5,978 research outputs found
Dynamical entanglement purification using chains of atoms and optical cavities
In the framework of cavity QED, we propose a practical scheme to purify
dynamically a bipartite entangled state using short chains of atoms coupled to
high-finesse optical cavities. In contrast to conventional entanglement
purification protocols, we avoid CNOT gates, thus reducing complicated pulse
sequences and superfluous qubit operations. Our interaction scheme works in a
deterministic way, and together with entanglement distribution and swapping,
opens a route towards efficient quantum repeaters for long-distance quantum
communication.Comment: 13 pages, 6 figures, revised version with incorporated erratu
Diffraction of a Bose-Einstein condensate from a Magnetic Lattice on a Micro Chip
We experimentally study the diffraction of a Bose-Einstein condensate from a
magnetic lattice, realized by a set of 372 parallel gold conductors which are
micro fabricated on a silicon substrate. The conductors generate a periodic
potential for the atoms with a lattice constant of 4 microns. After exposing
the condensate to the lattice for several milliseconds we observe diffraction
up to 5th order by standard time of flight imaging techniques. The experimental
data can be quantitatively interpreted with a simple phase imprinting model.
The demonstrated diffraction grating offers promising perspectives for the
construction of an integrated atom interferometer.Comment: 4 pages, 4 figure
The QCD phase diagram from analytic continuation
We present the crossover line between the quark gluon plasma and the hadron
gas phases for small real chemical potentials. First we determine the effect of
imaginary values of the chemical potential on the transition temperature using
lattice QCD simulations. Then we use various formulas to perform an analytic
continuation to real values of the baryo-chemical potential. Our data set
maintains strangeness neutrality to match the conditions of heavy ion physics.
The systematic errors are under control up to MeV. For the
curvature of the transition line we find that there is an approximate agreement
between values from three different observables: the chiral susceptibility,
chiral condensate and strange quark susceptibility. The continuum extrapolation
is based on 10, 12 and 16 lattices. By combining the analysis for these
three observables we find, for the curvature, the value .Comment: 14 pages, 4 figures, revised versio
Characterization of aerosol plumes in nanosecond laser ablation of molecular solids at atmospheric pressure
Ablation of molecular solids with pulsed ultraviolet lasers at atmospheric pressure is an important process in (bio-)organic mass spectrometry. Of practical importance for analytical sampling and analysis are the plume formation and expansion. Plumes formed by atmospheric-pressure laser ablation of anthracene and 2,5-dihydroxybenzoic acid (2,5-DHB) were studied by light scattering imaging, which showed significant material release in the form of aerosols. The monitored plume expansion dynamics could be fitted to the drag-force model, yielding initial plume velocities of 150m/s for anthracene and 43m/s for DHB. While the angle of incidence does not affect the plume direction and propagation, a large dependence of the plume-expansion velocity on the laser pulse energy could be found, which is limited at atmospheric pressure by the onset of plasma shielding. With respect to analytical applications, the efficiency of sampling of the laser ablation products by a capillary could be experimentally visualize
The Ekman-Hartmann layer in MHD Taylor-Couette flow
We study magnetic effects induced by rigidly rotating plates enclosing a
cylindrical MHD Taylor-Couette flow at the finite aspect ratio . The
fluid confined between the cylinders is assumed to be liquid metal
characterized by small magnetic Prandtl number, the cylinders are perfectly
conducting, an axial magnetic field is imposed \Ha \approx 10, the rotation
rates correspond to \Rey of order . We show that the end-plates
introduce, besides the well known Ekman circulation, similar magnetic effects
which arise for infinite, rotating plates, horizontally unbounded by any walls.
In particular there exists the Hartmann current which penetrates the fluid,
turns into the radial direction and together with the applied magnetic field
gives rise to a force. Consequently the flow can be compared with a Taylor-Dean
flow driven by an azimuthal pressure gradient. We analyze stability of such
flows and show that the currents induced by the plates can give rise to
instability for the considered parameters. When designing an MHD Taylor-Couette
experiment, a special care must be taken concerning the vertical magnetic
boundaries so they do not significantly alter the rotational profile.Comment: 9 pages, 6 figures; accepted to PR
Probing Elemental Abundances in SNR 1987A Using XMM-Newton
We report on the latest (2007 Jan) observations of supernova remnant (SNR)
1987A from the XMM-Newton mission. Since the 2003 May observations of Haberl et
al. (2006), 11 emission lines have experienced increases in flux by factors ~ 3
to 10, with the 775 eV line of O VIII showing the greatest increase; we have
observed 6 lines of Fe XVII and Fe XVIII previously unreported by XMM-Newton. A
two-shock model representing plasmas in non-equilibrium ionization is fitted to
the EPIC-pn spectra, yielding temperatures of ~ 0.4 and ~ 3 keV, as well as
elemental abundances for N, O, Ne, Mg, Si, S and Fe. We demonstrate that the
abundance ratio of N and O can be constrained to less than ~20% accuracy.
Within the same confidence interval, the same analysis suggests that the C+N+O
abundance varies from ~ 1.1 to 1.4 X 10^-4. Normalizing our obtained abundances
by the Large Magellanic Cloud (LMC) values of Hughes, Hayashi & Koyama (1998),
we find that O, Ne, Mg and Fe are under-abundant, while Si and S are
over-abundant, consistent with the findings of Aschenbach (2007). Such a result
has implications for both the single-star and binary accretion/merger models
for the progenitor of SNR 1987A. In the context of the binary merger scenario
proposed by Morris & Podsiadlowski (2006, 2007), material forming the inner,
equatorial ring was expelled after the merger, implying that either our derived
Fe abundance is inconsistent with typical LMC values or that iron is
under-abundant at the site of the progenitor star of SNR 1987A.Comment: 14 pages, 10 diagrams (2 omitted). Accepted by Ap
An in-depth look at prior art in fast round-robin arbiter circuits
Arbiters are found where shared resources exist such as busses, switching fabrics, processing elements. Round-robin is a fair arbitration method, where requestors get near-equal shares of a common resource or service. Round-robin arbitration (RRA) finds use in network switches/routers and processor boards/systems as well as many other applications that have concurrency. Today's electronic systems require arbiters with hundreds of ports (e.g., switching fabrics with virtual I/O queues) and clock speeds near the limits of even the latest microelectronics fabrication processes/libraries. Achieving high clock speeds in the presence of large number of ports is only possible with highly parallel arbiter architectures. This paper presents an in-depth literature survey of previous work on this problem. It looks at RRA work in the literature in a bigger context, then defines the typical RRA problem (RRA_typical), and specifically investigates work on fast architectures that solve the RRA_typical problem. There are five such works that are really competitive. This report takes a very in-depth look at these works. It explains each architecture and how/why it works from a unique perspective that cannot be found in the original publication of that architecture. It also proposes improvements to these architectures. We wrote generators for the improved versions of these architectures. We will share a summary of synthesis results in this report – although a detailed account of how these results were obtained and their analysis is the subject of another (upcoming) publicatio
Dynamics of charged fluids and 1/L perturbation expansions
Some features of the calculation of fluid dynamo systems in
magnetohydrodynamics are studied. In the coupled set of the ordinary linear
differential equations for the spherically symmetric dynamos, the
problem represented by the presence of the mixed (Robin) boundary conditions is
addressed and a new treatment for it is proposed. The perturbation formalism of
large expansions is shown applicable and its main technical steps are
outlined.Comment: 16 p
Experimental partitioning of halogens and other trace elements between olivine, pyroxenes, amphibole and aqueous fluid at 2 GPa and 900–1,300 °C
We present new partition coefficients for various trace elements including Cl between olivine, pyroxenes, amphibole and coexisting chlorine-bearing aqueous fluid in a series of high-pressure experiments at 2 GPa between 900 and 1,300 °C in natural and synthetic systems. Diamond aggregates were added to the experimental capsule set-up in order to separate the fluid from the solid residue and enable in situ analysis of the quenched solute by LA–ICP–MS. The chlorine and fluorine contents in mantle minerals were measured by electron microprobe, and the nature of OH defects was investigated by infrared spectroscopy. Furthermore, a fluorine-rich olivine from one selected sample was investigated by TEM. Results reveal average Cl concentrations in olivine and pyroxenes around 20 ppm and up to 900 ppm F in olivine, making olivine an important repository of halogens in the mantle. Chlorine is always incompatible with Cl partition coefficients D Cl olivine/fluid varying between 10−5 and 10−3, whereas D Cl orthopyroxene/fluid and D Cl clinopyroxene/fluid are ~10−4 and D Cl amphibole/fluid is ~5 × 10−3. Furthermore, partitioning results for incompatible trace element show that compatibilities of trace elements are generally ordered as D amph/fluid ≈ D cpx/fluid > D opx/fluid > D ol/fluid but that D mineral/fluid for Li and P is very similar for all observed silicate phases. Infrared spectra of olivine synthesized in a F-free Ti-bearing system show absorption bands at 3,525 and ~3,570 cm−1. In F ± TiO2-bearing systems, additional absorption bands appear at ~3,535, ~3,595, 3,640 and 3,670 cm−1. Absorption bands at ~3,530 and ~3,570 cm−1, previously assigned to humite-like point defects, profit from low synthesis temperatures and the presence of F. The presence of planar defects could not be proved by TEM investigations, but dislocations in the olivine lattice were observed and are suggested to be an important site for halogen incorporation in olivine
Разработка способов, алгоритмов и программ обнаружения и исправления пакетных или независимых ошибок при передаче данных по каналам связи
Настоящая научно-квалификационная работа посвящена разработке способов, алгоритмов и программ обнаружения и исправления ошибок при передаче данных по каналам связи для обеспечения целостности и надёжности передаваемых команд и данных между устройствами вычислительно техники, а также при считывании данных из запоминающих устройств.The present scientific and qualification work is devoted to the development of methods, algorithms and programs for detecting and correcting errors in the transmission of data over communication channels to ensure the integrity and reliability of the transmitted commands and data between computing devices, as well as when reading data from memory devices
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