Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Shock compression of [001] single crystal silicon

Silicon is ubiquitous in our advanced technological society, yet our current understanding of change to its mechanical response at extreme pressures and strain-rates is far from complete. This is due to its brittleness, making recovery experiments difficult. High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon (using impedance-matched momentum traps) unveiled remarkable structural changes observed by transmission electron microscopy. As laser energy increases, corresponding to an increase in peak shock pressure, the following plastic responses are are observed: surface cleavage along {111} planes, dislocations and stacking faults; bands of amorphized material initially forming on crystallographic orientations consistent with dislocation slip; and coarse regions of amorphized material. Molecular dynamics simulations approach equivalent length and time scales to laser experiments and reveal the evolution of shock-induced partial dislocations and their crucial role in the preliminary stages of amorphization. Application of coupled hydrostatic and shear stresses produce amorphization below the hydrostatically determined critical melting pressure under dynamic shock compression.     

Design perspectives for creep-resistant magnesium die-casting alloys

The microstructure of die-cast magnesium alloys is highly non-uniform, which leads to a non-uniform distribution of the solidus/homologous temperature in the α(Mg) phase and a non-uniform distribution of deformation stresses and strains in the specimen during creep testing. Experimental observations suggest that significant creep deformation occurs in the α(Mg) phase in and adjacent to the eutectic regions while deformation in the primary α(Mg) dendrites is less pronounced. This article addresses the effect of the non-uniform as-cast microstructure on the creep resistance of die-cast magnesium alloys. Computational thermodynamic simulations were carried out to determine solute segregation, solidus temperature, and the corresponding homologous temperature distribution in the α(Mg) phase. Transmission electron microscopy studies provided evidence of non-uniform creep deformation in the creep-tested specimens. The results suggest that the creep resistance of magnesium alloys is determined by the weakest aggregate and/or phase in the alloy, viz., the α(Mg) phase in and adjacent to the eutectic regions. Microstructural design efforts that increase the homologous temperature or reinforce the eutectic α(Mg) phase hold significant promise for increasing the creep resistance of magnesium alloys.     

Exclusive 1,2-Reduction of Functionalised Conjugated Aldehydes with Sodium Triacetoxyborohydride

Functionalised α, β-unsaturated aldehydes were exclusively reduced to allylic alcohols with sodium-triacetoxyborohydride. Neither saturated alcohol nor saturated aldehydes are obtained. Conjugated ketones are not reduced.     

Syntheses of (4E,6E, 11Z)-4,6,11-hexadecatrienyl acetate and (4E, 6E, 11Z)-4,6,11-hexadecatrienal, female sex pheromones of eri-silkworm, Samia cynthia ricini (Lepidoptera: Saturniidae)

Syntheses of (4E,6E,11Z)-4,6,11-hexadecatrienyl acetate (1) and (4E,6E, 11Z)-4, 6,11-hexadecatrienal (2), female sex pheromones of eri-silkworm,Samia cynthia ricini have been achieved through Claisen ortho ester rearrangement of (6).     

Synthesis, characterization and kinetics of thermal decomposition of dimeric peroxycarbamates

Several dimeric peroxycarbamates (PCs) have been synthesized by using cycloaliphatic and aromatic diisocyanates with mono- and di-hydroperoxides. The reactions were carried out under suitable conditions either in the presence of T-12 (dibutyltin dilaurate) as catalyst or in the absence of this catalyst. The products were characterized by IR-spectra and molecular weight measurements from isocyanate and peroxygen analyses. Thermal decomposition kinetics of these PCs were studied in THF solution at 80, 90 and 100 °C; the reactions were found to be first-order and decomposition rate constants (k_d) were found. Activation energies and frequency factors for the decomposition were calculated. Activation energies were found to be in the range 67-121 kJ mol⁻¹ and frequency factors were of the order of 10¹¹-10¹⁵ s⁻¹ depending on the structure of the PC. The results for the PCs agree well with literature values.     

The Evolution of Bonding and Thermodynamic Properties of Boron‐Doped Small Carbon Clusters: An Ab Initio Study

Theoretical studies on BC_n (n=1–6) clusters are carried out using density functional theory, Møller–Plesset second‐order perturbation theory (MP2), coupled‐cluster calculations including up to triple excitations (CCSD(T)), and higher‐level approaches. All possible isomers depending on the positions of the boron atom are generated and the lowest‐energy isomers are determined for doublet and quartet electronic states. The three potential evolution paths of the clusters are determined as a function of their size. The energetic and electronic consequences for the increased size of structures differ significantly, which leads to representatives of the ground electronic state from different structural groups. The ab initio calculated thermal functions allow enhancements to the available atomization energies and improve the agreement between the calculated and experimental heat content.     

Spectroscopic Application of Realgar Using X-ray Fluorescence and Raman Spectroscopy

ABSTRACT

Samples of realgar ore were collected from the hydrothermal products of the Eocene volcanic material of the Erzurum region in Turkey. The prepared samples were analyzed by polarized energy dispersive X-ray fluorescence (PEDXRF) and by confocal Raman spectroscopy (CRS). The goal of this study was to figure out the chemical composition of realgar and its properties through PEDXRF and CRS and the optical characteristic features under the polarized microscope. The result of the XRF analysis shows the collected realgar samples are mainly composed of As, S, Si, and Mg in different proportions. The contents of As in realgar change from 36.55% through 31.49% to 5.97% in the analyzed samples. The strong peak of the realgar samples is at 352 cm^?1, and a weaker peak exists around 190 cm^?1. The accuracy and precision of the technique for chemical analysis is demonstrated by analyzing CRM 2126-81. The realgar ores were studied by use of CRS and polarized microscopy.