摘要:

The characteristics of impulse corona have been studied in a point‐to‐plane gap. Both positive and negative square voltage pulses of one‐ and two‐microsecond duration were used with various voltages and pulse repetition rates. The impulse corona in air is found to be quite similar to the d.c. corona, except that the phenomena are exaggerated by the relative absence of space charge inhibition. At higher voltages, the negative impulse corona was found to have a ``spike'' or streamer type of discharge superimposed on the regular Trichel pulse corona. By using the nonelectron‐attaching gases nitrogen and hydrogen, it is shown that these spikes are due to the negative ion space charge formed by the Trichel pulse in the gap. When the point is grounded, the intense field developed between this negative space charge and the positive space charge at the point is sufficient to cause a streamer to propagate.

ISSN:0021-8979    

DOI:10.1063/1.1698370

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Reference is made to the conjectural nature of our present views on the mechanism of extreme‐pressure lubrication. A differentiation is made betweenslidingandtearingso that sliding is defined as the relative motion of two solid bodies in frictional contact under the action of a tangential force with the frictional force increasing in direct proportion with the normal load. On the other hand, when the surfaces of the friction elements suffer macroscopic damage during relative motion, the frictional force increases at a more than proportionate rate with the normal load and a case of tearing is established.The general requirement made of a lubricant is the reduction of the frictional force. The requirement made of an extreme‐pressure lubricant is that it should reduce the frictional force at a sufficiently high value of the normal load for a pressure of at least 1.5×104kg‐wt./cm2to apply throughout the run, and in addition, the extreme‐pressure lubricant should prevent tearing or scoring of the surfaces at these comparatively high bearing pressures.A loaded revolving steel ball in frictional contact with a hardened steel block is a model of a bearing requiring extreme‐pressure lubrication. The temperature elevation at the rubbing contact should be a measure of the energy dissipated by friction, and this can be determined by connecting the rubbing contact to a galvanometer which records the thermal electromotive force generated at the contact. The record of the electromotive force represents the entire frictional history of the contact in every detail. Evidence was found that extreme‐pressure addition agents reduced the frictional force and extended the region of normal loads over which the frictional force was a direct proportion of the normal load.Various types of extreme‐pressure addition agents gave results which suggested the existence of an optimum dope concentration. In general, over the region of normal loads over which Amontons' law of the direct proportion between the frictional force and the normal load applied, lubricants which reduced the thermal electromotive forces generated at the rubbing contact also reduced the wear diameter. On the other hand, when tearing took place no such parallelism between friction and wear became apparent since the final wear diameter is the integrated result of the wear processes occurring during one run, whereas the record of the electromotive forces gives the details of the change of the frictional force in the course of such a run.It is suggested that the optimum dope concentration may be a function of two counteracting effects. On the one hand, the extreme‐pressure addition agent is likely to decrease the dielectric breakdown field strength of the thin layer of lubricant and to reduce thereby the electrostatic component of the frictional force. On the other hand, the lubricant becomes more corrosive with increasing concentration of the extreme‐pressure addition agents. As soon as appreciable corrosion takes place, tearing sets in and causes the frictional force to increase. Thus a balance will be struck between the reduction of the frictional force by diminishing its electrostatic component, and an increase of the frictional force owing to the corrosive action of the extreme‐pressure addition agents.Evidence was found to support this latter view when metallic films were wiped out by hand on metal blocks. It was then observed that under ``dry'' conditions the metallic films tended to reduce the thermal electromotive forces and that the films were more effective in reducing these forces in the order tin, copper, lead. On the other hand, in the presence of an extreme‐pressure lubricant of optimum dope concentration similar filmsincreasedthe thermal electromotive force, the increase being now in the order lead, tin, and copper, in which the corrosive action might be expected to be promoted by these films.An attempt was made to calibrate the thermal electromotive forces in terms of temperature.

ISSN:0021-8979    

DOI:10.1063/1.1698371

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A modified silica replica technique for electron microscopy has been developed involving direct condensation of silica upon the object. For improvement of the silica replica technique in general, the following new procedures are introduced:(a) The undesirable effects of brittleness of silica replica is largely obviated by use of a thin plastic supporting film.(b) A working method is introduced which completely avoids manual manipulation of the unsupported replicas.(c) A better definition of small structural elements of the specimen is obtained when a new method of condensing metallic vapors on a rotating replica is introduced; when compared to the usual shadowcasting, an improved two‐dimensional definition of the objects is achieved; also the combined use of rotary condensation and shadowcasting provides a better general definition of objects than would be obtainable by either method alone.Reproducibility of the morphology of crystals and particles by the modified silica replica is demonstrated with the electron micrographs.

ISSN:0021-8979    

DOI:10.1063/1.1698372

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

An automatic method is proposed for recording systematically the density distributions resulting from all permutations of sign of a given set of Fourier coefficients.It is suggested that the device could be used in conjunction with analog computers of the type now being built by Pepinski, and relay circuits for this purpose are given.

ISSN:0021-8979    

DOI:10.1063/1.1698373

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A simple systematic method, based on a theorem stated and proven here, is presented of obtaining a formula of the formz=f(x, y) from an experimental curve (Fig. 1) in whichyis kept constant and a second experimental curve (Fig. 2) in whichxis kept constant. Questions of the sufficiency of the original data are automatically answered by this method. Several examples are given to illustrate the procedure explicitly.

ISSN:0021-8979    

DOI:10.1063/1.1698374

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Exact, explicit expressions are obtained for the field of a radiating periodic point dipole located in medium 1 at the center of a spherical shell of medium 2, which is bounded by medium 3. The values of &egr;, &mgr;, &sgr; and the shell radii are arbitrary. The reflected and transmitted fields are examined in various special cases. When the shell radii become infinite, the fields agree with those obtained by R. K. Luneberg for the case of plane waves normally incident on a flat plate of medium 2 between media 1 and 3. When the radii are infinite and media 2 and 3 identical, the Fresnel formulas for normal incidence of plane waves on a plane interface between two half‐infinite media are obtained. When the radii are finite, media 2 and 3 identical and &mgr;1= &mgr;3, the results of C. T. Tai are obtained. For finite radii, media 1 and 3 identical, and shell thickness small compared to a wave‐length, the fields check the approximate results of J. B. Keller for the fields reflected and transmitted by a thin shell of any shape, when his results are specialized to the present case.

ISSN:0021-8979    

DOI:10.1063/1.1698375

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

For a plane dielectric sheet near a receiving antenna the power varies sinusoidally with distance, having a half‐wave period and an average proportional to the transmission coefficient. This is explained by assuming an equivalent antenna reflection, an assumption checked by special experiments. The theory includes phase and arbitrary incidence, for which the wave may be elliptically polarized. The reciprocal of received amplitudevs.polarization then gives a similar ellipse with 90° shift in orientation. Corresponding theory for transmitters shows that the reflection varies sinusoidally with half‐wave period and with average proportional to the reflection coefficient. For a distant sheet there is inverse‐distance attenuation. The effect of initial antenna mismatch is fully investigated. For any cylindrical surface, including corrugations or a plane, amplitude reflection varies with angle as the secondary power pattern. With a paraboloidal antenna of radiusaat wave‐length &lgr;, the reflection from a circular cylinder of radius &rgr; and reflection coefficientRis 6R(&lgr;p)½/13a; that from a narrow strip of width 2aqis (7Rq/80)(15−10q2+3q4); that from a narrow strip distantaq′from the axis is proportional toR(1−q′2)4. If the initial mismatch gives a reflectionr, and if the surfaces make an angle &thgr; with the axis, the above are multiplied by (1−r2) exp (4&thgr;2ln2/w) wherewis the antenna pattern half‐width. Corresponding results are given for corrugated surfaces and series of strips. Applications to radomes are discussed, and to pressurizing seal design and tolerances. All results are extensively verified experimentally.

ISSN:0021-8979    

DOI:10.1063/1.1698376

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698378

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698381

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698383

出版商:AIP    

年代:1949

数据来源: AIP