Estimation of optimal parameters yielding target amplitude–frequency response in nonlinear vibrating systems by a generalised cluster-based algorithm

Nonlinear Dynamics - Optimisation procedures for nonlinear vibrating systems are made cumbersome due to the fact that the regimes of periodic response are not known beforehand. Moreover, such...     

Digital Interferometric Measurement of Forced Convection Heat Transfer in a Miniature Rectangular Channel

Investigations have been performed on convective heat transfer in water flowing through mini-channels using the non intrusive technique of laser interferometry coupled with digital image processing. Optical glass channels, fabricated with metallic heating surfaces, were studied using a Mach-Zehnder interferometer configuration. Fringe patterns captured using a high-sensitivity CCD camera were analyzed digitally based on a calculation method developed for the liquid medium. Results of parametric studies were compared and contrasted with relevant theoretical solutions from the literature. Indication of the onset of turbulence at Reynolds numbers smaller than the conventional transition Reynolds number for large channels has also been noticed in the experimental investigation.     

Characterization of convective heat transfer in channels of small cross section using digital interferometry

Forced convection in channels of small cross sectional dimensions has been recommended as an effective heat removal method for electronic components and packages. Many of the experimental results reported in the literature on the heat transfer performance of small-cross section channels are of contradicting nature, even though some generally agreeing results are also found. One of the probable reasons for the deviations, as suggested by investigators, is the intrusive nature of measurement techniques, which interferes with the flow field. Hence a non intrusive measurement technique is preferable for temperature measurement in small channels. The present work is aimed at developing an interferometric method for convective heat transfer measurement in a liquid medium flowing through channels of small cross sectional dimensions, with hydraulic diameters ranging from 12 to 3 mm and characterizing the nature of fluid flow and heat transfer in these channels. Mach–Zehnder interferometric arrangement is used to obtain the temperature distributions in water flowing through the channels, which are further analyzed digitally to obtain the local heat transfer coefficients and Nusselt numbers. The results are compared and contrasted with classical results for channel flow and heat transfer, and attempt has been made to interpret the variations and deviations observed. The experimental study has been performed under different fluid velocities in the laminar flow regime, and under various wall heat fluxes corresponding to the heat dissipation range expected in microelectronic devices. Parametric variations for the heat transfer performance have been obtained and correlated using the experimental results.     

Regioselective synthesis of C-2 substituted imidazo[4,5-b]pyridines utilizing palladium catalysed C–N bond forming reactions with enolizable heterocycles

In this Letter we report a rapid and facile access to C2-substituted imidazo[4,5-b]pyridine analogues utilizing palladium mediated Buchwald–Hartwig cross-coupling reactions. The use of enolizable heterocycles as cross-coupling partners resulted in a wide range of imidazo[4,5-b]pyridine analogues which are prone to have medicinal relevance. Xantphos and Pd(OAc)₂ were found to be more effective for the coupling of 2-halo imidazo[4,5-b]pyridines with pyridone nucleophiles. A regioselective approach for the synthesis of 2-substituted 3H-imidazo[4,5-b]pyridine and 1H-imidazo[4,5-b]pyridine is also reported.     

Mössbauer and magnetic studies on nanocrystalline NiFe2O4 particles prepared by ethylene glycol route

NiFe₂O₄ nanoparticles have been synthesized by co-precipitation method at 145°C in N₂ atmosphere using ethylene glycol as solvent and capping agent. This gives the promising synthesis route for nanoparticles at low temperature. The as-synthesized NiFe₂O₄ is subsequently heated at 400°C, 500°C, 700°C and 800°C. Crystallite size increases with the heat treatment temperature. The heat treatment temperature has direct effect on the electron paramagnetic resonance and intrinsic magnetic properties. The room temperature Mössbauer spectrum of the 800°C heated sample shows the two sextets pattern indicating that the sample is ferrimagnetic and Fe^3?+? ions occupy both tetrahedral and octahedral sites of spinel structure.     

Design,synthesis and molecular docking studies of some 1-(5-(2-fluoro-5-(trifluoromethoxy)phenyl)-1,2,4-oxadiazol-3-yl)piperazine derivatives as potential anti-inflammatory agents

Molecular Diversity - We herein report the facile synthesis of a series of 3,5-substituted-1,2,4-oxadiazole derivatives in good to excellent yields. The anti-inflammatory potential of the newly...     

Use of molecular electrostatic potential for quantitative assessment of inductive effect

Density functional theory computations at the B3LYP/6-31G(d,p) level have been carried out for three types of model compounds, viz. (i) 4-substituted bicyclo[2.2.2]octane carboxylic acids, (ii) anions of 4-substituted bicyclo[2.2.2]octane carboxylic acids and (iii) 4-substituted quinuclidines where the substituents are NO(2), CN, Cl, Br, CF(3), F, CHO, CH(2)Cl, COOH, COCH(3), CONH(2), OH, OCH(3), C(6)H(5), NH(2), H, CH(3), CH(2)CH(3), CH(CH(3))(2), and C(CH(3))(3) to study the dependencies between molecular electrostatic potential minimum (V(min)) and the inductive substituent constant sigma(I). All the three model systems show excellent linear correlation between V(min) and sigma(I) suggesting that the calculation of V(min) parameter in these systems offers a simple and efficient computational approach for the evaluation of inductive substituent constants. The calculated linear equation for the models (i), (ii), and (iii) are V(min) = 12.982 sigma(I)- 48.867, V(min) = 13.444 sigma(I)- 182.760, and V(min) = 18.100 sigma(I)- 65.785, respectively. Considering the simplicity of the quinuclidine model, V(min) value at the nitrogen lone pair region of a 4-substituted quinuclidine system is recommended for the evaluation of sigma(I). Further, the additivity effect of sigma(I) is tested on multiply substituted quinuclidine and bicyclo[2.2.2]octane carboxylic acid derivatives using the V(min) approach and the results firmly supported the additivity rule of inductive effect. The systems showing considerable deviations from the additivity rule are easily recognized as those showing either steric effect or intramolecular hydrogen bond interactions at the V(min) response site. However, the distance relation of sigma(I) is not well represented in the caged molecular systems.     

Microwave enhanced Suzuki coupling: a diversity-oriented approach to the synthesis of highly functionalised 3-substituted-2-aryl/heteroaryl imidazo[4,5-b]pyridines

A modified approach for the synthesis of 3-substituted 2-aryl/heteroaryl imidazo[4,5-b]pyridines utilising palladium catalysed cross-coupling reactions under microwave enhanced conditions has been achieved. utilisation of (A-^taphos)₂PdCl₂-catalysed cross-coupling reactions enables rapid derivatization of this (imidazo[4,5-b]pyridines) pharmaceutically relevant core. This catalytic system is compatible with a broad spectrum of arylboronic acids—electron rich, electron poor, and heteroarylboronic acids.     

Design,Synthesis, and Biological Evaluation of 3,5‐Disubstituted 2‐Pyrazineamide Derivatives as Antitubercular Agents

A novel series of 3,5‐disubstituted‐2‐pyrazineamide derivatives ( 5a–5o ) were synthesized and studied for their potential as antitubercular agents. Among them, the compounds 5a , 5g , and 5m showed the good minimal inhibitory concentration of 20, 25, and 25 μg/mL, respectively. The compound 5a displayed excellent minimum inhibitory concentration of 10 μg/mL and is four times more potent compared with the standard drug, rifampicin concentration. In silico docking studies revealed that the compounds 5a and 5c can bind strongly in the active site of 2FUM enzyme and prevent enzyme–substrate interactions. In addition, in silico docking studies were calculated, and based on the data obtained, compound 5a displayed excellent drug‐like properties.     

A rapid approach for the copper,amine, and ligand-free Sonogashira coupling of 4-methyl-7-nonafluorobutylsulfonyloxy coumarins under microwave irradiation

A rapid, efficient, and reliable access for the synthesis of an assortment of 4-methyl-7-alkyl/aryl/heteroaryl alkynyl coumarins has been developed by the copper, amine, and ligand-free Sonogashira cross-coupling reaction of 4-methyl-7-nonafluorobutylsulfonyloxy coumarin with various terminal alkynes under microwave irradiation. In the presence of a suitable catalyst, base, and solvent, the coupling reaction proceeded smoothly to give the diaryl alkynes in satisfactory to exceptional yields. Nonaflates coupled more efficiently than the corresponding triflates which yielded the detriflated product as well as the hydrolyzed product as competing side products along with the required product. The utilization of TBAF·3H₂O as a mild base as well as a solvating agent was the key for success of the reaction.