Strong exciton-plasmon coupling in semiconducting carbon nanotubes

We study theoretically the interactions of excitonic states with surface electromagnetic modes of small-diameter (~1 nm) semiconducting single-walled carbon nanotubes. We show that these interactions can result in strong exciton-surface-plasmon coupling. The exciton absorption line shape exhibits Rabi splitting ~0.1 eV as the exciton energy is tuned to the nearest interband surface plasmon resonance of the nanotube. We also show that the quantum confined Stark effect may be used as a tool to control the exciton binding energy and the nanotube band gap in carbon nanotubes in order, e.g., to bring the exciton total energy in resonance with the nearest interband plasmon mode. The exciton-plasmon Rabi splitting we predict here for an individual carbon nanotube is close in its magnitude to that previously reported for hybrid plasmonic nanostructures artificially fabricated of organic semiconductors on metallic films. We expect this effect to open up paths to new tunable optoelectronic device applications of semiconducting carbon nanotubes.Comment: 22 pages, 8 figures, accepted for PR

Influence of AC electric field on the charge generation in albumin solution in a flow-based AFM-fishing system

The work was supported by the Russian Ministry of Education and Science, Agreement No. 14.613.21.0063, universal identifier RFMEFI61317X0063

Experimental Constraints on the Neutrino Oscillations and a Simple Model of Three Flavour Mixing

A simple model of the neutrino mixing is considered, which contains only one right-handed neutrino field, coupled via the mass term to the three usual left-handed fields. This is a simplest model that allows for three-flavour neutrino oscillations. The existing experimental limits on the neutrino oscillations are used to obtain constraints on the two free mixing parameters of the model. A specific sum rule relating the oscillation probabilities of different flavours is derived.Comment: 10 pages, 3 figures in post script, Latex, IFT 2/9

МЕТОДЫ ОБУЧЕНИЯ Z-КЛАССИФИКАТОРОВ

The use of genetic and gradient algorithms for learning classifiers based on Z-model was considered. Combined method of consistent applying this algorithms was offered. The resulting method allows to calculate all model parameters including integer ones and provides acceptable model training quality.Рассмотрено использование генетического и градиентного алгоритмов для обучения классификаторов, основанных на Z-модели. Предлагается комбинированный метод, суть которого состоит в их последовательном применении для предварительного и окончательного обучения. Полученный метод позволяет настраивать все параметры модели, включая целочисленные, и обеспечивает приемлемое качество настройки Z-модели классификации

Вероятностный анализ срыва автосопровождения видеосистемой мобильного робота

The article is devoted to the development of a methodology for estimating the probability of an object auto tracking failure by the mobile robot video system under the influence of external factors caused by random vibrations of the mobile platform. The mathematical formulation of the probabilistic analysis problem is based on the processes representation occurring in the system by a vector stochastic differential equation. The condition for the auto tracking failure is the exit of the tracked object from the of the video system field of view and non-return to it within a specified time. The probability of auto-tracking failure depends on the dynamic tracking system properties and is described by a recurrent formula that accounts the probability of an object being out of the field of view and the probability of its non-return. The method of calculating the failure probability includes the solution of two ordinary differential equations systems for probabilistic moments. One system of equations characterizes the probability density of tracked object location coordinates distribution in an open area of space. Another system of equations characterizes the change in time of the probability density of the tracked object coordinates, which is outside the video system field of view. A simplified example is given that clearly illustrates the evolution of the system probabilistic characteristics under the study in space and time.Статья посвящена разработке методики оценки вероятности срыва автосопровождения объекта видеосистемой мобильного робота под действием внешних факторов, обусловленных случайными колебаниями мобильной платформы. Математическая постановка задачи вероятностного анализа основана на представлении процессов, происходящих в системе, векторным стохастическим дифференциальным уравнением. Условием срыва автосопровождения считается выход отслеживаемого объекта из поля зрения видеосистемы и невозврат в него в течение заданного времени. Вероятность срыва автосопровождения зависит от динамических свойства системы слежения и описывается рекуррентной формулой, в которой учитывается вероятность нахождения объекта вне поля зрения и вероятность его невозврата. Методика расчета вероятности срыва включает в себя решение двух систем обыкновенных дифференциальных уравнений для вероятностных моментов. Одна система уравнений характеризует плотность вероятности распределения координат нахождения сопровождаемого объекта в открытой области пространства. Другая система уравнений характеризует изменение во времени плотности вероятности координат сопровождаемого объекта, находящегося за пределами поля зрения видеосистемы. Приведен упрощенный пример, который наглядно иллюстрирует эволюцию вероятностных характеристик исследуемой системы в пространстве и во времени

Catalysis of iron core formation in Pyrococcus furiosus ferritin

The hollow sphere-shaped 24-meric ferritin can store large amounts of iron as a ferrihydrite-like mineral core. In all subunits of homomeric ferritins and in catalytically active subunits of heteromeric ferritins a diiron binding site is found that is commonly addressed as the ferroxidase center (FC). The FC is involved in the catalytic Fe(II) oxidation by the protein; however, structural differences among different ferritins may be linked to different mechanisms of iron oxidation. Non-heme ferritins are generally believed to operate by the so-called substrate FC model in which the FC cycles by filling with Fe(II), oxidizing the iron, and donating labile Fe(III)–O–Fe(III) units to the cavity. In contrast, the heme-containing bacterial ferritin from Escherichia coli has been proposed to carry a stable FC that indirectly catalyzes Fe(II) oxidation by electron transfer from a core that oxidizes Fe(II). Here, we put forth yet another mechanism for the non-heme archaeal 24-meric ferritin from Pyrococcus furiosus in which a stable iron-containing FC acts as a catalytic center for the oxidation of Fe(II), which is subsequently transferred to a core that is not involved in Fe(II)-oxidation catalysis. The proposal is based on optical spectroscopy and steady-state kinetic measurements of iron oxidation and dioxygen consumption by apoferritin and by ferritin preloaded with different amounts of iron. Oxidation of the first 48 Fe(II) added to apoferritin is spectrally and kinetically different from subsequent iron oxidation and this is interpreted to reflect FC building followed by FC-catalyzed core formation

Приближенная математическая модель оценки влияния вибраций на навесные элементы видеосистемы мобильного робота

The problem of constructing and applying of mathematical model for assessing the influence of vibrations on the attached elements of the video system of a mobile robot is solved. This robot is considered as a mobile platform for placing of the special equipment for various purposes. The analysis of mathematical models and the results of experimental studies of vibrations of multi-support wheeled machine and its structural elements has been conducted. On the basis of this analysis, the form of a stochastic mathematical model of vibrations of the structure of a mobile robot has been substantiated. The vibration model is specified as a correlation function or spectral density of a random process for various conditions of the robot’s movement. Differential equations of the shaping filter for modeling а random vibration process with given characteristics are presented. Differential equations for the probabilistic moments of the vibration process are presented. Based on the equations for the probabilistic moments and the proposed formula, an assessment of events, which consist in exceeding the vibration amplitude of a given level was carried out. These events are named as outliers of a random process and characterize the range within the basic properties of the equipment installed on the mobile platform are preserved. An analytical study of a mathematical model to determine the intensity of emissions of a random vibration process has been carried out. The probabilistic characteristics of the vibration process and the intensity of emissions are determined. The obtained theoretical results make it possible to assess the performance of the elements of a video system installed on a mobile platform and to formulate the basic requirements for tolerances for their parameters. The results of computer modeling clearly showed the efficiency of the proposed mathematical model for assessing the influence of vibrations.Решается задача построения и применения математической модели оценки влияния вибраций на навесные элементы видеосистемы мобильного робота. Данный робот рассматривается в качестве подвижной платформы для размещения специального оборудования различного предназначения. Проведен анализ математических моделей и результатов экспериментальных исследований колебаний (вибраций) элементов конструкции многоопорных колесных машин. На основе данного анализа обоснован вид стохастической математической модели вибраций конструкции мобильного робота. Модель вибраций задана в виде корреляционной функции или спектральной плотности случайного процесса для различных условий перемещения робота. Представлены дифференциальные уравнения формирующего фильтра для моделирования случайного процесса вибраций с заданными характеристиками. Приведены дифференциальные уравнения для вероятностных моментов процесса вибраций. На основе уравнений для вероятностных моментов и предложенной формулы проведена оценка событий, которые заключаются в превышении амплитудой вибраций заданного уровня. Эти события называются выбросами случайного процесса и характеризуют диапазон, внутри которого сохраняются основные свойства оборудования, установленного на подвижной платформе. Проведено аналитическое исследование математической модели для определения интенсивности выбросов случайного процесса вибраций. Определены вероятностные характеристики процесса вибраций и интенсивности выбросов. Полученные теоретические результаты позволяют оценить работоспособность элементов видеосистемы, установленной на подвижной платформе и сформулировать основные требования к допускам на их параметры. Результаты компьютерного моделирования наглядно показали работоспособность предложенной математической модели оценки влияния вибраций

Crystal structure of the ferritin from the hyperthermophilic archaeal anaerobe Pyrococcus furiosus

The crystal structure of the ferritin from the archaeon, hyperthermophile and anaerobe Pyrococcus furiosus (PfFtn) is presented. While many ferritin structures from bacteria to mammals have been reported, until now only one was available from archaea, the ferritin from Archaeoglobus fulgidus (AfFtn). The PfFtn 24-mer exhibits the 432 point-group symmetry that is characteristic of most ferritins, which suggests that the 23 symmetry found in the previously reported AfFtn is not a common feature of archaeal ferritins. Consequently, the four large pores that were found in AfFtn are not present in PfFtn. The structure has been solved by molecular replacement and refined at 2.75-Å resolution to R = 0.195 and Rfree = 0.247. The ferroxidase center of the aerobically crystallized ferritin contains one iron at site A and shows sites B and C only upon iron or zinc soaking. Electron paramagnetic resonance studies suggest this iron depletion of the native ferroxidase center to be a result of a complexation of iron by the crystallization salt. The extreme thermostability of PfFtn is compared with that of eight structurally similar ferritins and is proposed to originate mostly from the observed high number of intrasubunit hydrogen bonds. A preservation of the monomer fold, rather than the 24-mer assembly, appears to be the most important factor that protects the ferritin from inactivation by heat