773 research outputs found
Induction of morphological aberrations by enzyme inhibition in Drosophila melanogaster
Zusatz zum Futter vonDrosophila melanogaster von 5-Fluoro-2-deoxyuridin oder Aminopterin induziert überzählige Skutellar- und Dorsozentralborsten sowie gekerbte Flügel. Diese Modifikationen wurden als Konsequenz von Enzymhemmung interpretiert
Gapless finite- theory of collective modes of a trapped gas
We present predictions for the frequencies of collective modes of trapped
Bose-condensed Rb atoms at finite temperature. Our treatment includes a
self-consistent treatment of the mean-field from finite- excitations and the
anomolous average. This is the first gapless calculation of this type for a
trapped Bose-Einstein condensed gas. The corrections quantitatively account for
the downward shift in the excitation frequencies observed in recent
experiments as the critical temperature is approached.Comment: 4 pages Latex and 2 postscript figure
Crying Without Tears:Dimensions of Crying and Relations With Ocular Dryness and Mental Well-Being in Patients With Sjogren's Syndrome
This study examined dimensions of crying and its relations with ocular dryness and mental well-being in patients with Sjogren's syndrome, a systemic autoimmune disease with dryness as primary symptom. Three-hundred patients with Sjogren's syndrome completed questionnaires on crying, dryness, and well-being. The crying questionnaire revealed four dimensions: "Cryability" (comprising both crying sensibility and ability to cry), Somatic consequences, Frustration, and Suppression. Compared to 100 demographically-matched control participants from the general population, patients scored low on Cryability and high on Somatic consequences and Frustration. The crying dimensions generally showed significant but weak associations with ocular dryness and mental well-being in patients. This is the first quantitative study indicating that crying problems are more common in patients with Sjogren's syndrome than in the general population. Perhaps, patients who experience problems with crying could be helped to rely on other ways of expressing emotions than crying in tear-inducing situations.</p
Thermodynamic properties of confined interacting Bose gases - a renormalization group approach
A renormalization group method is developed with which thermodynamic
properties of a weakly interacting, confined Bose gas can be investigated.
Thereby effects originating from a confining potential are taken into account
by periodic boundary conditions and by treating the resulting discrete energy
levels of the confined degrees of freedom properly. The resulting density of
states modifies the flow equations of the renormalization group in momentum
space. It is shown that as soon as the characteristic length of confinement
becomes comparable to the thermal wave length of a weakly interacting and
trapped Bose gas its thermodynamic properties are changed significantly. This
is exemplified by investigating characteristic bunching properties of the
interacting Bose gas which manifest themselves in the second order coherence
factor
The Energy of a Trapped Interacting Bose Gas
A Bose gas in an external potential is studied by means of the semi-classical
approximation. Analytical results are derived for the energy of an interacting
Bose gas in a generic power-law trapping potential. An expression for the
chemical potential below the critical temperature is also obtained. The
theoretical results are in qualitative agreement with a recent energy
measurement.Comment: 6 pages, REVTex, one figure
Single-collision scattering of keV-energy Kr ions off a polycrystalline Cu surface
In the keV-energy regime, the scattering of krypton ions off a copper sample has been studied. In addition to the broad energy spectrum arising from multiple-collision scattering, the energy distributions of the backscattered ions exhibit prominent peaks at energies where single-collision (SC) scattering peaks are expected. Such SC peaks were shown to be absent in Sn – Mo/Ru scattering, systems of similar mass ratio and thus similar kinetics. The present Kr on Cu results allow for a comparison to a simulation package as SRIM. An important difference found between the present experiment and the predictions of SRIM is that the SC contribution is observed to decrease with scattering angle, whereas SRIM predicts this contribution to be constant. The intensity of the experimental SC peaks, though much weaker than in the SRIM simulations, may be used as markers to improve SRIM in its description of low-energy heavy particle scattering off surfaces
Kinetic Theory of Collective Excitations and Damping in Bose-Einstein Condensed Gases
We calculate the frequencies and damping rates of the low-lying collective
modes of a Bose-Einstein condensed gas at nonzero temperature. We use a complex
nonlinear Schr\"odinger equation to determine the dynamics of the condensate
atoms, and couple it to a Boltzmann equation for the noncondensate atoms. In
this manner we take into account both collisions between
noncondensate-noncondensate and condensate-noncondensate atoms. We solve the
linear response of these equations, using a time-dependent gaussian trial
function for the condensate wave function and a truncated power expansion for
the deviation function of the thermal cloud. As a result, our calculation turns
out to be characterized by two dimensionless parameters proportional to the
noncondensate-noncondensate and condensate-noncondensate mean collision times.
We find in general quite good agreement with experiment, both for the
frequencies and damping of the collective modes.Comment: 10 pages, 8 figure
Condensate growth in trapped Bose gases
We study the dynamics of condensate formation in an inhomogeneous trapped
Bose gas with a positive interatomic scattering length. We take into account
both the nonequilibrium kinetics of the thermal cloud and the Hartree-Fock
mean-field effects in the condensed and the noncondensed parts of the gas. Our
growth equations are solved numerically by assuming that the thermal component
behaves ergodically and that the condensate, treated within the Thomas-Fermi
approximation, grows adiabatically. Our simulations are in good qualitative
agreement with experiment, however important discrepancies concerning details
of the growth behaviour remain.Comment: 28 pages, 11 figures. Changes made to the introduction, Sec. VI, Sec.
VII, and included additional growth curves in Fig. 1
Collisionless modes of a trapped Bose gas
We calculate the excitation frequencies of the m=0 monopole and m=2
quadrupole modes in the collisionless regime by solving a non-linear
Schroedinger equation for the condensate, coupled to a collisionless Boltzmann
equation for the quasiparticles. Since the dynamics of the noncondensate cloud
is also taken into account, the theory satisfies the Kohn theorem. The spectrum
turns out to be strongly temperature dependent and we compare our results with
experiment.Comment: 6 pages of LaTeX and 1 postscript figure. Contribution to the meeting
`New directions in atomic phycics' held in Cambridge this mont
Quadrupole collective modes in trapped finite-temperature Bose-Einstein condensates
Finite temperature simulations are used to study quadrupole excitations of a
trapped Bose-Einstein condensate. We focus specifically on the m=0 mode, where
a long-standing theoretical problem has been to account for an anomalous
variation of the mode frequency with temperature. We explain this behavior in
terms of the excitation of two separate modes, corresponding to coupled motion
of the condensate and thermal cloud. The relative amplitudes of the modes
depends sensitively on the temperature and on the frequency of the harmonic
drive used to excite them. Good agreement with experiment is found for
appropriate drive frequencies.Comment: 4 pages, 3 figure
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