The log delta log t method for the determination of the coefficient of consolidation

The behaviour of saturated soils undergoing consolidation is very complex, It may not follow Terzaghi's theory over the entire consolidation process, Different soils may behave in such a way as to fit into Terzaghi's theory over some specific stages of the consolidation process (percentage of consolidation), This may be one of the reasons for the difficulties faced by the existing curve-fitting procedures in obtaining the coefficient of consolidation, c(v). It has been shown that the slope of the initial linear portion of the theoretical log U-log T curve is constant over a wider range of degree of consolidation, U, when compared with the other methods in use, This initial well-defined straight line in the log U-log T plot intersects the U = 100% line at T = pi/4, which corresponds to U = 88.3%, The proposed log delta-log t method is based on this observation, which gives the value of c(v) through simple graphical construction, In the proposed method, which is more versatile, identification of the characteristic straight lines is very clear; the intersection of these lines is more precise and the method does not depend upon the initial compression for the determination of c(v).

Chromatographic methods for determination of nimesulide and for stability studies

Simple and rapid HPLC, GC, and TLC procedures have been developed for detection and determination of nimesulide, a non-pharmacopeial drug, in preformulation and dosage form. Use of these techniques has enabled separation of impurities and the precursor in the bulk material and in formulations. Isocratic reversed-phase HPLC was performed on a C-18 column with methanol-water-acetic acid, 67:32:1 (v/v), as mobile phase and UV detection at 230 nm. Calibration curves were linear over the concentration range 100-1000 mug mL(-1) with a good correlation coefficient (0.9993) and a coefficient of variation of 1.5%. Gas chromatography was performed on an OV-17 packed column with temperature programming and flame-ionization detection. The lower limit of determination by HPLC and GC was 4 ppm. Thin-layer chromatography of nimesulide was performed on silica gel G with toluene-ethyl acetate, 8:2, as mobile phase. Stability testing of the drug was performed under different temperature, humidity, and UV-radiation conditions.

Determination of the reactivity ratios for the oxidative copolymerizations of indene with methyl, ethyl and butyl acrylates

Full Paper: The copolyperoxides of various compositions of indene with methyl acrylate, ethyl acrylate and butyl acrylate have been synthesized by the free-radical-initiated oxidative copolymerization. The compositions of copolyperoxide obtained from H-1 and C-13 NMR spectra have been used to determine the reactivity ratios of the monomers. The copolyperoxides contain a greater proportion of the indene units in random placement. The NMR studies have shown irregularities in the copolyperoxide chain due to the cleavage reactions of the propagating peroxide radical. The thermal analysis by differential scanning calorimetry suggests alternating peroxide units in the copolyperoxide chain. From the activation energy for the thermal degradation, it was inferred that degradation occurs via the dissociation of the peroxide (O-O) bonds of the copolyperoxide chain. The flexibility of the polyperoxides in terms of glass transition temperature (T-g) has also been examined.

On the explicit determination of the polar decomposition in n-dimensional vector spaces

A method for the explicit determination of the polar decomposition (and the related problem of finding tensor square roots) when the underlying vector space dimension n is arbitrary (but finite), is proposed. The method uses the spectral resolution, and avoids the determination of eigenvectors when the tensor is invertible. For any given dimension n, an appropriately constructed van der Monde matrix is shown to play a key role in the construction of each of the component matrices (and their inverses) in the polar decomposition.

A determination of the structure of the intramolecular charge transfer state of 4-dimethylaminobenzonitrile (DMABN) by time-resolved resonance Raman spectroscopy

Picosecond time-resolved resonance Raman spectra of the A (intramolecular charge transfer, ICT) state of DMABN, DMABN-d(6) and DMABN-N-15 have been obtained. The isotopic shifts identify the nu (s)(ph-N) mode as a band at 1281 cm(-1). The similar to 96 cm(-1) downshift of this mode from its ground state frequency rules out the electronic coupling PICT model and unequivocally supports the electronic decoupling TICT model. However, our results suggest some pyramidal character of the A state amino conformation.

High contrast imaging and thickness determination of graphene with in-column secondary electron microscopy

We report a new method for quantitative estimation of graphene layer thicknesses using high contrast imaging of graphene films on insulating substrates with a scanning electron microscope. By detecting the attenuation of secondary electrons emitted from the substrate with an in-column low-energy electron detector, we have achieved very high thickness-dependent contrast that allows quantitative estimation of thickness up to several graphene layers. The nanometer scale spatial resolution of the electron micrographs also allows a simple structural characterization scheme for graphene, which has been applied to identify faults, wrinkles, voids, and patches of multilayer growth in large-area chemical vapor deposited graphene. We have discussed the factors, such as differential surface charging and electron beam induced current, that affect the contrast of graphene images in detail. (C) 2011 American Institute of Physics. doi:10.1063/1.3608062]

Calcium ruthenates: Determination of Gibbs energies of formation using electrochemical cells

Metallic Ru has been found to coexist separately with CaO, RuO2, and the interoxide phases, Ca2RuO4, Ca3Ru2O7, and CaRuO3, present along the pseudobinary system CaO-RuO2. The standard Gibbs energies of formation (Df((ox))G(o)) of the three calcium ruthenates from their component oxides have been measured in the temperature range 925-1350 K using solid-state cells with yttria-stabilized zirconia as the electrolyte and Ru+RuO2 as the reference electrode. The standard Gibbs energies of formation (Deltaf((ox))G(o)) of the compounds can be represented by Ca2RuO4:Deltaf((ox))G(o)/J mol(-1)=-38,340-6.611 T (+/-120), Ca3Ru2O7 : Df((ox))G(o)/J mol(-1)=-75,910-11.26 T (+/-180), and CaRuO3 : Deltaf((ox))G(o)/J mol(-1)=-35,480-3.844 T(+/-70). The data for Ca2RuO4 corresponds to the stoichiometric composition, which has an orthorhombic structure, space group Pbca, with short c axis ("S'' form). The structural features of the ternary oxides responsible for their mild entropy stabilization are discussed. A three-dimensional oxygen potential diagram for the system Ca-Ru-O is developed as a function of composition and temperature from the results obtained. Using the Neumann-Kopp rule to estimate the heat capacity of the ternary oxides relative to their constituent binary oxides, the standard enthalpies of formation of the three calcium ruthenates from the elements and their standard entropies at 298.15 K are evaluated. (C) 2003 The Electrochemical Society.

Determination of critical micelle concentration by hyper-Rayleigh scattering

The critical micelle concentration (CMC) of several surfactants that contain an NLO chromophore, either at the hydrocarbon tail, or at the hydrophilic headgroup, or even as a counterion, was determined by hyper-Rayleigh scattering (HRS). In all cases, the HRS signal exhibited a similar variation with surfactant concentration, wherein the CMC is inferred from a rather unprecedented drop in the signal intensity. This drop is attributed to the formation of small pre-micellar aggregates, whose concentrations become negligible above CMC. In addition, a probe molecule, which upon protonation yielded a species with significantly enhanced HRS intensity, was developed and its utility for the determination of the CIVIC of simple fatty acids was demonstrated.

Determination of solid fraction evolution during solidification of aluminum alloy in presence of linear electromagnetic stirring

In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process parameters such as cooling rate, stirring intensity and in estimating the total solidification time. In the present work, a new method of estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al-Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with non-dendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Schiel equation.

Theoretical determination of HI vertical scale heights in the dwarf galaxies DDO 154, Ho II, IC 2574 and NGC 2366

In this paper, we model dwarf galaxies as a two-component system of gravitationally coupled stars and atomic hydrogen gas in the external force field of a pseudo-isothermal dark matter halo, and numerically obtain the radial distribution of HI vertical scale heights. This is done for a group of four dwarf galaxies (DDO 154, Ho II, IC 2574 and NGC 2366) for which most necessary input parameters are available from observations. The formulation of the equations takes into account the rising rotation curves generally observed in dwarf galaxies. The inclusion of self-gravity of the gas into the model at par with that of the stars results in scale heights that are smaller than what was obtained by previous authors. This is important as the gas scale height is often used for deriving other physical quantities. The inclusion of gas self-gravity is particularly relevant in the case of dwarf galaxies where the gas cannot be considered a minor perturbation to the mass distribution of the stars. We find that three out of four galaxies studied show a flaring of their HI discs with increasing radius, by a factor of a few within several disc scale lengths. The fourth galaxy has a thick HI disc throughout. This flaring arises as a result of the gas velocity dispersion remaining constant or decreasing only slightly while the disc mass distribution declines exponentially as a function of radius.