10,182 research outputs found
The dominant spin relaxation mechanism in compound organic semiconductors
Despite the recent interest in "organic spintronics", the dominant spin
relaxation mechanism of electrons or holes in an organic compound semiconductor
has not been conclusively identified. There have been sporadic suggestions that
it might be hyperfine interaction caused by background nuclear spins, but no
confirmatory evidence to support this has ever been presented. Here, we report
the electric-field dependence of the spin diffusion length in an organic
spin-valve structure consisting of an Alq3 spacer layer, and argue that this
data, as well as available data on the temperature dependence of this length,
contradict the notion that hyperfine interactions relax spin. Instead, they
suggest that the Elliott-Yafet mechanism, arising from spin-orbit interaction,
is more likely the dominant spin relaxing mechanism.Comment: Accepted for publication in Physical Review
A survey of max-type recursive distributional equations
In certain problems in a variety of applied probability settings (from
probabilistic analysis of algorithms to statistical physics), the central
requirement is to solve a recursive distributional equation of the form X =^d
g((\xi_i,X_i),i\geq 1). Here (\xi_i) and g(\cdot) are given and the X_i are
independent copies of the unknown distribution X. We survey this area,
emphasizing examples where the function g(\cdot) is essentially a ``maximum''
or ``minimum'' function. We draw attention to the theoretical question of
endogeny: in the associated recursive tree process X_i, are the X_i measurable
functions of the innovations process (\xi_i)?Comment: Published at http://dx.doi.org/10.1214/105051605000000142 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
How to Combine Fast Heuristic Markov Chain Monte Carlo with Slow Exact Sampling
Use each of n exact samples as the initial state for a MCMC sampler run for m
steps. We give confidence intervals for accuracy of estimators which are always
valid and which, in certain settings, are almost as good as the intervals one
would obtain if the (unknown) mixing time of the chain were known.Comment: 14 page
A latent factor model for spatial data with informative missingness
A large amount of data is typically collected during a periodontal exam.
Analyzing these data poses several challenges. Several types of measurements
are taken at many locations throughout the mouth. These spatially-referenced
data are a mix of binary and continuous responses, making joint modeling
difficult. Also, most patients have missing teeth. Periodontal disease is a
leading cause of tooth loss, so it is likely that the number and location of
missing teeth informs about the patient's periodontal health. In this paper we
develop a multivariate spatial framework for these data which jointly models
the binary and continuous responses as a function of a single latent spatial
process representing general periodontal health. We also use the latent spatial
process to model the location of missing teeth. We show using simulated and
real data that exploiting spatial associations and jointly modeling the
responses and locations of missing teeth mitigates the problems presented by
these data.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS278 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The determinants of aid in the post-cold war era
The authors estimate the responsiveness of aid to recipient countries' economic and physical needs, civil/political rights, and government effectiveness. They look exclusively at the post-Cold War era and use fixed effects to control for the political, strategic, and other considerations of donors. They find that aid and per capita income have been negatively related, while aid has been positively related to infant mortality, rights, and government effectiveness.Foreign aid program
Is there too little immigration? an analysis of temporary skilled migration
This paper presents a model of legal migration of temporary skilled workers from one source country to two host countries, both of which can control their levels of such immigration. Because of complementarities between capital and labor, the return on capital is positively related to the level of immigration. Consequently, when capital is immobile, host nations’ optimal levels of immigration are positively related to their capital endowments. Further, when capital is mobile between the host nations, the common return on capital is a function of the levels of immigration in both countries, meaning that immigration is a public good. As a result, when immigration imposes costs on host countries, the Nash equilibrium results in free riding and less immigration than would occur in the cooperative equilibrium. These results are qualitatively unaltered when capital mobility extends to the source nation.Emigration and immigration
Immigration and outsourcing: a general equilibrium analysis
We analyze the effects of outsourcing in the presence of a minimum wage by presenting a general-equilibrium model with an oligopolistic export sector and a competitive import-competing sector. An outsourcing tax is politically popular because it switches jobs to unemployed natives. It is also economically sound because it raises national income. An export subsidy may or may not be justified on welfare grounds. Increased international competition has no effect on the level of outsourcing, but the direction of its effect on unemployment and national income depends on the relative factor intensities of the two sectors.Immigrants ; Labor market ; Contracting out
Complex small-scale structure in the infrared extinction towards the Galactic Centre
A high level of complex structure, or ``granularity'', has been observed in
the distribution of infrared-obscuring material towards the Galactic Centre
(GC), with a characteristic scale of 5arcsec - 15arcsec, corresponding to 0.2 -
0.6pc at a GC distance of 8.5kpc. This structure has been observed in ISAAC
images which have a resolution of 0.6arcsec, significantly higher than that of
previous studies of the GC.
We have discovered granularity throughout the GC survey region, which covers
an area of 1.6deg x 0.8deg in longitude and latitude respectively (300pc x
120pc at 8.5kpc) centred on Sgr A*. This granularity is variable over the whole
region, with some areas exhibiting highly structured extinction in one or more
wavebands and other areas displaying no structure and a uniform stellar
distribution in all wavebands. The granularity does not appear to correspond to
longitude, latitude or radial distance from Sgr A*. We find that regions
exhibiting high granularity are strongly associated with high stellar
reddening.Comment: 5 pages, 3 figures, accepted for publication in ApJ
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