548 research outputs found
Design of Semi-active Magnetorheological Valve with Non-magnetic Bypass
The paper presents a methodology of designof a semi-active magnetorheological (MR) valve. Themethodology was composed of the non-Newtonian fluid flowanalysis and FEM analysis of a magnetic circuit. Based onthe present methodology a MR valve was designed. The MRvalve achieves damping force 1600 N at a velocity of 0.15m/s. The time response was determined to 6 ms
First 10 kg of Naked Germanium Detectors in Liquid Nitrogen installed in the GENIUS-Test-Facility
The first four naked high purity Germanium detectors were installed
successfully in liquid nitrogen in the GENIUS-Test-Facility (GENIUS-TF) in the
GRAN SASSO Underground Laboratory on May 5, 2003. This is the first time ever
that this novel technique aiming at extreme background reduction in search for
rare decays is going to be tested underground. First operational parameters are
presented.Comment: 10 pages, latex2e, 8 figures, Was presented (first presentation) at
4th International Conference on Particle Physics Beyond the Standard Model
BEYOND'2003, Castle Ringberg, Germany, 9-14 June, 2003, Springer, Heidelberg,
Germany, 2003, edited by H.V. Klapdor-Kleingrothau
New Directions in Degenerate Dipolar Molecules via Collective Association
We survey results on the creation of heteronuclear Fermi molecules by tuning
a degenerate Bose-Fermi mixture into the neighborhood of an association
resonance, either photoassociation or Feshbach, as well as the subsequent
prospects for Cooper-like pairing between atoms and molecules. In the simplest
case of only one molecular state, corresponding to either a Feshbach resonance
or one-color photoassociation, the system displays Rabi oscillations and rapid
adiabatic passage between a Bose-Fermi mixture of atoms and fermionic
molecules. For two-color photoassociation, the system admits stimulated Raman
adiabatic passage (STIRAP) from a Bose-Fermi mixture of atoms to stable Fermi
molecules, even in the presence of particle-particle interactions. By tailoring
the STIRAP sequence it is possible to deliberately convert only a fraction of
the initial atoms, leaving a finite fraction of bosons behind to induce
atom-molecule Cooper pairing via density fluctuations; unfortunately, this
enhancement is insufficient to achieve a superfluid transition with present
ultracold technology. We therefore propose the use of an association resonance
that converts atoms and diatomic molecules (dimers) into triatomic molecules
(trimers), which leads to a crossover from a Bose-Einstein condensate of
trimers to atom-dimer Cooper pairs. Because heteronuclear dimers may possess a
permanent electric dipole moment, this overall system presents an opportunity
to investigate novel microscopic physics.Comment: 10 pages, 5 figures, 77+ references, submitted to Euro. Phys. J.
topical issue on "Ultracold Polar Molecules: Formation and Collisions
Tremendous bleeding complication after vacuum-assisted sternal closure
Vacuum-assisted closure (VAC) of complex infected wounds has recently gained popularity among various surgical specialties. The system is based on the application of negative pressure by controlled suction to the wound surface. The effectiveness of the VAC System on microcirculation and the promotion of granulation tissue proliferation are proved. No contraindications for the use in deep sternal wounds in cardiac surgery are described. In our case report we illustrate a scenario were a patient developed severe bleeding from the ascending aorta by penetration of wire fragments in the vessel. We conclude that all free particles in the sternum have to be removed completely before negative pressure is used
Dynamics of positive- and negative-mass solitons in optical lattices and inverted traps
We study the dynamics of one-dimensional solitons in the attractive and
repulsive Bose-Einstein condensates (BECs) loaded into an optical lattice (OL),
which is combined with an external parabolic potential. First, we demonstrate
analytically that, in the repulsive BEC, where the soliton is of the gap type,
its effective mass is \emph{negative}. This gives rise to a prediction for the
experiment: such a soliton cannot be not held by the usual parabolic trap, but
it can be captured (performing harmonic oscillations) by an anti-trapping
inverted parabolic potential. We also study the motion of the soliton a in long
system, concluding that, in the cases of both the positive and negative mass,
it moves freely, provided that its amplitude is below a certain critical value;
above it, the soliton's velocity decreases due to the interaction with the OL.
At a late stage, the damped motion becomes chaotic. We also investigate the
evolution of a two-soliton pulse in the attractive model. The pulse generates a
persistent breather, if its amplitude is not too large; otherwise, fusion into
a single fundamental soliton takes place. Collisions between two solitons
captured in the parabolic trap or anti-trap are considered too. Depending on
their amplitudes and phase difference, the solitons either perform stable
oscillations, colliding indefinitely many times, or merge into a single
soliton. Effects reported in this work for BECs can also be formulated for
optical solitons in nonlinear photonic crystals. In particular, the capture of
the negative-mass soliton in the anti-trap implies that a bright optical
soliton in a self-defocusing medium with a periodic structure of the refractive
index may be stable in an anti-waveguide.Comment: 22pages, 9 figures, submitted to Journal of Physics
Stability of dark solitons in a Bose-Einstein condensate trapped in an optical lattice
We investigate the stability of dark solitons (DSs) in an effectively
one-dimensional Bose-Einstein condensate in the presence of the magnetic
parabolic trap and an optical lattice (OL). The analysis is based on both the
full Gross-Pitaevskii equation and its tight-binding approximation counterpart
(discrete nonlinear Schr{\"o}dinger equation). We find that DSs are subject to
weak instabilities with an onset of instability mainly governed by the period
and amplitude of the OL. The instability, if present, sets in at large times
and it is characterized by quasi-periodic oscillations of the DS about the
minimum of the parabolic trap.Comment: Typo fixed in Eq. (1): cos^2 -> sin^
New limits on dark--matter WIMPs from the Heidelberg--Moscow experiment
New results after 0.69 kg yr of measurement with an enriched 76Ge detector of
the Heidelberg--Moscow experiment with an active mass of 2.758 kg are
presented. An energy threshold of 9 keV and a background level of 0.042
counts/(kg d keV) in the energy region between 15 keV and 40 keV was
reached.The derived limits on the WIMP--nucleon cross section are the most
stringent limits on spin--independent interactions obtained to date by using
essentially raw data without background subtraction.Comment: 8 pages (latex) including 5 postscript figures and 2 tables. To
appear in Phys. Rev. D, 15. December 199
Vortices in a Bose-Einstein condensate confined by an optical lattice
We investigate the dynamics of vortices in repulsive Bose-Einstein
condensates in the presence of an optical lattice (OL) and a parabolic magnetic
trap. The dynamics is sensitive to the phase of the OL potential relative to
the magnetic trap, and depends less on the OL strength. For the cosinusoidal OL
potential, a local minimum is generated at the trap's center, creating a stable
equilibrium for the vortex, while in the case of the sinusoidal potential, the
vortex is expelled from the center, demonstrating spiral motion. Cases where
the vortex is created far from the trap's center are also studied, revealing
slow outward-spiraling drift. Numerical results are explained in an analytical
form by means of a variational approximation. Finally, motivated by a discrete
model (which is tantamount to the case of the strong OL lattice), we present a
novel type of vortex consisting of two pairs of anti-phase solitons.Comment: 10 pages, 6 figure
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