摘要:

If a thermionically emitting cathode is used in an arc discharge the heat feedback from the gaseous plasma to the solid surface provides the continuity of the arc process. The response time of the temperature fluctuation of the solid‐surface material is found to be at least an order‐of‐magnitude longer than that of the plasma, therefore, the rate process is necessarily controlled by the slowest branch in the process, namely, the solid material. Based on this logic, the initial stages of electric arc ignition and cathode spot growth are analyzed for a thermionically emitting cathode. A feedback heat‐transfer process which couples the plasma and the solid surface is hypothesized to govern these phenomena. While the model chosen has been simplified to the extent that quantitative significance may be lost, however, several previously observed qualitative features of arcs are explained, one of which is the need for a minimum current density for the persistence of a thermionic arc. The cathode spot growth can also be accounted for by this hypothetical model.

ISSN:0021-8979    

DOI:10.1063/1.1659482

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The axial distribution of voltage induced near the inner wall of a 3.8‐cm‐diam tube confining an rf argon induction plasma at atmospheric pressure was measured at a flow rate of 115 cm3/sec with a water‐cooled ring probe. Also measured as functions of probe position were the excitation frequency, voltage, and current on the inductor coil. The plasma reduced the probe voltage to about 60% of its value in the absence of the plasma. After correction for the effects of cooling and displacement of the plasma by the probe, the total induced voltage around the circumference of the plasma at the midsection was found to be 64 V. The corresponding value for electric‐field intensity was 6 V/cm. This value falls between published values obtained by indirect methods and is in fair agreement with prediction on the basis of a one‐dimensional theory.

ISSN:0021-8979    

DOI:10.1063/1.1659483

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An analytical discussion of a theoretical model of Fingero‐imbibition in a cracked porous medium, of small inclination, is presented in this paper. The phenomenon is assumed to occur in a double‐phase displacement process involving two immiscible liquids of small viscosity difference in which the injection is initiated by imbibition and the consequential displacement of the relatively more viscous native liquid produces fingers. The nonlinear differential system governing this phenomenon is mathematically formulated and an approximate solution, using a perturbation technique, has been obtained.

ISSN:0021-8979    

DOI:10.1063/1.1659484

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A passive mechanical device for slowly expanding the yaw cone of a spinning sounding rocket is described in mathematical detail. The equations of motion for the system are solved and approximations useful for design are developed. The device has been used for sky scanning in the infrared and results of a test flight are presented.

ISSN:0021-8979    

DOI:10.1063/1.1659485

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Measurements obtained in the temperature range 0.1°–1°K illustrate the influence of the thermal boundary resistance on the thermal conductance of a suspension of copper particles in an amorphous dielectric.

ISSN:0021-8979    

DOI:10.1063/1.1659486

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The steady‐flow viscosity&eegr;(&ggr;˙),the loss modulusG″(&ohgr;), and the storage modulusG′(&ohgr;) for five linear polyethylene melts (190°C) were measured using the Weissenberg rheogoniometer and the Instron rheometer. An excellent agreement was observed between the experimentalG′(&ohgr;) andG″(&ohgr;) values and those calculated from the relaxation spectrum obtained from&eegr;(&ggr;˙)using the relation&eegr;(&ggr;˙)=∫H(ln&tgr;)h(&thgr;)g(&thgr;)3/2&tgr;d ln&tgr;,  &thgr;=&ggr;˙&tgr;/2.Here, &ggr;˙ is the shear rate, &ohgr; is the radian frequency, and &tgr; is the relaxation time. The functionsg(&thgr;) andh(&thgr;) are expressed asg(&thgr;)=(2/&pgr;)[cot−1&thgr;+&thgr;/(1+&thgr;2)]  and  h(&thgr;)=(2/&pgr;)[cot−1&thgr;+&thgr;(1−&thgr;2)/(1+&thgr;2)2].No coordinate shift was required. An interative procedure was used in such an interconversion. The first approximation to the spectrumH1(ln&tgr;) was(2/&pgr;)[&eegr;(&ggr;˙)×&ggr;˙]and the corresponding viscosity was&eegr;1(&ggr;˙).The successive approximations were expressed by the equationHK(ln&tgr;)=HK−1(ln&tgr;)+p&ggr;˙[&eegr;(&ggr;˙)−&eegr;K−1(&ggr;˙)],wherep=2/&pgr; andK≥2. In all cases, only six iterations were required to achieve satisfactory convergence. The relaxation spectra so obtained from viscosity measurements at large shearing deformation were in excellent agreement with those calculated fromG″(&ohgr;) measured in oscillatory experiments carried at small deformation.

ISSN:0021-8979    

DOI:10.1063/1.1659487

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A theoretical model for the thermal lens and birefringent effects induced in a continuously pumped Nd:YAG rod is developed. Experimental measurements of these effects using a 6328‐Å probe are described and compared to theory. Excellent agreement between the two types of measurements and theory is obtained. The thermally birefringent and bifocusing phenomena are suggested as causes of reductions in the polarized and fundamentalTEM00powers from a high‐power multimode Nd:YAG laser. Typical results are described using a laser which operates in the 200−300‐W range of average powers.

ISSN:0021-8979    

DOI:10.1063/1.1659488

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A theoretical treatment of the diffraction of a monochromatic Gaussian light beam by reflection off a single‐frequency ultrasonic surface wave is presented. With a suitable incident‐light‐beam diameter a discrete diffraction pattern is formed. The form and the frequency spectrum of the light in the pattern are stated in detail for the limiting case of small‐sound‐beam intensity. A description is given of experiments which verify the theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.1659489

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The flux‐density distribution and its stability in the mixed state of type II superconductors in the presence of a stationary longitudinal magnetic field are considered in the connection with the critical conduction current and the longitudinal magnetization. It is believed that the theory similates reasonably well the behavior of the superconductors. It is found that the flux pinning by imperfections in the superconductors becomes ineffective in the longitudinal field because of the induced helical vibrations of pinned flux lines.

ISSN:0021-8979    

DOI:10.1063/1.1659490

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A simplified model is used to study the response to a slowly changing uniform magnetic field of a wire consisting of fine filaments of superconductor embedded in a normal metal matrix, the entire wire being twisted about its axis. Expressions for the critical twist pitch, the power loss in the normal metal, and the time constant are obtained.

ISSN:0021-8979    

DOI:10.1063/1.1659491

出版商:AIP    

年代:1970

数据来源: AIP