Market Access, Openness and Growth

This paper identifies a causal effect of openness to international trade on growth. It does so by using tariff barriers of the United States as instruments for the openness of developing countries. Trade liberalization by a large trading partner causes an expansion in the trade of other countries. Trade expansion induced by greater market access appears to cause a quantitatively large acceleration in the growth rates of developing countries. Eliminating existing developed world tariffs would increase developing country trade to GDP ratios by one third and growth rates by 0.6 to 1.6 percent per annum.

Improved Limits on Spin-Mass Interactions

Very light particles with CP-violating couplings to ordinary matter, such as axions or axion-like particles, can mediate long-range forces between polarized and unpolarized fermions. We describe a new experimental search for such forces between unpolarized nucleons in two 250 kg Pb weights and polarized neutrons and electrons in a $^3$He-K co-magnetometer located about 15 cm away. We place improved constrains on the products of scalar and pseudoscalar coupling constants, $g^n_p g^N_s < 4.2\times10^{-30}$ and $g^e_p g^N_s < 1.7\times10^{-30}$ (95% CL) for axion-like particle masses less than $10^{-6}$ eV, which represents an order of magnitude improvement over the best previous neutron laboratory limit

NMR detection with an atomic magnetometer

We demonstrate detection of NMR signals using a non-cryogenic atomic magnetometer and describe several novel applications of this technique. A water free induction decay (FID) signal in a 0.5 $\mu$T field is detected using a spin-exchange-relaxation-free K magnetometer and the possibility of using a multi-channel magnetometer for 3-D MRI requiring only a single FID signal is described. We also demonstrate detection of less than $10^{13}$ $^{129}$Xe atoms whose NMR signal is enhanced by a factor of 540 due to Fermi-contact interaction with K atoms. This technique allows detection of less than $10^{9}$ $^{129}$Xe spins in a flowing system suitable for remote NMR applications

New classes of systematic effects in gas spin co-magnetometers

Atomic co-magnetometers are widely used in precision measurements searching for spin interactions beyond the Standard Model. We describe a new $^3$He-$^{129}$Xe co-magnetometer probed by Rb atoms and use it to identify two general classes of systematic effects in gas co-magnetometers, one associated with diffusion in second-order magnetic field gradients and another due to temperature gradients. We also develop a general and practical approach for calculating spin relaxation and frequency shifts due to arbitrary magnetic field gradients and confirm it experimentally.Comment: 5 pages, 4 figure

High-Temperature Alkali Vapor Cells with Anti-Relaxation Surface Coatings

Antirelaxation surface coatings allow long spin relaxation times in alkali-metal cells without buffer gas, enabling faster diffusion of the alkali atoms throughout the cell and giving larger signals due to narrower optical linewidths. Effective coatings were previously unavailable for operation at temperatures above 80 C. We demonstrate that octadecyltrichlorosilane (OTS) can allow potassium or rubidium atoms to experience hundreds of collisions with the cell surface before depolarizing, and that an OTS coating remains effective up to about 170 C for both potassium and rubidium. We consider the experimental concerns of operating without buffer gas and with minimal quenching gas at high vapor density, studying the stricter need for effective quenching of excited atoms and deriving the optical rotation signal shape for atoms with resolved hyperfine structure in the spin-temperature regime. As an example of a high-temperature application of antirelaxation coated alkali vapor cells, we operate a spin-exchange relaxation-free atomic magnetometer with sensitivity of 6 fT/sqrt(Hz) and magnetic linewidth as narrow as 2 Hz.Comment: 8 pages, 5 figures. The following article appeared in Journal of Applied Physics and may be found at http://link.aip.org/link/?jap/106/11490