The Quest for Purchasing Power Parity with a Series-specific Unit Root Test Using Panel Data

A unit root testing procedure is presented that exploits the well-established power advantages of panel estimation while rectifying a deficiency in other panel unit root tests. This procedure, which takes into account contemporaneous cross-correlation and heterogeneous serial correlation of the regression residuals, allows determination of which members of the panel reject the null hypothesis of a unit root and which do not. Applying the procedure to real exchange rates yields results that are in broad agreement with those obtained from single-equation unit root tests. There is little evidence that a unit root can be rejected in dollar-based real exchange rates for the floating rate period.Marketing,

Finite groups can be generated by a pi-subgroup and a pi'-subgroup

Answering a question of Dan Haran and generalizing some results of Aschbacher-Guralnick and Suzuki, we prove that given a set of primes pi, any finite group can be generated by a pi-subgroup and a pi'-subgroup. This gives a free product description of a countably generated free profinite group.Comment: We generalized the main result in the previous version, simplified the proof and give an application to profinite groups. In the latest version, we also proved a result about generation by Sylow subgroup

Temperature can enhance coherent oscillations at a Landau-Zener transition

We consider sweeping a system through a Landau-Zener avoided-crossing, when that system is also coupled to an environment or noise. Unsurprisingly, we find that decoherence suppresses the coherent oscillations of quantum superpositions of system states, as superpositions decohere into mixed states. However, we also find an effect we call "Lamb-assisted coherent oscillations", in which a Lamb shift exponentially enhances the coherent oscillation amplitude. This dominates for high-frequency environments such as super-Ohmic environments, where the coherent oscillations can grow exponentially as either the environment coupling or temperature are increased. The effect could be used as an experimental probe for high-frequency environments in such systems as molecular magnets, solid-state qubits, spin-polarized gases (neutrons or He3) or Bose-condensates.Comment: 4 Pages & 4 Figs - New version: introduction extended & citations adde

Quantum critical behavior in strongly interacting Rydberg gases

We study the appearance of correlated many-body phenomena in an ensemble of atoms driven resonantly into a strongly interacting Rydberg state. The ground state of the Hamiltonian describing the driven system exhibits a second order quantum phase transition. We derive the critical theory for the quantum phase transition and show that it describes the properties of the driven Rydberg system in the saturated regime. We find that the suppression of Rydberg excitations known as blockade phenomena exhibits an algebraic scaling law with a universal exponent.Comment: 4 pages, 3 figures, published versio

Accessibility as a determinant of retail sales

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of City and Regional Planning, 1962.Includes bibliographical references (leaf 63).by Robert Breuer.M.C.P

Bell-state preparation for electron spins in a semiconductor double quantum dot

A robust scheme for state preparation and state trapping for the spins of two electrons in a semiconductor double quantum dot is presented. The system is modeled by two spins coupled to two independent bosonic reservoirs. Decoherence effects due to this environment are minimized by application of optimized control fields which make the target state to the ground state of the isolated driven spin system. We show that stable spin entanglement with respect to pure dephasing is possible. Specifically, we demonstrate state trapping in a maximally entangled state (Bell state) in the presence of decoherence.Comment: 9 pages, 4 figure