The effect of improved satellite line shapes on the argon Heβ spectral feature

The effect of the interference term in the electron broadening of the Li-like satellites to the Ar Heβ line has been investigated in the standard Stark broadening theory. Although the interference term has negligible or small effect on satellite lines with spectator electrons in n = 2 and n = 3 shells, it shows significant narrowing for lines with n = 4 spectator electrons. Nevertheless, the improved n = 4 satellite line shape makes a small difference in the emergent intensity distribution of the composite spectral feature. Accordingly, this change in line shape does not affect previous diagnosis of plasma conditions in Ar-doped ICF implosion cores.     

Frequency dependent electron collisional widths for opacity calculations

It is shown that theoretical Rosseland mean opacities are sensitive to spectral line shape models. Due to computational constraints, however, opacity codes typically use Voigt or Lorentz profiles. Both of these profiles have an incorrect far wing behavior that can significantly overestimate the photon absorption. A new line profile is proposed, based on second-order line broadening theory, which is both more physical and relatively fast to compute.     

Turbulent statistical characteristics associated to the north wind phenomenon in southern Brazil with application to turbulent diffusion

A parameterization for the transport processes in a shear driven planetary boundary layer (PBL) has been established employing turbulent statistical quantities measured during the north wind phenomenon in southern Brazil. Therefore, observed one-dimensional turbulent energy spectra are compared with a spectral model based on the Kolmogorov arguments. The good agreement obtained from this comparison leads to well defined formulations for the turbulent velocity variance, local decorrelation time scale and eddy diffusivity. Furthermore, for vertical regions in which the wind shear forcing is relevant, the eddy diffusivity derived from the north wind data presents a similar profile to those obtained from the non-extensive statistical mechanics theory. Finally, a validation for the present parameterization has been accomplished, using a Lagrangian stochastic dispersion model. The Prairie Grass data set, which presents high mean wind speed, is simulated. The analysis developed in this study shows that the turbulence parameterization constructed from wind data for north wind flow cases is able to describe the diffusion in a high wind speed, shear-dominated PBL.     

Effective action in a general chiral model: Next to leading order derivative expansion in the worldline method

We present a formalism to determine the imaginary part of a general chiral model in the derivative expansion. Our formalism is based on the worldline path integral for the covariant current that can be given in an explicit chiral and gauge covariant form. The effective action is then obtained by integrating the covariant current, taking account of the anomaly.     

“Click-switch” – one-step conversion of organic azides into photochromic diarylethenes for the generation of light-controlled systems

Diarylethenes (DAEs) are an established class of photochromic molecules, but their effective incorporation into pre-existing targets is synthetically difficult. Here we describe a new class of DAEs in which one of the aryl rings is a 1,2,3-triazole that is formed by “click” chemistry between an azide on the target and a matching alkyne–cyclopentene–thiophene component. This late-stage zero-length linking allows for tight integration of the DAE with the target, thereby increasing the chances for photomodulation of target functions. Nineteen different DAEs were synthesized and their properties investigated. All showed photochromism. Electron-withdrawing groups, and in particular −M-substituents at the triazole and/or thiophene moiety resulted in DAEs with high photo- and thermostability. Further, the chemical nature of the cyclopentene bridge had a strong influence on the behaviour upon UV light irradiation. Incorporation of perfluorinated cyclopentene led to compounds with high photo- and thermostability, but the reversible photochromic reaction was restricted to halogenated solvents. Compounds containing the perhydrogenated cyclopentene bridge, on the other hand, allowed the reversible photochromic reaction in a wide range of solvents, but had on average lower photo- and thermostabilities. The combination of the perhydrocyclopentene bridge and electron-withdrawing groups resulted in a DAE with improved photostability and no solvent restriction. Quantum chemical calculations helped to identify the photoproducts formed in halogenated as well as non-halogenated solvents. For two optimized DAE photoswitches, photostationary state composition and reaction quantum yields were determined. These data revealed efficient photochemical ring closure and opening. We envision applications of these new photochromic diarylethenes in photonics, nanotechnology, photobiology, photopharmacology and materials science.

New photochromic diarylethenes are reported in which one aryl ring is a 1,2,3-triazole that is formed by “click” chemistry between an azide on the target and a matching alkyne–cyclopentene–thiophene component.     

Hidden Conformations in Aspergillus niger Monoamine Oxidase are Key for Catalytic Efficiency

Enzymes exist as an ensemble of conformational states, whose populations can be shifted by substrate binding, allosteric interactions, but also by introducing mutations to their sequence. Tuning the populations of the enzyme conformational states through mutation enables evolution towards novel activity. Herein, Markov state models are used to unveil hidden conformational states of monoamine oxidase from Aspergillus niger (MAO‐N). These hidden conformations, not previously observed by any other technique, play a crucial role in substrate binding and enzyme activity. This reveals how distal mutations regulate MAO‐N activity by stabilizing these hidden, catalytically important conformational states, but also by modulating the communication pathway between both MAO‐N subunits.     

Dynamic 3D axisymmetric problems in continuously non-homogeneous piezoelectric solids

The meshless local Petrov-Galerkin (MLPG) method is used to analyze transient dynamic problems in 3D axisymmetric piezoelectric solids with continuously inhomogeneous material properties. Both mechanical and thermal loads are considered here. A 3D axisymmetric body is created by rotation of a cross section around an axis of symmetry. Axial symmetry of geometry and boundary conditions reduces the original 3D boundary value problem into a 2D problem. The cross section is covered by small circular sub-domains surrounding nodes randomly spread over the analyzed domain. A unit step function is chosen as test function, in order to derive local integral equations on the boundaries of the chosen sub-domains, called local boundary integral equations (LBIE). These integral formulations are either based on the Laplace transform technique or the time-difference approach. The local integral equations are non-singular and take a very simple form, despite of inhomogeneous and anisotropic material behaviour across the analyzed structure. Spatial variation of all physical fields (or of their Laplace transforms) at discrete time instants are approximated on the local boundary and in the interior of the sub-domain by means of the moving least-squares (MLS) method. The Stehfest algorithm is applied for the numerical Laplace inversion, in order to retrieve the time-dependent solutions.     

A theoretical study on the reaction mechanism for the bergman cyclization from the perspective of the electron localization function and catastrophe theory

The reaction mechanism associated with the Bergman cyclization of the (Z)-hexa-1,5-diyne-3-ene to render p-benzyne has been analyzed by means of a combined use of the electron localization function (ELF) and the catastrophe theory on the basis of density functional theory (DFT) calculations (B3LYP/6-31G(d)). The complex electronic rearrangements of this reaction can be highlighted using this novel quantum mechanical perspective. Five domains of structural stability of the ELF occurring along the intrinsic reaction path as well as four catastrophes (fold-cusp-fold-cusp) responsible for the changes in the topology of the system have been identified. The multiple factors that occur along the intrinsic reaction coordinate path are presented and discussed in a consistent way. The topological analysis of ELF and catastrophe theory reveals that mechanical deformation of the C1-C2-C3 unit and closed-shell repulsion between terminal acetylene groups lead to an early formation of diradicaloid character at C2 and C5 atoms. Immediately after the transition structure (TS) is reached, the open-shell-singlet biradical becomes stable. Meanwhile, C1 and C6 atoms are preparing to be covalently bonded; that will finally occur at a distance of 1.791 A. In addition, a separation of the ELF into in-plane (sigma) and out-of-plane (pi) contributions allows us to discuss the aromaticity profiles; sigma-aromaticity appears in the vicinities of the TS, while pi-aromaticity takes place in the final stage of the reaction path, once the ring has been formed.     

Direct vapor phase propylene epoxidation over deposition-precipitation gold-titania catalysts in the Presence of H2/O2: Effects of support, neutralizing agent, and pretreatment

The effects of titanium connectivity, deposition solution neutralizing agent, and catalyst pretreatment were examined for a series of Au-on-titanium-containing supports for the direct gas-phase epoxidation of propylene using hydrogen and oxygen. The degree of titanium isolation was examined using pure titania, monolayer-titania on silica, submonolayer-titania on silica, and titanium silicalite-1 (TS-1) supports. Activity and selectivity were shown to increase as the degree of titanium isolation increased, with TS-1 and submonolayer-titania supports providing the best stability and yield. Isolation of the titanium was found to significantly reduce the cracking of propylene to ethanal and carbon dioxide. Sodium carbonate was found to be the best neutralizing agent for catalysts prepared using deposition-precipitation (DP). DP with ammonium hydroxide gave catalysts with reduced selectivity and activity. Titania-modified silica was found to produce better catalysts when the support was not calcined prior to gold deposition. Similarly, calcination was detrimental to catalysts prepared via deposition of a 2 nm gold colloid onto titania-modified supports even though the gold did not sinter. The beneficial effects of Ti site isolation and support acid/base control are best seen at higher temperatures, where only a few catalysts can maintain selectivity.     

Review of combinatorial problems induced by spatial forest harvesting planning

In the last two decades forest planning and management has become very much focused on spatially oriented decisions, due to the introduction of spatial details, such as road building, and environmental concerns, like wildlife protection, biodiversity, reducing erosion and improving water quality. This has led to modeling transformations and extensions in planning forest activities, as mixed integer decision variables are necessary to account for spatial restrictions. These new models are much harder to solve due to the added combinatorial complexity. In this paper, we discuss issues of modeling spatial criteria, as well as algorithms that have been developed to solve them, both heuristic and exact. We present these results as they have evolved in a state-of-the-art structure.