Metallo-dielectric diamond and zinc-blende photonic crystals

It is shown that small inclusions of a low absorbing metal can have a dramatic effect on the photonic band structure. In the case of diamond and zinc-blende photonic crystals, several complete photonic band gaps (CPBG's) can open in the spectrum, between the 2nd-3rd, 5th-6th, and 8th-9th bands. Unlike in the purely dielectric case, in the presence of small inclusions of a low absorbing metal the largest CPBG for a moderate dielectric constant (epsilon<=10) turns out to be the 2nd-3rd CPBG. The 2nd-3rd CPBG is the most important CPBG, because it is the most stable against disorder. For a diamond and zinc-blende structure of nonoverlapping dielectric and metallo-dielectric spheres, a CPBG begins to decrease with an increasing dielectric contrast roughly at the point where another CPBG starts to open--a kind of gap competition. A CPBG can even shrink to zero when the dielectric contrast increases further. Metal inclusions have the biggest effect for the dielectric constant 2<=epsilon<=12, which is a typical dielectric constant at near infrared and in the visible for many materials, including semiconductors and polymers. It is shown that one can create a sizeable and robust 2nd-3rd CPBG at near infrared and visible wavelengths even for a photonic crystal which is composed of more than 97% low refractive index materials (n<=1.45, i.e., that of silica glass or a polymer). These findings open the door for any semiconductor and polymer material to be used as genuine building blocks for the creation of photonic crystals with a CPBG and significantly increase the possibilities for experimentalists to realize a sizeable and robust CPBG in the near infrared and in the visible. One possibility is a construction method using optical tweezers, which is analyzed here.Comment: 25 pp, 23 figs, RevTex, to appear in Phys Rev B. For more information look at http://www.amolf.nl/research/photonic_materials_theory/moroz/moroz.htm

Spin-orbit lateral superlattices: energy bands and spin polarization in 2DEG

The Bloch spinors, energy spectrum and spin density in energy bands are studied for the two-dimensional electron gas (2DEG) with Rashba spin-orbit (SO) interaction subject to one-dimensional (1D) periodic electrostatic potential of a lateral superlattice. The space symmetry of the Bloch spinors with spin parity is studied. It is shown that the Bloch spinors at fixed quasimomentum describe the standing spin waves with the wavelength equal to the superlattice period. The spin projections in these states have the components both parallel and transverse to the 2DEG plane. The anticrossing of the energy dispersion curves due to the interplay between the SO and periodic terms is observed, leading to the spin flip. The relation between the spin parity and the interband optical selection rules is discussed, and the effect of magnetization of the SO superlattice in the presence of external electric field is predicted.Comment: 6 pages, 5 figures, reported at the International Conferences "Nanophysics and Nanoelectronics" (Nizhny Novgorod, Russia, March 2006) and "Nanostructures: Physics and Technology" (St Petersburg, Russia, June 2006

Persistent currents in multicomponent Tomonaga-Luttinger liquid: application to mesoscopic semiconductor ring with spin-orbit interaction

We study persistent currents in semiconductor ballistic rings with spin-orbit Rashba interaction. We use as a working model the multicomponent Tomonaga-Luttinger liquid which arises due to the nonparabolic dispersion relations of electrons in the rings with rather strong spin-orbit coupling. This approach predicts some new characteristic features of persistent currents, which may be observed in experimental studies of semiconductor ballistic rings.Comment: 13 pages, 8 figure

A superconvergent representation of the Gersten-Nitzan and Ford-Webber nonradiative rates

An alternative representation of the quasistatic nonradiative rates of Gersten and Nitzan [J. Chem. Phys. 1981, 75, 1139] and Ford and Weber [Phys. Rep. 1984, 113, 195] is derived for the respective parallel and perpendicular dipole orientations. Given the distance d of a dipole from a sphere surface of radius a, the representations comprise four elementary analytic functions and a modified multipole series taking into account residual multipole contributions. The analytic functions could be arranged hierarchically according to decreasing singularity at the short distance limit d ---> 0, ranging from d^{-3} over d^{-1} to ln (d/a). The alternative representations exhibit drastically improved convergence properties. On keeping mere residual dipole contribution of the modified multipole series, the representations agree with the converged rates on at least 99.9% for all distances, arbitrary particle sizes and emission wavelengths, and for a broad range of dielectric constants. The analytic terms of the representations reveal a complex distance dependence and could be used to interpolate between the familiar d^{-3} short-distance and d^{-6} long-distance behaviors with an unprecedented accuracy. Therefore, the representations could be especially useful for the qualitative and quantitative understanding of the distance behavior of nonradiative rates of fluorophores and semiconductor quantum dots involving nanometal surface energy transfer in the presence of metallic nanoparticles or nanoantennas. As a byproduct, a complete short-distance asymptotic of the quasistatic nonradiative rates is derived. The above results for the nonradiative rates translate straightforwardly to the so-called image enhancement factors Delta, which are of relevance for the surface-enhanced Raman scattering.Comment: 30 pages including 6 figure

Rashba effect in 2D mesoscopic systems with transverse magnetic field

We present semiclassical and quantum mechanical results for the effects of a strong magnetic field in Quantum Wires in the presence of Rashba Spin Orbit coupling. Analytical and numerical results show how the perturbation acts in the presence of a transverse magnetic field in the ballistic regime and we assume a strong reduction of the backward scattering interaction which could have some consequences for the Tomonaga-Luttinger transport. We analyze the spin texture due to the action of Spin Orbit coupling and magnetic field often referring to the semiclassical solutions that magnify the singular spin polarization: results are obtained for free electrons in a twodimensional electron gas and for electrons in a Quantum Wire. We propose the systems as possible devices for the spin filtering at various regimes.Comment: 12 pages, 12 figures, to appear in Phys. Rev.

Persistent Current of Free Electrons in the Plane

Predictions of Akkermans et al. are essentially changed when the Krein spectral displacement operator is regularized by means of zeta function. Instead of piecewise constant persistent current of free electrons on the plane one has a current which varies linearly with the flux and is antisymmetric with regard to all time preserving values of $\alpha$ including $1/2$. Different self-adjoint extensions of the problem and role of the resonance are discussed.Comment: (Comment on "Relation between Persistent Currents and the Scattering Matrix", Phys. Rev. Lett. {\bf 66}, 76 (1991)) plain latex, 4pp., IPNO/TH 94-2

Exploiting Nonlinear Recurrence and Fractal Scaling Properties for Voice Disorder Detection

Background: Voice disorders affect patients profoundly, and acoustic tools can potentially measure voice function objectively. Disordered sustained vowels exhibit wide-ranging phenomena, from nearly periodic to highly complex, aperiodic vibrations, and increased &#x22;breathiness&#x22;. Modelling and surrogate data studies have shown significant nonlinear and non-Gaussian random properties in these sounds. Nonetheless, existing tools are limited to analysing voices displaying near periodicity, and do not account for this inherent biophysical nonlinearity and non-Gaussian randomness, often using linear signal processing methods insensitive to these properties. They do not directly measure the two main biophysical symptoms of disorder: complex nonlinear aperiodicity, and turbulent, aeroacoustic, non-Gaussian randomness. Often these tools cannot be applied to more severe disordered voices, limiting their clinical usefulness.&#xd;&#xa;&#xd;&#xa;Methods: This paper introduces two new tools to speech analysis: recurrence and fractal scaling, which overcome the range limitations of existing tools by addressing directly these two symptoms of disorder, together reproducing a &#x22;hoarseness&#x22; diagram. A simple bootstrapped classifier then uses these two features to distinguish normal from disordered voices.&#xd;&#xa;&#xd;&#xa;Results: On a large database of subjects with a wide variety of voice disorders, these new techniques can distinguish normal from disordered cases, using quadratic discriminant analysis, to overall correct classification performance of 91.8% plus or minus 2.0%. The true positive classification performance is 95.4% plus or minus 3.2%, and the true negative performance is 91.5% plus or minus 2.3% (95% confidence). This is shown to outperform all combinations of the most popular classical tools.&#xd;&#xa;&#xd;&#xa;Conclusions: Given the very large number of arbitrary parameters and computational complexity of existing techniques, these new techniques are far simpler and yet achieve clinically useful classification performance using only a basic classification technique. They do so by exploiting the inherent nonlinearity and turbulent randomness in disordered voice signals. They are widely applicable to the whole range of disordered voice phenomena by design. These new measures could therefore be used for a variety of practical clinical purposes.&#xd;&#xa

Дистанционное образование в России в контексте обучения иностранным языкам

Every year the interest of youth in a foreign language as a means of international communication increases. New professions arise that require knowledge of a foreign language. Knowledge of a foreign language is a mandatory requirement for business communication and running anywhere in the world, evidence, and guarantee of competitiveness, professional socialization of the modern young generation. One of the priority tasks of the language training system is the improvement of teaching methods, the search for innovative methods, and advanced technologies for teaching languages. The article describes the current trends in Russian education, which are associated with the spread of distance education. It is proved that distance education is becoming increasingly important in terms of language training. It is shown that modern trends in education are associated, first of all, with the need to overcome the contradictions between the content of training and the requirements for the personality of the future specialist, the traditional organization of the educational process and the patterns of interpersonal and intercultural interaction.Cada año aumenta el interés de los jóvenes en un idioma extranjero como medio de comunicación internacional. Surgen nuevas profesiones que requieren el conocimiento de un idioma extranjero. El conocimiento de un idioma extranjero es un requisito obligatorio para la comunicación empresarial y la ejecución en cualquier parte del mundo, evidencia y garantía de competitividad, socialización profesional de la generación joven moderna. Una de las tareas prioritarias del sistema de capacitación en idiomas es la mejora de los métodos de enseñanza, la búsqueda de métodos innovadores y las tecnologías avanzadas para la enseñanza de idiomas. El artículo describe las tendencias actuales en la educación rusa, que están asociadas con la difusión de la educación a distancia. Está comprobado que la educación a distancia se está volviendo cada vez más importante en términos de capacitación en idiomas. Se muestra que las tendencias modernas en educación están asociadas, en primer lugar, con la necesidad de superar las contradicciones entre el contenido de la capacitación y los requisitos para la personalidad del futuro especialista, la organización tradicional del proceso educativo y los patrones de interpersonal e interacción intercultural.&nbsp;С каждым годом увеличивается интерес молодежи к иностранному языку как средству международного общения. Появляются новые специальности, требующие владения иностранным языком.Знание второго и последующих языков – это обязательное требование для делового общения и ведения бизнеса в любой точке мира, свидетельство и залог конкурентоспособности, профессиональной социализации современного молодого поколения.Одними из приоритетных задач системы языковой подготовки являются совершенствование методов обучения, поиск инновационных методов и передовых технологий обучения языкам.В данной статье описываются современные тенденции российского образования, связанные с распространением дистанционного обучения. Доказывается, что дистанционное обучение приобретает все большее значение в плане языковой подготовки. Показано, что современные тенденции в образовании связаны, в первую очередь, с необходимостью преодоления противоречий между содержанием подготовки и требованиями к личности будущего специалиста, традиционной организацией образовательного процесса и закономерностями межличностного и межкультурного взаимодействия

Pauli problem for a spin of arbitrary length: A simple method to determine its wave function

The problem of determining a pure state vector from measurements is investigated for a quantum spin of arbitrary length. Generically, only a finite number of wave functions is compatible with the intensities of the spin components in two different spatial directions, measured by a Stern-Gerlach apparatus. The remaining ambiguity can be resolved by one additional well-defined measurement. This method combines efficiency with simplicity: only a small number of quantities have to be measured and the experimental setup is elementary. Other approaches to determine state vectors from measurements, also known as the ‘‘Pauli problem,’’ are reviewed for both spin and particle systems