Conductance relaxation in Langmuir-Blodgett manganese phthalocyanine (PcMn) films in inhomogeneous electrical field

The conductance relaxation of Langmuir-Blodgett films of manganese phthalocyanine in inhomogeneous electrical field was studied. Inhomogeneous electrical field was achieved by using the lateral surface of reverse-biased Si p-n junction. The conductance of new film increases up to saturation with the characteristic time about 10 hours. After that the film has been kept in air for a long time (about 50 days), on application of the back bias the conductance slowly decreased with the characteristic time more than 10 hours. These properties are associated with appearance or disappearance of the bonds between molecular stacks in the film

Low-frequency magnetic sensing by magnetoelectric metglas/bidomain LiNbO3 long bars

We present an investigation into the magnetic sensing performance of magnetoelectric bilayered metglas / bidomain LiNbO3 long thin bars operating in a cantilever or free vibrating regime and under quasi-static and low-frequency resonant conditions. Bidomain single crystals of Y+128o-cut LiNbO3 were engineered by an improved diffusion annealing technique with a polarization macrodomain structure of the “head-to-head” and “tail-to-tail” type. Long composite bars with lengths of 30, 40 and 45 mm, as well as with and without attached small tip proof masses, were studied. ME coefficients as large as 550 V/cm∙Oe, corresponding to a conversion ratio of 27.5 V/Oe, were obtained under resonance conditions at frequencies of the order of 100 Hz in magnetic bias fields as low as 2 Oe. Equivalent magnetic noise spectral densities down to 120 pT/Hz1/2 at 10 Hz and to 68 pT/Hz1/2 at a resonance frequency as low as 81 Hz were obtained for the 45 mm long cantilever bar with a tip proof mass of 1.2 g. In the same composite without any added mass the magnetic noise was shown to be as low as 37 pT/Hz1/2 at a resonance frequency of 244 Hz and 1.2 pT/Hz1/2 at 1335 Hz in a fixed cantilever and free vibrating regimes, respectively. A simple unidimensional dynamic model predicted the possibility to drop the low-frequency magnetic noise by more than one order of magnitude in case all the extrinsic noise sources are suppressed, especially those related to external vibrations, and the thickness ratio of the magnetic-to-piezoelectric phases is optimized. Thus, we have shown that such systems might find use in simple and sensitive room-temperature low-frequency magnetic sensors, e.g., for biomedical applications.publishe

Astrometric Control of the Inertiality of the Hipparcos Catalog

Based on the most complete list of the results of an individual comparison of the proper motions for stars of various programs common to the Hipparcos catalog, each of which is an independent realization of the inertial reference frame with regard to stellar proper motions, we redetermined the vector $\omega$ of residual rotation of the ICRS system relative to the extragalactic reference frame. The equatorial components of this vector were found to be the following: $\omega_x = +0.04\pm 0.15$ mas yr$^{-1}$, $\omega_y = +0.18\pm 0.12$ mas yr$^{-1}$, and $\omega_z = -0.35\pm 0.09$ mas yr$^{-1}$.Comment: 8 pages, 1 figur

Magnetoelectric metglas/bidomain y + 140°-cut lithium niobate composite for sensing fT magnetic fields

We investigated the magnetoelectric properties of a new laminate composite material based on y+140°-cut congruent lithium niobate piezoelectric plates with an antiparallel polarized “head-to-head” bidomain structure and metglas used as a magnetostrictive layer. A series of bidomain lithium niobate crystals were prepared by annealing under conditions of Li2O outdiffusion from LiNbO3 with a resultant growth of an inversion domain. The measured quasi-static magnetoelectric coupling coefficient achieved |αE31| = 1.9 V·(cm·Oe)–1. At a bending resonance frequency of 6862 Hz, we found a giant |αE31| value up to 1704 V·(cm·Oe)–1. Furthermore, the equivalent magnetic noise spectral density of the investigated composite material was only 92 fT/Hz1/2, a record value for such a low operation frequency. The magnetic-field detection limit of the laminated composite was found to be as low as 200 fT in direct measurements without any additional shielding from external noises.publishe

HD 69686: A Mysterious High Velocity B Star

We report on the discovery of a high velocity B star, HD 69686. We estimate its space velocity, distance, surface temperature, gravity, and age. With these data, we are able to reconstruct the trajectory of the star and to trace it back to its birthplace. We use evolutionary tracks for single stars to estimate that HD 69686 was born 73 Myr ago in the outer part of our Galaxy ($r \sim 12$ kpc) at a position well below the Galactic plane ($z \sim -1.8$ kpc), a very unusual birthplace for a B star. Along the star's projected path in the sky, we also find about 12 other stars having similar proper motions, and their photometry data suggest that they are located at the same distance as HD 69686 and probably have the same age. We speculate on the origin of this group by star formation in a high velocity cloud or as a Galactic merger fragment.Comment: 28 pages, 6 figures, accepted for publication in Ap

Бидоменные сегнетоэлектрические кристаллы: свойства и перспективы применения

Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) are among the most important and most widely used materials of coherent and nonlinear optics, as well as acoustics. High degree of uniformity and reproducibility has become the foundation of technology for manufacturing high-quality crystals, absorbed by many suppliers around the world. However, the above areas do not limit the use of LiNbO3 and LiTaO3 due to their unique piezoelectric and ferroelectric properties. One promising application of crystals is the design of electromechanical transducers for precision sensors and actuators. In this respect, the high thermal stability of the piezoelectric and mechanical properties, the lack of hysteresis and creep make it possible to create electromechanical converters with wide operating temperature range, that is beyond the capability of commonly used ferroelectric ceramics. The main advantage of LiNbO3 and LiTaO3 over other single-crystal piezoelectrics is ferroelectric domain structure regulation toward targeted impact on the device characteristics. One of the most striking examples of electromechanical transducer design through domain engineering is the formation of a so-called bidomain ferroelectric structure in crystal. It represents a single-crystalline plate with two macrodomains with opposite directions of spontaneous polarization vectors separated by a charged domain wall. High switching fields make inversion domains stable at temperatures up to 1000 °C. This review summarizes the main achievements in the formation of bidomain structure and near surface inversion domains in LiNbO3 and LiTaO3 crystals. We present the domain structure virtualization methods in crystals and non-destructive methods for controlling the domain boundary position. The report contains a comparative analysis of the methods for forming inversion domains in crystals, and the patterns and technological control methods of the domain structure are discussed. The basic physical models have been proposed in the literature to explain the effect of the inversion domains formation. In the present paper we outline what one sees as strengths and weaknesses of these models. The strategies of crystallographic cut selection to create devices based on bidomain crystals are briefly discussed. We provide examples of the implementation of devices based on bidomain crystals such as actuators, sensors, acoustic transducers, and waste energy collection systems.Ниобат лития (LiNbO3) и танталат лития (LiTaO3) относятся к важнейшим и наиболее широко применяемым материалам когерентной и нелинейной оптики, а также акустики. Высокие требования, предъявляемые к однородности и воспроизводимости характеристик, стали основой для создания промышленной технологии выпуска высококачественных кристаллов, освоенной многими предприятиями мира. Однако использование LiNbO3 и LiTaO3 не ограничивается перечисленными выше областями техники благодаря выраженным пьезо- и сегнетоэлектрическим свойствам. Одним из перспективных направлений использования кристаллов является создание на их основе электромеханических преобразователей для прецизионных сенсоров и актюаторов. При этом высокая термическая стабильность пьезоэлектрических и механических свойств, отсутствие гистерезиса и крипа позволяют создавать электромеханические преобразователи, способные работать в широком диапазоне температур, недостижимом для обычно используемых для этих целей сегнетокерамических материалов. Главным преимуществом LiNbO3 и LiTaO3 перед другими монокристаллическими пьезоэлектриками является возможность направленного воздействия на характеристики устройств путем управления сегнетоэлектрической доменной структурой кристаллов. Одним из наиболее ярких примеров использования доменной инженерии для создания электромеханических преобразователей на основе кристаллов является формирование в них так называемой бидоменной структуры — двух доменов макроскопического размера, расположенных в одной кристаллической пластине, имеющих встречно направленные векторы спонтанной поляризации и разделенных заряженной доменной стенкой. Высокие коэрцитивные поля переключения делают инверсные домены стабильными вплоть до температуры Кюри (порядка 1140 °C у LiNbO3 и 600 °C у LiTaO3). В обзоре рассмотрены основные достижения в области формирования бидоменной структуры и приповерхностных инверсных доменов в кристаллах LiNbO3 и LiTaO3. Представлены методы визуализации доменной структуры в кристаллах и неразрушающие методы контроля положения междоменной границы. Проведен сравнительный анализ методов формирования инверсных доменов в кристаллах, обсуждены закономерности и технологические приемы управления доменной структурой. Приведены основные физические модели, предложенные в литературе для объяснения эффекта образования инверсных доменов, рассмотрены их сильные и слабые стороны. Кратко перечислены способы выбора кристаллографического среза для создания устройств, в которых используются бидоменные кристаллы. Приведены примеры реализации устройств на основе бидоменных кристаллов: актюаторов, сенсоров, акустических преобразователей, систем сбора бросовой энергии

Robust estimation of microbial diversity in theory and in practice

Quantifying diversity is of central importance for the study of structure, function and evolution of microbial communities. The estimation of microbial diversity has received renewed attention with the advent of large-scale metagenomic studies. Here, we consider what the diversity observed in a sample tells us about the diversity of the community being sampled. First, we argue that one cannot reliably estimate the absolute and relative number of microbial species present in a community without making unsupported assumptions about species abundance distributions. The reason for this is that sample data do not contain information about the number of rare species in the tail of species abundance distributions. We illustrate the difficulty in comparing species richness estimates by applying Chao's estimator of species richness to a set of in silico communities: they are ranked incorrectly in the presence of large numbers of rare species. Next, we extend our analysis to a general family of diversity metrics ("Hill diversities"), and construct lower and upper estimates of diversity values consistent with the sample data. The theory generalizes Chao's estimator, which we retrieve as the lower estimate of species richness. We show that Shannon and Simpson diversity can be robustly estimated for the in silico communities. We analyze nine metagenomic data sets from a wide range of environments, and show that our findings are relevant for empirically-sampled communities. Hence, we recommend the use of Shannon and Simpson diversity rather than species richness in efforts to quantify and compare microbial diversity.Comment: To be published in The ISME Journal. Main text: 16 pages, 5 figures. Supplement: 16 pages, 4 figure

Анизотропия деформации плаcтин монокристаллов ниобата лития Y + 128°–среза с бидоменной структурой

Bidomain single crystals of lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) are promising material for usage as actuators, mechanoelectrical transducers and sensors working in a wide temperature range. It is necessary to take into account anisotropy of properties of crystalline material when such devices are designed. Inthis study we investigated deformations of bidomain round shaped Y + 128°-cut wafers of lithium niobate in an external electric field. Dependencies of piezoelectric coefficients on rotation angles were calculated for lithium niobate and lithium tantalate and plotted for the crystal cuts which are used for bidomain ferroelectric structure formation. In experiment, we utilized external heating method and long-time annealing with lithium out-diffusion method in order to create round bidomain lithium niobate wafers. In order to obtain dependencies of the bidomain crystals’ movements on the rotation angle with central fastening and external electric field application optical microscopy was used. We also modeled a shape of the deformed bidomain wafer with a suggestion that the edge movement depends on the radial distance to the fastening point quadratically. In conclusion, bidomain Y + 128°-cut lithium niobate wafer exhibits saddle-like deformation when DC electric field is applied.Бидоменные монокристаллы ниобата лития (LiNbO3) и танталата лития (LiTaO3) являются перспективным материалом для создания на их основе актюаторов, механоэлектрических преобразователей и сенсоров, способных работать в широком диапазоне температур. При изготовлении таких устройств необходимо учитывать анизотропию свойств используемого материала. Исследованы деформации бидоменных пластин ниобата лития Y + 128°-среза круглой формы под действием внешнего электрического поля. Рассчитаны угловые зависимости пьезоэлектрических модулей кристаллов ниобата и танталата лития и построены их графики для срезов, используемых при изготовлении пластин с бидоменной сегнетоэлектрической структурой. Стационарным внешним нагревом и длительным отжигом с аутдиффузией лития сформированы бидоменные структурыв круглых пластинах ниобата лития. Методом оптической микроскопии получены зависимости перемещения краев бидоменных кристаллов от угла поворота вокруг нормалей пластин при центральном точечном закреплении и приложении внешнего электрического поля. Проведено моделирование формы деформированной пластины в предположении квадратичной зависимости перемещения краев от радиального расстояния до точки закрепления. Сделан вывод о седлообразном характере деформации бидоменной пластины Y + 128°-среза при приложении постоянной разности потенциалов

Novel hybrid organic/inorganic 2D quasiperiodic PC: from diffraction pattern to vertical light extraction

Recently, important efforts have been dedicated to the realization of a fascinating class of new photonic materials or metamaterials, known as photonic quasicrystals (PQCs), in which the lack of the translational symmetry is compensated by rotational symmetries not achievable by the conventional periodic crystals. As ever, more advanced functionality is demanded and one strategy is the introduction of non-linear and/or active functionality in photonic materials. In this view, core/shell nanorods (NRs) are a promising active material for light-emitting applications. In this article a two-dimensional (2D) hybrid a 2D octagonal PQC which consists of air rods in an organic/inorganic nanocomposite is proposed and experimentally demonstrated. The nanocomposite was prepared by incorporating CdSe/CdS core/shell NRs into a polymer matrix. The PQC was realized by electron beam lithography (EBL) technique. Scanning electron microscopy, far field diffraction and spectra measurements are used to characterize the experimental structure. The vertical extraction of the light, by the coupling of the modes guided by the PQC slab to the free radiation via Bragg scattering, consists of a narrow red emissions band at 690 nm with a full width at half-maximum (FWHM) of 21.5 nm. The original characteristics of hybrid materials based on polymers and colloidal NRs, able to combine the unique optical properties of the inorganic moiety with the processability of the host matrix, are extremely appealing in view of their technological impact on the development of new high performing optical devices such as organic light-emitting diodes, ultra-low threshold lasers, and non-linear devices