Photoluminescence Studies of Pr<Superscript>3+</Superscript> Doped Lead Germanate Glass

The Pr³⁺doped PbO-GeO₂ glass samples have been synthesized by melting and quenching process. The nephelauxetic ratio, covalency and bonding parameter which provides the information about the type of bonding between the rare earth ion and neighbor oxygen atoms calculated. The optical parameters such as radiative transition probabilities, radiative lifetime, branching ratios etc. of Pr³⁺ ions have been determined by Judd-Ofelt analysis. An upconversion emission using the excitation at ~594 nm supported by energy transfer process due to dipole-dipole interaction in the ¹D₂ metastable state has been found.     

Aminolysis of Epoxides in Ionic Liquid 1-Ethylpyridinium Trifluoroacetate as Green and Efficient Reaction Medium

Aminolysis of epoxides has been carried out using the ionic liquid 1-ethylpyridinium trifluoroacetate ([EtPy][TFA]) as reaction medium. The reactions went smoothly under mild conditions without any catalyst to afford corresponding β-aminoalcohols in high conversions. Moreover, further enhancement in the conversions was observed when AlCl₃ was used as Lewis acid catalyst.     

An environmentally friendly,cost effective synthesis of quinoxalines: the influence of microwave reaction conditions

A convenient, environmentally friendly and novel synthesis of quinoxalines using silica gel as the catalyst is described. The choice of microwave conditions has been shown to have a substantial impact on the reaction outcome with closed-vessel microwave irradiation resulting in the formation of quinoxalines in high yields and short reaction times. Preliminary mechanistic investigations have indicated that a slight build-up in pressure has a major impact on the reaction outcome.     

Piecewise static policies for two-stage adjustable robust linear optimization

Mathematical Programming - In this paper, we consider two-stage adjustable robust linear optimization problems under uncertain constraints and study the performance of piecewise static policies....     

On the power and limitations of affine policies in two-stage adaptive optimization

We consider a two-stage adaptive linear optimization problem under right hand side uncertainty with a min–max objective and give a sharp characterization of the power and limitations of affine policies (where the second stage solution is an affine function of the right hand side uncertainty). In particular, we show that the worst-case cost of an optimal affine policy can be times the worst-case cost of an optimal fully-adaptable solution for any δ > 0, where m is the number of linear constraints. We also show that the worst-case cost of the best affine policy is times the optimal cost when the first-stage constraint matrix has non-negative coefficients. Moreover, if there are only k ≤ m uncertain parameters, we generalize the performance bound for affine policies to , which is particularly useful if only a few parameters are uncertain. We also provide an -approximation algorithm for the general case without any restriction on the constraint matrix but the solution is not an affine function of the uncertain parameters. We also give a tight characterization of the conditions under which an affine policy is optimal for the above model. In particular, we show that if the uncertainty set, is a simplex, then an affine policy is optimal. However, an affine policy is suboptimal even if is a convex combination of only (m + 3) extreme points (only two more extreme points than a simplex) and the worst-case cost of an optimal affine policy can be a factor (2 − δ) worse than the worst-case cost of an optimal fully-adaptable solution for any δ > 0.     

Operational matrix approach for solution of integro-differential equations arising in theory of anomalous relaxation processes in vicinity of singular point

In this paper we study the numerical solution of singular Abel–Volterra integro-differential equations, which are typical for the theory of anomalous diffusion and viscoelastic delayed stresses. The proposed method is based on application of the operational and almost operational matrices to derivatives and integrals in a vicinity of the kernel’s singular point. As examples, two orthonormal systems are considered: Bernstein polynomials and Legendre wavelets. The methods convert the singular integro-differential equation in to a system of algebraic equations that implies two advantages: (i) one does not need to introduce artificial smoothing factors into the singular integrand and (ii) the direct estimation of computational error around singular point is possible via the obtained explicit expression. The examples of numerical solution and their discussion are presented.     

Diorganotin(IV) complexes of 2-chloridophenylacetohydroxamic acid as prospective antimicrobials: synthesis,characterization, and biological properties

New diorganotin(IV) complexes [Me₂Sn(2-ClC₆H₄CH₂CONHO)₂] (1) and [n-Bu₂Sn(2-ClC₆H₄CH₂CONHO)₂] (2) have been synthesized by reactions of Me₂SnCl₂ and n-Bu₂SnCl₂ with potassium 2-chloridophenylacetohydroxamate (2-ClPhAHK = 2-ClC₆H₄CH₂CONHOK) in 1:2 molar ratio in MeOH+C₆H₆ solvent medium and characterized by elemental analyses, molar conductivity, molecular weight determinations and spectroscopic techniques (IR, ¹H, ¹³C, and ¹¹⁹Sn NMR) and mass spectrometry. Bonding through carbonyl and hydroxamic oxygens (O,O coordination) and distorted-octahedral geometry around tin is proposed. The electrochemical behavior of 1 and 2 studied by cyclic voltammetry shows quasi-reversible reductions. Thermal behavior of 1 and 2 in N₂ shows decomposition in one step affording SnO as the residue. The in vitro antimicrobial activity assay against pathogenic Gram-negative bacteria viz. Salmonella typhi, Escherichia coli; Gram-positive Bacillus cereus and Staphylococcus aureus and fungi Aspergillus niger and Alternaria alternata by MIC method revealed their significant antimicrobial potential relative to the respective standard Chloramphenicol and Nystatin drugs.     

Correction to: Comparative qualitative analysis of different classes of compounds in selected Australian and Indian Eucalyptus and Corymbia species: a convenient de‑replication method for the eucalypts

JPC – Journal of Planar Chromatography – Modern TLC -     

Tribological behavior of Al-based self-lubricating composites

Abstract

Aluminum-based composites containing either SiC (Al10%SiC) as the hard phase or a combination of SiC and MoS₂ (Al10%SiC4%MoS₂) have been synthesized following stir casting route. To overcome the poor wetting characteristics, magnesium was added in one of the composites (Al10%SiC4%MoS₂4%Mg) to improve the bonding between matrix and second phase. The results suggested an enhancement in hardness and strength of the composite containing SiC–MoS₂ and Mg, thus indicating the effectiveness of Mg addition in improving the interfacial bonding strength. Tribological performance of the composites has been examined by carrying out pin-on-disk wear tests under dry sliding conditions at different normal loads of 9.8, 14.7, 19.6, and 24.5 N and at a constant sliding speed of 1 m/s. Both the friction coefficient and the wear rate have been found to reduce with addition of MoS₂; however, bonding between the matrix and reinforcements was not good. Al10%SiC4%MoS₂4%Mg has shown the best tribological performance at all the loads in terms of the lowest friction coefficient and the lowest wear rate. The wear mechanism has been found to be a combination of adhesion and abrasion as indicated by the presence of some abrasive grooves and delaminated flakes at the worn surface and the X-ray examination of wear debris for all the materials used in the present investigation.