9,625 research outputs found
Relativistic r-modes in Slowly Rotating Neutron Stars: Numerical Analysis in the Cowling Approximation
We investigate the properties of relativistic -modes of slowly rotating
neutron stars by using a relativistic version of the Cowling approximation. In
our formalism, we take into account the influence of the Coriolis like force on
the stellar oscillations, but ignore the effects of the centrifugal like force.
For three neutron star models, we calculated the fundamental -modes with
and 3. We found that the oscillation frequency of the
fundamental -mode is in a good approximation given by , where is defined in the corotating frame at the
spatial infinity, and is the angular frequency of rotation of the
star. The proportional coefficient is only weakly dependent on
, but it strongly depends on the relativistic parameter ,
where and are the mass and the radius of the star. All the fundamental
-modes with computed in this study are discrete modes with distinct
regular eigenfunctions, and they all fall in the continuous part of the
frequency spectrum associated with Kojima's equation (Kojima 1998). These
relativistic -modes are obtained by including the effects of rotation higher
than the first order of so that the buoyant force plays a role, the
situation of which is quite similar to that for the Newtonian -modes.Comment: 22 pages, 8 figures, accepted for publication in Ap
Momentum-Resolved Ultrafast Electron Dynamics in Superconducting Bi2Sr2CaCu2O8+delta
The non-equilibrium state of the high-Tc superconductor Bi2Sr2CaCu2O8+delta
and its ultrafast dynamics have been investigated by femtosecond time- and
angle-resolved photoemission spectroscopy well below the critical temperature.
We probe optically excited quasiparticles at different electron momenta along
the Fermi surface and detect metastable quasiparticles near the antinode. Their
decay through e-e scattering is blocked by a phase space restricted to the
nodal region. The lack of momentum dependence in the decay rates is in
agreement with relaxation dominated by Cooper pair recombination in a boson
bottleneck limit
r-modes in Relativistic Superfluid Stars
We discuss the modal properties of the -modes of relativistic superfluid
neutron stars, taking account of the entrainment effects between superfluids.
In this paper, the neutron stars are assumed to be filled with neutron and
proton superfluids and the strength of the entrainment effects between the
superfluids are represented by a single parameter . We find that the
basic properties of the -modes in a relativistic superfluid star are very
similar to those found for a Newtonian superfluid star. The -modes of a
relativistic superfluid star are split into two families, ordinary fluid-like
-modes (-mode) and superfluid-like -modes (-mode). The two
superfluids counter-move for the -modes, while they co-move for the
-modes. For the -modes, the quantity is
almost independent of the entrainment parameter , where and
are the azimuthal wave number and the oscillation frequency observed by an
inertial observer at spatial infinity, respectively. For the -modes, on
the other hand, almost linearly increases with increasing . It
is also found that the radiation driven instability due to the -modes is
much weaker than that of the -modes because the matter current associated
with the axial parity perturbations almost completely vanishes.Comment: 14 pages, 4 figures. To appear in Physical Review
Super Schrodinger algebra in AdS/CFT
We discuss (extended) super Schrodinger algebras obtained as subalgebras of
the superconformal algebra psu(2,2|4). The Schrodinger algebra with two spatial
dimensions can be embedded into so(4,2). In the superconformal case the
embedded algebra may be enhanced to the so-called super Schrodinger algebra. In
fact, we find an extended super Schrodinger subalgebra of psu(2,2|4). It
contains 24 supercharges (i.e., 3/4 of the original supersymmetries) and the
generators of so(6), as well as the generators of the original Schrodinger
algebra. In particular, the 24 supercharges come from 16 rigid supersymmetries
and half of 16 superconformal ones. Moreover, this superalgebra contains a
smaller super Schrodinger subalgebra, which is a supersymmetric extension of
the original Schrodinger algebra and so(6) by eight supercharges (half of 16
rigid supersymmetries). It is still a subalgebra even if there are no so(6)
generators. We also discuss super Schrodinger subalgebras of the superconformal
algebras, osp(8|4) and osp(8^*|4).Comment: 19pp; references added and title changed. version to appear in J.
Math. Phy
Hyperfine interaction and magnetoresistance in organic semiconductors
We explore the possibility that hyperfine interaction causes the recently
discovered organic magnetoresistance (OMAR) effect. Our study employs both
experiment and theoretical modelling. An excitonic pair mechanism model based
on hyperfine interaction, previously suggested by others to explain magnetic
field effects in organics, is examined. Whereas this model can explain a few
key aspects of the experimental data, we, however, uncover several fundamental
contradictions as well. By varying the injection efficiency for minority
carriers in the devices, we show experimentally that OMAR is only weakly
dependent on the ratio between excitons formed and carriers injected, likely
excluding any excitonic effect as the origin of OMAR.Comment: 10 pages, 7 figures, 1 tabl
Dense Molecular Gas In A Young Cluster Around MWC 1080 -- Rule Of The Massive Star
We present CS , CO , and CO , observations with the 10-element Berkeley Illinois Maryland Association
(BIMA) Array toward the young cluster around the Be star MWC 1080. These
observations reveal a biconical outflow cavity with size 0.3 and 0.05 pc
for the semimajor and semiminor axis and 45\arcdeg position angle.
These transitions trace the dense gas, which is likely the swept-up gas of the
outflow cavity, rather than the remaining natal gas or the outflow gas. The gas
is clumpy; thirty-two clumps are identified. The identified clumps are
approximately gravitationally bound and consistent with a standard isothermal
sphere density, which suggests that they are likely collapsing protostellar
cores. The gas kinematics suggests that there exists velocity gradients
implying effects from the inclination of the cavity and MWC 1080. The
kinematics of dense gas has also been affected by either outflows or stellar
winds from MWC 1080, and lower-mass clumps are possibly under stronger effects
from MWC 1080 than higher-mass clumps. In addition, low-mass cluster members
tend to be formed in the denser and more turbulent cores, compared to isolated
low-mass star-forming cores. This results from contributions of nearby forming
massive stars, such as outflows or stellar winds. Therefore, we conclude that
in clusters like the MWC 1080 system, effects from massive stars dominate the
star-forming environment in both the kinematics and dynamics of the natal cloud
and the formation of low-mass cluster members. This study provides insights
into the effects of MWC 1080 on its natal cloud, and suggests a different
low-mass star forming environment in clusters compared to isolated star
formation.Comment: 42 pages, 5 tables, and 13 figures, accepted for publication in Ap
Scanning tunneling spectroscopic studies of the pairing state of cuprate superconductors
Quasiparticle tunneling spectra of both hole-doped (p-type) and electron-doped (n-type) cuprates are studied using a low-temperature scanning tunneling microscope. The results reveal that neither the pairing symmetry nor the pseudogap phenomenon is universal among all cuprates, and that the response of n-type cuprates to quantum impurities is drastically different from that of the p-type cuprates. The only ubiquitous features among all cuprates appear to be the strong electronic correlation and the nearest-neighbor antiferromagnetic Cu2+-Cu2+ coupling in the CuO2 planes
R-modes of neutron stars with a solid crust
We investigate the properties of -mode oscillations of a slowly rotating
neutron star with a solid crust, by taking account of the effects of the
Coriolis force. For the modal analysis we employ three-component neutron star
models that are composed of a fluid core, a solid crust and a surface fluid
ocean. For the three-component models, we find that there exist two kinds of
-modes, that is, those confined in the surface fluid ocean and those
confined in the fluid core, which are most important for the -mode
instability. The -modes do not have any appreciable amplitudes in the solid
crust if rotation rate of the star is sufficiently small. We find that the core
-modes are strongly affected by mode coupling with the crustal torsional
(toroidal) modes and lose their simple properties of the eigenfunction and
eigenfrequency as functions of the angular rotation velocity . This
indicates that the extrapolation formula, which is obtained in the limit of
, cannot be used to examine the -mode instability of rapidly
rotating neutron stars with a solid crust unless the effects of mode coupling
with the crustal torsional modes are correctly taken into account.Comment: 10 pages, 3 figures, revised version accepted for publication in the
Ap
Crustal Oscillations of Slowly Rotating Relativistic Stars
We study low-amplitude crustal oscillations of slowly rotating relativistic
stars consisting of a central fluid core and an outer thin solid crust. We
estimate the effect of rotation on the torsional toroidal modes and on the
interfacial and shear spheroidal modes. The results compared against the
Newtonian ones for wide range of neutron star models and equations of state.Comment: 15 page
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