bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric Properties of Er-Doped HfTiO Films for High-K Gate Stacks
Authors: Li Xianfei , Wu Ping , Wang Hui , Pei Yili , Chen Sen , Zhang Shiping
Published: August 2012

HfTiErO and HfTiO thin films (∼50nm), as potential replacements for traditional SiO2 gate dielectric materials, were prepared on n-Si (100) substrates by radio frequency magnetron sputtering. The dielectric characteristics of HfTiErO were compared with those of HfTiO. The structure of HfTiErO was analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The growth of HfTiErO and HfTiO were observed by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Experimental results indicate that as the Er content increases, the dielectric constant (k) can increase to the maximum (∼20.2) and then decrease. In comparison with HfTiO, HfTiErO films (the atomic ratio of Hf:Ti:Er was 1:0.16:0.10) can exhibit a higher relative permittivity (increasing by 54% compared with HfTiO), a smoother interface, a better surface microscopy and a lower interface trap density in C-V curves.
Experimental Investigation of EHD Flow Regimes Map in an Electrostatic Air-Oil Droplets Separator
Authors: Kong Xiangling , Alshehhi Mohamed , Goharzadeh Afshin
Published: August 2012

The applications of ESPs in liquid droplets separation have not been implemented thoroughly as in dust separation. In this paper, flow visualization measurements of the electrohydrodynamic (EHD) flow field in a narrow wire-plate electrostatic precipitator (ESP) were conducted when the primary gas flow was seeded with oil droplets with average diameter of 2μm. The EHD flow field was visualized under wide range of operating conditions by a high speed camera. The tested gas velocities were from 0 to 0.5m/s, and a positive DC voltage varying from 0 to 16kV was applied to the ESP. Experimental results clearly confirmed formation of the secondary flow and the EHD flow patterns changed significantly during corona discharge, depending on the gas velocity and applied voltage. Six typical EHD flow patterns were summarized based on the visualization and an EHD flow regime map was plotted against Reynolds number (Re) and electrohydrodynamic number (Ehd), which represents the relationship between inertial forces and electrical forces. The EHD flow structures were pronounced for high applied voltage (high Ehd) and low gas velocity (low Re) and the primary flow acted to suppress the formation of EHD flow. The EHD flow patterns obtained with oil droplets showed different characteristics, compared to EHD flow with solid particles from previous studies, when both electrics and inertial forces are weak. The high adhesive forces of oil droplets might be the main cause of these differences.
Molecular Dynamics of Crack Growth in Nickel and Nickel-Aluminum Bi-Metallic Interface System Under Cyclic Loading
Authors: Purohit Yojna , Mohan Ram
Published: August 2012

Molecular dynamics simulations using embedded atom method inter-atomic potential were used to study crack propagation under cyclic loading in a Ni single crystal and a Ni-Al bi-metallic system. The crack in Ni-Al initiates and propagates from Ni towards the Ni-Al interface. The cyclic loading was applied in a strain controlled manner with constant amplitude of maximum strains (emax) applied to the two systems. The crack growth and propagation mechanism of a crack propagating in Ni were compared with the crack growth and propagation of a surface crack in Ni-Al at two different values of emax. Our results suggest that depending on the maximum value of the applied strain (emax), the crack propagates either by fatigue cleavage of the atomic bonds in the crack plane or by void nucleation in the regions near the crack tip. The creation of voids slows down crack growth in both the Ni and Ni-Al at higher value of emax. A comparison of crack growth under tensile and cyclic loading (emax, 0.046) suggest that plastic deformation around crack tip dominate crack propagation during tensile loading that result in slower crack growth (due to early nucleation of dislocations at the crack tip), when compared to crack growth under cyclic loading.
Widening Absorption Band of Grating Structure With Complex Dual-Groove Grating
Authors: Jiao Y. , Liu L. H. , Hsu P.-f.
Published: August 2012

The wavelength-selective radiative properties are becoming noticeable requirements in various technological fields. There have been many researches focus on the radiative properties of periodic microstructured surface of metals. However, the spectral bandwidth of high absorptance is often too narrow by applying the conventional grating structures. In order to solve this problem, in this paper we propose two novel periodic grating structures, which can widen the spectral bandwidth of high absorptance. One of the new periodic grating structures, called dual-groove grating, is constructed by adding a rectangular groove at the bottom of the simple binary grating’s groove through a secondary microscale processing. The other novel grating structure, which is called complex dual-groove grating, is constructed by superposing a dual-groove grating and a simple binary grating within one period. Aluminum grating structure is taken as an example to show how the geometric parameters based on the novel structure widen the spectral bandwidth of high absorptance within mid-infrared and far-infrared spectra. The rigorous coupled-wave analysis (RCWA) is used to calculate the absorptance of periodic grating structures. The results show that, two close absorption peaks and three connecting absorption peaks are obtained respectively for the two novel periodic grating structures. These two novel structures may widen the effective spectral bandwidth of high absorptance of the microscale periodic grating structures.
Vibration Reduction by Passive and Semi-Active Friction Joints
Authors: Gaul Lothar , Becker Jens
Published: August 2012

Reduction of structural vibrations is of major interest in mechanical engineering for lowering sound emission of vibrating structures, improving accuracy of machines and increasing structure durability. Besides optimization of the mechanical design or various types of passive damping treatments, active structural vibration control concepts are efficient means to reduce unwanted vibrations. In this contribution, two different semi-active control concepts for vibration reduction are proposed that adapt the normal force of attached friction dampers. Thereby, semi-active control concepts generally possess the advantage over active control that the closed loop is intrinsically stable and that less energy is required for the actuation than in active control. In the chosen experimental implementation, a piezoelectric stack actuators is used to apply adjustable normal forces between a structure and an attached friction damper. Simulation and experimental results of a benchmark structure with passive and semi-actively controlled friction dampers are compared for stationary narrow-band excitation.
Stiffness Characterization Using a Dynamic Heart Phantom and Magnetic Resonance Imaging
Authors: Yan Karen Chang , McDonough Mary Kate , Pilla James J. , Xu Chun
Published: August 2012

Heart disease is the number one cause of death in the United States [1]. Cardiac Magnetic Resonance Imaging (MRI) technology can be used to diagnose and evaluate a number of diseases and conditions such as coronary artery disease, damage caused by a heart attack, heart failure, and heart valve problems etc. Given the inherent difficulty in imaging the heart in motion, many efforts have been made to improve cardiac motion tracking and eliminate motion related artifacts. A dynamic heart phantom (DHP) capable of simulating true physiological motions is a valuable research tool for improving quality of MR images and determining critical diagnostic information. For instance, MR images have been used to quantify myocardial strain and estimate soft tissue material parameters and in turn to learn about cardiac structure and function [2–4]. In these studies, heart phantoms made of rubber like materials with known material properties are often used as a mean of validation.
Biomedical Engineering Design Education at King Saud University: A First of Its Kind Approach
Authors: Ranu Harcharan Singh , Bhullar Aman Sweet
Published: August 2012

Biomedical Engineering in the Millennium is building the future of biology and medicine. New products, from biotechnology and novel devices for diagnosis and treatment, are marketed through interactions between universities, medical centers, small start-up companies, and large, more established firms. The role of biomedical engineering in the 21st century has already been highlighted by Ranu as far as research, education and space age technologies are concerned. Therefore, educating the modern biomedical engineering students in design processes is extremely important. This paper highlights how biomedical engineering design is taught for the first time to King Saud University students in Saudi Arabia. The conclusion drawn from this is that for the first time an innovative design course has been developed to teach the biomedical engineering students at King Saud University to meet the needs of tomorrow’s biomedical engineers.
Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator
Authors: Shinn Aaron F. , Vanka S. Pratap
Published: August 2012

Large Eddy Simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported with the jet modeled using a plenum/pipe configuration. This configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.
The Effect of Microstructural and Geometrical Features on Fatigue Performance in Mg AZ31 Friction Stir Spot Welds
Authors: Jordon J. B.
Published: August 2012

The relationship of microstructural and geometrical features to fatigue performance is investigated in friction stir spot welds made using AZ31 magnesium alloy sheets. Lap-shear coupons were spot welded using two sets of welding parameters. Optical microscopy of the initial state of the microstructure of each set of spot welds revealed differences in the hook formation, sheet thickness in the weld zone, and nugget diameter. Both sets of welds were fatigue tested in load control until failure at various load ratios. Optical microscopy of the failed coupons revealed differences in the fracture mode between the two sets of coupons. A linear elastic fracture mechanics model was used to correlate the fatigue life in the two processes. The fatigue model, which is a function of hook size, sheet thickness, and nugget diameter, showed good correlation to the experimental results. The model was also employed to show that the fatigue of the friction stir spot welds was most sensitive to the sheet thickness in the weld zone, followed by hook height, and then nugget diameter.
High-Q Gallium Nitride Nanowire Resonators With Piezoresistive Readout
Authors: Gray Jason M. , Rogers Charles T. , Bertness Kris A. , Sanford Norman A.
Published: August 2012

We report on the fabrication and piezoresistive readout of doubly-clamped c-axis GaN nanowire (NW) mechanical resonators. As-grown GaN-NW resonators have demonstrated exceptional mechanical quality factors (Q, defined as resonance frequeny over full width at half maximum power) in the range of 104–105 [1]. This work confirms the NWs can retain this high Q even after removal from the growth substrate and placement on lithographically-defined test structures, with a highest Q to date of 26,000 at 10−5 Pa and 8 K. Wires range from 100–500 nm in diameter and 15–18 micrometers in length. We fabricate the devices using a combination of lithographic patterning and dielectrophoresis to suspend NWs over 8 or 10 micrometer gaps. We deposit an electrostatic gate ∼1 micrometer away from the NW to induce vibration, with readout utilizing the piezoresistivity of GaN. Observed resonances range from 9–36 MHz, consistent with a Young’s modulus of roughly 300 GPA. At room temperature and under vacuum, Q for these fabricated devices is typically around 103, significantly lower than the 104–105 range of the as-grown wires. However, the larger Q can be recovered by cooling the substrate. We find that by ∼10 K, Q increases by an order of magnitude to above 104. We will discuss the temperature dependence, as well as fabrication and processing effects, on the NW resonance and Q.
Getting Hands-On Experience From Simple Experiments and Model Development in Thermal-Fluid Courses
Authors: Li Xianchang , Zhou Jiang
Published: August 2012

When the engineering students transition from their sophomore to junior year, they start experiencing a large number of abstract concepts each semester. For most of students who do not have much experience in engineering, it is difficult to link these new concepts to physical problems, and the formulas associated with the new concepts make little or no sense to them. To help students get more experience, hands-on experiments can be effective. This paper first describes several simple experiments that can be demonstrated in classroom and conducted at home. Fluid Mechanics was chosen as a trial course in this study. The experiments are designed to cover the important aspects of Fluid Mechanics such as the minor/major loss of a pipe flow, the drag of an immersed object, and the application of linear momentum equations. The second approach to enhance the learning experience is to make a physical model. For both fluid mechanics and thermodynamics, an open-ended course project was assigned to the students, and the project required the students to develop a system model and complete the analysis. The outcome was evaluated through the student feedback as well as coursework, and the results indicate that this practice can help the students understand the concepts better and sustain their interest in the topics.
Optimization of Heat Exchanger Networks
Authors: Fakheri Ahmad , Leanos Alex
Published: August 2012

Various graphical and iterative methods for the optimization of Heat Exchanger Networks (HENs) have been provided. This paper proposes a new alternative approach, based on two ideas. The first is that the optimum solution must be where the efficiencies of the individual heat exchangers are high, and the second idea is that in a heat exchanger network, it is desirable to maximize entropy generation as a result of heat transfer, and minimize entropy generation due to other effects, such as stream mixing. These two ideas provide a simple process for optimizing a network of four heat exchangers, and the concept can potentially be extended to larger systems.
Mixtures of CO2-SF6 as Working Fluids for Geothermal Plants
Authors: Sabau Adrian S. , Yin Hebi , Pawel Steven J. , Gruszkiewicz Miroslaw , McFarlane Joanna , Conklin James C. , Qualls Lou A.
Published: August 2012

In this paper, mixtures of CO2 and SF6 were evaluated as working fluids for geothermal plants based on property measurements, molecular dynamics modeling, thermodynamic cycle analysis, and materials compatibility assessment. The CO2 - SF6 was evaluated for a reservoir temperature of 160°C. Increasing the efficiency for these low reservoir sources will increase the options available for geothermal energy utilization in more sites across the country. The properties for the mixtures were obtained either from thermodynamic property measurements and molecular dynamics simulations. Optimum compositions of the CO2 - SF6 were identified for a well reservoir temperature and a given water-cooling condition. Concerning the global warming potential, it was estimated that the equivalent CO2 emissions per 1kWh for a Rankine cycle operating with 100% SF6 would be approximately of 7.6% than those for a coal-fired power plant.
Meso-Scale Oil Condition Sensor
Authors: McClelland Bradley D. , Rorrer Ronald A. L.
Published: August 2012

With advances in vehicle electronics and instrumentation, there has become an increasing demand for sensors to monitor the various systems of vehicles. One fruitful area for exploration is oil condition monitoring. There are a variety of devices that have been researched and some commercial sensors based upon indirect measures of oil condition based upon temperature history and mileage. In this work, a meso-scale oscillatory device has been built to monitor the condition of oil while in use. Specifically, the device measures the viscosity, dielectric constant, and temperature of the oil. These measurements were chosen based on their importance to the function of oil. This is especially true of viscosity, which is known to be a major indicator of the overall condition of the lubricant. Tests showing the operation of the device, including measurements of oil samples from actual engines, are shown. Other tests include the detection of fuel contamination and metal wear particle presence. The device presented here could be easily incorporated into the onboard electronics of a modern vehicle in order to monitor the condition of the oil and determine when oil replacement is necessary.
Incorporation of Manufacturing Process Design Into the Senior Capstone Design Course
Authors: Gallagher Douglas V. , Rorrer Ronald A. L.
Published: August 2012

At the University Colorado Denver, a manufacturing process design course was specifically created to raise the level of the as constructed senior design projects in the department. The manufacturing process design course creates a feed forward loop into the senior design course, while the senior design course generates a feedback loop into the process design course. Every student and student project has the opportunity to utilize CNC mills and lathes where appropriate. Specific emphasis is placed upon the interfaces from solid models to CAM models and subsequently the interface from CAM models to the machine tool. Often the construction of many senior design projects approaches the level of blacksmithing due to time constraints and lack of fabrication background. Obviously, most engineering students have neither the time nor the ability to become expert fabricators. However, the wide incorporation of CNC machining in the program allows, an opportunity to not only raise the quality of their prototypes, but also to immerse in the hands on experience of living with the ramifications of their own design decisions in manufacturing. Additionally, some of the art of fabrication is turned into the science of fabrication. The focus of this paper will be primarily on examining the effect of formal incorporation of the manufacturing process in the capstone design course.
Bifurcation Characteristics of an Impacted Cantilevered Beam for Off-Resonance Excitation
Authors: Dick Andrew J.
Published: August 2012

Analytical and numerical methods are applied in order to study the response behavior of the constrained motion of a cantilevered beam for off-resonance excitation. Studies are conducted by using a multi-mode representation of the beam in order to accurately depict the influence of the bifurcation on the spatial response behavior. When modeling this system, the periodic collisions of the cantilevered beam with the compliant material result in a discontinuous force being applied to the free end of the beam. The constraining material is modeled by using the Kelvin-Voigt model. Due to the coupling of the damping and stiffness properties of the modal responses when in contact with the constraining material, a simplified single-mode approximation is used. A shooting method is used with the analytical solution of the simplified model in order to study the qualitative behavior of the system. Preliminary results using the analytical solution agree with the numerical results. The results of the shooting method reveal multiple stable solutions and suggest the presence of additional unstable periodic solutions.
Enhancement of Electronics Cooling in the OH-58D Kiowa Warrior
Authors: Davis Timothy J. , Helm Aaron M. , Sullivan Michael D. , Tamm Gunnar , Hodges Chris D.
Published: August 2012

The Bell OH-58 Kiowa helicopter was first introduced in 1969 and has undergone several retrofits to the present OH-58D Kiowa Warrior (KW) model. The KW has become heavily loaded with electronics for communications, weapons and sensors to enhance its overmatch capability against the enemy. However, the ability to cool the heating load of these systems is being stretched thin, especially in current hot operational environments. As a result, electrical component failure has resulted in reduced operational availability and extended maintenance periods. This paper presents a theoretical study performed by cadets and faculty at the U.S. Military Academy, in support of a request by Army PEO Aviation to explore alternatives. The thermal and flow characteristics of the current KW electronics bays are analyzed to identify weaknesses and potentials for quick retrofits. Several novel solutions are proposed and assessed, including redirection and enhancement of the flow, as well as cooling of the intake air or direct cooling of the electronics through mechanical, thermoelectric, evaporative and heat pipe methods.
Domestic and Global New Building Construction: A Tool for Selecting Green and Sustainable Building Systems and Components
Authors: Mina Odette , Ciocci Richard
Published: August 2012

This paper provides an overview of how to design a cost effective and environmentally responsible, green and sustainable, commercial building. Specifically included is the selection process for proper building components which will identify all factors that must receive design phase consideration and ultimately lead to the desired outcome. The process takes into consideration the appropriate aspects of various green building environmental assessment tools, such as, Leadership in Energy and Environmental Design (LEED), Green Globes (GG), Building Research Establishment Environmental Assessment Method (BREEAM), to identify important elements for design, construction, operation and maintenance of a building. Such a selection process involves many building components, but the focus of this paper is roofing systems. Specifically, the roofing system selection process will use a weighting scheme, which will be described later in this paper. This example selection process will illustrate how to identify all important factors that must be considered when choosing the best environmentally responsible and sustainable building components that are appropriate for the specific design and construction project. The weighting scheme will be useful and applicable not only for specific projects at the local level but globally as well. Factors taken into consideration are building use; geographic location and climate; budget; and any additional considerations deemed necessary by the design and construction project team.
Conversion of a Dune Buggy to a Hybrid Vehicle as a Systems Design Course Project
Authors: Yilmaz Emin
Published: August 2012

Department of Technology has purchased a used Dune Buggy years ago. It had a 6.8 horsepower Honda G65 engine with a centrifugal clutch to move the vehicle. Students in EDTE 341-Transportation Technologies course have tried, twice, to fix the engine, but they were not successful. As a student design project in ETME 475-Mechanical Systems Design course, during spring semester of 2009, three Mechanical Engineering Technology (MET) students, with the help of one Electrical/Electronics Engineering Technology (EET) student, have converted the vehicle to a hybrid vehicle. The purpose of the design project was to convert an internal combustion engine (ICE) driven Dune Buggy to a hybrid vehicle. ICE and Electric motor (EM) sizes were kept at about 6HP and cost was limited to no more than $3000. ETME 475 is a three credit-hour course with two credit hours for lecture and one credit hour (two lab contact hours) for laboratory. Laboratory time is used to discuss the project(s) and cover basic knowledge needed for the specific project(s). Along with regular textbook homework sets, students are assigned to turn in project related assignments. Most weeks, both homework and project assignments were due. First half of the semester was spent on designing the hybrid vehicle. Second half of the semester was spent constructing it. There were three students enrolled in the course. One EET student worked on the project to do electrical/instrumentations systems design and wiring. At the end of the semester, Dune Buggy was able to move with the EM. However ICE stalled as soon as the magnetic clutch was engaged. The following semester, fall semester of 2009, another MET student worked on the project to modify wiring and replace the magnetic clutch with a centrifugal clutch. This work was done under two credit-hour, ETME 499-Independent Research in Mechanical Engineering course. At the end of the semester, the Dune Buggy was fully operational with EM and ICE, one at a time, or both at the same time. Two additional MET students worked on the vehicle during the spring semester of 2011 as one of their low-tech projects to improve safety by covering cover exposed areas of the dune buggy and paint it. This paper discusses the details and coordination of the project as a design project for senior level Mechanical Systems Design course.
Thermal Performance and Reliability of Large-Area Bonded Interfaces in Power Electronics Packages
Authors: Narumanchi Sreekant , DeVoto Douglas , Mihalic Mark , Popp Tim , McCluskey Patrick
Published: August 2012

In automotive power electronics packages (e.g., insulated gate bipolar transistor [IGBT] packages), conventional polymeric thermal interface materials (TIMs) such as greases, gels, and phase-change materials pose a bottleneck to heat removal and are also associated with reliability concerns. High thermal performance bonded interfaces have become an industry trend. However, due to mismatches in the coefficient of thermal expansion between materials/layers and the resultant thermomechanical stresses, there could be voids and crack formations in these bonded interfaces as well as delaminations, which pose a problem from a reliability standpoint. These defects manifest themselves in increased thermal resistance in the package, which acts as a bottleneck to heat removal from the package. Hence, the objective of this research is to investigate and improve the thermal performance and reliability of novel bonded interface materials for power electronics packaging applications. Thermal performance and reliability of bonds/joints is presented for bonds based on a thermoplastic (polyamide) adhesive with embedded micron-sized carbon fibers, sintered silver (Ag), and conventional lead (Pb)-based solder materials. These materials form a bond between 50.8 mm × 50.8 mm footprint direct-bond-copper (DBC) substrate and copper (Cu) base plate samples. Samples undergo thermal cycling (−40°C to 150°C) for up to 2,000 cycles as an upper limit. Damage occurrence is monitored every 100 temperature cycles by several non-destructive techniques, including steady-state thermal resistance measurement, acoustic microscopy, and high-voltage potential testing. This yields a consistent story on the thermal performance and reliability of large-area joints under accelerated stress conditions.
Thermal Conductivity of Heat Treated and Non-Heat Treated Individual Multiwalled Carbon Nanotubes
Authors: Bifano Michael F. P. , Kaul Pankaj B. , Prakash Vikas
Published: August 2012

Thermal conductivity measurements of commercially available CVD grown individual multiwalled carbon nanotubes (MWCNTs) are reported. The measurements are performed using the three-omega-based Wollaston T-Type probe method inside a scanning electron microscope (SEM). An average 385% increase in thermal conductivity is measured for those MWCNTs samples which undergo a 20 hour 3000°C post annealing heat treatment. However, in most samples qualitatively characterized defects are found to negate any advantage of the heat treatment process. The highest thermal conductivity measured is 893.0 W/mK and is of a heat-treated sample. These results will help to improve the quality of MWCNT production and aid in the development of highly efficient CNT-structured thermal management devices and engineering materials.
Molecular Dynamics Modeling of Thermal Conductance at Atomically Clean and Disordered Silicon/Aluminum Interfaces
Authors: Choi Woon Ih , Kim Kwiseon , Narumanchi Sreekant
Published: August 2012

Thermal resistance between layers impedes effective heat dissipation in electronics packaging applications. Thermal conductance for clean and disordered interfaces between silicon (Si) and aluminum (Al) was computed using realistic Si/Al interfaces and classical molecular dynamics with the modified embedded atom method potential. These realistic interfaces, which include atomically clean as well as disordered interfaces, were obtained using density functional theory. At 300 K, the magnitude of interfacial conductance due to phonon-phonon scattering obtained from the classical molecular dynamics simulations was approximately five times higher than the conductance obtained using analytical elastic diffuse mismatch models. Interfacial disorder reduced the thermal conductance due to increased phonon scattering with respect to the atomically clean interface. Also, the interfacial conductance, due to electron-phonon scattering at the interface, was greater than the conductance due to phonon-phonon scattering. This suggests that phonon-phonon scattering is the bottleneck for interfacial transport at the semiconductor/metal interfaces. The molecular dynamics modeling predictions for interfacial thermal conductance for a 5 nm disordered interface between Si/Al are in-line with recent experimental data in the literature.
Aerodynamic Bicycle Helmet Design Using a Truncated Airfoil With Trailing Edge Modifications
Authors: Sims Bradford W. , Jenkins Peter E.
Published: August 2012

Aerodynamic drag contributes the majority of the resistance experienced by a competitive cyclist. Low aerodynamic drag is a key quality of high performance equipment and many aerodynamic helmets have been developed. These helmets are designed with a teardrop shape that attempts to maintain attached air flow. This shape provides a drag reduction when the athlete has their head up and is looking forward but has adverse effects if the athlete rotates their head down. A helmet design that helps maintain attached airflow while presenting reduced frontal area when the athlete’s head is down could significantly improve performance. The aerodynamic improvements of applying a truncated airfoil shape with a trailing edge modification to a helmet design were investigated. SolidWorks Flow Simulation was used to evaluate the aerodynamic forces. A common production helmet design was progressively truncated to determine the optimal truncation length and the effects of multiple trailing edge modifications were tested. A specific truncation length with a trailing edge base cavity was found to provide similar head up performance but significantly better head down performance compared to the production design. Scale models of the final improved design and the production helmet were tested in the wind tunnel to verify the computational results.
A Framework for Integrating Design Education, Research and Outreach: The Center for Innovation and Engineering at West Point
Authors: Floersheim Bruce , Klosky J. Ledlie , Flynn Matthew
Published: August 2012

The Department of Civil and Mechanical Engineering at West Point has recently established a multi-disciplinary research and educational outreach center that has a two-fold mission: enhance the undergraduate educational experience of students and assist in solving real-world technical problems, supporting global Army operations. This is accomplished by tying projects directly to the undergraduate education mission and gaining efficiency by consolidating administrative and outreach functions for multiple existing research programs. The paper describes the Center for Innovation and Engineering (CIE), its lines of effort, and several past and current initiatives. Assessment data from students participating in the senior capstone design course, which is closely tied to the CIE, reinforces the importance of multi-disciplinary, client-based projects in the engineering education experience.
Novel Nano-Structured High-Performance Thermoelectric Materials and Devices
Authors: Jovanovic Velimir , Ghamaty Saeid , Bass John C. , Krommenhoek Daniel
Published: August 2012

Recent developments of high-performance nano-structured thermoelectric (TE) materials show that these materials have much higher conversion efficiencies than the state-of-the-art (SOTA) thermoelectrics. In these new quantum well (QW) materials, the carrier and barrier materials (in this case SiGe and Si) are confined in alternating layers less than 10 nm thick, and this confinement has been shown to result in greatly improved TE properties (Seebeck coefficient, electrical resistivity and thermal conductivity) leading to higher TE Figure of Merit, ZT, conversion efficiencies and Coefficient of Performance (COP) for cooling applications than for SOTA bulk thermoelectrics. From the most recent QW test data, ZTs greater than 3 at room temperature have been obtained which constitutes a significant improvement over the SOTA bulk thermoelectrics which have ZTs less than 1. The QW TE materials with ZTs greater than 3 lead to conversion efficiencies greater than 20 percent and higher COPs than for the SOTA vapor-compression cooling systems, which allow for much wider commercial applications, particularly in the applications such as the waste-heat recovery from truck engines and power plants, refrigeration and air conditioning, where the SOTA bulk TE modules were shown to be technically feasible but economically unjustified due to low conversion efficiencies. With higher efficiency QW materials, these applications become economically attractive. In a recent QW test, a conversion efficiency corresponding to 60 percent of the Carnot efficiency was measured and this is believed to be the highest such value ever measured for a TE material. For power generation applications, QW TE generators can be designed for capacities ranging from milliwatts to kilowatts and for cooling applications with capacities ranging from watts to several tons of refrigeration. This involves the transition from the nano scale QW thin films to macro scale TE devices. This paper discusses the status of the prototype QW TE generators and coolers being designed and fabricated, and the latest test results.
Optimal Preview Control of Structural Vibrations Under Earthquake Excitations
Authors: Shahrabi A. F. , Ahmadi G.
Published: August 2012

Active vibration control of structures under earthquake excitation has attracted considerable attention in the recent years. In this study, attention was given to optimal preview control methodology for protection of building with and without base isolation systems against earthquakes. A three-story building model was used and several earthquake records including El Centro, Mexico City and Tabas earthquake records were used as excitation. Acceleration and displacement responses of the structure with active preview control were evaluated and the results are compared with those for the unprotected buildings. It was shown that using properly designed active preview control systems can effectively reduce the acceleration transmitted to structures during a major earthquake. The study was repeated for a base isolated structure. It was shown that that the using the information obtain from the preview sensors in the active control strategy would improve the system performance significantly. The influence of the preview time on the system performance was also studied. It was found that the range of preview time needed for improved performance is quite small but depends on the frequency contend of the earthquake excitation.
Effects of Layer Placement in Isotropic Layer Pairs for Producing Equivalent Mass Anisotropy
Authors: Cai Liang-Wu , Sa´nchez-Dehesa Jose´
Published: August 2012

Mass-anisotropy is an important ingredient for acoustic cloaking. In recent years, the idea of using two isotropic layer to effectively mimic an mass-anisotropic layer has created an intense interest. In this paper, this equivalency is studied, with a particular focus on how to place the two layers. It is found that the proper placement is to place the heavier layer of the pair closer to the center, and that a proper placement plays a significant role in the effectiveness of the resulting cloak. It is also noted that the equivalency does not provide sufficient conditions to completely determine the material properties of the two isotropic layers. This leaves the choices wide open as what other additional conditions can be imposed on the relation between the bulk modulus of the two layers. Three choices are examined in this paper: matching the modulus, the impedances, and the sound speeds, of the two layers. It is found that a proper layer placement is more important than these choices.
Exact/Approximated Geometrical Determinations of IMRT Photon Pencil-Beam Path Through Alloy Static Wedges in Radiotherapy Using the Anisothropic Analytic Algorithm (AAA)
Authors: Casesnoves F.
Published: August 2012

Static wedge filters are commonly used in Radiation Therapy, Forward and/or Inverse Planning, to obtain a conformal optimized dose distribution, both in the tumor target and organs at risk zones (OARs); in other words, the Treatment Planning Optimization (TPO) zone and annexes. We have calculated the exact 2D/3D geometrical pathway of the Photon-Beam through the usual alloy static wedges, in order to get a better dose determination related to the Beam Intensity Attenuation Factor(s), after the beam has passed through the alloy wedge. The Radiotherapy model used to develop this mathematical task is the classical Superposition-Convolution Algorithm, so-called AAA (Anisothropic Analytical Algorithm). In addition, we present some optimal geometrical approximations to make the computational calculations quicker in IMRT, and reduce the planning-system routine time. The practical objective is to provide a general formulation into the AAA Model Coordinates System (depending on Collimator and Wedge Angles) that also can be applied with simple changes of coordinates to other models, if necessary. These transformations are also explained for the convenience of the TPO selected for a particular model. As a result, it is possible to determine the best individual treatment dose distribution for each patient, and conform the tumor volume and shape accurately in the technical planning process related to the selected wedges. Geometrical and Computational techniques are detailed and developed for a clear reading. Finally, we show basic simulations and numerical examples for Standard Manufacturing wedge filters of straight sloping surface, to check the accuracy and errors of the approximated calculations. Simulations results give low RMS and Relative Error values for standard wedge filters of 15°, 30°, 45°, and 60°.
Radial Impeller Design Optimization Matched for High Efficiency Fans
Authors: Epple Philipp , Semel Matthias , Smith Henrik , Litfin Oliver , Delgado Antonio
Published: August 2012

Radial fans and blowers are widely used in many different fields, such as heater blowers or fans and blowers for vacuum cleaners. Although the impellers for these fans are already quite well optimized, it is possible to increase the efficiency of the fan matching the impeller properly to it. A very common fan optimization strategy is to increase the efficiency of the radial impeller, keeping its operating point, i.e. the flow rate of maximum efficiency. However, in most of these cases the impeller is not matched to the fan and hence this procedure will not deliver the best fan, even if the efficiency of the impeller is improved. In order to understand how an optimization of the fan has to be done, a theoretical treatment is presented. Detailed theoretical formulas are presented and discussed. In order to validate the theory, a series of well directed impellers and fans was designed, CAD models constructed and using ANSYS CFX finally the corresponding flow simulation was performed. It is shown how the impellers have to be modified in order to shift the flow rate of maximum efficiency without significant decrease in efficiency. Finally a detailed experimental study was performed at the test rig conforming the German engineering norm DIN 24 163 [1]. Here the theoretical achievements were systematically verified at the test rig for vacuum cleaner fans. It is shown how to, based on this theory, from the very beginning design the radial impellers such that they are perfectly matched to the full fan. In such a way it is shown how to increase the efficiency of radial fans and blowers substantially.
Thermal Conductivity Measurement of Thin Nanowires
Authors: Wingert Matthew C. , Moon Jaeyun , Chen Zack , Xiang Jie , Chen Renkun
Published: August 2012

Semiconductor nanowires hold great promise for applications such as nano-electronics and energy conversion. A detailed knowledge of the thermal properties of the nanowire materials is essential for proper thermal management in nano-devices and thermal energy conversion. Prior thermal measurements on individual nanowires have shown that nanowires have reduced lattice thermal conductivity and, in some cases, enhanced thermoelectric properties. However, such thermal measurements are limited to nanowire thermal conductance of the order of 1 nW/K and are typically limited to nanowire diameters greater than 20 nm. Measurements to obtain the thermal conductivities of single nanowires with smaller diameter nanowires, which may exhibit even lower thermal conductivity and possibly quantum confinement effect at low temperature, have proven elusive. Herein, we demonstrated an experimental technique with improved measurement sensitivity that is capable of measuring the thermal conductance of 10 pW/K. This more sensitive technique overcomes several issues with current instrumentations and provides a tool for characterizing the properties of much smaller diameter nanowires, such as nanowires with 1 W/m-K thermal conductivity, 10 nm diameter and 1 μm length. Measurement enabled by this measurement platform will improve our understanding of thermal transport in confined nanostructures.
Is Synthetic Composite Bone a Substitute for Natural Bone in Screw Bending Tests?
Authors: James Thomas P. , Andrade Brendan A.
Published: August 2012

Composite replica bones have been used extensively for biomechanical studies. These studies normally rely upon the overall tensile, compressive, and bending strength of large replica bones, such as the tibia and femur. In this study, highly localized behavior of composite bone was scrutinized by examining the material’s response to cortical screws in bending. Of interest was localized deformation of the composite material as compared to the response of natural bone under similar loading conditions. Cortical screw deflection in a laminated composite bone was compared to deflection in a bovine bone under quasi-static loading. The laminated composite bone consisted of short glass fiber reinforced epoxy as a cortical bone substitute, while polyurethane foam was used as a cancellous bone substitute. A new laser projection method was used to make comparative measurements of the slope of the screw head near to the applied load. Initial results indicate that composite bone is a reliable substitute for natural bone in quasi-static studies of cortical screw deflection.
Design of Acoustic Filters Using Acoustic and Elastic Resonators
Authors: Sharma B. , Sun C. T.
Published: August 2012

Recently, investigators have experimentally demonstrated that high transmission loss at low frequencies can be obtained using membrane type resonators. Mass loaded membranes have been shown to produce high transmission loss at the anti-resonance frequency [1], while an array of membranes has been experimentally demonstrated to exhibit a cut-off frequency below which all waves are attenuated [2]. Also, an array of side holes on a cylindrical tube has been shown to exhibit a similar cut-off frequency [3].
A Semi-Active Damper Design for Use in a Terrain Adaptive Ankle Prosthesis
Authors: LaPre` Andrew , Sup Frank
Published: August 2012

State-of-the-art commercial ankle prostheses enable amputees to walk on level ground replicating the passive biomechanics of able-bodied persons reasonably well. However, when navigating uneven terrains (such as slopes and stairs) these devices do not allow the ankle to adjust to the ground at each step in order to maintain stable contact. At these instances, the probability of falling is greatly increased. In contrast, the natural ankle adapts passively (i.e. no net positive power is required) just after heel strike allowing the foot to conform to the ground. This paper focuses on developing a continuously variable damper that can be paired with a carbon fiber foot in order to replicate the passive adaption dynamics of the human ankle. Presented in this paper are the performance specifications, the mathematical model, and the resulting device design for the semi-active damping system. The design consists of a hydraulic actuator, coupled to a servo control valve which modulates the damping. The system is designed to replicate the dynamic damping range of an able-bodied ankle joint by achieving flow rates as high as 2.0 liters per minute at 1.0 MPa, and operate at up to 20 MPa.
Inverse Problem for the Estimation of Skin Cancerous Region Parameters by Thermal Analysis
Authors: Luna Jose Manuel , Romero-Mendez Ricardo , Hernandez-Guerrero Abel , Elizalde-Blancas Francisco
Published: August 2012

Malignant melanoma is the most aggressive skin cancer since it metastasizes rapidly. The existence of a quantitative, non-expensive, and non-invasive diagnostic screening tool for the evaluation of pigmented lesions would be invaluable for the early detection of malignant melanoma. Based on the fact that this cancerous skin lesion has higher metabolism, as well as an increased blood flow, it has been conjectured that it has higher temperature compared to surrounding healthy skin, temperature than can be measured by infrared thermography. Therefore, it is possible to explore the relationship between the characteristics (size and heat produced) of the neoplasm and the resulting temperature distribution on the skin surface to evaluate the development of the lesion. In our investigation the Dual Reciprocity Boundary Element Method (DRBEM) has been coupled to the Simulated Annealing Technique (SAT) in an inverse procedure to estimate simultaneously the depth and heat produced by skin malignant neoplasms at early stages. The SAT was used to estimate neoplasm parameters by minimizing an objective function that involves the skin surface temperature profiles obtained from simulated data to those obtained numerically by the DRBEM. Results are presented for neoplasms of Clark levels II–IV to demonstrate the feasibility of the proposed methodology.