1,721,071 research outputs found
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
Analysis of JLab E12-14-012 Ti(e,e′p) Data and Determination of the Ti Spectral Function
No full textFuture long baseline neutrino oscillation experiments like the Deep Underground Neutrino Experiment (DUNE) rely on Liquid Argon Time Projection Chamber (LArTPC) detectors. The reconstruction of neutrino flavors and energy through interactions with Argon is a critical issue for assuring the DUNE success. The neutrino-Argon nuclear cross section is one of the biggest sources of uncertainty in measuring possible Charge-Parity Violation (CPV) in the neutrino (ν) sector and decoupling background like matter-effects. This thesis summarizes the exclusive electron scattering measurement of the Jefferson Lab E12-14-012 experiment. The E12-14-012 experiment goals are to explore the Ti(e,e′p) and Ar(e,e′p) reactions in a wide range of kinematics in order to determine the spectral function of protons and neutrons in Argon. The measurements made in E12-14-012 are the first of their kind in argon and are a pivotal step in understanding the electron-Argon interaction and its relation to neutrino scattering. Titanium was specifically chosen under an assumption that its protons can be a proxy for argon neutron spectral functions. The analysis of the exclusive electron scattering in titanium is described in detail in this thesis.M.S.While considerable progress has been made in understanding the power of the atom, nucleons (protons and neutrons) trapped in medium-to-heavy nuclei have properties that we still need to understand. The purpose of this thesis is to explore the nuclear investigation conducted at Jefferson Lab (JLab) in Newport News, Virginia. Specifically, we follow the data analysis of the JLab Hall A Experiment E12-14-012 which seeks to quantify the nuclear energy momentum distributions of nucleons in complex nuclei like titanium and argon. These measurements, the first of their kind experimentally, are done to provide a reliable model for lepton-nucleus interactions. Modeling lepton-nucleus interactions in argon is of paramount importance, as argon is the primary target medium in future long baseline neutrino oscillation experiments like DUNE. Neutrinos are notoriously difficult to measure; and therefore, when they interact, we only measure the interaction products as they come out of the nucleus. Sometimes the products of the primary interaction will not escape the nucleus and have to be modelled to accurately estimate the incoming neutrino energy. The analysis on titanium provided in this thesis is a bridge for argon interactions with leptons, where titanium is used to determine argon neutron momentum and energy distributions
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
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
Gamma Veto Detectors in the KOPIO Experiment
No full textKOPIO is an experiment designed to search for the CP-symmetry-violating reaction KL⁰ → π⁰νν̅. Measurement of the branching ratio of this reaction, depending on the accuracy of the measurement, could be the most precise measurement of the CP-violation parameters of the Standard Model to date. The KL⁰ → π⁰νν̅ reaction is exceedingly rare, with an expected branching ratio of (2.6 ± 1.2) ·10⁻¹¹ . The rareness of this reaction means two things: 1) that we need prodigious numbers of kaons, and 2) that a multitude of "improper" decays will have to be screened out by means of a veto detector system, part of which is being designed here at Virginia Tech.
This detector must be able to detect the passage of daughters of the undesired decay reactions (charged particles and gammas). It must be operational inside a magnetic field, and must have signal timing fast enough to accommodate the rate at which these decays occur. A detector consisting of alternating layers of scintillator and lead, with wavelength-shifting fibers embedded in the scintillator, provides the characteristics sought after. This paper presents methodology used in design and construction of this detector, as well as results of signal property tests, using both cosmic rays and gammas as event triggers. Also included is a discussion on transporting the detector signal outside of the magnetic field so it can be read by photomultiplier tubes resting outside of the sweeping magnet.Master of Scienc
Aspects of Supersymmetry
No full textThis thesis is devoted to a discussion of various aspects of supersymmetric quantum field theories in four and two dimensions. In four dimensions, = 1 supersymmetric quantum gauge theories on various four-manifolds are constructed. Many of their properties, some of which are distinct to the theories on flat spacetime, are analyzed. In two dimensions, general = (2, 2) nonlinear sigma models on S² are constructed, both for chiral multiplets and twisted chiral multiplets. The explicit curvature coupling terms and their effects are discussed. Finally, = (0, 2) gauged linear sigma models with nonabelian gauge groups are analyzed. In particular, various dualities between these nonabelian gauge theories are discussed in a geometric content, based on their Higgs branch structure.Ph. D
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
Gamma-ray emission from Galactic millisecond pulsars: Implications for dark matter indirect detection
No full textThe Fermi Large Area Telescope has observed a gamma-ray excess toward the center of the Galaxy at ~ GeV energies. The spectrum and intensity of the excess are consistent with the annihilation of dark matter with a mass of ~100 GeV and a velocity-averaged cross section of ~ 1e-26 cubic centimeter per second. In the meantime, a population of unresolved millisecond pulsars (MSPs) in the Galactic center remains a possible source of the excess. Furthermore, recent analyses have shown that the excess prefers the spatial morphology of the stellar bulge distribution in the Galactic center, supporting a MSP origin. The new discovery makes it imperative to further study the signals from MSPs.
This dissertation studies the gamma-ray emission from Galactic millisecond pulsars to provide new insights into the origin of the Galactic center excess. Using the GALPROP code, we simulate the propagation of e± injected by the putative MSPs in the Galactic bulge and calculate the inverse Compton (IC) emission caused by the e± losing energy in the interstellar radiation field. We find recognizable features in the spatial maps of the IC. Above TeV energies, the IC morphology tends to follow the distribution of the injected e±. Then, we study the Cherenkov Telescope Array (CTA) sensitivity to the IC signal from MSPs. We find that the CTA has the potential to robustly discover the IC signature when the MSP e± injection efficiencies are in the range ≈ 2.9-74.1%. The CTA can also discriminate between an MSP and a dark matter origin for the radiating e± based on their different spatial maps.
Next, we analyze the Fermi data from directions of Galactic globular clusters. The globular clusters are thought to be shining in gamma rays because of the MSP population they host. By analyzing their gamma-ray spectra, we reveal evidence for an IC component in the high-energy tail of Fermi data. Based on the IC component in the globular cluster spectra, the e± injection efficiency of millisecond pulsars is estimated to be slightly smaller than 10%.
Finally, we study the spatial morphology of the 511 keV signal toward the Galactic center using data from INTEGRAL/SPI. We confirm that the 511 keV signal also traces the old stellar population in the Galactic bulge, which is similar to the Fermi GeV excess. Using a 3D smoothing kernel, we find that the signal is smeared out over a characteristic length scale of 150 ± 50 pc. We show that positron propagation prior to annihilation can explain the overall phenomenology of the 511 keV signal.Doctor of PhilosophyDark matter means matter that does not interact with light; therefore, they are invisible to traditional observations. We know that dark matter exists based on plenty of gravitational evidence: the motions of stars in galaxies, the large-scale structure of the Universe, the temperature fluctuations in the cosmic microwave background. However, we still know very little about the particle nature of dark matter. Detecting dark matter is one of the most extensive missions of modern physics. In indirect detection, the dark matter particles are expected to annihilate or decay in the cosmos, producing messenger particles that include gamma rays, cosmic rays, and neutrinos. Astronomical observations could detect those signals and confirm the nature of dark matter. However, understanding the astrophysical sources is essential for indirect detection of dark matter as they may emit similar signals. For a recent example, the Fermi Large Area Telescope launched by NASA is the most sensitive gamma-ray telescope in the energy range of ~ 100 MeV to ~ 100 GeV. It has detected an excess of gamma-ray signals toward the Galactic center consistent with what we expect from dark matter annihilation. However, millisecond pulsars, a type of fast rotating neutron stars, may also generate similar gamma-ray signals. Therefore, the origin of the signal remains unsettled.
In this dissertation, we study different prospective of the gamma-ray emission from the millisecond pulsars in the Milky Way. We first study the inverse Compton signal from the millisecond pulsars in the Galactic bulge, caused by the relativistic e± injected by the millisecond pulsars. We find that the signal traces the original distribution of the e± above TeV energies. Next generation ground-based gamma-ray observatories like the Cherenkov Telescope Array (CTA) could be used to detect the signal. We study the CTA sensitivity to such an inverse Compton signal. We find that CTA can detect the inverse Compton signal from millisecond pulsars and discriminate it from a dark matter signal. We also study the gamma-ray emission from globular clusters in the Milky Way. They are dense collections of old stars orbiting our Galaxy, and they are known for hosting many millisecond pulsars. We reveal evidence for inverse Compton emission from the gamma-ray data of globular clusters. Our discovery helps us better understand the high-energy property of millisecond pulsars. Last, we study the morphology of the Galactic 511 keV signal caused by positron annihilation. Compact objects including millisecond pulsars are potential sources of the positrons. We find that the old stellar distribution with a smearing scale of ~ 150 pc best describes the 511 keV signal. Positron propagation from their sources prior to annihilation could explain the measured smearing scale
Novel Electromagnetic Properties of Elementary Particles
Full text linkQuantum electrodynamics is our most precisely and stringently tested theory. What happens when some non electrically charged elementary particles couple to the photon? We discuss neutrino electromagnetic properties, a dark photon portal to dark matter and magnetic monopoles produced by cosmic rays in the milky way. We don't just discuss these models, but show how to place(in some cases) leading constraints on these models using future particle physics experiments or astrophysics. The Deep Underground Neutrino Experiment will have the highest muon neutrino flux yet, and will be able to constrain neutrino electromagnetic properties better than current terrestrial experiments. Dark matter is known to be cold, but a subcomponent could be hot or boosted, if this is a dark photon which necessarily couples to the photon, we could see this in future gaseous detectors which are better suited because they have less in-medium effects than liquid Xenon for example. Monopoles of TeV scale masses can be produced by Cosmic Ray - Interstellar Medium collisions. These monopoles would impact the well measured 10−6 Gauss galactic magnetic field or it's production mechanism allowing us to place constraints on monopole cross section.Doctor of PhilosophyQuantum electrodynamics is the most stringently tested and precise theory. The photon is the force carrier particle of quantum electrodynamics. We explore the interaction of the photon with some other particles that are not charged(do not directly interact with the photon. The first particle we explore is the neutrino which is a neutral very weakly interacting particle that oscillates between different flavors it is produced and detected in. The Deep Underground Neutrino Experiment(DUNE) is a future experiment to measure these oscillations. We could also measure the interaction between the neutrino and the photon at DUNE. Dark matter is a placeholder for matter that only seems to interact gravitationally and seems to be cold. We still hope for some weak interactions to explain it's abundance in the universe. One way it could interact would be through the dark photon- a new force carrier which couples to the standard photon as well. These dark photons could be a fast moving subcomponent of dark matter. We could potentially detect these at future gaseous detectors where in medium effects are suppressed as compared to for example liquid xenon. Magnetic monopoles are a well motivated candidate which could explain the quantization of electric charge. Cosmic rays are charged particle moving through the galaxy carrying most of the radiation energy density in the galaxy. These fast moving particles could collide with particles at rest in the galaxy producing monopoles. These monopoles accelerate in the magnetic fields of the milky way. The fact that the magnetic field in the galacxy still exists allows us to place a bound on this monopole production cross section
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