bluuebunny/crossref_metadata_2025 huggingface dataset:
Methods and Characterization of Pick and Place Microassembly
Authors: Subramaniam V. , Last M. E. , Pister K. S. J.
Published: April 2008

Microassembly of MEMS structures using serial pick-and place has been demonstrated as a method for constructing complex three-dimensional microstructures. A new methodology to perform pick-and-place microassembly using a 3 DOF micromanipulator is demonstrated here. In this approach, the "pick" operation is performed on one chip, while the "place" operation is performed on a second chip mounted orthogonally to it under a microscope. This removes the need for the rotation of parts during assembly as required in previous works thus creating a significantly simpler assembly process. Also new in this work is the characterization of the contact resistance and the rigidity of assembled microstructures. The contact resistance of assembled microparts coated with 30nm of gold is measured to be approximately 12Ωusing a four-point measurement. The force required to pull out a micropart from a socket (into which it is assembled) is characterized along all three axes and found to be over 5mN in each case. The relationship between the force taken to engage the sockets and the force to pull out a micropart is measured to be linear. An electrostatic inchworm motor with extended range and a vertical thermal actuator are demonstrated which are manufactured using microassembly. Thus this assembly process with mechanically rigid assemblies is shown to have a number of potential applications.
A Survey on Failure Prognosis Research: Theory and Applications
Authors: Mohammadpour Javad , Grigoriadis Karolos M. , Franchek Matthew A. , Zwissler Benjamin J.
Published: April 2008

The paper presents a survey of recent advances in the area of failure prognosis and highlights some of the engineering applications in this area. The theoretical aspects of data-driven and model-based prognosis and damage modeling are summarized. The paper also reviews a recently proposed intelligent modelbased diagnosis/prognosis structure and its components. Finally, some of the important industrial applications, in which prognosis techniques have been employed for anticipating failure occurrence and determining useful remaining life are discussed.
High-Speed Visualization of Bubbles Interacting With a Solid Surface
Authors: Khoja Suleman , Attinger Daniel
Published: April 2008

Bubbles around a solid surface moving in a fluid at high Reynolds number drastically reduce the associated turbulent drag. In this paper, we present experiments on the interaction of air bubbles with a solid wall. The design of an experimental setup is described, that allows generating bubbles with diameters of 0.4 to 2 mm and observes their interaction with a solid wall whose angle with the horizontal can be controlled. Depending on the bubble size and angle of inclination of the solid wall, the bubbles bounce off or slide along the wall. High-speed visualizations of the bubble-wall interactions are performed for values of Reynolds and Weber number ranging from 40 to 560 and 0.04 to 1.80 respectively. Our experimental results are compared with the work of Tsao and Koch [Physics Fluids 9, 44 (1997)].
Piezoelectric Networks for Vibration Suppression of Mistuned Bladed Disks
Authors: Yu Hongbao , Wang K. W.
Published: April 2008

Extensive investigations have been conducted to study the vibration localization phenomenon and the excessive forced response that can be caused by mistuning in bladed disks. Most previous researches have focused on attacking the mistuning issue in the bladed disk, such as reducing the sensitivity of the structure to mistuning through mechanical tailoring, or design optimization. Few have focused on developing effective vibration control methods for such systems. This study extends the piezoelectric network concept, which has been utilized for mode delocalization in periodic structures, to the control of mistuned bladed disks under engine order excitation. A piezoelectric network is synthesized and optimized to effectively suppress the excessive vibration in the bladed disk caused by mistuning. One of the merits of such an approach is that the optimum design is independent of the number of spatial harmonics, or engine orders. Local circuits are first formulated by connecting inductors and resistors with piezoelectric patches on the individual blades. While these local circuits can function as conventional damped absorber when properly tuned, they do not perform well for bladed disks under all engine order excitations. To address this issue, capacitors are introduced to couple the individual local circuitries. Through such networking, an absorber system that is independent of the engine order can be achieved. Monte Carlo simulation is performed to investigate the effectiveness of the network for bladed disk with a range of mistuning level of its mechanical properties. The robustness issue of the network in terms of detuning of the electric circuit parameters is also studied. Finally, negative capacitance is introduced and its effect on the robustness of the network is investigated.
Flame-Surface Interaction and Flamelet Microstructure Over Single and Multiple Solid Fuel Segments in a Channel Cross Flow
Authors: Long Yang , Jahangirian Saeed , Wichman Indrek S.
Published: April 2008

The goal of this research is to study flamelets near solid fuel segments embedded in a non-combustible binder material. Flame attachment to surfaces in problems such as spreading flames, fires, and surface-burning propellants is a complicated process. The flame heats the surface, which decomposes into volatiles, which leave the surface as the gaseous fuel that mixes with incoming oxidizer, feeding further combustion. An interesting flame shape called the "flamelet" appears in narrow-channel combustion, microgravity combustion, and combustion over heterogeneous fuels. The model examined here develops a simple description of flamelet attachment and examines the details of the localized near-surface heat transfer and gas phase combustion. In essence, the "flame microstructure" near the surface is described as it interacts with the surface, including the heat flux from the flame, the surface heat flux, their dependence on flame microstructural parameters, and the sensitivity of the flame structure in response to changes in these parameters. Where possible, numerical solutions are compared with analytical formulas and calculations, and extensions are made to describe more general cases.
Computational Modeling of Lateral Amygdala Neurons During Acquisition and Extinction of Conditioned Fear, Using Hebbian Learning
Authors: Li Guoshi , Cheng Stacy , Ko Frank , Raunch Scott L. , Quirk Gregory , Nair Satish S.
Published: April 2008

The amygdaloid complex located within the medial temporal lobe plays an important role in the acquisition and expression of learned fear associations (Quirk et al. 2003) and contains three main components: the lateral nucleus (LA), the basal nucleus (BLA), and the central nucleus (CE) (Faber and Sah, 2002). The lateral nucleus of the amygdala (LA) is widely accepted to be a key site of plastic synaptic events that contributes to fear learning (Pare, Quirk, LeDoux, 2004). There are two main types of neurons within the LA and the BLA: principal pyramidal-like cells which form projection neurons and are glutamatergic and local circuit GABAergic interneurons (Faber and Sah, 2002). In auditory fear conditioning, convergence of tone [conditioned stimulus (CS)] and foot-shock [unconditioned stimulus (US)] inputs potentiates the synaptic transmission containing CS information from the thalamus and cortex to LA, which leads to larger responses in LA in the presentation of subsequent tones only. The increasing LA responses disinhibit the CE neurons via the intercalated (ITC) cells, eliciting fear responses via excessive projections to brain stem and hypothalamic sites (Pare, Quirk, LeDoux, 2004). As a result, rats learn to freeze to a tone that predicts a foot-shock. Once acquired, conditioned fear associations are not always expressed and repeated presentation of the tone CS in the absence of US causes conditioned fear responses to rapidly diminish, a phenomenon termed fear extinction (Quirk et al. 2003). Extinction does not erase the CS-US association, instead it forms a new memory that inhibits conditioned response (Quirk et al. 2003)
Role of Indoor Air Distribution in Performance of Heat Pump Systems in Energy-Efficient Residential Buildings
Authors: Jal-Alzadeh-Azar Ali A. , Anderson Ren , Gawlik Keith
Published: April 2008

This paper demonstrates the potential impact of indoor air distribution on the energy consumption of central HVAC systems with cognizance of human thermal comfort. The study focuses on a hypothetical high-performance house incorporating a split heat pump system. The air distribution of this building incorporates high sidewall supply-air registers and near-floor, wall-mounted return-air grilles. Heating-mode stratification resulting from this prevalent configuration is a prime example of situations in which challenges regarding energy efficiency, comfort, and ventilation effectiveness emerge. These challenges underline the importance of adopting a comprehensive design strategy for high-performance buildings. Two indoor air distribution scenarios were analyzed: (1) theoretically well mixed and (2) poorly mixed, representing a realistic case. The former scenario was evaluated using an analytical approach, whereas the latter was investigated through computational fluid dynamics (CFD) simulations. For heating mode, the results indicated the presence of a pronounced thermal stratification resulting from poor air mixing. At 50% of the design heating load, for the well-mixed case, the HVAC system energy consumption was significantly higher. Considerably better air distribution performance was observed with cooling mode, in which the relative energy penalty for the well-mixed scenario was noticeably less. In real-world applications where measures must be taken to achieve near perfectly mixed indoor conditions for better comfort, the energy use is expected to be even higher. However, in the absence of such measures, the thermostat setpoint is likely to be readjusted, leading to a higher energy use without necessarily improving the overall comfort level, as demonstrated in this paper. The limitation of increasing the supply-air flow rate to enhance air mixing and diffusion is also discussed in terms of the system moisture removal capability.
Opportunities for Thermoelectric Energy Conversion in Hybrid Vehicles
Authors: Headings Leon , Marano Vincenzo , Jaworski Christopher , Guezennec Yann , Washington Gregory , Heremans Joseph P. , Rizzoni Giorgio
Published: April 2008

Much analysis has been performed on the application of thermoelectrics in automobiles, but the low efficiency of the materials has so far limited their use. As a result, little has been done in the physical design of how to most efficiently utilize thermoelectrics in a vehicle's energy system. However, much progress has been and continues to be made in the field of thermoelectric materials. Developments in the areas of nanostructured materials have produced materials with double the efficiency of current commercially available materials. This, coupled with a growing need for the reduced consumption of fossil fuels and production of greenhouse gases, has generated renewed interest in the application of thermoelectrics in automotive systems. Hybrid-electric vehicle (HEV) designs have provided significant improvements in fuel efficiency and continue to evolve. This modified energy management strategy introduces new components and energy distributions which force traditional designs to be reconsidered. For example, the temperature and quantity of thermal energy transferred through the exhaust and radiator are lowered. Also, the IC engine may not be run continuously, creating difficulties in maintaining temperature in the catalytic converter, powering belt-driven accessories, and regulating cabin temperature. This contributes to an increased demand for electrical energy. Finally, the power electronics are typically liquid cooled (order of 60-65 °C) and the high voltage battery packs must be kept cool (typically below 45 °C) to maximize their life. A detailed computer model which captures the details of the energy transfers in HEV's, including thermal loads will be used to assess the unique thermal requirements of hybrid vehicles under average engine loads. Based on these requirements, specific thermal energy management strategies will be proposed. These modified systems will be added to the computer model in order to evaluate their potential using currently available thermoelectrics materials. Finally, the preferred thermal energy management system will be selected as the basis for future design optimization.
Designing Functional Products in the Best Interest of the User — With a Factor 10 Reduction in Life Cycle Cost : Example, a (Solar) Airconditioning System
Authors: Dartnall John , Adhikari Arjun K. , McNab John
Published: April 2008

There is increasing interest in Life Cycle Design with the purpose of raising sustainability and reducing energy and material consumption. By increasing energy efficiency, selecting more suitable materials and lessening maintenance requirements it is practical to reduce life cycle cost. Conventional Heat pump air conditioners operate to effect a healthy and comfortable indoor environment. They are large consumers of energy, partly due to the need to exhaust air (with consequent energy wastage) from the conditioned building so that healthy ventilation air may be introduced in its place. Rather than drawing all the energy from community electricity and gas supplies, the designer should design these systems so they recover as much energy as is feasible from both building exhaust air and the environment. A low life cycle cost solar air conditioner design is described that obtains under peak load more than 90% of its energy from a combination of building exhaust air and insolation with a reduction in life cycle cost approaching a factor of 10. In basic terms, with a reduction of a factor of 3 in energy consumption along with a life increase also of a factor of 3 it is possible to approach a factor of 10 improvement in product life cycle cost.
Generation of Controllable Nano-Gaps on Single Wall Carbon Nanotube
Authors: Jeong Jaesun , Chung Gu Hyun , Buttner William J. , Hunter Gary W. , Stetter Joseph R. , Wang Rong
Published: April 2008

We demonstrated the application of the atomic force microscope (AFM) in generation of controllable nano-gaps on single wall carbon nano-tubes (SWCNTs). Tapping mode AFM combined with interleave mode was used to image and manipulate the CNTs. By precise control of the loading force and the scan rate, we were able to generate desired gaps on CNT nanowires ranging from 10.6 nm to 58.8 nm. The gap size dependence on loading force and scan rate was discussed. Such a structure can be applied in fabrication of capacitancebased nano-device toward sensor applications.
Fabrication and Characterization of a Carbon Nanofiber Reinforced Liquid Crystalline Polymer
Authors: Rohatgi A. , Thomas J. P. , Pogue W. R. , Baucom J. N.
Published: April 2008

Our group at the Naval Research Laboratory is studying hierarchical arrangements of materials at multiple length scales and how such arrangements can be used to yield novel properties. We are investigating nanocomposites comprising a thermotropic liquid crystalline polymer (LCP) matrix reinforced with carbon nanofibers for potential structure + conduction multifunctional applications. The LCP matrix is known for its inherent hierarchical microstructure, and its fracture surface is typically characterized by fibrils ranging in size from nanometer to micrometer. The carbon nanofibers being compounded with the LCP matrix are vapor-grown carbon nanofibers (VGCF) and pre-processing techniques are being developed to eventually replace VGCF with single-wall carbon nanotubes (SWNT). Composites with VGCF content of 0, 1, 2, 5 and 10 wt.% were extruded using a twin-screw extruder to yield monofilaments in the range of 0.5 to 2 mm in diameter. The mechanical properties of extruded filaments were determined via quasi-static tensile tests and fracture surfaces examined under a scanning electron microscope. Porosity and hierarchical fibrillar structures were commonly observed in the fracture surfaces of tensile tested LCP and LCP-VGCF filaments. The LCP-VGCF filaments showed a maximum increase in strength and modulus of 20% and 35%, respectively, at 1-2 wt.% VGCF content. The dependence of mechanical properties on VGCF content was attributed to the interplay between the extrusion process parameters, VGCF dispersion and molecular alignment of LCP. In another set of experiments, LCP was thermo-mechanically pre-processed using a laboratory scale double-roll mixer and extruded using a Maxwell mixing extruder to yield monofilaments in the range of 0.2 to 0.7 mm. At 0.2 mm diameter, filaments of un-pre-processed and pre-processed neat LCP showed almost identical mechanical properties. At 0.7 mm diameter, however, pre-processed LCP filaments showed 10% and 30% degradation in strength and modulus, respectively, relative to un-pre-processed LCP. The lowered mechanical properties of pre-processed LCP were attributed to its chemical degradation during thermo-mechanical processing. Over the diameter range from 0.2 to 2 mm and irrespective of prior processing or extrusion method, the modulus and strength of neat LCP filaments increased with decreasing diameter. The strength and modulus dependence on filament diameter could be explained by the "skin-core" effect typically seen in liquid crystalline polymers. Future work will involve optimizing processing parameters for simultaneous enhancements in mechanical properties and electrical/thermal conductivity in LCP-VGCF/LCP-SWNT filaments.
Three-Dimensional Shear Driven Thin Liquid Film in a Duct
Authors: Lan H. , Friedrich M. , Armaly B. F. , Drallmeier J. A.
Published: April 2008

Measurements and predictions of three-dimensional shear driven thin liquid films by turbulent air flow in a duct are reported. FLUENT - CFD code is used to perform the numerical simulations and the Reynolds Averaged Navier-Stokes and continuity equations along with the Volume of Fluid (VOF) model and the realizable k-ε turbulence model are implemented for this task. Film thickness and width are reported as a function of air flow rate, liquid film volume flow rate and surface tension, and a comparison with preliminary measured results is made. The thickness of the shear driven liquid film is measured using an interferometric technique that makes use of the phase shift between the reflection of incident light from the top and bottom surfaces of the thin liquid film. The spatial resolution is determined based on the spot size of the incident light, which for the current configuration of the transmitting optics is approximately 10 microns. The resulting fringe pattern is imaged using a high-speed imaging camera operating at 2000 frames per second. The technique has proved successful in measuring thickness between 100 and 900 microns in these shear driven films. Simulation results reveal that higher gas flow velocity decreases the film thickness but increases its width, while higher liquid film flow rate increases the film thickness and increases its width. Reasonable comparison appears to exist between preliminary measured and simulated results.
Modeling and Parametric Study of a Ceramic High Temperature Heat Exchanger and Chemical Decomposer
Authors: Ponyavin Valery , Chen Yitung , Mohamed Taha , Trabia Mohamed , Wilson Merrill , Hechanova Anthony E.
Published: April 2008

It is proposed to use ceramic high temperature heat exchanger as a sulfuric acid decomposer for hydrogen production within the sulfur iodine thermo-chemical cycle. The decomposer is manufactured using fused ceramic layers that allow creation of channels with dimensions below one millimeter. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer, stresses and chemical reactions in the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. Temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis. Results of this research can be used as a basis for investigation optimal design of the decomposer that can provide maximum chemical decomposition performance while maintaining stresses within design limits.
A Dynamic Model of Recompression HCCI Combustion Including Cylinder Wall Temperature
Authors: Roelle Matthew J. , Ravi Nikhil , Jungkunz Adam F. , Gerdes J. Christian
Published: April 2008

In a Homogeneous Charge Compression Ignition (HCCI) engine, pre-compression gas temperature and cylinder wall temperature are two of the conditions that determine combustion timing. However, they operate in completely different dynamic realms. The pre-compression gas temperature will stabilize in just a few cycles. Conversely, the cylinder wall temperature requires a minute or more. To predict combustion timing under changing thermal conditions, this paper describes a multi-state continuous-time model of HCCI combustion achieved with exhaust recompression and a discrete model of cylinder wall temperature updated once per cycle. The continuous model is necessary to capture ignition on each cycle. Wall temperature changes so little every cycle, it is only updated between combustion cycles. This scheme is investigated by comparing experimental and simulated fuel step changes, which alter residual gas temperature quickly and cylinder wall temperature slowly. Dynamic comparisons show several similar behaviors and provide insight into the physical processes.
The Integration of Student Design Competitions and Academic Curricula
Authors: Lumkes John H.
Published: April 2008

This paper discusses various aspects and models of how student design competitions can be integrated into a typical undergraduate curriculum. University models range from no involvement—where the professional society chapter or even a separate group of students operate autonomously—to models where the competition activities are intimately integrated with the capstone senior design requirements. Each model exhibits different strengths and weakness, these being examined in terms of student experiences and feedback, ABET criteria, benefits to the university, and cost to the university. A case study demonstrates the potential for integration and the perspectives of students, advisors, and organizers are considered.
Fault Diagnostics of Industrial Robots Using Support Vector Machines and Discrete Wavelet Transforms
Authors: Datta A. , Patel S. , Mavroidis C. , Antoniadis I. , Krishnasamy J. , Hosek M.
Published: April 2008

In this paper we address the problem of fault diagnostics in industrial robots. The goal was to develop a method that automatically, accurately and in a generic way could identify and classify faults once they occur for any type of industrial robot used. Although a large number of diagnosis methods and relevant applications for industrial equipment already exist, the current research in the area of fault diagnosis of industrial robotic manipulators is rather poor, due to the large variability of faults, the unsteady and non-uniform operating conditions, the small amount of sensors used in industrial manipulators and the rather limited time records of the equipment. These restrictions present key challenges of the current research to be undertaken. In this paper we present a novel approach to perform fault diagnostics of industrial robotic systems using Support Vector Machines (SVM) and Discrete Wavelet Transform based feature extraction. Experimental results are obtained from an industrial manipulator used in the semi-conductor industry.
Development of a More Efficient Defrost Control System for Residential Heat Pumps
Authors: Yilmaz Emin
Published: April 2008

The purpose of this research project was to design a more efficient defrost control system for residential heat pumps. Defrost systems are used to melt the accumulated ice on evaporator coils of outdoor units. The purpose of the new control system is to prevent the initiation of defrost cycle when there is no substantial ice accumulation on the outdoor unit. Two of the envisioned ice accumulation sensing methods were (a). Increase in pressure loss across the evaporator coil and (b). Resistance change across two electrodes when ice bridges the electrodes. A differential pressure sensor was used to sense an increase in pressure loss across outdoor coil for this research project. Results indicate that, although maximum time interval of 90 minutes was used, about 55% of defrost cycles initiated were not necessary since there was no ice to melt. An ASYST based data acquisition system was used to monitor, measure and store key parameters. It is expected that with the new control system one can improve efficiency by about 3%. A similar project has been undertaken on a heat pump recently installed on our HVAC experimental unit as an undergraduate research project. Installation of temperature and humidity controlled enclosure, and thermocouples have been completed. Some preliminary results were reported. If any, other results will be reported at the meeting.
Effects of H2-Enrichment on the Propagation Characteristics of CH4-Air Flames
Authors: Briones Alejandro M. , Aggarwal Suresh K. , Katta Vishwanath R.
Published: April 2008

The propagation of H2-enriched CH4-air triple flames in a nonpremixed jet is investigated numerically. The flames are ignited in a nonuniform jet-mixing layer downstream of the burner. A comprehensive, time-dependent computational model is used to simulate the transient ignition and flame propagation phenomena. The model employs a detailed description of methane-air chemistry and transport properties. Following ignition a well-defined flame is formed that propagates upstream towards the burner along the stoichiometric mixture fraction line. As the flame propagates upstream, the flame speed, which is defined as the normal flamefront velocity at the leading edge with respect to the local gas velocity, increases above or decreases below to the corresponding unstretched laminar flame speed of the stoichiometric planar premixed flame. Although the flame curvature varies as a function of axial position, the flame curvature remains nearly constant for a given flame. As hydrogen is added to the fuel stream the flame curvature during flame propagation remains nearly constant. During the flame propagation process, the hydrodynamic stretch dominates over the curvature-induced stretch. Hydrogen increases the heat release and the component of the velocity perpendicular to the flame increases across the surface, whereas the tangential component remains unchanged. This jump in the perpendicular velocity component bends the velocity vector toward the stoichiometric mixture fraction line. This redirection of the flow is accommodated by the divergence of the streamlines ahead of the flame, resulting in the decrease of the velocity and increase in the hydrodynamic stretch.
Development of Mechanical Engineering Curricula at the University of Minho
Authors: Teixeira J. C. F. , Silva J. C. F. L. , Flores P.
Published: April 2008

The implementation of the Bologna protocol in the EU has set new goals for the whole higher education system as: a) a quality assessment for university courses; b) a framework for the exchange of students and academics and c) an opportunity for changing the teaching/learning procedures and methodologies. Within the context, the mechanical engineering curricula at the University of Minho has been comprehensively formulated in order to meet these and future challenges and expectations. The whole process has been based upon various cornerstones: the legal framework for the higher education system; the introduction of new learning methodologies and an accurate survey and understanding of the existing strong and week points of the previous experience. For this purpose, a comprehensive evaluation has been carried out with former students and a detailed map has been formulated regarding their professional careers and experiences. Furthermore, a discussion has been carried out in order to define the mission of the graduate in Mechanical Engineering. In brief, such mission may be referred by his ability to participate in the wealth creation through technology based innovation. Within this context, the curriculum has been structured in order to meet such goals. In addition to strong foundations in physics and mathematics, new subjects are introduced into the curriculum. The whole education is based upon project development which stimulates the students initiative, responsibility and their ability to integrate knowledge. Throughout the curriculum, students are enrolled into research projects developed in the department and it is expected that a few selected projects may be taken into a quasi industrial stage.
On Modeling and to Impact Dynamic Equations of Multi-Rigid-Link Robotics Having Simultaneous Collisions With Frictional Impulses
Authors: Mu Xiuping , Wu Qiong , Mu Yanping
Published: April 2008

Impact plays an important role in robotic manipulations. As robotic manipulators interact with their environment or objects, the motion of the system varies discontinuously and large impulsive forces are created at the surface of contact and are transmitted through the system, particularly when the motion of the manipulator is fast. With the demands for more precise and faster performance of robotic manipulators and minimizing potential damage of the system, being able to better simulate and control impact has become essential. In this paper, the impact dynamics describing simultaneous collisions of multi-link robotics with frictional impulses are investigated. The solutions for the after-impact velocities and impulses are provided in a closed form which can be easily employed for simulating robotic system contact states. The results are also important for the motion planning and impact control of robotic systems with contact tasks.
The Effect of Surface Processing on the Protein Adsorption and Tribomechanical Properties of Ultra-High-Molecular Weight Polyethylene
Authors: Karuppiah K. S. Kanaga , Sundararajan Sriram , Xu Zhi-Hui , Li Xiaodong
Published: April 2008

Ultra-high molecular weight polyethylene (UHMWPE) is a popular choice for the liner material of the acetabular cup and forms one of the articulating surfaces in total joint replacements (TJRs). Evaluating the tribological characteristics of UHMWPE on immediate contact with the physiological fluid is essential to understand pathways and mechanisms of eventual failure. In this study, the friction response and interfacial shear strength of a UHMWPE - ceramic interface was quantified using atomic force microscopy (AFM) before and after exposure to bovine serum albumin (BSA) solution. A 10% protein solution concentration was used to closely mimic protein levels in human physiological fluid. Medical grade UHMWPE samples with two different surface finishing treatments, milling and melting/reforming were used in the experiments. Friction response as a function of normal load was monitored on a particular area on each sample. Fluorescence microscopy was used to assess the protein adsorption on the test area. The interfacial shear strength of the interface was calculated from the friction data using contact mechanics. Contact angle measurements were also performed on the surfaces to evaluate the surface energies before and after protein adsorption. Correlations between the friction behavior and surface energy of the surfaces are discussed.
Multi-Axis Electromagnetic Moving-Coil Micro-Actuator
Authors: Golda Dariusz , Culpepper Martin L.
Published: April 2008

This paper presents the design and proposed fabrication of an electromagnetic (EM) micro-actuator capable of independent force output in two orthogonal axes of motion. This actuator enables independently controlled in- and out-of-plane motion when coupled with a suitable flexure. An electromagnetic force model is presented. Simulation results indicate that the actuator can output several mNewtons per square millimeter of footprint in two orthogonal axes with electrical bandwidth greater than 1 MHz. In addition, we show that the micro-actuator may be designed to eliminate parasitic force and torque by tuning the coil geometry. A bench-level prototype nanopositioner has been designed and built with centimeter-scale prototype actuator coils and magnets. Predicted static displacement matches the measured values to within 5%. Efforts to further miniaturize the device are described, including a four-mask micro-fabrication process that is to be used to fabricate two-axis actuators for a six-axis nanopositioner. Parts of these processes have been used to create prototype micro-coils that sustain current densities greater than 1000 A/mm2.
An Experimental and Theoretical Investigation of Nonlinear Vibrations of Piezoelectrically-Driven Microcantilevers
Authors: Mahmoodi S. Nima , Jalili Nader
Published: April 2008

The nonlinear vibrations of a piezoelectrically-driven microcantilever beam are experimentally and theoretically investigated. A part of the microcantilever beam surface is covered by a piezoelectric layer, which acts as an actuator. Practically, the first resonance of the beam is of interest, and hence, the microcantilever beam is modeled to obtain the natural frequency theoretically. The bending vibrations of the beam are studied considering the inextensibility condition and the coupling between electrical and mechanical properties in piezoelectric materials. The nonlinear term appears in the form of quadratic due to presence of piezoelectric layer, and cubic form due to geometry of the beam (mainly due to the beam's inextensibility). Galerkin approximation is utilized to discretize the equations of motion. The obtained equation is simulated to find the natural frequency of the system. In addition, method of multiple scales is applied to the equations of motion to arrive at the closed-form solution for natural frequency of the system. The experimental results verify the theoretical findings very closely. It is, therefore, concluded that the nonlinear approach could provide better dynamic representation of the microcantilever than previous linear models.
An Adaptive Self-Sensing Strategy for Piezoelectrically-Actuated Microcantilevers Used in Ultra-Small Mass Sensing Applications
Authors: Gurjar Miheer , Jalili Nader
Published: April 2008

This paper presents a mathematical model of a self-sensing microcantilever beam for mass sensing applications. Equations of motion are derived for a microcantilever beam with a tip mass and a piezoelectric patch actuator deposited on the cantilever surface. In the self-sensing mode, the same piezoelectric patch is used for actuation and sensing. Selfinduced voltage signals, which are extracted using a capacitive bridge mechanism, reveal frequency information of the vibrating beam, which in turn, reveals the particle mass. Equations of motion are obtained using the extended Hamilton's principle by considering the microcantilever as a distributed- parameters system. Two methods to estimate the unknown tip mass are presented. The first one is based on an inverse solution to the characteristic equation problem, while the second method uses a constraint-based optimization approach to estimate the tip mass. To improve the self-sensing performance, the need for adaptive estimation of the piezoelectric capacitance is stressed and an online estimation mechanism is presented. Simulations are presented to demonstrate the ability of the model to detect tip mass up to 0.1 femtogram (1 femtogram = 10-15 gm). Further simulation results demonstrate the working of constraint optimization method and adaptive self-sensing mechanism.
Tube Side Corrosion in Heat Exchangers: A Case Study
Authors: Ribeiro Antonio Carlos , Dalprat-Franco L. C.
Published: April 2008

Tube side corrosion in heat exchangers is a major concern in the design and operation of these equipment. This paper describes a particularly serious occurrence of what was interpreted to be Microbiologically Increased Corrosion (MIC) in a carbon steel condenser that lead to premature failure of the tubes by perforated corrosion pits. The photographs in the text illustrate the problem and proposed cures are discussed in the conclusions.
Effect of Processing Parameters on the Cellular Morphology and Mechanical Properties of Thermoplastic Polyolefin (TPO) Microcellular Foams
Authors: Wong Steven , Naguib Hani E. , Park Chul B.
Published: April 2008

In this study, the effects of processing parameters on the cellular morphologies and mechanical properties of TPO70 (Thermoplastic Polyolefin) microcellular foams are investigated. Microcellular closed cell TPO70 foams were prepared using a two-stage batch process method. The microstructure of these foamed samples was controlled by carefully altering the processing parameters such as saturation pressure, foaming temperature and foaming time. The foam morphologies were characterized in terms of the cell density, foam density and average cell size. Elastic modulus, tensile strength, and elongation at break of the foamed TPO70 samples were measured for different cell morphologies. The findings show that the mechanical properties were significantly affected by the foaming parameters which varied with the cell morphologies. The experimental results can be used to predict the microstructure and mechanical properties of microcellular polymeric TPO70 foams prepared with different processing parameters.
Nexus Materials: A Vision Just Beyond the Horizon
Authors: Brei Diann
Published: April 2008

In future applications, materials will need to extend beyond that of the bulk response or even simple engineered behavior. This paper attempts to articulate an integrated vision and even push it further to the next realm of materials defined here as Nexus materials, the synergistic connection that weaves it all together. The applications in mind will demand complex functionality such as higher order actuation across surfaces/volumes, distributed conformal sensing, and full-spectrum instantaneous color change. Looking beyond the horizon, the level of complexity needs to be raised to radical state change (not just by a few percent) where the material properties can be grossly changed on command by electrical, magnetic, thermal, optical or chemical control stimuli. While it is desirable to have multiple states, the materials should be situationally functional with the ability to change key properties over time to economically accommodate changing situations- in contrast to current multifunctional materials that are time invariant. The research in nanomaterials holds the promise that one day it will be possible to design and build up materials from the bottom up into ultrahierachial systems like nature. It may be possible to achieve truly intrinsic intelligence with control and supporting elements such as power onsite via energy harvesting. However, the level of integration has to evolve beyond the discrete laminated structures of the 1990's and the discretely integrated composites of the 2000's to continuously integrated materials where the phases are indistinguishable. This doesn't mean no interfaces, but does implies minimizing the parasitic interfaces (typically extrinsic) and maximizing the helpful symbiotic interfaces (typically intrinsic). To achieve this vision, a new wholistic approach will be required that synergistically uses the design space, coupling multiple fields (piezoelectric, magnetostriction, shape memory, etc.). This alternative engineering paradigm will hopefully lead to new classes of material systems - Nexus materials - that make the ultimate, synergistic connection between the past and the future and are just beyond the horizon.
Seperation of Nanoparticles by Gravitational Sedimentation
Authors: Jayatissa Ahalapitiya H. , Dadi Anathramprasad
Published: April 2008

Preparation of nanocrystalline titanium oxide particles by wet chemical method and the separation of these particles by gravitational sedimentation were investigated. A colloidal form of titanium oxide was synthesized by the reaction between titanium fluoride containing solution and hydroxyl ions in an aqueous medium under controlled conditions. Colloidal precipitates produced by this reaction can have different size particles. This titanium oxide suspension was separated using a large liquid column in which different size particles can be collected in different region of the column. Raman and X-ray diffraction were used to investigate the structural properties of these nanocrystalline titanium oxides. The properties of asproduced particles were compared with the properties of annealed samples at different temperatures. As-produced particles had the anatase structure while it was not changed when annealed below 700 °C. High temperature (>700 °C) annealed particles had the rutile structure. The grain size of asproduced samples was varied in the range of 7–90 nm. This study with titanium oxide as the model material indicates that the gravitational sedimentation is a very promising technique to separate a mixture of different size nanoparticles.
Constitutive Modeling for Porous PLGA 85/15 Scaffold in Compression
Authors: Leung Linus , Perron Josee , Naguib Hani E.
Published: April 2008

Constitutive modeling of stress-strain relationship of open-celled PLGA 85/15 foams under compression was studied. A constitutive model for compressive behavior was directly derived from the morphology of a unit cubic cell. These constitutive equations describe the stress-strain relationship as a function of the foam's material properties and cell morphology, such as elastic modulus, yield stress, relative density, cell strut thickness, and cell size. To verify this model, uniaxial compression testing was performed on foam samples. Using the gas foaming/salt leaching method, the samples were prepared by using different foaming parameters such as salt/polymer mass ratio, saturation pressure, and saturation time. The comparisons of theoretical and experimental data demonstrate that the constitutive model using a cubic unit cell accurately describes the behavior of PLGA foams with low relative densities under compression.
Relevance of High Productivity Machining Development and Testing to Engineering Technology Education
Authors: Bruce R. Gregg , Garg Nitin
Published: April 2008

A brief introduction to high-speed, high-productivity machining is followed by analysis of the applicability of high-productivity machining coursework to manufacturing-related engineering and engineering technology education. Typically, undergraduate students know and learn little about this emerging manufacturing technology. This paper presents the current educational environment and analyzes the need for coursework to promote learning in this and other advanced manufacturing technologies to help students of engineering and engineering technology succeed in today's competitive manufacturing environment.
Modeling Leakage With Mica-Based Compressive Seals for Solid Oxide Fuel Cells
Authors: Green Christopher K. , Streator Jeffrey L. , Haynes Comas
Published: April 2008

Fuel cells represent a promising energy alternative to the traditional combustion of fossil fuels. In particular, solid oxide fuel cells (SOFCs) have been of interest due to their high energy densities and potential for stationary power applications. One of the key obstacles precluding the maturation and commercialization of planar SOFCs has been the lack of a robust sealant. This paper presents a computational model of leakage with the utilization of mica-based compressive seals. A finite element model is developed to ascertain the macroscopic stresses and deformations in the interface. In conjunction with the finite element model is a microscale contact mechanics model that accounts for the role of surface roughness in determining the mean interfacial gap at the interface. An averaged Reynolds equation derived from mixed lubrication theory is applied to model the leakage flow across the rough, annular interface. The composite model is applied as a predictive tool for assessing how certain physical parameters (i.e., seal material composition, compressive applied stress, surface finish, and interfacial conformity) affect seal leakage rates.
Manufacturing of Single Poly(Lactic Acid) Composites
Authors: Li Ruihua , Yao Donggang
Published: April 2008

An approach of utilizing slowly crystallizing dynamics for fabrication of poly(lactic acid) (PLA) single-polymer composites (SPCs) was investigated. As a slowly crystallizing polymer, PLA can be prepared as two distinct physical forms, amorphous (or near-amorphous) PLA and highly crystalline PLA. In this study, near-amorphous PLA films and highly crystalline PLA fibers were combined to form a SPC using a rapid hot compaction method at a temperature about 40°C below PLA's melting temperature. It was found that, by rapidly heating an amorphous-crystalline lamination above PLA's glass transition temperature during manufacturing, amorphous films can be fused and good adhesion between the amorphous film and the crystalline fiber can be achieved. Mechanical testing showed that the tearing strength of the SPC is almost half an order higher that that of the original PLA film.
Microtiter Plate-Based Microfluidic Platforms: Sealing, Leakage Testing, and Performance of a 96-Well SPRI Device
Authors: Park D. S. , Hupert M. , Guy J. , Datta P. , Lee J.-B. , Witek M. , You B. H. , Soper S. A. , Nikitopoulos D. D. , Murphy M. C.
Published: April 2008

Highly parallelized biochemical analysis is a significant step toward achieving high throughput processing of patient samples for diagnosis and treatment monitoring. The standard microtiter plate is used to carry out multiple reactions for high throughput screening. By incorporating polymer microfluidic devices at each well in the microtiter plate format, the capability of the format could be significantly enhanced for high throughput processing of large numbers of biochemical samples in a cost-effective manner. Low cost replication of the microtiter plates is done using micro molding techniques, so microfabrication technology for making large area mold inserts (LAMIs) containing microfluidic devices at each well of a microtiter plate format is needed. A large area mold insert (LAMI) in the footprint of the standard microtiter plate was fabricated using an SU-8 based UV-LIGA technique. Excellent lithography results, with vertical sidewalls, were obtained by utilizing flycutting to minimize SU-8 film thickness variation and a UV filter for attenuating high absorbance UV wavelengths. Overplating of nickel in the SU-8 polymeric molds was used to make high quality metallic mold inserts with vertical sidewalls. Micro molding of polycarbonate (PC) was done using hot embossing, resulting in good replication fidelity over the large surface area. Thermal fusion bonding of the molded PC chips yielded good sealing results and the developed polymer microfluidic platforms showed good fluidic uniformity.
Utilizing Disk Shaped Thermistors to Experimentally Determine the Prandtl Number Dependence Ranging From Vapors to Liquids
Authors: Kobus Chris J. , Wu Dan , Guessous Laila
Published: April 2008

The current research utilizes disk-shaped thermistors to indirectly measure the convective heat transfer coefficient in the case of natural convection. Thermistors are resistors which have a resistance that is extremely temperature sensitive, so that experiments can be run with exceptional resolution. Not only can the convective heat transfer be indirectly measured, but so can the surface temperature, without the need for external temperature sensors which can interfere with the phenomena itself. Utilizing these themistors, heat transfer data was taken utilizing a variety of fluids from gasses (Pr = 0.72) to heavy oils (Pr ~ 1000). From the experimental data, it was shown that the classical Nusselt-Rayleigh type correlation does not accurately predict the Prandtl number dependence for this geometry, and a new dimensionless correlation is proposed.