摘要:

In a commercial electron diffraction camera some alkaline earth metals (from Be to Sr) or Al, Ni, or Mo were evaporated onto outgassed metal sheets or glass slides, using the starting pressure of 0.1&mgr; of mercury. The diffraction patterns of the thinnest layers (to about 103A) presented, regardless of the evaporation speed used, the pattern of the oxide of the evaporated metal exclusively. The diffraction pattern of the metal space lattice itself was growingly observed with Be, Al, Ni, and Mo only afteruninterruptedevaporation until layer thicknesses of about 1&mgr; were reached. When Mg, Ca, and Sr were evaporated, no patterns without, at least, the most intensive oxide rings could be attained under the vacuum conditions given in the apparatus.The results are in accord with some earlier findings of Langmuir, Beeching, Darbyshire, and Beischer, and clear up some hitherto not fully explained effects with stepwise evaporated layers. The appearance of oxide patterns is always accompanied by strong improvements of the vacuum in the evaporation compartment by the arising metal vapors, i.e., by the well‐known gettering effect.

ISSN:0021-8979    

DOI:10.1063/1.1698232

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Some layers presenting the space lattice pattern of the metal (Be, Mg, Al, Mo, or Ni) were heated for constant periods. Beginning with a distinctly marked threshold temperature, the interference rings of the oxide space lattice appeared while, simultaneously, the metal space lattice pattern diminished, entirely disappearing with another higher lying temperature. The oxidation temperature ranges (for ten‐minute heating periods) of Be, Mg, and Al were measured. With glucinum it is equal to that within which, Kollath stated, there was a strong increase of the emissivity of beryllium secondary emission cells.An elementary calculation gives an inferior time limit to oxidation of the observable surface layer. The surface layer of polished metals is considered; the high secondary emissivity in the case of glucinum, together with the usually supposed Beilby layer giving only two broad diffuse diffraction rings, points to the existence of a random liquid‐like network of BeO molecules on the surface of polished beryllium secondary emission cells.

ISSN:0021-8979    

DOI:10.1063/1.1698242

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A simple theory for stress‐strain rate analyses during plastic flow of anisotropic sheet metals is proposed for the work hardening range. The effect of orientation on the yield strength in simple tension and biaxial tension was discussed for various types of symmetry. The theory appears to be approximately correct for mild steel plates that exhibit planar isotropy.

ISSN:0021-8979    

DOI:10.1063/1.1698231

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The resolving power of the electron microscope and the contrast in the image are calculated for different conditions of focusing, illumination and aperture. These conditions can change the limit of resolution by a factor of about 3. The contrast in the image of an atom is appreciably increased by defocusing and spherical aberration. Nevertheless, the contrast improves when the numerical value of the aberration constant is diminished. The effect of different methods of spherical correction is discussed briefly.

ISSN:0021-8979    

DOI:10.1063/1.1698233

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

This paper presents typical data on the internal friction of twelve single crystals of zinc oscillating longitudinally. The measurements of decrement were made at frequencies of 41 kc and 57 kc. (a) Zinc of three grades of purity was used. The behavior of decrement as a function of stress amplitude for these different materials was found to depend less on the purity of the metal than has been reported previously (see references 1 and 2). (b) For one crystal the decrement showed little rise from its initial value of 2×10−5at very low stress amplitudes up to stress amplitudes nearly three times the static elastic limit. Considerable similarity of behavior of the decrement as a function of stress amplitude resolved into the basal plane has been found for a number of crystals with a wide range of orientation. The obtaining of these consistent results depended on the use of appropriate annealing and etching techniques. (c) The decrement of a well annealed crystal increased with rising temperature at all stress amplitudes throughout the temperature range −75°C to 150°C. (d) The prior application of static stress far below the static elastic limit has been found to increase the decrement at high stress amplitudes without affecting that at very low stress amplitudes. This increase was a function of the stress amplitude at which the decrement was measured, and of the prior static stress,L. The observations fitted a relation of the form log&Dgr;=C1+C2L, whereC1depended on the amplitude of measurement andC2was approximately constant.

ISSN:0021-8979    

DOI:10.1063/1.1698234

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Certain mathematical representations of a limiter and discriminator are postulated. On this basis, and on the basis of the statistics of narrow‐band random noise, the output signal voltage and r.m.s. noise output voltage are calculated for a limiter and discriminator fed by an f‐m carrier and narrow‐band random noise. The output signal‐to‐noise ratio can thus be expressed as a function of the input signal‐to‐noise ratio. The former is plottedversusthe latter in Fig. 5, for several different degrees of limiting. A sharp increase in the output signal‐to‐noise ratio from far below the input signal‐to‐noise ratio to only 0.9 db below it is found to occur as the latter increases through the range 0 db to 6 db. For the sake of comparison, Fig. 5 also shows the corresponding curve for square law detection of an a‐m carrier, as well as that for f‐m without a limiter. It is to be emphasized that these results pertain to the unfiltered discriminator output; consideration of filtering, which is generally present in a receiver to a considerable extent, requires a determination of the spectral distribution of the discriminator output noise.

ISSN:0021-8979    

DOI:10.1063/1.1698235

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The application of ultrasonic methods to the determination of the elastic constants of solids is considered in some detail. It is shown that a rotating plate technique in which ultrasonic transmission is plotted as a function of the angle of incidence of the waves allows determination of the velocities of dilatation and shear waves in the plate. From these data, Poisson's ratio and the mechanical moduli may be determined. Details of an apparatus for making such measurements are given. The elastic constants of several metals have been measured with this equipment and the values obtained are shown to be in agreement with previous published data. In addition, measurements of a number of thermoplastic and thermosetting resins have been made successfully. It has been found that in the case of Melmac Resin 26–8B there is no variation in the elastic constants as a function of cure time.

ISSN:0021-8979    

DOI:10.1063/1.1698236

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A simple theoretical analysis of the superconducting bolometer in transition is shown to be useful in predicting phenomena such as the shape of the transition curve and the dependence of the bolometer time constant upon the current magnitude. The analysis holds for bolometer currents smaller than a critical value which is equal to the square root of the ratio of the bolometer cooling constant to the bolometerdR/dT. For bolometers constructed in this laboratory this critical current value falls between 15 and 30 ma.Qualitative extension of the theory to the case of large bolometer currents is made by considering the presence of regions at different temperatures within the bolometer and by summarizing the possible effects of the magnetic field due to the bolometer current upon the transition. Experimentally obtained transition curves are given for both small and large bolometer currents.

ISSN:0021-8979    

DOI:10.1063/1.1698237

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

This paper gives calculations and computations, based on simple ideal conditions, of the possible disturbances of underground temperatures caused by uplift and denudation. The effects of the speed of denudation, the rate of uplift, and the time during which these two processes may have been operating, are illustrated by numerical tables applying to some specific ideal situations. The resulting disturbance of the heat flow in the earth (which is evaluated by making use of underground temperature gradients) is discussed. It is shown that uplift and denudation increase the heat flow above its equilibrium value, but that no very large increase is likely to occur unless the equilibrium heat flow is small and the speed of denudation is large.

ISSN:0021-8979    

DOI:10.1063/1.1698238

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

TheE‐plane radiation pattern has been measured at short distances and bothEandH‐plane patterns at relatively great distances from the mouths of several electromagnetic horns. Measured values are compared with values calculated by the Kirchhoff formula and in addition the distant patterns are compared with values calculated by the corrected formula due to Stratton and Chu.For the range of horn length and aperture considered, the Kirchhoff formula gives satisfactory agreement in theE‐plane for angles as great as twenty degrees and at distances as short as one foot from the mouth of the horn; theH‐plane predictions are not as satisfactory.

ISSN:0021-8979    

DOI:10.1063/1.1698239

出版商:AIP    

年代:1949

数据来源: AIP