1,588 research outputs found
Radiation environment along the INTEGRAL orbit measured with the IREM monitor
The INTEGRAL Radiation Environment Monitor (IREM) is a payload supporting
instrument on board the INTEGRAL satellite. The monitor continually measures
electron and proton fluxes along the orbit and provides this information to the
spacecraft on board data handler. The mission alert system broadcasts it to the
payload instruments enabling them to react accordingly to the current radiation
level. Additionally, the IREM conducts its autonomous research mapping the
Earth radiation environment for the space weather program. Its scientific data
are available for further analysis almost without delay.Comment: 5 pages, 7 figures, accepted for publication in A+A letter
Design and Evaluation of a Device for Measuring 3D-Micromotions of Press-Fit Femoral Stem Prostheses
Controlling the stability transfer between oppositely traveling waves and standing waves by inversion-symmetry-breaking perturbations
The effect of an externally applied flow on symmetry degenerated waves
propagating into opposite directions and standing waves that exchange stability
with the traveling waves via mixed states is analyzed. Wave structures that
consist of spiral vortices in the counter rotating Taylor-Couette system are
investigated by full numerical simulations and explained quantitatively by
amplitude equations containing quintic coupling terms. The latter are
appropriate to describe the influence of inversion symmetry breaking
perturbations on many oscillatory instabilities with O(2) symmetry.Comment: 4 pages, 4 figure
A numerical investigation on the vortex formation and flow separation of the oscillatory flow in jet pumps
A two-dimensional computational fluid dynamics model is used to predict the
oscillatory flow through a tapered cylindrical tube section (jet pump) placed
in a larger outer tube. Due to the shape of the jet pump, there will exist an
asymmetry in the hydrodynamic end effects which will cause a time-averaged
pressure drop to occur that can be used to cancel Gedeon streaming in a
closed-loop thermoacoustic device. The performance of two jet pump geometries
with different taper angles is investigated. A specific time-domain impedance
boundary condition is implemented in order to simulate traveling acoustic wave
conditions. It is shown that by scaling the acoustic displacement amplitude to
the jet pump dimensions, similar minor losses are observed independent of the
jet pump geometry. Four different flow regimes are distinguished and the
observed flow phenomena are related to the jet pump performance. The simulated
jet pump performance is compared to an existing quasi-steady approximation
which is shown to only be valid for small displacement amplitudes compared to
the jet pump length.Comment: The following article has been accepted by the Journal of the
Acoustical Society of America. After it is published, it will be found at:
http://scitation.aip.org/JAS
Study of timing performance of Silicon Photomultiplier and application for a Cherenkov detector
Silicon photomultipliers are very versatile photo detectors due to their high
photon detection efficiency, fast response, single photon counting capability,
high amplification, and their insensitivity to magnetic fields. At our
institute we are studying the performance of these photo detectors at various
operating conditions. On the basis of the experience in the laboratory we built
a prototype of a timing Cherenkov detector consisting of a quartz radiator with
two mm MPPCs S10362-33-100C from Hamamatsu Photonics as
photodetectors. The MPPC sensors were operated with Peltier cooling to minimize
thermal noise and to avoid gain drifts. The test measurements at the DANE
Beam-Test Facility (BTF) at the Laboratori Nazionali di Frascati (LNF) with
pulsed 490 MeV electrons and the results on timing performance with Cherenkov
photons are presented.Comment: Conference proceedings of 12th Vienna Conference on Instrumentation
201
Jet pumps for thermoacoustic applications: design guidelines based on a numerical parameter study
The oscillatory flow through tapered cylindrical tube sections (jet pumps) is
characterized by a numerical parameter study. The shape of a jet pump results
in asymmetric hydrodynamic end effects which cause a time-averaged pressure
drop to occur under oscillatory flow conditions. Hence, jet pumps are used as
streaming suppressors in closed-loop thermoacoustic devices. A two-dimensional
axisymmetric computational fluid dynamics model is used to calculate the
performance of a large number of conical jet pump geometries in terms of
time-averaged pressure drop and acoustic power dissipation. The investigated
geometrical parameters include the jet pump length, taper angle, waist diameter
and waist curvature. In correspondence with previous work, four flow regimes
are observed which characterize the jet pump performance and dimensionless
parameters are introduced to scale the performance of the various jet pump
geometries. The simulation results are compared to an existing quasi-steady
theory and it is shown that this theory is only applicable in a small operation
region. Based on the scaling parameters, an optimum operation region is defined
and design guidelines are proposed which can be directly used for future jet
pump design.Comment: The following article has been accepted by the Journal of the
Acoustical Society of America. After it is published, it will be found at
http://scitation.aip.org/JAS
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Noble gases from the interstellar medium trapped on the MIR space station and analyzed by in vacuo etching
Introduction: The composition of the present interstellar medium (ISM) provides an important benchmark in cosmochemistry. It serves as a reference for galactic chemical evolution (GCE) models, solar mixing predictions and provides information for understanding Big Bang nucleosynthesis. The present-day ISM 3He abundance allows, combined with the protosolar 3He, deduced from the Jovian atmosphere or meteorites [1,2], tracing the GCE over the past 4.56 Ga. 3He/4He = (2.5 0.6) x 10-4 has been determined for the local ISM [3]. However, the uncertainty is too large to better constrain GCE models and - in combination with the present-day solar wind value - the protosolar D/H [4]
Treatment of gastrointestinal hemorrhage
Background: We assessed the value of selective arteriography in the diagnosis and management of acute gastrointestinal hemorrhage. Methods: We reviewed the records of 107 consecutive patients who had gastrointestinal hemorrhage and underwent selective arteriography between January 1992 and October 2003: 10 had upper gastrointestinal bleeding, 79 had lower gastrointestinal bleeding, and 18 had varicose bleeding with portal hypertension. Selective embolization was attempted in 15 patients to obtain hemostasis. Angiographic findings were reviewed and prospective reports were compared with the final diagnosis and outcome. Results: Of 129 angiographic studies, 36 correctly revealed the bleeding site and 93 were negative. Extravasation was seen in 24 cases at the level of stomach (n = 2), duodenum (n = 1), small bowel (n = 5), or colon (n = 16). Indirect signs of bleeding sources were identified in 12 patients (stomach in one, small bowel in four, large bowel in four, liver in three). Transcatheter embolization induced definitive hemostasis in 11 of 15 patients (73%), namely in the stomach (n = 2), small bowel (n = 3), colon (n = 7), and liver (n = 3). Three patients required surgery after embolization. Conclusion: Abdominal arteriography may localize gastrointestinal bleeding sources in approximately one-third of cases. Selective embolization may provide definitive hemostasis in most instance
Calculation of thermoacoustic functions with computational fluid dynamics
Thermoacoustic functions are important parameters of one-dimensional codes used for the design of thermoacoustic engines. The thermal and viscous thermoacoustic functions allow the inclusion of three dimensional effects in one-dimensional codes. These functions are especially important in the regenerator of a thermoacoustic engine, where the thermoacoustic heat pumping occurs. Even though analytical solutions were derived for uniform pores, the thermoacoustic functions for complex geometries such as stacked screen or random fiber regenerators cannot be calculated analytically. In order to gain more insight into the geometry induced complex flow fields, the procedure of Udea, et al. (2009) to estimate the thermoacoustic functions was applied in computational fluid-dynamic simulations. By using two measurement locations outside of the regenerator and modeling the regenerator as an array of uniform pores it is possible to estimate the thermoacoustic functions for complex geometries. Furthermore, a correction method is proposed to quantify the entrance effects at the beginning and end of a regular pore. The simulations are first validated for a uniform cylindrical pore with the help of the analytical solution. Then the correction method is successfully applied to a cylindrical pore with the results closely matching the analytical solution
Calcium antagonist induced vasodilation in peripheral, coronary and cerebral vasculature as important factors in the treatment of elderly hypertensives
Increased arteriolar tone is the pathophysiological hallmark of essential hypertension and is determined by the intracellular free calcium concentration in the vascular smooth muscle cell. Calcium influx is an important determinant of vasoconstriction and excess calcium influx-dependent vasoconstriction has been shown by plethysmographical studies in patients with essential hypertension. Calcium antagonists acutely lower BP by reducing calcium influx, calcium concentration and peripheral resistance. The degree of the attendant sympathetic nerve reflex activation and counter-regulatory mechanisms determines the antihypertensive response of the individual. Chronic monotherapy with a calcium antagonist results in an antihypertensive response, which is directly related to the patient's age and pretreatment BP and indirectly related to plasma renin levels. The resulting reduction in after-load neither leads to reduced cerebral blood flow in hypertensive patients, nor aggravates congestive heart failure. Calcium antagonists are a useful alternative to diuretics, primarily in older patients with low renin levels, either alone or combined with any other antihypertensive drug, and provide effective and safe control of blood pressur
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