Think globally, buy locally: International agreements and government procurement

Abstract Do international treaties constrain national governments? The answer appears to be "yes" when it comes to the use of traditional barriers to trade, such as tariffs. Yet, while many governments have cut tariffs to comply with international agreements, they have often raised non-tariff barriers in their place. One increasingly prominent non-tariff barrier is discrimination in public procurement. Governments frequently discriminate against foreign suppliers in favor of domestic ones when buying goods and services. In an attempt to reduce procurement discrimination, international organizations, such as the World Trade Organization, have devoted ever more attention to members' procurement practices. Additionally, a growing number of preferential trade agreements seek to regulate public procurement. It remains unclear, however, whether international rules are effective in changing governments' purchasing behavior. Using original data, we find that neither multilateral nor preferential procurement agreements substantially reduce governments' propensity to "buy national." These results illustrate the difficulty of regulating non-transparent policy areas via international treaties

Propagating Coherent Acoustic Phonon Wavepackets in InMnAs/GaSb

We observe pronounced oscillations in the differential reflectivity of a ferromagnetic InMnAs/GaSb heterostructure using two-color pump-probe spectroscopy. Although originally thought to be associated with the ferromagnetism, our studies show that the oscillations instead result from changes in the position and frequency-dependent dielectric function due to the generation of coherent acoustic phonons in the ferromagnetic InMnAs layer and their subsequent propagation into the GaSb. Our theory accurately predicts the experimentally measured oscillation period and decay time as a function of probe wavelength.Comment: 4 pages, 4 figure

Photoresonance and conductivity of surface electrons on liquid ³He

Resonance variations of the in-plane conductivity of surface electrons (SEs) over liquid ³He induced by microwave (MW) radiation of a fixed frequency are experimentally and theoretically studied for low temperature scattering regimes (T < 0.5 K). The system was tuned to resonance by varying the amplitude of the vertical electric field which shifts the positions of SE Rydberg levels. The line-shape change and reversing of the sign of the effect are found to be opposite to that reported previously for weak vertical electric fields. A theoretical analysis of conductivity of the SE system heated due to decay of electrons excited to the second Rydberg level by the MW explains well the line-shape variations observed. It shows also that shifting the MW resonance into the range of weak vertical fields leads to important qualitative changes in the line-shape of SE conductivity which are in agreement with observations reported previously

Effects of electron-electron interactions on the electronic Raman scattering of graphite in high magnetic fields

We report the observation of strongly temperature-dependent, asymmetric spectral lines in electronic Raman scattering spectra of graphite in a high magnetic field up to 45 T applied along the c-axis. The magnetic field quantizes the in-plane motion, while the out-of-plane motion remains free, effectively reducing the system dimension from three to one. Optically created electron-hole pairs interact with, or shake up, the one-dimensional Fermi sea in the lowest Landau subbands. Based on the Tomonaga-Luttinger liquid theory, we show that interaction effects modify the van Hove singularity to the form $(\omega-\Delta)^{2\alpha-1/2}$ at zero temperature. At finite temperature, we predict a thermal broadening factor that increases linearly with the temperature. Our model reproduces the observed temperature-dependent line-shape, determining $\alpha$ to be $\sim$0.05 at 40 T

Magnetophonon resonance in graphite: High-field Raman measurements and electron-phonon coupling contributions

We perform Raman scattering experiments on natural graphite in magnetic fields up to 45 T, observing a series of peaks due to interband electronic excitations over a much broader magnetic field range than previously reported. We also explore electron-phonon coupling in graphite via magnetophonon resonances

Ultrahigh-Field Hole Cyclotron Resonance Absorption in InMnAs Films

We have carried out an ultrahigh-field cyclotron resonance study of p-type In1-xMnxAs films, with Mn composition x ranging from 0% to 2.5%, grown on GaAs by low-temperature molecular-beam epitaxy. Pulsed magnetic fields up to 500 T were used to make cyclotron resonance observable in these low-mobility samples. The clear observation of hole cyclotron resonance is direct evidence of the existence of a large number of itinerant, effective-mass-type holes rather than localized d-like holes. It further suggests that the p-d exchange mechanism is more favorable than the double exchange mechanism in this narrow gap InAs-based dilute magnetic semiconductor. In addition to the fundamental heavy-hole and light-hole cyclotron resonance absorption appearing near the high-magnetic-field quantum limit, we observed many inter-Landau-level absorption bands whose transition probabilities are stronglydependent on the sense of circular polarization of the incident light.Comment: 8 pages, 10 Postscript figure