Browsing by Subject "Density"
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Item Correlating mechanical properties of cancellous bone in the rat with various density measures(Texas A&M University, 2004-09-30) Ramaswamy, RamyaThis study focussed on the reduced platen compression (RPC) testing of the cancellous bone of the proximal tibia. The objective of this study was to improve the current testing methods with an emphasis on the location of the RPC specimens, and to correlate the mechanical properties of the rodent cancellous bone with the various density measures. Analytical studies were made to assess the effect of the size and shape of the platen based on the values from mechanical testing of the cancellous bone. RPC specimens are made from transverse slices of the proximal tibia metaphysis. Specimen location was determined using planar radiograph method at a distance of 1.75 mm distal to the growth plate. The distance from the top of the proximal tibia to the line at 1.75 mm distal to the growth plate was measured and this distance is termed as the first cut distance. Specimen thickness of 2 mm was then cut for the RPC test. Endocortical method was followed to determine the platen sizing for RPC testing. The cancellous bone was then tested in compression to failure. Correlations were performed between the mechanical properties of the cancellous bone and the density measures from pQCT and radiographic techniques. SigmaStat and TableCurve 2D were used to perform the correlations and estimate the P value for the correlation. Linear and power law fits were made for all the correlations. Based on this study, several improvements to the reduced platen compression test were recommended. An improved specimen location method was developed. However, it requires a corrective distance to account for the tissue that cannot be identified in the radiographic analysis. A new method for estimating the density of the cancellous bone that is directly tested by the platen was developed. Correlations between the density of the cancellous bone and the mechanical properties show that, there is a strong correlation between ultimate stress and aluminum layer intensity. Elastic modulus correlates best with the last batch tested in this study. Recommendations for future study include advanced technology like finite element analysis and custom shaped platens to enhance RPC testing.Item CO₂ solubility and dissolution rate: the epic battle between ions and CO₂ for water, energy and space(2015-12) Gilbert, Kimberly Dawn; Bennett, Philip C. (Philip Charles), 1959-; Cardenas, Meinhard B; Breecker, Daniel O; Zhang, Tongwei; Cygan, Randall TCO₂ dissolution into deep subsurface brines is regarded as a viable means of reducing CO₂ atmospheric emissions. Dissolved ions affect CO₂ solubility (CCO₂) and the rate of dissolution, but the mechanisms of the effect are not clearly understood and thus CCO₂ prediction is difficult. We measured CCO2 and solution density up to 140°C and 35.5 MPa-PCO₂ in water, NaCl, CaCl₂, Na2SO₄, and NaHCO₃ solutions up to 3.4 molal and Bravo Dome mixed brine. CCO₂ weakly correlated to ionic strength and water activity. Strong correlations (R² > 0.92) were identified between CCO₂ and each of ΔGhydr, ΔHhydr, ΔShydr, and the electrostricted water concentration, ha; calculated from ion concentration and hydration number. Traditional empirical CCO₂ prediction models require extensive experimental work to determine parameters. We use a novel prediction approach by applying a mole balance on water, then evaluating the energy required to remove water from hydrated ions to solvate CO₂. The resulting model developed using moderated multiple regression shows that CCO₂ is dependent on CO₂fugacity (f), temperature (T), ha, and the solution hydration energy (G): all of which are specified or previously catalogued variables. A model (R²=0.92) is generated from 503 data points from this study and literature and includes the squares of each variable and interactions. Interactions between f, T, ha and G evaluated using spot-light analysis indicate that: 1) competition for water molecules significantly impacts CCO₂; 2) T and f interact to exacerbate a decrease in open water structure concentration; and 3) hydrated ions may dampen thermal agitation and reduce open structure collapse caused by increased T. The interactions of this research are likely extensible to the dissolution of any non-polar gas into a salt solution. CO₂ dissolution rate measurements demonstrated that convection occurred in experimental reactors with dissolving CO₂; however, the system was diffusion limited due to a thin diffusion layer. Density measurements revealed salt solution volume decreases with increasing CO₂, which results in: 1) faster mass transfer of dissolved CO₂ and 2) increased CO₂ total storage capacity (TSC). In 1 m Na₂SO₄ at 60°C and 10 MPa volume decreases yielded a 20% TSC increase.Item Density and Temperature in Quantum Nuclear Systems(2014-10-01) Zheng, HuaOne of the goals of nuclear physics is to study the Equation of State (EOS) of nuclear matter. In order to create the nuclear matter at different densities, we collide different nuclei and detect the fragments after the collisions with different beam energies in the laboratory. Then we extract information about finite nuclei by analyzing the collected data with different assumptions. As we know, quantum effects play an important role in many systems: the Cosmic Microwave Background (CMB) radiation, the specific heat of different metals, the suppression of density uctuations in a trapped Fermi gas, the enhancement of density fluctuations in a trapped Bose gas, the observation of Fermi pressure in trapped mixed Fermi and Bose gases, etc. The nucleus is a quantum many body system made of strongly interacting fermions, protons and neutrons (nucleons). Therefore, we are dealing with fermions and bosons in the nucleus-nucleus collisions. It is clear that we need to take into account the genuine quantum nature of particles when we extract the physical quantities for the EOS. In the past, some methods have employed the classical limit of low density and high temperature, e.g. double ratio thermometer, while other methods (e.g. two particle correlation) implement some quantum effects but they are only able to calculate one physical quantity, i.e. density p or temperature T. We would like to develop a method which takes into account the quantum nature of particles to extract the temperature and density of nuclear matter created in heavy-ion collisions. In this dissertation, we propose a new thermometer which includes quantum effects as manifested in quadrupole momentum fluctuations and multiplicity fluctuations of the detected particles. In the same framework, we are able to calculate the density of the studied particles. To test our method, we use the Constrained Molecular Dynamics (CoMD) model, which incorporates the Pauli principle, and we simulate the 40Ca + 40Ca collisions at different beam energies at impact parameter b = 1 fm up to 1000 fm/c. Later, we apply our method to do data analysis and extract the temperatures and densities for fermions and bosons respectively. The Fermi quenching for fermions is found in the simulation data. It has been confirmed in different experimental data. We also studied the possible Bose-Einstein condensate (BEC) for bosons in the same framework with CoMD and CoMD? which includes the boson correlations. Comparing the results with neutron case, we can see that the Coulomb effects play a role in the data analysis. To explore our method even further, we introduce the Coulomb correction for charged particles (both fermions and bosons). A method borrowed from electron scattering was adopted and applied to classical as well as quantum systems. In the model calculations, it was observed that when taking into account those effects, the T of p and n (as well as composite fermions in the classical case) are very similar, while the densities are not affected by the corrections. But for bosons, the temperatures and densities are very similar to the neutron case.Item Differential density lipoprotein profiling for the characterization of Lipoprotein(a)(Texas A&M University, 2006-10-30) Espinosa Garcia, Irma LeticiaLipoprotein(a) (Lp(a)) has been described as an emerging risk factor for cardiovascular disease. The complexity of the Lp(a) molecule sets a challenge for the determination of the risk it represents for the cardiovascular system. The objective of the present study was to develop a rapid method for the separation, purification, density measurement, and characterization of Lp(a) from serum using a procedure that is isoform independent. The objective was met by linking ultracentrifugation with affinity separations for the specific separation of Lp(a) from other lipoproteins. The mean density distribution of Lp(a) was determined by a differential density lipoprotein profile (DDLP). For DDLP, the lipoprotein density distribution of a serum sample with elevated Lp(a) levels was determined by ultracentrifugation using NaBiEDTA complex as a density gradient. Lp(a) was removed from a second aliquot of the same serum sample by carbohydrate affinity using wheat germ agglutinin (WGA). WGA was demonstrated to have high specificity for Lp(a) in serum. The Lp(a)-depleted sample was ultracentrifuged to obtain a lipoprotein density distribution in the absence of Lp(a). A DDLP was obtained after subtracting the Lp(a)-depleted lipoprotein density profile from the untreated lipoprotein density profile. DDLP gives relevant information of the lipoproteins in serum such as density, Lp(a) isoform, and subclass characteristics. Lp(a) was quantitatively removed from serum with a recovery efficiency of more than 80%. Lp(a) was purified by ultracentrifugation. Lp(a) obtained in this way retained its inherent density and immunoreactivity. Lp(a) was further characterized by gel electrophoresis and Western blot as well as by capillary electrophoresis. Capillary electrophoresis demonstrated to be a powerful analytical technique for the characterization of Lp(a) and apoprotein(a) isoforms. The major outcome of this research was the effectiveness of using affinity separations coupled with density ultracentrifugation for the isolation of pure Lp(a) from serum and its isoform characterization based on density and electromobility. The methodology developed and described here are relevant in a clinical setting for the analysis of Lp(a).Item Effects of local environmental factors and spatial habitat characteristics on the density of a marine gastropod, Megastraea undosa (Wood 1828)(2010-08) Abshire, Courtney Burke; Gonzalez-Guzman, Laura Imelda; Keitt, Timothy H.The ability to identify and define factors which affect the abundance of marine species has been a primary goal of many ecologists. The need to accurately quantify the relationship between an organism and its environment is of critical importance in cases where that organism is the object of commercial harvest and tied to the economic well being of communities. This is especially evident for communities located along the Pacific coast of the Baja California peninsula where local fishing cooperative and their associated communities are dependent on the continuing successful harvest of a limited number of marine species, one of these being the marine gastropod Megastraea undosa (Wood, 1828). I conducted a multi-scale observational study investigating the effects of scale and selected local environmental and regional habitat characteristics of subtidal rocky reefs on the density of M. undosa. The study showed that M. undosa density varied significantly at two scales: quadrat (m2) and reef (100s m2). At the reef level, area and percent total cover were found to have a significant positive relationship with M. undosa density. No measured variable showed a significant association to M. undosa density at the quadrat level. Results suggest that both local and regional factors combine to affect M. undosa density and that their impacts on M. undosa density warrants further study.Item Effects of Vegetation Structure and Elevation on Lower Keys Marsh Rabbit Density(2012-02-14) Dedrickson, AngelaThe Lower Keys marsh rabbit (Sylvilagus palustris hefneri, LKMR), 1 of 3 subspecies of Sylvilagus palustris, is endemic to the Lower Florida Keys. The LKMR is listed as an endangered species due to predation by feral and free roaming domestic cats (Felis catus) and raccoons (Procyon lotor), road mortality, effects of storm surges, sea level rise, the small declining metapopulation size, and possible habitat loss from hardwood encroachment. The purpose of this study was to determine the current LKMR density on lands managed by the United States Navy, Naval Air Station Key West and evaluate how vegetation structure and patch elevation effect LKMR population density. I conducted fecal pellet counts to determine LKMR density, collected vegetation data using percent composition of ground cover, Robel range pole, and point-centered quarter methods, and obtained data on patch area and elevation. I used simple linear regression to assess the relationship between LKMR density and 9 measured vegetation characteristics, patch area, and patch elevation to determine which variables have an influence on LKMR density and the relationship between them. In my examination of the simple regression models, 6 out of the 11 variables appeared to influence LKMR population density. The average per patch percent composition of nonliving material and grasses, maximum height of vegetation at the range pole, distance to nearest woody vegetation, patch elevation, and visual obstruction readings (VOR) individually accounted for 26.4%, 30.4% , 18.1%, 8.5%, 6.8%, and 1.4% of the variability in LKMR density, respectively. According to the regression models, LKMR density increased in patches with greater amounts of grasses and with greater distance to woody vegetation. Habitat management is vital to the recovery of the LKMR and needs to focus on providing greater amounts of grasses and reducing the amount of woody vegetation encroachment to enhance LKMR population density.Item Estimating density of Florida Key deer(Texas A&M University, 2006-08-16) Roberts, Clay WaltonFlorida Key deer (Odocoileus virginianus clavium) were listed as endangered by the U.S. Fish and Wildlife Service (USFWS) in 1967. A variety of survey methods have been used in estimating deer density and/or changes in population trends for this species since 1968; however, a need to evaluate the precision of existing and alternative survey methods (i.e., road counts, mark-recapture, infrared-triggered cameras [ITC]) was desired by USFWS. I evaluated density estimates from unbaited ITCs and road surveys. Road surveys (n = 253) were conducted along a standardized 4-km route each week between January 1999??December 2000 (total deer observed, n = 4,078). During this same period, 11 ITC stations (1 camera/42 ha) collected 5,511 deer exposures. Study results found a difference (P < 0.001) between methods with road survey estimates lower (76 deer) than ITC estimates (166 deer). Comparing the proportion of marked deer, I observed a higher (P < 0.001) proportion from road surveys (0.266) than from ITC estimates (0.146). Lower road survey estimates are attributed to (1) urban deer behavior resulting in a high proportion of marked deer observations, and (2) inadequate sample area coverage. I suggest that ITC estimates are a reliable and precise alternative to road surveys for estimating Key deer densities on outer islands. I also evaluated density estimates from 3 road survey methods. Road survey methods (n = 100) were conducted along a standardized 31-km route where markresight, strip-transect, and distance sampling data were collected between June 2003?? May 2004. I found mark-resight estimates to be lower ( x = 384, 95% CI = 346??421) than strip-transect estimates ( x = 854, 95% CI = 806??902) and distance estimates ( x = 523, 95% CI = 488??557). I attribute low mark-resight estimates to urban deer behavior resulting in a higher proportion of marked deer observations along roadways. High strip-transect estimates also are attributed to urban deer behavior and a reduced effective strip width due to dense vegetation. I propose that estimates using distance sampling eliminate some of these biases, and recommend their use in the future.Item Experimental Characterization and Molecular Study of Natural Gas Mixtures(2011-08-08) Cristancho Blanco, Diego EdisonNatural Gas (NG) plays an important role in the energy demand in the United States and throughout the world. Its characteristics as a clean, versatile and a sustainable source of energy makes it an important alternative within the spectra of energy resources. Addressing industrial and academic needs in the natural gas research area requires an integrated plan of research among experimentation, modeling and simulation. In this work, high accuracy PpT data have been measured with a high pressure single sinker magnetic suspension densimeter. An entire uncertainty analysis of this apparatus reveals that the uncertainty of the density data is less that 0.05% across the entire ranges of temperature (200 to 500) K and pressure (up to 200 MPa). These characteristics make the PpT data measured in this study unique in the world. Additionally, both a low pressure (up to 35 MPa) and a high pressure (up to 200 MPa) isochoric apparatus have been developed during the execution of this project. These apparatuses, in conjunction with a recently improved isochoric technique, allow determination of the phase envelope for NG mixtures with an uncertainty of 0.45% in temperature, 0.05% in pressure and 0.12% in density. Additionally, an innovative technique, based upon Coherent Anti-Stokes Raman Scattering (CARS) and Gas Chromatography (GC), was proposed in this research to minimize the high uncertainty introduced by the composition analyses of NG mixtures. The collected set of P?T and saturation data are fundamental for thermodynamic formulations of these mixtures. A study at the molecular level has provided molecular data for a selected set of main constituents of natural gas. A 50-50% methane-ethane mixture was studied by molecular dynamics simulations. The result of this study showed that simulation time higher than 2 ns was necessary to obtain reasonable deviations for the density determinations when compared to accurate standards. Finally, this work proposed a new mixing rule to incorporate isomeric effects into cubic equations of state.Item High accuracy p-rho-t measurements up to 200 MPa between 200 K and 500 K using a compact single sinker magnetic suspension densimeter for pure and natural gas like mixtures(2009-06-02) Atilhan, MertHighly accurate density data is required for engineering calculations to make property estimations in natural gas custody transfer through pipelines. It is also essential to have accurate pressure-volume-temperature (PVT) data for developing equations of state (EOS). A highly accurate, high pressure and temperature, compact single sinker magnetic suspension densimeter has been used for density measurements. First, the densimeter is calibrated against pure component densities for which very reliable data are available. After validating its performance, the densities of four light natural gas mixtures that do not contain components heavier than hexane and two heavy gas mixtures containing hexane and heavier components having fractions more than 0.2 mole percent were measured. The light mixtures were measured in the temperature range of 250 to 450 K and in the pressure range of 10 to 150 MPa (1450 to 21,750 psi); the heavy mixtures were measured in the range of 270 to 340 K and in the pressure range of 3 to 35 MPa (500 to 5,000 psi). Out of those, the data for only four light natural gas mixtures have been presented in the dissertation due to confidentiality agreements that are still in force. A force transmission error and uncertainty analysis was carried out. The total uncertainty was calculated to be 0.11%. Data calculated in this work is compared with the current industry standard EOS for natural gas systems (AGA8-DC92 EOS) and GERG EOS, which is the most recently developed EOS for natural gas systems. The data measured as a part of this research should be used as reference quality data, either to modify the parameters of AGA8-DC92 EOS and GERG EOS or to develop a more reliable equation of state with wider ranges of pressure and temperature.Item Spectroscopic measurement of n[subscript e] and T[subscript e] profiles using atomic and kinetic models for Argon in the Texas Helimak(2013-05) Dodd, Kenneth Carter; Gentle, Kenneth W.Profiles for electron density and temperature were determined in a self-consistent way using line emission spectroscopy and collisional radiative models for neutral and singly ionized Argon (Ar I and Ar II) in the Texas Helimak. Neutral Argon density profiles were calculated using a kinetic gas model. Electron-impact excitation and Ionization rates were corrected to account for the electron velocity distribution deviating slightly from a true Maxwellian distribution due to inelastic electron-neutral collisions. Results show an electron temperature which roughly agrees with probe diagnostics. This method gives an electron density that is about twice as high, which may be possible from a power balance perspective.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.