5,924 research outputs found
A Review of the Role of Melatonin in Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is a troubling disease experienced worldwide. The presentation of symptoms varies from patient to patient, and current prescription treatments can be inadequate in resolving symptoms. This article explores the available scientific literature supporting the use of melatonin in alleviating IBS symptoms
Accretion disc-corona and jet emission from the radio-loud narrow-line Seyfert 1 galaxy RX J1633.3+4719
We perform X-ray/ultraviolet (UV) spectral and X-ray variability studies of
the radio-loud narrow-line Seyfert 1 (NLS1) galaxy RX J1633.3+4719 using
XMM-Newton and Suzaku observations from 2011 and 2012. The 0.3-10 keV spectra
consist of an ultrasoft component described by an accretion disc blackbody
(kT_in = 39.6^{+11.2}_{-5.5} eV) and a power law due to the thermal
Comptonization ({\Gamma} = 1.96^{+0.24}_{-0.31}) of the disc emission. The disc
temperature inferred from the soft excess is at least a factor of 2 lower than
that found for the canonical soft excess emission from radio-quiet NLS1s. The
UV spectrum is described by a power law with photon index 3.05^{+0.56}_{-0.33}.
The observed UV emission is too strong to arise from the accretion disc or the
host galaxy, but can be attributed to a jet. The X-ray emission from RX
J1633.3+4719 is variable with fractional variability amplitude =13.5 per cent. In contrast to radio-quiet active galactic nuclei
(AGN), X-ray emission from the source becomes harder with increasing flux. The
fractional rms variability increases with energy and the rms spectrum is well
described by a constant disc component and a variable power-law continuum with
the normalization and photon index being anticorrelated. Such spectral
variability cannot be caused by variations in the absorption and must be
intrinsic to the hot corona. Our finding of possible evidence for emission from
the inner accretion disc, jet and hot corona from RX J1633.3+4719 in the
optical to X-ray bands makes this object an ideal target to probe the disc-jet
connection in AGN.Comment: 12 pages, 11 figures, 3 tables, Published in MNRA
Embedded AGN and star formation in the central 80 pc of IC 3639
[Abridged] Methods: We use interferometric observations in the -band with
VLTI/MIDI to resolve the mid-IR nucleus of IC 3639. The origin of the nuclear
infrared emission is determined from: 1) the comparison of the correlated
fluxes from VLTI/MIDI with the fluxes measured at subarcsec resolution
(VLT/VISIR, VLT/ISAAC); 2) diagnostics based on IR fine-structure line ratios,
the IR continuum emission, IR bands produced by polycyclic aromatic
hydrocarbons (PAH) and silicates; and 3) the high-angular resolution spectral
energy distribution. Results: The unresolved flux of IC 3639 is at , measured with three different baselines in
VLTI (UT1-UT2, UT3-UT4, and UT2-UT3; -), making this the
faintest measurement so far achieved with mid-IR interferometry. The correlated
flux is a factor of - times fainter than the VLT/VISIR total flux
measurement. The observations suggest that most of the mid-IR emission has its
origin on spatial scales between and (-). A composite scenario where the star formation component dominates
over the AGN is favoured by the diagnostics based on ratios of IR
fine-structure emission lines, the shape of the IR continuum, and the PAH and
silicate bands. Conclusions: A composite AGN-starburst scenario is able to
explain both the mid-IR brightness distribution and the IR spectral properties
observed in the nucleus of IC 3639. The nuclear starburst would dominate the
mid-IR emission and the ionisation of low-excitation lines (e.g. [NeII]) with a net contribution of . The AGN accounts for the
remaining of the mid-IR flux, ascribed to the unresolved component
in the MIDI observations, and the ionisation of high-excitation lines (e.g.
[NeV] and [OIV]).Comment: Accepted for publication in A&
Heavy boson production through the collision of an ultrahigh-energy neutrino on a target nucleon
We discuss W and Z production through the deep inelastic neutrino-nucleon
scattering in the context of the standard model SU(3)x SU(2)x U(1) of the
strong and electroweak interactions. We find the cross section rates for the
process neutrino + nucleon --> lepton(-) + W(+) + X for the case of
ultrahigh-energy neutrinos colliding on a target nucleon.Comment: 20 pages, 6 figure
Experiments on the culture of Penaeus monodon in the salt pan area at Tuticorin
The paper embodies the results of growth and production of Penaeus monodon cultured during 1988-89 in the salt pan
area at Tuticorin. The overall growth rate of the hatchery produced seeds stocked in ponds varied from 25.1 mm/5.85
g to 35.2 mm/9.8g per month and the best growth was associated with low stocking density. The post-larvae attained
marketable size of 32 g in about 140 days. Supplementary feed consisted of 7-9 ingredients with protein value of 38%.
The conversion ratio varied from 1:1:5 to 1:1.91
Muon Pair Production by Electron-Photon Scatterings
The cross section for muon pair productions by electrons scattering over
photons, , is calculated analytically in the leading order. It is
pointed out that for the center-of-mass energy range, ,
the cross section for is less than b. The differential
energy spectrum for either of the resulting muons is given for the purpose of
high-energy neutrino astronomy. An implication of our result for a recent
suggestion concerning the high-energy cosmic neutrino generation through this
muon pair is discussed.Comment: a comment added, to appear in Phys. Rev. D, Rapid Communicatio
Thresholded Covering Algorithms for Robust and Max-Min Optimization
The general problem of robust optimization is this: one of several possible
scenarios will appear tomorrow, but things are more expensive tomorrow than
they are today. What should you anticipatorily buy today, so that the
worst-case cost (summed over both days) is minimized? Feige et al. and
Khandekar et al. considered the k-robust model where the possible outcomes
tomorrow are given by all demand-subsets of size k, and gave algorithms for the
set cover problem, and the Steiner tree and facility location problems in this
model, respectively.
In this paper, we give the following simple and intuitive template for
k-robust problems: "having built some anticipatory solution, if there exists a
single demand whose augmentation cost is larger than some threshold, augment
the anticipatory solution to cover this demand as well, and repeat". In this
paper we show that this template gives us improved approximation algorithms for
k-robust Steiner tree and set cover, and the first approximation algorithms for
k-robust Steiner forest, minimum-cut and multicut. All our approximation ratios
(except for multicut) are almost best possible.
As a by-product of our techniques, we also get algorithms for max-min
problems of the form: "given a covering problem instance, which k of the
elements are costliest to cover?".Comment: 24 page
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