516 research outputs found
Self-trapping of a binary Bose-Einstein condensate induced by interspecies interaction
The problem of self-trapping of a Bose-Einstein condensate (BEC) and a binary
BEC in an optical lattice (OL) and double well (DW) is studied using the
mean-field Gross-Pitaevskii equation. For both DW and OL, permanent
self-trapping occurs in a window of the repulsive nonlinearity of the GP
equation: . In case of OL, the critical nonlinearities
and correspond to a window of chemical potentials
defining the band gap(s) of the periodic OL. The
permanent self-trapped BEC in an OL usually represents a breathing oscillation
of a stable stationary gap soliton. The permanent self-trapped BEC in a DW, on
the other hand, is a dynamically stabilized state without any stationary
counterpart. For a binary BEC with intraspecies nonlinearities outside this
window of nonlinearity, a permanent self trapping can be induced by tuning the
interspecies interaction such that the effective nonlinearities of the
components fall in the above window
IRS Spectra of Solar-Type Stars: \break A Search for Asteroid Belt Analogs
We report the results of a spectroscopic search for debris disks surrounding
41 nearby solar type stars, including 8 planet-bearing stars, using the {\it
Spitzer Space Telescope}. With accurate relative photometry using the Infrared
Spectrometer (IRS) between 7-34 \micron we are able to look for excesses as
small as 2% of photospheric levels with particular sensitivity to weak
spectral features. For stars with no excess, the upper limit in a
band at 30-34 m corresponds to 75 times the brightness of our
zodiacal dust cloud. Comparable limits at 8.5-13 m correspond to
1,400 times the brightness of our zodiacal dust cloud. These limits correspond
to material located within the 1 to 5 AU region that, in our solar
system, originates from debris associated with the asteroid belt. We find
excess emission longward of 25 m from five stars of which four also
show excess emission at 70 m. This emitting dust must be located around
5-10 AU. One star has 70 micron emission but no IRS excess. In this case, the
emitting region must begin outside 10 AU; this star has a known radial velocity
planet. Only two stars of the five show emission shortward of 25 \micron
where spectral features reveal the presence of a population of small, hot dust
grains emitting in the 7-20 m band. The data presented here strengthen the
results of previous studies to show that excesses at 25 \micron and shorter
are rare: only 1 star out of 40 stars older than 1 Gyr or % shows an
excess. Asteroid belts 10-30 times more massive than our own appear are rare
among mature, solar-type stars
Unenhanced helical computed tomography vs intravenous urography in patients with acute flank pain: accuracy and economic impact in a randomized prospective trial
Abstract.: Unenhanced helical computed tomography (UHCT) has evolved into a well-accepted alternative to intravenous urography (IVU) in patients with acute flank pain and suspected ureterolithiasis. The purpose of our randomized prospective study was to analyse the diagnostic accuracy of UHCT vs IVU in the normal clinical setting with special interest on economic impact, applied radiation dose and time savings in patient management. A total of 122 consecutive patients with acute flank pain suggestive of urolithiasis were randomized for UHCT (n=59) or IVU (n=63). Patient management (time, contrast media), costs and radiation dose were analysed. The films were independently interpreted by four radiologists, unaware of previous findings, clinical history and clinical outcome. Alternative diagnoses if present were assessed. Direct costs of UHCT and IVU are nearly identical (310/309 Euro). Indirect costs are much lower for UHCT because it saves examination time and when performed immediately initial abdominal plain film (KUB) and sonography are not necessary. Time delay between access to the emergency room and start of the imaging procedure was 32h 7min for UHCT and 36h 55min for IVU. The UHCT took an average in-room time of 23min vs 1h 21min for IVU. Mild to moderate adverse reactions for contrast material were seen in 3 (5%) patients. The UHCT was safe, as no contrast material was needed. The mean applied radiation dose was 3.3mSv for IVU and 6.5mSv for UHCT. Alternative diagnoses were identified in 4 (7%) UHCT patients and 3 (5%) IVU patients. Sensitivity and specificity of UHCT and IVU was 94.1 and 94.2%, and 85.2 and 90.4%, respectively. In patients with suspected renal colic KUB and US may be the least expensive and most easily accessable modalities; however, if needed and available, UHCT can be considered a better alternative than IVU because it has a higher diagnostic accuracy and a better economic impact since it is more effective, faster, less expensive and less risky than IVU. In addition, it also has the capability of detecting various additional renal and extrarenal pathologie
Discovery of an 86 AU Radius Debris Ring Around HD 181327
HST/NICMOS PSF-subtracted coronagraphic observations of HD 181327 have
revealed the presence of a ring-like disk of circumstellar debris seen in 1.1
micron light scattered by the disk grains, surrounded by a di use outer region
of lower surface brightness. The annular disk appears to be inclined by 31.7
+/- 1.6 deg from face on with the disk major axis PA at 107 +/-2 deg . The
total 1.1 micron flux density of the light scattered by the disk (at 1.2" < r <
5.0") of 9.6 mJy +/- 0.8 mJy is 0.17% +/- 0.015% of the starlight. Seventy
percent of the light from the scattering grains appears to be confined in a 36
AU wide annulus centered on the peak of the radial surface brightness (SB)
profile 86.3 +/- 3.9 AU from the star, well beyond the characteristic radius of
thermal emission estimated from IRAS and Spitzer flux densities assuming
blackbody grains (~ 22 AU). The light scattered by the ring appears bilaterally
symmetric, exhibits directionally preferential scattering well represented by a
Henyey-Greenstein scattering phase function with g = 0.30 +/- 0.03, and has an
azimuthally medianed SB at the 86.3 AU radius of peak SB of 1.00 +/- 0.07 mJy
arcsec^-2. No photocentric offset is seen in the ring relative to the position
of the central star. A low surface brightness diffuse halo is seen in the
NICMOS image to a distance of ~ 4" Deeper 0.6 micron HST/ACS PSF-subtracted
coronagraphic observations reveal a faint outer nebulosity, asymmetrically
brighter to the North of the star. We discuss models of the disk and properties
of its grains, from which we infer a maximum vertical scale height of 4 - 8 AU
at the 87.6 AU radius of maximum surface density, and a total maximum dust mass
of collisionally replenished grains with minimum grain sizes of ~ 1 micron of ~
4 M(moon).Comment: 45 pages, 15 figures, accepted for publication in Ap
Infrared color selection of massive galaxies at z > 3
We introduce a new color-selection technique to identify high-redshift,
massive galaxies that are systematically missed by Lyman-break selection. The
new selection is based on the H_{160} and IRAC 4.5um bands, specifically H -
[4.5] > 2.25 mag. These galaxies, dubbed "HIEROs", include two major
populations that can be separated with an additional J - H color. The
populations are massive and dusty star-forming galaxies at z > 3 (JH-blue) and
extremely dusty galaxies at z < 3 (JH-red). The 350 arcmin^2 of the GOODS-N and
GOODS-S fields with the deepest HST/WFC3 and IRAC data contain 285 HIEROs down
to [4.5] 3) HIEROs, which
have a median photometric redshift z ~4.4 and stellar massM_{*}~10^{10.6} Msun,
and are much fainter in the rest-frame UV than similarly massive Lyman-break
galaxies (LBGs). Their star formation rates (SFRs) reaches ~240 Msun yr^{-1}
leading to a specific SFR, sSFR ~4.2 Gyr^{-1}, suggesting that the sSFRs for
massive galaxies continue to grow at z > 2 but at a lower growth rate than from
z=0 to z=2. With a median half-light radius of 2 kpc, including ~20% as compact
as quiescent galaxies at similar redshifts, JH-blue HIEROs represent perfect
star-forming progenitors of the most massive (M_{*} > 10^{11.2} Msun) compact
quiescent galaxies at z ~ 3 and have the right number density. HIEROs make up
~60% of all galaxies with M_{*} > 10^{10.5} Msun identified at z > 3 from their
photometric redshifts. This is five times more than LBGs with nearly no overlap
between the two populations. While HIEROs make up 15-25% of the total SFR
density at z ~ 4-5, they completely dominate the SFR density taking place in
M_{*} >10^{10.5} Msun galaxies, and are therefore crucial to understanding the
very early phase of massive galaxy formation.Comment: ApJS, in pres
Broad-band gravitational-wave pulses from binary neutron stars in eccentric orbits
Maximum gravitational wave emission from binary stars in eccentric orbits
occurs near the periastron passage. We show that for a stationary distribution
of binary neutron stars in the Galaxy, several high-eccentricity systems with
orbital periods in the range from tens of minutes to several days should exist
that emit broad gravitational-wave pulses in the frequency range 1-100 mHz. The
space interferometer LISA could register the pulsed signal from these system at
a signal-to-noise ratio level in the frequency range Hz during one-year observational time. Some detection
algorithms for such a signal are discussed.Comment: 17 pages, LATEX, 3 figures, Astronomy Letters, 2002, in press; typos
corrected, refference adde
Grassroots Creative Hubs: Urban Regeneration, Recovered Industrial Factories and Cultural Production in Buenos Aires and Rio de Janeiro
This chapter examines the nature, functioning and politics of grassroots creative hubs as contained in refurbished industrial factories. The renewal and transformation of factories into arts and cultural venues has been a key feature of post-industrial urbanism in the last three decades. Examples abound across the world, from railway and power stations to post office buildings and chocolate factories, these recovered infrastructures have been re-signified as cultural facilities â performing or multi-arts centres, galleries, cultural centres, creative economy laboratories, incubators and museums. These initiatives, be that they are led by local governments or community groups, are part of broader urban strategies for revitalising historical centres, revalorising cultural heritage and creating work opportunities as well as resources for tourism and business investment. But can a factory building be considered a creative hub? Does the materiality of these urban artefacts provide a solution to the oftentransient nature of ephemeral cultural urbanism?
Refurbishing old industrial factories and warehouses for cultural use and creative production has been the subject of much investigation since the 1980s-1990s, mainly through the study of culture-led urban regeneration and gentrification (Zukin, 1989; Montgomery, 1995; Evans and Shaw, 2004; Mommaas, 2004; Pratt, 2009), and more recently, creative industry clusters and districts (Evans, 2009; Zukin and Braslow, 2011; OâConnor and Gu, 2012). These studies have pointed out the problems that arise from the organisation, management and long-term sustainability of converted industrial sites, as well as from the policy uses and abuses that often pave the way to real-estate development and social displacement.
Drawing on insights from urban sociology and critical geography, the chapter conducts a case-study analysis of two cultural and creative economy factories in Latin America: FĂĄbrica Bhering in Rio de Janeiro, Brazil, and IMPA, la FĂĄbrica Cultural in Buenos Aires, Argentina. The chapter is comprised of three sections: the first discusses whether recovered industrial factories can be thought of as creative hubs in relation to ephemeral cultural urbanism; the second examines the two case-studies in the context of Brazil and Argentina; and the third offers concluding remarks. Overall the chapter contributes a Latin American perspective on culture-led urban regeneration to the study of creative hubs. Particularly, grassroots creative initiatives of urban renewal are presented as an alternative to the exclusionary gentrification processes to which creative hubs and other territorial forms of creativity are often related to, in times largely shaped by neoliberal operations driven by real-estate interests and alliances between political and economic urban elites
A combined VANDELS and LEGA-C study: the evolution of quiescent galaxy size, stellar mass, and age from z = 0.6 to z = 1.3
We study the relationships between stellar mass, size, and age within the quiescent population, using two mass-complete spectroscopic samples with log10(Mâ/Mâ) > 10.3, taken from VANDELS at 1.0 < z < 1.3, and LEGA-C at 0.6 < z < 0.8. Using robust Dn4000 values, we demonstrate that the well-known 'downsizing' signature is already in place by z 1.1, with Dn4000 increasing by 0.1 across a 1 dex mass interval for both VANDELS and LEGA-C. We then proceed to investigate the evolution of the quiescent galaxy stellar mass-size relation from z -1.1 to z -0.7. We find the median size increases by a factor of 1.9 ± 0.1 at log10(Mâ/Mâ) = 10.5, and see tentative evidence for flattening of the relation, finding slopes of α = 0.72 ± 0.06 and α =\0.56\pm 0.04 for VANDELS and LEGA-C, respectively. We finally split our sample into galaxies above and below our fitted mass-size relations, to investigate how size and Dn4000 correlate. For LEGA-C, we see a clear difference, with larger galaxies found to have smaller Dn4000 at fixed stellar mass. Due to the faintness and smaller numbers of the VANDELS sample, we cannot confirm whether a similar relation exists at z -1.1. We consider whether differences in stellar age or metallicity are most likely to drive this size-Dn4000 relation, finding that any metallicity differences are unlikely to fully explain the observed offset, meaning smaller galaxies must be older than their larger counterparts. We find the observed evolution in size, mass, and Dn4000 across the -2 Gyr from z âŒ1.1 to z âŒ0.7 can be explained by a simple toy model in which VANDELS galaxies evolve passively whilst experiencing a series of minor mergers
A combined VANDELS and LEGA-C study: the evolution of quiescent galaxy size, stellar mass, and age from z = 0.6 to z = 1.3
We study the relationships between stellar mass, size and age within the
quiescent population, using two mass-complete spectroscopic samples with
, taken from VANDELS at
, and LEGA-C at . Using robust D4000 values, we
demonstrate that the well-known 'downsizing' signature is already in place by
, with D4000 increasing by across a 1
dex mass interval for both VANDELS and LEGA-C. We then proceed to investigate
the evolution of the quiescent galaxy stellar mass-size relation from
to . We find the median size increases by a factor of
at , and
see tentative evidence for flattening of the relation, finding slopes of
and for VANDELS and LEGA-C
respectively. We finally split our sample into galaxies above and below our
fitted mass-size relations, to investigate how size and D4000 correlate.
For LEGA-C, we see a clear difference, with larger galaxies found to have
smaller D4000 at fixed stellar mass. Due to the faintness and smaller
numbers of the VANDELS sample, we cannot confirm whether a similar relation
exists at . We consider whether differences in stellar age or
metallicity are most likely to drive this size-D4000 relation, finding
that any metallicity differences are unlikely to fully explain the observed
offset, meaning smaller galaxies must be older than their larger counterparts.
We find the observed evolution in size, mass and D4000 across the
Gyr from to can be explained by a simple toy
model in which VANDELS galaxies evolve passively, whilst experiencing a series
of minor mergers.Comment: 14 pages, 9 figures, submitted to MNRA
Measuring star formation in high-z massive galaxies: A mid-infrared to submillimeter study of the GOODS NICMOS Survey sample
We present measurements of the mean mid-infrared-to-submillimeter flux
densities of massive (M\ast \approx 2 \times 10^11 Msun) galaxies at redshifts
1.7 < z < 2.9, obtained by stacking positions of known objects taken from the
GOODS NICMOS Survey (GNS) catalog on maps: at 24 {\mu}m (Spitzer/MIPS); 70,
100, and 160{\mu}m (Herschel/PACS); 250, 350, 500{\mu}m (BLAST); and 870{\mu}m
(LABOCA). A modified blackbody spectrum fit to the stacked flux densities
indicates a median [interquartile] star-formation rate of SFR = 63 [48, 81]
Msun yr^-1 . We note that not properly accounting for correlations between
bands when fitting stacked data can significantly bias the result. The galaxies
are divided into two groups, disk-like and spheroid-like, according to their
Sersic indices, n. We find evidence that most of the star formation is
occurring in n \leq 2 (disk-like) galaxies, with median [interquartile] SFR =
122 [100,150] Msun yr^-1, while there are indications that the n > 2
(spheroid-like) population may be forming stars at a median [interquartile] SFR
= 14 [9,20] Msun yr^-1, if at all. Finally, we show that star formation is a
plausible mechanism for size evolution in this population as a whole, but find
only marginal evidence that it is what drives the expansion of the
spheroid-like galaxies.Comment: Accepted by MNRAS. 10 pages, 3 figures, 3 table
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