Testing the validity of THz reflection spectra by dispersion relations

Complex response function obtained in reflection spectroscopy at terahertz range is examined with algorithms based on dispersion relations for integer powers of complex reflection coefficient, which emerge as a powerful and yet uncommon tools in examining the consistency of the spectroscopic data. It is shown that these algorithms can be used in particular for checking the success of correction of the spectra by the methods of Vartiainen et al [1] and Lucarini et al [2] to remove the negative misplacement error in the terahertz time-domain spectroscopy.Comment: 17 pages, 4 figure

Spin dynamics and magnetic-field-induced polarization of excitons in ultrathin GaAs/AlAs quantum wells with indirect band gap and type-II band alignment

The exciton spin dynamics are investigated both experimentally and theoretically in two-monolayer-thick GaAs/AlAs quantum wells with an indirect band gap and a type-II band alignment. The magnetic-field-induced circular polarization of photoluminescence, $P_c$, is studied as function of the magnetic field strength and direction as well as sample temperature. The observed nonmonotonic behaviour of these functions is provided by the interplay of bright and dark exciton states contributing to the emission. To interpret the experiment, we have developed a kinetic master equation model which accounts for the dynamics of the spin states in this exciton quartet, radiative and nonradiative recombination processes, and redistribution of excitons between these states as result of spin relaxation. The model offers quantitative agreement with experiment and allows us to evaluate, for the studied structure, the heavy-hole $g$ factor, $g_{hh}=+3.5$, and the spin relaxation times of electron, $\tau_{se} = 33~\mu$s, and hole, $\tau_{sh} = 3~\mu$s, bound in the exciton.Comment: 17 pages, 16 figure

Dipole excited states in 11^{11}Li with complex scaling

The 1$^-$ excitations of the three--body halo nucleus $^{11}$Li are investigated. We use adiabatic hyperspherical expansion and solve the Faddeev equations in coordinate space. The method of complex scaling is used to compute the resonance states. The Pauli forbidden states occupied by core neutrons are excluded by constructing corresponding complex scaled phase equivalent two-body potentials. We use a recently derived neutron--core interaction consistent with known structure and reaction properties of $^{10}$Li and $^{11}$Li. The computed dipole excited states with $J^\pi=1/2^+$, $J^\pi=3/2^+$, and $J^\pi=5/2^+$ have energies ranging from 0.6 MeV to 1.0 MeV and widths between 0.15 MeV and 0.65 MeV. We investigate the dependence of the complex energies of these states on the $^{10}$Li spectrum. The finite spin 3/2 of the core and the resulting core-neutron spin-spin interaction are important. The connection with Coulomb dissociation experiments is discussed and a need for better measurements is pointed out.Comment: 28 pages, 6 figures, Nuclear Physics A, in pres

Evolution of mitochondrial genomes in Baikalian amphipods

© 2016 The Author(s).Background: Amphipods (Crustacea) of Lake Baikal are a very numerous and diverse group of invertebrates generally believed to have originated by adaptive radiation. The evolutionary history and phylogenetic relationships in Baikalian amphipods still remain poorly understood. Sequencing of mitochondrial genomes is a relatively feasible way for obtaining a set of gene sequences suitable for robust phylogenetic inferences. The architecture of mitochondrial genomes also may provide additional information on the mechanisms of evolution of amphipods in Lake Baikal. Results: Three complete and four nearly complete mitochondrial genomes of Baikalian amphipods were obtained by high-throughput sequencing using the Illumina platform. A phylogenetic inference based on the nucleotide sequences of all mitochondrial protein coding genes revealed the Baikalian species to be a monophyletic group relative to the nearest non-Baikalian species with a completely sequenced mitochondrial genome - Gammarus duebeni. The phylogeny of Baikalian amphipods also suggests that the shallow-water species Eulimnogammarus has likely evolved from a deep-water ancestor, however many other species have to be added to the analysis to test this hypothesis. The gene order in all mitochondrial genomes of studied Baikalian amphipods differs from the pancrustacean ground pattern. Mitochondrial genomes of four species possess 23 tRNA genes, and in three genomes the extra tRNA gene copies have likely undergone remolding. Widely varying lengths of putative control regions and other intergenic spacers are typical for the mitochondrial genomes of Baikalian amphipods. Conclusions: The mitochondrial genomes of Baikalian amphipods display varying organization suggesting an intense rearrangement process during their evolution. Comparison of complete mitochondrial genomes is a potent approach for studying the amphipod evolution in Lake Baikal

Alternative evaluations of halos in nuclei

Data for the scattering of 6He, 8He, 9Li, and 11Li from hydrogen are analyzed within a fully microscopic folding model of proton-nucleus scattering. Current data suggest that of these only 11Li has a noticeable halo. For 6He, we have also analysed the complementary reaction 6Li(gamma,pi)6He(gs). The available data for that reaction support the hypothesis that 6He may not be a halo nucleus. However, those data are scarce and there is clearly a need for more to elicit the microscopic structure of 6He.Comment: 18 pages, 8 figures (added 4 figures), added reference. Version accepted for publication in Phys. Rev.

Анализ механизма перехода в предельное состояние жилых домов серии 111 при Спитакском землетрясении 1988 г.

The study aimed at investigating the reaction of aresidential building (Series 111 nine-story block section) to seismic impacts that can lead to destruction of the building. The article presents the results of the retrospective analysis of the seismic resistance of nine-story block sections in the city of Gyumri (Leninakan) under the influence of the 07.12.1988 Spitak earthquake. The seismic resistance of the block section was calculated using the ‘pushover analysis’ method. Direct dynamic calculations were performed using a model of complex elastoplastic deformation of a mechanical system with two degrees of freedom. An external impact was represented by the earthquake records taken at the Ghukasyan station. Macroseismic survey data collected after the 1988 earthquake are presented. The block sections of Series 111 multistory residential buildings were designedbythe Armenian research and design institutions ArmNIISA and Armgosproekt in 1975 for construction in the Armenian Republic on sites with seismicity of 7–8 points. Vibration tests were conducted to test the strength of anine-storey block section in Yerevan in 1976, and it was discovered that the actual seismic resistance of the building did not comply with the current earthquake-resistant construction standards. However, the test results were ignored. On December 7, 1988, the earthquake took place, and the Series 111 buildings collapsed in the cities of Gyumri (Leninakan) and Vanadzor (Kirovokan). In the State Commission Report regarding the Series 111 design, it was concluded that considering the damage due to the violations of the design and construction standards and taking into account the inspection calculations, the accepted design solutions of the residential buildings did not meet the requirements of the regulatory documents for buildings designed to sustain seismicity of 8 points. Such design should not be used for seismic areas and must be critically revised. The retrospective analysis performed by the authors of this article on the basis of experimental data not only confirmed the conclusions of the State Commission, but also made it possible to establish a mechanism for the transition of Series 111 block-sections to the limit state. Unfortunately, the state management of the construction industry failed to use this information and did not take any urgent preventive actions.In fact, the authoritiesof the USSR supported the position of the Gosstroy of Armenia and allowed them to continue the construction of Series 111 residential buildings with minor changes. It was impossible to prevent the Spitak earthquake, but proper preventive actions could have reduced the amount of social and economic damage incurred due to the earthquake. The consequences of obvious design and construction errors discovered 12 years before the Spitak earthquake were ‘written off’and explained by the natural disaster, including underestimated standard seismicity, features of the engineering-geological settings, and the unfavorable spectrum of theactual impact. Thousands of people lost their life, and huge material damage was caused due to the loss of Series 111 residential buildings (300000square meters). Such was the price of professional incompetence and departmental ambitions.Целью настоящей статьи является исследование реакции 9-этажной блок-секции серии 111 на сейсмические воздействия вплоть до разрушения. Изложены результаты ретроспективного анализа сейсмостойкости 9-этажных блок-секций в г. Гюмри (Ленинакане) под воздействием Спитакского землетрясения 07.12.1988 г. Выполнены расчеты сейсмостойкости блок-секции по методу «pushoveranalysis», а также прямой динамический расчет модели сложного упругопластического деформирования механической системы с двумя степенями свободы. В качестве внешнего воздействия использованы записи землетрясения на ст. Гукасян. Приведены данные макросейсмического обследования последствий землетрясения 1988 г. Типовые проекты блок-секций многоэтажных жилых домов серии 111, разработанные в 1975 г. в АрмНИИСА и Армгоспроекте, предназначались для строительства в Армянской ССР на площадках с сейсмичностью 7–8 баллов. Проведенные в 1976 г. в г. Ереване вибрационные испытания 9-этажной блок-секции жилого дома серии 111 показали, что фактическая сейсмостойкость здания не соответствует действующим нормам. Игнорирование результатов вибрационных испытаний привело к тотальному обрушению домов этой серии в городах Гюмри (Ленинакан) и Ванадзор (Кировакан) 7 декабря 1988 г. В Заключении Государственной комиссии в отношении проектов серии 111 отмечено, что характер нарушений норм и данные поверочных расчетов свидетельствуют, что принятые конструктивные решения рассмотренных жилых домов не отвечают требованиям нормативных документов для зданий с расчетной сейсмичностью 8 баллов. Проекты не могут применяться для строительства в сейсмических районах без коренной переработки. Результаты ретроспективного анализа, выполненного авторами статьи на основе экспериментальных данных, не только подтвердили выводы Государственной комиссии, но и позволили установить механизм перехода блок-секции серии 111 в предельное состояние. К сожалению, тогдашнее руководство строительной отраслью страны не сумело использовать эту информацию для принятия срочных превентивных мер. Союзные органы фактически поддержали позицию Госстроя Армении, разрешив продолжить строительство жилых домов серии 111 с незначительными замечаниями. Предотвратить Спитакское землетрясение было невозможно, но социальный и экономический ущерб от него можно было уменьшить за счет превентивных мероприятий. Последствия очевидных проектных и строительных ошибок, вскрытых за 12 лет до Спитакского землетрясения, списали за счет стихии: заниженной нормативной сейсмичности, особенностей инженерно-геологического строения, неблагоприятного спектрального состава воздействия, что действительно имело место. В итоге – тысячи погибших и материальный ущерб от потери жилищного фонда серии 111 в объеме 300 тыс. м2. Такова цена профессиональной некомпетентности и ведомственных амбиций

Algorithm of Quasiuniform Filling of Reachable Set for Nonlinear Control System

In this paper, we propose an algorithm of obtaining points that uniformly fill the volume of the reachable set, and even for a small number of elements results in a cloud quasiuniform approximation of the set. To solve the task of finding each additional point is to solve the optimization problem. Minimized function describes the uniformity and depends on the Euclidean distance between the elements of the approximation. It is designed to be equal or close to zero, if the distance exceeds the desired threshold value. Thus, a lower bound for the optimal value of the functional is pre-defined, so we save computing time for the random component of global optimization algorithms. "The tunnel ideology" underlies this algorithm. Besides local descent mechanisms it assumes that there are also transition mechanisms from a local extremum with the current record functional value to lower value extrema attraction domains. As a globalizing mechanism we use a nonlocal search in random directions repeated several times at each iteration of the algorithm. To improve the reliability of the proposed method of algorithm construction a recurrent random multistart is also included. The article includes the results of computational experiments on test examples and its comparison with calculations obtained by the method based on the Pontryagin maximum principle \cite{Gornov}. The designed method of reachable set approximation is applicable for two-dimensional systems and multidimensional ones as well. The experiments showed the efficiency of the approach and results comparison confirmed the accuracy the obtained approximations

Dynamics of Vacancy Formation and Distribution in Semiconductor Heterostructures: Effect of Thermally Generated Intrinsic Electrons

The effect of thermally generated equilibrium carrier distribution on the vacancy generation, recombination, and mobility in a semiconductor heterostructure with an undoped quantum well is studied. A different rate of thermally generated equilibrium carriers in layers with different band gaps at annealing temperatures forms a charge-carrier density gradient along a heterostructure. The nonuniform spatial distribution of charged vacancy concentration that appears as a result of strong dependence in the vacancy formation rate on the local charge-carrier density is revealed. A model of vacancy-mediated diffusion at high temperatures typical for post-growth annealing that takes into account this effect and dynamics of nonequilibrium vacancy concentration is developed. The change of atomic diffusivity rate in time that follows on the of spatial vacancy distribution dynamics in a model heterostructure with quantum wells during a high-temperature annealing at fixed temperatures is demonstrated by computational modeling