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1.
Инвентарный номер: нет.
   
   K 79


    Koverda, V. P.
    The origin of 1/f fluctuations and scale transformations of time series at nonequilibrium phase transitions / V. P. Koverda, V. N. Skokov // Physica A. - 2005. - Vol.346, №3-4. - С. 203-216
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
FLUCTUATIONS -- POWER SPECTRA -- NONEQUILIBRIUM PHASE TRANSITIONS
Аннотация: Investigations of the dynamics of heat and mass transfer show that in crisis and transient conditions one can observe high-energy fluctuations with a power spectrum inversely proportional to the frequency (flicker or 1/f fluctuations). Such a spectrum presupposes energy transient from high to lower frequency modes and the possibility of large-scale catastrophic events in a system. Theory shows that such fluctuations arise in a system owing to the simultaneous progress of interacting phase transitions in the presence of a white noise of sufficient intensity. The distributions functions of fluctuations during scale transformations of a system of stochastic equations describing the 1/f noise generations have been investigated. It is shown that the Gaussian distributions of a random process with a 1/f spectrum under a roughness of a scale change to exponential distribution characteristic of the statistics of extreme events. The probability of such events should be taken into account in predicting the stability of different heat transfer regimes

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2.
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   K 79


    Koverda, V. P.
    Statistics of low-frequency pulsations in critical regimes of heat mass exchange with phase transitions / V. P. Koverda, V. N. Skokov, A. V. Reshetnikov // Journal of Engineering Thermophysics. - 2007. - Vol.16, №3. - С. 130 -138
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
FLUCTUATION -- IRREGULAR HIGH-ENERGY -- 1 / F СПЕКТРЫ
Аннотация: Experimental investigation of fluctuation dynamics in critical and transitional modes of heat mass exchange shows existence of irregular high-energy pulsations with power spectrum inversely proportional to the frequency—so called 1/f spectrum. Such regimes are characterized by the fact that an essential part of the pulsations energy is connected with very slow processes and mean that large high-energy bursts are possible in the system. Another characteristic feature of such regimes is scale invariance of the fluctuations distribution function. According to the theory, the 1/f fluctuations can emerge in physical systems due to simultaneous phase transitions in presence of sufficiently intensive white noise. This paper is devoted to detailed investigation of relaxation processes at steadying of stationary stochastic process in non-equilibrium phase transitions in system of two nonlinear stochastic differential equation. Such an information reveals statistical patterns of particular large-scale low-frequency bursts. Discontinuous “forgetting” of the initial conditions takes place. It is shown by numerical methods that distributions of duration and maximal values of the low-frequency extreme bursts have the power-like form. Experimental investigation results of statistical characteristics of fluctuation processes at ultrasonic cavitation and flash boiling of overheated water jets are presented. Results of the experiments carried out fit conclusions of the theoretical model for interacting heterogeneous phase transitions

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3.
Инвентарный номер: нет.
   
   S 45


   
    Self-organized criticality and 1/f-noise at interacting nonequilibrium phase transitions / V. N. Skokov, A. V. Reshetnikov, V. P. Koverda, V. P. Koverda, A. V. Vinogradov // Physica A. - 2001. - Vol.293, № 1-2. - С. 1-12
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
SELF-ORGANIZED CRITICALITY -- 1/f FLUCTUATIONS -- POWER SPECTRA
Аннотация: Oscillatory combustion regimes were experimentally investigated under the conditions of ignitable liquid boiling-up before the reaction front. Fluctuations with a power spectral density inversely proportional to frequency (1/f-noise) were observed and the power-law character of distribution functions was found. The phenomena are connected with the intersection and interaction of nonequilibrium phase transitions. A mathematical model describing the initiation of 1/f fluctuations at the interaction of a subcritical phase transition and supercritical one in a space-distributed system was suggested

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4.
Инвентарный номер: нет.
   


   
    1/f noise and self-organized criticality in crisis regimes of heat and mass transfer / V. N. Skokov, V. P. Koverda, A. V. Reshetnikov, V. P. Skripov, N. A. Mazheiko, A. V. Vinogradov // International Journal of Heat and Mass Transfer. - 2003. - Vol. 46, № 10. - С. 1879-1883
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
1/f-NOISE -- FLUCTUATIONS -- FLICKER NOISE
Аннотация: Thermal fluctuations under the transition from nucleate to film boiling of water on a wire heater and fluctuations of jet form during an outflow of superheated liquid from a pressure vessel were experimentally investigated. It has been found that power spectrum of the fluctuations has got a low frequency component corresponding to a 1/f law (flicker noise).??The effect given is connected with the occurrence of nonequilibrium phase transitions in the systems: a crisis of heat transfer under the transition from nucleate to film boiling and a crisis of a flow in boiling-up of superheated liquid jet??

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5.
Инвентарный номер: нет.
   
   K 79


    Koverda, V. P.
    Statistics of fluctuations with a 1/f spectrum at phase transitions in a spatially distributed system / V. P. Koverda, V. N. Skokov // Physica A. - 2011. - Vol. 390, № 13. - С. 2468-2479
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
1/f-NOISE -- FIRST PASSAGE TIME -- AVALANCHES
Аннотация: A study has been made on the statistics of fluctuations in a spatially distributed system, which describes the interaction of nonequilibrium phase transitions. It is shown that at a certain intensity of external white noise acting on phase transitions, the time and spatial spectra of fluctuations have power laws S(f)∼f−α and S(k)∼k−γ. The dependence of the exponents α and γ on the value of the diffusion coefficient determining the spatial interaction of fluctuations have been found. Extreme low-frequency fluctuations has been revealed and distribution functions of their duration P(τ)∼τ−β and size P(s)∼s−ν have been determined. It has been found that the exponent α of the frequency dependence of time spectra and the exponent β of the distribution function of the fluctuation duration are related by the relation α+β=2. The exponent of the spatial spectrum γ and the exponent of the size distribution function ν are related by a similar relation: γ+ν=2. The results of experimental studies on fluctuations in a typical nonequilibrium phase transition such as transient modes of water boiling on a wire heater are presented. It was demonstrated that the critical exponents, which describe the power dependence of power spectra of fluctuations and the amplitude distribution of extreme surges, are related by the relation α+β=2 both in experiments and in the theoretical model of interacting heterogeneous phase transitions

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6.
Инвентарный номер: нет.
   
   K 79


    Koverda, V. P.
    Statistics of avalanches in stochastic processes with a 1/fα spectrum / V. P. Koverda, V. N. Skokov // Physica A. - 2009. - Vol.388, №9. - С. 1804-1812
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
1/f-NOISE -- AVALANCHES -- FIRST PASSAGE TIME
Аннотация: The results of numerical investigation of the Brownian motion in a two-dimensional potential field formed under the coupling of phase transitions at the conditions of the criticality induced by white noise are presented. The suggested system of stochastic equations at the white noise intensity that corresponds to the criticality of a noise-induced transition describes stationary random processes with power spectra S(f)∼f−α, where the exponent α varies in the range 0.8≤α≤1.8. The exponent α was found by the direct FFT method from numerical realizations of the Brownian motion processes. The exponent β of the distribution function P(τ)∼τ−β of the duration of low frequency extreme fluctuations was determined by numerical methods from the distributions of time of the first passage across a potential barrier with different realizations of white noise. The low frequency extreme fluctuations in many properties are similar to avalanches considered in models of self-organized criticality. The exponents α and β were determined directly from numerical realizations of random processes independently of each other. It is shown that the exponents α and β are related by the relation α+β=2.

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7.
Инвентарный номер: нет.
   
   D 98


   
    Dynamics of transition processes and structure formation in critical heat-mass transfer regimes during liquid boiling and cavitation / A. N. Pavlenko, V. P. Koverda, A. V. Skokov, A. V. Reshetnikov, A. V. Vinogradov, A. S. Surtaev // Journal of Engineering Thermophysics. - 2009. - Vol.18, №1. - С. 20-38
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
CRITICAL PHENOMENA -- FALLING FILMS -- LIQUID CAVITATION
Аннотация: The results of experimental studies concerning the development of critical phenomena and structure formation in the process of boiling in falling films and during liquid cavitation are given. In conditions of stepwise and periodic pulsed surges of a thermal load, the parameters of formed metastable regular structures and critical parameters of heat-releasing surface drying are shown to be determined by the dynamics of moving wetting boundaries in the process of system self-organization. In the case of high-intensity heat fluxes, decomposition of a falling film is determined by propagation regimes of self-maintaining boiling fronts with a complex shape of intermediate structures. The study of ultrasonic cavitation of water, glycerin, and vacuum oil shows that structures of interacting gas-vapor bubbles (having the form of fractal clusters) are formed near the emitter surface. Spatial structures are characterized by a low-frequency divergence of the power spectra and a scale-invariant function of the fluctuation distributions. The experimental results are in good qualitative agreement with the numerical simulations performed within the theory of 1/f fluctuations in the case of nonequilibrium phase transitions in a spatially distributed system

\\\\expert2\\NBO\\Journal of Engineering Thermophysics\\2009, V.18, N 1. P. 20-38.pdf
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8.
Инвентарный номер: нет.
   
   V 70


    Vinogradov, A. V.
    Spectral Characteristics of Fluctuations in Ultrasonic Cavitation of Water and Glycerin / A. V. Vinogradov // Heat Transfer Research. - 2008. - Vol.39, №6. - С. 519-527
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
FLUCTUATION -- ACOUSTIC CAVITATION -- GLYCERIN
Аннотация: The results of experimental investigation of the dynamics of fluctuations in acoustic cavitation of water and glycerin are presented. Near the radiator surface the structures in interacting vapor-gas bubbles having the form of fractal clusters were formed. Using the method of photometric scanning of transmitted laser radiation, the dynamics of fluctuations was investigated. In the transient regime the range of the power of fluctuations changed inversely proportional to frequency. The distributions of local fluctuations differ from Gaussian ones and reveal the properties of scale invariance. The qualitative behavior of the frequency dependence of the spectral density of fluctuations on change in the power of an ultrasonic radiator was investigated. It is shown that the raise of the high-frequency boundary of the flicker behavior point to the buildup of instability and may serve as a precursor of possible large-scale overshoots

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9.
Инвентарный номер: нет.
   
   B 73


   
    Boiling up of jets of superheated ethanol-water solutions / A. V. Reshetnikov, A. V. Vinogradov, V. N. Begletsov, V. N. Skokov, V. P. Koverda // Journal of Engineering Thermophysics. - 2007. - Vol.16, №4. - С. 244-248
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
EVOLUTION OF THE SHAPES -- SUPERHEATED AQUEOUS SOLUTIONS -- LOW-BOILING LIQUID
Аннотация: The stability and evolution of the shapes of jets of strongly superheated aqueous solutions of ethanol flowing out of a high-pressure chamber are experimentally investigated at various initial parameters. It has been found that a low-boiling liquid causes shifting to lower temperatures of the boundaries between various kinds of boiling-up jets, such as cylindrical, conical, and open. Large-scale pulsations of the jet shapes are observed in the temperature range from 454 to 484 K, where the jet completely breaks down. The conditions for the formation of large-scale low-frequency pulsations with a power spectrum diverging inversely proportional to the frequency f (1/f spectra) have been revealed. Such fluctuations prove that the flow is unstable and large-scale low-frequency ejections are possible

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10.
Инвентарный номер: нет.
   
   S 68


    Smolyak, B. M.
    The effect of ac magnetic fields on the lifting power of levitating superconductors / B. M. Smolyak, G. V. Ermakov, L. I. Chubraeva // Superconductor Science and Technology. - 2007. - Vol.20, №4. - С. 406-411
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
LEVITATION FORCE -- SUPERCONDUCTING SUSPENSION -- LIFTING FORCE
Аннотация: This study deals with the decrease in the levitation force under the action of an ac field up to the frequency at which oscillations of the superconducting suspension are limited by inertia. The lifting force was measured as a function of the ac field amplitude and the exposure time. It was shown that the force quickly decreased at the moment the ac field was applied and then continued diminishing, but at a lower rate. A qualitative model was proposed, taking into account two effects of the ac field on the magnetization of the levitating superconductor: a complete destruction of the critical state in some section of the superconductor (to a depth λac) and the initiation of a faster magnetic relaxation in the region where the induction gradient is preserved

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