• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 298
  • 96
  • 71
  • 43
  • 24
  • 13
  • 7
  • 7
  • 4
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 704
  • 704
  • 122
  • 100
  • 96
  • 94
  • 85
  • 75
  • 66
  • 63
  • 63
  • 59
  • 53
  • 47
  • 45
  • 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

Infrared photodissociation of gas phase ions : single photon and multiphoton events

Odeneye, Michael Adetunji January 2000 (has links)
No description available.
12

Imaging stars through the atmosphere

Tuthill, Peter George January 1994 (has links)
No description available.
13

Frequency-selective excitation and non-linear data processing in nuclear magnetic resonance

Davies, S. J. January 1988 (has links)
No description available.
14

Image reconstruction for emission optical projection tomography

Darrell, Alexander Louis January 2010 (has links)
Emission Optical Projection Tomography (eO PT) is a relatively new imag- ing modality that bridges a gap between micro Magnetic Resonance Imag- ing and Confocal Laser Scanning Microscopy. eO PT can be used to image the anatomy and gene expression of intact biological specimens at high resolution and thus provides an alternative to time consuming methods such as serial sectioning. Tomographic image reconstruction for eOPT is currently performed using the Filtered Back Projection algorithm which, while being fast, does not account for the physics of image formation and thus can result in reconstructions of reduced resolution and questionable quantitative consistency. This thesis describes work that was done on eOPT in three areas, including image formation, tomographic reconstruction, and memory savings, the latter of which were required to bring implementation of 3D iterative reconstruction algorithms within reach for the relatively high-resolution eO PT imaging modality. In the area of image formation, measurements were taken to reveal the effects of optical blurring, diffraction and charge-coupled device (CCD) camera noise. Accurate models of each of these phenomena were developed and compared against the measurements. The subject of image reconstruction was first addressed with a modi- fication to the FBP algorithm designed to correct for the quantitative inaccuracies suspected of being introduced by the FBP algorithm when reconstructing specimens consisting of very fine detail. This was done by incorporating the quantitative aspects of the model of image formation into the FBP algorithm. The full model of image formation was incorpo- rated into the iterative Maximum Likelihood Expectation Maximisation (MLEM) algorithm. The third strand of this thesis focuses on various memory saving meth- ods developed to enable the implementation and testing of a variation of MLEM known as the Ordered Subsets Expectation Maximisation (OSEM). , Without such memory saving methods, the implementation of an iterative 3D reconstruction algorithm such as MLEM or OSEM using a full model of image formation would have remained beyond the capacity of modern computers for the foreseeable future, requiring several Terabytes of RAM. Comparisons were made between the quality of and the time required to produce FBP and OSEM reconstructions of the same data sets given the availability of limited computing resources. The feasibility of adopting OSEM reconstructions as an alternative to FBP reconstructions was dis- cussed, based on the use of currently available cutting edge computing hardware.
15

Studies of anorectal function using high resolution anorectal manometry in health and faecal incontinence

Carrington, Emma V. January 2017 (has links)
Faecal incontinence (FI) is a prevalent complaint in Western populations and causes significant disability. Impaired motor function of the anal canal is a common pathophysiological feature and assessment of sphincteric function with manometry is a routine part of symptom assessment. High-resolution anorectal manometry (HRAM) may provide a more detailed understanding of anorectal function, however its clinical utility has not been established. Aims The principal aims of this thesis were to: (1) Explore existing practices of anorectal manometry (2) Examine current evidence supporting the use of HRAM (3) Develop and validate a protocol for the performance of HRAM (4) Define normal values for traditional measures of sphincteric function using HRAM (5) Develop and validate novel measures of sphincteric function, and explore whether they improve diagnostic accuracy in patients with FI (6) Examine anorectal function over a prolonged period with HRAM to evaluate the phenomenon of anal sampling (referred to in this thesis as transient anal sphincter relaxations [TASRs]) Methods The following methods were used: (1) A worldwide survey of current practices of anorectal manometry (2) A systemic review of the literature (3) Prospective studies (both standard and prolonged) of anal function in healthy volunteers and patients with FI Results The practice of anorectal manometry is markedly variable internationally with no two centres surveyed employing the same methods. Within the 62 centres surveyed, there were 16 combinations of ways in which squeeze data were reported. A review of the literature demonstrated a growing evidence base for the use of HRAM however there is a paucity of data that confirm added benefits of HRAM over conventional manometry. A standardized protocol for HRAM was developed to allow the reporting of traditional measures of anorectal function. Novel measures derived from HRAM were developed which demonstrate increased sensitivity for the detection of impaired sphincteric control in patients with FI (sensitivity of traditional measure [conventional squeeze increment] 36% vs. 59% for the novel HRAM measure [5-second squeeze profile]). Transient anal sphincter relaxations (TASRs) were characterized using HRAM. In health, TASRs are often perceived by the individual as the urge to pass wind (39% of events) and their frequency increases following meal consumption. Conversely in FI, TASRs are a rare occurrence and are generally not perceived (only one patient (1/10 [10%]) with FI reported GI sensations associated with TASR events). Conclusions Anorectal manometry is in need of standardization. Novel measures derived from HRAM may improve diagnostic utility and further exploration of TASR characteristics might give insight into the pathophysiology of FI.
16

High resolution spectroscopic studies of ����S�����O��� and �����S�����O���

Barber, Jeffrey 28 April 2003 (has links)
Graduation date: 2003
17

Synthetic Aperture Sonar Motion Estimation and Compensation

Cook, Daniel A. 09 April 2007 (has links)
Synthetic aperture sonar (SAS) is the underwater acoustic counterpart to stripmap-mode synthetic aperture radar (SAR). Current seagoing SAS systems are deployed on unmanned robotic vechicles, commonly referred to as autonomous underwater vehicles (AUVs). As with SAR, SAS imaging is ideally done with a straight-line collection trajectory. However, SAS is far more susceptible to image degradation caused by the actual sensor trajectory deviating from a pefectly straight line. Unwanted motion is virtually unavoidable in the sea due to the influence of currents and wave action. In order to construct a perfectly-focused SAS image the motion must either be constrained to within one-eighth of a wavelength over the synthetic aperture, or it must be measured with the same degree of accuracy and then accounted for in the processing software. Since the former is not possible, the latter approach must be taken. The technique known as redundant phase centers (RPC) has proven to be insrumental in solving the problem of SAS motion compensation. In essence, RPC simply refers to the practice of overlapping a portion of the receiver array from one ping (transmission and reception) to the next. The signals observed by this overlapping portion will be identical except for a time shift proportional to the relative motion between pings. The time shifts observed by the RPC channels of the receiver array are scalars representing the projection of the array receiver locations onto the image slant plane, and these time shifts can be used to compensate for the unwanted platform motion. This thesis presents several extensions to the standard RPC technique in which the RPC time delays are combined with the AUV's on-board navigation data. The scalar time delays are decomposed into the components induced by the six degrees of freedom of the motion: i.e., the linear and angular velocities. Thus, the time delays observed in the image slant plane can be used to refine the motion estimate in an absolute frame of reference external to the AUV. Creating a high-resolution SAS image of the sea floor in an automatic fashion demands accurate and robust motion estimation. The performance of the motion estimation schemes presented is demonstrated using actual field data collected from an assortment of current research SAS systems.
18

A high-resolution study of the electronic structure of NbSe3 in normal and charge density wave states with angle resolved photoemission spectroscopy /

Rocha, Matthew Paul, January 2003 (has links)
Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 166-167). Also available for download via the World Wide Web; free to University of Oregon users.
19

New devices and techniques for high resolution astronomical spectroscopy and a new study of old stars /

Keller, Luke David, January 1999 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 110-113). Available also in a digital version from Dissertation Abstracts.
20

High resolution spectroscopy of scandium monohalides

Xia, Ye, 夏晔 January 2012 (has links)
This thesis reports the study of the molecular and electronic structure of scandium monohalides using the technique of laser ablation/reaction with supersonic free jet expansion used for producing the target molecules and laser induced fluorescence (LIF) spectroscopy for recording their electronic transition spectrum. The scandium diatomic molecules studied in this work were scandium monoiodide (ScI) and scandium monobromide (ScBr), which were produced by the reaction of Sc atoms with 2% CH3I and 2% C2H5Br gases seeded in Ar carrier gas, respectively. The LIF spectrum of the electronic transition of ScI and ScBr were recorded in the visible and near infrared spectral region between 613 and 854 nm. The analysis of the high resolution electronic spectra of ScI and ScBr yielded molecular constants and information of electronic structures. For all the transition bands observed, rotationally-resolved transition lines were fit to a theoretical model to retrieve molecular constants for both upper and lower electronic states. For the ScI molecule, seven vibrational bands of the D1П –X^1 Σ^+ system were recorded and analyzed. Accurate molecular constants for the v = 0 – 2 levels of the D^1П state and the v = 0 – 3 levels of the X^1 Σ^+ state were obtained. The equilibrium bond lengths, re (Å), for the electronic states of ScI were determined as follows: ScI X^1 Σ^+ D^1П r_e(Å) 2.6078 2.7146 For the ScBr molecule, three electronic transition systems were recorded and analyzed, which include six vibrational bands of the C^1 Σ^+– X^1 Σ^+ system, seven vibrational bands of the e^3Δ–a^3Δsystem and two vibrational bands of the d3Φ – a3Δ system. Rotationally resolved transition lines of both Sc79Br and Sc81Br isotopes were observed and analyzed. Least-squares fitting of the measured line positions yielded accurate molecular constants for the v = 0 – 2 levels of the X^1 Σ^+ state, the v = 0 – 3 levels of the C^1 Σ^+ state, the v = 0 and 1 levels of the d3Φ state and the v = 0 – 2 levels of both e3Δ and a3Δ states, respectively. The equilibrium bond lengths, re (Å), determined for electronic states of ScBr are given as follows: ScBr X^1 Σ^+ a^3Δ C^1 Σ^+ r_e(Å) 2.3806 2.4767 2.4776 A molecular orbital (MO) energy level diagram has been used to examine the electronic configurations giving rise to the different observed electronic states of ScI and ScBr. An attempt has been made to put the MOs of all the scandium monohalides under a single picture. A comparison of the molecular constants for the different electronic states of scandium monohalides indicates a weakening of the chemical bonding between the scandium atom and the halogen atoms down the group. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Page generated in 0.1119 seconds