Theoretical study of the role of solvent Stark effect in electron transitions

The possible influence of the solvent Stark effect (SSE) on the solvatochromic shift in electron transitions has been analyzed by using the ASEP/MD (averaged solvent electrostatic potential from molecular dynamics) method. With this purpose, four molecules, two polar (acrolein and formaldehyde) and two non-polar (p-difluorobenzene and trans-difluoroethene) have been studied in solvents of diverse polarity. Independently of the nature of the system we found that the contribution of SSE on the average value of the solvent shift or on the multipole moment values is negligible. In the case of centro-symmetric molecules, our results permit to discard the SSE as cause of the solvent shift found, which must be assigned to the electrostatic interaction of the solute quadrupole and higher multipoles with the solvent. As the SSE values provide also a measure of the errors introduced by the mean field approximation (MFA), these results indicate that MFA permits a very accurate determination of the solvent shift at the same time that it reduces drastically the computational cost. Finally, a new procedure suited to the ASEP/MD method has been presented that permits to estimate the inhomogeneous broadening of spectral bands, complementing the information provided by mean field theories. This procedure does not need additional quantum calculations and its computational cost is minimal.     

Separation and Preconcentration by Dispersive Liquid�CLiquid Microextraction Procedure: Recent Applications

Dispersive liquid?Cliquid microextraction (DLLME) is a relatively novel miniaturized sample pre-treatment technique. DLLME has been applied for the analysis of a large variety of organic compounds and metal ions in different samples. This paper reviews the more recent applications of this procedure for sample preparation.     

Cyclodextrins in innovative engineering tools for risk-based environmental management

Experimental results, which may serve as basis for innovative applications of cyclodextrins (CDs) in environmental technologies, are presented here. Some newly developed CD-aided tools are used in sampling, measuring the concentration or testing the effect of contaminants in water and soil. The innovative methods such as the bacterial bioassays with CD-increased sensitivity or the CD-filled absorptive samplers for air and water sampling are utilised in environmental exposure, hazard and risk assessment. Technological developments aim the reduction of the risk of chemical substances in waters and soils. CD-aided environmental remediation is introduced through examples for the elimination of organic contaminants from water by CD-filters, and for the enhancement of the mobility and availability of soil contaminants in this way increasing the efficiency of soil remediation by water extraction, chemical oxidation, biodegradation, etc.     

Influence of rhodium additive on hydrogen electrosorption in palladium-rich Pd�CRh alloys

Hydrogen electrosorption into Pd-rich (>80?at.% Pd in the bulk) Pd?CRh alloys has been studied in acidic solutions (0.5?M H₂SO₄) using cyclic voltammetry and chronoamperometry. The influence of temperature (in the range between 283 and 328?K), electrode potential and alloy bulk composition on hydrogen electrosorption properties of Pd?CRh alloys is presented. It has been found that the additive of Rh to Pd?CRh alloys increases the maximum hydrogen solubility (for Rh bulk content below 10?at.%), decreases the potential of absorbed hydrogen oxidation peak and decreases the potential of the ???????? phase transition. Increasing temperature decreases the potential of absorbed hydrogen oxidation peak, the maximum hydrogen solubility, and the potential of the ???????? phase transition. The amounts of electrosorbed hydrogen for ??- and ??-phase boundaries, i.e., ??_max and ??_min, have been determined from the integration of the initial parts of current?Ctime responses in hydrogen absorption and desorption processes. The H/M ratio corresponding to ??_max increases with increasing Rh content, while for ??_min a maximum of H/M ratio is observed for the alloys containing ca. 95% Rh.     

The N- and C-terminal domains of parathyroid hormone-related protein affect differently the osteogenic and adipogenic potential of human mesenchymal stem cells

Parathyroid hormone-related protein (PTHrP) is synthesized by diverse tissues, and its processing produces several fragments, each with apparently distinct autocrine and paracrine bioactivities. In bone, PTHrP appears to modulate bone formation in part through promoting osteoblast differentiation. The putative effect of PTH-like and PTH-unrelated fragments of PTHrP on human mesenchymal stem cell (MSCs) is not well known. Human MSCs were treated with PTHrP (1-36) or PTHrP (107-139) or both (each at 10 nM) in osteogenic or adipogenic medium, from the start or after 6 days of exposure to the corresponding medium, and the expression of several osteoblastogenic and adipogenic markers was analyzed. PTHrP (1-36) inhibited adipogenesis in MSCs and favoured the expression of osteogenic early markers. The opposite was observed with treatment of MSCs with PTHrP (107-139). Moreover, inhibition of the adipogenic differentiation by PTHrP (1-36) prevailed in the presence of PTHrP (107-139). The PTH/PTHrP type 1 receptor (PTH1R) gene expression was maximum in the earlier and later stages of osteogenesis and adipogenesis, respectively. While PTHrP (107-139) did not modify the PTH1R overexpression during adipogenesis, PTHrP (1-36) did inhibit it; an effect which was partially affected by PTHrP (7-34), a PTH1R antagonist, at 1 µM. These findings demonstrate that both PTHrP domains can exert varying effects on human MSCs differentiation. PTHrP (107-139) showed a tendency to favor adipogenesis, while PTHrP (1-36) induced a mild osteogenic effect in these cells, and inhibited their adipocytic commitment. This further supports the potential anabolic action of the latter peptide in humans.     

An Algorithm to Find the Lineality Space of the Positive Hull of a Set of Vectors

The positive hull of a finite set of vectors, V{\cal V}, in d-dimensional space may or may not contain a lineality space L{\cal L}. This article presents an algorithm that identifies the vectors of V{\cal V} that belong to L{\cal L}. This is done by means of a sequence of supporting hyperplanes because every supporting hyperplane of the positive hull of V{\cal V} contains L{\cal L}. Computational results show the effectiveness of the algorithm, which is compared to the best procedure currently available (to the best knowledge of the author) that solves the same problem. The algorithm introduced here is especially efficient in the case of large problems, where cardinality and/or dimensions are large.     

Stability and convergence in discrete convex monotone dynamical systems

We study the stable behaviour of discrete dynamical systems where the map is convex and monotone with respect to the standard positive cone. The notion of tangential stability for fixed points and periodic points is introduced, which is weaker than Lyapunov stability. Among others we show that the set of tangentially stable fixed points is isomorphic to a convex inf-semilattice, and a criterion is given for the existence of a unique tangentially stable fixed point. We also show that periods of tangentially stable periodic points are orders of permutations on n letters, where n is the dimension of the underlying space, and a sufficient condition for global convergence to periodic orbits is presented.     

Coincidence theorems and its applications to equilibrium problems

Given two maps h : X ×K ? \mathbbR{h : X \times K \rightarrow \mathbb{R}} and g : X → K such that, for all x ? X, h(x, g(x)) = 0{x \in X, h(x, g(x)) = 0} , we consider the equilibrium problem of finding [(x)\tilde] ? X{\tilde{x} \in X} such that h([(x)\tilde], g(x)) 3 0{h(\tilde{x}, g(x)) \geq 0} for every x ? X{x \in X} . This question is related to a coincidence problem.     

Pivoting in Extended Rings for Computing Approximate Gr?bner Bases

It is well known that in the computation of Gr?bner bases arbitrarily small perturbations in the coefficients of polynomials may lead to a completely different staircase, even if the solutions of the polynomial system change continuously. This phenomenon is called artificial discontinuity in Kondratyev’s Ph.D. thesis. We show how such phenomenon may be detected and even “repaired” by using a new variable to rename the leading term each time we detect a “problem”. We call such strategy the TSV (Term Substitutions with Variables) strategy. For a zero-dimensional polynomial ideal, any monomial basis (containing 1) of the quotient ring can be found with the TSV strategy. Hence we can use TSV strategy to relax term order while keeping the framework of Gr?bner basis method so that we can use existing efficient algorithms (for instance the F ₅ algorithm) to compute an approximate Gr?bner basis. Our main algorithms, named TSVn and TSVh, can be used to repair artificial e{\epsilon}-discontinuities. Experiments show that these algorithms are effective for some nontrivial problems.