摘要:

The nucleation and growth of particles can be independently determined by simultaneous measurement of two quantities having different functional dependencies upon particle number and size. Light scattering and optical absorption are the two quantities chosen to observe the precipitation kinetics of a gold colloid. When an exposed photosensitive glass is treated at high temperatures, gold precipitates on a fixed number of sites. On the other hand, increasing the concentration of reactants causes spontaneous gold precipitation in which growth sites form continuously throughout the precipitation process. This indicates that the photosensitive reaction forms nuclei in a supersaturated solution which cannot nucleate spontaneously. In agreement with this, the experiment shows that the number of growth sites increases with exposure while the growth rate is the same for all exposures. Finally, assuming that the particles are spheres, absolute values are derived for the initial change of particle size with time and for the number of nuclei as a function of exposure.

ISSN:0021-8979    

DOI:10.1063/1.1722926

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Simplified equations for the cooling time of glass fibers to the solid state are deduced from the theory of heat conduction. The approximations made are based upon a value of the order of 1 for Nusselt's number. This value ofNuholds for comparable metallic fibers, as measured by Mueller, and is assumed to hold for glass fibers. The relation of pulling speed and flow rate to cooling time is shown. Calculations of cooling time of typical small glass fibers show that they are of the same order as the Maxwell relaxation time of the glass at roughly 900°C. The consequence of this correlation is discussed in terms of the high strength of fibers, and the high ``fictive'' temperature of fibers.

ISSN:0021-8979    

DOI:10.1063/1.1722953

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The cooling rate for fine glass fibers in the 6–16 &mgr; diameter range has been calculated by means of a new cooling equation. Typical strengthvsdiameter data are compared with the ratio of quenching time to the Maxwell relaxation;ts/&tgr;. Strength increases rapidly forts/&tgr; ≤ 1.0 and &tgr; is most probably of the order 10−4sec at 1100°C. The refractive index decreases slightly in the critical region but the change does not indicate a significant rise in the fictive with increased quenching. For this reason structural changes are considered of secondary importance as a factor contributing to high strength. New strength measurements of glass fibers fit a distribution law with reasonable accuracy. It is therefore concluded that the flaw theory of high strength is valid. The influence of ``hydrostatic'' cooling upon flaw generation is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722934

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Assuming that the resistivity of wave guide walls is not too large, the influence which energy losses have upon the shape of a pulse propagating along the wave guide is discussed. It is found that pulses are damped with a damping factor equal in the first approximation to that in a steady state.

ISSN:0021-8979    

DOI:10.1063/1.1722935

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A semidirect diffractometer method, requiring little or no specimen preparation, has been developed for the determination of fiber texture in wire or rod. The method is applied to cold‐drawn, high‐purity aluminum wire, which is found to have a double fiber texture: 80% of the specimen volume has a [111] texture and 20% a [100] texture.

ISSN:0021-8979    

DOI:10.1063/1.1722936

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

High‐velocity axial shocks have been produced in linear gas discharge systems by so shaping the discharge tube (and discharge) that a maximum amount of energy is coupled into the ionized gas before the shock is formed. Two methods of coupling energy into the gas are discussed along with their relative merits and shock velocities achieved by each method.

ISSN:0021-8979    

DOI:10.1063/1.1722937

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Field emission patterns were observed using a point made of a single crystal ofp‐type silicon. Stable patterns were obtained only after the point was distorted by heating in the presence of an electric field. The symmetry of the patterns agreed with the symmetry expected from the known orientation of the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1722938

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The behavior of germanium transistors in nuclear radiation fields is predicted by combining transistor theory and the experimentally observed changes in irradiated semiconductors. It is shown that the decay of minority carrier lifetime &tgr; in the base region usually controls the useful life of a transistor in a radiation field. Radiation induced changes of the conductivity place an ultimate limit on transistor life, but these changes occur at a much slower rate than those in &tgr;. The analysis predicts the following: (a) &agr;cb−1should be a linear function of bombardment time in a constant flux field; (b)p‐n‐punits should decay faster thann‐p‐nunits; (c) for a given resistivity type and structure the decay rate is proportional to the square of the transistor base width which in turn, is inversely proportional to the cutoff frequency of the amplification factor. Thus, high‐frequency units with their thin base regions decay more slowly than low‐frequency units. The predictions of the theory are compared with experimental observations on the behavior of irradiated transistors, and the agreement is found to be reasonably good.

ISSN:0021-8979    

DOI:10.1063/1.1722939

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The effect on the x‐ray diffraction pattern of deformation faults and twin faults occurring at random on the (211) planes of a b.c.c. lattice has been investigated. In single crystal reflections, deformation faults produce peak shifts and peak broadening, and twin faults produce a peak asymmetry and peak broadening. For a powder pattern it is necessary to average over the different components of a powder‐pattern peak; the peak shifts average out to zero, and the peak asymmetries to a quantity which is generally too small to measure. Both types of fault produce a line broadening which varies strongly from one powder peak to another. Thehkldependence of the broadening is the same for the two kinds of faults, and only a combination of the two probabilities can be measured. Measurements were made on samples of cold‐worked &bgr;‐brass filings in different states of annealing. There were no measurable peak shifts or peak asymmetries. The ratios of the effective particle size values could be explained only if a major part of the particle size broadening is due to faulting. The results are discussed in connection with measurements on other cold‐worked b.c.c. metals.

ISSN:0021-8979    

DOI:10.1063/1.1722940

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Tensile specimens of cast polymethyl methacrylate of five different molecular weights varying from 90 000 to 3 160 000 were broken by static loading and the fracture surfaces compared. The fracture appearance was fairly constant for a given molecular weight but there was a continuous development of certain features and a retrogression of others with changes in molecular weight. The series which was developed by varying the molecular weight was similar in appearance to that developed by Zandman by varying the rate of loading of polymethyl methacrylate. The higher molecular weight specimens corresponded in appearance to those obtained at the lower rates of loading. In the higher molecular weights, failure by ``separation'' was most marked whereas fracture by ``pulling out'' of polymer masses became more important at the lower molecular weights.

ISSN:0021-8979    

DOI:10.1063/1.1722941

出版商:AIP    

年代:1958

数据来源: AIP