Effect of the frozen-in magnetic field on the formation of Venus, plasma shell boundary: Experimental confirmation

A laboratory simulation of solar wind interaction with plasma shells of nonmagnetic planets is reported. It is shown that the momentum transfer from the plasma flow to the shell occurs due to the presence of a frozen-in magnetic field. Without a magnetic field frozen-in, the ionosphere has no sharp boundary and a shock wave does not form in the flow

Solar flare and CME predictions using numerical MHD simulations

According to observational and theoretical data the solar flare radiation and coronal mass ejection(CME) are manifestations of the same explosive process, which takes place high in the solar corona. In some solar flares one of these manifestations can be weak and can not be observed, in other flares both of these manifestations are present. CMEs are the most important cause of substorm appearances in the magnetosphere. For solar flare and CME predictions, it is need to have information about main processes of these explosive phenomena and to estimate the possibility of their occurrences. The energy for solar flare can be accumulated in a current sheet. For MHD simulation of this process the program PERESVET is developed that uses observed distributions of magnetic field on the photosphere as the boundary conditions. The MHD simulation showed, that the current sheet can be vertical, horizontal, or inclined to some angles to the photosphere depending on the magnetic field distribution on the photosphere and its evolution. The vertical current sheet can produce the CME, because the magnetic tension force accelerates plasma from the Sun. The CME prognosis is based on information about the position of current sheet in the solar corona

The mechanism of energy release and field-aligned current generation during substorms and solar flares

In this paper, the mechanisms of field-aligned current (FAC) and westward electrojet generation are considered on the base of space measurements and laboratory simulation. Upward and downward FAC are generated in the Earth magnetotail current sheet (CS) due to the tail earthward electric field. They are connected in the ionosphere by the Pedersen current. The FAC enhancement takes place during magnetic reconnection and explosive energy release at a substorm. Electron acceleration in upward FAC produces fast electron precipitation and aurora appearance. The westward electrojet (Hall current) is located between two opposite directed sheets of FAC. The current in the jet is determined by the Hall conductivity in the ionosphere. The similar current systems in the solar corona are responsible for energy transfer to the chromosphere during a solar flare. The solar flare model is built on the base of observations and 3D MHD numerical simulation for compressible resistive plasma

La momia y el herbolario: un ensayo sobre la historia de la arqueología del siglo XX

This paper compares the collections of Guido Bennati and Perfecto Paciente Bustamante, two medical practitioners, who, on the fringes of the law, contributed to the history of archaeology and ethnology in Argentina. The article reflects on the role of amateurs in science but, above all, on the frontier between learned and popular knowledge.Este trabajo compara las colecciones de Guido Bennati y Perfecto Paciente Bustamante, dos practicantes de la medicina quienes, al borde de la legalidad, forman parte de la historia de la arqueología y la etnología en la Argentina. De esta manera, el trabajo reflexiona sobre el papel de los aficionados en la ciencia y, ante todo, sobre la frontera entre el saber culto y el popular

Exchange Effects in the Invar Hardening: Fe0.65Ni0.35Fe_{0.65}Ni_{0.35} as a test case

An increase of the critical resolved shear stress of Invar alloys (Invar hardening) with a lowering temperature is explained. The effect is caused by a growth of the exchange interaction between dangling $d$-electron states of dislocation cores and paramagnetic obstacles (e.g., Ni atoms in FeNi alloys) which occurs below the Curie temperature. The spins of the two electrons align along the magnetization due to the exchange interaction with the surrounding atoms of the ferromagnetic. The exchange interaction between the dislocations and obstacles is enhanced in Invars due to a strong growth of the magnetic moments of atoms under the action of elastic strains near the dislocation cores. Parameters characterizing the exchange interaction are determined for the case of the Fe$_{0.65}$Ni$_{0.35}$ Invar. The influence of the internal magnetic field on the dislocation detachment from the obstacles is taken into account. The obtained temperature dependence of the critical resolved shear stress in the Fe$_{0.65}$Ni$_{0.35}$ Invar agrees well with the available experimental data. Experiments facilitating a further check of the theoretical model are suggested.Comment: 8 pages, 2 figure

Fine structure of the diamagnetic cavity boundary in comet Halley

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95105/1/jgra16786.pd

Local structure study of In_xGa_(1-x)As semiconductor alloys using High Energy Synchrotron X-ray Diffraction

Nearest and higher neighbor distances as well as bond length distributions (static and thermal) of the In_xGa_(1-x)As (0<x<1) semiconductor alloys have been obtained from high real-space resolution atomic pair distribution functions (PDFs). Using this structural information, we modeled the local atomic displacements in In_xGa_(1-x)As alloys. From a supercell model based on the Kirkwood potential, we obtained 3-D As and (In,Ga) ensemble averaged probability distributions. This clearly shows that As atom displacements are highly directional and can be represented as a combination of and displacements. Examination of the Kirkwood model indicates that the standard deviation (sigma) of the static disorder on the (In,Ga) sublattice is around 60% of the value on the As sublattice and the (In,Ga) atomic displacements are much more isotropic than those on the As sublattice. The single crystal diffuse scattering calculated from the Kirkwood model shows that atomic displacements are most strongly correlated along directions.Comment: 10 pages, 12 figure

Оптимизация процесса пассивации при изготовлении СВЧ-транзисторов на основе AlGaN/GaN гетероструктур методом ICP CVD

In present study is considered the influence of the regimes of passivating dielectric silicon nitride SiNx films deposition by the chemical vapor deposition in an inductively coupled plasma (ICP CVD) on the parameters of the high electron mobility transistors (HEMT) based on AlGaN/GaN heterostructures. By the investigation of dielectric material layers’ parameters was revealed the influence of RF and ICP generators power, working gases flows ratio on the films growth rate and perfection, also their effect on the CVC of passivated HEMT. With RF power increasing the deposition rate did not change, while its growth was observed with ICP power increasing. The transistor slope strongly decreases with RF power increasing, its maximum was achieved with a minimum RF power of 1 W. At the initial moment of deposition even at low values of RF power (at 3 W already) the transistor structure becomes completely inoperative. Shown, that the deposition process of dielectrics for the HEMT passivation must begin at the lowest possible RF power. An AlGaN/GaN UHF HEMT structure passivation process has been developed, allowing the deposition of conformal films and obtaining low drain-source currents in turn-off transistors without deterioration in the open state — at no more than 15 and 100 μA for 1,25 and 5 mm Т-gate width respectively (UG = –8 V and USD = 50 V).Рассмотрено влияние режимов нанесения пассивирующих диэлектрических пленок нитрида кремния SiNx методом плазмохимического осаждения из газовой фазы в индуктивно-связанной плазме (ICP CVD) на параметры транзисторов с высокой подвижностью электронов (HEMT) на основе гетероструктур AlGaN/GaN. На основании результатов исследования параметров полученных слоев диэлектрического материала определено влияние RF и ICP мощностей, соотношения потоков рабочих газов на скорость роста пленок и их совершенство, а также их влияние на вольт-амперные характеристики пассивируемых HEMT. Скорость осаждения при увеличении RF мощности практически не менялась, однако при увеличении ICP мощности наблюдался ее рост. При этом крутизна транзистора сильно снижалась с ростом RF мощности, ее максимум достигался при минимальной мощности RF = 1 Вт. В начальный момент роста, даже при невысоких значениях RF мощности (уже при 3 Вт), структура транзистора становилась полностью неработоспособной. Показано, что процесс осаждения диэлектрика для пассивации HEMT необходимо начинать при максимально низких значениях RF мощности. Отработан технологический процесс пассивации AlGaN/GaN СВЧ HEMT, позволяющий осаждать конформные пленки и получать низкие токи сток—исток транзисторов в закрытом состоянии без ухудшения характеристик в открытом состоянии — на уровне не более 15 и 100 мкА соответственно для общей ширины Т-образного затвора 1,25 и 5 мм (Uз = –8 В и Uс-и = 50 В)