• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2851
  • 1316
  • 345
  • 340
  • 168
  • 93
  • 69
  • 59
  • 44
  • 36
  • 26
  • 25
  • 21
  • 21
  • 21
  • Tagged with
  • 6638
  • 1250
  • 1185
  • 1075
  • 538
  • 514
  • 462
  • 440
  • 423
  • 416
  • 396
  • 356
  • 329
  • 317
  • 303
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
211

Synthesis of compounds with very large specific rotations

January 2020 (has links)
archives@tulane.edu / Abstract: A search in a research database for “large specific rotation” or anything similar produces few articles. Large specific rotation is not commonly used as an indicator for extraordinary chiroptical response. Alternatively, anisotropy factors obtained from circular dichroism spectra and calculated rotational strengths are more widely used to gauge chiroptical response. To another point, a search for “large chiroptical response” gives few articles that discuss pure organic compounds, and the result list is populated by organometallic clusters, nanostructures, and thin films. A search of the Reaxys database for organic compounds with [α]Ds larger than 1000 revealed that there are about 600, and there are only two that have [α]Ds larger than 10,000.30 We wondered if we could design a compound that would break the record in specific rotation and possess extraordinary chiroptical properties. Guided by time-dependent density functional theory (TD-DFT) calculations, various chiral, polycyclic aromatic compounds (PACs) were chosen as candidates to display extraordinary chiroptical properties, such as high optical rotation, strong circular dichroism, or a high degree of circularly polarized luminescence (CPL). PACs comprise a large class of organic compounds. In addition to synthetic PACs, numerous naturally occurring PACs exist in coal tar and as decomposition products of organic material. Since their pi electrons are delocalized, PACs have interesting and possibly useful electronic properties and a variety of applications. The PACs described in this dissertation, e.g., helical mesobenzanthrones, a cyclophane, are twisted pentacenes are chiral and have interesting optoelectronic properties. TD-DFT was primarily used to predict which compounds had the greatest potential to yield record-breaking specific rotations or other chiroptical properties, and ordinary DFT calculation were used to determine if these compounds had sufficiently high racemization barriers to be resolved at room temperature. With regard to specific rotation, the accuracy of TD-DFT calculations was examined by comparing experimental specific rotations to the calculated values. / 1 / Kelly Jane Dougherty
212

Cryopreservation of Equine Spermatozoa: Identification of Good and Poor Freezer Stallions and Effect of Sperm Density Per Straw

Fahad, Abed Sharqy 15 December 2012 (has links)
This study was carried out primarily to evaluate the cryo-tolerance of equine semen from four stallions through assessing the spermatozoa motion characteristics with Computer-Assisted Sperm Analysis (CASA). Four stallions were collected during the breeding season (summer). For each ejaculate, fresh and cryopreserved samples were taken for sperm motility characteristics evaluation. Data analysis demonstrated that sperm cells of stallions were significantly affected by (P<0.05) cryodamage. Stallion (A) was cryotolerant, and was classified as a good freezer, whereas stallion (D) was not and classified as a poor freezer regardless of the concentration of sperm. In addition, a concentration of 0.4 x 109 sperm cells/ml had higher percentages of rapid sperm and velocity parameters (P<0.05) compared to 0.8 x 109 sperm/ml. Further research is necessary to identify potential biomarkers for good and poor freezer stallions.
213

Effect of Crosslink Density on the Tearing of Gum Natural Rubber Cured with Dicumyl Peroxide (DCP)

Li, Yanxiao 22 May 2013 (has links)
No description available.
214

The Semiclassical Approximation and Strutinsky Smoothing

Jennings, Byron K. 11 1900 (has links)
<p> An expression for the semiclassical density of states for a particle in a smooth potential well is obtained from the Kirkwood expansion of the partition function. This expression for the semiclassical density of states is then shown to be essentially equivalent to the expression obtained from the Green's function method of Balian and Bloch.</p> <p> The Strutinsky shell correction to the nuclear binding energy is then analytically shown to be equivalent to the shell correction obtained from a consideration of the semiclassical partition function if certain restrictions on the Strutinsky smoothing parameter can be met.</p> / Thesis / Master of Science (MSc)
215

Study of Nuclear Level Densities from Deuteron-Induced Reactions on <sup>54,56,58</sup>Fe and <sup>63,65</sup>Cu

Ramirez, Anthony Paul D. January 2014 (has links)
No description available.
216

Low Excitation Corrections to the Density Of States

Jelovic, Andrijan 01 1900 (has links)
<p> We study a many particle system contained within a harmonic oscillator potential, with the single particle spacings equispaced and nondegenerate. We consider either fermions or bosons within this harmonic oscillator potential and derive the density of states for this system, with low excitation energy corrections. We extend our method for more than one species of fermions or bosons within this harmonic oscillator potential and compare our results with number-theoretic techniques. We move on to the degenerate harmonic oscillator potential and show that, for a fermion system, shell effects are contained within low excitation energy terms. We attempt to arrive at the density of states for an infinite number of bosons within the same potential. </p> / Thesis / Master of Science (MSc)
217

The Relationship Between Bone and Muscle Measures in Elite Adolescent Male Cross-Country Skiers Compared to Normally Active Matched Controls

Mark, Amy E. 06 1900 (has links)
Exercise associated muscle induced bone strain has potential osteogenic effects that may increase skeletal density, bone cross-sectional area and structural strength. Whether the effects of exercise and the muscle-bone relation are similar in weight bearing and nonweight bearing bones remains to be determined. This study compared bone density, geometry and biomechanical properties, and bone and muscle cross-sectional areas of 13 elite adolescent male cross-country skiers with height, weight, age and maturity matched non-athletic controls. Total bone mineral density (BMDror), and trabecular bone mineral density and total bone cross-sectional area (CSAror) were measured at the distal 4% of the radius (DR) of the dominant (D) and non-dominant (ND) arms, and tibia (DT) using peripheral quantitative computed tomography (pQCT); BMDror, CSAror, cortical BMD, cortical thickness (CrtTH) and area (CSAcoRr), stress-strain index polar, x, y, polar moment of inertia, axial moment of inertia, and muscle cross-sectional area (mCSA) were measured at the 66% length of the proximal tibia (PT) and proximal radius (PR) of the D and ND arms. Whole body BMD, whole body bone area, and hip areal bone mineral density were measured using dual energy X-ray absorptiometry (DXA). Speed of sound along the bone was measured using quantitative ultrasound (QUS) at the 1/3 DR and PT. There were no differences between the skiers and controls for any of the descriptive measures, however, there was a trend (p=0.06) for skiers to have lower percent body fat than controls. There were no differences between skiers and controls for the bone outcome measures using pQCT, DXA or QUS, except for CrtTH at the PT which was significantly higher in skiers (5.42±0.25mm, p=0.03) than controls (5.18±0.28mm). Cross-country skiers had increased CrtTH at the PT suggesting little differential effect of mechanical loading on bone density, geometry or biomechanical properties associated with skiing. / Thesis / Master of Science in Kinesiology
218

The Effect of Gymnastic Training on Bone Density in Prepubescent Females / Bone Density and Gymnastics

Dyson, Kerry 11 1900 (has links)
The effect of intense gymnastic training on bone mineral density was investigated in 16 elite prepubertal (9.82 ± 0.89 years) (mean ± SD) gymnasts (GYM) and 16 normoactive (9.87 ± 0.75 years) controls (CON). Pubertal status was determined according to the criteria of Tanner. Additionally the mother of each subject was recruited, and was included in all measurements as an estimate of hereditability. GYM were in elite pre-competitive or competitive programs for at least two years, and trained on average 18 hr per week. Areal bone mineral density (BMD) and body composition (%BF) was measured for the whole body, and BMD for the left hip and lumbar spine (L1-L4) by dual energy x-ray absorptiometry (DXA), and volumetric BMD for the distal radius by peripheral QCT (pQCT). There were no significant differences between groups for age, pubertal status or body mass; however GYM were significantly shorter (129.3 ± 5.7 vs. 136.7 ± 4.4 cm; P<0.01) and leaner (15.12 + 1.95 vs. 19.58 + 4.29 %BF) than CON. In an attempt to account for inter-group height differences, areal DXA measurements were converted to apparent bone mineral density (BMAD). GYM had significantly (P<0.05) greater femoral neck (0.698 ± 0.058 vs. 0.648 + 0.064 g.cm⁻²) and trochanteric (0.616 ± 0.060 vs. 0.530 + 0.084 g.cm⁻²) BMD. Additionally GYM had significantly greater whole body (0.101 ± 0.009 vs 0.094 ± 0.007 g.cm⁻³) BMAD than CON. GYM also had significantly greater total 367.75 ± 51.61 vs 307.37 ± 27.59 mg.cm⁻³), trabecular (207.93 ± 45.35 vs 163.76 ± 31.41 mg.cm⁻³) and cortical (496.94 ± 67.51 vs 429.80 ± 33.78 mg.cm⁻³) volumetric BMD than CON at the distal radius. There were no significant differences between mothers of GYM or CON for any of the variables studied. Significant daughter mother correlations existed only for lumbar spine BMD (r=0.55). These results suggest that participation in elite gymnastics prior to puberty elicits favourable whole body adaptations in bone mineral density, and also that striking regional differences are observed at the wrist, a site subjected to repetitive high impact loading during training. / Thesis / Master of Science (MSc)
219

The Influence of Soil Reconstruction Methods on Mineral Sands Mine Soil Properties

Meredith, Kelly Robyn 13 February 2008 (has links)
Significant deposits of heavy mineral sands (primarily ilmenite and zircon) are located in Virginia in Dinwiddie, Sussex and Greensville counties. Most deposits are located under prime farmland, and thus require intensive reclamation when mined. The objective of this study was to determine the effect of four different mine soil reconstruction methods on soil properties and associated rowcrop productivity. Treatments compared were 1) Biosolids-No Tillage, 2) Biosolids-Conventional Tillage, 3) Lime+NPK fertilized tailings (Control), and 4) 15-cm Topsoil over lime+P treated tailings. Treated plots were cropped to corn (Zea Mays L.) in 2005 and wheat (Triticum aestivum L.) in 2006. Yields were compared to nearby unmined prime farmland yields. Over both growing seasons, the two biosolids treatments produced the highest overall crop yields. The Topsoil treatment produced the lowest corn yields due to relatively poor physical and chemical conditions, but the effect was less obvious for the following wheat crop. Reclaimed land corn and wheat yields were higher than long-term county averages, but they were consistently lower than unmined plots under identical management. Detailed morphological study of 20 mine soil pedons revealed significant root-limiting subsoil compaction and textural stratification. The mine soils classified as Typic Udorthents (11), Typic Udifluvents (4) and Typic Dystrudepts (5). Overall, mined lands can be successfully returned to intensive agricultural production with comparable yields to long-term county averages provided extensive soil amendment and remedial tillage protocols are implemented. However, a significant decrease (~25 to 35%) in initial productivity should be expected relative to unmined prime farmland. / Master of Science
220

Density Reconsidered

Lyu, Jiayue 19 January 2022 (has links)
The work seeks to reconsider aspects of high density in urban architecture, exemplified in a site in Hong Kong, where currently urban housing, temple, commercial, office and other structures coexist. While a very high density of urban housing is in place, it does not consider qualities of living such as natural light and view in the apartment layouts. In addition to qualities directly related to living, the thesis also seeks to engage a notion of identity and individuality which is often absent in high density projects. The stereotypical image of mediocre high-density environments is a relentless repetition of stacked units which accommodates only very basic human needs of cooking and sleeping but does not offer high quality urban spaces where people can expand their otherwise tight dwelling. The investigation seeks to recognize the particularities of the Hong Kong site, including a temple complex which offers itself as a unique and peaceful moment, contrary to the hustle and bustle of the city. The relationship between dwellings and temple is a point of departure which architecturally expresses a deep respect for culture and context of Hong Kong. A good architectural density in this sense is a composite of diverse function and spaces that offer opportunities of activities that together form a sense of place. / Master of Architecture / This thesis explores what a reconsidered density in a city could benefit the immediate environment and offer a better living quality for the residents.

Page generated in 0.0317 seconds