417 research outputs found
Spontaneous arterial thrombosis in a patient with human immunodeficiency virus infection: Successful treatment with pharmacomechanical thrombectomy
AbstractPatients with human immunodeficiency virus (HIV) have various coagulation abnormalities as well as increased risk for development of clinical thrombosis and subsequent embolic events. We report acute lower leg ischemia caused by spontaneous atheroembolism with no identifiable source in a young patient with HIV infection. Treatment included percutaneous mechanical thrombectomy and thrombolysis, which reversed the arterial ischemia. Physicians should be aware of thromboembolic disease as a possible complication of HIV
A bimodal spacecraft bus based on a cermet fueled heat pipe reactor
Bimodal space reactor systems provide both thermal propulsion for the spacecraft orbital transfer and electrical power to the spacecraft bus once it is on station. These systems have the potential to increase both the available payload in high energy orbits and the available power to that payload. These increased mass and power capabilities can be used to either reduce mission cost by permitting the use of smaller launch vehicles or to provide increased mission performance from the current launch vehicle. A major barrier to the deployment of these bimodal systems has been the cost associated with their development. This paper describes a bimodal spacecraft bus with performance potential to permit more than 70% of the instrumented payload of the Titan IV/Centaur to be launched from the Atlas IIAS. The development cost is minimized by basing the design on existing component technologies
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Integrated X-ray testing of the electro-optical breadboard model for the XMM reflection grating spectrometer
X-ray calibration of the Electro-Optical Breadboard Model (EOBB) of the XXM Reflection Grating Spectrometer has been carried out at the Panter test facility in Germany. The EOBB prototype optics consisted of a four-shell grazing incidence mirror module followed by an array of eight reflection gratings. The dispersed x-rays were detected by an array of three CCDs. Line profile and efficiency measurements where made at several energies, orders, and geometric configurations for individual gratings and for the grating array as a whole. The x-ray measurements verified that the grating mounting method would meet the stringent tolerances necessary for the flight instrument. Post EOBB metrology of the individual gratings and their mountings confirmed the precision of the grating boxes fabrication. Examination of the individual grating surface`s at micron resolution revealed the cause of anomalously wide line profiles to be scattering due to the crazing of the replica`s surface
Spectroscopy of luminous z>7 galaxy candidates and sources of contamination in z>7 galaxy searches
We present three bright z+ dropout candidates selected from deep
Near-Infrared (NIR) imaging of the COSMOS 2 square degree field. All three
objects match the 0.8-8um colors of other published z>7 candidates but are
three magnitudes brighter, facilitating further study. Deep spectroscopy of two
of the candidates covering 0.64-1.02um with Keck-DEIMOS and all three covering
0.94-1.10um and 1.52-1.80um with Keck-NIRSPEC detects weak spectral features
tentatively identified as Ly-alpha at z=6.95 and z=7.69 in two of the objects.
The third object is placed at z~1.6 based on a 24um and weak optical detection.
A comparison with the spectral energy distributions of known z<7 galaxies,
including objects with strong spectral lines, large extinction, and large
systematic uncertainties in the photometry yields no objects with similar
colors. However, the lambda>1um properties of all three objects can be matched
to optically detected sources with photometric redshifts at z~1.8, so the
non-detection in the i+ and z+ bands are the primary factors which favors a z>7
solution. If any of these objects are at z~7 the bright end of the luminosity
function is significantly higher at z>7 than suggested by previous studies, but
consistent within the statistical uncertainty and the dark matter halo
distribution. If these objects are at low redshift, the Lyman-Break selection
must be contaminated by a previously unknown population of low redshift objects
with very strong breaks in their broad band spectral energy distributions and
blue NIR colors. The implications of this result on luminosity function
evolution at high redshift is discussed. We show that the primary limitation of
z>7 galaxy searches with broad filters is the depth of the available optical
data.Comment: 15 Pages, 15 figures, accepted to Ap
The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign
We present the results of a multisite photometric campaign on the pulsating
sdB star Balloon 090100001. The star is one of the two known hybrid hot
subdwarfs with both long- and short-period oscillations. The campaign involved
eight telescopes with three obtaining UBVR data, four B-band data, and one
Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal
resolution of 0.36microHz with a detection threshold of about 0.2mmag in
B-filter data.
Balloon 090100001 has the richest pulsation spectrum of any known pulsating
subdwarf B star and our analysis detected 114 frequencies including 97
independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz
region is most likely radial while the remaining ones in this region form two
nearly symmetric multiplets: a triplet and quintuplet, attributed to
rotationally split \ell=1 and 2 modes, respectively. We find clear increases of
splitting in both multiplets between the 2004 and 2005 observing campaigns,
amounting to 15% on average. The observed splittings imply that the rotational
rate in Bal09 depends on stellar latitude and is the fastest on the equator. We
use a small grid of models to constrain the main mode (f_1), which most likely
represents the radial fundamental pulsation. The groups of p-mode frequencies
appear to lie in the vicinity of consecutive radial overtones, up to the third
one. Despite the large number of g-mode frequencies observed, we failed to
identify them, most likely because of the disruption of asymptotic behaviour by
mode trapping. The observed frequencies were not, however, fully exploited in
terms of seismic analysis which should be done in the future with a larger grid
of reliable evolutionary models of hot subdwarfs.Comment: accepted for publication in MNRA
A survey for pulsating subdwarf B stars with the Nordic Optical Telescope
A search programme for pulsating subdwarf B stars was conducted with the
Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009. The
purpose of the programme was to significantly extend the number of rapidly
pulsating sdB stars to better understand the properties of this new group of
variable compact stars. Candidates were selected initially from the HS and HE
surveys, but were supplemented with additional objects from other surveys.
Short sequences of time-series photometry were made on the candidates to
determine the presence of rapid pulsations. In total twenty new pulsators were
found in this survey, most of which have already been published and some
extensively studied. We present four new short period pulsators, bringing the
total of such pulsators up to 49. We also give limits on pulsation amplitudes
for 285 objects with no obvious periodic variations, summarise the results of
the survey, and provide improved physical parameters on the composite pulsators
for which only preliminary estimates were published earlier.Comment: 17 pages, accepted for publication in A&
Individual-environment interactions in swimming: The smallest unit for analysing the emergence of coordination dynamics in performance?
Displacement in competitive swimming is highly dependent on fluid characteristics,
since athletes use these properties to propel themselves. It is essential for sport
scientists and practitioners to clearly identify the interactions that emerge between
each individual swimmer and properties of an aquatic environment. Traditionally, the
two protagonists in these interactions have been studied separately. Determining the
impact of each swimmer’s movements on fluid flow, and vice versa, is a major
challenge. Classic biomechanical research approaches have focused on swimmers’
actions, decomposing stroke characteristics for analysis, without exploring
perturbations to fluid flows. Conversely, fluid mechanics research has sought to
record fluid behaviours, isolated from the constraints of competitive swimming
environments (e.g. analyses in two-dimensions, fluid flows passively studied on
mannequins or robot effectors). With improvements in technology, however, recent
investigations have focused on the emergent circular couplings between swimmers’
movements and fluid dynamics. Here, we provide insights into concepts and tools that
can explain these on-going dynamical interactions in competitive swimming within
the theoretical framework of ecological dynamics
The Simons Observatory: Cryogenic Half Wave Plate Rotation Mechanism for the Small Aperture Telescopes
We present the requirements, design and evaluation of the cryogenic
continuously rotating half-wave plate (CHWP) for the Simons Observatory (SO).
SO is a cosmic microwave background (CMB) polarization experiment at Parque
Astron\'{o}mico Atacama in northern Chile that covers a wide range of angular
scales using both small (0.42 m) and large (6 m) aperture telescopes. In
particular, the small aperture telescopes (SATs) focus on large angular scales
for primordial B-mode polarization. To this end, the SATs employ a CHWP to
modulate the polarization of the incident light at 8~Hz, suppressing
atmospheric noise and mitigating systematic uncertainties that would
otherwise arise due to the differential response of detectors sensitive to
orthogonal polarizations. The CHWP consists of a 505 mm diameter achromatic
sapphire HWP and a cryogenic rotation mechanism, both of which are cooled down
to 50 K to reduce detector thermal loading. Under normal operation the
HWP is suspended by a superconducting magnetic bearing and rotates with a
constant 2 Hz frequency, controlled by an electromagnetic synchronous motor.
The rotation angle is detected through an angular encoder with a noise level of
0.07. During a cooldown, the rotor is held in
place by a grip-and-release mechanism that serves as both an alignment device
and a thermal path. In this paper we provide an overview of the SO SAT CHWP:
its requirements, hardware design, and laboratory performance.Comment: 19 pages, 21 figures, submitted to RS
Fine Particulate air Pollution is Associated with Higher Vulnerability to Atrial Fibrillation—The APACR Study
The acute effects and the time course of fine particulate pollution (PM2.5) on atrial fibrillation/flutter (AF) predictors, including P-wave duration, PR interval duration, and P-wave complexity, were investigated in a community-dwelling sample of 106 nonsmokers. Individual-level 24-h beat-to-beat electrocardiogram (ECG) data were visually examined. After identifying and removing artifacts and arrhythmic beats, the 30-min averages of the AF predictors were calculated. A personal PM2.5 monitor was used to measure individual-level, real-time PM2.5 exposures during the same 24-h period, and corresponding 30-min average PM2.5 concentration were calculated. Under a linear mixed-effects modeling framework, distributed lag models were used to estimate regression coefficients (βs) associating PM2.5 with AF predictors. Most of the adverse effects on AF predictors occurred within 1.5–2 h after PM2.5 exposure. The multivariable adjusted βs per 10-µg/m3 rise in PM2.5 at lag 1 and lag 2 were significantly associated with P-wave complexity. PM2.5 exposure was also significantly associated with prolonged PR duration at lag 3 and lag 4. Higher PM2.5 was found to be associated with increases in P-wave complexity and PR duration. Maximal effects were observed within 2 h. These findings suggest that PM2.5 adversely affects AF predictors; thus, PM2.5 may be indicative of greater susceptibility to AF
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