摘要:

The foundations and implications of the concepts essential to the thermodynamic analysis of nonequilibrium systems are investigated. Following a review of the background developments in irreversible thermodynamics the concept of thermostatic isolation is introduced. This provides a conceptual device whereby a thermostatic state may be established for any nonequilibrium system and a means of justifying extended use of basic relations of classical thermodynamics or thermostatics.The conventional development of the form of entropy production is outlined. This in general is the sum of extrinsic entropy production and intrinsic entropy production. The former occurs as the sum of products of generalized diffusion effects and property gradients and is the result of interactions with discrete adjacent systems. The latter occurs as the sum of products of generalized affinities and generalized reaction rates and is the result of interaction between geometrically coincident overlapping systems. Between the diffusion effect and gradients of extrinsic entropy production generally occur linear relations with phenomenological coefficients subject to the Onsager reciprocal relations. The intrinsic entropy production occurs as a relaxation phenomenon developed from the first‐order relaxation between the affinity and the displacement of the reaction from equilibrium.The relation of the ultimate limits of applicability of thermodynamics to the uncertainty in establishing thermostatic state under conditions of microscopic fluctuations is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721388

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The results of some experiments on millimeter wave and light generation by means of an undulator are described. After a brief survey of the theoretical background the design of a magnet system is discussed. An experiment is described in which a 100‐Mev electron beam from the Stanford linear accelerator passed through the undulator. Light radiated by the beam was observed and the plane of polarization determined. A small linear accelerator with good bunching action was used for an experiment on millimeter wave generation. At a beam energy of 3 Mev, radiation in a wavelength band below 1.9 millimeters was observed. A peak power output of the order of one watt was obtained. Millimeter waves generated in the accelerator tube were also observed.

ISSN:0021-8979    

DOI:10.1063/1.1721389

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Complex impedance‐matching problems are simplified substantially when they are studied in terms of appropriate circle transformations in theR‐Ximpedance plane. The geometric approach yields valuable insight into the behavior of specific networks and leads to the interesting Circle‐Locus Theorem which applies to any arbitrary, linear, reactive, two‐terminal‐pair network with lumped or distributed parameters (or a combination of both).

ISSN:0021-8979    

DOI:10.1063/1.1721390

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

In this paper a comparison is made between the index‐of‐refraction values measured on five metal‐strip test samples and values computed from four solutions that have appeared in the literature. Three of the samples are wave‐guide equivalents, and two are free‐space arrays. The techniques of measurement for the two types of structures are described briefly. It has been found that all four solutions have certain ranges of validity, but that only one is reliable over the full practical range of the design parameters. This solution, derived previously by the writer, is based on a transmission‐line equivalent circuit in which proximity effects are taken into account.

ISSN:0021-8979    

DOI:10.1063/1.1721391

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The problem of the design of transducers for the purpose of restoring the fidelity of a signal (which has been corrupted by noise), while preserving information in the sense of Shannon is shown to be a particular though unusual one of statistical inference and to be amendable to the methods of mathematical statistics.Adopting the view that the inference of the approximate form of a functions(t) (the signal) from the available mixture of the signal and the noise time seriesn(t) is the natural limiting case of inference from discrete series of random variables, it is seen that the transducer under discussion is the physical analog of a ``statistic''—in the sense of Fisher—and that the properties of the optimum transducer are equivalent to the statistical properties of sufficiency (preservation of information) and efficiency (maximization of fidelity).The case of a Gaussian signal to which Gaussian noise has been added is considered in detail. Using the probability density functional of the Gaussian time series, the maximum likelihood estimate (which in this case is efficient, hence sufficient) of the signal is derived, and it's physical analog is identified as the smoothing filter of Wiener with infinite lag.

ISSN:0021-8979    

DOI:10.1063/1.1721392

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The control and direction of electromagnetic waves is accomplished, in general, by the use of boundary materials and structures which produce desired effects on such waves when irradiated by them. An important class of boundary structure for this purpose is a surface having alternate areas of conducting and nonconducting material. Grids formed of a large number of parallel cylindrical conductors of circular cross section, uniformly spaced and lying in a common surface, are among the most generally useful of this class of boundary structure. Single layer parallel wire grids have received considerable study in the past. However, little information is available concerning the characteristics of multiple layers of such gridsAn analytical solution is obtained for the power transmission coefficient of a double grid system. Power transmission coefficients for various combinations of system parameters are computed from the analytical solution and tested experimentally. The solution is found to yield excellent correlation with experiment until the interwire spacing approaches the wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1721393

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The starting current of a simple model of the backward‐wave oscillator described by Kompfner and Williams has been calculated. The effect of space charge is included. The starting currentI0may be written in the formI0=4V0Z0a0(4QC)2&pgr;N3,whereV0is the beam voltage,Z0is the impedance of the circuit,Nis the length of the oscillator in wave‐lengths measured on the circuit anda0(4QC) is a dimensionless quantity which has been evaluated as a function of the space‐charge parameter 4QC.

ISSN:0021-8979    

DOI:10.1063/1.1721394

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A new vacuum technology is described which makes it possible to achieve working pressures as low as 10−10mm Hg in a routine and straightforward fashion. This is accomplished without the use of chemical getters, special traps, or refrigerants of any kind. Essential to this technology are several new instruments which have been especially developed for the production or measurement of ultra high vacua. These new tools have permitted us to carry out a number of researches concerning the phenomena which occur at very low pressures. The ultra high vacuum technology has also made possible a new experimental approach in the fields of gaseous and physical electronics.

ISSN:0021-8979    

DOI:10.1063/1.1721395

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A theory for the mean thermal gradient at the onset of convective flow of a fluid in a porous medium and heated from below, is given in variational form. Thermal equilibrium is not assumed, nor is viscosity assumed to be constant. An approximate solution is given for the theory, and is shown to agree quite well with published data. No attempt is made to maintain complete mathematical rigor in the derivations.

ISSN:0021-8979    

DOI:10.1063/1.1721396

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Probe measurements were made in the plasma of a low pressure mercury arc. The electron‐energy distributions showed depletions from a Maxwellian distribution in the high energy range. Coupling effects between adjacent probes were investigated and were found to be quite small but in the proper direction to agree with the Langmuir‐Tonks theory. Drift‐current distortion of the random electron‐energy distributions was measured with a bidirectional probe and compared with theory. A multisection probe extending from tube axis to tube wall allowed a determination of radial potential and density variations. Results over a pressure range from 3.4 microns to 35 microns showed good agreement with the ambipolar diffusion theory based on cumulative ionization. A direct calculation of ionization rate in the plasma was made from the ionization probability for a one‐step ionizing process; comparison of this calculation with the observed ionization rate at 1.7 microns indicated that at that pressure the ionization is half direct, half cumulative. For higher arc pressures cumulative ionization evidently predominates.

ISSN:0021-8979    

DOI:10.1063/1.1721397

出版商:AIP    

年代:1953

数据来源: AIP