The radiative leptonic decays D^0 \to e^+ e^-\gamma,\mu^+\mu^-\gamma in the standard model and beyond

We present a calculation of the rare decay modes and in the framework of the standard model. For the short distance part we have derived QCD corrections to the Wilson coefficients involved, including C₉. The latter is found to be strongly suppressed by the corrections, leading to diminished values for the branching ratios in the 10^-10 range. Within SM the exclusive decays are dominated by long distance effects. Non-resonant contributions are estimated using heavy quark and chiral symmetries to be at the level of , compared to the contributions arising from , with . The total SM branching ratio is predicted to be in the range (1-. We also consider contributions coming from MSSM with and without R parity conservation. The effects from MSSM are significant only for the R parity violating case. Such contributions enhance the branching ratio to , based on appropriately allowed values for C₉ and C₁₀. This selects as a possible probe of new physics. Received: 25 October 2002 / Published online: 24 January 2003     

Chemistry of organo halogenic molecules. Part XLVII. Stereochemistry of iodofluorination of 1,2- and 1,4-dihydronapthalene with (difluororiodo) methane

Reaction of (difluoroiodo)methane with 1,2-dihydronaphthalene resulted in the formation of vicinal iodofluorides; the reaction follows Markovnikov type regio-selectivity and is stereospecifically anti. Reaction with 1,4-dihydronaphthalene also occurs stereospecifically anti, and further elimination reaction leads to naphthalene.     

A Photosensitive Liquid Crystal Studied by 14N NMR, 2H NMR,and DFT Calculations

An azobenzene derivative, namely diheptylazobenzene, showing the nematic and smectic A liquid crystalline phases, was investigated by means of a combined approach based on NMR and DFT calculations. ¹⁴N NMR quadrupole‐ and chemical‐shift‐perturbed spectra were acquired in the whole mesophasic range, providing both experimental quadrupolar splittings and chemical shift anisotropy values. On the same mesogen, deuterium labelled at the α‐position of the hydrocarbon chain, ²H NMR quadrupole‐perturbed spectra were recorded. The analysis of these NMR data was performed with the help of ab initio calculations, in vacuo and by taking into account the effect of the anisotropic environment typical of liquid crystals, by using the IEF‐PCM model. The geometry optimizations of the azomesogen in the trans and cis configurations were performed by DFT calculations employing the combination of B3LYP functional with the 6‐311G(d) basis set. The analysis of experimental NMR data was performed by considering the trans configuration as the most populated one and the corresponding quadrupolar tensors and chemical shielding tensors were determined at the DFT level of theory. The main result of this work is the determination of a relatively high and temperature‐dependent molecular biaxiality of the trans state of this azomesogen.     

Synthesis of CDE molecular fragments related to sendanin mediated by titanocene(III)

A practical, brief, and diastereoselective synthesis of limonoid CDE fragments from a readily available starting material is described. The key step was the titanocene(III)-promoted cyclization of unsaturated epoxylactones, readily prepared from α-cyclocitral. In this way, we confirm the viability of our procedure for the synthesis of a limonoid model with different functionalization patterns. We also report the antifeedant activity of epoxylactones 18 and 19, which show significant antifeedant activity against Spodoptera littoralis and Spodoptera frugiperda, two insect species with different feeding ecologies.     

A New Technique for Translating Discrete Hybrid Automata into Piecewise Affine Systems

The paper proposes a new translation algorithm that translates a hybrid system described as a discrete hybrid automaton (DHA) into an equivalent piecewise affine (PWA) system. The translation algorithm exploits, among others, a new technique for cell enumeration in hyperplane arrangement, all proposed in this paper. The new translation technique enables the transfer of several analysis and synthesis tools developed for PWA systems to a DHA class of hybrid systems.     

Oxidative Halogenation with “Green” Oxidants: Oxygen and Hydrogen Peroxide

It is difficult to imagine organic chemistry without organo‐halogen compounds and the molecular halogens needed for their preparation. The halogens have very different reactivity, with iodine usually requiring some form of activation, while others are reactive and hazardous chemicals. To avoid their use, various modified reagents have been discovered (N‐bromo‐ and N‐chlorosuccinimide, Selectfluor…?), but halogens are used to prepare these reagents and when they are used the atom economy is poor. A better approach, which is based on biomimetric research on oxidative halogenation in nature, consists of generating the halogenating reagent in situ under acidic conditions from a halide salt. The result of such a reaction has been halogenation with 100 % halogen atom economy. Suitable oxidants for the oxidation of halides are hydrogen peroxide and oxygen.     

Handling large amounts of chemical data

The main aspects of handling large amounts of complex information, in general, and spectroscopic data, in particular, are described and discussed. In the first part, the basic terms and procedures are defined and illustrated with examples from different spectrometries. The items such as the representation of complex data of different types, measurement — and information — pace, metrics of a multi-dimensional space, different types of transformations, information content of a given representation, the concept of a frame, the holistic and reductionistic aspect of information are explained in more detail.In the second part, the organization of complex data with the intention of forming an expert system is discussed. Emphasis is put on the clustering of data, on the criteria for clustering, and on the ways and means governing the formation of hierarchies of clusters and frames they represent. Furtheron, a model for an expert system (which is able to acquire new information, i. e. which is able to learn, and to use the acquired knowledge for predicting the structural features of unknown compounds) based on the hierarchical organization of a large amount of data is outlined.Finally, the prospects and limitations of expert systems based on the hierarchical clustering of large data collections are discussed.