Absence of Localization in Certain Field Effect Transistors

We review some experimental and theoretical results on the metal-to-insulator transition (MIT) observed at zero magnetic field (B=0) in several two-dimensional electron systems (2DES). Scaling of the conductance and magnetic field dependence of the conductance provide convincing evidence that the MIT is driven by Coulomb interactions among the carriers and is dramatically sensitive to spin polarization of the carriers.Comment: 8 pages, LaTeX, figure label change

Modeling the optical properties of hexagonal GaN

An adjustable broadening function instead of the conventional Lorentzian one is incorporated in the dielectric function model for hexagonal GaN. One-electron contributions at E 1 critical points and higher-state (m>1) exciton terms, which were incorrectly disregarded in the previous study, are taken into account. Model parameters were determined using the acceptance-probability-controlled simulated annealing. As a result, excellent agreement with experimental data for both real and imaginary parts in the range from 1.5 to 10 eV is obtained. Average discrepancy between experimental and calculated data for the real part of the index of refraction equals 2.75×10 -4, and for the imaginary part is 1.66×10 -3. © 1998 American Institute of Physics.published_or_final_versio

Modeling the optical constants of hexagonal GaN, InN, and AlN

Optical constants of hexagonal GaN (in the range 1.5-10 eV), InN (in the range 2-10 eV), and AlN (in the range 6-20 eV) for E⊥c are modeled using a modification of Adachi's model of optical properties of semiconductors. Model parameters are determined using the acceptance-probability-controlled simulated annealing method. The employed model uses an adjustable broadening function instead of the conventional Lorentzian one. The broadening can vary over a range of functions with similar kernels but different wings. Therefore, excessive absorption inherent to Lorentzian broadening due to the large wings of a Lorentz function can be reduced, yielding better agreement with experimental data. As a result, excellent agreement with experimental data is obtained; the relative rms errors for the real part of the index of refraction are below 2% for all three materials, and, for the imaginary part, below 5% for GaN and below 3% for InN and AlN. © 1999 American Institute of Physics.published_or_final_versio

Genetic algorithms for reflective filters design

A genetic algorithm (GA) with adaptive mutations has been employed for the design of Bragg reflectors. The algorithm enables three different design types: (a) composition and thickness of each layer are optimized; (b) two compositions are chosen for the two alternating materials, and the thickness of each layer is optimized; (c) composition and thickness of two layers are chosen and the pair is repeated. The algorithm enables the finding of the optimal design for two chosen incident and final media, and it is capable of taking into account the existence of a finite optically thick substrate. The algorithm is very versatile and can be applied for the design of refractive filters using various materials. We have demonstrated application of this algorithm to the design of AlxGa1-xN reflectors, as well as organic and dielectric reflectors.published_or_final_versio

Dielectric function models for describing the optical properties of hexagonal GaN

Several different models have been employed for modeling the dielectric function of hexagonal GaN in the range from 1 to 10 eV. Models are compared in terms of number of parameters required, intricacy of model equations, and possibility of accurate estimation of important physical parameters, such as energies of critical points and exciton binding energies. Shortcomings and advantages of each model are discussed in detail. Excellent agreement with the experimental data for GaN has been achieved with three of the investigated models. It has also been shown that an assumption of adjustable broadening instead of a purely Lorentzian one improves the agreement with the experimental data and enables elimination of excessive absorption below the gap which is inherent to the models with Lorentzian broadening. © 2001 American Institute of Physics.published_or_final_versio

Modeling the optical constants of Hg xCd 1-xTe alloys in the 1.5-6.0 eV range

The optical constants of Hg xCd 1-xTe as a function of energy and composition x are modeled over a wide spectral range from 1.5 to 6 eV. The model employed represents an extension of Adachi's model and incorporates the adjustable broadening function rather than the conventional Lorentzian one. In this way, greater flexibility of the model is achieved, enabling us to obtain an excellent agreement with the experimental data. The relative rms errors obtained for all compositions are below 2.5% for the real part and below 6% for the imaginary part of the index of refraction. The lowest rms errors are obtained for x = 0 (0.6% for the real part and 0.7% for the imaginary part of the index of refraction), and the highest for the x = 0.91 (2.4% for the real part and 5.8% for the imaginary part). © 1999 American Institute of Physics.published_or_final_versio

Comment on 'Optical properties of CdTe1-xSx (0 <= x<= 1): experiment and modeling' [J. Appl. Phys. 85, 7418 (1999)]

Wei et al. [J. Appl. Phys. 85, 7418 (1999)] performed the room temperature spectroscopic ellipsometry to determine the dielectric function of CdTe1–xSx films. They have fit the obtained dielectric function using the Holden's model dielectric function [Phys. Rev. B 56, 4037 (1997)], and derived conclusions about the line shape at the band gap E0. However, their description of the fitting procedure is ambiguous, and some model parameters in Table I [J. Appl. Phys. 85, 7418 (1999)] are missing which makes it impossible to reproduce their calculations. Furthermore, the results of Wei et al. [J. Appl. Phys. 85, 7418 (1999)] do not represent conclusive proof of the advantages of their approach over other models available in the literature. © 2000 American Institute of Physics.published_or_final_versio

Factor V Leiden and thrombosis in patients with systemic lupus erythematosus: a meta-analysis.

The aim of this study was to perform a meta-analysis of the association between the factor V Leiden polymorphism (FVL) and thrombosis among patients with systemic lupus erythematosus (SLE) and/or antiphospholipid antibody (aPL) positivity. Included studies recruited patients based on SLE or aPL-positive status, confirmed subjects' SLE diagnosis as defined by the American College of Rheumatology, and documented thrombotic events. Excluded studies were non-English or considered only arterial thrombosis. Individual patient data, available from 5 studies, together with unpublished data from 1210 European-American SLE patients from the UCSF Lupus Genetics Collection genotyped for FVL, were further analyzed. Seventeen studies (n=2090 subjects) were included in the initial meta-analysis. Unadjusted odds ratios (OR) were calculated to assess association of FVL with thrombosis. The OR for association of thrombosis with FVL was 2.88 (95% confidence interval (CI) 1.98-4.20). In the secondary analysis with our individual patient dataset (n=1447 European-derived individuals), SLE subjects with the FVL polymorphism still had more than two times the odds of thrombosis compared to subjects without this polymorphism, even when adjusting for covariates such as gender, age and aPL status. SLE and/or aPL-positive patients with the FVL variant have more than two times the odds of thrombosis compared to those without this polymorphism

Lorenz System Parameter Determination and Application to Break the Security of Two-channel Chaotic Cryptosystems

This paper describes how to determine the parameter values of the chaotic Lorenz system used in a two-channel cryptosystem. The geometrical properties of the Lorenz system are used firstly to reduce the parameter search space, then the parameters are exactly determined, directly from the ciphertext, through the minimization of the average jamming noise power created by the encryption process.Comment: 5 pages, 5 figures Preprint submitted to IEEE T. Cas II, revision of authors name spellin

Modeling the optical constants of wide-bandgap materials

Calculations of the optical constants of hexagonal GaN (in the range 1-10 eV), InN (in the range 2-20 eV), A1N (in the range 6-20 eV) and 6H-SiC (in the range 1-30 eV) for the component perpendicular to the c axis are presented. The employed model is modified Adachi's model of the optical properties of semiconductors. In the employed model, damping constant rdescribing broadening phenomenon is replaced with the frequency dependent expression 1(w). In such a manner, type of broadening represents adjustable parameter of the model, allowing broadening to vary over a range of functions with similar kernels but different wings. Excellent agreement with experimental data is obtained for all investigated materials. Obtained relative rms errors for the real and imaginary parts of the index of refraction are equal to 3.5% and 5.2% for 6HSiC in the 1-30 eV range, 1 .7% and 4.1% for GaN in the 1.5-10 eV range, 1.2% and 2.5% for InN in the 2-10 eV range and 1 .5% and 1.9% for A1N in the 6-20 eV range.published_or_final_versio