479 research outputs found
Large-N transition temperature for superconducting films in a magnetic field
We consider the -component Ginzburg-Landau model in the large limit,
the system being embedded in an external constant magnetic field and confined
between two parallel planes a distance apart from one another. On physical
grounds, this corresponds to a material in the form of a film in the presence
of an external magnetic field. Using techniques from dimensional and
-function regularization, modified by the external field and the
confinement conditions, we investigate the behavior of the system as a function
of the film thickness . This behavior suggests the existence of a minimal
critical thickness below which superconductivity is suppressed.Comment: Revtex, two column, 4 pages, 2 figure
Laser Spectroscopy of Niobium Fission Fragments: First Use of Optical Pumping in an Ion Beam Cooler Buncher
A new method of optical pumping in an ion beam cooler buncher has been developed to selectively enhance ionic metastable state populations. The technique permits the study of elements previously inaccessible to laser spectroscopy and has been applied here to the study of Nb. Model independent mean-square charge radii and nuclear moments have been studied for Nb to cover the region of the N=50 shell closure and N≈60 sudden onset of deformation. The increase in mean-square charge radius is observed to be less than that for Y, with a substantial degree of β softness observed before and after N=60
Off-line studies of the laser ionization of yttrium at the IGISOL facility
A laser ion source is under development at the IGISOL facility, Jyvaskyla, in
order to address deficiencies in the ion guide technique. The key elements of
interest are those of a refractory nature, whose isotopes and isomers are
widely studied using both laser spectroscopic and high precision mass
measurement techniques. Yttrium has been the first element of choice for the
new laser ion source. In this work we present a new coupled dye-Ti:Sapphire
laser scheme and give a detailed discussion of the results obtained from laser
ionization of yttrium atoms produced in an ion guide via joule heating of a
filament. The importance of not only gas purity, but indeed the baseline vacuum
pressure in the environment outside the ion guide is discussed in light of the
fast gas phase chemistry seen in the yttrium system. A single laser shot model
is introduced and is compared to the experimental data in order to extract the
level of impurities within the gas cell.Comment: 18 pages submitted to NIM
The Stromlo Missing Satellites Survey
The Stromlo Missing Satellites (SMS) program is a critical endeavor to
investigate whether cold dark matter cosmology is flawed in its ability to
describe the matter distribution on galaxy scales or proves itself once again
as a powerful theory to make observational predictions. The project will
deliver unprecedented results on Milky Way satellite numbers, their
distribution and physical properties. It is the deepest, most extended survey
for optically elusive dwarf satellite galaxies to date, covering the entire
20,000 sq deg of the Southern hemisphere. 150TB of CCD images will be analysed
in six photometric bands, 0.5-1.0 mag fainter than SDSS produced by the ANU
SkyMapper telescope over the next five years. (For more details see:
http://msowww.anu.edu.au/~jerjen/SMS_Survey.html)Comment: 4 pages, 1 figure, in "Galaxies in the Local Volume" (Sydney, 8-13
July 2007), eds B. Koribalski and H. Jerjen, Springer Astrophysics and Space
Science Proceedings, p. 18
A sextupole ion beam guide to improve the efficiency and beam quality at IGISOL
The laser ion source project at the IGISOL facility, Jyvaskyla, has motivated
the development and construction of an rf sextupole ion beam guide (SPIG) to
replace the original skimmer electrode. The SPIG has been tested both off-line
and on-line in proton-induced fission, light-ion and heavy-ion induced
fusion-evaporation reactions and, in each case, has been directly compared to
the skimmer system. For both fission and light-ion induced fusion, the SPIG has
improved the mass-separated ion yields by a factor of typically 4 to 8.
Correspondingly, the transmission efficiency of both systems has been studied
in simulations with and without space charge effects. The transport capacity of
the SPIG has been experimentally determined to be 10^12 ions/s before space
charge effects start to take effect. A direct comparison with the simulation
has been made using data obtained via light-ion fusion evaporation. Both
experiment and simulation show an encouraging agreement as a function of
current extracted from the ion guide.Comment: Latex formatted, submitted to NIM B, 17 pages with 22 .eps figure
Dynamics of Fermionic Four-Wave Mixing
We study the dynamics of a beam of fermions diffracted off a density grating
formed by fermionic atoms in the limit of a large grating. An exact description
of the system in terms of particle-hole operators is developed. We use a
combination of analytical and numerical methods to quantitatively explore the
Raman-Nath and the Bragg regimes of diffraction. We discuss the limits in
diffraction efficiency resulting from the dephasing of the grating due the
distribution of energy states occupied by the fermions. We propose several
methods to overcome these limits, including the novel technique of ``atom
echoes''.Comment: 8 pages, 7 figure
Solum depth spatial prediction comparing conventional with knowledge-based digital soil mapping approaches
Solum depth and its spatial distribution play an important role in different types of environmental studies. Several approaches have been used for fitting quantitative relationships between soil properties and their environment in order to predict them spatially. This work aimed to present the steps required for solum depth spatial prediction from knowledge-based digital soil mapping, comparing the prediction to the conventional soil mapping approach through field validation, in a watershed located at Mantiqueira Range region, in the state of Minas Gerais, Brazil. Conventional soil mapping had aerial photo-interpretation as a basis. The knowledge-based digital soil mapping applied fuzzy logic and similarity vectors in an expert system. The knowledge-based digital soil mapping approach showed the advantages over the conventional soil mapping approach by applying the field expert-knowledge in order to enhance the quality of final results, predicting solum depth with suited accuracy in a continuous way, making the soil-landscape relationship explicit
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
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