On the expansion of a quantum field theory around a topological sector

The idea of treating quantum general relativistic theories in a perturbative expansion around a topological theory has recently received attention, in the quantum gravity literature. We investigate the viability of this idea by applying it to conventional Yang–Mills theory on flat spacetime. This theory admits indeed a formulation as a modified topological theory, like general relativity. We find that the expansion around the topological theory coincides with the usual expansion around the free abelian theory, though the equivalence is non-trivial. In this context, the technique appears therefore to be viable, but not to bring particularly new insights. On the other hand, we point out that the relation of this expansion with the actual quantum BF theory is far from being transparent. Some implications for gravity are discussed.     

Investigation on porosity changes of Lecce stone due to conservation treatments by means of x‐ray nano‐ and improved micro‐computed tomography: preliminary results

Cultural heritage materials are subject to continuous chemical and physical changes depending on the establishment of a dynamic equilibrium with the environment in which they are placed. In particular, different phenomena can take place, such as formation of black crusts, corrosion of the material, internal cracks. Lecce stone, a biocalcarenite mainly used for historical buildings in South Italy, has a high total porosity. In order to prevent its deterioration, different kinds of hydrophobic organic products are applied on the surface of the restored artefacts. Since the efficacy of the treatments depends mostly on the penetration depth and the distribution of the products in the pores, porosity and internal structure of the stone material were mainly investigated in this research. Micro x‐ray computed tomography (µ‐CT) has been used to study and characterize the internal structure of different samples, untreated and treated with protective products. The porosity and other parameters of the rock were then calculated and compared, before and after the conservation treatment, in order to highlight the changes due to the application of the product. On the other hand, small pieces of the untreated and treated samples were analysed by sub‐micron resolution x‐ray tomography where it was possible to see the distribution of the products inside the pores. Copyright © 2007 John Wiley & Sons, Ltd.     

Functionalisation of saturated hydrocarbons. Part XI. Oxidation of cedrol, β- and γ-eudesmol,sclareol, manoyl oxide, 1,9-dideoxyforskolin,methyl trans-dihydroiasmonate,and tetrahydrolinalool by the ‘Gif system’

The oxidation of cedrol ( 1 ), β- and γ-eudesmol ( 6 and 7 , resp.), sclareol ( 14 ) manoyl oxide ( 15 ), 1,9-dideoxyforskolin ( 22 ) (±)-methyl trans-dihydrojasmonate ( 28 ), and tetrahydrolinalool ( 32 ) nearly all of natural terpenoid origin, by the ‘Gif system’ has afforded a number of novel products ( 3 , 11 , and 12 , 16/17 , 18/19 , 26 , 29–31 , and ketones corresponding to 34–35 , res.). The structures of these compounds were established by spectroscopic techniques including 2D-NMR and, where appropriate, by comparison with authentic samples.     

On the stability of wideband beam patterns with respect to weighting and envelope fluctuations

This paper presents a study on the worsening caused by a random perturbation of the weighting window (modeling, in this way, the uncertainty on the channel sensitivity), or by an alteration of the shape of the transmitted pulse, for a wideband array. In the stability evaluation, main-lobe width and signal to noise ratio evaluated at different dB levels of the beam pattern play the role of quality parameters. Two different profiles of the weighting window have been used for this analysis: a typical raised cosine, and a window optimized by a Simulated Annealing procedure. Also for the pulse envelope, two distinct shapes have been chosen: perfectly Gaussian and experimentally measured. The analysis of the obtained results provides useful hints about the amount and the kind of the beam pattern worsening, when realistic fluctuations occur. Moreover, the results show that the weighting windows provided by the simulated annealing procedure are particularly robust to such fluctuations.     

High-precision lattice QCD confronts experiment

The recently developed Symanzik-improved staggered-quark discretization allows unquenched lattice-QCD simulations with much smaller (and more realistic) quark masses than previously possible. To test this formalism, we compare experiment with a variety of nonperturbative calculations in QCD drawn from a restricted set of "gold-plated" quantities. We find agreement to within statistical and systematic errors of 3% or less. We discuss the implications for phenomenology and, in particular, for heavy-quark physics.     

Quantum mechanical study of stereoselectivity in the oxazaborolidine-catalyzed reduction of acetophenone

Chiral oxazaborolidines, known as CBS catalysts after the work of Corey, Bakshi and Shibata, are used for the stereoselective reduction of prochiral ketones to secondary chiral alcohols. Due to their relative low cost, ease of use, and high selectivity, their popularity has remarkably grown in the last 15 years. Oxazaborolidine-catalyzed reductions have been much studied, both experimentally and computationally, by means of semiempirical methods. Though, a more accurate high level quantum mechanical study on the complete system, capable of elucidating reliably the origins of stereoselectivity, is still lacking. Therefore, the acetophenone (PhMK) reduction with Corey's oxazaborolidine has been modeled for the first time with ab initio and DFT-B3LYP calculations on the complete system as well as with AM1. Calculations on the complexation of BH(3) to CBS, which can occur only in a cis fashion with respect to the hydrogen on the stereogenic C-4 carbon atom, have allowed us to confirm the great rigidity of Corey's catalyst, possibly determining its excellent enantioselectivity. Acetophenone-CBS-BH(3) complexes were characterized at various levels of theory, and it was found that the picture obtained depends heavily on the method adopted. A computational strategy for identifying the hydride transfer transition states of the competing pathways was developed and tested, using a model system for which the transition state geometry was already known. The application of the TS search method to the reduction of acetophenone allowed the characterization of the TS's for the competing pathways in this reaction, making it possible to predict with good quantitative accuracy the stereochemical outcome of the reaction at all the levels of theory adopted. The characterization of the intermediate oxazadiboretane products confirmed that the highly exothermic hydride transfer provides the thermodynamical drive for the reaction.     

Facile determination of the protecting group location of Nim-protected histidine derivatives by 1H-15N heteronuclear correlation NMR

The positioning of the imidazole protecting group of several histidine derivatives was determined by means of (1)H-(15)N heteronuclear multiple-bond correlation NMR experiments. The cross-peak originated from the three-bond correlation between the histidine side-chain H(beta) and the imidazole N(pi) was used for the identification of the N(pi) signal in the (15)N spectrum. Therefore, based on the fact that the signal of the substituted imidazole nitrogen appears always at lower chemical shift (delta) than the unsubstituted one, the position of the blocking group could easily be inferred. The obtained data confirmed previous findings that were accomplished with other less generally applicable spectroscopic or crystallographic techniques.     

Direct and indirect role of Fe doping in NiOOH monolayer for water oxidation catalysis**

Water oxidation activity of pristine NiOOH is greatly enhanced by doping it with Fe. However, the precise role of Fe is still being debated. Using a first-principles DFT+U approach, we investigate the direct and indirect roles of Fe in enhancing the oxygen evolution reaction (OER) activity of NiOOH monolayers. Considering two Mars-Van-Krevelen mechanisms of OER based on the source of O−O bond formation, we show that a mechanism involving the coupling of lattice oxygen is generally more favorable than water nucleophilic attack on lattice oxygen. On doping with Fe, the overpotential of NiOOH is reduced by 0.33 V, in excellent agreement with experimental findings. Introducing Fe at active sites results in different potential determining steps (PDS) in the two mechanisms. The Ni sites in pristine and Fe-doped NiOOH have the same PDS regardless of the mechanism. The Fe sites not only have the lowest overpotential but also decrease the overpotential for Ni sites.     

Visualizing a Single-Crystal-to-Single-Crystal [2+2] Photodimerization through its Lattice Dynamics: An Experimental and Theoretical Investigation

In homogeneous solid-state reactions, the single-crystal nature of the starting material remains unchanged, and the system evolves seamlessly through a series of solid solutions of reactant and product. Among [2+2] photodimerizations of cinnamic acid derivatives in the solid state, those involving salts of the 4-aminocinnamic acid have been recognized to proceed homogeneously in a “single-crystal-to-single-crystal” fashion by X-ray diffraction techniques. Here the bromide salt of this compound class is taken as a model system in a Raman spectroscopy study at low wavelengths, to understand how such a mechanism defines the trend of the crystal lattice vibrations during the reaction. Vibrational mode calculations, based on dispersion corrected DFT simulations of the crystal lattices involved in the transformation, have assisted the interpretation of the experiments. Such an approach has allowed us to clarify the spectral signatures and to establish a correlation between the dynamics of the monomer and dimer systems in a process where chemical progress and crystal structural changes are demonstrated to occur simultaneously.     

Removal and sensing of emerging pollutants released from (micro)plastic degradation: Strategies based on boron-doped diamond electrodes

The negative impacts of microplastics on the environment and human health cannot be unnoticed. Several classes of emerging pollutants with endocrine-disrupting properties such as bisphenol A and its analogs, phthalates, among others, have been reported to migrate out of plastics entering the aquatic environment. Thus, this review aims to draw attention to the significant potential of the boron-doped diamond electrode to contribute to the implementation of mitigation actions for microplastic pollutants. The latest studies in the two main fields of the use of the boron-doped diamond electrode, that is, treatment of wastewater by electrochemical oxidation and a as sensor for pollutants monitoring, are herein reviewed and their main findings highlighted.