Abstract: A detailed discussion of data obtained over the past 15 years concerning the damping of mechanical vibrations in the kilocycle and megacycle range is given. The dependence of the decrement and modulus change on the variables of frequency and strain‐amplitude and many other parameters is compared with predictions of the dislocation theory developed in an earlier paper. Although general agreement is obtained, and many interesting quantitative results are found, it is not possible to say that the theory agrees everywhere since not all the necessary parameters are known well enough theoretically. A number of new experiments are suggested which may permit stronger conclusions to be made. This part may be read independently of the earlier paper by the reader who does not wish to follow the development of the theory in detail.

Abstract: Propagation of compressive waves generated by high explosive in Armco iron may, under certain conditions, occur with three stable shocks, which are characterized by abrupt and possibly quasi‐discontinuous change of pressure. The characteristics of these have been investigated experimentally and found to be consistent with the hypothesis of a polymorphic transition in iron at about 0.13 megabar. The same phenomenon has been observed in mild steel.

Abstract: Various kinds of silica glass and natural and synthetic crystals have been irradiated with fast neutrons at temperatures of ∼250°C and above 300°C In the glasses, asymmetric paramagnetic resonance lines resulting from the irradiation have been observed with apparent g values of 20013±00006 and 20090±00007, and half‐widths of ≈17 gauss and ≈40 gauss, respectively Two groups of lines were found in the natural crystals and have been associated with the two lines in the glasses, the two lines in the glasses being the envelope of the lines in the crystals when they are summed over random orientations with respect to the magnetic field On the basis of g values, absence of common impurity and of hyperfine splitting, and the thermal stability of the lines, it is concluded that the observed resonances in the silica glasses and crystals have their origin in defects in the basic SiO4 tetrahedra generated by fast neutrons and primary and secondary knockons From preliminary optical bleaching data in neutron i

Abstract: Scattering by a spherical obstacle of a plane longitudinal wave propagating in an isotropically elastic solid is computed. Expressions for the scattered wave and the total scattered energy are given. Three special types of obstacle—an isotropically elastic sphere, a spherical cavity, and a rigid sphere—are discussed in detail, especially for Rayleigh scattering. The result for the isotropically elastic sphere is compared with the well‐known result of scattering of a plane wave propagating in an ideal fluid by a sphere of another ideal fluid.

Abstract: Tensile tests have been performed on whiskers of iron, copper, and silver 1.2 to 15 μ in diameter. The strongest whiskers which were less than 4 μ in diameter exhibited resolved elastic shear strengths of from two to six percent of their shear moduli. Stress‐strain determinations on iron have shown that large deviations from Hooke's law occur beyond two percent strain. As the whiskers increase in size, their strengths decrease with considerable scatter.

Abstract: A dynamic method has been developed for the study of the pyroelectric effect. Transient currents produced in single crystals of barium titanate when subjected to flashes of light are shown to be pyroelectric in origin. The illumination results in a small change in the temperature of the crystal which, in turn, causes the polarization to change. This change is recorded as a current in the external circuit. It is shown that from room temperature up to the Curie point, the pyroelectric current is consistent with the polarization as a function of temperature, as determined from hysteresis loop measurements. The technique proves to be a sensitive and nondestructive method for studying the state of polarization of a crystal.The technique is used to study the pyroelectric effect induced by applied static electric fields at temperatures above the Curie point. The results are consistent with Devonshire's theory of the ferroelectricity of BaTiO3, and they confirm that the Curie point transition is of the first order.

Abstract: The switching time ts and the switching current imax have been measured as a function of applied field E and of the size of the sample. It has been observed that the ``activation field'' α for the nucleation of new domains is inversely proportional to the thickness of the sample. This behavior can be explained by assuming a surface layer. The thickness of this layer has been calculated to be of the order of 10−4 cm. The same way we can explain the thickness dependence of the 60‐cycle coercive field strength. Furthermore, it has been found that the switching time depends to a first approximation linearly on the thickness of the sample if the field E is kept constant. This can be explained by assuming a domain wall motion primarily in the forward direction or by assuming a nucleation mechanism. The maximum velocity of the domain growth was found to be of the order of the velocity of sound. The switching time does not depend on electrode area.

Abstract: When an explosive detonates underwater it creates a bubble of gas which performs damped radial oscillations of large amplitude. The usual theory of these oscillations treats the water as incompressible and yields undamped oscillations of constant period. We have modified this theory by taking account of the compressibility of the water. Our theory predicts damped oscillations of diminishing period. Comparison of the predicted and observed radius‐time curves for one particular case shows fairly good agreement. Radius‐time curves for four representative cases have been computed with a large number of periods in each case. These can be used to describe a variety of explosions.

Abstract: Precipitates formed by copper diffused into silicon crystals were studied by optical means using an infrared image tube. Linear aggregates are identified as dislocations by correlation with etch pits. Dislocations in as‐grown crystals are usually curvilinear. Dislocation loops formed during plastic deformation consist of straight‐line composite portions and pure screw portions, all of which lie in 〈110〉 directions. Precipitates frequently are not found on screw dislocations; when present they differ in detail from those on composites. Interactions between adjacent dislocations can be seen. Etch pits associated with either composite or screw dislocations are similar in form, indicating that the pits formed in as‐grown crystals by the technique described identify all the dislocations. Dislocation loops enter from the surface upon deformation of crystals with relatively few grown‐in dislocations. Dislocation loops formed entirely within the crystal in patterns consistent with operation of the Frank‐Read mech...

Abstract: A modified Landau‐Lifshitz equation is solved for a single‐domain sphere and an infinitely‐wide thin single‐domain sheet of ferromagnetic material neglecting anisotropy. The external magnetic field is switched from one direction to its opposite instantaneously at the initial time and the behavior of the magnetization vector is investigated thereafter. It is shown that there is a critical value of the damping constant corresponding to the minimum value of the (repetitive) magnetization reversal time. If the damping constant is larger than the critical value, the magnetization vector moves slower; if it is smaller, the magnetization vector moves faster but oscillates so that it takes longer time until it comes to a rest at the final position. The critical values of the Landau‐Lifshitz damping constant λ are γM for the sphere and 0.013γM for the thin sheet, where γ and M are the gyromagnetic ratio and the magnetization, respectively. The computed minimum switching time for the thin sheet of 4–79 molybdenum Permalloy is of the order of 10−9 sec.

Abstract: A formula for the resolution of the field ion microscope is derived by considering that most of the ions originate from rebounding molecules after random elastic collision with the surface. Cooling the tip with solid N2 or liquid H2 in order to obtain a large accommodation coefficient drastically reduces the lateral velocity of the ions in a helium operated microscope. As a result the potential resolution for a tip of radius 1000 A is improved to 1.5 A. Photographs show the individual atoms of a tungsten surface. The actual resolution is sufficient to resolve neighboring atoms with 2.74 A separation.

Abstract: Colloidal silica of 30, 20, 10, and 5% concentrations by weight have been used to produce small‐angle scattering. The resulting scattering showed plateaus which varied in angular position with concentration in the very small angle portion and then showed an approximation to the single particle scattering in the larger small angle region. This scattering from individual scattering centers followed that predicted by Debye. Average distances of separation of randomly spaced particles as determined from the particle‐to‐particle scattering plateaus checked those calculated from the concentrations. In addition, scattering from various sized particles ranging from diameters of 100 to 500 000 A were measured. Two theories, a refraction and reflection or ray theory and a diffraction or wave theory, have been applied to the analysis of this scattering. A comparison of the particle sizes as obtained using these two theories with the particle size as obtained by means other than x‐ray scattering shows that for the la...

Abstract: When water flows over glass which has been treated with the vapor of dimethyldichlorosilane and thus made water repellent, slipping on the boundary between the solid surface and the water takes place. This is is shown in capillary tubes of various diameters. The amount of slipping is small, but measurable. It disappears or becomes extremely small in case of turbulent flow.

Abstract: Following a brief comparison of three collision‐seeking types of navigation—pure pursuit, constant‐bearing collision, and proportional navigation—the usual definition of planar proportional navigation is extended to three dimensions. Based upon a simple criterion for optimum navigation to the line‐of‐sight motion, a proper formulation is found in terms of the geodesic and normal curvatures of the missile path on the surface generated by the line of sight. By a suitable choice of a reference coordinate system, the missile‐target kinematic relationships are then linearized, assuming relatively small deviations of the missile from a collision course. Upon combining these ``geometry feedback'' equations with the equations of guidance, the missile trajectory is found to be given in terms of two independent linear differential equations of identical form and of one higher order than the missile transfer function. Typical solutions are found for some simple cases. The character of the trajectory is shown to depend on an ``effective navigation constant'' proportional to the missile navigation constant (or gain) and the ratio of missile speed to closing speed; a value of this parameter greater than two is found to be necessary to insure finite terminal missile acceleration. Two example trajectories are calculated from both the exact and the linearized trajectory equations to indicate the accuracy of the linearization.

Abstract: A theory for uniform field breakdown in air at microwave frequencies is developed and applied with success to predicting values of breakdown over a wide range of experimental conditions. Three distinct types of breakdown are treated; c.w. (continuous wave) breakdown, single pulse breakdown, and multipulse breakdown. The conditions for breakdown are determined from a solution of the electron continuity equation for an average electron, in which electron ionization, attachment, and diffusion are the dominant mechanisms. Modulation of the electron average energy at twice the frequency of the applied field becomes important at either high pressure or low frequency and modifies the values of the breakdown field. The breakdown field strengths are shown to be determined from a single curve for each type of breakdown power, either c.w. or pulsed. These theoretical curves are in accordance with the experimental results, thus verifying the assumption and the values of the coefficients used in the theory.

Abstract: In the extrusion of an amorphous, un‐cross‐linked polymer through a capillary, there is a critical stress at and beyond which the emerging stream becomes irregular in shape. This effect appears to originate in the approach to the capillary rather than within the capillary. Tearing or fracture of the molten polymer appears to occur in this region.

Abstract: It is shown that reagent CP‐4 plus ferric ions can be used to detect the positions of dislocations in LiF crystals. The technique is highly selective and both edge and screw (110) [110] dislocations can be detected and distinguished. A double etching method is used to observe, for the first time, the glide and climb of individual dislocations in LiF.

Abstract: A fundamental study of graphite sliding contacts shows that atmospheric concentrations of only a few parts per million of the larger organic molecules are sufficient to prevent the severe wear of graphite which occurs in a dry atmosphere. The experimental results suggest roughly the empirical rule that the minimum relative ``humidity'' of a vapor for effective lubrication decreases logarithmically with chain length in the region 5 to 15 A.

Abstract: The progress of an isothermal chemical reaction on a catalytic surface, which is located in a laminar hydrodynamic flow field of large Reynolds number, is analyzed. Past analytical investigations have been restricted primarily to chemical reactions in fully velocity developed flow fields subject frequently to one or both of the following approximations. (i) The actual velocity distribution is replaced by a flow of uniform velocity. (ii) The concentrations of the reactants on the catalytic surface are prescribed subject to certain hypotheses concerning the rate controlling mechanism.In this investigation the principal aim has been to calculate the actual surface concentration in a laminar boundary layer flow without unduly sacrificing the hydrodynamic features or introducing unnecessary assumptions about the effective over‐all reaction mechanism. The method presented, which is related to an analysis of convective heat transfer from a nonisothermal surface, is applicable to arbitrary catalytic reaction mech...

Abstract: Measurements of neutron irradiation effects upon the Young's modulus and logarithmic decrement of a set of copper single crystals of 99.999% purity have been made at room temperature. Interpretations of the results can best be given in terms of an oscillating dislocation line mechanism in which the oscillations are suppressed by the presence of interstitial atoms, vacancies, or some combination thereof. Comparisons of the results with the predictions of impurity line pinning are given. It is shown that an interpretation in this sense leads to generally accepted values for the dislocation densities and average segment lengths.

Abstract: Photoconductive (PC) and photoelectromagnetic (PEM) effects have been observed in p‐type InSb single crystals of high purity at 77°K (extrinsic range) and 301°K (intrinsic range). Because of the large electron mobilities in InSb, and because the variation of the PEM response with magnetic field was found to be strongly dependent on surface treatment, it was necessary to develop a new theoretical model to describe the PEM effect, permitting the evaluation of bulk lifetime and both electron and hole mobilities. In addition, the model affords an interpretation of Hall and magnetoresistance effects in intrinsic InSb. When the PEM effect is analyzed using impurity or thermal scattering, assuming Boltzmann statistics, the result does not fit the data so well as the simple model presented here.

Abstract: An apparatus has been constructed for the study of deformation under tension of single and polycrystalline ice. Deformations down to 10−5 cm could be measured. Deformation of single and polycrystals was investigated as a function of time, stress, and temperature. Whereas the strain rate for polycrystalline ice decreases with time, that for single glacier ice increases linearly with time. The deformation for fine‐grained polycrystalline ice consists of an instantaneous elastic deformation, a transient creep and a steady state creep. Deformation curves can be represented by empirical equations. The recovery curves on removal of the loads have also been investigated and the plastic flow has been deduced from the residual deformation after complete recovery. This plastic flow was found to be Newtonian within the range of stresses investigated and the viscosity coefficients can be represented by an exponential relationship as follows: η1 = 7.5·e+16100/RT poises, where 16 100 calories is the energy of activatio...

Abstract: Experimental measurements of jet velocity and of penetration velocity as functions of depth of penetration are described for lined cavity charges fired into several types of target material and under a variety of experimental conditions. The results show that the hydrodynamic theory of penetration of Pugh and of Hill, Mott, and Pack describes very accurately the early stages of the penetration process. Strength of the target becomes an appreciable factor in the later stages, however. A simple modification of the theory is described which appears to account adequately for these strength effects. Some alterations in ideas concerning the mechanism of penetration by the jet after fracture are also described.

Abstract: A variational method is presented which is used to calculate the energy appearing in the various diffracted orders set up when a plane wave is incident upon a periodic reflecting surface. Either the first or the second boundary condition can be so treated. A sample problem is worked showing that if the average absolute slope of the reflecting surface is small (segments of surface with large slope may be included) and if the displacement of the surface is not large compared with the wavelength of the incident radiation, the formulation gives results correct to within a few percent. The calculation shows the existence of Wood anomalies; these are discussed in the paper.