Marwan E. Nusair

Bio: Marwan E. Nusair is an academic researcher from American University of Beirut. The author has contributed to research in topics: Pulse-Doppler radar & Waveguide (electromagnetism). The author has an hindex of 7, co-authored 12 publications receiving 16978 citations.

Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis

Abstract: We assess various approximate forms for the correlation energy per particle of the spin-polarized homogeneous electron gas that have frequently been used in applications of the local spin density a...

Police radar detectors for detecting radar signals and determining the directional origin of the signal source

Abstract: A police radar detector detects both the presence of radar signals incident upon a motor vehicle using the detector and also determines the direction of origin of the source of detected radar signals and alerts the operator of the motor vehicle of the presence and source direction of the radar signals. The radar detector includes at least two antennas and preferably three or more antennas with detector circuitry shared among the antennas in a single detector housing. One of the antennas is directed generally toward the front of the motor vehicle and, for a three antenna embodiment, the second and third antennas are directed at angles of generally 120° to the left and 120° to the right of the front of the vehicle. As the police speed radar frequency bands are scanned or swept, each potential radar signal which is detected is processed to determine the direction of origin of the signals. To determine the direction of origin of sensed radar signals, the signals are detected in all antennas with the signal strengths in the different antennas being compared to determine the direction of origin of the signals. It is preferred to identify the direction of the radar source as being to the front of the vehicle, to the rear of the vehicle, to the left side of the vehicle or to the right side of the vehicle.

Motor vehicle radar detector including amplitude detection

Abstract: A radar detector for use in a motor vehicle employs amplitude detection to sense the presence of radar signals commonly used to monitor the speed of such motor vehicles. Amplitude signals are generated by down-converting received signals using a series of mixers, one of which is swept to insure signal detection, and compared to a threshold which is controlled such that noise is detected by the comparison on average a selected period of time. Detected amplitude signals must persist for a given period of time before they are considered to be potentially valid radar signals. After passing the first test of persistence, the signals are verified by means of frequency modulating the first of the series of mixers, detecting the frequency modulation and correlating the detected frequency modulation to determine whether the signal is valid and if so, to which radar frequency band the signal belongs. A first embodiment of the radar detector monitors the X band (10.475-10.575 Ghz), the Ku band (13.400-13.500 Ghz), the K band (24.025-24.275 Ghz), and the Ka band (34.200-35.200 Ghz) and a second embodiment monitors all of these radar signal bands plus and expanded Ka band (34.200-35.200 Ghz).

Double-ridge waveguide to microstrip coupling

Abstract: A method and apparatus for coupling a double-ridge wavguide to a microstrip circuit. A lower ridge of a coupling section of waveguide is expanded by gradually increasing its width such that at the beginning of the coupling the lower ridge is equal to the width of the lower ridge of the double-ridge waveguide to be coupled and at the end of the coupling the width of the lower ridge is equal to the full width of the coupling. This flaring of the lower ridge creates an electrically conductive surface for receiving a ground plane for the microstrip circuit. Additionally, the upper ridge is altered gradually such that at the beginning of the coupling the ridge gap is equal to the gap in the double-ridge waveguide and at the end of the coupling the ridge gap is equal to the sum of the thicknesses of the dielectric substrate, the microstrip line, and the ground plane of the microstrip circuit. The upper ridge is gradually tapered over the length of the coupling and then sharply tapered adjacent the microstrip end of the coupling so that the width of the upper ridge is changed to the width of the microstrip line and the impedance of the coupling matches the impedance of the microstrip circuit. The sidewalls of the coupling may also be tapered inwardly or outwardly if needed for impedance matching.

The Fermi contact contribution to the Knight shift in Be from self-consistent spin-polarized calculations

Abstract: The linear augmented plane wave method in the muffin-tin approximation was used to perform self-consistent spin-polarized calculations of the electron number density n(r) and spin (magnetic moment) density m(r) in metallic Be, within the framework of the spin density functional formalism. For the exchange-correlation functional we used the recent accurate results of Vosko et al. in the local spin density approximation. The Fermi contact contribution to the Knight shift is proportional to the sum of three spin densities (evaluated at the nucleus) arising from (i) the valence electrons at the Fermi surface, (ii) the core electrons, and (iii) the valence electrons below the Fermi surface. We find a 90% cancellation between (i) and (ii) which greatly magnifies the significance of the relatively small effect (iii). Although our contact term is still positive in sign, its magnitude is nearly one-fourth of the previous smallest first principles result and thus requires a smaller orbital diamagnetic contribution ...

Self-interaction correction to density-functional approximations for many-electron systems

Abstract: The exact density functional for the ground-state energy is strictly self-interaction-free (i.e., orbitals demonstrably do not self-interact), but many approximations to it, including the local-spin-density (LSD) approximation for exchange and correlation, are not. We present two related methods for the self-interaction correction (SIC) of any density functional for the energy; correction of the self-consistent one-electron potenial follows naturally from the variational principle. Both methods are sanctioned by the Hohenberg-Kohn theorem. Although the first method introduces an orbital-dependent single-particle potential, the second involves a local potential as in the Kohn-Sham scheme. We apply the first method to LSD and show that it properly conserves the number content of the exchange-correlation hole, while substantially improving the description of its shape. We apply this method to a number of physical problems, where the uncorrected LSD approach produces systematic errors. We find systematic improvements, qualitative as well as quantitative, from this simple correction. Benefits of SIC in atomic calculations include (i) improved values for the total energy and for the separate exchange and correlation pieces of it, (ii) accurate binding energies of negative ions, which are wrongly unstable in LSD, (iii) more accurate electron densities, (iv) orbital eigenvalues that closely approximate physical removal energies, including relaxation, and (v) correct longrange behavior of the potential and density. It appears that SIC can also remedy the LSD underestimate of the band gaps in insulators (as shown by numerical calculations for the rare-gas solids and CuCl), and the LSD overestimate of the cohesive energies of transition metals. The LSD spin splitting in atomic Ni and $s\ensuremath{-}d$ interconfigurational energies of transition elements are almost unchanged by SIC. We also discuss the admissibility of fractional occupation numbers, and present a parametrization of the electron-gas correlation energy at any density, based on the recent results of Ceperley and Alder.

Chemistry with ADF

Abstract: We present the theoretical and technical foundations of the Amsterdam Density Functional (ADF) program with a survey of the characteristics of the code (numerical integration, density fitting for the Coulomb potential, and STO basis functions). Recent developments enhance the efficiency of ADF (e.g., parallelization, near order-N scaling, QM/MM) and its functionality (e.g., NMR chemical shifts, COSMO solvent effects, ZORA relativistic method, excitation energies, frequency-dependent (hyper)polarizabilities, atomic VDD charges). In the Applications section we discuss the physical model of the electronic structure and the chemical bond, i.e., the Kohn–Sham molecular orbital (MO) theory, and illustrate the power of the Kohn–Sham MO model in conjunction with the ADF-typical fragment approach to quantitatively understand and predict chemical phenomena. We review the “Activation-strain TS interaction” (ATS) model of chemical reactivity as a conceptual framework for understanding how activation barriers of various types of (competing) reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis. Finally, we include a brief discussion of exemplary applications in the field of biochemistry (structure and bonding of DNA) and of time-dependent density functional theory (TDDFT) to indicate how this development further reinforces the ADF tools for the analysis of chemical phenomena. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 931–967, 2001

Density-Functional Theory for Time-Dependent Systems

Abstract: The response of an interacting many-particle system to a time-dependent external field can usually be treated within linear response theory. Due to rapid experimental progress in the field of laser physics, however, ultra-short laser pulses of very high intensity have become available in recent years. The electric field produced in such pulses can reach the strength of the electric field caused by atomic nuclei. If an atomic system is placed in the focus of such a laser pulse one observes a wealth of new phenomena [1] which cannot be explained by traditional perturbation theory. The non-perturbative quantum mechanical description of interacting particles moving in a very strong time-dependent external field therefore has become a prominent problem of theoretical physics. In principle, it requires a full solution of the time-dependent Schrodinger equation for the interacting many-body system, which is an exceedingly difficult task. In view of the success of density functional methods in the treatment of stationary many-body systems and in view of their numerical simplicity, a time-dependent version of density functional theory appears highly desirable, both within and beyond the regime of linear response.