Activities in dilute solutions of chromium and iron in nickel at 1600° by mass spectrometry

Binary and ternary alloys of chromium and iron with nickel were studied. The total solute content ranged from 1 to 10 at. pct. The first-order interaction coefficients for chromium are ε_Cr ^(Cr)= 1.8 ±2.0, and ε_Cr ^(Fe) = 0.6 ± 5.0 (twice standard deviation). The relative partial molar enthalpy of liquid chromium in nickel at 1550° and at 5 pct chromium is −2200 cal per g-atom. An unusual result was obtained for iron in the form of a minimum in the experimental ln(I_Fe ^N _Ni/I_Ni ^N _Fe)-curve. Formerly Postdoctoral Fellow, Department of Metallurgical Engineering, Ohio State University, Columbus, Ohio. Formerly N. S. F. Trainee at Ohio State University.     

Laser-beam modulation using grating diffraction effects

An optical-diffraction modulator, using an electro-optic crystal excited by a periodic array of metallic conductors, is described. The operation of the device is in some ways similar to that of an acoustoelectric modulator; it differs from it in that it has a bandwidth, potentially very wide, which extends from d.c. It may therefore find application as a baseband modulator.     

The minority-carrier injection in the completely depleted MSM structure

The effect of the semiconductor parameters on the injection of carriers in a metal-semiconductor-metal structure was analyzed. It was assumed that the semiconductor is completely depleted when no external voltage is applied. We found that in that case minority carrier injection dominates over majority carrier injection. Consequently, numerical analysis shows that the current density in a metal-n-type semiconductor-metal structure increases with increasing electron barrier height and/or with decreasing donor concentration. The hole injection current dominates over the electron injection current. These relationships are opposite to those occurring both in a single MS junction and in a partly-depleted MSM junction where the minority carrier injection ratio is known to be negligibly small.     

Studies on vesicourethral reflexes. II. Urethral sphincteric responses to spinal cord stimulation

A bipartite bladder model was developed with and without complete muscular separation in order to isolate and analyze separately sphincteric and detrusor responses. Spinal cord stimulation of the sacral micturition center evoked responses in the detrusor compartment as well as in the urethral sphincteric compartment. The micturition center was easily definable in the spinal cord at a variable point lying in the segment L51/2 to L6 vertebral levels. It was not possible to isolate a separate detrusor center from a sphincteric center. They did overlap-with the sphincteric center extending both above and below the detrusor center. Parameters of stimulation were tested and it was noted that 1 to 3 v, frequency of 10 to 15 cps, and duration of 1 msec gave the optimal responses. Complte muscular separation did not alter sphincteric response to spinal cord stimulation. Nerve-mediated impulses resulted in rise in detrusor pressure and a simultaneous rise in urethral pressure that interfered with proper voiding and hindered bladder emptying. This problem remains to be solved before central spinal cord stimulation for the purpose of controlled bladder evacuation becomes fully effective.     

Finite element analysis of deformation of strain-softening materials

A finite element analysis of strain-softening materials is presented in which the shear band of prescribed thickness is assumed to exist within elements where maximal stress intensity is reached. The incremental stiffness matrix of the element is derived including shear band deformation. Examples presented in the Paper demonstrate that the load-displacement curve and the displacement field are not sensitive to the mesh size used in the solution.     

Mechanism of high-temperature sulphide corrosion of metals and alloys

Sulfidation appears to be considerably more suitable than oxidation for studying the high-temperature behaviour of metals. Sulfide scales are formed at considerably higher rates and at lower temperatures, in addition it is much easier to work with the radioactive sulfide isotope. The experiments can be conducted in sulfur vapour or in hydrogen/hydrogen sulfide mixtures; differences are due only to different sulfur partial pressures. Sulfide scale is formed on pure metals (e. g. Cu, Ag, Ni) as well as in binary or ternary alloys. (e. g. FeNi, NiCr, CuZn, CoCr, FeCrAl) with consistantly reproducible results. Irrespective of scale thickness and structure the reaction rates are always controlled by outward diffusion with the high defect concentration favouring high reaction rates. Since various metals tend to form low melting metal/metal sulfide eutectics, it is necessary to keep temperatures below the particular melting point. Contrary to inner oxidation there is no inner sulfidation. The protective action of sulfide scale is considerably inferior to that of oxide scale. According to the results of the present compilation no material has become available which combines sufficient scaling resistance with good high-temperature mechanical properties. Solution of this problem may perhaps be found by adding rare earth metals.