摘要:

This paper deals with bearings supported on metal beams under mechanical stress in the axial direction. Because of a phenomenon related to the bending of long columns under axial compression the torque of the total arrangement can be made zero or even negative. Such a bearing can be designed with two decisive advantages, absolutely no friction, and practically no restoring torque as far as small angles of rotation are concerned. Two different types of beam bearings are treated, and their equations for precalculation are derived. Furthermore, the influences of temperature, external forces, and the angle of rotation on the torque of the bearing are investigated. Finally, a combination of two different beam bearings is shown to offer a possible compensation for these unfavorable effects.

ISSN:0021-8979    

DOI:10.1063/1.1698360

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

For a definite Mach number, given byM2= 4/(3−&ggr;), all Mach lines in a steady plane two‐dimensional potential flow of a perfect gas with expansion exponent &ggr; have zero curvature. The use and significance of this relation are discussed, and the hypothetical expansion law consistent with straight Mach lines is deduced.

ISSN:0021-8979    

DOI:10.1063/1.1698361

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The structure of thin metallic films was studied by means of electron diffraction and electron microscopy. Microcrystal size can be correlated with the melting point of the metals, those with high melting points producing continuous films of small unoriented microcrystals while those with low melting points produce large microcrystals oriented preferentially with respect to the substrate. The effects of varying experimental conditions on the film structure of selected metals are reported. The electron beam of the electron microscope affects metals with low melting points most directly, producing melting, sublimation or crystallization. Variations in the velocity of the impinging atom, obtained by passing thermal atoms through a mechanical velocity selector, produce no effect for metals whose vapor is monatomic. Antimony whose vapor is found to consist of polyatomic molecules as well as atoms produces films whose grain size seems to vary with the size of the molecules forming the antimony film. The rate of evaporation merely determines whether zinc or cadmium films may or may not be formed while for antimony films it also determines the type of the films formed. Those formed by rapid evaporation consist of small crystallites while those formed by slow evaporation consist of large amorphous patches. This effect is explained on basis of the mobility of the atoms on the substrate, the mobility time being determined to be less than 2×10−5second. The mobility time and therefore the structure depends upon the type of substrate. The degree of vacuum is critical when the residual vapor reacts with the film being formed, but if no reaction takes place between residual vapor and film, pronounced variation for films formed in a vacuum are produced only when the pressure is above 10−2mm of mercury.

ISSN:0021-8979    

DOI:10.1063/1.1698362

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A method is described for determining the variation of the resistance (R) and the reactance (X) of an electrical network from mechanical plots of the numerators and denominators (both functions of the angular frequency &ohgr;) occurring in the expressions forRandX. From the expressions,R = N(&ohgr;)/D(&ohgr;) andX = N′(&ohgr;)/D(&ohgr;), mechanical plots ofN, N′, andD versus&ohgr; can be obtained with a mechanical harmonic synthesizer, and the values ofRorXcorresponding to any value of &ohgr; may then be determined by taking the ratios of the ordinates ofNandD, orN′andD, corresponding to the desired value of &ohgr;.

ISSN:0021-8979    

DOI:10.1063/1.1698363

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The theory of the hardness is reviewed and measurements are made with respect to the application of hardness data to contact problems, particularly for the determination of the real contact area. The ball indentation method is recommended, with hardnessHdefined as the ratioP/Smbetween the contact loadPand the mouth areaSmof the indentation. This hardness is not a single valued material constant but is a function of the specific depthDof the indentation, whereDis the ratio between the actual depth and the radius of curvature of the indentation. The variation ofHwith geometric and metallurgical conditions is discussed together with some empirical formulae to describe the experimental results. The relation between the hardness and the yield point is discussed. A comparison with Brinell and Rockwell hardness numbers is also made. The indentation which two crossed cylindrical rods produce in each other is found to give nearly the same hardness as the ball indentation tests ifDexceeds a certain value.

ISSN:0021-8979    

DOI:10.1063/1.1698364

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Short cylindrical antennas have been loaded to resonate at frequencies lower than their natural frequencies by means of dielectric sheaths of cylindrical and conical form. These loadings are compared experimentally with loading by means of metal disks at the ends of the antennas. Resistances at resonance calculated by the Poynting vector method for two assumed current distributions are compared with the experimental results. It is shown that for a given current distribution at resonance, the antenna radiation resistance depends only on the antenna length in wave‐lengths. Particular loading methods alter the current distributions. Those which produce more nearly uniform current distributions yield higher radiation resistances.

ISSN:0021-8979    

DOI:10.1063/1.1698365

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A method is described for measuring the amplitude distribution of high frequency current along some simple types of antennas. Measured curves for some cases are given and compared with some frequently assumed curves. Some of the measured distributions were integrated numerically to determine the driving point resistances. The driving point resistances were measured for geometrically similar antennas in some cases. Deviations from usually assumed curves are significant, but do not bring about large errors in the calculated resistances.

ISSN:0021-8979    

DOI:10.1063/1.1698366

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Signal‐to‐noise ratios at the output of an f‐m receiver are determined as functions of the input signal‐to‐noise ratio, clipping level, and i‐f and audio filter characteristics when random (fluctuation) noise accompanies the signal to be observed. Both narrow and broad band f‐m are examined. Specific calculations are made for sinusoidal frequency modulation, and it is indicated how data for this simple type of signal may be related to the more complex phenomenon of speech. The concept of the signal‐to‐noise ratio is redefined to describe more accurately the sensing of a signal in noise, since the conventional definition for f‐m proves inadequate and misleading, except for strong carriers. Extensive comparisons are made with a‐m reception employing a half‐wave linear rectifier, and it is found that for moderate and weak (<3 db) signals a‐m requires less input signal power against the same noise background than does f‐m to achieve the same desired output. This is particularly evident for weak signals. Only when the signal is strong (>10 db) is f‐m superior to a‐m; here broad band f‐m with very heavy limiting is needed. Narrow band f‐m at its best (no limiting) is comparable with or inferior to a‐m at high signal levels. Limiting proves to be detrimental in narrow‐band operation for all cases involving fluctuation noise, whereas heavy limiting is essential for successful broad‐band performance. Furthermore, the shape of the i‐f response becomes important in the latter, while it is not in the former. A large number of curves illustrating the average and mean‐square signal and noise outputs, etc., and signal‐to‐noise ratios for various conditions of operation are included.

ISSN:0021-8979    

DOI:10.1063/1.1698367

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A theoretical investigation has been made of the power dissipation by eddy currents in a metallic surface at microwave frequencies in the presence of regular parallel grooves or scratches whose dimensions are comparable to the eddy current skin depth. The eddy current equation has been integrated numerically for grooves of various shapes and sizes transverse to the direction of induced current flow, and the corresponding losses are calculated and plotted. The power dissipation is increased by about 60 percent over its value for a smooth surface when the root‐mean‐square deviation of the grooved surface from an average plane is equal to the skin depth; the exact shape of the grooves is not critical. The increase in eddy current losses caused by grooves parallel to the current is shown in a particular case to be only about one‐third as great as the increase caused by transverse grooves of similar size. The effect on losses of an isolated narrow crack or fissure transverse to the current is briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.1698368

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Flash radiographic techniques as applied to Army Ordnance problems are discussed. The feasibility of using microsecond x‐ray bursts in the study of internal ballistic and explosive phenomena is discussed and illustrated by selected flash radiographs.

ISSN:0021-8979    

DOI:10.1063/1.1698369

出版商:AIP    

年代:1949

数据来源: AIP