48,687 research outputs found
Orbital Decay of the PSR J0045-7319/B Star Binary System: Age of Radio Pulsar and Initial Spin of Neutron Star
Recent timing observations of PSR J0045-7319 reveal that the neutron star/B
star binary orbit is decaying on a time scale of |\Porb/\dot\Porb|=0.5 Myr,
shorter than the characteristic age ( Myr) of the pulsar (Kaspi et
al.~1996a). We study mechanisms for the orbital decay. The standard weak
friction theory based on static tide requires far too short a viscous time to
explain the observed \dot\Porb. We show that dynamical tidal excitation of
g-modes in the B star can be responsible for the orbital decay. However, to
explain the observed short decay timescale, the B star must have some
significant retrograde rotation with respect to the orbit --- The retrograde
rotation brings lower-order g-modes, which couple much more strongly to the
tidal potential, into closer ``resonances'' with the orbital motion, thus
significantly enhancing the dynamical tide. A much less likely possibility is
that the g-mode damping time is much shorter than the ordinary radiative
damping time. The observed orbital decay timescale combined with a generic
orbital evolution model based on dynamical tide can be used as a ``timer'',
giving an upper limit of Myr for the age of the binary system since the
neutron star formation. Thus the characteristic age of the pulsar is not a good
age indicator. Assuming standard magnetic dipole braking for the pulsar and no
significant magnetic field decay on a timescale \lo 1 Myr, the upper limit
for the age implies that the initial spin of the neutron star at birth was
close to its current value.Comment: AASTeX, 9 pages, 3 ps figures. ApJ Letters, in pres
Geometrical and electronic structures of the (5, 3) single-walled gold nanotube from first-principles calculations
The geometrical and electronic structures of the 4 {\AA} diameter perfect and
deformed (5, 3) single-walled gold nanotube (SWGT) have been studied based upon
the density-functional theory in the local-density approximation (LDA). The
calculated relaxed geometries show clearly significant deviations from those of
the ideally rolled triangular gold sheet. It is found that the different
strains have different effects on the electronic structures and density of
states of the SWGTs. And the small shear strain can reduce the binding energy
per gold atom of the deformed SWGT, which is consistent with the experimentally
observed result. Finally, we found the finite SWGT can show the
metal-semiconductor transition.Comment: 11 pages, 4 figure
Constructions of the soluble potentials for the non-relativistic quantum system by means of the Heun functions
The Schr\"{o}dinger equation where
is rewritten as a more popular form of a second order
differential equation through taking a similarity transformation
with . The Schr\"{o}dinger invariant
can be calculated directly by the Schwarzian derivative and the
invariant of the differential equation . We
find an important relation for moving particle as and thus
explain the reason why the Schr\"{o}dinger invariant keeps constant.
As an illustration, we take the typical Heun differential equation as an object
to construct a class of soluble potentials and generalize the previous results
through choosing different as before. We get a more general
solution through integrating
directly and it includes all
possibilities for those parameters. Some particular cases are discussed in
detail.Comment: 11 page
A complex environment around Cir X-1
We present the results of an archival 54 ks long Chandra observation of the
peculiar source Cir X--1 during the phase passage 0.223-0.261. A comparative
analysis of X-ray spectra, selected at different flux levels of the source,
allows us to distinguish between a very hard state, at a low countrate, and a
brighter, softer, highly absorbed spectrum during episodes of flaring activity,
when the unabsorbed source luminosity is about three times the value in the
hard state. The spectrum of the hard state clearly shows emission lines of
highly ionized elements, while, during the flaring state, the spectrum also
shows strong resonant absorption lines. The most intense and interesting
feature in this latter state is present in the Fe K alpha region: a very
broadened absorption line at energies ~ 6.5 keV that could result from a
smeared blending of resonant absorption lines of moderately ionized iron ions
(Fe XX - Fe XXIV). We also observe strong resonant absorption lines of Fe XXV
and Fe XXVI, together with a smeared absorption edge above 7 keV. We argue that
the emitting region during the quiescent/hard state is constituted of a purely
photo-ionized medium, possibly present above an accretion disk, or of a
photo-ionized plasma present in a beamed outflow. During the flaring states the
source undergoes enhanced turbulent accretion that modifies both the accretion
geometry and the optical depth of the gas surrounding the primary X-ray source.Comment: Accepted for publication in Ap
Exact solution of Schrodinger equation for Pseudoharmonic potential
Exact solution of Schrodinger equation for the pseudoharmonic potential is
obtained for an arbitrary angular momentum. The energy eigenvalues and
corresponding eigenfunctions are calculated by Nikiforov-Uvarov method.
Wavefunctions are expressed in terms of Jacobi polynomials. The energy
eigenvalues are calculated numerically for some values of l and n with n<5 for
some diatomic molecules.Comment: 10 page
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Internalisation of membrane progesterone receptor-α after treatment with progesterone: Potential involvement of a clathrin-dependent pathway
This article has been made available through the Brunel Open Access Publishing Fund.Internalisation and recycling of seven trans-membrane domain receptors is a critical regulatory event for their signalling. The mechanism(s) by which membrane progesterone receptor-α (mPRα) number is regulated on the cell surface is unclear. In this study, we investigated the cellular distribution of mPRα and mechanisms of mPRα trafficking using a cell line derived from a primary culture of human myometrial cells (M11) as an experimental model. RT-PCR and immunofluorescent analysis demonstrated expression of mPRα in M11 cells with mPRα primarily distributed on the cell surface under basal conditions. For the first time, plasma membrane localisation of mPRα was confirmed using immuno-gold transmission electron microscopy. Stimulation of M11 cells with progesterone (P4, 100 nM) resulted in internalisation of mPRα from the plasma membrane to the cytoplasm (10 min) and subsequent partial translocation back to the cell surface (20 min). We investigated potential endocytotic pathways involved in trafficking of mPRα after its internalisation. Partial co-localisation of clathrin with mPRα was obvious after 10 min of P4 treatment. Of note, chlorpromazine (inhibitor of clathrin-mediated pathway) inhibited the endocytosis of mPRα, whereas treatment with nystatin (inhibitor of caveolae-mediated pathway) did not affect internalisation. Collectively, these data suggest that mPRα is expressed on the cell surface of M11 cells and undergoes endocytosis after P4 stimulation primarily via a clathrin-mediated pathway.This article is available through the Brunel Open Access Publishing Fun
NMR study of a bimesogenic liquid crystal with two nematic phases
Recent interest in bimesogenic liquid crystals showing two nematic phases has led us to investigate the nematic mean-field interactions in these nematic phases by using rigid solutes as probes. The nematic potential that is modelled by two independent Maier-Saupe terms is successful in fitting the observed dipolar couplings (order parameters) of para-, meta- and ortho-dichlorobenzene solutes in both the nematic phases of 39 wt% of 4-n-pentyl-4′-cyanobiphenyl (5CB) in α,ω-bis(4-4′-cyanobiphenyl)nonane (CB_C9_CB) to better than the 5% level. The derived liquid-crystal potential parameters G₁ and G₂ for each solute in the N and Ntb phases will be discussed. The most interesting observation is that G1 (associated with size and shape interactions) is almost constant in the Ntb phase, whereas G₂ (associated with longer-range electrostatic interactions) has large variation, even changing sign
Spin-Kick Correlation in Neutron Stars: Alignment Conditions and Implications
Recent observations of pulsar wind nebulae and radio polarization profiles
revealed a tendency of the alignment between the spin and velocity directions
in neutron stars. We study the condition for spin-kick alignment using a toy
model, in which the kick consists of many off-centered, randomly-oriented
thrusts. Both analytical considerations and numerical simulations indicate that
spin-kick alignment cannot be easily achieved if the proto-neutron star does
not possess some initial angular momentum, contrary to some previous claims. To
obtain the observed spin-kick misalignment angle distribution, the initial spin
period of the neutron star must be smaller than the kick timescale. Typically,
an initial period of a hundred milliseconds or less is required.Comment: 17 pages, 8 figures. Accepted by Ap
Algebraic approach to the Hulthen potential
In this paper the energy eigenvalues and the corresponding eigenfunctions are
calculated for Hulthen potential. Then we obtain the ladder operators and show
that these operators satisfy SU(2) commutation relation.Comment: 8 Pages, 1 Tabl
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