Comparison of Lithium Divertor Options for the DEMO-FNS Tokamak

Technical Physics - The choice of an idea for a divertor with evaporating liquid lithium that meets the requirements for removing the thermal load from the edge plasma and provides an acceptable...     

Stability of a random process with a 1/f spectrum under deterministic action

The stability of the resultant process, which appears upon the interaction of a random process having a 1/f spectrum with a deterministic action, is analyzed using the entropy maximum principle. Under the action of a harmonic force, stable resultant processes are divided into two branches depending on the amplitude of the harmonic force. Due to an exponential relaxation upon an increase in the damping coefficient, the resultant process acquires the Lorentz spectrum without high-energy low-frequency spikes.     

Effect of hydrogenation on spin-reorientation phase transitions and magnetic anisotropy constants of RFe11Ti single crystals (R=Lu, Ho, and Er)

The magnetic anisotropy and spin-reorientation phase transitions in single crystals of the RFe₁₁Ti (R=Lu, Ho, and Er) compounds and their hydrides are investigated. Measurements are carried out on capacitance and torque magnetometers. The magnetic anisotropy constants K ₁ and K ₂ are determined by the mathematical processing of experimental magnetization curves in terms of the phenomenological theory of the anisotropic ferromagnet magnetization. It is demonstrated that the hydrogenation strongly affects the magnitude and the sign of magnetic anisotropy constants, as well as the spin-reorientation phase transitions. The hydrogenation of the HoFe₁₁Ti compound leads to the change in sign of the magnetic anisotropy constant K ₁. The inference is made that a change in the atomic volume and the axial ratio c/a cannot result in the observed effects. A change in the magnetic anisotropy constants upon hydrogenation is primarily due to the change in the interaction of the quadrupole moment of a 4f electron subshell of rare-earth ions with surrounding ions of the crystal lattice and also with valence and conduction electrons.     

1/f Noise in a nonequilibrium phase transition: Experiment and mathematical model

The results of an experimental investigation of a high-power source of broad-band 1/f noise, which can be generated in a system of two interacting nonequilibrium phase transitions, are presented. This process takes place when a normal conductor-superconductor phase transition is superposed on the critical liquid-vapor transition in a boiling coolant. A mathematical model describing a nonequilibrium phase transition in a complicated nonlinear system with two interacting order parameters, which involves the conversion of white noise into stochastic fluctuations of the order parameters with 1/f and 1/f ² spectra, is proposed. The properties of the model fluctuations with a 1/f spectrum agree qualitatively with the experimentally observed properties. A characteristic difference between the model fluctuations with a 1/f ² spectrum and random walks is also noted. Zh. éksp. Teor. Fiz. 113, 1748–1757 (May 1998)     

Fluctuations with a 1/f α spectrum in nonequilibrium phase transitions in a spatially distributed system

Statistics of fluctuations in a spatially distributed system describing the interaction of nonequilibrium phase transitions is studied. It is shown that for a certain value of the intensity of external white noise acting on phase transitions, the time and spatial spectra of fluctuations exhibit power dependences S(f) ～ f ^?α and S(k) ～ k ^?γ. The dependence of exponents α and γ on the diffusion coefficient determining the spatial interaction of fluctuations is determined. Extremal low-frequency fluctuations are singled out and the distribution functions of their duration (P(τ) ～ τ^?β) and size (P(s) ～ s^?ν)) are constructed. It is found that exponent α in the time spectral dependence and exponent β in the duration of fluctuations are connected via the relation α + β = 2. Exponents γ and ν in the spatial spectral dependence and in the size distribution function are connected via an analogous relation (γ + ν = 2).     

Special elements of the lattice of epigroup varieties

We describe right-hand skew Boolean algebras in terms of a class of presheaves of sets over Boolean algebras called Boolean sets, and prove a duality theorem between Boolean sets and étalé spaces over Boolean spaces.     

Scaling of 1/<Emphasis Type="Italic">f</Emphasis> noise in nonequilibrium phase transitions

Investigation of the dynamics of fluctuations of heat and mass transfer reveals that its crisis and transient modes exhibit high-energy pulsations with a power spectrum that is inversely proportional to frequency (flicker or 1/f fluctuations). Such a spectrum suggests energy transfer from high-to low-frequency modes and the possibility of large-scale catastrophic outbursts in the system being considered. The theory shows that such fluctuations arise in the system owing to the simultaneous occurrence of interacting phase transitions in the presence of white noise having a sufficiently high intensity. The distribution of fluctuations for scale transformations of the set of stochastic equations that describe the generation of 1/f noise is investigated. It is shown that, under a scale transformation, the Gaussian distribution of a random process having a 1/f spectrum passes to an exponential distribution, which is characteristic of the statistics of extreme outbursts. The probability of such outbursts must be taken into account in predicting the stability of various heat-transfer modes.     

Relaxation and power spectra of low-frequency fluctuations in foams

The dynamics of foam formation in a water-glycerin solution was studied to establish the relationship between the relaxation characteristics and the fluctuation power spectrum for a stochastic process. Foaming occurred during the dissociation of the gas-saturated solution and during bubbling of the solution through a porous filter. Two types of relaxation of the foam—exponential and power-law—were revealed. The power-law type of relaxation was observed upon exposure to ultrasound. Relationships between the type of relaxation and the distribution of lowfrequency fluctuations and power spectra was established.