62,549 research outputs found
Continuous phase transition of a fully frustrated XY model in three dimensions
We have used Monte Carlo simulations, combined with finite-size scaling and
two different real-space renormalization group approaches, to study a fully
frustrated three-dimensional XY model on a simple cubic lattice. This model
corresponds to a lattice of Josephson-coupled superconducting grains in an
applied magnetic field . We find that the
model has a continuous phase transition with critical temperature , where is the XY coupling constant, and critical exponents
, , and , where , , and describe the critical behavior of the
specific heat, helicity modulus, and correlation length. We briefly compare our
results with other studies of this model, and with a mean-field approximation.Comment: 34 pages, 13 figures, 1 table, Phys. Rev. B in pres
Policy spillovers in a regional target-setting regime
The present UK government has introduced a decentralised, target-driven framework for the delivery of regional policy in England. This paper analyses the operation of such a regime when there are spatial spillovers about which the government is uninformed. It stresses the simple idea that spillovers in such a setting normally lead to a sub-optimal allocation of policy expenditures. A key result is that the existence of negative spillovers on some policies generates expenditure switching towards those policies. The extent of the expenditure switching is related to a number of factors: the size of the spillovers; the initial policy weights in the government's welfare function; the number of agencies; the extent of their knowledge of spillovers; and their degree of collusion. Such expenditure switching is generally not welfare maximising
Superdiffusive nonequilibrium motion of an impurity in a Fermi sea
We treat the nonequilibrium motion of a single impurity atom in a
low-temperature single-species Fermi sea, interacting via a contact
interaction. In the nonequilibrium regime, the impurity does a superdiffusive
geometric random walk where the typical distance traveled grows with time as
for the -dimensional system with . For nonzero
temperature , this crosses over to diffusive motion at long times with
diffusivity . These results apply also to a nonzero
concentration of impurity atoms as long as they remain dilute and
nondegenerate.Comment: 5 pages, 1 figure, to appear in Phys. Rev.
Ballistic spreading of entanglement in a diffusive nonintegrable system
We study the time evolution of the entanglement entropy of a one-dimensional
nonintegrable spin chain, starting from random nonentangled initial pure
states. We use exact diagonalization of a nonintegrable quantum Ising chain
with transverse and longitudinal fields to obtain the exact quantum dynamics.
We show that the entanglement entropy increases linearly with time before
finite-size saturation begins, demonstrating a ballistic spreading of the
entanglement, while the energy transport in the same system is diffusive. Thus
we explicitly demonstrate that the spreading of entanglement is much faster
than the energy diffusion in this nonintegrable system.Comment: 7 pages, 7 figures. Published version. Supplementary material adde
Opulent Operetta and Marvelous Musicals
Program listing performers and works performe
Junior Recital, Micah Baldwin, tenor & Jasmin Ward, soprano
Junior RecitalMicah Baldwin, tenor & Jasmin Ward, sopranoDavid Kim, pianoTuesday, April 16, 2019 at 7:30pmRecital Hall / James W. Black Music Center1015 Grove Avenue / Richmond, Va
Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems
We study optimal delivery strategies of one common and independent
messages from a source to multiple users in wireless environments. In
particular, two-layered superposition of broadcast/multicast and unicast
signals is considered in a downlink multiuser OFDMA system. In the literature
and industry, the two-layer superposition is often considered as a pragmatic
approach to make a compromise between the simple but suboptimal orthogonal
multiplexing (OM) and the optimal but complex fully-layered non-orthogonal
multiplexing. In this work, we show that only two-layers are necessary to
achieve the maximum sum-rate when the common message has higher priority than
the individual unicast messages, and OM cannot be sum-rate optimal in
general. We develop an algorithm that finds the optimal power allocation over
the two-layers and across the OFDMA radio resources in static channels and a
class of fading channels. Two main use-cases are considered: i) Multicast and
unicast multiplexing when users with uplink capabilities request both
common and independent messages, and ii) broadcast and unicast multiplexing
when the common message targets receive-only devices and users with uplink
capabilities additionally request independent messages. Finally, we develop a
transceiver design for broadcast/multicast and unicast superposition
transmission based on LTE-A-Pro physical layer and show with numerical
evaluations in mobile environments with multipath propagation that the capacity
improvements can be translated into significant practical performance gains
compared to the orthogonal schemes in the 3GPP specifications. We also analyze
the impact of real channel estimation and show that significant gains in terms
of spectral efficiency or coverage area are still available even with
estimation errors and imperfect interference cancellation for the two-layered
superposition system
Spotted Seals, Phoca largha, in Alaska
The worldwide literature on management of spotted seals, Phoca largha, was reviewed and updated, and aerial surveys weref lown in 1992 and 1993 to determine the species' distribution and abundance in U.S. waters. In April, spotted seals were found only in the Bering Sea ice front. In June, they were seen along deteriorating ice floes and fast ice in Norton Sound. Surveys along most of Alaska's western coast in August and September found over 2,500 spotted seals in Kuskokwim Bay and concentrations of 100-400 seals around Nunivak Island, Scammon Bay, Golovnin Bay/Norton Sound, Cape Espenberg/Kotzebue Sound, and Kasegaluk Lagoon. All of these sites have been used by spotted seals in the past. The sum of the highest counts, irrespective of year, was 3,570 seals (CV =0.06). This is not an abundance estimate for all spotted seals in the Bering Sea, because it does not account for animals in the water, and we did not survey the Asian coast and some islands. Also, spotted seals and harbor seals, Phoca vitulina, are too similar in appearance to be identified accurately from the air, so our results probably include a mix of these species where their ranges overlap
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