materials is to form and maintain a protective oxide film along the structural material surfaces by active oxygen control technology. The oxidation process of metals in lead bismuth eutectic (LBE) environment is investigated numerically at a mesoscopic scale. An improved stochastic cellular automaton model based on an improved Moore neighborhood is proposed to investigate the development of a continuous oxide layer of metals in LBE. The ionization of metal and the oxidation reaction were simulated with consideration of the transport of oxygen along the grain boundary and the diffusion of metallic ions. The model was benchmarked with a pure diffusion process, both with the analytical solution and with the previous work. Significant agreement was reached between the data. The developed model is also mapped with the experimental data from an LBE loop. A parametric study was conducted in order to check the importance of the main explicit parameters of the mesoscopic model. The boundary condition at the far end of the specimen has been investigated for the CA model.
Sensitivity Analysis on Three-Dimensional Numerical Simulation of Liquified Natural Gas Sloshing in Tank
Authors: Kang Chang-Wei , Zhang Baili , Lou Jing , Lee Sing-Kwan , Wu Jer-Fang , Seah Ah-Kuan
Published: August 2009

A series of sensitivity analyses is carried out against flow models (i.e. inviscid, laminar and turbulent models), mesh size and scaling factor based on Froude scale laws on the time history of sloshing impact pressures and computational requirements. In order to capture the complex wave breaking and gas trapping phenomena associated with the violent liquid sloshing motion, a free surface tracking approach called Volume of Fluid (VOF) method is employed. The computational results show that the inviscid flow model based on Euler equation would provide a reasonably accurate impact load prediction and with efficient computing time. This is because the inertia force is the dominant factor in the sloshing movement compared to the localized viscous effect. For mesh sensitivity analysis, 5mm and 10mm mesh size models have been simulated for 20 cycles. It is found that 5mm resolution provides better results than 10mm. Further mesh refinement is expected to provide better results, but with significant computational power requirement. Finally, the full-scale simulation results have also been compared against the model scale results. The simulated impact pressures derived from model scale based on the Froude scale law agree with those of calculated from the full scale simulation.
Fabrication of Single and Multi-Layer Fibrous Biomaterial Scaffolds for Tissue Engineering
Authors: Nain Amrinder S. , Miller Eric , Sitti Metin , Campbell Phil , Amon Cristina
Published: August 2009

For regenerative medicine applications, we need to expand our understanding of the mechanisms by which nature assembles and functionalizes specialized complex tissues to form a complete organism. The first step towards this goal involves understanding the underlying complex mechanisms of highly organized behavior spanning not only diverse scientific fields, but also nano, micro and macro length-scales. For example, an engineered fibrous biomaterial scaffold possessing the hierarchal spatial properties of a native extracellular matrix (ECM) can serve as a building block upon which living cells are seeded for repair or regeneration. The hierarchical nature of ECM along with the inherent topological constraints of fiber diameter, fiber spacing, multi-layer configurations provide different pathways for living cells to adapt and conform to the surrounding environment. Our previously developed Spinneret based Tunable Engineered Parameters (STEP) technique to deposit biomaterial scaffolds in aligned configurations has been used for the first time to deposit single and multi-layer biological scaffolds of fibrinogen. Fibrinogen is a very well established tissue engineering scaffold material, as it improves cellular interactions and allows scaffold remodeling compared to synthetic polymers. Current state-of-the-art fiber deposition techniques lack the ability to fabricate scaffolds of desired fiber dimensions and orientations and in this study we present fabrication and aligned deposition of fibrinogen fiber arrays with diameters ranging from sub-200 nm to sub-microns and several millimeters in length. The fabricated scaffolds are then cultured with pluripotent mouse C2C12 cells for seven days and cells on the scaffolds are observed to elongate resembling myotube morphology along the fiber axis, spread along intersecting layers and fuse into bundles at the macroscale. Additionally, we demonstrate the ability to deposit poly (lactic-co-glycolic acid) (PLGA), Polystyrene (PS) biomaterial scaffolds of different diameters to investigate the effects of topological variations on cellular adhesion, proliferation and migration. Previous studies have indicated cells making right angle transitions upon encountering perpendicular double layer fibers and cellular motion is thwarted in the vicinity of diverging fibers. Current ongoing studies are aimed at determining the effects of fiber diameter and fiber spacing on mouse C2C12 cellular adhesion and migration, which are envisioned to aid in the design of future scaffolds for tissue engineering possessing appropriate material and geometrical properties.
Evaluation of the Effect of Cement Viscosity on Cement Mantle in Total Knee Arthroplasty
Authors: Paliwal Manish , Kern Brian , Allan D. Gordon
Published: August 2009

Aseptic loosening of the tibial implant remains one of the major reasons of failure in Total Knee Arthroplasty (TKA). The cement viscosity at the time of application to the bone is of great importance to ensure a long-term success of the arthroplasty, as it influences the cement penetration and stability of the prosthesis. Currently, there are number of cements available with a wide range of viscosities and set times. High viscosity faster-setting cements may significantly reduce operating room times. However, the concern is that this positive feature may be at the expense of decreased penetration into the bone, and hence reduced stability of the construct. The use of four cement types ((DePuy II (DePuy Inc. Warsaw, IN), Endurance (DePuy Inc. Warsaw, IN), Simplex-P (Stryker Corp Kalamazoo, MI), and Palacos (Zimmer, Inc, Warsaw, IN)) were compared and evaluated during TKA using surrogate tibiae, with respect to the depth of cement penetration according to the Knee Society Total Knee Arthroplasty Roentgenographic Evaluation System. On radiographic analysis of the implanted surrogate tibiae, it was found that Simplex had the maximum commulative penetration of 19.2 mm in seven zones in Mediolateral view, and 12.7 mm in three zones in anteroposterior view. In zone seven, the difference was statistically significant when comparing Simplex with Palacos (11 mm vs 4.6 mm, two-tailed P value = 0.035), somewhat significant with Depuy 2 (11 mm vs 6 mm, two tailed P value = 0.08), but the different was not significant when compared with Endurance (11 mm vs 10 mm, two-tailed P value = 0.6345). In Zone 5, the difference was statistically significant with Simplex vs Endurance (0.3 mm vs 2.2 mm, P = 0.028), and with Simplex vs Depuy 2 (0.3 mm vs 2.17 mm, P = 0.012). This study enhances the understanding of the relation between cement viscosities and cement penetration into cancellous bone during TKA.
Non-Equilibrium Thin-Film Flow in Rotating Disk and Cone
Authors: Leung Wallace Woon-Fong
Published: August 2009

The acceleration of a continuous feed liquid stream in a film “down” the rotating cone and disk is of great interest in centrifuges [1, 2], thin-film reactors and process intensifiers. The mechanism of feed acceleration is determined by an interaction of several different effects. Circumferential viscous forces act to increase the angular momentum. The centrifugal field thus produced establishes a body-force component along the cone/disk surface, thereby driving the flow “down” toward larger radius. The longitudinal flow is however impeded by longitudinal resistance forces. These different effects compete with each other as the flow proceeds, never quite coming to an unchanging equilibrium state. An approximate integral method which was used to explore the “near-equilibrium” flow behavior in earlier work has been extended to investigate the case with large departure from equilibrium. The latter exhibits complicated highly nonlinear effect. Despite this, useful information can be obtained from the theoretical analysis. Experimental results on feed acceleration of liquid streams at various feed rates and rotation speeds in a rotating cone have been used to validate the study. The theoretical study with complementary experimental tests provides insights into how continuous liquid stream in form of a thin film is being accelerated using rotating cones and disks, and the associated shear rates involved. The latter has important bearing in processing shear-sensitive mammalian cells in biopharmaceutical separation with centrifuges and mass transfer in thin-film reactors.
Computational and Experimental Studies on Cavity Filling Process by Cold Gas Dynamic Spray
Authors: Takana Hidemasa , Li HongYang , Ogawa Kazuhiro , Kuriyagawa Tsunemoto , Nishiyama Hideya
Published: August 2009

Real-time computational simulations on cavity filling process by cold gas dynamic spray and powder jet deposition process with covering from micro to macroscale were carried out in order to give an insight for their advanced applications to joining, crack repair and dental treatment. It was made clear that shock wave appears in front of the substrate due to under-expansion of jet, even in a micro nozzle-substrate distance in the powder jet deposition process. By clarifying the relation between shock wave, cavity configuration and particle in-flight behavior in supersonic jet in detail, optimum cavity configuration for cavity filling process has been proposed both numerically and experimentally. When the the shock wave covers up the cylindrical cavity, cavity cannot be filled at all. Under the condition of shock wave appearing inside the cylindrical cavity, cone-shape deposition was formed due to the back flow jet near the cavity side wall. By adopting cone-shape cavity, cavity can be filled completely resulting from the suppression of the back flow jet near the cavity side wall.
Spatial Electrostrictive Actuation of Circular Cylindrical Tubes
Authors: Huang Shih-Lin , Chu Chin-Chou , Chang Chien C. , Tzou Horn-Sen
Published: August 2009

Circular cylindrical shells are common components in aerospace structures and many other engineering systems, e.g., rockets, tubes, piping systems, peristaltic pumps, storage tanks, etc. Electromechanical actuators laminated on the shell surfaces can certainly strengthen the shell when needed. Or, regulated inputs to the surface actuators can introduce prescribed surface waves to control the shell oscillation. This study is to evaluate spatial actuation characteristics of circular cylindrical shells using segmented electrostrictive actuators. Electrostrictive actuations induced by surface laminated electrostrictive actuators are defined first. Governing equations of a hybrid circular cylindrical shell/electrostrictive actuator system are formulated. The total electrostrictive actuation and its contributing circumferential membrane/bending and longitudinal bending components are evaluated with respect to shell modal characteristics, design parameters and control voltages. The actuator’s quadratic behavior only generate a positive control force or moment and thus an actuator patch can suppress (or amplify) the vibration in the positive (or negative) displacement. Accordingly, the quadratic electrostrictive actuation suggests that appropriate input voltage(s) need to be carefully applied to specific actuator(s) or regions in order to control, but not to amplify, the shell oscillations. Based on the spatially distributed modal actuation, generic design guidelines and optimal actuation locations are proposed.
A Case Study of Conceptual Design Analysis of Stove Brackets Using Finite Element Method
Authors: Va´zquez Diego , Medelli´n Hugo , Ca´rdenas Antonio , de la Garza Alonso
Published: August 2009

Advanced engineering techniques for analysis are modern tools used for companies to enhance the design and manufacturing cycles of new or existing products. Finite element method has become one of the most used tools in the design process of products. This paper presents a case study regarding a design change of the brackets that support the gas jet in stoves. Using the finite element method, the mechanical performance of the existing brackets is compared with the performance of the new proposed bracket. This comparison is used to evaluate the feasibility of carrying out the design change. The benefit of the new design is a reduction of materials, production costs and production times. Experimental analysis of the materials and the validation of the finite element solutions were also performed. The results of the experimental analysis and FEM simulation are discussed and presented. Finally, the performance of the existing and the new brackets under several load cases is compared and the results suggest that the product design change is feasible.
Switching Bifurcation and Chaos in an Extended Fermi-Acceleration Oscillator
Authors: Luo Albert C. J. , Guo Yu
Published: August 2009

The Fermi acceleration oscillator is extensively used to interpret many physical and mechanical phenomena. To understand dynamic behaviors of a particle (or a bouncing ball) in such a Fermi oscillator, a generalized Fermi acceleration model is developed. This model consists of a particle moving vertically between a fixed wall and the piston in a vibrating oscillator. The motion switching bifurcation of a particle in such a generalized Fermi oscillator is investigated through the theory of discontinuous dynamical systems. The analytical conditions for the motion switching are developed for numerical predictions. Thus, periodic motions in the Fermi-acceleration oscillator are given and the corresponding local stability and bifurcation are presented. Periodic and chaotic motions in such an oscillator are presented via the displacement time-history. From switching bifurcation and period-doubling bifurcation, parameter maps of periodic and chaotic motions will be developed for a global view of motions in the Fermi acceleration oscillator. To illustrate motion switching phenomena, the acceleration responses of the particle and base in the Fermi oscillator are presented. Poincare mapping sections are also used to illustrate chaos, and energy dissipation in chaotic motions can be evaluated.