1,721,001 research outputs found
A precision measurement of the (129)Xe electric dipole moment using dual noble gas masers.
No full textThis dissertation describes a measurement of the permanent electric dipole moment (EDM) in 129Xe. An EDM violates both parity and time reversal, and so its size sets limits on the CP-violating parameters of the Standard Model and its extensions. Two species of noble gas Zeeman masers were employed to achieve this precision. Zeeman masers are tools that permit very long running times and the advantages of in situ magnetometry. The Bloch equations that model the maser behavior are derived, and their solution predicts the maser polarizations for different system settings. Details of the construction of the apparatus (particularly the EDM cells employed) are provided. Over a six month period the experiment achieved a statistical sensitivity of 2.84 x 10-27 e cm but was limited by a systematic effect whose origin is unknown. Various approaches for identifying and eliminating this systematic are discussed.PhDAtomic physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132459/2/9963883.pd
Toward precision D coefficient measurement in polarized neutron decay and the development of A helium-3 neutron polarizer.
No full textI describe the search for possible time reversal symmetry violation by measurement of the coefficient D in polarized neutron decay. This relates to the triple product among the neutron polarization vector, electron momentum, and proton momentum in the neutron decay rate (w\sim{-}\\sigma\sb{n}\cdot(\vec p\sb{e}\times\vec p\sb{p})). With the improvements in neutron polarization (97%), an optimal octagonal detector geometry, and neutron spin transport system, about 15\times10\sp6 decay events were selected from data acquired at the Cold Neutron Research Facility at NIST, Gaithersburg. I have developed techniques for extracting D from the positive and negative triple product decay rates. My preliminary result is D=(12.1\pm13.4)\times10\sp{-4} where the uncertainty is statistical only. The false D resulting from the instrumental factor (\sigma\sb{\kappa}) and neutron polarization uncertainty (\sigma\sb{P}) are negligible. I also estimate the false D of the asymmetric transverse polarization (ATP) effect with an upper limit 5\times10\sp{-4} for the preliminary analysis of the initial data. I also describe development of an optical pumping/spin exchange neutron spin filter and obtained 40% neutron polarization for 2 A neutrons with a 10 amagat-cm 35 cm\sp3 polarized \sp3He cell.PhDAtomic physicsNuclear physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131448/2/9909910.pd
A precision measurement of the neutron spin structure functions using a polarized (3)He target.
No full textThis thesis describes a precision measurement of the neutron spin dependent structure function, g\sbsp{1}{n}(x). The measurement was made by the E154 collaboration at SLAC using a longitudinally polarized, 48.3 GeV electron beam, and a \sp3He target polarized by spin exchange with optically pumped rubidium. A target polarization as high as 50% was achieved. The elements of the experiment which pertain to the polarized \sp3He target will be described in detail in this thesis. To achieve a precision measurement, it has been necessary to minimize the systematic error from the uncertainty in the target parameters. All of the parameters of the target have been carefully measured, and the most important parameters of the target have been measured using multiple techniques. The polarization of the target was measured using nuclear magnetic resonance techniques, and has been calibrated using both proton NMR and by measuring the shift of the Rb Zeeman resonance frequency due to the \sp3He polarization. The fraction of events which originated in the \sp3He, as measured by the spectrometers, has been determined using a physical model of the target and the spectrometers. It was also measured during the experiment using a variable pressure \sp3He reference cell in place of the polarized \sp3He target. The spin dependent structure function g\sbsp{1}{n}(x) was measured in the Bjorken x range of 0.014 x 0.7 with an average Q\sp2 of 5 (GeV/c)\sp2. One of the primary motivations for this experiment was to test the Bjorken sum rule. Because the experiment had smaller statistical errors and a broader kinematic coverage than previous experiments, the behavior of the spin structure function g\sbsp{1}{n}(x) could be studied in detail at low values of the Bjorken scaling variable x. It was found that g\sbsp{1}{n}(x) has a strongly divergent behavior at low values of x, calling into question the methods commonly used to extrapolate the value of g\sbsp{1}{n}(x) to low x. The precision of the measurement made by the E154 collaboration at SLAC puts a tighter constraint on the extrapolation of g\sbsp{1}{n}(x) to low x, which is necessary to evaluate the Bjorken sum rule.PhDAtomic physicsHigh energy physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131098/2/9825346.pd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Laser-polarized xenon-129 magnetic resonance spectroscopy and imaging. The development of a method for <italic>in vivo</italic> perfusion measurement.
No full textThis thesis presents in vivo nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) studies with laser-polarized 129Xe delivered to living rats by inhalation and transported to tissue via blood flow. The results presented herein include the observation, assignment, and dynamic measurement of 129Xe resonances in the brain and body, the first one- and two-dimensional chemical-shift-resolved images of 129Xe in blood, tissue, and gas in the thorax, and the first images of 129Xe in brain tissue. These results establish that laser-polarized 129Xe can be used as a magnetic resonance tracer in vivo. NMR resonances at 0, 191, 198, and 209 ppm relative to the 129 Xe gas resonance are observed in the rat thorax and assigned to 129Xe in gas, fat, tissue, and blood respectively. Resonances at 189, 192, 195, 198, and 209 ppm are observed in the brain, and the 195 and 209 ppm resonances are assigned to 129Xe in grey matter, and blood, respectively. The design and construction of a laser-polarized 129Xe production and delivery system is described. This system produces liter-volumes of laser-polarized 129Xe by spin-exchange optical-pumping. It represented an order of magnitude increase over previously reported production volumes of polarized 129Xe. At approximately 3--7% polarization, 157 cc-atm of xenon is produced and stored as ice every 5 minutes. This reliable, effective, and simple production method for large volumes of 129Xe can be applied to other areas of research involving the use of laser-polarized noble gases. A model of the in vivo transport of laser polarized 129Xe to tissue under realistic experimental NMR conditions is described. Appropriate control of the NMR parameters is shown to allow tissue perfasion and 129Xe tissue T1 to be extracted from measurement of the steady-state 129Xe tissue signal. In vivo rodent 129Xe NMR results are used to estimate the signal-to-noise ratio of this technique, and an inhaled 30% xenon/70% O2 mixture polarized to 5% is estimated to provide sufficient SNR in rodent grey matter. Application to the measurement of regional cerebral blood flow and neuronal activation is discussed.PhDAtomic physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123958/2/3001042.pd
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Towards a Measurement of the Electric Dipole Moment of radon-223.
No full textThe observed baryon asymmetry in the universe requires a greater degree of CP violation than is contained in the CP-violating Standard Model processes discovered thus far. Since the permanent electric dipole moment (EDM) of a particle, atom, or molecule is a CP-odd observable, any nonzero measurement of an EDM above the small Standard Model background would indicate a new source of CP violation. The nuclear structure of 223Rn is expected to enhance its sensitivity to CP-violating interactions relative to 199Hg, currently the most sensitive atomic EDM result, motivating the development of the Radon EDM experiment. In anticipation of radon production at TRIUMF, we performed a series of studies to improve the design and predict the expected precision of the Radon EDM experiment. We designed and tested a prototype gas transfer apparatus that collects a sample of noble gas from a beam and transfers it to a measurement cell, achieving a transfer efficiency of about 40%. We recently improved this to greater than 90%. We studied the polarization and relaxation of radon using samples of 209Rn produced at SUNY Stony Brook's Nuclear Structure Laboratory and polarized it via spin-exchange with optically pumped rubidium. We constructed equations for the anisotropy of the gamma rays emitted by polarized 209Rn as a function of the rubidium polarization, the spin-exchange cross section sigmaSE, the wall-binding temperature T0, the quadrupole relaxation rate Ginfinity2 , and the cell temperature. Using rubidium polarization values measured by electron spin resonance, our radon polarization data indicated that a silane-based wall coating improved the relaxation rate in our cells. For T 0 = 350 K and sigmaSE = 2.5 x 10 -5A2, we found Ginfinity2 = 0.14 +/- 0.02 Hz in uncoated cells and Ginfinity2 = 0.042 +/- 0.012 Hz in coated cells. We used the coated-cell results to obtain a conservative estimate of the Radon EDM precision, 3 x 10-26e · cm at TRIUMF using gamma-ray anisotropies. Coupled with the enhancement effects, this indicates sensitivity to CP violation similar to that of 199Hg in the first phase of the Radon EDM experiment.PhDAtomic physicsNuclear physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127179/2/3441653.pd
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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