摘要:

The electrical impedance of a lossy conductor is a complicated function of time (or frequency) because of the skin effect. By solving the diffusion equation for magnetic fields in conductors of several prototypical shapes, the impedance can be calculated as a function of time for a step function of current. The solution suggests an electrical circuit representation that allows calculation of time‐dependent voltages and currents of arbitrary waveforms. A technique using an operational amplifier to determine the current in such a conductor by measuring some external voltage is described. Useful analytical approximations to the results are derived.

ISSN:0021-8979    

DOI:10.1063/1.337434

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A sensor with a high sensitivity and an excellent selectivity for ammonia gas was prepared by using sputtered ZnO thin films. The sensor exhibited an increase of resistance for exposure to ammonia gas whereas it exhibited a decrease of resistance for exposure to many other gases such as inflammable and organic gases. The resistance change and the selectivity of the sensor were enhanced by doping group III metal impurities such as Al, In, and Ga. The lower limit of the detection for ammonia gas was about 1 ppm at a working temperature of 350 °C.

ISSN:0021-8979    

DOI:10.1063/1.337435

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A method of measuring the thermal conductivity of materials during transient heating or cooling is proposed based on the continuous recording of the temperature difference between sample surfaces when known heat flux is supplied to one of the sample surfaces by a heater. The analysis of the solution of the heat conduction equation for a measuring system consisting of two platelike samples separated by a heater shows that the transient heating or cooling significantly influences the temperature distribution within the samples. It follows from the theoretical consideration that this effect as well as the effects resulting from heat generation or absorption in the samples during phase transitions can be eliminated by subtracting the results of two measurements conducted with different powers supplied by the heater. The condition for validity of this procedure is the small temperature difference between sample surfaces which can be achieved by the selection of appropriate temperature change rate or sample thickness.

ISSN:0021-8979    

DOI:10.1063/1.337436

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In this paper, an apparatus for measurements of the thermal conductivity of materials as a continuous function of the temperature is described. It works on the principle of continuous recording of the temperature difference between the surfaces of the sample caused by the flux of heat while the ambient temperature is linearily changed. The theoretical background described in the preceding paper by E. Piorkowska and A. Galeski [J. Appl. Phys.60, ▪▪▪▪ (1986)] showed that the utilization of the results of two continuous measurements with different heat fluxes makes it possible to eliminate all components of the thermal response of the sample except the one depending on the heat flux and the thermal conductivity only. Testing measurements were conducted on samples of several nonmetalic materials. The results obtained indicate high precision of the method and the apparatus and reveal new possibilities of studying the thermal conductivity of materials during phase transitions.

ISSN:0021-8979    

DOI:10.1063/1.337437

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The energy required to produce an electron‐ion pair (i.p.),W, for the &agr;‐particle irradiated gases CF4, C2F6, C3F8, andn‐C4F10has been measured and found to be 34.3, 34.5, 34.4, and 34.2 eV/ i.p., respectively. The large values ofWfor these perfluorocarbons (PFCs) are attributed to their large cross sections for electron impact‐induced dissociation. The constancy ofWfor this group of molecules is discussed with respect to the constancy of the ratio (∼0.68) of the respective (energy integrated) total ionization cross section to the total (energy integrated) inelastic scattering cross section.Wvalues are also reported for the binary gas mixtures Ar/CF4, Ar/C2F6, Ar/C3F8, and CH4/CF4which have conduction and insulation properties suitable for use in diffuse discharge opening switches. TheWvalues for these binary mixtures (and for C2H2/CF4, C2H2/C2F6, and C2H2/C3F8) increase with the amount of PFCs in the mixture and (contrary to the Ar/C2H2mixture) exhibit no Jesse effect. The ternary gas mixtures Ar/C2H2/PFC (=CF4, C2F6, C3F8) containing ≲10% PFC were found to exhibit a pronounced Jesse effect which is a function of the content of the PFC in the mixture and the electron scattering cross section of the PFC itself. Substantial increases in ionization can be achieved by adding to the Ar/PFC binaries 1–3% of C2H2. An analysis of theWdata yielded information on the partition of the &agr; particle’s energy among the gas components and indicated that the rate constant for energy transfer from excited argon atoms (Ar*) to the PFC is smaller than that from Ar* to C2H2; it showed, also, that the rate constant for energy transfer from Ar* to C2H2is ∼104larger than that for collisional deexcitation of Ar* by ground‐state Ar atoms. The quantitative measurements reported herewith and the parameters deduced from a simple modeling of the data permit the tailoring of ternary gas mixtures with substantial current increases over those achieved in the binary Ar/PFC (=CF4, C2F6, C3F8) mixtures which possess the desirable conduction and insulation characteristics for pulsed power opening switches.

ISSN:0021-8979    

DOI:10.1063/1.337792

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Experimental and theoretical studies are reported on formation of primary particles during evaporation of metals into a host gas in an evaporation chamber. The developed theory explains present and previous experimental observations of this process. The dependence of primary particle size on host gas pressure, host‐gas molecular weight and source temperature has been explained. Particle thermophoresis has been shown to cause formation of the so‐called ‘‘smoke shell’’ observed surrounding the vapor source. Coalescence of primary particles has been shown not to be an important growth process for the primary particles, although for longer times primary particle coagulation produces the chains of primary particles observed experimentally.

ISSN:0021-8979    

DOI:10.1063/1.337438

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Electromagnetic fields from switching on and off a constant current distributed over a plate of finite extent are studied. Such current distribution will set up a magnetostatic field and an electric dipole field behind the initial transient pulse. Over an area equal to that of the plate, there is a finite volume in which the strengths of theEandHfields of the transient pulse do not decrease with distance. This finite volume decreases as the inverse of the distance from the source so that the energy contained in this volume also decreases as the inverse of the distance traveled.

ISSN:0021-8979    

DOI:10.1063/1.337439

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Measurement of microwave Cerenkov radiation in air exhibits the diffraction pattern predicted in earlier work. The radiation appears only at harmonics of the frequency of periodic electron bunches. Angular distribution power measurements are presented for frequencies of 2.86, 5.71, 8.57, and 11.42 GHz corresponding to the fundamental and the first three harmonics of anS‐band rf linac.

ISSN:0021-8979    

DOI:10.1063/1.337440

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The performance characteristics of small‐period electromagnet wigglers of novel design are measured and compared with theoretical expectations. Field measurements for wigglers driven by dc, ac, and short‐pulse current sources are reported. Fields as high as 1 kG have been readily obtained in a double‐sided 3.9‐mm‐period wiggler. These performance capabilities allow the design of high‐power free electron laser oscillators and ‘‘optical klystron’’ amplifiers in the near‐millimeter regime using modest electron beam energies in the range 200–400 keV. Oscillator and amplifier designs for operation at 150 and 300 GHz are presented. The generation of 1.2 MW of 150‐GHz radiation with >50% efficiency is predicted.

ISSN:0021-8979    

DOI:10.1063/1.337441

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Laser direct‐write metallization in metallo‐organic films involves complex thermal profiles and changes in optical properties that affect the spatial resolution, chemical purity, and electrical properties of the resulting features. Compositional profiles of the metal features, determined by scanning Auger electron spectroscopy, are reported and correlated with the chemistry of the laser‐initiated thermal reaction and the observed feature structure. Studies of the changes in optical properties of the films by conventional thermal decomposition offer important insights into the reaction mechanisms. We also report an optimized development procedure for the laser‐exposed samples.

ISSN:0021-8979    

DOI:10.1063/1.337442

出版商:AIP    

年代:1986

数据来源: AIP