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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

Implementation and assessment of bi-radionuclide seeds for permanent implant prostate brachytherapy

Nuttens, Vincent E 20 March 2008 (has links)
Interstitial brachytherapy using permanent seeds is a common modality for the treatment of early stage prostate cancer. It consists of inserting hundreds of radioactive seeds (size of a grain of rice) in the prostate by means of transperineal needles. In this procedure, dose delivery to healthy surrounding organs at risk (OAR) and dose homogeneity within the prostate are of prime concern. Placement errors should therefore be minimized to avoid unacceptable area underdosage or overdosage. At present, brachytherapy seeds can be loaded with three different radionuclides: iodine-125 (<sup>125</sup>I: 28.37 keV; 59.40 days), palladium-103 (<sup>103</sup>Pd: 20.74 keV; 16.991 days), and cesium-131 (<sup>131</sup>Cs: 30.45 keV; 9.689 days). Long or short term morbidity is the main drawback of <sup>125</sup>I and <sup>131</sup>Cs due to their deeper penetration in the normal tissues. However, both provide a good homogeneity of the dose distribution within the prostate. By contrast, <sup>103</sup>Pd offers a short penetration depth that reduces the dose to OAR. Nevertheless, it could result in cold spot (underdosage) where a recurrence of the cancer could appear. A compromise had to be found between good implant uniformity and low dose to OAR. We propose therefore to study if the combination of two radionuclides inside the same seed could be a solution. Two mixtures were considered: <sup>103</sup>Pd<sub>0.75</sub>-<sup>125</sup>I<sub>0.25</sub> and <sup>103</sup>Pd<sub>0.25</sub>-<sup>131</sup>Cs<sub>0.75</sub>. The subscripts denote the fractions of internal activity of each radionuclide. The work is subdivided into three steps. First we adapt the AAPM TG-43U1 dosimetry formalism used by the physician to make multiple-radionuclides sources compatible with Treatment Planning Systems (TPS). Then the dose distributions around the bi-radionuclide seeds are determined. Second, the prescription doses for both sources are derived using the linear quadratic model for tumor cell surviving fraction. They were computed using mono-radionuclide implants as benchmarks. Finally, treatment plans and Dose-Volume Histograms parameters have been computed on real patients virtually implanted with bi-radionuclide seeds and the results were compared with the mono-radionuclide one. These parameters can then be used to evaluate the Normal Tissue Complication Probability (NTCP) of urethra, the most exposed organ at risk in prostate brachytherapy. First, dosimetry results show that, from a pure physical point of view (i.e. without tissue reponse), the dose distributions of both mixtures lies in between that for <sup>103</sup>Pd and <sup>125</sup>I/<sup>131</sup>Cs. The compromise between homogeneity and reduced dose at large distance can be reached. Second, the averaged prescription doses for the Pd-I mixture are 142<sup>+15</sup><sub>-16</sub>Gy and 142<sup>+6</sup><sub>-8</sub>Gy using <sup>103</sup>Pd and <sup>125</sup>I as benchmarks, respectively. The values for the Pd Cs mixture are 128<sup>+13</sup><sub>-13</sub>Gy and 115<sup>+6</sup><sub>-7</sub>Gy, using <sup>103</sup>Pd and <sup>131</sup>Cs, respectively, as benchmarks. Finally, urethral NTCP results fall in the 19 to 23% range. However, they are affected by large uncertainties, making the comparison difficult. At present, no conclusion could be drawn about the efficiency of bi-radionuclide brachytherapy in comparison with mono-radionuclide using the available models. Permanent seed prostate brachytherapy suffers a lot from the lack of precision on radiobiological modelling parameters. A better knowledge of their values could significantly improve the predicting models and therefore lead to better treatment outcome.
2

Beta-decay, beta-delayed neutron emission and isomer studies around <sup>78</sup>Ni

Rajabali, Mustafa Moiz 01 December 2009 (has links)
A study of nuclei with few nucleons outside the closed shell provides benchmarks for the nuclear shell model especially in this modern era of physics where exotic doubly magic nuclei can be tested. The subject of this thesis is to experimentally investigate the properties of nuclei near 78Ni and to confront them with the predictions of modern large scale shell model calculations. In this regard, an experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL) to measure excited states in 71-73Ni populated via the beta-decay of 71-73Co. Data collected from this experiment lead to partial level schemes for 71Ni and 73Ni and to improvements of existing level schemes for 70Ni and 72Ni. An objective of this experiment was to investigate the changes in excitation energy of the 5/2- state relative to the 9/2+ ground state as well as the search for the 1/2- isomeric state in odd-mass nickel isotopes approaching 78Ni. A second experiment was performed also at the NSCL where a two nucleon removal reaction from 73Cu was used to populate the low lying yrast states in 71Ni. Results from this in-beam experiment aided in constructing the level scheme of 71Ni. Systematics in shell model calculations using realistic interactions for odd mass 69-77Ni reveal a steady increase in energy spacing between the 1/2- level and 9/2+ ground state - suggesting an increased role of the g9/2 correlations, but an almost constant energy separation between the 5/2- and 1/2- excited states. Using data from the two experiments, the position of the 5/2- state in 71Ni and 73Ni and 1/2- state in 71Ni were identified. The decay of 74,76Ni into 74,76Cu was also investigated. Low lying states revealed new level schemes which are presented with an interpretation of the position of 1+ states populated via allowed GT transitions. A second project in this thesis is on the design and development of a detector system using a dual micro channel plate configuration. The system was built to detect and measure nanosecond isomers in neutron rich 73-76Cu and 76Zn isotopes. The design of the instrument and preliminary beam and alpha source tests done on the system are discussed.
3

Nucleosynthesis of <sup>16</sup>O Under Quiescent Helium Burning

Matei, Catalin 29 December 2006 (has links)
No description available.
4

Intracellular calcium stores and sodium-calcium exchanger in cardiac myocytes:experimental and computer simulation study

Han, C. (Chunlei) 27 November 2001 (has links)
Abstract Cytosolic Ca2+, [Ca2+]I , has a key role in intracellular signalling during excitation-contraction coupling (E-C coupling) in cardiac myocytes. The sarcoplasmic reticulum (SR) is a main intracellular Ca2+ store and the Na+-Ca2+ exchanger (NaCaX) is a major mechanism to extrude Ca2+ for balancing the Ca2+ influx via L-type Ca2+ channels during excitation. Furthermore, [Ca2+]I also affects the configuration of the action potential (AP). The present study, by combination of animal experiments and computer simulations, investigated the roles of [Ca2+]I, SR and NaCaX in cardiac myocytes, in Ca2+-induced Ca2+ release (CICR) and in modulation of APs. The following were studied: (I) the stretch-induced effects on rat atrium and the role of [Ca2+]I in modulation of AP; (II) the role of the SR in modulation in rat atrium by stretch; (III) the role of NaCaX; (IV) the role of [Ca2+]I in modulation of action potential duration (APD) in myocytes with short and long action potential duration. In isolated rat atrial preparations, the physiological or moderate stretch stimulus caused two- phasic rise of developed contraction, rapid and slow phases, accompanied with slow increments of [Ca2+]I and prolongations of action potentials durations in continuous recordings. In sustained stretch, the APD and [Ca2+]I were all increased significantly when intra-atrial pressure increased from 1 to 3 mmHg. In computer simulations, employing a rat atrial model (RA model), it was found that stretch-activated channels and increased Tn C affinity for Ca2+ alone could not produce the changes in the experiments. Only after both mechanisms applied to model cells, the main experimental findings could be mimicked (I). The prolongation of APD induced by stretch in rat atrial preparations was reversed after depleting the Ca2+ content of the SR by application of the SR functional inhibitors, ryanodine, thapsigargin and caffeine (II). In the computer simulation using modified guinea pig ventricular model, the Ca2+ entry via the reversal of NaCaX was found to be accounting 25% of the total activator Ca2+ for triggering Ca2+ release from the SR during normal excitation. This contribution increases with elevated [Na+]i (III). In a guinea pig ventricular model (GPV model) and a RA model were employed for investigating the regulation of APD by [Ca2+]I-dependent membrane currents. Increased SR Ca2+ content produced an elevated [Ca2+]I in both model cells, leading to prolongation of APD in the RA model but shortening in the GPV model. Increased [Ca2+]I enhances the NaCaX current in the same scale in both models, but inhibits L-type Ca current much more in the GPV model than the RA model (IV). In conclusion, (I) Stretch-induced [Ca2+]I increase prolongs the rat atrial AP by enhancing the NaCaX inward current. Stretch-activated channels (SACs) and increased affinity of TnC for Ca2+ are main general factors responsible for the variety of changes of cardiac muscles induced by stretch. (II) The SR plays a crucial role in the modulation of myocytes by accumulating the additional Ca2+ influx via sarcolemma during stretch. (III) The NaCaX contributes a small part for activator Ca2+ for calcium release from the SR during normal cardiac E-C coupling. However, this contribution is [Na]i-dependent, and in some pathological conditions, it may be a potential factor for cardiac arrhythmogenesis. (IV) Different effects on the NaCaX and L-type channels induced by increased [Ca2+]I leads to the dispersion of the change of APD in myocytes with long and short AP during inotropic interventions that increase the [Ca2+]I.
5

Numerical calculations of quasiparticle dynamics in a Fermi liquid

Virtanen, T. (Timo) 08 March 2011 (has links)
Abstract The problem of describing a system of many interacting particles is one of the most fundamental questions in physics. One of the central theories used in condensed matter physics to address the problem is the Fermi liquid theory developed by L. D. Landau in the 1956. The theory describes interacting fermions, and can be used to explain transport phenomena of electrons in metals and dynamics of helium three. Even when the theory is not directly applicable, it forms a basis against which other, more sophisticated theories can be compared. this thesis the Fermi liquid theory is applied to 3He-4He-mixtures at temperatures where the bosonic 4He part is superfluid, and the mechanical properties of the system are largely determined by the 3He component, treated as a degenerate normal Fermi liquid. The dynamics of strongly interacting liquid 3He can be described as a collection of quasiparticles, elementary excitations of the system, which interact only weakly. In 3He-4He mixtures the interactions can be continuously tuned by changing the temperature and the concentration of the mixture. The scattering time of quasiparticles depends on temperature, and thus the transition from the hydrodynamic limit of continuous collisions at higher temperatures to the collisionless ballistic limit at low temperatures can be studied. This gives invaluable information on the role of the interactions in the dynamics of the system. In this work, by using the Fermi liquid theory and Boltzmann transport equation, the dynamics of helium mixture disturbed by a mechanical oscillator is described in the full temperature range. The solution necessarily is numeric, but new analytical results in the low temperature limit are obtained as well. The numerical approach enables one to study various boundary conditions thoroughly, and allows application of the theory to a specic geometry. It is shown that in order to explain the experimental observations, it is necessary to take into account the reflection of quasiparticles from the walls of the container. For suitable choice of oscillator frequency and container size, second sound resonances are observed at higher temperatures, while in the ballistic limit quasiparticle interference can be seen. The numerical results are in quantitative agreement with experiments, thus attesting the accuracy of Fermi liquid theory. In particular, the previously observed decrease of inertia of a mechanical oscillator immersed in helium at low temperatures is reproduced in the calculations, and is explained by elasticity of the fluid due to Fermi liquid interactions.
6

Diseño e Implementación de un Curso para la Gestión/Tipificación de Proyectos en Telecomunicaciones

Cerda Espinoza, Mauricio Alexis January 2007 (has links)
No description available.
7

Photoproduction of K<sup>*+</sup>¿¿/¿¿<sup>0</sup> and K<sup>0</sup>¿¿<sup>+</sup> from the Proton Using CLAS at Jefferson Lab

Tang, Wei January 2012 (has links)
No description available.
8

Electronic Properties of Silicon-based Nanostructures

Guzman-Verri, Gian Giacomo 08 December 2006 (has links)
No description available.
9

Estrogen modulation of MPP <sup>+</sup> - induced Dopamine secretion in the Corpus Striatum and Nucleus accumbens of the Rat Brain

Arvin, Michael, Jr. January 1998 (has links)
No description available.
10

Iodinated Polyhedral Boranes for Cancer Detection

Palmer, Alycia M. 20 October 2011 (has links)
No description available.

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