Static conductivity of charged domain wall in uniaxial ferroelectric-semiconductors

Using Landau-Ginzburg-Devonshire theory we calculated numerically the static conductivity of both inclined and counter domain walls in the uniaxial ferroelectrics-semiconductors of n-type. We used the effective mass approximation for the electron and holes density of states, which is valid at arbitrary distance from the domain wall. Due to the electrons accumulation, the static conductivity drastically increases at the inclined head-to-head wall by 1 order of magnitude for small incline angles theta pi/40 by up 3 orders of magnitude for the counter domain wall (theta=pi/2). Two separate regions of the space charge accumulation exist across an inclined tail-to-tail wall: the thin region in the immediate vicinity of the wall with accumulated mobile holes and the much wider region with ionized donors. The conductivity across the tail-to-tail wall is at least an order of magnitude smaller than the one of the head-to-head wall due to the low mobility of holes, which are improper carries. The results are in qualitative agreement with recent experimental data for LiNbO3 doped with MgO.Comment: 20 pages, 6 figures, 1 appendi

Domain wall conduction in multiaxial ferroelectrics

The conductance of domain wall structures consisting of either stripes or cylindrical domains in multi-axial ferroelectric-semiconductors is analyzed. The effects of the domain size, wall tilt and curvature, on charge accumulation, are analyzed using the Landau-Ginsburg Devonshire (LGD) theory for polarization combined with Poisson equation for charge distributions. Both the classical ferroelectric parameters including expansion coefficients in 2-4-6 Landau potential and gradient terms, as well as flexoelectric coupling, inhomogeneous elastic strains and electrostriction are included in the present analysis. Spatial distributions of the ionized donors, free electrons and holes were found self-consistently using the effective mass approximation for the respective densities of states. The proximity and size effect of the electron and donor accumulation/depletion by thin stripe domains and cylindrical nanodomains are revealed. In contrast to thick domain stripes and thicker cylindrical domains, in which the carrier accumulation (and so the static conductivity) sharply increases at the domain walls only, small nanodomains of radius less then 5-10 correlation length appeared conducting across entire cross-section. Implications of such conductive nanosized channels may be promising for nanoelectronics.Comment: 39 pages, 11 figures, 3 tables, 4 appendice

Distinct genetic control of parasite elimination, dissemination, and disease after Leishmania major infection

Elimination of pathogens is the basis of host resistance to infections; however, relationship between persisting pathogens and disease has not been clarified. Leishmania major infection in mice is an important model of host–pathogen relationship. Infected BALB/c mice exhibit high parasite numbers in lymph nodes and spleens, and a chronic disease with skin lesions, splenomegaly, and hepatomegaly, increased serum IgE levels and cytokine imbalance. Although numerous gene loci affecting these disease symptoms have been reported, genes controlling parasites’ elimination or dissemination have never been mapped. We therefore compared genetics of the clinical and immunologic symptomatology with parasite load in (BALB/c × CcS-11) F2 hybrids and mapped five loci, two of which control parasite elimination or dissemination. Lmr5 influences parasite loads in spleens (and skin lesions, splenomegaly, and serum IgE, IL-4, and IFNγ levels), and Lmr20 determines parasite numbers in draining lymph nodes (and serum levels of IgE and IFNγ), but no skin or visceral pathology. Three additional loci do not affect parasite numbers but influence significantly the disease phenotype—Lmr21: skin lesions and IFNγ levels, Lmr22: IL-4 levels, Lmr23: IFNγ levels, indicating that development of L. major-caused disease includes critical regulations additional to control of parasite spread

Modeling of ICRH slow wave propagation and absorption in Wendelstein 7-X stellarator

The propagation and absorption of slow waves in the plasma of the Wendelstein 7-X stellarator was investigated by the ray tracing. The aim of the work was to obtain a qualitative picture of the penetration into the plasma of a wave excited by the potential difference between the antenna conductors and the antenna box. For this, a ray code was used, which performs calculations in the magnetic configuration of the stellarator obtained by the VMEC code. A strong influence of the type of magnetic configuration (“higher mirror”, “lower mirror”, or standard configuration) on the propagation and absorption of a slow wave was found.Поширення і поглинання повільної хвилі в плазмі стеларатора Вендельштейн 7-Х було досліджено методом променевих траєкторій. Мета роботи – отримання якісної картини проникнення в плазму хвилі, що збуджується за рахунок різниці потенціалів між провідниками антени і антенним боксом. Для цього використаний променевий код, який виконував розрахунки в магнітній конфігурації стеларатора, що отримана кодом VMEC. Виявлено сильний вплив виду магнітної конфігурації (посилені гофри, зменшені гофри або стандартна конфігурація) на поширення і поглинання повільної хвилі.Распространение и поглощение медленной волны в плазме стелларатора Вендельштейн 7-Х было исследовано методом лучевых траекторий. Цель работы – получение качественной картины проникновения в плазму волны, возбуждаемой за счет разности потенциалов между проводниками антенны и антенным боксом. Для этого использован лучевой код, который выполнял расчеты в магнитной конфигурации стелларатора, полученной кодом VMEC. Обнаружено сильное влияние вида магнитной конфигурации (усиленные гофры, уменьшенные гофры или стандартная конфигурация) на распространение и поглощение медленной волны

17 O MAS NMR studies of oxo-based olefin metathesis catalysts: a critical assessment of signal enhancement methods

International audienceThe DFS enhancement method as applied to 17O MAS NMR was critically assessed, first on NaPO3, a simple binary glass system, and in a second step, on a series of catalysis-related organometallic molecules and materials. The robustness of DFS was investigated for the wide range of anisotropic parameters (quadrupolar coupling and chemical shift anisotropy) encountered in these samples. Emphasis has been put on the variation of signal enhancements with respect to the DFS final sweep frequency, pulse amplitude and pulse duration, while line shape distortion issues were also addressed. Finally, the robustness of DFS enhancement of the 17O MAS NMR signal is shown through its successful application to silica-supported olefin metathesis catalysts

Some Features of Particle Orbit Behavior in LHD Configurations

"Localizations of helically trapped particle losses on the last closed magnetic surface in different LHD configurations are studied. The effects of electric field, finite beta and bootstrap current are taken into account. It is shown that the angular location of the helically trapped particle losses may be controlled by the change of vertical field coil currents.

On the use of 17 O NMR for understanding molecular and silica-grafted tungsten oxo siloxide complexes

International audience17 O-labelled tungsten siloxide complexes and grafted materials were prepared and characterized by 17 O MAS NMR, with input from DFT calculations. Guidelines linking 17 O NMR parameters and the tungsten oxo species coordination sphere are proposed

Gradient Heatmetry Advances

The paper describes a unique method of heat flux measurement, i.e., gradient heatmetry. Gradient heatmetry is performed using gradient heat flux sensors (GHFS) developed on the anisotropic thermoelements basis. The principle of GHFS’ operation leads to the fact that their response time is about 10 ns, and the volt-watt sensitivity does not depend on the thickness. GHFS are compared with other types heat flux sensors, with the GHFS features depending on the materials being described. The theory and examples of gradient heatmetry applications in thermophysical experiment are provided