摘要:

A photo‐density method for the determination of diffusion of radioactive tracer is presented and compared in detail to a thin section analysis method. The method is no doubt applicable to similar tracer problems such as metal diffusion studies. The proper analysis of an emulsion exposed by decaying Na24which had been allowed to diffuse into glass is given. The necessity for making and using an emulsion gamma‐curve for the tracer in this analysis is shown.

ISSN:0021-8979    

DOI:10.1063/1.1698323

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

This paper summarizes the experimental and theoretical status of the optical chronograph developed in the course of ballistic research at the Naval Research Laboratory. The instrument, together with a simple procedure for analysis of data, is capable of yielding the position, velocity, and deceleration of a non‐plastically deforming small arms projectile during the armor penetration process, which lasts from 30 to 150 microseconds. Decelerations have been observed up to 5×107ft./sec.2. The longitudinal vibrations induced in projectiles during impact were observed by a shadow‐photography technique which yields time‐displacement curves from the motion of the trailing face of a projectile during penetration. The precision of the derived decelerations, about 4 percent, is sufficient to permit the evaluation of strain‐rate and inertia effects during high speed indentation by means of conical indenters at strain‐rates approaching 2×105/sec.

ISSN:0021-8979    

DOI:10.1063/1.1698324

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Of the criteria that are used in the design of servomechanisms, the so‐called ``minimum mean‐square'' error criterion is used quite widely in cases where the undesirability of the error increases with its magnitude. There is, however, an important class of applications, particularly in the field of ballistics, where a more appropriate criterion can be defined as the probability that the error be less than some prescribed tolerance. The problem of maximization of this probability is shown to reduce to a number of implicit equations whose solution in practice must be carried out by cut and trial. It is further shown that under certain conditions the maximization of probability yields the same values for the design constants as the minimization of mean‐square error. These conditions are discussed for the general case as well as for certain specific cases which are important in practice.

ISSN:0021-8979    

DOI:10.1063/1.1698325

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A concentrated polymer solution is sheared by a rod oscillating axially with a very small amplitude in a closed tube. The rod is driven by a coil in a magnetic field; from electrical measurements on the coil, the mechanical resistance and reactance of the system are calculated by transducer relationships. Equations are given for obtaining the dynamic viscosity, &eegr;′, and rigidity,G′, of the solution. In the case of some polymer solutions, the audiofrequency range covered by the present apparatus falls in the dispersion zone where &eegr;′ andG′change rapidly with frequency. In other cases the frequency range covered appears to be at the upper end of the dispersion zone; &eegr;′ is far smaller than the viscosity in steady flow, andG′changes very little with frequency. The advantages and limitations of the method are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1698326

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

It is shown that in close packing of spheres, two types of interstice exist, bounded by six and by four convex spherical surfaces. These are termed ``square'' and ``triangular.'' They are connected by a continuous labyrinth through which a ball not exceeding (2/√3−1)rin radius can be threaded. In both cubic and hexagonal arrangements, their shape and size are identical, but their distribution differs. RadiiRfornsmaller balls, which can take up patterns with cubic symmetry within each square interstice, are calculated for values ofnup to 27 and plotted. The expression(R/r)=(2−1)/n12is used as a test for efficiency of packing.WhenR/ris plotted against the density increment attributable to this interstitial packing, a set of spires is obtained. Atn=8 andn=9 (R/rbeing, respectively, 0.2289 and 0.2166) twin peaks of 13 percent and 12 percent appear, which are accentuated by first entry of a sphere into the triangular interstice atR/r= 0.22475; this contributes another 3 percent. The peak of 16 percent atn=21,R/r= 0.1782, is also reinforced by first entry of 4 spheres in a body‐centered tetrahedron at 0.1716, which gives an additional 6 percent density increment. Applications to bulk storage, ceramics, and interstitial compounds and solid solutions are considered. None of the special packs gives a density increment (∂&Dgr;square+∂&Dgr;triangular)/&Dgr; even approaching the 26 percent for fine spherical filler close packed in the interstices.

ISSN:0021-8979    

DOI:10.1063/1.1698327

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Measurements are described of the potential variation of fine ribbon probes embedded in standard barium and strontium oxide coatings. Observations were made with 19 tubes at values of pulsed emission as high as 50 amperes/cm2. Results were as follows: (a) values of resistance were found ranging from 2 to 230 ohms‐cm2; (b) potential gradients were adequate to admit dielectric breakdown as a cause of sparking; (c) the curve of resistancevs. emission passes through a maximum and, at different temperatures, this maximum occurs at the same probe potential; (d) with BaO or mixed cathodes of higher values of resistance the resistance is largely at the interface, for low resistance coatings no observations on this matter were obtained; (e) the two best tubes as regards high emission without sparking had the lowest values of coating resistance; (f) the resistance of SrO cathodes is an order of magnitude higher than that of BaO or mixed cathodes; (g) superposition of d.c. upon pulsed emission gives a pronounced decrease of resistance.

ISSN:0021-8979    

DOI:10.1063/1.1698328

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Small angle x‐ray scattering measurements are made on samples of colloidal gold of radius from 50 to 400 angstroms. Copper (1.54 angstrom wave‐length) and aluminum (8.32 angstrom wave‐length) radiation are used.The usual method of analysis is shown to be valid only for particles of radius less than 120 wave‐lengths. Extension of the method to larger particles is achieved, giving improved electron microscope correlation.The use of longer wave‐lengths and optimum shaped slits are shown to reduce geometry errors sufficiently to give clear evidence of predicted intensity maxima. The first three secondary shape function maxima are observed.An additional interference maximum attributable to particle‐to‐particle interference is observed. The position and magnitude of this maximum are correctly predicted by an expression based on earlier fluid scattering theory.

ISSN:0021-8979    

DOI:10.1063/1.1698329

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Both the spherical and the chromatic aberration of electron microscope objectives may, in principle, be corrected with the aid of a uniform retarding field acting as a mirror. Such an arrangement has the drawback of requiring a conducting film in the ray path and the insertion of the specimen in a region of high field strength. The employment of concave electron mirrors with concentrated field distribution, forming a real image of approximately unity magnification, is free from this drawback. The formulas for spherical and chromatic aberration, presented in a form suitable for calculation, are applied to a characteristic electron mirror field of this type (&PHgr; =C+tanh(sinhz)). It is found that the aberration coefficients of the mirror are so large, however, that this method of aberration correction encounters serious practical difficulties.

ISSN:0021-8979    

DOI:10.1063/1.1698330

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A new sweep frequency ionosphere sounding equipment is described. The equipment records ionosphere virtual height as a function of frequency over the range from 1 to 25 megacycles. Special features of the device are high power output, good receiver sensitivity, and anti‐jamming circuits.

ISSN:0021-8979    

DOI:10.1063/1.1698331

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The thermionic and photoelectric work functions and the temperature variation of coating conductivity have been measured for an oxide cathode. Thermionic and photoelectric currents were measured in both retarding and accelerating fields. The two work functions are found to be different, but not by the amount predicted by applying simple semi‐conductor theory to the data. Photoelectric currents fit a Fowler plot rather well over a limited range of frequencies. The large decrease in work function with applied field, the poor ``saturation'' of thermionic currents typical of oxide cathodes, and the behavior of the photoelectric currents in accelerating fields all suggest that one is dealing with a ``patchy'' surface. Applying ``checkerboard'' patch theory to the experimental data, one finds that most of the data is accounted for by assuming patches about 3×10−4cm on a side differing in work function by about 0.2 volt.

ISSN:0021-8979    

DOI:10.1063/1.1698332

出版商:AIP    

年代:1949

数据来源: AIP