689 research outputs found
Perceived stress in HIV-infected individuals: Phsyiological and psychological correlates
The purpose of this study was to determine the correlation of perceived stress with selected physiological and psychological factors in an HIV-infected, predominantly African American population and to assess the multivariable effects on perceived stress. The variables that correlated significantly with perceived stress were entered into a backward stepwise regression model. Pearson’s r analysis showed significant correlations between perceived stress and state and trait anxiety, depression, HIV-related symptoms, sleep quality, daytime sleepiness and fatigue. State and trait anxiety, depression and fatigue retained significance (p\u3c0.1) in the final regression model. These factors explained approximately 80% of the variance in perceived stress. The significant interactions of multiple physiological and psychological correlates suggest that perceived stress is a complex outcome with a multifactorial etiology. Further, the model suggests that psychological factors may contribute to perceived stress in this population more than physiological factors such as HIV-related symptomatology or stage of disease
Focusing Vacuum Fluctuations II
The quantization of the scalar and electromagnetic fields in the presence of
a parabolic mirror is further developed in the context of a geometric optics
approximation. We extend results in a previous paper to more general
geometries, and also correct an error in one section of that paper. We
calculate the mean squared scalar and electric fields near the focal line of a
parabolic cylindrical mirror. These quantities are found to grow as inverse
powers of the distance from the focus. We give a combination of analytic and
numerical results for the mean squared fields. In particular, we find that the
mean squared electric field can be either negative or positive, depending upon
the choice of parameters. The case of a negative mean squared electric field
corresponds to a repulsive Van der Waals force on an atom near the focus, and
to a region of negative energy density. Similarly, a positive value corresponds
to an attractive force and a possibility of atom trapping in the vicinity of
the focus.Comment: 26 pages, 15 figures; additional discussion added in Sects. IV and I
Diffraction of a released bose-einstein condensate by a pulsed standing light wave
We study the diffraction of a released sodium Bose-Einstein condensate by a pulsed standing light wave. The width of the momentum distribution of the diffracted atoms exhibits strong oscillations as a function of the pulse duration, corresponding to periodic focusing and collimation of the condensate inside the standing light wave. Applications of this thick grating regime of diffraction to atom interferometry are discussed
Loading of a Rb magneto-optic trap from a getter source
We study the properties of a Rb magneto-optic trap loaded from a commercial
getter source which provides a large flux of atoms for the trap along with the
capability of rapid turn-off necessary for obtaining long trap lifetimes. We
have studied the trap loading at two different values of background pressure to
determine the cross-section for Rb--N collisions to be 3.5(4)x10^{-14} cm^2
and that for Rb--Rb collisions to be of order 3x10^{-13} cm^2. At a background
pressure of 1.3x10^{-9} torr, we load more than 10^8 atoms into the trap with a
time constant of 3.3 s. The 1/e lifetime of trapped atoms is 13 s limited only
by background collisions.Comment: 5 pages, 5 figure
Chiral Supergravitons Interacting with a 0-Brane N-Extended NSR Super-Virasoro Group
We continue the development of the actions, S_{AFF}, by examining the cases
where there are N fermionic degrees of freedom associated with a 0-brane. These
actions correspond to the interaction of the N-extended super Virasoro algebra
with the supergraviton and the associated SO(N) gauge field that accompanies
the supermultiplet. The superfield formalism is used throughout so that
supersymmetry is explicit.Comment: PACS: 04.65.+e, 11.15.-q, 11.25.-w, 12.60.
Focusing Vacuum Fluctuations
The focusing of the vacuum modes of a quantized field by a parabolic mirror
is investigated. We use a geometric optics approximation to calculate the
energy density and mean squared field averages for scalar and electromagnetic
fields near the focus. We find that these quantities grow as an inverse power
of the distance to the focus. There is an attractive Casimir-Polder force on an
atom which will draw it into the focus. Some estimates of the magnitude of the
effects of this focusing indicate that it may be observable.Comment: 20 pages, 4 figures; typos corrected, two refs and some comments
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An ansatz for the nonlinear Demkov-Kunike problem for cold molecule formation
We study nonlinear mean-field dynamics of ultracold molecule formation in the
case when the external field configuration is defined by the level-crossing
Demkov-Kunike model, characterized by a bell-shaped coupling and finite
variation of the detuning. Analyzing the fast sweep rate regime of the strong
interaction limit, which models a situation when the peak value of the coupling
is large enough and the resonance crossing is sufficiently fast, we construct a
highly accurate ansatz to describe the temporal dynamics of the molecule
formation in the mentioned interaction regime. The absolute error of the
constructed approximation is less than 3*10^-6 for the final transition
probability while at certain time points it might increase up to 10^-3.
Examining the role of the different terms in the constructed approximation, we
prove that in the fast sweep rate regime of the strong interaction limit the
temporal dynamics of the atom-molecule conversion effectively consists of the
process of resonance crossing, which is governed by a nonlinear equation,
followed by atom-molecular coherent oscillations which are basically described
by a solution of the linear problem, associated with the considered nonlinear
one.Comment: Accepted for publication in J. Contemp. Phys. (Armenian National
Academy of Sciences) 8 pages, 4 figure
Evaporative cooling of trapped fermionic atoms
We propose an efficient mechanism for the evaporative cooling of trapped
fermions directly into quantum degeneracy. Our idea is based on an electric
field induced elastic interaction between trapped atoms in spin symmetric
states. We discuss some novel general features of fermionic evaporative cooling
and present numerical studies demonstrating the feasibility for the cooling of
alkali metal fermionic species Li, K, and Rb. We also
discuss the sympathetic cooling of fermionic hyperfine spin mixtures, including
the effects of anisotropic interactions.Comment: to be publishe
Quantum Limits of Stochastic Cooling of a Bosonic Gas
The quantum limits of stochastic cooling of trapped atoms are studied. The
energy subtraction due to the applied feedback is shown to contain an
additional noise term due to atom-number fluctuations in the feedback region.
This novel effect is shown to dominate the cooling efficiency near the
condensation point. Furthermore, we show first results that indicate that
Bose--Einstein condensation could be reached via stochastic cooling.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Atom capture by nanotube and scaling anomaly
The existence of bound state of the polarizable neutral atom in the inverse
square potential created by the electric field of single walled charged carbon
nanotube (SWNT) is shown to be theoretically possible. The consideration of
inequivalent boundary conditions due to self-adjoint extensions lead to this
nontrivial bound state solution. It is also shown that the scaling anomaly is
responsible for the existence of bound state. Binding of the polarizable atoms
in the coupling constant interval \eta^2\in[0,1) may be responsible for the
smearing of the edge of steps in quantized conductance, which has not been
considered so far in literature.Comment: Accepted in Int.J.Theor.Phy
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