RESUMO

The photochemical activation of Al atoms in cryogenic matrices to induce their reaction with methane has been experimentally studied before. Here, a theoretical study of the nonadiabatic transition probabilities for the ground ((2)P:3s(2)3p(1)) and the lowest excited states ((2)S:3s(2)4s(1) and (2)D:3s(2)3d(1)) of an aluminum atom interacting with a methane molecule (CH(4)) was carried out through ab initio Hartree-Fock self-consistent field calculations. This was followed by a multiconfigurational study of the correlation energy obtained by extensive variational and perturbational configuration interaction analyses using the CIPSI program. The (2)D state is readily inserted into a C-H bond, this being a prelude to a sequence of avoided crossings with the initially repulsive (to CH(4)) lower lying states (2)P and (2)S. We then use a direct extension of the Landau-Zener theory to obtain transition probabilities at each avoided crossing, allowing the formation of an HAlCH(3) intermediate that eventually leads to the final pair of products H+AlCH(3) and HAl+CH(3).

RESUMO

Transition probabilities on the interaction of the ground and the lowest excited states of gold Au ((2)S:5d(10)6s(1), (2)D:5d(9)6s(2), and (2)P:5d(10)6p(1)) with silane (SiH(4)) are studied through ab initio Hartree-Fock self-consistent field calculations, where the atom's core is represented by relativistic effective core potentials. These calculations are followed by a multiconfigurational self-consistent field study. The correlation energy is accounted for through extensive variational and perturbative second order multireference Moller-Plesset configuration interaction analysis of selected perturbations obtained by iterative process calculations using the CIPSI program package. It is found that the Au atom in the ((2)P:5d(10)6p(1)) state inserts in the Si-H bond. In this interaction its corresponding D (2)A(') potential energy surface is initially attractive and only becomes repulsive after encountering an avoided crossing with the initially repulsive C (2)A(') surface linked to the Au((2)D:5d(9)6s(2))-SiH(4) fragments. The A, B, and C (2)A(') curves derived from the Au((2)D:5d(9)6s(2)) atom interaction with silane are initially repulsive, each one of them showing two avoided crossings, while the A (2)A(') curve goes sharply downwards until it meets the X (2)A(') curve interacting adiabatically, which is linked with the Au((2)S:5d(10)6s(1))-SiH(4) moieties. The A (2)A(') curve becomes repulsive after the avoided crossing with the X (2)A('), curve. The lowest-lying X (2)A(') potential leads to the HAuSiH(3) X (2)A(') intermediate molecule. This intermediate molecule, diabatically correlated with the Au((2)P:5d(10)6p(1))+SiH(4) system which lies 3.34 kcal/mol above the ground state reactants, has been carefully characterized as have the dissociation channels leading to the AuH+SiH(3) and H+AuSiH(3) products. These products are reached from the HAuSiH(3) intermediate without any activation barrier. The Au-SiH(4) calculation results are successfully compared to experiment. Landau-Zener theory of avoided crossings is applied to these interactions considering the angle theta instead of the distance r as the reaction coordinate.

RESUMO

BACKGROUND: Thanks to defense mechanisms, organisms have had to adapt themselves to an adverse natural setting that causes acute and chronic stress. This adaptive response that tries to protect the cells against lethal insults uses its own defense systems. MATERIAL AND METHODS: Prospective, observational, descriptive pilot study with analytic components to determine the baseline preoperative TNF levels of 35 patients undergoing total knee arthroplasty due to gonarthrosis. Ten patients with a diagnosis of infected total knee arthroplasty were also included. In order to find differences and possible associations, the Mann-Whitney U test or the Fisher test was used to compare the variables between the non-infected group of patients and the group with the infection complication. RESULTS: We found a statistically significant difference; higher levels of fibrinogen, erythrocyte sedimentation rate, C-reactive protein, TNF-alpha and temperature were found in the infected patients; temperature was not clinically relevant. CONCLUSIONS: In the absence of a diagnostic specificity, the combined determinations of acute phase reactants may be useful to detect the presence and intensity of the inflammatory and infectious processes.

Assuntos

RESUMO

The magnetic field dependent viscosity (magnetoviscosity) of dilute suspensions of magnetic tri-axial ellipsoidal particles suspended in a Newtonian fluid and under applied shear and magnetic fields was studied numerically. Brownian dynamics simulations were performed to compute the intrinsic magnetoviscosity of the suspension. Results are presented for the response of dilute suspensions of ellipsoidal particles to constant magnetic and shear flow fields. Suspensions of ellipsoidal particles show a significant effect of aspect ratio on the intrinsic magnetoviscosity of the suspension, and this effect is more pronounced as the aspect ratio becomes more extreme. The use of an effective rotational diffusion coefficient D(r,eff) collapses the normalized intrinsic magnetoviscosity of all suspensions to a master curve as a function of Péclet number with the Langevin parameter alpha=(mu(0)muH)/(k(B)T) as parameter, up to a critical value of alpha for which the results for suspensions of spherical particles deviate from those of suspensions of ellipsoids. This discrepancy is attributed to the action of the shear-torque on the ellipsoidal particles, which tends to orient these particles in the direction of maximum deformation of the simple shear flow, and which does not act on spherical particles.

RESUMO

The interactions of Ga((2)P:4s(2)4p(1), (2)S:4s(2)5s(1), and (2)P:4s(2)5p(1)) with SiH(4) are studied by means of Hartree-Fock self-consistent field (SCF) and multiconfigurational SCF followed by extensive variational and perturbational second-order multireference Møller-Plesset configuration by perturbation selected by iterative process calculations, using relativistic effective core potentials. The Ga atom in its (2)P(4s(2)5p(1)) state can spontaneously insert into the SiH(4). The Ga atom in its (2)S(4s(2)5s(1)) state is inserted into the SiH(4). In this interaction the 3 (2)A(') potential energy surface initially attractive becomes repulsive after meeting the 2 (2)A(') surface linked with the Ga((2)P:4s(2)4p(1))+SiH(4) fragments. The two (2)A(') curves (2 (2)A(') and X (2)A(')) derived from the interaction of Ga((2)P:4s(2)4p(1)) atom with silane molecule are initially repulsive. The 2 (2)A(') curve after an avoided crossing with the 3 (2)A(') curve goes down until it meets the X (2)A(') curve. The 2 (2)A(') curve becomes repulsive after the avoided crossing with the X (2)A(') curve. The X (2)A(') curve becomes attractive only after its avoided crossing with the 2 (2)A(') curve. The lowest-lying X (2)A(') potential leads to the HGaSiH(3)X (2)A(') intermediate molecule. This intermediate molecule, diabatically correlated with the Ga((2)S:4s(2)5s(1))+SiH(4) fragments, which lies 1.5 kcal/mol above the ground state reactants leads to the GaH+SiH(3) or H+GaSiH(3) products through the dissociation channels. These products are reached from the HGaSiH(3) intermediate without activation barriers. This work shows that the Ga atom at its first excited state in the presence of silane molecules in gas phase leads to the formation of SiH(3) radicals, H atoms, GaH hydrides, as well as gallium silicide molecules.

Assuntos

Assuntos

Assuntos

Assuntos