13,138 research outputs found
Free-fall accretion and emitting caustics in wind-fed X-ray sources
In wind-fed X-ray binaries the accreting matter is Compton cooled and falls
freely onto the compact object. The matter has a modest angular momentum
and accretion is quasi-spherical at large distances from the compact object.
Initially small non-radial velocities grow in the converging supersonic flow
and become substantial in the vicinity of the accretor. The streamlines with
(where and are the mass and radius of the compact
object) intersect outside and form a two-dimensional caustic which emits
X-rays. The streamlines with low angular momentum, , run into
the accretor. If the accretor is a neutron star, a large X-ray luminosity
results. We show that the distribution of accretion rate/luminosity over the
star surface is sensitive to the angular momentum distribution of the accreting
matter. The apparent luminosity depends on the side from which the star is
observed and can change periodically with the orbital phase of the binary. The
accretor then appears as a `Moon-like' X-ray source.Comment: 8 pages, accepted to MNRA
Electrically Controlled Pumping of Spin Currents in Topological Insulators
Pure spin currents are shown to be generated by an electrically controlled
quantum pump applied at the edges of a topological insulator. The electric
rather than the more conventional magnetic control offers several advantages
and avoids, in particular, the necessity of delicate control of magnetization
dynamics over tiny regions. The pump is implemented by pinching the sample at
two quantum point contacts and phase modulating two external gate voltages
between them. The spin current is generated for the full range of parameters.
On the other hand, pumping via amplitude modulation of the inter-boundary
couplings generates both charge and spin currents, with a pure charge current
appearing only for special values of the parameters for which the Bohm-Aharonov
flux takes integer values. Our setup can therefore serve to fingerprint the
helical nature of the edges states with the zeros of the pumped spin and charge
currents occurring at distinct universal locations where the Fabry-Perot or the
Aharonov-Bohm phases take integer values.Comment: 5 pages, 5figure
Stability of a stochastically perturbed model of intracellular single-stranded RNA virus replication
Replication of single-stranded RNA virus can be complicated, compared to that
of double-stranded virus, as it require production of intermediate antigenomic
strands that then serve as template for the genomic-sense strands. Moreover,
for ssRNA viruses, there is a variability of the molecular mechanism by which
genomic strands can be replicated. A combination of such mechanisms can also
occur: a fraction of the produced progeny may result from a stamping-machine
type of replication that uses the parental genome as template, whereas others
may result from the replication of progeny genomes. F. Mart\'{\i}nez et al. and
J. Sardany\'{e}s at al. suggested a deterministic ssRNA virus intracellular
replication model that allows for the variability in the replication
mechanisms.
To explore how stochasticity can affect this model principal properties, in
this paper we consider the stability of a stochastically perturbed model of
ssRNA virus replication within a cell. Using the direct Lyapunov method, we
found sufficient conditions for the stability in probability of equilibrium
states for this model. This result confirms that this heterogeneous model of
single-stranded RNA virus replication is stable with respect to stochastic
perturbations of the environment
Feasibility of the optical fiber clock
We explore the feasibility of a compact high-precision Hg atomic clock based
on a hollow core optical fiber. We evaluate the sensitivity of the
- clock transition in Hg and other divalent atoms to the fiber
inner core surface at non-zero temperatures. The Casimir-Polder interaction
induced - transition frequency shift is calculated for the atom
inside the hollow capillary as a function of atomic position, capillary
material, and geometric parameters. For atoms on the axis
of a silica capillary with inner radius and
optimally chosen thickness , the atom-surface
interaction induced - clock transition frequency shift can be
kept on the level . We also estimate
the atom loss and heating due to the collisions with the buffer gas, lattice
intensity noise induced heating, spontaneous photon scattering, and residual
birefringence induced frequency shifts.Comment: 8 pages, 5 figures, submitte
Multipolar Origin of the Unexpected Transverse Force Resulting from Two-Wave Interference
We propose a theoretical study on the electromagnetic forces resulting from
the superposition of a TE and TM plane waves interacting with a sphere.
Specifically, we first show that, under such an illumination condition, the
sphere is subjected to a force transverse to the propagation direction of the
waves. We then analyze the physical origin of this counter-intuitive behavior
using a multipolar decomposition of the electromagnetic modes involved in that
scattering process. This analysis reveals that interference effects, due to the
two-wave illumination, lead to a Kerker-like asymmetric scattering behavior
resulting in this peculiar transverse force
New insights into the Jahn–Teller effect in NO_3 via the dark à 2E" state
The recent cavity ringdown (CRD) measurement of the forbidden Ã^2 E"←X~^2 A2' transition of the nitrate radical NO_3 reveals a rich, well-resolved spectrum in the near-infrared. The spectroscopic detail provides a new window onto the Jahn–Teller (JT) and pseudo-Jahn–Teller (PJT) effects in NO_3. This paper reviews the current experimental evidence for vibronic coupling in the à state and discusses the theoretical issues in the context of new preliminary EOMIP/CCSD and CCSD(T) calculations. The theoretical results to date indicate that the à 2E" state of NO_3 undergoes a relatively strong JT distortion which may require inclusion of higher order vibronic couplings. The intensity of this transition may involve multiple intensity borrowing mechanisms via PJT coupling among the X~, à and B~ states
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