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Title: Massively parallel computation and porting of EPIC research hydro code on Cray-T3D.
Creator: Dutta, Arindum., Florida Atlantic University, Tsai, Chi-Tay
Abstract/Description: The objective of the work is to verify the feasibility of converting a large FEA code into a massively parallel FEA code in terms of computational speed and cost. Sequential subroutines in the Research EPIC hydro code, a Lagrangian finite element analysis code for high velocity elastic-plastic impact problems, are individually converted into parallel code using Cray Adaptive Fortran (CRAFT). The performance of massively parallel subroutines running on 32 PEs on Cray-T3D is faster than their...
Show moreThe objective of the work is to verify the feasibility of converting a large FEA code into a massively parallel FEA code in terms of computational speed and cost. Sequential subroutines in the Research EPIC hydro code, a Lagrangian finite element analysis code for high velocity elastic-plastic impact problems, are individually converted into parallel code using Cray Adaptive Fortran (CRAFT). The performance of massively parallel subroutines running on 32 PEs on Cray-T3D is faster than their sequential counterparts on Cray-YMP. At next stage of the research, Parallel Virtual Machine (PVM) directives is used to develop a PVM version of the EPIC hydro code by connecting the converted parallel subroutines running on multiple PEs of T3D to the sequential part of the code running on single PE. With an incremental increase in the massively parallel subroutines into the PVM EPIC hydro code, the performance with respect to speedup of the code increased accordingly. The results indicate that significant speedup can be achieved in the EPIC hydro code when most or all of the subroutines are massively parallelized.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/15249
Subject Headings: Parallel processing (Electronic computers), Computer programs, coding theory, Supercomputers
Format: Document (PDF)

Title: Finite Element Modeling of Dislocation Multiplication in Silicon Carbide Crystals Grown by Physical Vapor Transport Method.
Creator: Chen, Qingde, Tsai, Chi-Tay, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Silicon carbide as a representative wide band-gap semiconductor has recently received wide attention due to its excellent physical, thermal and especially electrical properties. It becomes a promising material for electronic and optoelectronic device under high-temperature, high-power and high-frequency and intense radiation conditions. During the Silicon Carbide crystal grown by the physical vapor transport process, the temperature gradients induce thermal stresses which is a major cause of...
Show moreSilicon carbide as a representative wide band-gap semiconductor has recently received wide attention due to its excellent physical, thermal and especially electrical properties. It becomes a promising material for electronic and optoelectronic device under high-temperature, high-power and high-frequency and intense radiation conditions. During the Silicon Carbide crystal grown by the physical vapor transport process, the temperature gradients induce thermal stresses which is a major cause of the dislocations multiplication. Although large dimension crystal with low dislocation density is required for satisfying the fast development of electronic and optoelectronic device, high dislocation densities always appear in large dimension crystal. Therefore, reducing dislocation density is one of the primary tasks of process optimization. This dissertation aims at developing a transient finite element model based on the Alexander-Haasen model for computing the dislocation densities in a crystal during its growing process. Different key growth parameters such as temperature gradient, crystal size will be used to investigate their influence on dislocation multiplications. The acceptable and optimal crystal diameter and temperature gradient to produce the lowest dislocation density in SiC crystal can be obtained through a thorough numerical investigation using this developed finite element model. The results reveal that the dislocation density multiplication in SiC crystal are easily affected by the crystal diameter and the temperature gradient. Generally, during the iterative calculation for SiC growth, the dislocation density multiples very rapidly in the early growth phase and then turns to a relatively slow multiplication or no multiplication at all. The results also show that larger size and higher temperature gradient causes the dislocation density enters rapid multiplication phase sooner and the final dislocation density in the crystal is higher.
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Date Issued: 2015
PURL: http://purl.flvc.org/fau/fd/FA00004489, http://purl.flvc.org/fau/fd/FA00004489
Subject Headings: Computational grids, Crystals -- Mathematical models, Differential equations -- Data processing, Dislocations in crystals, Engineering mathematics, Finite element method
Format: Document (PDF)

Title: Design of micromixer and microfludic control system.
Creator: Li, Lin, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Micromixer is one of the most significant components of microfluidic systems, which manifest essential applications in the field of chemistry and biochemistry. Achieving complete mixing performance at the shortest micro channel length is essential for a successful micromixer design. We have developed five novel micromixers which have advantages of high efficiency, simple fabrication, easy integration and ease for mass production. The design principle is based on the concept of splitting...
Show moreMicromixer is one of the most significant components of microfluidic systems, which manifest essential applications in the field of chemistry and biochemistry. Achieving complete mixing performance at the shortest micro channel length is essential for a successful micromixer design. We have developed five novel micromixers which have advantages of high efficiency, simple fabrication, easy integration and ease for mass production. The design principle is based on the concept of splitting-recombination and chaotic advection. Numerical models of these micromixers are developed to characterize the mixing performance. Experiments are also carried out to fabricate the micromixers and evaluate the mixing performance. Numerical simulation for different parameters such as fluids properties, inlet velocities and microchannel cross sectional sizes are also conducted to investigate their effects on the mixing performance. The results show that critical inlet velocities can be predicted for normal fluid flow in the micromixers. When the inlet velocity is smaller than the critical value, the fluids mixing is dominated by mechanism of splitting-recombination, otherwise, it is dominated by chaotic advection. If the micromixer can tolerate higher inlet velocity, the complete mixing length can be further reduced. Our simulation results will provide valuable information for engineers to design a micromixer by choosing appropriate geometry to boost mixing performance and broaden implicational range to fit their specific needs. Accurate and complicated fluidic control, such as flow mixing or reaction, solution preparation, large scale combination of different reagents is also important for bio-application of microfluidics. A proposal microfluidic system is capable of creating 1024 kinds of combination mixtures. The system is composed of a high density integrated microfluidic chip and control system. The high density microfluidic chip, which is simply fabricated through soft lithography technique, contains a pair of 32 flow channels that can be specifically addressed by each 10 actuation channels based on principle of multiplexor in electronic circuits. The corresponding hardware and software compose the control system, which can be easy fabricated and modified, especially for prototype machine developing. Moreover, the control system has general application. Experiments are conducted to verify the feasibility of this microfluidic system for multi-optional solution combination.
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Date Issued: 2013
PURL: http://purl.flvc.org/fau/fd/FA0004033
Subject Headings: Flow visualization, Fluidic devices -- Design, Microelectromagnetical systems, Microfluidics -- Design
Format: Document (PDF)

Title: 3D-Printed Flexible Polylactic Acid/ Thermoplatic Polyurethane (PLA/TPU) Stents for Esophageal Malignancies.
Creator: Lin, Maohua, Kang, Yunqing, Tsai, Chi-Tay, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Palliation therapy for dysphagia using esophageal stents is the current treatment of choice for those patients with inoperable esophageal malignancies. However, the stents currently used in the clinical setting, regardless of the type of metal mesh or plastic mesh stents (covered/uncovered), may cause complications, such as tumor ingrowth and stent migration into the stomach. Furthermore, metal mesh stents have limited capacities for loading anti-cancer drugs. To effectively reduce/overcome...
Show morePalliation therapy for dysphagia using esophageal stents is the current treatment of choice for those patients with inoperable esophageal malignancies. However, the stents currently used in the clinical setting, regardless of the type of metal mesh or plastic mesh stents (covered/uncovered), may cause complications, such as tumor ingrowth and stent migration into the stomach. Furthermore, metal mesh stents have limited capacities for loading anti-cancer drugs. To effectively reduce/overcome those complications and enhance the efficacy of drug release, we designed and 3D-printed a tubular, flexible polymer stent with spirals, and then load anti-cancer drug, paclitaxel, on the stent for drug release. Non- spiral 3D-printed tubular and mesh polymer stents served as controls. The self-expansion and anti migration properties, cytotoxicity, drug release profile, and cancer cell inhibition of the 3D-printed stent were fully characterized. Results showed the self-expansion force of the 3D-printed polymer stent with spirals was slightly higher than the stent without spirals. The anti-migration force of the 3D-printed stent with spirals was significantly higher than the anti-migration force of a non-spiral stent. Furthermore, the stent with spirals significantly decreased the migration distance compared to the migration distance of the non-spiral 3D-printed polymer stent. The in vitro cytotoxicity of the new stent was examined through the viability test of human esophagus epithelial cells, and results indicated that the polymer stent does not have any cytotoxicity. The results of in vitro cell viability of esophageal cancer cells further indicated that the paclitaxel in the spiral stent treated esophageal cancer cells much more efficiently than that in the mesh stent. Furthermore, the results of the in vitro drug release profile and drug permeation showed that the dense tubular drug-loaded stent could efficiently be delivered more paclitaxel through the esophageal mucosa/submucosa layers in a unidirectional way than mesh stent that delivered less paclitaxel to the esophageal mucosa/submucosa but more to the lumen. In summary, these results showed that the 3D-printed dense polymer stent with spirals has promising potential to treat esophageal malignancies.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013230
Subject Headings: Paclitaxel, Stents, Esophageal Neoplasms, 3-D printing, Polymers in medicine
Format: Document (PDF)

Title: Dislocation reduction in gallium arsenide crystals grown from Czochralski process.
Creator: Subramanyam, Narayanaswamy., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The dislocation density in the Gallium Arsenide (GaAs) crystal is generated by the excessive thermal stresses during Czochralski (CZ) growth process. A constitutive equation which couples the dislocation density with the plastic deformation is employed to simulate the dislocation density in the crystal. The temperature distribution in the crystal during growth process is obtained by solving the quasi-steady-state (QSS) heat transfer equation. The thermal stresses induced by the temperature...
Show moreThe dislocation density in the Gallium Arsenide (GaAs) crystal is generated by the excessive thermal stresses during Czochralski (CZ) growth process. A constitutive equation which couples the dislocation density with the plastic deformation is employed to simulate the dislocation density in the crystal. The temperature distribution in the crystal during growth process is obtained by solving the quasi-steady-state (QSS) heat transfer equation. The thermal stresses induced by the temperature distribution are calculated by finite element method. The resolved shear stress (RSS) in each slip system is obtained by stress transformation. The dislocation motion and multiplication in each slip system are simulated using the constitutive equation and the total dislocation density in the crystal is obtained. The dislocation density is also found to be affected by the growth orientation, growth speed, ambient temperature and the radius of the crystal. The dislocation density in GaAs crystals grown from different growth orientation and crystal radius at various ambient temperatures will be calculated so that the influence of these growth parameters on the dislocation density can be understood. Consequently, one can control the growth parameters to reduce the dislocation density generated in the crystal during the CZ growth process.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/14982
Subject Headings: Dislocations in crystals, Gallium arsenide semiconductors, Crystal growth
Format: Document (PDF)

Title: Crystallographic finite element modeling for dislocation generation in semiconductor crystals grown by VGF process.
Creator: Sheu, Gary., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The generation and multiplication of dislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals grown by the Vertical Gradient Freeze (VGF) process is predicted using a transient crystallographic finite element model. This transient model is developed by coupling microscopic dislocation motion and multiplication to macroscopic plastic deformation in the slip system of the grown crystals during their growth process. During the growth of InP and GaAs crystals,...
Show moreThe generation and multiplication of dislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals grown by the Vertical Gradient Freeze (VGF) process is predicted using a transient crystallographic finite element model. This transient model is developed by coupling microscopic dislocation motion and multiplication to macroscopic plastic deformation in the slip system of the grown crystals during their growth process. During the growth of InP and GaAs crystals, dislocations are generated in plastically deformed crystal as a result of crystallographic glide caused by excessive thermal stresses. The temperature fields are determined by solving the partial differential equation of heat conduction in a VGF crystal growth system. The effects of growth orientations and growth parameters (i.e., imposed temperature gradients, crystal radius and growth rate) on dislocation generation and multiplication in GaAs and InP crystals are investigated using the developed transient crystallographic finite element model. Dislocation density patterns on the cross section of GaAs and InP crystals are numerically calculated and compared with experimental observations. For crystals grown along [001] and [111] orientations, the results show that more dislocations are generated as the temperature gradient, the crystal growth rate and the crystal radius increase. For the same growth process, it shows that the crystal grown along [111] orientation is a favorable growth direction to grow lower dislocation density crystals. All the results show a famous "W" shape and four fold symmetry dislocation density pattern in GaAs and InP crystals grown from both orientations regardless of crystal growth parameters, which agree well with the patterns observed in actual grown crystals. Therefore, this developed crystallographic model can be employed by crystal grower to design an optimal growth parameters and orientations for growing low dislocation density in advanced semiconductor and optical crystals.
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Date Issued: 2005
PURL: http://purl.flvc.org/fcla/dt/12171
Subject Headings: Surface chemistry, Gallium arsenide semiconductors, Dislocations in crystals, Crystal growth, Semiconductors--Materials
Format: Document (PDF)

Title: Finite element modeling for dislocation generation in semiconductor crystals grown from the melt.
Creator: Zhu, Xinai., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Dislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals are generated by excessive stresses that are induced during the crystal growth process, and the fabrication and packaging of microelectronic devices/circuits. The presence of dislocations has adverse effects on the performance, lifetime and reliability of the GaAs and InP-based devices/circuits. It is well known that dislocation density can be significantly reduced by doping impurity atoms into the GaAs and InP...
Show moreDislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals are generated by excessive stresses that are induced during the crystal growth process, and the fabrication and packaging of microelectronic devices/circuits. The presence of dislocations has adverse effects on the performance, lifetime and reliability of the GaAs and InP-based devices/circuits. It is well known that dislocation density can be significantly reduced by doping impurity atoms into the GaAs and InP crystal and/or decreasing the thermal stresses in these crystals during their growth process. In order to reduce the dislocation density generated in the GaAs and InP crystals, the influence of crystal growth parameters and doping impurity atoms on the dislocations reduction in GaAs and InP crystals has to be understood. Therefore, a transient finite element model was developed to simulate the dislocation generation in GaAs and InP crystals grown from the melt. A viscoplastic constitutive equation that couples a microscopic dislocation density with a macroscopic plastic deformation is employed to formulate this transient finite element model, where the dislocation density is considered as an internal state variable and the doping impurity is represented by a drag-stress in this constitutive model. GaAs and InP single crystals grown by the vertical gradient freeze (VGF) process were adopted as examples to study the influences of doping impurity and growth parameters on dislocations generated in these grown crystal. The calculated results show that doping impurity can significantly reduce dislocation generation and produces low-dislocation-density or dislocation free GaAs and InP single crystals. It also shows that the dislocations generated in GaAs and InP crystals increase as the crystal diameter and imposed temperature gradient increase, but do not change or increase slightly as the crystal growth rate increases. Therefore, this finite element model can be effectively used by crystal growers to select acceptable levels of doping impurity, crystal diameter, temperature gradient, and growth rate to produce the lowest dislocation density in GaAs and InP crystals through a thorough numerical investigation using this developed finite element model.
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Date Issued: 2004
PURL: http://purl.flvc.org/fcla/dt/12072
Subject Headings: Dislocations in crystals, Gallium arsenide semiconductors, Indium phosphide, Metal crystals--Growth
Format: Document (PDF)

Title: Finite element modeling of dislocation multiplication in microelectronic and optoelectronic devices/circuits.
Creator: Wang, Xueming., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Two-dimensional and three-dimensional methodologies are developed to determine the dislocation multiplication in microelectronic and optoelectronic devices/circuits. A two-dimensional finite element code is developed to simulate the dislocation multiplication in microelectronic and optoelectronic devices/circuits. Example two-dimensional analyses are performed and analysis results are presented. The three-dimensional methodology is successfully implemented using ANSYS APDL Language within the...
Show moreTwo-dimensional and three-dimensional methodologies are developed to determine the dislocation multiplication in microelectronic and optoelectronic devices/circuits. A two-dimensional finite element code is developed to simulate the dislocation multiplication in microelectronic and optoelectronic devices/circuits. Example two-dimensional analyses are performed and analysis results are presented. The three-dimensional methodology is successfully implemented using ANSYS APDL Language within the ANSYS program. A three dimensional heterojunction bipolar transistor model is generated. CFD-thermal and structural analyses are performed to determine temperature fields and dislocation densities, which are calculated as functions of time, thickness of the thermal shunt, and heat generation rates.
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Date Issued: 2005
PURL: http://purl.flvc.org/fcla/dt/12182
Subject Headings: Finite element method, Computational grids, ANSYS (Computer systems), Semiconductors--Materials--Analysis
Format: Document (PDF)

Title: Finite element modeling of composite laminates with embedded piezoelectric structures including debonding.
Creator: Suarez, Beatriz., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Piezoelectric sensors are one of the primary devices used in smart structures because of their capability to act as both, sensors and actuators. A finite element model has been developed to predict elastic behavior and electrical response of laminate composites with embedded piezoelectric sensors. Correlations with experimental results indicate that the model is capable of forecasting the elastic and electrical response of the structure with good accuracy. The important issue of debonding of...
Show morePiezoelectric sensors are one of the primary devices used in smart structures because of their capability to act as both, sensors and actuators. A finite element model has been developed to predict elastic behavior and electrical response of laminate composites with embedded piezoelectric sensors. Correlations with experimental results indicate that the model is capable of forecasting the elastic and electrical response of the structure with good accuracy. The important issue of debonding of any of the faces of the sensors is also studied in the current work. Finite element results indicate significant changes in the elastic response caused by debonding, as well as unreliable electrical outputs.
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Date Issued: 1998
PURL: http://purl.flvc.org/fcla/dt/15603
Subject Headings: Finite element method, Piezoelectric materials, Laminated materials, Smart structures
Format: Document (PDF)

Title: Impact analysis of a piezo-transducer-vibrator.
Creator: Karabiyik, Necati., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Piezo-Transducer-Vibrators are miniature devices that emit both audio and silent signals and are currently targeted for use as an integral part of wristwatch technology. Utilizing nonlinear finite element analysis is essential for obtaining a greater understanding of the system response under varying conditions. Dyna3D nonlinear finite element code is applied in this analysis with the focus on the mechanical aspects of the vibrator. Four impact variables, the velocity, the plate gap, the...
Show morePiezo-Transducer-Vibrators are miniature devices that emit both audio and silent signals and are currently targeted for use as an integral part of wristwatch technology. Utilizing nonlinear finite element analysis is essential for obtaining a greater understanding of the system response under varying conditions. Dyna3D nonlinear finite element code is applied in this analysis with the focus on the mechanical aspects of the vibrator. Four impact variables, the velocity, the plate gap, the weight and the velocity angle are studied to determine the effects on the system response. Each impact variable is assigned three separate values, creating twelve programs for analysis. For each program, responses to impact conditions are studied demonstrating the deformed mode shapes, maximum principal stresses and maximum displacements using state database plots and time-history plots.
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Date Issued: 1994
PURL: http://purl.flvc.org/fcla/dt/15008
Subject Headings: Piezoelectric transducers, Finite element method, Wrist watches, Vibrators
Format: Document (PDF)

Title: Paper curl modeling.
Creator: Lu, Wentao, Florida Atlantic University, Tsai, Chi-Tay, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: A computational approach for characterization of curl of paper under humidity changes is presented. Asymmetric papers with nonuniform through-thickness fiber orientation distribution are considered. Testing of the constituent layers of the papers considered was conducted at various constant relative humidities to obtain the mechanical properties, moisture content, moisture expansion coefficients and stress relaxation curves. Experiments were performed on asymmetric two-ply laboratory made...
Show moreA computational approach for characterization of curl of paper under humidity changes is presented. Asymmetric papers with nonuniform through-thickness fiber orientation distribution are considered. Testing of the constituent layers of the papers considered was conducted at various constant relative humidities to obtain the mechanical properties, moisture content, moisture expansion coefficients and stress relaxation curves. Experiments were performed on asymmetric two-ply laboratory made papers to determine the curl response under moisture loading. The influence of viscoelastic stress relaxation on the curl response was first investigated. Geometrically nonlinear finite element analysis was conducted. It was found that the curvatures relax at an increasing rate with increasing humidities because of moisture enhanced viscoelastic dominance. Computed time-dependent curvatures were compared to experimental measurements which verified the mode shape and time-dependent relaxation response. Geometrically nonlinear finite element analysis revealed that initial deflections may strongly influence the subsequent curl behavior. A sheet with initial curvatures may undergo a bifurcation transition (buckling curl response) if the curvatures strongly interact. After the bifurcation transition, the sheet may or may not assume an unexpected shape. Experiments showed sensitivity of the response to the directions of the initial curvatures, and there are indications of a bifurcation as a result of curvature interaction. A two-ply laminate model was used to analyze curvatures of various asymmetric papers. Differences in fiber orientation distribution and principal fiber orientation angle between the two plies were considered. The analysis showed that the sheet typically bifurcated into a cylindrical and/or twisted shape. A sheet with known through-thickness fiber orientation demonstrated a complex curl response that could be simulated using the approach presented, given that the initial curl shape is known.
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Date Issued: 2000
PURL: http://purl.flvc.org/fcla/dt/12626
Subject Headings: Paper--Testing, Paper--Mechanical properties, Papermaking
Format: Document (PDF)

Title: The prediction of dislocation generation during gallium arsenide crystal growth.
Creator: Liu, Ping., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Thermal stresses are induced by temperature variations in gallium arsenide(GaAs) crystal growth. The thermal stresses cause plastic deformations by dislocation and dynamic interaction in the crystal. In this study, firstly the temperature distribution in the Czochralski technique (CZ) growth of GaAs crystal is obtained according to the Jordan model. Secondly a visco-plastic response function for the GaAs crystal is developed from the Haasen model. Finally a nonlinear finite element model is...
Show moreThermal stresses are induced by temperature variations in gallium arsenide(GaAs) crystal growth. The thermal stresses cause plastic deformations by dislocation and dynamic interaction in the crystal. In this study, firstly the temperature distribution in the Czochralski technique (CZ) growth of GaAs crystal is obtained according to the Jordan model. Secondly a visco-plastic response function for the GaAs crystal is developed from the Haasen model. Finally a nonlinear finite element model is employed to simulate the dislocation generation during CZ growth of GaAs crystal.
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Date Issued: 1991
PURL: http://purl.flvc.org/fcla/dt/14780
Subject Headings: Gallium arsenide semiconductors, Dislocations in crystals, Crystal growth
Format: Document (PDF)

Title: Thermal and stress analysis of heterojunction bipolar transistor.
Creator: Rivero, Jose Fernando., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The objective of this work is to perform the current induce thermal stress analysis of heterojunction bipolar transistor and to determine the implications of the variation of the thermal shunt thickness. A thesis presented on multi-physics using finite element analysis, covering fluid, thermal and stress with fatigue life analysis of a microelectronic heterojunction bipolar transistor.
Date Issued: 2001
PURL: http://purl.flvc.org/fcla/dt/12834
Subject Headings: Junction transistors, Thermal analysis
Format: Document (PDF)

Title: Thermal analysis of a heterojunction bipolar transistor.
Creator: Kokkalera, Subbaiya U., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The Heterojunction Bipolar Transistor (HBT) is capable of delivering high current density at microwave frequencies and are now being implemented in microwave circuitry as high power amplifiers. The heat generated during device operation is dissipated through the Gallium Arsenide substrate. Because of its poor thermal conductivity the junction temperature rise can be large enough to degrade and thermally limit the performance of the device. The power HBT with multiple emitter fingers are...
Show moreThe Heterojunction Bipolar Transistor (HBT) is capable of delivering high current density at microwave frequencies and are now being implemented in microwave circuitry as high power amplifiers. The heat generated during device operation is dissipated through the Gallium Arsenide substrate. Because of its poor thermal conductivity the junction temperature rise can be large enough to degrade and thermally limit the performance of the device. The power HBT with multiple emitter fingers are susceptible to the thermal effect due to non-uniform temperature distribution. This results in a thermal effect called thermal runaway causing thermal-induced current instability and hot spot formation thus destroying the device. Thermal shunt technique which has been developed to suppress this non-uniform temperature involves fabrication of a thick metal thermal shunt connecting all the fingers thus forming a strong thermal coupling between the emitter fingers. In this thesis 2 and 3-dimensional thermal simulations were carried out using Finite Element techniques to study the thermal behavior of the HBT's as a function of thermal shunt and other device design configurations such as the number of emitter fingers, thickness of thermal shunt, emitter spacing, Silicon as a substrate material, power variation etc. The results are projected as a design guideline for HBT device.
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Date Issued: 1994
PURL: http://purl.flvc.org/fcla/dt/15081
Subject Headings: Junction transistors, Thermal analysis, Microwave circuits
Format: Document (PDF)

Title: Evolution and application of a parallel algorithm for explicit transient finite element analysis on SIMD/MIMD computers.
Creator: Das, Partha S., Florida Atlantic University, Case, Robert O., Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The development of a parallel data structure and an associated elemental decomposition algorithm for explicit finite element analysis for massively parallel SIMD computer, the DECmpp 12000 (MasPar MP-1) machine, is presented, and then extended to implementation on the MIMD computer, Cray-T3D. The new parallel data structure and elemental decomposition algorithm are discussed in detail and is used to parallelize a sequential Fortran code that deals with the application of isoparametric...
Show moreThe development of a parallel data structure and an associated elemental decomposition algorithm for explicit finite element analysis for massively parallel SIMD computer, the DECmpp 12000 (MasPar MP-1) machine, is presented, and then extended to implementation on the MIMD computer, Cray-T3D. The new parallel data structure and elemental decomposition algorithm are discussed in detail and is used to parallelize a sequential Fortran code that deals with the application of isoparametric elements for the nonlinear dynamic analysis of shells of revolution. The parallel algorithm required the development of a new procedure, called an 'exchange', which consists of an exchange of nodal forces at each time step to replace the standard gather-assembly operations in sequential code. In addition, the data was reconfigured so that all nodal variables associated with an element are stored in a processor along with other element data. The architectural and Fortran programming language features of the MasPar MP-1 and Cray-T3D computers which are pertinent to finite element computations are also summarized, and sample code segments are provided to illustrate programming in a data parallel environment. The governing equations, the finite element discretization and a comparison between their implementation on Von Neumann and SIMD-MIMD parallel computers are discussed to demonstrate their applicability and the important differences in the new algorithm. Various large scale transient problems are solved using the parallel data structure and elemental decomposition algorithm and measured performances are presented and analyzed in detail. Results show that Cray-T3D is a very promising parallel computer for finite element computation. The 32 processors of this machine shows an overall speedup of 27-28, i.e. an efficiency of 85% or more and 128 processors shows a speedup of 70-77, i.e. an efficiency of 55% or more. The Cray-T3D results demonstrated that this machine is capable of outperforming the Cray-YMP by a factor of about 10 for finite element problems with 4K elements, therefore, the method of developing the parallel data structure and its associated elemental decomposition algorithm is recommended for implementation on other finite element code in this machine. However, the results from MasPar MP-1 show that this new algorithm for explicit finite element computations do not produce very efficient parallel code on this computer and therefore, the new data structure is not recommended for further use on this MasPar machine.
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Date Issued: 1997
PURL: http://purl.flvc.org/fcla/dt/12500
Subject Headings: Finite element method, Algorithms, Parallel computers
Format: Document (PDF)

Title: The finite element method as a parametric tool in the design and analysis of a pressure vessel having a threaded closure.
Creator: Merkl, Garrett Andrew., Florida Atlantic University, Case, Robert O., Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The finite element method is a very powerful tool used to analyze a variety of problems in engineering. This thesis looks at the finite element method as a tool and several important modeling features of concern. A well known finite element software package, ANSYS, will be used to demonstrate a diverse number of its capabilities, and several procedures followed in solving a specific engineering problem. The subject matter involves a nonlinear contact analysis of a pressure vessel having a...
Show moreThe finite element method is a very powerful tool used to analyze a variety of problems in engineering. This thesis looks at the finite element method as a tool and several important modeling features of concern. A well known finite element software package, ANSYS, will be used to demonstrate a diverse number of its capabilities, and several procedures followed in solving a specific engineering problem. The subject matter involves a nonlinear contact analysis of a pressure vessel having a threaded closure. The choice of this application is prompted by an interest in better understanding how the finite element method is implemented in the design and analysis of different pressure vessel parameters. A parametric finite element analysis was performed. Load and stress distributions along the threaded region of the vessel were examined for parameters including number of threads, thread pitch, diameter ratio, closure plug length, and thread profile.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/15243
Subject Headings: Finite element method, Pressure vessels--Design and construction, Strains and stresses--Mathematical models
Format: Document (PDF)

Finite element method (6)	+ -
Dislocations in crystals (5)	+ -
Gallium arsenide semiconductors (4)	+ -
Crystal growth (3)	+ -
Computational grids (2)	+ -

Junction transistors (2)	+ -
Thermal analysis (2)	+ -
3-D printing (1)	+ -
ANSYS (Computer systems) (1)	+ -
Algorithms (1)	+ -
Computer programs (1)	+ -
Crystals -- Mathematical models (1)	+ -
Differential equations -- Data processing (1)	+ -
Engineering mathematics (1)	+ -
Esophageal Neoplasms (1)	+ -
Flow visualization (1)	+ -
Fluidic devices -- Design (1)	+ -
Indium phosphide (1)	+ -
Laminated materials (1)	+ -
Metal crystals--Growth (1)	+ -
Microelectromagnetical systems (1)	+ -
Microfluidics -- Design (1)	+ -
Microwave circuits (1)	+ -
Paclitaxel (1)	+ -
Paper--Mechanical properties (1)	+ -
Paper--Testing (1)	+ -
Papermaking (1)	+ -
Parallel computers (1)	+ -
Parallel processing (Electronic computers) (1)	+ -
Piezoelectric materials (1)	+ -

Tsai, Chi-Tay (16)	+ -
College of Engineering and Computer Science (15)	+ -
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