Browsing by Subject "Strain"
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Item A phenomenological approach to understanding the changes in marital intimacy for caregivers married to a spouse with Alzheimer's Disease(Texas Tech University, 2005-05) Adams, Mark S.; Harris, Steven M.; Tacon, Anna M.; Stelle, Charlie D.; Wampler, Karen S.Alzheimer’s disease or a related dementia (ADRD) can create enormous strain and burden for family caregivers. But the potential for relationship disruption via changes in intimacy seem to be the greatest for couples in long-term marriages. I conducted intensive interviews with spouses who provide care for their partner with ADRD. I wanted to better understand how some spousal caregivers had managed to maintain a sense of continuity in their marital intimacy, and to understand what may have kept others from maintaining that same closeness. I also explored the role of physical intimacy and/or sexuality in facilitating the process of marital continuity. I proceeded from the assumption that people want to feel close to those they love and that a person can be active in creating that closeness. I believe that the sexual relationship holds a great potential for maintaining feelings of closeness and connection. I used a phenomenological approach to describe, analyze, and interpret data of spouses' lived experiences. Then I attempted to extrapolate those experiences into clinical interventions or suggestions to assist clinicians who may work with similar couples. My analysis shows that spouses who provide care for their partner with ADRD moved through a process of change that affected their opportunities for further intimacy. The disease processes eventually led to a diagnosis of ADRD for the impaired spouse. A sense of uncertainty or ambiguity grew as the symptoms of the disease increased. Caregiving spouses were faced with the challenge of emotionally and psychologically separating the symptoms of ADRD from the personhood of their partner. The growing ambiguity was usually accompanied by challenges (both emotional and practical) to cope and adjust to the new dynamics. Adjustment and working through the challenges did not automatically mean that the spouse who was providing care would feel emotionally close to his or her partner, although it was much more likely. There is one last overarching influence that affects the whole process – marital history. This study has implications for clinical theory and interventions for practitioners working with couples or spouses who provide care to a partner with ADRD.Item Computaional modeling of membrane mechanics(Texas Tech University, 2006-08) Kundomal, Chellaram A.; Seshaiyer, Padmanabhan; Martin, Clyde F.; Schovanec, LawrenceIn this work we analyze mechanics of thin membranes. After a brief review on the backgrounds and methods, this thesis develops a systematic approach to understanding membrane mechanics. The two essential mathematical tools employed include Principle of Virtual Work and the finite element method. More specifically after defining suitable measures of deformation of an arbitrary body, we describe how one can apply the Principle of Virtual Work for a fully dynamic application. We employ the finite element method to a quasi-static application which results in a system of nonlinear equations. These equations are solved by the Newton-Raphson procedure for systems. The computational methodology discussed in this work was implemented in Maple for two different membrane materials: neo-Hookean and Mooney-Rivlin.Item Exploration of voltage controlled manganite phase transitions as probed with magnetic force microscopy(2010-05) Ruzicka, Frank Joseph; de Lozanne, Alejandro L.; Tsoi, Maxim; Shih, Chih-Kang; Markert, John T.; Shi, LiLow-temperature magnetic force microscopy was used to study the phase diagram of a La1/3Pr1/3Ca1/3MnO3 thin film grown on a (110) NdGaO3 (NGO) substrate by pulsed laser deposition. Traditionally, one can observe the phase change at the nanoscale level as the sample is cooled from room temperature through the transition temperature to liquid nitrogen temperatures, but in this case a fixed voltage ranging from 0 V to 31 V was applied before each cooling cycle. From in and ex situ transport measurements, it is observed that the temperature of the peak of the transition increases with applied field; however, the MFM images show that the magnetic transition begins at a lower temperature with the same increase in field. Thus, this dissertation shows that a new voltage control exists for the phase transition in certain manganites.Item Fold-related brittle structures and associated strain in a limestone bed of the Carmel Formation, San Rafael Swell, Utah(2015-12) Laciano, Peter Joseph; Marrett, Randall; Cloos, Mark; Ukar, EstibalitzThe San Rafael Swell (SRS) is a basement-cored Laramide uplift located in central-eastern Utah. The SRS is bounded on the east by a 70 km long monocline, a fault-propagation fold, with excellent exposure of sedimentary strata including the Carmel Formation. This monocline is an ideal natural laboratory for studying brittle deformation associated with folding. Qualitative and quantitative observations for brittle structures in a limestone bed near the base of the Carmel Fm. were made in a wide range of bedding dip, curvature, and fold domains. Kinematic data was collected for 2942 structures (1865 veins, 746 stylolites, 314 faults) in 30 locations in order to calculate principal directions of strain. Additionally, data was collected along 71 scanlines at 19 of those locations in order to estimate structure intensities and strain magnitudes. Dekameter-displacement thrust faults, acting as ramps between inferred layer-parallel faults, accommodate orders of magnitude more strain than all other observed brittle structures. These faults are only found in segments of the monocline where bedding dip is high, but curvature is low, which provides strong evidence that limb rotation more strongly controls strain magnitudes than layer bending in the SRS. The trishear model effectively predicts SRS monocline geometry, specifically observed limb thickening, broad, curved hinges, and progressively rotating limb. This is likely due to the dominance of thick, homogeneous rock packages, such as the Navajo Sandstone, in the SRS monocline. In contrast, strain localization within the Carmel Fm. is poorly predicted by trishear: there is strong evidence of flexural slip, and folding induced structure orientations and calculated principal strain directions remain consistent relative to bedding. These strain directions are inconsistent with trishear forward models produced by workers such as Zuluaga et al. (2014) that do not stay consistent relative to bedding. These divergences are likely due to the fact that trishear is a kinematic model that assumes rock homogeneity, while the Carmel Fm. is stratigraphically and mechanically heterogeneous. Because this heterogeneity appears to have a strong effect on strain localization, kink band models likely better estimate strain localization in the Carmel limestone bed as well as other layers in folded heterogeneous strata. The monocline’s interpreted transition from layer-parallel shortening to extension at the steepest locations in the monocline, and thus at most advanced stage of folding, enabled estimation of the dip of the basement fault beneath the SRS as ~30°. This shallow dip contrasts with the steep dip (~60°) assumed for the SRS by Zuluaga et al. (2014) and observed in the Kaibab uplift (Huntoon and Sears, 1975; Tindall, 2000), but is consistent with a recent estimation of 20-40° for the SRS by Davis and Bump (2009) using trishear modeling.Item History and Analysis of Distributed Acoustic Sensing (DAS) for Oilfield Applications(2013-05-15) Kimbell, JeremiahThe inherent nature of distributed acoustic sensing technology is a direct result of two key components: optical fiber and the speed of light. Because the speed of light is constant and optical fiber is an isolated medium, combining the two creates a mechanism insulated from environmental interference that effectively ?moves? at the speed of light. This process is most visible in the telecommunications industry where the technology transports large amounts of data over significant distances at very high speeds. The same factors that make optical fiber excellent for transporting data (high speed and low environmental interference) also make the technology very applicable for precise measuring applications. Because optical fiber is insulated, a change to the fiber will have a pronounced (measurable) effect. These measurable effects manifest themselves as changes in the amount of light that is reflected within the optical fiber. This change in reflected light can be measured and quantified to indicate both the specific location along the fiber where the change in reflection occurred and the magnitude of the change in reflection. Knowing both the location of the affected area and the extent to which the reflection changed allows for precise measuring and subsequently, educated inferences about what caused the changes initially. The ability of optical fiber to detect changes at myriad intervals over long distances has particular appeal for functions involving remote and hard to get to environments. Both of these conditions are inherent to the petroleum industry and provide substantial incentive for investigating DAS for oilfield applications.Item Investigation of Transfer Function Analysis as a Means to Predict Strain on Rat Tibiae from Ankle Torque Waveforms(2010-07-14) Bouse, ScottElectrical Muscle Stimulation (EMS) is used as a countermeasure in animal disuse studies that seek to determine which forms of exercise are most effective in mitigating the effects of disuse atrophy on bone and muscle. Although EMS has been used for many years in our lab and others, few researchers have been able to quantify the levels of strain on rat tibiae during EMS and far fewer have investigated the causal relationship between torque produced at the ankle and strain on the tibia. This thesis sought to investigate the relationship between ankle torque and tibial strain by using a combination of techniques, namely: (1) the addition of rosette strain gages, (2) improved synchronization between ankle torque and tibial strain recordings, and (3) spectral analysis between torque and strain waveforms. In previous work, few methods existed to align torque and strain recordings temporally, as those data were recorded on separate computers and synchronizing events were not captured. Attempting to create a torque-strain crossplot with unsynchronized data does not always yield valid results, so a method of reliably synchronizing those data is required. This thesis developed methods to capture simultaneous (synchronizing) events in both torque and strain recordings and then used those captured events to synchronize data between two computers. Following that synchronization, stiffness calculations were run on torque-strain crossplots to determine linear-model relationships between torque and strain for each method of synchronization. The results from those regressions were then used to determine if one or more synchronization techniques are superior to others, in terms of repeatability or precision. The results of these analyses have shown that using portions of the curves can dramatically increase computing speed while providing high levels of repeatability in synchronization measures. After synchronization techniques had been investigated, 3-element rosette data were used to calculate the principal strains on the surface of the tibiae, and the percentage of principal strains that are accounted for in the axial direction. Since the strain environment changes along the axis of the bone, the principal strain data were plotted versus the distance from proximal epiphysis to rosette gage, and statistical analysis was presented. After rosette data were analyzed, the torque and strain data pairs were fed into a signal processing suite for the purpose of transfer function calculation. Using the synchronization methods outlined above, two means of synchronization were compared in the transfer function program. Results for these analyses demonstrated that transfer functions are slightly dependent on synchronization methods, but that calculated gains do not differ between synchronization techniques. The specific shapes of the transfer functions highlight the relative attenuation/amplification of frequencies in torque and strain signals. Specifically, a range of frequencies, commonly called a band, between 24 and 32Hz is attenuated by the soft tissues and mechanical linkages in the lower leg of rats. This finding gives researchers looking to increase or decrease modeling stimulus to bone a new piece of information about the relative efficiency of EMS exercise. For example, EMS performed at 24-25Hz might produce less strain in the tibia than EMS at 22-23Hz, despite the 22-23Hz stimulation producing marginally less torque.Item Mechanical stress and circuit aging aware VLSI CAD(2010-12) Chakraborty, Ashutosh; Pan, David Z.; Abraham, Jacob; Orshansky, Michael; Saxena, Prashant; Touba, NurWith the gradual advance of the state-of-the-art VLSI manufacturing technology into the sub-45nm regime, engineering a reliable, high performance VLSI chip with economically attractive yield in accordance with Moore's law of scaling and integration has become extremely difficult. Some of the most serious challenges that make this task difficult are: a) the delay of a transistor is strongly dependent on process induced mechanical stress around it, b) the reliability of devices is affected by several aging mechanisms like Negative Bias Temperature Instability (NBTI), hot carrier injection (HCI), etc and c) the delay and reliability of any device are strongly related to lithographically drawn geometry of various features on wafer. These three challenges are the main focus of this dissertation. High performance fabrication processes routinely use embedded silicon-germanium (eSiGe) technology that imparts compressive mechanical stress to PMOS devices. In this work, cell level timing models considering flexibility to modulate active area to change mechanical stress, were proposed and exploited to perform timing optimization during circuit placement phase. Analysis of key physical synthesis optimization steps such as gate sizing and repeater insertion was done to understand and exploit mechanical stress to significantly improve delay of interconnect and device dominated circuits. Regarding circuit reliability, the proposed work is focused on reducing the clock skew degradation due to NBTI effect specially due to the use of clock gating technique for achieving low power operation. In addition, we also target the detrimental impact of burn-in testing on NBTI. The problem is identified and a runtime technique to reduce clock skew increase was proposed. For designs with predictable clock gating activities, a zero overhead design time technique was proposed to reduce clock skew increase over time. The concept of using minimum degradation input vector during static burn-in testing is proposed to reduce the impact of burn-in testing on parametric yield. Delay and reliability strongly depend on dimension of various features on the wafer such as gate oxide thickness, channel length and contact position. Increased variability of these dimensions can severely restrict ability to analyze or optimize a design considering mechanical stress and circuit reliability. One key technique to control physical variability is to move towards regular fabrics. However, to make implementation on regular fabrics attractive, high quality physical design tools need to be developed. This dissertation proposes a new circuit placement algorithm to place a design on a structured ASIC platform with strict site and clock constraints and excellent overall wirelength. An algorithm for reducing the clock and leakage power dissipation of a structured ASIC by reducing spine usage is then proposed to allow lower power dissipation of designs implemented using structured ASICs.Item Quantifying the strain response in the rat tibia during simulated resistance training used as a disuse countermeasure(2009-05-15) Jeffery, Jay MelvinDisuse of weight bearing bones has been shown to cause bone loss. This poses a health concern for people exposed to microgravity, such as astronauts. Animal studies are used to study factors related to bone loss and countermeasures to prevent bone loss. This study used a hindlimb unloaded (HU) rat model to simulate microgravity and a muscle stimulation countermeasure to simulate resistive exercise. Uniaxial strain gages were implanted on the antero-medial aspect of the proximal tibia to measure the mechanical strain during a typical exercise session. In a separate but parallel study, the exercise was shown to be an effective countermeasure to disuse related bone loss. The current study sought to understand the loading of the bone during the exercise. To determine if the strain response changes during a protocol using this countermeasure, strains were measured on a group of weight bearing animals and a group that were hind limb unloaded and received the countermeasure for 21 days. Strain magnitudes and rates were considered and related to torques at the ankle joint. No significant differences in strain magnitudes were noted between the baseline control group and the hindlimb unloaded group that received the countermeasure. The two kinds of contractions used in an exercise session are isometric and eccentric. The isometric contractions are used to adjust the stimulation equipment for the eccentric contractions, which constitute the exercise. Peak strain levels during the isometric contractions ranged from 900 to 2200 microstrain while the eccentric were 38% lower and ranged from 600 to 1400. Eccentric strain rates were 62% lower than the isometric contractions strain rates. These results indicate that the strain environment during the isometric contractions may be causing more of the osteogenic response than the eccentric contractions, which have previously been thought to be the primary part of the countermeasure.Item Strain and modulation doping in epitaxial Si/Ge core-shell nanowire heterostructures(2015-12) Dillen, David Carl; Tutuc, Emanuel, 1974-; Banerjee, Sanjay K; Dodabalapur, Ananth; Yu, Edward T; Korgel, Brian AFor over five decades, silicon based electronics relied on scaling of individual field-effect transistors (FETs) for improvements in integrated circuit performance. Recently, however, further enhancement of packing density and switching speed was limited by the increase in power consumption of short channel devices. New materials and device geometries were introduced to help expand CPU performance while also decreasing power dissipation. Semiconducting nanowires have also been recognized for potential applications as channel material in highly scaled FETs. These structures present opportunities for strain and energy band engineering through the use of radial, or core-shell, heterostructures. To fully exploit the benefits of radial heterostructures, however, requires knowledge of elastic strain distributions and energy band alignments, necessitating the development of new characterization methods. This is especially true in Si/Ge material systems, where a large lattice mismatch over 4% is possible. In this thesis, we grow Si/Ge core-shell nanowires and demonstrate multiple techniques to characterize the nanoscale heterostructure, including strain measurements and extraction of valence band offsets. We grow Ge-SixGe1-x core-shell nanowires and measure the elastic strain using Raman spectroscopy. The Ge core’s Raman spectrum is consistent with a compressive strain in this region due to lattice mismatch with the SixGe1-x shell. The strain distribution and expected Raman peak positions are calculated using continuum elasticity models and lattice dynamic theory, finding excellent agreement to experimental data. We also demonstrate radial modulation doping in Ge-SixGe1-x core-shell nanowire heterostructures by doping a portion of the SixGe1-x shell with boron during growth. The modulation doped nanowire FETs show an enhanced low temperature hole mobility and also a decoupling of transport between core and shell. Through comparison to finite-element calculations, we extract the valence band offset at the core-shell interface. Lastly, we grow coherently strained Si-SixGe1-x core-shell nanowires and characterize the structure using Raman spectroscopy. We first optimize the Si nanowire growth process to favor the diamond crystal structure and to minimize sidewall coverage by Au catalyst, followed by epitaxial growth of the SixGe1-x shell using the Si nanowire as substrate. Raman measurements on core-shell samples indicate a tensile strain in the Si core and a compressive strain in the SixGe1-x shell, both consistent with calculations of the strain and the strain-induced shift of the Raman peaks in this structure.Item Thru-thickness bending stress distribution at elevated temperatures(Texas A&M University, 2005-08-29) Christian, Lee ConnerDuring the bending of flange plate used for dapped girders some highway bridge fabricators are experiencing cracking of the flange plate particularly when heat is used in assisting the bending process. Due to the extreme strains experienced during the fabrication process, investigating this problem requires the use of a finite element analysis. The fabrication process was broken down into two parts, first the heating of the plate through the use of either a furnace or an acetylene torch (thermal), and the second was the bending process (structural). The five different temperatures collected during the thermal analysis were a uniform temperature of 75oF, a 1100oF uniform temperature as a result of furnace heating, both five and ten minutes of air-cooling after the plate had reached a uniform temperature of 1100oF, and the temperature gradient after heating the flange plate to a surface temperature of 1200oF though the use of an acetylene torch. After the thermal analysis was completed, the resulting temperatures were imported into the structural model. The plate thicknesses analyzed were one, one and a half, and two inches, assuming both 50 and 70 ksi yield strengths. To achieve a 90 degree six-inch radius bend the plate was bent in five separate locations. The result of this analysis showed that with the introduction of temperature gradients into thefabrication process, the strains along the plate??s extreme fibers increased. The model further showed that for both a one and a half and two-inch thick plate the extreme fiber strains exceeded ten percent, which further adds to the increased risk of the flange plate cracking during fabrication. The highest residual stresses through the plate??s thickness occurred during cold bending. The residual stresses through the plate??s thickness decreased when the fabrication process was carried out at elevated temperatures. When steel exceeds a strain of 10 to 16 percent during the fabrication process, the plate becomes susceptible to cracking. This strain limit was exceeded for plate thicknesses of one and a half and two inches.Item Use of a BCD for compaction control(Texas A&M University, 2005-11-01) Li, YanfengCompaction of soil is essential in the construction of highways, airports, buildings, and bridges. Typically compaction is controlled by measuring the dry density and the water content of the compacted soil and checking that target values have been achieved. There is a current trend towards measuring the soil modulus instead or in addition to density. The reasons are that the density measurements are made using nuclear density meter, an undesirable tool in today??s political environment and that pavement design uses moduli as an input parameter. Although there are many apparatus available to measure soil modulus in the field such as Falling Weight Deflectometer, Dynamic Cone Penetrometer and Seismic Pavement Analyzer, a light weight and easy to use device which can measure the soil modulus fast and accurately is in great need. Briaud Compaction Device (BCD) is a portable device which can measure a soil modulus in several seconds. The principle of the BCD is to use the bending of a plate resting on the ground surface as an indicator of the modulus of the soil below. Numerical simulations show that within a certain range, the soil modulus is simply related to the plate bending. Strain gauges are glued on the top of the plate of BCD and a double half Wheatstone bridge is used to measure the strain. BCD tests were done in parallel with plate tests of the same size. A good correlation was found between the ratio of the plate pressure over the bending strain measured with a BCD and the reload soil modulus obtained from the plate test. This correlation can be incorporated into the BCD processor to display the soil modulus directly. To transit from dry density based compaction control to modulus based compaction control, BCD tests were also performed in the laboratory on top of a soil sample compacted inside the Proctor mold followed by plate tests. That way, a soil modulus versus water content curve is developed which parallels the approach for the dry density versus water content. The soil modulus versus water content curve can be used to provide the target values for compaction control in the field.