36,405 research outputs found
Observation of Magnetic Moments in the Superconducting State of YBaCuO
Neutron Scattering measurements for YBaCuO have identified
small magnetic moments that increase in strength as the temperature is reduced
below and further increase below . An analysis of the data shows
the moments are antiferromagnetic between the Cu-O planes with a correlation
length of longer than 195 \AA in the - plane and about 35 \AA along the
c-axis. The origin of the moments is unknown, and their properties are
discusssed both in terms of Cu spin magnetism and orbital bond currents.Comment: 9 pages, and 4 figure
Neutron Scattering Studies of the Magnetic Fluctuations in YBa_2Cu_3O_{7-\delta}
Neutron scattering measurements have been made on the spin fluctuations in
YBa_2Cu_3O_{7-\delta} for different oxygen doping levels. Incommensurability is
clearly observed for oxygen concentrations of 6.6 and 6.7 and is suggested for
the 6.93. Measurements of the resonance for the O_{6.6} concentration show that
it exists in a broadened and less intense form at temperatures much higher than
T_c.Comment: 9 pages, 4 gif figures, Proceedings of Spectroscopies in Novel
Superconductors, Cape Cod, Massachusetts, Sept, 199
Additivity of Entangled Channel Capacity for Quantum Input States
An elementary introduction into algebraic approach to unified quantum
information theory and operational approach to quantum entanglement as
generalized encoding is given. After introducing compound quantum state and two
types of informational divergences, namely, Araki-Umegaki (a-type) and of
Belavkin-Staszewski (b-type) quantum relative entropic information, this paper
treats two types of quantum mutual information via entanglement and defines two
types of corresponding quantum channel capacities as the supremum via the
generalized encodings. It proves the additivity property of quantum channel
capacities via entanglement, which extends the earlier results of V. P.
Belavkin to products of arbitrary quantum channels for quantum relative entropy
of any type.Comment: 17 pages. See the related papers at
http://www.maths.nott.ac.uk/personal/vpb/research/ent_com.htm
Behavior of X-Ray Dust Scattering and Implications for X-Ray Afterglows of Gamma-Ray Bursts
The afterglows of gamma-ray bursts (GRBs) have commonly been assumed to be
due to shocks sweeping up the circum-stellar medium. However, most GRBs have
been found in dense star-forming regions where a significant fraction of the
prompt X-ray emission can be scattered by dust grains. Here we revisit the
behavior of dust scattering of X-rays in GRBs. We find that the features of
some X-ray afterglows from minutes to days after the gamma-ray triggers are
consistent with the scattering of prompt X-ray emission from GRBs off host dust
grains. This implies that some of the observed X-ray afterglows (especially
those without sharp rising and decaying flares) could be understood with a
dust-scattering--driven emission model.Comment: ApJ, in pres
A nucleon-pair and boson coexistent description of nuclei
We study a mixture of s-bosons and like-nucleon pairs with the standard
pairing interaction outside a inert core. Competition between the nucleon-pairs
and s-bosons is investigated in this scenario. The robustness of the BCS-BEC
coexistence and crossover phenomena is examined through an analysis of pf-shell
nuclei with realistic single-particle energies in which two configurations with
Pauli blocking of nucleon-pair orbits due to the formation of the s-bosons is
taken into account. When the nucleon-pair orbits are considered to be
independent of the s-bosons, the BCS-BEC crossover becomes smooth with the
number of the s-bosons noticeably more than that of the nucleonpairs near the
half-shell point, a feature that is demonstrated in the pf-shell for several
values of the standard pairing interaction strength. As a further test of the
robustness of the BCS-BEC coexistence and crossover phenomena in nuclei,
results are given for B(E2; 0^{+}_{g}->2^{+}_1) values of even-even 102-130Sn
with 100Sn taken as a core and valence neutron pairs confined within the 1d5/2,
0g7/2, 1d3/2, 2s1/2, 1h11/2 orbits in the nucleon-pair orbit and the s-boson
independent approximation. The results indicate that the B(E2) values are well
reproduced.Comment: 5.1 pages, 3 figures, LaTe
Pseudogap and incommensurate magnetic fluctuations in YBa_2Cu_3O_{6. 6}
Unpolarized inelastic neutron scattering is used to study the temperature and
wave vector dependence of the dynamical magnetic susceptibility,
, of a well characterized single crystal
( K). We find that a pseudogap opens in the spin fluctuation spectrum
at temperatures well above . We speculate that the appearance of the low
frequency incommensurate fluctuations is associated with the opening of the
pseudogap. To within the error of the measurements, a gap in the spin
fluctuation spectrum is found in the superconducting state.Comment: 6 pages, 3 ps figs, Proceedings of ICNS, Physica B, to be publishe
Image Properties of Embedded Lenses
We give analytic expressions for image properties of objects seen around
point mass lenses embedded in a flat CDM universe. An embedded lens in
an otherwise homogeneous universe offers a more realistic representation of the
lens's gravity field and its associated deflection properties than does the
conventional linear superposition theory. Embedding reduces the range of the
gravitational force acting on passing light beams thus altering all quantities
such as deflection angles, amplifications, shears and Einstein ring sizes.
Embedding also exhibits the explicit effect of the cosmological constant on
these same lensing quantities. In this paper we present these new results and
demonstrate how they can be used. The effects of embedding on image properties,
although small i.e., usually less than a fraction of a percent, have a more
pronounced effect on image distortions in weak lensing where the effects can be
larger than 10%. Embedding also introduces a negative surface mass density for
both weak and strong lensing, a quantity altogether absent in conventional
Schwarzschild lensing. In strong lensing we find only one additional quantity,
the potential part of the time delay, which differs from conventional lensing
by as much as 4%, in agreement with our previous numerical estimates.Comment: 17 pages, 6 figure
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