Competitive hydrogenation in binary diene systems on a palladium catalyst

Summary Hydrogenations of individual C₅ dienic substrates (1,3-cyclopentadiene, isoprene, 1,4-pentadiene, cis-1,3-pentadiene, trans-1,3-pentadiene) and their binary mixtures on a heterogeneous palladium catalyst were studied in cyclohexane at 25°C and 2 MPa. Selectivities of the competitive hydrogenations were determined and the substrates relative adsorption coefficients calculated. Effects of the diene structure on their reactivity and the stability of the surface complex are discussed. It was found that differences in selectivity of the competitive hydrogenations of C₅ dienes are caused by the difference both in adsorptivity values and in reactivity of adsorbed molecules. The presence of a five-membered ring in the C₅ dienes leads, , in significant reduction of surface complex stability as compared with acyclic structures of C₅ dienes. On the other hand, it has a very positive effect on the rate of surface reaction.     

First-order invariant Einstein-Cartan variational structures

A first-order invariant Einstein-Cartan structure is a Lagrangian structure on a differential manifold defined by a generally invariant Lagrangian depending on a metric field, a connection field, and the first derivatives of these fields. Moreover, it is assumed that the metric and connection fields satisfy the so-called compatibility condition. In this paper the problem of finding all such invariant Einstein-Cartan structures is discussed. It is shown that each Lagrangian of these structures depends only on certain tensors constructed from the metric and the connection fields, which means that all the Lagrangians can be described within the framework of the classical theory of invariants. The maximal number of functionally independent Lagrangians is determined as a function of the dimension of the underlying manifold.     

Reversible two-photon optical data storage in coumarin-based copolymers

A functionalized polymer film allowing for a complete and straightforward second-harmonic generation (SHG)-assisted high-contrast writing-reading-erasing-writing sequence is proposed. The whole process is supported by the reversible photoinduced dimerization of a coumarin chromophore and enables efficient optical data storage that can be detected only by SHG imaging.     

Lagrange theory in fibered manifolds

Some basic notions and theorems of the Lagrange theory in fibered manifolds are stated, with the stress on coordinate-free formulation of the theory.     

Principal bundle structure on jet prolongations of frame bundles

In this paper, we introduce the structure of a principal bundle on the r-jet prolongation J ^r FX of the frame bundle FX over a manifold X. Our construction reduces the well-known principal prolongation W ^r FX of FX with structure group G _n ^r . For a structure group of J ^r FX we find a suitable subgroup of G _n ^r . We also discuss the structure of the associated bundles. We show that the associated action of the structure group of J ^r FX corresponds with the standard actions of differential groups on tensor spaces.     

Physiological and Biochemical Parameters of Common Duckweed Lemna minor after the Exposure to Tetracycline and the Recovery from This Stress

In this study, the ability of Lemna minor L. to recover to normal growth, after being degraded in a tetracycline-containing medium, was extensively investigated. The plants were exposed to tetracycline (TC) at concentrations of 1, 2.5, and 10 mM. Subsequently, their physiological status was analysed against the following criteria: rate of plant growth; free radical accumulation; antioxidant enzyme activity; chlorophyll content; HSP70 protein content; cell membrane permeability, and mitochondrial activity. The study showed that duckweed can considerably recover from the damage caused by antibiotics, within a week of cessation of stress. Of the plant properties analysed, mitochondrial activity was the most sensitive to antibiotic-induced disturbances. After transferring the plants to a tetracycline-free medium, all plant parameters improved significantly, except for the mitochondrial activity in the plants grown on the medium containing the highest dose of tetracycline. In the plants treated with this antibiotic at the concentration of 10 mM, the proportion of dead mitochondria increased and was as high as 93% after one week from the beginning of the recovery phase, even after the transfer to the tetracycline-free medium.