Solution phase evolution of AuSe nanoalloys in Triton X-100 under UV-photoactivation

A solution phase UV-irradiation technique has been exploited to produce an AuSe nanoalloy through fusion of preformed Au (photoproduced) and Se (chemically prepared) in a micellar (TX-100) medium.     

Instability of Interfaces in the Antiferromagnetic XXZ Chain at Zero Temperature

 For the antiferromagnetic, highly anisotropic XZ and XXZ quantum spin chains, we impose periodic boundary conditions on chains with an odd number of sites to force an interface (or kink) into the chain. We prove that the energy of the interface depends on the momentum of the state. This shows that at zero temperature the interface in such chains is not stable. This is in contrast to the ferromagnetic XXZ chain for which the existence of localized interface ground states has been proven for any amount of anisotropy in the Ising-like regime. Received: 15 August 2002 / Accepted: 8 January 2003 Published online: 14 April 2003 RID="⋆" ID="⋆" ? Copyright rests with the authors. Reproduction of the entire article for non-commercial purposes is permitted. Communicated by M. Aizenman     

Does Solvent Influence the Ground-state Tautomeric Population of Hypericin?¶

Nuclear magnetic resonance measurements indicate that hypericin exists in the same "normal" tautomeric form irrespective of whether the solvent is dimethyl sulfoxide or tetrahydrofuran. This result is discussed in the context of previous experimental and theoretical work. It is concluded that solvent perturbations cannot induce tautomerization in hypericin.     

Accelerated Bergman cyclization of porphyrinic-enediynes

The Bergman cyclization of simple diethynylporphyrinic-enediynes exhibits a double activation barrier to the formation of Bergman cyclized product. Addition of H-atom acceptor accelerates the formation of the picenoporphyrin, indicating that the second barrier is rate limiting.     

Are messages of R-parity violating supersymmetry hidden within top quark signals?

In an R-parity nonconserving supersymmetric theory, the lighter stop can dominantly decay into b&mgr; and btau if R-parity breaking has to explain the neutrino mass and mixing pattern suggested by the data on atmospheric muon neutrinos. This should give rise to dilepton + dijet and single - lepton + jets, signals identical with those of the top quark at the Fermilab Tevatron. One can thus constrain the stop parameter space using the current top search data and can similarly look for the first signals of supersymmetry at the upgraded runs of the Tevatron.     

Diffusion and transport phenomena in a collisional magnetoplasma having both streaming and temperature anisotropy: Collisional kinetics

Boltzmann-transport equation is analytically solved for two-component magnetoplasma using Chapman-Enskog analysis to include collisional diffusion transport having anisotropies in both streaming velocity and temperature components. The modified collisional integrals are analytically solved with flux integrals and perturbed kinetic equation to arrive at drift diffusion velocity and resulting transport coefficients which are markedly affected by both streaming and temperature anisotropy. The early isotropic results are recovered in the limit V ₀ = 0 and T _‖ = T _⊥ which reduce to eqs (11.30) and (11.31) of [1] and eqs (2.7) and (2.13) of [2]. The electrical resistivity (η_⊥) diminishes sharply in fusion temperature limit kT _⊥ = 1 keV. The shape of the curves for both electrical resistivity and thermal conductivity is rectangular hyperbolic. However, for low thermal ratio (T _‖/T _⊥ < 1), the curves are raised up and for high thermal ratio (T _‖/T _⊥ > 1), they are lowered down the isotropic case (T _‖/T _⊥ > 1), showing comparatively diminished magnitudes of the quantities.      

Littrow-type discretely tunable, Q-switched Nd:YAG laser around 1.3 μm

An all-solid-state, side diode array pulse pumped Nd:YAG laser tunable for six wavelengths ranging from 1318.8 nm to 1356.0 nm is developed. The tunability is obtained by using a grating in Littrow mode that also serves as an output coupler. The configuration ensures a line width as low as 0.04 nm. Thermal effects limit the maximum average power to 250 mW for an average absorbed pump power of 8.0 W in the free-running condition. An acousto-optic Q-switching of the laser provides pulses of width 251 ns with peak power of 733 W for an average pump power of 11.5 W. The laser may find application in microsurgery and dermatology. PACS 42.55.Xi; 42.60.-v; 42.60.Fc; 42.60.Gd; 42.62.Be     

Thin Nd:YAG slab laser pumped by lens duct coupled diode laser stacks

High power continuous wave operation of a diode face-pumped thin Nd:YAG slab laser is reported. A novel pumping geometry for a thin Nd:YAG slab using cylindrical lens duct coupled diode laser stacks is demonstrated. In a close-coupled resonator, a maximum laser output power of 260 W in multimode operation is obtained. This corresponds to a slope efficiency of 34% and an optical-to-optical efficiency of 27%, respectively. In high-brightness operation, a polarized laser output of 70 W has been obtained with a beam quality factor close to 4 in both directions. The polarization contrast ratio is >100. PACS 42.55.Xi; 42.60.Pk; 42.60.By     

Spinning cone water film power meter for high-power CO2 lasers

A laser power meter based on water as an absorbing medium has been developed to measure multi-kilowatt CO₂ laser power with high sensitivity and accuracy. Water absorbs CO₂ laser radiation readily within a very thin layer. Though water has large thermal capacity, due to short absorption length, it could vapourize at high laser powers. In order to circumvent this problem, this power meter has a centre cone and a rapidly spinning water film as the calorimetric medium. The unique feature in this development is the centre cone, which diverges the beam and reduces the power density thus reduces the possibility of vapourization. This minimizes the error in measurements. Due to the rapidly moving fluid film, it exhibits fast response at low as well as high power levels.     

Polarization switching properties of spray deposited CsNO3: PVA composite films

The ferroelectric and switching properties of spray deposited cesium nitrate: poly (vinyl alcohol) composite films at different substrate temperatures (T _s ) have been studied. The optimum value of remanent polarization was obtained in the film deposited at T _s =200°C, which may be due to larger structural distortion (c/a ratio) and less porosity as revealed by x-ray diffraction and field emission scanning electron microscope (FESEM) analysis. The switching current transients have been analyzed by nucleation limited switching model (NLS) with the Lorentzian distribution function. This model gives excellent agreement with the experimental polarization current throughout the whole time range. The switching parameters were determined in the composite films deposited at different T _s and found to be optimum at T _s =200°C. The effect of pulse amplitude on the domain switching properties has also been studied and analyzed. The peak value of polarization current exhibits an exponential dependence on the external applied field.