bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative Viscosity Due to Magnetic Properties of a Semi-Dense Colloidal Dispersion Composed of Ferromagnetic Rod-Like Particles With Magnetic Moment Normal to the Particle Axis
Authors: Sakuda Yasuhiro , Satoh Akira
Published: May 2009

We have investigated the negative viscosity of a colloidal dispersion composed of ferromagnetic rod-like particles, which have a magnetic moment normal to the particle axis. A simple shear flow problem has been treated to clarify the particle orientational distribution and rheological properties of such a semi-dense dispersion, under circumstances of an external magnetic field applied in the direction normal to the shear plane of a simple shear flow. The results obtained here are summarized as follows. For the cases of a very strong magnetic field and magnetic interactions between particles, the magnetic moment of the rodlike particles is significantly restricted in the magnetic field direction, so that the particle approximately aligns in the shear flow direction. Also, the particle can easily rotate around the axis of the cluster almost freely even in a simple shear flow. Characteristic orientational properties of the particle cause negative viscosity, as in the previous study for a dilute dispersion. However, magnetic particle-particle interactions have a function to make such negative viscosity decrease.
Growth of Carbon Nanotubes on Metal Containing Amorphous Carbon (A-C:M) Films
Authors: Yung K. P. , Wei J. , Tay B. K.
Published: May 2009

In this study, carbon nanotubes were grown from metal containing amorphous carbon (a-C:M). a-C:M were deposited by two different techniques: RF magnetron sputtering and filtered cathodic vacuum arc (FCVA). X-ray diffraction (XRD) and atomic force microscopy (AFM) were deployed to analyze the chemical structure and morphology of the catalyst layers, respectively. The morphology of the carbon nanotubes growth was studied under Scanning electron microscopy (SEM). It was found that carbon nanotubes growth from sputtered a-C:Fe film are random orientated, while the nanotubes from FCVA a-C:M are well-aligned. SEM and AFM studies also show that the diameter of the nanotubes grown on sputtered a-C:Fe film is proportional to that of the annealed catalyst particles grain size. However, the diameter of the nanotubes from FCVA a-C:Fe film was found to be much smaller than the grain size of the catalyst particles.
Physical-Based Simulations of Mechanical Watches and Clocks
Authors: Tam L. C. , Kong Tom , Du R.
Published: May 2009

Mechanical watches and clocks are intricate mechanical devices that fascinate millions of people around the world. In general, a mechanical watch is made of some 100 components. Among these components, the escapement plays a vital role in controlling the timekeeping accuracy. An escapement usually consists of an escape wheel, which receives energy provided by the mainspring through the gear train, and a pallet fork, which controls the oscillation. Owing to its complex nature, few have built a mathematical model for the escapement. In this paper, we present a physical-based simulation model for the Graham Escapement (the oldest and the most common escapement for clocks), and a model for the Swiss Lever Escapement (the most popular escapement for mechanical watches). The models are developed based on a commercial software system RecurDyn® [1]. The simulation helps to understand the kinetics as well as the dynamics of the escapements.
Finite Element Modeling of Brain Tissue Retraction for Neurosurgical Simulation
Authors: Adachi Kazuhiko , Inoue Yoshiaki , Kanki Hiroshi , Fujita Atsushi , Kohmura Eiji
Published: May 2009

The simulation capability for intraoperative brain tissue deformation by the surgical procedures using computational Finite Element analysis is demonstrated in this paper. Our research group has been developing the patient-specific three-dimensional Finite Element brain deformation model consisting of precise anatomical structures, i.e., brain parenchyma with both gyri and sulci on the surface, falx cerebri, and tentorium, in order to evaluate brain shift during navigation surgery without additional acquisition of intraoperative imaging. In this study, both gray and white matters of the brain tissues were modeled as homogeneous nonlinear hyper-viscoelastic material. The falx cerebri with tentorium was modeled as linear elastic material which is much stiffer than the brain tissue. The skull was modeled as a rigid body. In the numerical simulation, the computation of the intraoperative cerebellum tissue deformation due to retraction by spatula for posterior fossa surgery was conducted by ABAQUS/Explicit. The illustrative results successfully demonstrate the interaction between brain tissue and spatula.
Directed Hierarchical Self Assembly: Active Fluid Mechanics at the Micro and Nanoscales
Authors: Krishnan Mekala , Tolley Michael T. , Lipson Hod , Erickson David
Published: May 2009

Directed hierarchical self assembly (DHSA) involves the purposeful assembly of a series of different subunits over multiple length scales to create arbitrarily shaped, large structures. We are developing a two stage DHSA procedure comprising of a coarse “far field” fluidic process which brings the sub-elements into the general vicinity of the assembly point and a fine “near field” process which completes the process. In the experiments presented here our sub-elements comprise of lithographically patterned silicon “microtiles” which are 500μm in size and contain a series of functional elements. The far-field assembly of these tiles is controlled fluid dynamically by modulating the translational and rotational shear forces applied to the tiles with a microfluidic structure. The near-field assembly is controlled through on board (i.e. on tile) microchannel jets/sinks, the strengths of which are modulated through the assembly or disassembly of thermally actuated gel based microvalves. This provides two fundamental levels of system control, namely control of the magnitude and direction of fluid flow, as well as addressability and control of each assembled component through on tile valves. In this paper we present our preliminary work on the fundamental fluid mechanics of this assembly at these two stages. In the first section we look at fluid motion and forces using CFD based numerical simulations. In the second we study a valving system based on an aqueous solution of a triblock copolymers that form a gel at temperatures near room temperature.
Optofluidic Transport: Optical Waveguides as Microfluidic “Train Tracks”
Authors: Yang Allen H. J. , Schmidt Bradley , Mandal Sudeep , Lipson Michal , Erickson David
Published: May 2009

In this work we demonstrate optofluidic [1] transport and trapping of dielectric particles using the intense electromagnetic energy in the evanescent field of optically excited microphotonic waveguides. A conceptual overview of the transport mechanism is presented along with the detailed optofluidic theory which describes the transport. Experimental results for straight and curved waveguides are presented along with details of our experimental technique. The final section details our recent work on developing a stability condition for this form of transport.
Validity Evaluations of On-Line Driver Modeling and State Assessment
Authors: Chen Liang-Kuang , Peng Meng-Hsuan
Published: May 2009

Although driver steering control models and on-line model identification have been studied extensively, the application of the driver models to driver state assessment is seldom investigated. Furthermore, the validity level, or confidence index, of the on-line modeling and assessment of driver behavior is not reported in the literature. In this paper, on-line system identification techniques are applied to the determination of driver model parameters and model validity estimation. The driver steering control model is estimated on-line using system identification techniques. The on-line driver state assessment is achieved using probabilistic neural network (PNN), and the validity of the assessment is derived from the likelihood function inside the PNN. Preliminary results show that the computed validity indices agree with expectation reasonably well. More driving simulator experiments will be conducted to validate the proposed indices.
Generation of SI Nanoparticles Using Plasma Technology for Novel Device and Energy Storage Application
Authors: Kim Kwangsu , Cho Yonghyun , Kim Youngjin , Kim Taesung
Published: May 2009

Silicon nanoparticles are widely studied as a building block for various applications. M. L. Ostraat et al.[1] and S. Koliopoulou et al.[2] studied NFGM (nano floating gate memory), and S. Oda[3] studied electron characteristics of Si nanoparticles. H. Shirai et al.[4] studied optical characteristics of crystalline silicon nanoparticles. In addition, silicon nanoparticles can be applied for energy devices such as 2nd generation battery. In this paper, we investigated the generation of Si nanoparticles using pulse plasma technology. An inductively-coupled plasma chamber with RF power (13.56 MHz) was designed for this study. DC-bias was applied between the substrate and grounded grid installed above the substrate to increase the particle collection efficiency and to avoid film formation on the substrate. Moreover, in order to control the structure of silicon nanoparticle, we implemented heater inside the substrate. Experiments were performed with various pulse periods to generate nanoparticles with various sizes. Transmission electron microscopy (TEM) was used to measure the shape, structure and size of nanoparticles. TEM images showed that the generated nanoparticles have spherical shape with highly monodisperse size distribution. The structure is originally amorphous but we could change its structure to crystal by annealing. We employed a widely used plasma technology, so we except that it can be easily applied to industry with small modification.
Effect of Load Disturbances on Multiplexed Force Control of McKibben Actuators
Authors: Jouppila V. , Ellman A.
Published: May 2009

Traditionally in fluid power systems each actuator is provided with its own control valve that is often quite an expensive and weighty component. By using multiplexed control, where a single control valve is shared among a number of actuators, it is possible to achieve cost and weight savings. The control system can be carried out with one pressure regulator and several high-speed on/off valves which form the multiplexer unit. The McKibben actuator has characteristics such as hermetic construction and almost frictionless operation which enable its use especially in force control applications. The muscle can maintain its pressure and thus the generated force for a relatively long time after it is disconnected from the pressure line. It has been proven [Jouppila & Ellman, 2006] that multiplexed force control of pneumatic muscles is an option for applications where multiple actuators have similar tasks with low dynamics. In this paper the effect of different load disturbances on the multiplexed force control system is investigated. The system is basically an open-loop configuration where the pressure regulator controls the system pressure. Thus, the system is sensitive to load variations because there is no feedback loop from the muscles. In the testing procedure the McKibben actuators with similar tasks are controlled with the multiplexing technique. The system behavior is studied when one of the muscles is displaced from its original position. The effects of using different frequencies and amplitudes for the load variation are studied. The purpose is to find the boundaries in which the pressure regulator is able to compensate the disturbance effects. Simulations are first used to investigate how sensitive the system is to the load variations. Also the pressure regulator’s capability for error compensation is studied. Actual measurements are used to verify the simulation results.
The Design of an Interactive Socially Assistive Robot for Patient Care
Authors: Nejat Goldie , Allison Brian , Gomez Nadia , Rosenfeld Andrew
Published: May 2009

It is anticipated that the use of assistive robots will be one of the most important service applications of robotic systems of the future. In this paper, a unique non-contact socially assistive robot consisting of a human-like demeanor is presented for utilization in hospital wards and veteran homes to study its role and impact on the well-being of patients, addressing patient’s needs and its overall effect on the quality of patient care. The robot will be an embodied entity that will participate in hands-off non-contact social interaction with a patient during the convalescence, rehabilitation or end-of-life care stage. The robot has been designed as a platform to incorporate the three design parameters of embodiment, emotion and non-verbal dialog to encourage natural interactions between the patient and itself. For perception, we describe the first application of utilizing varying intensity depth imaginary, via a 3D camera, for non-contact and non-restricting 3D gesture recognition and characterization.
A Method to Simulate Structural Intensity Fields in Plates and General Structures Induced by Spatially and Temporally Random Excitation Fields
Authors: Daley Michael J. , Hambric Stephen A.
Published: May 2009

The structure-borne power in bending waves is well understood, and has been studied by many investigators in ideal beam and plate structures. Most studies to date, however, have considered only the structural intensity induced by deterministic, localized drives. Many structures of practical interest are excited by spatially random pressure fields, such as diffuse and turbulent boundary layer pressure fluctuations. Additionally, such studies typically employ finite differencing techniques to estimate the shear, bending and twisting components of intensity, and are therefore only applicable to simple homogenous uniform structures such as thin plates and beams. Often, however, finite differencing techniques are not applicable to practical structures of interest. The present study introduces a new method to compute the structural intensity induced by spatially random pressure fields in general structures which does not require the use of finite differencing techniques. The results of this method are validated using those obtained using finite-difference based techniques in a thin plate. The simulated fields from the new analytic technique are shown to be similar to those estimated via finite difference-based techniques, thus validating this new method. Both methods show intensity patterns different from those caused by deterministic point drives. The new general method may be applied in the future to complex non-homogenous structures which include discontinuities and curvature.
Functional Electrical Stimulation of a Quadriceps Muscle Using a Neural-Network Adaptive Control Approach
Authors: Tang Yan , Leonessa Alexander
Published: May 2009

Functional electrical stimulation (FES) has been used to facilitate persons with paralysis in restoring their motor functions. In particular, FES-based devices apply electrical current pulses to stimulate the intact peripheral nerves to produce artificial contraction of paralyzed muscles. The aim of this work is to develop a model reference adaptive controller of the shank movement via FES. A mathematical model, which describes the relationship between the stimulation pulsewidth and the active joint torque produced by the stimulated muscles in non-isometric conditions, is adopted. The direct adaptive control strategy is used to address those nonlinearities which are linearly parameterized (LP). Since the torque due to the joint stiffness component is non-LP, a neural network (NN) is applied to approximate it. A backstepping approach is developed to guarantee the stability of the closed loop system. In order to address the saturation of the control input, a model reference adaptive control approach is used to provide good tracking performance without jeopardizing the closed-loop stability. Simulation results are provided to validate the proposed work.
Performance Evaluation of Parallel Flow Microchannel Heat Exchanger Subjected to External Heat Transfer
Authors: Mathew B. , Hegab H.
Published: May 2009

In this paper the effect of constant external heat transfer on the performance of a two fluid balanced parallel flow microchannel heat exchanger is analyzed. A mathematical model is developed for predicting the effectiveness-NTU relationship of both the fluids. Theoretical analysis is presented for various cases of external heating over a wide range of NTU. External heating improved the effectiveness of the cold fluid but degraded the effectiveness of the hot fluid while external cooling produced the opposite changes in the effectiveness of the coolants. The extent of improvement or degradation depended on the level of external heating/cooling. A term referred to as performance factor is used to assess the degree of improvement or degradation of the effectiveness of the individual fluids. Experiments conducted on two microchannel heat exchangers by subjecting the coolants to 5% and 10% external heating have been presented in this paper. The experimental value of NTU varied from 0.42 to 1.76. Good agreement is observed between the theoretical predictions and experimental results. The results presented in this paper are nondimensional; thus they can be utilized irrespective of the dimensions of parallel flow microchannel heat exchangers as well as the type of coolant.
Isometric Stress Analysis and Current-Voltage Characteristics of Some Nanoclay Dielectric Elastomer Compounds
Authors: Nurminen N. , Ellman A. , Jouppila V. , Paajanen M. , Karesoja M.
Published: May 2009

The electromechanical properties of elastomer material change when different levels of stretching are applied to the elastomer film. The generated stress and expansion of the EAP material depend on the electric field across the material and its relative permeability. Some of the best known commercial dielectric elastomer materials are based on acrylic elastomers, e.g. 3M VHB 4910 or 4905 adhesive tape. In this work, the VHB 4910 tape was used as a reference material for different types of acrylic nanoclay compound materials. These new type of nanoclay elastomer compounds were tested because the addition of clay into the elastomer was assumed to increase its actuating performance. Different voltage and pre-stretching levels were used in the measurements. Current-voltage characteristics and isometric stress measurements were used to study the energy efficiency, frequency dependent behavior, reactivity and isometric stress performance of the EAP materials. Based on the electromechanical characterization and material properties, a general hyperelastic material model was developed. According to the preliminary tests, the nanoclay compound seems to be a bit stiffer than VHB 4910 resulting in a greater isometric stress response.
Gradients of Stiffness Guide Neurite Growth in 3D Collagen Gels
Authors: Sundararaghavan Harini G. , Shreiber David I.
Published: May 2009

One approach to enhance nerve and spinal cord regeneration following injury is to implant a biomaterial scaffold to ”bridge” the gap of the injury. Structural/mechanical anisotropy has been suggested as a means of orienting this growth axially. We have spatially varied the mechanical properties of a 3D collagen gel to direct growth axially and unidirectionally. Gradients of mechanical properties were generated in collagen gels by exposing the collagen to a 0–1mM gradient of genipin, a cell-tolerated crosslinking agent, for 12hrs via microfluidics. The gradient of stiffness was confirmed via a gradient of genipin-induced fluorescence intensity, which we have previously correlated to the storage modulus of collagen gels. The growth of neurites from isolated chick embryo dorsal root ganglia (DRG) in the presence of these gradients was evaluated after 5 days in culture. In control cases, neurites grew into the collagen gel and up either side of the cross-channel to approximately equal lengths. A 20% difference in differential growth was observed in control experiments. In contrast, when presented a gradient of shear modulus from ∼365Pa – 60Pa, neurites elected to grow down the gradient of stiffness to the compliant side, with an almost 300% difference. Interestingly, the length of neurites in gels with gradients was significantly greater than the length of those grown in gels with uniform, untreated gels with high compliance. Control of neurite growth, cell migration, and other aspects of cell behavior in 3D scaffolds via mechanical properties offers vast potential for tissue engineering and other regenerative therapies.
Self Assembly of Metallic Quantum Dots
Authors: Salac David , Lu Wei
Published: May 2009

Experiments have shown that metallic quantum dots without a coherent lattice or lattice mismatch with the substrate can undergo ordering. Here we show that this ordering can arise due to electrostatic interactions within the system. We show that the contact potential induces repulsive charge clouds in the substrate. The size-dependent repulsion and van der Waal attraction lead to ordered nanoscale structures.
Secondary Breakup of Electrically Charged Newtonian Drops
Authors: Guildenbecher Daniel R. , Sojka Paul E.
Published: May 2009

An experimental investigation was conducted to determine the secondary breakup morphology of electrically charged drops. Movies of drop breakup in a high speed air stream were recorded for drops charged between 0 and 60% of the Rayleigh charge limit. The conventional Weber number was found to be insufficient to classify the breakup morphology of charged drops. Rather an electrostatic Weber number was defined to account for the presence of the electrostatic surface stress. When the electrostatic Weber number was used in place of the classical Weber number, the observed breakup morphology was found to be similar to that proposed by previous researchers for uncharged drops. It is therefore concluded that secondary breakup of electrically charged drops can be characterized using the wealth of available literature on uncharged Newtonian drops, provided the electrostatic Weber number is used, and that the charge relaxation time is much smaller than the breakup time.
Free Vibration Analysis of Double Curvature Thin Walled Structures by a B-Spline Finite Element Approach
Authors: Carminelli Antonio , Catania Giuseppe
Published: May 2009

This paper presents a free vibration analysis of general double curvature shell structures using B-spline shape functions and a refinement technique. The shell formulation is developed following the well known Ahmad degenerate approach including the effect of the shear deformation. The formulation is not isoparametric, as a consequence the assumed displacement field is described through non-uniform B-spline functions of any degree. A solution refinement technique is considered by means of a high continuity p-method approach. The eigensolution of a plate, and of single and double curvature shells are obtained by numerical simulation to test the performance of the approach. Solutions are compared with other available analytical and numerical solutions, and discussion follows.
Modeling of Dynamically Loaded Open-Cell Metallic Foams
Authors: Romero Pedro A. , Cuitin˜o Alberto M.
Published: May 2009

Heterogeneous cellular materials such as metallic and polymeric open-celled foams are preferable in many engineering applications requiring mitigation of energy during sudden impact loading. This brief communication presents an approach for modeling dynamically loaded open-cell metallic foams. It is implicitly assumed that there exists a length scale separation where the microstructural dimensions are much smaller than the macroscopic dimensions. In this context, a macroscopic point translates into a microscopic array of identical unit cells sharing the same macroscopic fields. Dictated by a model for the metallic cell wall constitutive behavior, the effective unit cell response is then obtained from a structural micromechanical model which enforces the principle of minimum action on a representative 3D unit cell. The effective macroscopic response at every node in the FEM mesh (equilibrium, stresses, stress tangents) is then provided by the unit cell microscopic model. The present theory allows one to define a constitutive formulation for lightweight, open-celled foams based on clear and quantifiable parameters such as microstructural topology and ligament properties while capturing the effects of dynamic loading via viscous dissipation at ligament level and microinertia at unit cell level. History of deformation is considered at ligament level while axial and bending deformation are considered at unit cell level. As observed experimentally, the resulting macroscopic FEM simulations clearly demonstrate how the material undergoes heterogeneous deformation during cellular structure collapse.
Study of Vehicle Dynamic Modeling Fidelity on Haptic Collaboration in Steer-by-Wire Systems
Authors: Naik Anand P. , Lee Leng-Feng , Krovi Venkat N.
Published: May 2009

The Steer-By-Wire (SBW) paradigm for vehicle control offers many advantages over traditional use of mechanical steering systems but comes at the cost of loss of proprioception (“road feel”). To this end, haptic interfaces for SBW systems have been proposed to restore the intimacy of interactive control back to the driver. However, the degree of realism for the interaction is dependent on the fidelity of the underlying computational vehicle dynamics model. Hence we focus on quantitative comparative testing of the role of vehicle dynamics modeling fidelity for haptic SBW tasks. Additionally the SBW paradigm can simplify implementation of shared/collaborative control (steering) of the underlying mechanical system (vehicle). Possibilities range from sharing of control between multiple individual users or between user and automation technology. Performance evaluation of 3 modes of shared control vs. individual control of driving was carried out and preliminary analysis of results is presented in the paper.
Efficient Parallel Computer Simulation of the Motion Behaviors of Closed-Loop Multibody Systems
Authors: Duan Shanzhong , Ries Andrew
Published: May 2009

This paper presents an efficient parallelizable algorithm for the computer-aided simulation and numerical analysis of motion behaviors of multibody systems with closed-loops. The method is based on cutting certain user-defined system interbody joints so that a system of independent multibody subchains is formed. These subchains interact with one another through associated unknown constraint forces fc at the cut joints. The increased parallelism is obtainable through cutting joints and the explicit determination of associated constraint forces combined with a sequential O(n) method. Consequently, the sequential O(n) procedure is carried out within each subchain to form and solve the equations of motion while parallel strategies are performed between the subchains to form and solve constraint equations concurrently. For multibody systems with closed-loops, joint separations play both a role of creation of parallelism for computing load distribution and a role of opening a closed-loop for use of the O(n) algorithm. Joint separation strategies provide the flexibility for use of the algorithm so that it can easily accommodate the available number of processors while maintaining high efficiency. The algorithm gives the best performance for the application scenarios for n>>1 and n>>m, where n and m are number of degree of freedom and number of constraints of a multibody system with closed-loops respectively. The algorithm can be applied to both distributed-memory parallel computing systems and shared-memory parallel computing systems.
Optimization of a Light-Weight Composite Blast Containment Vessel Structural Response
Authors: Thota Jagadeep , Ayyaswamy Ashok K. , Trabia Mohamed B. , O’Toole Brendan J.
Published: May 2009

This paper proposes an optimization technique for increasing the structural integrity of a light-weight composite blast containment vessel. The vessel is cylindrical with two hemispherical ends. It has a steel liner that is internally reinforced with throttles and gusset plates and wrapped with a basalt-plastic composite. A finite element model of the blast containment vessel was proposed and verified in an earlier work. The parameters of the vessel are incorporated within an iterative optimization procedure to decrease the peak strains within the vessel, which are caused by internal blast loading due to an explosive charge placed at the center of the vessel. The procedure is validated for different initial guesses of the design variables.
Microscale Laser-Induced Fluorescence Method for Non-Intrusive Temperature Measurement
Authors: Chamarthy Pramod , Wereley Steven T. , Garimella Suresh V.
Published: May 2009

Ratiometric Laser Induced Fluorescence (LIF) Thermometry is applied for temperature measurements in a ‘T’ junction, using microscale visualization methods. Rhodamine B (RhB) and Rhodamine 110 (Rh110) are used as the temperature-dependent and temperature-independent dye, respectively. The temperature responses of the two dyes were carefully measured for different concentrations. A novel normalization procedure for the calibration curve is proposed to render the technique system-independent. The mixing plane between a hot and a cold fluid stream for three different temperatures and three different flow rate ratios is visualized using 4X and 10X magnifications.
An Experimental Investigation of the Effects of Functional Group Structure on Particulate Matter and NO Emissions of Oxygenated Hydrocarbons
Authors: Perez Carlos , Walton Stephen M. , Wooldridge Margaret S.
Published: May 2009

The effects of alkyl group size on nitric oxide and soot emissions in small esters was investigated using a multi-element diffusion burner (a Hencken burner) and pool fires at atmospheric pressure. The esters were chosen to examine chemical structure characteristics, e.g. carboxylic acid length, while holding other parameters constant (molecular weight, and C:H:O ratio), to determine the effects of various structural parameters on the particulate matter and NO emissions. The esters were chosen to vary alkyl chain length from one to four carbons in both their alcohol and carboxylic acid groups with the largest ester chosen containing 5 carbons in total. Increasing the carbon content increased the relative sooting tendencies of the esters. Within the isomer pairs considered, the sooting tendency was higher for compounds with longer alcohol groups compared to longer carboxylic groups. Although the NO results were convolved with temperature and structural effects are not isolated, the NO emissions were significantly affected by the addition of the esters to a baseline methane flame.
Micro Electro Discharge Machining of CNT-Based Nanocomposite Materials
Authors: Wan Yi , Kim Dae-Wook , Jang Jae-Soon , Park Young-Bin
Published: May 2009

Since the discovery of carbon nanotubes (CNTs), there has been great interest in CNT-based composites. Well-developed micromachining processes are necessary to realize micron-size CNT-based composite products. Micro electro discharge machining (micro-EDM) has been applied into many challenge-to-cut materials such as ceramic composites. In this study, micro-EDM is used to machine CNT-reinforced polymer composites in the micro scale. CNT-based polymer composites were fabricated using solution casting, in which CNTs were dispersed in the polymer-solvent solution via high energy sonication, followed by precipitation and hot pressing. The investigation uses design of experiments (DOE) approach to screen of influential input factors for process measures. A 2 level fractional factorial design was used with four input factors; CNT loading on the workpiece, μ-EDM supply voltage, pulse on-time duration, and pulse on-time ratio. With 16 μ-EDM experiments, supply voltage was found to be most influential to the material-removal-rate (MRR). Scanning electron microscope (SEM) was used to investigate characteristics of the machined CNT-based nanocomposite surfaces.
Effect of Uniaxial Deformation, Annealing and Carbon Nanotubes on the Morphology and Mechanical Properties of Poly (Butylene Terephthalate) and PBT Nanocomposites
Authors: Mago Gaurav , Dutreuil Jerry A. , Fisher Frank T. , Kalyon Dilhan M.
Published: May 2009

The goal of this investigation is to elucidate the interrelations between the strain-induced crystallization behavior, morphology and mechanical properties of poly (butylene terephthalate) PBT and its nanocomposites with multi-walled carbon nanotubes (MWNTs). The mechanical properties of semicrystalline polymers such as PBT depend upon the processing conditions, which affect the crystallization behavior and the resulting crystal morphology developed within the processed sample. PBT is observed to undergo strain-induced crystallization during uniaxial deformation, with concomitant changes in the polymer crystal as a function of the applied strain history. In the current work polymer morphology was investigated with wide angle XRD, differential scanning calorimetry (DSC) and polarized light microscopy (PLM). DSC results indicate an increase in crystallinity due to strain-induced crystallization during uniaxial cold-stretching, which was further confirmed with XRD analysis of the samples. Analyses of the samples under polarized light pre- and post-stretching clearly show that there is a transformation of the spherulitic crystals of the pre-stretch morphology into elongated oblong crystals, as the imposed strain exceeds a critical value. Annealing of PBT was done under different conditions to probe the effects of changes in the crystallinity obtained upon thermal treatment on polymer morphology and mechanical properties. The annealed samples were found to have high crystallinity, high Young’s modulus, and low yield stress values as compared to unannealed samples processed under similar conditions. To investigate the effects of nanoparticle loadings on PBT crystal morphology and mechanical properties, pure PBT was melt mixed with different concentrations of multi-walled carbon nanotubes (MWNTs). Due to the increased nucleation rate effect associated with the incorporation of MWNTs, the PBT crystallization temperature was increased and the crystal size decreased with the increasing concentration of MWNTs. Tensile tests performed on PBT and their nanocomposite samples revealed decreases in the elongation at break values. Research is ongoing to understand the relationship between the MWNT loading levels and mechanical properties along with study of orientation of MWNTs under tensile load and its effect on strain-induced crystallization.
An Integrated Micron-Resolution Particle Image Velocimeter/Optical Tweezers (μPIVOT) for Microenvironment Investigations
Authors: Lingwood James K. , Ne`ve Nathalie , Kohles Sean S. , Tretheway Derek C.
Published: May 2009

A novel instrument has been developed (μPIVOT) to manipulate and characterize the mechanical environment in and around microscale objects by integrating two laser-based techniques: micron-resolution particle image velocimetry (μPIV) and optical tweezers (OT). While the μPIVOT enables a new realm of microscale studies, it still maintains the individual capabilities of each optical technique. Ongoing investigations will provide a unique perspective towards understanding microscale phenomena including cell biomechanics, non-Newtonian fluid flow, and single particle or particle-particle hydrodynamics.
High-Fidelity Reconstruction and Computational Modeling of Metallic Microstructure
Authors: Qidwai M. A. Siddiq , Geltmacher A. B. , Lewis A. C. , Rowenhorst D. J. , Spanos G.
Published: May 2009

The end-objective of this research is to identify critical microstructural features in metals that precipitate plastic flow, and therefore, cause degradation of mechanical performance at higher scales. The material focus is a titanium alloy-β21s. The three-dimensional (3D) microstructure in the mesoscale range was obtained using serial sectioning, optical microscopy, electron backscatter diffraction (EBSD) and computerized 3D reconstruction techniques. The reconstructed volumes, comprising hundreds of beta-Ti grains, provide information on morphology and crystallography. This data was used as input into 3D finite element models to analyze the spatial evolution of state variables, such as stress, strain and crystallographic slip under simple loading conditions. Single crystal hypoelasticity and the assumption of resolved shear stress causing crystal slip were used to represent microstructural material behavior. Evolution of plastic flow with applied loading was analyzed at grain boundary interfaces where most flow occurred. Rendering of large reconstructions into faithful but lean finite element meshes was identified to be the critical issue in simulating accurate material behavior near grain boundaries, establishing definite structure-property relationships at mesoscale and reducing the computational cost.
Design and Performance of a Fuel Cell Plant Heat Recovery System
Authors: Ryan Robert G. , Brown Tom
Published: May 2009

A 1 MW Direct Fuel Cell® (DFC) power plant began operation at California State University, Northridge (CSUN) in January, 2007. This plant is currently the largest fuel cell plant in the world operating on a university campus. The plant consists of four 250 kW DFC300MA™ fuel cell units purchased from FuelCell Energy, Inc., and a waste heat recovery system which produces dual heating hot water loops for campus building ventilation heating, and domestic water and swimming pool heating water for the University Student Union (USU). The waste heat recovery system was designed by CSUN’s Physical Plant Management and engineering student staff personnel to accommodate the operating conditions required by the four individual fuel cell units as well as the thermal energy needs of the campus. A Barometric Thermal Trap (BaTT) was designed to mix the four fuel cell exhaust streams prior to flowing through a two stage heat exchanger unit. The BaTT is required to maintain an appropriate exhaust back pressure at the individual fuel cell units under a variety of operating conditions and without reliance on mechanical systems for control. The two stage heat exchanger uses separate coils for recovering sensible and latent heat in the exhaust stream. The sensible heat is used for heating water for the campus’ hot water system. The latent heat represents a significant amount of energy because of the high steam content in the fuel cell exhaust, although it is available at a lower temperature. CSUN’s design is able to make effective use of the latent heat because of the need for swimming pool heating and hot water for showers in an adjacent recreational facility at the USU. Design calculations indicate that a Combined Heat and Power efficiency of 74% is possible. This paper discusses the integration of the fuel cell plant into the campus’ energy systems, and presents preliminary operational data for the performance of the heat recovery system.
An Efficient O(N) Algorithm for Computer Simulation of Rigid Body Molecular Dynamics
Authors: Duan Shanzhong , Ries Andrew
Published: May 2009

Molecular dynamics is effective for a nano-scale phenomenon analysis. There are two major computational costs associated with computer simulation of atomistic molecular dynamics. They are calculation of the interaction forces and formation/solution of equations of motion. In this paper, an O(N) (order N) procedure is presented for calculation of the interaction forces and formation/solution of equations of motion. For computational costs associated with potentials or interaction forces, an internal coordinate method is used. Use of the internal coordinate method makes application of multi-rigid body molecular dynamics to an atomistic molecular system become possible. The algorithm based on the method makes the calculation considerably more practical for large-scale problems encountered in molecular dynamics such as conformation dynamics of polymers. For computational costs associated with formation/solution of equations of motion, Kane method and the internal coordinate method are used for recursive formation and solution of equations of motion of an atomistic molecular system. However, in computer simulation of atomistic molecular dynamics, the inclusion of lightly excited all degrees of freedom of an atom, such as inter-atomic oscillations and rotation about double bonds with high frequencies, introduces limitations to the simulation. The high frequencies of these degrees of freedom force the use of very small integration step sizes, which severely limit the time scales for the atomic molecular simulation over long periods of time. To improve this, holonomic constraints such as strictly constant bond lengths and bond angles are introduced to freeze these high frequency degrees of freedom since they have insignificant effect on long time scale processes in conformational dynamics. In this way, the procedure developed in multibody dynamics can be utilized to achieve higher computing efficiency and an O(N) computational performance can be realized for formation/solution of equations of motion.
Realization-Preserving Structure and Order Reduction of Nonlinear Energetic System Models Using Energy Trajectory Correlations
Authors: Ersal Tulga , Fathy Hosam K. , Stein Jeffrey L.
Published: May 2009

Previous work by the authors developed algorithms for simplifying the structure of a lumped dynamic system model and reducing its order. This paper extends this previous work to enable simultaneous model structure and order reduction. Specifically, it introduces a new energy-based metric to evaluate the relative importance of energetic connections in a model. This metric (1) accounts for correlations between energy flow patterns in a model using the Karhunen-Loe`ve expansion; (2) examines all energetic connections in a model, thereby assessing the relative importance of both energetic components and their interactions, and enabling both order and structural reduction; and (3) is realization-preserving, in the sense of not requiring a state transformation. A reduction scheme based on this metric is presented and illustrated using a simple example.
Plastic Mesoscale Combustors/Heat Exchangers
Authors: Sanford Lindsay L. , Huang Shuo-Yu J. , Lin ChienShung , Lee Jungmin , Ahn Jeongmin , Ronney Paul D.
Published: May 2009

Recent experimental and theoretical studies of heat-recirculating combustors have demonstrated the importance of thermal conduction through the structure of the combustor on its performance. In particular, this solid-phase heat conduction inevitably degrades performance via transfer of heat out of the reaction zone to the surrounding structure, which is then lost to ambient. This in turn leads to a reduction of reaction temperature and thus sustainable reaction rates. By use of platinum-based catalysts in spiral counterflow “Swiss roll” heat-recirculating combustors, we have been able to sustain nearly complete combustion of propane-air mixtures at temperatures less than 150 °C using combustors built with titanium (thermal conductivity (k) of 7 W/m°C). Such low temperatures suggest that high-temperature polymers (e.g. polyimides, k ∼ 0.3 W/m°C) may be employed as a combustor material. With this motivation, a polyimide Swiss roll combustor was built using CNC milling and tested over a range of Reynolds numbers with propane fuel and Pt catalyst. The combustor survived prolonged testing at temperatures up to 450 °C. Reynolds numbers as low as 2 supported combustion, with thermal power as low as 3 watts and temperatures as low as 72 °C. These initial results suggest that polymer combustors may prove more practical for meso- or microscale thermochemical devices due to their lower thermal conductivity and ease of manufacturing. Applications to electric power generation via single-chamber solid oxide fuel cells are discussed.
A Global Engineering Design Clinic Experience in Engineering Education: Lessons Learned
Authors: Pezeshki C. , Racicot K. , Zbib H.
Published: May 2009

Though the establishment of clinics for students to participate in engineering activities with partners around the world has achieved a high profile recently, there are major difficulties to surmount in developing workable structures for such enterprises. As with many engineering education endeavors, the focus of initiating global engineering programs is often on the hard technology to enable students to work collaboratively across distances. Too often, the soft technology aspect, such as coordinated work practice, is overlooked during the process of set-up and initial operation. It is relatively straightforward (though not particularly easy) to acquire the necessary technology and apply it to a lab development scenario. But it is not ‘global engineering’ unless there are collaborative partners across the world, on the other end of the Internet cable. In this paper, we will discuss a case study involving the setup of hard technology, such as computers, telecommunications, and integration of video into the curriculum. Equally important, we will discuss the generation of partners with similar work practice, project management, and pedagogical styles, and ways to facilitate interaction between students in different programs in different international locations, while satisfying sponsoring institutions and corporations.
A Method to Estimate Critical Tire Properties Using Non-Linear Tire Models
Authors: Edwards Dustin L. , Bevly David M.
Published: May 2009

This paper describes a method to estimate lateral and longitudinal cornering stiffness, as well as the maximum tire force. Knowledge of these parameters can be critical for certain vehicle control systems that need to understand the tire’s limits, especially during turning maneuvers and acceleration. In this study, an extended Kalman filter is used along with the Dugoff or Fiala tire model to estimate these parameters. The pros and cons are discussed for estimation with both the Dugoff and Fiala tire models. An inertial measurement unit (IMU), a dual GPS antenna, and wheel speed sensors implemented on a test bed are used to evaluate the performance of the algorithms. A transformation matrix derived from a bicycle model is used to convert acceleration measurements into force measurements. The force measurements are then fed into the extended Kalman filter to estimate the parameters. Although this algorithm is post-processed, it can easily be used in real-time estimation. The experiment is performed on an asphalt surface to test its performance. The effects of vehicle roll can be significant for vehicles that exhibit large roll angles, but it is assumed to be negligible in this study.