8,015 research outputs found
Development of a general purpose airborne simulator
Variable stability system development for General Purpose Airborne Simulator /GPAS
Demonstration of an inductively coupled ring trap for cold atoms
We report the first demonstration of an inductively coupled magnetic ring trap for cold atoms. A uniform, ac magnetic field is used to induce current in a copper ring, which creates an opposing magnetic field that is time-averaged to produce a smooth cylindrically symmetric ring trap of radius 5 mm. We use a laser-cooled atomic sample to characterize the loading efficiency and adiabaticity of the magnetic potential, achieving a vacuum-limited lifetime in the trap. This technique is suitable for creating scalable toroidal waveguides for applications in matter-wave interferometry, offering long interaction times and large enclosed areas
Environmental factors influence both abundance and genetic diversity in a widespread bird species.
Genetic diversity is one of the key evolutionary variables that correlate with population size, being of critical importance for population viability and the persistence of species. Genetic diversity can also have important ecological consequences within populations, and in turn, ecological factors may drive patterns of genetic diversity. However, the relationship between the genetic diversity of a population and how this interacts with ecological processes has so far only been investigated in a few studies. Here, we investigate the link between ecological factors, local population size, and allelic diversity, using a field study of a common bird species, the house sparrow (Passer domesticus). We studied sparrows outside the breeding season in a confined small valley dominated by dispersed farms and small-scale agriculture in southern France. Population surveys at 36 locations revealed that sparrows were more abundant in locations with high food availability. We then captured and genotyped 891 house sparrows at 10 microsatellite loci from a subset of these locations (N = 12). Population genetic analyses revealed weak genetic structure, where each locality represented a distinct substructure within the study area. We found that food availability was the main factor among others tested to influence the genetic structure between locations. These results suggest that ecological factors can have strong impacts on both population size per se and intrapopulation genetic variation even at a small scale. On a more general level, our data indicate that a patchy environment and low dispersal rate can result in fine-scale patterns of genetic diversity. Given the importance of genetic diversity for population viability, combining ecological and genetic data can help to identify factors limiting population size and determine the conservation potential of populations
Demonstration of a Quantum Gate using Electromagnetically Induced Transparency
We demonstrate a native gate between two individually
addressed neutral atoms based on electromagnetically induced transparency
(EIT). This protocol utilizes the strong long-range interactions of Rydberg
states to enable conditional state transfer on the target qubit when operated
in the blockade regime. An advantage of this scheme is it enables
implementation of multi-qubit CNOT gates using a pulse sequence independent
of qubit number, and provides an simple gate for efficient implementation of
quantum algorithms and error correction. We achieve a loss corrected gate
fidelity of , and prepare an
entangled Bell-state with ,
limited at present by laser power. We present a number of technical
improvements to advance this to a level required for fault-tolerant scaling.Comment: 6 pages, 5 figures plus Supplementary Materia
Optically-induced lensing effect on a Bose-Einstein condensate expanding in a moving lattice
We report the experimental observation of a lensing effect on a Bose-Einstein
condensate expanding in a moving 1D optical lattice. The effect of the periodic
potential can be described by an effective mass dependent on the condensate
quasi-momentum. By changing the velocity of the atoms in the frame of the
optical lattice we induce a focusing of the condensate along the lattice
direction. The experimental results are compared with the numerical predictions
of an effective 1D theoretical model. Besides, a precise band spectroscopy of
the system is carried out by looking at the real-space propagation of the
atomic wavepacket in the optical lattice.Comment: 5 pages, 4 figures; minor changes applied and typos corrected; a new
paragraph added; some references updated; journal reference adde
Stellar black holes at the dawn of the universe
It is well established that between 380000 and 1 billion years after the Big
Bang the Inter Galactic Medium (IGM) underwent a "phase transformation" from
cold and fully neutral to warm (~10^4 K) and ionized. Whether this phase
transformation was fully driven and completed by photoionization by young hot
stars is a question of topical interest in cosmology. AIMS. We propose here
that besides the ultraviolet radiation from massive stars, feedback from
accreting black holes in high-mass X-ray binaries (BH-HMXBs) was an additional,
important source of heating and reionization of the IGM in regions of low gas
density at large distances from star-forming galaxies. METHODS. We use current
theoretical models on the formation and evolution of primitive massive stars of
low metallicity, and the observations of compact stellar remnants in the near
and distant universe, to infer that a significant fraction of the first
generations of massive stars end up as BH-HMXBs. The total number of energetic
ionizing photons from an accreting stellar black hole in an HMXB is comparable
to the total number of ionizing photons of its progenitor star. However, the
X-ray photons emitted by the accreting black hole are capable of producing
several secondary ionizations and the ionizing power of the resulting black
hole could be greater than that of its progenitor. Feedback by the large
populations of BH-HMXBs heats the IGM to temperatures of ~10^4 K and maintains
it ionized on large distance scales. BH-HMXBs determine the early thermal
history of the universe and mantain it as ionized over large volumes of space
in regions of low density. This has a direct impact on the properties of the
faintest galaxies at high redshifts, the smallest dwarf galaxies in the local
universe, and on the existing and future surveys at radio wavelengths of atomic
hydrogen in the early universe.Comment: 7 pages, 2 figures, accepted to be published in Astronomy and
Astrophysic
The Distance to the Large Magellanic Cloud from the Eclipsing Binary HV2274
The distance to the Large Magellanic Cloud (LMC) is crucial for the
calibration of the Cosmic Distance Scale. We derive a distance to the LMC based
on an analysis of ground-based photometry and HST-based spectroscopy and
spectrophotometry of the LMC eclipsing binary system HV2274. Analysis of the
optical light curve and HST/GHRS radial velocity curve provides the masses and
radii of the binary components. Analysis of the HST/FOS UV/optical
spectrophotometry provides the temperatures of the component stars and the
interstellar extinction of the system. When combined, these data yield a
distance to the binary system. After correcting for the location of HV2274 with
respect to the center of the LMC, we find d(LMC) = 45.7 +/- 1.6 kpc or DM(LMC)
= 18.30 +/- 0.07 mag. This result, which is immune to the metallicity-induced
zero point uncertainties that have plagued other techniques, lends strong
support to the ``short'' LMC distance scale as derived from a number of
independent methods.Comment: 6 pages, including 2 pages of figures. Newly available optical (B and
V) photometry has revealed -- and allowed the elimination of -- a systematic
error in the previously reported determination of E(B-V) for HV2274. The new
result is E(B-V) = 0.12 mag (as compared to the value of 0.083 reported in
the original submission) and produces a DECREASE in the distance modulus of
HV2274 by 0.12 mag. ApJ Letters, in pres
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