GaCl3- and TiCl4-catalyzed insertion of isocyanides into a C-S bond of dithioacetals

The insertion reaction of isocyanide into a C-S bond of dithioacetals is catalyzed by GaCl3 or TiCl4 to afford thioimidates containing an alpha-alkylthio group. Balanced thiophilicity of these Lewis acids is critical for efficient catalysis.     

Analysis of hydrophilic metabolites by high-performance liquid chromatography-mass spectrometry using a silica hydride-based stationary phase

A novel silica hydride-based stationary phase was used to evaluate the retention behavior in the aqueous normal-phase (ANP) mode of standards representing three classes of metabolites. The effects on retention behavior of amino acids, carbohydrates and small organic acids were examined by altering the column temperature, and by adding different additives to both the mobile phase and sample solvent. Gradient mode results revealed the repeatability of retention times to be very stable for these compound classes. At both 15 and 30 degrees C, excellent RSD values were obtained with less than 1% variation for over 50 injections of an amino acid mixture. The ability to separate the 19 nonderivatized amino acid standards, organic acids and carbohydrates was demonstrated as well as the potential for this material to separate polar metabolites in complex fluids such as urine.     

Compositionally graded quaternary electron blocking layer for efficient deep ultraviolet AlGaN-based light-emitting diodes

Optical Review - We present the enhancement of ultraviolet (UV) light-emitting diodes (LEDs) using numerical analysis. We have employed a compositionally graded quaternary (AlInGaN) electron...     

Synthesis and Characterization of Some Thallium Cyclopentadienide Fused Ring Pyridazines

Thallium cyclopentadiene (Cp) salts are important precursors for the synthesis of a variety of compounds having materials and commercial applications. The synthesis of 5,6-fused ring thallium Cp pyridazines 2a–d from previously reported 5,6-fused ring pyridazines is described herein. This route was quite general, and features an efficient and convenient two-step synthesis of a series of TlCp salts in a THF solution of thallium ethoxide. Full characterization of newly formed TlCp salts 3a–d are reported.     

Optimization of modular machining lines

The paper summarizes the main results of the author’s Ph.D. thesis presented in December 2006 at the école des Mines de Saint étienne. The work was supervised by Alexandre Dolgui and Xavier Delorme. The thesis is written in French and is available upon request from the author. Its purpose is to provide decision support in the design and reconfiguration of modular machining lines with multi-spindle units. This design problem is defined as the selection of spindle units to perform a set of operations needed to produce the parts and subsequently their assignment to workstations. The corresponding optimization problem is solved using different models based on integer and constraint programming.      

Regularity of the Rotation Number for the One-Dimensional Time-Continuous Schr?dinger Equation

Starting from results already obtained for quasi-periodic co-cycles in $SL(2, \mathbb R),$ we show that the rotation number of the one-dimensional time-continuous Schr?dinger equation with Diophantine frequencies and a small analytic potential has the behavior of a $\frac{1}{2}-$ H?lder function. We give also a sub-exponential estimate of the length of the gaps which depends on its label given by the gap-labeling theorem.     

Joint project of fishery and poultry - A bioeconomic model

This paper considers the optimal joint harvest of prawns and poultry in a linked bioeconomic system. Through the cultivation process, poultry and prawns are reciprocal predators of one another. Prawns of non-marketable quality are fed to the birds, and birds which perish (in greater numbers in the face of increased density) are fed to prawns, along with a lot of other things that one does not usually consider prawns to eat (hogs, broken rice, etc.). The paper derives optimality conditions for the joint “effort” imposed in each of these industries, where effort is somehow analogous to the control variable in classical Gordon-Schaefer fishery problems. Growth of both species is governed by parameters as well as externally applied nutrients and the biomass of the other species available as supplemental nutrition. Analysis of the boundedness of this dynamical system is discussed. The conditions for local and global stability are derived. Finally, an optimal harvesting policy is discussed by applying Pontryagin’s Maximal Principle. Due to linearity of the objective function with respect to the control variable, the solution is bang-bang in this control and the best policy is to reach the singular equilibrium as quickly as possible by switching to the singular control.     

Recent synthetic methodologies for pyridopyrazines: An update

Abstract

Among heterocyclic compounds, pyridopyrazines are the scaffolds that have gained considerable attention on academic and industrial level due to their widespread applications as intermediates in the preparation of advanced and biologically potent pharmaceutical materials. Many pyridopyrazine derivatives are available in market to cure various pharmacological disorders. These candidates can be synthesized via a number of synthetic routes using various reagents like cyclocondensation of diaminopyridines with carbonyl compounds or their derivatives etc. In the present review, we have elaborated all these protocols along with different factors and reaction conditions such as use of metal catalyst, solvent-free and microwave irradiation, one-pot synthesis etc. that have resulted in high regioselectivity and yields. The review focuses on the synthetic methodologies developed in the last decade for different pyridopyrazine derivatives.