Photo-driven Molecular Wankel Engine B13+_{13}^+

We report a molecular Wankel motor, the dual-ring structure B13+, driven by circularly-polarized infrared electromagnetic radiation, under which a guided uni-directional rotation of the outer ring is achieved with rotational frequency of the order of 300 MHz.Comment: 5 pages, 4 figure

Skin and Proximity Effects in Electrodes and Furnace Shells

A review of two-dimensional (2D) analytical models of skin and proximity effects in large industrial furnaces with three electrodes arranged in an equilateral triangle is given. The models cover three different cases: one electrode only, three electrodes where two are approximated by line currents, and induced shell currents where all electrodes are approximated by line currents. The first two models show how the skin and proximity effects depend on electrode material properties and size, and the distance between the electrodes. The third model shows how the strength of the induced shell currents will depend on electrode position and furnace size. These models are compared to numerical studies including distributed electrodes and shell currents. The analytical models are accurate when induced shell currents can be disregarded. However, strong shell currents may have a significant impact on the current distribution within the electrodes. This electrode-shell proximity effect competes with the electrode-electrode proximity effect. Finally, the 2D models have been compared with three-dimensional (3D) case studies of large industrial furnaces. In 3D, the shell currents are significantly smaller than what are predicted by the 2D models, but they are sufficiently strong to cause a significant correction of the electrode current density.Skin and Proximity Effects in Electrodes and Furnace ShellspublishedVersio

Understanding Scale-Up of High-Current Electrodes

A simple and generic model for the heat distribution in electrodes for primary metal production has been investigated. The equations have been analyzed focusing on understanding the scale-up of electrodes under both direct current (DC) and alternating current (AC) conditions. The analysis provides a theoretical foundation for Westly’s empirical scale-up rule. For graphite and small carbon electrodes, the current-carrying capacity is limited by the ohmic heating, which controls the lateral heat flux and the temperature at the electrode periphery. For these electrodes, the current capacity is higher for DC than for AC. For large carbon or Søderberg electrodes, the electrode current must be limited to avoid large thermal stresses and subsequent breakages, especially in connection with shutdowns or considerable current fluctuations. Thermally, the current capacity is then limited by the maximum temperature difference between the center and the periphery. For this case, AC electrodes can carry more current than DC.Understanding Scale-Up of High-Current ElectrodespublishedVersio

Toward accurate QM/MM reaction barriers with large QM regions using domain based pair natural orbital coupled cluster theory

The hydroxylation reaction catalyzed by p-hydroxybenzoate hydroxylase and the Baeyer–Villiger reaction catalyzed by cyclohexanone monooxygenase are investigated by means of quantum mechanical/molecular mechanical (QM/MM) calculations at different levels of QM theory. The geometries of the stationary points along the reaction profile are obtained from QM/MM geometry optimizations, in which the QM region is treated by density functional theory (DFT). Relative energies are determined from single-point QM/MM calculations using the domain-based local pair natural orbital coupled cluster DLPNO-CCSD(T) method as QM component. The results are compared with single-point DFT/MM energies obtained using popular density functionals and with available experimental and computational data. It is found that the choice of the QM method strongly affects the computed energy profiles for these reactions. Different density functionals provide qualitatively different energy barriers (variations of the order of 10 kcal/mol in both reactions), thus limiting the confidence in DFT/MM computational predictions of energy profiles. On the other hand, the use of the DLPNO-CCSD(T) method in conjunction with large QM regions and basis sets makes it possible to achieve high accuracy. A critical discussion of all the technical aspects of the calculations is given with the aim of aiding computational chemists in the application of the DLPNO-CCSD(T) methodology in QM/MM calculations

Hybrid Dynamics Simulation Engine for Metalloproteins

Quality computational description of metalloproteins is a great challenge due to the vast span of time- and lengthscales characteristic of their existence. We present an efficient new method that allows for robust characterization of metalloproteins. It combines quantum mechanical (QM) description of the metal-containing active site, and extensive dynamics of the protein captured by discrete molecular dynamics (DMD) (QM/DMD). DMD samples the entire protein, including the backbone, and most of the active site, except for the immediate coordination region of the metal. QM operates on the part of the protein of electronic and chemical significance, which may include tens to hundreds of atoms. The breathing quantum-classical boundary provides a continuous mutual feedback between the two machineries. We test QM/DMD using the Fe-containing electron transporter protein, rubredoxin, and its three mutants as a model. QM/DMD can provide a reliable balanced description of metalloproteins’ structure, dynamics, and electronic structure in a reasonable amount of time. As an illustration of QM/DMD capabilities, we then predict the structure of the Ca2+ form of the enzyme catechol O-methyl transferase, which, unlike the native Mg2+ form, is catalytically inactive. The Mg2+ site is ochtahedral, but the Ca2+ is 7-coordinate and features the misalignment of the reacting parts of the system. The change is facilitated by the backbone adjustment. QM/DMD is ideal and fast for providing this level of structural insight

Preclinical evidence implicating corticotropin-releasing factor signaling in ethanol consumption and neuroadaptation

The results of many studies support the influence of the corticotropin-releasing factor (CRF) system on ethanol (EtOH) consumption and EtOH-induced neuroadaptations that are critical in the addiction process. This review summarizes the preclinical data in this area after first providing an overview of the components of the CRF system. This complex system involves hypothalamic and extra-hypothalamic mechanisms that play a role in the central and peripheral consequences of stressors, including EtOH and other drugs of abuse. In addition, several endogenous ligands and targets make up this system and show differences in their involvement in EtOH drinking and in the effects of chronic or repeated EtOH treatment. In general, genetic and pharmacological approaches paint a consistent picture of the importance of CRF signaling via type 1 CRF receptors (CRF1) in EtOH-induced neuroadaptations that result in higher levels of intake, encourage alcohol seeking during abstinence and alter EtOH sensitivity. Furthermore, genetic findings in rodents, non-human primates and humans have provided some evidence of associations of genetic polymorphisms in CRF-related genes with EtOH drinking, although additional data are needed. These results suggest that CRF1 antagonists have potential as pharmacotherapeutics for alcohol use disorders. However, given the broad and important role of these receptors in adaptation to environmental and other challenges, full antagonist effects may be too profound and consideration should be given to treatments with modulatory effects.The authors were supported by the Department of Veterans Affairs; NIH NIAAA grants P60AA010760, R24AA020245 and U01AA013519 and NIH NIDA grant P50DA018165, during the writing of this manuscript. The authors have no financial conflict of interest to disclose

Granular flow described by fictitious fluids: a suitable methodology for process simulations

The flow of granular materials is often present in metallurgical reactors. Metallurgical simulations are typically multidisciplinary and the granular flow will often have a significant effect on the temperature distribution. The flow of bulk materials exhibits patterns that can be very different from fluid flows. Standard fluid flow methods are not applicable to describe such flows. For simple bulk flows with plug flow sections and mass flow hoppers, a reasonable flow field can, however, be computed with a standard CFD tool. The trick is to apply appropriate, nonstandard, moving wall boundary conditions. This simple approach does not work for complex flow cases, including sections with one or more free boundaries. For such cases, we apply the Discrete Element Method (DEM), which has emerged to be the preferred choice for simulation of granular flow. A suitable method has been developed to compute the volume averaged flow field by DEM and then import it into a code for multiphysics simulations. To reduce the high computational cost of DEM simulations a hybrid approach is recommended. DEM simulations are then used for the complex flow regions while the simple model is used wherever applicable. In the multiphysics program the flow field is forced to be equal, or very close to, the DEM results by applying a suitable volume force.publishedVersio

Granular flow described by fictitious fluids: a suitable methodology for process simulations

The flow of granular materials is often present in metallurgical reactors. Metallurgical simulations are typically multidisciplinary and the granular flow will often have a significant effect on the temperature distribution. The flow of bulk materials exhibits patterns that can be very different from fluid flows. Standard fluid flow methods are not applicable to describe such flows. For simple bulk flows with plug flow sections and mass flow hoppers, a reasonable flow field can, however, be computed with a standard CFD tool. The trick is to apply appropriate, nonstandard, moving wall boundary conditions. This simple approach does not work for complex flow cases, including sections with one or more free boundaries. For such cases, we apply the Discrete Element Method (DEM), which has emerged to be the preferred choice for simulation of granular flow. A suitable method has been developed to compute the volume averaged flow field by DEM and then import it into a code for multiphysics simulations. To reduce the high computational cost of DEM simulations a hybrid approach is recommended. DEM simulations are then used for the complex flow regions while the simple model is used wherever applicable. In the multiphysics program the flow field is forced to be equal, or very close to, the DEM results by applying a suitable volume force