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

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

Transition of fertility and birth control population of the Timocka krajina

Демографска транзиција условљена недовољним рађањем карактерише савремене негативне демографске процесе који су започети у земљама Европе, а током друге половине 20.века постају одлика развијених земаља и земаља у развоју усвајањем ниских репродуктивних норми. Овај период одликује Друга демографска транзиција са променама у систему вредности, породичним односима и фертилитетним одликама становништва, као и са усвајањем метода контроле рађања. Простор Тимочке крајине се одликује демографском транзицијом плодности женског становништва већ крајем 19.века, условљавајући негативни тренд демографског развоја који представља претечу екстремно ниског фертилитета Србије. Ови процеси су детерминисани историјским процесима на овом простору, култролошким, етничким, историјским наслеђем и укорењеним облицима репродуктивног понашања становништва, тако да је поред друштвеног, привредног и економског развоја, значајна и специфичност демографског развитка простора. Трансформација проширене у просту репродукцију, и достизање нивоа фертилитета женског становништва недовољног за просту замену генерација детерминише на самом почетку 21.века, да се овај простор Срије, налази у одмаклој фази демографске транзиције са дубоком биолошком депопулацијом. Достигнути ниво транзиције фертилитета и транзиције контроле рађања на простору Тимочке крајине праћен је и интензивним просторним кретањима кроз историјске етапе, наглашавајући губитак популационе снаге којим се одликује овај простор више од једног века, као и другим одликама становништва и друштва одређених историјских етапа. Зато је значајно и научно оправдано сагледати ове феномене и кроз доступне изворе научне и стручне литературе са подацима о овом простору. Циљ у овој докторској дисертацији је утврдити и научно аргументовати основне карактеристике и специфичности демографског развитка, транзиције фертилитета и 5 транзиције контроле рађања Тимочке крајине...The demographic transition caused by insufficient birth rate is characteristic for modern negative demographic processes which started in European countries, and during the second half of the 20th century became a distinctive feature of developed and developing countries by accepting low reproductive norms. This period is marked as Second demographic transition with changes in value system, family relations and fertility features of the population, as well as accepting the methods of birth control. The Timocka krajina region started having a demographic transition of the fertility of female population at the end of the 19th century, which caused a negative trend of demographic development leading to an extremely low fertility rate in Serbia. These processes are determined by historical events in this region and by cultural, ethnical and historical legacy and forms of reproductive behavior of the population, so that beside social, industrial and economical factors, another important factor is the specific demographic development of the region. The transformation from expanded to simple reproduction rate and reaching the fertility level of female population which is inadequate for the plain replacement of generations determines that this region of Serbia is in the late phase of a demographic transition towards deep biological depopulation. The reached level of fertility transition and birth control transition in Timocka krajina region is accompanied by intensive migration through historical times, which marks the loss of work force which was characteristic for this area for more than a century like other features of the population and societies at different historical times. Thus it is important and scientifically justified to observe these phenomena through available sources of scientific and technical publications about this region. The aim of this dissertation is determining and scientifically argumenting the basic characteristics and specificity of demographic development of fertility transition and transition of birth control in Timocka krajina region. The task of this research is a scientific exploration of the influence of traditional and historical legacy and modern demographic development, migrational components and non-demographic influence on the establishment and formation of demographic flows and levels of transition of fertility and birth control, temporal and spatial characterisation of demographic processes and the consequences of 8 biological depopulation, with establishing phases, stages and the consequences of demographic aging, disturbing of relations of age contigents of female population, as well a scientific analysis of mutual dependency of the development of population and the area it inhabits..

Distributed Air Traffic Control Simulator

During initial training air traffic control students acquire theoretical knowledge in various fields including air traffic management, aircraft performance, air traffic control equipment and systems, navigation and others. This paper proposes a simulator and explains its use and features that allows students to gain a practical insight into their coursework in order to complement their training. The goal of the simulator is to realistically implement all the key functionalities needed to cover the topics that were presented in class. The simulator offers a user friendly, distributed, and multi-role environment that can be deployed on regular PCs. Moreover, this paper discusses and resolves some of the main conceptual and implementational issues that were faced during simulator development

The Effect of Shelter on Oxidative Stress and Aggressive Behavior in Crested Newt Larvae (Triturus spp.)

Shelters are important for animal survival. Provision of adequate hiding places allow animals to express their natural sheltering behavior and it can have different positive effects on cortisol levels, physiological processes and mental performance. Although the absence of a refuge activates some stress response, its effect on oxidative stress has not been adequately examined. This study investigated whether the presence/absence of a shelter modifies the oxidative status (the antioxidant system and oxidative damage) and aggressive behavior of crested newt larvae (Triturus macedonicus and its hybrid with T. ivanbureschi). Our results show that individuals reared with shelters had lower values of the tested antioxidant parameters (catalase, glutathione peroxidase, glutathione S-transferase and glutathione), indicating a lower production of reactive species than individuals reared without shelter. The same pattern was observed in both T. macedonicus and its hybrid. Contrary to the activation of some physiological pathways, shelter availability did not significantly affect the rate of intraspecific aggressive behavior. The physiological benefits of shelter use can be manifested as a lower requirement for investment in the energy necessary for the maintenance of the upregulated antioxidant defenses, activation of repair systems and synthesis of endogenous antioxidants. This study highlights the importance of shelter provision, which may be valuable in habitat restoration and animal conservation studies

Invertible Zero-Shot Recognition Flows

© 2020, Springer Nature Switzerland AG. Deep generative models have been successfully applied to Zero-Shot Learning (ZSL) recently. However, the underlying drawbacks of GANs and VAEs (e.g., the hardness of training with ZSL-oriented regularizers and the limited generation quality) hinder the existing generative ZSL models from fully bypassing the seen-unseen bias. To tackle the above limitations, for the first time, this work incorporates a new family of generative models (i.e., flow-based models) into ZSL. The proposed Invertible Zero-shot Flow (IZF) learns factorized data embeddings (i.e., the semantic factors and the non-semantic ones) with the forward pass of an invertible flow network, while the reverse pass generates data samples. This procedure theoretically extends conventional generative flows to a factorized conditional scheme. To explicitly solve the bias problem, our model enlarges the seen-unseen distributional discrepancy based on a negative sample-based distance measurement. Notably, IZF works flexibly with either a naive Bayesian classifier or a held-out trainable one for zero-shot recognition. Experiments on widely-adopted ZSL benchmarks demonstrate the significant performance gain of IZF over existing methods, in both classic and generalized settings

Quantum Cascade Laser Design for Tunable Output at Characteristic Wavelengths in the Mid-Infrared Spectral Range

We present a method for systematic optimization of quantum cascade laser active region, based on the use of the genetic algorithm. The method aims at obtaining a gain-maximized structure, designed to emit radiation at specified wavelengths suitable for direct absorption by pollutant gasses present in the ambient air. After the initial optimization stage, we introduce a strong external magnetic field to tune the laser output properties and to slightly modify the emission wavelength to match the absorption lines of additional compounds. The magnetic field is applied perpendicularly to the epitaxial layers, thus causing two dimensional continuous energy subbands to split into series of discrete Landau levels. This affects all the relevant relaxation processes in the structure and consequently the lifetime of carriers in the upper laser level. Furthermore, strong effects of band nonparabolicity result in subtle changes of the lasing wavelength at magnetic fields which maximize the gain, thus providing a path for fine tuning of the output radiation properties. Numerical results are presented for GaAs/Al(x)Ga(1-x)As based quantum cascade laser structures designed to emit at particular wavelengths in the mid infrared part of the spectrum.11th Annual Conference of the Materials-Research-Society-of-Serbia (YUCOMAT 2009), Aug 31-Sep 04, 2009, Herceg Novi, Montenegr

Humidity sensing properties of nanocrystalline pseudobrookite (Fe2TiO5) based thick films

Pseudobrookite based nanopowder was obtained by solid state synthesis of starting hematite and anatase nanopowders in the weight ratio 55:45. Structural and morphological properties were analyzed using X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV/Vis diffuse reflectance spectroscopy, Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM) confirming the formation of nanocrystalline pseudobrookite. The obtained powder was mixed with a binder (ethyl cellulose), dispersant (alpha-terpinol) and adhesion agents (acetic acid and distilled water) to obtain a thick film paste. It was screen printed on alumina substrate with interdigitated PdAg electrodes and fired at 600 degrees C for 30 min. Formation of a porous nanocrystalline thick film structure was shown using Scanning electron microscopy (SEM), while Hall measurements enabled determination of carrier mobility. Change of impedance response in the frequency range 42 Hz-1 MHz with humidity was analyzed at room temperature (25 degrees C) and 50 degrees C in the relative humidity range 30-90% and 40-90%, respectively. At 42 Hz, and room temperature the impedance reduced similar to 28 times, while at 50 degrees C it reduced similar to 147 times in the relative humidity range 40-90%. The sensor showed rapid response (16 s) and relatively low hysteresis (8.39% at 25 degrees C and 2.64% at 50 degrees C) showing that this is a promising material for application in humidity sensing