Nonparabolicity effects and the spin-split electron dwell time in symmetric III-V double-barrier structures

We start from the fourth order nonparabolic and anisotropic conduction band bulk dispersion relation to obtain an one-band effective Hamiltonian which we apply to an AlGaSb symmetric double-barrier structure with resonant energies significantly (more than 200meV) above the well bottom. The spin-splitting is described by the k3 Dresselhaus spin-orbit coupling term modifying only the effective mass of the spin eigenstates in the investigated structure. Apart from the bulk-like resonant energy shift due to the band nonparabolicity, we obtain a substantial shift depending on the choice of boundary conditions for the envelope functions at interfaces between different materials. The shift of resonant energy levels leads to the change of spin-splitting and the magnitude of the dwell times. We attempt to explain the influence of both the nonparabolicity and boundary conditions choice by introducing various effective masses

Quantization of a gauge theory on a curved noncommutative space

We study quantization of a gauge analogon of the Grosse-Wulkenhaar model: we find divergent one-loop contributions to the 1-point and 2-point Green functions. We obtain that five counterterms are necessary for renormalization and that all divergences are logarithmic.Comment: 23 pages, 3 figure

AdS-inspired noncommutative gravity on the Moyal plane

We consider noncommutative gravity on a space with canonical noncommutativity that is based on the commutative MacDowell-Mansouri action. Gravity is treated as gauge theory of the noncommutative $SO(1,3)_\star$ group and the Seiberg-Witten (SW) map is used to express noncommutative fields in terms of the corresponding commutative fields. In the commutative limit the noncommutative action reduces to the Einstein-Hilbert action plus the cosmological term and the topological Gauss-Bonnet term. After the SW expansion in the noncommutative parameter the first order correction to the action, as expected, vanishes. We calculate the second order correction and write it in a manifestly gauge covariant way.Comment: 22 pages, no figures, final versio

Non-commutative SU(N) gauge theories and asymptotic freedom

In this paper we analyze the one-loop renormalization of the $\theta$-expanded $\rm SU(N)$ Yang-Mills theory. We show that the {\it freedom parameter} $a$, key to renormalization, originates from higher order non-commutative gauge interaction, represented by a higher derivative term $b h \theta^{\mu\nu}\hat F_{\mu\nu}\star\hat F_{\rho\sigma}\star\hat F^{\rho\sigma}$. The renormalization condition fixes the allowed values of the parameter $a$ to one of the two solutions: $a=1$ or $a=3$, i.e. to $b=0$ or to $b=1/2$, respectively. When the higher order interaction is switched on, ($a=3$), pure non-commutative SU(N) gauge theory at first order in $\theta$-expansion becomes one-loop renormalizable for various representations of the gauge group. We also show that, in the case $a=3$ and the adjoint representation of the gauge fields, the non-commutative deformation parameter $h$ has to be renormalized and it is asymptotically free.Comment: 16 pages, no figure

Simple algorithm for computing the stiffness matrix of composite cross-section

The paper proposes an algorithm for computing the stiffness matrix of composite cross-sections made of two or more different materials. Irrespective of the cross-section geometry, the calculation puts forward a numerical solution applying the finite element method (FEM). The cross-section is discretised into fibers and integration over the section area is performed numerically. The required geometric characteristics and stiffness matrix of the entire cross-section are formed by the assembling procedure. Beam theory equations are used for calculating stresses and strains at characteristic points of the cross-section. Materially nonlinear behaviour of concrete and steel is considered. The advantage of the proposed numerical algorithm is that results of satisfying accuracy are obtained in only a few iterations. The algorithm is implemented in own computer program with a straightforward input data procedure

Time delay in thin slabs with self-focusing Kerr-type nonlinearity

Time delays for an intense transverse electric (TE) wave propagating through a Kerr-type nonlinear slab are investigated. The relation between the bidirectional group delay and the dwell time is derived and it is shown that the difference between them can be separated into three terms. The first one is the familiar self interference time, due to the dispersion of the medium surrounding the slab. The other two terms are caused by the nonlinearity and oblique incidence of the TE wave. It is shown that the electric field distribution along the slab may be expressed in terms of Jacobi elliptic functions while the phase difference introduced by the slab is given in terms of incomplete elliptic integrals. The expressions for the field intensity dependent complex reflection and transmission coefficients are derived and the multivalued oscillatory behavior of the delay times for the case of a thin slab is demonstrated

Towards automated design of quantum cascade lasers

We present an advanced technique for the design and optimization of GaAs/AlGaAs quantum cascade laser structures. It is based on the implementation of the simulated annealing algorithm with the purpose of determining a set of design parameters that satisfy predefined conditions, leading to an enhancement of the device output characteristics. Two important design aspects have been addressed: improved thermal behavior, achieved by the use of higher conduction band offset materials, and a more efficient extraction mechanism, realized via a ladder of three lower laser states, with subsequent pairs separated by the optical phonon energy. A detailed analysis of performance of the obtained structures is carried out within a full self-consistent rate equations model of the carrier dynamics. The latter uses wave functions calculated by the transfer matrix method, and evaluates all relevant carrier–phonon and carrier–carrier scattering rates from each quantized state to all others within the same and neighboring periods of the cascade. These values are then used to form a set of rate equations for the carrier density in each state, enabling further calculation of the current density and gain as a function of the applied field and temperature. This paper addresses the application of the described procedure to the design of lambda~9 µm GaAs-based mid-infrared quantum cascade lasers and presents the output characteristics of some of the designed optimized structures. © 2005 American Institute of Physic

Edem mozga kod zavisnika od droge

Background/Aim. The effect of drugs leaves permanent consequences on the brain, organic in type, followed by numerous manifestations, and it significantly affects the development of mental dysfunctions. The clinicians are often given a task to estimate a patient's personality during treatment or during experts estimate of a drug addict. The aim of this research was to determine the differences, if any, in characteristics of addicts experience and personality traits in drug addicts with or without cerebral edema. Methods. The research was conducted on a sample of 252 male drug addicts, the average age of 23.3 (SD = 4.3) years. Cerebral edema was confirmed on magnetic resonance (MR) images of the brain performed during the treatment of the addicts. The participants were tested by the psychologists using Minnesota Multiphasic Personality Inventory (MMPI-201) test, and the data were processed using canonical discriminate analysis within the SPSS program. The dependent variable in the study was cerebral edema. A block of independent variables, designed for the requirements of this study, consisted of two subgroups. The first one consisted of 12 variables describing the relevant characteristics of drug abuse. The second subgroup consisted of 8 psychopathological tendencies in the personality defined by the mentioned test. Results. Cerebral edema was confirmed in 52 (20.63%) of the drug addicts. The differences between the groups of drug addicts with and without cerebral edema were determined in the following: the time span of taking drugs (0.301), use of alcohol parallel with drugs (0.466), and treatment for addiction (0.603). In the drug addicts with a cerebral edema, MMPI-201 confirmed the increase in the scales for hypochondria, psychopathic deviations and psychastenia, and the decrease in the scales for schizophrenia and depression. Conclusion. Our study confirmed a possible connection between cerebral edema and personality traits in a number of the examined drug addicts. Considering the fact that practice often requires personality estimation, regardless whether it is about treatment or expert's estimate, it is necessary to further research in this direction.Uvod/Cilj. Dejstvo droge ostavlja trajne posledice organskog tipa, na mozak, praćene brojnim neurološkim manifestacijama, i bitno utiče na razvoj psihičkih poremećaja. Kliničarima se često postavlja zadatak da procene ličnost tokom lečenja ili veštačenja zavisnika od droge. Cilj istraživanja bio je utvrđivanje karakteristika narkomanskog staža i osobina ličnosti kod zavisnika od droge sa i bez edema mozga. Metode. Istraživanje je sprovedeno u grupi od 252 zavisnika od droge muškog pola, prosečne starosti 23,3 (SD = 4,3) godine. Za vreme lečenja zavisnika od droge rađena je magnetna rezonanca mozga, a za procenu psihopatoloških tendencija ličnosti korišćen je Minnesota Multiphasic Personality Inventory (MMPI-201) test. Za obradu podataka korišćena je kanonička diskriminativna analiza u sklopu SPSS programa. Zavisna varijabla u istraživanju bio je edem mozga. Blok nezavisnih varijabli, sačinjen za potrebe ovog istraživanja, sastojao se od dve podgrupe. Prvu je činilo 12 varijabli kojima se opisuju relevantna obeležja zavisnosti od droga. Drugu je činilo 8 psihopatoloških tendencija ličnosti definisanih pomenutim testom. Rezultati. Edem mozga utvrđen je kod 52 (20,63%) zavisnika od droge. Razlike između grupa zavisnika od droge sa i bez edema mozga utvrđene su u dužini narkomanskog staža (0,301), korišćenju alkohola paralelno sa drogama (0,466) i lečenju zavisnosti (0,603). Kod zavisnika od droge sa cerebralnim edemom na MMPI-201 testu utvrđene su povišene skale hipohondrije, psihopatske devijacije i psihastenije, a sniženje skala šizofrenije i depresije. Zaključak. Kod jednog broja ispitivanih zavisnika od droge potvrđena je sumnja u mogućnost povezanosti edema mozga i osobina ličnosti. S obzirom na to da praksa često iziskuje potrebu za procenom ličnosti, bilo da se radi o lečenju ili veštačenju, neophodno je nastaviti istraživanja u ovom pravcu

(Non)renormalizability of the D-deformed Wess-Zumino model

We continue the analysis of the $D$-deformed Wess-Zumino model which was started in the previous paper. The model is defined by a deformation which is non-hermitian and given in terms of the covariant derivatives $D_\alpha$. We calculate one-loop divergences in the two-point, three-point and four-point Green functions. We find that the divergences in the four-point function cannot be absorbed and thus our model is not renormalizable. We discuss possibilities to render the model renormalizable.Comment: 19 pages; version accepted for publication in Phys.Rev.D; new section with the detailed discussion on renormalizabilty added and a special choice of coupling constants which renders the model renormalizable analyze