177,239 research outputs found
Lipase catalysed resolution of (R)- and (S)-1-trimethylsilyl-1-alkyn-3-ols: Useful intermediates for the synthesis of optically active gamma-lactones
No full textVarious (R)- and (S)-1-trimethylsilyl-1-alkyn-3-ols, chiral building units useful for the synthesis of biologically active compounds, have been efficiently resolved by enantioselective acetylation mediated by immobilized lipase PS. The resolution is applied to the synthesis of (R)- and (S)-5-octyl-2-(5H)-furanone
Reduced collagen cross links : the first synthesis of all the possible (2S,2'S)-stereoisomers of 5-hydroxylysinonorleucine and of 5,5'-dihydroxylysinonorleucine in enantiomerically pure form
No full textThe paper reports the first enantioselective synthesis of all the possible collagen reduced cross links as described: ydroxylysinonorleucines I (R1 = R3 = R4 = H, R2 = OH; R1 = R2 = R4 = H, R3 = OH) and dihydroxylysinonorleucines I (R1 = R3 = H, R2 = R4 = OH; R3 = R4 = H, R1 = R2 = OH and R2 = R4 = H, R1 = R3 = OH). The Williams' glycine template methodol. was used both for the introduction of a stereogenic at the ?-position and for an easy protection of the amino acidic functionalities during the synthesis of the dimeric amino acids
Facile and rapid regeneration of free amino acids from N-benzyloxycarbonyl-5-oxazolidinones and from N-benzyloxycarbonylamino derivatives by treatment with BCl3 in dichloromethane
No full textReaction of benzyloxycarbonyl-5-oxazolidinones and of N-benzyloxycarbonylamino acids with BCl3 in dichloromethane at room temperature affords the corresponding free amino acids
On the basic properties and the structure of power cells
No full textAltres ajuts: acords transformatius de la UABGiven a set T⊆R and a nonnegative function r defined on T, we consider the power of x∈R with respect to the sphere with center t∈T and radius rt, that is, px,t:=x-t-rt, with · denoting the Euclidean distance. The corresponding power cell of s∈T is the set (Formula presented.) We study the structure of such cells and investigate the assumptions on r that allow for generalizing known results on classical Voronoi cells
A convenient two step transformation of tyrosine into the antihypertensive amino acid (S)-4-hydroxy-3-hydroxymethylphenylalanine
No full textTreatment of tyrosine with paraformaldehyde and catalytic amounts of p-toluenesulfonic acid, at reflux in toluene, directly generates benzyl (S)-4-(4H-1,3-benzodioxin-6-ylmethyl)-5-oxo-1,3-oxazolane-3-carboxylate, which on treatment with boron trichloride in dichloromethane, affords (S)-4-hydroxy-3-hydroxymethylphenylalanine
Comprehensive reconstruction of the external nose
No full textNasal defects can take place most often after oncological procedures or traumatic avulsions. Substance abuse is a more and more frequent cause of severe nasal deformities. Rarely even congenital diseases such as arhinia can lead to the need of complex nasal reconstructions. Whereas small defects of the skin are easily repaired with local flaps, more complex reconstructions must address the inner lining, the outer lining and the skeletal framework to obtain ideal results. The inner lining can be successfully reconstructed with mucosal flaps from the septum or the turbinate. Alternatively a previously skin-grafted forehead flap is usually sufficient. Major defects of the inner lining on the other hand require microvascular flaps. The workhorse of major reconstructions of the nasal skin is the forehead flap. It is ideal in terms of color and texture match, it is extremely reliable and if some technical aspects are respected, the results that are obtained are predictable. The reconstruction of the skeletal and cartilaginous framework is of the uttermost importance. Minor defects are easily reconstructed with small cartilaginous grafts harvested from the septum or the ear. On the other hand, the workhorse for major nasal reconstructions is the rib graft. This allows performing composite bony and cartilaginous reconstructions with enough tissue to rebuild the dorsum and the alae. Here the Authors present their experience with nasal reconstructions in nasal defects resulting from oncological procedures, from substance abuse and in arhinia
On an equilibrium problem with complementarity constraints formulation of pay-as-clear electricity market with demand elasticity
No full textWe consider a model of pay-as-clear electricity market based on a Equilibrium Problem with Complementarity Constraints approach where the producers are playing a noncooperative game parameterized by the decisions of regulator of the market (ISO). In the proposed approach the bids are assumed to be convex quadratic functions of the production quantity. The demand is endogenously determined. The ISO problem aims to maximize the total welfare of the market. The demand being elastic, this total welfare take into account at the same time the willingness to pay of the aggregated consumer, as well as the cost of transactions. The market clearing will determine the market price in a pay-as-clear way. An explicit formula for the optimal solution of the ISO problem is obtained and the optimal price is proved to be unique. We also state some conditions for the existence of equilibria for this electricity market with elastic demand. Some numerical experiments on a simplified market model are also provided
Spatial equilibrium problems: the carbon leakage effect on cement sector under different environmental policies
No full textThis paper proposes a Generalized Nash Game problem (GNEP) to study the possible cement production relocation from countries subject to environmental regulation to areas where environmental policies are not applied or are more lenient. This phenomenon takes the name of “carbon leakage” effect. This analysis is based on an oligopolistic partial equilib- rium model with a detailed technological representation of the cement market. An existence result for this GNEP is also provided
Census Transform Based Optical Flow for Motion Detection during Different Sinusoidal Brightness Variations
No full textThis work is a first approach of the implementation of a specific Optical Flow algorithm for motion detection in cases where the brightness variation is represented by a sine wave, whose characteristics vary across the different image sectors. The final goal would be the implementation of such an algorithm in thermal films recording a component undergoing a sinusoidal load. Mapping the motion field all over the thermal video time history, and deriving it in order to obtain a strain map, would enable both the simultaneous measurement of stress (by performing Thermoelastic Stress Analysis) and strain by a unique video, and the possibility of stress calibration, thus linking the digital levels in output to real stress values. In this scenario, the authors present the implementation of Census Transform based Optical Flow on a simulated video, where the brightness variation is modeled like the superimposition of sine waves equal for all pixels and different Gaussian spatial distributions frame after frame. The latter is used for creating different sine patterns for each image sector
Chemoselective synthesis of sialic acid 1,7-lactones
No full textThe chemoselective synthesis of the 1,7-lactones of N-acetylneuraminic acid, N-glycolylneuraminic acid, and 3-deoxy-D-glycero-D-galacto-nononic acid is accomplished in two steps: a simple treatment of the corresponding free sialic acid with benzyloxycarbonyl chloride and a successive hydrogenolysis of the formed 2-benzyloxycarbonyl 1,7-lactone. The instability of the 1,7-lactones to protic solvents has been also evidenced together with the rationalization of the mechanism of their formation under acylation conditions. The results permit to dispose of authentic 1,7-sialolactones to be used as reference standards and of a procedure useful for the preparation of their isotopologues to be used as inner standards in improved analytical procedures for the gas liquid chromatography-mass spectrometry (GLC-MS) analysis of 1,7-sialolactones in biological medi
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