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61.
C. V. Yelamaggad Manoj Mathews Uma Hiremath Geetha Nair D. S. Shankar Rao S. Krishna Prasad 《Liquid crystals》2013,40(8):899-908
A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C8) while the number of methylene units in the central spacer was varied from C3 to C11. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C9 to C11 methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced. 相似文献
62.
Metabolic analysis with high-resolution nuclear magnetic resonance (NMR) enables simultaneous investigation of numerous chemical
species in response to biochemical changes in subjects. When the analysis involves comparing two or more NMR spectra, it is
essential to properly align them because small variations across different spectra influence the alignment and thus, interfere
with direct comparisons between samples. We propose a new alignment method within the Bayesian modeling framework. The proposed
method allows us to estimate the amplitude and phase shifts simultaneously and to obtain robust results in the existence of
noise. Effectiveness of our proposed method is demonstrated through real NMR spectra in human plasma and a comparison study
with dynamic time warping and correlated optimized warping, two widely used alignment methods in spectral data. 相似文献
63.
Hiremath R Basile JA Varney SW Swift JA 《Journal of the American Chemical Society》2005,127(51):18321-18327
The control of crystal polymorphism is a long-standing issue in solid-state chemistry, which has many practical implications for a variety of commercial applications. At least four different crystalline forms of 1,3-bis(m-nitrophenyl) urea (MNPU), a classic molecular crystal system, are known to crystallize from solution in various concomitant combinations. Herein we demonstrate that the introduction of gold-thiol self-assembled monolayers (SAMs) of substituted 4'-X-mercaptobiphenyls (X = H, I, and Br) into the crystallization solution can serve as an effective means to selectively template the nucleation and growth of alpha-, beta-, and gamma-MNPU phases, respectively. Polymorph control in the presence of SAM surfaces persists under a variety of solution conditions and consistently results in crystalline materials with high phase purity. The observed selectivity is rationalized on the basis of long-range two-dimensional geometric lattice matching and local complementary chemical interactions at the SAM/crystal interfaces. 相似文献
64.
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66.
Summary Ninhydrin in the presence of SnCl2 in 0.2M citrate buffer (pH 5) is proposed as a new reagent for the Spectrophotometric assay of chloramphenicol (CP), CP esters and CP in pharmaceutical formulations such as tablets, capsules, eye drops, eye ointments, ear drops and injections. The method is based on hydrolysis of chloramphenicol with 4M NaOH and subsequent treatment with ninhydrin reagent. The resulting violet colour exhibits maximum absorption at 570 nm. The Beer's law limits, molar absorptivity, effect of time and reagent concentration, and interference studies are reported.
Eine neue spektrophotometrische Methode zur Bestimmung von Chloramphenicol
Zusammenfassung Für die spektrophotometrische Bestimmung von Chloramphenicol (CP) und CP-Estern in pharmazeutischen Präparaten (Tabletten, Pillen, Augentropfen, Augensalben, Ohrentropfen und Injektionspräparaten) wurde als neues Reagens Ninhydrin mit SnCl2 in 0,2M Citratpuffer (pH 5) vorgeschlagen. Das Verfahren beruht auf der Hydrolyse von CP mit 4M NaOH und nachfolgender Behandlung mit dem Ninhydrinreagens. Die sich dabei ergebende Violettfärbung hat ihr Absorptionsmaximum bei 570 nm. Die Gültigkeitsgrenzen des Beerschen Gesetzes, die molare Absorbanz, der Einfluß der Zeit und der Reagenskonzentration sowie die Störfaktoren wurden angegeben.相似文献
67.
Summary The title complex has been synthesized and characterized by elemental and spectral analysis. The NiII chelate forms adducts with heterocyclic nitrogen bases, which were characterized spectrophotometrically in solution. Bidentate and unsaturated monodentate bases form hexacoordinate adducts with 11 and 12 metalligand stoichiometries, respectively, whilst saturated nitrogen bases form pentacoordinate adducts with 11 stoichiometry. The results are discussed in terms of basicities and steric properties of the bases. 相似文献
68.
Kumar P Hiremath US Yelamaggad CV Rossberg AG Krishnamurthy KS 《The journal of physical chemistry. B》2008,112(31):9270-9274
We report on the electric-field-generated effects in the nematic phase of a twin mesogen formed of bent-core and calamitic units, aligned homeotropically in the initial ground state and examined beyond the dielectric inversion point. The bend-Freedericksz (BF) state occurring at the primary bifurcation and containing a network of umbilics is metastable; we focus here on the degenerate planar (DP) configuration that establishes itself at the expense of the BF state in the course of an anchoring transition. In the DP regime, normal rolls, broad domains, and chevrons (both defect-mediated and defect-free types) form at various linear defect-sites, in different regions of the frequency-voltage plane. A significant novel aspect common to all these patterned states is the sustained propagative instability, which does not seem explicable on the basis of known driving mechanisms. 相似文献
69.
Surface roughness effects in a short porous journal bearing with a couple stress fluid 总被引:3,自引:0,他引:3
In this paper, a theoretical study of the effect of surface roughness in hydrodynamic lubrication of a porous journal bearing with couplestress fluid as lubricant is made. The modified Reynolds equations accounting for the couple stresses and randomized surface roughness structure are mathematically derived. The Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effects of surface roughness on the static characteristics of a short porous journal bearing with couplestress fluid as lubricant. Further, it is assumed that, the roughness asperity heights are small compared to the film thickness. It is observed that, the effects of surface roughness on the bearing characteristics are more pronounced for couplestress fluids as compared to the Newtonian fluids. 相似文献
70.
The present paper deals with the study of heat transfer characteristics in the laminar boundary layer flow of an incompressible
viscous fluid over an unsteady stretching sheet which is placed in a porous medium in the presence of viscous dissipation
and internal absorption or generation. Similarity transformations are used to convert the governing time dependent nonlinear
boundary layer equations into a system of non-linear ordinary differential equations containing Prandtl number, Eckert number,
heat source/sink parameter, porous parameter and unsteadiness parameter with appropriate boundary conditions. These equations
are solved numerically by applying shooting method using Runge-Kutta-Fehlberg method. Comparison of numerical results is made
with the earlier published results under limiting cases. The effects of the parameters which determine the velocity and temperature
fields are discussed in detail. 相似文献