Isotopic replacement in ionic systems: the 4He2+ + 3He -> 3He4He+ + 4He reaction

Full quantum dynamics calculations have been carried out for the ionic reaction 4He2+ + 3He and state-to-state reactive probabilities have been obtained using both a time-dependent (TD) and a time-independent (TI) approach. An accurate ab-initio potential energy surface has been employed for the present quantum dynamics and the two sets of results are shown to be in agreement with each other. The results for zero total angular momentum suggest a marked presence of atom exchange (isotopic replacement) reaction with probabilities as high as 60%. The reaction probabilities are only weakly dependent on the initial vibrational state of the reactants while they are slightly more sensitive to the degree of rotational excitation. A brief discussion of the results for selected higher total angular momentum values is also presented, while the l-shifting approximation [1] has been used to provide estimates of the total reaction rates for the title process. Such rates are found to be large enough to possibly become experimentally accessible

Density Functional Theory for the Photoionization Dynamics of Uracil

Photoionization dynamics of the RNA base Uracil is studied in the framework of Density Functional Theory (DFT). The photoionization calculations take advantage of a newly developed parallel version of a multicentric approach to the calculation of the electronic continuum spectrum which uses a set of B-spline radial basis functions and a Kohn-Sham density functional hamiltonian. Both valence and core ionizations are considered. Scattering resonances in selected single-particle ionization channels are classified by the symmetry of the resonant state and the peak energy position in the photoelectron kinetic energy scale; the present results highlight once more the site specificity of core ionization processes. We further suggest that the resonant structures previously characterized in low-energy electron collision experiments are partly shifted below threshold by the photoionization processes. A critical evaluation of the theoretical results providing a guide for future experimental work on similar biosystems

First-principles study of electron transport through C20C_{20} cages

Electron transport properties of C$_{20}$ molecules suspended between gold electrodes are investigated using first-principles calculations. Our study reveals that the conductances are quite sensitive to the number of C$_{20}$ molecules between electrodes: the conductances of C$_{20}$ monomers are near 1 G$_{0}$, while those of dimers are markedly smaller, since incident electrons easily pass the C$_{20}$ molecules and are predominantly scattered at the C$_{20}$-C$_{20}$ junctions. Moreover, we find both channel currents locally circulating the outermost carbon atoms.Comment: 8 pages and 3 figure

Correction of hypovitaminosis D improved global longitudinal strain earlier than left ventricular ejection fraction in cardiovascular older adults after orthopaedic surgery

Background Cardiovascular diseases and insufficient levels of vitamin D are risk factors for adverse surgical outcomes, and they are both commonly present among older adults undergoing orthopaedic surgery. Giving the cardiovascular effects of vitamin D, pre-operative diagnosis of hypovitaminosis D would be a valuable step for the implementation of supplementation protocols. We investigated if the normalization of serum 25 [OH] D could ameliorate cardiac performance of older adults suffering from cardiovascular diseases. Methods We enrolled 47 older adults scheduled for major orthopaedic surgery and suffering from hypovitaminosis D. Patients underwent 6-months calcifediol supplementation with a starting dose at first post-operative day of 50 \u3bcg/die in liquid preparation. Down-Titration to 20 \u3bcg/die at 3-months assessment was planned. Cardiac performance was evaluated by measuring left ventricular ejection fraction (LVEF) and global longitudinal strain (GLS) during pre-operative assessments and at 1-month, 3-months, 6-months follow-ups. Results Six months of calcifediol supplementation were associated with a significant improvement of both LVEF (+ 3.94%; 95% CI: -4.0789 to -0.8232; P < 0.01) and GLS (+ 18.56%; Z = -5.895; P < 0.0001). Conclusions Calcifediol supplementation normalized serum 25 [OH] D concentration after 1-month treatment. GLS offered better insights into myocardial contractile amelioration than LVEF, thus being useful for detecting earlier subclinical changes that may anticipate hemodynamic modifications

Energies and density distributions of (4He)N clusters doped with Br2(X): A Hartree-like approach

10 págs.; 8 figs.; 2 tabs.; PACS numberssd: 36.40.Mr, 31.15.Ar, 33.20.Fb, 33.80.GjEnergies and density distributions of the helium atoms in Br2(X) - (4He)N clusters are calculated using a quantum >Hartree-like> approach in which the dopant molecule and the 4He atoms play the role of the nuclei and electrons, respectively, of the original Hartree formulation. A detailed generalization of the methodology is presented. The validity of this treatment is assessed by comparing energies and density distributions for N =2 up to N=18 with those obtained by performing quantum diffusion Monte Carlo (DMC) calculations. The present Hartree model shows good agreement with the DMC calculations, the main difference being that the DMC density distributions of the He atoms are more isotropic than those generated via the model. The treatment is extended to larger (up to N=60) clusters and saturation effects are analyzed and discussed. ©2005 The American Physical Society.This work has been partially supported by the Italy-Spain Integrated Action Programme HI02-74, DGICYT Spanish Grant No. BFM2001-2179, European TMR network Grant No. HPRN-CT-1999-0005, and Cineca sGrant No. HPRI-CT- 1999-00048d. F.A.G. and C.DiP. thank the Research Committee of the University of Rome La Sapienza. M.P.deL.-C. was supported by the “Ramón and Cajal” Programme and J.J. by the Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, U.S. Department of Energy under Contract No. W-31-109-Eng-38.Peer Reviewe

Ab initio van der Waals interactions in simulations of water alter structure from mainly tetrahedral to high-density-like

The structure of liquid water at ambient conditions is studied in ab initio molecular dynamics simulations using van der Waals (vdW) density-functional theory, i.e. using the new exchange-correlation functionals optPBE-vdW and vdW-DF2. Inclusion of the more isotropic vdW interactions counteracts highly directional hydrogen-bonds, which are enhanced by standard functionals. This brings about a softening of the microscopic structure of water, as seen from the broadening of angular distribution functions and, in particular, from the much lower and broader first peak in the oxygen-oxygen pair-correlation function (PCF), indicating loss of structure in the outer solvation shells. In combination with softer non-local correlation terms, as in the new parameterization of vdW-DF, inclusion of vdW interactions is shown to shift the balance of resulting structures from open tetrahedral to more close-packed. The resulting O-O PCF shows some resemblance with experiment for high-density water (A. K. Soper and M. A. Ricci, Phys. Rev. Lett., 84:2881, 2000), but not directly with experiment for ambient water. However, an O-O PCF consisting of a linear combination of 70% from vdW-DF2 and 30% from experiment on low-density liquid water reproduces near-quantitatively the experimental O-O PCF for ambient water, indicating consistency with a two-liquid model with fluctuations between high- and low-density regions

Double strand breaks in DNA resulting from double-electron-emission events

A mechanism of double strand breaking (DSB) in DNA due to the action of two electrons is considered. These are the electrons produced in the vicinity of DNA molecules due to ionization of water molecules with a consecutive emission of two electrons, making such a mechanism possible. This effect qualitatively solves a puzzle of large yields of DSBs following irradiation of DNA molecules. The transport of secondary electrons, including the additional electrons, is studied in relation to the assessment of radiation damage due to incident ions. This work is a stage in the inclusion of Auger mechanism and like effects into the multiscale approach to ion-beam cancer therapy.Comment: 4 pages, 3 figure