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Unified Treatment (unified + treatment)

Distribution by Scientific Domains
Engineering28%
Chemistry28%

Selected Abstracts

Multi-user detection in OFDM systems using CDMA and multiple antennas

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2003
Christoph Degen
This paper deals with linear multi-user detection in orthogonal frequency division multiplexing (OFDM) systems. The separation of concurrently transmitted signals is based on space division and code division multiple access (SD/CDMA). The examined OFDM schemes are compared against frequency domain equalization for single-carrier transmission schemes (SC/FDE). Both show strong similarities. Therefore in this paper, we focus on a unified treatment of multi-user detection systems based on OFDM or SC/FDE. The trade-off between exploitation of diversity and user separation is analyzed for different spreading techniques and a varying number of receive antennas. The performance is evaluated in terms of both uncoded and coded bit error ratio (BER). Furthermore, a novel time domain spreading technique for OFDM systems is proposed for which the peak-to-average transmitter power ratio (PAPR) is independent of the applied spreading code. Copyright © 2004 AEI [source]

The Raman effect,a unified treatment of the theory of Raman scattering by molecules.

JOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2003
Derek A. Long, John Wiley & Sons, Pp 597.
No abstract is available for this article. [source]

A multiple-scattering theory of circular and linear dichroism for photoemission and photoabsorption

JOURNAL OF SYNCHROTRON RADIATION, Issue 1 2002
S. Di Matteo
A unified treatment of circular dichroism, both natural and magnetic, in (spin-resolved) photoemission and photoabsorption from core levels is given, valid in the many-body case and for extended systems, together with an extension of the formalism to treat linear dichroism. The reduction of this scheme to a one-electron picture in the framework of multiple scattering theory is briefly discussed and shows the intimate connection of the two spectroscopies via a generalized optical theorem. Plausibility arguments are given that in correlated d -band systems screening and relaxation effects are not so drastic as in other cases, due to the autoscreening action of the excited photoelectron, so that the final density of states is much like the initial unperturbed one. It is shown how to exploit this point of view to obtain in favorables cases separated orbital and spin moment radial (surface) distribution maps from dichroic magnetic EXAFS spectra (photoelectron diffraction patterns) related to the ground state. Dichroic natural spectra, both in photoemission and absorption, are shown to be sensitive only to atoms in chiral geometry. [source]

The design of excitation pulses for spin systems using optimal control theory: With application to NMR spectroscopy

OPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 5 2009
Naum I. Gershenzon
Abstract This paper considers the use of optimal control theory in designing radio frequency excitation pulses for magnetic spin systems satisfying Bloch dynamics. Such pulses are required in applications of nuclear magnetic resonance to initially transfer sample magnetization vectors to the transverse plane. Once transferred, signals released by nuclei as they respond to a static magnetic field normal to the transverse plane are then analyzed and interpreted. Continuous time deterministic optimal control theory is employed to determine time-dependent pulse amplitudes and frequencies that minimize the distance between final magnetization vectors and a chosen target vector. Pulses are designed to excite a range of resonant frequencies and to tolerate miscalibration errors in applied fields. The model presented permits a unified treatment of the control problem as considered by a variety of authors, and a thorough mathematical analysis of the existence, and characteristics of, optimal excitation pulses. Practical numerical algorithms for designing optimal pulses are given, and the effectiveness of the algorithms is illustrated by comparing the pulses that they generate with those commonly used in high-resolution spectroscopy. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Granger's representation theorem: A closed-form expression for I(1) processes

THE ECONOMETRICS JOURNAL, Issue 1 2005
Peter Reinhard Hansen
Summary, The Granger representation theorem states that a cointegrated vector autoregressive process can be decomposed into four components: a random walk, a stationary process, a deterministic part, and a term that depends on the initial values. In this paper, we present a new proof of the theorem. This proof enables us to derive closed-form expressions of all terms of the representation and allows a unified treatment of models with different deterministic specifications. The applicability of our results is illustrated by examples. For example, the closed-form expressions are useful for impulse response analyses and facilitate the analysis of cointegration models with structural changes. [source]

Flavours of pseudo-height

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 606 2005
A. A. White
Various functions of pressure have been used as vertical coordinate in atmospheric dynamics. Some of these are called pseudo-heights, or described as height-like, although they could equally well be called pseudo-thicknesses and described as thickness-like. Three pseudo-heights are reviewed here, and a unified treatment is presented in which two appear as specializations of the third. The common feature is a standard temperature profile which is a function only of pressure, and the two specializations arise when that function is chosen to represent either an isothermal atmosphere or an isentropic atmosphere. Neither of these choices,or any other reasonable function of pressure,itself introduces approximation. Under quasi-geostrophic approximation, the need for a non-zero mean-state stratification means that a second reference-temperature profile must be introduced if isentropic pseudo-height is used as vertical coordinate. © Crown copyright 2005. [source]

Relativistic Scott correction for atoms and molecules

COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 1 2010
Jan Philip Solovej
We prove the first correction to the leading Thomas-Fermi energy for the ground state energy of atoms and molecules in a model where the kinetic energy of the electrons is treated relativistically. The leading Thomas-Fermi energy, established in [25], as well as the correction given here, are of semiclassical nature. Our result on atoms and molecules is proved from a general semiclassical estimate for relativistic operators with potentials with Coulomb-like singularities. This semiclassical estimate is obtained using the coherent state calculus introduced in [36]. The paper contains a unified treatment of the relativistic as well as the nonrelativistic case. © 2009 Wiley Periodicals, Inc. [source]