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The Langmuir monolayer at an air–water interface shows remarkably different surface pressure (π)–area (A) isotherm, when measured with the surface normal of a Wilhelmy plate parallel or perpendicular to the direction of compression of the monolayer. Such difference arises due to difference in stress exerted by the monolayer on the plate in different direction. In this article, we report the effect of changing the direction of substrate normal with respect to the compression of the monolayer during Langmuir–Blodgett (LB) film deposition on the morphology of the films. The morphology of the LB film of stearic acid is studied using an atomic force microscope. The morphology of the LB films is found to be different due to difference in the stress in different directions. The role of such surface morphology on the alignment of a nematic liquid crystal (LC) in LC cells is studied. The granular texture of LB films of stearic acid supports the homogeneous alignment of the LC whereas the uniform texture supports the homeotropic alignment of the LC. 相似文献
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Summary A convenient electroanalytical technique for the simultaneous determination of lead, cadmium, copper and zinc in human blood and teeth is described. The method is based on differential pulse anodic stripping voltammetry at the static mercury drop electrode (SMDE). Optimum conditions for the anodic stripping of Pb, Cd, Cu and Zn were determined using ammonium acetate and dilute nitric acid (pH 2) as electrolytes. Interferences from other metals were not observed and the estimations were reproducible within a standard deviation of±4%. Low blank values and high sensitivity of the method allowed the determinations at sub-ppb levels with an electrolysis time of 1–3 min. The accuracy of the method has been tested by comparison with the results obtained by mass spectrometry and atomic absorption spectrometry. The results and findings are discussed in brief.
Bestimmung von Blei, Cadmium, Kupfer und Zink in menschlichen Geweben mit Hilfe der Differentialpuls-Anodic Stripping Voltammetrie
Zusammenfassung Eine vorteilhafte elektroanalytische Methode zur Bestimmung von Pb, Cd, Cu und Zn in menschlichem Blut und in Zähnen wird beschrieben. Das Verfahren beruht auf der Differentialpuls-Anodic Stripping Voltammetrie an der statischen Quecksilbertropfelektrode. Mit Hilfe von Ammoniumacetat und verdünnter Salpetersäure (pH 2) als Trägerelektrolyten wurden die optimalen Bedingungen ausgearbeitet. Störungen durch andere Metalle wurden nicht beobachtet. Die Standardabweichung betrug ±4%. Infolge der niedrigen Blindwerte und der hohen Empfindlichkeit konnten Bestimmungen im Sub-ppb-Bereich mit Elektrolysezeiten von 1–3 min durchgeführt werden. Die Genauigkeit der Methode wurde durch Vergleich mit massenspektrometrischen und AAS-Untersuchungen bewiesen. Die Ergebnisse werden kurz diskutiert.相似文献
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An alternative semianalytical representation of diatomic vibrational energy levels to the Dunham expansion, is presented in the form of an expansion over Newton polynomials. This latter representation produces smaller variances and correlation coefficients than Dunham's representation, especially for light molecules. The method is illustrated by application to the vibrational levels of the ground state of the H2 molecule. Extension of the method to vibrational-rotational levels is discussed briefly. 相似文献
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Bianchi Type-V Magnetized String Cosmological Model with Variable Magnetic Permeability for Viscous Fluid distribution 下载免费PDF全文
We investigate the Bianchi type-V magnetized string cosmological model with variable magnetic permeability for viscous fluid distribution. The magnetic field is due to an electric current produced along the x-axis. Thus the magnetic field is in yz-plane and F23 is the only non-vanishing component of electromagnetic field tensor Fij. To obtain the deterministic model in terms of cosmic time t, we assume the condition ξθ const where ξ is the coefficient of bulk viscosity and θ the expansion in the model. 相似文献
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K. D. Singh Mudher K. Krishnan R. R. Khandekar M. B. Yadav N. C. Jayadevan D. D. Sood 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(1):183-191
Rubidium uranium trisulphate [Rb2U(SO4)3] was prepared as a high purity compound of uranium in different lots of 250 g each. The compound was characterised and evaluated
by chemical, atomic spectrosopic, infrared, X-ray diffraction and thermogravimetric methods for its use as a chemical assay
standard for uranium. The compound is stoichiometric, pure, homogeneous and stable in atmospheric conditions. The solubility
studies showed that Rb2U(SO4)3 is easily soluble in mineral acids. An experiment based on Randomised Block Design was carried out to assign a value to the
uranium content in Rb2U(SO4)3 from the statistically analysed chemical data. The assigned value of [34.167±0.042]% to the uranium content is in close agreement
with the theoretical value of 34.152%. Based on these studies, Rb2U(SO4)3 is recommended as a chemical assay standard for uranium. 相似文献
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Gulati K Longley EJ Dorko MJ Bittinger KL Siska PE 《The Journal of chemical physics》2004,120(18):8485-8493
Relative doubly differential cross sections for the Penning ionization of H(2) by spin-state-selected metastable He (1s2s) are reported at center-of-mass collision energies E of 3.1 and 4.2 kcal/mol in a crossed supersonic beam experiment employing a rotatable mass spectrometer detector. The measurements are sufficiently dense in velocity space as to avoid having to functionalize the differential cross sections in order to transform the intensities into the c.m. The H(2) (+) product is scattered sharply forward, c.m. Deltatheta<10 degrees half-width at half-maximum, with respect to the incident direction of H(2) at both energies for both spin states. On the average the products have lost energy upon recoil, mean recoil energy E(')相似文献
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Enantiomeric separation of a melatonin agonist Ramelteon using amylose-based chiral stationary phase
Sachin D. Patil Nandkumar Khandekar Gajanan B. Kasawar K.A. Shaikh 《Arabian Journal of Chemistry》2013,6(1):103-109
A new simple isocratic chiral liquid chromatographic method was developed for the enantiomeric purity of Ramelteon[(S)-N-[2-(1,6,7,8-tetrahydro-2H-indeno[5,4-b]furan-8-yl) ethyl]-propionamide], a melatonin agonist in bulk drugs. The chromatographic separation was achieved on Chiralpak AD-H, 250 mm × 4.6 mm, 5 μm column using a mobile phase system consisting of n-hexane, ethanol and methanesulfonic acid in the ratio of 900:100:0.1 (v/v/v). The mobile phase was pumped on the column at the flow rate of 1 mL min?1. Addition of methane sulfonic acid in the mobile phase enhanced chromatographic efficiency and resolution between the enantiomers. The resolution between the enantiomers was found to be more than four. The developed method was subsequently validated and proved to be accurate and precise. The experimentally established limit of detection and quantification of (R)-enantiomer were found to be 25.5 and 77.2 ng ml?1, respectively, for 20 μl injection volumes. The percentage recovery of (R)-enantiomer was ranged from 98.5 to 101.9 in bulk drug samples of Ramelteon. The stability of Ramelteon sample in analytical solution was checked for about 48 h at room temperature and was found to be stable for about 48 h. The proposed method was found to be suitable and accurate for the quantitative determination of (R)-enantiomer in drug substance. 相似文献
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Path integration of a Lagrangian related to an electron gas in a random potential is carried out within the framework of Feynman's
polygonal approach. The integration is direct and does not require the knowledge of an auxiliary measure or the artificial
coupling of the system to external forces. 相似文献