Some new techniques for scattered-light photoelasticity

This paper describes some new techniques for determining the directions of the secondary principal stresses and their difference in scattered-light photoelasticity. These new techniques do not employ the compensator and are capable of obtaining the same degree of accuracy as the compensator method.     

On the nullification of stress-concentration factors by stress equalization

During a recent design study involving a critically stressed “tongue-and-groove” type compression joint of dissimilar materials, a novel technique was conceived for nullifying the effects of an otherwise high local stress-concentration factor. In principle, the nominal stresses in the tongue-and-groove portions of the joint are forced to be uniform. For idealizedfit conditions, the stress concentration in the fillet under this stress-equalized condition is theorized to approach unity (1.00). In the present paper, experimental verification is provided.     

Displacement field around a circular hole in a viscoelastic plate

Moiré experimental techniques are used to measure displacement fields in viscoelastic plates undergoing large deformations at elevated temperatures. These experimental procedures are applicable to determining displacement fields in nonlinear materials. As preliminary information, the material properties are determined from creep studies. The moiré method is used to determine the strains under constant load and isothermal conditions. Tests are conducted for several combinations of load and temperature for 2.5 decades of time. Assuming thermorheologically simple behavior, the data are shifted to establish the creep extensional compliance over ten decades in time. The constitutive equations are formulated as integral equations, the kernels of which are the functions that were measured in this work. These equations are solved exactly for the infinitesimal case. The finite case is then approximated by an incremental superposition of a series of successiye infinitesimal solutions. The results are applied to a plate initially containing a circular hole, and are shown to agree closely with the experimental measurements.     

Photoelastic concrete similutide with CR-39 reinforced with epoxy and glass

This investigation was undertaken to study the similitude of models for reinforced concrete beams by photoelasticity. All previous attempts of model analysis have not maintained the correct modular ratio of reinforcing rod to the beam material. The material problem of obtaining the necessary rods was solved. The material exploratory investigation revealed suitable reinforcing plastics that have opened a wide range of model analyses for reinforced concrete. The models fabricated provided a study in correlation of models and prototype. A sample of the stresses obtained with a photoelastic interferometer is given to demonstrate the practical application of the model analysis.     

On the influence of a flexural biasing state on the velocity of piezoelectric surface waves

A system of linear electroelastic equations for small fields superposed on a bias is applied in the determination of the velocity of acoustic surface waves in piezoelectric substrates subject to flexural biasing stresses. The influence of the biasing stresses appears in the boundary conditions as well as the differential equations. Direct calculations performed for both quartz and lithium niobate when the spatial variation of the flexural biasing state is omitted indicate that the biasing stresses in the boundary conditions have an important influence of the surface wave velocity. In addition, perturbation calculations are performed which include the influence of the spatial variation of all flexural biasing terms and it is shown that, for substrate thickness-to-wavelength ratios well within the practical range, the spatial variation in the biasing state has an appreciable effect on the velocity of acoustic surface waves.     

The slow motion of two touching fluid spheres along their line of centers

The creeping motion along their line of centers of two fluid spheres in contact is analyzed. An exact solution is presented. Corrections to the Hadamard—Rybezynski equation are tabulated for various particle radii ratios and particle fluid to external fluid viscosity ratios. In the limit of infinite particle viscosity, these corrections are shown to agree with previous calculations for rigid spheres.     

Methods correlating data on the heat conductivity of dissociating gases

This article describes three methods of correlating experimental data on the heat conductivity of dissociating systems with a single chemical reaction. Criterial equations for the coefficients of thermal conductivity are given.In studies on dissociating gases, the problem of determining the physical constants of the transport phenomena and, in particular, the coefficient of thermal conductivity is of special interest. In such investigations, however, experimental methods in the high-temperature range are complicated and need further development, while in the case of polyatomic mixtures in which chemical reactions are taking place the practical computations are cumbersome and inaccurate. Therefore, the development of general methods of correlating the available experimental data on the heat conductivity of chemically reacting gases is of definite importance. In this article three methods of evaluating experimental data are discussed in relation to dissociating gases.     

Fractional Derivatives Applied to Phase-Space Reconstructions

The concept and application of phase-space reconstructions are reviewed. Fractional derivatives are then proposed for the purpose of reconstructing dynamics from a single observed time history. A procedure is presented in which the fractional derivatives of time series data are obtained in the frequency domain. The method is applied to the Lorenz system. The ability of the method to unfold the data is assessed by the method of global false nearest neighbors. The reconstructed data is used to compute recurrences and correlation dimensions. The reconstruction is compared to the commonly used method of delays in order to assess the choice of reconstruction parameters, and also the quality of results.     

Ähnliche Grenzschichtlösungen zweiter Ordnung für Strömungs- und Temperaturgrenzschichten an longitudinal gekrümmten Wänden mit Grenzschichtbeeinflussung

Zusammenfassung Für die inkompressible, stationäre Strömungs- und Temperaturgrenzschicht an longitudinal gekrümmten Wänden mit Grenzschichtbeeinflussung werden unter Berücksichtigung der Glieder zweiter Ordnung, d. h. mit Berücksichtigung der Verdrängung und des metrischen Krümmungseinflusses ähnliche Lösungen angegeben. Die Lösungen erstrecken sich auf Wände, deren Krümmungk proportional zu einer Potenz der Bogenlängex ist. In dieser Familie von Wandkurven sind die Staupunktströmung an einem Zylinder und die Strömungen an Keilen mit gekrümmten Keilflanken eingeschlossen. Dabei ist der Öffnungswinkel des Keils mit dem Krümmungsverlauf der Keilflanken verknüpft.

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Similarity solutions are given for incompressible, steady hydrodynamic and thermal boundary layers on longitudinally curved walls with boundary layer interference considering second order terms i. e. allowing for displacement and metric curvature influence. The solution apply to walls with curvaturek proportional to a power of the arc lengthx. Involved in this family of wall-curves is the stagnation point flow on a cylinder and the flow along wedges with curved walls. Here, the angle of the wedge is connected to the curvature of the wedge-walls.

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Mit Unterstützung der Aerospace Research Laboratories durch das U. S. Air Force European Office of Aerospace Research.     

What are gene patents and why are people worried about them?

This article examines what it means to patent a gene. Numerous ethical concerns have been raised about the effects of such patents on clinical medical practice as well as on research and development. We describe what kinds of inventions are covered by human gene patents, give several examples and summarize the small body of empirical research performed in the US examining the effects of these patents. There is little evidence that early fears about gene patenting placing substantial restraints on research and clinical medicine have come to fruition. Nonetheless, there are areas of concern, and policy makers, physicians and the public should be alert to ensure that the net social benefits of patenting human genes are maintained.