摘要:

The equation logR=A+B/(T+&thgr;) for the resistanceRof a thermistor atT°K is proposed. Least square analyses of the most precise resistance‐temperature data available for three different thermistor materials show that the equation is a considerable improvement over its predecessors; the standard relative errors of fit are 0.4 percent, 0.17 percent, and 0.91 percent.

ISSN:0021-8979    

DOI:10.1063/1.1699586

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The spark described here provides a high intensity light source, whose effective duration approaches 10−7second. The light intensity is nine hundred times greater than that obtained using RG8U cable cut for 10−7second duration discharge. The cable described here is coaxial with silver conductors fired on the dielectric, a compound of barium titanate. The gain in light intensity is apparently due to both the higher capacity of the barium titanate cable and its very low characteristic impedance.

ISSN:0021-8979    

DOI:10.1063/1.1699587

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Spectral and total emissivity measurements of thoria‐coated tungsten filaments show that irreversible and reversible changes of the emissivity occur. &egr;&lgr; (&lgr;=0.65&mgr;) varies from 0.2 to 0.7 and &egr;tfrom 0.2 to 0.5.Certain variations of the thermal radiation can be related to changes of thermionic emission.Passage of current through the coating affects emissivity and thermionic emission. This is shown by measuring infra‐red radiation and electron current simultaneously. The existing relationship between emissivity and thermionic activation is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1699588

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The dynamic characteristics of a discharge can be determined by making square‐wave changes of arc current. This is done by putting the discharge tube in the plate circuit of a group of pentodes connected in parallel and supplied with a square‐wave signal superimposed on a d.c. bias.Probes operated at constant current are very useful in recording the characteristics of a modulated discharge. For measuring electron temperature (Te), two identical probes are centered about points having the same space potential. If the probes are operated at different fixed currents on the straight line part of the probe characteristic, the voltage between them is proportional toTe. Longitudinal voltage gradient or radial potential differences may be recorded by use of identical probes operated at the same current.A probe operated at a suitable current will follow roughly the variations in space potential of the adjacent region of the discharge. Another probe made sufficiently negative with respect to such a probe will collect only positive ions. A probe made 0–10 volts positive with respect to the constant‐current one gives records from which electron concentrations can be computed. In this case, a bias connection without current flow is obtained by use of a cathode‐follower with two stages of direct‐coupled amplification.The oscillograph amplifier used for dynamic probe records must be either a differential one or one with ungrounded power supply. In the latter case, the stray capacitance is many times larger; but fairly reliable records can be obtained if the arc current is 0.1 ampere or more, and if the time constant for the decay of the transient effects being measured is at least 10 microseconds. The oscilloscope amplifier and any preamplifier used for recording spectral intensities should be direct‐coupled.

ISSN:0021-8979    

DOI:10.1063/1.1699589

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The radiation patterns have been measured for five dielectric rods of circular cross section which were excited in theTM0,1mode. These rods were each 0.870&lgr;0in diameter, and the lengths were 2&lgr;0, 4&lgr;0, 6&lgr;0, 8&lgr;0, and 10&lgr;0. The theoretical radiation patterns have been computed by means of equivalent surface electric and magnetic currents. Excellent agreement is obtained when it is assumed that the diameter of the surface on which these currents are distributed is 0.65 of the diameter of the dielectric rod. Representative experimental and theoretical patterns are shown for the full 360°.

ISSN:0021-8979    

DOI:10.1063/1.1699590

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A total of 350 back‐reflection ZnO powder x‐ray diffraction lines on 25 photographic films have been measured and analysed by the Cohen analytical least squares extrapolation method to yielda=(3.2495±0.00002)A,c=(5.2069±0.00011)A; where the stated errors are the probable errors. The statistical reliability of the results is emphasized.In the measurement of the Debye‐Scherrer ring radii the accuracy obtained with a metric scale and indicator (employing no optical lens system) and with a dividing engine equipped with a microscope are compared and the former simpler method is found more reliable. It is concluded that the use of precision measuring instruments for observing diffraction ring radii are unnecessary and even undesirable apparently because the magnifying power of the optical system of precision micrometers leads to uncertainties in settings on photographic lines.

ISSN:0021-8979    

DOI:10.1063/1.1699591

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The manner in which a sphere behaves when it enters the water from air depends on the rate at which energy is taken from it, and most of this energy is utilized in setting water into motion. The virtual mass is a partial measure of this motion. An investigation of virtual mass for spheres shortly after vertical water entry is described. The spheres used had specific gravities between 1.06 and 16.77 and impact velocities ranged from 21 to 103 ft./sec. The value of the virtual‐mass coefficient was found to be much smaller than had previously been estimated, an average value of 0.08 being obtained. The method used recognizes the dependence ofCDon sphere speed and depth, and makes comparisons only where these parameters have the same value.

ISSN:0021-8979    

DOI:10.1063/1.1699592

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The strain‐time behavior of annealed platinum wires at constant stress and temperature is reported for a wide range of experimental conditions, namely: 1550 to 78°K, 900 to 40,000 p.s.i., 0.001 to 0.1 strain, 10−1to 10−6min.−1strain rate.The following relations were found to describe the results satisfactorily:&sgr;=A&egr;˙n|&egr;,T;   &sgr;=BepT|&egr;,&egr;˙,&egr;=Cta|&sgr;,T;   Q∼log&sgr;|&egr;;   ∂n∂T=∂p∂log&egr;˙|&egr;,where &sgr;=stress, &egr;=strain, &sgr;=strain rate,T=absolute temperature,Q=activation energy for rate of deformation,t=time, andA, B, C, a, n, andpare constants.

ISSN:0021-8979    

DOI:10.1063/1.1699593

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The effect of magnetic field on the high frequency breakdown of gases has been studied. The presence of energy resonance and the modification of diffusion are shown experimentally and explained theoretically. An application is made of both the average electron theory and the Boltzmann theory, and the correspondence between these two theories is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1699594

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The quantum mechanical problem of the interaction of a charged macroscopic body with a metal surface is treated by means of the variation method. The resulting expression for the interaction energy is the same as that obtained by the classical image force method except for three correction terms. These corrections are caused by the change in kinetic energy associated with the concentration of the electrons on the surface of the metal, the reduction in the electron‐electron interaction energy in the metal resulting from the anti‐symmetrization of the wave function and the effect of the finite thickness of the surface charge. It is found that these terms are negligible except for distances between the charged body and metal surface such that surface structure effects are important.

ISSN:0021-8979    

DOI:10.1063/1.1699595

出版商:AIP    

年代:1950

数据来源: AIP