1,654 research outputs found
Photon Bunching at TeV Energies
Harwit, Protheroe, and Biermann (1999) recently proposed that Bose-Einstein
photon bunching might significantly affect the interpretation of Cerenkov
counts of TeV gamma photons. Here, we show that a combination of two recent
results of Aharonian et al. (2000) and Aharonian et al. (2001) permits us to
set new, more stringent upper limits of on the fractional amount
of photon bunching in the 7-10 TeV radiation from Markarian 501. Potential
bunching at even higher energies should nevertheless continue to be
investigated for this and other TeV sources, since a clear understanding of TeV
energy spectra is required to unambiguously determine the spectral energy
density of the mid-infrared extragalactic background
Defining Museum Intervention: An Analysis of James Putnam\u27s Time Machine
In his 2001 publication Art and Artifact: The Museum as Medium, independent curator James Putnam coins the term ‘museum intervention’ to describe a type of artwork created by some artists as a means to critique organizing principles of the museum. Putnam’s book analyzes examples of museum interventions, including his own 1994 exhibition, Time Machine: Ancient Egypt and Contemporary Art, but fails to offer a definition for the term. This thesis analyzes the trajectory of exhibition practices leading to the publication of the new term through an examination of historical changes in museum display. The paper then analyzes examples of museum intervention included in Putnam’s book in order to develop a definition for the term. The paper examines Time Machine in relation to the new definition and, contrary to Putnam’s assertions, concludes that the exhibition is not a museum intervention
Revisiting the Hanbury Brown-Twiss set-up for fractional statistics
The Hanbury Brown-Twiss experiment has proved to be an effective means of
probing statistics of particles. Here, in a set-up involving edge-state
quasiparticles in a fractional quantum Hall system, we show that a variant of
the experiment composed of two sources and two sinks can be used to unearth
fractional statistics. We find a clear cut signature of the statistics in the
equal-time current-current correlation function for quasiparticle currents
emerging from the two sources and collected at the sinks.Comment: 4 pages, 3 figure
Measuring Societal Biases in Text Corpora via First-Order Co-occurrence
Text corpora are used to study societal biases, typically through statistical
models such as word embeddings. The bias of a word towards a concept is
typically estimated using vectors similarity, measuring whether the word and
concept words share other words in their contexts. We argue that this
second-order relationship introduces unrelated concepts into the measure, which
causes an imprecise measurement of the bias. We propose instead to measure bias
using the direct normalized co-occurrence associations between the word and the
representative concept words, a first-order measure, by reconstructing the
co-occurrence estimates inherent in the word embedding models. To study our
novel corpus bias measurement method, we calculate the correlation of the
gender bias values estimated from the text to the actual gender bias statistics
of the U.S. job market, provided by two recent collections. The results show a
consistently higher correlation when using the proposed first-order measure
with a variety of word embedding models, as well as a more severe degree of
bias, especially to female in a few specific occupations
A Monte-Carlo Assessment Of The Life Cycle Impacts of Geothermal Energy For Power And Transportation
Increasing awareness of environmental issues surrounding power generationand transportation has increased interest in renewable energy sources such as geothermal.Renewable energy extraction is not without environmental cost, however; drillingoperations and construction of the facilities required for utilization can be resource intensive. Complete life cycle analysis (LCA) allows for impactcomparison between competing methods of power generation. The results are modular, allowingfor use in other product life cycles. One such life cycle is that of the transportation vehicle. An analysis of vehicle life cycles involving geothermal energy is performed employingthe The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model. Geothermal power haslarge variations between plants owing to differences in the hydrothermalreservoir chemistry and thermodynamic conditions. Due to these variations, a stochastic approachwas used to determine the amount of variation that is likely to be seen using this energy source.The results show geothermal power to have low environmental impact relative to othermethods of energy production for use in transportation
Quantum atom optics with fermions from molecular dissociation
We study a fermionic atom optics counterpart of parametric down-conversion
with photons. This can be realized through dissociation of a Bose-Einstein
condensate of molecular dimers consisting of fermionic atoms. We present a
theoretical model describing the quantum dynamics of dissociation and find
analytic solutions for mode occupancies and atomic pair correlations, valid in
the short time limit. The solutions are used to identify upper bounds for the
correlation functions, which are applicable to any fermionic system and
correspond to ideal particle number-difference squeezingComment: Changes in response to referees' comments, updated reference
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