An innovative extensional viscometer for low-viscosity and low-elasticity liquids

A spinline-type extensional viscometer is described in which an innovative method of tensile stress measurement is employed. A limited amount of liquid flows through a vertical capillary at a constant flow rate under the influence of a constant pressure head. The drainage time decreases when the liquid stream leaving the capillary is stretched by the application of vacuum. These drainage times are measured in a manner similar to that used for intrinsic viscosity measurements. The measured difference in drainage times, with and without stretching, is trivially related to the extensional stress at the capillary exit, and this provides a very simple method of accurately determining fluid stretching forces having a magnitude as low as 10^-4 N; stresses at other axial locations in the stretched liquid jet are obtained by means of a force balance in the usual manner. The validity of the proposed technique is demonstrated by obtaining the expected results for a Newtonian oil having a shear viscosity of 56.2 mPa-s. Also presented are preliminary data on polyethylene oxide-in-water solutions having an even lower shear viscosity.     

Application of rainbow schlieren deflectometry for concentration measurements in an axisymmetric helium jet

 The rainbow schlieren deflectometry technique was used to measure oxygen concentrations in a laminar, isothermal helium jet discharged vertically into ambient air. The concentration distributions were inferred from the color schlieren image by taking into consideration the sampling interval and noise in measurements, especially near the jet center. Excellent quantitative agreement was reached between measurements from schlieren and a continuous sampling probe. This work demonstrates the capability of the schlieren technique for providing accurate, spatially-resolved, nonintrusive, full-field of view measurements of species concentration in an isothermal binary system. Because the basic quantity measured is the refractive index, the present schlieren technique can be extended for quantitative measurements of other scalar flow properties related to the refractive index. Received: 21 April 1997 / Accepted: 14 November 1997     

On Spatial Effects of Modelling in Linear Viscoelasticity

The parameters of a linear model of a viscoelastic material are determined by testing the material in homogeneous (i.e. spatially constant) states. Some of the qualitative properties of the behaviour of the material observed in the tests may be unexpectedly lost if the material is confined, so that the behaviour varies in space and is thus not homogeneous. One such property is the (Lyapunov) stability of the deformation. To ensure that the material possesses these properties it is necessary to impose some additional restrictions on the model parameters. These restrictions are found by analysing the boundary value problems for viscoelastic bodies of various shapes and subjected to various boundary conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Castes, migration, immunogenetics and infectious diseases in south India

It has been said that the grandest genetic experiment of nature has been conducted in south India in the name of the caste system. One can expect the frequency of an infectious disease to be equal to the product of the frequencies of various indicated loci/alleles, whether physiological, hormonal or immunological, in an endemic area. The sympatrically isolated caste and sub-caste populations of southern India, with differing origins, migration patterns and breeding habits, differ significantly in their HLA and other immune repertoire and are ideal models to study and test this hypothesis. The prevalence of a number of major infectious diseases, including TB and leprosy, are reviewed in different communities in the light of their genetic history.     

Oscillations of a wedge in a free stream with particular reference to parachutes

The phenomenon of coupled breathing and longitudinal oscillations of a wedge-mass system in a free stream is examined. As a first step the unsteady pressure distribution on the surface of the oscillating wedge is calculated. For dynamic equilibrium of the wedge-mass system, the moment about the apex of the wedge must be zero. This condition establishes the amplitude and phase relation between breathing and longitudinal oscillations. As a final step the equation of motion of the store is used to calculate the frequency of the breathing oscillations. This frequency is shown to be dependent on four parameters. These parameters include the Froude number, the rigging line length to wedge breadth ratio and the rigging line stiffness and damping. Current results are compared with Hume and Stevens [1] experimental results.     

Limiting energy characteristics of pulsed tea co2 lasers

The article presents the results of experimental studies on the determination of the characteristics of the process of absorption of large specific electrical energy densities in a wide range of pressures (0.1–0.5 atm CO₂?2N₂?0.5H₂). The presence of limitations (E₀/p ≥45 V/cm · torr, Q/p=? 1 J/cm³ · atm) which are responsible for the region of existence of a diffusional discharge was established, which made it possible to determine the relationship between the limiting electrical energy density which can be absorbed in the discharge, the initial parameters of the system, and the amount of radiated energy.     

Conductor destruction in electrical explosion

Conductor damage has been examined when the current is switched off at various stages in electrical explosion. If the switching is fairly rapid, kink instability growth is accompanied by formation of vapor bubbles at the kinks within the volume of the liquid metal. Later switching results in vapor bubbles uniformly distributed along the conductor. Cumulative ejection occurs under certain conditions. A qualitative interpretation is given.     

A technique for generating shear waves in cylindrical shells under radial impact

Experimental techniques are developed to study and measure the shear-wave velocity in an aluminum cylindrical shell subjected to a radial impact. The radial impact is obtained by exploding an electrical detonator inserted in plastic plugs mounted on the end of the shell. Strain gages, mounted on the outside surface of the shell at various axial locations, are used to obtain oscilloscope traces from which the shear-wave velocity can be calculated.     

Optimum transmission of elastic waves through joints

An elastic wave transmitting system (e.g. a nonuniform elastic rod) consisting of an input section with constant impedance, a joint with variable impedance, and an output section with constant impedance is considered. The efficiency of energy transmission (the ratio of transmitted to incident elastic wave energy) is determined and the following optimization problem is solved for two sample cases: Given the properties of the wave transmitting system and a limited duration of the incident wave, determine the shape of this wave such that the efficiency of energy transmission is maximized. In the first case (a joint with constant impedance) the optimization problem leads to a matrix eigenvalue problem. In the second case (a joint with concentrated mass) it leads to an eigenvalue problem for an integral equation. The efficiencies obtained for the optimum incident waves are compared with those obtained for rectagular incident waves an it is found that the differences are generally small. The results, which are discussed with particular reference to the transmission of elastic wave energy through drill rod joints, can also be interpreted for e.g. shallow water waves and electromagnetic waves in a transmission line.     

Development of high-temperature biaxial-strain transducer for use to 1033°K (1400°F)

This study involved the development and evaluation of a high-temperature biaxial-strain transducer for measurement of strains up to 5 percent at temperatures approaching 1033°K (1400°F). The design requirements for transducer were established by specifications prepared by the Pressure Vessel Research Committee (PVRC) of the Welding Research Council. These specifications reflect the needs of the national laboratories and private industry as they relate to safety and structural-behavior studies of nuclear and advanced fossil-fuel systems, including piping, piping components, heat exchangers, and other pressure equipment. It was concluded, on the basis of the results from this study, that the transducer should perform satisfactorily at temperatures to at least 866°K (1100°F), and perhaps to 1033°K (1400°F). This paper should be of particular interest to those involved in high-temperature strain measurements or structural-behavior studies of energy systems (nuclear and fossil fuel) and components (piping, pumps, valves, heat exchangers, reactor components, etc).