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 $B_h \sim A \kappa^h /h$ and we estimate that the growth constant $\kappa = 5.161930154(8)$ and the amplitude $A=0.2808499(1)$.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, $\tau_1=1.00014(2)$, appears to exclude the conjecture $\tau_1=1$. The critical point and the exponents $\nu_{\parallel}$ and $\nu_{\perp}$ 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 $t$-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