Photoconduction and photocontrolled collective effects in the Peierls conductor TaS3_3

Light illumination of thin crystals of CDW conductor TaS$_3$ is found to result in dramatic changes of both linear ($G$) and nonlinear conduction. The increase of $G$ is accompanied by suppression of the collective conduction, growth of the threshold field $E_T$, and appearance of the switching and hysteretic behavior in the nonlinear conduction. The effects in the nonlinear conduction are associated with increase of CDW elasticity due to illumination that leads in particular to appearance of a relation $E_T\propto G^{1/3}$ expected for the one-dimensional pinning.Comment: RevTeX4, 4 pages, 4 postscript figures. Revised manuscript, new title, new Fig. 1, text corrections. Journal reference adde

Experimental evidence of ageing and slow restoration of the weak-contact configuration in tilted 3D granular packings

Granular packings slowly driven towards their instability threshold are studied using a digital imaging technique as well as a nonlinear acoustic method. The former method allows us to study grain rearrangements on the surface during the tilting and the latter enables to selectively probe the modifications of the weak-contact fraction in the material bulk. Gradual ageing of both the surface activity and the weak-contact reconfigurations is observed as a result of repeated tilt cycles up to a given angle smaller than the angle of avalanche. For an aged configuration reached after several consecutive tilt cycles, abrupt resumption of the on-surface activity and of the weak-contact rearrangements occurs when the packing is subsequently inclined beyond the previous maximal tilting angle. This behavior is compared with literature results from numerical simulations of inclined 2D packings. It is also found that the aged weak-contact configurations exhibit spontaneous restoration towards the initial state if the packing remains at rest for tens of minutes. When the packing is titled forth and back between zero and near-critical angles, instead of ageing, the weak-contact configuration exhibits "internal weak-contact avalanches" in the vicinity of both the near-critical and zero angles. By contrast, the stronger-contact skeleton remains stable

Origin of slow-drift shadow bursts in Jovian decameter radio emission with quasi-harmonic structure

An explanation is proposed for the appearance of slowly drift shadow bursts in the dynamic spectrum of Jupiter against the background of decameter radio emission with a quasi-harmonic structure. Background radio emission is caused by hot ions with a loss cone type distribution function, which generate ion cyclotron waves due to the effect of double plasma resonance. A flow of hot ions with a distribution function of the Maxwell type is injected into the source region, fills the loss cone of generating ions and interrupts the generation of ion cyclotron waves due to the filling of the loss cone. The condition under which instability breaks down is obtained, and the optimal values of the parameters of the injected ions necessary for the occurrence of bursts in absorption are determined

Spatially resolved microwave pulsations of a flare loop

A microwave burst with quasi-periodic pulsations was studied with high spatial resolution using observations with the Nobeyama Radioheliograph (NoRH). We found that the time profiles of the microwave emission at 17 and 34 GHz exhibit quasi-periodic (with two well defined periods P 1 = 14–17 s and P 2 = 8–11 s) variations of the intensity at different parts of an observed flaring loop. Detailed Fourier analysis shows the P 1 spectral component to be dominant at the top, while the P 2 one near the feet of the loop. The 14–17 s pulsations are synchronous at the top and in both legs of the loop. The 8–11 s pulsations at the legs are well correlated with each other but the correlation is not so obvious with the pulsations at the loop top. For this P 2 spectral component, a definite phase shift, P 2 /4 ≈ 2.2 s, between pulsations in the northern leg and loop top parts of the loop have been found. The length of the flaring loop is estimated as L = 25 Mm (≈34 ) and its average width at half intensity at 34 GHz as about 6 Mm (≈8 ). Microwave diagnostics shows the loop to be filled with a dense plasma with the number density n 0 ≈ 10 11 cm −3, penetrated by the magnetic field changing from B 0 ≈ 100 G near the loop top up to B 0 ≈ 200 G near the north footpoint. A comparative analysis of different MHD modes of the loop demonstrates the possibility of the simultaneous existence of two modes of oscillations in the loop: the global sausage mode, with the period P 1 = 14–17 s and the nodes at the footpoints, and a higher harmonics mode (possibly with the radial wave number l > 1), with P 2 = 8–11 s

One-dimensional conduction in Charge-Density Wave nanowires

We report a systematic study of the transport properties of coupled one-dimensional metallic chains as a function of the number of parallel chains. When the number of parallel chains is less than 2000, the transport properties show power-law behavior on temperature and voltage, characteristic for one-dimensional systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let