4,688 research outputs found
Emergence of atom-light-mirror entanglement inside an optical cavity
We propose a scheme for the realization of a hybrid, strongly
quantum-correlated system formed of an atomic ensemble surrounded by a
high-finesse optical cavity with a vibrating mirror. We show that the steady
state of the system shows tripartite and bipartite continuous variable
entanglement in experimentally accessible parameter regimes, which is robust
against temperature
Electric field effect on superconductivity at complex oxide interfaces
We examine the enhancement of the interfacial superconductivity between
LaAlO and SrTiO by an effective electric field. Through the
breaking of inversion symmetry at the interface, we show that a term coupling
the superfluid density and an electric field can augment the superconductivity
transition temperature. Microscopically, we show that an electric field can
also produce changes in the carrier density by relating the measured
capacitance to the density of states. Through the electron-phonon induced
interaction in bulk SrTiO, we estimate the transition temperature.Comment: 7 Pages, Submitted to Physical Revie
Thermal barrier coatings issues in advanced land-based gas turbines
The Department of Energy's Advanced Turbine System (ATS) program is aimed at forecasting the development of a new generation of land-based gas turbine systems with overall efficiencies significantly beyond those of current state-of-the-art machines, as well as greatly increased times between inspection and refurbishment, improved environmental impact, and decreased cost. The proposed duty cycle of ATS turbines will require the use of different criteria in the design of the materials for the critical hot gas path components. In particular, thermal barrier coatings will be an essential feature of the hot gas path components in these machines. While such coatings are routinely used in high-performance aircraft engines and are becoming established in land-based turbines, the requirements of the ATS turbine application are sufficiently different that significant improvements in thermal barrier coating technology will be necessary. In particular, it appears that thermal barrier coatings will have to function on all airfoil sections of the first stage vanes and blades to provide the significant temperature reduction required. In contrast, such coatings applied to the blades and vances of advanced aircraft engines are intended primarily to reduce air cooling requirements and extend component lifetime; failure of those coatings can be tolerated without jeopardizing mechanical or corrosion performance. A major difference is that in ATS turbines these components will be totally reliant on thermal barrier coatings which will, therefore, need to be highly reliable even over the leading edges of first stage blades. Obviously, the ATS program provides a very challenging opportunity for TBC's, and involves some significant opportunities to extend this technology
Additional application of the NASCAP code. Volume 1: NASCAP extension
The NASCAP computer program comprehensively analyzes problems of spacecraft charging. Using a fully three dimensional approach, it can accurately predict spacecraft potentials under a variety of conditions. Several changes were made to NASCAP, and a new code, NASCAP/LEO, was developed. In addition, detailed studies of several spacecraft-environmental interactions and of the SCATHA spacecraft were performed. The NASCAP/LEO program handles situations of relatively short Debye length encountered by large space structures or by any satellite in low earth orbit (LEO)
Induced polarization at a paraelectric/superconducting interface
We examine the modified electronic states at the interface between
superconducting and ferro(para)-electric heterostructures. We find that
electric polarization and superconducting order parameters can be
significantly modified due to coupling through linear terms brought about by
explicit symmetry breaking at the interface. Using an effective action and a
Ginzburg-Landau formalism, we show that an interaction term linear in the
electric polarization will modify the superconducting order parameter at
the interface. This also produces modulation of a ferroelectric polarization.
It is shown that a paraelectric-superconductor interaction will produce an
interface-induced ferroelectric polarization.Comment: 4 pages, 3 figures, Submitted to Phys. Rev.
Additional application of the NASCAP code. Volume 2: SEPS, ion thruster neutralization and electrostatic antenna model
The interactions of spacecraft systems with the surrounding plasma environment were studied analytically for three cases of current interest: calculating the impact of spacecraft generated plasmas on the main power system of a baseline solar electric propulsion stage (SEPS), modeling the physics of the neutralization of an ion thruster beam by a plasma bridge, and examining the physical and electrical effects of orbital ambient plasmas on the operation of an electrostatically controlled membrane mirror. In order to perform these studies, the NASA charging analyzer program (NASCAP) was used as well as several other computer models and analytical estimates. The main result of the SEPS study was to show how charge exchange ion expansion can create a conducting channel between the thrusters and the solar arrays. A fluid-like model was able to predict plasma potentials and temperatures measured near the main beam of an ion thruster and in the vicinity of a hollow cathode neutralizer. Power losses due to plasma currents were shown to be substantial for several proposed electrostatic antenna designs
A lower bound for the BCS functional with boundary conditions at infinity
We consider a many-body system of fermionic atoms interacting via a local
pair potential and subject to an external potential within the framework of BCS
theory. We measure the free energy of the whole sample with respect to the free
energy of a reference state which allows us to define a BCS functional with
boundary conditions at infinity. Our main result is a lower bound for this
energy functional in terms of expressions that typically appear in
Ginzburg-Landau functionals.Comment: 32 page
Common humpback whale (Megaptera novaeangliae) sound types for passive acoustic monitoring
Author Posting. © Acoustical Society of America, 2011. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 129 (2011): 476-482, doi:10.1121/1.3504708.Humpback whales (Megaptera novaeangliae) are one of several baleen whale species in the Northwest Atlantic that coexist with vessel traffic and anthropogenic noise. Passive acoustic monitoring strategies can be used in conservation management, but the first step toward understanding the acoustic behavior of a species is a good description of its acoustic repertoire. Digital acoustic tags (DTAGs) were placed on humpback whales in the Stellwagen Bank National Marine Sanctuary to record and describe the non-song sounds being produced in conjunction with foraging activities. Peak frequencies of sounds were generally less than 1 kHz, but ranged as high as 6 kHz, and sounds were generally less than 1 s in duration. Cluster analysis distilled the dataset into eight groups of sounds with similar acoustic properties. The two most stereotyped and distinctive types (“wops” and “grunts”) were also identified aurally as candidates for use in passive acoustic monitoring. This identification of two of the most common sound types will be useful for moving forward conservation efforts on this Northwest Atlantic feeding ground.This paper was funded by the National Oceanic
and Atmospheric Administration (NOAA)’s National
Marine Sanctuaries Program. It was also sponsored in part
by the University of Hawaii Sea Grant College Program,
School of Ocean and Earth Science and Technology, under
Institutional Grant No. NA05OAR4171048 from the NOAA
Office of Sea Grant, Department of Commerce
Mechanical Control of Spin States in Spin-1 Molecules and the Underscreened Kondo Effect
The ability to make electrical contact to single molecules creates
opportunities to examine fundamental processes governing electron flow on the
smallest possible length scales. We report experiments in which we controllably
stretch individual cobalt complexes having spin S = 1, while simultaneously
measuring current flow through the molecule. The molecule's spin states and
magnetic anisotropy were manipulated in the absence of a magnetic field by
modification of the molecular symmetry. This control enabled quantitative
studies of the underscreened Kondo effect, in which conduction electrons only
partially compensate the molecular spin. Our findings demonstrate a mechanism
of spin control in single-molecule devices and establish that they can serve as
model systems for making precision tests of correlated-electron theories.Comment: main text: 5 pages, 4 figures; supporting information attached; to
appear in Science
- …