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Articles 1 - 30 of 34
Full-Text Articles in Engineering
A Nonlocal Model For Coupled Damage-Plasticity Incorporating Gradients Of Internal State Variables At Multiscales, Robert J. Dorgan
A Nonlocal Model For Coupled Damage-Plasticity Incorporating Gradients Of Internal State Variables At Multiscales, Robert J. Dorgan
LSU Doctoral Dissertations
The thermodynamically consistent formulation and the subsequent numerical implementation of a gradient enhanced continuum coupled damage-plasticity model as a constitutive framework to model ill-posed localization problems is presented. By the introduction of "nonlocal," gradient-enhanced measures in the plasticity potential function and yield criterion and in the damage potential function and damage criterion, the proposed model introduces microstructural characteristic material length scales which allows the size of localized zones to be predicted based on material constants, as opposed to local models where the loss of ellipticity causes the localized zones to be mesh dependent.
The gradient model proposed introduces non-linear functions …
Experimental And Computational Analysis Of Random Cylinder Packings With Applications, Wenli Zhang
Experimental And Computational Analysis Of Random Cylinder Packings With Applications, Wenli Zhang
LSU Doctoral Dissertations
Random cylinder packings are prevalent in chemical engineering applications and they can serve as prototype models of fibrous materials and/or other particulate materials. In this research, comprehensive studies on cylinder packings were carried out by computer simulations and by experiments. The computational studies made use of a collective rearrangement algorithm (based on a Monte Carlo technique) to generate different packing structures. 3D random packing limits were explored, and the packing structures were quantified by their positional ordering, orientational ordering, and the particle-particle contacts. Furthermore, the void space in the packings was expressed as a pore network, which retains topological and …
Spectral Analysis Of Total Suspended Solids Mixtures For Solids Composition Determination, Curtis W. Sutherland
Spectral Analysis Of Total Suspended Solids Mixtures For Solids Composition Determination, Curtis W. Sutherland
LSU Doctoral Dissertations
Total Suspended Solids (TSS) analysis provides an initial and very basic measure for study and characterization of water quality. The present tedious procedures used for the identification of different solids constituents present in TSS and for the classification or insight into the origins of those solids are time-consuming and expensive. The research reported herein investigates the use of instrumental analysis using reflectance spectra of TSS as an attractive alternative to sufficiently characterize and identify TSS in a more rapid and economical method that could be used to study TSS transport and to identity TSS points of origin. For this investigative …
A Distribution Kinetics Approach For Polymer Crystallization And Phase Separation, Jiao Yang
A Distribution Kinetics Approach For Polymer Crystallization And Phase Separation, Jiao Yang
LSU Doctoral Dissertations
The mechanism of polymer crystallization is extensively studied and still far away from consensus. This research adopted cluster size distribution kinetics approach to explore the kinetics of polymer crystallization and phase separation within spinodal region. The kinetics of polymer crystallization is studied by integrating nucleation, crystal growth and ripening. Population balance equations based on crystal size distribution and concentration of amorphous polymer segments are solved numerically and the related differential moment equations are also solved. The model accounts for nucleation and crystal growth. Different mass dependences of growth and dissociation rate coefficients are proposed to investigate the fundamental features of …
Structural Performance Of Approach Slab And Its Effect On Vehicle Induced Bridge Dynamic Response, Xiaomin Shi
Structural Performance Of Approach Slab And Its Effect On Vehicle Induced Bridge Dynamic Response, Xiaomin Shi
LSU Doctoral Dissertations
Differential settlement often occurs between the bridge abutment and the embankment soil. It causes the approach slab to lose its contacts and supports from the soil and the slab will bend in a concave manner. Meanwhile, loads on the slab will also redistribute to the slab ends, which may result in faulting (or "bump") at the slab ends. Once a bump forms, repeating traffic vehicles can deteriorate the expansion joint in turn. In this case, the vehicle receives an initial disturbance before it reaches the bridge. This excitation introduces an extra impact load on the bridge and affects its dynamic …
A Micromechanical Approach For Predicting The Complex Shear Modulus And Accumulated Shear Strain Of Asphalt Mixtures From Binder And Mastics, Cristian Druta
A Micromechanical Approach For Predicting The Complex Shear Modulus And Accumulated Shear Strain Of Asphalt Mixtures From Binder And Mastics, Cristian Druta
LSU Doctoral Dissertations
Asphalt mixtures are particulate composite materials consisting of uniformly distributed mineral aggregates, asphalt binder and air voids. Mixtures of asphalt binder and filler, also called mastics, are often assumed to behave as simple viscoelastic materials, where the binders are stiffened by the filler. Because the workability and performance of bituminous mixes are known to be affected by the filler-asphalt mixture (or mastic) properties, this study is intended for performing rheological tests on asphalt binder and mastics and use the results in order to estimate performance parameters of asphalt mixture. The present work uses the PG64-22 asphalt binder test data initially …
A State-Space Approach To Blind Estimation Of Mimo Wireless Channels, Hesham Mahmoud Zarif Amin Badr
A State-Space Approach To Blind Estimation Of Mimo Wireless Channels, Hesham Mahmoud Zarif Amin Badr
LSU Doctoral Dissertations
This dissertation focuses on blind channel estimation in wireless communications such that the estimated channel admits the minimum phase property. It assumes only the second order statistics of the transmitted signal at the receive side. Our proposed approach is based on the generalized spectral factorization because of the deficient normal rank for the power spectral density (PSD) function of the received signal. We will show the relationship between the generalized spectral factorization and inner-outer factorizations where the inner is square with smaller size. The inner-outer factorization is in turn related to the generalized Kalman filtering in which the dimension of …
Tribological Aspects Of Journal Bearings Focusing On The Stribeck Curve, Xiaobin Lu
Tribological Aspects Of Journal Bearings Focusing On The Stribeck Curve, Xiaobin Lu
LSU Doctoral Dissertations
The dissertation focuses on the frictional characteristics of journal bearings as represented by the Stribeck curve. The behavior of lift-off speed and the factors that affect it are explored. An equation is proposed for predicting the lift-off speed. The comparison between the experimental results of oil- and grease-lubricated journal bearings with a mixed elastohydrodynamic lubrication model for line contacts is indicative of good agreement in the mixed lubrication regime. Efforts are made to modify the surface profile of bushing by putting dimples on its surface. Experimental results show that with proper dimensions of dimples, the friction performance of journal bearings …
Mimo-Ofdm Communication Systems: Channel Estimation And Wireless Location, Zhongshan Wu
Mimo-Ofdm Communication Systems: Channel Estimation And Wireless Location, Zhongshan Wu
LSU Doctoral Dissertations
In this new information age, high data rate and strong reliability features our wireless communication systems and is becoming the dominant factor for a successful deployment of commercial networks. MIMO-OFDM (multiple input multiple output-orthogonal frequency division multiplexing), a new wireless broadband technology, has gained great popularity for its capability of high rate transmission and its robustness against multi-path fading and other channel impairments. A major challenge to MIMO-OFDM systems is how to obtain the channel state information accurately and promptly for coherent detection of information symbols and channel synchronization. In the first part, this dissertation formulates the channel estimation problem …
Integrated Circuit Metrology By Multilevel Patterning Technology, Li Jiang
Integrated Circuit Metrology By Multilevel Patterning Technology, Li Jiang
LSU Doctoral Dissertations
A low cost, high accuracy method is described in detail for measuring image placement in integrated circuit manufacture. The method measures both the overlay between levels and the absolute placement of features in a single level. The overlay is measured by a technique which views multiple levels separately. The absolute distances between features on a test wafer are measured by comparing the features to precision gratings. Optical imaging techniques are described for viewing and analyzing the grating images, as well as for measuring distortions in the observing microscope and a video camera. These techniques permit image placement measurements to be …
Active Control Of Spray Combustion, Onur Tuncer
Active Control Of Spray Combustion, Onur Tuncer
LSU Doctoral Dissertations
Effect of a forced dilution air jet on air-fuel spray mixing and emissions has been investigated. Temperature measurements have been made at a number of forcing frequencies in the range of 100-1100 Hz and blowing ratios between 6-15. Open-loop flame response to forcing has also been acquired by recording pressure and heat release spectra. The results show that the mean temperature field inside the flame can be altered due to jet modulation. Significant effects are observed by forcing at locations close to the dump plane. Enhancements in temperature of the order of 100–200 ˚C, and reduction in pattern factor of …
An Adaptive Multi-Scale Computational Method For Modeling Nonlinear Deformation In Nanoscale Materials, Wenming Wang
An Adaptive Multi-Scale Computational Method For Modeling Nonlinear Deformation In Nanoscale Materials, Wenming Wang
LSU Doctoral Dissertations
In this dissertation a coupled multi-scale computational model for simulating nonlinear deformation processes in crystalline metals at finite temperatures is developed. The computational model uses the finite element method to model the coarse scale response of the material. The constitutive response in the finite element will be modeled through interatomic potentials acting on the underlying homogeneous crystal lattice that characterizes its nanostructure. An adaptive remeshing technique is proposed to automatically delineate regions of severe deformation where homogeneity of the microstructure/deformation is violated. In these regions the finite element will be replaced by a set of deformed atoms which interact with …
A Plasticity-Damage Model For Plain Concrete, Umit Cicekli
A Plasticity-Damage Model For Plain Concrete, Umit Cicekli
LSU Doctoral Dissertations
A plastic-damage model for plain concrete is developed in this work. The model uses two different yield criteria: one for plasticity and one for damage. In order to account both for compression and tension loadings, the damage criterion is divided into two parts: one for compression and a second for tension. The superscripts (+) and (-) in this work are used to represent tension and compression cases, respectively. The total stress is decomposed into tension and compressions components. The total strain is decomposed into elastic and plastic parts. The strain equivalence concept is used such that the strains in the …
Data-Driven Fault Detection Using Trending Analysis, Min Luo
Data-Driven Fault Detection Using Trending Analysis, Min Luo
LSU Doctoral Dissertations
The objective of this research is to develop data-driven fault detection methods which do not rely on mathematical models yet are capable of detecting process malfunctions. Instead of using mathematical models for comparing performances, the methods developed rely on extensive collection of data to establish classification schemes that detect faults in new data. The research develops two different trending approaches. One uses the normal data to define a one-class classifier. The second approach uses a data mining technique, e.g. support vector machine (SVM) to define multi class classifiers. Each classifier is trained on a set of example objects. The one-class …
Towards A Generalized Team Task Complexity Model, Ashok Darisipudi
Towards A Generalized Team Task Complexity Model, Ashok Darisipudi
LSU Doctoral Dissertations
The objective of this research was to develop and validate a generalized team task-complexity model and framework by drawing on the literature from various team and task factors grouped into three task-dimensions, which compose task-complexity space and how these affect the task-performance. A number of task typologies have been presented in the teams' literature to better define and understand the critical role of the tasks and the associated team processes. In addition, most of the research work has defined team measures as highly abstract concepts not capable of providing the quantitative comparison of team performances from various domains. This research …
Uv-Liga Micro-Fabrication Of Inertia Type Electrostatic Transducers And Their Application, Seok Jae Jeong
Uv-Liga Micro-Fabrication Of Inertia Type Electrostatic Transducers And Their Application, Seok Jae Jeong
LSU Doctoral Dissertations
This dissertation discusses the design, working principles, static & dynamic analysis and simulation, mechanics of material, applied MEMS technology, micro-fabrication, and experimental testing of two types of micro-transducers: micro-power relay and micro-accelerometer. Several possible design concepts were proposed, and the advantages and disadvantages of electrostatic working principles were also discussed. Transducers presented in this research used electrostatic force as a driving force in the micro-relay and capacitance as a sensing parameter in the micro-accelerometer. There was an analogy between the micro-relay and the micro-accelerometer in their theoretical approach and fabrication processes. The proposed micro-transducers (micro-relay and micro-accelerometer) were fabricated using …
Exploring The Hot-Carrier Effect On The Wireless Transceivers, Sameer R. Herlekar
Exploring The Hot-Carrier Effect On The Wireless Transceivers, Sameer R. Herlekar
LSU Doctoral Dissertations
Phase noise can be regarded as the most severe cause of performance degradation in the wireless communication systems. The hot-carriers (HCs), found in the CMOS synchronization circuits, are the high-energy charge carriers that degrade the MOSFET devices’ performance by increasing the threshold voltage required to operate the MOSFETs. The HC effect manifests itself as the phase noise whose level increases with the continued MOSFET operation and such increases result in the performance degradation of the voltage-controlled oscillator (VCO) built on the MOSFETs. The HC effect is particularly evident in the short-channel MOSFET devices. In this dissertation, we analyze the wireless …
Theory Of Curvature-Dependent Disjoining Pressure And Its Application To Liquid Films, Jin Zhang
Theory Of Curvature-Dependent Disjoining Pressure And Its Application To Liquid Films, Jin Zhang
LSU Doctoral Dissertations
A liquid film of thickness h < 100 nm is subject to additional intermolecular forces, which are collectively called disjoining pressure Pi. Since Pi dominates at small film thicknesses, it determines the stability and wettability of thin films. Current theory for uniform films gives Pi = Pi(h). It becomes unbounded as h -> 0. We present a theory of curvature-dependent disjoining pressure. The new Pi depends on the curvature hxx, slope hx, and h. When this theory is implemented for Lennard-Jones liquid films, the new Pi is bounded as h -> 0. We show that this Pi captures three regimes of drop behavior (complete wetting, partial wetting, and pseudo partial wetting) without altering the signs of the long and short-range interactions. We also find that a drop with a uniform film is linearly stable, whereas a drop without a uniform film is unstable. Evaporating thin films is …
Ultra-Violet Lithography Of Thick Photoresist For The Applications In Biomems And Micro Optics, Ren Yang
Ultra-Violet Lithography Of Thick Photoresist For The Applications In Biomems And Micro Optics, Ren Yang
LSU Doctoral Dissertations
UV lithography of thick photoresist is widely used in microelectromechanical systems (MEMS) and micro-optoelectromechanical systems (MOEMS). SU-8 is a typical negative tone thick photoresist for micro systems, and can be used for both structural material and pattern transfer. This dissertation presents an effort to comprehensively study these important subjects. The first part, and the most fundamental part of this dissertation concentrated on the numerical analysis and experimental study of the wavelength dependent absorbance of SU-8 and the diffraction effects on the sidewall profiles of the microstructures made using UV lithography of SU-8. This study has laid the foundation for all …
Theoretical And Experimental Study On Cable Vibration Reduction With A Tmd-Mr Damper, Wenjie Wu
Theoretical And Experimental Study On Cable Vibration Reduction With A Tmd-Mr Damper, Wenjie Wu
LSU Doctoral Dissertations
Stay cables are vulnerable to dynamic excitations because of their low intrinsic damping. Excessive cable vibrations cause frequent maintenance and are detrimental to the safety of the entire bridge. Targeting the severe cable vibration problem, in addition to using the existing Magnetorheological (MR) damper, the current study proposes a new type of damper, called the Tuned Mass Damper-Magnetorheological (TMD-MR) damper. Theoretical and experimental investigations for the damper performance on the cable vibration reduction are conducted, which provides the necessary research support for practical implementation. Experiments on the individual MR damper are carried out first to gain some experience on the …
System Optimization For Realizing A Miniaturized Gas Chromatograph Sensor For Rapid Chemical Analysis, Abhinav Bhushan
System Optimization For Realizing A Miniaturized Gas Chromatograph Sensor For Rapid Chemical Analysis, Abhinav Bhushan
LSU Doctoral Dissertations
Rapid and comprehensive on-site analysis of chemicals in applications ranging from industrial process control to homeland security is of significant importance to improve the environment and save human life. The need for sensors that are fast, reliable, and portable has never been greater. For the challenging task of on-site instrumentation, where power sources can be limited, shrinking the size of the device is the most effective way to conserve power. Although gas chromatography is a mature technique well suited for these applications, current instrumentation has deficiencies that limit its usage. Speed of analysis and non portability are severe hindrances to …
Distribution Dynamics Of Complex Systems, Young-Pyo Jeon
Distribution Dynamics Of Complex Systems, Young-Pyo Jeon
LSU Doctoral Dissertations
A complex system is defined as a system with many interdependent parts having emergent self-organization; analyzing and designing such complex systems is a new challenge. A common observable structure of many complex systems is the network, which is connections among nodes, and thus inherently difficult to describe. The goal of this research is to introduce an effective methodology to describe complex systems, and thus we will construct a population balance (distribution kinetics) model based on the association-dissociation process to describe the evolution of complex systems. Networks are commonly observed structures in complex systems with interdependent parts that self-organize. How networks …
Use Of Polyhydroxyalkanoates For Denitrification In Recirculating Aquaculture Systems, Maria Teresa Gutierrez-Wing
Use Of Polyhydroxyalkanoates For Denitrification In Recirculating Aquaculture Systems, Maria Teresa Gutierrez-Wing
LSU Doctoral Dissertations
Increasing demand of aquacultural products is driving the industry toward more intensive culture practices. Aquacultural operations are constrained by limitations on the availability high quality waters and regulatory pressures on the discharges. Recirculating systems can address these issues by reducing the amount of water required in the operation. Closed systems are especially suited where biosecurity is important. In closed systems, nitrate accumulates, limiting the time the water can be reused. In marine inland systems, water reuse reduces the cost of salt for make up water. To increase the water reuse time, some form of nitrate removal process must be incorporated …
Optical Control Plane: Theory And Algorithms, Stefan Alexandru Pascu
Optical Control Plane: Theory And Algorithms, Stefan Alexandru Pascu
LSU Doctoral Dissertations
In this thesis we propose a novel way to achieve global network information dissemination in which some wavelengths are reserved exclusively for global control information exchange. We study the routing and wavelength assignment problem for the special communication pattern of non-blocking all-to-all broadcast in WDM optical networks. We provide efficient solutions to reduce the number of wavelengths needed for non-blocking all-to-all broadcast, in the absence of wavelength converters, for network information dissemination. We adopt an approach in which we consider all nodes to be tap-and-continue capable thus studying lighttrees rather than lightpaths. To the best of our knowledge, this thesis …
Electrodeposition Of Cocu Nanostructures, Yutong Li
Electrodeposition Of Cocu Nanostructures, Yutong Li
LSU Doctoral Dissertations
Electrodeposition is a key component in the microelectronic industry because it has the following advantages: low cost, easy operation and the capability to deposit into irregular geometries such as recessed and curved areas. In this dissertation, CoCu alloys were investigated to fabricate multilayers, microdevices and microposts. All of these multilayer structures were composed of nanometric copper and cobalt-rich layers in order to obtain magnetoresistance, a phenomenon where the resistance of multilayer structures decreases with increases of external magnetic field. An investigation was carried out in order to evaluate appropriate plating conditions during multilayered thin film deposition, with the aim to …
Intercarrier Interference Suppression For The Ofdm Systems In Time-Varying Multipath Fading Channels, Xiaozhou Huang
Intercarrier Interference Suppression For The Ofdm Systems In Time-Varying Multipath Fading Channels, Xiaozhou Huang
LSU Doctoral Dissertations
Due to its spectral efficiency and robustness over the multipath channels, orthogonal frequency division multiplexing (OFDM) has served as one of the major modulation schemes for the modern communication systems. In the future, the wireless OFDM systems are expected to operate at high carrier-frequencies, high speed and high throughput mobile reception, where the fasting time-varying fading channels are encountered. The channel variation destroys the orthogonality among the subcarriers and leads to the intercarrier interference (ICI). ICI poses a significant limitation to the wireless OFDM systems. The aim of this dissertation is to find an efficient method of providing reliable communication …
Electrodeposited Metal Matrix Nanocomposites As Thin Films And High Aspect Ratio Microstructures For Mems, Alonso Lozano Morales
Electrodeposited Metal Matrix Nanocomposites As Thin Films And High Aspect Ratio Microstructures For Mems, Alonso Lozano Morales
LSU Doctoral Dissertations
The electrodeposition of metal-matrix nanocomposites as thin film and high aspect ratio microstructures (HARM’s) for MicroElectroMechanical Systems (MEMS) components is examined. The effect of -Al2O3 nanopowder on copper reduction from acidic and basic electrolytes is examined with rotating disk electrodes (RDE’s). At pH 0.2, regions of copper inhibition and enhancement are identified in the kinetic regime. Low particle loading (12.5 g/L) results in an inhibited copper rate, while, high particle concentration (60 g/L) does both, inhibits the rate at low overpotentials and accelerates it at higher overpotentials, depending on the electrode rotation rate. At pH 8 the presence of particles …
Compiler Optimization Techniques For Scheduling And Reducing Overhead, Tong-Chai Wang
Compiler Optimization Techniques For Scheduling And Reducing Overhead, Tong-Chai Wang
LSU Doctoral Dissertations
Exploiting parallelism in loops in programs is an important factor in realizing the potential performance of processors today. This dissertation develops and evaluates several compiler optimizations aimed at improving the performance of loops on processors. An important feature of a class of scientific computing problems is the regularity exhibited by their access patterns. Chapter 2 presents an approach of optimizing the address generation of these problems that results in the following: (i) elimination of redundant arithmetic computation by recognizing and exploiting the presence of common sub-expressions across different iterations in stencil codes; and (ii) conversion of as many array references …
Design And Evaluation Of Automated, Continuous Culture Techniques For Brachionus Rotundiformis, Zhengzhong Zhang
Design And Evaluation Of Automated, Continuous Culture Techniques For Brachionus Rotundiformis, Zhengzhong Zhang
LSU Doctoral Dissertations
A 40-L recirculating rotifer turbidostat (RRT) pilot system consisting of a rotifer reactor, biofilter, foam fractionator, feed container, harvester, and two air-lift pumps was designed to produce B. rotundiformis, a small (S-type) rotifer, that is increasingly demanded for production of small-gape marine finfish larvae. The system’s automatic monitoring (turbidity, pH, conductivity and temperature) and controlling (turbidity, pH, feeding and harvesting) were performed by a Rugid™ computer. A 4 (temperature) x 3 (salinity) study indicated that a 30oC/15 ppt treatment is the most favorable to the growth of B. rotundiformis. Under these conditions, the effect of harvest rate on rotifer system …
Design And Fabrication Of Micro Transducers Using Cured Su-8 Polymer As Main Structural Material, Wen Dai
Design And Fabrication Of Micro Transducers Using Cured Su-8 Polymer As Main Structural Material, Wen Dai
LSU Doctoral Dissertations
Polymer based micro-transducers have many advantages over the traditional silicon based micro-transducers, such as easy integration with metal structures, design flexibility, and low fabrication costs. The characteristics of micro-transducers include converting electrical signals to/from mechanical response, the ability to sustain loading, sensitivity to external excitation, and etc. Some of the difficulties in realizing these characteristics include: characterizing material mechanical properties, techniques for producing electrically conductive polymer structures, and reliable fabrication procedures. In this dissertation, research addressing these difficulties is presented. The developed techniques are demonstrated in the design and fabrication of a SU-8 polymer based comb-drive micro-actuator. The micro-actuator used …