摘要:

The origin of distortion in electron microscope projection lenses is discussed and the serious nature of its effect on the measurement of particle size distributions is pointed out. Methods of measuring distortion are described. By means of first‐order theory it is shown to be possible to correct distortion by the use of a two element projection lens. The degree of correction obtainable is shown to be satisfactory for most practical purposes. A double gap projection lens polepiece and the correction of distortion obtained with it are described.

ISSN:0021-8979    

DOI:10.1063/1.1707732

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

A distinction is drawn between the focusing properties of single crystals with regard to x‐ray diffraction and the parafocusing properties of microcrystalline powder layers. A discussion of these parafocusing properties and of the absorption term, which arises in the diffraction of x‐rays from powder layers, is followed by a discussion of various types of powder goniometers. Their characteristic properties are compared. The application of parafocusing conditions to the design of a goniometer for quantitative evaluations and of back reflection cameras is discussed in greater detail.

ISSN:0021-8979    

DOI:10.1063/1.1707733

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

Two methods are described for obtaining x‐ray diffraction patterns of oxide‐coated cathodes. One method is used in the study of the conversion process in forming the oxide cathode while the other method is utilized in measuring the thermal expansion coefficients of barium, strontium, and thorium oxides. The conversion of an equal molar barium‐strontium carbonate solid solution, (BaSr)CO3, involves (1) crystal growth in the carbonate, (2) decomposition to the mixed oxides, BaO and SrO, (3) formation of the oxide solid solution, (BaSr)O, and (4) crystal growth in the oxide. A similar sequence of events is observed in the conversion of a mixed carbonate, BaCO3+SrCO3. Crystal and particle size growth of carbonates and crystal growth of oxides are investigated and possible relationships are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1707734

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

Two methods for bringing out a partially collimated electron beam from a betatron or synchrotron are discussed. Both of the methods become easier as the size of the accelerator is increased. One method makes use of a perturbing magnetic field to focus the electrons as they are made to leave the field of the accelerator by means of orbit expansion. The other method makes use of a pulsed deflecting system where the deflecting field is applied during a time short compared to the period of revolution of the electrons.

ISSN:0021-8979    

DOI:10.1063/1.1707735

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

A graphical ray tracing scheme is described which gives improved accuracy for tracing particle orbits of the type encountered in the cyclotron, betatron, and synchrotron. The method allows a large increase in scale factor by elimination of the necessity of a compass arm. The motion of the particle is deduced from the motion of a working point, related to the instantaneous center of curvature of the particle orbit.

ISSN:0021-8979    

DOI:10.1063/1.1707736

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

A discussion is given of the application of infra‐red absorption methods of analysis for light gases which do not obey Beer's law of absorption due to pressure broadening. Some of these gases do not obey Beer's law in the pure state or when contaminated by foreign gases. The method of analysis depends upon the nature and intensity of the pressure broadening effect of the different components in the sample upon each other. Data are presented showing the nature of some of these effects and illustrating the accuracy obtainable for certain types of analyses. The instrumentation used in routine gas analyses by infra‐red in this laboratory is described.

ISSN:0021-8979    

DOI:10.1063/1.1707737

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

Two means are described for minimizing the effects of lead loss in determining the electrical properties of thin filaments as a function of temperature. In both cases the filaments are supported at the mid‐points of filamentary U's. In one case the U's are made of finer wire than the main filament so that lead loss is reduced. In the other case, alternating current is passed through the U's so that the temperature of the main filament is maintained uniform down to its points of support.

ISSN:0021-8979    

DOI:10.1063/1.1707738

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

A method has been established for the measurement of the viscosity of high polymers at low rates of shear in the range 104to 109poises using a parallel plate plastometer. This is based on a mathematical criterion for separating the viscous portion of the deformation from the ``elastic'' and ``delayed elastic'' components. Experimentally, the plate separation is measured at a given temperature as a function of time. The theory furnishes a relation, which is also the criterion for predominantly viscous deformation, between viscosity, plate separation, applied load, and time. This relation, a modified form of Stefan's equation, is used for calculating the viscosity from the experimentally observed quantities. The method has been applied to polyethylene and vinyl chloride‐acetate resin compounds. The viscosity‐temperature behavior of these materials is shown to be simple over the temperature range studied; that is, log viscosity varies linearly with the reciprocal of the absolute temperature. Data are presented which show that polyethylene resins and polyethylene resin‐paraffin wax mixtures follow Flory's relation; that is, log viscosity varies linearly with the square root of the weight average molecular weight. Accordingly, the parallel plate plastometer offers promising possibilities for the empirical determination of the weight average molecular weight of these materials. Data are also presented on plasticized vinyl chloride‐acetate resin systems which point to a close parallel between the effects of increasing temperature and increasing plasticizer concentration.

ISSN:0021-8979    

DOI:10.1063/1.1707739

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

Numerous researches on metals, rocks, glass, rubber, and textiles are cited to show that what may be regarded asnormalcreep in amorphous and polycrystalline solids conforms to the general relation&egr;=&egr;1+at+blogt,where &egr; is the total strain at timet, &egr;1is a parameter interpretable as the approximate initial strain, anda, bare other parameters. A special form of this equation, havinga= 0, has been frequently applied. Reference is made to several other studies on the same class of solids, which have established for normal relaxation the relation&sgr;=&sgr;1−&bgr;logt,where &sgr; is the stress at timet, &sgr;1is the stress at unit time, and &bgr; is a parameter. A theoretical foundation for both equations is provided by the reaction‐rate theory of plastic flow. Observations in the present study indicate that creep extension in cotton and rayon tire cords over prolonged periods of time follows the above creep equation, and, in general, is not adequately represented by an equation omitting the termat. From the presence of this term in the equation, the existence of a component of the viscous type in tire cord growth is deduced. The pattern of creep recovery in cotton tire cord appears to be set by the behavior of the cord in creep extension.

ISSN:0021-8979    

DOI:10.1063/1.1707741

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

Tire‐cord fatigue tests are characterized and interpreted in terms of the following parameters: magnitude and frequency of the cyclic stroke, average load, minimum load, temperature, and humidity. By varying one test parameter at a time, it is shown that the effects of creep and degradation are minimized by using a high frequency and a high stroke. The relative rating of two samples of rayon depends on the parameters of the test and on the modulus and twist structure of the samples. Fatigue breakdown is interpreted in terms of progressive fracture under localized strains occurring at the peak stress of the cycle. A comparison of the fatigue behavior of rubbers, metals, and tire cord suggests they may all involve the same basic process of crack growth.

ISSN:0021-8979    

DOI:10.1063/1.1707742

出版商:AIP    

年代:1946

数据来源: AIP