16,397 research outputs found
Creation of collective many-body states and single photons from two-dimensional Rydberg lattice gases
The creation of collective many-body quantum states from a two-dimensional
lattice gas of atoms is studied. Our approach relies on the van-der-Waals
interaction that is present between alkali metal atoms when laser excited to
high-lying Rydberg s-states. We focus on a regime in which the laser driving is
strong compared to the interaction between Rydberg atoms. Here energetically
low-lying many-particle states can be calculated approximately from a quadratic
Hamiltonian. The potential usefulness of these states as a resource for the
creation of deterministic single-photon sources is illustrated. The properties
of these photon states are determined from the interplay between the particular
geometry of the lattice and the interatomic spacing.Comment: 12 pages, 8 figure
Anisotropic effect of field on the orthorhombic-to-tetragonal transition in the striped cuprate (La,Nd)_{2-x}Sr_xCuO_4
The Nd-doped cuprate La_{2-y-x}Nd_ySr_xCuO_4 displays a first-order phase
transition at T_d (= 74 K for x=0.10, y = 0.60) to a low-temperature tetragonal
(LTT) phase. A magnetic field H applied || the a-axis leads to an increase in
T_d, whereas T_d is decreased when H || c. These effects show that magnetic
ordering involving both Nd and Cu spins plays a key role in driving the LTO-LTT
transition. Related anisotropic effects are observed in the uniform
susceptibility and the in-plane magnetoresistance.Comment: 5 pages, 5 figure
Feedback control of unstable cellular solidification fronts
We present a numerical and experimental study of feedback control of unstable
cellular patterns in directional solidification (DS). The sample, a dilute
binary alloy, solidifies in a 2D geometry under a control scheme which applies
local heating close to the cell tips which protrude ahead of the other. For the
experiments, we use a real-time image processing algorithm to track cell tips,
coupled with a movable laser spot array device, to heat locally. We show,
numerically and experimentally, that spacings well below the threshold for a
period-doubling instability can be stabilized. As predicted by the numerical
calculations, cellular arrays become stable, and the spacing becomes uniform
through feedback control which is maintained with minimal heating.Comment: 4 pages, 4 figures, 1 tabl
A Case Study of On-the-Fly Wide-Field Radio Imaging Applied to the Gravitational-wave Event GW 151226
We apply a newly-developed On-the-Fly mosaicing technique on the NSF's Karl
G. Jansky Very Large Array (VLA) at 3 GHz in order to carry out a sensitive
search for an afterglow from the Advanced LIGO binary black hole merger event
GW 151226. In three epochs between 1.5 and 6 months post-merger we observed a
100 sq. deg region, with more than 80% of the survey region having a RMS
sensitivity of better than 150 uJy/beam, in the northern hemisphere having a
merger containment probability of 10%. The data were processed in
near-real-time, and analyzed to search for transients and variables. No
transients were found but we have demonstrated the ability to conduct blind
searches in a time-frequency phase space where the predicted afterglow signals
are strongest. If the gravitational wave event is contained within our survey
region, the upper limit on any late-time radio afterglow from the merger event
at an assumed mean distance of 440 Mpc is about 1e29 erg/s/Hz. Approximately
1.5% of the radio sources in the field showed variability at a level of 30%,
and can be attributed to normal activity from active galactic nuclei. The low
rate of false positives in the radio sky suggests that wide-field imaging
searches at a few Gigahertz can be an efficient and competitive search
strategy. We discuss our search method in the context of the recent afterglow
detection from GW 170817 and radio follow-up in future gravitational wave
observing runs.Comment: 11 pages. 6 figures. 1 table. Accepted for publication in ApJ Letter
Why Global Inequality Matters: Derivative Global Egalitarianism
This article integrates empirical and normative discussions about why global economic inequalities matter in critically examining an approach known as derivative global egalitarianism (DGE). DGE is a burgeoning perspective that opposes excessive global economic inequality not based on the intrinsic value of equality but inequality\u27s negative repercussions on other values. The article aims to advance the research agenda by identifying and critically evaluating four primary varieties of DGE arguments from related but distinct literatures, which span a number of disciplines, including economics, international relations, and political philosophy. Overall, DGE offers a number of persuasive arguments as to why current levels of global inequality are of concern, but aspects of DGE beg further philosophical and empirical examination. By situating DGE within the wider theoretical and empirical contexts, this article provides resources for its critical assessment and theoretical development
Spin susceptibility, phase diagram, and quantum criticality in the electron-doped high Tc Superconductor Ba[Fe(1-x)Co(x)]2As2
We report a systematic investigation of Ba[Fe(1-x)Co(x)]2As2 based on
transport and 75-As NMR measurements, and establish the electronic phase
diagram. We demonstrate that doping progressively suppresses the uniform spin
susceptibility and low frequency spin fluctuations. The optimum superconducting
phase emerges at x_c~0.08 when the tendency toward spin ordering completely
diminishes. Our findings point toward the presence of a quantum critical point
near x_c between the SDW (spin density wave) and superconducting phases.Comment: 5 Figure
Rare charm meson decays D->Pl^+l^- and c->ul^+l^- in SM and MSSM
We study the nine possible rare charm meson decays D->Pl^+l^-
(P=pi,K,eta,eta') using the Heavy Meson Chiral Lagrangians and find them to be
dominated by the long distance contributions. The decay D^+ -> pi^+l^+l^- with
the branching ratio 1*10^(-6) is expected to have the best chances for an early
experimental discovery. The short distance contribution in the five Cabibbo
suppressed channels arises via the c->ul^+l^- transition; we find that this
contribution is detectable only in the D->pi l^+l^- decay, where it dominates
the differential spectrum at high-q^2. The general Minimal Supersymmetric
Standard Model can enhance the c->ul^+l^- rate by up to an order of magnitude;
its effect on the D->Pl^+l^- rates is small since the c->ul^+l^- enhancement is
sizable in low-q^2 region, which is inhibited in the hadronic decay.Comment: 17 page
Science and Film-making
The essay reviews the literature, mostly historical, on the relationship between science and film-making, with a focus on the science documentary. It then discusses the circumstances of the emergence of the wildlife making-of documentary genre. The thesis examined here is that since the early days of cinema, film-making has evolved from being subordinate to science, to being an equal partner in the production of knowledge, controlled by non-scientists
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