Propagation of wave packets in randomly stratified media

The propagation of a narrow-band signal radiated by a point source in a randomly layered absorbing medium is studied asymptotically in the weak-scattering limit. It is shown that in a disordered stratified medium that is homogeneous on average a pulse is channelled along the layers in a narrow strip in the vicinity of the source. The space-time distribution of the pulse energy is calculated. Far from the source, the shape of wave packets is universal and independent of the frequency spectrum of the radiated signal. Strong localization effects manifest themselves also as a low-decaying tail of the pulse and a strong time delay in the direction of stratification. The frequency-momentum correlation function in a one-dimensional random medium is calculated.Comment: 11 pages, 3 figures, Revtex-4. Submitted to Phys. Rev.

Synthesis of Few-layer Graphene Sheets via Chemical and Thermal Reduction of Graphite Oxide

Few-layer graphene sheets were produced from graphite oxide (GO) chemical and thermal reduction. For the chemical reduction of GO as reducing agents were used hydrazine hydrate, hydroxylammonium chloride, sodium borohydride and sodium sulfite. The reduced material was characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, X-ray diffraction, Fourier transform infrared and Raman spectroscopy. A comparison of the deoxygenation efficiency of graphene oxide suspension by different method or reductants has been made, revealing that the highest degree of reduction was achieved by thermal reduction and using hydrazine hydrate and hydroxylammonium chloride as a reducing agents. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3506

Preparation of Amino-Functionalized Graphene Sheets and their Conductive Properties

Amino-functionalized graphene sheets were prepared through chemical reduction by hydrazine hy-drate, amination or amidation of graphite oxide. For amination of graphite oxide were used polyamine such as ethylenediamine, diethylenetriamine and triethylenetetramine. Addition of amine groups to graphene is identified by Fourier transform infrared spectroscopy, Raman spectroscopy, elemental analysis and ther-mogravimetry. Scanning electron microscopy data indicate that the organic amine is not only as nitrogen sources to obtain the nitrogen-doped graphene but also as an important modification to control the assem-bly of graphene sheets in the 3D structures. The electrical conductivity of the materials obtained by amina-tion and amidation of graphene is much smaller than that of reduced graphite oxide. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3563

Electro-Conductive Composites Based on Metal Oxides and Carbon Nanostructures

Optimal conditions were found for the formation of carbon-oxide composites by the treatment of mixtures of oxides of aluminum or titanium with carbon nanotubes and nanofibers in a planetary ball mill. The dependences of the electrical conductivity of composites on the content of carbon nanomaterials (1-5% by mass) were determined. It is shown that the addition of 3%(wt) of CNT to the oxides leads to a sharp increase in the electrical conductivity: from 5.0×10-8 to 2.8×10-4 S/cm for Al2O3 and from 5.0×10-6 to 2.2×10-2 S/cm for TiO2. It was shown that the carbon-oxide composites are promising carriers of the catalysts of electrode processes in electrochemical devices. It was revealed that Pt/TiO2 - CNT catalyst containing 5% (mass) of carbon nanotubes has the best catalytic activity in oxygen reduction, in an electrode-modeling cathode of a fuel cell. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3512

Radio frequency control of particle detrpping / retrapping process in a stellarator type device

The possibility to study experimentally the effect of AC electric field on the transit particles is considered on the example of the small stellarator device. This study is important for the development of scenario for the ambipolar electric field control in plasma due to injection of the particles into plasma core in the fusion devices.Розглянута можливість експериментального вивчення впливу змінного електромагнітного поля на частинки з перехідними траєкторіями на прикладі невеличкого пристрою стелараторного типу. Таке вивчення важливе для розвитку сценарію контролю амбіполярного електричного поля в плазмі в термоядерних системах за допомогою інжекції частинок у центр плазми.Рассмотрена возможность экспериментального изучения влияния переменного электрического поля на частицы с переходными траекториями на примере небольшого прибора стеллараторного типа. Это изучение важно для развития сценария контроля амбиполярного электрического поля в плазме в термоядерных системах, чего можно достичь инжекцией частиц в центр плазмы

Self-consistent penning-malmberg trap

Self-consistent interaction of electrons with electric fields observed in drive space of velocity spread impulse electron beam in longitudinal homogeneous magnetic field during and after the injecting impulse was investigated. The mechanism by which non-neutral electron plasma is accumulated and confined has been studied. Physical behavior of non-neutral plasma has been studied in various non-neutral particle traps, a typical of which is Penning–Malmberg trap. It is a cylindrical trap where the radial motion of the non-neutral particles is constrained by magnetic field, while the longitudinal motions are constrained by electrostatic potential well. When used as an electron trap, the electrons from a thermal cathode are injected parallel to the magnetic field while the cathode side of the electrostatic well is open. By closing the wall dynamically, the electrons that fail to escape during the well closure are trapped. In our experiments the holding electrostatic walls arise self-consistently, simultaneously with injection of an electron beam in the space of drift. Seized there are those particles that at the moment of formation of the trap were in the space of drift

Charged particles accumulation in drift space of warm electron beam during non-stationary virtual cathod existence

In this paper, the properties and the formation of collective electromagnetic trap for electron beam that propagates in a conducting cylinder are described. It is shown that the electron beam provides the development of an electrostatic instability in the above-mentioned conditions. The instability leads to the appearance of a non-stationary virtual cathode and the formation of electrostatic potential trap. This phenomenon takes place in the central region of the drive space where the amplitude of the electrostatic potential has two maxima. The trap confines electrons during its formation and keeps them inside the drift tube. Once seized in the trap, electrons have rather low temperature and are unstable to diocotron oscillations. During the evolution of diocotron instability the spatial charge redistribution takes place in the cross-section of the beam, which is probably connected with the drift of electrons in longitudinal magnetic field. This process is accompanied not only by azimuthal redistribution of the beam density, but also by radial transfer of electrons across magnetic field, which leads to the increase of the radial beam dimensions and to the injection of electrons onto the walls of the drift chamber. The variations of the radial beam dimensions, and, hence, the spatial charge redistribution in longitudinal direction lead to the corresponding variation of the longitudinal distribution of electric potential, and appearance of self-consistent field of 'potential pit' type in central region of the drive space

Using of electron cyclotron resonance discharge in ion beam sputtering systems for space charge compensation

The possibility of using a magnetic mirror in the output gap of ion source with a closed electron drift to generating of an additional gas discharge by using the electron-cyclotron resonance to compensate of the ion beam space charge is studied. The first experiments have shown that an additional microwave discharge generated in the region of the annular gap when the microwave power is applied. An additional plasma source of electrons provides the maintenance and intensification of the gas discharge in the accelerator with an anode layer.Вивчено можливість використання пастки пробочного типу у вихідному зазорі джерела іонів із замкнутим електронним дрейфом для генерації додаткового газового розряду з використанням електронно-циклотронного резонансу та компенсації просторового заряду іонного пучка. Перші експерименти показали, що генерується додатковий НВЧ-розряд в області кільцевого зазору при подачі НВЧ-потужності. Додаткове плазмове джерело електронів забезпечує підтримку та інтенсифікацію газового розряду в прискорювачі з анодним шаром.Изучена возможность использования ловушки пробочного типа в выходном зазоре источника ионов с замкнутым электронным дрейфом для генерации дополнительного газового разряда с использованием электронно-циклотронного резонанса и компенсации пространственного заряда ионного пучка. Первые эксперименты показали, что генерируется дополнительный СВЧ-разряд в области кольцевого зазора при подаче СВЧ-мощности. Дополнительный плазменный источник электронов обеспечивает поддержание и интенсификацию газового разряда в ускорителе с анодным слоем

Features of Magnetocaloric Effect in Er(Co-Fe)2 Laves Phases

In this work the results of measurements of heat capacity (CP) and magnetocaloric effect (MCE) in Er(Co1-хFeх)2 system in the concentration range 0.07 ≤ x ≤ 0.80 are presented. Phase composition was controlled by X-ray difraction analysis. Heat capacity was measured in the temperature range 77-320 K. MCE has been studied within the temperature range 5-670 K in magnetic fields up to 70 kOe. It was found that Fe concentration increase caused the table-like (plateau) MCE temperature dependence for both magnetic entropy change date and direct ∆T-effect measurements independently on Fe concentration. The possible reasons of such behavior are discussed