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.     

Face-to-face arene-arene binding energies: dominated by dispersion but predicted by electrostatic and dispersion/polarizability substituent constants

Parallel face-to-face arene-arene complexes between benzene and substituted benzenes have been investigated at the MP2(full)/6-311G** and M05-2X/6-311G** levels of theory. A reasonably good correlation was found between the binding energies and the ∑|σ(m)| values of the substituted aromatics. It is proposed that a substituent |σ(m)| value informs on both the aromatic substituent dispersion/polarizability and the effect the substituent has on the aromatic electrostatics. Supporting this hypothesis, a combination of electrostatic (∑σ(m)) and dispersion/polarizability (∑M(r)) substituent constant terms gives an excellent, and statistically significant, correlation with the benzene-substituted benzene binding energy. Symmetry adapted perturbation theory energy decomposition calculations show the dominant attractive force is dispersion; however, the sum of all nonelectrostatic forces is essentially a constant, while the electrostatic component varies significantly. This explains the importance of including an electrostatic term when predicting benzene-substituted benzene binding energies.     

Activation of the pre-supplementary motor area but not inferior prefrontal cortex in association with short stop signal reaction time – an intra-subject analysis

Background  

Our previous work described the neural processes of motor response inhibition during a stop signal task (SST). Employing the race model, we computed the stop signal reaction time (SSRT) to index individuals' ability in inhibitory control. The pre-supplementary motor area (preSMA), which shows greater activity in individuals with short as compared to those with long SSRT, plays a role in mediating response inhibition. In contrast, the right inferior prefrontal cortex (rIFC) showed greater activity during stop success as compared to stop error. Here we further pursued this functional differentiation of preSMA and rIFC on the basis of an intra-subject approach.     

Predicting DNA–intercalator binding: the development of an arene–arene stacking parameter from SAPT analysis of benzene‐substituted benzene complexes

A series of substituted naphthalimides were synthesized and intercalated into the DNA sequence d(GCGCGCGC)₂, and an experimental ΔT_m value was obtained. Two‐parameter QSAR analyses were performed to generate a theoretical ΔT_m value. Although by no means exhaustive in terms of parameter selection, the correlations did not yield statistics that indicated the models met the threshold for significance at the 95% confidence level. Rather than continue with an exhaustive search of all possible QSAR parameters, a one‐parameter QSAR analysis was performed utilizing a novel arene–arene stacking parameter, designated Π^π, developed from Symmetry‐Adapted Perturbation Theory (SAPT) energy decomposition studies of calculated benzene‐substituted benzene dimer binding energies. The QSAR analysis using the Π^π stacking parameter yielded statistics suggesting the model was significant at the 95% confidence level. The approach of developing a novel QSAR parameter via SAPT calculations, rather than exhaustively searching all traditional QSAR parameters, is presented both as a new approach for QSAR studies and as a unique application of SAPT. Copyright © 2013 John Wiley & Sons, Ltd.