17,484 research outputs found
Creation of Dirac Particles in the Presence of a Constant Electric Field in an Anisotropic Bianchi I Universe
In this article we compute the density of Dirac particles created by a
cosmological anisotropic Bianchi I universe in the presence of a constant
electric field. We show that the particle distribution becomes thermal when one
neglects the electric interaction.Comment: 9 page
Reflectance of Polytetrafluoroethylene (PTFE) for Xenon Scintillation Light
Gaseous and liquid xenon particle detectors are being used in a number of
applications including dark matter search and neutrino-less double beta decay
experiments. Polytetrafluoroethylene (PTFE) is often used in these detectors
both as electrical insulator and as a light reflector to improve the efficiency
of detection of scintillation photons. However, xenon emits in the vacuum
ultraviolet wavelength region (175 nm) where the reflecting properties of PTFE
are not sufficiently known.
In this work we report on measurements of PTFE reflectance, including its
angular distribution, for the xenon scintillation light. Various samples of
PTFE, manufactured by different processes (extruded, expanded, skived and
pressed) have been studied. The data were interpreted with a physical model
comprising both specular and diffuse reflections. The reflectance obtained for
these samples ranges from about 47% to 66% for VUV light. Fluoropolymers,
namely ETFE, FEP and PFA were also measured
Decoherence and Entanglement Dynamics in Fluctuating Fields
We study pure phase damping of two qubits due to fluctuating fields. As
frequently employed, decoherence is thus described in terms of random unitary
(RU) dynamics, i.e., a convex mixture of unitary transformations. Based on a
separation of the dynamics into an average Hamiltonian and a noise channel, we
are able to analytically determine the evolution of both entanglement and
purity. This enables us to characterize the dynamics in a concurrence-purity
(CP) diagram: we find that RU phase damping dynamics sets constraints on
accessible regions in the CP plane. We show that initial state and dynamics
contribute to final entanglement independently.Comment: 10 pages, 5 figures, added minor changes in order to match published
versio
Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System
©2019. American Geophysical Union. All Rights Reserved.Subglacial water ïŹow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5â to 10âHz seismic tremor that we associate with subglacial water ïŹow,
that is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequencyâdependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in meltâwater
input. We suggest that conduit formation requires sustained water input and that multiconduit ïŹow paths can be distinguished from singleâconduit ïŹow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely ïŹows through a singleâconduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable conïŹgurations that last 3â7 days, while tremor produced by singleâconduit ïŹow remains more stationary.
We also ïŹnd that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2â6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.Raw seismic data described in this paper are available through the Incorporated Research Institutions for Seismology Data Management Center (http://ds.iris.edu/mda/ZQ? timewindow=2015â2016; Amundson et al., 2015). The raw weather data used in this paper can be found through the Arctic Data Center (https://doi.org/ 10.18739/A2H98ZC7V; Bartholomaus & Walter, 2018). Python code developed to carry out the analyses presented here is available at https://github.com/ voremargot/SeismicâTremorâRevealsâ SpatialâOrganizationâandâTemporalâ Changesâof SubglacialâWaterâSystem and https://github.com/ tbartholomaus/med_spec. This study was made possible with support from the University of Texas Institute for Geophysics and the University of Idaho. We thank Ginny Catania for the loan of weather stations. J. P. W.'s and J. M. A.'s contributions to this work were supported by the U.S. National Science Foundation (OPPâ1337548 and OPPâ 1303895). T. C. B. thanks Dylan Mikesell for an early conversation, which inspired the analysis presented here.Ye
Stability and effects of organic solvents on endopeptidases from the gastric fluid of the marine crab Cancer pagurus
The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst. II.The optically thin phase and the structure of the ejecta in recurrent novae
We continue our study of the physical properties of the recurrent nova T Pyx,
focussing on the structure of the ejecta in the nebular stage of expansion
during the 2011 outburst. The nova was observed contemporaneously with the
Nordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R
~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration),
and with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble
Space Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar.
28 (absolute fluxes). We use standard plasma diagnostics (e.g. [O III] and [N
II] line ratios and the H line fluxes) to constrain electron densities
and temperatures. Using Monte Carlo modeling of the ejecta, we derive the
structure and filling factor from comparisons to the optical and ultraviolet
line profiles. The ejecta can be modeled using an axisymmetric conical --
bipolar -- geometry with a low inclination of the axis to the line of sight,
i=15+/-5 degrees, compatible with published results from high angular
resolution optical spectro-interferometry. The structure is similar to that
observed in the other short orbital period recurrent novae during their nebular
stages. We show that the electron density scales as as expected from a
ballistically ejected constant mass shell; there is no need to invoke a
continuing mass outflow following the eruption. The derived mass for the ejecta
with filling factor f ~ 3%, M_ej ~ 2E-6$M_sun is similar to that obtained for
other recurrent nova ejecta but inconsistent with the previously reported
extended optically thick epoch of the explosion. We suggest that the system
underwent a common envelope phase following the explosion that produced the
recombination event. Implications for the dynamics of the recurrent novae are
discussed. (truncated)Comment: accepted for publication in A&A (10 Nov. 2012), 10 pgs, 16 fig
Subchondral bone density distribution of the talus in clinically normal Labrador Retrievers
Background: Bones continually adapt their morphology to their load bearing function. At the level of the subchondral bone, the density distribution is highly correlated with the loading distribution of the joint. Therefore, subchondral bone density distribution can be used to study joint biomechanics non-invasively. In addition physiological and pathological joint loading is an important aspect of orthopaedic disease, and research focusing on joint biomechanics will benefit veterinary orthopaedics. This study was conducted to evaluate density distribution in the subchondral bone of the canine talus, as a parameter reflecting the long-term joint loading in the tarsocrural joint.
Results: Two main density maxima were found, one proximally on the medial trochlear ridge and one distally on the lateral trochlear ridge. All joints showed very similar density distribution patterns and no significant differences were found in the localisation of the density maxima between left and right limbs and between dogs.
Conclusions: Based on the density distribution the lateral trochlear ridge is most likely subjected to highest loads within the tarsocrural joint. The joint loading distribution is very similar between dogs of the same breed. In addition, the joint loading distribution supports previous suggestions of the important role of biomechanics in the development of OC lesions in the tarsus. Important benefits of computed tomographic osteoabsorptiometry (CTOAM), i.e. the possibility of in vivo imaging and temporal evaluation, make this technique a valuable addition to the field of veterinary orthopaedic research
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