Dual differential interferometer

A dual two-beam differential interferometer that measures both the amplitude and orientation of propagating, broadband surface acoustic waves is disclosed. Four beams are focused on a surface. The four reflected beams are separated into two pairs. The two pairs are detected to produce two signals that are used to compute amplitude and orientation

The Politics of Hydroelectric Power in Alaska: Rampart and Devil Canyon -- A Case Study

Originally published January 1978, revised October 1978. OWRT Agreement No. 14-34-0001-7003 Project No. A-060-ALAS. Completion Report.Hydroelectric power in Alaska has had a curious history--and an instructive one. This study focuses on three separate projects: Eklutna, Rampart, and Devil Canyon. The Eklutna project functions today; Rampart was not constructed; and the Devil Canyon project is still in the planning stage. Yet for all their differences in location, goals, and fate, the projects were related; and, taken together, their histories highlight all the essential political elements involved in hydroelectric power construction. There is still a fourth project which is functioning today--the Snettisham installation near Juneau which is not considered in this paper. A complex decision-making process determines the progress of such large projects. In following these three Alaskan projects, we can gain a better perspective on the roles of the several government agencies and the public; thus we can assess some of the inherent complexities. Such an assessment fully substantiates the conclusion that it takes more than moving dirt to build a dam.The work upon which this completion report is based was supported by funds provided by the U. S. Department of the Interior, Office of Water Research and Technology as authorized under the Water Resources Research Act of 1964, Public Law 88-379, as amended

Photonic properties of one-dimensionally-ordered cold atomic vapors under conditions of electromagnetically induced transparency

We experimentally study the photonic properties of a cold-atom sample trapped in a one-dimensional optical lattice under the conditions of electromagnetically induced transparency. We show that such a medium has two photonic band gaps. One of them is in the transparency window and gives rise to a Bragg mirror, which is spectrally very narrow and dynamically tunable. We discuss the advantages and the limitations of this system. As an illustration of a possible application we demonstrate a two-port all-optical switch

A microscopic modeling of phonon dynamics and charge response in metallic BaBiO3_3

We use our recently proposed microscopic modeling in the framework of linear response theory to investigate the complete phonon dispersion, the phonon density of states, certain phonon-induced electronic charge distributions and charge fluctuations (CF's) for anomalous soft modes of metallic BaBiO$_{3}$ in its simple cubic phase where superconductivity with $T_{c}$ up to 32 K appears. The theoretical approach already has been applied successfully to the cuprate high-temperature superconductors (HTSC's), simple ionic crystals (NaCl, MgO) and perovskite oxides (SrTiO$_{3}$, BaTiO$_{3}$). It is well suited for materials with a strong component of ionic binding and especially for "ionic" metals. In particular, the giant phonon anomalies related to the breathing vibration of the oxygen as found experimentally in superconducting doped Ba$_{0.6}$K$_{0.4}$BiO$_{3}$, resembling those observed in the high $T_{c}$ cuprates, are investigated. The origin of these anomalies is explored and attributed to a strong nonlocal coupling of the displaced oxygen ions to CF's of ionic type, essentially of the Bi6s- and Bi6p orbital. This points to the importance of both of these states at the Fermi energy. Starting from an ab-initio rigid ion model (RIM) we calculate the effect on the lattice dynamics and charge response of the most important electronic polarization processes in the material, i.e. CF's and dipole fluctuations (DF's). Taking into account these electronic degrees of freedom in linear response theory, we obtain a good agreement with the measured phonon dispersion and in particular with the strong phonon anomalies.Comment: Additional comparison with the cuprate HTSC's. A slightly shorter version has been published in PR

Accelerated convergence for incompressible flow calculations

Two improved algorithms which solve the steady-state Navier-Stokes equations, PISO and SIMPLER, are studied. Computations were carried out on progressively finer grids for the driven cavity and flow over a backward-facing step. The effects of relaxation factor, number of grid nodes and number of sweeps through the pressure equations are studied to evaluate the performance of the PISO and SIMPLER schemes. Results show that these improved schemes accelerate the convergence rate of the solution generally by a factor of two as compared to the SIMPLE method