Successive phase transitions of [(PyO)(H/D)][AuCl4] (PyO=C5H5NO)

³⁵Cl NQR as well as heat capacity measurements of [(PyO)H][AuCl₄] and its deuterated analog [(PyO)D][AuCl₄] revealed successive phase transitions at 70.5 and 62.5 K, and at 71 and 63 K, respectively. The NQR frequency varied continuously through the upper transition point while discontinuously through the lower transition point. In the intermediate-temperature phase a remarkable decrease in the signal intensity was observed. These NQR observations as well as the feature of the heat capacity anomaly in which a broad peak is succeeded by a sharp peak with decreasing temperature suggest a possibility of normal-incommensurate-commensurate phase sequence.     

Experimental study of a broad-band XeCl double-pass amplifier with SBS mirror

An oscillator-amplifier XeCl laser system has been used to experimentally investigate the effectiveness of a liquid stimulated Brillouin scattering (SBS) mirror for correcting the spatial aberrations of broad-band laser radiation in a double-pass amplifier. It has been found that the SBS amplifier performance is strongly dependent on the intensity I _p exciting the Brillouin medium. A good beam reconstruction has been attained at I _p1GW/cm², whereas highly aberrated output beams have been delivered by the SBS amplifier for I _p>1 GW/cm². By comparing the broad-band SBS amplifier performance to that of the same amplifier with a dielectrically coated flat mirror at one end, it has been found that the use of a SBS mirror is advantageous to obtain lower divergence output beams only for low energy pump beams (<1 mJ).     

Stimulated Brillouin scattering in magnetized diffusive semiconductor plasmas

Using the hydrodynamical model and following the coupled mode approach, detailed analytical investigation of stimulated Brillouin scattering is performed in an electrostrictive semiconductor. The total induced current density including diffusion current density and the effective Brillouin susceptibility are obtained under off-resonant laser irradiation. The analysis deals with the qualitative behaviour of the Brillouin gain and transmitted intensity with respect to excess doping concentration and magnetic field. Efforts are directed towards optimizing the doping level and magnetic field to achieve maximum Brillouin gain at pump intensities far below the optical damage threshold level. It is found that by immersing a moderately doped semiconductor in a sufficiently strong magnetic field in transverse direction, one can achieve resonant enhancement of Brillouin gain provided the generated acoustic mode lies in the dispersionless regime.     

Proton irradiation defects in (fluoranthene)2PF6

Electron spin resonance and electron–proton double resonance (Overhauser shift method) are used for the comparison of proton radiation damaged and as-grown (fluoranthene)₂PF₆ single crystals. Chemical modification and various consequences of the nonuniform distribution of radiation induced defects in this quasi-one-dimensional organic conductor with defect dependent Peierls transition are worked out.     

Stimulated brillouin scattering in SF6 with a free-running XeCl laser as pump

A XeCl laser system without dispersive elements is used to investigate near threshold reflectivity and phase-conjugation (PC) fidelity of stimulated Brillouin scattering (SBS) mirrors with SF₆ as the active medium. Using different focal-length lenses to focus the broadband laser radiation into the Brillouin medium, it was found that at threshold the effective interaction length for SBS is equal to the confocal parameter and that the SBS gain is equal to its steady-state value for monochromatic pumping. High PC-fidelity values ranging from 0.8–1.0 were found under most of the experimental conditions investigated.     

Accelerated D-Dimensional Compactified Universe in Gauss--Bonnet--Dilatonic Scalar Gravity from D-Brane/M-Theory

We discuss a particular d-dimensional Gauss- Ronnet-dilatonie universe compactified on S^1 motivated from Mtheory. We examine the time-evolution of the dynamical equations where many interesting consequences are revealed and discussed in some details. Under reasonable conditions, the discussed model can provide a mechanism to realize, in higher-dimensions （d 〉 4）, the accelerated expansion of the universe in the presence of dark energy, without the presence of phantom energy and without the contraction of some internal dimension.     

Phantom Energy with Variable G and Λ

We investigate a cosmological model of a phantom energy with a variable cosmological constant （∧） depending on the energy density （ρ） as ∧∝ρ^α,α=const and a variable gravitational constant G. The model requires α 〈 0 and a negative gravitational constant. The cosmological constant evolves with time as ∧ ∝ t^-2. For ω 〉 - 1 and α 〈 -1 the cosmological constant ∧ 〈 0, G 〉 0 and ρ decrease with cosmic expansion. For ordinary energy （or dark energy）, i.e.ω 〉 -1, we have -1 〈 α〈 0 and β 〉 0 so that G〉0 increases with time and p decreases with time. Cosmic acceleration with dust particles is granted, provided -2/3 〈α〈 0 and ∧〉0.     

Investigation of the non-linear loss properties of magnetic fluids subject to large alternating fields

The non-linear relaxational properties of a water-based magnetic fluid are investigated by means of measuring the frequency dependent complex susceptibility, χ(ω) in the presence of an external potential. The results obtained are discussed in terms of the magnetic analogue of the Coffey and Paranjape model as modified by Déjardin. The loss processes in the magnetic fluid in the non-linear region are investigated in the context of the loss tangent, tan(δ), and the power dissipation per unit volume. These measurements are of importance because of the continuing interest in the clinical applications of magnetic fluids, where large alternating magnetic fields can be applied to magnetic fluids to induce loss processes and heating effects, often driving the magnetic fluid into the non-linear region of magnetisation. We evaluate the increment of the susceptibility, Δχ, due to the non-linear response, through measurement of χ(ω), and extend this formulism to the non-linear increment of the loss tangent, Δ tan(δ) and the increment of the heating rate, ΔU_heat.     

Cosmology with weak lensing surveys

Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening matter. The distortions are due to fluctuations in the gravitational potential, and are directly related to the distribution of matter and to the geometry and dynamics of the Universe. As a consequence, weak gravitational lensing offers unique possibilities for probing the Dark Matter and Dark Energy in the Universe. In this review, we summarise the theoretical and observational state of the subject, focussing on the statistical aspects of weak lensing, and consider the prospects for weak lensing surveys in the future.