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 ${\bf H} = (\Phi_0/a^2)(1/2,1/2,1/2)$. We find that the model has a continuous phase transition with critical temperature $T_c = 0.681 J/k_B$, where $J$ is the XY coupling constant, and critical exponents $\alpha/\nu = 0.87 \pm 0.01$, $v/\nu = 0.82 \pm 0.01$, and $\nu = 0.72 \pm 0.07$, where $\alpha$, $v$, and $\nu$ 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 $\sim t^{d/(d+1)}$ for the $d$-dimensional system with $d\geq 2$. For nonzero temperature $T$, this crosses over to diffusive motion at long times with diffusivity $D\sim T^{-(d-1)/2}$. 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 $K$ 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 $K$ 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 $K$ 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 $K$ 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