摘要:

Pressure‐temperature equilibria curves for a series of some 20 rare‐earth arsenates and rare‐earth vanadates which undergo the reconstructive transition zircon (Zr SiO4) &lrarr2; scheelite (CaWO4) type structure in the region 10 000–60 000 atm were obtained. From these curves, a set of data were extracted representing (with a fair approximation to corresponding states) the change of equilibrium pressure for a transition as a function of the radius of the rare‐earth ion. The result is a V‐shaped curve for both vanadates and arsenates showing a minimum transformation pressure near Dy3+or Ho3+. An interesting even‐odd effect is noted.

ISSN:0021-8979    

DOI:10.1063/1.1729706

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The high‐frequency spectral noise voltage appearing across a metallic conductor electrically heated to high temperatures is experimentally found to be in agreement with the Nyquist theorem even though the conductor is far from thermodynamic equilibrium. Furthermore, because of the thermal origin of the nonlinearities in the current‐voltage characteristic the proper value of resistance to use in the Nyquist expression corresponds to the voltage/current ratio, rather than the differential resistance at the operating point. At frequencies below that corresponding to the thermal time constant of the conductor, an additional noise voltage caused by temperature fluctuations is detected. The observed magnitude and spectrum of this noise voltage is in very good agreement with a simple calculation of temperature fluctuations due to heat conduction.

ISSN:0021-8979    

DOI:10.1063/1.1729707

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Waves moving through a medium in which the wave velocity is a function of time and space suffer frequency changes. If the velocity modulation is small and adiabatic, very elementary kinematic considerations define these frequency changes. For a uniformly moving velocity pattern the frequency change suffered by a portion of the wave is shown to depend only on the wave velocity at the input and output end of the modulating system, and not on the intermediate velocities experienced by the wave. Electro‐optic modulation and deflection experiments are treated in this framework. The paper is intended to present a particularly simple viewpoint, and does not arrive at really new results.

ISSN:0021-8979    

DOI:10.1063/1.1729708

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The presence of fluctuations in the discharge parameters introduces errors into Langmuir probe measurements. Previous work by Garscadden and Emeleus considered the effects of fluctuations in the individual parameters. In this paper a generalized small‐amplitude theory of the effects of these fluctuations is given and also a large signal theory for single‐frequency oscillations. The results of Garscadden and Emeleus can be deduced from these, but additional terms are predicted due to cross modulation occurring when the various fluctuations are correlated. The large signal theory has been checked experimentally in a mercury‐vapor discharge at a pressure of about 1 &mgr;. Further experimental measurements with injected broadband noise signals confirm certain features of the generalized theory. The errors caused by fluctuations are discussed and it is concluded that although electron temperatures may still be measured accurately in their presence, serious errors can be incurred in the measurement of electron saturation current and number density.

ISSN:0021-8979    

DOI:10.1063/1.1729709

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A simple method for measuring thermal diffusivity is considered. It consists in suddenly heating one end of a sample and measuring the time it takes for a heat wave to arrive at the other end. This paper considers the application of this method for two kinds of boundary conditions relating to the heat input. These conditions correspond to step‐function heating (a) by radiation and (b) by a good contact to a constant‐temperature heat source, such as liquid metal.In addition to consideration of the effects on the analytic solution due to radiation heat loss, other factors which affect the accuracy and sensitivity of the technique are discussed. The heat‐wave method is related to many other techniques for measuring thermal diffusivity, ranging from Angstrom's original method to several pulse heating techniques which have been described recently. The interrelationships between these different techniques are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1729710

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The flash technique for measuring thermal diffusivity is analyzed for the case of a cylindrical‐shaped specimen of radiusr0and thicknessato determine the effects of radiation at high temperatures, finite duration of the heat pulse, and the feasibility of low temperature measurements. It is found that the flash diffusivity method is useful in two complementary limits: (1) pulse time &tgr; short compared to the characteristic thermal response timetc, (2) &tgr;/tcof the order 1 to 10. The former case corresponds to the original description of Parker, Jenkins, and Abbott, while the latter case is suitable at very low temperatures. Moreover, it is shown that there is an optimum specimen thicknessafor a given material and pulse time &tgr;, in the sense that a higher temperature can be reached before any corrections have to be made to the Parkeret al.analysis.

ISSN:0021-8979    

DOI:10.1063/1.1729711

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Experiments have been carried out on Te‐doped (∼1–3×1018cm−3) GaAs crystals in which changes innare measured when Li is introduced by diffusion and again after the Li is removed. The amounts of Li removed are determined by chemical analyses. It is found that two Li atoms introduced cause a loss of one electron, corresponding to a (Li+Li=) pair. Acceptors remain during the removal of Li which are postulated to be Ga vacancies. The kinetics of the disappearance of the ``vacancies'' have been investigated. The process appears to be diffusion controlled with an activation energy corresponding to 5–6 eV. The equilibria reached show an increasing ``vacancy'' solubility with decreasing temperature. A model in which Ga vacancies form stable pairs with Te atoms is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1729712

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

It is predicted theoretically that because of its time‐dependent mechanical properties, the rolling behavior of a wear fragment of viscoelastic material trapped between two moving surfaces is complex. If the moving surfaces are smooth and unlubricated, the fragment may either roll with a velocity equal to half the relative velocity between the surfaces, or it may reach a terminal rolling velocity beyond which increases in surface speed cannot drive it. If the surfaces are lubricated, the tractive force tending to roll the fragments arises from the friction of surface asperities sliding through the fragment. The rolling behavior then depends on the ratio of the size of the asperity to the size of the fragment. A critical value of this ratio exists. Above it, the fragment rolls at a velocity always slightly less than half that of the surfaces because of slip. Below the critical ratio, the fragment cannot be driven beyond a certain maximum velocity. Slip always takes place between the fragment and the surface, and increases with increasing surface velocity. Beyond the maximum rolling velocity, an increase of surface velocity leads to a decrease in the rolling velocity of the fragment.

ISSN:0021-8979    

DOI:10.1063/1.1729713

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A quantitative theory of the scattering from systems in which a precipitating phase is undergoing diffusion‐controlled growth is worked out by means of a Fourier transform method, and is applied to experimental data on light scattering from phase‐separated glasses. The theory predicts an initial inverse eighth‐power dependence of turbidity on wavelength, a great excess of backward scattering over forward scattering, and under certain conditions a minimum in the plot of intensity against scattering angle, all of which are in agreement with observation.

ISSN:0021-8979    

DOI:10.1063/1.1729714

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The Hall coefficient and conductivity have been measured during pile‐irradiation for a number of zone‐refined,p‐type silicon crystals with initial resistivities of 1, 8, and 100 &OHgr;‐cm. To supply the magnetic field for the Hall measurements, a small electromagnet was used. The conductivity of zone‐refined silicon shows much faster changes with irradiation than pulled silicon samples of equivalent resistivity. The 100‐&OHgr;‐cm samples exhibit a monotonic nonlinear decrease of ln&sgr;, conductivity, vs &phgr;f, integrated fast flux, whereas the other samples with initial Fermi levels closer to the valence band have one or two regions of linear decrease in ln&sgr; vs &phgr;fbefore the nonlinear decrease region is observed. The Hall mobility for the 100‐&OHgr;‐cm samples decreases and becomes negative as a result of the carrier density decreasing with irradiation. In the case of the 8‐&OHgr;‐cm sample, the Hall mobility decreases with irradiation whereas the 1‐&OHgr;‐cm sample shows no change in Hall mobility with irradiation up to the maximum integrated flux used in the present experiment. The origins of the dependence of ln&sgr; on &phgr;fas well as the behavior of the Hall coefficient and Hall mobility with irradiation are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1729715

出版商:AIP    

年代:1963

数据来源: AIP