74 research outputs found
Kaon Condensation in Neutron Star Matter with Hyperons
Based on the Kaplan-Nelson Lagrangian, we investigate kaon condensation in
dense neutron star matter allowing for the explicit presence of hyperons. Using
various models we find that the condensate threshold is sensitive to the
behavior of the scalar density; the more rapidly it increases with baryon
density, the lower is the threshold for condensation. The presence of hyperons,
particularly the , shifts the threshold for condensation to a
higher density. In the mean field approach, with hyperons, the condensate
amplitude grows sufficiently rapidly that the nucleon effective mass vanishes
at a finite density and a satisfactory treatment of the thermodynamics cannot
be achieved. Thus, calculations of kaon-baryon interactions beyond the mean
field level appear to be necessary.Comment: 13 pages, latex, 3 figures by fax/mail from [email protected]
Cold Quark Matter
We perform an O(alpha_s^2) perturbative calculation of the equation of state
of cold but dense QCD matter with two massless and one massive quark flavor,
finding that perturbation theory converges reasonably well for quark chemical
potentials above 1 GeV. Using a running coupling constant and strange quark
mass, and allowing for further non-perturbative effects, our results point to a
narrow range where absolutely stable strange quark matter may exist. Absent
stable strange quark matter, our findings suggest that quark matter in compact
star cores becomes confined to hadrons only slightly above the density of
atomic nuclei. Finally, we show that equations of state including quark matter
lead to hybrid star masses up to M~2M_solar, in agreement with current
observations. For strange stars, we find maximal masses of M~2.75M_solar and
conclude that confirmed observations of compact stars with M>2M_solar would
strongly favor the existence of stable strange quark matter.Comment: 51 pages, 11 figures, v2: minor modifications and additional
reference
The challenge of improving the diagnostic yield from metanephrine testing in suspected phaeochromocytoma and paraganglioma
Background Plasma-free metanephrines (PFM) or urinary fractionated metanephrines (UFM) are the preferred biochemical tests for the diagnosis of phaeochromocytoma and paraganglioma (PPGL). Borderline increased results should be followed up to either exclude or confirm diagnosis. Methods We extracted all PFM and UFM results reported by our laboratory over a six-month period from the laboratory information system. We categorized patients with borderline increased results according to whether follow-up testing had been performed as suggested in the initial laboratory report. Questionnaires were then sent to all requesting doctors and medical notes reviewed where available. Results Two hundred and four patients with borderline increased PFM or UFM were identified. Sixty-five (38.5%) of 169 patients with borderline increased PFM had a repeat test out of which 36 were normal and 29 did not normalize. Of 35 patients with borderline increased UFM, 17 (48.6%) had subsequent PFM measurement, out of which 15 were normal. Questionnaires were returned to 106 (52%) patients. Of these, the most frequent indication for testing was hypertension ( n = 50); 15 patients had an incidental adrenal mass and two of these patients were diagnosed with a phaeochromocytoma. Conclusion Only 38% of patients with borderline increased PFM had a repeat PFM measurement. This was not significantly higher when compared with the 28% in a previous audit that we reported in 2010 ( P = 0.10). Forty-nine per cent of patients with a borderline increased UFM had a repeat UFM or PFM measurement. There remains a substantial possibility of missed detection of PPGL
Electro-kinetic technology as a low-cost method for dewatering food by-product
Increasing volumes of food waste, intense environmental awareness, and stringent legislation have imposed increased demands upon conventional food waste management. Food byproducts that were once considered to be without value are now being utilized as reusable materials, fuels, and energy in order to reduce waste. One major barrier to the valorization of food by-products is their high moisture content. This has brought about the necessity of dewatering food waste for any potential re-use for certain disposal options. A laboratory system for experimentally characterizing electro-kinetic dewatering of food by-products was evaluated. The bench scale system, which is an augmented filter press, was used to investigate the dewatering at constant voltage. Five food by-products (brewer’s spent grain, cauliflower trimmings, mango peel, orange peel, and melon peel) were studied. The results indicated that electro-kinetic dewatering combined with mechanical dewatering can reduce the percentage of moisture from 78% to 71% for brewer’s spent grain, from 77% to 68% for orange peel, from 80% to 73% for mango peel, from 91% to 74% for melon peel, and from 92% to 80% for cauliflower trimmings. The total moisture reduction showed a correlation with electrical conductivity (R2¼0.89). The energy consumption of every sample was evaluated and was found to be up to 60 times more economical compared to thermal processing
Cooling of Dark-Matter Admixed Neutron Stars with density-dependent Equation of State
We propose a dark-matter (DM) admixed density-dependent equation of state
where the fermionic DM interacts with the nucleons via Higgs portal. Presence
of DM can hardly influence the particle distribution inside neutron star (NS)
but can significantly affect the structure as well as equation of state (EOS)
of NS. Introduction of DM inside NS softens the equation of state. We explored
the effect of variation of DM mass and DM Fermi momentum on the NS EOS.
Moreover, DM-Higgs coupling is constrained using dark matter direct detection
experiments. Then, we studied cooling of normal NSs using APR and DD2 EOSs and
DM admixed NSs using dark-matter modified DD2 with varying DM mass and Fermi
momentum. We have done our analysis by considering different NS masses. Also DM
mass and DM Fermi momentum are varied for fixed NS mass and DM-Higgs coupling.
We calculated the variations of luminosity and temperature of NS with time for
all EOSs considered in our work and then compared our calculations with the
observed astronomical cooling data of pulsars namely Cas A, RX J0822-43, 1E
1207-52, RX J0002+62, XMMU J17328, PSR B1706-44, Vela, PSR B2334+61, PSR
B0656+14, Geminga, PSR B1055-52 and RX J0720.4-3125. It is found that APR EOS
agrees well with the pulsar data for lighter and medium mass NSs but cooling is
very fast for heavier NS. For DM admixed DD2 EOS, it is found that for all
considered NS masses, all chosen DM masses and Fermi momenta agree well with
the observational data of PSR B0656+14, Geminga, Vela, PSR B1706-44 and PSR
B2334+61. Cooling becomes faster as compared to normal NSs in case of
increasing DM mass and Fermi momenta. It is infered from the calculations that
if low mass super cold NSs are observed in future that may support the fact
that heavier WIMP can be present inside neutron stars.Comment: 24 Pages, 15 Figures and 2 Tables. Version accepted in The European
Physical Journal
Kaon Zero-Point Fluctuations in Neutron Star Matter
We investigate the contribution of zero-point motion, arising from
fluctuations in kaon modes, to the ground state properties of neutron star
matter containing a Bose condensate of kaons. The zero-point energy is derived
via the thermodynamic partition function, by integrating out fluctuations for
an arbitrary value of the condensate field. It is shown that the vacuum
counterterms of the chiral Lagrangian ensure the cancellation of divergences
dependent on , the charge chemical potential, which may be regarded as an
external vector potential. The total grand potential, consisting of the
tree-level potential, the zero-point contribution, and the counterterm
potential, is extremized to yield a locally charge neutral, beta-equilibrated
and minimum energy ground state. In some regions of parameter space we
encounter the well-known problem of a complex effective potential. Where the
potential is real and solutions can be obtained, the contributions from
fluctuations are found to be small in comparison with tree-level contributions.Comment: 40 pages RevTeX, 3 epsf figure
Hydrogen Epoch of Reionization Array (HERA)
The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to
measure 21 cm emission from the primordial intergalactic medium (IGM)
throughout cosmic reionization (), and to explore earlier epochs of our
Cosmic Dawn (). During these epochs, early stars and black holes
heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is
designed to characterize the evolution of the 21 cm power spectrum to constrain
the timing and morphology of reionization, the properties of the first
galaxies, the evolution of large-scale structure, and the early sources of
heating. The full HERA instrument will be a 350-element interferometer in South
Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz.
Currently, 19 dishes have been deployed on site and the next 18 are under
construction. HERA has been designated as an SKA Precursor instrument.
In this paper, we summarize HERA's scientific context and provide forecasts
for its key science results. After reviewing the current state of the art in
foreground mitigation, we use the delay-spectrum technique to motivate
high-level performance requirements for the HERA instrument. Next, we present
the HERA instrument design, along with the subsystem specifications that ensure
that HERA meets its performance requirements. Finally, we summarize the
schedule and status of the project. We conclude by suggesting that, given the
realities of foreground contamination, current-generation 21 cm instruments are
approaching their sensitivity limits. HERA is designed to bring both the
sensitivity and the precision to deliver its primary science on the basis of
proven foreground filtering techniques, while developing new subtraction
techniques to unlock new capabilities. The result will be a major step toward
realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table
Optimizing Sparse RFI Prediction using Deep Learning
Radio Frequency Interference (RFI) is an ever-present limiting factor among
radio telescopes even in the most remote observing locations. When looking to
retain the maximum amount of sensitivity and reduce contamination for Epoch of
Reionization studies, the identification and removal of RFI is especially
important. In addition to improved RFI identification, we must also take into
account computational efficiency of the RFI-Identification algorithm as radio
interferometer arrays such as the Hydrogen Epoch of Reionization Array grow
larger in number of receivers. To address this, we present a Deep Fully
Convolutional Neural Network (DFCN) that is comprehensive in its use of
interferometric data, where both amplitude and phase information are used
jointly for identifying RFI. We train the network using simulated HERA
visibilities containing mock RFI, yielding a known "ground truth" dataset for
evaluating the accuracy of various RFI algorithms. Evaluation of the DFCN model
is performed on observations from the 67 dish build-out, HERA-67, and achieves
a data throughput of 1.6 HERA time-ordered 1024 channeled
visibilities per hour per GPU. We determine that relative to an amplitude only
network including visibility phase adds important adjacent time-frequency
context which increases discrimination between RFI and Non-RFI. The inclusion
of phase when predicting achieves a Recall of 0.81, Precision of 0.58, and
score of 0.75 as applied to our HERA-67 observations.Comment: 11 pages, 7 figure
HI 21cm Cosmology and the Bi-spectrum: Closure Diagnostics in Massively Redundant Interferometric Arrays
New massively redundant low frequency arrays allow for a novel investigation
of closure relations in interferometry. We employ commissioning data from the
Hydrogen Epoch of Reionization Array to investigate closure quantities in this
densely packed grid array of 14m antennas operating at 100 MHz to 200 MHz. We
investigate techniques that utilize closure phase spectra for redundant triads
to estimate departures from redundancy for redundant baseline visibilities. We
find a median absolute deviation from redundancy in closure phase across the
observed frequency range of about 4.5deg. This value translates into a
non-redundancy per visibility phase of about 2.6deg, using prototype
electronics. The median absolute deviations from redundancy decrease with
longer baselines. We show that closure phase spectra can be used to identify
ill-behaved antennas in the array, independent of calibration. We investigate
the temporal behavior of closure spectra. The Allan variance increases after a
one minute stride time, due to passage of the sky through the primary beam of
the transit telescope. However, the closure spectra repeat to well within the
noise per measurement at corresponding local sidereal times (LST) from day to
day. In future papers in this series we will develop the technique of using
closure phase spectra in the search for the HI 21cm signal from cosmic
reionization.Comment: 32 pages. 11 figures. Accepted to Radio Scienc
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