8,350 research outputs found
Spontaneously modulated spin textures in a dipolar spinor Bose-Einstein condensate
Helical spin textures in a Rb F=1 spinor Bose-Einstein condensate are
found to decay spontaneously toward a spatially modulated structure of spin
domains. This evolution is ascribed to magnetic dipolar interactions that
energetically favor the short-wavelength domains over the long-wavelength spin
helix. This is confirmed by eliminating the dipolar interactions by a sequence
of rf pulses and observing a suppression of the formation of the short-range
domains. This study confirms the significance of magnetic dipole interactions
in degenerate Rb F=1 spinor gases
The Evolution of Luminous Compact Blue Galaxies: Disks or Spheroids?
Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies
characterized by high luminosities, blue colors, and high surface brightnesses.
Residing at the high luminosity, high mass end of the blue sequence, LCBGs sit
at the critical juncture of galaxies that are evolving from the blue to the red
sequence. Yet we do not understand what drives the evolution of LCBGs, nor how
they will evolve. Based on single-dish HI observations, we know that they have
a diverse range of properties. LCBGs are HI-rich with M(HI)=10^{9-10.5} M(sun),
have moderate M(dyn)=10^{10-12} M(sun), and 80% have gas depletion timescales
less than 3 Gyr. These properties are consistent with LCBGs evolving into
low-mass spirals or high mass dwarf ellipticals or dwarf irregulars. However,
LCBGs do not follow the Tully-Fisher relation, nor can most evolve onto it,
implying that many LCBGs are not smoothly rotating, virialized systems. GMRT
and VLA HI maps confirm this conclusion revealing signatures of recent
interactions and dynamically hot components in some local LCBGs, consistent
with the formation of a thick disk or spheroid. Such signatures and the high
incidence of close companions around LCBGs suggest that star formation in local
LCBGs is likely triggered by interactions. The dynamical masses and apparent
spheroid formation in LCBGs combined with previous results from optical
spectroscopy are consistent with virial heating being the primary mechanism for
quenching star formation in these galaxies.Comment: 4 pages, 1 figure, to appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Se
The Nature of Nearby Counterparts to Intermediate Redshift Luminous Compact Blue Galaxies I. Optical/H I Properties and Dynamical Masses
We present single-dish H I spectra obtained with the Green Bank Telescope,
along with optical photometric properties from the Sloan Digital Sky Survey, of
20 nearby (D < 70 Mpc) Luminous Compact Blue Galaxies (LCBGs). These ~L*, blue,
high surface brightness, starbursting galaxies were selected with the same
criteria used to define LCBGs at higher redshifts. We find these galaxies are
gas-rich, with M(HI) ranging from 5*10^8 to 8*10^9 M_sun, and M(HI)/L_B ranging
from 0.2 to 2 M_sun/L_sun, consistent with a variety of morphological types of
galaxies. We find the dynamical masses (measured within R_25) span a wide
range, from 3*10^9 to 1*10^11 M_sun. However, at least half have dynamical
mass-to-light ratios smaller than nearby galaxies of all Hubble types, as found
for LCBGs at intermediate redshifts. By comparing line widths and effective
radii with local galaxy populations, we find that LCBGs are consistent with the
dynamical mass properties of Magellanic (low luminosity) spirals, and the more
massive irregulars and dwarf ellipticals, such as NGC 205.Comment: 33 pages, 8 figures, accepted by Ap
The Nature of Nearby Counterparts to Intermediate Redshift Luminous Compact Blue Galaxies II. CO Observations
We present the results of a single-dish beam-matched survey of the three
lowest rotational transitions of CO in a sample of 20 local (D < 70 Mpc)
Luminous Compact Blue Galaxies (LCBGs). These ~L*, blue, high surface
brightness, starbursting galaxies were selected with the same criteria used to
define LCBGs at higher redshifts. Our detection rate was 70%, with those
galaxies having Lblue<7e9 Lsun no detected. We find the H2 masses of local
LCBGs range from 6.6e6 to 2.7e9 Msun, assuming a Galactic CO-to-H2 conversion
factor. Combining these results with our earlier HI survey of the same sample,
we find that the ratio of molecular to atomic gas mass is low, typically 5-10%.
Using a Large Velocity Gradient model, we find that the average gas conditions
of the entire ISM in local LCBGs are similar to those found in the centers of
star forming regions in our Galaxy, and nuclear regions of other galaxies. Star
formation rates, determined from IRAS fluxes, are a few solar masses per year,
much higher per unit dynamical mass than normal spirals. If this rate remains
constant, the molecular hydrogen depletion time scales are short, 10-200 Myr.Comment: accepted for publication in the ApJ (vol 625
Monitoring Tropospheric Gases with Small Unmanned Aerial Systems (sUAS) during the Second CLOUDMAP Flight Campaign
Small unmanned aerial systems (sUAS) are a promising technology for atmospheric monitoring of trace atmospheric gases. While sUAS can be navigated to provide information with higher spatiotemporal resolution than tethered balloons, they can also bridge the gap between the regions of the atmospheric boundary layer (ABL) sampled by ground stations and manned aircraft. Additionally, sUAS can be effectively employed in the petroleum industry, e.g., to constrain leaking regions of hydrocarbons from long gasoducts. Herein, sUAS are demonstrated to be a valuable technology for studying the concentration of important trace tropospheric gases in the ABL. The successful detection and quantification of gases is performed with lightweight sensor packages of low-power consumption that possess limits of detection on the ppm scale or below with reasonably fast response times. The datasets reported include timestamps with position, temperature, relative humidity, pressure, and variable mixing ratio values of ~400 ppm CO2, ~1900 ppb CH4, and ~5.5 ppb NH3. The sensor packages were deployed aboard two different sUAS operating simultaneously during the second CLOUDMAP flight campaign in Oklahoma, held during 26–29 June 2017. A Skywalker X8 fixed wing aircraft was used to fly horizontally at a constant altitude, while vertical profiles were provided by a DJI Phantom 3 (DJI P3) quadcopter flying upward and downward at fixed latitude-longitude coordinates. The results presented have been gathered during 8 experiments consisting of 32 simultaneous flights with both sUAS, which have been authorized by the United States Federal Aviation Authority (FAA) under the current regulations (Part 107). In conclusion, this work serves as proof of concept showing the atmospheric value of information provided by the developed sensor systems aboard sUAS
Trajectory design strategies that incorporate invariant manifolds and swingby
Libration point orbits serve as excellent platforms for scientific investigations involving the Sun as well as planetary environments. Trajectory design in support of such missions is increasingly challenging as more complex missions are envisioned in the next few decades. Software tools for trajectory design in this regime must be further developed to incorporate better understanding of the solution space and, thus, improve the efficiency and expand the capabilities of current approaches. Only recently applied to trajectory design, dynamical systems theory now offers new insights into the natural dynamics associated with the multi-body problem. The goal of this effort is the blending of analysis from dynamical systems theory with the well established NASA Goddard software program SWINGBY to enhance and expand the capabilities for mission design. Basic knowledge concerning the solution space is improved as well
Stimfit: A fast visualization and analysis environment for cellular neurophysiology
Stimfit is a free cross-platform software package for viewing and analyzing electrophysiological data. It supports most standard file types for cellular neurophysiology and other biomedical formats. Its analysis algorithms have been used and validated in several experimental laboratories. Its embedded Python scripting interface makes Stimfit highly extensible and customizable
Impact of Medicare denials on noninvasive vascular diagnostic testing
AbstractPurpose: The purpose of this study was to evaluate the impact of Medicare coverage limitations and claim denials on noninvasive vascular diagnostic testing. Methods: All Medicare claims for noninvasive vascular diagnostic studies from January 1, 1999, to December 31, 1999, were identified from the hospital billing database according to Current Procedural Terminology codes for carotid artery duplex ultrasound scan, venous duplex ultrasound scan, and lower-extremity arterial Doppler scan. Reasons for Medicare denial of payment for these tests were reviewed and a cost analysis was performed. Results: During the 1-year period, there were 1096 noninvasive vascular diagnostic studies performed on Medicare patients. Of these 1096 tests, 176 (16.1%) were denied by Medicare (19.6% of 408 carotid duplex ultrasound scans, 16.8% of 345 venous duplex ultrasound scans, and 11.1% of 343 lower-extremity arterial Doppler scans). Of the noninvasive vascular tests denied by Medicare, an abnormal result was present in 72.5% of carotid duplex ultrasound scans, 32.8% of venous duplex ultrasound scans, and 78.9% of lower-extremity arterial Doppler scans. Overall, 88.1% of all initially denied claims (N = 176) were ultimately reimbursed by Medicare after resubmission, including 77.1% of the 118 claims denied based on compliance rules for “medical necessity.” Conclusion: Because of coverage limitations, Medicare denials of noninvasive vascular diagnostic tests can lead to potential uncompensated physician and hospital technical fees if denied claims are unrecognized. Vascular laboratories performing these tests need to review compliance with Medicare guidelines. Improvements may need to be made at both the provider and Medicare carrier levels in obtaining reimbursement for appropriately ordered noninvasive vascular diagnostic studies. (J Vasc Surg 2001;34:846-53.
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