31,994 research outputs found
Semiconductor optical amplifiers: performance and applications in optical packet switching [Invited]
Semiconductor optical amplifiers (SOAs) are a versatile core technology and the basis for the implementation of a number of key functionalities central to the evolution of highly wavelength-agile all-optical networks. We present an overview of the state of the art of SOAs and summarize a range of applications such as power boosters, preamplifiers, optical linear (gain-clamped) amplifiers, optical gates, and modules based on the hybrid integration of SOAs to yield high-level functionalities such as all-optical wavelength converters/regenerators and small space switching matrices. Their use in a number of proposed optical packet switching situations is also highlighted
Search procedures revisited
Search Procedures reflects on a series of studies carried out over a four year period in the late 1970s. It was published at an interesting time for Information Retrieval. Written before Information Retrieval became synonymous with online information seeking it focuses on Information Retrieval within Public Libraries, then the major location for everyday information seeking. While many of his contemporaries focused on information seeking in academic or special library settings, Peter chose instead to focus a setting that was visited by a more diverse set of people with a broader range of information needs
Modelling and simulation of small-scale embedded generation systems
Advances in heat and power production are leading to a revolution in how buildings are perceived as an energy system. The rapid development of fuel cells, photovoltaic facades, cogeneration and the evolution of ducted windturbines allows the designer to envisage a building providing much of its own heat and power through local embedded generation (EG). However, the addition of heat and power production to the building increases it complexityas an energy system. New design issues must be addressed such as the integration of EG with traditional HVAC and power systems; optimal demand and supply matching; demand side management and its impact on environmentalperformance; interaction of the EG system with the local electricity network, etc
RDWIA analysis of 12C(e,e'p) for Q^2 < 2 (GeV/c)^2
We analyze data for 12C(e,e'p) with Q^2 < 2 (GeV/c)^2 using the relativistic
distorted-wave impulse approximation (RDWIA) based upon Dirac-Hartree wave
functions. The 1p normalization extracted from data for Q^2 > 0.6 (GeV/c)^2 is
approximately 0.87, independent of Q^2, which is consistent with the predicted
depletion by short-range correlations. The total 1p and 1s strength for E_m <
80 MeV approaches 100% of IPSM, consistent with a continuum contribution for 30
< E_m < 80 MeV of about 12% of IPSM. Similarly, a scale factor of 1.12 brings
RDWIA calculations into good agreement with 12C(e,e'p) data for transparency.
We also analyzed low Q^2 data from which a recent NDWIA analysis suggested that
spectroscopic factors might depend strongly upon the resolution of the probe.
We find that momentum distributions for their empirical Woods-Saxon wave
functions fit to low Q^2 data for parallel kinematics are too narrow to
reproduce data for quasiperpendicular kinematics, especially for larger Q^2,
and are partly responsible for reducing fitted normalization factors.Comment: 19 pages, 14 figures, to be submitted to PR
Application of the Kelly Criterion to Ornstein-Uhlenbeck Processes
In this paper, we study the Kelly criterion in the continuous time framework
building on the work of E.O. Thorp and others. The existence of an optimal
strategy is proven in a general setting and the corresponding optimal wealth
process is found. A simple formula is provided for calculating the optimal
portfolio for a set of price processes satisfying some simple conditions.
Properties of the optimal investment strategy for assets governed by multiple
Ornstein-Uhlenbeck processes are studied. The paper ends with a short
discussion of the implications of these ideas for financial markets.Comment: presented at Complex'2009 (Shanghai, Feb. 23-25
Shell tile thermal protection system
A reusable, externally applied thermal protection system for use on aerospace vehicles subject to high thermal and mechanical stresses utilizes a shell tile structure which effectively separates its primary functions as an insulator and load absorber. The tile consists of structurally strong upper and lower metallic shells manufactured from materials meeting the thermal and structural requirements incident to tile placement on the spacecraft. A lightweight, high temperature package of insulation is utilized in the upper shell while a lightweight, low temperature insulation is utilized in the lower shell. Assembly of the tile which is facilitated by a self-locking mechanism, may occur subsequent to installation of the lower shell on the spacecraft structural skin
Electronic structure induced reconstruction and magnetic ordering at the LaAlOSrTiO interface
Using local density approximation (LDA) calculations we predict
GdFeO-like rotation of TiO octahedra at the -type interface between
LaAlO and SrTiO. The narrowing of the Ti bandwidth which results
means that for very modest values of , LDA calculations predict charge
and spin ordering at the interface. Recent experimental evidence for magnetic
interface ordering may be understood in terms of the close proximity of an
antiferromagnetic insulating ground state to a ferromagnetic metallic excited
state
Schottky barriers at hexagonal boron nitride/metal interfaces: a first principles study
The formation of a Schottky barrier at the interface between a metal and
hexagonal boron nitride (h-BN) is studied using density functional theory. For
metals whose work functions range from 4.2 to 6.0 eV, we find Schottky barrier
heights for holes between 1.2 and 2.3 eV. A central role in determining the
Schottky barrier height is played by a potential step of between 0.4 and 1.8 eV
that is formed at the metal|h-BN interface and effectively lowers the metal
work function. If h-BN is physisorbed, as is the case on fcc Cu, Al, Au, Ag and
Pt(111) substrates, the interface potential step is described well by a
universal function that depends only on the distance separating h-BN from the
metal surface. The interface potential step is largest when h-BN is
chemisorbed, which is the case for hcp Co and Ti (0001) and for fcc Ni and Pd
(111) substrates
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