12 research outputs found
Phase Fluctuations in Bose-Einstein Condensates
We demonstrate the existence of phase fluctuations in elongated Bose-Einstein
Condensates (BECs) and study the dependence of those fluctuations on the system
parameters. A strong dependence on temperature, atom number, and trapping
geometry is observed. Phase fluctuations directly affect the coherence
properties of BECs. In particular, we observe instances where the phase
coherence length is significantly smaller than the condensate size. Our method
of detecting phase fluctuations is based on their transformation into density
modulations after ballistic expansion. An analytic theory describing this
transformation is developed.Comment: 11 pages, 7 figure
Observation of Phase Fluctuations in Bose-Einstein Condensates
The occurrence of phase fluctuations due to thermal excitations in
Bose-Einstein condensates (BECs) is studied for a variety of temperatures and
trap geometries. We observe the statistical nature of the appearence of phase
fluctuations and characterize the dependence of their average value on
temperature, number of particles and the trapping potential. We find pronounced
phase fluctuations for condensates in very elongated traps in a broad
temperature range. The results are of great importance for the realization of
BEC in quasi 1D geometries, for matter wave interferometry with BECs, as well
as for coherence properties of guided atom laser beams.Comment: 4 pages, 4 figure
Reflection of thermal atoms by a pulsed standing wave
Reflection of thermal atoms by a pulsed standing wave
with a duration in the nanosecond range is studied. The momentum
distribution of the reflected atoms is determined by calculations
based on the adiabatic atom-photon interactions. It is shown that
with a proper choice of the field intensity and the pulse duration the
standing-wave pattern functions as a row of independent atom
mirrors. At an optimum choice of the parameter values, the fraction of
the elastically reflected atoms is more than 20% . Furthermore, we
show that the pulsed standing-wave mirror can be used to manipulate their final momentum distribution.
When using laser pulses with an intensity of several tens of
MW/cm2, tens of thousands of atoms can be reflected by a single
laser pulse
Reflection of atoms from a pulsed evanescent wave
Atomic motion in a pulsed evanescent wave, with a pulse duration on
the order of the lifetime of the excited state, is calculated using
the semiclassical Bloch-equation approach. The equations for the
internal atomic motion are solved using two approximations based on
high laser intensity and on slow atomic velocity. The center-of-mass
motion in the field under the effect of the dipole force is
subsequently determined by numerical integration. As an example, the
calculations show that the maximum normally incident velocity allowing
a sodium atom to be reflected is approximately 35 m/s when using a
laser pulse of 7 ns duration. Our results also
demonstrate that the velocity distribution of the reflected atoms may
considerably differ from the distribution of the incident atoms due to
different deceleration and acceleration times in a short laser
pulse. This effect may lead to an average slowing-down of the
reflected part of a thermal particle beam
Pulsed standing wave deflection of sodium atoms
We study the deflection of sodium atoms by a resonantly tuned pulsed
standing wave of high field intensity. The effects of the phase
fluctuations of the pulsed laser field on the momentum distribution of
the deflected atoms are experimentally determined. The results are
explained using a theoretical model based on the generalized density
matrix formalism of two-level atoms
Observation of phase fluctuations in elongated bose-einstein condensates
The occurrence of phase fluctuations due to thermal excitations in Bose-Einstein condensates (BECs) is studied for a variety of temperatures and trap geometries. We observe the statistical nature of the appearance of phase fluctuations and characterize the dependence of their average value on temperature, number of particles, and the trapping potential. We find pronounced phase fluctuations for condensates in very elongated traps in a broad temperature range. The results are of great importance for the realization of BEC in quasi-1D geometries, for matter wave interferometry with BECs, as well as for coherence properties of guided atom laser beams. © 2001 American Physical Society
Fatigue and health-related quality of life depend on the disability status and clinical course in RRMS
Abstract
Background: Fatigue is a prominent and disabling symptom of multiple sclerosis (MS), impairing quality of life. The disease course of relapsing remitting MS (RRMS) is individual.
Objectives: We aimed to study the effects of demographic and clinical characteristics, as well as lifestyle risk factors on experienced fatigue and health-related quality of life (HRQoL) among RRMS patients, comparing benign and severe disease types.
Methods: Altogether 198 Finnish RRMS patients were recruited for this real-life cross-sectional study. Self-reported questionnaires were used to evaluate fatigue and HRQoL by using Fatigue Scale for Motor and Cognitive Functions and 15D health-related quality of life questionnaires. Patients were categorized into subgroups based on the current disability status measured by the Expanded Disability Status Scale (EDSS) cut-off value of 4.5, and by retrospective clinical course divided into benign and aggressive RRMS.
Results: All in all, 73% of the RRMS patients suffered from fatigue. Lower HRQoL had a strong correlation with more prominent fatigue (r = -0.719). Higher EDSS was associated with more prominent fatigue and lower HRQoL in the whole RRMS cohort. Older age at the disease onset was associated with more prominent fatigue and decreased HRQoL in the groups of aggressive RRMS and EDSS > 4.5. In the groups of EDSS ≤ 4.5 and benign RRMS, a higher number of used disease-modifying treatments (DMTs) was associated with more pronounced fatigue and reduced HRQoL. In addition, higher BMI was associated with lower HRQoL in patients with benign RRMS. Side effects (45 %) and lack of efficacy (26 %) were the most common reasons for discontinuing a DMT. Cessation due to side effects was the only reason that was significantly associated with more prominent fatigue and lower HRQoL. Use of nicotine products, gender, or disease duration were not associated with fatigue or HRQoL.
Conclusions: Individuals with severe RRMS and higher EDSS scores are more prone to experience fatigue and lower HRQoL. In addition, fatigue and lower HRQoL are more commonly observed among RRMS patients with older age at disease onset and in those with multiple DMT switches