5,247 research outputs found
Minimal-memory realization of pearl-necklace encoders of general quantum convolutional codes
Quantum convolutional codes, like their classical counterparts, promise to
offer higher error correction performance than block codes of equivalent
encoding complexity, and are expected to find important applications in
reliable quantum communication where a continuous stream of qubits is
transmitted. Grassl and Roetteler devised an algorithm to encode a quantum
convolutional code with a "pearl-necklace encoder." Despite their theoretical
significance as a neat way of representing quantum convolutional codes, they
are not well-suited to practical realization. In fact, there is no
straightforward way to implement any given pearl-necklace structure. This paper
closes the gap between theoretical representation and practical implementation.
In our previous work, we presented an efficient algorithm for finding a
minimal-memory realization of a pearl-necklace encoder for
Calderbank-Shor-Steane (CSS) convolutional codes. This work extends our
previous work and presents an algorithm for turning a pearl-necklace encoder
for a general (non-CSS) quantum convolutional code into a realizable quantum
convolutional encoder. We show that a minimal-memory realization depends on the
commutativity relations between the gate strings in the pearl-necklace encoder.
We find a realization by means of a weighted graph which details the
non-commutative paths through the pearl-necklace. The weight of the longest
path in this graph is equal to the minimal amount of memory needed to implement
the encoder. The algorithm has a polynomial-time complexity in the number of
gate strings in the pearl-necklace encoder.Comment: 16 pages, 5 figures; extends paper arXiv:1004.5179v
Influence of Melissa officinalis essential oil and its formulation on Typhlodromips swirskii and Neoseiulus barkeri (Acari: Phytoseiidae)
The toxicity of Melissa officinalis L. essential oil and its formulation (Melissacide) were evaluated against eggs and females of two predatory phytoseiid mites, Typhlodromips swirskii (Athias Henriot) and Neoseiulus barkeri (Hughes), using direct spray. Results indicate that both tested materials were potent on predatory females than egg stage. Typhlodromips swirskii was proved to be more sensitive to the oil and formulation than N. barkeri.
Females mortality were (62-100%) in T. swirskii, and (46-69%) in N. barkeri, when both predatory mites were sprayed with LC50 and LC90 of the oil and Melissacide reported on Tetranychus urticae Koch. Females of both predators were suffered from reduction in food consumption when sprayed with two sublethal concentrations of Melissacide, while insignificant differences reported in daily number of eggs deposited by females of T. swirskii, when sprayed with its LC25 value of Melissacide and control
Magnetically Torqued Thin Accretion Disks
We compute the properties of a geometrically thin, steady accretion disk
surrounding a central rotating, magnetized star. The magnetosphere is assumed
to entrain the disk over a wide range of radii. The model is simplified in that
we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal
component of the magnetic field as a function of radial distance. We find a
solution for the angular velocity profile tending to corotation close to the
central star, and smoothly matching a Keplerian curve at a radius where the
viscous stress vanishes. The value of this ''transition'' radius is nearly the
same for both of our adopted B-field models. We then solve analytically for the
torques on the central star and for the disk luminosity due to gravity and
magnetic torques. When expressed in a dimensionless form, the resulting
quantities depend on one parameter alone, the ratio of the transition radius to
the corotation radius. For rapid rotators, the accretion disk may be powered
mostly by spin-down of the central star. These results are independent of the
viscosity prescription in the disk. We also solve for the disk structure for
the special case of an optically thick alpha disk. Our results are applicable
to a range of astrophysical systems including accreting neutron stars,
intermediate polar cataclysmic variables, and T Tauri systems.Comment: 9 sharper figs, updated reference
Force-Free Models of Magnetically Linked Star-Disk Systems
Disk accretion onto a magnetized star occurs in a variety of astrophysical
contexts, from young stars to X-ray pulsars. The magnetohydrodynamic
interaction between the stellar field and the accreting matter can have a
strong effect on the disk structure, the transfer of mass and angular momentum
between the disk and the star, and the production of bipolar outflows, e.g.,
plasma jets. We study a key element of this interaction - the time evolution of
the magnetic field configuration brought about by the relative rotation between
the disk and the star - using simplified, largely semianalytic, models. We
first discuss the rapid inflation and opening up of the magnetic field lines in
the corona above the accretion disk, which is caused by the differential
rotation twisting. Then we consider additional physical effects that tend to
limit this expansion, such as the effect of plasma inertia and the possibility
of reconnection in the disk's corona, the latter possibly leading to repeated
cycles in the evolution. We also derive the condition for the existence of a
steady state for a resistive disk and conclude that a steady state
configuration is not realistically possible. Finally, we generalize our
analysis of the opening of magnetic field lines by using a non-self-similar
numerical model that applies to an arbitrarily rotating (e.g. keplerian) disk.Comment: 75 pages, 22 figures, 2 tables. Submitted to Astrophysical Journa
"Propeller" Regime of Disk Accretion to Rapidly Rotating Stars
We present results of axisymmetic magnetohydrodynamic simulations of the
interaction of a rapidly-rotating, magnetized star with an accretion disk. The
disk is considered to have a finite viscosity and magnetic diffusivity. The
main parameters of the system are the star's angular velocity and magnetic
moment, and the disk's viscosity, diffusivity. We focus on the "propeller"
regime where the inner radius of the disk is larger than the corotation radius.
Two types of magnetohydrodynamic flows have been found as a result of
simulations: "weak" and "strong" propellers. The strong propeller is
characterized by a powerful disk wind and a collimated magnetically dominated
outflow or jet from the star. The weak propeller have only weak outflows. We
investigated the time-averaged characteristics of the interaction between the
main elements of the system, the star, the disk, the wind from the disk, and
the jet. Rates of exchange of mass and angular momentum between the elements of
the system are derived as a function of the main parameters. The propeller
mechanism may be responsible for the fast spinning-down of the classical T
Tauri stars in the initial stages of their evolution, and for the spinning-down
of accreting millisecond pulsars.Comment: 18 pages, 16 figures, ApJ (accepted), added references, corrected
typos; see animation at
http://astrosun2.astro.cornell.edu/us-rus/disk_prop.ht
The Propeller Regime of Disk Accretion to a Rapidly Rotating Magnetized Star
The propeller regime of disk accretion to a rapidly rotating magnetized star
is investigated here for the first time by axisymmetric 2.5D
magnetohydrodynamic simulations. An expanded, closed magnetosphere forms in
which the magnetic field is predominantly toroidal. A smaller fraction of the
star's poloidal magnetic flux inflates vertically, forming a magnetically
dominated tower. Matter accumulates in the equatorial region outside
magnetosphere and accretes to the star quasi-periodically through elongated
funnel streams which cause the magnetic field to reconnect. The star spins-down
owing to the interaction of the closed magnetosphere with the disk. For the
considered conditions, the spin-down torque varies with the angular velocity of
the star omega* as omega*^1.3 for fixed mass accretion rate. The propeller
stage may be important in the evolution of X-ray pulsars, cataclysmic variables
and young stars. In particular, it may explain the present slow rotation of the
classical T Tauri stars.Comment: 5 pages with 4 figures, LaTeX, macros: emulapj.sty, avi movies are
available at http://www.astro.cornell.edu/us-russia/disk_prop.ht
HEALING POTENCY OF HAEMATOCOCCUS PLUVIALIS EXTRACT FOR TREATING TYPE 2 DIABETES IN RATS
Objective: The present study aims to evaluate the antidiabetic effect of ethanolic extract of Haematococcus pluvialis (H. pluvialis) in streptozotocin (STZ)-induced diabetic rats.Methods: The antidiabetic activity of H. pluvialis was investigated by the determination of glucose and insulin levels, aspartate (AST), alanine transaminases (ALT), lipid profile including total cholesterol (TC), triglycerides (TG), low-density lipoprotein-cholesterol (LDL-C) and high-density-lipoprotein-cholesterol (HDL-C). Histopathological examination of pancreas and liver were also carried out.Results: The results revealed that the levels of glucose, TC, TG, LDL-C as well as AST and ALT enzyme activities were increased significantly in diabetic rats. While, insulin and HDL-C levels decreased significantly in STZ-induced diabetic rats. The remediation of diabetic rats with H. pluvialis attenuated the elevated levels of glucose, TC, TG, LDL-C as well as AST and ALT activities in diabetic rats. Besides, it improved insulin, HDL-C levels, pancreas and hepatic architectures.Conclusion: H. pluvialis extract has a promising antidiabetic potency through attenuation of several metabolic disorders associated diabetes
MYCOBACTERIUM AVIUM SUBSP. PARATUBERCULOSIS IN RAW CAPRINE MILK
ABSTRACT One hundred and fifty individual caprine milk samples were analyzed for Mycobacterium avium subsp. paratuberculosis (MAP). Out of 150 samples tested for MAP, 53 (35.33%) samples could be detected by Enzyme-Linked Immunosobent Assay (ELISA) technique. However, one (0.67%) sample was found positive in Polymerase Chain Reaction (PCR) method and failed to be isolated from all the examined samples
A Solar Prominence Model
We propose a model for solar prominences based on converging flow observed in
the chromosphere and photosphere. In contrast with existing models we do not
apply a shearing motion along the neutral line. Instead we assume that bipolar
loops approaching on different sides of the neutral line have a non-vanishing
magnetic helicity of the SAME sign. In the converging flow the individual loops
kink and develop a skew. For loops of the same helicity the skew is in the same
sense. As a result the `chiral' symmetry of an aligned distribution of loops is
broken and the reconnecting loop system forms a filament with the observed
magnetic orientation and anchoring of the barbs in regions of parasytic
polarity. The filament consists of a number of individual strands of coaxial
coronal electric currents each of which is current neutralised. The filament
material is suspended in dips in the magnetic field and the transverse field
direction coincides with that in the Kuperus-Raadu model. Above the filament a
cavity forms with an overlying arcade consisting of the outer portions of the
reconnected loops.Comment: 17 pages, Late
- …