A valuable, inexpensive Cui/n-heterocyclic carbene catalyst for the selective diboration of styrene

The complexes [Cu(NHC)(NCMe)]BF4 (NHC=N-heterocyclic ligand), with bis(catecholato)diboron (B2(cat)2) as the boron source, efficiently catalyze the diboration of styrene with very high degrees of conversion. With the appropriate NHC ligand, the reaction proceeds quantitatively toward the diborated derivative PhCH(Bcat)--CH2(Bcat). The [styrene]/[B2(cat)2] ratio also has a strong effect on the selectivity: the use of an excess of styrene allows modification of the selectivity toward the formation solely of the monoborated derivative, PhCH2--CH2(Bcat). DFT calculations suggest that no oxidative addition processes take place at copper, but that intermediates containing coordinated sigma-bonds are involved in the catalytic cycle.     

Rank tests for functional data based on the epigraph,the hypograph and associated graphical representations

Advances in Data Analysis and Classification - Visualization techniques are very useful in data analysis. Their aim is to summarize information into a graph or a plot. In particular, visualization...     

THE UV PROTEIN FLUORESCENCE OF PURPLE MEMBRANE AND ITS APOMEMBRANE

The ultraviolet fluorescence of the purple membrane of H. halobium and its apomembrane was characterized by measuring emission spectra, polarization, decay lifetimes and the changes induced by pH and temperature. The fluorescence quantum yields of the two membranes are 0.024 × 0.003 and 0.17 × 0.03, respectively. The emission, which shows lifetimes in the 0.4 to 4 ns range, was assigned to heterogeneous populations of emitters, consisting, probably, of two tryptophans in the purple membrane and seven or eight residues in the apomembrane. Acrylamide quenching experiments showed that the accessibility of this neutral quencher to the fluorophors is reduced greatly in both membranes. Fluorimetric methods were also used in an attempt to monitor the purple complex reconstitution process. It was concluded that the fluorescence quantum yields of any monomers, dimers and trimers present in the partially reconstituted membranes should be very similar.
Finally, based on the spectroscopic results and on specific folding patterns of the seven α-helical regions of bacteriorhodopsin (Stoeckenius and Bogomolni, 1982), it is proposed that Trp 137, Trp 138 (and perhaps Trp 10) of the protein molecule are the most plausible fluorophors in the purple membrane. It is also suggested that the protein in the apomembrane takes a more open configuration which is permeable to small ions and molecules.     

The nonlinear diffusion-convection equation on the semiline with time-dependent flux at the origin

The nonlinear diffusion-convection equation is considered as a phenomenological model of two-phase flow in a semi-infinite porous medium. For such a model the initial/boundary value problem is solved with a general initial datum and a boundary condition at the origin representing a time-dependt t flux. The problem is reduced to a linear integral equation of Volterra type in one dependent variable; in some cases of applicative interest this equation can be solved by quadratures.Dipleave while serving as Secretary-General of Pugwash Conferences on Sciences and World Affairs, Geneva-London-Rome.Dipartimento de Fisica, Universita di Roma La Sapienza, 00185 Roma, Italy. Instituto Nazionale di Fisica Nucleare, Sezione di Roma, Dipartimento di Fisica, Universita di Perugia, 06100 Perugia, Italy. Translated from Teoreticheskaya i Matemaaticheskaya Fizika, Vol. 99, No. 2, pp. 211–219, May, 1994.     

Modelling the air transport with complex networks: A short review

Air transport is a key infrastructure of modern societies. In this paper we review some recent approaches to air transport, which make extensive use of theory of complex networks. We discuss possible networks that can be defined for the air transport and we focus our attention to networks of airports connected by flights. We review several papers investigating the topology of these networks and their dynamics for time scales ranging from years to intraday intervals, and consider also the resilience properties of air networks to extreme events. Finally we discuss the results of some recent papers investigating the dynamics on air transport network, with emphasis on passengers traveling in the network and epidemic spreading.     

Elastic rods in life- and material-sciences: A general integrable model

The study of elastic deformations in thin rods has recently seen renewed interest due to the close connection between these systems and coarse-grained models of widespread application in life- and material-sciences. Until now, the analysis has been restricted to the solution of equilibrium equations for continuous models characterized by constant bending and twisting elastic moduli and/or by isotropic rod section. However, more realistic models often require more general conditions: indeed this is the case whenever microscopic information issuing from atomistic simulations is to be transferred to analytic or semi-analytic coarse-grained or macroscopic models. In this paper we will show that integrable, indeed solvable, equations are obtained under quite general conditions and that regular (e.g. circular helical) solutions emerge from reasonable choices of elastic stiffnesses.     

On the modeling of collective learning dynamics

This paper deals with the modeling of the collective learning dynamics of two systems of a heterogeneously distributed population. The first one evolves autonomously towards higher levels of knowledge, while the second system learns from the first one. The approach is based on the mathematical kinetic theory for active particles. The modeling focuses on applications to life sciences.