54,905 research outputs found
Chiral spin-wave excitations of the spin-5/2 trimers in the langasite compound Ba3NbFe3Si2O14
The inelastic scattering of neutrons from magnetic excitations in the
antiferromagnetic phase of the langasite compound Ba3NbFe3Si2O14 is analyzed
theoretically. In the calculations presented, the strongly coupled spin-5/2 Fe
triangles are accounted for as trimerized units. The weaker interactions
between the trimers are included within the mean-field/random-phase
approximation. The theory is compared with linear spin-wave theory, and a model
is developed which leads to good agreement with the published results from
unpolarized and polarized neutron-scattering experiments.Comment: 10 pages, 9 figure
A parallel algorithm for the enumeration of benzenoid hydrocarbons
We present an improved parallel algorithm for the enumeration of fixed
benzenoids B_h containing h hexagonal cells. We can thus extend the enumeration
of B_h from the previous best h=35 up to h=50. Analysis of the associated
generating function confirms to a very high degree of certainty that and we estimate that the growth constant and the amplitude .Comment: 14 pages, 6 figure
Honeycomb lattice polygons and walks as a test of series analysis techniques
We have calculated long series expansions for self-avoiding walks and
polygons on the honeycomb lattice, including series for metric properties such
as mean-squared radius of gyration as well as series for moments of the
area-distribution for polygons. Analysis of the series yields accurate
estimates for the connective constant, critical exponents and amplitudes of
honeycomb self-avoiding walks and polygons. The results from the numerical
analysis agree to a high degree of accuracy with theoretical predictions for
these quantities.Comment: 16 pages, 9 figures, jpconf style files. Presented at the conference
"Counting Complexity: An international workshop on statistical mechanics and
combinatorics." In celebration of Prof. Tony Guttmann's 60th birthda
"Fear" and Offshoring: The Scope and Potential Impact of Imports and Exports of Services
Commentators, including Princeton University's Alan Blinder, estimate 40 million jobs could be at risk of being offshored over the next 20 years and suggest American workers should specialize in services that can be delivered face-to-face. In contrast, Jensen and Kletzer expect the process of globalization in services will proceed much as it has in manufacturing: They estimate only 15-20 million jobs are at risk of being offshored to low-wage, labor-abundant countries; approximately 40 percent of these jobs will be in the manufacturing sector, long considered "at risk." They expect these losses to be offset by job gains in high-wage activities from services exporting. The United States will retain its comparative advantage in high-skill, high-wage production and increase these activities in tradable service industries as trade barriers diminish. While the loss of low-wage activities that are offshored and the gain from high-wage service exports will cause dislocation, the globalization of services production is likely to have productivity-enhancing effects similar to the impact of globalization in the manufacturing sector, offering significant potential to improve living standards in the United States and around the world.
Low-density series expansions for directed percolation II: The square lattice with a wall
A new algorithm for the derivation of low-density expansions has been used to
greatly extend the series for moments of the pair-connectedness on the directed
square lattice near an impenetrable wall. Analysis of the series yields very
accurate estimates for the critical point and exponents. In particular, the
estimate for the exponent characterizing the average cluster length near the
wall, , appears to exclude the conjecture . The
critical point and the exponents and have the
same values as for the bulk problem.Comment: 8 pages, 1 figur
Generalized contour deformation method in momentum space: two-body spectral structures and scattering amplitudes
A generalized contour deformation method (GCDM) which combines complex
rotation and translation in momentum space, is discussed. GCDM gives accurate
results for bound, virtual (antibound), resonant and scattering states starting
with a realistic nucleon-nucleon interaction. It provides a basis for full
off-shell -matrix calculations both for real and complex input energies.
Results for both spectral structures and scattering amplitudes compare
perfectly well with exact values for the separable Yamaguchi potential.
Accurate calculation of virtual states in the Malfliet-Tjon and the realistic
CD-Bonn nucleon-nucleon interactions are presented.
GCDM is also a promising method for the computation of in-medium properties
such as the resummation of particle-particle and particle-hole diagrams in
infinite nuclear matter. Implications for in-medium scattering are discussed.Comment: 15 pages, revte
Tradable Services: Understanding the Scope and Impact of Services Outsourcing
We develop a new empirical approach to identify tradable service activities. Contrary to conventional views of service activities as nontradable, we find a significant number of service industries and occupations that appear tradable and substantial employment in these tradable activities. Workers employed in tradable service activities differ from those employed in tradable manufacturing and nontradable services. Workers in tradable service activities have higher skill levels and are paid higher wages than manufacturing workers or workers in nontradable service activities. In general, we find little evidence that tradable service activities have lower employment growth than other service activities. However, evidence suggests lower employment growth at the lowest end of the skill distribution. There is also evidence of higher worker displacement rates in tradable services. Workers displaced from tradable service activities are different from displaced manufacturing workers: Displaced tradable service workers have higher skills and higher predisplacement earnings than displaced manufacturing workers.services, offshoring, trade, labor, information technology, jobs
Connecting the Micro-dynamics to the Emergent Macro-variables: Self-Organized Criticality and Absorbing Phase Transitions in the Deterministic Lattice Gas
We reinvestigate the Deterministic Lattice Gas introduced as a paradigmatic
model of the 1/f spectra (Phys. Rev. Lett. V26, 3103 (1990)) arising according
to the Self-Organized Criticality scenario. We demonstrate that the density
fluctuations exhibit an unexpected dependence on systems size and relate the
finding to effective Langevin equations. The low density behavior is controlled
by the critical properties of the gas at the absorbing state phase transition.
We also show that the Deterministic Lattice Gas is in the Manna universality
class of absorbing state phase transitions. This is in contrast to expectations
in the literature which suggested that the entirely deterministic nature of the
dynamics would put the model in a different universality class. To our
knowledge this is the first fully deterministic member of the Manna
universality class.Comment: 8 pages, 12 figures. Changes in the new version: Reference list has
been correcte
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