55 research outputs found
Spacelab 3 Mission Science Review
Papers and abstracts of the presentations made at the symposium are given as the scientific report for the Spacelab 3 mission. Spacelab 3, the second flight of the National Aeronautics and Space Administration's (NASA) orbital laboratory, signified a new era of research in space. The primary objective of the mission was to conduct applications, science, and technology experiments requiring the low-gravity environment of Earth orbit and stable vehicle attitude over an extended period (e.g., 6 days) with emphasis on materials processing. The mission was launched on April 29, 1985, aboard the Space Shuttle Challenger which landed a week later on May 6. The multidisciplinary payload included 15 investigations in five scientific fields: material science, fluid dynamics, life sciences, astrophysics, and atmospheric science
A Proposed Hypothetical Exploration Mission in the Flamsteed Crater Region of the Moon
A hypothetical 14-day lunar surface mission is proposed for two astronauts to investigate the lunar terrain and larger features about a preselected landing site. Because the Surveyor I spacecraft soft-landed in the Flamsteed Crater region and demonstrated that an unmanned- spacecraft can safely land in this particular area, this site will , for purposes of this paper, be considered a suitable site in which to carry out a proposed scientific exploration mission.By Otha H. Vaughan, Jr.Abstract -- Summary -- Introduction -- Objectives -- Supporting Equipment -- Guidelines and Constraints -- Mission Profile -- Time Line Analysis -- Concluding Remarks
Nonlinear quantum model for atomic Josephson junctions with one and two bosonic species
We study atomic Josephson junctions (AJJs) with one and two bosonic species
confined by a double-well potential. Proceeding from the second quantized
Hamiltonian, we show that it is possible to describe the zero-temperature AJJs
microscopic dynamics by means of extended Bose-Hubbard (EBH) models, which
include usually-neglected nonlinear terms. Within the mean-field approximation,
the Heisenberg equations derived from such two-mode models provide a
description of AJJs macroscopic dynamics in terms of ordinary differential
equations (ODEs). We discuss the possibility to distinguish the Rabi,
Josephson, and Fock regimes, in terms of the macroscopic parameters which
appear in the EBH Hamiltonians and, then, in the ODEs. We compare the
predictions for the relative populations of the Bose gases atoms in the two
wells obtained from the numerical solutions of the two-mode ODEs, with those
deriving from the direct numerical integration of the Gross-Pitaevskii
equations (GPEs). Our investigations shows that the nonlinear terms of the ODEs
are crucial to achieve a good agreement between ODEs and GPEs approaches, and
in particular to give quantitative predictions of the self-trapping regime.Comment: Accepted for the publication in J. Phys. B: At. Mol. Opt. Phy
Finite-Size Studies on the SO(5) Symmetry of the Hubbard Model
We present numerical evidence for the approximate SO(5) symmetry of the
Hubbard model on a 10 site cluster. Various dynamic correlation functions
involving the operators, the generators of the SO(5) algebra, are studied
using exact diagonalisation, and are found to possess sharp collective peaks.
Our numerical results also lend support on the interpretation of the recent
resonant neutron scattering peaks in the YBCO superconductors in terms of the
Goldstone modes of the spontaneously broken SO(5) symmetry.Comment: 4 pages, Rev-Tex, includes 2 eps figure
Atomic Josephson junction with two bosonic species
We study an atomic Josephson junction (AJJ) in presence of two interacting
Bose-Einstein condensates (BECs) confined in a double well trap. We assume that
bosons of different species interact with each other. The macroscopic wave
functions of the two components obey to a system of two 3D coupled
Gross-Pitaevskii equations (GPE). We write the Lagrangian of the system, and
from this we derive a system of coupled ordinary differential equations (ODE),
for which the coupled pendula represent the mechanic analogous. These
differential equations control the dynamical behavior of the fractional
imbalance and of the relative phase of each bosonic component. We perform the
stability analysis around the points which preserve the symmetry and get an
analytical formula for the oscillation frequency around the stable points. Such
a formula could be used as an indirect measure of the inter-species s-wave
scattering length. We also study the oscillations of each fractional imbalance
around zero and non zero - the macroscopic quantum self-trapping (MQST) - time
averaged values. For different values of the inter-species interaction
amplitude, we carry out this study both by directly solving the two GPE and by
solving the corresponding coupled pendula equations. We show that, under
certain conditions, the predictions of these two approaches are in good
agreement. Moreover, we calculate the crossover value of the inter-species
interaction amplitude which signs the onset of MQST.Comment: Accepted for the publication in J. Phys. B: At. Mol. Opt. Phy
Transiting exoplanets from the CoRoT space mission III. The spectroscopic transit of CoRoT-Exo-2b with SOPHIE and HARPS
We report on the spectroscopic transit of the massive hot-Jupiter
CoRoT-Exo-2b observed with the high-precision spectrographs SOPHIE and HARPS.
By modeling the radial velocity anomaly occurring during the transit due to the
Rossiter-McLaughlin (RM) effect, we determine the sky-projected angle between
the stellar spin and the planetary orbital axis to be close to zero
lambda=7.2+-4.5 deg, and we secure the planetary nature of CoRoT-Exo-2b. We
discuss the influence of the stellar activity on the RM modeling. Spectral
analysis of the parent star from HARPS spectra are presented.Comment: A&A Letters (in press), 5 pages, 2 figure
The pd <--> pi+ t reaction around the Delta resonance
The pd pi+ t process has been calculated in the energy region around the
Delta-resonance with elementary production/absorption mechanisms involving one
and two nucleons. The isobar degrees of freedom have been explicitly included
in the two-nucleon mechanism via pi-- and rho-exchange diagrams. No free
parameters have been employed in the analysis since all the parameters have
been fixed in previous studies on the simpler pp pi+ d process. The
treatment of the few-nucleon dynamics entailed a Faddeev-based calculation of
the reaction, with continuum calculations for the initial p-d state and
accurate solutions of the three-nucleon bound-state equation. The integral
cross-section was found to be quite sensitive to the NN interaction employed
while the angular dependence showed less sensitivity. Approximately a 4% effect
was found for the one-body mechanism, for the three-nucleon dynamics in the p-d
channel, and for the inclusion of a large, possibly converged, number of
three-body partial states, indicating that these different aspects are of
comparable importance in the calculation of the spin-averaged observables.Comment: 40 Pages, RevTex, plus 5 PostScript figure
Phase Space Analysis of Quintessence Cosmologies with a Double Exponential Potential
We use phase space methods to investigate closed, flat, and open
Friedmann-Robertson-Walker cosmologies with a scalar potential given by the sum
of two exponential terms. The form of the potential is motivated by the
dimensional reduction of M-theory with non-trivial four-form flux on a
maximally symmetric internal space. To describe the asymptotic features of
run-away solutions we introduce the concept of a `quasi fixed point.' We give
the complete classification of solutions according to their late-time behavior
(accelerating, decelerating, crunch) and the number of periods of accelerated
expansion.Comment: 46 pages, 5 figures; v2: minor changes, references added; v3: title
changed, refined classification of solutions, 3 references added, version
which appeared in JCA
Population structure of the malaria vector Anopheles moucheti in the equatorial forest region of Africa
<p>Abstract</p> <p>Background</p> <p><it>Anopheles moucheti </it>is a major malaria vector in forested areas of Africa. However, despite its important epidemiological role, it remains poorly known and insufficiently studied. Here, levels of genetic differentiation were estimated between different <it>A. moucheti </it>populations sampled throughout its distribution range in Central Africa.</p> <p>Methods</p> <p>Polymorphism at ten microsatellite markers was compared in mosquitoes sampled in Cameroon, the Democratic Republic of Congo and an island on Lake Victoria in Uganda. Microsatellite data were used to estimate genetic diversity within populations, their relative long-term effective population size, and the level of genetic differentiation between them.</p> <p>Results</p> <p>All specimens collected in Tsakalakuku (Democratic Republic of Congo) were identified as <it>A. m. bervoetsi </it>while other samples consisted of <it>A. m. moucheti</it>. Successful amplification was obtained at all microsatellite loci within all <it>A. m. moucheti </it>samples while only six loci amplified in <it>A. m. bervoetsi</it>. Allelic richness and heterozygosity were high for all populations except the island population of Uganda and <it>A. m. bervoetsi</it>. High levels of genetic differentiation were recorded between <it>A. m. bervoetsi </it>and each <it>A. m. moucheti </it>sample as well as between the island population of <it>A. m. moucheti </it>and mainland populations. Significant isolation by distance was evidenced between mainland populations.</p> <p>Conclusion</p> <p>High levels of genetic differentiation supports complete speciation of <it>A. m. bervoetsi </it>which should henceforth be recognized as a full species and named <it>A. bervoetsi</it>. Isolation by distance is the main force driving differentiation between mainland populations of <it>A. m. moucheti</it>. Genetically and geographically isolated populations exist on Lake Victoria islands, which might serve as relevant field sites for evaluation of innovative vector control strategies.</p
- …