摘要:

The spectral character of the stimulated emission from ruby has been investigated; we found that the zero-fieldsplitting(0.38 cm−1)of the4A2ground level and the cavity optical length and its reflectivity determinethe spectral character of this emission. At 300°K the system is induced into oscillation in a number of cavitymodes separated by&Dgr;v¯ = (2l&egr;12)−1, wherelis the length of the resonator and&egr;12is the index of refraction forthe ordinary ray. AtT≅80°KtheE¯(2E) → ±32(A2)and theE¯(2E) → ±12(4A2)transitions were identifiedin the stimulated emission spectrum. Each can oscillate in an axial cavity mode (or modes) plus an off-axismode at the center of the transition. At 4.2°K the system oscillates in off-axis modes, unless the length of thecavitylis such that it has axial resonances coincident with the transition frequencies. An analysis of thetemperature dependence of the oscillation threshold for the separate transitions is presented and is comparedwith the observed behavior.

ISSN:0021-8979    

DOI:10.1063/1.1931137

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Beryl crystals containing transition metal ions can he grown from a number of mineralizing fluxes. OftheseV2O5appears to be particularly advantageous for growing beryl by transfer methods. TheCr3+containingcrystals grown by this method are particularly suitable for microwave device applications as indicatedby a resonance linewidth of 100 Mc at the X band.

ISSN:0021-8979    

DOI:10.1063/1.1931138

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

In papers I and II of this series, it was concluded on the basis of theory and a limited number of experimentalsamples that the over-all differential probabilityp′of single fracture, as a function of the mean fragmentdimensionx, should show the presence of three peaks. These correspond to the effect of internal flawsof facial and volume type, and of surficial flaws. This result is verified experimentally with good statisticsfrom the mean of data for 36 specimens fractured in gelatin by Bergstrom, Sollenberger, and Mitchell. Theeffect in this over-all distribution of the exoclastic fragments produced by surficial flaws was subtracted out.The resulting endoclastic differential probabilitypfor the 36 specimens, corresponding to the effect of internalflaws only, shows with good statistics the presence of two peaks arising from facial and volume flaws.The result of I that the number of fragments cumulated over fragment volumes down to a lower limitvshould vary asv−23for small fragment size is confirmed by measurements for specimens that underwentsingle rather than plural fracture.

ISSN:0021-8979    

DOI:10.1063/1.1931139

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Prior work in paper I on the size distribution of the fragments in single fracture of a three-dimensional solid is extended to the two-dimensional case (that of a thin plate). The underlying physical assumptions are the two-dimensional analogs of those made in I. These assumptions yield directly the probabilityd&pgr; (c,a)of formation of a fragment with perimeter and area in the rangesctoc+dcandatoa+da, respectively, ase−RdRin the general case, withRlinear incanda. The derivation yielding this Poisson form requires no assumption on the shape of a fragment. The numberdv (c,a)of fragments with perimeter and area in the rangesctoc+dcandatoa+da, respectively, is evaluated as the product ofd&pgr; (c,a)by thea priorinumber of particles with these values ofcanda. The distribution functiondv (c,a)meets the necessary physical requirement that the fracture process conserve surface area independently of particle shape. By assuming that all fragments are geometrically similar, one can replaced&pgr; (c,a)anddv (c,a)by forms,&pgr;(x)dxandv(x)dx, respectively, which depend only on a mean linear dimensionxof a fragment. The moments of the distribution corresponding to the total number and total perimeter of the fragments are divergent; this anomaly is explained as the result of neglect of depletion of Griffith flaws.

ISSN:0021-8979    

DOI:10.1063/1.1931140

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Experimental data corresponding to the exoclastic fragmentsfrom spherical glass specimens fractured in gelatin in the course ofthe work on paper II are used to test the theoretical predictionsof paper IV; the fragments in question are those engendered bysurficial flaws of the specimen. The data on the fragments consistof measurements of the spherical surface corresponding to theoriginal surface of the specimen, and of the core surface. The lattersurface appears on many of the exoclastic fragments; it arisesthrough failure under compression of the central core of thespecimen to produce the endoclastic fragments. The over-allprobability of fracture determined only by the original sphericalsurface on the fragments shows the presence in the correspondingdistribution of three component distributions, corresponding ingeneral to the larger fragments, those of intermediate size, andthe smaller fragments. The first distribution is identified as arisingfrom fragmentation through activation of surficial flaws in thecore surface, and agreement of the data with theory is good.By eliminating fragments from the over-all distribution for whichthe data are correlated with theory in this manner, the seconddistribution in question is identified as corresponding to fragmentationthrough activation of surficial flaws in the original sphericalsurface of the specimen. Excellent agreement of the data with thetheory of IV is obtained. The remaining distribution probablyarises from particles formed by activation of internal flaws (althoughoriginal surface of the specimen appears on the fragments).The results yield numerical values of surficial flaw densities.

ISSN:0021-8979    

DOI:10.1063/1.1931141

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Explosively generated plane waves were passed through plates of duraluminum, iron, and steels of variouscompositions and heat treatments. X-cut quartz disks of large diameter-to-thickness ratios (≥5) were usedto obtain continuous stress-time profiles of elastic-plastic wave structures associated with yielding. For timesless than wave transit time through the disk, the short-circuit current output is directly proportional to thespecimen-to-quartz interface stress up to 21 kbar. The incident wave profile in the specimen is then determinedfrom the interface stress-time profile on the basis of an assumed model. Advantages of the techniqueare excellent time resolution, high sensitivity, and relative simplicity of use. The profiles for duraluminum,normalized SAE 1018 steel, and normalized Armco iron exhibit a relatively slow rise to the yield stress,subsequent stress relaxation, except in duraluminum, and then a gradual rising transition into the plasticwave. In comparison, SAE 4340 and other tool steel profiles exhibit a faster initial rise, no stress relaxation,and a steeper transition into the plastic wave. The dynamic yield stress in the tool steels increases withRockwell hardness, and the separation between the elastic and plastic wavefronts decreases. In general, asthe specimen thickness is increased, the dynamic yield stress decreases and the initial rise time increases.

ISSN:0021-8979    

DOI:10.1063/1.1931142

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The elastic energy released as a crack passes parallel to a slip band has been calculated. This energy maybe large enough to explain observations of (110) cracking in NaCl-type ionic crystals.

ISSN:0021-8979    

DOI:10.1063/1.1931143

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The problem of electromagnetic wave propagation along a dielectric cylinder of elliptical cross section isconsidered. Two infinite determinants representing the characteristic equations for the two types of hybridwaves (theeHEmn, and the0HEmnwaves) are derived. It is found that there exists two dominant waveswhich possess zero cutoff frequencies. The characteristic roots of these two dominant waves are computedfor various values of eccentricity and relative dielectric constant. Theoretical propagation constants for thedominant waves are verified by experiments.

ISSN:0021-8979    

DOI:10.1063/1.1931144

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

This paper discusses how the fluorescence from semiconductors might be useful in constructing an opticalmaser. Attention is given to the sharp line emission which occurs at low temperatures in CdS and whicharises from excitons bound to impurities. Some recent experimental results are summarized which giveinformation concerning the fluorescent efficiency and the depth to which crystals are excited using ultravioletlight for excitation. Possible maser geometries are discussed and the opportunities for using an evacuatedground state are pointed out. There appear to be several severe difficulties in the way of success. Theseare partly associated with the small depth of penetration of the exciting light, with the low fluorescent efficienciesavailable and with the inability to grow large perfect crystals with controlled impurity content. Animprovement in the art of crystal growing is probably necessary before the effects described here can beexpected to result in a useful optical maser.

ISSN:0021-8979    

DOI:10.1063/1.1931145

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A detailed study of the Cu-Au system between 25–50 at. % Au was made to determine the range of stabilityof the long period superlattices found in this system. The single-crystal thin film technique was usedto make the samples, and the structure was determined using electron diffraction. It was found that a one-dimensionallong period superlattice exists as an equilibrium phase from about 30% Au, substantiatingScott's original observation, to 60% Au. From about 30% to 38% Au, the antiphase structure is theCu3AuIItype, while at higher Au content, the structure is the CuAu II type. The domain sizeMwas found to decreasecontinuously from a value of about 10 at 30% Au to 5 at 50% Au, regardless of the change in structurewhen crossing the phase region betweenCu3Auand CuAu. Small amounts of Al added to a samplehaving the CuAu II structure and an Au content of 40%, decreased the domain size in a manner identicalto that observed for stoichiometric CuAu II. The addition of Al to a sample having an Au content of 27.5%,where an antiphase structure is not observed, resulted in the formation of an antiphase structure for whichthe period could be predicted by our present theory. Qualitative arguments are presented to explain theappearance of these structures. Particular emphasis is placed on the role of the antiphase domain boundaryenergy and the electron energy in determining the formation and period of the superlattice.

ISSN:0021-8979    

DOI:10.1063/1.1931146

出版商:AIP    

年代:1962

数据来源: AIP