Topological and leading particle cross sections for 147 GeV/c π− -p interactions

Results are reported based on a study of π^?p interactions at 147 GeV/c in the FERMILAB 30-inch Proportional Wire Hybrid Bubble Chamber System. We have measured the topological cross sections and separated two-prong elastic and inelastic channels. In addition, we have extracted leading particle cross sections using the increased momentum resolution of the downstream proportional wire chambers. We have compared our results with experiments and predictions of a simple fragmentation hyphothesis.     

Cross sections and charged multiplicity distributions for π−p and K−p interactions at 147 GeV/c

The results presented in this paper were obtained from a 105 000 frame exposure of the FNAL Hybrid Proportional Wire Chamber-30 inch Bubble Chamber System, in a tagged beam of 147 GeV/c negative particles. Elastic, total and topological cross sections were obtained for both π^?p and K^?p interactions. Comparisons with other data, taken with various beam particles over large momentum intervals, show good agreement with KNO scaling, and similarity in the scaling behavior of σ_n for the different beam particles.     

Steric and electronic contributions to conformational effects on chemical shifts of acyclic alcohols

Our calculations on bi- and polycyclic alcohols reveal that the Mulliken charge distribution and chemical shift patterns due to hyperconjugation of lone pairs on oxygen with neighboring groups break down or are attenuated for certain spatial relationships of the hydroxyl group. Since in strained ring systems other effects on these parameters may be present, we applied a similar analysis to acyclic alcohols. Calculations at the B3LYP/6-31G^* level on conformers of methanol, ethanol, 1- and 2-propanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 2-butanol, 2-methyl-2-butanol, 1- 2- and 3-pentanol and 2-methyl-3-pentanol, where hyperconjugation may be present, reveal steric effects as modifiers of hyperconjugative patterns affecting carbon-13 chemical shifts in such alcohols. Contrary to what is observed in bi- and policyclic systems, where electrostatic effects interfere with effects due to hyperconjugation, these steric effects may be the main cause for the attenuation of deshielding of nuclei that are subject to hyperconjugation. Electrostatic effects are also present but they do not interfere with hyperconjugation by lone pairs. Conformational effects fall off sharply after the third carbon in the chain.     

Towards an insight on the photoluminescence of disordered CaWO4 from a joint experimental and theoretical analysis

A joint experimental and theoretical study has been carried out to rationalize for the first time the photoluminescence (PL) properties of disordered CaWO₄ (CWO) thin films. From the experimental side, thin films of CWO have been synthesized following a soft chemical processing, their structure has been confirmed by X-ray diffraction data and corresponding PL properties have been measured using the 488 nm line of an argon ion laser. Although we observe PL at room temperature for the crystalline thin films, the structurally disordered samples present much more intense emission. From the theoretical side, first principles quantum mechanical calculations, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline (CWO-c) and asymmetric (CWO-a) periodic model. Electronic properties are analyzed in the light of the experimental results and their relevance in relation to the PL behavior of CWO is discussed. The symmetry breaking process on going from CWO-c to CWO-a creates localized electronic levels above the valence band and a negative charge transfer process takes place from threefold, WO₃, to fourfold, WO₄, tungsten coordinations. The correlation of both effects seems to be responsible for the PL of amorphous CWO.     

Temperature dependence of the ESR linewidth in KFeS2

The ESR linewidth in KFeS₂ has been measured in the range 80–340 K. The linewidth is found to decrease steadily as the temperature is increased, without any discontinuity or singularity at the transition temperature T_N=245 K. In the paramagnetic state, the region of enhanced linewidth extends further above T_N than for two-and three-dimensional compounds such as K₂MnF₄ and MnF₂.     

Magnesium in biological samples by spectrophotometric measurement of the 8-quinolinolate extract

Conditions for the simple, rapid and sensitive determination of magnesium in biological samples have been determined. Commercially available solvents and reagents are used without further purification. Magnesium is separated and converted to a form which may be measured spectrophotometrically in a single extraction as the 8-quinolinolate in 1,1,2-trichloroethane. The extraction of other 8-quinolinolates is prevented by the addition of tartrate and cyanide to the buffer solution. Adequate sensitivity is obtained (absorbance of 0.4 for 20 μg of magnesium), and even greater sensitivity is possible by reducing the volumes of both aqueous and organic phases.