1,912 research outputs found
Dynamical stabilization of matter-wave solitons revisited
We consider dynamical stabilization of Bose-Einstein condensates (BEC) by
time-dependent modulation of the scattering length. The problem has been
studied before by several methods: Gaussian variational approximation, the
method of moments, method of modulated Townes soliton, and the direct averaging
of the Gross-Pitaevskii (GP) equation. We summarize these methods and find that
the numerically obtained stabilized solution has different configuration than
that assumed by the theoretical methods (in particular a phase of the
wavefunction is not quadratic with ). We show that there is presently no
clear evidence for stabilization in a strict sense, because in the numerical
experiments only metastable (slowly decaying) solutions have been obtained. In
other words, neither numerical nor mathematical evidence for a new kind of
soliton solutions have been revealed so far. The existence of the metastable
solutions is nevertheless an interesting and complicated phenomenon on its own.
We try some non-Gaussian variational trial functions to obtain better
predictions for the critical nonlinearity for metastabilization but
other dynamical properties of the solutions remain difficult to predict
Superconductivity Under Pressure in FeSe1-xTex Studied by DC Magnetic Measurements
AbstractSuperconductivity under pressure in FeSe1−xTex with x=0.7 (TC∽14K) has been investigated by the measurements of DC magnetization using high quality single crystal specimens. It has been found that TC increases and makes a maximum of ∽15K at 1GPa but rapidly decreases above 1GPa under hydrostatic pressure using liquid Ar as pressure transmitting media (PTM). In contrast, TC is found to increase up to 18K at 2.5GPa then decrease gradually under nearly uniaxial pressure along c-axis using NaCl as PTM. It is also found that TC reaches a maximum of 16K at 1GPa but is nearly pressure independent above 1GPa under nearly uniaxial pressure along a-axis. These behaviors suggest that the superconductivity is suppressed by the isotropic compression but is enhanced (not changed) by the uniaxial compression along c-axis (a-axis)
Testing the Evolution of the Correlations between Supermassive Black Holes and their Host Galaxies using Eight Strongly Lensed Quasars
One of the main challenges in using high redshift active galactic nuclei to
study the correlations between the mass of the supermassive Black Hole (MBH)
and the properties of their active host galaxies is instrumental resolution.
Strong lensing magnification effectively increases instrumental resolution and
thus helps to address this challenge. In this work, we study eight strongly
lensed active galactic nuclei (AGN) with deep Hubble Space Telescope imaging,
using the lens modelling code Lenstronomy to reconstruct the image of the
source. Using the reconstructed brightness of the host galaxy, we infer the
host galaxy stellar mass based on stellar population models. MBH are estimated
from broad emission lines using standard methods. Our results are in good
agreement with recent work based on non-lensed AGN, demonstrating the potential
of using strongly lensed AGNs to extend the study of the correlations to higher
redshifts. At the moment, the sample size of lensed AGN is small and thus they
provide mostly a consistency check on systematic errors related to resolution
for the non-lensed AGN. However, the number of known lensed AGN is expected to
increase dramatically in the next few years, through dedicated searches in
ground and space based wide field surveys, and they may become a key diagnostic
of black hole and galaxy co-evolution.Comment: 12 pages, 4 figures, 3 tables. MNRAS in press. Comments welcom
The Grism Lens-Amplified Survey from Space (GLASS). IX. The dual origin of low-mass cluster galaxies as revealed by new structural analyses
Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the
Grism Lens-Amplified Survey from Space, we analyze 2200 cluster and 1748 field
galaxies at to determine the impact of environment on galaxy
size and structure at , an unprecedented limit at these
redshifts. Based on simple assumptions--we find no significant
differences in half-light radii () between equal-mass cluster or field
systems. More complex analyses-)-reveal local density
) to induce only a ( confidence) reduction in
beyond what can be accounted for by color, Sersic index (), and
redshift () effects.Almost any size difference between galaxies in high- and
low-density regions is thus attributable to their different distributions in
properties other than environment. Indeed, we find a clear color-
correlation in low-mass passive cluster galaxies () such
that bluer systems have larger radii, with the bluest having sizes consistent
with equal-mass star-forming galaxies. We take this as evidence that
large- low-mass passive cluster galaxies are recently acquired systems
that have been environmentally quenched without significant structural
transformation (e.g., by ram pressure stripping or starvation).Conversely,
of small- low-mass passive cluster galaxies appear to have been
in place since . Given the consistency of the small- galaxies'
stellar surface densities (and even colors) with those of systems more than ten
times as massive, our findings suggest that clusters mark places where galaxy
evolution is accelerated for an ancient base population spanning most masses,
with late-time additions quenched by environment-specific mechanisms are mainly
restricted to the lowest masses.Comment: The accepted version. The catalog is available through the GLASS web
page (http://glass.astro.ucla.edu), or
https://www.astr.tohoku.ac.jp/~mtakahiro/Publication/Morishita17
Suggestions for a way forward to further evaluate ageing error for Southern Hemisphere minke whales.
Paper SC/59/O8 provides a very helpful perspective and suggestions to help clarify the use of Antarctic minke whale age data in the commercial and research permit periods. On the basis of the paper, some areas for further work suggest themselves and these are outlined below. We recognise that these involve, in some cases, quite substantial additional work but believe that this will assist considerably in addressing the issues raised inter alia at the JARPA review meeting as well as during past IA sub-committee meetings and allow the valuable analyses involving both commercial and scientific permit data to be undertaken. The second experiment is designed to confirm the proposal in SC/59/O8 to limit analyses to using only data for animals aged six years and over
Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization
Within one billion years of the Big Bang, intergalactic hydrogen was ionized
by sources emitting ultraviolet and higher energy photons. This was the final
phenomenon to globally affect all the baryons (visible matter) in the Universe.
It is referred to as cosmic reionization and is an integral component of
cosmology. It is broadly expected that intrinsically faint galaxies were the
primary ionizing sources due to their abundance in this epoch. However, at the
highest redshifts (; lookback time 13.1 Gyr), all galaxies with
spectroscopic confirmations to date are intrinsically bright and, therefore,
not necessarily representative of the general population. Here, we report the
unequivocal spectroscopic detection of a low luminosity galaxy at . We
detected the Lyman- emission line at {\AA} in two separate
observations with MOSFIRE on the Keck I Telescope and independently with the
Hubble Space Telescope's slit-less grism spectrograph, implying a source
redshift of . The galaxy is gravitationally magnified by
the massive galaxy cluster MACS J1423.8+2404 (), with an estimated
intrinsic luminosity of mag and a stellar mass of
solar masses. Both are an order of
magnitude lower than the four other Lyman- emitters currently known at
, making it probably the most distant representative source of
reionization found to date
The Grism Lens-Amplified Survey from Space (GLASS). XII. Spatially Resolved Galaxy Star Formation Histories and True Evolutionary Paths at z > 1
Modern data empower observers to describe galaxies as the spatially and
biographically complex objects they are. We illustrate this through case
studies of four, systems based on deep, spatially resolved, 17-band
+ G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full
spectrum rest-UV/-optical continuum fitting, we characterize these galaxies'
observed kpc-scale structures and star formation rates (SFRs) and
reconstruct their history over the age of the universe. The sample's
diversity---passive to vigorously starforming; stellar masses to ---enables us to draw spatio-temporal inferences
relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass
progenitors). Specifically, we find signs that bulge mass-fractions () and
SF history shapes/spatial uniformity are linked, such that higher s
correlate with "inside-out growth" and central specific SFRs that peaked above
the global average for all starforming galaxies at that epoch. Conversely, the
system with the lowest had a flat, spatially uniform SFH with normal peak
activity. Both findings are consistent with models positing a feedback-driven
connection between bulge formation and the switch from rising to falling SFRs
("quenching"). While sample size forces this conclusion to remain tentative,
this work provides a proof-of-concept for future efforts to refine or refute
it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data
amenable to this and more sophisticated analyses. These samples---spanning
representative mass, redshift, SFR, and environmental regimes---will be ripe
for converting into thousands of sub-galactic-scale empirical windows on what
individual systems actually looked like in the past, ushering in a new dialog
between observation and theory.Comment: 18 pp, 15 figs, 3 tables (main text); 5 pp, 5 figs, 1 table
(appendix); Submitted to AAS Journals 1 October 201
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