3-Sasakian manifolds, 3-cosymplectic manifolds and Darboux theorem

We present a compared analysis of some properties of 3-Sasakian and 3-cosymplectic manifolds. We construct a canonical connection on an almost 3-contact metric manifold which generalises the Tanaka–Webster connection of a contact metric manifold and we use this connection to show that a 3-Sasakian manifold does not admit any Darboux-like coordinate system. Moreover, we prove that any 3-cosymplectic manifold is Ricci-flat and admits a Darboux coordinate system if and only if it is flat.     

The first total synthesis of the (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid and related analogs with antileishmanial activity

The first total synthesis of the marine cyclopropane fatty acid (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid was accomplished in eight steps and in 9.1% overall yield starting from 1-bromo-12-methyltridecane. The cis analog (±)-17-methyl-cis-4,5-methyleneoctadecanoic acid was also synthesized but in seven steps and in 16.4% overall yield. With the two isomeric cyclopropane fatty acids at hand it was possible to unequivocally corroborate the trans relative configuration of the naturally occurring fatty acid by gas chromatographic co-elution of the corresponding methyl esters. The cis isomer was cytotoxic to Leishmania donovani promastigotes with an IC₅₀ of 300.2 ± 4.2 μM.     

How Does Photoreceptor UVR8 Perceive a UV‐B Signal?

UVR8 is the only known plant photoreceptor that mediates light responses to UV‐B (280–315 nm) of the solar spectrum. UVR8 perceives a UV‐B signal via light‐induced dimer dissociation, which triggers a wide range of cellular responses involved in photomorphogenesis and photoprotection. Two recent crystal structures of Arabidopsis thaliana UVR8 (AtUVR8) have revealed unusual clustering of UV‐B‐absorbing Trp pigments at the dimer interface and provided a structural framework for further mechanistic investigation. This review summarizes recent advances in spectroscopic, computational and crystallographic studies on UVR8 that are directed toward full understanding of UV‐B perception at the molecular level.     

STM studies of cyclohexene hydrogenation/dehydrogenation and its poisoning by carbon monoxide on Pt(1 1 1)

A scanning tunneling microscope that can be operated in ultra high vacuum (<10⁻⁹ Torr) as well as at high pressures (1 − 10³ Torr) has been utilized to study the structures formed by cyclic C₆ hydrocarbons adsorbed on a platinum (1 1 1) crystal surface. Catalytic reactions of cyclohexene were also studied in the presence of hydrogen at pressures (up to 200 mTorr) and 300 K-350 K temperature range. Cyclohexane and cyclohexene produced the same adsorbed structure, which is attributed to the partially dehydrogenated π-allyl (C₆H₉). 1,3-Cyclohexadiene produced structures similar to those produced by benzene. In contrast 1,4-cyclohexadiene forms a structure that we attribute to intact molecular 1,4-cyclohexadiene. During reaction the STM images appear disordered, indicative of rapid diffusion of surface species. Addition of 5 mTorr of CO stops the catalytic activity and forms an ordered structure on the surface.     

Classical spin-field model of a one-dimensional ferromagnet in an external magnetic field

The low temperature field dependent magnetization and susceptibility of the linear ferromagnet CsNiF₃ are compared with calculations for a one-dimensional classical spin field model.     

Affine Projections on Adapted Subalgebras of Continuous Functions

In this paper we study a particular class of positive projections defined on an adapted subalgebra of continuous real-valued functions. Among other things, we characterize the existence of such projections in terms of representing measures concentrated on the Choquet boundary and we show their strong connection with the abstract Dirichlet problem. Finally we show how to construct Korovkin subsets for such projections. Mathematics Subject classification (2000): Primary:47B38, 47B65, 31C99. Secondary 46E25, 41A36.     

EXAFS study of iron monomers and dimers isolated in solid argon

We report a study of local structure of iron monomers and dimers isolated in a rare gas Ar matrix using extended X-ray absorption fine structure measurements. The results have been compared with Mössbauer measurements on such systems. The interatomic distance found for Fe₂ in these measurements is 1.87 ± 0.13 Å.     

Dynamics of surface catalyzed reactions; the roles of surface defects, surface diffusion, and hot electrons

The mechanism that controls bond breaking at transition metal surfaces has been studied with sum frequency generation (SFG), scanning tunneling microscopy (STM), and catalytic nanodiodes operating under the high-pressure conditions. The combination of these techniques permits us to understand the role of surface defects, surface diffusion, and hot electrons in dynamics of surface catalyzed reactions. Sum frequency generation vibrational spectroscopy and kinetic measurements were performed under 1.5 Torr of cyclohexene hydrogenation/dehydrogenation in the presence and absence of H(2) and over the temperature range 300-500 K on the Pt(100) and Pt(111) surfaces. The structure specificity of the Pt(100) and Pt(111) surfaces is exhibited by the surface species present during reaction. On Pt(100), pi-allyl c-C6H9, cyclohexyl (C6H11), and 1,4-cyclohexadiene are identified adsorbates, while on the Pt(111) surface, pi-allyl c-C6H9, 1,4-cyclohexadiene, and 1,3-cyclohexadiene are present. A scanning tunneling microscope that can be operated at high pressures and temperatures was used to study the Pt(111) surface during the catalytic hydrogenation/dehydrogenation of cyclohexene and its poisoning with CO. It was found that catalytically active surfaces were always disordered, while ordered surface were always catalytically deactivated. Only in the case of the CO poisoning at 350 K was a surface with a mobile adsorbed monolayer not catalytically active. From these results, a CO-dominated mobile overlayer that prevents reactant adsorption was proposed. By using the catalytic nanodiode, we detected the continuous flow of hot electron currents that is induced by the exothermic catalytic reaction. During the platinum-catalyzed oxidation of carbon monoxide, we monitored the flow of hot electrons over several hours using a metal-semiconductor Schottky diode composed of Pt and TiO2. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path, resulting in the ballistic transport of hot electrons through the metal. The electron flow was detected as a chemicurrent if the excess electron kinetic energy generated by the exothermic reaction was larger than the effective Schottky barrier formed at the metal-semiconductor interface. The measurement of continuous chemicurrent indicated that chemical energy of exothermic catalytic reaction was directly converted into hot electron flux in the catalytic nanodiode. We found the chemicurrent was well-correlated with the turnover rate of CO oxidation separately measured by gas chromatography.     

3-Quasi-Sasakian manifolds

In the present article we carry on a systematic study of 3-quasi-Sasakian manifolds. In particular, we prove that the three Reeb vector fields generate an involutive distribution determining a canonical totally geodesic and Riemannian foliation. Locally, the leaves of this foliation turn out to be Lie groups: either the orthogonal group or an abelian one. We show that 3-quasi-Sasakian manifolds have a well-defined rank, obtaining a rank-based classification. Furthermore, we prove a splitting theorem for these manifolds assuming the integrability of one of the almost product structures. Finally, we show that the vertical distribution is a minimum of the corrected energy.