2,488 research outputs found
Magnetic and Electronic Phase Diagram and Superconductivity in the Organic Superconductors k-(BEDT-TTF)2X
The magnetic susceptibility of the organic superconductors -(h8 or
d8-ET), Cu(NCS) and Cu[N(CN)]Br has been studied. A
metallic phase below 37 38 K for Cu[N(CN)]Br and
46 50 K for Cu(NCS) has an anisotropic temperature
dependence of the susceptibility and the charge transport. Partial
charge-density-wave or charge fluctuation is expected to coexist with the
metallic phase instead of the large antiferromagnetic fluctuation above
. The phase diagram and the superconductivity of -(ET)
are discussed in connection with this phase.Comment: 5 pages, 4figures, REVTeX, references are corrected, accepted for
pubication in Phys. Rev.
Viscous diffusion and photoevaporation of stellar disks
The evolution of a stellar disk under the influence of viscous evolution,
photoevaporation from the central source, and photoevaporation by external
stars is studied. We take the typical parameters of TTSs and the Trapezium
Cluster conditions. The photoionizing flux from the central source is assumed
to arise both from the quiescent star and accretion shocks at the base of
stellar magnetospheric columns, along which material from the disk accretes.
The accretion flux is calculated self-consistently from the accretion mass loss
rate. We find that the disk cannot be entirely removed using only viscous
evolution and photoionization from the disk-star accretion shock. However, when
FUV photoevaporation by external massive stars is included the disk is removed
in 10^6 -10^7yr; and when EUV photoevaporation by external massive stars is
included the disk is removed in 10^5 - 10^6yr.
An intriguing feature of photoevaporation by the central star is the
formation of a gap in the disk at late stages of the disk evolution. As the gap
starts forming, viscous spreading and photoevaporation work in resonance.
There is no gap formation for disks nearby external massive stars because the
outer annuli are quickly removed by the dominant EUV flux. On the other hand,
at larger, more typical distances (d>>0.03pc) from the external stars the flux
is FUV dominated. As a consequence, the disk is efficiently evaporated at two
different locations; forming a gap during the last stages of the disk
evolution.Comment: 27 pages, 11 figures, accepted for publication in Ap
Disentangling the dynamical origin of P11 Nucleon Resonances
We show that two almost degenerate poles near the threshold and
the next higher mass pole in the partial wave of scattering
evolve from a single bare state through its coupling with , and
reaction channels. This finding provides new information on
understanding the dynamical origins of the Roper and
resonances listed by Particle Data Group. Our results for the resonance poles
in other partial waves are also presented.Comment: Improved version, accepted Phys. Rev. Let
AUTORADIOGRAPHIC ANALYSIS OF LYMPHOPOIESIS AND LYMPHOCYTE MIGRATION IN MICE BEARING MULTIPLE THYMUS GRAFTS
Lymphopoiesis was studied in 3-month-old normal C57Bl mice and in 3-month-old C57Bl mice carrying from 12 to 48 C57Bl thymus grafts using tritiated thymidine labeling. Thymus graft lymphopoiesis was found to be identical with that of normal thymus tissue and the presence of thymus grafts was found to have no influence on host thymus lymphopoiesis. No evidence was found that the massive amounts of thymus graft tissue in the mice affected any parameter of host lymph node lymphopoiesis nor was any evidence detected for the migration of thymic lymphocytes from these massive deposits of thymus graft tissue either to host lymph nodes and blood or to other organs in the host animal. It is concluded that the majority of small lymphocytes produced in the thymus and thymus graft tissue do not migrate from these tissues but die locally at the end of their intrathymic life span of 3 to 4 days
Dynamical coupled-channels analysis of 1H(e,e'pi)N reactions
We have performed a dynamical coupled-channels analysis of available
p(e,e'pi)N data in the region of W < 1.6 GeV and Q^2 < 1.45 (GeV/c)^2. The
channels included are gamma^* N, pi N, eta N, and pi pi N which has pi Delta,
rho N, and sigma N components. With the hadronic parameters of the model
determined in our previous investigations of pi N --> pi N, pi pi N reactions,
we have found that the available data in the considered W < 1.6 GeV region can
be fitted well by only adjusting the bare gamma^* N --> N^* helicity amplitudes
for the lowest N^* states in P33, P11, S11 and D13 partial waves. The
sensitivity of the resulting parameters to the amount of data included in the
analysis is investigated. The importance of coupled-channels effect on the
p(e,e' pi)N cross sections is demonstrated. The meson cloud effects, as
required by the unitarity conditions, on the gamma^* N --> N^* form factors are
also examined. Necessary future developments, both experimentally and
theoretically, are discussed.Comment: 14 pages, 11 figures. Version to appear in PR
Halting planet migration by photoevaporation from the central source
The recent discovery of Jupiter-mass planets orbiting at a few AU from their
stars compliments earlier detections of massive planets on very small orbits.
The short period orbits strongly suggest that planet migration has occurred,
with the likely mechanism being tidal interactions between the planets and the
gas disks out of which they formed. The newly discovered long period planets,
together with the gas giant planets in our solar system, show that migration is
either absent or rapidly halted in at least some systems. We propose a
mechanism for halting type-II migration at several AU in a gas disk.
Photoevaporation of the disk by irradiation from the central star can produce a
gap in the disk at a few AU, preventing planets outside the gap from migrating
down to the star. This would result in an excess of systems with planets at or
just outside the photoevaporation radius.Comment: 12 pages, 3 figures, accepted for publication by ApJ Letter
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