Solitary Elastic Waves and Elastic Wavelets

A new group of wavelets that have the form of solitary waves and are the solutions of the wave equations for dispersive media is proposed to call elastic wavelets. That this group includes well-known Mexican-hat wavelets is proved. It is proposed to use elastic wavelets to study local features of the profile evolution of a solitary wave in an elastic dispersive medium     

A New X-ray Medical-Image-Enhancement Method Based on Multiscale Shannon–Cosine Wavelet

Because of noise interference, improper exposure, and the over thickness of human tissues, the detailed information of DR (digital radiography) images can be masked, including unclear edges and reduced contrast. An image-enhancement algorithm based on wavelet multiscale decomposition is proposed to address the shortcomings of existing single-scale image-enhancement algorithms. The proposed algorithm is based on Shannon–Cosine wavelets by taking advantage of the interpolation, smoothness, tight support, and normalization properties. Next a multiscale interpolation wavelet operator is constructed to divide the image into several sub-images from high frequency to low frequency, and to perform different multi-scale wavelet transforms on the detailed image of each channel. So that the most subtle and diagnostically useful information in the image can be effectively enhanced. Moreover, the image will not be over-enhanced and combined with the high contrast sensitivity of the human eye’s visual system in smooth regions, different attenuation coefficients are used for different regions to achieve the purpose of suppressing noise while enhancing details. The results obtained by some simulations show that this method can effectively eliminate the noise in the DR image, and the enhanced DR image detail information is clearer than before while having high effectiveness and robustness.     

Molecular MC SCF calculations by direct minimization

Calculations on the H₂CO ground state and excited states at the equilibrium planar geometry, using the single excitation MC SCF method, are described for two basis sets. The results obtained by a full calculation including all the electrons are compared with those obtained by a pseudopotential version of the method including only the valence electrons. The results agree quite well both with each other and with the observed values.     

Structural and electronic properties of the [FeFe] hydrogenase H-cluster in different redox and protonation states. A DFT investigation

The molecular and electronic structure of the Fe 6S 6 H-cluster of [FeFe] hydrogenase in relevant redox and protonation states have been investigated by DFT. The calculations have been carried out according to the broken symmetry approach and considering different environmental conditions. The large negative charge of the H-cluster leads, in a vacuum, to structures different from those observed experimentally in the protein. A better agreement with experimental data is observed for solvated complexes, suggesting that the protein environment could buffer the large negative charge of the H-cluster. The comparison of Fe 6S 6 and Fe 2S 2 DFT models shows that the presence of the Fe 4S 4 moiety does not affect appreciably the geometry of the [2Fe] H cluster. In particular, the Fe 4S 4 cluster alone cannot be invoked to explain the stabilization of the mu-CO forms observed in the enzyme (relative to all-terminal CO species). As for protonation of the hydrogen cluster, it turned out that mu-H species are always more stable than terminal hydride isomers, leading to the conclusion that specific interactions of the H-cluster with the environment, not considered in our calculations, would be necessary to reverse the stability order of mu-H and terminal hydrides. Otherwise, protonation of the metal center and H 2 evolution in the enzyme are predicted to be kinetically controlled processes. Finally, subtle modifications in the H-cluster environment can change the relative stability of key frontier orbitals, triggering electron transfer between the Fe 4S 4 and the Fe 2S 2 moieties forming the H-cluster.     

Structure and energetics of Fe2(CO)8 singlet and triplet electronic states

The singlet and triplet state potential energy surfaces (PES) of Fe2(CO)8 are explored by means of density functional theory (DFT) techniques. The two PES have different global mimima: the dibriged C(2v) isomer for the singlet and the unbridged D(2d) isomer for the triplet. The sign of the energy gap between singlet and triplet global minima depends on the type of adopted DFT functional: hybrid functionals predict the triplet is more stable than the singlet, but the opposite applies to generalized gradient approximated (GGA) functionals. The analysis of the computed CO stretching frequencies demonstrates that the experimental data for the unbridged form is compatible also with the unbridged triplet D(2d) isomer. Starting from these two facts, the electronic structure of unbridged D(2d) Fe2(CO)8 is discussed herein. Single-point energy computations at the coupled-cluster single and double (CCSD) level favor the D(2d) triplet state.     

A photocatalytic water splitting device for separate hydrogen and oxygen evolution

A two-compartment Plexiglas cell has been set up and tested for separate hydrogen and oxygen production from photocatalytic water splitting on a thin TiO2 layer deposited by magnetron sputtering on a flat Ti electrode inserted between the two cell compartments.     

DFT characterization of key intermediates in thiols oxidation catalyzed by amavadin

Amavadin is an unusual octa-coordinated V(IV) complex isolated from Amanita muscaria mushrooms. The outer-sphere catalytic properties of such a complex toward several oxidation reactions are well known. Nevertheless, a remarkable example exists, in which the V(V) (d(0)) oxidized form of amavadin is able to electro-catalyze the oxidation of some thiols to the corresponding disulfides through an inner-sphere mechanism (Guedes da Silva et al. J. Am. Chem. Soc.1996, 118, 7568-7573.) The reaction mechanism implies the formation of an amavadin-substrate intermediate, whose half-life is about 0.3 s. By means of Density Functional Theory (DFT) computations and Quantum Theory of Atoms in Molecules (QTAIM) analysis of the electron density, we have first characterized the stereoelectronic features of the V(IV) (inactive) and V(V) (active) states of amavadin. Then, the formation of the V(V) complex with methyl mercaptoacetate (MMA), which has been chosen as a prototypical substrate, has been characterized both thermodynamically and kinetically. DFT results reveal that protonation of V(V) amavadin at a carboxylate oxygen not directly involved in the V coordination, favors MMA binding into the first coordination sphere of vanadium, by substitution of the amavadin carboxylate oxygen with that of the substrate and formation of an S-HO hydrogen bond interaction. The latter interaction can promote SH deprotonation and binding of the thiolate group to vanadium. The kinetic and thermodynamic feasibility of the V(V)-MMA intermediates formation is in agreement, along with electrochemical experimental data, also with the biological role exerted by amavadin. Finally, the presence of an ester functional group as an essential requisite for MMA oxidation has been rationalized.     

Cubic Nonlinearity in Elastic Materials: Theoretical Prediction and Computer Modelling of New Wave Effects

Our object of interest is nonlinear interaction of waves in elastic materials. The new model of a material is proposed that takes into account the mechanism of simultaneous quadratic and cubic nonlinear deformations. Introduction of cubic nonlinearity into the model makes the general wave picture more complicated and creates new possibilities for the wave analysis. We present four possibilities for the evolution of profiles of plane harmonic waves. It is noted that quadratic and cubic nonlinearities emerge first of all in the second and third harmonics generation, respectively. Further, we discuss the results of computer modelling of the wave profile evolution. The influence of the progress of second and third harmonics on the wave profile evolution is studied separately. We study separately how second and third harmonics influence the evolution of the wave profile. We also investigate how the progress of harmonics depends on the initial frequency and amplitude. We find two distinct schemes of the evolution progress: the scheme (in) with four stages for the second harmonics and the scheme with three stages for the third harmonics. As a result the influence of both harmonics could be observed simultaneously, and such a case is demonstrated in the paper. Nevertheless this phenomenon is not necessarily present in every material which explains the absence of experimental observations of the third harmonics by this time.