bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on Quenching of a Small Metal Sphere in Nanofluids
Authors: Kim H. , Buongiorno J. , Hu L. W. , McKrell T. , DeWitt G.
Published: August 2009

The objective of this research is to systematically investigate the quenching characteristics of a hot sphere in nanofluids. The experiments are carried out with a small (9.5 mm) stainless steel sphere with initial temperatures near 1000 °C. Alumina nanofluids and deionized water are tested at low volume concentrations (less than 0.1% by volume) and saturated conditions (100 °C). The results show that the quenching behavior in nanofluids is nearly identical to that in pure water. Moreover it is found that some nanoparticles accumulate on the sphere surface during the quenching process. Such accumulation of nanoparticles on the surface promotes the destabilization of the vapor film in subsequent quenching experiments, thus accelerating the return to nucleate boiling at higher temperature than that in the clean surface case.
Design of Superhydrophobic Surfaces for Optimum Roll-Off and Droplet Impact Resistance
Authors: Varanasi Kripa K. , Deng Tao , Hsu Ming F. , Bhate Nitin
Published: August 2009

We study the wetting behavior of water droplets on superhydrophobic arrays of lithographically fabricated square posts. To determine the droplet wetting state, we measure static contact angles and compare the results to predictions for equilibrium Cassie and Wenzel states. Surprisingly, we find that roll-off angles are minimized on surfaces expected to induce Wenzel-like wetting in equilibrium. We argue that droplets on these surfaces are metastable Cassie droplets whose internal Laplace pressure is insufficient to overcome the energy barrier required to completely wet the posts. These metastable Cassie droplets show superior roll-off properties because the effective length of the contact line that is pinned to the surface is reduced. We develop a model that can predict the transition between the metastable Cassie and Wenzel regimes by comparing the Laplace pressure of the drop to the capillary pressure associated with the wetting energy barrier of the textured surface. In the case of impacting droplets the water hammer and Bernoulli pressures must be compared with the capillary pressure. Experiments with impacting droplets show very good agreement with this simple pressure-balance model. Together these models can be used to optimize texture design for droplet-shedding and droplet-impact resistant surfaces.
Collaborative Agent Based Optimization of Draw Die Design
Authors: Ding Y. , Nye T. J.
Published: August 2009

In this paper we consider the problem of automatically determining optimal drawbead sizes and blankholder forces when designing draw dies for stamped parts. A network of software agents, each implementing a different numerical optimization technique, was used in combination with metal forming simulation software to optimize process variables. Three test cases were used of varying complexity from a rectangular cup to the NUMISHEET’99 automobile front door panel simulation benchmark. It was found that the performance of each agent (and optimization technique) depended strongly on the complexity of the problem. More interestingly, for a given amount of computational effort, a network of collaborating agents using different optimization techniques always outperformed agents using a single technique in terms of both the best solution found and in the variance of the collection of best solutions.
Improved Micro-Patterning of Soft-Polymers and Elastomers Using Conformally Coated Omni-Coat Nanofilms
Authors: Pan Feng , Lee John , Di Sciullo Jones Alex , Huang Adam
Published: August 2009

This paper describes the basic Direct Polymer Patterning On Substrate Technique (DPPOST) process and a modified process currently under development to provide higher robustness in the fabrication process, with the goal of achieving near 100% patterning yields. The patterning of soft-polymers and elastomers has gained interest in the last decade as the material of choice for lab-on-the chip applications; i.e., forming micro-fluidic and bio-reactor chambers. Recently, a lithographically compatible patterning method for soft-polymers and elastomers have been demonstrated by using SU-8® hard polymer resists as robust lift-off molds. This patterning technology, DPPOST, has the ability to form a wide range of structural features found in MEMS, from tens of millimeter structures to micrometer level resolutions. It has been used to embed nano-particles, such as carbon-black (∼45nm mean radius) and metal particles, and allows lithographic alignment of electrodes on micro-fluidic channels previously not possible with soft-lithography fabricated PDMS devices. The modified-DPPOST process uses conformal coating of Omnicoat™ nano-films to provide a barrier between the SU-8® and the patterned polymer, hence reducing stiction during the release process.
A Weibull Failure Theory for Contact Loading in Gears With Asymmetric Teeth
Authors: Dhorje M. , Ekwaro-Osire S. , Khandaker M. P. H. , Karpat F.
Published: August 2009

Meshing gear pairs have regions of high stress gradients due to contact loading. In other applications, high stress gradients can also be generated due to geometric irregularities, material mismatch, or thermal mismatch. In meshing gear pairs, the extent of the region with a high stress gradient depends on the material and the geometric properties. It is common that failure, through crack initiation, will occur in the region of high stress and strain gradients. The conventional Weibull failure theory fails to accurately predict the probability of failure of components with high stress gradients. In this research, the contact loading in a gear pair, with asymmetric teeth, is analyzed. Thus, the objective of this work is to develop a Weibull failure theory to handle the high stress gradients due to contact loading in gear pairs with asymmetric teeth. The modified Weibull failure theory developed uses the weight function approach to account for the variation of the critical stress along the face of natural flaws. For contacting gear teeth, it is demonstrated that the modified Weibull failure theory generates monotonous trends for the probability of failure with respect to increasing Weibull modulus.
Uncertainty Analysis for Biomechanical Injury of Cervical Spine Column
Authors: Jang Taek Hyun , Ekwaro-Osire Stephen , Gill J. Brian , Hashemi Javad
Published: August 2009

Uncertain parameters exist in complex structures, such as the cervical spine, and they may produce unexpected significant influences on the structures. Therefore, for an accurate injury analysis of the cervical spine, it is essential to consider the uncertainties contained in the cervical spine components. For this research, motions segment of finite element C5-C6 motion segment was created and validated based on experimental data under various loading conditions. Young’s moduli of the cervical spine components were considered random variables. Then, based on the sensitivity analysis, Young’s moduli of the disc annulus and nucleus were considered random fields. Each random field was discretized into three and four sets of random variables for the disc annulus and nucleus, respectively. Using sets of random variables discretized from a random field, the sensitivities of the sensitive parameters were reduced to less than 0.05, in which the randomness may be ignored without losing analysis accuracy. The variance for probabilistic injury function was also decreased after random field analysis procedure. Moreover, considering material properties to be a random field, the reliability also increased. Reliability increased by 12.69% when Young’s modulus of both the disc annulus and nucleus were considered random fields.
Microfabricated Nanowire Diluter for Controlled Assembly of Nanowires
Authors: Yoon Hyeun Joong , Yang Jin Ho , Yang Sang Sik , Yang Eui-Hyeok
Published: August 2009

The controlled assembly of nanowires is essential for nanoscale processes. The dielectrophoretic (DEP) assembly process enables a very simple and efficient assembly; however, controlling the number and dimension of nanowires to bridge electrodes is extremely intricate. The micromachined nanowire diluter presented in this paper can automatically dilute and sort nanowires in solution without requiring conventional centrifuge equipment. The device consists of a glass substrate with an array of gold electrode pairs and a PDMS microchannel. Nickel nanowires (30 μm-long) were fabricated by a template-directed electrodeposition process using nanoporous alumina templates. A liquid solution containing nanowires was injected into an inlet of the diluter. Pulsed voltages were applied to 16 pairs of electrodes. The nanowires were subsequently trapped or released in the microchannel at specific pulsed electric fields. As a result, the number of nanowires at the outlet of the channel was dramatically reduced, implying that the device presented here can effectively dilute nanowire suspensions for controlled assembly.
Fabrication of 3-D Superhydrophobic Micro-Ratchets via Combined Thermal Imprint Lithography and Photolithography
Authors: Ok Jeong Tae , Lopez-On˜a Eugene , Park Daniel Sang-Won , Wong Harris , Park Sunggook
Published: August 2009

Ratcheted structures with superhydrophobicity have potential to drive motion of liquid drops in microfluidic devices. We report development of a new process to integrate microscale pillars with varied periods of ratchets from sub-micrometer to 1.5 mm in SU-8. For the fabrication, an hierarchical mixed process of thermal imprint lithography and optical UV-lithography was employed. Use of Ni ratchets as stamps and a hydrophobic silane coating on the stamp surfaces significantly improved imprinting performance into SU-8. We have successfully demonstrated fabrication of ratcheted micropillars as well as submicrometer ratchets integrated into micropillars. In addition, we will discuss optimization of the SU-8 imprinting process and the air gap compensation for photolithography of ratcheted SU-8 layers, which are essential for the fabrication.
Complete Design of a VTOL UAV by a Large Group of Students
Authors: Kiefer Renaud , Vedrines Marc , Kiefer Franc¸ois
Published: August 2009

This paper deals with the complete design and implementation of a small unmanned air vehicle (UAV) in the framework of a project course for engineers. This project takes place within an international contest organised by the french defence and aerospace agency. The objective is to design an autonomous air vehicle that will be able to be operated by soldiers on the battlefield, with embedded sensors and camera, which will be able to explore an urban environment, and detect targets or threads such as snipers. Our team won the first edition of the contest two year ago and is again selected with eleven other teams to take part in the new challenge next year. Our way of running this project is quite unusual on the education point of view for several reasons. In the challenging scientific area of aerospace engineering, an entire vehicle (mechanical parts as well as electronic parts) is designed, manufactured, tested and operated by students, thus involving a lot of students of different background. For instance, mechatronics students are coordinating the project, helped by students in mechanical engineering, fluid mechanics, composite structures, manufacturing, topography, physics and electronics. The main challenge is to coordinate large groups of students of different faculties and different levels, as there are more than 40 students working on the same project at the same time. The group of students studying mechatronics is currently working on this project since September 2006 and will go on until they graduate in june 2009. The aerodynamics structure is an elliptic wing within a 70 cm diameter sphere. The UAV should take of and land vertically and then fly horizontally. This challenging transition between vertical and horizontal flight is currently under study and has been carried out successfully by another team operating a more classical airplane. Moreover, the project organisation and design process is currently analysed and deals as a case study for researchers in the area of engineering design. This is also interesting as it is generally not possible to analyse the entire design process in an industrial environment. The technical aspects of the project as well as the project organisation, collaborative design tools and project management tools will be presented. The success and failures of the project organisation will be explained and the analysis from problem base learning point of view commented.
Individual Excitation of Closely Spaced Modes Using Sine Testing Techniques for Structural Qualification
Authors: Ryan Jordan , Lu Bei
Published: August 2009

Structural qualification testing is critically important to structures in aerospace applications where a unique set of challenges exists. Often testing requirements for large, lightweight aerospace structures cannot be satisfied with conventional static testing for strength qualification; under these circumstances, vibration testing is used. The objective of such vibration testing is to load each component of an aerospace structure with the appropriate peak acceleration. Mode shapes are exploited towards this end, however for a large structure composed of multiple components, modes of predominant motion of each component may be closely spaced in the frequency domain. The difficulty of exciting each to a different peak response level without exceeding the target peak response acceleration on the other is greatly increased. This paper experimentally investigates a near-resonance sine burst testing technique, which is compared with the typical swept sine method. The sinusoidal inputs are designed so that the peak responses of two closely spaced modes are independently controlled to achieve correct test loads. The experimental results provide a guideline for strength qualification testing of aerospace structures.
Biomechanical Device Towards Quantitative Massage
Authors: Zeng Hansong , Zhao Yi , Butterfield Timothy , Agarwal Sudha , Furqan Haq , Best Thomas
Published: August 2009

Massage therapies are widely employed for improving and recovering tissue functions and physical activities. It is generally believed that such therapies would promote health and well-being by many possible mechanisms, including fastening muscle blood flow, parasympathetic activity, releasing relaxation hormones and inhibiting muscle tension, neuromuscular excitability and stress hormones. Nonetheless, most of current research is based on statistics and thus qualitative, preventing the in-depth study of the effectiveness. This is partially due to the lack of appropriate tools for quantitative loading and in situ assessment of tissue performance. To address this, we develop a biomechanical device to mimic massage therapies by applying controllable mechanical forces to animal tissues during cyclic mechanical motions. The device can apply compressive loads normal to the tissue surface and generate lengthwise motion along the tissue surface. Mechanical forces are applied with controllable magnitudes, frequencies and durations. Tissue mechanical response is recorded and correlated to the loading parameters. The changes of bulk tissue compliance and viscoelastic properties under various loading conditions are evaluated. The improvement of tissue functions and inhibition of muscle inflammation are examined. The results show that the peak torque production increased after massage, which suggests the recovery of muscle functions. A reduced number of infiltrating leukocytes is also observed in the subject muscle fibers after massage. Findings of this study suggest that the biomechanical device offers a quantitative analysis of massage actions, which will help to determine the optimal range of loading conditions required for safe and effective use of massage therapies.
Temperature-Dependent Permeability of Microporous Membranes for Vapor Venting Heat Exchangers
Authors: Marconnet Amy M. , David Milnes P. , Rogacs Anita , Flynn Roger D. , Goodson Kenneth E.
Published: August 2009

Improved flow regime stability and lower pressure drop may be possible in two-phase microfluidic heat exchangers through the use of a hydrophobic membrane for phase separation. Past research on vapor-venting heat exchangers showed that membrane mechanical and hydrodynamic properties are crucial for heat exchanger design. However, previous characterizations of hydrophobic membranes were primarily carried out at room temperatures with air or nitrogen, as opposed to liquid water and steam at the elevated operating temperature of the heat exchangers. This work investigates laminated PTFE, unlaminated PTFE, and nylon membranes and quantifies the permeability of the membranes to air and steam. The pressure drop across the membrane as a function of fluid flow rate and temperature characterizes the membrane permeability. This work will facilitate more focused experimental work and predictive modeling on optimizing membrane properties and will help with the development of more effective vapor venting heat exchangers.
Investigation of Thermal Performance of Primary and Secondary Thermoelectric Modules
Authors: Khalsa Simranjit , Nnanna A. G. Agwu
Published: August 2009

This paper reports the findings of an investigation on application of secondary thermoelectric (TE) module as a heat exchanger for the primary TE module. The experimental system consists of two commercially available thermoelectric modules arranged thermally in series with a heat sink and an integrated circuit (IC) chip. Heat produced from the IC chip is transferred to the heat sink via the TE modules. A total of nine experimental setups were analyzed using measured temperature data to assess the efficacy of the setups. Experimental evidence shows that the secondary TE module provides additional cooling advantage. The cooling capacity for a system with secondary TE module is 10.95W compared to 3.5W for systems where secondary modules are non-existent. The respective coefficient of performance, COP = Qc/Qp are 2.43 and 0.78. The use of a secondary TE module as a heat exchanger for the primary thermoelectric module is ineffective when compared with liquid-cooled heat exchanger. Results further showed that during early stages of heating and cooling processes, there exists lag in response time between the integrated circuits chip. This could result in over-heating or under-cooling the IC chip.
Investigation of Fiber Optic Sensor for Monitoring of Ammonia
Authors: Shastry Sistla S. , Abdi Abdeq M. , Nnanna A. G. Agwu
Published: August 2009

Detection and characterization of chemical contaminants in water network is paramount for water quality and water security. The current trend of monitoring the presence of contaminants is the batch sampling technique, where sample of water is collected and analyzed in the laboratory. While this technique is accurate, it fails to provide immediate information. In this work, the authors investigate the effectiveness of utilizing a fiber optics based sensor for detecting ammonia in water. In order for the system to sense ammonia, a small portion of the cladding of the fiber optic cable is stripped and replaced by a porous polymer material. A novel procedure of etching the glass cladding is reported. The modified cladding when interacts with ammonia causes a change in intensity of the electromagnetic wave flowing through the cable. The change in intensity caused by the modified cladding is studied parametrically which will help in forming a correlation between concentration of ammonia and absorbance.
Inverse Problems With Errors in the Independent Variables Errors-in-Variables, Total Least Squares, and Bayesian Inference
Authors: Emery A. F.
Published: August 2009

Most practioners of inverse problems use least squares or maximum likelihood (MLE) to estimate parameters with the assumption that the errors are normally distributed. When there are errors both in the measured responses and in the independent variables, or in the model itself, more information is needed and these approaches may not lead to the best estimates. A review of the error-in-variables (EIV) models shows that other approaches are necessary and in some cases Bayesian inference is to be preferred.
Critical Heat Flux by High Velocity Liquid Flow in Narrow Rectangular Channel
Authors: Sakurai Hisashi , Koizumi Yasuo , Ohtake Hiroyasu
Published: August 2009

Experiments of critical heat flux of extremely thin-fast plate jet film sub-cooled flow were conducted. The extremely thin-fast film-type jet of sub-cooled water was erupted into a stagnant pool. The heat transfer is augmented by the fast jet flow on the heat transfer surface. Vapor generated on the surface is easily taken away from the surface by the fast jet flow and leaves upward from the surface. The static head of water in the pool depress down the fast film-type jet flow on to the heat transfer surface and may collapse the vapor film that is formed between the heat transfer surface and the fast film flow. All these combine to have the possibility to improve the critical heat flux. In the experiments, the liquid sub-cooling was in the range of 30 ∼ 70 K. The thickness of the jet film was 0.2 mm and 0.5 mm. The width of the jet film was 2 mm. The velocity of the erupting jet film was 5.0 ∼ 32 m/s. The heat transfer surface was 2.0 × 2.0 mm heated electrically. The heat transfer surface was placed on the bottom of the pool. The fast-thin film jet was erupted on the bottom of the pool parallel to the heat transfer surface. Bubble behavior generated on the heat transfer surface was recorded by a high speed video camera at 10,000 frames/s. The highest critical heat flux obtained up to now is 3.2 × 107 W/m2. The analytical model of the critical heat flux for the present flow system will be presented.
Analytical Study of the Instability Between Two Liquids Flowing in a Channel and Subjected to Parallel or Normal Electric Field
Authors: Uguz A. Kerem , Aubry Nadine
Published: August 2009

The electro-hydrodynamic linear stability of a flat interface between two viscous, immiscible and incompressible liquids in plane Poiseuille flow has been shown to be useful in microfluidic devices. In some applications (e.g., material deposition) stability is desired, and in others (e.g., mixing or drop formation) instability needs to be induced. Depending on the direction of the electric field, i.e., parallel or normal to the flat interface, and in the case of fast electric times, it was shown analytically and without solving the complete set of equations that the electric field can either stabilize or destabilize the interface [1]. In this paper, we fully solve the equations and determine the maximum growth rates and the critical wavenumbers in the conductivity versus permittivity ratio space.
Adaptive Methods for Non-Linear Empirical Similitude Method
Authors: Tadepalli Srikanth , Wood Kristin L.
Published: August 2009

Several problems in engineering realm pose modeling and simulation difficulty due to severe non–linear behavior and debilitating singular or stiff conditions that act as additional impediments. In many such instances advanced numerical schemes are employed to either relax or simplify the PDE that defines the physical process to obtain reasonable output from the simulation. Digressing from this traditional approach, we present an experimental similitude method in this paper to analyze non–linear systems. Combined with the use of original mapping algorithms, we discuss the benefits of empirical similarity techniques and present a heat transfer example for exposition.
A Simple Approach for Thermal Analysis of Regenerative Cooling of Rocket Engines
Authors: Naraghi Mohammad H. , Foulon Matthieu
Published: August 2009

A simple model for thermal analysis of regenerative cooled rocket engines is developed. In this model the multi-dimensional heat conduction in the engine wall is analyzed using the fin effect of cooling channel side walls. A one-dimensional model for the cooling channel flow and heat transfer is used. The coolant properties are evaluated based on the NIST database. The present model is used to perform thermal analysis on two engines: the Space Shuttle Main Engine (a liquid hydrogen cooled engine) and a liquid oxygen cooled engine. Given the simplicity of the present approach its results compare well with other comprehensive models.
A Theory for Interactions of Two Dynamical Systems
Authors: Luo Albert C. J.
Published: August 2009

In this paper, a generalized theory for interactions of two separable dynamical systems is presented. The corresponding mathematical conditions are developed to determine the motion complexity of the two systems, which is caused by the interaction between two systems. This theory presents a different point of view about the interactions of dynamical system.
Controlling Mixing Inside a Droplet by Time Dependent Rigid-Body Rotation
Authors: Chabreyrie Rodolphe , Vainchtein Dmitri , Chandre Cristel , Singh Pushpendra , Aubry Nadine
Published: August 2009

The use of microscopic discrete fluid volumes (i.e., droplets) as microreactors for digital microfluidic applications often requires mixing enhancement and control within droplets. In this work, we consider a translating spherical liquid droplet to which we impose a time periodic rigid-body rotation which we model using the superposition of a Hill vortex and an unsteady rigid body rotation. This perturbation in the form of a rotation not only creates a three-dimensional chaotic mixing region, which operates through the stretching and folding of material lines, but also offers the possibility of controlling both the size and the location of the mixing. Such a control is achieved by judiciously adjusting the three parameters that characterize the rotation, i.e., the rotation amplitude, frequency and orientation of the rotation. As the size of the mixing region is increased, complete mixing within the drop is obtained.
Obtaining the Sensed Temperatures From a Detailed Model of a Welded Thermocouple
Authors: Woolley Jonathan W. , Bestor Michael A. , Weaver Mark L. , Woodbury Keith A.
Published: August 2009

When imbedded in dissimilar materials subject to large temperature gradients, thermocouples are known to yield erroneous (bias) temperature measurements. It has been established that the bias error may be accounted for with an appropriate computational model and the measured temperatures may be corrected with an appropriate kernel function. In this work, a thermocouple with a welded bead is considered. Early two-dimensional models considered the thermocouple to be a single wire with effective thermal properties. The model in the current investigation is three-dimensional and represents the sensor as two wires, each with unique thermal properties. The welded bead is represented as a separate entity with properties distinct from those of the wires. The problem of determining what location in the three-dimensional model corresponds to the measured temperature is considered. Earlier models have considered the sensed temperature to be the temperature at the tip of the two-dimensional thermocouple or, in three-dimensional models, the temperature at the center of the volume of the welded bead. In the current work, a theory is set forth for identifying the location at which the temperature is sensed by a thermocouple. This theory is in line with traditional thermoelectric theory and is supported with experimental evaluation with thermal imaging as well as examination of thermocouples by scanning electron microscopy and energy dispersive X-ray analysis. The significance of accurate modeling of the sensed temperatures is demonstrated with a numerical experiment.
Design and Numerical Modeling of an On-Board Chemical Release Module for Motion Control of Bacteria-Propelled Swimming Micro-Robots
Authors: Behkam Bahareh , Nain Amrinder S. , Amon Cristina H. , Sitti Metin
Published: August 2009

On/off motion control of bacteria-propelled synthetic bodies was previously achieved using a chemical switching technique. A chemical agent (CuSO4) directly binds to the rotor of the flagellar motor inhibiting it. When desired, a second chemical agent (EDTA) is introduced, which binds to the CuSO4 molecules, freeing the motor and allowing the bacteria to resume its motion [1]. To facilitate localized delivery of the control agents and reduce the diffusion time, we propose an on-board chemical release scheme for the first time. The proposed microfluidic motion control module contains two sets of optomechanically responsive nanocomposite paraffin wax micro-valves which can be independently actuated. To demonstrate the feasibility of the concept, a transient two-dimensional mass transfer numerical model is developed and the transient concentration profiles of the diffused chemicals at different locations on the robot body is studied. The results of this work provide crucial information required to determine the number, size, and location of the required micro-valves.
Effect of Sintering Temperature on Mechanical Properties of Electrospun Silica Nanofibers
Authors: Shendokar Sachin , Kelkar Ajit , Mohan Ram , Bolick Ron , Chandekar Gautam
Published: August 2009

Mechanical Properties of materials depend upon the crystal structure, presence of dislocations and slip planes in the unit cells. Nano-structures due to its nano scale size are expected to have defect free unit cells and hence posses very good mechanical properties. Electrospinning provides simple and cost effective means to produce nanofibers on a mass scale. These electrospun nanofibers could be subsequently used in woven composites to improve interlaminar properties. This paper addresses manufacturing of silica nanofibers by electrospinning and effect of sintering temperature on properties of these fibers. Electrospinning produces nanofibers by stretching liquid droplet emanating from spinnerate under the combined action of Columbic forces due to applied voltage and repulsion of charged ions. When the formed electrospun silica nanofibers are sintered at different temperatures, there is variation SiO2 content due to evaporation of solvents. This results into variation in the mechanical properties of electrospun silica nanofibers based on the sintering temperature. Differential Scanning Calorimetric (DSC) studies are carried out to relate variation in SiO2 content with sintering temperature. The mechanical properties of these electrospun fibers under various sintering temperatures are ascertained by evaluating their performance of composite laminates with electrospun interlaminate layers.
A Hybrid PD-Fuzzy Controller for Atomic Force Microscopes
Authors: Payam Amir Farrokh , Abdel-Rahman Eihab M.
Published: August 2009

This paper presents two fuzzy-based controllers designed to scan non-contact atomic force microscopes (AFM) over a specimen surface. Firstly, we develop a conventional fuzzy controller to achieve asymptotic probe tip tracking for bounded tip trajectories. Secondly, a hybrid PD-fuzzy controller is designed for the same purpose where the PD gains are tuned online by means of fuzzy logic. Finally, we compare the efficacy and requirements of the two controllers and compare their results to those of other recently proposed controllers for the same purpose. We show improved performance using both of our controllers; the most significant advantage being increased controller bandwidth and thus faster AFM scan rates. However, the PD-fuzzy controller is found to impose more realistic actuation demands on the plant than the Fuzzy controller.
Cure Kinetics of Neat and Nanophased Polyurethane Foams
Authors: Mohan Sriram , Balakrishnan Anandh , Saha Mrinal C.
Published: August 2009

In this work, the isothermal cure behavior of a two part polyurethane foam system has been evaluated at temperatures between 25°C–80°C via a rheokinetic method. An ATD CSS 1000-Advanced Polymer Analyzer (APA) rheometer operating in torsion mode was used for this purpose. In the first phase of our work, neat polyurethane foams were investigated and the effects of cure temperature on the final cure modulus and density were documented. The testing procedure consisted of measuring G* as a function of time. The data obtained was fit to a generalized cure kinetics model to evaluate various parameters such as rate constants, reaction orders and activation energies. The rate constants as a function of temperature exhibited a straight line Arrhenius relationship. In the second phase of the work, 1% by weight of cloisite-15A nanoclay was used to manufacture nanocomposite foams. Isothermal cure tests were performed on the nanocomposite foam sample at 25°C. A preliminary investigation of the effect of nanoclay infusion on the final cure properties revealed no significant change. However the nanoclay foam sample exhibited higher reaction rates than its neat counterpart at the same temperature. The cell structures of these foams were studied using a JEOL 960 Scanning Electron Microscope. The micrographs supported the observations that neat foam samples showed an increased density and modulus at lower temperatures than at higher temperatures. The nanoclay sample also showed a higher density relative to its neat counterpart.
A Test Setup for Evaluation of Harmonic Distortions in Precision Inertial Sensors
Authors: Spiewak S. A. , Ludwick S. J. , Hauer G.
Published: August 2009

Steadily improving performance of inertial sensors necessitates significant enhancement of the methods and equipment used for their evaluation. As the nonlinearity of sensors decreases and gets close to that of the exciters, new challenges arise. One of them, addressed in this research, is a superposition of errors caused by the nonlinearity of tested devices with nonlinear distortions of excitation employed for experimental evaluation. This can lead to a cancellation, at least partial, of the effects of both imperfections and underestimation of the actual distortions of the evaluated sensors. We implement and analyze several system architectures and components of applicable motion generation systems from the viewpoint of satisfying the relevant, often conflicting requirements posed by the evaluation of high performance sensors. Robust mechanical integration of the guidance, actuation and measurement functions emerges as a key factor for achieving the needed quality of generated test patterns. We find precision air bearing stages such as ABL1500 series (Aerotech) most suitable for implementing the needed experimental setup. We propose an architecture with two reciprocating stages, implement and evaluate its core components, and illustrate its performance with experimental results.
A Linearly Tunable MEMS Capacitor With Segmented Electrode and Enhanced Structure
Authors: Shavezipur Mohammad , Hashemi Seyed Mohammad , Khajepour Amir , Nieva Patricia
Published: August 2009

This research presents a novel linearly tunable MEMS capacitor with flexible electrode and modified structural stiffness. The capacitor is designed for PolyMUMPs as a standard three-structural-layer fabrication process. The moving electrode is divided into segments interconnected through torsional springs. Under each connecting point (node) two flexible and rigid steps are located. The flexible steps are cantilever beams, and as the bias voltage increases, they touch their corresponding nodes and consequently their stiffnesses are added to the total structural stiffness. This is the core idea of the proposed design to linearize the capacitance-voltage (C-V) response. An analytical model is developed to investigate the behavior of the new capacitor. In this model, the governing equations of the capacitor are numerically solved to obtain the system’s C-V response. An optimization problem with different design variables, such as dimensions of the segments or the beams stiffness coefficients, is solved to maximize the linearity of the C-V curves. The numerical results demonstrate drastic improvement in capacitors performance, where a highly linear C-V response and a maximum tunability of 94% is reached.
Mechanical and Electrical Properties of Micro-Lines Fabricated by Laser-Assisted Maskless Microdeposition
Authors: Alemohammad Hamidreza , Toyserkani Ehsan
Published: August 2009

The present paper is concerned with the analysis of the microstructural properties of silver micro-lines produced by Laser-Assisted Maskless Microdeposition (LAMM). LAMM is a laser based direct write method used in microscale layered manufacturing. In LAMM, liquid-suspended nanoparticles of a variety of materials are deposited in a layer-by-layer fashion and cured by a laser radiation. In this work, conductive micro-lines of silver with widths of 20 μm are fabricated, and their microstructures as well as electrical and mechanical properties are studied. Investigations show that the microstructures are affected by the laser power and the laser scanning velocity. To find the effect of laser processing parameters on the electrical performance of the samples, the conductivity of the samples are expressed in terms of the effective energy absorbed during laser radiation. It is shown that the conductivity of the sintered samples is increased up to 2 × 105 S.m−1 by raising the effective energy density. In addition, mechanical properties, i.e. modulus of elasticity of one of the fabricated samples are obtained using the nanoindentation test.
Development of a Linearly Tunable Modified Butterfly-Shape MEMS Capacitor
Authors: Shavezipur Mohammad , Hashemi Seyed Mohammad , Khajepour Amir , Nieva Patricia
Published: August 2009

This paper presents a novel geometry and modified structural stiffness for electrostatically actuated MEMS tunable capacitors. The design is based on parallel-plate configuration and four triangular plates are put together to form a butterfly shape flexible moving electrode. Each triangle is suspended by three uneven supporting beams. The capacitor is also equipped with extra beams, called here the “middle beams”, located under the triangles’ corners (nodes). An analytical model is developed to solve the governing equations of a triangular-plate electrode with uneven sides and supporting beams, where the stiffness of the middle beams is gradually added to the system as actuation voltage increases. The numerical simulations reveal that each triangle can be individually tuned up to 150% and the capacitance-voltage (C-V) response is broken into small sections due to added middle beams. Using the model developed in this paper and by design optimization, a linear C-V response is obtained, where the tunability in linear region reaches 100%. The simplicity of the proposed design allows the device to be fabricated using a three-structural-layer process such as PolyMUMPs and could therefore be monolithically integrated with other RF devices and ICs. Moreover, adding additional insulator layer on top of the fixed electrode increases the tunability to over 200% displaying a smooth and low sensitive response.
Measurement of Budding Yeast Growth Rate With MOSFET-Based Microfluidic Coulter Counters
Authors: Sun Jiashu , Li Deyu , Stowers Chris , Boczko Erik
Published: August 2009

Many bioassays are performed on an ensemble of cells and assay results depend crucially on the state of cells relative to one another. If the cells in the ensemble are disordered with respect to one variable, then the measurements that depend on that variable are confounded by averaging. One solution to this is to maintain the cell cycle synchrony for the cells in the ensemble. To do this, it is extremely important to accurately measure the cell growth rate. For example, the volume growth rate of budding yeast is closely linked to many aspects of the cell cycle. Therefore, investigation of the volume growth rate of budding yeast has become an appealing research topic because of its important implications in achieving cell cycle synchrony. In this paper, we report on applications of novel microfluidic sensing technique to measure the volume growth rate of individual budding yeast. We apply our recently developed MOSFET-based microfluidic Coulter counters to detect the volume of budding yeast when it is translocated through the sensing aperture forth and back, controlled by adjusting the direction of electroosmotic flow inside the microfluidic device. Our results indicate that because of the enhanced sensitivity of the MOSFET-based microfluidic Coulter counter, it is possible to measure the volume growth rate of individual budding yeast over its whole cell cycle. The measurement results clearly showed the volume growth of the individual budding yeast.
A Mechanical Fatigue Damage Evolution Model for PB-Free Solder Materials
Authors: Ladani Leila J. , Razmi Jafar
Published: August 2009

Evaluating state of damage in a ductile material as it experiences mechanical fatigue and cyclic loading poses much complexity and has been the subject of many researches. This study revisits the anisotropic damage model developed by Lemaitre (1992) and proposes to use his model combined with a micro-mechanics and mechanism based damage evolution model (Energy Partitioning Damage Evolution (EPDE)) and also a Unified Creep Plasticity-based model to predict the state of damage. The model is examined for pure shear and is applied to Pb-free solder materials. New anisotropic damage model exponents are generated using experimental data for Pb-free solder for both EPDE and UPC-based models and are compared with exponents generated previously under the assumption of isotropic and homogenous damage evolution.
Influence of Mechanical Load on Enzymatic Cleavage of Native Collagen
Authors: Zareian Ramin , Ruberti Jeffrey W.
Published: August 2009

It has been hypothesized that collagen fibrils in native tissue are “strain-stabilized” and thus protected (to some extent) from enzyme attack by the application of mechanical load. If true, collagen and its complement native enzymes (MMPs) could comprise the basis of “smart” structure which is intrinsically load-adaptive. If strain protection of collagen significantly reduces the activity of bacterial collagenase (BC-Clostridium Histolyticum), then benchtop “sculpting” of collagenous matrix for tissue engineering may be practical. In this investigation, we have quantified the enzymatically-induced creep of uniaxially-loaded (0.25 N) and unloaded control bovine corneal tissue strips (∼6.0 mm × 0.7 mm × 17 mm) which were exposed to BC (0.05 mM). Experimental and control strips were loaded for 15 minutes (initial creep-in) then exposed to the BC at which point the controls were unloaded. After 35 minutes of degradation, unloaded controls were re-loaded and the dynamic strain was recorded. All unloaded control specimens were significantly compromised mechanically compared to experimentals and could not hold the applied load for more than a few minutes following reloading. From the data is clear that strain protects the loaded fibrils. How that protection is manifested remains an open question.
Investigation of Moisture Sensitivity Related Failure Mechanism of Quad Flat No-Lead (QFN) Packages
Authors: Zhang Minshu , Lee S. W. Ricky
Published: August 2009

Interfacial delamination is a long existing problem in the moisture preconditioning process and reflow. The failure is caused by the competition between interfacial strength and hygrothermal stress. Many simulations based on the finite element model have been applied to study the failure mechanism of this phenomenon. However, the difficulty in obtaining material properties of mini-size packages, the lack of experiment investigation of interfacial adhesion and the less-understood moisture analysis will always bring many challenges to simulations. To avoid the above issues, dummy QFN packages were fabricated as the test vehicle for the investigation of the moisture related failure. The major advantage of using dummy packages is that all material properties could be traced and all geometric parameters could be determined without ambiguities. With everything under control, failure modes could be generated within expectation. This would provide a good experiment comparison for future finite element analysis. In this study, several experiment procedures were implemented to establish the relationship between material selection and moisture sensitivity level (MSL) test performance. They were package fabrication, mechanical tests for interfacial adhesion, C-SAM and cross-section inspections. Based on the experimental results, features of the moisture related failure mechanism are presented in this paper.
Challenges in Teaching Applied Thermodynamics
Authors: Karimi Amir
Published: August 2009

Most Mechanical Engineering programs offer a course in applied thermodynamics either as a requirement or as an elective for an undergraduate degree. Student success in this course depends on their preparation on fundamental concepts gained in an introductory course in thermodynamics. The divide in background knowledge among students creates a challenge for an instructor teaching the applied thermodynamics course. This paper explains how students’ background knowledge of the fundamental concepts is evaluated at the beginning of the semester. It provides a description of an approach adapted in teaching the course in order to close the gap in background knowledge among students. Through assessment results, this paper demonstrates how the adapted teaching method has improved student success. Other challenges for instruction and student assessment are discussed in this paper.
Fundamental Study on Impact Oscillations Between a Pantograph and an Overhead Rigid Conductor Line in a Railway Current Collection System
Authors: Kitajo Kotaro , Yoshizawa Masatsugu , Kawamura Satoshi
Published: August 2009

The contact problems between the rigid conductor line and the pantograph in a current railway system are studied from the viewpoint of nonlinear dynamics. It is assumed that there are impact oscillations between the rigid conductor line and the pantograph under the state of contact loss. The rigid conductor line pantograph system is modeled with a spring-supported beam excited by an oscillating body. First, we approached as an impact problem and theoretically examined by using this model. As a result, periodical impact oscillations were shown in low moving velocities of body. Second, we employed the method of mapping to clarify impact problems, and we obtained the relationship of the state of the system at the arbitrary impact to that at the next impact. Finally, the experiments are conducted with the simple experimental model using dimensionless parameters which are equal to the one of the analytical model.
Transient Motion of a Rigid Body Through a Narrow Tube and Characteristics of Surrounding Fluid Flow
Authors: Otsuka Tatsuya , Ishii Daichi , Maeda Toru , Yoshizawa Masatsugu
Published: August 2009

A multibody transportation system that moves with fluid inside a small-diameter tube has been studied by a lot of researchers. It is expected to be developed for future engineering applications such as a micro machine that transports medicines to a certain part of a body. This paper deals with the flow characteristics around a single rigid body and transient motion of the body when a body is influenced by pressure force from upstream. The model considered a body smaller than a diameter of a tube so that the force on the body can be numerically and analytically estimated as viscous friction force. It was assumed that the flow is axisymmetric, laminar and taken to be Newtonian and incompressible. It was obtained that the axial component of the fluid velocity decreases and pressure increases near the body like stagnation flow. Moreover, the pressure rapidly increases behind the body and decreases in front of the body with increasing diameter of the body.