3,240 research outputs found
SSX MHD Plasma Wind Tunnel
A new turbulent plasma source at the Swarthmore Spheromak Experiment (SSX) facility is described. The MHD wind tunnel configuration employs a magnetized plasma gun to inject high-beta plasma into a large, well-instrumented, vacuum drift region. This provides unique laboratory conditions approaching that in the solar wind: there is no applied background magnetic field in the drift region and has no net axial magnetic flux; the plasma flow speed is on the order of the local sound speed (M ~ 1), so flow energy density is comparable to thermal energy density; and the ratio of thermal to magnetic pressure is of order unity (plasma β ~ 1) so thermal energy density is also comparable to magnetic energy density. Results presented here and referenced within demonstrate the new capabilities and show how the new platform is proving useful for fundamental plasma turbulence studies
Développement d'un Test Sérologique Contre le Virus de la Chorioméningite Lymphocytaire
Les Arenavirus sont une famille de virus à ARN très diversifiée avec plus de 23 espèces recensées dans le monde, divisées en deux Clades majeures (Emonet et al., 2009). Ils sont classifiés en Arenavirus du Nouveau Monde versus de l'Ancien Monde (Buchmeier, de la Torre, and Peters, 2007) (Fig. 1). Parmi les Arenavirus, sept sont connus pour être les agents causales de fièvres hémorragiques foudroyantes : Les virus Lassa, Junin, Machupo, Guanarito, Sabia, Chapare et Lujo. Les Arenavirus infectent, de façon spécifique, des espèces de rongeurs qui sont le réservoir naturel déterminant ainsi leur distribution géographique (Clegg, 2002). On retrouve le virus de la chorioméningite lymphocytaire (LCMV) à la fois en Europe et aux Amériques. Le rongeur infecté est le vecteur de transmission à l'Homme. Les maladies associées aux infections par les Arenavirus hémorragiques ont un haut taux de mortalité allant de 15 à 30% et sont à haut risque épidémiologique en raison de l'absence de vaccin et de traitement efficace. Pour ces raisons, ces Arenavirus sont classifiés comme pathogènes à haut risque par le centre pour le contrôle des maladies (CDC) (Borio et al., 2002)
New Class of Compact Stars at High Density
We discuss the equation of state for cold, dense quark matter in perturbation
theory, and how it might match onto that of hadronic matter. Certain choices of
the renormalization scale correspond to a strongly first order chiral
transition, and may generate a new class of small and very dense quark stars.
The results for the mass-radius relation are compatible with the recent
determination of the mass and the radius of an isolated neutron star by Pons et
al.Comment: Latex, 7 pages, 4 figures. Presented at the International Conference
on Statistical QCD, Bielefeld, Germany, 26-30 August 2001. Requires
espcrc1.st
Temporal and Spatial Turbulent Spectra of MHD Plasma and an Observation of Variance Anisotropy
The nature of MHD turbulence is analyzed through both temporal and spatial
magnetic fluctuation spectra. A magnetically turbulent plasma is produced in
the MHD wind-tunnel configuration of the Swarthmore Spheromak Experiment (SSX).
The power of magnetic fluctuations is projected into directions perpendicular
and parallel to a local mean field; the ratio of these quantities shows the
presence of variance anisotropy which varies as a function of frequency.
Comparison amongst magnetic, velocity, and density spectra are also made,
demonstrating that the energy of the turbulence observed is primarily seeded by
magnetic fields created during plasma production. Direct spatial spectra are
constructed using multi-channel diagnostics and are used to compare to
frequency spectra converted to spatial scales using the Taylor Hypothesis.
Evidence for the observation of dissipation due to ion inertial length scale
physics is also discussed as well as the role laboratory experiment can play in
understanding turbulence typically studied in space settings such as the solar
wind. Finally, all turbulence results are shown to compare fairly well to a
Hall-MHD simulation of the experiment.Comment: 17 pages, 17 figures, Submitted to Astrophysical Journa
The properties of the D-meson in dense matter
We study the D-meson spectral density in dense matter within the framework of
a coupled-channel self-consistent calculation taking, as bare meson-baryon
interaction, a separable potential. Our coupled-channel model generates
dynamically the resonance. The medium modifications of the
D-meson properties due to Pauli blocking and the dressing of D-mesons, nucleons
and pions are also discussed. We found that the coupled-channel effects in the
self-consistent process reduce the in-medium effects on the D-meson compared to
previous works.Comment: 4 pages, 4 figures, to appear in the proceedings of Strangeness in
Quark Matter 2004 (SQM2004), Cape Town, South Africa, 15-20 September 200
Possible Signatures Of Dissipation From Time-Series Analysis Techniques Using A Turbulent Laboratory Magnetohydrodynamic Plasma
The frequency spectrum of magnetic fluctuations as measured on the Swarthmore Spheromak Experiment is broadband and exhibits a nearly Kolmogorov 5/3 scaling. It features a steepening region which is indicative of dissipation of magnetic fluctuation energy similar to that observed in fluid and magnetohydrodynamic turbulence systems. Two non-spectrum based time-series analysis techniques are implemented on this data set in order to seek other possible signatures of turbulent dissipation beyond just the steepening of fluctuation spectra. Presented here are results for the flatness, permutation entropy, and statistical complexity, each of which exhibits a particular character at spectral steepening scales which can then be compared to the behavior of the frequency spectrum
A new possible quark-hadron mixed phase in protoneutron stars
The phase transition from hadronic matter to quark matter at high density
might be a strong first order phase transition in presence of a large surface
tension between the two phases. While this implies a constant-pressure mixed
phase for cold and catalyzed matter this is not the case for the hot and lepton
rich matter formed in a protoneutron star. We show that it is possible to
obtain a mixed phase with non-constant pressure by considering the global
conservation of lepton number during the stage of neutrino trapping. In turn,
it allows for the appearance of a new kind of mixed phase as long as neutrinos
are trapped and its gradual disappearance during deleptonization. This new
mixed phase, being composed by two electric neutral phases, does not develop a
Coulomb lattice and it is formed only by spherical structures, drops and
bubbles, which can have macroscopic sizes. The disappearance of the mixed phase
at the end of deleptonization might lead to a delayed collapse of the star into
a more compact configuration containing a core of pure quark phase. In this
scenario, a significant emission of neutrinos and, possibly, gravitational
waves are expected.Comment: 4 pages, 4 figure
Hyperons and massive neutron stars: the role of hyperon potentials
The constituents of cold dense matter are still far from being understood.
However, neutron star observations such as the recently observed pulsar PSR
J1614-2230 with a mass of 1.97+/-0.04 M_solar help to considerably constrain
the hadronic equation of state (EoS). We systematically investigate the
influence of the hyperon potentials on the stiffness of the EoS. We find that
they have but little influence on the maximum mass compared to the inclusion of
an additional vector meson mediating repulsive interaction amongst hyperons.
The new mass limit can only be reached with this additional meson regardless of
the hyperon potentials. Further, we investigate the impact of the nuclear
compression modulus and the effective mass of the nucleon at saturation density
on the high density regime of the EoS. We show that the maximum mass of purely
nucleonic stars is very sensitive to the effective nucleon mass but only very
little to the compression modulus.Comment: 24 pages, 8 figure
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