ISSN:0021-8979    

DOI:10.1063/1.1699651

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

One factor inherent in most electron microscopes is the magnetic asymmetry (astigmatism) in the objective lens. This is often due to imperfect machining, localized defects (impurities) in the iron, or grain anisotropies. The lapping technique described herein effectively reduces the effect of imperfect machining (misalignment of components). Critical faces and the bores through the pole piece are lapped with a series of powders (alumina) which increase in fineness until the final process is that of polishing. A set of jigs and laps (brass and hard wood) are described; their specifications and use so as to properly alter the critical pole piece surfaces are also described. Electron micrographs illustrating the value of this lapping procedure in the improvement in objective lens symmetry are included.

ISSN:0021-8979    

DOI:10.1063/1.1699652

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The permeability of a number of thin organic films toward oxygen and nitrogen has been measured. For an ethyl cellulose film the studies were extended to include CO2, A, He, and H2. The enrichment of a binary gas mixture in a single stage of permeation has been calculated for the extreme cases of perfect mixing and no mixing. Application of these results indicates that the use of a fractional permeation process may be of practical importance in effecting the separation of oxygen from air, helium from natural gas, and hydrogen from coke‐oven gas, as examples.

ISSN:0021-8979    

DOI:10.1063/1.1699653

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Part I has described the d.c. current‐voltage characteristics obtained for typical Si and Ge crystal rectifiers, has given a summary of the published theories of the rectifier, and has shown that none of these theories accounts for the principal features of the observed characteristics. Part II describes the multicontact theory, an extension of the diode theory, and shows that this theory does account for the behavior of the observed characteristics. There also is described a graphical treatment, based upon the multicontact theory, which may be used in the analysis of experimental characteristics. The multicontact theory assumes that the contact potential at the metal‐semiconductor surface varies from spot to spot. It is shown that an exponential distribution function for contact potentials may be used to account for the observed logarithmic slopes and that the observed temperature behavior of the characteristics may be explained by assuming that the distribution function varies with temperature in a manner dependent upon the nature of the contact.

ISSN:0021-8979    

DOI:10.1063/1.1699654

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An analysis of a sampling servo mechanism with an error‐clamping device and linear forward and return paths is given. The method leads to a determination of the continuous output of the system in terms of quadratures and gives explicitly the value of the output at the discrete sampling instants. Frequently this is all that is needed in order to study the output variation with time. The question of stability is discussed and a criterion for testing the stability of the system is given in terms of the system parameters.

ISSN:0021-8979    

DOI:10.1063/1.1699655

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The variations in velocity of dilatational waves in the pressure range 0 to 15,000 lb./in.2and temperature range 30° to 90°C have been measured for samples of polystyrene, Lucite, and polyethylene. The velocity of rotational waves was also measured for polystyrene and Lucite. In polyethylene no trace of a rotational wave could be identified. The elastic moduli and Poisson's ratio are computed over the experimental range.

ISSN:0021-8979    

DOI:10.1063/1.1699656

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A method for the summation of certain types of Fourier series by the use of Laplace transforms is presented. The procedure enables one to easily obtain graphical representations of functions defined by Fourier series in many cases of practical importance.

ISSN:0021-8979    

DOI:10.1063/1.1699657

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

It is shown that when certain plausible assumptions are fulfilled simple scaling laws govern the times required to produce, by sintering at a given temperature, geometrically similar changes in two or more systems of solid particles which are identical geometrically except for a difference of scale. It is suggested that experimental studies of the effect of such a change of scale may prove valuable in identifying the predominant mechanism responsible for sintering under any particular set of conditions, and may also help to decide certain fundamental questions in fields such as creep and crystal growth.

ISSN:0021-8979    

DOI:10.1063/1.1699658

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A resonant bar method for obtaining the dynamic elastic properties of a thin cement layer is discussed. Formulas are deduced for the calculation of Young's modulus from the measured resonant frequency and band width of two similar steel bars, cemented end‐to‐end. The accuracy of the method is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1699659

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An electronic apparatus which assists in the finding of the roots of polynomials is described. The device accepts the coefficients of polynomials of degree 10 or less and yields the absolute magnitude of the roots to a precision of 0.01 relative to the largest coefficient in the polynomial and an angular accuracy of 0.3 degree on the angle of the root.The method used is the electronic analog of the expression&ohgr;=anzn=anrn cosn&thgr;+janrn sinn&thgr;.Sinn&thgr; and cosn&thgr; are generated by a motor‐driven commutator. The radiusris controlled manually. Hence a plot of &ohgr; is placed on the oscilloscope for a fixedras a function of &thgr;. To find the rootris manipulated until &ohgr; crosses the origin in the &ohgr;‐plane. The value of &thgr; is found by inserting a pip on the intensity of the oscilloscope under a variable phase control. When this pip is moved to the origin of the &ohgr;‐plane the phase meter indicates the angle of the root in thezplane.

ISSN:0021-8979    

DOI:10.1063/1.1699660

出版商:AIP    

年代:1950

数据来源: AIP