Evolution of Fields in a Second Order Phase Transition

We analyse the evolution of scalar and gauge fields during a second order phase transition using a Langevin equation approach. We show that topological defects formed during the phase transition are stable to thermal fluctuations. Our method allows the field evolution to be followed throughout the phase transition, for both expanding and non-expanding Universes. The results verify the Kibble mechanism for defect formation during phase transitions.Comment: 12 pages of text plus 17 diagrams available on request, DAMTP 94-8

Strong Decays of Strange Quarkonia

In this paper we evaluate strong decay amplitudes and partial widths of strange mesons (strangeonia and kaonia) in the 3P0 decay model. We give numerical results for all energetically allowed open-flavor two-body decay modes of all nsbar and ssbar strange mesons in the 1S, 2S, 3S, 1P, 2P, 1D and 1F multiplets, comprising strong decays of a total of 43 resonances into 525 two-body modes, with 891 numerically evaluated amplitudes. This set of resonances includes all strange qqbar states with allowed strong decays expected in the quark model up to ca. 2.2 GeV. We use standard nonrelativistic quark model SHO wavefunctions to evaluate these amplitudes, and quote numerical results for all amplitudes present in each decay mode. We also discuss the status of the associated experimental candidates, and note which states and decay modes would be especially interesting for future experimental study at hadronic, e+e- and photoproduction facilities. These results should also be useful in distinguishing conventional quark model mesons from exotica such as glueballs and hybrids through their strong decays.Comment: 69 pages, 5 figures, 39 table

Stereodivergent cyclopropanation of unactivated alkenes with heme proteins

Cyclopropyl motifs are present in a variety of compounds important to pharmaceutical, agrochemical, and fragrance industries. The asymmetric synthesis of cyclopropanes is often performed under harsh conditions with toxic, precious metal chiral catalysts. In 2013, the first example of biocatalytic alkene cyclopropanation was reported, using an engineered cytochrome P450 enzyme [1]. Since then, several heme proteins were reported to cyclopropanate a variety of styrenyl alkenes [2], but none have been shown to asymmetrically cyclopropanate more challenging substrates such as unactivated, aliphatic alkenes using the native iron-heme cofactor. Here we report that heme proteins can cyclopropanate unactivated alkenes and that stereoselectivity and activity can be tuned by directed evolution. A few rounds of site-saturation mutagenesis and screening yielded four protein variants with high enantio- and diastereoselectivity for complementary isomers, enabling stereodivergent synthesis of aliphatic cyclopropanes. These iron-porphyrin proteins are fully genetically encoded, and the reactions can be performed under mild, aqueous conditions with whole cells or purified protein. The protein enhances the activity of the native iron-heme cofactor, giving access to a broad array of cyclopropanated products. This example showcases the ability to quickly and efficiently engineer proteins for non-natural biocatalytic function. [1] P.S. Coelho, E.M. Brustad, A. Kannan, F.H. Arnold, Olefin cyclopropanation via carbene transfer catalyzed by engineered cytochrome P450 enzymes., Science. 339 (2013) 307–10. [2] O.F. Brandenberg, R. Fasan, F.H. Arnold, Exploiting and engineering hemoproteins for abiological carbene and nitrene transfer reactions, Curr. Opin. Biotechnol. 38 (2017) in press

Large-scale unit commitment under uncertainty: an updated literature survey

The Unit Commitment problem in energy management aims at finding the optimal production schedule of a set of generation units, while meeting various system-wide constraints. It has always been a large-scale, non-convex, difficult problem, especially in view of the fact that, due to operational requirements, it has to be solved in an unreasonably small time for its size. Recently, growing renewable energy shares have strongly increased the level of uncertainty in the system, making the (ideal) Unit Commitment model a large-scale, non-convex and uncertain (stochastic, robust, chance-constrained) program. We provide a survey of the literature on methods for the Uncertain Unit Commitment problem, in all its variants. We start with a review of the main contributions on solution methods for the deterministic versions of the problem, focussing on those based on mathematical programming techniques that are more relevant for the uncertain versions of the problem. We then present and categorize the approaches to the latter, while providing entry points to the relevant literature on optimization under uncertainty. This is an updated version of the paper "Large-scale Unit Commitment under uncertainty: a literature survey" that appeared in 4OR 13(2), 115--171 (2015); this version has over 170 more citations, most of which appeared in the last three years, proving how fast the literature on uncertain Unit Commitment evolves, and therefore the interest in this subject

Beam on Nonlinear Winkler Foundation and Modified Neutral Plane Solution for Calculating Downdrag Settlement

The neutral plane solution has been widely used to estimate downdrag settlements and drag loads mobilized in piles in consolidating soil profiles. Pile settlement is typically assumed equal to soil settlement at the neutral plane depth corresponding to effective stress conditions at the end of consolidation. This paper demonstrates that, in general, pile settlement is not equal to soil settlement at the neutral plane depth; rather, it is the relative velocity between the pile and soil that is zero at the neutral plane depth. A beam on nonlinear Winkler foundation (BNWF) solution, in which the shaft friction capacity is proportional to effective stress, is utilized to demonstrate that pile settlement is not equal to soil settlement at the neutral plane depth, because the neutral plane depth evolves as consolidation progresses. The BNWF solution also shows that pile settlement depends on drainage conditions, with more settlement occurring when consolidation occurs first near the top of the consolidating soil layer, and less settlement occurring when consolidation initiates at the bottom. A modified neutral plane solution that is amenable to hand calculation is formulated to account for the evolution of neutral plane depth on pile settlement. Finally, the proposed BNWF and modified neutral plane solutions are compared with measurements of downdrag settlement from a centrifuge test program. The proposed methods produced more accurate estimates of pile settlement than the traditional neutral plane solution. © 2013 American Society of Civil Engineers

The impact of recent developments in technologies which enable the increased use of biocatalysts

While biocatalytic transformations are very powerful in enantioselective synthesis, frequently occurring under mild conditions, and proceed with extraordinary selectivity, there are practical challenges associated with the use of biocatalysis, such as limited substrate scope, stability, and reusability. Recent technological developments, for example immobilization, continuous flow, and molecular biology, all contribute towards enhancing the use of enzymes in synthesis

FEM analysis of dynamic soil-pile-structure interaction in liquefied and laterally spreading ground

A two-dimensional nonlinear dynamic finite element (FE) model was developed and calibrated against dynamic centrifuge tests to study the behavior of soil-pile-structure systems in liquefied and laterally spreading ground during earthquakes. The centrifuge models included a simple structure supported on pile group. The soil profiles consisted of a gently sloping clay crust over liquefiable sand over dense sand. The FE model used an effective stress pressure dependent plasticity model for liquefiable soil and a total stress pressure independent plasticity model for clay, beam column elements for piles and structure, and interface springs that couple with the soil mesh for soil-structure interaction. The FE model was evaluated against recorded data for eight cases with same set of baseline parameters. Comparisons between analyses and experiments showed that the FE model was able to approximate the soil and structural responses and reproduce the lateral loads and bending moments on the piles reasonably well. © 2013, Earthquake Engineering Research Institute