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Showing papers by "Indian Institute of Science published in 1971"


Journal ArticleDOI
TL;DR: In this article, the authors used a hot wire in a turbulent boundary layer in air to measure the frequent periods of activity (to be called "bursts") noticed in turbulent signal that has been passed through a narrow band-pass filter.
Abstract: Using a hot wire in a turbulent boundary layer in air, an experimental study has been made of the frequent periods of activity (to be called ‘bursts’) noticed in a turbulent signal that has been passed through a narrow band-pass filter. Although definitive identification of bursts presents difficulties, it is found that a reasonable characteristic value for the mean interval between such bursts is consistent, at the same Reynolds number, with the mean burst periods measured by Kline et al. (1967), using hydrogen-bubble techniques in water. However, data over the wider Reynolds number range covered here show that, even in the wall or inner layer, the mean burst period scales with outer rather than inner variables; and that the intervals are distributed according to the log normal law. It is suggested that these ‘bursts’ are to be identified with the ‘spottiness’ of Landau & Kolmogorov, and the high-frequency intermittency observed by Batchelor & Townsend. It is also concluded that the dynamics of the energy balance in a turbulent boundary layer can be understood only on the basis of a coupling between the inner and outer layers.

432 citations


Journal ArticleDOI
TL;DR: In this article, a constant-dihedral angle relation for cyclic oligopeptide structures was calculated from conformational theory, using eight examples in which the number of theoretical assumptions were least, and the best values of the coefficients A, B, and C in the expression J(θ) = Acos2θ + B cos θ + Csin2 ǫ + csin2ǫ were found by a least-squares procedure to be 7.9, −1.55, and 1.35.
Abstract: Proton magnetic resonance data and conformational calculations of a series of model compounds containing a NH-CαH group substituted as in peptides have been used to generate a proton–proton coupling constant–dihedral angle relation for the peptide unit. For those substances used in which the dihedral angle about the N-Cα bond is not fixed, the angle distribution was calculated from conformational theory. Using eight examples in which the number of theoretical assumptions were least, the best values of the coefficients A, B, and C in the expression J(θ) = Acos2θ + B cosθ + Csin2θ were found by a least-squares procedure to be 7.9, −1.55, and 1.35, respectively. This relation gives reasonable values for the dihedral angles ϕ in cyclic oligopeptide structures for which the availability of both NMR data and other structural information allow comparison. When applied to N-acetylamino acid N-methylamides having side chains extending beyond Cβ, however, agreement with the calculated conformational distribution was found for Leu, Met, and Trp, but observed values of J were larger than expected for Val, He, Phe, and Tyr, These disagreements are considered to be the result of interactions not yet taken into account in the usual conformational calculations.

162 citations


Journal ArticleDOI
TL;DR: Pore-size distribution data for pores of diameters down to 0.016 μm were obtained by mercury porosimetry for a number of laboratory-prepared specimens.
Abstract: Pore-size distribution data for pores of diameters down to 0.016 μm were obtained by mercury porosimetry for a number of laboratory-prepared specimens. Statically-compacted specimens of a kaolinite, an illite, and Boston Blue Clay were evaluated, and changes in the pore-size distribution of the kaolinite were followed as a function of increasing amount of static compaction. In this clay several distinct classes of pore sizes were recognized. Initial compaction reduced the gross pore sizes without influencing the finer classes. After the elimination of the gross pores, further compaction was at the expense of an intermediate class of pores above about 0.14 μm in diameter, pores finer than this being unaffected. Specimens of the kaolinite prepared from a slurry or by sedimentation showed substantially different pore-size distributions from the compacted clay. Drying shrinkage tended to eliminate the larger pores while leaving the smaller ones unaffected. Pore-size distribution appears to be a sensitive parameter with which to follow the effects of microstructural changes which may influence the engineering behavior of the material.

111 citations


Journal ArticleDOI
TL;DR: In this article, a unified theory for obtaining the transient response of second-order nonlinear systems by the Krylov-Bogoliubov method is presented, which covers all three cases when the roots of the corresponding linear equation are real, complex conjugate, or pure imaginary.
Abstract: A unified theory is presented for obtaining the transient response of second-order non-linear systems by the Krylov-Bogoliubov method. The method is a generalization of Bogoliubov's asymptotic method and covers all three cases when the roots of the corresponding linear equation are real, complex conjugate, or pure imaginary. It is shown that by suitable substitution for the roots in the general result, that the solution corresponding to each of the three cases can be obtained. The solution for the equation governing the motion of a simple pendulum with and without damping derived from the general solution reduces to that obtained by Popov's [4] method.

60 citations


Journal ArticleDOI
TL;DR: In this article, the Galerkin method is applied to evaluate the vibration characteristics of simply-supported unsymmetric trapezoidal plates, with the deflection surface expressed in terms of a Fourier sine series in transformed coordinates.

59 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a successful investigation for the identification of singularities and concentrations at sharp corners at the intersection of two or more interfaces and/or edges in two dimensional domains governed by harmonic and biharmonic types of equations.
Abstract: Elastizitatstheoretische Losungen fur das Verhalten verbundener oder nicht verbundener zusammengesetzter Bereiche mit scharfen Ecken sind oft, gleichgultig ob sie mit funktionalen Methoden oder mit der Methode der finiten Elemente gewonnen worden sind, unbefriedigend, weil das angewendete Verfahren den Charakter und die Grose der Spannungskonzentrationen in solchen Ecken nicht ohne weiteres erkennen last. Sind aber die Moglichkeit von Spannungskonzentrationen und ihr Charakter erst einmal geklart, so kann durch Verfeinerung der Analysis auch in den Bereichen der Spannungsspitzen ein hoher Grad von Genauigkeit erzielt werden. In der Arbeit wird ein wirksames Untersuchungsverfahren zur Identifizierung der Singularitaten und Spannungskonzentrationen in scharfen Ecken, in denen zwei oder mehr Grenzflachen und/oder Kanten in zweidimensionalen, von Gleichungen des harmonischen oder biharmonischen Typs beherrschten Bereichen zusammentreffen, geboten. Mit Hilfe einer bestimmten Vorgehensweise last sich fur verschiedene physikalische Probleme, fur die die einzelnen Gleichungstypen gelten, der mathematische Ansatz fur die Grenzflachen und Kantenbedingungen vereinheitlichen und eine einheitliche Behandlung von Problemen mit verschiedenen Kombinationen von Grenzflachen- und Kantenbedingungen erreichen. Es wird die Anwendung auf einige typische Elastizitatsprobleme gezeigt. Die hier fur Grenzflachen zwischen Isotropiebereichen dargestellte Methode last sich auf den Fall von Anisotropiebereichen ausdehnen. Elasticity solutions for bonded or unbonded composite domains with sharp corners whether by functional methods or by finite element formulations are often unsatisfactory, because the procedure applied cannot by itself identify the nature and magnitude of the stress concentrations at such corners. Once the possibility and nature of stress concentrations in a problem are clearly identified, the analysis can be refined and a high degree of accuracy achieved in the peak stress regions. This paper presents a successful investigation for the identification of singularities and concentrations at sharp corners at the intersection of two or more interfaces and/or edges in two dimensional domains governed by harmonic and biharmonic types of equations. A procedure is chosen to standardize the mathematical statement of the interface and edge conditions for different physical problems governed by each class of equations and to achieve a unified treatment of problems with various combinations of interface and edge conditions. It is applied to some typical problems in elasticity. The method presented here for interfaces between isotropic regions, can be extended to interfaces between aeolotropic regions.

59 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compare two genres of ecoulement, i.e., adiabatique and co-occurrence, for the propagation of ondes de choc, and compare avec l'exposant obtenu par l'integration numerique des equations de similarite.
Abstract: Nous avons etudie les ondes de choc spheriques et cylindriques convergentes pres du centre (ou de l'axe) de l'implosion, lorsque celles-ci sont devenues intenses et que l'ecoulement qui les suit est devenu «semblable a lui-meme», ayant «oublie» les conditions initiales. Un tel ecoulement devient probablement isotherme a cause de l'echange thermique intense par conduction ou par rayonnement. Nous avons donc etudie un ecoulement isotherme a un moment donne, plutot que l'ecoulement adiabatique habituellement suppose (Guderley, 1942). Les deux genres d'ecoulement sont compares. Nous avons calcule l'exposant de la loi de la propagation des ondes de choc par la regle caracteristique de Whitham (1958) pour des valeurs differentes de γ=c p/c v; nous l'avons compare avec l'exposant exact obtenu par l'integration numerique des equations de similarite. Les deux valeurs ne concordent pas aussi bien que lorsque l'on admet que l'ecoulement qui suit l'onde de choc est adiabatique.

55 citations


Journal ArticleDOI
TL;DR: A new accurate model for sensitivity in power systems is obtained and used in conjunction with linear programming for the solution of load-shedding problems with a minimum loss of loads.
Abstract: This paper obtains a new accurate model for sensitivity in power systems and uses it in conjunction with linear programming for the solution of load-shedding problems with a minimum loss of loads. For cases where the error in the sensitivity model increases, other linear programming and quadratic programming models have been developed, assuming currents at load buses as variables and not load powers. A weighted error criterion has been used to take priority schedule into account; it can be either a linear or a quadratic function of the errors, and depending upon the function appropriate programming techniques are to be employed.

54 citations


Journal ArticleDOI
TL;DR: In this article, a hybrid technique combining continuum and finite element concepts is proposed for finite element analysis with stress singularities, where each region of stress concentration is covered by one large primary element whose description includes term(s) identifying the type and order of concentration, while the remaining structure is split into a few secondary elements.
Abstract: An important limitation of finite element analysis, namely, the need for a large number of small elements in regions of finite or infinite stress concentrations and the difficulties of convergence in such cases, is well known. Rao1 suggested a possibility of overcoming this by developing hybrid techniques combining continuum and finite element concepts. In such techniques, each region of stress concentration is covered by one large primary element whose description includes term(s) identifying the type and order of concentration, while the remaining structure is split into a few secondary elements which are conventional finite elements. In this paper a procedure incorporating this concept is developed and its effectiveness is clearly demonstrated by successful application to two important examples, one of them with stress singularities. The concept, in fact, can be applied equally well to other two- and three-dimensional problems of continua with discontinuities and concentrations.

48 citations



Journal ArticleDOI
TL;DR: In this article, the effect of coordination on the vibration spectra of trichloroacetates of Cu, Ca, Sr and Ba was investigated in order to determine the shifts of the antisymmetric and symmetric COO − stretching frequencies.

Journal ArticleDOI
TL;DR: In this article, the vibration of simply supported skew plates having a linear variation in thickness in one direction is considered, and approximate analysis is made by using Lagrange's equations employing the double Fourier sine series in oblique co-ordinates to represent the deflected surface.

Journal ArticleDOI
TL;DR: In this article, the buckling problems of simply supported skew plates with in-plane stresses represented in terms of orthogonal components were considered by using the Rayleigh-Ritz method, employing a double Fourier sine series in oblique coordinates.
Abstract: The buckling problems of simply supported skew plates with in-plane stresses represented in terms of orthogonal components are considered by using the Rayleigh-Ritz method, employing a double Fourier sine series in oblique coordinates. Results for the buckling coefficients for different combinations of side-ratio and skew angle are provided mainly when each of the in-plane stresses is acting singly. Results include buckling coefficients under positive shear which are hitherto unavailable in the literature.

Journal ArticleDOI
TL;DR: In this paper, the effect of anions on the coordination of diphenyl sulphoxide (DPSO) with thorium(IV) was investigated, and it was shown that DPSO is coordinated to the metal ion through its oxygen.
Abstract: Thorium(IV) is known to form high coordination-number complexes. An attempt has therefore been made to determine the effect of anions on the coordination complexes of diphenyl sulphoxide (DPSO) with thorium(IV). The complexes formed have the formulae [Th(DPSO)6](ClO4)4, [Th(DPSO)4Cl4], [Th(DPSO)4Br4], [Th(DPSO)6I2]I2, [Th(DPSO)4(NCS)4]and [Th(DPSO)3(NO3)4]. In all the complexes, DPSO is coordinated to the metal ion through its oxygen. The electrical conductances in nitrobenzene and in nitromethane, and ebullioscopic molecular weights in acetonitrile, show that the perchlorate and iodide complexes behave as 1:4 and 1:2 electrolytes, respectively; while the other complexes are monomeric and non-electrolytes. The infrared spectra of the solid complexes indicate the ionic nature of the perchlorate, the bidentate nature of the nitrate and the coordination of the thiocyanate through its nitrogen. [Th(DPSO)4Cl4], [Th(DPSO)4Br4]and [Th-(DPSO)3 (NO3)4]decompose endothermically while [Th(DPSO)6](ClO4)4 and [Th(DPSO)4(NCS)4]decompose exothermically, both in air and in nitrogen. The perchlorate complex has octahedral symmetry around the thorium, the halo- and the thiocyanato complexes are 8-coordinate, probably with square antiprismatic structures, while the nitrate complex is 11-coordinate

Journal ArticleDOI
TL;DR: In this article, the activities of delta-aminolaevulate synthetase and delta-aminoevulate dehydratase have been assayed in Saccharomyces cerevisiae during glucose repression and de-repression.
Abstract: The activities of delta-aminolaevulate synthetase and delta-aminolaevulate dehydratase have been assayed in Saccharomyces cerevisiae during glucose repression and de-repression. delta-Aminolaevulate dehydratase increased concomitantly with the increase in oxygen uptake during the de-repression phase caused by the depletion of glucose in the medium. delta-Aminolaevulate synthetase showed an oscillatory behaviour and a spurt in its activity always preceded the increase in oxygen uptake. The activity of both the enzymes was lowered if the cells were incubated with glucose or cycloheximide, but not with chloramphenicol.

Journal ArticleDOI
TL;DR: In this article, the stability constants of cuprous and cupric complexes were derived using polarographic and redox potential measurements, by reducing cupric ion with copper gauze until equilibrium.

Journal ArticleDOI
TL;DR: In this paper, a linearization technique for non-linear oscillations with second-order ODEs was proposed, based on approximation of the nonlinear function by a linear function such that the error is least in the weighted mean square sense.

Journal ArticleDOI
01 Sep 1971
TL;DR: In this paper, a cuprous sulfide pellet suspended in a stream of air was used to measure the evolution of SO2 titrimetrically, and rate controlling mechanisms for these two intervals have been proposed based on interface chemical reaction, mass transfer resistance, and heat transfer concepts.
Abstract: The oxidation rate of a cuprous sulfide pellet suspended in a stream of air was followed by measuring the evolution of SO2 titrimetrically. Thin thermocouples embedded in the center of the sample recorded the variation of temperature during oxidation. The reaction was found to be topochemical and the sample temperature was found to be higher than its surroundings initially for about half an hour. After this initial period, the sample temperature decreased to that of the surroundings and remained constant during the rest of the period of over 5 hr. The apparent activation energy from the experimental data was found to be different for the initial (nonisothermal) and subsequent (isothermal) periods. Rate controlling mechanisms for these two intervals have been proposed based on interface chemical reaction, mass transfer resistance, and heat transfer concepts. Fair agreement is found between the theoretical rates based on transport mechanisms and those obtained experimentally.

Journal ArticleDOI
TL;DR: In this paper, the authors dealt with the shear strength characteristics of saturated, remoulded, montmorillonite and Kaolinite clays as affected by changes in soil structure.

Journal ArticleDOI
TL;DR: In this paper, the low-temperature plastic flow of alpha-zirconium was studied by employing constantrate tensile tests and differential-stress creep experiments and it was concluded that overcoming the Peierls energy humps by the formation of kink pairs in a length of dislocation is the rate-controlling mechanism.
Abstract: The low-temperature plastic flow of alpha-zirconium was studied by employing constantrate tensile tests and differential-stress creep experiments. The activation parameters, enthalpy and area, have been obtained as a function of stress for pure, as well as commercial zirconium. The activation area is independent of grain size and purity and falls to about 9b2 at high stresses. The deformation mechanism below about 700° K is found to be controlled by a single thermally activated process, and not a two-stage activation mechanism. Several dislocation mechanisms are examined and it is concluded that overcoming the Peierls energy humps by the formation of kink pairs in a length of dislocation is the rate-controlling mechanism. The total energy needed to nucleate a double kink is about 0.8 eV in pure zirconium and 1 eV in commercial zirconium

Journal ArticleDOI
TL;DR: In this article, the approximate solutions of non-linear autonomous systems by the application of ultraspherical polynomials are obtained by a generalized averaging technique based on the ultraspheric polynomial expansions.

Journal ArticleDOI
TL;DR: In this paper, an approach, starting with the bubble formation model of Khurana and Khumar, has been presented, which is found to be reasonably applicable to the formation of both bubbles and drops from single submerged nozzles.

Journal ArticleDOI
TL;DR: The purpose of this prelimiiiary note is to point out the possibility of making such tests and to indicate some results which show reasonable agreement with data obtained from infrared arid NMR studies.
Abstract: The variation of energy of the conformation of a dipeptide unit with the dihedral angles \phi and \psi is a fundamental aspect, which is of great importance to the study of protein structure. Good reviews are available dealing with the energy changes associated with the variation of different parameters such as bond lengths, bond angles, dihedral angles etc. Also recently, attempts have been made to obtain satifactory expression for hydrogen bond energy as a function of the parameters relating to it . Although various results of interest in relation to the conformation of polypeptides and proteins have been worked out from such theory, the theoretical results have not been dirertly tested in many cases in relation to available data from physicochemical studies on a dipeptide unit, or fragments of simple compounds which sufficiently approximate to it. The purpose of this prelimiiiary note is to point out the possibility of making such tests and to indicate some results which show reasonable agreement with data obtained from infrared arid NMR studies.

Journal ArticleDOI
01 Dec 1971
TL;DR: In this article, the relative stabilities of the right and left-handed α-helical structures of poly-L-alanine have been investigated, by calculating their conformational energies (V).
Abstract: Making use of the empirical potential functions forpeptide NH .. O bonds, developed in this laboratory, the relative stabilities of the rightand left-handed α-helical structures of poly-L-alanine have been investigated, by calculating their conformational energies (V). The value of Vmin of the right-handed helix (αP) is about — 10.4 kcal/mole, and that of the left-handed helix (αM) is about — 9.6 kcal/mole, showing that the former is lower in energy by 0.8 kcal/mole. The helical parameters of the stable conformation of αP aren ∼ 3.6 andh ∼ 1.5 A. The hydrogen bond of length 2.85 A and nonlinearity of about 10° adds about 4.0 kcal/ mole to the stabilising energy of the helix in the minimum enregy region. The energy minimum is not sharply defined, but occurs over a long valley, suggesting that a distribution of conformations (ϕ, ψ) of nearly the same energy may occur for the individual residues in a helix. The experimental data of a-helical fibres of poly-L-alanine are in good agreement with the theoretical results for αP. In the case of proteins, the mean values of (ϕ, ψ) for different helices are distributed, but they invariably occur within the contour for V = Vmin + 2 kcal/mole for αP.

Journal ArticleDOI
TL;DR: In this paper, the condensation of isonitrosoacetylacetone in the presence and in the absence of nickel(II) has been investigated and the nature of bonding of the ligand to the metal ion is discussed.

Journal ArticleDOI
TL;DR: In this article, the elastic stability of polar orthotropic annular plates subjected to in-plane uniform radial edge pressures has been considered, and the Rayleigh-Ritz method with simple polynomials as admissible functions has been employed in the analysis.
Abstract: In this paper, elastic stability of polar orthotropic annular plates subjected to in-plane uniform radial edge pressures has been considered. The Rayleigh-Ritz method with simple polynomials as admissible functions has been employed in the analysis. It has been established that spectra of eigenvalues for axisymmetric buckling are identical for free-free, simply supported-free, and free-simply supported combinations of edge conditions. For a hole ratio of 1/2, numerical estimates to the least axisymmetric buckling loads have been obtained for all combinations of free, simply supported, and clamped boundary conditions for two loading cases, namely: (1) when the outer edge alone is subjected to uniform presure, and (2) when both edges are subjected to equal pressures. Some interesting effects of the rigidity ratio on these buckling loads have been brought out.

Journal ArticleDOI
TL;DR: In this article, the Galerkin method with the flutter mode represented in terms of a double series of beam characteristic functions is employed for the supersonic panel flutter problem.
Abstract: The supersonic panel flutter problem of clamped skew panels with in-plane forces is formulated on the basis of the classical, small deflection, thin plate theory using oblique coordinates. The two-dimensional, static approximation is made use of for the aerodynamic loading. Galerkin method with the flutter mode represented in terms of a double series of beam characteristic functions is employed. Results of numerical calculations made for unstressed panels for different combinations of side ratio, angle of skew, and angle of yaw are presented here. The majority of the calculations were made using 16 terms in the series. Convergence is examined in a few typical cases. The dynamic pressure parameter for flutter is found to increase monotonically with the angle of skew for side ratio 1 and to decrease initially before beginning to increase for side ratio 0.5. The results are also compared with those obtained earlier for simply supported panels.


Journal ArticleDOI
TL;DR: In this article, a single crystal ESR study of copper diethyldithiocarbamate has shown evidence for the presence of coupled pairs of Cu++ ions and the zero field splitting parameter D = 276 × 10−4 cm−1.

Journal ArticleDOI
TL;DR: In this paper, the steady laminar viscous hypersonic flow of an electrically conducting fluid in the region of the stagnation point of an insulating blunt body in the presence of a radial magnetic field is studied by similarity solution approach, taking into account the variation of the product of density and viscosity across the boundary layer.
Abstract: In this paper, the steady laminar viscous hypersonic flow of an electrically conducting fluid in the region of the stagnation point of an insulating blunt body in the presence of a radial magnetic field is studied by similarity solution approach, taking into account the variation of the product of density and viscosity across the boundary layer. The two coupled non-linear ordinary differential equations are solved simultaneously using Runge-Kutta-Gill method. It has been found that the effect of the variation of the product of density and viscosity on skin friction coefficient and Nusselt number is appreciable. The skin friction coefficient increases but Nusselt number decreases as the magnetic field or the total enthalpy at the wall increases.