We apply first principles calculations to compare the carbon and boron nitride nanotube unzipping under atomic oxygen impact. We show that the attack of several oxygen atoms can cause bond breaking in nanotubes, but the structure of boron nitride nanotubes is less damaged than the structure of carbon ones. With increasing diameter, the structural damage of nanotubes reduces
Aim. The main stages of scientific activity of V.A. Solntsev from the student's bench to the leader of the scientific school on radiophysics and microwave electronics are investigated. Method. Based on the primary publications, the main directions of the creative path of the scientist, whom determined the electronic age of the time, are analyzed. Results. It is shown how timely V.A. Solntsev found a substitute for research and calculation methods that ceased to satisfy the demands of science and production, and resolutely went on to develop new principles of amplification and generation, accurately determining the expiration time of previous methods and principles and giving way only to the routine apparatus. Discussion. Great educational work and scientific and organizational role of the outstanding scientist were noted. © 2018 Saratov State University. All rights reserved.
The paper deals with cyclostationarity as a natural extension of stationarity as the key property in designing the widely-used models of random processes. The comparative example of two processes, one is wide-sense stationary and the other is wide-sense cyclostationary, is given in the paper and reveals the lack of the conventional stationary description based on one-dimensional autocorrelation functions. It is shown that two significantly different random processes appear to be characterized by exactly the same autocorrelation function while their two-dimensional autocorrelation functions provide outlook where the difference between processes of two above-mentioned classes becomes much clearer. More concise representation by expanding the two-dimensional autocorrelation function to its Fourier series where the cyclic frequency appears as the transform parameter is illustrated. The closed-form expression for the components of the cyclic autocorrelation function is also given for the random process which is an infinite pulse train made of rectangular pulses with randomly varying amplitudes.
Diffraction of light in a non-homogeneous acoustic field produced by a wedge-shaped piezoelectric transducer is studied theoretically. Electrical, acoustic and acousto-optic characteristics of cells with the wedge-shaped transducers are calculated. Most attention is focused on special features of these cells operation at transducer’s third harmonic frequency. It is shown that the acoustic field has a complicated amplitude and phase structure which varies with ultrasound frequency. The dependence of the acousto-optic diffraction efficiency on the acoustic wave amplitude and the phase mismatch is studied. It is established that the diffraction efficiency can approach 100% despite a noticeable phase mismatch. Optimal values of acoustic power and light incidence angles are found. It is revealed that due to the wedge-like form of the transducer the frequency band at the third harmonic can be several times increased with retaining a high value of the electric-to-acoustic power conversion.
The construction of a contactless adaptive vibration sensor based on an externally modulated reflectometer-type fiber-optic transducer is discussed. The sources of measurement error and ways of reducing them are determined. An experimental prototype fiber-optic contactless adaptive vibration sensor and a method for correcting its transfer function are described.
Cloud applications bring new challenges to the design of network elements, in particular the burstiness of traffic workloads. A shared memory switch is a good candidate architecture to exploit buffer capacity; in this work, we analyze the performance of this architecture. Our goal is to explore the impact of additional traffic characteristics such as varying processing requirements and packet values on objective functions. The outcome of this work is a better understanding of the relevant parameters for buffer management to achieve better performance in dynamic environments of data centers. We consider a model that captures more of the properties of the target architecture than previous work and consider several scheduling and buffer management algorithms that are specifically designed to optimize its performance. In particular, we provide analytic guarantees for the throughput performance of our algorithms that are independent from specific distributions of packet arrivals. We furthermore report on a comprehensive simulation study which validates our analytic results.
In this paper we discuss some variations of the notion of separating code for alphabets of arbitrary size. We show how the original definition can be relaxed in two different ways, namely almost separating and almost secure frameproof codes, yielding two different concepts. The new definitions enable us to obtain codes of higher rate, at the expense of satisfying the separating property partially. These new definitions become useful when complete separation is only required with high probability, rather than unconditionally. We also show how the codes proposed can be used to improve the rate of existing constructions of families of fingerprinting codes.
The problem of measuring the temperatures of the radio-electrical components of printed circuits is investigated. A temperature measuring sensor (thermocouple) and possible errors are considered. A systematic error compensation method is proposed to ensure the necessary accuracy of measurements made with the temperature sensor. © 2015 Springer Science+Business Media New York
The article gives a review of existing methods of network-on-chip design based on the approach in which mapping of the characteristic tasks graph is performed on a given regular topology. The networks-on-chip synthesis problem is generally characterized. The analysis and comparison of standard topologies (mesh and torus) with circulant topologies are performed. Advantages and disadvantages of mesh and torus topologies usage, and the effect, achieved by their application to various implementations of networks on chip, are analyzed. Extension of the scope of solutions for standard regular network topologies mesh and torus on the circulant topologies with better characteristics is proposed. This will make it possible to take advantage of the deterministic approach, but with the use of more effective NoC topologies optimized for a particular task.
Various wireless networks scenarios involve dissemination of large amounts of control information. This limits the channel resources available for transmission of the user data. This problem is especially crucial in dense networks, sensor networks, and high-mobility networks (e.g., networks of vehicles and drones). Several methods for dissemination of control information are known. This study is focused on the promising method called differential update. The idea behind it is that control messages sent by stations should contain only the information modified since the transmission of the previous message. An analytical model of this method has been developed. It allows one to estimate the average amount of transmitted control information and the reliability and promptness of its delivery to neighboring stations. An algorithm for adaptive tuning of parameters of the differential update method has been developed on the basis of this model. Simulation results obtained with NS-3 simulator demonstrate that the proposed algorithm minimizes the amount of sent control information while satisfying the set of requirements on reliability and promptness of its delivery.
Models of rectangular and axially symmetric resonator slow-wave structures, which are built using transmission matrix for determining the characteristics of the slow-wave structures in different operation modes, are investigated. Elements of the transmission matrix are determined from the results of 3D simulation with the use of the HFSS software. In the analysis of the dispersion characteristics, slow-wave structures with two microwave propagation channels are studied and simulated using a 4×4 transmission matrix.
Original Russian Text © N.P. Kravchenko, S.V. Mukhin, S.A. Presnyakov, 2017, published in Radiotekhnika i Elektronika, 2017, Vol. 62, No. 7, pp. 693–702.
The results of this study were reported at the 2nd All-Russia Conference on Problems of Microwave Electronics, Moscow Institute of Electronics and Mathematics, Higher School of Economics (National Research University), Moscow, October 26−28, 2015.
Models of slow-wave structures are used in simulating millimetre band devices are considered in the research. It is reasonable to use axially-symmetric slow-wave structures (SWS) for designing millimetre band traveling wave tubes (TWT). Simulating of considered slow-wave structure's 3D model produced in HFSS software package . The program that is outlined in  is used for calculation of dispersion characteristics. The model of slow-wave structure cell bases on the results of calculation. The nature of the distribution of the electromagnetic field in the system depends on the interaction features of electrons and the field in the TWT with slow-wave structure. The discrete approach described in  is the most common for solving this type of problems. It is electrodynamically justified to use difference equation for description of the discrete interaction in a traveling wave tube, in which the phase of the field in the interaction gaps in the longitudinal direction remains constant. The difference form of the electrodynamic theory of excitation allows to justify the use of one or another mathematical model for constructing a finite-difference equation . The coefficients of the finite-difference equation have a certain electrodynamic significance because they are calculated through the transmission matrix coefficients of the 2-N pole. Mathematical model of discrete interaction becomes more accurate when accuracy of coefficients of the finite-difference equation increases. In the research the 2-N pole is sextopole that appears form octopole in case of excitation current absence. The resulting sextopole is a mathematical model of the slow-wave structure cell. Coefficients of the obtained 2-N pole justifies accuracy, realism and recuperation of Electrodynamic characteristics of the simulated resonator slow-wave structure. Specification of discrete interaction processes in traveling-wave tubes, and electrodynamic processes in the SWS is ensured by the correct selection of the transmission matrix coefficients.
The paper presents the results of research that can be put into the development and research of non-contact rapid method for assessing the quality of the assembly and installation of EM designs. To achieve the objectives, studied the behavior of the mechanical connection of the contact pairs, namely the definition of the contribution of R,L,C parameters contact joints in the modulation level and the spectral composition of the electromagnetic radiation mechanical contact pair
A new method for estimating the number of errors guaranteed to be corrected by a low-density parity-check code is proposed. The method is obtained by analyzing edges with special properties of an appropriate Tanner graph. In this paper we consider binary LDPC codes with constituent single-parity-check and Hamming codes and an iterative decoding algorithm. Numerical results obtained for the proposed lower bound exceed similar results for the best previously known lower bounds.
In this paper the slow-wave structures and their models, which are used for development of the millimeter range devices, are considered. The travelling-wave tubes (TWTs) of the millimeter range use rectangular and axially-symmetric resonator slow-wave structures. Analysis of these slow-wave structures was performed using HFSS program for 3D-modeling . Dispersion characteristics were calculated by program outlined in the paper . These characteristics are used to build the model of the slow-wave structure’s cell. The peculiarities of the interaction between the electrons and the field in the TWT with resonator slow-wave structures are determined by the nature of the field distribution in such structure. The discrete approach is the most common for solving problems of this type . The difference form of the electrodynamic excitation theory applied to the description of the discrete interaction is justifying the use of a mathematical model.
For a description of the TWT with the discrete interaction, in which the phase of the field in the interaction gaps in the longitudinal remains constant, the use of the difference equation is electrodynamically reasonable.
The more precisely defined the coefficients of the finite difference equations, the more accurate the mathematical model of the discrete interaction becomes. These coefficients have a certain electrodynamic meaning and are defined via coefficients of the quadripole transmission matrix derived from the sextopole if there is no the exciting current. The accuracy of the restoration of the electrodynamic characteristics of the modeled resonator slow-wave structures is determined by the coefficients of the quadripole obtained. Therefore, the correct selection of these coefficients provides a correct description of the discrete processes of interaction in travelling-wave tubes as well as the electrodynamic processes in the slow-wave structures.
Researchers face fundamental challenges applying the stochastic geometry framework to analysis of terahertz (THz) communications systems. The two major problems are the principally new propagation model that now includes exponential term responsible for molecular absorption and blocking of THz radiation by the human crowd around the receiver. These phenomena change the probability density function (pdf) of the interference from a single node such that it no longer has an analytical Laplace transform (LT) preventing characterization of the aggregated interference and signal-to-interference ratio (SIR) distributions. The expected use of highly directional antennas at both transmitter and receiver adds to this problem increasing the complexity of modeling efforts. In this paper, we consider Poisson deployment of interferers in ℜ 2 and provide accurate analytical approximations for pdf of interference from a randomly chosen node for blocking and non-blocking cases. We then derive LTs of pdfs of aggregated interference and SIR. Using the Talbot’s algorithm for inverse transform we provide numerical results indicating that failure to capture atmospheric absorption, blocking or antenna directivity leads to significant modeling errors. Finally, we investigate the response of SIR densities to a wide range of system parameters highlighting the specific effects of THz communications systems. The model developed in this paper can be used as a building block for performance analysis of realistic THz network deployments providing metrics such as outage and coverage probabilities.
In this paper, we describe the Desmos supercomputer that consists of 32 hybrid nodes connected by a low-latency highbandwidth Angara interconnect with torus topology. This supercomputer is aimed at cost-effective classical molecular dynamics calculations. Desmos serves as a test bed for the Angara interconnect that supports 3D and 4D torus network topologies, and verifies its ability to unite massively-parallel programming systems speeding-up effectively MPI-based applications. We describe the Angara interconnect presenting typical MPI benchmarks. Desmos benchmarks results for GROMACS, LAMMPS, VASP and CP2K are compared with the data for other HPC systems. Also, we consider the job scheduling statistics for several months of Desmos deployment.
Temperature dependences of low field Hall resistivity H are used to separate anomalous (a H) and nor- mal (RHB) contributions to Hall effect in chiral magnet MnSi (Tc 29.1K). It is found that the transition between paramagnetic (T > Tc) and magnetically ordered (T < Tc) phases is accompanied by the change inanomalous Hall resistivity from low temperature behavior governed by Berry phase effects (aH = μ0S22M,T < Tc) to high temperature regime dominated by skew scattering (aH = μ0S1M, T > Tc). The crossover between the intrinsic (2) and extrinsic () contributions to anomalous Hall effect develops together with the noticeable increase of the charge carriers’ concentration estimated from the normal Hall coefficient (from n/nMn(T > Tc) 0.94 to n/nMn(T < Tc) 1.5, nMn 4.2 · 1022 cm−3). The observed features may corre- spond to the dramatic change in Fermi surface topology induced by the onset of long range magnetic order in MnSi.
We report results of the high frequency (60GHz) electron spin resonance (ESR) study of the quantum criti- cal metallic system Mn1−xFexSi. The ESR is observed for the first time in the concentration range 0 < x < 0.24 at temperatures up to 50K. The application of the original experimental technique allowed carrying out line shape analysis and finding full set of spectroscopic parameters, including oscillating magnetization, line width and g factor. The strongest effect of iron doping consists in influence on the ESR line width and spin relaxation is marked by both violation of the classical Korringa-type relaxation and scaling behavior. Additionally, the non-Fermi-liquid effects in the temperature dependence of the ESR line width, which may be quantitatively described in the theory of W¨olfle and Abrahams, are observed at quantum critical points x 0.11 and xc 0.24.
. This paper presents a novel rodent avoidance test. We have devel-oped a specialized device and procedures that expand the possibilities for exploration of the processes of learning and memory in a psychophysiological experiment. The device consists of a current stimulating electrode-platform and custom software that allows to control and record real-time experimental pro-tocols as well as reconstructs animal movement paths. The device can be used to carry out typical footshock-avoidance tests, such as passive, active, modified active and pedal-press avoidance tasks. It can also be utilized in the studies of prosocial behavior, including cooperation, competition, emotional contagion and empathy. This novel footshock-avoidance test procedure allows flexible current-stimulating settings. In our work, we have used slow-rising current. A test animal can choose between the current rise and time-out intervals as a signal for action in footshock avoidable tasks. This represents a choice between escape and avoid-ance. This method can be used to explore individual differences in decision-making and choice of avoidance strategies. It has been shown previously that a behavioral act, for example, pedal-pressing is ensured by motivation-dependent brain activity (avoidance or approach). We have created an experimental design based on tasks of instrumental learning: pedal-pressing in an operant box results in a reward, which is either a piece of food in a feeder (food-acquisition behavior) or an escape-platform (footshock-avoidance behavior). Data recording and analysis were performed using custom software, the open source Accord.NET Framework was used for real-time object detection and tracking.