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121.
A high-power wideband traveling-wave tube with stepwise changes in the diameter of the drift channel
E. M. Il’ina S. A. Myatezhnikov I. V. Polyakov 《Journal of Communications Technology and Electronics》2007,52(8):943-948
Results of the design of a high-power wideband (in the band 8–18 GHz) traveling-wave tube (TWT) with stepwise changes in the diameter of the drift channel are presented. The TWT is stable against self-excitation by a backward wave at high values of the accelerating voltage. It is shown that the output section of the device can be increased by a factor of 1.5 and the operating current can be raised by a factor of 1.3. These increases are attained owing to the 1.27-GHz diversity of the π-type frequencies of sections with different values of the channel diameter and owing to growth of the starting current corresponding to self-excitation by the backward wave. Application of the TWT with the interaction space that has steps of the channel diameter improved the electron efficiency by a factor of 1.2 and increased the output power by a factor of 1.6. 相似文献
122.
Andrey Sarikov Jens Schneider Martin Muske Ina Sieber Stefan Gall 《Thin solid films》2007,515(19):7465-7468
The aluminium-induced layer-exchange process allows to grow thin large-grained polycrystalline Si films on foreign substrates. A characteristic feature of these films is the preferential (100) orientation of Si grains, favourable for subsequent epitaxial thickening at low temperatures. In this work, a model based on the preferential nucleation is proposed, which elucidates a possible origin of the preferential (100) orientation and its sensitivity to the preparation and process conditions. The probability of Si nuclei to have respective orientation is attributed to the nucleation barrier, i.e. the critical value of the change of the Gibbs energy during nucleation. The preferential orientation is formed statistically by the nuclei having the lowest nucleation barriers. 相似文献
123.
The 2-D problem of diffraction by a gap between two orthogonal semi-infinite barriers is considered. The method of reflections
is applied and the diffraction problem is reformulated as a propagation problem on a multi-sheet surface. An auxiliary problem,
with a single incident wave, is formulated. By applying an embedding formula the auxiliary problem is reduced to that of finding
a set of edge Green’s functions for the surface. The edge Green’s functions are proven to satisfy two sets of differential
equations: the coordinate equations and the spectral equation. Although too complicated to be solved analytically, these ordinary differential equations offer some advantages over partial
differential equations or integral equations. 相似文献
124.
L. P. Kholpanov Yu. S. Polyakov 《Journal of Engineering Physics and Thermophysics》2007,80(6):1140-1153
A model of turbulent heat-and mass transfer with nonlinear sources (sinks) that appear as a result of chemical reactions of
the first and second orders has been developed. The conjugation condition (equality of temperatures and local fluxes) at the
reactor — coolant interface was used for this purpose. A finite-difference numerical solution by the alternating direction
method is obtained. The influence of the coefficients of turbulent viscosity on heat-and mass transfer is investigated. The
model has been tested on the example of modeling fast polymerization processes. It has been established in practical calculations
of the processes of fast polymerization that instead of the model with variable coefficients of transfer and velocities of
liquid motion one can use its approximation with constant coefficients of transfer and velocities of liquid motion.
__________
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 73–85, November–December, 2007. 相似文献
125.
Results are given of LDA measurements of averaged and fluctuation velocities of glass particles during their deposition in smooth and dimpled narrow pipes. Experiments reveal a decrease in the axial component of averaged velocity of particles and a significant increase in fluctuation velocities of particles during their motion in a pipe with dimples. 相似文献
126.
Elena Filatova Aleksei Konashuk Yuri Petrov Evgeny Ubyivovk Andrey Sokolov Andrei Selivanov 《Science and Technology of Advanced Materials》2016,17(1):274-284
We have studied the stability of the resistive switching process in the Al/(In2O3)0.9(SnO2)0.1/TiO2 assembly grown by atomic layer deposition. Besides electrical characterization the effect of electric field on the atomic electronic structure of the TiO2 layer was studied using near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The region of the current instability in the I-V characteristics was revealed. Presumably this current instability is supported by the amorphous structure of the TiO2 film but is initiated by the surface morphology of the Al substrate. A formation of the O2 molecules was established which occurs specifically in the region of the current instability that is a result of electrical Joule heating manifestation. 相似文献
127.
Temperature‐Dependent Exciton and Trap‐Related Photoluminescence of CdTe Quantum Dots Embedded in a NaCl Matrix: Implication in Thermometry 下载免费PDF全文
Sergii Kalytchuk Olga Zhovtiuk Stephen V. Kershaw Radek Zbořil Andrey L. Rogach 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(4):466-476
Temperature‐dependent optical studies of semiconductor quantum dots (QDs) are fundamentally important for a variety of sensing and imaging applications. The steady‐state and time‐resolved photoluminescence properties of CdTe QDs in the size range from 2.3 to 3.1 nm embedded into a protective matrix of NaCl are studied as a function of temperature from 80 to 360 K. The temperature coefficient is found to be strongly dependent on QD size, with the highest sensitivity obtained for the smallest size of QDs. The emission from solid‐state CdTe QD‐based powders is maintained with high color purity over a wide range of temperatures. Photoluminescence lifetime data suggest that temperature dependence of the intrinsic radiative lifetime in CdTe QDs is rather weak, and it is mostly the temperature‐dependent nonradiative decay of CdTe QDs which is responsible for the thermal quenching of photoluminescence intensity. By virtue of the temperature‐dependent photoluminescence behavior, high color purity, photostability, and high photoluminescence quantum yield (26%–37% in the solid state), CdTe QDs embedded in NaCl matrices are useful solid‐state probes for thermal imaging and sensing over a wide range of temperatures within a number of detection schemes and outstanding sensitivity, such as luminescence thermochromic imaging, ratiometric luminescence, and luminescence lifetime thermal sensing. 相似文献
128.
Virus Matryoshka: A Bacteriophage Particle—Guided Molecular Assembly Approach to a Monodisperse Model of the Immature Human Immunodeficiency Virus 下载免费PDF全文
Pooja Saxena Li He Andrey Malyutin Siddhartha A. K. Datta Alan Rein Kevin M. Bond Martin F. Jarrold Alessandro Spilotros Dmitri Svergun Trevor Douglas Bogdan Dragnea 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(42):5862-5872
Immature human immunodeficiency virus type 1 (HIV‐1) is approximately spherical, but is constructed from a hexagonal lattice of the Gag protein. As a hexagonal lattice is necessarily flat, the local symmetry cannot be maintained throughout the structure. This geometrical frustration presumably results in bending stress. In natural particles, the stress is relieved by incorporation of packing defects, but the magnitude of this stress and its significance for the particles is not known. In order to control this stress, we have now assembled the Gag protein on a quasi‐spherical template derived from bacteriophage P22. This template is monodisperse in size and electron‐transparent, enabling the use of cryo‐electron microscopy in structural studies. These templated assemblies are far less polydisperse than any previously described virus‐like particles (and, while constructed according to the same lattice as natural particles, contain almost no packing defects). This system gives us the ability to study the relationship between packing defects, curvature and elastic energy, and thermodynamic stability. As Gag is bound to the P22 template by single‐stranded DNA, treatment of the particles with DNase enabled us to determine the intrinsic radius of curvature of a Gag lattice, unconstrained by DNA or a template. We found that this intrinsic radius is far larger than that of a virion or P22‐templated particle. We conclude that Gag is under elastic strain in a particle; this has important implications for the kinetics of shell growth, the stability of the shell, and the type of defects it will assume as it grows. 相似文献
129.
130.
Ana S.R. Brásio Andrey Romanenko João Leal Lino O. Santos Natércia C.P. Fernandes 《Journal of Process Control》2013,23(10):1471-1479
The economic performance of an industrial scale semi-batch reactor for biodiesel production via transesterification of used vegetable oils is investigated by simulation using nonlinear model predictive control (NMPC) technology. The objective is to produce biodiesel compliant to the biodiesel standards at the minimum costs. A first-principle model is formulated to describe the dynamics of the reactor mixture temperature and composition. The feed oil and mixture composition are characterized using a pseudo-component approach, and the thermodynamic properties are estimated from group contribution methods. The dynamic model is used by the NMPC framework to predict the optimal control profiles, where a multiple shooting based dynamic optimization problem is solved at every sampling time. Simulation results with the economic performance of an industrial scale semi-batch reactor are presented for control configurations manipulating the methanol feed flow rate and the heat duty. 相似文献