569 research outputs found
TEMPERATURE AND RELATIVITY
We investigate whether inertial thermometers moving in a thermal bath behave
as being hotter or colder. This question is directly related to the classical
controversy concerning how temperature transforms under Lorentz
transformations. Rather than basing our arguments on thermodynamical
hypotheses, we perform straightforward calculations in the context of
relativistic quantum field theory. For this purpose we use Unruh-DeWitt
detectors, since they have been shown to be reliable thermometers in
semi-classical gravity. We believe that our discussion helps in definitely
clarifying this issue.Comment: 9 pages, 1 figure available upon reques
Surface Effects in Magnetic Microtraps
We have investigated Bose-Einstein condensates and ultra cold atoms in the
vicinity of a surface of a magnetic microtrap. The atoms are prepared along
copper conductors at distances to the surface between 300 um and 20 um. In this
range, the lifetime decreases from 20 s to 0.7 s showing a linear dependence on
the distance to the surface. The atoms manifest a weak thermal coupling to the
surface, with measured heating rates remaining below 500 nK/s. In addition, we
observe a periodic fragmentation of the condensate and thermal clouds when the
surface is approached.Comment: 4 pages, 4 figures; v2: corrected references; v3: final versio
All-optical formation of a Bose-Einstein condensate for applications in scanning electron microscopy
We report on the production of a F=1 spinor condensate of 87Rb atoms in a
single beam optical dipole trap formed by a focused CO2 laser. The condensate
is produced 13mm below the tip of a scanning electron microscope employing
standard all-optical techniques. The condensate fraction contains up to 100,000
atoms and we achieve a duty cycle of less than 10s.Comment: 5 pages, 4 figure
Wave function recombination instability in cold atom interferometers
Cold atom interferometers use guiding potentials that split the wave function
of the Bose-Einstein condensate and then recombine it. We present theoretical
analysis of the wave function recombination instability that is due to the weak
nonlinearity of the condensate. It is most pronounced when the accumulated
phase difference between the arms of the interferometer is close to an odd
multiple of PI and consists in exponential amplification of the weak ground
state mode by the strong first excited mode. The instability exists for both
trapped-atom and beam interferometers.Comment: 4 pages, 5 figure
Review of lobomycosis and lobomycosis-like disease (LLD) in Cetacea from South America. Scientific Committee document SC/60/DW13, International Whaling Commission, June 2008, Santiago, Chile
Caused by a yeast-like organism known as Lacazia loboi, Lobomycosis (or lacaziosis) naturally affects humans, common bottlenose dolphins (Tursiops truncates) inhabiting coastal waters from southern Brazil to Gulf of Mexico and Atlantic coast of Florida, as well as botos-cinza (Sotalia guianensis). These species are usually found in coastal waters, subject to runoff provided by large rivers and a considerable burden of associated contaminants. Histological and morphological studies demonstrated that the etiological agent of L. loboi infecting humans is different from the one found to infected dolphins. Moreover, it likely that dolphin-human infections do not occur although infected bottlenose dolphins were from populations engaged in cooperative fishing that involve a relative small number of dolphins and humans. The records of Lobomycosis and Lobomycosis-like disease (LLD) in Tramandaà estuary (29o58´S), Rio Grande do Sul, Brazil, represent the southernmost distribution of L. loboi. On the other hand, the northernmost distribution of this disease is reported in the southern portion of Indian River Lagoon (27°25´N), Florida, USA. LLD seems to be more widespread, infecting both toothed small cetaceans and baleen whales, from the tropical Atlantic to the Pacific. Future studies should evaluate the association with impaired immune function in affected dolphins and the emergency of Lobomycosis. It may be associated with an immunosuppressive factor of environmental origin, such as exposure to pesticides or other agricultural or industrial contaminants, introduced through runoff or point sources of pollution, altering conditions to favour disease emergence. Lobomycosis should be assigned as neglected tropical disease, as should be the case of LLD, if future investigations indicate their connection as an emerging pathogen, its pathogenicity and environment requirements
Magnetic Field Effects on Neutron Diffraction in the Antiferromagnetic Phase of
We discuss possible magnetic structures in UPt based on our analysis of
elastic neutron-scattering experiments in high magnetic fields at temperatures
. The existing experimental data can be explained by a single-{\bf q}
antiferromagnetic structure with three independent domains. For modest in-plane
spin-orbit interactions, the Zeeman coupling between the antiferromagnetic
order parameter and the magnetic field induces a rotation of the magnetic
moments, but not an adjustment of the propagation vector of the magnetic order.
A triple-{\bf q} magnetic structure is also consistent with neutron
experiments, but in general leads to a non-uniform magnetization in the
crystal. New experiments could decide between these structures.Comment: 5 figures included in the tex
Atomic diffraction from nanostructured optical potentials
We develop a versatile theoretical approach to the study of cold-atom
diffractive scattering from light-field gratings by combining calculations of
the optical near-field, generated by evanescent waves close to the surface of
periodic nanostructured arrays, together with advanced atom wavepacket
propagation on this optical potential.Comment: 8 figures, 10 pages, submitted to Phys. Rev.
Stability and collapse of localized solutions of the controlled three-dimensional Gross-Pitaevskii equation
On the basis of recent investigations, a newly developed analytical procedure
is used for constructing a wide class of localized solutions of the controlled
three-dimensional (3D) Gross-Pitaevskii equation (GPE) that governs the
dynamics of Bose-Einstein condensates (BECs). The controlled 3D GPE is
decomposed into a two-dimensional (2D) linear Schr\"{o}dinger equation and a
one-dimensional (1D) nonlinear Schr\"{o}dinger equation, constrained by a
variational condition for the controlling potential. Then, the above class of
localized solutions are constructed as the product of the solutions of the
transverse and longitudinal equations. On the basis of these exact 3D
analytical solutions, a stability analysis is carried out, focusing our
attention on the physical conditions for having collapsing or non-collapsing
solutions.Comment: 21 pages, 14 figure
Time-of-flight and activation experiments on 147Pm and 171Tm for astrophysics
The neutron capture cross section of several key unstable isotopes acting as branching points in the s-process are crucial for stellar nucleosynthesis studies, but they are very challenging to measure due to the difficult production of sufficient sample material, the high activity of the resulting samples, and the actual (n,Îł) measurement, for which high neutron fluxes and effective background rejection capabilities are required. As part of a new program to measure some of these important branching points, radioactive targets of 147Pm and 171Tm have been produced by irradiation of stable isotopes at the ILL high flux reactor. Neutron capture on 146Nd and 170Er at the reactor was followed by beta decay and the resulting matrix was purified via radiochemical separation at PSI. The radioactive targets have been used for time-of-flight measurements at the CERN n-TOF facility using the 19 and 185 m beam lines during 2014 and 2015. The capture cascades were detected using a set of four C6D6 scintillators, allowing to observe the associated neutron capture resonances. The results presented in this work are the first ever determination of the resonance capture cross section of 147Pm and 171Tm. Activation experiments on the same 147Pm and 171Tm targets with a high-intensity 30 keV quasi-Maxwellian flux of neutrons will be performed using the SARAF accelerator and the Liquid-Lithium Target (LiLiT) in order to extract the corresponding Maxwellian Average Cross Section (MACS). The status of these experiments and preliminary results will be presented and discussed as well
Characterization of the n-TOF EAR-2 neutron beam
The experimental area 2 (EAR-2) at CERNs neutron time-of-flight facility (n-TOF), which is operational since 2014, is designed and built as a short-distance complement to the experimental area 1 (EAR-1). The Parallel Plate Avalanche Counter (PPAC) monitor experiment was performed to characterize the beam prole and the shape of the neutron 'ux at EAR-2. The prompt Îł-flash which is used for calibrating the time-of-flight at EAR-1 is not seen by PPAC at EAR-2, shedding light on the physical origin of this Îł-flash
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