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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.
11

Neutron Density Depression Due to an Oblate Spheroidal Detector

Trammell, Margaret Ruth 01 1900 (has links)
In this paper, two projects have been undertaken. First, Workman's calculations have been checked to a higher degree of approximation to determine the accuracy of his method. Second, a new set of boundary conditions has been developed for obtaining solutions of the neutron diffusion equation which do not depend on the solution of the equation inside the detector.
12

Techniques for Handling Multilayered Media in the FDTD Method

Çapoğlu, İlker R. 06 July 2007 (has links)
We introduce supplemental methods for the finite-difference time-domain (FDTD) analysis of planar multilayered media. The invariance is allowed to be disturbed by any imperfection, provided that these imperfections are local and therefore can be contained within an FDTD simulation grid. We specifically investigate two FDTD methods that were not previously developed for general multilayered media: the near-field-to-far-field transform (NFFFT) and the total-field/scattered-field (TF/SF) boundary (or the plane-wave injector). The NFFFT uses the FDTD output on a virtual surface surrounding the local imperfections and calculates the radiated field. The plane wave injector builds an incident plane wave inside a certain boundary (TF/SF boundary) while allowing any scattered fields created by the imperfections inside the boundary to exit the boundary with complete transparency. The NFFFT is applicable for any lossless multilayered medium, while the plane-wave injector is applicable for any lossy multilayered medium. After developing the respective theories and giving simple examples, we apply the NFFFT and the plane-wave injector to a series of problems. These problems are divided into two main groups. In the first group, we consider plane-wave scattering problems involving perfectly-conducting objects buried in multilayered media. In the second group, we consider problems that involve radiating structures in multilayered media. Specifically, we investigate the reciprocity of antennas radiating in the presence of an ungrounded dielectric slab using the methods developed in this study. Finally, we present our previous work on an entirely different subject, namely, the theoretical analysis of the input admittance of a prolate-spheroidal monopole fed by a coaxial line through a ground plane.
13

Measuring dark matter profiles non-parametrically in dwarf spheroidal galaxies

Jardel, John Raymond 23 June 2014 (has links)
Although exotic objects like supermassive black holes (SMBHs) and dark matter halos do not emit or interact with light, we can still detect them across the vastness of space. By observing the gravitational dance of objects we can see, astronomers are able to infer the mass of the invisible objects they orbit. This has led to the discovery that nearly every massive galaxy hosts a SMBH at its center, and has confirmed that every galaxy is embedded in an extended halo of dark matter. However, the practice of inferring mass from the motions of bright kinematics tracers has many complications, not the least of which is that we seldom observe more than the line-of-sight component of the instantaneous velocity of a star. Consequently, astronomers must build dynamical models of the galaxies they wish to study. These models often rely on overly restrictive assumptions, or are crippled by degeneracies amongst their parameters and lack predictive power. In this thesis, I introduce a significant advancement into the field of dynamical modeling. My modeling technique is based on the powerful principle of orbit superposition, also known as Schwarzschild Modeling. This technique is robust to many of the degeneracies associated with dynamical modeling, and has enjoyed much success in measuring the SMBHs and dark matter halos of large elliptical or bulge-dominated galaxies. I use it in Chapter 2 to accurately measure the SMBH in the Sombrero Galaxy (NGC 4594) and to constrain its dark matter halo. Unfortunately, when measuring dark matter halos with Schwarzschild Modeling, the modeler is required to adopt a parameterization for the dark matter density profile. Often this is precisely the quantity one wishes to measure. To avoid this reliance on a priori parameterizations, I introduce a technique that calculates the profile non-parametrically. Armed with this powerful new technique, I set out to measure the distribution of dark matter in the halos of some of the smallest galaxies in the Universe. These dwarf spheroidal galaxies (dSphs) orbit the Milky Way as satellites, and their dark matter content has been studied extensively. However, the models used to probe their halos have been simplistic and required overly restrictive assumptions. As a result, robust conclusions about their dark matter content have remained elusive. Into this controversial and active area of study, I bring Non-Parametric Schwarzschild Modeling. The results I find offer the most robust and detailed measurements of the dark matter profiles in the dSphs to date. I begin my study with the first application of standard Schwarzschild Modeling to any dSph galaxy by using it in Chapter 3 on Fornax. This chapter details the process of re-tooling Schwarzschild Modeling for the purpose of measuring these small galaxies. In Chapter 4, I introduce the fully non-parametric technique, and apply it to Draco as proof of concept. Chapter 5 presents the main results of this thesis. Here I apply Non-Parametric Schwarzschild Modeling to Draco, Carina, Fornax, Sculptor, and Sextans. By relaxing the assumption of a parameterization for the dark matter profile, I find a variety of profile types in these five galaxies---some of which are consistent with past observations, others consistent with predictions from simulations, and still others were completely unanticipated. Finally, in Chapter 6 I describe the modeling of these galaxies in more detail. I demonstrate the accuracy of Non-Parametric Schwarzschild Modeling by recovering a known dark matter profile from artificial simulated data. I also expound upon the modeling results by presenting the detailed orbit structure of the five dSphs. Lastly, I compare my results to hydrodynamical simulations to explore the link between dark matter profile type and the baryon content of the dSphs. / text
14

The study of Chinese herbal medicinal compound on implantation : in vitro spheroid-endometrium co-culture

Cheung, Hoi-yan, 張凱恩 January 2013 (has links)
Traditional Chinese medicine (TCM) plays an important role in the Chinese healthcare system for over five thousand years. It includes the use of herbal medicine, acupuncture, Tui Na (推拿), and diet therapy. TCM helps to maintain a balance of Yin-Yang (阴阳), Five Phases (五行), Meridians (经络) and Qi (气) inside the body. In practise, pregnant women take tocolytic drugs to tonify the blood and qi to provide a continuous supply of nutrients for baby. Traditional Chinese herbal medicines usually prescribed as a complex formula to produce synergistic or agonistic effect to maintain a well balance of the above components in human bodies. Moreover, TCM usually cannot produce immediate effect on patients, therefore, the efficacy of individual component remains largely unknown. This study aims to investigate whether Chinese tocolytic drug components could modulate fertility by affecting the in vitro spheroid (blastocyte surrogate) attachment process by using trophoblastic (JEG-3) and endometrial epithelial (Ishikawa) cells to mimic the embryo-endometrial implantation process. Nine Chinese herbal medicinal compounds (Atractylenolide I(白术内酯), Atractylenolide II(白术内酯II), Atractylenolide III(白术内酯III), Paeoniflorin(芍药苷), Albiflorin(芍药内酯苷), Nuzhenide(女贞子甙), Ecliptasaponin A(旱莲甙A), Wedelolactone(蟛蜞菊内酯) and Columbianadin(二氢欧山芹醇当归酸酯)) which are commonly found in traditional Chinese tocolytic drug formula were selected to study (1) the toxicity of the drugs on trophoblastic (JEG-3) and endometrial epithelial (Ishikawa) cells growth, (2) the effect of three tocolytic drugs (Atractylenolide I, Atractylenolide II and Atractylenolide III) on spheroid attachment, and (3) their effect of the expression of Wingless (Wnt) signaling molecules (Active-β-Catenin, Axin-2, β-catenin, E-cadherin, GSK-3β, and Mucin-1). It was found that the nine compounds, Atractylenolide I, Atractylenolide II, Atractylenolide III, Paeoniflorin, Albiflorin, Nuzhenide, Ecliptasaponin A, Wedelolactone and Columbianadin did not affect cell viability at 25μM, 25μM, 5μM, 0.2μM, 125μM, 125μM, 125μM, 5μM and 25μM, respectively, by cell proliferation assay. However, at these concentrations, the spheroid attachment was not significantly increased by Atractylenolide I, Atractylenolide II and Atractylenolide III. Interestingly, the protein expression of GSK-3β and Active-β-catenin were up-regulated by the three compounds in both cells and JEG-3 cells respectively. The expressions of Axin-2 and E-cadherin were up-regulated by Atractylenolide III in Ishikawa cells and Atractylenolide II in JEG-3 cells. Atractylenolide I and Atractylenolide III increase the Ishikawa cells expression of Active-β-catenin and β-catenin respectively and together suppress the JEG-3 cells Mucin-1 and β-catenin expression. In conclusion, the nine tocolytic compounds have different effect on cell proliferation. Atractylenolide I, Atractylenolide II and Atractylenolide III did not enhance the attachment rate of JEG-3 spheroid onto Ishikawa monolayer. However, they affected Wnt-signaling molecules expression, suggesting that they may modulate endometrial receptivity. Further experiments are needed to study their combined effect on co-culture and expression of Wnt-signaling molecules. / published_or_final_version / Obstetrics and Gynaecology / Master / Master of Medical Sciences
15

Newtonian vs. MOND Gravity: Dwarf Spheroidal Galaxies With Central Massive Black Holes

Hogsett, Elijah Glen 18 July 2023 (has links)
No description available.
16

The MOND External Field Effect on Dwarf Spheroidal Galaxies

Blankartz, Benjamin David 03 August 2017 (has links)
No description available.
17

Prolate Spheroidal Sequence Based Transceivers for  Time-Frequency Dispersive Channels

Said, Karim A. 12 July 2017 (has links)
Most existing transceivers are Fourier-centric where complex sinusoids play a central role in the internals of the core building blocks. From the channel perspective, complex sinusoids constitute the fundamental effects in the wireless baseband equivalent channel model; exemplified by the time-invariant and time-varying transfer functions in static and time-varying channel conditions respectively. In addition, complex sinusoids are used as signaling waveforms for data transmission through the channel. The dominant mode of transmission in modern communications is in the form of finite time duration blocks having approximately finite bandwidth. As a result, the time-frequency space becomes projected to a time-frequency subspace having essentially limited support where complex sinusoids suffer from leakage effects due to the finite time extent of a block. In addition, Kronecker delta signals (duals of complex sinusoids) suffer from the same vulnerability due to the finite extent bandwidth. Gabor signaling bases using non-rectangular pulse shapes can attain good confinement in the time-frequency space, however, at the expense of completeness which reduces the utilization efficiency of the time-frequency signaling resources. Over a signaling block period, a doubly dispersive (DD) channel is projected onto an essentially limited time-frequency subspace. In this subspace, the Discrete Prolate Spheroidal (DPS) basis matched to the channel parameters is known to be optimally compact in representing the channel using a basis expansion decomposition. Unlike the Discrete Fourier Transform (DFT) basis which lacks compactness due to the leakage effect. Leakage in the expansion coefficients of a particular channel using the DFT basis has a direct correspondence with the Inter-Symbol Interference (ISI) between the DFT signaling components when transmitted through the same channel. For the DPS basis, however, the correspondence is not as obvious. Nevertheless, DPS when used for signaling results in ISI compactness in the form of an exponential decay of distant ISI components. The efficacy of DPS signaling in DD channels in addition to its efficiency in modeling DD channels motivates the investigation of a new transceiver baseband architecture where DFT is supplanted by DPS. / Ph. D.
18

Prolate Shaped Dark Matter Halo And The Galactic Warp

Rahul Nath, R 11 1900 (has links) (PDF)
The physical explanation for the existence of the galactic warp is one of the major research areas in Astronomy. People have proposed various theories but nobody has yet given a convincing explanation. Most of the spiral galaxies are observed to be warped which reveals that the galactic warp is a stable characteristic. In the theory of kinematic bending wave, warp is considered as a wave that is propagated through the galactic disk with a speed called pattern speed. If the pattern initially had straight line of nodes, according to bending wave theory, the warp would tend to wind up rapidly in the gravitational field of galactic disk. But still we observe warped galaxies in the sky. In the literature, it has been claimed that the winding problem of galactic warp may be solved by incorporating the effect of gravitational field of the dark matter halo in which the galactic disk is embedded. Recently some works on the dynamics of galactic disk claim that the shape of the dark matter halo is pro late spheroid. In this thesis, the effect of the gravitational field of a prolate spheroidal dark matter halo with varying eccentricity to the galactic warp is calculated and discussed. Chapter1 gives the general introduction of the topics discussed in the following chapters. The structure of the spiral galaxy, their classifications, and the disk dynamics are discussed in the first few sections. One of the revolutionary concepts that emerged in the previous century was the existence of the dark matter. Presently tracing the mass distribution and the constituent particles of dark matter is one of the major research areas in theoretical and experimental physics. In this thesis, the effect of a particular type of mass distribution in dark matter halo on the warp is discussed in detail. In the next few sections, the following topics are discussed namely; how the concept of dark matter came into astrophysics, how to measure the total mass inside a given radius and what are the different distributions used for various purposes. A new theory called Modified Newtonian Mechanism was also proposed in the previous century as an alternative to the dark matter concept which is also discussed briefly. Kinematic bending wave theory and the winding problem of the galactic warp is also discussed in detail. In the last section a relation between the pattern speed of the warp and the shape of the dark matter halo is obtained. The calculation of the potential of a prolate spheroidal mass distribution with varying eccentricity is not done in any literature as we know. The calculation of the potential and the patten speed of prolate spheroidal mass distributions and of the galactic disk are described in chapter 2. The calculations of oblate spheroidal mass distribution are also discussed in this chapter but that is out of main theme. In chapter 3 we apply the equations obtained in the Chapter 2 to one simple toy model and to the Galaxy. The rotation curve and the pattern speed of a warp in the gravitational field of prolate spheroidal mass distribution of varying eccentricity are described. Usually the Milky Way disk is treated as an in infinitesimally thin disk but for our calculations the three dimensional but thin disk is used. The usually people use some approximation to calculate the potential due to galactic infinitesimal thin disk. The difference of the work from earlier works done by different people(with the approximation mentioned in above line) is also discussed in this Chapter. Chapter 4 discusses the summary of the entire work.
19

Foil Depression Factors for Disc-shaped Detectors

Gallagher, Tom Lewis 06 1900 (has links)
The generalized data which are presented in this thesis are the culmination of the determination of the foil depression factor using oblate spheroidal coordinates.
20

Error bounds for digital communication over spatially modulated channels.

January 1969 (has links)
Also issued as a Ph.D. thesis in the Dept. of Electrical Engineering, 1968. / Bibliography: p.91-93.

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