bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Power Deposition Patterns for Single Pulse High Temperature Therapies With Temperature-Dependent Perfusion
Authors: Cheng Kung-Shan
Published: April 2008

The blood perfusion has been know to be an important factor of a thermal therapy, furthermore there were experiments shown that both normal tissue and tumor have different temperature-dependent perfusions. Since it has been shown by a recent study that the optimal power deposition patterns producing uniform tumor thermal dose distributions exist for thermal treatments ranging from the conventional hyperthermia to the high temperature therapy, this motivates performing a study on the optimal power deposition patterns for the high temperature therapy. This study showed that there are such optimal power deposition patterns for different tumor sizes by applying a 5-sec heating pulse with different out-tumor heat patterns even when the tumor and normal tissue both have different temperature-dependent perfusions. With this short heating, the optimal power patterns for temperature dependent perfusion models are almost identical to the corresponding constant perfusion models. In addition to this perfusion-independence, when tumor size is at least 4cm, even the treatment times from both perfusion models are almost the same. Furthermore, the simulations also showed that the optimal power deposition patterns are not sensitive to the out-tumor heating patterns, provided the heating applicator is not poorly focused. Results of the study motivate the thermal treatment community to perform more studies on the short-time high-temperature therapy to benefit these blood perfusion independences.
Cooling Limit Approach for Single-Pulse Thermal Therapies
Authors: Cheng Kung-Shan
Published: April 2008

Based upon the commonly used Sapareto-Dewey thermal dose formula, a thermal treatment is divided into four periods: 1) period-1 is from 37°C to 43°C, 2) period-2 is from 43°C to Tpeak, 3) period-3 is from Tpeak to 43°C, and 4) period-4 is 43°C to 38°C. A recent study derived a closed form thermal dose formula based on a combined term, the “effective cooling frequency,” revealed that one can determine the best performance of a thermal therapy by concentrating on the cooling periods: period-3 and period-4. As an extension, this study used a closed-form temperature solution to investigate the influences from both cooling terms (perfusion and thermal conduction) separately. The results determined the upper bound of the peak temperature for pulses with different focal sizes under different blood perfusion values. Under practical settings, no pulse should introduce peak temperature higher than 67°C to avoid overdosing when the desired thermal dose is 240CEM43°C. It also showed that pulses with focal size smaller than or equal to 4 mm benefit the perfusion independence for the following quantities: the upper bound on the peak temperature, the treatment size, and the time/temperature for which 90% thermal dose is accumulated. Thus the conduction dominates the cooling process for each single pulse heated by the highly focused SFUS applicators when the pulses are properly isolated temporally. Results from this study further provide an estimation of the closest distance between two pulses and the time/temperature to re-activate the consecutive pulses. Thus the results can guide the researchers to design more efficient treatment protocol for multiple-pulse thermal therapies.
Thermal Transport in Novel Silicon Transistors
Authors: Etessam-Yazdani Keivan , Liu Wenjun , Yang Yizhang , Asheghi Mehdi
Published: April 2008

This manuscript investigates the relevance and impact of nanoscale thermal phenomena in the state-of-the-art semiconductor device technologies such as: silicon-on-insulator (SOI), strained silicon, and tri-gate CMOS transistors. The experimental data and predictions for thin silicon layer thermal conductivity and the solutions of the Boltzmann transport equations (BTE) for phonon transport in strained-Si/Ge bi-layer configuration are used to estimate the thermal resistance of the SOI, tri-gate, and strained-silicon-on-SiGe-on-insulator (SGOI) transistors, respectively. In particular, the impact of SiGe underlayer and interface roughness on the lateral thermal conductivity of the silicon layer at room temperature is investigated. In order to avoid the complexity of the BTE for predictions of the temperature distribution, Lumped Analytical (LA) models are introduced that are simple to implement and also adequate enough to capture the sub-continuum effects. It is concluded that the SOI, SGOI and tri-gate transistors are all susceptible to self-heating for very thin silicon device layers.
Modeling of Screw-Plate Systems for Mandibular Fracture Repair
Authors: Chaudhary Naresh , Lovald Scott , Wagner Jon , Khraishi Tariq , Kelly James , Wood John
Published: April 2008

Fractures of the mandible are a common form of traumatic injury. These fractures may be repaired using miniplates secured to cortical bone with screws. In the present research, the authors measure the pull-out strengths of cortical screws using a standard test paradigm and develop a finite element model to analyze forces acting on these screws. Pull-out strengths are measured in a tri-laminate synthetic material that mimics the cortical layers and cancellous bone of the mandible. A finite-element (FE) model is developed to analyze the mechanics of deformation of the model bone during the pullout process. Issues that are important for the proper modeling of both normal and fractured mandibles are also considered.
Mathematical Clothing Modeling in a Digital Human Environment
Authors: Man Xiaolin , Swan Colby C.
Published: April 2008

A new motivation for mathematical clothing modeling, namely to quantify the impact of clothing on digital human models in virtual environments, is discussed. After a brief review of previous mathematical clothing modeling works, a nonlinear finite element approach with contact is exercised with good results on a variety of draping problems. A micromechanical approach for predicting fabric effective mechanical properties based on fiber properties and texture is proposed.
Method for Generating 3D-Viewing Window for Web-Based E-Catalog
Authors: Lee Deuk-Hee , Park Sehyung , Ha Sungdo , Lee Yunyeong
Published: April 2008

This paper presents a framework-based procedure to generate three-dimensional electronic catalogs (3d e-catalogs), which link three-dimensional viewing windows (3d viewing windows) to e-catalogs. The 3d viewing windows include the three-dimensional interactive and event-driven objects (3d objects) of products for e-catalogs; the 3d viewing windows view and manipulate the 3d objects. The framework provides users with the template models of 3d viewing windows and 3d objects; the template model of a 3d viewing window is defined in HTML and the template model of a 3d object is defined in VRML. Users will specify the components of the template models, and complete the 3d viewing windows including the 3d objects of the new products to be displayed in 3d e-catalogs. In addition, the framework presents the way to get hierarchical 3d models from CAD models of products.
Neural Nets and Optic Flow for Autonomous Micro-Air-Vehicle Navigation
Authors: Oh Paul Y. , Green William E. , Barrows Geoffrey
Published: April 2008

Reconnaissance, surveillance and target acquisition tasks in near-Earth environments like forests, caves, tunnels and buildings is a grand challenge. Micro-air-vehicles are a future line of bird-sized flying assets designed to address such a challenge. Needed are light-weight and miniature sensor suites that can provide autonomous collision avoidance in complex environments. Our demonstrations with optic flow microsensors have been promising but controller gain-tuning is often tedious. This paper describes the use of neural nets to automate gain tuning. The overall effect delivers collision avoidance over wide ranges of lighting conditions, contrast and surface textures.
A Monolithic Micro Four-Bar Mechanism With Flexure Hinges
Authors: Lee Sang-Joon John , Yee Raymond K. , Kelley Reginald , Martin Roy , Sadaka Alain , Hsu Tai-Ran
Published: April 2008

A monolithic micro four-bar mechanism was fabricated in silicon to examine motion amplification as well as the effect of non-ideal geometric profiles in its flexure hinges. Through-wafer deep reactive ion etching (DRIE) was used to produce high-aspect-ratio flexure joints that allow compliant motion within the plane of a silicon wafer. The flexures were approximately 20 microns wide and 530 microns deep, micromachined through the entire wafer thickness. A taper angle of approximately 0.5 degree narrowing toward the bottom of the wafer was measured in the flexure cross section. A finite element model was developed to predict the output rotation of one link in response to the displacement applied at the drive link. For a 1-micron linear input, the model predicted a 0.39-degree angular displacement for the output link. This showed close agreement with experimental data that measured 0.41 degree. An enhanced finite element model that accounted for the tapered cross-section, however, predicted a slightly smaller input/output relation of 0.37 degree per micron.
Thin Film In-Plane Silicon Thermal Conductivity Dependence on Molecular Dynamics Surface Boundary Conditions
Authors: Gomes Carlos J. , Madrid Marcela , Amon Cristina H.
Published: April 2008

The in-plane thermal conductivity of thin silicon films is predicted using equilibrium molecular dynamics, the Stillinger-Weber potential and the Green-Kubo relationship. Film thicknesses range from 2 to 200 nm. Periodic boundary conditions are used in the directions parallel to the thin film surfaces. Two different strategies are evaluated to treat the atoms on the surfaces perpendicular to the thin film direction: adding four layers of atoms kept frozen at their crystallographic positions, or restraining the atoms near the surfaces with a repulsive potential. We show that when the thin-film thickness is smaller than the phonon mean free path, the predictions of the in-plane thermal conductivity at 1000K differ significantly depending on the potential applied to the atoms near the surfaces. In this limit, the experimentally observed trend of decreasing thermal conductivity with decreasing film thickness is predicted when the surface atoms are subject to a repulsive potential in addition to the Stillinger-Weber potential, but not when they are limited by frozen atoms.
Fluid Dynamics in a Hemodialysis Graft
Authors: Lee Sang-Wook , Loth Francis , Fischer Paul F. , Grogan Jennifer K. , Bassiouny Hisham S.
Published: April 2008

Arteriovenous (AV) grafts for hemodialysis access typically have a high flow rate environment which creates significant pressure and velocity fluctuations downstream of venous anastomosis. We investigate a blood flow dynamics using direct numerical simulation within a subject-specific geometry with pulsatile flow conditions based on animal study. The irregularity of local geometry creates disturbed flow patterns and breaks the symmetry. This study demonstrates the importance of accurate representation of subject-specific geometry and realistic flow inlet conditions.
A Cam-Controlled, Single Actuator-Driven Leg Mechanism for Legged Vehicles
Authors: Wan Xiaonan , Song Shin-Min
Published: April 2008

Leg design is crucial to the performance of a legged vehicle. To achieve good walking efficiency, a leg should be able to generate a horizontal straight line by a single actuator in the walking phase. In the return phase, additional actuator(s) is used to lift and place the foot. In this paper, a study of a cam-controlled, single-actuator-driven leg is presented. It does not require additional actuator for the return motion. In addition, the legs are driven by continuous, constant speed rotary input and they move in a constant speed. Therefore, it is conceivable that the legged vehicle can be driven by a traditional rotary engine. The cam curve is designed to have connectivity of third derivative (jerk). The driving torque is analyzed. The gait and stability related to such leg mechanism are discussed. This leg mechanism has the potential to be the leg of a practical and affordable walking machine.
Fire Suppression in Microgravity: Dynamics of a Polydispersed Water Mist Around an Obstacle
Authors: Lewis S. J. , Delplanque J.-P.
Published: April 2008

The work presented here aims at characterizing the dynamics of water mist during fire suppression events in cluttered spaces. To this end, a numerical model for a polydispersed water-mist is used. A sectional approach is used to describe the mist behavior. The distributions of the parameters characterizing the mist (size, speed, and direction at injection) are discretized in classes, and they are chosen using a Monte Carlo method. The fate of the droplets in each class is determined by calculating the history of a representative droplet for each class using a Lagrangian approach. The dynamics of the representative droplets and their heat and mass transfer histories are tracked. An extended-film model is used to evaluate droplet evaporation. This mist model interacts in a one-way coupled manner with a pre-calculated flow field around hot obstacles.
Structural Design Optimization of Side/Rear Impact Guards Using a Coupled Genetic Algorithm Finite Element Method
Authors: Liu De-Shin , Lin Nan-Chun , Huang Chao-Chin , Meng Yin-Lee
Published: April 2008

Underride protective structure can reduce serious injures when passenger cars collide with the rear end or side of the heavy vehicle. This paper describes the use of Genetic Algorithm (GA) coupled with a dynamic, inelastic and large deformation finite element (FE) code LS-DYNA to search optimal design of the Side/Rear impact guards. In order to verify the accuracy of the FE model, the simulation results were compared with real experiments follow with the regulation ECE R73. The validated FE model then used to study the optimal design base on under running distance and total amount of energy absorbing capacity. The results from this study shown that this newly developed method not only can found multi-objective design parameters but also can reduce computational time significantly.
Generalized Prediction for Subcooled Water Flow Boiling CHFs Versus Outlet Subcoolings for Flow Velocities at Outlet Pressures in Various Tubes
Authors: Sakurai Akira , Fukuda Katsuya
Published: April 2008

The mechanisms and corresponding correlations for the subcooled water flow boiling CHFs for outlet subcoolings in a vertical tube having an inside diameter, D, and length-to-diameter, L/D, ratio for a flow velocity with outlet pressure as a parameter were previously clarified by the authors based on the existing flow boiling CHF data measured using the tubes having the diameters ranging from 0.4 to 12 mm, and the L/D ratios ranging from 2.4 to 96.6 for the flow velocities ranging from 5 to 130 m/s, at the pressures ranging from 0.34 to 17.2 MPa. Namely the CHF, qcr,sub, versus outlet subcooling, Δsub,out, for a flow velocity with outlet pressure as a parameter were divided into four regions for outlet subcoolings: first the CHF decreased down to minimum one (first region), secondly it increased up to maximum one (second region), thirdly it decreased down to minimum one (third region), and finally it again increased monotonously with an increase in outlet subcooling. The CHFs belonging to third region became significant with a decrease in diameter for the smaller tubes with diameters such as around 1 mm, and on the other hand, those almost disappeared with an increase in diameter for the larger tubes with the diameters such as around 9 mm. The CHFs belonging to second region significantly depending on the pressure and tube diameter, and those belonging to fourth region being almost independent of the pressure, and tube inside diameter, D, and length-to-diameter, L/D, ratio were well expressed by the unified subcooled water flow boiling CHF correlations representing the CHF resulting from the hydrodynamic instability, HI, and those representing the CHF resulting from the heterogeneous spontaneous nucleation, HSN, on the inside surface near the exit of heated tube respectively. In the present paper, the generalized evaluation of the maximum qcr,sub of the qcr,sub data belonging to 2nd region resulting from the HI unsolved before was realized solving the simultaneous equations consisted with the unified qcr,sub correlation representing qcr,sub resulting from the HI previously derived and the generalized correlation for the Δsub,out,max at corresponding qcr,sub,max newly derived.
Mixed-Model Assembly Quality: An Approach to Prevent Human Errors
Authors: Cheldelin Brent , Ishii Kosuke
Published: April 2008

Mixed-model production is the manufacture of similar products on a single assembly line (see Fig. 1). This assembly technique is gaining popularity in a multitude of production environments. Benefits of this include: reduced investment costs, reduced fluctuation in production due to customer demand, and smaller production facilities. For some world-class manufacturers, mixed-model production also causes increased commonality amongst products on each assembly line thus leading to reduced inventory levels and number of stock-keeping units (SKU). However, a systematic approach is lacking in most companies leading to an increase in human assembly errors due to the increase in process complexity. In response, many companies focus on automation, lean-manufacturing, and JIT parts delivery along with other forms of technology and error-proofing devices. Unfortunately, there are two problems with this approach. First, how does a company with low production volume justify the investment in automation, technology, and error-proofing devices to alleviate these types of errors? Second, employing these fixes after the problems exist leads to sub-optimal designs. With product life-cycles shrinking (Shibata, 2001) and development times shortening even more severely (see Fig. 2), companies cannot afford to fix problems after they find them in production. Companies need to address the problem in the design stage. The authors propose a multi-phase approach to managing mixed-model assembly errors in low to mid-volume assembly environments. First, companies should employ mixed-model FMEA during preliminary design to drive commonality and eliminate errors at the systems level. Second, a geometry-based comparison function based off CAD system data that can identify similar parts during detailed design is needed. An automated comparison technique alerts the designer to potential assembly problems of individual parts. Third, when parts must be physically similar, this information must be transferred to manufacturing so appropriate technologies are employed to error-proof the assembly operation.
Virtual Automated Transit System (VATS) and Intelligent Transportation Systems (ITS) Application to Intermodal Freight Movements in Northeastern Illinois
Authors: Amirouche Farid , Mahmudi Khurram , Zavattero David
Published: April 2008

This paper addresses the issues faced by local and state governments concerning increasing traffic congestions, inadequate roadway design and traffic safety problems caused by the freight truck traffic; on the other hand, the freight industry is seeking to improve productivity by having easy access and direct routes between the intermodal facilities and the interstate highway system.
A Novel Self-Aligned Microcoil Formation for Magnetic Actuator Applications
Authors: Chang Hung-Pin , Lin Jason , Chang Ruisheng , Lin Puo-Han , Bachman Mark , Reinicke Bob , Barbarits Joe , Li G. P.
Published: April 2008

A novel self-aligned lithographic technique has been developed to overcome difficulties in forming a high resolution, high aspect-ratio electroforming in polymer molds. This technique is capable of building a micro coil device with high-density, high aspect-ratio features, which is useful for magnetic actuator applications. The relatively straightforward technique has excellent potential for scaling to batch manufacturing.
Buoyancy Driven Microfluidics
Authors: Chen Z. , Qian S. , Wang J. , Bau H. H.
Published: April 2008

It is not surprising that the use of buoyancy as a driving force in microfluidic systems has attracted little or no attention. Buoyant forces are proportional to the volume and do not scale favorably as the device size is reduced. Nevertheless, in certain biotechnological applications, one can produce sufficiently large buoyancy forces to generate fluid motion at velocities on the order of mm/s even in conduits with equivalent diameters of a few hundreds of microns. One example is the thermal polymerase chain reaction (PCR) for DNA amplification. In this process, the reagents’ temperature varies from about 55°C to 94°C. Such large temperature variations can induce significant buoyant forces. Another class of systems that can be driven by buoyant forces is rotating laboratories on a chip (lab on a CD). In such laboratories, large centrifugal accelerations may induce significant buoyant forces even when the temperature variations are relatively small. These temperature variations can be used to propel and control fluid flow.
Mechanical Properties of Matrix Hybrid Thick-Composites
Authors: Hamada Hiroyuki , Nakai Asami , Eto Kazuya , Sugimoto Kenichi
Published: April 2008

For the purpose of more safety boats, the large thickness of outer plates is required to increase flexural stiffness, strength and impact properties. Some problems in mechanical properties are generated by increasing in thickness because the effect of interlaminar shearing of Thick-composites on whole mechanical properties is greater than that of thin-composites. We have investigated the matrix hybrid composite with two kinds of unsaturated polyester, one was hard type resin with low toughness and the other was flexible type resin with low modulus and high toughness. In this study, matrix hybrid composite was focused and applied to Thick-composites. First, the flexural properties were investigated and the micro fracture progress was precisely observed with in-situ observation using replica method. Then, impact properties of the Thick-composites were examined and the availability of matrix hybrid composite was investigated. It was concluded that the matrix hybrid composite achieved high performance in both static and impact load.
Applying Functional Modeling as a Unifying Basis for Design for Six Sigma Execution
Authors: Hutcheson Ryan S. , Donndelinger Joseph A. , McAdams Daniel A. , Stone Robert B.
Published: April 2008

This paper explores the applicability of the most recently developed methods in functional modeling to Design for Six Sigma transfer function development and requirements flowdown. An example created during a collaborative research project between the General Motors R&D Center and the University of Missouri – Rolla is used to demonstrate the benefits of using standardized functional modeling during conceptual design. The proposed standard for creating the functional models is the Functional Basis. The Functional Basis is a list of function and flow terms that can be used to describe electro-mechanical systems. The example presented in this paper is based on the parking brake system of a passenger car. Module heuristics, function-based rules for partitioning systems, were used to define the sub-systems during the requirements flowdown example. The functional modeling techniques used in this example provide a standard method of capturing current engineering design knowledge while allowing additional knowledge to be discovered.
Models for Reliability of Fine-Pitch BGAs and CSPs in Shock and Drop Impact
Authors: Lall Pradeep , Panchagade Dhananjay , Liu Yueli , Johnson Wayne , Suhling Jeff
Published: April 2008

Drop-induced failures are most dominant in portable electronic products. In this study, explicit finite element models have been used to study the transient dynamics of printed circuit boards during drop from 6 ft. Methodologies for modeling components using smeared property formulations have been investigated. Reduced integration element formulations examined include – shell and solid elements. Model predictions have been validated with experimental data. Results show that models with smeared properties can predict transient-dynamic response of board assemblies in drop-impact, fairly accurately. High-speed data acquisition system has been used to capture in-situ strain, continuity and acceleration data in excess of 1 million samples per second. Ultra high-speed video at 40,000 fps per second has been used to capture the deformation kinematics. Component types examined include – plastic ball-grid arrays, tape-array BGA, QFN, and C2BGA. Model predictions have been correlated with experimental data. Impact of experimental error sources on model correlation with experiments also has been investigated.
Prognosis Methodologies for Health Management of Electronics and MEMS Packaging
Authors: Lall Pradeep , Islam Nokibul , Rahim Kaysar , Suhling Jeff
Published: April 2008

The current state-of-art in managing system reliability is geared towards the development of life-prediction models for unaged pristine materials under known loading conditions based on relationships such as the Paris’s Power Law [Paris, et. al 1960, 1961], Coffin-Manson Relationship [Coffin 1954; Tavernelli, et. al. 1959; Smith, et. al. 1964; Manson, et. al. 1964] and the S-N Diagram. There is need for methods and processes which will allow interrogation of complex systems and sub-systems to determine the remaining useful life prior to repair or replacement. This capability of determination of material or system state is called “prognosis”. In this paper, a methodology for prognosis-of-electronics has been demonstrated with data of leading indicators of failure for accurate assessment of product damage significantly prior to appearance of any macro-indicators of damage. Proxies for leading indicators of failure have been developed including – micro-structural evolution characterized by average phase size and interfacial stresses at interface of silicon structures. Structures examined include – electronics package, MEMS Packages and interconnections on a metal backed printed circuit board typical of electronics deployed in harsh environments. Since, an aged material knows its state the research presented in this paper focuses on enhancing the understanding of material damage to facilitate proper interrogation of material state. Mathematical relationship has been developed between phase growth rate and time-to-1-percent failure to enable the computation of damage manifested and a forward estimate of residual life.
A New Method for the Solder Ball Pull Test Using a Shape Memory Alloy Tube
Authors: Lo Jeffery , Lau Dennis , Lee S. W. Ricky , Chan Simon , Chan Frank , Chau K. C.
Published: April 2008

The solder ball shear test is a commonly used method to evaluate the attachment strength of solder balls. However, some previous studies indicated that the solder ball shear test may not be suitable for showing the effect of intermetallic compound (IMC) growth due to thermal aging. This is because the IMC layer is thin and not susceptible to the shear loading. Since the IMC layer consists of brittle materials, the ball pull test should be a better method to evaluate the solder ball attachment strength. The major challenge of conducting a solder ball pull test is how to grip the solder ball. This paper presents an innovative method for conducting the solder ball pull test. A shape memory alloy (SMA) tube is used to grip the solder ball and pull it off from the substrate. The inner diameter of the SMA tube is originally smaller than the diameter of the solder ball under testing. Once the temperature is raised to higher than the switching temperature of SMA, the SMA tube will expand radially, resulting an inner diameter larger than the solder ball. After the SMA tube cools down, the tube contracts and grips the solder ball firmly. The solder ball can then be pulled off from the attached substrate by frictional force. A prototype of the aforementioned solder ball pull test device has been developed. Some preliminary testing results are presented in this paper.
Enhanced DMFC Performance via Electro-Hydraulic Pulsing
Authors: Haynes Comas , Leahy Scott , Lay Leonard , McCarthy Larry , Parekh David
Published: April 2008

Direct methanol fuel cells (DMFCs) are an attractive fuel cell choice option, particularly because of the capability to use liquid fuel without need for processing. The phenomenon of methanol crossover, however, substantially reduces cell power output and efficiency. The present work shows the benefits of periodically pulsed fuel supply and current load on the performance of a DMFC. It is determined that the enhanced performance resultant from such electro-hydraulic (EH) pulsing is realized due to temporary, cyclic mitigations of methanol crossover (as well as unstably high voltages given high frequency electronic pulsing).
Phonon Band Structure and Thermal Transport Correlation in a Two-Atom Unit Cell
Authors: McGaughey A. J. H. , Hussein M. I. , Kaviany M. , Hulbert G. M.
Published: April 2008

The phononic band structure and thermal conductivity of a family of a two-atom unit cell Lennard-Jones crystals are predicted using molecular dynamics simulations. The structure consists of alternating layers of atoms with different masses, leading to anisotropic thermal properties. An increase in the mass ratio results in an increase in the width of the band gap and a decrease in the value of its central frequency. The thermal conductivity decreases with an increase in the mass ratio, and in all cases is lower than that for a monatomic unit cell. The thermal conductivity increases with an increase in the ratio of the central gap frequency to its width. The rate of this increase decreases and becomes less temperature-dependent at lower mass ratios. The results could be utilized towards the development of guidelines for the design of materials with extreme thermal transport properties.
MEMS Based High Sensitivity Calorimetry
Authors: Zhang Shu , Yang Yizhang , Barmak Katayun , Rabin Yoed , Asheghi Mehdi
Published: April 2008

The fundamental study of phase transformations continues to be a key for successful implementation of metals and alloys in micro- and nano-scale structures in integrated circuitry and magnetic recording devices and systems. The thermodynamic and thermokinetic properties of extremely thin layers can be altered due to the relative effect of boundaries and interfaces on the volume of the material. Calorimetry at the nano-scale requires measurement sensitivity on the order of 1 nJ or better, which requires improved thermal design, development of thermal modeling, and development of experimental measurement techniques. In this report, the specific heat of 144 nm thick CoFe layer is measured, using frequency-domain Joule heating and thermometry (3ω-technique), on Cu/SiO2 and Cu/SiO2/CoFe suspended bridges. Analyses of the heat transfer in suspended structures are performed to establish guidelines for design and fabrication of small-scale differential scanning calorimeters.
Investigation of Fractional Characteristic of Molecular Motion by Molecular Dynamics Simulation
Authors: Liu Chao , Wan Liming , Zhang Xinming , Zeng Danling
Published: April 2008

Molecular dynamics simulation (MDS) is adopted to investigate the characteristic of fractional motion of molecules in liquid phase, vapor phase and liquid-vapor interface in the paper. Based on the theory of mean free path and Shannon sampling theorem, the way to determine a universal criterion of time step of simulation is presented. It is shown that there exists difference in the regular pattern of molecular motion in the state of liquid and vapor phase. The fractional features are different for different matter states. Under the condition of same temperature, the characteristic fractional number of molecular motion in liquid state is greater than one in vapor state. It is shown that the fractional dimension numbers in the X, Y and Z direction of the liquid-vapor interface are different. This proves that the liquid-vapor interface has anisotropic character.
Comparison of Thermomechanical and Stress Wave Induced Laser Repair Techniques for Stiction-Failed Microcantilevers
Authors: Koppaka Sai B. , Mackin Thomas J. , Phinney Leslie M.
Published: April 2008

Surface micromachined structures with high aspect ratios are often utilized as sensor platforms in microelectromechanical systems (MEMS) devices. These structures generally fail by stiction or adhesion to the underlying substrate during operation, or related initial processing. Such failures represent a major disadvantage in mass production of MEMS devices with highly compliant structures. Fortunately, most stiction failures can be prevented or repaired in a number of ways. Passive approaches implemented during fabrication or release include: (1) utilizing special low adhesion coatings and (2) processing with low surface energy rinse agents. These methods, however, increase both the processing time and cost and are not entirely effective. Active approaches, such as illuminating stiction-failed microstructures with pulsed laser irradiation, have proven to be very effective for stiction repair [1–5]. A more recent and promising method, introduced by Gupta et al. [6], utilized laser-induced stress waves to repair stiction-failed microstructures. This approach represents a logical extension of the laser spallation technique for debonding thin films from substrates [7–9]. The method transmits stress waves into MEMS structures by laser-irradiating the back side of the substrate opposite the stiction-failed structures. This paper presents an experimental study that compares the stress wave repair method with the thermomechanical repair method on identical arrays of stiction-failed cantilevers.
Design of Fuzzy Logic-Based Controller in Roll Grinding System With Double Regenerative Chatter
Authors: Yuan LiHong , Ja¨rvenpa¨a¨ V. M. , Keskinen Erno
Published: April 2008

This paper proposes application of fuzzy logic control (FLC) to do vibration control for the roll-grinding machine system with double regenerative chatter. In this paper, a multiple-degree-of-freedom (MDOF) model is developed to represent the dynamics behaviors of this kind of system. The dynamic system has double delays and lumped cutting parameters which make vibration control challenging. Numerical simulation shows that FLC can dramatically reduce the vibration levels compared to a convention control method.
Correlation of Heat Transfer Data to Film Thickness Data of the Thin Film Found in Spray Cooling
Authors: Pautsch Adam G. , Shedd Timothy A.
Published: April 2008

As electronic circuit design and packaging technology progresses, the density and power levels of electronic components is increasing at a nearly exponential rate. The higher heat loads dissipated by these devices are nearing the limits of traditional cooling techniques. One method capable of removing heat fluxes as high as 100 W/cm2 is spray cooling. This process involves the impingement of liquid droplets onto a heated surface, forming a thin two-phase film. In order to create reliable models of the heat transfer during spray cooling, the behavior of the film must be understood. This paper presents an investigation into the behavior of the thin film found in spray cooling. A study was performed to relate experimental measurements of the heat transfer coefficients to experimental measurements of film thickness as they vary spatially over a die surface. Both a single nozzle and a multi-nozzle array were investigated. Measured heat transfer coefficients ranged from 0.2 to 1.2 W/m2K and film thicknesses ranged from 90 to 300 μm.
Investigating Methods of Heat Recovery From Low-Temperature PEM Fuel Cells in CHP Applications
Authors: Jalalzadeh-Azar Ali A.
Published: April 2008

Heat recovery from low-temperature proton exchange membrane (PEM) fuel cells poses a number of challenges. In response to these challenges, thermodynamic assessments of proposed heat recovery methods are studied in the context of combined heat and power (CHP) for building applications. Preheating combustion air in conjunction with desiccant dehumidification and absorption cooling technologies is one of the two strategies examined in this study. The other approach integrates the PEM fuel cell with a water-loop heat pump (WLHP) for direct heat recovery. As the primary objective, energy-saving potentials of the adopted heat recovery strategies are estimated with respect to various benchmarks. The quantified energy-saving potentials are translated into effective CHP performance indices and compared with those typically specified by the manufacturers for service hot water applications. The need for developing CHP performance protocols is also discussed in light of the proposed energy recovery techniques—thereby, accomplishing the secondary objective.
Computational Fluid Dynamics and Solid Mechanics Analyses of a Patient-Specific AAA Pre- and Post-EVAR
Authors: Scotti Christine M. , Finol Ender A. , Viswanathan Siddharth , Shkolnik Aleksandr , DiMartino Elena S. , Vorp David A. , Amon Cristina H.
Published: April 2008

The establishment of a new pathway for blood flow immediately following endovascular aneurysm repair (EVAR) results in morphological changes and remodeling of the aneurismal sac. While EVAR is a minimally invasive surgical intervention, failure of the endovascular graft (EVG) may occur in which there is downstream migration and endoleak formation, creating a repressurization of the aneurismal sac and an increased risk of rupture. While the mechanism of aneurysm rupture and EVG failure is fundamental in nature, the factors that most significantly contribute to the end result are not yet fully understood. Mechanically, both are the consequence of an exerted force or disturbance exceeding the strength of a given material, whether it is the aneurismal arterial wall or the interaction that exists between the graft and wall. Embedded within this causal relationship are the contributions of arterial wall remodeling, intraluminal thrombus formation, and the dynamics that exists within the lumen. Several studies have been performed to examine these factors individually as they affect shear stress, the development of vortices, and the mechanical stress experienced along the arterial wall. However, a complete investigation is needed to study an anatomically realistic geometry operating under physiological conditions. The computational analyses conducted in this investigation address the confluence of these factors as they are modeled within an accurate patient-specific abdominal aortic aneurysm (AAA) reconstructed from CT scan data prior to and after EVAR. Our results verify the pressure-dominated characteristic of the flow and the negligible contribution of the dynamic and frictional force components; both are in good agreement with previously published results for analytical estimation of flow-induced forces in EVGs. [1]
Fluid-Coupled Vibrations of Immersed Spent Nuclear Racks: A Nonlinear Model Accounting for Squeeze-Film and Dissipative Phenomena
Authors: Moreira Miguel , Antunes Jose´
Published: April 2008

Fluid-coupling effects lead to a complex dynamical behavior of immersed spent fuel assembly storage racks. Predicting their responses under strong earthquakes is of prime importance for the safety of nuclear plant facilities. In the near-past we introduced a simplified linearized model for the vibrations of such systems, in which gap-averaged velocity and pressure fields were described analytically in terms of a single space-coordinate for each fluid inter-rack channel. Using such approach it was possible to generate and assemble a complete set of differential-algebraic equations describing the multi-rack fluid coupled system dynamics. Because of the linearization assumptions, we achieved computation of the flow-structure coupled modes, but also time-domain simulations of the system responses. However, nonlinear squeeze-film and dissipative flow effects, connected with very large amplitude responses and/or relatively small water gaps, cannot be properly accounted unless the linearization assumption is relaxed. Such is the aim of the present paper. Here, using a similar approach, we generalize our theoretical model to deal with nonlinear flow effects. Besides that the proposed methodology can be automatically implemented in a symbolic computational environment, it is much less computer-intensive than finite element formulations. Using the proposed technique, computations of basic flow-coupled rack configurations subjected to impulse excitations are presented, in order to highlight the essential features of such systems as well as the relevance of squeeze-film and dissipative effects. Finally, more realistic simulations of complex system responses to strong seismic excitations are presented and discussed.
Rapid Consolidation of TiB2 via Plasma Pressure Compaction
Authors: Kothari Kunal B. , Wereley Norman M. , Radhakrishnan Ramachandran
Published: April 2008

This paper reports on the microstructure and mechanical properties of titanium diboride (TiB2) consolidated by plasma pressure compaction (P2C)*. Titanium diboride powder with 2.5 wt% of silicon nitride (Si3N4) used as a sintering aid was rapidly consolidated via P2C at 1500°C. This rapid consolidation process inhibits grain growth and ensures high strength and ductility of the consolidated material. Microstructure of the consolidated material was characterized via optical microscopy, scanning electron microscopy and wavelength dispersive spectroscopy. The consolidated specimens showed 93.5% densification with no apparent porosity. The morphology of the consolidated sample as studied by chemical composition analysis was found to be similar to that of the powder. The flexure strength, fracture toughness, Young’s modulus and Vicker hardness of the consolidated specimens were measured at room temperature. The mechanical properties were found to be equivalent if not superior to the typical mechanical properties reported in the literature.
Two-Dimensional Thermal Performance Analysis of a Semi-Transparent Spectral Zirconia Thermal Barrier Coating
Authors: Uppu Nalini , Mensah Patrick F. , Diwan Ravinder
Published: April 2008

The performance of an aero engine can be increased in two ways: one by reducing the air requirement for the cooling of the turbine blades and secondly by increasing the turbine inlet temperature (TIT) that is operating temperature of the turbine blades. Taking into account the latter approach the blade material must withstand high temperatures of above 1350°C. For this enhancing purpose, protective coatings called the thermal barrier coatings (TBC) are being employed. The thermal barrier coating mainly consists of two layers; one is the metallic coating MCrAlY, which is the premiere layer over the substrate Ni based super alloy. The other is the ceramic layer made of Yttria Stabilized Zirconia (YSZ). Apart from these two layers, an intermediate layer of Al2O3 is formed by the oxidation of the aluminum in MCrAlY called the diffusion layer which also enhances the adhesion between the two layers. M stands for Nickel or Cobalt. The present study is an investigation on the in-situ thermal performance of TBCs by considering the ceramic layer as a semi-transparent media and varying its thickness and simultaneously increasing the operating temperature on its other boundary surface. The above thermal boundary value problem is modeled in 2-dimensions and solved numerically using the discrete ordinate model for radiative heat transfer in a commercial computational fluid dynamics and heat transfer software. Two samples of Ni based super alloy substrate with dimensions 40 × 100 × 3mm are considered; one sample with a thickness of 0.25 mm ceramic layer and the other sample with 1 mm coating thickness for transient thermal analysis. Simulated transient temperature histories are presented for use in a thermo-mechanical analysis in order to predict the failure modes in the TBC. The temperature distribution in TBC coating mainly depends on the radiative effects combined with heat conduction and convection and radiation at the material boundaries.
An Economic Analysis Model With Environmental Strategies Embedded for End-of-Life Management of Electronic Products
Authors: Yuan Chris Y. , Zhang Hong Chao
Published: April 2008

With huge amount of electronic products becoming obsolete each year, more and more Original Equipment Manufacturers (OEMs) and recycling companies engage in economic pursuits from the End-of-Life (EOL) management of the electronic wastes, while the increasing environmental concerns from society and governmental agencies ask for proper considerations of environmental strategies during the EOL management process to reduce the environmental impact of these electronic products. This paper proposes an economic analysis model with environmental strategies embedded for the management of EOL electronic products, in which both economic and environmental factors are well considered. The purpose of this model is to help OEMs and recyclers in economic and environmental analysis of their EOL management processes.
Solidification and Melting of Gallium in the Presence of Magnetic Field: Experimental Simulation of Low Gravity Environment
Authors: Charmchi M. , Zhang H. , Li W. , Faghri M.
Published: April 2008

Phase change in a simulated low gravity environment is the central topic of this research work. The application of a transverse magnetic field gives rise to Lorentz forces that can dampen the convective flows especially the buoyancy driven flows. The flow suppression depends on a dimensionless parameter namely the Hartmann number. This paper presents the experimental results for sidewall solidification and melting and therefore, addresses the fixed solid phase conditions. Gallium is used as phase change material (PCM) and both melting and solidification processes are investigated. The effects of an applied magnetic field on phase change rate and on the shape of the solid/melt interface are studied. The solid thickness is measured via ultrasonic techniques and the solid/melt interface is mapped using florescent light shadowgraphy through a transparent window. The presented data consist of temperature history, ultrasonic detection of the interface, florescent light shadowgraphy and solid phase volume fraction. The presence of the magnetic field had a marked effect on melting and natural convection whereas; phase change convection was noticeable in the solidification cases.
Analysis of Homogeneous Charge Compression Ignition (HCCI) Engines for Cogeneration Applications
Authors: Aceves Salvador M. , Martinez-Frias Joel , Reistad Gordon M.
Published: April 2008

This paper presents an evaluation of the applicability of Homogeneous Charge Compression Ignition Engines (HCCI) for small-scale cogeneration (less than 1 MWe) in comparison to five previously analyzed prime movers. The five comparator prime movers include stoichiometric spark-ignited (SI) engines, lean burn SI engines, diesel engines, microturbines and fuel cells. The investigated option, HCCI engines, is a relatively new type of engine that has some fundamental differences with respect to other prime movers. Here, the prime movers are compared by calculating electric and heating efficiency, fuel consumption, nitrogen oxide (NOx) emissions and capital and fuel cost. Two cases are analyzed. In Case 1, the cogeneration facility requires combined power and heating. In Case 2, the requirement is for power and chilling. The results show that HCCI engines closely approach the very high fuel utilization efficiency of diesel engines without the high emissions of NOx and the expensive diesel fuel. HCCI engines offer a new alternative for cogeneration that provides a unique combination of low cost, high efficiency, low emissions and flexibility in operating temperatures that can be optimally tuned for cogeneration systems. HCCI engines are the most efficient engine technology that meets that oncoming 2007 CARB NOx standards for cogeneration engines. The HCCI engine appears to be a good option for cogeneration systems and merits more detailed analysis and experimental demonstration.