11,649 research outputs found
Raman scattering in a Heisenberg {\boldmath } antiferromagnet on the triangular lattice
We investigate two-magnon Raman scattering from the Heisenberg
antiferromagnet on the triangular lattice, considering both the effect of
renormalization of the one-magnon spectrum by 1/S corrections and final-state
magnon-magnon interactions. The bare Raman intensity displays two peaks related
to one-magnon van-Hove singularities. We find that 1/S self-energy corrections
to the one-magnon spectrum strongly modify this intensity profile. The central
Raman-peak is significantly enhanced due to plateaus in the magnon dispersion,
the high frequency peak is suppressed due to magnon damping, and the overall
spectral support narrows considerably. Additionally we investigate final-state
interactions by solving the Bethe-Salpeter equation to . In contrast to
collinear antiferromagnets, the non-collinear nature of the magnetic ground
state leads to an irreducible magnon scattering which is retarded and
non-separable already to lowest order. We show that final-state interactions
lead to a rather broad Raman-continuum centered around approximately twice the
'roton'-energy. We also discuss the dependence on the scattering geometry.Comment: 7 pages, 5 figure
Teaching Locals New Tricks: Foreign Experts as a Channel of Knowledge Transfers
Gains from productivity and knowledge transmission arising from the presence of foreign firms have received a good deal of empirical attention, but theoretical micro-foundations for this mechanism are limited. Here we develop a dynamic model in which foreign experts may train domestic workers who work with them. Gains from training can in turn be decomposed into two types: (a) obtaining knowledge and skills at a lower cost than if they were self-learnt at home, (b) producing domestic skilled workers earlier in time than if the domestic economy had to rediscover the relevant knowledge through "reinventing the wheel." We use fixed effects and nearest neighbour matching estimators on a panel of plant-level data for Colombia that identifies the use of foreign experts, to show that these experts have substantial, although not always immediate, positive effects on the wages of domestic workers and on the value added per worker.
Snca and Bdnf gene expression in the VTA and raphe nuclei of midbrain in chronically victorious and defeated male mice
The study aimed to analyze the mRNA levels of Snca and Bdnf genes in the ventral tegmental area (VTA) and raphe nuclei of the midbrain in male mice that had each won or defeated 20 encounters in daily agonistic interactions. Groups of animals that had the same winning and losing track record followed by a no-fight period for 14 days were also studied. Snca mRNA levels were increased in the raphe nuclei in the losers and in the VTA of the winners. After fighting deprivation Snca mRNA levels were decreased to the control level in both groups. Snca mRNA levels were similar to the control level in the VTA of the losers and in the raphe nuclei of the winners. However Snca gene expression was increased in these areas after no-fight period in the winners and losers in comparison with respective mRNA levels in the undeprived animals. Significant positive correlations were found between the mRNA levels of Snca and Bdnf genes in the raphe nuclei. It was concluded, that social experience affects Snca gene expression depending on brain areas and functional activity of monoaminergic systems in chronically victorious or defeated mice
The Influence of Budgeting Based on Performance on the Effectiveness of Financial Control and the Effectiveness of Performance Control at Tomohon City Government
Budgeting based on performance is the answer to use as a tool for measuring and accounting for government performance. It is a method of budgeting for management to link any funding outlined in activities with expected outputs and outcomes, including efficiency in achieving results from those outputs. The purpose of this study is to know the budgeting based on performance on the effectiveness of financial control and effectiveness of performance control. The object of this research was conducted at local government work unit (SKPD) of Tomohon local government using simple regression analysis to know influence of budgeting based on performance to effectiveness of financial control and effectiveness of performance control from 14 service in Tomohon city. The results of this study support a causal relationship between budgeting based on performance with the effectiveness of financial control and effectiveness of performance control. It can be used as a tool to achieve effectiveness in financial control
Eccentricity and Spin-Orbit Misalignment in Short-Period Stellar Binaries as a Signpost of Hidden Tertiary Companions
Eclipsing binaries are observed to have a range of eccentricities and
spin-orbit misalignments (stellar obliquities). Whether such properties are
primordial, or arise from post-formation dynamical interactions remains
uncertain. This paper considers the scenario in which the binary is the inner
component of a hierarchical triple stellar system, and derives the requirements
that the tertiary companion must satisfy in order to raise the eccentricity and
obliquity of the inner binary. Through numerical integrations of the secular
octupole-order equations of motion of stellar triples, coupled with the spin
precession of the oblate primary star due to the torque from the secondary, we
obtain a simple, robust condition for producing spin-orbit misalignment in the
inner binary: In order to excite appreciable obliquity, the precession rate of
the stellar spin axis must be smaller than the orbital precession rate due to
the tertiary companion. This yields quantitative requirements on the mass and
orbit of the tertiary. We also present new analytic expressions for the maximum
eccentricity and range of inclinations allowing eccentricity excitation
(Lidov-Kozai window), for stellar triples with arbitrary masses and including
the non-Keplerian potentials introduced by general relativity, stellar tides
and rotational bulges. The results of this paper can be used to place
constraints on unobserved tertiary companions in binaries that exhibit high
eccentricity and/or spin-orbit misalignment, and will be helpful in guiding
efforts to detect external companions around stellar binaries. As an
application, we consider the eclipsing binary DI Herculis, and identify the
requirements that a tertiary companion must satisfy to produce the observed
spin-orbit misalignment.Comment: 19 pages, 15 figures, accepted for publication in MNRA
Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters
Many exoplanetary systems containing hot Jupiters are observed to have highly
misaligned orbital axes relative to the stellar spin axes. Kozai-Lidov
oscillations of orbital eccentricity/inclination induced by a binary companion,
in conjunction with tidal dissipation, is a major channel for the production of
hot Jupiters. We demonstrate that gravitational interaction between the planet
and its oblate host star can lead to chaotic evolution of the stellar spin axis
during Kozai cycles. As parameters such as the planet mass and stellar rotation
period vary, periodic islands can appear in an ocean of chaos, in a manner
reminiscent of other dynamical systems. In the presence of tidal dissipation,
the complex spin evolution can leave an imprint on the final spin-orbit
misalignment angles.Comment: 26 pages, 13 figures. Includes supplementary materials. To be
published in the September 12, 2014 edition of Science Magazine. For
additional information, please visit
http://astro.cornell.edu/~dong/sciencepaper.htm
Vortex nucleation by collapsing bubbles in Bose-Einstein condensates
The nucleation of vortex rings accompanies the collapse of ultrasound bubbles
in superfluids. Using the Gross-Pitaevskii equation for a uniform condensate we
elucidate the various stages of the collapse of a stationary spherically
symmetric bubble and establish conditions necessary for vortex nucleation. The
minimum radius of the stationary bubble, whose collapse leads to vortex
nucleation, was found to be about 28 healing lengths. The time after which the
nucleation becomes possible is determined as a function of bubble's radius. We
show that vortex nucleation takes place in moving bubbles of even smaller
radius if the motion made them sufficiently oblate.Comment: 4 pages, 5 figure
Runaway Merger Shocks in Galaxy Cluster Outskirts and Radio Relics
Moderately strong shocks arise naturally when two subclusters merge. For
instance, when a smaller subcluster falls into the gravitational potential of a
more massive cluster, a bow shock is formed and moves together with the
subcluster. After pericenter passage, however, the subcluster is decelerated by
the gravity of the main cluster, while the shock continues moving away from the
cluster center. These shocks are considered as promising candidates for
powering radio relics found in many clusters. The aim of this paper is to
explore the fate of such shocks when they travel to the cluster outskirts, far
from the place where the shocks were initiated. In a uniform medium, such a
"runaway" shock should weaken with distance. However, as shocks move to large
radii in galaxy clusters, the shock is moving down a steep density gradient
that helps the shock to maintain its strength over a large distance.
Observations and numerical simulations show that, beyond , gas density
profiles are as steep as, or steeper than, , suggesting that there
exists a "Habitable zone" for moderately strong shocks in cluster outskirts
where the shock strength can be maintained or even amplified. A characteristic
feature of runaway shocks is that the strong compression, relative to the
initial state, is confined to a narrow region just behind the shock. Therefore,
if such a shock runs over a region with a pre-existing population of
relativistic particles, then the boost in radio emissivity, due to pure
adiabatic compression, will also be confined to a narrow radial shell.Comment: 9 pages, 8 figures; published in MNRA
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