Some algorithms for discrete time queues with finite capacity

We consider a discrete time queue with finite capacity and i.i.d. and Markov modulated arrivals. Efficient algorithms are developed to calculate the moments and the distributions of the first time to overflow and the regeneration length. Results are extended to the multiserver queue. Some illustrative numerical examples are provided. This revised version was published online in June 2006 with corrections to the Cover Date.     

Silica-supported tungstic acid (STA): A recyclable catalyst for the synthesis of 1H-indazolo [1,2-b]phthalazine-trione and spiro-triazolo[1,2-a]indazole-tetraone derivatives under solvent-free condition

Abstract

An efficient one-pot synthesis of 1?H-indazolo[1,2-b]phthalazine-trione and spiro-triazolo[1,2-a]indazole-tetraone derivatives via three-component condensation reaction of phthalhydrazide or 4-phenylurazole, aldehydes or isatins and dimedone in the presence of a catalytic amount of silica-supported tungstic acid (STA), as a heterogeneous solid acid catalyst under solvent-free conditions is presented. This ecofriendly protocol offers several advantages such as a cost-effective procedure with excellent yields, short reaction time, simple workup, recovery and reusability of catalyst with broad scope of usable substrates. This has made the protocol sustainable and economic.     

Simple and Efficient Method for the Synthesis of Benzimidazole Derivatives using Monoammonium Salt of 12‐Tungstophosphoric Acid

Benzimidazoles have been synthesized in very good yield from o‐phenylenediamine and aromatic aldehydes in the presence of monoammonium salt of 12‐tungstophosphoric acid [(NH₄)H₂PW₁₂O₄₀], an efficient heterogeneous catalyst. This catalyst has the advantages of simple workup procedure, water insolubility, and good activity with high yield for the synthesis of benzimidazole derivatives.     

Simple and Efficient Method for Acetylation of Alcohols,Phenols, Amines,and Thiols Using Anhydrous NiCl2 Under Solvent-Free Conditions

Solvent-free acetylation of alcohols, phenols, amines, and thiols with acetic anhydride (Ac₂O) in the presence of 0.1 mol% (13 mg) anhydrous NiCl₂, an inexpensive and easily available catalyst, is described. Excellent yields, short reaction time, and mild reaction conditions are important features of this method.     

Vinyl Polymerization of Ethyl Acrylate Initiated by TI3+-Ascorbic Acid Redox System

The application of polymers at ever-increasing temperatures has given impetus to research on the chemistry of thermal decomposition. In recent years polymers have been used for a variety of high-temperature applications, such as cooking vessels, motor insulation, and re-entry vehicle heat shields. Interest in chemistry of decomposition has been found in such industries as tobacco and grinding-wheels. Because of the vast number of polymers that are available and the variety of applications thousands of papers have appeared in the literature. Rather than give a complete review the purpose of this paper is to give a brief survey of topics that have been emphasized in the author's research, namely kinetics, mechanisms, and gaseous decomposition products at elevated temperatures.     

Use of ultrasound in leather processing Industry: Effect of sonication on substrate and substances – New insights

Influence of ultrasound (US) on various unit operations in leather processing has been studied with the aim to improve the process efficiency, quality, reduce process time and achieve near-zero discharge levels in effluent streams as a cleaner option. Effect of US on substrate (skin/leather) matrix as well as substances used in different unit operations have been studied and found to be useful in the processing. Absorption of US energy by leather in process vessel at different distances from US source has been measured and found to be significant. Effect of particle-size of different substances due to sonication indicates positive influence on the diffusion through the matrix. Our experimental results suggest that US effect is better realized for the cases with pronounced diffusion hindrance. Influence of US on bioprocessing of leather has been studied and found beneficial. Attempts have also been made to improve the US aided processing using external aids. Operating US in pulse mode operation could be useful in order to reduce the electrical energy consumption. Use of US has also been studied in the preparation of leather auxiliaries involving mass-transfer resistance. Preliminary cost analysis carried out for ultrasound-assisted leather-dyeing process indicates scale-up possibility. Therefore, US application provide improvement in process efficiency as well as making cleaner production methods feasible. Hence, overall results suggest that use of US in leather industry is imminent and potential viable option in near future.     

Diversity-oriented one-pot synthesis of furan based densely substituted biheteroaryls via isocyanide insertion

A facile and efficient acid-catalyzed cascade reaction for the synthesis of novel biheteroaryl structural motifs containing densely functionalized furans has been developed. The reaction sequence involves a Knoevenagel condensation of arylglyoxals with aroyl or heteroaroylacetonitrile and subsequently an isocyanide insertion via formal [4+1] cycloaddition followed by rapid [1,3]-H shift to afford uniquely decorated novel biheterocycles. Furthermore, the scope of the methodology was extended to diverse biheteroaryls by employing 3-(2-furyl)-3-oxopropanenitrile, 3-cyanoacetyl-1-methylindole, 3-oxo-3-(1H-pyrrol-2-yl)propanenitrile, 3-(1H-indol-3-yl)-3-oxopropanenitrile, 3-Oxo-3-(2-thienyl)propionitrile and benzoylacetonitriles.     

Thiosemicarbazone Scaffold as a Multidentate Ligand for Transition‐Metal Ions: Synthesis,Characterization, In Vitro Antimicrobial,Anthelmintic, DNA Cleavage,and Cytotoxic Studies

New series of Schiff bases derived from o‐substituted thiosemicarbazides and 8‐formyl‐7‐hydroxy‐4‐methylcoumarin have been synthesized and their coordination tendency toward Co(II), Ni(II), and Cu(II) metal ions is studied. Analytical, spectral (IR, UV‐Vis, ESR, and FAB‐mass), magnetic, and thermal studies suggests octahedral geometry of the type ML₂ for all the Co(II), Ni(II), and Cu(II) complexes. The complexes are soluble in DMF/DMSO and are non‐electrolytes. The Schiff bases and their metal complexes have been screened for antibacterial (Escherichia coli, Staphylococcus aureus, Salmonella typhi, and Pseudomonas aeruginosa) and antifungal activities (Aspergillus flavus, Aspergillus niger, and Cladosporium) by minimum inhibitory concentration method. DNA cleavage is studied by agarose gel electrophoresis method. Metal (II) complexes show good anthelmintic activity when compared to Schiff bases.     

Preorganizing linear (self-complementary) quadruple hydrogen-bonding arrays using intramolecular hydrogen bonding as the sole force

[structures: see text] In this article we describe a rational approach for prefixing multiple cooperative binding sites in an ideal spatial arrangement on a structurally rigid backbone, constrained exclusively by intramolecular hydrogen bonding. The idea is exemplified by the ability of the self-assembling constructs 1a-e and 2a,b to form hydrogen-bonded dimers, whose structural preorganization has been solely effected by intramolecular hydrogen bonding. The readily accessible amidinourea backbone has been used as a common platform for the construction of a variety of such self-assembling systems. ESI mass spectrometry and single-crystal X-ray diffraction studies have been particularly effective in investigating the self-assembling propensities of these systems. Remarkably, most the H-bonded dimers reported herein undergo an unusual mode of self-assembly, using intermolecular four-membered ring hydrogen-bonded interaction, affording extended supramolecular networks.     

Convenient high yield and stereoselective synthesis of O-glycopeptides using N-α-Fmoc-Tyr/Ser[β-d-Glc(OAc)4]OPfp generated in solution

Fmoc-AA-OPfp (AA=Tyr or Ser) (1 equiv) was reacted with β-d-Glc(OAc)₅ (6 equiv) in the presence of BF₃.Et₂O (6 equiv) in CH₂Cl₂ at room temperature for 2 h, and the glycosylation reaction mixture was used directly to couple to the amino group of the peptide resin without isolation and purification of the Fmoc-AA[β-d-Glc(OAc)₄]-OPfp. Moreover, the -OAc protecting groups of glucose was removed just prior to releasing the peptide from the resin using 6 mM NaOMe in 85% DMF-MeOH. The crude product obtained by TFA cleavage contained >90% of the target O-glycopeptide, and the 500 MHz ¹H NMR analysis revealed that the glycosylation reaction was nearly stereoselective (>97% β-anomer). This method is rapid and stereoselective, and can now be exploited for the routine synthesis of O-glycopeptides.