12,152 research outputs found
Supersonic turbulence in 3D isothermal flow collision
Colliding supersonic bulk flows shape observable properties and internal
physics of various astrophysical objects, like O-star winds, molecular clouds,
galactic sheets, binaries, or gamma-ray bursts. Using numerical simulations, we
show that the bulk flows leave a clear imprint on the collision zone, its mean
properties and the turbulence it naturally develops. Our model setup consists
of 3D head-on colliding isothermal hydrodynamical flows with Mach numbers
between 2 and 43. Simulation results are in line with expectations from
self-similarity: root mean square Mach numbers (Mrms) scale linearly with
upstream Mach numbers, mean densities remain limited to a few times the
upstream density. The density PDF is not log-normal. The turbulence is
inhomogeneous: weaker in the zone center than close to the confining shocks. It
is anisotropic: while Mrms is generally supersonic, Mrms transverse to the
upstream flow is always subsonic. We argue that uniform, isothermal, head-on
colliding flows generally disfavor isotropic, supersonic turbulence. The
anisotropy carries over to other quantities like the density variance - Mach
number relation. Structure functions differ depending on whether they are
computed along a line-of-sight perpendicular or parallel to the upstream flow.
We suggest that such line-of-sight effects should be kept in mind when
interpreting turbulence characteristics derived from observations.Comment: 20 pages, 14 figures, 4 tables, accepted by Astronomy and
Astrophysic
Weakly-entangled states are dense and robust
Motivated by the mathematical definition of entanglement we undertake a
rigorous analysis of the separability and non-distillability properties in the
neighborhood of those three-qubit mixed states which are entangled and
completely bi-separable. Our results are not only restricted to this class of
quantum states, since they rest upon very general properties of mixed states
and Unextendible Product Bases for any possible number of parties. Robustness
against noise of the relevant properties of these states implies the
significance of their possible experimental realization, therefore being of
physical -and not exclusively mathematical- interest.Comment: 4 pages, final version, accepted for publication in PR
Ifosfamide with regional hyperthermia in soft-tissue sarcomas
For high-risk soft tissue sarcomas (HR-STS) of adults, new treatment strategies are needed to improve outcome with regard to local control and overall survival. Therefore, systemic chemotherapy has been integrated either after (adjuvant) or before (neoadjuvant) optimal local treatment by surgery and radiotherapy in HR-STS. The combination with regional hyperthermia as a new treatment strategy seems to open a new therapeutic window. Copyright (C) 2003 S. Karger AG, Basel
Laser Doppler system for measuring three dimensional vector velocity Patent
Describing laser Doppler velicometer for measuring mean velocity and turbulence of fluid flo
Simultaneous observations of haemolymph flow and ventilation in marine spider crabs at different temperatures: a flow weighted MRI study
In vivo magnetic resonance imaging (MRI) and angiography were applied to the marine spider crab Maja squinado for a study of temperature effects and thermal tolerance. Ventilation and haemolymph circulation were investigated during progressive cooling from 12°C to 2°C. The anatomical resolution of MR images from Maja squinado obtained with a standard spin echo sequence were suitable to resolve the structures of various internal organs. The heart of the animal could be depicted without movement artifacts. The use of a flow compensated gradient echo sequence allowed simultaneous observations of ventilation, reflected by water flow through the gill chambers as well as of haemolymph flow. Simultaneous investigation of various arteries was possible by use of flow weighted MRI. In addition to those accessible by standard invasive flow sensitive doppler sensors, flow changes in gill, leg arteries and the venous return could be observed. Both ventilation and haemolymph flow decreased during progressive cooling and changes in haemolymph flow varied between arteries. Haemolymph flow through the Arteria sternalis, some gill and leg arteries was maintained at low temperatures indicating a reduced thermal sensitivity of flow in selected vessels. In support of previous invasive studies of haemolymph flow as well as heart and ventilation rates, the results demonstrate that the operation of gills and the maintenance of locomotor activity are critical for cold tolerance. A shift in haemolymph flow between arteries likely occurs to ensure the functioning of locomotion and ventilation in the cold
Predictors of course and outcome in hypochondriasis after cognitive-behavioral treatment
Background. Predictors of treatment outcome were evaluated in a clinical sample suffering from hypochondriasis. Methods: The sample consisted of 96 patients with hypochondriacal disorder according to DSM-IV or high syndrome scores on the Illness Attitude Scales (IAS) or Whiteley Index (WI). After intense inpatient cognitive-behavioral treatment (CBT), 60% of the patients were classified as responders because of substantial improvements or recovery from hypochondriacal symptomatology. Results: Non-responders were characterized by a higher degree of pre-treatment hypochondriasis, more somatization symptoms and general psychopathology (SCL-90R), more dysfunctional cognitions related to bodily functioning, higher levels of psychosocial impairments, and more utilization of the health care system as indicated by the number of hospital days and costs for inpatient treatments and medication. No predictive value was found for sociodemographic variables, comorbidity with other mental disorders and chronicity. Multiple linear regression showed that pre-treatment variables significantly predicted IAS scores at post-treatment (R-2 = 0.59), changes during treatment (0.10), IAS scores at follow-up two years later (0.41) and changes between baseline and follow-up (0.25). Conclusions: The results demonstrate the relevance of various psychopathological variables and health care utilization as important indicators for outcome and further course of clinical hypochondriasis. Copyright (C) 2002 S. Karger AG, Basel
Spatial displays as a means to increase pilot situational awareness
Experiences raise a number of concerns for future spatial-display developers. While the promise of spatial displays is great, the cost of their development will be correspondingly large. The knowledge and skills which must be coordinated to ensure successful results is unprecedent. From the viewpoint of the designer, basic knowledge of how human beings perceive and process complex displays appears fragmented and largely unquantified. Methodologies for display development require prototyping and testing with subject pilots for even small changes. Useful characterizations of the range of differences between individual users is nonexistent or at best poorly understood. The nature, significance, and frequency of interpretation errors associated with complex integrated displays is unexplored and undocumented territory. Graphic displays have intuitive appeal and can achieve face validity much more readily than earlier symbolic displays. The risk of misleading the pilot is correspondingly greater. Thus while some in the research community are developing the tools and techniques necessary for effective spatial-display development, potential users must be educated about the issues so that informed choices can be made. The scope of the task facing all is great. The task is challenging and the potential for meaningful contributions at all levels is high indeed
The multiplicity of \phi\ Phe revisited
The chemically peculiar B star Phe was, until very recently,
considered a triple system, even though the data were not conclusive and the
orbits rather uncertain. Very recent results by Korhonen et al. (2013) provided
a revised orbit, different from the then available astrometric Hipparcos orbit.
Additional spectroscopic data, obtained with the BESO spectrograph at Cerro
Armazones, confirm the newly found orbit, even though the resulting radial
velocities do not allow to improve on the recent orbit. We combine the latter
with the Hipparcos measurements to secure the astrometric orbit, and derive the
inclination of the system. Using evolutionary tracks, we can finally constrain
all the parameters of the two components in this system.
We confirm the mass of the primary, 3 M, and find that the companion
has a mass of 0.9 M. The inclination of the system is , and is potentially eclipsing; we predict the time of the next
conjunction. Given that the eccentricity of the orbit and the exact value of
the semi-amplitude of the radial velocity relies on just one set of points, we
also urge observers to measure radial velocities at the next periastron passage
in April 2015.Comment: 5 papes, accepted as Research Note in Astronomy and Astrophysic
Glass transition of hard spheres in high dimensions
We have investigated analytically and numerically the liquid-glass transition
of hard spheres for dimensions in the framework of mode-coupling
theory. The numerical results for the critical collective and self
nonergodicity parameters and exhibit
non-Gaussian -dependence even up to . and
differ for , but become identical on a scale
, which is proven analytically. The critical packing fraction
is above the corresponding Kauzmann packing
fraction derived by a small cage expansion. Its quadratic
pre-exponential factor is different from the linear one found earlier. The
numerical values for the exponent parameter and therefore the critical
exponents and depend on , even for the largest values of .Comment: 11 pages, 8 figures, Phys. Rev. E (in print
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