Effects of surface crossing in chemical reactions - The H3/plus/ system

Potential energy surfaces for singlet states of H3/plus

A crossed beam study of the reaction N/plus/ plus O2 yields NO/plus/ plus O

Studying reaction N/plus/ plus O2 yields NO/plus/ plus O as function of collision energy using crossed beam

Nonadiabatic Dynamics in Open Quantum-Classical Systems: Forward-Backward Trajectory Solution

A new approximate solution to the quantum-classical Liouville equation is derived starting from the formal solution of this equation in forward-backward form. The time evolution of a mixed quantum-classical system described by this equation is obtained in a coherent state basis using the mapping representation, which expresses $N$ quantum degrees of freedom in a 2N-dimensional phase space. The solution yields a simple non-Hamiltonian dynamics in which a set of $N$ coherent state coordinates evolve in forward and backward trajectories while the bath coordinates evolve under the influence of the mean potential that depends on these forward and backward trajectories. It is shown that the solution satisfies the differential form of the quantum-classical Liouville equation exactly. Relations to other mixed quantum-classical and semi-classical schemes are discussed.Comment: 28 pages, 1 figur

Possible Local Spiral Counterparts to Compact Blue Galaxies at Intermediate Redshift

We identify nearby disk galaxies with optical structural parameters similar to those of intermediate-redshift compact blue galaxies. By comparing HI and optical emission-line widths, we show that the optical widths substantially underestimate the true kinematic widths of the local galaxies. By analogy, optical emission-line widths may underrepresent the masses of intermediate-z compact objects. For the nearby galaxies, the compact blue morphology is the result of tidally-triggered central star formation: we argue that interactions and minor mergers may cause apparently compact morphology at higher redshift.Comment: 5 pages, uses emulateapj5 and psfig. To appear in ApJ

Self-Regulated Growth of Supermassive Black Holes in Galaxies as the Origin of the Optical and X-ray Luminosity Functions of Quasars

We postulate that supermassive black-holes grow in the centers of galaxies until they unbind the galactic gas that feeds them. We show that the corresponding self-regulation condition yields a correlation between black-hole mass (Mbh) and galaxy velocity dispersion (sigma) as inferred in the local universe, and recovers the observed optical and X-ray luminosity functions of quasars at redshifts up to z~6 based on the hierarchical evolution of galaxy halos in a Lambda-CDM cosmology. With only one free parameter and a simple algorithm, our model yields the observed evolution in the number density of optically bright or X-ray faint quasars between 2<z<6 across 3 orders of magnitude in bolometric luminosity and 3 orders of magnitude in comoving density per logarithm of luminosity. The self-regulation condition identifies the dynamical time of galactic disks during the epoch of peak quasar activity (z~2.5) as the origin of the inferred characteristic quasar lifetime of ~10 million years. Since the lifetime becomes comparable to the Salpeter e-folding time at this epoch, the model also implies that the Mbh-sigma relation is a product of feedback regulated accretion during the peak of quasar activity. The mass-density in black-holes accreted by that time is consistent with the local black-hole mass density of ~(0.8-6.3) times 10^5 solar masses per cubic Mpc, which we have computed by combining the Mbh-sigma relation with the measured velocity dispersion function of SDSS galaxies (Sheth et al.~2003). Applying a similar self-regulation principle to supernova-driven winds from starbursts, we find that the ratio between the black hole mass and the stellar mass of galactic spheroids increases with redshift as (1+z)^1.5 although the Mbh-sigma relation is redshift-independent.Comment: 10 pages, 5 figures, submitted to Ap

Ehrenfest dynamics is purity non-preserving: a necessary ingredient for decoherence

We discuss the evolution of purity in mixed quantum/classical approaches to electronic nonadiabatic dynamics in the context of the Ehrenfest model. As it is impossible to exactly determine initial conditions for a realistic system, we choose to work in the statistical Ehrenfest formalism that we introduced in Ref. 1. From it, we develop a new framework to determine exactly the change in the purity of the quantum subsystem along the evolution of a statistical Ehrenfest system. In a simple case, we verify how and to which extent Ehrenfest statistical dynamics makes a system with more than one classical trajectory and an initial quantum pure state become a quantum mixed one. We prove this numerically showing how the evolution of purity depends on time, on the dimension of the quantum state space $D$, and on the number of classical trajectories $N$ of the initial distribution. The results in this work open new perspectives for studying decoherence with Ehrenfest dynamics.Comment: Revtex 4-1, 14 pages, 2 figures. Final published versio

Coherent dynamics of photoinduced nucleation processes

We study the dynamics of initial nucleation processes of photoinduced structural change of molecular crystals. In order to describe the nonadiabatic transition in each molecule, we employ a model of localized electrons coupled with a fully quantized phonon mode, and the time-dependent Schr\"odinger equation for the model is numerically solved. We found a minimal model to describe the nucleation induced by injection of an excited state of a single molecule in which multiple types of intermolecular interactions are required. In this model coherently driven molecular distortion plays an important role in the successive conversion of electronic states which leads to photoinduced cooperative phenomena.Comment: 14 pages, 5 figure

The Principal Axis of the Virgo Cluster

Using accurate distances to individual Virgo cluster galaxies obtained by the method of Surface Brightness Fluctuations, we show that Virgo's brightest ellipticals have a remarkably collinear arrangement in three dimensions. This axis, which is inclined by 10 to 15 degrees from the line of sight, can be traced to even larger scales where it appears to join a filamentary bridge of galaxies connecting Virgo to the rich cluster Abell 1367. The orientations of individual Virgo ellipticals also show some tendency to be aligned with the cluster axis, as does the jet of the supergiant elliptical M87. These results suggest that the formation of the Virgo cluster, and its brightest member galaxies, have been driven by infall of material along the Virgo-A1367 filament.Comment: 8 pages, 4 figures, accepted for publication in ApJ Letter

Risk and protective factors for meningococcal disease in adolescents: matched cohort study

Objective: To examine biological and social risk factors for meningococcal disease in adolescents. Design: Prospective, population based, matched cohort study with controls matched for age and sex in 1:1 matching. Controls were sought from the general practitioner. Setting: Six contiguous regions of England, which represent some 65% of the country’s population. Participants: 15-19 year olds with meningococcal disease recruited at hospital admission in six regions (representing 65% of the population of England) from January 1999 to June 2000, and their matched controls. Methods: Blood samples and pernasal and throat swabs were taken from case patients at admission to hospital and from cases and matched controls at interview. Data on potential risk factors were gathered by confidential interview. Data were analysed by using univariate and multivariate conditional logistic regression. Results: 144 case control pairs were recruited (74 male (51%); median age 17.6). 114 cases (79%) were confirmed microbiologically. Significant independent risk factors for meningococcal disease were history of preceding illness (matched odds ratio 2.9, 95% confidence interval 1.4 to 5.9), intimate kissing with multiple partners (3.7, 1.7 to 8.1), being a university student (3.4, 1.2 to 10) and preterm birth (3.7, 1.0 to 13.5). Religious observance (0.09, 0.02 to 0.6) and meningococcal vaccination (0.12, 0.04 to 0.4) were associated with protection. Conclusions: Activities and events increasing risk for meningococcal disease in adolescence are different from in childhood. Students are at higher risk. Altering personal behaviours could moderate the risk. However, the development of further effective meningococcal vaccines remains a key public health priority

Orientation isotope effect in ion–molecule reactions

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/67/10/10.1063/1.434632.A simple kinematicmodel is proposed to account for the kinetic isotope effect (KIE) upon the reactions of simple ions X+ with HD. This model is based upon (1) the fact that the displacement of the center of polarizability from the center of mass in the HD molecule will affect the alignment of the reactants, (2) the fact that, for many ions X+, reaction must occur by a surface crossing mechanism, and (3) the assumption that the ratio XH+/(XH++XD+) equals the fraction of intimate collisions in which the H end of HD is oriented towards the ion at the moment the reactants pass over the centrifugal barrier in the effective radial potential (or cross over to the X–HD+ surface if the crossing occurs before the centrifugal barrier is reached). Use of the ion–induced dipole potential for the reactants permits the derivation of an analytic expression for the KIE. With no adjustable parameters, this model accounts quantitatively for the very different KIE’s observed in the reactions of Ar+ and Kr+ with HD at low collision energies