Structural and dielectric properties of Bi modified PLZT ceramics

Polycrystalline samples of bismuth (Bi) doped lead lanthanum zirconate titanate (PLZT) with the general formula Pb_0.9(La_1−zBi_z)_0.1(Zr_0.65Ti_0.35)_0.975O₃, where [z=0.0, 0.3, 0.5, 0.7] near the morphotropic phase boundary (MPB) has been synthesized by a solid solution mixing technique. Some aspect of crystal structure of the compound at room temperature was studied using X-ray diffraction (XRD) technique. Detailed studies of dielectric constant (ε) and dielectric loss () obtained both as a function of frequency (100 Hz-100 kHz) at room temperature (RT) and temperature (RT-600 K) at 10 kHz suggest that compounds undergo ferroelectric-paraelectric phase transition of diffuse type. Both ac and dc conductivity have been studied over a wide range of temperature. The activation energy (E_a) of the samples was calculated from the plot of ac conductivity vs. inverse of absolute temperature. The temperature variation of resistivity shows that the compounds have negative temperature coefficient of resistance (NTCR).     

Near-threshold production of the multistrange Xi- hyperon

The yield for the multistrange Xi(-) hyperon has been measured in 6A GeV Au+Au collisions via reconstruction of its decay products pi(-) and Lambda, the latter also being reconstructed from its daughter tracks of pi(-) and p. The measurement is rather close to the threshold for Xi(-) production and therefore provides an important test of model predictions. The measured yield for Xi(-) and Lambda are compared for several centralities. In central collisions the Xi(-) yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multistrange hadron production approaches chemical equilibrium in high baryon density nuclear matter.     

Comparison of source images for protons, pi-'s, and lambda's in 6A GeV Au+Au collisions

Source images are extracted from two-particle correlations constructed from strange and nonstrange hadrons produced in 6A GeV Au+Au collisions. Very different source images result from pp vs p Lambda vs pi(-)pi(-) correlations. Scaling by transverse mass can describe the apparent source size ratio for p/pi(-) but not for Lambda/pi(-) or Lambda/p. These observations suggest important differences in the space-time emission histories for protons, pions, and neutral strange baryons produced in the same events.     

Lasing without population inversion from autoionizing states

Summary We show that in case of (1+1)-photon resonant absorption to and emission from an autoionizing state embedded into a continuum, the gain profile can be modified significantly in the presence of a parallel near-resonant channel leading to another autoionizing state embedded into a different continuum. Due to the coupling between two channels via cross-photoionization (i.e. ionization from the intermediate state of one channel to the continuum of another channel) the gain can be obtained around three different frequencies leading to lasing without population inversion. Results of parametric calculations are presented.     

(T1u+T1g)⊗(hg+τ1u)vibronic interaction and superconductivity in C 60 n− fullerides

The closeness of low-lying T_1u and T_1g levels of C ₆₀ ⁻ could enable their mixing under an odd parity vibration of (T_{1 u} + T_{1 g} ⊗ (h_g + τ_{1 u})type. In addition, the two levels are susceptible to Jahn-Teller interaction due to five-fold degenerate h_g vibrations. This complex problem of (T_1u+T_1g)⊗(h_g+τ_1u) vibronic interaction is transformed to a form similar to T_2g ⊗ (ε_g + τ_2g) vibronic problem of octahedral symmetry. The problem is analysed in an infinite coupling model and compared with the experimental spectroscopic results for the C ₆₀ ⁻ radical. The resulting parameters are used to calculate the pair-binding energy and superconducting transition temperature in C ₆₀ ⁿ⁻ fullerides. Vibronic mixing with the T_1g level is found to be responsible for maximising the pair-binding energy at the doping level n=3. It is also found to be an important source of T_c enhancement.     

Optogalvanic detection of NaNe molecule

Summary The formation of NaNe molecule has been detected in a hollow cathode lamp containing traces of sodium and neon using the optogalvanic technique. Two broad continuum peaks have been observed in the structure. They have been analysed to result due to transitions {Na(3s) + Ne(2p ⁶)}²Σ¹→ →{Na*(3p) + Ne(2p ⁶)}²Π,²Σ and {Na*(3p) + Ne(2p ⁶)}²Π,²Σ→{Na*(5s) + Ne(2p ⁶)}²Σ¹. A third peak in between these is probably due to a two-photon transition from 3s→5s of Na in NaNe. The authors of this paper have agreed to not receive the proofs for correction.     

Thermogravimetric analysis of some higher carboxylate derivatives of chromium(III)

Theoretical considerations of the effects of electric fields on the solid-state reactions involved in the formation of Portland cement clinker suggest that fields should assist both the generation of active oxides from the raw components of the mix and their combination to form the various clinker phases. Consideration of the semiconductor properties of calcium oxide suggests that the formation of this compound from the calcium carbonate starting material could be enhanced under some conditions by field-dependent electrodesorption of CO₂ from the particle surfaces, and the dehydroxylation of kaolinite to form a reactive aluminosilicate is also known to be field-assisted. The observed effects of electric fields on the interoxide reactions involved in clinker formation can be explained in terms of a simple model which takes into account the relative diffusivities and electrical mobilities of the various ions, the oxygen packing of the matrices through which diffusion occurs, and the relative orientations of the reactant grains with respect to the field direction.