bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiments With the Powered Arm Cobot
Authors: Kim Songho , Peshkin Michael , Colgate J. Edward
Published: April 2008

The Arm cobot is a three degree-of-freedom manipulator intended for direct physical interaction with a human operator. The Arm cobot can operate as a passive device, such that the cobot sets the end-effector’s allowed direction of motion, while the human operator provides all motive forces. Previous work with the passive Arm cobot involved displaying free motion and virtual paths and surfaces. This paper presents experimental results with a powered Arm cobot. In one experiment, the Arm cobot is commanded to track a user-defined trajectory, while in another experiment, we show an improved free motion controller.
Surface Reconstruction of In Vivo Geometry Based on Medical Images Using Multilevel Radial Basis Functions
Authors: Kuan Yoke Kong , Fischer Paul F. , Loth Francis
Published: April 2008

Compactly supported radial basis functions (RBFs) were used for surface reconstruction of in vivo geometry, translated from two dimensional (2D) medical images. RBFs provide a flexible approach to interpolation and approximation for problems featuring unstructured data in three-dimensional space. Point-set data are obtained from the contour of segmented 2-D slices. Multilevel RBFs allow smoothing and fill in missing data of the original geometry while maintaining the overall structure shape.
An Introduction Into X-Ray Micromachining Using Synchrotron Radiation
Authors: Goettert Jost
Published: April 2008

Micro production technologies are a driving factor in today’s continuous effort of developing new, highly functional products. The need for increased functionality is met by decreasing the size of individual components as well as consequently miniaturizing components for non-electronic properties including optical, mechanical, and fluidic functions. An important factor in this approach his the right material for a given task and the ability to shape it into the desired geometry as well as to combine micro components in a cost-effective way to build more complex modules and micro systems. One micro production technology that meet several of the above mentioned needs is the LIGA process, a combination of three major fabrication processes — x-ray based micromachining or deep x-ray lithography (DXRL), electroplating, and molding. In x-ray lithography the unique properties of synchrotron radiation, especially high intensity of collimated x-ray photons, permit patterning of extremely precise, very tall primary microstructures up to several millimeters in height with micrometer lateral dimensions and sub-micrometer details (so-called High-Aspect Ratio Microstructures, HARM). These microstructures are attractive for mechanical and optical components in MEMS (MicroElectroMechanicalSystems) devices. While x-ray lithography is crucial to achieve a primary microstructure with superior features, the use of synchrotron radiation is limiting the material choice to only a few polymer materials, so-called x-ray resists. Additional processes including electroplating and molding, however, open up a huge selection of engineering materials such as metals, ceramics, and also a large number of polymers and allow MEMS engineers to combine structural and material properties to build the next generation MEMS devices. This paper is primarily focusing on the DXRL process. Process fundamentals including equipment and infrastructure, x-ray masks, resists, typical structure geometries as well as patterning accuracy will be discussed. A few examples will illustrate ongoing efforts of commercializing this technology and also indicate future areas of applications.
On Non-Axisymmetrical Transverse Vibrations of Circular Plates of Convex Parabolic Thickness Variation
Authors: Caruntu Dumitru I.
Published: April 2008

This paper presents an approach for finding the solution of the partial differential equation of motion of the non-axisymmetrical transverse vibrations of axisymmetrical circular plates of convex parabolical thickness. This approach employed both the method of multiple scales and the factorization method for solving the governing partial differential equation. The solution has been assumed to be harmonic angular-dependent. Using the method of multiple scales, the partial differential equation has been reduced to two simpler partial differential equations which can be analytically solved and which represent two levels of approximation. Solving them, the solution resulted as first-order approximation of the exact solution. Using the factorization method, the first differential equation, homogeneous and consisting of fourth-order spatial-dependent and second-order time-dependent operators, led to a general solution in terms of hypergeometric functions. Along with given boundary conditions, the first differential equation and the second differential equation, which was nonhomogeneous, gave respectively so-called zero-order and first-order approximations of the natural frequencies and mode shapes. Any boundary conditions could be considered. The influence of Poisson’s ratio on the natural frequencies and mode shapes. Any boundary conditions could be considered. The influence of Poisson’s ratio on the natural frequencies and mode shapes could be further studied using the first-order approximations reported here. This approach can be extended to nonlinear, and/or forced vibrations.
Interfacial Adhesion of Nanoporous Zeolite Thin Films
Authors: Hu Lili , Wang Junlan , Li Zijian , Li Shuang , Yan Yushan
Published: April 2008

Nanoporous zeolite thin films are promising candidates as future low-k materials. During the integration with other semiconducting materials, the high stresses resulted from the synthesis process can cause the film to fracture or delaminate from the substrates. Evaluating the interfacial adhesion of zeolite thin films is very important in achieving high performance low-k materials. In this work, laser spallation technique is utilized to investigate the interfacial strength of zeolite thin films from three different synthesis processes. The preliminary results show that the fully crystalline zeolite thin films from hydro-thermal in-situ and seeded growth methods have a stronger interface than that from the spin-on process. Effort is also being made to compare the interfacial strength of the zeolite films between the two hydro-thermal methods. This is the first time that the interfacial strength of zeolite thin films is quantitatively evaluated. The results have great significance in the future applications of low-k zeolite thin films.
Hydrodynamic Performance of Meso Scale Gas Journal Bearings
Authors: Kim Daejong , Bryant Michael D.
Published: April 2008

Recent advancement of micro machining technology enabled a fabrication of micro scale gas bearings for high performance miniature scale rotating machinery. This paper presents recent development of micro gas bearings fabricated through X-ray lithography, and suggests fabrication method of various meso scale (~mm) gas journal bearings, which include Rayleigh step gas journal bearings, pressure dam bearings, grooved pressure dam bearings. Also presented are simulations performed using orbit method for the suggested meso scale gas bearings with diameter of 2mm, length of 2mm, and clearance of 1~2 micron. Pan’s first order slip model was adopted to simulate molecular rarefaction effects. The rotor mass was 0.3g, simulating very small Laser scanner unit. From the simulations, Rayleigh step journal bearing had highest threshold speed reaching 300,000 rpm. Effects of molecular rarefaction in sub micron bearing clearance on the dynamic performance at very high bearing numbers, were also investigated.
Two-Medium Model for the Bond Line Thickness of Particle Filled Thermal Interface Materials
Authors: Hu Xuejiao , Govindasamy Senthil , Goodson Kenneth E.
Published: April 2008

Thermal interface materials (TIMs) are widely used in electronics packaging. Increasing heat generation rates require lower values of the TIM thermal resistance, which depends on the material thermal conductivity and the TIM thickness, or the bond line thickness (BLT). The variation of the TIM thickness is not well understood. The major difficulty comes from the complexity of TIMs as condensed particle systems, especially when the TIM thickness is squeezed to several multiples of the filler particle diameter. This confined heterogeneous structure makes the behavior of TIMs different from that of homogeneous fluids. In this study, we propose a two-medium model for the BLT. The variation of BLT with attachment pressure is modeled using two parameters: the viscidity of the fluids and the interactions of particles. The predictions are compared with the measurements for TIMs made of aluminum oxide particles (sizes: 0.6–6 microns, volume fractions: 30%–50%) and silicon oil (kinematic viscosity: 100 cst and 1000 cst). Reasonable agreement is obtained for different applied pressures. Results indicate that the impact of the particle interactions is an important factor governing the variation of the TIM BLT, especially when the BLT is small.
Construction and Validation of a Complaint Model of the Cerebrospinal Fluid System With Fluid Filled Syrinx
Authors: Martin Bryn A. , Kalata Wojciech , Oshinski John N. , Loth Francis , Royston Thomas J.
Published: April 2008

A simplified model of the cerebrospinal fluid (CSF) system with compliant fluid filled syrinx has been constructed, tested, and verified to closely mimic the in-vivo flow conditions observed through MRI imaging of the pathological CSF system with syringomyelia. The model is subjected to a MRI derived CSF flow waveform from a patient with Syringomyelia through use of a computer controlled pulsatile pump. Model geometry, flow waveform, and spinal cord compliance are obtained at three axial locations along the system through MRI image processing techniques. MRI testing was conducted with the syrinx open and closed to the external environment. Results indicate that the internal and external flow waveforms were in opposite directions when the syrinx was closed and in unison when the syrinx was open. The observed flow waveform and compliance measurements closely mimicked the in-vivo case when the syrinx is open to the external environment.
Agent-Based Distributed Collaborative Sourcing of Stamped Parts
Authors: Ding Y. , Nye T. J.
Published: April 2008

Metal stampings are an important manufactured product. Their production cycle includes the steps of part design, process and tooling design, tooling construction, and production. Each of these activities may be performed within departments of a single manufacturing plant, but more commonly are separated across firms and are widely distributed geographically. To be most effective, this process should be performed concurrently, with considerable flows of information along the supply chain. Research on Agent-based systems shows they are very promising in this type of task as individual agents can wrap particular domain knowledge and analysis algorithms, are always available to respond and are able to autonomously form networks as needed to complete product and process design tasks. In this paper we examine the particular case where alternate suppliers may be selected to supply components to the supply chain. Agents are used to connect the suppliers to the supply chain network. Each supplier firm’s agent understands the firm’s production capabilities, costs and capacity loading, and is able to negotiate with a broker agent representing the stamped part customer. A prototype system is described, and case studies are used to show the benefits of an Agent-based approach to this supply chain problem.
Thermal Transport Phenomena in Buoyancy-Driven Nanofluids
Authors: Nnanna A. G. Agwu , Fistrovich Tom , Malinski Kurt , Choi S. U. S.
Published: April 2008

This paper presents an experimental investigation of the thermal transport phenomena in buoyancy-driven nanofluids. The experimental model for this study is a rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls. The nanofluids were confined within the enclosure. Simulations were performed to measure the transient and steady-state temperature response of the nanofluids to applied load. Experimental observation shows settling of the nanoparticle at low heat loads and a remixing of the nanofluid at higher loads. At high loads, the buoyancy force increased hence increasing the re-circulatory motion of the nanofluid. This may be one method of addressing the settling of nanoparticles in nanofluid. For natural convection in an enclosure, this paper shows that the thermal behavior of nanofluids is identical to pure fluids. Temperature data collected during the experiment were used to study the variation of Nusselt number with Rayleigh number.
Well Resolved Wall Pressure Measurements in a High Reynolds Number Turbulent Boundary Layer
Authors: Perkins Brendan F.
Published: April 2008

In order to better understand boundary layer turbulence at high Reynolds number, the fluctuating wall pressure was measured within the turbulent boundary layer that forms over the salt playa of Utah’s west desert. Pressure measurements simultaneously acquired from an array of nine microphones were analyzed and interpreted. The wall pressure intensity was computed and compared with low Reynolds number data. This analysis indicated that the variance in wall pressure increases logarithmically with Reynolds number. Computed autocorrelations provide evidence for a hierarchy of surface pressure producing scales. Space-time correlations are used to compute broadband convection velocities. The convection velocity data indicate an increasing value for larger sensor separations. To the author’s knowledge, the pressure measurements are the highest Reynolds number, well resolved measurements of fluctuating surface pressure to date.
Constructal Optimization of the Coupling Between a Hot and a Cold Stream for Power and Refrigeration
Authors: Ordonez Juan C. , Vargas Jose V. C.
Published: April 2008

The first part of this paper reviews some basic results regarding the extraction of power from a hot stream. The second part of the paper outlines the thermodynamic optimization of the coupling between a hot and a cold stream for refrigeration under a total heat transfer area constraint, via constructal theory. The refrigeration system is driven by a hot stream of single-phase fluid that is subsequently discharged into the ambient. The irreversibility is due to three heat exchangers and the discharging of the used stream. It is shown that the thermodynamic optimum is pinpointed by an optimal ratio between the mass flow rates of the hot stream and the stream that is heated by the hot stream, and by an optimal distribution of the heat exchanger area inventory among the three heat exchangers of the installation. The robustness of the optima found is investigated regarding to the variation of the design and operating parameters. The connection between constructal theory and the thermodynamic optimization employed in this paper is the end product: the optimal matching of the streams. It represents configuration (architecture, geometry) derived from principle. If design is approached in this manner (constructal theory), design becomes science, not art.
Self-Sensing Actuators in Electrohydraulic Valves
Authors: Yuan Qing Hui , Li Perry Y.
Published: April 2008

Self-sensing refers to extracting the position information from the electromagnetic signals instead of from a physical position sensor. Self-sensing actuator has the benefit of significantly reducing hardware effort. In this paper, we investigate self-sensing actuators applied in direct acing proportional valves. The study is based on the configuration of a dual-solenoid actuator where each solenoid provides the independent single direction force. By considering the electrical dynamics of the solenoids and the nonlinear constraint between the two solenoids, an observer for the flux linkages is obtained. The position estimate is then calculated based on the flux linkage estimates. Both simulation and experiments verify the validity of the proposed algorithm.
Self-Calibration of Push-Pull Solenoid Actuators in Electrohydraulic Valves
Authors: Yuan Qing Hui , Li Perry Y.
Published: April 2008

System parameters for solenoid actuators are important for high performance control and for self-sensing. Due to the non-linearities in the solenoid actuators, parameter identification procedures that aim to obtain the electro-mechanical property can be complex and time consuming. In this paper, a self-calibration procedure for solenoid actuators in push-pull configurations is proposed. Utilizing the fact that the inductances of the solenoids share the same parameters as those for the electromagnetic force, the parameters for the electromagnetic force can be obtained from the easily obtainable electrical signals such as the voltage and current signals, and two inexpensive on-off sensors. The calibration procedure involves only actuating the solenoid actuator back and forth. Simulation study is presented to verify the method.
Fabrication and Testing of High Aspect Ratio Metal Micro-Gas Chromatograph Columns
Authors: Bhushan Abhinav , Yemane Dawit , Goettert Jost , Overton Edward B. , Murphy Michael C.
Published: April 2008

Micro gas chromatograph (GC) separation columns were fabricated and tested. Rectangular columns with high aspect ratio have inherent benefits over traditional tubular columns and can easily be integrated into a GC sensor system for rapid chromatographic analysis. The 2 m long, 50 μm wide, 500 μm tall columns were fabricated out of electroplated nickel through deep X-ray lithography using the LIGA technique. Critical fabrication issues including reproducible fabrication of compact footprint, deep columns and sealing of the metal columns were addressed. Experiments were conducted to establish the relationship between column head pressure and flow rate. Methane samples analyzed using hydrogen as a carrier gas on uncoated columns showed very little dispersion suggesting that there was no internal leakage in the columns. The sensor performance data compares well with other micro GC sensor systems.
Design in the Thermal Fluids Engineering
Authors: Sadeghipour Sadegh M. , Asheghi Mehdi
Published: April 2008

Design is seen as the magic word and being a design engineer is considered to be the key to success in the job market by many of the mechanical engineering students. However, it is always assumed that the mechanical systems not the thermal engineers are indeed design engineers by education and practice. This notion probably stems from the fact that most of the thermal fluid courses in mechanical engineering curriculum seem to have been defined and developed to prepare undergraduate students for going to graduate school rather than the job market. The undergraduate courses usually emphasize on the theories with less attention to the design and application aspects. Perhaps, the responsibility of thermal engineering educators is to correct this notion by emphasizing more on the application and design in the existing courses or alternatively to develop and offer new courses on more applied topics. In this paper, we will report an integrated approach in teaching topics in fins and fin assemblies, which includes class lectures, laboratory experiments, ANSYS simulations and design competition. In this manuscript, we will report on the details of this approach including the procedures, methods, our observations, and the students’ feedbacks.
Dynamic Simulation and Analysis of a Passively Self-Stabilizing Hexapedal Running Robot
Authors: Clark Jonathan E. , Cutkosky Mark R. , Thelen Darryl G.
Published: April 2008

The Sprawl family of robots have demonstrated that fast and robust locomotion is possible over uneven terrain with only feed-forward control. In the absence of feed-back, the speed, efficiency, and stability of the system are largely functions of how well the physical system is tuned. This work describes the development of a dynamic model used to investigate the effects of design changes on system stability and performance. Simulation results show the surprisingly large region of configurations that result in stable locomotion, and how the shape of this region changes as a function of the passive properties of the hips. Understanding of this is critical since peak performance, as measured by running speed, tends to occur on the boundary of stable configurations. Simulation results were used to quantitatively redesign the legs of a version of the robot configured to run outdoors. Implementation of the design changes resulted in doubling the robot’s speed.
Influence of Transverse Fins Attached to the Heated Wall of a Rayleigh-Be´nard Cavity
Authors: Hitt Darren L. , Campo Antonio
Published: April 2008

In this article we examine the augmentation of classic Rayleigh-Be´nard convection by the addition of periodically-spaced tranverse fins attached to the heated, lower plate. The respective impacts of the fin size, the fin spacing and the thermal conductivity of the fin material are examined through numerical simulations for different laminar Rayleigh numbers and reported it terms of the Nusselt number. With the exception of very closely spaced fins, the heat transport is observed to exceed that of the idealized Rayleigh-Be´nard case. It is found that local heat transport maxima and minima do exist for specific fin spacings and that the maxima become more pronounced at higher Rayleigh numbers. For ‘small fins’ the fin spacing corresponding to maximum heat transport is such that the fin spacing is approximately equal to the enclosure height.
Titanium Bulk Micromachining for BioMEMS Applications: A DEP Device as a Demonstration
Authors: Zhang Yanting , Parker Emily R. , Rao Masa P. , Aimi Marco F. , Mezic Igor , MacDonald Noel C.
Published: April 2008

Titanium has been widely used as a biomedical material in orthopedics, dentistry, cardiology, and cardiovascular surgery due to the excellent biostability and biocompatibility that results from its spontaneous formation of a highly passivating oxide layer in air and blood. However, little research has been done on the development of titanium for bioMEMS applications. This is likely due to the immaturity of titanium bulk micromachining technology to date. Here we report the application of new high-aspect-ratio bulk titanium micromachining techniques recently developed within our group towards the fabrication of a titanium-based multi-frequency traveling wave dielectrophoresis (DEP) device targeted for the separation of bioparticles. The device serves to illustrate the potential of these techniques for enabling the realization of novel bioMEMS devices with enhanced functionality and capability.
A Preliminary Theoretical Investigation for Developing an Artificial Meniscus
Authors: Singh A. , Vaziri A. , Nayeb-Hashemi H.
Published: April 2008

Analysis of the stress distribution within cartilages of the human knee joint in response to external loads can help to understand the causes of pathological cartilage degeneration and lead to prevention of injury. Wilson et al [1] demonstrated that by modeling the cartilage material as isotropic, type-2 damage can be explained and with the assumption of transverse isotropic properties, type-1 damage could be explained. In this study, we explore the effect of meniscectomy on the shear stress distribution through the knee joint cartilages by modeling the cartilage as three layers and considering the biphasic properties of the top, middle and deep zones. The results of the analysis indicate that complete meniscectomy of the knee joint induces the maximum shear stress at the cartilages surface to increase substantially. This suggests the need for developing an artificial meniscus that could replace the damaged one.
Clumping and Packing of Hair Arrays Manufactured by Nanocasting
Authors: Majidi Carmel , Groff Richard , Fearing Ron
Published: April 2008

The gecko’s remarkable dry adhesive system, consisting of arrays of heirarchically structured hairs made from a stiff material, has motivated widespread interest in creating a synthetic dry adhesive whose adhesive properties derive more from its geometry than its bulk material properties. Recently, methods for synthesizing simple hair arrays have been developed. It has been observed that micro and nanosized synthetic hairs often adhere together to form clumps. This paper introduces several models and guidelines for predicting clumping conditions through hair geometry and lattice structure, and presents our methods for casting hair arrays.
Multi-Axial Fatigue Damage Models of Fiber Reinforced Composites
Authors: Yang N. H. , Nayeb-Hashemi H. , Vaziri A.
Published: April 2008

Fiberglass reinforced composites are extensively used in various structural components. In order to insure their structural integrity, their monotonic and fatigue properties under multiaxial stress fields must be understood. Combined in-phase tension/torsion loading is applied to [±45°]4 E-glass/epoxy composite tubes under monotonic and fatigue conditions to determine the effects of multiaxial loading on its failure. Various monotonic and fatigue damage criteria are proposed. These models considered failure mode (failure plane), the energy method and the effective stress-strain method. It is observed for the majority of experiments, the failure initiated at the outer lamina layer at 45° to the tube axis. A damage criterion for multiaxial monotonic loading is proposed considering both normal and shear stress contributions on the plane of failure. The experimental data show an excellent agreement with this proposed model for various loading conditions. Other failure models are currently under investigation utilizing the stresses and strains at the composite laminate as well as stress and strain at the outer lamina layer. Multiaxial fatigue failure models are proposed considering again the plane of failure. Since the plane of the failure is subjected to mean and cyclic stresses (shear and normal) and mean and cyclic strains (shear and normal), the fatigue damage models consider the contributions of these stresses and strains to the fatigue life of the composite tube. In addition to the fatigue damage model based on the plane of failure, a multi-axial fatigue failure model is proposed considering the mean and cyclic energy during fatigue experiments. The experimental data show a good correlation between the proposed damage parameters and fatigue life of specimens with some scatter of the data. Other fatigue failure models are currently under investigation considering the loading frequency and visco-elastic properties of the composite.
Enhanced Heat Transfer Through the Use of Nanofluids in Forced Convection
Authors: Faulkner Daniel J. , Rector David R. , Davidson Justin J. , Shekarriz Reza
Published: April 2008

Much attention has been paid in recent years to the use of nanoparticle suspensions for enhanced heat transfer. The majority of this work has focused on the thermal conductivity of these nanofluids, which can be as much as 2.5 times higher than that of the plain base fluid. The present work moves beyond measurements of non-flowing liquids, to explore the role that nanofluids can play in enhancing convective heat transfer within microscale channels. A unique pseudo-turbulent flow regime is postulated, which simulates turbulent behavior at very low Reynolds numbers, in what are nominally laminar flows. The resulting fluid mixing has the potential to raise the average convective heat transfer coefficient within the channel. Numerical modeling, using the lattice Boltzmann method, confirms the existence of the pseudo-turbulent flow regime. Finally, experimental results are presented which demonstrate a significant heat transfer enhancement when using nanofluids in forced convection. The current results are especially relevant to microchannel heatsinks, where the low Reynolds numbers impose limitations on the maximum Nusselt number achievable.
Thermal Conductivity Measurement of the ZnS-SiO2 Dielectric Films for Optical Data Storage Applications
Authors: Li Chun-Teh , Yang Yizhang , Sadeghipour Sadegh M. , Asheghi Mehdi
Published: April 2008

The amorphous/crystalline phase formation during writing or erasure of the written marks, in the rewritable phase change (PC) optical recording media, is controlled by the temperature distribution in the media and its variation with time. Temperature distribution, on the other hand, strongly depends on the thermal properties of its constituent layers in particular the ZnS-SiO2 dielectric layer that separates the phase change media from the substrate and aluminum heat sink. The reported values for the thermal conductivity of thin dielectric layers are however limited in the literature. In this manuscript, we report thermal conductivity data for dielectric layers of thickness near 50, 100 and 225 nm using the steady sate Joule-heating and electrical resistance thermometry technique. The boundary resistance at the interface is estimated to be near 7.0×10−8 m2 K W−1, which would limit the thermal time constant for cooling of PC layer and potentially impact data rate and jitter in optical recording technology.
Stress Analysis of Pin-Loaded Composite Plates
Authors: Stone James J.-S. , Ju Shen-Haw , Rowlands Robert E.
Published: April 2008

The frictional contact of the pin-loaded joint in composite plates was studied. This included the effects of pin clearance and variations in material and geometry. Full-filed displacements were measured by high sensitivity moire´ interferometry. Considerable effort was expended to develop a loading frame, relevant fixtures and monitoring capability to ensure that the plate was loaded uniformly through its thickness, particularly at the pin-loaded hole. Numerical techniques were prepared for processing the optical fringe data. A reliable finite element model for a bolted joint was also formulated. The efficient finite element program, which is capable of handling friction and/or clearance at the loaded hole, has been validated analytically, experimentally and numerically.
Water and Solute Active Transport Through Model Epidermis: Contribution of Electrodiffusion
Authors: Falkenberg Cibele Vieira , Georgiadis John G.
Published: April 2008

As part of a research program focusing on the role of human skin as a transport barrier, we formulate a coarse-grained model of the epidermis consisting of free extracellular water, live cells, and inert extracellular matrix subject to the coupling between molecular diffusive flux and electrokinetic flux (or electrodiffusion, as expressed by the Nernst-Planck equation). This polyphasic mathematical model accounts for active transport of physiologically-relevant solutes across the membrane of the live cells (keratinocytes), diffusion in the extracellular matrix and redistribution of water. The volume of the cell phase is regulated by the fluxes of water and Na+, K+ and Cl− ions across the cell membrane and is controlled according to the time-delay scheme introduced in the model of Hernandez & Cristina (1998). Computing the transient response of a 100 μm-thick viable epidermis layer exposed to a hyposmotic shock reveals that accounting for the electrokinetic flux in the extracellular domain has negligible effect on the results. This result suggests that a significant simplification of the model can be made in terms of decoupling the extracellular variation of the electrostatic field from the diffusion problem during the study of complex transepidermal transport.
Investigation of the Transition From Plane Strain to Plane Stress in Orthogonal Metal Cutting
Authors: Pednekar Vasant , Madhavan Vis , Adibi-Sedeh Amir H.
Published: April 2008

It is widely known that in practical orthogonal machining experiments, interior sections of the deforming material undergo plane strain deformation whereas material near the side faces of the workpiece undergoes plane stress deformation. This study is aimed at investigating the plane strain to plane stress transition using 3D coupled thermo-mechanical finite element analysis of orthogonal machining. The temperature, stress, strain and strain-rate distributions along different planes of the workpiece are analyzed to obtain estimates of the fraction of material undergoing plane strain deformation for different widths of cut. While it is found that the deformation in the mid-section of the workpiece is close to that observed in 2D plane strain simulations, the deformation along the side faces is quite different from that observed in 2D plane stress simulations, due to the constraint imposed upon the material along the sides by the material in the middle. Though the chip thickness along the sides is smaller than the chip thickness in the middle, the strain, strain-rate, and temperature fields along the side face and mid-section are quite similar. This study confirms that accurate maps of temperature, strain and strain-rate in plane strain deformation can be obtained by observing the side faces. It is found that for the cutting conditions used, a width to depth-of-cut ratio of twenty (not ten, as is commonly assumed) results in a close approximation to plane strain deformation through more than 90% of the width of the work material. For a width to depth-of-cut ratio of ten, significant deviations are observed in the stresses, with respect to their corresponding values in plane strain. Recommendations for the width of cut to depth of cut ratio to be used in experiments for other cutting conditions can be developed based upon similar studies.
Acute Thoracic Vertebral Injury Thresholds
Authors: Truman Mari S. , Ferrara Lisa A. , Milks Ryan , Gordon Illya , Eckhardt Jason
Published: April 2008

This study measures select static and dynamic characteristics of the human mid-thoracic spine, and compares them to previously published data for the thoraco-lumbar and cervical regions. Little information is available on the acute injury threshold for mid-thoracic intervertebral discs. The aim of this study was to characterize injury thresholds for the thoracic spine. Non-destructive combined flexion-compression loading experiments were conducted on 5 fresh human T5-T10 functional spinal units (FSU) at quasi-static and physiologic strain rates, and the resulting load-deflection responses were converted into global and local stiffness. Subsequently, 29 thoracic vertebrae (T5-T10) from 6 spines were subjected to moderate to severe impact loading in flexion. The peak forces and pressures were not statistically different between the thoracic disc levels. However, the mean injury forces and pressures were statistically different from mean failure forces found in the literature for both the lumbar and cervical spine regions, with the thoracic values falling between the cervical and lumbar values.
Self-Aligned Micro Bubble Arrays by Using Surface Tension
Authors: Meng De-Sheng , Kim Chang-Jin
Published: April 2008

This paper describes the theory and experiments involve in the capture of bubbles onto a patterned surface. Guided by surface free energy, bubbles can automatically attach to the energetically favorable locations (bubble-traps) and align into bubble arrays. Bubble capturing potential φbc is proposed as the quantity to evaluate the surface’s “affinity” for bubbles. A bubble-trap can therefore be viewed as an area with locally maximum positive φbc. Two types of bubble-traps are proposed and evaluated. Type I bubble-traps are hydrophobic patterns on a hydrophilic flat surface. Type II bubble-traps are concave conic pits surrounded by a hydrophilic flat surface. Simulation of bubble capturing potential φbc explains the bubble-capturing behavior for both cases and predicts a better performance for type II bubble-traps. Experiments agree well with the theoretical prediction and suggest promising applications.
Parallelogram Micromachine for Low Cost Micromechanics
Authors: Huerta L. Ruiz , Caballero-Ruiz A. , Marin-Aguilar E. , Velasco-Herrera G. , Baidyk T. , Kussul E.
Published: April 2008

This paper describes the experience of the Laboratory of Micromechanics and Mechatronics in the production of low cost micromechanics. A case of study is discussed and explained. The importance of applying simple mechanisms and high level control systems is presented. The basic elements and components needed to develop a high resolution micromachine tool are presented. This case of study is a MicroMachine Tool of 800nm of resolution in its three translational axes. Every single axis is able to move along 20mm. The configuration of the axes is not conventional, thanks to the use of parallel elements that results in semi circular movements.
Field Demonstration of Pumping Power Reduction in a Hydronic HVAC System With Drag-Reducing Surfactant Additives
Authors: Gasljevic K. , Matthys E. F.
Published: April 2008

A field test of the use of drag-reducing additives in hydronic cooling systems was conducted in a medium-size building on the UCSB campus. The purpose of the demonstration was to show that pumping power can be significantly reduced through the use of surfactant additives, to investigate adverse effects on overall heat transfer in heat exchangers, and also to investigate a more challenging system with dominant discrete pressure drops. The field test was considered to be very successful on all counts, especially considering the relatively small size of the building and the complex nature of the piping network. About 15% pumping power reduction was achieved overall, with a nominal pumping power of 22.5 kW. The heat transfer issues were found to be manageable and the measurements also confirmed that a 50% pumping power reduction is a realistic expectation for larger buildings, integrated complex of more buildings, and particularly for district cooling or heating systems.
Numerical Investigation of Adiabatic and Conjugate Film Cooling Effectiveness on a Single Cylindrical Film-Cooling Hole
Authors: Silieti Mahmood , Divo Eduardo , Kassab Alain J.
Published: April 2008

This paper documents a computational investigation of the film-cooling effectiveness of a 3-D gas turbine endwall with one cylindrical cooling hole. The simulations were performed for an adiabatic and conjugate heat transfer models. Turbulence closure was investigated using five different turbulence models; the standard k-ε model, the RNG k-ε model, the realizable k-ε model, the standard k-ε model, as well as the SST k-ω model. Results were obtained for a blowing ratio of 2.0, and a coolant-to-mainflow temperature ratio of 0.54. The simulations used a dense, high quality, O-type, hexahedral grid. The computed flow/temperature fields are presented, in addition to local, two-dimensional distribution of film cooling effectiveness for the adiabatic and conjugate cases. Results are compared to experimental data in terms of centerline film cooling effectiveness downstream cooling-hole, the predictions with realizable k-ε turbulence model exhibited the best agreement especially in the region for (x/D ≤ 6). All turbulence models predicted the jet lift-off. Also, the results show the effect of the conjugate heat transfer on the temperature (effectiveness) field in the film-cooling hole region and, thus, the additional heating up of the cooling jet itself.
Factors Affecting the Finishing Characteristics of an Internal Magnetic Abrasive Finishing Process for High Purity Fittings
Authors: Yamaguchi Hitomi , Shinmura Takeo , Sekine Megumi
Published: April 2008

In the case of internal finishing of the bent section of a complex shaped tube, such as found in high purity fittings, by a magnetic abrasive finishing process, the magnetic field at the finishing area and, therefore, the finishing force are hardly uniform over the entire finishing area due to the geometry. This affects the abrasive behavior against the inner surface of the bent section, changing the finishing characteristics of SUS304 stainless steel fittings. In practice, non-uniformities in the surface finish remain at the bent section between the inside, outside, and lateral regions. This unevenness combines to cause difficulties in achieving uniform finishing. Magnetic abrasive is generally supplied with ferrous particles, and the ferrous particles experience greater magnetic force and play a role in pressing the magnetic abrasive against the target surface. This paper studies the finishing mechanism in view of the relationship between the magnetic field, the ferrous particles mixed with magnetic abrasive, and the finishing characteristics. The experiments identify the finishing conditions required for successfully diminishing the non-uniformity in the finished surface, and methods are recommended to satisfy the required conditions. The experiments using the proposed methods show the feasibility of producing a uniformly finished mirror surface.
Experimental Study of an Ultra-High Performance, 3-D Micro Convective Heat Sink With a Constructal Plumbing System
Authors: Moreno R. , Tao Y.-X.
Published: April 2008

This paper presents the fabrication and results of an experimental study carried out to determine the thermal fluid performance of a 3-D, active micro convective heat sink having high surface-to-volume ratio geometry. The heat sink consists of an array of elemental units arranged in parallel. Each unit is constructed as a network of nearly fractal geometry. The design of each unit uses the constructal method to minimize the point-to-point temperature difference within the heat sink and Murray’s Law to minimize pressure drop across the device. One elemental unit of the heat sink was manufactured using the tape casting fabrication method with thick silver film techniques. An experiment was conducted using water as the coolant under laminar flow conditions to obtain the pressure drop and heat transfer characteristics of the 3-D micro convective heat sink. The results were then compared with theoretical calculations.
Lattice Boltzmann Simulation of Flow and Heat Transfer Characteristics in a Symmetrically Bifurcated Microchannel
Authors: Xing Keqiang , Tao Yong
Published: April 2008

The lattice Boltzmann method (LBM) as a relatively new numerical scheme has recently achieved considerable success in simulating fluid flows and associated transport phenomena. However, application of this method to heat transfer problems has been at a stage of infancy. In this work, a thermal lattice Boltzmann model is employed to simulate a two-dimensional, steady flow in a symmetric bifurcation under constant temperature and constant heat flux boundary conditions. The bifurcation effects on the heat transfer and fluid flow are investigated and comparisons are made with the straight tube. Also, different bifurcation angles are simulated and the results are compared with the work of the other researchers.
Frost Density Measurement for Evaporator Defrosting Control
Authors: Iragorry J. , Tao Y.-X.
Published: April 2008

In frost growth control on finned surfaces, the most important frost properties are thickness and density. As shown in previous work, the frost thickness can be related to the temperature difference between frost surface and the fin or tube. The frost temperature can be obtained by using an infrared thermometer. A frost density sensor is designed. A set of strain gages are installed in a flexible beam element (HDPE), which deflection caused by frost accretion is related to the change in frost density. A prototype of the sensor is tested for distributed frost weight and for artificial probe tip-loads. The relation between the sensor signal and frost weight is obtained for the cases studied. The combination of frost top temperature and weight variation signals can be used to control the defrost process.
Fluid Slip of Flow Past a Hydrophobic Wall Sphere
Authors: Fujita Takao , Watanabe Keizo
Published: April 2008

The possibility of fluid slip has received considerable attention in recent years. Laminar drag reduction is achieved by using a hydrophobic wall with fluid slip. Fluid slip is closely related to the gas-liquid interface formed at a solid surface with many fine grooves. The friction generated by the solid boundary is modified considerably because the gas-liquid interface provides a zero-shear stress boundary condition. The purpose of this study is to experimentally clarify the flow characteristics and drag reduction of a hydrophobic wall sphere by visualizing flow and by measuring the drag. In addition, the flow patterns were numerically analyzed by applying a wet boundary condition for fluid slip. The flow visualization results showed that the Vortex Loop was not exist at Re < 400 in the hydrophobic wall sphere and the separation point moved downstream compared with that of a conventionally smooth sphere. Drag reduction occurred in the flow and the maximum drag reduction ratio was 14.6% at Re=93.2. In this simulation, the flow patterns for the numerical simulation results agreed with those of the flow visualization results.
Determining Moldability and Parting Directions for Polygons With Curved Edges
Authors: McMains Sara , Chen Xiaorui
Published: April 2008

We consider the problem of whether a given geometry can be molded in a two part, rigid, reusable mold with opposite removal directions. We describe an efficient algorithm for solving the opposite direction moldability problem for a 2D “polygon” bounded by edges that may be either straight or curved. We introduce a structure, the normal graph of the polygon, that represents the range of normals of the polygon’s edges, along with their connectivity. We prove that the normal graph captures the directions of all lines corresponding to feasible parting directions. Rather than building the full normal graph, which could take time O(n log n) for a polygon bounded by n possibly curved edges, we build a summary structure in O(n) time and space, from which we can determine all feasible parting directions in time O(n).
Decomposition-Based Assembly Synthesis for Structural Stiffness and Dimensional Integrity
Authors: Lyu Naesung , Lee Byungwoo , Saitou Kazuhiro
Published: April 2008

A method for optimally synthesizing multi-component structural assemblies of an aluminum space frame (ASF) vehicle body is presented, which simultaneously considers structural stiffness, manufacturing and assembly cost and dimensional integrity under a unified framework based on joint libraries. The optimization problem is posed as a simultaneous determination of the location and feasible types of joints in a structure selected from the predefined joint libraries, combined with the size optimization for the cross sections of the joined structural frames. The structural stiffness is evaluated by finite element analyses of a beam-spring model modeling the joints and joined frames. Manufacturing and assembly costs are estimated based on the geometries of the components and joints. Dimensional integrity is evaluated as the adjustability of the assembly for the given critical dimensions. The optimization problem is solved by a multi-objective genetic algorithm. An example on an ASF of the mid-size passenger vehicle is presented, where the representative designs in the Pareto set are examined with respect to the three design objectives.