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  • 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.
1

Structural studies of some disordered molybdates and manganates and manganates

Cooper, Steven P. January 1999 (has links)
No description available.
2

A study of simple glassforming aqueous electrolyte solutions

Ansell, Stuart January 1995 (has links)
No description available.
3

Thermal neutron scattering by some molecular liquids

Garawi, M. S. January 1987 (has links)
No description available.
4

Development of high pressure and cryogenic techniques, and their application to neutron diffraction

Ridley, Christopher James Taylor January 2017 (has links)
Neutron diffraction is an extremely powerful technique in condensed matter research; it can be used to measure crystallographic structures, including some of those undeterminable using X-rays. It is also perhaps the most powerful technique for determining magnetic structures, and for probing the strength of magnetic interactions, revealing information beyond that extractable from a magnetometer. High pressure is used by many condensed matter researchers as an additional thermodynamic variable, or tool to perturb otherwise stable systems, and has been used with neutron diffraction for many years. When coupled with low temperatures, this has led to the discovery of an enormous range of non-ambient phases of matter, with a range of exotic properties, some of which are discussed in this thesis. Pressure has a very strong effect on the magnetic properties of a material, with many of the most unusual magnetic phases existing only at extremely low temperatures, or pressures which can only be reached on very small samples. The main topic for this thesis is the study, development, and implementation of new techniques to combine low temperatures, high pressures, and neutron diffraction measurements from micro sized samples. A new pressure cell has been designed, tested, and commissioned with neutron beam time on the WISH diffractometer at the ISIS neutron facility. The cell is compact, with a total mass of approximately 5 kg, and is capable of generating large loads in excess of 4.5 tonnes force. Depending on the sample size used with the cell, the opposed anvil system is capable of generating a range of different pressures beyond what is widely available for low temperature neutron diffraction measurements. To save wasted experimental time in cooling and warming the device, the cell is capable of varying the applied load continuously down to 5 K, whilst the sample pressure can also be measured in-situ using a compact spectrometer system. Obtaining refineable neutron diffraction data from the small samples (< 1mm3) possible in an opposed anvil pressure cell is challenging due to extremely low ratios of signal-to-background when compared with large volume pressure cells. Finite element analysis (FEA) was performed to minimise the mass of the cell, whilst also minimising the amount of supporting material in the beam. Despite this, the signal from the sample is typically very weak; to overcome this, a novel 3D printed device has been designed and tested to collimate extremely small samples, removing much of the background signal from the surrounding material. It has enabled neutron data to be collected from samples an order of magnitude smaller than previously measurable in the cell. To maximise the pressures achievable in the pressure cell, for a given sample volume, an extended FEA study was performed to understand the evolutions of stresses in the cell, and understand the limitations of using sapphire as an anvil material. To complement this work, a compact piston cylinder cell has also been designed for a combination of different measurements. One of the key challenges in high pressure research is in knowing, or ensuring, that the conditions the sample is under are approximately the same for a variety of different measurements. Since different instruments, and techniques, may not allow for the same apparatus to be used between them, this is not always possible. A compact clamped piston cylinder cell has been designed, suitable for in-situ electrical measurements, with additional potential for simultaneous neutron diffraction measurements. The device is demonstrated through an ultrasonic characterisation of the compound UGe2. In addition to the information obtainable from neutron diffraction, much can be learnt from studying the transport properties of a material. This information can be used alongside neutron data to provide a full understanding of how a material behaves. One technique of interest measures how the electrical properties of a material changes under applied magnetic field. This is difficult to achieve under pressure due to the often anisotropic construction of the pressure cell affecting the magnetic field on the sample in different orientations, and the challenge in getting wires to the sample under pressure. This thesis presents the design, and preliminary testing, of an ultra compact high symmetry piston cylinder cell designed to be taken to sub-Kelvin temperatures and rotationally oriented in applied magnetic field. The spherical construction of the cell means that the field on the sample position is, to a very close approximation, identical in all orientations. Finally, this thesis presents a study of the binary alloy Pd3Fe under pressure. Pd3Fe was recently reported to undergo a large-volume collapse under high pressure at room temperature, resulting in near zero thermal expansion]. There are several competing theories on the mechanism behind this process. To investigate further, a series of single crystal Pd3Fe samples were grown, cut, prepared, and extensively analysed. The results of this study suggest that the cause for the large volume collapse may not be magnetic in nature, as previously expected.
5

Quantum and classical aspects of hydrogen bond dynamics

Ikram, Abarrul January 1996 (has links)
No description available.
6

Mechanism of cellular uptake of HIV-TAT peptide & effects of TAT-SOD against ultraviolet induced skin damage

Chen, Xiaochao January 2013 (has links)
TAT peptide is one of the best-characterised cell penetrating peptides (CPPs) derived from the transactivator of transcription protein from the human immunodeficiency virus 1 (HIV-1). TAT peptide is able to cross the cell membrane and deliver various biomolecules into cells with low immunogenicity and no toxicity. However, the exact mechanism of internalization still remains a subject of controversy. Lamellar neutron scattering was used to determine the location of TAT peptide in the negativelycharged phospholipids bilayers. The results reveal two locations, one in the peripheral aqueous phase between the adjacent bilayers and the second one below the glycerol backbone region of the lipid bilayer. A concentrationindependent membrane thinning above a peptide concentration threshold (1mol%) and a contiguous transbilayer water channel at the largest peptide concentration (10mol%) were also found. This evidence led to the suggestion that the toroidal pore model might be involved in the transmembrane mechanism at high peptide concentration. Another set of neutron diffraction experiments examined the interaction between the TAT peptide and neutral phospholipids showed that TAT peptide preferentially intercalated into the hydrophobic core and the glycerol backbone region of the neutral lipid bilayer at the lowest peptide concentration investigated (0.1mol%), indicating that the insertion did not require negatively-charged phospholipids. There was also clear evidence for the concentration-dependent reorientation of TAT peptide. A plasmid containing the human copper-zinc SOD gene linked with the coding sequence for a 11-aa HIV-TAT peptide (pGEX-TAT-SOD, 513bp) was constructed and used to express a recombinant fusion protein in Escherichia coli strain BL21 (DE3). High-level expression of TAT-SOD soluble protein with a GST tag (44-kDa) was achieved under optimal expression conditions and a small-scale glutathione affinity column or large-scale ion-exchange chromatography used for its purification. The potential protective effect of TAT-SOD against UV-induced cell damage was studied on UVC-irradiated MDCK epithelial cells. Before any further clinical study, the UV full-length absorption of TAT-SOD protein was measured. The results showed the potential UV protective effect of TAT-SOD was not due to the physical absorption of UV irradiation. In a preclinical study with five healthy volunteers, the penetration of TAT-SOD through human stratum corneum on the inner upper arm was identified by the tape stripping and specific SOD activity analysis. Significant increases on SOD activity were found on the outer layers of stratum corneum in TAT-SOD treated group, compared to placebo treated control, indicating that the TAT peptide assisted SOD to penetrate into the human stratum corneum . In a clinical study with ten healthy volunteers, eight showed a significant increase of minimal erythema dose (MED) with TAT-SOD pre-treatment. The median blood flow value of ten subjects at the UVB-irradiated site decreased with TAT-SOD pretreatment. Taken together, this evidence showed that TATvi SOD did have a marked protective effect against UVB induced skin damage. In a second clinical study, five healthy volunteers were challenged with a series of UVB doses. Skin punch biopsies were taken from four test sites on the lower back for H&E and immunohistochemical staining analysis. UVB-induced apoptotic sunburn cell (SBC) formation, p53 up-regulation and thymine dimer formation in epidermis were not attenuated by pretreatment with TAT-SOD. These data suggest that transdermal superoxide scavenger TAT-SOD reduced the UVB-induced inflammation, but did not abrogate the direct DNA damage of UVB irradiation on the skin. However, the hope of TAT-SOD could reduce UVA indirect DNA damage remains.
7

Lattice Strain Response of Zr-2 During Biaxial Deformation

Campbell, Dale 13 January 2014 (has links)
Pseudo-plane strain compression tests are carried out on rolled plate Zircaloy-2 using different combinations of loaded and constrained sample directions relative to the plate principal directions. Lattice strains are measured for 17 out of 18 possible measureable sample directions. The inability to obtain true plane strain led to little effect of the compression rig on deformation during elastic loading; however noticeable differences are seen when compared to similar uniaxial data for Zircaloy-2 in the plastic region. Work hardening increased with increased constraint and was affected by the configuration of loaded and constrained sample directions. Constraint showed significant effects on twinning when twinning was present. For the RD loaded cases the initiation of twinning occurs at -318 MPa for the RD/ND case (RD loaded, ND constrained direction) and -420 MPa for the RD/TD case. Intensity profiles of the (0002) and {101 ̅ 0} indicate that more twinning occurs in the RD/TD case than the RD/ND case. For TD/YD an amplification of twinning was seen in the TD/RD when compared to the TD/ND. This is indicated both by texture results as well as the intensity profiles of the (0002) and {101 ̅ 0}. Using the experimental data an elastic-plastic self-consistent (EPSC) code was used to probe the micromechanical processes that are occurring when the compression rig is operated. The experimental data was used further to constrain the hardening parameters of the EPSC code using an inverse approach. The EPSC code was able to capture the relative activity of the twinning characteristics found by the experimental data but unable to truly capture the evolution of the (0002) lattice strains when twinning occurs. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2014-01-13 11:24:21.692
8

Orientacoes preferenciais em niobio determinadas por difracao de neutrons

UENO, S.I.N. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:50:39Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:59Z (GMT). No. of bitstreams: 1 00051.pdf: 1323615 bytes, checksum: 560d14914e0156e890a27864c7db81e2 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP
9

Difracao multipla de neutrons em um cristal de aluminio

PARENTE, CARLOS B.R. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:23:49Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:52Z (GMT). No. of bitstreams: 1 01106.pdf: 7271038 bytes, checksum: 0782814eac2bd5593952b215dd48d0e7 (MD5) / Tese (Doutoramento) / IEA/T / Instituto de Fisica, Universidade de Sao Paulo - IF/USP
10

Orientacoes preferenciais em niobio determinadas por difracao de neutrons

UENO, S.I.N. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:50:39Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:59Z (GMT). No. of bitstreams: 1 00051.pdf: 1323615 bytes, checksum: 560d14914e0156e890a27864c7db81e2 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

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