Showing papers by "Indian Institute of Science published in 1969"

On the criteria for reverse transition in a two-dimensional boundary layer flow

Abstract: Experiments on reverse transition were conducted in two-dimensional accelerated incompressible turbulent boundary layers. Mean velocity profiles, longitudinal velocity fluctuations and the wall-shearing stress (TW) were measured. The mean velocity profiles show that the wall region adjusts itself to laminar conditions earlier than the outer region. During the reverse transition process, increases in the shape parameter (H) are accompanied by a decrease in the skin friction coefficient (Cf). Profiles of turbulent intensity (u’2) exhibit near similarity in the turbulence decay region. The breakdown of the law of the wall is characterized by the parameter \[ \Delta_p (= u[dP/dx]/\rho U^{*3}) = - 0.02, \] where U* is the friction velocity. Downstream of this region the decay of fluctuations occurred when the momentum thickness Reynolds number (R) decreased roughly below 400.

A nonstationary random process model for earthquake accelerograms

Abstract: Though many models for the simulation of earthquake records have been suggested, they are either unrealistic or restricted to a qualitative simulation. If the basic mechanism of earthquakes at different places is similar the underlying mathematical pattern of the different recordings may also be alike. Due to the complexities involved in analyzing the fundamental mechanism, a search for the common pattern must be carried out among the few available ground acceleration records. An attempt has been made in this paper in this direction. An analysis of past records shows that the strength of the oscillations exhibited by the number of zero crossings and extremes in a given interval and the nonstationary random nature revealed by the time-dependent variance function are important characteristics. Using this information a stationary random process modulated by a deterministic function has been developed. Almost all types of known records can be generated from this model by varying its parameters. Approximate methods have also been developed for estimating these parameters in artificial simulation. To test the model, ensembles of a single pulse, a ten-second, a thirty-second and a very long record have been simulated and analyzed for relative velocity and time response spectra. Many quantities realized in the records compare well with the corresponding ones fixed beforehand. Suggestions are made for using the model in aseismic design.

Flexure of Simply Supported Thick Homogeneous and Laminated Rectangular Plates

Abstract: A three-dimensional, linear, small deformation theory of elasticity solution by the direct method is given for the flexure of simply supported homogeneous, isotropic, thick rectangular plates under arbitrary loading. This solution, in terms of infinite series is formally exact and yields accurate numerical results without undue effort. Numerical results are presented for uniformly distributed normal load on the top surface. The results from Reissner's theory of thick plates and the predictions of thin plate theory are compared with the values from the present exact solution. The analysis is readily extended for laminated plates of isotropic materials. Numerical results are also given for a three-ply laminate under uniformly distributed normal load on the top surface, and are used to assess the accuracy of thin plate theory predictions for laminates. Fur das Biegeproblem einer einfach unterstutzten, homogenen, isotropen, dicken, beliebig belasteten Rechteckplatte wird auf direktem Wege uber eine dreidimensionale lineare Theorie kleiner elastischer Verformungen eine Losung gewonnen. Sie erscheint in der Gestalt unendlicher Reihen, ist formal exakt und liefert ohne unzumutbaren Aufwand genaue numerische Resultate. Solche werden fur den Fall einer uber die obere Randflache gleichformig verteilten Normallast angegeben und mit den Ergebnissen der Reissnerschen Theorie dicker Platten und mit den Voraussagen einer Theorie dunner Platten verglichen. Die verwendete Analysis last sich leicht auf geschichtete Platten aus isotropen Materialien ausdehnen. Fur eine Dreischichtplatte, auf deren obere Randflache eine gleichformig verteilte Normallast wirkt, werden die numerischen Ergebnisse mitgeteilt und dazu benutzt, die Genauigkeit der von der Theorie dunner Platten gemachten Voraussagen einzuschatzen.

Analysis of Natural Half-Wave-Length Power Transmission Lines

Abstract: This paper provides additional theoretical information on half-wave-length power transmission. The analysis is rendered more general by consideration of a natural half-wave line instead of a short line tuned to half-wave. The effects of line loading and its power factor on the voltage and current profiles of the line and ganerator excitation have been included. Some of the operating problems such as charging of the line and synchronization of the half-wave system are also discussed. The inevitability of power-frequency overvoltages during faults is established. Stability studies have indicated that the use of switching stations is not beneficial. Typical swing curves are also presented.

On an asymptotic method of Krylov-Bogoliubov for overdamped nonlinear systems

Abstract: A general asymptotic method based on the work of Krylov-Bogoliubov is developed to obtain the response of nonlinear over damped systems. A second-order system with both roots real is treated first and the method is then extended to higher-order systems. Two illustrative examples show good agreement with results obtained by numerical integration.

Performance of Tuned Half-Wave-Length Power Transmission Lines

Abstract: The basic concepts of tuned half-wave lines were covered by Hubert and Gent [1]. In this paper the problem of overvoltages during faults and the stability of the system incorporating such tuned lines are discussed. The type of tuning bank and the line arrangements that will be satisfactory from the point of view of stability are suggested. The behavior of a line tuned by distributed capacitor is analyzed, and its performance is compared with the other type of tuned line.

Structure of ferroverdin.

Abstract: FERROVERDIN, a green iron-containing pigment, was isolated in 1955 by Chain, Tonolo and Carilli1 from an unidentified species of Streptomyces. It was at first assigned the formula C30H24O8N2Fe and the iron was shown by measurements of magnetic susceptibility to be in the ferrous state2. Later the ligand present was proved to be the p-vinyl phenyl ester of 3-nitroso-4-hydroxy-benzoic acid3,4. X-ray crystallographic measurements were undertaken to find the atomic arrangement in this unusual complex; they show, in two different crystal structures, that each iron atom is attached to three nitrosophenyl ligands and that the charge is balanced by sodium ions.

The neurotoxicity of β-N-oxalyl-l-αβ-diaminopropionic acid, the neurotoxin from the pulse Lathyrus sativus

Abstract: Intraperitoneal administration of β-N-oxalyl-l-αβ-diaminopropionic acid, the neurotoxin from Lathyrus sativus, to 12-day-old rats causes typical convulsions within 10min. There is a striking accumulation of glutamine in the brain, and chronic ammonia toxicity is indicated. There are no changes in the amounts of urea, aspartic acid and glutamic acid in the brain. Adult rats, even when injected with a dose of excess of β-N-oxalyl-l-αβ-diaminopropionic acid, do not develop symptoms, and there are no changes in the amounts of glutamine or ammonia in the brain. A significant concentration of β-N-oxalyl-l-αβ-diaminopropionic acid can be detected in the brain of the young rat but not in that of the adult animal. It is concluded that β-N-oxalyl-l-αβ-diaminopropionic acid interferes with the ammonia-generating or -fixing mechanisms in the brain and leads to chronic ammonia toxicity.

Effect of Vibration on Heat Transfer From Spheres

Abstract: The effect of vibration on free and forced convection heat transfer from spheres was investigated. Test spheres made of copper were subjected to sinusoidal vibration in the vertical plane, this being perpendicular to the direction of airstream in the case of forced convection studies. In free convection studies the amplitude of vibration was varied from 4 mm to 25.5 mm and the frequency of vibration from 150 cpm to 930 cpm. It was found that the effect of vibration on Nusselt number was negligible for values of vibrational Reynolds number less than 200. For values of vibrational Reynolds number greater than 200, the vibration increased the heat transfer coefficient considerably and values of heat transfer coefficients as high as seven times the free convection values without vibration were obtained. The following correlations were obtained for heat transfer from spheres to air: free convection without vibration, NNu = 2 + 0.401 (NGr)0.25 for 4 × 103 < NGr < 6 × 104 and free convection with vibration: hvho = 0.83 (NRe)v0.5(a/D)0.1(NGr)0.251.28 In the case of forced convection studies with vibration, the amplitude of vibrations varied between 4 mm and 12.4 mm, and the frequency of vibration from 200 cpm to 1600 cpm. The flow velocity was varied from 24.5 ft/sec to 84 ft/sec. The results in the absence of vibration could be represented by: NNu = 0.304 (NRe )0.56 or NNu = 2 + 0.222 (NRe )0.587 in the range 6 × 103 < NRe < 3.3 × 104 . Nusselt numbers were not found to be affected by the imposition of vibrational velocity even as high as 19.6 percent of the flow velocity.

Method of variation of parameters for overdamped non-linear systems†

Abstract: A simple analytical method is developed to obtain the time response of second-order non–linear overdamped systems with a small non–linearity based on the Krylov— Bogoliubov method of variation of parameters. The solutions obtained for different initial conditions for a second–order system whose linear equation has real roots show good agreement with those obtained by numerical integration.

The Boltzmann collision integrals for a combination of Maxwellians

Abstract: The gain and loss integrals in the Boltzmann equation for a rigid sphere gas are evaluated in closed form for a distribution which can be expressed as a linear combination of Maxwellians. Application to the Mott-Smith bimodal distribution shows that the gain is also bimodal, but the two modes in the gain are less pronounced than in the distribution. Implications of these results for simple collision models in non-equilibrium flow are discussed.

Activation of liver succinate dehydrogenase in rats exposed to hypobaric conditions.

Abstract: 1. On brief exposure of rats to hypobaric conditions, the activity of hepatic mitochondrial succinate dehydrogenase was raised from the basal state to a ;partially activated state'. This was further raised to ;fully activated state' by preincubation of mitochondria with succinate, as was the activity in mitochondria from normal rats. 2. On washing mitochondria with the homogenizing sucrose medium the activity excess obtained on preincubation with succinate was lost in mitochondria from both normal and treated rats. 3. The enzyme in the ;partially activated state' from animals exposed to hypobaric conditions was stable to the washing procedure but was labilized and reverted to a low basal state of activity on freezing and thawing of the isolated mitochondria. 4. The results suggest that activation of succinate dehydrogenase under hypobaric conditions represents a conformational change leading to a stable, partially activated, form of the enzyme system: this is the first evidence of physiological modulation of this rate-limiting step in the control of the rate of oxidation of succinate.

Minimum error solutions of the Boltzmann equation for shock structure

Abstract: ‘Best’ solutions for the shock-structure problem are obtained by solving the Boltzmann equation for a rigid sphere gas by applying minimum error criteria on the Mott-Smith ansatz. The use of two such criteria minimizing respectively the local and total errors, as well as independent computations of the remaining error, establish the high accuracy of the solutions, although it is shown that the Mott-Smith distribution is not an exact solution of the Boltzmann equation even at infinite Mach number. The minimum local error method is found to be particularly simple and efficient. Adopting the present solutions as the standard of comparison, it is found that the widely used v 2 x -moment solutions can be as much as a third in error, but that results based on Rosen's method provide good approximations. Finally, it is shown that if the Maxwell mean free path on the hot side of the shock is chosen as the scaling length, the value of the density-slope shock thickness is relatively insensitive to the intermolecular potential. A comparison is made on this basis of present results with experiment, and very satisfactory quantitative agreement is obtained.

A note on the damping and oscillations of a fluid drop moving in another fluid

Abstract: The oscillations of a drop moving in another fluid medium have been studied at low values of Reynolds number and Weber number by taking into consideration the shape of the drop and the viscosities of the two phases in addition to the interfacial tension. The deformation of the drop modifies the Lamb's expression for frequency by including a correction term while the viscous effects split the frequency into a pair of frequencies—one lower and the other higher than Lamb's. The lower frequency mode has ample experimental support while the higher frequency mode has also been observed. The two modes almost merge with Lamb's frequency for the asymptotic cases of a drop in free space or a bubble in a dense viscous fluid but the splitting becomes large when the two fluids have similar properties. Instead of oscillations, aperiodic damping modes are found to occur in drops with sizes smaller than a critical size ($\sim\hat{\rho}\hat{ u}^2/T $). With the help of these calculations, many of the available experimental results are analyzed and discussed.

Studies on the positional integrity of glyceride fatty acids during digestion and absorption in rats

Abstract: 1. Rats previously starved for 24hr. were separately given by intraduodenal injections 0·5ml. of a dispersion containing 10mg. of sodium taurocholate, with 50mg. of glycerol 1,3-dioleate 2[1-14C]-palmitate, glycerol 1,2-dioleate 3[1-14C]-palmitate, a mixture of [1-14C]palmitic acid and triolein, or a mixture of [1-14C]-palmitic acid and oleic acid. 2. At the end of 30min., the net amounts, and the radioactivity, of the neutral-lipid components recovered from the intestinal lumen and mucosa, and the position of the labelled palmitic acid in the mucosal triglycerides, were determined. 3. When glycerol 1,3-dioleate 2[1-14C]-palmitate was administered, most of the labelled acid was retained in the di- and monoglycerides of the lumen; the triglycerides were the major components containing the radioactivity in the mucosa and 75–80% of the labelled acid was located at the β-position of these triglycerides. 4. When glycerol 1,2-dioleate 3[1-14C]-palmitate was administered, the labelled acid was readily split off in the lumen and virtually no radioactivity could be traced in the monoglyceride fraction; in the intestinal mucosa, triglycerides were again the chief components containing most of the radioactivity, and 80–85% of the labelled acid was esterified at the outer positions of the glycerol. 5. When [1-14C]palmitic acid mixed with triolein was administered, the concentrations of free fatty acids increased markedly in the intestinal lumen and mucosa, and 80–88% of the radioactivity of the mucosal triglycerides was located at the outer positions of the glycerol. 6. When [1-14C]palmitic acid mixed with oleic acid was administered, the labelled acid accumulated in the lumen as well as in the cell, and it was randomly incorporated into all three positions of the mucosal triglycerides.

A three dimensional elasticity solution for rectangular prism under end loads

Abstract: Fur ein Rechteckprisma, an dessen Enden vorgegebene Krafte wirken, wird auf der Grundlage der die dreidimensionale Elastizitatstheorie beherrschenden Gleichungen das Problem des dreidimensionalen elastischen Verhaltens gelost. Die Losung hat die Form eines Galerkin-Vektors, dessen Komponenten in Doppel-Fourier-Reihen entwickelt sind, die der zugrunde liegenden biharmonischen Gleichung genugen und so gewahlt sind, das sie alle Randbedingungen befriedigen. Es werden Rechteckprismen mit symmetrischen oder exzentrischen Normalkraften an den Enden untersucht und fur typische Falle numerische Ergebnisse angegeben. Die gewonnenen Ergebnisse werden mit denen der zweidimensionalen Theorie verglichen.