K-space Prony’s method for generating the basis functions of multi-Gaussian beam models

The expansion coefficients of a multi-Gaussian ultrasonic beam model are obtained by a new approach that applies Prony´s method in a K-space domain. This method allows the fitting of the Gaussian beam directly at the face of the transducer with very high computational efficiency. It is demonstrated that the K-space Prony’s method can be used to accurately model the transducer field of planar and focused piston transducers, as well as probes that do not act as pistons. The choice of parameters appearing in the method and their influence on performance are discussed.     

STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—IX. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRUM OF THE BACTERIOCHLOROPHYLLIDE a ANION RADICAL

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for 19 doublet states of the anion radical of ethyl bacteriochlorophyllide a (Et-BChl a˙), and are employed in a resolution of the electronic absorption spectrum, as well as in a comparison with a previously reported study of the electronic states and spectrum of the anion radical of ethyl bacteriopheophorbide a (Et-BPheo a˙). The lowest two excited doublet states, D₁ and D₂, of Et-BChl a˙ are found to be approximately degenerate and are predicted to contribute to the experimentally observed absorption at 10000 cm^?1. In contrast, the D₂←D₀ transition in Et-BPheo a˙ is predicted to contribute to the 11000 cm^?1 absorption, while the D₁←D₀ transition appears at approximately 8600 cm^?1 with a low oscillator strength (f= 0.002). The prominent visible absorption at ～15700 cm^?1 in both molecules is found to be due to the D₄← D₀ transition. Another difference between the predicted spectra of the two molecules appears in the low-energy shoulder of the Soret band. Here, two intense transitions, D₁₀←D₀ and D₁₁←D₀, are predicted for Et-BChl a˙, as opposed to three fairly intense transitions, D₇←D₀, D₈←D₀ and D₉←D₀, for Et-BPheo a˙, differences which may provide a means of distinguishing between the two molecules using resonance Raman spectroscopy. The remainder of the Soret band of Et-BChl a˙ above 26000 cm^?1 consists of a number of closely-spaced transitions to states D₁₂←D₁₈. The intense transitions D₁₂←D₀, D₁₃←D₀, D₁₄←D₀ are predicted to contribute to the Soret maximum near 30000 cm^?1. The ground state spin densities of the two molecules are similar, with the minor difference of somewhat less spin density located on the methine carbon atoms of Et-BChl a˙ compared with Et-BPheo a˙.     

Predicting Fluid Flow Regime,Permeability, and Diffusivity in Mudrocks from Multiscale Pore Characterisation

Transport in Porous Media - In geoenergy applications, mudrocks prevent fluids to leak from temporary (H2, CH4) or permanent (CO2, radioactive waste) storage/disposal sites and serve as a source...     

Steady-state and transient electron transport within bulk wurtzite zinc oxide

We study the steady-state and transient electron transport that occurs within bulk wurtzite zinc oxide using an ensemble semi-classical three-valley Monte Carlo simulation approach. We find that for electric field strengths in excess of 180 kV/cm, the steady-state electron drift velocity associated with bulk wurtzite zinc oxide exceeds that associated with bulk wurtzite gallium nitride. We also present evidence to suggest that the negative differential mobility exhibited by the velocity-field characteristic associated with bulk wurtzite zinc oxide is not related to transitions to the upper valleys. The transient electron transport that occurs within bulk wurtzite zinc oxide is studied by examining how electrons, initially in thermal equilibrium, respond to the sudden application of a constant electric field. From these transient electron transport results, we conclude that for devices with dimensions smaller than 0.1 μm, gallium nitride based devices will offer the advantage, owing to their superior transient electron transport, while for devices with dimensions greater than 0.1 μm, zinc oxide based devices will offer the advantage, owing to their superior high-field steady-state electron transport.     

Group 4 transition-metal atom reactions with CS2 and OCS: infrared spectra and density functional calculations of SMCS, SM-(eta2-CS), SMCO, and OMCS in solid argon

Laser-ablated titanium, zirconium, and hafnium atoms were reacted with CS2 and OCS molecules during condensation in excess argon. With CS2, the SMCS and S-M(eta2-CS) products were formed on sample deposition. Photolysis increased both complexes, while annealing favored the lower energy S-M(eta2-CS) side-bound isomer. The OCS reactions produced SMCO, OMCS, and the simple M(eta2-CO)S adduct. Product absorptions are identified by comparison with density functional theory frequency calculations and isotopic substitutions. Investigations with OCS emphasized differences in the CS and CO bond insertion products.     

Matrix infrared spectra and density functional calculations of transition metal hydrides and dihydrogen complexes

Metal hydrides are of considerable importance in chemical synthesis as intermediates in catalytic hydrogenation reactions. Transition metal atoms react with dihydrogen to produce metal dihydrides or dihydrogen complexes and these may be trapped in solid matrix samples for infrared spectroscopic study. The MH(2) or M(H(2)) molecules so formed react further to form higher MH(4), (H(2))MH(2), or M(H(2))(2), and MH(6), (H(2))(2)MH(2), or M(H(2))(3) hydrides or complexes depending on the metal. In this critical review these transition metal and dihydrogen reaction products are surveyed for Groups 3 though 12 and the contrasting behaviour in Groups 6 and 10 is discussed. Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate. 104 references are cited.     

Combined triple and double bonds to uranium: the N≡U=N-H uranimine nitride molecule prepared in solid argon

Reactions of laser-ablated U atoms with N(2) and H(2) mixtures upon codeposition in excess argon at 5 K gave strong NUN and weak UN infrared absorptions and new bands at 3349.7, 966.9, 752.4, and 433.0 cm(-1) for the unusual new U(V) molecule N≡U=N-H, uranimine nitride, containing both triple and double bonds. This identification is based on D and (15)N isotopic substitution and comparison with frequencies computed by density functional theory for the (2)Δ ground state NUNH. Calculated bond lengths are compared to those of the (1)Σ(g)(+) ground state of U(VI) uranium dinitride N≡U≡N, the (2)Φ ground state of the isoelectronic nitride oxide N≡U=O, and the (3)A ground state of the U(IV) uranimine dihydride HN=UH(2) molecule, which have all been prepared in solid argon matrices. Mulliken bond orders based on the CASSCF orbitals for N≡U=N-H are 2.91, 2.19, and 1.05, respectively. Here, the terminal nitride is effectively a triple bond, just as found for N≡U≡N. The solid argon matrix is a convenient medium to isolate reactive terminal uranium nitrides for examination of their spectroscopic properties.