Pion Tensor Generalized Parton Distributions in a Covariant Constituent Quark Model

The pion tensor generalized parton distributions are evaluated within a covariant, analytic constituent quark model. The generalized form factors for the first two Mellin moments and the probability densities of polarized quarks in the impact parameter space are derived and compared with lattice QCD and quark model results.     

A suitable preparation of <Emphasis Type="Italic">N</Emphasis>-sulfonyl-1,2,3,4-tetrahydroisoquinolines and their ring homologs with a reusable Preyssler heteropolyacid as catalyst

The preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines, N-sulfonyl-2,3,4,5-tetrahydro-1H-2-benzazepines and N-sulfonyl-1,2,3,4,5,6-hexahydrobenzazocine was catalyzed by a Preyssler heteropolyacid, H₁₄[NaP₅W₃₀O₁₁₀], (PA), supported on silica (PASiO₂40) with excellent yields by means of the Pictet–Spengler reaction of N-aralkylsulfonamides with s-trioxane. The reactions proceed with 0.5 mol% of silica-supported catalyst in toluene at 70°C. The catalyst can be recycled without appreciable loss of the catalytic activity.     

Tungstophosphoric Acid Supported on Zirconia: A Recyclable Catalyst for the Green Synthesis on Quinoxaline Derivatives under Solvent-Free Conditions

Abstract

A green, simple, and fast procedure has been developed for the preparation of quinoxaline derivatives by a condensation of 1,2-diamines with 1,2-dicarbonyl compounds in the presence of zirconium oxide modified with tungstophosphoric acid (H₃PW₁₂O₄₀) as a heterogeneous catalyst, in a solvent-free medium using conventional heating. Quinoxaline derivatives were formed in short-time periods and excellent yields (65–100%). The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions without appreciable loss of the catalytic activity.

Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional text.     

Dynamic and generalized Wentzell node conditions for network equations

Motivated by a neurobiological problem, we discuss a class of diffusion problems on a network. The celebrated Rall lumped soma model for the spread of electrical potential in a dendritical tree prescribes that the common cable equation must be coupled with particular dynamic conditions in some nodes (the cell bodies, or somata). We discuss the extension of this model to the case of a whole network of neurons, where the ramification nodes can be either active (with excitatory time‐dependent boundary conditions) or passive (where no dynamics take place, i.e. only Kirchhoff laws are imposed). While well‐posedness of the system has already been obtained in previous works, using abstract tools based on variational methods and semigroup theory we are able to prove several qualitative properties, including asymptotic behaviour, regularity of solutions, and monotonicity of the semigroups in dependence on the physical coefficients. Copyright © 2006 John Wiley & Sons, Ltd.     

Selective detection of echoEPR signals due to naturally substituted13C radicals in a single crystal of ammonium tartrate

Echo-detected electron paramagnetic resonance (echoEPR) profiles for irradiated deuterated ammonium tartrate single crystals depend strongly on the delays between pulses of the echo sequence. This is mainly due to instantaneous and spectral diffusion that plays a crucial role in determining the decay of the echo at every field position: the dephasing rate 1/7_M depends on the number of spins excited by the pulses and on the total number of interacting spins. A rigorous simulation of the echoEPR profiles at different delays requires the evaluation of the modulation pattern (ESEEM) and of the dephasing processes at every field position. From the simulations, information on the microscopic radical concentration, and on the electron-electron flip-flop rates of the single radical species can be obtained. Natural isotope¹³C substitution generates low-concentration radicals with relaxation properties different from the equivalent¹²C-substitued radicals. The different behavior is discussed.     

Simple and Friendly Sulfones Synthesis Using Aqueous Hydrogen Peroxide with a Reusable Keggin Molybdenum Heteropolyacid,Immobilized on Aminopropyl-Functionalized Silica

Keggin molybdenum heteropolyacid (H₃PMo₁₂O₄₀), immobilized on aminopropyl-functionalized silica catalysts, were made using two immobilization methods: incipient wetness and equilibrium adsorption. The material prepared for the equilibrium adsorption technique was found to be a highly efficient, ecofriendly, and recyclable heterogeneous catalyst for the selective oxidation of sulfides to sulfones in excellent yields, under mild reaction condition using 35% w/v aqueous hydrogen peroxide as the oxidant.     

Effect of gamma-irradiation on the levels of total and cis/trans isomers of beta-carotene in dehydrated parsley

Ionizing radiation is a method for preservation of foods that use the high energy of gamma rays or accelerated electrons, thereby ionizing molecules. The most important precursor of vitamin A is β-carotene, a carotenoid with pro-vitamin A activity. The highly unsaturated chain confers the instability of β-carotene, and some reactions, as isomerisation, can reduce the characteristics of pro-vitamin A. The present study investigated whether increasing doses of 0, 10 and 20 kGy lower the total β-carotene level and if an enhancement of cis-isomers occurred on samples of dehydrated parsley. No differences were observed of either fractions analyzed at doses applied in this study, nor did it contribute to the decrease of vitamin A.     

Resonance assisted synchronization of coupled oscillators: frequency locking without phase locking

Frequency locking without phase locking of two coupled nonlinear oscillators is experimentally demonstrated. This synchronization regime is found for two coupled laser modes, beyond the phase-locking range fixed by Adler's equation, because of a resonance mechanism. Specifically, we show that the amplitudes of the two modes exhibit strong fluctuations that produce average frequency synchronization, even if the instantaneous phases are unlocked. The experimental results are in good agreement with a theoretical model.     

Interference of coherent polariton beams in microcavities: polarization-controlled optical gates

We demonstrate, theoretically and experimentally, a polarization-controlled optical gate based on a degenerate polariton-polariton scattering process occurring in semiconductor microcavities. Because of the interference between coherent polaritons, this process is observed in the case of polaritons generated from two collinearly polarized coherent pump beams. On the contrary, if the beams are cross polarized, the scattering is suppressed.