摘要:

The radiation from fast electron beams passing through a succession of electric or magnetic fields of alternating polarity is examined. The radiation of maximum frequency is emitted in the forward direction. If the deflecting fields are not too large, a semiqualitative argument shows that the maximum frequency is the lowest possible harmonic. The frequencies emitted are determined by studying the Doppler effect, and the angular distribution of radiated energy as well as the total radiation are calculated in a simple straight‐forward manner with reference to well‐known formulas of special relativity. The question of the coherence of the radiation is discussed. The spectral distribution of radiated energy is then calculated more exactly. It is concluded that several applications of the radiation appear possible. A scheme for obtaining millimeter‐waves of considerable power is outlined. The upper limit of the power in a band extending down to a wave‐length of 1 millimeter is calculated to be of the order of several kilowatts for a beam of one ampere and an energy of 1.5 megavolt. The use of the radiation for speed monitoring of beams with energies up to 1000 megavolt is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1700002

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

In the investigated range of 5×10−3to 10−7mm Hg, the breakdown voltage over insulators in high vacuum is independent of pressure. Currents of 10−11to 10−8ampere were observed in the region below breakdown voltage by detecting x‐ray quanta with a Geiger‐Mueller counter. Pinhole camera x‐ray pictures revealed that practically all radiations originate from an area on the anode a distance from the insulator, with a weaker radiation coming from a ring immediately adjacent to the insulator. Current‐voltage relationships as usually observed in these experiments indicate a roughness factor and an emitting area on the cathode similar to previous findings in vacuum gaps. Current bursts were observed which did not develop into complete breakdown. Oscilloscopic observations revealed that sometimes at breakdown over insulators the voltage on the test sample drops to 2.5 kv; in other cases it falls to less than 100 volts. The low voltage arc‐like discharge extinguishes at a current of about one ampere for copper electrodes in contact with Pyrex glass. When a resistance in series with the test sample is increased to keep the maximum current below one ampere, no stable discharge is observed. As in a vacuum gap, the breakdown voltage over an insulator is increased by successive breakdowns. Part of this ``conditioning'' is permanent. The nonpermanent part is dependent on the state of the test sample prior to conditioning. The anode does not appear to influence conditioning. When the resistance in series with the test sample allows a discharge current above one ampere to flow, a fast conditioning usually occurs which results in a high permanent breakdown voltage.

ISSN:0021-8979    

DOI:10.1063/1.1700003

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A theoretical and experimental analysis of the current‐voltage (dc) characteristic of a parallel‐plate condenser through which the small, airborne, charged particles of an aerosol are passed continuously shows that a charge‐weighted distribution of radius (or radius squared)‐charge ratio may be obtained when certain experimental conditions are satisfied. Examination of such a distribution for an aerosol (particles less than a micron in diameter) before and after passage through a small (20‐liter) settling chamber shows that the classes of particles in the distribution that are easiest to collect in the condenser are also the classes that disappear most rapidly in the chamber. It is pointed out that the methods employed would become less tedious and more powerful when used with a dispersion of constant‐size particles, and that they are well adapted for certain fundamental investigations of aerosol properties.

ISSN:0021-8979    

DOI:10.1063/1.1700004

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Fracturing, or scabbing, of a material near a free surface as the result of a transient compressional stress wave of high intensity impinging on that surface has been observed for many years; however, little quantitative data that relate the fracture to the nature of the stress wave and the physical properties of the material seem to exist. The phenomenon has been investigated for five metals, 1020 steel, 4130 steel, 24S‐T4 aluminum alloy, brass, and copper, by using an explosive charge to induce a high intensity stress wave in the metal. The distribution of pressure within the wave was determined by a modified Hopkinson‐bar type of experiment.Scabbing has been found to be governed principally by the spatial distribution of pressure within the wave and a critical normal fracture stress &sgr;cthat is characteristic of the material and perhaps the state of stress. Numerical values of &sgr;cwere obtained for each of the five metals.

ISSN:0021-8979    

DOI:10.1063/1.1700005

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Permanent magnets have been successfully utilized to energize magnetic lens pole pieces for high resolution electron microscopy at direct magnifications of 7000 times with 30‐kilovolt electrons, and 6000 times at 50 kilovolts. Stray magnetic fields, which have previously limited high magnification and high resolution, have been minimized by using two circuit gaps in parallel and by surrounding the assembly with a magnetic shield connected to the external pole pieces of the two gaps. Magnetomotive forces of 1400 gilberts have been obtained. A single magnet, magnets in bucking arrangement, and configurations involving magnets disposed either radially or parallel to the optical axis of the lens, have been successfully utilized. The effects of various magnetic circuit parameters on the design and operation of the lens system have been studied.

ISSN:0021-8979    

DOI:10.1063/1.1700006

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

It is common knowledge that in cyclically stressed ferromagnetic materials an energy loss due to internal friction is observed; this part of loss disappears when the material is brought to saturation or above the Curie temperature. It is also known that a stress, applied to a ferromagnetic material, produces a motion of Weiss domains from their rest position.The scope of this paper is to verify experimentally the following hypothesis: in cyclically stressed ferromagnetic materials, energy loss because of magneto‐elastic internal friction is induced by a domain motion due to the applied stress itself.The ratioIr/Is(whereIr=residual induction, andIs=saturation intrinsic induction) has been chosen as an index of the domain position; its measure has been carried out by normal ballistic method on a permeameter rigged with a torsion applying device.Energy loss was measured by means of a torsion pendulum; a coil allowed the saturation of specimen in order to separate magneto‐elastic from purely mechanical losses. Plotting curves ofIr/Isand of magneto‐elastic losses as a function of applied stress and comparing them for each tested material, it has been found that they, besides having the same shape, show abrupt slope variations at practically the identical value of stress. It has further been observed that a specimen presenting only a low percent variation ofIr/Isratio (i.e., in which domains had slightly moved from their rest position) showed also moderate magneto‐elastic losses. These results appear to confirm assumptions made about the magneto‐elastic internal friction in ferromagnetic materials. The reason why motion of domains takes place in an essentially irreversible way still remains unknown.

ISSN:0021-8979    

DOI:10.1063/1.1700007

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Existing calculations on the tunnel effect through thin films in contacts apply to very weak and very strong electric fields. It is the main purpose of the present paper to complete the picture by the treatment of intermediate cases, which are important for many contact applications.

ISSN:0021-8979    

DOI:10.1063/1.1700008

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The problem of the diffraction of a plane electromagnetic wave by the convex surface of a paraboloid of revolution is examined. Expressions for the components of the incident wave, the scattered wave, and the refracted wave are obtained and are written in such a form that boundary conditions can be satisfied over a paraboloidal surface &xgr;=&xgr;0. The analysis is then restricted to the case of a perfectly conducting paraboloid and a wave whose wave front is perpendicular to the axis of rotation. The amplitude of the scattered wave is plotted as a function of the distance along the axis of rotation for three paraboloids. One of these curves is compared with the scattered field produced by a sphere whose radius is equal to the radius of curvature of the paraboloid at the nose.

ISSN:0021-8979    

DOI:10.1063/1.1700009

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A steady‐state temperature distribution is found for the case of a periodically varying point source of heat, immersed in a homogeneous isotropic infinitely extended fluid, moving with a constant velocity. The phase velocity of the generated temperature wave is discussed. If the phase velocity in a stationary medium isV0, and the fluid velocityv>V0, the phase velocity in a moving medium is given byV=v[1+½(V0/v)4−(5/8)(V0/v)8+…]. For practical cases one can usually assumeV=v, with an error of less than 0.1 percent, even whenV0is as large as 20 percent ofv.

ISSN:0021-8979    

DOI:10.1063/1.1700010

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The accuracy of a V‐2 type ballistic rocket which is guided to the termination of propulsion and is in free flight thereafter is investigated. The effect of the rotation of the earth and the re‐entry into the atmosphere on the accuracy is considered and the errors due to lack of thrust control are analyzed.

ISSN:0021-8979    

DOI:10.1063/1.1700011

出版商:AIP    

年代:1951

数据来源: AIP