bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Adhesive Curing Condition on Bonding Strength in Auto Body Assembly
Authors: Wu Xin , Hao Hongqi
Published: April 2008

The bonding strength of metal-to-metal lap joining of a two-part epoxy-based adhesive employed in an automotive assembly line was investigated under different heating rates (10°C/min to 6000°C/min), peak temperatures (room to 250°C), and holding times. The results indicate that bonding strength is mainly controlled by the peak curing temperature and the heating rate. The maximum bonding strength appears between 70–110°C, but the value of it depends on the heating rate. At heating rates of 10°C/min, 50°C/min, and 100°C/min the peak strength decreases with increasing heating rate. However, further increase in heating rate to 2000–6000°C/min resulted in higher peak bonding strength. The microstructures and fractured surfaces after shear testing were examined by a scanning electron microscope (SEM). The results revealed that many gas bubbles (voids) were formed during the adhesive curing process, and the fracture process was controlled by the link of the voids. At low heating rates (10–100°C/min) the mean void size and volume fraction increase with heating rate and peak temperature, causing the weakening to the bonding strength. But at very high heating rates (2000–6000°C/min) the rapid hardening of the adhesive suppressed the development of gas bubbles, so the mean void size and volume fraction were low, and the bonding strength was high. This result indicates that to effectively improve the adhesive bonding strength, both the chemical reaction (degree of cure) and physical response (gas bubble formation) need to be optimized.
Manipulation of Microfluidic Flows Using Time Dependent Wall Temperatures
Authors: Mautner Tom
Published: April 2008

One module in a bioagent detector currently under development involves a flow-through PCR module [1] [3] [4]. Conventional, flow-through PCR devices utilize three heaters to obtain the required temperatures in each zone, the length of which is specified by the required sample residence times. An alternate design uses two wall heaters with substrate conduction supplying the center zone temperature. The concept of using a conduction based PCR device led to an extensive computational study of various channel wall temperature profiles that would produce enhanced mixing in a variety of microfluidic devices. The results are applicable to micro channel designs in general even tough motivated by the conduction based PCR configuration. The lattice Boltzmann (LB) method was used to perform low Reynolds number (typically Re=0.10) simulations for two and three dimensional channel geometries having various wall temperature distributions. The momentum and thermal lattice Boltzmann equations were coupled via a body force term in the momentum equation. Initial computations using two- and three-heater configurations in two dimensions demonstrated excellent comparisons with published data provided that both the top and bottom walls were heated. If only one wall was heated, large vertical thermal gradients occurred resulting in non-uniform temperature fields. However, when the same conditions were applied to three dimensional channels, lower temperatures were observed in the center of the channel regardless of the wall temperatures or channel aspect ratio. Parametric studies were performed to evaluate the effects of thermal coupling, thermal diffusion coefficients, entrance temperatures, wall temperature configurations and channel geometry. If was found that moderate variation of the thermal diffusion coefficient produced only minor differences in the temperature field, and large changes in the thermal coupling magnitude demonstrated transition from natural to forced convection flows. The simulations also indicate that the largest effect on flow and temperature uniformity arises from the applied wall temperature distribution (various thickness channel walls). It was found, in 2D, that if the channel wall starts from ambient temperature, the applied heating, on the outer surfaces only, may not result in the desired wall or fluid temperatures. However, once the channel walls are heated to a uniform temperature, excellent temperature distributions are obtained for both thick and thin channel walls. Additionally, a checkerboard pattern of wall heaters was used to test its application to promoting mixing. Results were favorable in creating enhanced mixing; however, the temperature pattern did not produce uniform temperature profiles in the channel.
Free-Oscillation One-Dimensional Numerical Solutions of the Advective Stefan Problem
Authors: Rodri´guez N. J. , Jua´rez-Herna´ndez A. , Marti´nez L. G. Tra´paga
Published: April 2008

Mathematical Modelling of heat conduction-convection requires methods that are efficient and accurate. This is of paramount importance for modeling complex problems of value for the heat transfer community. In this paper, a One-dimensional Substantial Capacitance method with solutions free from oscillations is presented. The method is derived by equating energy and heat control volume equations. The method can be readily implemented into a standard finite element method (FEM) code. Resulting FEM equations are similar to those used to model classical heat-conduction. A 1-D semi-infinite bar is employed to perform numerical testing. Five methods are employed for code validation and these are analytical, Bubnov-Galerkin, Petrov-Galerkin, Substantial Capacitance and Finite Difference schemes (FDS); the approach is shown to be accurate, stable and computationally competitive.
Processing and Properties of Graphene-Based Nanocomposites
Authors: Wong Shing-Chung , Sutherland Eric M. , Yerramaddu Suchitra , Wouterson Erwin , Uhl Fawn M. , Webster Dean
Published: April 2008

Fabrication of carbon nanotubes is expensive, particularly for the purifying process required to make them widely accepted for reinforcements and structural composite applications. Instead of trying to discover lower cost processes for nanotubes, we seek to develop an alternative nanoscale carbon material with comparable properties that can be produced cost-effectively and in larger quantities. These carbon nanomaterials are referred to as nanoscale graphene platelets (NGP). In this study, we fabricated and studied graphene-based nanocomposites by (1) exfoliating carbon or graphite materials using acid treatment, thermal and microwave expansion, and (2) examined the electrical and dielectric properties of the graphite reinforced polymers. Less than 1 wt% filler content was required to reach the percolation threshold (φc) of transition in electrical conductivity and dielectric properties. Molecular dynamics simulation was employed to characterize the increase in elastic moduli for graphene platelets embedded in polymer matrices at molecular scale.
Influence of Rearrangement of Actin Cytoskeleton on the Overall Material Properties of ATDC5 Cells During Chondrogenesis
Authors: Ayyalasomayajula Madhavi , Salihu Sydha , Kish Vincent , Mukherjee Nilay
Published: April 2008

ATDC5 cells, a prechondrocytic cell line, were cultured in 2% agarose gel-cell constructs. A major reorientation of actin structure (stress-fiber to punctate) was observed during the chondrogenesis of these cells. 2D finite element models of cell (considered as a composite with embedded actin fibers) in a 500μ3 gel were created for days 1 (prechondrocytes), 5, 8 & 12 (chondrocytes) of culture. The response of the cells to uniaxial compression of the gel-cell construct was studied. The model predicted that, as a result of rearrangement of actin, the cells became more compliant and less anisotropic. When the gel size was reduced to 20μ3, RUTL (Ratio of radial deformations of cell in the Transverse direction to Loaded direction) became significantly different between prechondrocytes and chondrocytes. The difference in force required to compress a 20μ3 gel-cell construct containing a prechondrocyte vs a chondrocyte to 15% deformation was 103nN (152.3 vs 48.8 nN). This information can be used to build MEMS based devices that can mechanically distinguish between the different cell types.
Balancing the Speed and Fidelity of Automotive Powertrain Models Through Surrogation
Authors: Kozaki Tetsuji , Mori Hiroshi , Fathy Hosam K. , Gopalswamy Swaminathan
Published: April 2008

The growing use of model-based engineering for powertrain design and validation imposes conflicting modeling requirements. Vehicle powertrain models must be accurate enough for design optimization, and fast enough for real-time verification on hardware-in-the-loop platforms. Because these two requirements conflict, one finds two families of powertrain models today: high-fidelity models and real-time models. Model surrogation can bridge the gap between these two families by extracting powertrain models accurate enough for optimization and fast enough for real time. This paper systematically derives surrogate torque converter, clutch friction, and clutch hydraulics models. Using these models, the simulation speeds for two automatic transmissions improve significantly without appreciable loss of accuracy.
Creation of Nano-Scaled Surface Structure for the Enhancement of Boiling Heat Transfer
Authors: Ngai Sho , Leontiev A. I. , Lloyd John R. , Malyshenko S. P.
Published: April 2008

The present research is an experimental investigation of nucleate pool boiling heat transfer enhancement on a surface with micro/nano-scaled surface structures. Glancing Angle Deposition (GLAD) was employed to fabricate porous surfaces in this study. The thin film microstructure consists of closely packed columns oriented in the plane of incidence formed due to a self-shadowing mechanism. Boiling heat transfer from the nano-structured surface was compared to that of a smooth reference surface and the commercial High Flux surface. The results of this study have shown that nano-structured films created by the GLAD process increase the nucleation site density as compared to the smooth surface. This research has opened up new areas in the field of heat transfer, which motivate new surface coating concepts to enhance the understanding of boiling heat transfer on nano-structured films.
Structural Constitutive Characterization of the Vocal Fold: Modeling the Fibrous and the Interstitial Matrix Proteins
Authors: Chan Roger W. , Siegmund Thomas H. , Zhang Kai , Tirunagari Neeraj , Fu Min
Published: April 2008

The extracellular matrix (ECM) of the human vocal fold is a highly specialized soft connective tissue with a layered microstructure that is optimally tuned for vibration and sound production in response to a unique set of biomechanical stimuli in vivo, including oscillation at amplitudes up to 3–4 mm at magnitudes of acceleration > 200g and at high frequencies (> 100Hz). The vocal fold ECM, commonly called the lamina propria or mucosa, consists of biomacromolecules of two major classes distributed in different densities: (1) fibrous proteins including collagen and elastin fibers that are denser in the deep layers of the ECM, and (2) interstitial proteins like glycosaminoglycans and structural glycoproteins that are scattered throughout the entire ECM [1,2]. Nonlinear viscoelastic response of the vocal fold ECM under different loading conditions has been reported, including strain rate-dependence and hysteresis of tensile stress-strain curves, and nonlinear stress-strain behavior under large-strain shear [3,4].
Active-Vision for the Autonomous Surveillance of Dynamic, Multi-Object Environments
Authors: Bakhtari Ardevan , Naish Michael D. , Benhabib Beno
Published: April 2008

This paper presents a novel method for the coordinated selection and positioning of groups of active-vision cameras for the autonomous surveillance of an object-of-interest as it travels through a multi-object workspace with an a priori unknown trajectory. Several approaches have been previously proposed to address the problem of sensor selection and control. However, these have primarily relied on off-line planning methods and only infrequently utilized on-line planning to compensate for unexpected variations in a target’s trajectory. The method proposed in this paper, on the other hand, uses a real-time dispatching algorithm, which eliminates the need for any a priori knowledge of the target’s trajectory and, thus, is robust to unexpected variations in the environment. Experiments have shown that the use of dynamic sensors along with a dispatching algorithm can tangibly improve the performance of an active-surveillance system.
CFD-Based Aeroelastic Analysis in Transonic Flow Regime
Authors: He Chunlei , Choi Sangbum , Mirmirani D. , Wu Chivey
Published: April 2008

The aeroelastic instability behavior of the AGARD445.6 wing at transonic flight speed is investigated by using Finite Element-based unsteady CFD simulations and automated three-dimensional unstructured meshing. A general-purpose multidisciplinary computer program called STARS (Structural Analysis RoutineS), developed at NASA Dryden Flight Research Center is employed as the tool for this study. The computational results on flutter boundaries of the wing structure are compared with wind tunnel data, and have been found to be satisfactory.
Parameter Optimizing for Piecewise Linear Isolator
Authors: Narimani A. , Golnaraghi M. F.
Published: April 2008

In this paper we have studied the effect of end stops in an isolator. While subjected to excessive base excitation the stops prevent the system from excessive relative displacement particularly around the resonance frequency. Although stoppers prevent the undesired motion they increase the transmitted force that is undesirable in suspension systems. This system is modeled as a piecewise linear system where the nonlinearity cannot be considered small. Therefore we have adopted an averaging method which leads to analytical frequency response of the piecewise linear system at resonance. Using this analytical method we are able to obtain the range of the parameters, which minimize the relative displacement of the system. Further more using the RMS optimization methods the transmitted force in the system is optimized.
The Impact of Direct Competency Testing (DCT)
Authors: Marchetta Jeffrey G. , Hochstein John I. , Tan Teong E.
Published: April 2008

Direct Competency Testing (DCT) was developed and implemented to measure the ability of mechanical engineering students to correctly solve problems in the fundamental areas for each course in the mechanical engineering curriculum. Almost 10 years since the inception of DCT, an effort is made to assess the efficacy of DCT as a measure of student ability. Qualitative and quantitative assessments are conducted to evaluate the impact of administration, documentation, and evaluation of DCT on students and faculty. Student surveys focus on the perception of competency testing as a component of coursework and whether DCT is a reasonable measure of learning. Faculty survey results yield historical data of student DCT and provide perceptions of the effectiveness of DCT in mechanical engineering coursework. The impact of DCT on program accreditation and the connection to EC2000 criteria are examined. Evidence is provided that competency testing helps instructors assess a minimum threshold above which to evaluate the success of their students and that the majority of students believed DCT was a valuable component of an engineering curriculum. Results are presented to support the merit of continuing and further refining the methods for DCT.
Nonlinear Isolator Optimization Using RMS Cost Function
Authors: Narimani A. , Golnaraghi M. F.
Published: April 2008

In this paper using a modified averaging method the frequency response of a general nonlinear isolator is obtained. Stiffness and damping characteristics are considered cubic functions of displacement and velocity through the isolator. Analytical results are compared with those obtained by numerical integration in order to validate the closed form solution for strongly nonlinear isolator. While increasing the nonlinearity in the system improves the response of the isolator, stability and jump avoidance conditions set boundary limits for the parameters. The effects of nonlinear parameters to avoid jump phenomenon are discussed in detail. The set of parameters where the system behaves regularly are found and the nonlinear isolator is optimized based on RMS optimization method. Using this method the RMS function of absolute acceleration of the sprung mass is minimized versus the RMS function of relative displacement.
A Tool to Integrate Design for Assembly During Product Platform Design
Authors: Pandit Amar , Siddique Zahed
Published: April 2008

To survive in the current market, many companies are moving toward design and development of product families using a platform approach. To effectively develop a family of products companies have to consider both component and assembly perspective. The assembly perspective has many issues associated with it for developing common platforms, which includes assemblability evaluation for the entire family. Application of Design for Assembly techniques to evaluate product family will require modifications to the current single product DFA method. The purpose of this paper is to extend the current DFA technique for product family and platform design. Specifically, we integrate the product family architecture with DFA evaluation. Product family concepts related to assembly are used to develop new product family DFA guidelines. A product family DFA tool that utilizes these extensions has been developed and is presented in the paper. The application of this product family DFA extensions and tool are illustrated using a Walkman product family.
Dynamic Reconfigurable Machine Tool Controller
Authors: Li Wei , Red W. Ed , Jensen C. Greg , Davis Tyler
Published: April 2008

This paper presents a dynamic reconfigurable control strategy based on the Direct Machining And Control (DMAC) research at Brigham Young University. We propose a reconfigurable framework which will allow a DMAC compliant machine to be controlled by a variety of applications and control laws. This Reconfigurable Mechanism for Application Control (RMAC) paradigm uses a hierarchical architecture to configure a mechanism into a device driver for direct control by an application like CAD/CAM. The paradigm is one of a mechanism device driver assigned to each mechanism class or model, and uses only the master model to control the mechanism. The traditional M&G code language is no longer necessary since motion entities (NURBS, lines, arcs, etc) are passed directly to the mechanism. The design strategy of using dynamic-link libraries (DLL) to form a mechanism device driver permits a mechanism to assume different operating configurations, depending on the number of axes and machine resolution. For example, the machine can perform as a material removal machine in one instant, and then, by loading a new device driver, act as a Coordinate Measuring Machine (CMM). This strategy is possible because DMAC is a software and networked-based control architecture. Both the CAD/CAM planning software and the real-time control software reside on the same PC. The CAM process plan can thus directly control the machine without need for process plan decomposition into the forms supported by the native controller. The architectural framework is explained in detail and the methodology for control software reconfiguration into a device driver is presented. For demonstration purposes three device drivers will be implemented on one machine to demonstrate feasibility and usefulness.
Mechanical Behavior of Electrodeposited Copper Film at Elevated Temperatures
Authors: Read D. T. , Cheng Y.-W. , Geiss R.
Published: April 2008

The temperature dependence of the strength of a thin copper electrodeposit has been measured, by microtensile testing, from room temperature to 150 °C. The ultimate tensile strength decreased from around 240 MPa at room temperature to just above 200 MPa at 150 °C. The yield strength followed a similar trend. Elongation to failure increased slightly with temperature. The Young’s modulus, as measured by the unload-load slope, was well below the values expected based on averaging single-crystal elastic constants at all test temperatures. The effect of strain rate on strength at room temperature, using a range of over a decade, was low, with a weak trend upward.
Compact Models for Transient Conduction or Viscous Transport in Non-Circular Geometries With a Uniform Source
Authors: Muzychka Y. S. , Yovanovich M. M.
Published: April 2008

Transient heat conduction in solid prismatic bars of constant cross-sectional area having uniform heat generation and unsteady momentum transport in infinitely long ducts of arbitrary but constant cross-sectional area are examined. In both cases the solutions are mathematically modeled using a transient Poisson equation. By means of scaling analysis a general asymptotic model is developed for an arbitrary non-circular cross-section. Further, by means of a novel characteristic length scale, the solutions for a number of fundamental shapes are shown to be weak functions of geometry. The proposed models can be used to predict the dimensionless mean flux at the wall and the area averaged temperature or velocity for the tube, annulus, channel and rectangle for which exact series solutions exist. Due to the asymptotic nature of the proposed models, it is shown that they are also applicable to other shapes at short and long times for which no solutions or data exist. The root mean square (RMS) error based on comparisons with exact results is between 2.2–7.6 percent for all data considered.
Effects of Combustor Acoustics on Fuel Spray Dynamics
Authors: Chishty Wajid A. , Vandsburger Uri , Saunders William R. , Baumann William T.
Published: April 2008

An experimental liquid fuel LDI combustor, developed to study thermoacoustic instability processes and to test active combustion control systems, was found to demonstrate three distinct stability regimes, with system characteristics not reported in earlier literature. These observations led to a series of further investigations, both in reactive and non-reactive conditions, to gain an insight into effects of combustor acoustics on fuel spray dynamics. This paper presents only the non-reacting flow results, from both experimental and modeling investigations. The experimental setup and construction details of an isothermal acoustic rig are presented. Phase-locked PDA measurements of droplet velocities and diameters from a simplex atomizer spray were acquired, with and without combustor swirl co-airflow, under varying acoustic forcing conditions and spray feed pressures. Measurements made at four locations in the spray are related, in the paper, to these variations in mean and unsteady inputs. The dynamic behavior of the spray is then presented in terms of frequency response characteristics related to acoustic fields imposed on the spray. Finally, results from non-reacting spray modeling, predicting droplet trajectories, are reported. The modeling was done using the deterministic separated flow approach. These trajectories are compared to the reported experimental results to support preliminary explanations for the unique experimental observations of the swirl-stabilized kerosene flame in a single can combustor geometry.
Heat Transfer Devices With Self-Rewetting Fluids
Authors: Abe Yoshiyuki , Tanaka Kotaro , Yokoyama Takuya , Iwasaki Akira
Published: April 2008

The authors have been proposing the utilization of “self-rewetting fluids” as a new phase change heat transfer media, especially in space applications. Self-rewetting fluids show a quite unique thermophysical behavior—an increase in the surface tension with increasing temperature. Since self-rewetting fluids are non-azeotropic compositions of dilute aqueous solutions of alcohols, the Marangoni effects due to both temperature gradient and concentration gradient work in the same direction in the course of liquid/vapor phase change, and induce a strong liquid flow to hotter interface. A series of terrestrial experiments for conventional heat pipes with self-rewetting fluids have been conducted, and compared with those with water as a reference. Appreciable heat transfer performance improvement from water heat pipes was recognized. Furthermore, a series of low gravity experiments for wickless heat pipes with a self-rewetting fluid have also been conducted by using parabolic flights of aircraft. The heat transfer performance of wickless heat pipes in low gravity was evaluated, and superior characteristics was confirmed.
Effects of Valve Design and Orientation on Flow Induced Platelet Activation in Mechanical Heart Valves
Authors: Yin Wei , Alemu Yared , Jesty Jolyon , Bluestein Danny
Published: April 2008

A study was conducted to estimate the thromboembolic potential of different Mechanical Heart Valve (MHV) designs and the effect of valve orientation (valve axial misalignment during implantation) on it. CFD simulations of turbulent, transient, non-Newtonian blood flow patterns generated by two types of MHVs (monoleaflet and bileaflet) and the effect of valve orientation were conducted using the Wilcox k-ω turbulence model. Platelet shear stress histories (cumulative effect of shear stress and time) were calculated and averaged over a large number of platelet trajectories within the flow field, and compared with in vitro Platelet Activity State (PAS) measurements conducted in a left ventricular assist device (LVAD) model. Platelets were circulated in the LVAD with Carbomedics bileaflet and Bjork-Shiley monoleaflet MHVs correspondingly. The PAS measurement indicated that PAS induced by the tilted St. Jude bileaflet MHV and the untilted valve was very similar (P>0.1). The bileaflet MHV activated platelets at a rate of more than 2-fold than that observed with the monoleaflet MHV (P<0.05). This confirmed the CFD platelet shear stress histories, which clearly indicated a higher level of stimulation of platelets for the bileaflet MHV.
Electroosmotic Pumps Fabricated From Porous Silicon Membranes
Authors: Yao Shuhuai , Myers Alan M. , Posner Jonathan D. , Santiago Juan G.
Published: April 2008

Large flow rates per applied potential are obtained from electroosmotic (EO) pumps fabricated from n-type porous silicon. Porous silicon membranes have ideal geometries for EO pumping. These membranes have hexagonally packed, uniform pores with near-unity tortuosity and are well suited to maximize flow rate for a given applied voltage. The 350 μm thick membranes were passivated with a SiO2 layer and exhibit a maximum flow rate of 1.2 ml/min/cm2/V. This is 4.4 times higher than previously demonstrated silica-based frit EO pumps. LPCVD polysilicon deposition followed by wet oxidation was used to control the pore size. The impact of these coatings on the pump performance has also been characterized.
Transport Mechanisms in Electrokinetic Nanoscale Channels
Authors: Pennathur Sumita , Santiago Juan G.
Published: April 2008

We investigate electrokinetic transport in nanometer-scale fluidic channels. Our study includes numerical studies of nanofluidic transport of both charged and uncharged analytes in conditions of finite Debye layer thickness and high zeta potentials. The models are based on continuum mass transport and field theory. We also perform an experimental parametric study using etched nanoscale channels. Experimental results agree with model predictions and show that bulk electrokinetic transport in nanoscale channels depends strongly on the shape and size of the EDL and on the effects of transverse electrophoretic migration.
Chaotic Oscillations of a Post-Buckled Beam Constrained by an Axial Spring: Part 2 — Analysis
Authors: Maruyama Shinichi , Nagai Ken-ichi , Yamaguchi Takao , Hoshi Kazuaki
Published: April 2008

To compare with corresponding experiment, analytical results are presented on chaotic oscillations of a post-buckled beam constrained by an axial spring. The beam with an initial deflection is clamped at both ends. The beam is compressed to a post-buckled configuration by the axial spring. Then, the beam is subjected to both accelerations of gravity and periodic lateral excitation. Basic equations of motion includes geometrical nonlinearity of deflection and in-plane displacement. Applying the Galerkin procedure to the basic equation and using the mode shape function proposed by the author, a set of nonlinear ordinary differential equations is obtained with a multiple-degree-of-freedom system. Linear natural frequency due to the axial compression and restoring force of the post-buckled beam are obtained. Next, periodic responses of the beam are inspected by the harmonic balance method. Chaotic responses are obtained by the numerical integration of the Runge-Kutta-Gill method. Chaotic time responses are inspected by the Fourier spectra, the Poincare´ projections, the maximum Lyapunov exponents. Contribution of the number of modes of vibration to the chaos is also discussed by the principal component analysis. Chaotic response is generated within the sub-harmonic resonance responses of 1/2 and 1/3 orders. The maximum Lyapunov exponent corresponded to the sub-harmonic response of 1/2 order is greater than that of the sub-harmonic response of 1/3 order. By the inspection of the Lyapunov exponent on the chaotic response and the analysis with the multiple-degree-of-freedom system, more than three modes of vibration contribute to the chaos. Using the principal component analysis to the chaotic responses at multiple positions of the beam, the lowest mode of vibration contributes dominantly. Higher modes of vibration contribute to the chaos with small amount of amplitude.
Fatigue Correction Coefficient for Oscillating Cantilever Plates With Impact
Authors: Marsh Jay P. , Fan U. J.
Published: April 2008

A fatigue life prediction method for oscillating cantilevered thin plates subjected to both prescribed motion stresses and impact induced vibrational stresses is presented. The prescribed motion of the plate generates inertial stresses of a significant magnitude that would ordinarily produce finite life for the plate, but the inclusion of the impact events should reduce the life by a significant percentage. Experimental tests on thin steel plates subjected to high magnitude inertial loading combined with impact loading were performed on specimens of a low carbon, generic steel with no heat treatment (hot rolled A36). Experimental results are compared to theory with good correlation allowing for the development of a life reduction equation based on the ratio of impact energy to maximum, non-impact energy level, as well as other analytically derived values.
The Role of Tropomodulin in Cardiac Function and Remodeling
Authors: Bryan Andrea , Sung Amy , Lian Ian , Omens Jeffrey
Published: April 2008

Tropomodulin is an actin-capping protein in cardiac muscle, and is associated with both sarcomeric and cytoskeletal actin filaments. Homozygous knockout of erythrocyte tropomodulin (E-Tmod) is embryonically lethal, but heterozygous knockout (+/-) mice survive. Heterozygous E-Tmod knockout resulted in smaller right ventricle (RV) cavities and free walls compared to wild type. To investigate the effect of heterozygous tropomodulin knockout on mouse cardiac function and remodeling, mice (n=6 to 9) were subjected to 5 weeks of hypoxia to increase loading conditions on the RV via pulmonary hypertension. The effect of loading was determined by measuring the volume of RV anatomical features, and surface strain during the cardiac cycle. Although there was no significant change due to loading on RV cavity or free wall volume for wild type, geometrical measurements suggest that tissue had been redistributed. Under equal loading conditions, knockout mice exhibited a significant increase in volume for both RV features. RV epicardial function showed an increase in surface area strain at peak systole for hypoxic knockout mice. Thus it appears that heterozygous knockout of E-Tmod affects RV volume under normal and adverse loading conditions, as well as RV function.
A Generalized Time-Optimal Bi-Directional Scan Algorithm for Constrained Feedrate Optimization
Authors: Dong J. , Stori J. A.
Published: April 2008

The problem of generating an optimal feedrate trajectory has received a significant amount of attention in both the robotics and machining literature. The typical objective is to generate a minimum-time trajectory subject to constraints such as system limitations on actuator torques and accelerations. However, developing a computationally efficient solution to this problem while simultaneously guaranteeing optimality has proven challenging. The common constructive methods and optimal control approaches are computationally intensive. Heuristic methods have been proposed that reduce the computational burden but produce only near-optimal solutions with no guarantees. A two-pass feedrate optimization algorithm has been proposed previously in the literature by multiple researchers. However, no proof of optimality of the resulting solution has been provided. In this paper, the two-pass feedrate optimization algorithm is extended and generalized. The generalized algorithm maintains computationally efficiency, and supports the incorporation of a variety of state dependent constraints. By carefully arranging the local search steps, a globally optimal solution is achieved. Singularities, or critical points on the trajectory, which are difficult to deal with in optimal control approaches, are treated in a natural way in the generalized algorithm. A detailed proof is provided to show that the algorithm does generate a globally optimal solution under various types of constraints.
Scenario-Based Learning: An Innovative Approach to Teaching Basic Engineering Courses
Authors: Shih Angela , Mariappan Jawaharlal
Published: April 2008

Research has established that traditional linear, didactic approaches to teaching through lecturing are at best only tenuously connected to the ultimate aim of achieving competency. In order for classroom instruction to become relevant and meaningful, the process of learning must be motivating and exciting, and the basis of learning should be focused on discovering and not memorizing or regurgitation. We believe a guided discovery process is the most effective way to convert a passive classroom lecture into an engaging active learning experience. Scenario Based Learning (SBL) is an effective approach that provides an excellent framework for active learning. It offers an effective way of engaging learners and building competency mastery. This paper describes the initiatives currently underway at Cal Poly Pomona to develop and implement SBL approach to teach major concepts in basic freshmen and sophomore level engineering courses.
Thermodynamic Analysis of Magnetic Refrigerators
Authors: Rahman Muhammad M. , Rosario Luis
Published: April 2008

An analysis of a magnetic refrigeration cycle was carried out. The system consists of heat exchangers and beds of magnetic materials. The analysis considered that the system operates near room temperature in a magnetic field between 1 and 5 T and uses 3 kg of gadolinium (Gd) spheres packed in two magnetocaloric beds. The heat transfer fluid is water. The beds are periodically magnetized and demagnetized and the fluid flows are arranged to meet the cycle requirements. Sensitivity analysis has been performed. Cooling power, magnetic field, and temperature span trends are simulated. The cooling and heating effects were estimated based on the magnetocaloric effect of gadolinium. Findings indicate that the higher the magnetic field is the higher the cooling power with the same temperature span. It was also observed that the cooling power decreases with the increase in the temperature span for various magnetic fields. COP vs. temperature span was also considered. The trend indicates that COPactual/ COPCarnot decreases with an increase in the temperature span. These trends agreed with those shown by experimental data.
Predictions of Relative Humidity and Temperature in an Operating Room
Authors: Ho Son H. , Rosario Luis , Rahman Muhammad M.
Published: April 2008

This paper uses airflow simulations to evaluate different ventilation systems on an operating room (OR). This study compares air distribution systems for an operating room by use of computational fluid dynamics (CFD) modeling. The air supply distribution and exhaust arrangements were modeled for a directional air flow system where air moves across the space from the high-pressure supply area to the low pressure exhaust area. Calculations were done to model a typical operating room in a steady-state condition with inclusion of object such as surgical lights, operating table, heat sources such as surgical staff and a patient, side-wall supply grille and exhaust air grilles. The discharge angle for the side-wall supply grille was varied from 0 to 45 degrees. Air return locations were also studied. One and two air exhaust outlet sites inside the surgical suite were considered. In the two-exhaust outlet configuration, one position was close to the floor and the other position was high on the wall. Simulations with combinations of 1:0, 1:0.343, 0.343:1, and 1:1 flow rates between the two return locations were performed. Predictions for the air movement, room temperature, room relative humidity, and concentration of contaminants within the operating room are shown. Analysis of these predictions is discussed. The supply and exhaust conditions of the ventilation air flow are shown to play an important role in the control of air quality. Results show good agreement with experimental data.
A Criterion for the Formation of Micro Synthetic Jets
Authors: Timchenko V. , Reizes J. , Leonardi E. , de Vahl Davis G.
Published: April 2008

A synthetic jet actuator is a zero net mass flow device, which under appropriate conditions generates a continuous jet always directed away from the orifice. Because of limited experimental and computational data on micro-sized jets, there is a need for a criterion to determine the onset of the sustained jet regime. A numerical study of axisymmetric micro synthetic jets for a frequency range from 250 to 50,000 Hz, orifice diameters range from 20 to 200 μm, and Reynolds numbers from 6.5 to 35 has been performed in order to identify a general jet formation criterion. The parametric study has allowed us to develop a new criterion for the onset of micro synthetic jets with Stokes numbers less than 7.
Anabolic Fluid Flow as Dependent on It Dose and Frequency in Bone Formation and Inhibition of Bone Loss
Authors: Qin Yi-Xian , Kaplan Tamara , Lam Hoyan
Published: April 2008

Anabolic response of bone to interstitial fluid flow is strongly dependent on the dynamic components of the fluid pressure, implying that fluid flow is a critical regulatory component to bone mass and morphology. While the fluid stimulus can be potentially applied for therapeutic in promoting turnover, the hypothesis of fluid induced bone adaptation was evaluated in an avian ulna model using varied flow rates and magnitudes. Total of 12 one-year old male avian animals was used in this study. A sinusoidal fluid pressure was applied to the experimental ulna 10 min/day for 4 weeks. Three experimental groups of loading were performed at 1 and 30 Hz of fluid loading. The results reveal an increase of 22.7%±7.2 in trabecular volume for group of 30 Hz, 76mmHg loading, while it had only 0.5 % increase at 1Hz, 76 mmHg loading. Under physiologic fluid pressure, a higher flow rate of stimuli generates much higher remodeling response than a lower rate of loading. This implies that bone turnover may be sensitive to the dynamic components of fluid flow, thereby initiating the adaptive response.
Analysis of Indentation-Derived Yield Strength in Metallic Multilayers
Authors: Tan X. H. , Shen Y.-L.
Published: April 2008

The determination of overall mechanical properties of small-scale structures, such as nanolayered materials, frequently relies on the nanoindentation technique. In this study finite element modeling is employed to examine the relationship between indentation hardness and overall strength of multilayered composites. For simplicity the laminated structure is taken to consist of alternating layers of two elastic-perfectly plastic materials. The overall yield strength under uniform far-field loading is first quantified. Indentation loading of the layered structure is then simulated to cover a wide range of indentation depth from within one layer thickness to well into multiple layers. The systematic hardness values thus obtained are converted to corresponding flow stresses. It is found that the indentation-derived strength consistently underestimates the composite yield strength. Friction at the contact surface is also found to play a significant role. Relevant issues on applying indentation techniques to probe overall mechanical properties of metallic multilayered are discussed.
Micro Thin Film Temperature Sensors Embedded in Metal Structures
Authors: Choi Hongseok , Datta Arindom , Li Xiaochun
Published: April 2008

This paper studies the fabrication and calibration of thin film temperature sensors embedded in metal structures. Thin film thermocouples have been successfully fabricated on various metal substrates and advanced embedding techniques have been developed to ensure sensor function inside metal structures. Thin film thermocouple was insulated with multiple thin film layers (Al2O3 and Si3N4) by e-beam evaporating and plasma enhanced chemical vapor deposition (PECVD). The sensors are calibrated. These embedded thin film sensors provide superior spatial and temporal resolution that is not possible with traditional sensors used in various manufacturing processes. This research is significant in a way that it provides a new and improved route for in-situ monitoring of manufacturing process.
Experimental Investigation and Visualization of Two-Phase Flow and Water Transport in Microchannels
Authors: Hidrovo Carlos H. , Wang Fu-Min , Lee Eon Soo , Vigneron Se´bastien , Steinbrenner Julie E. , Paidipati Jay V. , Kramer Theresa A. , Eaton John K. , Goodson Kenneth E.
Published: April 2008

In this paper we present an overview of the experimental work carried out as part of research geared towards the understanding of two-phase flow in microchannels. The greater scope of the project is to use the knowledge gained towards the development of strategies to improve water management in fuel cell applications. We have conducted pressure versus flow rate experiments in microchannels with contrasting hydrophobic characteristics and under different liquid water injection conditions. These measurements have been complemented with flow visualization studies using white light and fluorescence. As expected, parameters associated to surface energy such as hydrophobicity have a big influence on the flow. Under hydrophobic conditions the formation of slugs or blobs of size comparable to that of the microchannel greatly impedes the flow of air, especially at low pressure drops. On the other hand liquid water effects under hydrophilic conditions are only noticeable at large injection rates (100 μL/min). In contrast to their hydrophobic counterparts, two-phase flow in hydrophilic microchannels is characterized by the formation of a thin film of liquid. Only when the thickness of the film becomes substantial does it have an effect on the air flow.
Noise Treatment Strategies for High Velocity HVAC Ducts in Ocean Going Fast Ferries
Authors: Neale J. , Leong S. S. , Barber T. , Byrne K. , Leonardi E.
Published: April 2008

This paper describes a study of strategies used to limit the flow generated noise encountered in the outlet diffusers of high velocity heating, ventilation and air conditioning (HVAC) duct systems. A circular jet of air was expanded using a 7° conical diffuser with a variety of outlet configurations and pipe lengths. Sound pressures were recorded for a jet diameter of 50 mm and a jet velocity of 15–60 ms−1 using a dual room reverberation suite. The design of the diffuser outlet was found to have a pronounced effect on the noise spectrum radiating from the duct outlet. The length and shape of the outlet duct downstream from the diffuser directly affect the noise radiating from it. Results are presented for a variety of outlet pipe lengths and geometric configurations. A numerical simulation of airflow through the conical diffuser was also completed using a large eddy simulation (LES) turbulence model for a range of jet velocities. An acoustic post processor was then used to predict the corresponding far-field sound pressure and sound power levels.
Studies on Thin Films (Dielectric and Metallic) Constituting Micro Thermo-Mechanical Sensors Embedded in Metal Structures
Authors: Datta Arindom , Choi Hongseok , Li Xiaochun
Published: April 2008

It is of interest to obtain the thermomechanical response of tools, equipment, and structural components in a real manufacturing environment. Microfabricated thin film thermocouples and strain gages are attractive for their small size and fast response. It is novel and challenging to fabricate these sensors on metal substrate and finally embed them into location of interest. Consequently, the materials (dielectric and metallic) constituting the sensor need to be characterized and optimized properly for reliability. We present here results of characterization and optimization of materials making a thermomechanical sensor to be embedded in metal structure.
Magnesium Matrix Nano-Composite Fabricated by Ultrasonic Dispersion of Nano-Sized SiC Particles in Molten Magnesium Alloy
Authors: Lan Jie , Li Xiaochun
Published: April 2008

The use of ultrasonic nonlinear effects to disperse nano-sized ceramic particles in molten metal has been studied and nanosized SiC particle reinforced AZ91D magnesium composites were fabricated. The microstructure of the composites was investigated by high resolution scanning electron microscopy (SEM), X-ray photo spectroscopy (XPS) and high resolution X-Ray Diffractometer(XRD) techniques. Experimental results show a nearly uniform distribution and good dispersion of the SiC nanoparticles within the magnesium matrix, although some of small agglomerates (less than 300nm) were found in matrix. The microhardness of composites have been improved significantly compared to that of pure AZ91D. The ultrasonic fabrication methodology is striking to rapidly produce a wide range of nano-sized particles reinforced metal matrix composites.
Lumped Modeling of Crosstalk Behavior of Thermal Inkjet Print Heads
Authors: Lee You-Seop , Kim Min Soo , Shin Seung Joo , Shin Suho , Kuk Keon , Sohn Dong Ki
Published: April 2008

This paper presents a lumped model to predict crosstalk characteristics of thermally driven inkjet print heads. The model is based on a heat conduction equation, an empirical pressure-temperature equation, and a nonlinear hydraulic flow-pressure equation. It has been simulated through the construction of a Kirchhoffian R-L-C network, and subsequently analyzed using SIMULINK and an electronic circuit simulation tool. Using the lumped R-C model, heating characteristics of the head are predicted to be in agreement with IR temperature measurements. The inter-channel crosstalk is simulated using the lumped R-L network. The values of viscous flow resistance, R and flow inertance, L of the inter-channels are adjusted to accord with the 3-D numerical simulation results of three adjacent jets. The crosstalk behaviors of a back shooter head as well as a top shooter head have been investigated. Predictions of the proposed lumped model of the meniscus oscillations are consistent with numerical simulations. Comparison of the lumped model with experimental results identifies that abnormal two-drop ejection phenomena are related to the increased meniscus oscillations because of the more severe crosstalk effects at higher printing speeds. Our model can be used as a design tool for a better design of thermal inkjet print heads to minimize crosstalk effects.