Aging phenomena in spin glasses and frustrated ferromagnets

An experimental protocol developed for spin glasses has been applied to a reentrant system. We compare the main features of the aging phenomena in both spin glass and ferromagnetic phases.     

Quantum phenomena in glasses at low temperatures

Glasses exhibit surprising low-temperature properties caused by the tunneling motion of small atomic clusters. We report here on recent dielectric measurements on a glass with the components BaO–Al₂O₃–SiO₂. In contrast to expectation, below 100 mK the dielectric properties become sensitive to weak magnetic fields. In this temperature range dielectric constant and dielectric loss show an oscillatory behavior with increasing magnetic field. Below 6 mK a phase transition within the ensemble of tunneling systems is observed.     

Aging, rejuvenation and memory phenomena in spin glasses

In this paper, we review several important features of the out-of-equilibrium dynamics of spin glasses. Starting with the simplest experiments, we discuss the scaling laws used to describe the isothermal aging observed in spin glasses after a quench down to the low-temperature phase. We report in particular new results on the sub-aging behaviour of spin glasses. We then discuss the rejuvenation and memory effects observed when a spin glass is submitted to temperature variations during aging, from the point of view of both energy landscape pictures and real-space pictures. We highlight the fact that both approaches point out the necessity of hierarchical processes involved in aging. Finally, we report an investigation of the effect of small temperature variations on aging in spin glass samples with various anisotropies which indicates that this hierarchy depends on the spin anisotropy.     

Chaotic phenomena of charged particles in crystal lattices

In this article, we have applied the methods of chaos theory to channeling phenomena of positive charged particles in crystal lattices. In particular, we studied the transition between two ordered types of motion; i.e., motion parallel to a crystal axis (axial channeling) and to a crystal plane (planar channeling), respectively. The transition between these two regimes turns out to occur through an angular range in which the particle motion is highly disordered and the region of phase space spanned by the particle is much larger than the one swept in the two ordered motions. We have evaluated the maximum Lyapunov exponent with the method put forward by Rosenstein et al. [Physica D 65, 117 (1993)] and by Kantz [Phys. Lett. A 185, 77 (1994)]. Moreover, we estimated the correlation dimension by using the Grassberger-Procaccia method. We found that at the transition the system exhibits a very complex behavior showing an exponential divergence of the trajectories corresponding to a positive Lyapunov exponent and a noninteger value of the correlation dimension. These results turn out to be linked to a physical interpretation. The Lyapunov exponents are in agreement with the model by Akhiezer et al. [Phys. Rep. 203, 289 (1991)], based on the equivalence between the ion motion along the crystal plane described as a "string of strings" and the "kicked" rotator. The nonintegral value of the correlation dimension can be explained by the nonconservation of transverse energy at the transition.     

Absorption phenomena in multicomponent phosphate glasses with Mn

The absorption and ESR spectra of multicomponent alumino-phosphate glasses doped with manganese (0·2–20 mol %) has been measured and compared with the absorption spectra of manganous and manganic ions in model solutions. The unirradiated glasses show in ultraviolet region increasing absorption below 200 nm with the shoulder at 235 nm and the absorption bands due to manganous oxygen complexes in octahedral symmetry. They are similar to the absorption bands of Mn²⁺ in concentrated H₃PO₄ acid. In irradiated glasses the bands at 200, 235, 275 (only if Mn is present) and a broad band at 540 nm appear. After the annealing at 450 C all radiation-induced bands disappear and the bands at 235 nm is more pronounced. The Mn³⁺ in H₃PO₄ solution exhibit the absorption spectrum with a weak band at 530 nm and a very intense band at 270 nm. It is therefore proposed that both the 540 and 275 nm bands in irradiated glasses can be assigned to octahedral oxygen complexes of Mn³⁺, i.e. to hole centres. The band at 200 nm which is practically independent of the modifiers (Be, Mg, Ca, Sr and Ba) is, therefore, associated with electron centres (electrons trapped in non-bridging oxygen vacancies). It is suggested that the band at 235 nm in irradiated and annealed glasses is associated with irreversible structural changes.The authors wish to express their appreciation to H.Dvoáková for preparing the solutions and E.Linhartová for careful measurements.     

Acoustic phenomena in filled porous glasses by time-resolved spectroscopy

We studied the propagation of ultrasonic acoustic waves in two porous glasses characterized by different pore diameters (4 and 200 nm) filled with carbon tetrachloride. Using a time-resolved optical spectroscopic technique (Transient Grating) we can measure the acoustic dynamics of these systems. The sound velocities, measured in both the samples, show high values compared with the sound velocity of bulk carbon tetrachloride; they cannot be predicted by the simple effective medium model, but are in good agreement with the estimate obtained from the Biot theory.     

Laser initiation and early stages of electrical breakdown in charged glasses

A single pulse from a neodymium laser is used to initial electrical breakdown in glasses which accumulate and preserve a space charge induced by a beam of rapid monoenergetic electrons. Laser initiation permits use of high-speed recording apparatus and study of the initial stage of electrical breakdown in the charged glasses. A time delay in electrical breakdown relative to the initiating optical radiation was observed and measured, corresponding to the time of formation of a conductive channel between the region of space-charge localization and the specimen surface. Growth rates of the conductive channel are determined for surface and volume initiation, and possible mechanisms of laser initiation are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 72–77, July, 1988.     

Nonlinear electrohydrodynamic phenomena and droplet generation in charged jets of conducting liquid

Phenomena occurring at the tip of a charged conducting jet are analyzed in detail using numerical methods developed for axially symmetric flows. Universal mechanisms (independent of the method for producing the jet) for droplet formation with different ratios of the Laplace and electrical pressures on the lateral surface are identified. An explanatory analysis is given for all of the nonlinear stages of the classical Rayleigh instability of a charged conducting drop, beginning with the formation of a jet at the surface of the drop and culminating in the generation of a developed jet of secondary droplets. Zh. Tekh. Fiz. 69, 1–9 (November 1999)     

Correlation phenomena in the Cherenkov radiation of accelerated multiply charged ions

Correlation phenomena occurring in Cherenkov radiation are considered which are related to fluctuations of the charge states of multiply charged accelerated ions in a medium. The additional correlation contribution to the radiation is determined by the root-mean-square deviation of the ion charge from its equilibrium value and is responsible for the nonzero radiation yield in the event that the threshold condition is not fulfilled. Numerical estimates of the radiation yield of heavy ions in the optical and X-ray frequency ranges are given. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 41–46, January, 2009.     

Spectral method in quantum theory of channeling phenomena of fast charged particles in crystals

We show the possibility of using the spectral method to determine the quantum characteristics of interaction between fast charged particles and crystal when the channeling occurs. Basing on this method, we have developed the procedure for calculation of particles transversal motions eigenlevels for plane channeling. We considered origin of new levels with increasing of particle's energy and zone structure forming from these levels with increasing number of potential wells. We discuss also the possibility of using the spectral method in number of other problems of quantum theory of channeling.     

Correlation of highly charged ion and X-ray emissions from the laser-produced plasma in the presence of non-linear phenomena

Flux of X-ray radiation emitted from the Ta plasma, produced by the fundamental (1ω) and the third harmonic (3ω) frequencies of the high-power iodine laser PALS, was studied in dependence on the laser focus position. One or two (three) maxima, corresponding to the hard or soft component of the emitted spectrum, can appear, according to the experimental conditions. These dependencies are compared with those published by other authors, and also with our results concerning the highly charged ion generation. At laser intensities above I _L～ 10¹⁴ W/cm², the participation of non-linear processes in the pre-formed plasma was confirmed.     

On the mechanoelectrical coupling in the cochlear outer hair cell

Outer hair cell electromotility, a manifestation of the interconnection between the mechanical and electrical processes occurring in outer hair cells, is believed to be an important contribution to the active cochlea. Two modes of mechanoelectrical coupling in the outer hair cell wall are studied: the potential shift caused by mechanical loading under the wall charge preservation conditions and the current (transferred charge) caused by mechanical loading under the voltage-clamp conditions. By using the previously reported elastic moduli of the wall and components of the active force, the potential shift under the charge preservation conditions is derived. This shift is expressed in terms of the wall strains and the active force derivatives with respect to the wall potential. The magnitudes of the potential shift corresponding to the conditions of cell inflation, axial stretch (compression), and the micropipet aspiration are estimated. In the last case, the distribution of the potential shift along the cell wall is also demonstrated. The potential shift can reach -20(-)-40 mV under the conditions of the micropipet aspiration or cell inflation. Such shift is much smaller under the condition of cell stretch (compression). The current and the charge transfer caused by the cell stretch under the voltage-clamp conditions is analyzed, and shows good agreement of predictions with experimental data.     

Wall Recombination in Glow Discharges

We derived a model describing the radial distribution of the ion and electron densities and the radial electric field strength in the positive column of a glow discharge. The set of equations related to the plasma consists of the equations for particle and momentum conservation for the ions and electrons and the Poisson-equation. In a novel approach, the necessary boundary conditions in our model result from a system of balance equations for the charge carriers on the insulated wall surrounding the positive column.     

Effect of humidity on the parameters of mechanoelectrical transformations in concretes

An increase in the humidity of a cement solution from 0 to 8% is found to result in an exponential decrease in the principal spectral maximum of its electric response to an impact excitation according to the change in the electrical resistivity. A physical model is proposed for the mechanoelectrical transformations occurring in a wet heterogeneous material, and this model agrees well with the experimental data.