4,441 research outputs found
Economic geography : real or hype?
Economic geography has become a mantra for many economists, geographers, and regional scientists. Previous studies have tested the importance of economic geography for production activities and found a significant association between them. Most of these studies, however, have not taken into account that economic geography influences location decisions at the firm level. The authors show a potential bias that can arise when firm location choices are not considered in estimating the contribution of economic geography to industry performance. Their analysis using microdata of Indian manufacturingfirms shows there is an upward bias in the contribution of economic geography to productivity when firm location choices are not considered in the analysis.Economic Theory&Research,Banks&Banking Reform,Environmental Economics&Policies,Water and Industry,Labor Policies,Economic Theory&Research,Environmental Economics&Policies,Banks&Banking Reform,Water and Industry,National Urban Development Policies&Strategies
Economic structure, productivity, and infrastructure quality in southern Mexico
There are large and sustained differences in the economic performance of sub-national regions in most countries. The authors examine the economic structure and productivity in Southern Mexico and compare it with the rest of the country. The authors use firm level data from Mexican manufacturing to test the relative importance of firm level characteristics (such as human capital and technology adoption) compared with external characteristics (such as infrastructure quality and regulatory environment) in explaining productivity differentials. The authors find that the economic structure of Southern Mexico is considerably different from the rest of the country, with the economic landscape dominated by micro enterprises and a relative specialization in low productivity activities. This, coupled with low skill levels and fewer skill upgrading opportunities, reduces the performance of Southern firms. Productivity differentials between Southern firms and others, however, only exist for micro enterprises. The econometric analysis shows that while employee training and technology adoption enhance productivity, access to markets by improving transport infrastructure that link urban areas also have important productivity effects.Labor Policies,Economic Theory&Research,Municipal Financial Management,Environmental Economics&Policies,Banks&Banking Reform,Environmental Economics&Policies,Economic Theory&Research,Banks&Banking Reform,Municipal Financial Management,Microfinance
Quantitative study of molecular N_2 trapped in disordered GaN:O films
The structure of disordered GaN:O films grown by ion-assisted deposition is
investigated using x-ray absorption near-edge spectroscopy and Raman
spectroscopy. It is found that between 4 and 21 % of the nitrogen in the films
is in the form of molecular N_2 that interacts only weakly with the surrounding
matrix. The anion to cation ratio in the GaN:O host remains close to unity, and
there is a close correlation between the N_2 fraction, the level of oxygen
impurities, and the absence of short-range order in the GaN:O matrix.Comment: 5 pages, 3 figure
Coarsening Dynamics of an Antiferromagnetic XY model on the Kagome Lattice: Breakdown of the Critical Dynamic Scaling
We find a breakdown of the critical dynamic scaling in the coarsening
dynamics of an antiferromagnetic {\em XY} model on the kagome lattice when the
system is quenched from disordered states into the Kosterlitz-Thouless ({\em
KT}) phases at low temperatures. There exist multiple growing length scales:
the length scales of the average separation between fractional vortices are
found to be {\em not} proportional to the length scales of the quasi-ordered
domains. They are instead related through a nontrivial power-law relation. The
length scale of the quasi-ordered domains (as determined from optimal collapse
of the correlation functions for the order parameter )
does not follow a simple power law growth but exhibits an anomalous growth with
time-dependent effective growth exponent. The breakdown of the critical dynamic
scaling is accompanied by unusual relaxation dynamics in the decay of
fractional () vortices, where the decay of the vortex numbers is
characterized by an exponential function of logarithmic powers in time.Comment: 13 pages, 26 figure
Spatially Resolved Stellar Populations of Eight GOODS-South Active Galactic Nuclei at z ~ 1
We present a pilot study of the stellar populations of eight active galactic nucleus (AGN) hosts at z ~ 1 and compare with (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the Great Observatories Origins Deep Survey South field obtained with the laser guide star adaptive optics system at Keck Observatory. We combine these K' data with B, V, i, and z imaging from the Advanced Camera for Surveys on Hubble Space Telescope to give multicolor photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGNs as inferred from their high X-ray luminosities (LX > 10^42 erg s^–1) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [O III] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there are only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR spectral energy distributions of the strong Type II AGNs indicate that they are excited to Luminous InfraRed Galaxy (LIRG) status via galactic starbursting, while the strong Type I AGNs are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGNs at z ~ 1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are by-products of this starbursting
Tracing the Spiral Structure of the Outer Milky Way with Dense Atomic Hydrogen Gas
We present a new face-on map of dense neutral atomic hydrogen (HI) gas in the
outer Galaxy. Our map has been produced from the Leiden/Argentine/Bonn (LAB) HI
21-cm line all-sky survey by finding intensity maxima along every line of sight
and then by projecting them on the Galactic plane. The resulting face-on map
strikingly reveals the complex spiral structure beyond the solar circle, which
is characterized by a mixture of distinct long arcs of HI concentrations and
numerous 'interarm' features. The comparison with more conventional spiral
tracers confirms the nature of those long arc structures as spiral arms. Our
map shows that the HI spiral structure in the outer Galaxy is well described by
a four-arm spiral model (pitch angle of 12 deg) with some deviations, and gives
a new insight into identifying HI features associated with individual arms.Comment: 24 pages, 10 figures, 3 tables; accepted for publication in PAS
Optical Spectroscopy of Active Galactic Nuclei in SA57
The cosmological evolution of X-ray-selected and optically selected Active
Galactic Nuclei (AGNs) show different behaviours interpreted in terms of two
different populations. The difference is evident mainly for low luminosity AGNs
(LLAGNs), many of which are lost by optical photometric surveys. We are
conducting a spectroscopical study of a composite sample of AGN candidates
selected in SA57 following different searching techniques, to identify low
luminosity AGNs and break down the sample into different classes of objects.
AGN candidates were obtained through optical variability and/or X-ray emission.
Of special interest are the extended variable objects, which are expected to be
galaxies hosting LLAGNs. Among the 26 classified objects a fair number (9) show
typical AGN spectra. 10 objects show Narrow Emission Line Galaxy spectra, and
in most of them (8/10) optical variability suggests the presence of LLAGNs.Comment: 7 pages, 8 figures, to appear in A&
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