Küppers-Lortz instability in rotating Rayleigh-Bénard convection in a porous medium

The Darcy-Lapwood-Brinkman model with the Boussinesq approximation is used to study Küppers-Lortz (KL) instability in the nonlinear regime of rotating Rayleigh-Bénard convection in a sparsely packed porous medium near the onset of stationary convection. The threshold Taylor numbers and critical angles for the onset of KL instability are obtained for different values of Λ, M for finite Prandtl numbers (1.5≤Pr≤100). Heat transfer is studied from Nusselt number at the onset of stationary convection.     

Polycatenar oligophenylene liquid crystals

We report the synthesis of oligophenylene polycatenar liquid crystals incorporating 1,4‐disubstituted phenyl rings joined by a direct carbon carbon bond and some pyrimidine analogues. The nature of the linkages does appear to affect the mesomorphism significantly. The ratio of the aromatic core to the aliphatic chains is varied systematically by changing the number of 1,4‐disubstituted phenyl rings and the length of the aliphatic chains. This strongly influences the transition temperatures of the mesophases. Some of the compounds are columnar over an extended temperature range of more than 200°C with melting points below room temperature. We suggest that a combination of the poor overlap of the conjugated electron system of the molecular cores making up the columnar structure and the high concentration of aliphatic chains leads to a low charge‐carrier mobility.     

Zinc Oxide Modified Au Electrode as Sensor for an Efficient Detection of Hydrazine

ZnO nanoparticles (ZnO NPs) prepared by microwave heating technique are used to modify a gold electrode (ZnO/Au) for the hydrazine detection study. The synthesized product is well characterized by various techniques. Detailed electrochemical investigation of the oxidation of hydrazine on the ZnO/Au electrode in 0.02 M phosphate buffer solution (PBS) of pH 7.4 was carried out. A very low detection limit of 66 nM (S/N=4) and a wide linearity in current for a concentration range from 66.0×10^?3 to 415 µM was achieved by amperometry. The electrode was found to be stable for over a month when preserved in PBS.     

Hydrogen bond nature in formamide (CYHNH2···XH; YO,S, Se,Te; XF,HO, NH2) complexes at their ground and low‐lying excited states

A theoretical study on the nature of hydrogen bond for formamide and its heavy complexes (CYHNH₂···XH; Y?O, S, Se, Te; X?F, HO, NH₂) was performed on the basis of density functional theory and the quantum chemistry analysis. Except for the CYHNH₂···NH₃ complexes, the substitution of O atom at formamide with less electronegative atoms (S, Se, and Te) is found to weaken the hydrogen bond (H‐bond). This substitution results in cyclic structure of hydrated and ammoniated formamide complexes by the formation of bifunctional H‐bonds (Y···H₄X; X···H₃C). Natural bond orbital analysis indicates that the H‐bond is weakened because of less charge transfer from a lone pair orbital of H‐bond acceptor to antibonding orbital of H‐bond donor. The quantum theory of atoms in molecules analysis reveals that the acyclic structure with single H‐bond stabilizes the complexes more than the cyclic structure formed by bifunctional H‐bonds. Natural energy decomposition analysis (NEDA) and block‐localized wavefunction energy decomposition (BLW‐ED) analyses show that the H‐bond stabilization energies of NEDA and BLW‐ED have good correlation with the dissociation energy of formamide complexes and charge transfer from donor to acceptor atom play an important role in H‐bonding. We have also studied the low‐lying electronic excited states (T₁, T₂, and S₁) for CYHNH₂···H₂O complexes to explore the nature of H‐bond on the basis of electronegativity and found that NEDA also establishes a good correlation with relative electronic energy (with respect to their ground state) and H‐bond strength at their excited states. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrodeposition of cobalt with tunable morphology from reverse micellar solution

Electrodeposition of cobalt on a copper electrode was successfully performed from aqueous and reverse micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), using constant potential electrolysis method. The potential to be applied for electrodeposition was judged from the cyclic voltammetric behavior of cobalt(II) in aqueous and reverse micellar solutions of CTAB at different compositions. The morphology, dimension, and crystallinity of cobalt deposited onto a copper substrate were evaluated from scanning electron microscopy (SEM) images and X-ray diffraction technique. The cobalt deposited on copper from aqueous solution does not show any definite shape and size, while the deposition from reverse micellar solutions occurred with definite shapes such as star-, flower-, and nanorod-like structures depending on the composition. The slow kinetics governed by the reverse micelles associated with the deposition brings about oriented growth of cobalt onto the copper substrate and offers the potential to electrochemically tune cobalt deposit with desirable morphology.     

Spectrophotometric method for quantitative determination of montelukast in bulk,pharmaceutical formulations and human serum

A simple ultraviolet spectrophotometric method for the estimation of montelukast in methanol has been devised and been compared with the existing pharmacopoeial RP-HPLC method for estimation of the drug. The limit of detection of montelukast at 283 nm was 75.2 ng/mL. The calibration was linear in the range of 3–45 μg/mL. Analytical parameters such as stability, selectivity, accuracy and precision have been established for the method in MONAKA® tablets and in human serum and evaluated statistically to assess the application of the method. The method was validated under the ICH and USP guidelines and found to comprise the advantages for simplicity, stability, sensitivity, reproducibility and accuracy for using as an alternate to the existing non-spectrophotometric methods for the routine analysis of the drug in pharmaceutical formulations and in pharmaceutical investigations involving montelukast.     

Analysis of thermo-magnetic fluctuations above the glass-transition temperature in Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1O8+δ (0.000 ≤ x ≤ 0.180) system

The resistivity of Bi_1.6Pb_0.5Sr_2−xEu_xCa_1.1Cu_2.1O_8+δ (0.000 ≤ x ≤ 0.180) superconductor has been measured as a function of temperature and magnetic field. The resistivity shows a glassy behavior even at higher temperatures and magnetic fields for the Eu-doped samples as compared with the Eu free sample. The values of glass-transition temperature [T_g], magnetic field dependent activation energy [U₀(B)] and the temperature and magnetic field dependent activation energy [U₀(B,T)] are found to be maximum for optimal doping levels (x = 0.135) which shows that the flux lines are effectively pinned in this sample. Also for temperatures below the superconducting transition temperature (T_C), a scaling of measured resistivity curves in magnetic field (B = 0.4 and 0.8 T) is obtained and this scaling is quite useful for better understanding of the behavior of the flux vortices in high temperature superconductors.     

Influence of sintering temperature on microstructure,critical current density and pinning potential of superconducting Bi1.6Pb0.5Sr1.8Dy0.2Ca1.1Cu2.1O8+δ ceramics

The influence of sintering temperature on the microstructure, critical current density (J_C), pinning potential values (U₀) and flux pinning properties of Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ superconductor has been investigated. The samples are prepared by the solid-state route and sintered at temperatures ranging from 846 to 860 °C. A systematic correlation between the sintering temperature, Lotgering index, J_C, U₀ and flux pinning properties has been found. The samples sintered at lower sintering temperature (846 °C) have more grain boundaries with smaller grains while those sintered at a higher temperature (856 °C) contain larger grains with good texturing. The flux pinning force (F_P) calculated from the field dependent J_C values shows that the irreversibility lines (IL) of the Dy-doped samples shift towards higher fields to different extents depending on the sintering temperature. The maximum value of F_P = 1697 kN m^?3 is obtained for the sample sintered at 846 °C and the peak position of F_P is obtained at 0.96 T as against 616 kN m^?3 and 0.52 T for the sample sintered at 856 °C. The U₀ values calculated by Anderson's function is maximum for the sample sintered at 846 °C. But the self-field J_C value of this sample is lower than that of the samples sintered at 856 °C. The samples sintered at 856 °C show best self-field J_C due to the improved microstructure. The changes in microstructure followed by very high enhancement of self-field J_C, J_C(B) characteristics, F_P and U₀ values within a narrow temperature range, are of great scientific and technological significance and the results are explained on the basis of microstructural variation with respect to sintering temperature, hole optimization and formation of point defects due to the doping of Dy atoms in Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ system.     

Simultaneous Determination of Ceftriaxone Sodium and Non Steroidal Anti‐Inflammatory Drugs in Pharmaceutical Formulations and Human Serum by RP‐HPLC

An accurate, sensitive and least time consuming reverse phase high performance liquid chromatographic (RP‐HPLC) method for the estimation of ceftriaxone in the presence of non steroidal anti‐inflammatory drugs in formulation and human serum has been developed and validated. Chromatographic separation was conducted on prepacked Purospher Star, C18 (5 μm, 250 × 4.6 mm) column at room temperature using methanol:water:acetonitrile (80:15:5 v/v/v) as a mobile phase, pH adjusted at 2.8 with ortho‐phosphoric acid and at a flow rate of 1.0 mL/minute, while UV detection was performed at 270 nm. The results obtained showed a good agreement with the declared content. The method shows good linearity in the range of 2.5‐25 μg/mL ceftriaxone serum concentrations with a correlation coefficient 0.999 (inter‐ and intra‐day RSD < 2.0%). The limit of detection and quantification for ceftriaxone and NSAID's in pharmaceutical formulation and serum were in the range 0.51‐1.54 μg/mL. Analytical recovery was >98.1%. The proposed method may be used for the quantitative analysis of commonly administered non steroidal anti‐inflammatory drugs i.e. tiaprofenic acid, naproxen sodium, flurbiprofen, diclofenac acid and mefenamic acid alone or in combination with ceftriaxone from raw materials, dosage formulations and in serum. The established HPLC method is rapid, accurate and selective, because of its sensitivity and reproducibility.     

Synthesis of 8-Aroyl-9-hydroxy-7,9,11-triaryl-3-oxo(or thioxo)-2,4-diazaspiro[5.5]undecane-1,5-diones

A number of 8-aroyl-9-hydroxy-7,9,11-triaryl-3-oxo(or thioxo)-2,4-diazaspiro[5.5]undecane-1,5-diones 3a–g were synthesized from the reaction of 1,3-diaryl-2-propen-1-ones 2a–d with barbituric acid 1a and 2-thiobarbituric acid 1b in 50% aqueous ethanol under refluxing conditions without using any catalyst. The structures of the compounds were confirmed by ultraviolet, infrared, ¹H and ¹³C NMR, mass, and elemental analysis.