摘要:

An investigation was made of the effects of nonuniformity in the magnetic fields and in the test specimens employed in the measurement of nuclear magnetic resonance absorption. Particular attention was given to the determination of relative integrated line intensity from derivative maxima independently of the uniformity of concentration of the subject nuclei through the available sample volume. The principal objective was to devise techniques applicable to granular hygroscopic materials. A technique applicable for the low‐moisture range was tested for materials containing 7 to 16 percent water and found to be satisfactory.

ISSN:0021-8979    

DOI:10.1063/1.1721984

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The so‐called gap problem in antenna theory is considered critically. It is shown that whereas there exist problems related to transmission‐line end‐effect and coupling between antenna and line, there is no gap, and hence no gap problem, when a physically realizable complete transmitting system is considered rather than an antenna with a fictitious mathematically convenient driving mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1721985

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The linearized theory of slender bodies in arbitrary motion at zero angle of attack has been worked out. The results have been applied to a smooth body accelerating uniformly through sonic velocity. The results theory can be used to estimate the nonlinear or transonic effects.For an accelerating body, the parameter (bl/c2)½is important where 2b= acceleration, 2l= length of body,c= sound speed at infinity. For sufficiently high (bl/c2)½, transonic effects can be neglected. Using linearized theory to estimate the ratio of nonlinear terms in the differential equation gives&lgr;=nonlinear termssignificant linear terms=34(&ggr;+1)&dgr;2(bl/c2)12log2&dgr;2c2bl12−94,where &dgr; = thickness ratio of body. The result above is evaluated at the maximum thickness of a symmetric parabolic arc body at the instant it passes through sonic velocity. For &lgr;<1 transonic effects can be neglected while for &lgr;>1 they begin to dominate. For practical applications the result shows that there is a possibility of a sufficiently long and slender missile accelerating fast enough to avoid transonic effects (e.g., 50 feet long, 5 percent thick, 3gacceleration). For conventional aircraft, transonic effects will dominate. An interesting side result is that when the acceleration is sufficiently large so that transonic effects do not matter the drag coefficient near sonic speed is independent of the acceleration (CD≐3&dgr;2for parabolic arc body).

ISSN:0021-8979    

DOI:10.1063/1.1721986

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The electron optical properties of a cylindrical space charge cloud are derived. The possibility of achieving a system free from either spherical or chromatic aberration by combining a space charge lens with a space charge free converging lens is examined. It is concluded that the achromatization of a thin electric or magnetic lens is possible only if the resultant action of the combination is divergent. The correction of the spherical aberration of a high quality lens, such as an electron microscope objective, is shown to be impossible on account of electron interaction effects.

ISSN:0021-8979    

DOI:10.1063/1.1721987

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The present work is an extension of the author's prior work on the radiation characteristics of and current distribution in a conical helix, the helix used in the present case having a pitch angle much lower than of that studied previously. In this case the condition of the phase velocity adjusting itself automatically to maintain maximum directivity condition (which enables the radiation to be confined in the axial mode over a large band of frequencies) does not hold. Nevertheless the major fraction of energy could be radiated in the axial direction when the geometry of the helix and the distance of the apex from the ground were properly chosen, the conical helix together with the ground being regarded as tapered transmission lines (with the ground as one and the helix wire—with the distance of its elements from the ground line increasing continually,—as the other line).Measurements of the field intensity and the current distribution were made in the frequency range of 100 Mc/sec to 500 Mc/sec with a conical helix antenna arrangement as follows. The helix was of six turns, the radius increasing uniformly from 5 cm at the apex to 65 cm at the base within an axial distance of 60 cm. The apex of the helix was placed at a distance of 17.5 cm from the ``ground'' provided by a 6‐ft square copper netting of close mesh. It was found that within the range of frequency measured the major fraction of the energy was radiated in the axial direction. Theoretical expressions forE&phgr;andE&thgr;were derived by assuming a linear current distribution, and the calculated radiation patterns were found to agree with the experimentally determined ones.

ISSN:0021-8979    

DOI:10.1063/1.1721988

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The diffraction of electromagnetic waves by circular apertures in extended conducting screens and by complementary obstacles was investigated experimentally to determine the structure of the field in the near zone. Techniques for measuring both the electric and magnetic field distributions are presented and the general experimental problems are discussed. Data are given for the tangential components of the electric and magnetic vectors in the principal planes in the immediate neighborhood of the diffracting structures, and axial distributions for the corresponding components. The results extend the range of the data available previously. The predicted uniformity of the tangential magnetic field in the aperture plane, for the case of a wave incident normally, is verified. An experimental test was made also of the electromagnetic Babinet principle.

ISSN:0021-8979    

DOI:10.1063/1.1721989

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The electron microscope examination of the surfaces of bulk clays by replica techniques is difficult because of the porosity of the clays and the necessity of using hydrofluoric acid to dissolve the clay from the replicas. The surfaces of some bulk endellite clays were examined by means of collodion, silica, and preshadowed replicas. Collodion and two‐step silica replicas were unreliable and difficult to use because of penetration of the collodion or plastic into the pores of the clay. Collodion strippings were of some value in removing layers of clay particles from the surface for direct examination in the microscope. Best results were obtained with the preshadowing technique which employed a shadowing layer of platinum backed by a layer of evaporated carbon or by Parlodion. Micrographs of replicas prepared by the latter technique show the surface of a highly porous endellite clay to consist of tubes in various orientations.

ISSN:0021-8979    

DOI:10.1063/1.1721990

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721991

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721992

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721993

出版商:AIP    

年代:1955

数据来源: AIP