Showing papers by "Istanbul University published in 1974"

Mean velocity and longitudinal dispersion of heavy particles in turbulent open-channel flow

Abstract: This paper deals with the motion of a heavy particle in a turbulent flow in an open channel with a smooth bottom. For the case when the particle stays in suspension in the main body of the flow almost all the time, (a) the probability density function of the projection on a cross-sectional plane of the particle position at any instant, and (b) the mean velocity and longitudinal dispersion coefficient of particles are determined analytically by employing the Eulerian formulation and applying the Aris moment transformations. It is found that the mean particle velocity decreases and the longitudinal dispersion coefficient of particles increases with the fall velocity.

Seasonal Changes in Dimensions and Viability of the Developing Eggs of the Cornish Pilchard (Sardina pilchardus Walbaum) off Plymouth

Abstract: The fishery for the Cornish Pilchard is generally regarded as a northern extension of the much greater fishery for the Atlantic Sardine in the Bay of Biscay. Most of the pilchards taken there are four years old or more, and younger specimens are rare in commercially caught samples. It has been suggested, therefore, that the population is maintained by migration of older fish from the northern Bay of Biscay, where there are large numbers of 2-year olds. This area is presumed to act as a ‘nursery ground’ for any young fish surviving from the more northerly spawnings (Furnestin, 1944; Hickling, 1945; Le Gall, 1950).

A Method of Digital Computation for SCR Circuits

Abstract: It is shown in this paper that it is possible to derive generalized equations for computation of electrical circuits containing SCR elements. Any classical method of circuit analysis can be used applying the nonlinear mathematical model given for the SCR. In order to get this model, a binary logic state variable is doped to the equation which is obtained by a Boolean function. The derivation of this mathematical model and the application of the method to an impulse-commutated inverter with an RL load are presented.

The Abundance and Distribution of Eggs and Larvae of Teleost Fishes off Plymouth in 1969 and 1970: Part 3. Eggs of Pilchard ( Sardina Pilchardus Walbaum) and Sprat ( Sprattus Sprattus (L.))

Abstract: Pilchard eggs were collected over a grid of 30 stations visited on 14 cruises from August 1969 to November 1970. The samples were taken with oblique tows of a 1 m terylene net at 4 knots, the average volume of water filtered being 750 m 3 . The formalin preserved eggs were graded into the series of stages described by Gamulin & Hure. No very early eggs were found, but from the occurrence of stage 2 eggs it is deduced that most spawning takes place in the early hours of darkness, between 20.00 and 24.00 h B.S.T.: some spawning must also occur all round the clock. There were two main peaks of spawning, June-July and October-November, when large numbers of eggs were found inshore; the average numbers reached 196 per m 2 water column in July and 30 per m 2 water column in October. Smaller numbers of eggs were taken in the other months of the year, mostly offshore, and with a minimum in December–February. In the spring (March-May) the area sampled was well clear of the main area of spawning of pilchard in the approaches to the Channel, north or northwest of Ushant. During the peak months no particular part of the sampling area appeared to be especially favoured for spawning. The significance of the two main peaks of spawning is discussed in relation to the problem of recruitment of fish to the population. As an alternative to the accepted hypothesis that young pilchard move back to the Bay of Biscay for maturation it is suggested that some of them, at least, may survive and mature in the Channel.

The effects of chronic reserpine and nialamide treatment on the free amino acid levels of rat brain.

Abstract: Free amino acid levels were determined in the brains of rats treated chronically with reserpine and nialamide. The results were compared with those obtained 3 days after such treatment was discontinued.

A piezoelectric model for nerve conduction.

Abstract: The early studies of the electrical conductance of nerve membrane were explained by a single cell model with different batteries for the action potential. Hodgkin and Huxley proposed that the action potential is propagated along a lossless transmission line.’ After 1960, some of the experiments performed on perfused giant axonz-’ gave some interesting results that could not be explained solely by these assumptions and this model. With the latter experimental results in mind, Wei”’ utilized the Danielli-Davson model, which is based on the dipole structure of the membrane, to explain the action potential in physical terms. Experimental data from other authors support the dipole concept of the m e m b ~ a n e . ~ . ~ Fukadalo-l2 measured piezoelectricity in many living organs. The anisotropy of the piezoelectric modulus is caused by collagen and elastin fibers that exhibit this property. Theoretical investigation of piezoelectricity in helical polymer chains has been undertaken by Kasai.I3 With these observations as a framework, the action potential can be explained by a local electrical phenomenon in association with a dipole membrane effect, which propagates along the nerve by the piezoelectric properties of the membrane.

The onset of natural convection in a horizontal air layer heated from below

Abstract: In this work, the beginning of the instability (onset of convection) of an air layer of infinite width and depth heated from underneath with a constant heat flux is studied. In the theoretical part, the instability is studied using the quasi-static assumption. The functional relationship of Rayleigh number vs. horizontal wave number of the disturbance is obtained in a digital computer using Green's Fonctions for the case of Prandtl number equal to one. Furthermore in order to make a comparison with similar investigations, limiting cases of infinite and very small Prandtl numbers are also taken into consideration.-In the experimental part, Rayleigh numbers corresponding to the onset of manifest convection based on visual observations are investigated by optical methods under various heat fluxes. The average value measured is found to be 145.

On the evaluation of constituent matrices

Abstract: A computationally simple algorithm for the evaluation of constituent mutrices of a given matrix A with distinct and/or multiple eigenvalues is presented. The method, although based on the use of resolving polynomials does not require matrix inversion, nor does it require inverse Laplace transform techniques.

New transformations in signal-flow graphs extended to multi-inputs

Abstract: The new transformations given by Acar for signal-flow graphs with a single input are extended to signal-flow graphs with more than one input. The extended transformations allow changes in several transmittances simultaneously.

Formulation of the sensitivity function using signal-flow graphs

Abstract: An equation is obtained which gives the derivatives of the graph transfer functions with respect to a parameter of interest when the parameter is the transmittance of many branches and when the graph transfer functions are in the bilinear form of the parameter. This equation is useful for evaluating the sensivity functions of active RLC network functions by variation of the passive or active parameters of interest.

Comparative Studies on Water Uptake and Water Permeability of Potato Tissue under the Effect of Indoleacetic Acid, Chloramphenicol and Actinomycin D

Abstract: The water uptake of potato tuber tissue under the influence of chloramphenicol and actinomycin D was compared with that of indoleacetic acid. Both antibiotics decreased the water absorption as compared to the effect of indoleacetic acid. This decrease, in the early hours (3 to 6 h), is due to diminished water permeability. In the later period (6 to 48 h), it is instead a result of a reduction in wall extensibility.

Synthesis of transfer functions by signal-flow graphs

Abstract: A new procedure is given for the synthesis of voltage transfer functions. It is shown that the well known circuits of Lovering and Brugler can also be derived easily by this method. It is also indicated that a simplification can be obtained in the RC:-RC decomposition method. which is in the proposed procedure.

A logic approach in the simplex method of linear programming

Abstract: The purpose of this paper is to show a logic of direct approach for the simplex method on L.P. From the characteristics of the objective function and the constraints, L.P. problems can be classified as follows : Form Objective Constraint function A) Standard Max cTx Ax0 B) Nonstandard Type I Max cTx Ax>b, x>0 Type II Min cTx Ax0 Type III Min cTx Ax0 Type IV Max cTx Ax>/ 0 Type V Min cTx Ax>^ 4.b, x>0 Preliminaries: A linear programming model has been constructed from three parts. The influence of characteristics of each part can be considered as in the following order: objective function, R.H.S. (right-hand side) and left-hand side. The proposed method involves two concepts with respect to criteria. The first concept is that the direction of objective function should be always kept in an objective policy, and is characterized by the coefficient of objective function. The second concept is related to the determination of the optimal condition. These concepts are connected with the definition of the key capacity factor Wb.

Taste thresholds of phenylthiocarbamate.

Abstract: The common frequency of the nontasting gene for phenylthiocarbamate (about 28%) has been found both in Indian adults and in Indian children aged between 6 and 11 years. However, a much lower frequency (less than 11%) was obtained when both Turkish adults and Turkish children aged between 6 and 11 years were tested. On the other hand. English children under the age of 7 years possessed a higher frequency (up to 60%). English children aged 9 years or older had a frquency comparable with that of English adults (about 28%). It was found that between the ages of 7 and 9 many English nontaster children became tasters, which accounts for the observed change in frequency. The reasons for these variations are being investigated.

The shape and position of bubbles at horizontal liquid surfaces

Abstract: The scope of this investigation comprises the determination of the shape and position of a gas bubble floating at the horizontal surface of a liquid. — A starting point towards the solution of this problem is provided by Laplace's law, but this equation is soluble analytically in very few cases only. It is shown that the most useful parameters can be obtained from Princen's table which is a modified version of Bashford and Adams table and other dimensions can be evaluated from the equations as proposed in the context. It is suggested that r√c should be used as the fundamental dimensionless shape parameter and further the radius r of the equivalent sphere can be related to original radius r0 of the bubble by means of a correction factor. — This system has also been studied experimentally. A photographic technique has been used, both the length xc and the height h of upper part of the bubble at the surface have been measured on photographs thus allowing a sensitive test of the theory.