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Articles 19171 - 19200 of 30244

Full-Text Articles in Mechanical Engineering

Shield Design For Maximum Deformation In Shape-Shifting Surfaces, Daniel Eduardo Perez Jan 2013

Shield Design For Maximum Deformation In Shape-Shifting Surfaces, Daniel Eduardo Perez

USF Tampa Graduate Theses and Dissertations

This research presents the initial studies and results on shield design for Shape-Shifting Surfaces (SSSs) seeking maximum compression and maximum expansion of a unit-cell. Shape-Shifting Surfaces (SSSs) are multilayered surfaces that are able to change shape while maintaining their integrity as physical barriers. SSSs are composed of polygonal unit-cells, which can change side lengths and corner angles. These changes are made possible by each side and corner consisting of at least two different shields, or layers of material. As the layers undergo relative motion, the unit-cell changes shape. In order for the SSS to retain its effectiveness as a barrier, …

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Supercritical Co2 Brayton Cycles For Solar-Thermal Energy, Brian D. Iverson, Thomas M. Conboy, James J. Pasch, Alan M. Kruizenga Jan 2013

Supercritical Co2 Brayton Cycles For Solar-Thermal Energy, Brian D. Iverson, Thomas M. Conboy, James J. Pasch, Alan M. Kruizenga

Faculty Publications

Of the mechanisms to improve efficiency for solar-­‐thermal power plants, one of the most effective ways to improve overall efficiency is through power cycle improvements. As increases in operating temperature continue to be pursued, supercritical CO2 Brayton cycles begin to look more attractive despite the development costs of this technology. Further, supercritical CO2 Brayton has application in many areas of power generation beyond that for solar energy alone.

One challenge particular to solar-­‐thermal power generation is the transient nature of the solar resource. This work illustrates the behavior of developmental Brayton turbomachinery in response to a fluctuating thermal input, much …

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Molten Carbonates As An Effective Oxygen Reduction Catalyst For 550–650°C Solid Oxide Fuel Cells, Yunhui Gong, Xue Li, Lingling Zhang, Whitney Tharp, Changyong Qin, Kevin Huang Jan 2013

Molten Carbonates As An Effective Oxygen Reduction Catalyst For 550–650°C Solid Oxide Fuel Cells, Yunhui Gong, Xue Li, Lingling Zhang, Whitney Tharp, Changyong Qin, Kevin Huang

Faculty Publications

We report the first study that investigates the use of molten carbonates as an effective catalyst to promote electrochemical oxygen reduction reaction (ORR) at the cathode of intermediate temperature solid oxide fuel cells (IT-SOFCs). A series of binary Li-K carbonate compositions were incorporated into the porous backbones of a commercial cathode assembled in symmetrical impedance cells for electrochemical characterization. Within the temperature range of 550–650◦C, we observed that the polarization and ohmic area-specific resistances of the original sample can be significantly reduced by the introduction of molten carbonates. A new ORR charge-transfer model involving two intermediate species CO5 2− and …

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Carbon Dioxide Absorption And Channelling In Closed Circuit Rebreather Scrubbers, Shona Cunningham Jan 2013

Carbon Dioxide Absorption And Channelling In Closed Circuit Rebreather Scrubbers, Shona Cunningham

Theses

Closed Circuit Rebreathers (CCRs) are a type of Self Contained Underwater Breathing Apparatus (SCUBA) used predominantly by the diving community. CCR technologies have become prevalent within the commercial, military and technical diving communities over recent years. CCRs work by recycling breathing gas, by-passing the gas through a carbon dioxide (CO2) chemical scrubber and topping the resultant scrubbed gas up with pure oxygen to maintain the oxygen content at a level which supports life. One of the main dangers currently faced by divers using this equipment is the risk of CO2 poisoning if the scrubber fails. This failure …

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Application Of Nano-Imprint Lithography For Next Generation Carbon Nanotube-Based Devices, Svitlana Fialkova Jan 2013

Application Of Nano-Imprint Lithography For Next Generation Carbon Nanotube-Based Devices, Svitlana Fialkova

Dissertations

This research report addresses the development of 3D carbon nanostructures that can provide unique capabilities for manufacturing carbon nanotube (CNT) electronic components, electrochemical probes, biosensors and tissue scaffolds. The shaped CNT arrays were grown on patterned catalytic substrate by chemical vapor deposition (CVD) method. The new fabrication process for catalyst patterning based on combination of nano-imprint lithography (NIL), magnetron sputtering and reactive etching techniques was proposed and studied. The optimal process parameters for each technique were evaluated. The catalyst was made by deposition of Fe and Co nanoparticles over alumina support layer on Si/SiO2 substrate. The metal particles were …

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Metal-Based Microchannel Heat Exchangers : Manufacturing And Heat Transfer Testing, Bin Lu Jan 2013

Metal-Based Microchannel Heat Exchangers : Manufacturing And Heat Transfer Testing, Bin Lu

LSU Doctoral Dissertations

This dissertation focuses on improving the functionality of metal-based microchannel heat exchangers (MHEs), as well as pushing this technology toward real-world applications. Design optimization was carried out on MHEs for performance maximization. Double-layered microchannel layout was experimentally studied, and a significant reduction on liquid flow pressure drop penalty was achieved. Other than water, another commonly-used coolant, ethylene glycol, was applied to MHEs, and flow and heat transfer characteristics were quantified. Transient Liquid Phase (TLP) bonding was used for joining Cu structures. For further understanding of the MHE heat transfer, a detailed examination was carried out on the TLP bonding interface …

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A Study On The Cleaning And Modification Of Metal Surfaces By Direct Current Cathodic Electrolytic Plasma Process, Jiandong Liang Jan 2013

A Study On The Cleaning And Modification Of Metal Surfaces By Direct Current Cathodic Electrolytic Plasma Process, Jiandong Liang

LSU Doctoral Dissertations

The processes of surface treatments or surface modifications, more formally known as surface engineering, tailor the surfaces of engineering materials. The treatments are usually intended to change physical properties such as thermal or electrical conductivity, modify the surface dimensions, i.e. roughness, etc. A novel surface treatment method, Electrolytic Plasma Process (EPP), was developed for coating purposes, in its early developmental stage. In this work, the major effort is to avoid using any environmental hazardous chemical (coatings) and to extend such its application to some new fields. The general response of the substrate material under electrolytic plasma process was summarized including …

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The Effect Of Isostatic Pressing On The Dielectric Properties Of Screen Printed Ba0.5Sr0.5Tio3 Thick Films, Siwei Wang, Lingling Zhang, Jiwei Zhai, Fanglin Chen Jan 2013

The Effect Of Isostatic Pressing On The Dielectric Properties Of Screen Printed Ba0.5Sr0.5Tio3 Thick Films, Siwei Wang, Lingling Zhang, Jiwei Zhai, Fanglin Chen

Faculty Publications

Ba0.5Sr0.5TiO3 thick films with B2O3–Li2O glass sintering aid were prepared by the screen printing method on Al2O3 substrates. A 200 MPa isostatic pressure was applied to the films before sintering. After being sintered at 950∘C, lower porosity and denser microstructure was obtained compared with the films without isostatic pressing. The dielectric constant and dielectric loss were 238 and 0.0028, respectively. A tunability of 61.7% was obtained for the isostatic pressed films, a 27.8% enhancement compared to unpressurized films. These results suggest that isostatic pressing …

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A Simple Model For The In-Plane Rotational Response Of A Disk Resonator In Liquid: Resonant Frequency, Quality Factor, And Optimal Geometry, Mohomad S. Sotoudegan, Stephen M. Heinrich, Fabien Josse, Nicholas J. Nigro, Isabelle Dufour, Oliver Brand Jan 2013

A Simple Model For The In-Plane Rotational Response Of A Disk Resonator In Liquid: Resonant Frequency, Quality Factor, And Optimal Geometry, Mohomad S. Sotoudegan, Stephen M. Heinrich, Fabien Josse, Nicholas J. Nigro, Isabelle Dufour, Oliver Brand

Civil and Environmental Engineering Faculty Research and Publications

No abstract provided.

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Monitoring Damage Initiation And Growth In Composite Structures By Acoustic Emission Method, Kassahun Mekonnen Asamene Jan 2013

Monitoring Damage Initiation And Growth In Composite Structures By Acoustic Emission Method, Kassahun Mekonnen Asamene

Dissertations

In this dissertation, acoustic emission technique is examined as candidate for monitoring the integrity of polymer matrix structural members. Acoustic emission technique has so far been largely limited to laboratory tests and field applications have been mostly limited to qualification tests of aerospace structures. The lack of quantitative indications of damage in composite structural members associated with the complex nature of damage in these materials has been a limiting factor. Generally, a number of failure modes operate simultaneously at a site of damage, and each of these failure modes generates a different type of acoustic emission signal. In addition, issues …

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Representing Intersubject Variability With A Statistical Shape And Alignment Model Of The Knee, Chandreshwar Rao Jan 2013

Representing Intersubject Variability With A Statistical Shape And Alignment Model Of The Knee, Chandreshwar Rao

Electronic Theses and Dissertations

Prior statistical shape models have not considered multiple structures in the knee joint to characterize anatomic variation which are required to investigate joint mechanics further for the successful knee replacement. Accordingly, the study's objective was to develop statistical shape and alignment model (SSAM) to capture intersubject variability and demonstrate the ability to generate realistic instances for use in finite element analysis (FEA). SSAM described the variability in the training set of 20 subjects with a series of modes of variation obtained by performing principal component analysis (PCA). PCA produced modes of variation with the first 3 modes representing 70% and …

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Review Of Electrochemical And Electrodischarge Machining, Kamlakar P. Rajurkar, M. M. Sundaram, A. P. Malshe Jan 2013

Review Of Electrochemical And Electrodischarge Machining, Kamlakar P. Rajurkar, M. M. Sundaram, A. P. Malshe

Department of Mechanical and Materials Engineering: Faculty Publications

Electrochemical and electro-discharge machining processes are the two major electro-machining processes with unique capabilities. Electrical Discharge Machining (EDM) and Electrochemical Machining (ECM) offer a better alternative or sometimes the only alternative in generating accurate 3-D complex shaped macro, micro and nano features and components of difficult–to-machine materials. Technological advances reported in electrochemical and electro discharge machining processes, which reflect the state of the art in academic and industrial research and applications, are briefly reviewed in this paper.

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Wire Electro-Discharge Machining Of Titanium Alloy, Farnaz Nourbakhsh, Kamlakar P. Rajurkar, Ajay P. Malshe, Jian Cao Jan 2013

Wire Electro-Discharge Machining Of Titanium Alloy, Farnaz Nourbakhsh, Kamlakar P. Rajurkar, Ajay P. Malshe, Jian Cao

Department of Mechanical and Materials Engineering: Faculty Publications

This paper presents an experimental investigation of wire electro-discharge machining (WEDM) of titanium alloy. The objective is to investigate the effect of seven process parameters including pulse width, servo reference voltage, pulse current, and wire tension on process performance parameters (such as cutting speed, wire rupture and surface integrity). A Taguchi L18 design of experiment (DOE) has been applied. All experiments have been conducted using Charmilles WEDM. It was also found that the cutting speed increases with peak current and pulse interval. Surface roughness was found to increase with pulse width and decrease with pulse interval. The Analysis of Variance …

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Selective Detection And Automated Counting Of Fluorescently-Labeled Chrysotile Asbestos Using A Dual-Mode High-Throughput Microscopy (Dm-Htm) Method, Myoung-Ock Cho, Hyo Mi Chang, Donghee Lee, Yeon Gyu Yu, Hwataik Han, Jung Kyung Kim Jan 2013

Selective Detection And Automated Counting Of Fluorescently-Labeled Chrysotile Asbestos Using A Dual-Mode High-Throughput Microscopy (Dm-Htm) Method, Myoung-Ock Cho, Hyo Mi Chang, Donghee Lee, Yeon Gyu Yu, Hwataik Han, Jung Kyung Kim

Department of Mechanical and Materials Engineering: Faculty Publications

Phase contrast microscopy (PCM) is a widely used analytical method for airborne asbestos, but it is unable to distinguish asbestos from non-asbestos fibers and requires time-consuming and laborious manual counting of fibers. Previously, we developed a high-throughput microscopy (HTM) method that could greatly reduce human intervention and analysis time through automated image acquisition and counting of fibers. In this study, we designed a dual-mode HTM (DM-HTM) device for the combined reflection and fluorescence imaging of asbestos, and automated a series of built-in image processing commands of ImageJ software to test its capabilities. We used DksA, a chrysotile-adhesive protein, for selective …

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Photovoltaic Device, Jinsong Huang, Bin Yang, Yongbo Yuan Jan 2013

Photovoltaic Device, Jinsong Huang, Bin Yang, Yongbo Yuan

Department of Mechanical and Materials Engineering: Faculty Publications

An apparatus includes a substrate; and a photoactive layer disposed on the substrate. The photoactive layer includes an electron acceptor material; an electron donor material; and a material having dipoles.

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Solution-Processed Nanoparticle Super-Float-Gated Organic Field-Effect Transistor As Un-Cooled Ultraviolet And Infrared Photon Counter, Yongbo Yuan, Qingfeng Dong, Bin Yang, Fawen Guo, Qi Zhang, Ming Han, Jinsong Huang Jan 2013

Solution-Processed Nanoparticle Super-Float-Gated Organic Field-Effect Transistor As Un-Cooled Ultraviolet And Infrared Photon Counter, Yongbo Yuan, Qingfeng Dong, Bin Yang, Fawen Guo, Qi Zhang, Ming Han, Jinsong Huang

Department of Mechanical and Materials Engineering: Faculty Publications

High sensitivity photodetectors in ultraviolet (UV) and infrared (IR) range have broad civilian and military applications. Here we report on an un-cooled solution-processed UV-IR photon counter based on modified organic field-effect transistors. This type of UV detectors have light absorbing zinc oxide nanoparticles (NPs) sandwiched between two gate dielectric layers as a floating gate. The photon-generated charges on the floating gate cause high resistance regions in the transistor channel and tune the source-drain output current. This ‘‘super-float-gating’’ mechanism enables very high sensitivity photodetectors with a minimum detectable ultraviolet light intensity of 2.6 photons/µm2s at room temperature as well …

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Analysis Of Electrically-Forced Vibrations Of Piezoelectric Mesa Resonators, Huijing He, Guo-Quan Nie, Jin-Xi Liu, Jiashi Yang Jan 2013

Analysis Of Electrically-Forced Vibrations Of Piezoelectric Mesa Resonators, Huijing He, Guo-Quan Nie, Jin-Xi Liu, Jiashi Yang

Department of Mechanical and Materials Engineering: Faculty Publications

We study the electrically forced thickness-shear and thickness-twist vibrations of stepped thickness piezoelectric plate mesa resonators made of polarized ceramics or 6-mm class crystals. A theoretical analysis based on the theory of piezoelectricity is performed, and an analytical solution is obtained using the trigonometric series. The electrical admittance, resonant frequencies, and mode shapes are calculated, and strong energy trapping of the modes is observed. Their dependence on the geometric parameters of the resonator is also examined.

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Constraint Enforcement Methods For Command Governor Based Adaptive Control Of Uncertain Dynamical Systems, Simon P. Schatz, Tansel Yucelen, Eric N. Johnsony, Florian Holzapfelz Jan 2013

Constraint Enforcement Methods For Command Governor Based Adaptive Control Of Uncertain Dynamical Systems, Simon P. Schatz, Tansel Yucelen, Eric N. Johnsony, Florian Holzapfelz

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Recently, research has been conducted in order to improve the transient behavior of adaptively controlled uncertain nonlinear dynamical systems. In this paper, an adaptive control architecture is extended in order to achieve predictable transient performance in the presence of state constraints. The methodology at hand is based on a robust command governor framework, which is a dynamical system adjusting the trajectory of a given command in order to track a certain desired closed-loop reference model both in transient time and steady-state. Specifically, the command, which is applied on the reference model and the actual system, is changed by the command …

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Consensus Protocols In Networked Multiagent Systems For Cluttered And Hostile Environments, Gerardo De La Torre, Eric N. Johnson, Tansel Yucelen Jan 2013

Consensus Protocols In Networked Multiagent Systems For Cluttered And Hostile Environments, Gerardo De La Torre, Eric N. Johnson, Tansel Yucelen

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Consensus refers to the agreement of networked agents upon certain quantities of interest and has widespread applications in diverse areas in science and engineering. This paper focuses on a new consensus protocol for networked multiagent systems operating in cluttered and hostile environments. Specifically, a consensus optimization algorithm is introduced that renders the Laplacian potential to be a nonincreasing function while minimizing a cost function and satisfying state and cost constraints. In addition, we show how to choose this cost function and the aforementioned constraints in order to decay the Laplacian potential to zero strictly. The proposed framework depends on a …

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Model Based Adaptive Control Of Underwater Vehicles For Improved Ocean Science, Christopher J. Mcfarland Jan 2013

Model Based Adaptive Control Of Underwater Vehicles For Improved Ocean Science, Christopher J. Mcfarland

Link Foundation Ocean Engineering and Instrumentation Fellowship Reports

Recent advances in unmanned underwater vehicle (UUV) capabilities have enabled oceanographic scientists to consider addressing research topics previously thought impractical or impossible. One such topic is the validation of high resolution computer models; long term deployments of coordinated UUV survey teams have been proposed to collect the density of measurements required. Another topic is the study of biological diversity in volatile areas; UUV intervention/sampling deployments have been proposed because of the inherent risks. In general, providing a high density of high accuracy measurements requires passing many targets as quickly and closely as possible. Similarly, efficacy for intervention/sampling deployments requires agile …

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Predicting Underwater Radiated Noise From Offshore Impact Pile Driving, Huikwan Kim Jan 2013

Predicting Underwater Radiated Noise From Offshore Impact Pile Driving, Huikwan Kim

Link Foundation Ocean Engineering and Instrumentation Fellowship Reports

Offshore wind turbines have been installed throughout Europe and are expected to be built in the United States water shortly. Offshore wind is an attractive option because 53% of the nation’s population lives in coastal area where energy cost and demands are high. Offshore winds tend to blow harder and more uniformly than on land [1]. However, structure borne noise and vibration generated by offshore impact pile driving radiate into and propagate through the air, water, and sediment media. The objective of this project is quantitatively predicting noise level around the piling location at sea to estimate the effects of …

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Approximate Dynamic Programming Based Solutions For Fixed-Final-Time Optimal Control And Optimal Switching, Ali Heydari Jan 2013

Approximate Dynamic Programming Based Solutions For Fixed-Final-Time Optimal Control And Optimal Switching, Ali Heydari

Doctoral Dissertations

"Optimal solutions with neural networks (NN) based on an approximate dynamic programming (ADP) framework for new classes of engineering and non-engineering problems and associated difficulties and challenges are investigated in this dissertation. In the enclosed eight papers, the ADP framework is utilized for solving fixed-final-time problems (also called terminal control problems) and problems with switching nature. An ADP based algorithm is proposed in Paper 1 for solving fixed-final-time problems with soft terminal constraint, in which, a single neural network with a single set of weights is utilized. Paper 2 investigates fixed-final-time problems with hard terminal constraints. The optimality analysis of …

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Automated Extraction And Classification Of Time-Frequency Contours In Humpback Vocalizations, Hui Ou, Whitlow W.L. Au, Lisa M. Zurk, Marc O. Lammers Jan 2013

Automated Extraction And Classification Of Time-Frequency Contours In Humpback Vocalizations, Hui Ou, Whitlow W.L. Au, Lisa M. Zurk, Marc O. Lammers

Electrical and Computer Engineering Faculty Publications and Presentations

A time-frequency contour extraction and classification algorithm was created to analyze humpback whale vocalizations. The algorithm automatically extracted contours of whale vocalization units by searching for gray-level discontinuities in the spectrogram images. The unit-to-unit similarity was quantified by cross-correlating the contour lines. A library of distinctive humpback units was then generated by applying an unsupervised, cluster-based learning algorithm. The purpose of this study was to provide a fast and automated feature selection tool to describe the vocal signatures of animal groups. This approach could benefit a variety of applications such as species description, identification, and evolution of song structures. The …

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Part Height Control Of Laser Metal Additive Manufacturing Process, Yu-Herng Pan Jan 2013

Part Height Control Of Laser Metal Additive Manufacturing Process, Yu-Herng Pan

Masters Theses

"Laser Metal Deposition (LMD) has been used to not only make but also repair damaged parts in a layer-by-layer fashion. Parts made in this manner may produce less waste than those made through conventional machining processes. However, a common issue of LMD involves controlling the deposition's layer thickness. Accuracy is important, and as it increases, both the time required to produce the part and the material wasted during the material removal process (e.g., milling, lathe) decrease. The deposition rate is affected by multiple parameters, such as the powder feed rate, laser input power, axis feed rate, material type, and part …

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Numerical Modeling Of Heat Transfer And Fluid Flow In Laser Metal Deposition By Powder Injection, Zhiqiang Fan Jan 2013

Numerical Modeling Of Heat Transfer And Fluid Flow In Laser Metal Deposition By Powder Injection, Zhiqiang Fan

Doctoral Dissertations

"Laser metal deposition is an additive manufacturing technique which allows quick fabrication of fully-dense metallic components directly from Computer Aided Design (CAD) solid models. A self-consistent three-dimensional model was developed for the laser metal deposition process by powder injection, which simulates heat transfer, phase changes, and fluid flow in the melt pool, The governing equations for solid, liquid and gas phases in the calculation domain have been formulated using the continuum model. The free surface in the melt pool has been tracked by the Volume of Fluid (VOF) method, while the VOF transport equation was solved using the Piecewise Linear …

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Kinematic And Dynamic Collision Statistics Of Cloud Droplets From High-Resolution Simulations, Bogdan Rosa, Hossein Parishani, Orlando Ayala, Wojciech W. Grabowski, Lian-Ping Wang Jan 2013

Kinematic And Dynamic Collision Statistics Of Cloud Droplets From High-Resolution Simulations, Bogdan Rosa, Hossein Parishani, Orlando Ayala, Wojciech W. Grabowski, Lian-Ping Wang

Engineering Technology Faculty Publications

We study the dynamic and kinematic collision statistics of cloud droplets for a range of flow Taylor microscale Reynolds numbers (up to 500), using a highly scalable hybrid direct numerical simulation approach. Accurate results of radial relative velocity (RRV) and radial distribution function (RDF) at contact have been obtained by taking advantage of their power-law scaling at short separation distances. Three specific but inter-related questions have been addressed in a systematic manner for geometric collisions of same-size droplets (of radius from 10 to 60 μm) in a typical cloud turbulence (dissipation rate at 400 cm2 s-3. Firstly, …

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Web-Based Virtual Learning For Digital Manufacturing Fundamentals For Automotive Workforce Training, Vukica Jovanovic, Nathan W. Hartman Jan 2013

Web-Based Virtual Learning For Digital Manufacturing Fundamentals For Automotive Workforce Training, Vukica Jovanovic, Nathan W. Hartman

Engineering Technology Faculty Publications

Automotive manufacturers are experiencing difficulties in hiring highly qualified workers with ability to adopt new technologies fast. This kind of ongoing need for training is slowing innovation. This problem is related to the difficulty in obtaining consistent training resources and services especially with lack of training for advanced manufacturing practices for specialised industry sectors. More and more occupations require degrees higher than secondary education because of the global need for so called ‘knowledge workers’. An example of an interactive learning programme, developed with the support of narrated presentation technology, podcasts and online access has been shown in this paper. Sixty …

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Assessment Of Abaqus Capabilities For Crack Growth And Calculation Of Energy Release Rate, Luis Alonso Hernandez Jan 2013

Assessment Of Abaqus Capabilities For Crack Growth And Calculation Of Energy Release Rate, Luis Alonso Hernandez

Open Access Theses & Dissertations

The purpose of this study was to benchmark ABAQUS modeling capabilities for crack propagation and calculation of energy release rate against closed-form analytical solutions. The crack growth capability for this study was evaluated using the following techniques: virtual crack closure technique (VCCT), X-FEM coupled with VCCT, and X-FEM coupled with cohesive segments. The capability of calculating the energy release rate was assessed by using the J-integral routine. A Double Cantilever Beam (DCB) specimen was used to conduct the study for mode I propagation, and a mixed mode bending (MMB) specimen was used to study the propagation for mixed mode I/II …

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Experimental Study On The Fabrication Of Advanced Materials For Energy Applications Using High Energy Mechanical Milling, Ashvin Kumar Narayana Swamy Jan 2013

Experimental Study On The Fabrication Of Advanced Materials For Energy Applications Using High Energy Mechanical Milling, Ashvin Kumar Narayana Swamy

Open Access Theses & Dissertations

The reaction of aluminum (Al) powder with water has the potential for on demand hydrogen generation. Conventional Al powders, however, react with water slowly due to a highly protective oxide layer on the particle surface. Current methods for Al activation involve harmful and expensive materials. The nano-scale Al powders also remain very expensive and have problems such as a large amount of oxide on the surface. The use of aluminum in an energy generation cycle is also hindered by the fact that, although Al is the most abundant metal in the Earth's crust, its recovery from ore consumes a lot …

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Effect Of Hafnium-Incorporation On The Microstructure And Dielectric Properties Of Cobalt Ferrite Ceramics, Stephen Josiah Wells Jan 2013

Effect Of Hafnium-Incorporation On The Microstructure And Dielectric Properties Of Cobalt Ferrite Ceramics, Stephen Josiah Wells

Open Access Theses & Dissertations

The effect of hafnium ion (Hf4+) incorporation in cobalt ferrite (CFO) was studied. Samples of Hf substituted CFO ceramic (CoFe2-xHfxO4), were synthesized in the laboratory with hafnium concentrations ranging from x=0.000 to x=0.200. X-ray diffraction scans show that the Hafnium CFO crystalizes in the inverse spinel phase. Inclusion of hafnium causes lattice expansion, increasing the lattice parameter from 8.374 í? for pure CoFe2O4 to 8.391 í? for the highest concentration of hafnium tested (x=0.020). The dielectric properties of CFO are greatly enhanced by inclusion of hafnium. The enhancement is due to the …

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