Intrinsic theory of projective changes in Finsler geometry

The aim of the present paper is to provide an intrinsic investigation of projective changes in Finsler geometry, following the pullback formalism. Various known local results are generalized and other new intrinsic results are obtained. Nontrivial characterizations of projective changes are given. The fundamental projectively invariant tensors, namely, the projective deviation tensor, the Weyl torsion tensor, the Weyl curvature tensor and the Douglas tensor are investigated. The properties of these tensors and their interrelationships are obtained. Projective connections and projectively flat manifolds are characterized. The present work is entirely intrinsic (free from local coordinates) (arXiv:?0904.?1602 [math.DG]).     

Molecular modeling simulation and experimental measurements to characterize chitosan and poly(vinyl pyrrolidone) blend interactions

Blends of chitosan and poly(vinyl pyrrolidone) (PVP) have a high potential for use in various biomedical applications and in advanced drug‐delivery systems. Recently, the physical and chemical properties of these blends have been extensively characterized. However, the molecular interaction between these two polymers is not fully understood. In this study, the intermolecular interaction between chitosan and PVP was experimentally investigated using ¹³C cross‐polarization magic angle‐spinning nuclear magnetic resonance (¹³C CP/MAS NMR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). According to these experimental results, the interaction between the polymers takes place through the carbonyl group of PVP and either the OH? C₆, OH? C₃, or NH? C₂ of chitosan. In an attempt to identify the interacting groups of these polymers, molecular modeling simulation was performed. Molecular simulation was able to clarify that the hydrogen atom of OH? C₆ of chitosan was the most favorable site to form hydrogen bonding with the oxygen atom of C?O of PVP, followed by that of OH? C₃, whereas that of NH? C₂ was the weakest proton donor group. The nitrogen atom of PVP was not involved in the intermolecular interaction between these polymers. Furthermore, the interactions between these polymers are higher when PVP concentrations are lower, and interactions decrease with increasing amounts of PVP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1258–1264, 2008     

Renormalized Solutions of Nonlinear Parabolic Equations in Weigthed Variable-Exponent Space

This article is devoted to study the existence of renormalized solutions for the nonlinear p(x)-parabolic problemin the Weighted-Variable-Exponent Sobolev spaces, without the sign condition and the coercivity condition.     

Existence of Renormalized Solutions of Nonlinear Elliptic Problems in Weighted Variable-Exponent Space

In this article, we study a general class of nonlinear degenerated elliptic problems associated with the differential inclusion $β(u)-div(a(x,Du)+F(u)) ∋ f$ in $Ω$ where $f ∈ L^1(Ω).$ A vector field $a(.,.)$ is a Carathéodory function. Using truncation techniques and the generalized monotonicity method in the framework of weighted variable exponent Sobolev spaces, we prove existence of renormalized solutions for general $L^1$-data.     

Angular dependence of the critical current density and the temperature scaling of the flux pinning force in YBCO thin film

In this paper, the critical current J_c(Θ) have been investigated as a function of magnetic-field angle Θ. Θ is the angle between the c-axis and the applied magnetic field direction. This investigation concerned three temperature values (60?K, 78?K and 81?K). The normalized pinning force f_p versus the normalized magnetic field h was also studied (f_p?=?F_p / F_pmax and h?=?H / H_max). The F_p expression was determined based on the Kramer model.The studied sample was a single crystal of YBaCuO thin film deposited by the ablation laser method on the surface (100) of a SrTiO₃ substrate.The results of this work show the existence of point core pinning of the normal centers in the low field regime and the occurrence of the flux creep in high field regime.     

Theoretical Density Functional Theory insights into the nature of chalcogen bonding between CX2 (X = S,Se, Te) and diazine from monomer to supramolecular complexes

Chalcogen bonding is a noncovalent interaction, highly similar to halogen and hydrogen bonding, occurring between a chalcogen atom and a nucleophilic region. Two density functional theory (DFT) approaches B3LY-D3 and B97-D3 were performed on a series of complexes formed between CX₂ (X = S, Se, Te) and diazine (pyridazine, pyrimidine and pyrazine). Chalcogen atoms prefer interacting with the lone pair of a nitrogen atom rather than with the π-cloud of an aromatic ring. CTe₂ and CSe₂ form a stronger chalcogen bond than CS₂. The electrostatic potential of CX₂ (X = S, Se and Te) reveals the presence of two equivalent σ-holes, one on each chalcogen atom. These CX₂ molecules interact with diazine giving rise to supramolecular interactions. Wiberg bond index and second-order perturbation theory analysis in NBO were performed to better understand the nature of the chalcogen bond interaction.     

Hemisynthesis,crystal structure and inhibitory effect of sesquiterpenic thiosemicarbazones and thiazolidin‐4‐ones on the corrosion behaviour of stainless steel in 1 M H2SO4 solution

Treatment of thiosemicarbazones prepared from sesquiterpenes with ethyl 2‐bromoacetate in the presence of sodium acetate afforded the corresponding thiazolidin‐4‐ones. The structures of all the newly synthesized compounds were established by considering spectral and single‐crystal X‐ray diffraction data. The title compound, ethyl 2‐((Z)‐2‐{(Z)‐[(1aR,5aR,9aS)‐1,1‐dichloro‐1a,5,5,7‐tetramethyl‐1a,2,3,4,5,5a,8,9‐octahydro‐1H‐benzo[a]cyclopropa[b][7]annulen‐8‐ylidene]hydrazono}‐4‐oxothiazolidin‐3‐yl)acetate, C₂₃H₃₁Cl₂N₃O₃S, 5 , crystallizes in the orthorhombic noncentrosymmetric space group P2₁2₁2₁ with Z = 4. Within the molecule in the crystal structure, the cyclohexene ring has an envelope conformation and the cycloheptane ring, to which it is fused, has a boat conformation. In the crystal, molecules are linked by C—H…Cl hydrogen bonds forming chains propagating along the b‐axis direction. The absolute configuration of the molecule in the crystal could be fully confirmed from anomalous dispersion effects [Flack parameter = ?0.04 (2)]. Thiosemicarbazones 1 and 2 are efficient inhibitors for steel corrosion in 1 M H₂SO₄ solution, with a maximum efficiency of 92.28% at 10^?3 M. Furthermore, thiosemicarbazone compounds were found to be more efficient than thiazolidin‐4‐one derivatives. In addition, cyclic voltammetry was used to characterize the tested molecules, as well to estimate the experimental value of the energy band gap.     

Existence results for periodic solutions of integro-dynamic equations on time scales

Using the topological degree method and Schaefer’s fixed point theorem, we deduce the existence of periodic solutions of nonlinear system of integro-dynamic equations on periodic time scales. Furthermore, we provide several applications to scalar equations, in which we develop a time scale analog of Lyapunov’s direct method and prove an analog of Sobolev’s inequality on time scales to arrive at a priori bound on all periodic solutions. Therefore, we improve and generalize the corresponding results in Burton et al. (Ann Mat Pura Appl 161:271–283, 1992)      

From imidates to vinyl-1,2,4-triazoles: Synthesis,mechanistic aspects and first issues of their reactivity

The reaction of variously substituted acylimidates with hydrazine derivatives represents an efficient and easy to set synthetic entry towards 5-vinyl-1,2,4-triazole derivatives. The construction of the triazole ring allows the installation of variety of substituent combination at the N(1), C(3) and C(5) positions of the five-membered heterocycle in good to high yields. The method reveals selective towards 5-vinyl-1,2,4-triazoles avoiding the potential formation of seven- and five-membered side-products as supported by theoretical calculations and NMR experiments. First lines of Pd-catalyzed arylation of the vinyl fragment towards 5-styryl-1,2,4-triazoles and Cu-catalyzed arylation at the N(1) site are finally described.     

Synthesis of imidazole derivatives: Ester and hydrazide compounds with antioxidant activity using ionic liquid as an efficient catalyst

The pyrrolidinium hydrogen sulfate (PHS) was used as an excellent ionic liquid catalyst for the preparation of many imidazoles moiety, which have biologically application via one-pot multicomponent reaction. Imidazoles were afforded through the reaction of equimolar from 1,2-diphenylethane-1,2-dione, ammonium acetate, different aromatic aldehydes, and ethyl glycinate hydrochloride. This method has the advantages of giving excellent yield, shortened reaction times, and ease of establishment. Moreover, the yielded of imidazoles components can be purified and crystallized by a nonchromatographic technique, and the catalyst can be reused. These entire novel synthesized components have been identified by spectral data: IR, NMR and mass spectra. These compounds have an in vivo antioxidant activity on experimental animals (rats).