Interfacial dynamics in transport-limited dissolution

Various model problems of ``transport-limited dissolution'' in two dimensions are analyzed using time-dependent conformal maps. For diffusion-limited dissolution (reverse Laplacian growth), several exact solutions are discussed for the smoothing of corrugated surfaces, including the continuous analogs of ``internal diffusion-limited aggregation'' and ``diffusion-limited erosion''. A class of non-Laplacian, transport-limited dissolution processes are also considered, which raise the general question of when and where a finite solid will disappear. In a case of dissolution by advection-diffusion, a tilted ellipse maintains its shape during collapse, as its center of mass drifts obliquely away from the background fluid flow, but other initial shapes have more complicated dynamics.Comment: 5 pages, 4 fig

Phase diagram of Pb(Zr,Ti)O3 solid solutions from first principles

A first-principles-derived scheme, that incorporates ferroelectric and antiferrodistortive degrees of freedom, is developed to study finite-temperature properties of PbZr1-xTixO3 solid solutions near its morphotropic phase boundary. The use of this numerical technique (i) resolves controversies about the monoclinic ground-state for some Ti compositions, (ii) leads to the discovery of an overlooked phase, and (iii) yields three multiphase points, that are each associated with four phases. Additional neutron diffraction measurements strongly support some of these predictions.Comment: 10 pages, 2 figure

Morphological changes in the brain in liver cirrhosis of alcoholic and viral etiology

Background. Hepatic encephalopathy is an actual problem of modern medicine. However, its pathogenesis and histological picture are currently insufficiently studied. Less is known about the impact of the nature of primary liver disease on pathogenesis and histological picture of hepatic encephalopathy. This determines the relevance of further morphological studies of the brain in the late stages of liver cirrhosis of various etiologies.The aim. To establish and compare the morphological changes in the brain in alcoholic liver cirrhosis and viral (hepatitis C virus (HCV)) cirrhosis.Materials and methods. The morphological study of the brain of 40 deceased in outcome of HCV-associated cirrhosis and 23 patients died in outcome of chronic alcoholism was carried out. Histological changes in various parts of the brain were studied using survey and elective stains. The immunohistochemical study of HCV NS3 and CD68 expression in different brain regions was performed in cases of HCV-infection.Results. The changes of neurons, glial cells and cerebral microvessels underlie in the basis of morphological picture of brain damage in both studied groups underlie that corresponds to the “classical” model of hepatic encephalopathy pathogenesis. At the same time, a number of morphological features were observed. The most prominent differences concerned the manifestations of the glial reaction. The productive changes of macroglial cells with the appearance of multiple Alzheimer’s astrocytes type 2 as well as spongious changes in subcortical white matter dominated in the observations of alcoholic cirrhosis. In contrast, microglia cells reaction (microgliosis) in white matter was noticed in HCV-associated cirrhosis.Conclusions. The differences in histological signs of brain in the terminal stages of liver disease of viral and alcoholic etiology are shown. They broaden current idea of morphological picture of hepatic encephalopathy, and may be used to study its pathogenesis

A combined theoretical and experimental study of the low temperature properties of BaZrO3

Low temperature properties of BaZrO3 are revealed by combining experimental techniques (X-ray diffraction, neutron scattering and dielectric measurements) with theoretical first-principles-based methods (total energy and linear response calculations within density functional theory, and effective Hamiltonian approaches incorporating/neglecting zero-point phonon vibrations). Unlike most of the perovskite systems, BaZrO3 does not undergo any (long-range-order) structural phase transition and thus remains cubic and paraelectric down to 2 K, even when neglecting zero-point phonon vibrations. On the other hand, these latter pure quantum effects lead to a negligible thermal dependency of the cubic lattice parameter below ~ 40 K. They also affect the dielectricity of BaZrO3 by inducing an overall saturation of the real part of the dielectric response, for temperatures below ~ 40 K. Two fine structures in the real part, as well as in the imaginary part, of dielectric response are further observed around 50-65 K and 15 K, respectively. Microscopic origins (e.g., unavoidable defects and oxygen octahedra rotation occurring at a local scale) of such anomalies are suggested. Finally, possible reasons for the facts that some of these dielectric anomalies have not been previously reported in the better studied KTaO3 and SrTiO3 incipient ferroelectrics are also discussed.Comment: 8 pages, 5 figures, submitted to Physical Review

Asymmetric dipolar ring

Describes a device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field

Влияние технологических факторов на прочность болтовых соединений из композиционных материалов

Наведено результати розрахунків дворядного двозрізного болтового з’єднання з елементами із полімерного композиційного матеріалу (ПКМ) для різних комбінацій таких технологічних факторів, як посадка болта в отвір і момент на ключі під час затягування. Розрахунки максимально наближені до реальної ситуації: використовували тривимірну геометричну і скінченноелементну моделі, задача розв’язувалася як пружна контактна з урахуванням силового навантаження, величин зазору/натягу в отворах, моменту затягування, тертя в з’єднанні. ПКМ моделювали як 3D-ортотропний матеріал. Розрахунки проводили на програмному комплексі FEMAP/NX NASTRAN, версія 10.2.0. Обчислення виконано відповідно до плану повного факторного експерименту: два фактори на трьох рівнях, всього дев’ять комбінацій. За результатами розрахунків побудовано регресійну модель, яка описує вплив вибраних технологічних факторів на величину максимального еквівалентного напруження за Мізесом у болтах з’єднання. Результати розрахунків засвідчили, що технологічні фактори, які супроводжують виготовлення болтового з’єднання, можуть істотно вплинути на напружено-деформований стан елементів з’єднання. Так, величина максимального еквівалентного напруження у розрахунках змінювалася від 782 до 1146 МПа, тобто різниця перевищувала 30 %. Зроблено висновок про перспективність застосування описаного підходу до проектування болтових з’єднань елементів з ПКМ, зокрема в авіабудуванні.The paper presents calculation results for a double lap bolted joint with elements made of polymer composite material (PCM) for different combinations of such processing factors as size of the bolt hole and tightening torque. These calculations are as close to real situation as possible: three-dimensional and finite-element models are used; the task is solved as thermoelastic and contact taking into account power load, amount of clearance and tightness in holes, tightening torque, friction within the joint. PCM was modeled as 3D-orthotropic material. The calculations were made using FEMAP/NX NASTRAN, version 10.2.0. We made calculations according to the plan of a complete factorial experiment: two factors at three levels, nine combinations altogether. Based on calculation results a regression model was developed. It describes the influence of selected processing factors on the volume of maximum equivalent stress by von Mises. The calculation results indicated that processing factors accompanying production of the bolted joint can significantly influence the stress and deformation state of joint elements. Thus, the maximum equivalent stress in calculations changed from 782 to 1146 MPa. So, the difference exceeded 30 %. We can conclude that the method application to design of bolted joint elements with PCM, particularly in aircraft building, is promising.Представлены результаты расчетов двухрядного двухсрезного болтового соединения с элементами из полимерного композиционного материала (ПКМ) для разных комбинаций таких технологических факторов, как посадка болта в отверстие и момент на ключе при затягивании. Расчеты максимально приближены к реальной ситуации: использовали трехмерную геометрическую и конечноэлементную модели, задача решалась как упругая контактная, с учетом силовой нагрузки, величин зазора/натяжения в отверстиях, момента затягивания, трения в соединении. ПКМ моделировали как 3D-ортотропний материал. Расчеты проводили в программном комплексе FEMAP/NX NASTRAN, версия 10.2.0. Вычисления выполнили в соответствии с планом полного факторного эксперимента: два фактора на трех уровнях, всего девять комбинаций. По результатам расчетов построили регрессионную модель, описывающую влияние избранных технологических факторов на величину максимального эквивалентного напряжения по Мизесу в болтах соединения. Результаты расчетов показали, что технологические факторы, сопровождающие изготовление болтового соединения, могут существенно повлиять на напряженно-деформированное состояние элементов соединения. Так, величина максимального эквивалентного напряжения в расчетах изменялась от 782 до 1146 МПа, т.е. различие превышало 30 %. Сделан вывод о перспективности применения описанного подхода к проектированию болтовых соединений элементов с ПКМ, в частности в авиастроении

Ferroelectric nanostructure having switchable multi-stable vortex states

A ferroelectric nanostructure formed as a low dimensional nanoscale ferroelectric material having at least one vortex ring of polarization generating an ordered toroid moment switchable between multi-stable states. A stress-free ferroelectric nanodot under open-circuit-like electrical boundary conditions maintains such a vortex structure for their local dipoles when subject to a transverse inhomogeneous static electric field controlling the direction of the macroscopic toroidal moment. Stress is also capable of controlling the vortex\u27s chirality because of the electromechanical coupling that exists in ferroelectric nanodots

Atomic excitation during recollision-free ultrafast multi-electron tunnel ionization

Modern intense ultrafast pulsed lasers generate an electric field of sufficient strength to permit tunnel ionization of the valence electrons in atoms. This process is usually treated as a rapid succession of isolated events, in which the states of the remaining electrons are neglected. Such electronic interactions are predicted to be weak, the exception being recollision excitation and ionization caused by linearly-polarized radiation. In contrast, it has recently been suggested that intense field ionization may be accompanied by a two-stage `shake-up' reaction. Here we report a unique combination of experimental techniques that enables us to accurately measure the tunnel ionization probability for argon exposed to 50 femtosecond laser pulses. Most significantly for the current study, this measurement is independent of the optical focal geometry, equivalent to a homogenous electric field. Furthermore, circularly-polarized radiation negates recollision. The present measurements indicate that tunnel ionization results in simultaneous excitation of one or more remaining electrons through shake-up. From an atomic physics standpoint, it may be possible to induce ionization from specific states, and will influence the development of coherent attosecond XUV radiation sources. Such pulses have vital scientific and economic potential in areas such as high-resolution imaging of in-vivo cells and nanoscale XUV lithography.Comment: 17 pages, 4 figures, original format as accepted by Nature Physic