10,412 research outputs found
Efficient-phase-encoding protocols for continuous-variable quantum key distribution using coherent states and postselection
We propose efficient-phase-encoding protocols for continuous-variable quantum
key distribution using coherent states and postselection. By these phase
encodings, the probability of basis mismatch is reduced and total efficiency is
increased. We also propose mixed-state protocols by omitting a part of
classical communication steps in the efficient-phase-encoding protocols. The
omission implies a reduction of information to an eavesdropper and possibly
enhances the security of the protocols. We investigate the security of the
protocols against individual beam splitting attack.Comment: RevTeX4, 8 pages, 9 figure
Identification of Xenopus SMC protein complexes required for sister chromatid cohesion
The structural maintenance of chromosomes (SMC) family is a growing family of chromosomal ATPases. The founding class of SMC protein complexes, condensins, plays a central role in mitotic chromosome condensation. We report here a new class of SMC protein complexes containing XSMC1 and XSMC3, Xenopus homologs of yeast Smc1p and Smc3p, respectively. The protein complexes (termed cohesins) exist as two major forms with sedimentation coefficients of 9S and 14S. 9S cohesin is a heterodimer of XSMC1 and XSMC3, whereas 14S cohesin contains three additional subunits. One of them has been identified as a Xenopus homolog of the Schizosaccharomyces pombe Rad21p implicated in DNA repair and the Saccharomyces cerevisiae Scc1p/Mcd1p implicated in sister chromatid cohesion. 14S cohesin binds to interphase chromatin independently of DNA replication and dissociates from it at the onset of mitosis. Immunodepletion of cohesins during interphase causes defects in sister chromatid cohesion in subsequent mitosis, whereas condensation is unaffected. These results suggest that proper assembly of mitotic chromosomes is regulated by two distinct classes of SMC protein complexes, cohesins and condensins
A High Stellar Obliquity in the WASP-7 Exoplanetary System
We measure a tilt of 86+-6 deg between the sky projections of the rotation
axis of the WASP-7 star, and the orbital axis of its close-in giant planet.
This measurement is based on observations of the Rossiter-McLaughlin (RM)
effect with the Planet Finder Spectrograph on the Magellan II telescope. The
result conforms with the previously noted pattern among hot-Jupiter hosts,
namely, that the hosts lacking thick convective envelopes have high
obliquities. Because the planet's trajectory crosses a wide range of stellar
latitudes, observations of the RM effect can in principle reveal the stellar
differential rotation profile; however, with the present data the signal of
differential rotation could not be detected. The host star is found to exhibit
radial-velocity noise (``stellar jitter') with an amplitude of ~30m/s over a
timescale of days.Comment: ApJ accepted, 9 pages, 9 figure
Mechanism of phase transitions and the electronic density of states in (La,Sm)FeAsOF from ab initio calculations
The structure and electronic density of states in layered
LnFeAsOF (Ln=La,Sm; =0.0, 0.125, 0.25) are investigated using
density functional theory. For the =0.0 system we predict a complex
potential energy surface, formed by close-lying single-well and double-well
potentials, which gives rise to the tetragonal-to-orthorhombic structural
transition, appearance of the magnetic order, and an anomaly in the specific
heat capacity observed experimentally at temperatures below 140--160 K.
We propose a mechanism for these transitions and suggest that these phenomena
are generic to all compounds containing FeAs layers. For 0.0 we demonstrate
that transition temperatures to the superconducting state and their dependence
on correlate well with the calculated magnitude of the electronic density
of states at the Fermi energy.Comment: 4 pages, 3 figures, 1 tabl
Potential Profiling of the Nanometer-Scale Charge Depletion Layer in n-ZnO/p-NiO Junction Using Photoemission Spectroscopy
We have performed a depth-profile analysis of an all-oxide p-n junction diode
n-ZnO/p-NiO using photoemission spectroscopy combined with Ar-ion sputtering.
Systematic core-level shifts were observed during the gradual removal of the
ZnO overlayer, and were interpreted using a simple model based on charge
conservation. Spatial profile of the potential around the interface was
deduced, including the charge-depletion width of 2.3 nm extending on the ZnO
side and the built-in potential of 0.54 eV
Relativistic Viscous Hydrodynamics for Multi-Component Systems with Multiple Conserved Currents
We would like to formulate relativistic dissipative hydrodynamics for
multi-component systems with multiple conserved currents. This is important for
analyses of the hot matter created in relativistic heavy ion collisions because
particle creations and annihilations of various particle species are frequently
taking place there. We show that consistent formulation in such systems
involves many non-trivialities, and derive constitutive equations that satisfy
Onsager reciprocal relations and describe the systems without ambiguity.Comment: 4 pages, no figures - To appear in the conference proceedings for Hot
Quarks 2010, June 21-26, La Londe-les-Maures, Franc
Describing transverse dynamics and space-time evolution at RHIC in a hydrodynamic model with statistical hadronization
A hydrodynamic model coupled to the statistical hadronization code
Therminator is used to study a set of observables in the soft sector at RHIC. A
satisfactory description of the pT-spectra and elliptic flow is obtained,
similarly to other hydrodynamic models. With the Gaussian initial conditions
the transverse femtoscopic radii are also reproduced, providing a possible
solution of the RHIC HBT puzzle.Comment: to appear in the conference proceedings for Quark Matter 2009, March
30 - April 4, Knoxville, Tennesse
200 A GeV Au+Au collisions serve a nearly perfect quark-gluon liquid
The specific shear viscosity (eta/s)_QGP of a Quark-Gluon-Plasma (QGP) at
temperatures T_c < T < 2T_c is extracted from the centrality dependence of the
eccentricity-scaled elliptic flow measured in ultra-relativistic heavy-ion
collisions. Coupling viscous fluid dynamics for the QGP with a microscopic
transport model for hadronic freeze-out we find that the eccentricity-scaled
elliptic flow is a universal function of charged multiplicity per unit overlap
area, (1/S)(dN_ch/dy), that depends only on the viscosity but not on the model
used for computing the initial fireball eccentricity. Comparing with
measurements we find 1 < (4pi)(eta/s)_QGP < 2.5 where the uncertainty range is
dominated by model uncertainties for the eccentricity values used to normalize
the measured elliptic flow.Comment: 4 pages, 2 figures, accepted by PR
Exact Analysis of Entanglement in Gapped Quantum Spin Chains
We investigate the entanglement properties of the valence-bond-solid states
with generic integer-spin . Using the Schwinger boson representation of the
valence-bond-solid states, the entanglement entropy, the von Neumann entropy of
a subsystem, is obtained exactly and its relationship with the usual
correlation function is clarified. The saturation value of the entanglement
entropy, , is derived explicitly and is interpreted in terms of
the edge-state picture. The validity of our analytical results and the
edge-state picture is numerically confirmed. We also propose a novel
application of the edge state as a qubit for quantum computation.Comment: 4 pages, 2 figure
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