26,108 research outputs found
Vection-induced gastric dysrhythmias and motion sickness
Gastric electrical and mechanical activity during vection-induced motion sickness was investigated. The contractile events of the antrum and gastric myoelectric activity in healthy subjects exposed to vection were measured simultaneously. Symptomatic and myoelectric responses of subjects with vagotomy and gastric resections during vection stimuli were determined. And laboratory based computer systems for analysis of the myoelectric signal were developed. Gastric myoelectric activity was recorded from cutaneous electrodes, i.e., electrogastrograms (EGGs), and antral contractions were measured with intraluminal pressure transducers. Vection was induced by a rotating drum. gastric electromechanical activity was recorded during three periods: 15 min baseline, 15 min drum rotation (vection), and 15 to 30 min recovery. Preliminary results showed that catecholamine responses in nauseated versus symptom-free subjects were divergent and pretreatment with metoclopramide HC1 (Reglan) prevented vection-induced nausea and reduced tachygastrias in two previously symptomatic subjects
Analysis of pressure distortion testing
The development of a distortion methodology, method D, was documented, and its application to steady state and unsteady data was demonstrated. Three methodologies based upon DIDENT, a NASA-LeRC distortion methodology based upon the parallel compressor model, were investigated by applying them to a set of steady state data. The best formulation was then applied to an independent data set. The good correlation achieved with this data set showed that method E, one of the above methodologies, is a viable concept. Unsteady data were analyzed by using the method E methodology. This analysis pointed out that the method E sensitivities are functions of pressure defect level as well as corrected speed and pattern
Evaluation of range and distortion tolerance for high Mach number transonic fan stages. Task 2: Performance of a 1500-foot-per-second tip speed transonic fan stage with variable geometry inlet guide vanes and stator
A 0.5 hub/tip radius ratio compressor stage consisting of a 1500 ft/sec tip speed rotor, a variable camber inlet guide vane and a variable stagger stator was designed and tested with undistorted inlet flow, flow with tip radial distortion, and flow with 90 degrees, one-per-rev, circumferential distortion. At the design speed and design IGV and stator setting the design stage pressure ratio was achieved at a weight within 1% of the design flow. Analytical results on rotor tip shock structure, deviation angle and part-span shroud losses at different operating conditions are presented. The variable geometry blading enabled efficient operation with adequate stall margin at the design condition and at 70% speed. Closing the inlet guide vanes to 40 degrees changed the speed-versus-weight flow relationship along the stall line and thus provided the flexibility of operation at off-design conditions. Inlet flow distortion caused considerable losses in peak efficiency, efficiency on a constant throttle line through design pressure ratio at design speed, stall pressure ratio, and stall margin at the 0 degrees IGV setting and high rotative speeds. The use of the 40 degrees inlet guide vane setting enabled partial recovery of the stall margin over the standard constant throttle line
Pion and Quark Annihilation Mechanisms of Dilepton Production in Relativistic Heavy-Ion Collisions
We revise the pion-pion and quark-quark annihilation mechanisms of dilepton
production during relativistic heavy-ion collisions. We focus on the
modifications caused by the specific features of intramedium pion states rather
than by medium modification of the rho-meson spectral density. The main
ingredient emerging in our approach is a form-factor of the multi-pion
(multi-quark) system. Replacing the usual delta-function the form-factor plays
the role of distribution which, in some sense, "connects" the 4-momenta of the
annihilating and outgoing particles. The difference between the c.m.s.
velocities attributed to annihilating and outgoing particles is a particular
consequence of this replacement and results in the appearance of a new factor
in the formula for the dilepton production rate. We obtained that the
form-factor of the multi-pion (multi-quark) system causes broadening of the
rate which is most pronounced for small invariant masses, in particular, we
obtain a growth of the rate for the invariant masses below two masses of the
annihilating particles.Comment: 6 pages, 6 figures, LaTex; to appear in Mod. Phys. Lett.
Entanglement in the dispersive interaction of trapped ions with a quantized field
The mode-mode entanglement between trapped ions and cavity fields is
investigated in the dispersive regime. We show how a simple initial preparation
of Gaussian coherent states and a postselection may be used to generate
motional non-local mesoscopic states (NLMS) involving ions in different traps.
We also present a study of the entanglement induced by dynamical Stark-shifts
considering a cluster of N-trapped ions. In this case, all entanglement is due
to the dependence of the Stark-shifts on the ions' state of motion manifested
as a cross-Kerr interaction between each ion and the field.Comment: 10 pages, 5 figures, corrected typo
Nonplanar integrability at two loops
In this article we compute the action of the two loop dilatation operator on
restricted Schur polynomials that belong to the su(2) sector, in the displaced
corners approximation. In this non-planar large N limit, operators that
diagonalize the one loop dilatation operator are not corrected at two loops.
The resulting spectrum of anomalous dimensions is related to a set of decoupled
harmonic oscillators, indicating integrability in this sector of the theory at
two loops. The anomalous dimensions are a non-trivial function of the 't Hooft
coupling, with a spectrum that is continuous and starting at zero at large N,
but discrete at finite N.Comment: version to appear in JHE
Probing the mechanical unzipping of DNA
A study of the micromechanical unzipping of DNA in the framework of the
Peyrard-Bishop-Dauxois model is presented. We introduce a Monte Carlo technique
that allows accurate determination of the dependence of the unzipping forces on
unzipping speed and temperature. Our findings agree quantitatively with
experimental results for homogeneous DNA, and for -phage DNA we
reproduce the recently obtained experimental force-temperature phase diagram.
Finally, we argue that there may be fundamental differences between {\em in
vivo} and {\em in vitro} DNA unzipping
The luminosity function of Palomar 5 and its tidal tails
We present the main sequence luminosity function of the tidally disrupted
globular cluster Palomar 5 and its tidal tails. For this work we analyzed
imaging data obtained with the Wide Field Camera at the INT (La Palma) and data
from the Wide Field Imager at the MPG/ESO 2.2 m telescope at La Silla down to a
limiting magnitude of approximately 24.5 mag in B. Our results indicate that
preferentially fainter stars were removed from the cluster so that the LF of
the cluster's main body exhibits a significant degree of flattening compared to
other GCs. This is attributed to its advanced dynamical evolution. The LF of
the tails is, in turn, enhanced with faint, low-mass stars, which we interpret
as a consequence of mass segregation in the cluster.Comment: 4 pages, 3 figures, to be published in the proceedings of the
conference "Satellites and tidal streams" held at La Palma, Canary Islands,
May 26 - 30, 200
Self consistent kinetic simulations of SPT and HEMP thrusters including the near-field plume region
The Particle-in-Cell (PIC) method was used to study two different ion
thruster concepts - Stationary Plasma Thrusters (SPT) and High Efficiency
Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in
the discharge chamber due to the different magnetic field configurations.
Special attention was paid to the simulation of plasma particle fluxes on the
thrusters channel surfaces. In both cases, PIC proved itself as a powerful
tool, delivering important insight into the basic physics of the different
thruster concepts. The simulations demonstrated that the new HEMP thruster
concept allows for a high thermal efficiency due to both minimal energy
dissipation and high acceleration efficiency. In the HEMP thruster the plasma
contact to the wall is limited only to very small areas of the magnetic field
cusps, which results in much smaller ion energy flux to the thruster channel
surface as compared to SPT. The erosion yields for dielectric discharge channel
walls of SPT and HEMP thrusters were calculated with the binary collision code
SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material
per hour was observed. For HEMP, thruster simulations have shown that there is
no erosion inside the dielectric discharge channel.Comment: 14 pages, 11 figures This work was presented at 21st International
Conference on Numerical Simulation of Plasmas (ICNSP'09
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