Showing papers by "University of Madras published in 1976"
TL;DR: In this paper, the authors derived the equation of motion for each three-dimensional spin vector and showed that in the continuum limit where the spins lie dense on a line, this set of equations reduces to a nonlinear partial differential equation.
Abstract: For a one-dimensional system of classical spins with nearest neighbour Heisenberg interaction we derive the equation of motion for each three-dimensional spin vector. In the continuum limit where the spins lie dense on a line this set of equations reduces to a nonlinear partial differential equation. In addition to spin-wave solutions we obtain some other special solutions of this equation. In particular we find solitary waves having total energy localised in a finite region, with velocity of propagation inversely proportional to the width of this region. Solutions of still another type are shown to have a diffusive character. The stability of such solutions and the possibility of interaction of two or more solitary waves have not yet been studied.
219 citations
TL;DR: In this article, new correlations have been proposed for estimation of gas phase holdup, characteristic velocity, interfacial area for mass transfer and mean bubble size of bubble swarms under dispersed and fluidized operation of bubble columns employing single and multi-orifice distributors.
Abstract: New correlations have been proposed for estimation of gas phase holdup, characteristic velocity, interfacial area for mass transfer and mean bubble size of bubble swarms under dispersed and fluidized operation of bubble columns employing single — and multi-orifice distributors. The analysis of results include available literature data of other investigators.
117 citations
TL;DR: A new secondary structure, which shows regularity within the experimental error, is noticed in alpha-chymotrypsin, and considering its extended nature, the name epsilon-helix has been suggested for the same.
Abstract: A new secondary structure, which shows regularity within the experimental error, is noticed in alpha-chymotrypsin, and considering its extended nature, the name epsilon-helix has been suggested for the same. The average observed values of phi and psi for this conformation are -93 degrees and +146 degrees, respectively. The helical parameters turn out to be n = 2.7 and h = 3.3 angstroms.
17 citations
TL;DR: In this article, a Fourier transform approach to the lineshapes of wide-line NMR spectra is proposed, which enables one to handle the general case of Voigt profile.
14 citations
TL;DR: In this article, the electronic bandstructure of zirconium, which has a HCP lattice structure, has been calculated using crystal potentials which include the effect of correlation as well as exchange.
Abstract: The electronic bandstructure of zirconium, which has a HCP lattice structure, has been calculated using crystal potentials which include the effect of correlation as well as exchange. Two methods, one due to Kohn and Sham (1965) and the other to Overhauser (1971) are used for calculating the exchange and correlation contributions to the crystal potential. With the inclusion of correlation the levels around the symmetry point K become well separated, and the entire set of bands is shifted by about 0.25 Ryd. The density of states has been obtained using one of the potentials. The bandstructure results are used to calculate the momentum density distribution of positron annihilation along the c axis.
11 citations
TL;DR: In this article, residence time distribution, axial mixing, and Peclet numbers for both phases in liquid spray columns are presented. Drop size distribution is of major interest, and correlating equations are presented for new correlating equation.
Abstract: New data on residence time distribution (RTD), axial mixing, and Peclet numbers for both phases in liquid spray columns are presented. Drop size distribution is of major interest. Continuous phase velocities affect RTD variance at high flow without appreciable effect on dispersed phase RTD variance. New correlating equations are presented.
11 citations
9 citations
TL;DR: In this paper, it was shown that the nuclei recoiling into the forward (or backward) hemisphere in the reaction μ − + A(J i = 0) → B(J f ≧ 1) + ν μ will not only be polarized but also aligned.
9 citations
TL;DR: In this paper, the synthesis of a wide variety of furo[2,3-b]quinolines starting from substituted 3-vinyl-2-quinolones is described.
Abstract: The synthesis of a wide variety of furo[2,3-b]quinolines starting from substituted 3-vinyl-2-quinolones is described. The procedure involves acetoxycyclisation of the vinyl-quinolone by treating with iodine in the presence of silver acetate and dehydroacetoxylation of the resulting 3-acetoxy-2,3-dihydrofuro[2,3-b]quinoline with phosphoric or polyphosphoric acid. The NMR spectra of the furoquinolines are discussed.
8 citations
TL;DR: In this article, a kinetic study of the thermal polymerisation of acrylonitrile initiated by the redox system V5+ -glycerol in sulfuric acid and perchloric acid was made in the temperature range 35-45°C.
Abstract: A kinetic study of the thermal polymerisation of acrylonitrile initiated by the redox system V5+ -glycerol in sulfuric acid and perchloric acid was made in the temperature range 35–45°C. The rates of polymerisation and V5+ disappearance wee measured with respect to their dependence on time, monomer, metal ion, glycerol, acid, and ionic strength. Experimental evidences provide support to a mechanism involving initiation by a free radical produced by the decomposition of the acyclic complex between V5+ and glycerol. The kinetics are consistent with a linear termination of polymerisation (1st order in respect of growing radicals) at higher concentration of V5+. The various rate and activation parameters were evaluated and an appropriate reaction scheme is proposed. The induction period and the polymerisation rate of the V5+ -glycerol system were compared with those involving polyhydroxy alcohol systems such as sorbitol and mannitol.
Gegenstand dieser Arbeit ist die Untersuchung der Kinetik der durch das Redoxsystem V5+ -Glyzerin angeregten thermischen Polymerisation von Acrylnitril in Gegenwart von Schwefel- oder Perchlorsaure im Temperaturbereich von 35–45°C. Polymerisationsgeschwindigkeit und die Geschwindigkeit des V5+ -Verbrauchs wurden hinsichtlich ihrer Abhangigkeit von der Zeit, der Monomer-, Metallion-, Glyzerin- und Saurekonzentration sowie der Ionenstarke untersucht. Die experimentellen Ergebnisse stutzen einen Mechanismus, der einen Start uber freie Radikale vorsieht, die aus dem Zerfall eines acyclischen V5+ -Glycerin-Komplexes resultieren. Die kinetischen Befunde sind mit der Annahme eines linearen Abbruchs (1. Ordnung bezuglich der Radikalketten) bei hoheren V5+ -Konzentrationen vereinbar. Die verschiedenen Geschwindigkeits- und Aktivierungsparameter wurden ermittelt und ein geeignetes Reaktionsschema vorgeschlagen. Die in diesem System auftretenden Induktionsperioden und Polymerisationsgeschwindigkeiten wurden mit den entsprechenden fur andere Polyhydroxy-Systeme (Mannit, Sorbit) registrierten Grosen vergleichen.
7 citations
01 Apr 1976
TL;DR: The mycoflora colonizing the litter of Atlantia monophylla Corr.
Abstract: The mycoflora colonizing the litter ofAtlantia monophylla Corr. andGymnosporia emarginata Laws. was analysed at monthly intervals during a one-year period. The fungi were grouped as ‘dominant’, ‘common’, ‘frequent’, ‘occasional’ and ‘rare’ depending on their percentage frequency. Only a few fungi appeared to be ‘dominant’ on each plant species and nearly half the number of species recorded occurred sporadically. Each plant had its own characteristic ‘dominant’ mycoflora which included mostly host specific forms. Many species were found to be common to both plant species, but the frequency and percentage occurrence of these species was different on both litter types.
TL;DR: The crystal structure of a new form of L-isoleucine hydrochloride monohydrate C6H13O2NHClH2O (termed form II) has been determined using three-dimensional photographic data as discussed by the authors.
Abstract: The crystal structure of a new form of L-isoleucine hydrochloride monohydrate C6H13O2NHClH2O (termed form II) has been determined using three-dimensional photographic data. This differs conformationally from the hydrochloride derivative (termed form I, Trommel and Bijvoet 1954) reported earlier. The crystal belongs to the orthorhombic space group P212121 with cell dimensions,a=5.87±0.01,b=24.77±0.02 andc=6.85±0.01 A and four molecules per cell,ρ
obs=1.240 g/cm3,ρ
cal=1.238 g/cm3,µ for CuKa=32.6 cm−1.
TL;DR: In this paper, the inner sphere oxidative path was observed in the oxidation of hexacyanoferrate(II) by peroxodiphosphate at pH = 10 and 26°C.
TL;DR: In this article, the angular correlation of positron annihilation radiation in halides of RX2 type to substantiate the model of positrons annihilating exclusively with anions in ionic substances is reported.
TL;DR: In this article, the angular correlation of two-photon annihilation in polycrystalline and single crystals of NaCl, KCl and KBr was measured using the Goldanskii and Prokopev model.
Abstract: Precision measurements of the angular correlation of two-photon annihilation in polycrystalline and single crystals of NaCl, KCl and KBr are presented. These show a small but systematic variation with crystal orientation. The differences in the angular distributions of different orientations show marked oscillations which extend well beyond the first Brillouin zone. Using the Goldanskii and Prokopev model of polaron states for positions in ionic crystals, the experimental FWHM are used to calculate the effective masses of positions and anion effective charges for different crystallographic directions. The observed variations of effective charge must be taken as the direct experimental evidence for ionic distortions from spherical symmetry. Consequently polaron masses of positrons are different in different directions.
TL;DR: In this paper, a spin-2 particle, described by a symmetric tensor wave function, moving in a homogeneous magnetic field (h.m.f.), is considered and an interaction involving a multiple of the Federbush term, besides the minimal interaction is considered.
Abstract: We present a systematic investigation of the problem of a spin-2 particle, described by a symmetric tensor wave function, moving in a homogeneous magnetic field (h.m.f.). An interaction involving a multiple of the Federbush term, besides the minimal interaction, is considered. By explicit solution of the wave equation with an external h.m.f., we show that the energy spectrum of the spin-2 particle, like that of the spin-3/2 particle (Rarita-Schwinger theory with minimal coupling) spills over into the complex plane. This happens even for arbitrarily small magnetic fields if the coupling is minimal, while the onset of the trouble is delayed till the field strength rises to 2m/sup 2//3e if the Federbush term is included. Our results also throw new light on the problem of the number of constraints, and bring into focus the associated breakdown of Lorentz invariance. We demonstrate that the correct number of constraints exists (irrespective of whether the Federbush term is present or not) if the electromagnetic field is a pure h.m.f.; but the number of constraints is too few for any other electromagnetic field (even one obtainable from a pure h.m.f. by a Lorentz transformation) unless the standard Federbush term is included. The results of ourmore » analysis are discussed in relation to a similar analysis for lower spins as well as their implications for higher-spin theories. (AIP)« less
TL;DR: The ammonium halides present an interesting system for positron angular correlation study in view of their polymorphism and the internal dynamics of ammonium ion Cohesive energy calculations have shown that ammonium ions are predominantly ionic and the hydrogen bonding contribution to cohesive energy is less than 3% as discussed by the authors.
Abstract: The ammonium halides present an interesting system for positron angular correlation study in view of their polymorphism and the internal dynamics of ammonium ion Cohesive energy calculations [1] have shown that ammonium ions are predominantly ionic and the hydrogen bonding contribution to cohesive energy is less than 3% It is shown here that the positron angular correlation is very sensitive to the nature of the chemical bond of the hydrogen ion with the lattice In the ordered phase, at a considerably lower temperature below the transition, the ammonium ion assumes a rigid configuration displaying the full effect of covalent bond The angular correlation broadens at this phase At higher phases the effect of covalency is washed out due to torsional oscillations and the angular correlation curve becomes narrower But in the phase I modification of NH4I, the width of angular distribution becomes larger indicating the creation of cation vacancies due to the relative instability of the ammonium ion in this lattice
Die Ammoniumhalogenide stellen ein interessantes System fur eine Untersuchung der Positronenwinkelkorrelation im Hinblick auf ihren Polymorphismus und die innere Dynamik des Ammoniums dar Berechnungen der Kohasionsenergie [1] haben gezeigt, das die Ammoniumionen vorwiegend ionisch gebunden sind und der Anteil der Wasserstoffbindung zur Kohasionsenergie kleiner als 3% ist Es wird hier gezeigt, das die Positronenwinkelkorrelation gegenuber der Natur der chemischen Bindung des Wasserstoffions mit dem Gitter sehr empfindlich ist In der geordneten Phase nimmt bei einer merklich tieferen Temperatur unterhalb des Ubergangs das Ammonium eine starre Konfiguration an, die den vollen Einflus der kovalenten Bindung zeigt Die Winkelkorrelation verbreitert sich in dieser Phase Bei hoheren Phasen wird der Einflus der Kovalenz infolge von Torsionsschwingungen verwaschen und die Winkelkorrelationskurve wird schmaler Jedoch wird in der Phase I von NH4J die Breite der Winkelverteilung groser und zeigt die Bildung von Kationenleerstellen an, die durch die relative Instabilitat des Ammoniumions in diesem Gitter hervorgerufen werden
TL;DR: In this article, semi-empirical calculations have been done on hexaphenyl benzene, triphenyl benene, and s-triphenyl triazine free molecules and the results are compared with X-ray crystal structure studies.
Abstract: Semi-empirical calculations have been done on hexaphenyl benzene, triphenyl benzene ands-triphenyl triazine free molecules and the results are compared with X-ray crystal structure studies. The conformation of isolated molecule differs from that found in crystals. The agreement improves when packing forces are also included in the minimum energy calculations.
TL;DR: In this article, the anomalous dispersion components of the stronger anomalous scatterers were calculated for four compounds, viz., zinc sulphide, L-α-glyceryl phosphoryl ethanolamine monohydrate, 1-β-arabinofurinosyl cytosine hydrochloride and lithium aluminium oxide.
Abstract: Using the Bijvoet difference data reported in the literature for four compounds,viz./it, zinc sulphide, L-α-glyceryl phosphoryl ethanolamine monohydrate, 1-β-arabinofurinosyl cytosine hydrochloride and lithium aluminium oxide, the anomalous dispersion components Δf″ of the stronger anomalous scatterer in each case is calculated accepting the theoretical values for the lighter anomalous scatterers. For MoKα radiation the values turn out to be Δf″zn=1.470 (85), and for CuKα Δf″P=0.430 (25) Δf″C1=0.715 (18) and Δf″A1=0.264 (21).
01 Mar 1976
TL;DR: In this article, experimental data on diffusivities involving organic amines diffusing in alcohols have been reported using the diaphragm cell technique, and experimental values have been compared with the predicted values by the generalized correlation proposed by Laddha and Smith.
Abstract: Experimental data on diffusivities involving organic amines diffusing in alcohols have been reported using the diaphragm cell technique. Experimental values have been compared with the predicted values by the generalized correlation proposed by Laddha and Smith.
01 Apr 1976
TL;DR: In this article, closed convex hull and extreme points are obtained for the class R (α) of univalent functions in U = {z:¦z ¦ α, 0 ≤ α β, 0 ⩽ β < 1, wheref ∈ R (β).
Abstract: Closed convex hull and extreme points are obtained for the classR (α) of univalent functions ƒ inU = {z:¦z ¦ α, 0 ≤ α β, 0 ⩽ β< 1, wheref ∈ R (α). Integral representations are given for the hulls of these two classes in terms of probability measures on suitable sets. These results are used to solve extremal problems. For example the upper bounds are determined for the coefficients of a function subordinate to some function in R(α) when 1/2 ≤ α < 1.