摘要:

The Seebeck coefficient &agr;, electrical conductivity &sgr;, and thermal conductivityKdata are given for a number of Ag2Te specimens measured at room temperature. The maximum value observed for the figure of merit &agr;2&sgr;/Kwas 1.3×10−3°C−1. The relationship betweenKand &sgr; was linear, andKelcould be expressed approximately by (&pgr;2/3) (k/e)2&sgr;T.Kphwas found to be 0.72×10−2w cm−1°C−1. There was no evidence of an ambipolar diffusion contribution toK. It is suggested that the small energy gap (0.02 ev) previously determined in this compound could account for the absence of a measurable ambipolar diffusion effect, the degeneracylike behavior ofKel, and the relatively low values of the Seebeck coefficient.

ISSN:0021-8979    

DOI:10.1063/1.1735932

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Techniques are developed for deriving both qualitative and quantitative information on the kinetics of gas desorption from measurements at continuously changing temperature. First‐ and second‐order processes can be distinguished immediately by the constancy of the end point of the former. Quantitative values for activation energy and frequency factors are deduced from the experimental time‐temperature curve and the instantaneous slopes of the evolution curve, even for systems with concentration‐dependent rate parameters. It is shown that for multiple desorption peaks, qualitative detection is simplified by slow heating, but may result in interconversion. The experimental basis of desorption measurements using the Bayard‐Alpert gauge is also analyzed, together with artifacts arising from negative pressures, bistable gauge operation, formation of new species in the gauge, and the delay in sensing density pulses transmitted through tubes.

ISSN:0021-8979    

DOI:10.1063/1.1735956

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A theoretical and experimental investigation of instability phenomena in synthesized plasmas is carried out. In the theoretical analysis the space charge and potential distributions are obtained for an idealized one‐dimensional model. The model consists of two face‐to‐face electrodes each emitting ions and electrons in any ratio and with a Maxwellian velocity distribution. The calculations show that no stable zero‐field solution is possible; instead, distributions with either a potential maximum or minimum in the center are obtained. For a range of values of the ratio &bgr; of injected ion to electron space‐charge density near unity (0.81 ≤&bgr;<1.235), double‐valued solutions to the problem are obtained. The actual solution into which the system settles depends on whether this range of &bgr; values is approached from above or below. Transitions from one such state to the other can occur at the limits of this &bgr; range. In the experimental investigation of a synthesized plasma, these instabilities, or state‐to‐state transitions, were found to be in good agreement with the theory. Oscillations triggered by state‐to‐state transitions were observed with a frequency corresponding to the ion transit time through the interelectrode space. These oscillations are not described by the steady‐state analysis.

ISSN:0021-8979    

DOI:10.1063/1.1735951

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Self diffusion coefficients for the two tracers In114and Sn113in the liquid alloy indium‐tin at the eutectic composition have been measured as a function of temperature in the range 200°C–450°C. The customary Arrhenius equation is used to describe the experimental results. For indium as a tracer we obtainedD=(42.5±5.7) 10−5 exp−2771±158RTcm2/sec,and for tinD=(11.7±1.7) 10−5 exp−1380±156RTcm2/sec.It is possible that the large difference between the two activation energies could be associated with properties of the eutectic composition.

ISSN:0021-8979    

DOI:10.1063/1.1735952

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Radiation‐temperature measurements of positive columns of glow discharges in helium, neon, and hydrogen were compared with calculations and with Langmuir probe measurements of the electron temperature. The microwave‐noise radiation was detected at a frequency of 3000 Mc. The plasma studied was illuminated by a blackbody source of known variable temperature. The blackbody temperature was adjusted until the received noise power became independent of the presence of the unknown plasma. At this point, the temperature of the two radiators is the same, irrespective of the magnitude of the plasma absorptivity.

ISSN:0021-8979    

DOI:10.1063/1.1735953

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The hypothetical model of ball lightning first suggested by P. L. Kapitza [Doklady Akad. Nauk S.S.S.R.101, No. 2, 245 (1955)] is considered in some detail in an attempt to uncover evidence which will substantiate or contradict the theory. Observers' reports of the phenomenon are summarized briefly. Pro and con arguments concerning Kapitza's scheme are given. A theoretical model in an ideal environment is examined. The radio‐frequency field suggested by Kapitza is considered, and the interference effects resulting from the reflection of a discrete band spectrum of linearly polarized waves from a perfect reflector are presented. The gaseous discharge is discussed, under the assumption that the ball lightning phenomenon is analogous to a point‐to‐plane corona discharge. It is determined that, given a sufficiently intense electric field, a horizontal discharge along one of the electric field antinodes, suggestive of horizontal lightning, can result. It is concluded that this exploratory work supports Kapitza's hypothesis, but that much more must be done before the theory is fully substantiated.

ISSN:0021-8979    

DOI:10.1063/1.1735954

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The use of dielectric waveguides in the form of small fibers as the mode selector in optical masers is considered. The fibers consist of a core of index of refractionn1which contains the maser material, surrounded by a cladding of lower indexn2. A comparison is made with the Fabry‐Perot interferometer used as a cavity. The principal advantages of the fiber for maser applications are the mode selection and the stronger mode coupling. It is shown that for core diameters just small enough to support only the twoHE11modes, the fraction of spontaneous emissions into the waveguide modes is given approximately by 1.4 (n1−n2)/(n1+n2). This could make maser action possible at much lower power levels. The major disadvantage is the difficulty of pumping into the small volume of the fiber. Schemes to overcome this difficulty are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1735955

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A pulse method for measuring thermal diffusivitity of metals has been developed. The temperature in an effectively infinite rod is zero everywhere up to the timet=0, when a very short heat pulse is introduced in the planex=0. The subsequent temperature histories of several points at different distances fromx=0 are recorded, and from these data the thermal diffusivity may be calculated. Since an experimental run lasts less than one minute, the requirements on the stability of the ambient temperature are not as stringent as in previously reported methods. The present method saves time without sacrificing accuracy, a maximum error of ±4% being estimated. Although this work was all done at room temperature, the specimens were mounted in a vacuum furnace which should permit measurements at elevated temperatures. The method was tested on commercial ``A'' nickel, giving a result in excellent agreement with previous values. Results are reported for four new steels developed by the Bethlehem Steel Company.

ISSN:0021-8979    

DOI:10.1063/1.1735957

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The distribution of current is computed in a cylindrical semiconductor specimen provided with cylindrical metallic end caps of the same diameter as that of the specimen and electrical lead wires of much smaller diameter. Nonuniformity of the longitudinal current density of 1% or less can be obtained in specimens with electrical resistivities at least 200 times greater than that of the end caps if the lengths of the specimens are at least equal to their diameters and if the length of each end cap is at least 0.3 diam.

ISSN:0021-8979    

DOI:10.1063/1.1735959

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The techniques of zone melting have been applied to AgCl and AgBr in an attempt to obtain large crystals of extremely high purity. By measuring distributions in ingots with deliberate impurity additions, both optimum conditions for zoning and distribution coefficients for several impurities were determined. For AgCl, zone melting in a chlorine atmosphere led to near‐ultimate distributions for Cu, Pb, Ni, and Fe after passage of 70 zones at a rate of 3 in./hr. The distribution coefficients determined were as follows: Cu, 0.4; Pb, 0.4; Ni, 1.4; and Fe, 0.7. Zone melting in vacuum resulted in similar distributions for Cu, Pb, and Ni, but Fe separated with an effective distribution coefficient slightly greater than one. Under these conditions, Mn and Cd separated in a direction opposite to that of zone travel, and Sn, Al, and Sr separated in the direction of zone travel. Zone refining of nominally pure AgCl resulted in crystals which probably contain less than one part in 109of Cu and Ni, less than one part in 108of Pb, and less than five parts in 108of Fe. Limited data on AgBr indicate that in this case, too, useful purification can be obtained. The dark electrical conductivity of the zoned crystals was found to be intrinsic above 315°K for AgCl and 300°K for AgBr.

ISSN:0021-8979    

DOI:10.1063/1.1735960

出版商:AIP    

年代:1961

数据来源: AIP