The problem of detecting nonlinear effects often arises in
investigations of different physical, engineering and other systems.
These can be, for example, nonlinear distortions in radio devices,
coupling of waves in nonlinear media, or nonlinear mechanisms of their
generation. A powerful tool for solving this problem is the use of
cumulants or their associated Fourier transforms, known as polyspectra.
However, the estimation of cumulants (or polyspectra) of real processes
(especially for fairly long realizations) requires considerable
computation resources, in particular, RAM. The present paper illustrates
the potentials of the so called “1½D-spectra”,
Γ(ω), for solving the problem of detecting weak
quadratic-type nonlinearities of random processes in the presence of
additive noise. This technique is a particular case of the bispectral
analysis being, however, it is much easier to use
The report consists of two parts. In the first part, the sampling analysis of weight windows is conducted on the basis of atomic functions (AF) and their application in problems of the classical method of synthetic aperture radar (SAR) is considered. The second part contains fundamentals of a modified method of synthetizing the aperture. The modified ambiguity function for different signals is probed. The lacks of the Ambiguity function are detected at a modified method. The paths of elimination of the indicated lacks are offered by introduction of weight processing in a technique of the modified method. The expediency of application of weight windows based on AF in reduced problems is empirically justified.
The influence of the bias voltage on the magnetoresistance of a magnetic tunneling junction with a step-like potential barrier has been studied theoretically in the frame of a two-band model of free electrons in ferromagnetic electrodes. It is shown that the dependence of the magnetoresistance of the magnetic tunneling junction on the bias voltage can vary according to the type and the thickness of the isolators forming a step-like tunneling potential barrier. It has been found out that the magnetoresistance of the magnetic tunneling junction can change its sign and oscillate with increasing bias voltage
The 2D problem of the stepped mitered waveguide bend is considered for both E and H polarizations of incident waves. The method used for analysis is the mode-matching technique (MMT). Geometric parameters of such a device that can provide a low level of return loss within the whole operating frequency band are found for WR90. It is proved that even 4 steps are enough to match the device to better than -30 dB.
Maybe the most aggressive phenomena in biology is the growth of
cancer cells. In this paper we propose a simple three-dimensional model
to simulate the growth of carcinoma, which includes cell proliferation,
reciprocal influence among cells, cell division and cell death. Every
simulated pattern growth is characterized by its gyration radius, number
of cells on tumor periphery and fractal dimension. We use the DLA model
and computer simulation to characterized the growth phenomenon. The
Application of DLA (diffusion-limited aggregation) model to generate
fractal structure is shown in this work. The similarity between this
computational model and some abnormal cell growth, are shown as well. We
use a hash function for the DLA in three-dimensional problem; the
possibility of developing studies in higher dimensions without affecting
the required time of the algorithm is shown. Also, a comparison between
the simulated patterns and explants of primary tumors is done
An unbiased finite impulse response (FIR) filtering algorithm is investigated for the GPS-based measurements of a local crystal clock. The algorithm is examined for the time interval error (TIE) measurements in presence of the uniformly distributed sawtooth noise induced by the multichannel GPS timing receiver. Based upon, we show that the unbiased FIR estimates are consistent with the reference (rubidium) measurements and fit them better than the standard Kalman filter
The Kontorovich-Lebedev transform is used for the solution of various problems of diffraction by a wedge. A failure of this transform is that it is applicable to a narrow class of functions not containing, in particular, a complete solution to the problem of diffraction. To overcome this problem a modified Kontorovich-Lebedev transform has previously been obtained in which the two-dimensional equation is reduced to an ordinary differential equation. The authors obtain a generalized radiation condition to give sense to this equation for the problem of plane wave diffraction by a wedge
General Newton-Kantorovich method and its new modification for piecewise-constant real permittivity profile reconstruction on the basis of multifrequency reflectometry data are described. The method of spectral analysis based on the chain-fraction approximation is proposed to be used as stage of modified Newton-Kantorovich method and is also described. Some results of numerical simulation are presented.
A new modification of quasi-optical dielectric resonator in the form of two dielectric hemidisks with a diametric slot between them in which another dielectric can be placed is investigated. In hemidisks the conditions for propagation of the whispering gallery mode waves is kept. The results of the frequency spectrum measurements in Ka-band for the resonators with one- and two-side displacement of the dielectric samples in the slot 1) symmetric one and 2) asymmetric one with radial conductor reflector) are presented and discussed. Evolution of resonator frequency spectrum in going from travelling wave regime to standing wave regime is followed.
The inversion states of a saturated traveling-wave three-level quantum paramagnetic amplifier have been investigated under conditions of bistable resonator pumping. The equations of motion for the vectorial order parameter have been obtained using adiabatic elimination of fast variables. The exact solutions for stationary inversion states have been found from these equations. For high-quality pump resonators, the isolated and the semi-isolated branches of the inversion ratio have been revealed in stationary solutions. The existence of the semi-isolated branches means a possibility of collapse of the inversion state under influence of a saturating signal. Revival of inversion is possible in this case only by the hard excitation of the pump system. This nonlinear phenomenon is of a qualitatively another nature than one described by us in arXiv:0901.0449v1 [nlin.AO], and may be observed at moderate Q-factor of pump resonator. Comment: 19 pages, 4 figures. Translated from Radiophysics and Electronics (Kharkov), 2008, N1
The stationary one-dimensional tight-binding Schredinger equation with a weak diagonal long-range correlated disorder in the potential is studied. An algorithm for constructing the discrete binary on-site potential exhibiting a hybrid spectrum with three different spectral components (absolutely continuous, singular continuous and point) ordered in any predefined manner in the region of energy and/or wave number is presented. A new approach to generating a binary sequence with the long-range memory based on a concept of additive Markov chains (Phys. Rev. E 68, 061107 (2003)) is used.
The microwave phonon stimulated emission (SE) has been experimentally and numerically investigated in a nonautonomous microwave acoustic quantum generator, called also microwave phonon laser or phaser (see previous works arXiv:cond-mat/0303188 ; arXiv:cond-mat/0402640 ; arXiv:nlin.CG/0703050) Phenomena of branching and long-time refractority (absence of the reaction on the external pulses) for deterministic chaotic and regular processes of SE were observed in experiments with various levels of electromagnetic pumping. At the pumping level growth, the clearly depined increasing of the number of coexisting SE states has been observed both in real physical experiments and in computer simulations. This confirms the analytical estimations of the branching density in the phase space. The nature of the refractority of SE pulses is closely connected with the pointed branching and reflects the crises of strange attractors, i.e. their collisions with unstable periodic components of the higher branches of SE states in the nonautonomous microwave phonon laser. Comment: 15 pages, 5 figures. Translated from Russian. Originally published in: Radiofizika i Elektronika (Kharkov), 2001, vol.6, no.1, pp.124-134
By using the network observation of subionospheric VLF/LF signals in
Japan and in Russia, we have found a significant ionospheric
perturbation prior to the recent 2011 3.11 Japan earthquake (EQ) in the
off-sea of the Tohoku area, which was an exceptionally huge plate-type
EQ. A remarkable anomaly (with decrease in the nighttime amplitude and
also with enhancement in dispersion) has been detected on March 5 and 6
on the propagation path from the NLK (Seattle, USA) transmitter to Chofu
(together with Kochi and Kasugai), and also we have observed the
corresponding VLF anomaly during a prolonged period of March 1 - 6, with
minima in the nighttime amplitude on March 3 and 4 on the path from JJI
(Miyazaki, Kyushu) to Kamchatka, Russia. This ionospheric perturbation
has been discussed extensively with respect to its reliability: (1) How
abnormal is this VLF/LF propagation anomaly ?, (2) how about the
temporal evolution of terminator times ?, (3) any solar-terrestrial
effects (especially the effect of geomagnetic storms) on the VLF/LF
propagation anomaly ?, (4) the effect of any other EQs and foreshock
activities on the VLF/LF anomaly ?, (5) any correlation with other
related phenomena ?, and (6) any other examples of VLF/LF propagation
anomaly for oceanic EQs ?. We then compared the temporal properties of
ionospheric perturbations for this EQ with those of a huge number of
inland EQs, and compared the corresponding spatial scale with the former
result of the same oceanic 2004 Sumatra EQ with nearly the same
magnitude. Finally, the generation mechanism of those seismo-ionospheric
perturbations is briefly commented.
A problem of accurate temperature stabilization and measurement arises during the development of low-temperature radiospectrometers designed for material dielectric parameter measurement in the millimeter waveband and in the wide temperature range. Thermometers used for measurement of low and ultra-low temperatures are usually based on the temperature dependence of particular material properties. Electric resistance thermometers are the most suitable for designing the circuits for temperature measurement and stabilization under the above-mentioned conditions. The temperature controller-stabilizer, being a precise automated block, designed for measurement and stabilization of temperature of the disk dielectric resonator in the 0.8 K/300 K temperature range is used in the cryodielectrometer of a gigahertz band. The four-wire circuit with alternating-current supply to the thermal sensors is applied. The specialized resistive sensors with different-sign temperature resistance coefficients are tested. The accuracy of resistance detection of about 0.05 % is provided. The accuracy of temperature stabilization is higher than ±0.01 K. Results of test experiments on the measurement of low-loss dielectric material parameters at low temperatures are presented.
The requirements to the electron beam quality in frequency multipliers are less strict as compared to those in the O-type backward wave tubes (BWT-O). Though having a lower output power than BWTs, multipliers are good candidates to be used in submillimeter waveband. Experimental research of frequency multipliers in millimeter waveband has been already undertaken. In these devices, the modulating function is performed by a klystron-type cavity fed by a powerful external cm-waveband oscillator. A slow-wave comb structure serves as a power take-off unit. In the submillimeter waveband, a two-stage klynotron-type oscillator seems to have all necessary characteristics to act as a multiplier, fulfilling two functions at the same time: A modulating oscillator and a power take-off. According to numerical theoretical studies, the electron bunching in a sheet beam in klynotrons occurs in a "layer-by-layer" manner: The more remote an electron layer from the comb surface, the more time is needed for electrons to bunch. In a remote layer electrons group into bunches after escaping the comb of the modulating structure; it means that a klynotron can be used as a beam modulator. The goal of this study was to justify this statement in experiments; we offer a description of a simple design of a multiplier klynotron and consider the outcome of its experimental performance research. In the modulating part of the klynotron the oscillations were generated at the wavelength λ ≈ 2.8 mm, and the wavelength of a signal generated in the take-off unit has a wavelength λ ≈ 0.93 mm. It was shown that it is possible to decrease the density of the focusing magnetic field in the device to 0.5 - 0.3 T, while a BWT of the same waveband requires a magnetic field of about 1.0 T.
A technique for calibrating data from the RM-08 microwave radiometer of an Okean-01 satellite and converting them to brightness temperatures is considered. Methods and results of interpreting thermal images of sea ice are presented and compared with the results of interpreting infrared images from the NOAA satellite.
Increasing of laser radiation power and improvement of its spatial-Time parameters remain one of the priority trends in upgrading quantum-optics devices. At the same time the problem of high-precision measurements of these parameters in the actual-use environment of lasers is important. The specific features of registration process appear at the measurements of highenergy laser pulse characteristics. They are caused by non-linearity behavior of interaction of powerful laser radiation with receiver. The objective of this paper is in determining of transfer function of the thin-wire bolometer of laser pulse energy on wavelength 1.06 μ with regard to non-linearity and non-uniformity of intensity distribution along the receiver. The heat-balance equation has been solved with regard to derived temperature dependencies of basic physical parameters of the bolometer. The dependencies of effective temperature of bolometer heating on the effective specific energy of incident laser radiation have been determined. The inverse function has been approximated with a polynomial of the second order. This function is a transfer one. Numerical values of coefficients of a cubic equation of measurements have been determined with their relative root-mean-square deviations. It allows us to carry out absolute measurements of energy parameters of laser radiation on wavelength 1.06 μ with thin-wire bolometer. Thus, the method of absolute calibration of thin-wire bolometer of laser pulse energy on wavelength 1.06 μ is substantiated.
Various implementations of solid-state erbium lasers with diode pumping are considered, namely, lasers based on the glass and crystal active elements; lasers pumped by ytterbium sensitizer and with resonant pumping; lasers with ATR-gate, with passive Q-switcher from a crystal of aluminum-magnesium spinel doped with cobalt, and with the integration of the properties of the passive Q-switcher into the active element.
Compact highly efficient 1.531 μ m laser is modeled. Methodology for calculating the parameters of such emitter is developed. Computer application is written to speed up the process of calculation and selection of the most technologically advanced interference coatings with predetermined reflection coefficients. Set of design and technological documentation for the production of the simulated Raman laser emitter is presented.
A modified method of carrier-phase ambiguity resolution of dual-frequency differential static carrier-phase GNSS observations at baselines up to 1000 km is proposed and verified. The developed method distinctive peculiarities which allowed to achieve high-reliability of carrierphase ambiguity resolution at intervals from 1 to 24 hours and obtain millimeters precision of positioning are described. The created domestic algorithmic high-precision positioning complex is competitive reliable and high-precision instrument for satellite observation processing and may be recommended for different practical applications.
Recently the trend connected with creation of new effective lasants representing the composites made of dye molecules and nanostructures of noble metals has been developing very rapidly. It is known that adding the nanoparticles of metals to the active media can be used for improving the media emission characteristics. Thus, for realization of this possibility it is necessary to research the nature of component interaction for each specific combination. In this paper, the dependence of fluorescence intensity of Rhodamine 6G and Sulforhodamine 101 liquid solutions on concentration of silver nanoparticles with a radius ∼ (32 ± 5) nm is investigated at different frequencies of exciting radiation. It was determined that the increase of the nanocomponent concentration increases fluorescence intensity of both dyes. It is shown that the fluorescence intensity increases when the wavelength of exciting radiation approaches the maximum of nanoparticle plasmon resonance range. Basing on the received dependences, the conclusion is drawn on existence of nanocomponent optimum concentration, exceeding of which will lead to suppression of fluorescence due to the increase of probability of non-radiative deactivation of molecules excited states.
Description and results of testing of the experimental radio meteor equipment for an atmosphere dynamics monitoring at 80-105 km altitudes which uses external terrestrial television broadcast signals for sounding have been presented. The main feature of the equipment is that all operations of a signal processing can be implemented on basis of a typical office computer with a sound card, without using of additional expensive measuring instrumentations.
The partial reflection technique was applied to experimentally investigate how the electron concentration in the middle-latitude ionospheric D-region varied at the sunrise terminator during the geomagnetic storm of November 7-11th, 2004. It was revealed that the electron concentration increased by 450-700% both immediately during the sunrise terminator passage and after it. The explanation to such phenomenon is based on the hypothesis about terminatorenhanced electron precipitation from the magnetosphere.
Compact electromagnetic radiation sources are an integral and important part of many modern applications, for which it is crucial to provide a continuous-wave (CW) operation with the output power of several watts or higher in millimeter and sub-millimeter ranges, for example, to enhance the sensitivity of DNP NMR spectroscopy. We used the results of performance tests of 2mm CW klynotrons to simulate the parameters of a CW klynotron with the central operating frequency of 130 GHz. On analyzing the performance characteristics of the sources the frequency dependence of the space charge, Pierce parameter and the system electrical length was defined. The obtained parameters were used to calculate the slow-wave structure (grating) and to simulate the operation parameters of klynotron tubes incorporating such structures. The simulation results served as a basis for designing klynotrons with homogeneous and four-stage slow-wave structures. The experimental part of the study was focused on a source with a homogeneous slow-wave structure which generated oscillations within the range 125-135 GHz. The dependences between the starting current, beam current and required focusing magnetic field were defined. The experimental test showed a good agreement between the empirical data and simulation results. The suggested method can be applied for simulating CW klynotrons in both millimeter and sub-millimeter ranges.
The results of development of the transceiver for 130-134 GHz band digital radio relay system are provided. The transceiver power amounted to 10 dBm, the receiver sensitivity was of about 10-11 W. Under the conditions of QAM-256 modulation the bit rate of 150 Mbps has been attained within the IF bandwidth of 25 MHz.
A programmable matrix FPGA has been used to develop a Fourier-spectrometer, which can be applied in spectroscopic research of molecular radiation in the Earth atmosphere. The analysis bandwidth of such spectrometer is 160 MGz, the spectrum resolution is 39 kHz. The spectrometer is a real-time device that can continuously accumulate signal's spectrum virtually without losing the observation time. Its receiving systems can operate both in the compensation and modulation modes. Spectrometer functions are controlled by a PC interfaced with the local Ethernet. In this paper, we present the results of testing the spectrometer as a component of a receiving system while observing CO molecule radiation from the Earth mesosphere.
At present submm wave sources are in great demand when many engineering issues have to be tackled. Specifically these are luggage scanning, photography of tumors, radars and coupling between large-size high-speed computers. These sources are bound to generate an output power from 1 to 50 W when using environmentally-friendly low-voltage electron flows. Among the electromagnetic radiation mm-wave sources the modification of an orotron is an obvious candidate for generating submm-waves. In this oscillator modification the binary comb is used instead of a plane periodical reflecting structure to ensure the wave slowing-down. This type of modification was referred to as an orbictron (abbr. open resonator, binary comb, electron). The critical factors that result in diminishing its efficiency, as the operating frequency increases, are sheet electron flow layering (lamination) effect and clipping of the HF-field amplitude in a rectangular channel where the interaction of electrons and electromagnetic waves takes place. These factors are due to the usage of the open resonator with marginally high loaded Q. A resonance effect in the binary comb of the orbictron has been detected. It showed that the HF-field amplitude in the electron-wave interaction space surpassed the field amplitude many times across the space between the operating surfaces of open resonator mirrors. This effect is apt to change radically the estimation of the required Q value of the orbictrons resonance system and eliminates the amplitude clipping problem. Using the channel for the sheet electron flow in the interaction space as the form of the binary comb's operating tapered-shaped surfaces (klynoorbictron) eliminates the problem of the sheet electron flow lamination (layering). The mathematical model that we have devised was applied to carry out an optimization search for promising variants of the orbictron-oscillator design in the 180 GHz range, with a 3.5 kV operating voltage of the electron flow and 0.1 F of the operating current. We have found the oscillator variants providing 10 to 12% efficiency with the quality factors not exceeding 1 000. It is shown that the efficiency tends to increase up to 14% owing to the use of klynotron effect (klynoorbictron) in the orbictron-oscillator, whereas the resonator Q-factor shows a three-fold decrease. The obtained results indicate that the orbictron and its modified designs of klynoorbictron hold a great promise as THz-range electromagnetic radiation sources.
A new technique is suggested to measure phase shifts of electromagnetic wavestransmitted through a 1D wire grating in the case of normal incidence. To implement theproposed technique an HCN-laser was involved which instruments are widely used in the capacity of THz-range sources of radiation. The output mirror of the laser was represented by the grating to be investigated and a solid mirror with an aperture. Physically the technique is based on determining the difference length of the laser resonator in the course of lasing in turnat two polarizations with the polarization vector being oriented inparallel and perpendicular to the grating wires.
The possible effect is discussed on the Schumann resonance records of the giant γ -ray flare from Sagittarius constellation (SGR 1806-20). We show that the dayside ionosphere modification is able to cause noticeable abrupt change in the power spectra global electromagnetic resonance. Spectral modifications gradually fade in time, so that usual spectra patterns are recovered in some time after the burst. A technique is proposed for measurements, which emphasizes the gamma burst effect.
We present experimental records containing extremely low frequency (ELF) pulses associated with the gamma ray flare of December 27, 2004. The GPS synchronized records were collected at observatories Moshiri (geographic coordinates 44.37 N; 142.24 E), Onagawa (38.43 N; 141.48 E), Esrange (67.83 N; 21.1 E), Karimshino (52.83 N; 158.13 E), Nagycenk (47.6 N; 16.7 E), and Hornsund (77.0N; 15.5E). Data demonstrate an exceptional similarity and contain characteristic pulses around the occurrence time of gamma flare. Our signal processing showed that in addition to fitting the arrival time of gamma rays, the following model predictions were confirmed: radio pulses contain the lowest Schumann resonance mode, the source polarity was positive, the magnetic field tends to be linearly polarized, and the source bearings correspond to the direction toward the sub-flare point. These properties are in accordance with the concept of a parametric electromagnetic pulse originating from a sizeable modification of the global electric circuit by the cosmic gamma flare.
Variations of the electron density in the midlatitude ionosphere D-region were studied experimentally with the help of the partial reflection method during the geomagnetic storm in December 2006. Their comparison with the results obtained before and after the geomagnetic storm is performed under the non-excited conditions. The quasi-periodic growth of the electron density in the D-region is detected during tens of minutes by more than 50⋯100% with the periods of 30⋯60 minutes.
Model of the pseudo-random sequence generator based on shift registers with a nonlinear feedback have been considered. The quantitative comparison is carried out including the amount feedback combinations, generating the sequence of maximum period with the shift registers having a linear feedback. Comparison of the generator performance based on the M-NLSFR and M-LSFR is carried out for the GF(2) and in expansion for the GF(2²) field.
Altitude, temporary and seasonal variations of the vertical component of the ionospheric plasma drift velocity obtained by the incoherent scatter radar of the Institute of ionosphere NAS and MES of Ukraine (Kharkiv) near the peak of the 24th cycle of solar activity are presented. Comparison of this data with ones obtained at low solar activity is performed. The instrumental and methodical features in determination of the plasma velocity are considered.
The development results of hardware computing system (HCS) for measurement of resonators characteristics with Q-factor values from dozens of units up to hundred thousand within the frequency bandwidth from 26 GHz to 37.5 GHz are provided. The measurements are based on recording and processing of amplitude-frequency characteristics (AFC) of resonators. The method for calculation of loaded O-factor, resonant frequency, relative amplitude of oscillations and level of the constant component of the signal, as well as the shift of phases between them on factors of approximation of the resonator AFC by fractional-rational function are suggested. It is shown, how using the factors of approximation of AFC of the reflection coefficient from the resonator the eigen Q-factor and the share of signal scattering power in a coupling element can be calculated. The results of tests demonstrating the system capabilities at studying the resonators with low- and high-quality factors are presented.
We examine electromagnetic pulse associated with an abrupt change of the height of the Earth-ionosphere cavity that was caused by intense gamma ray flare on 21:30:26.5 UT on December27, 2004. We demonstrate that parameters of observed extremely low frequency (ELF) radio pulse correspond to model expectations: the wave arrival angle is close to the direction towardthe epicenter of ionosphere modification, the pulsed waveform is similar to that computed, andits amplitude exceeds the level of the regular Schumann resonance background by a few times. Simultaneously, the pulse onset at the Karymshino observatory (52,827° N, 158,132° E) is ̃ 0.16 s in advance relative to the published time of modification in the VLF records.
With the increasing demand of millimeter-wave (mmWave) frequencies in 5G wireless communication technologies, investigations on techniques to improve spectral efficiency became an important aspect. There are mainly two techniques present in 5G wireless systems, named "hybrid beamforming,"that are used to reduce the system cost and "massive multi-input-multi-output (mMIMO)"to improve spectral efficiencies. In this paper, a single-cell downlink multi-user-mMIMO (MU-mMIMO) hybrid beamforming communication system is considered with multiple data streams per user that uses a generic channel model with accurate channel state information (CSI) and emphasizes partitioning of precoding into digital baseband domain and RF analog domain at transmitter (Tx) end, also combining the digital baseband domain and RF analog domain at the receiver (Rx) end. We believe that MU-mMIMO operation will be much more popular for 5G NR, considering the wide deployment of mMIMO in some major NR frequency bands. This paper gives a performance analysis of a MU-mMIMO hybrid beamforming communication system at 28 GHz frequency band with multiple number of base station (BS) antennas and quadrature amplitude modulation (QAM) schemes, and compares their performance. It also gives the tradeoff between beamforming gains to overcome path loss and reduce hardware cost and power consumption. Simulation results include receive constellation of the equalized symbols that give qualitative analysis and RMS EVM values for quantitative analysis.