ISSN:0021-8979    

DOI:10.1063/1.1707688

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

The microphysical structure of cuprene is described from electron micrographs and some suggestions are made concerning the mechanism of the formation of this substance. Cuprene samples prepared by polymerization of acetylene in the presence of finely divided cuprous oxide are shown to be composed of hollow fibers characterized by both longitudinal and transverse structure. The striking appearance in electron micrographs of this type of cuprene serves to identify it in clogging deposits taken from acetylene lines. This is illustrated by a deposit taken from a reactor used in the process of hydrogenation of acetylene to ethylene. Cuprene specimens formed by alpha‐ray bombardment of acetylene gas are shown to be composed of round particles joined by short, straight, thick necks which are about 500 to 1000A in length. These are samples of cuprene which have been bombarded further by alpha‐particles after their initial formation. An oxidized sample has round particles of mean diameter 4900A; an unoxidized sample has a mean diameter of 3800A for the round particles. There is evidence to suggest that alpha‐ray cuprene is liquid in nature. The two types of cuprene are so different physically that a change in nomenclature is in order.

ISSN:0021-8979    

DOI:10.1063/1.1707689

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

This paper presents a method of using sand in building models of two‐dimensional Fourier projections in crystal structure analysis. The machine for producing these models is described and the results are illustrated by projections of known structures. The mathematical principle of this method of summing Fourier series is identical to that which Bragg developed in England. The chief difference is in the use of sand instead of photographic film as the medium for producing contrasts in electronic density throughout the projection. The method herein described has a number of features which contribute to its usefulness: A two‐dimensional Fourier projection comprising the addition of one hundred and fifty terms may be made in about four hours by a single worker. The time required is not determined by the size of the unit cell. The subdivisions of the projection face are sufficiently fine to assure an accuracy as great as the x‐ray data from copper radiation will warrant when a scale of one angstrom to two centimeters is used. Upon embarking on a new structure problem, no changes in the equipment are necessary; as the initial set of templates suffices for all future work. The minimum interplanar spacing that the machine will accommodate is determined by the characteristics of copper radiation rather than the order (h, k, orl) by which the spacings are characterized. The resulting sand model of the projection is the same shape as the unit cell projection with regard to both the angle between the edges and the ratios of the edges of the cell. When the x‐ray data warrant, a distinction can be made between heavy atoms and lighter atoms by the differences in the height of the sand. Photographs of the projections (see Figs. 7 and 9) portray atoms as distinct spots.

ISSN:0021-8979    

DOI:10.1063/1.1707668

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

The distribution of the backscattered radiation of a long straight conductor shows a sharp return lobe perpendicular to its orientation. In horizontal observation such a ``rope'' would therefore give an appreciable echo only if it were almost exactly vertical. In practice no such effect will be observed since, because of wind and other disturbances, the rope will never be straight but actually over its whole length will pass through regions of space where the phase of the incident wave will change many times through its full range 2&pgr;. The effect of these irregularities will be to make the sharp dependence of the cross section upon the orientation of the rope disappear, and to give a cross section proportional to the total lengthLof the rope. In Section I, the wave‐length &lgr; is assumed to be large compared to the transverse dimensions of the rope. In Section II, the results are extended to include the case where the wave‐length &lgr; of the incident radiation is not necessarily large but is comparable with or even small compared to the widthdof a ribbon‐shaped rope. It is found that the cross section of such a rope can be written generally in the form &sgr; =KAf(&pgr;d/&lgr;), whereKis a numerical constant depending upon the deviations of the rope from the vertical and whereA = Ldis the area of the ribbon. The lengthLis assumed to be much greater than &lgr;. The functionfis evaluated by the use of a method developed by Morse and Rubenstein.

ISSN:0021-8979    

DOI:10.1063/1.1707669

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

The intrinsic viscosities of an extended series of linear methyl polysiloxane fluids, having dimethylsiloxane (Me2SiO) as the repeating unit, have been determined in toluene solution. These values have been correlated with their molecular weights, determined chemically and by osmotic pressure and light scattering measurements. The Staudinger equation was found applicable only for fluids of relatively low molecular weights, i.e., up to about 2500; for the higher polymers, the best correlation of intrinsic viscosity with number average molecular weight was found to be:[&eegr;]=2×10−4Mn0.66.This held reasonably well for molecular weights from 2500 to about 200,000. The bulk viscosities of the polysiloxane fluids were found to conform to the Flory relationship for melt viscosities; the expression:log visc. (cs. at 25∘C)=1.00+0.0123 Mn12appears to be reasonably valid for molecular weights above 2500.

ISSN:0021-8979    

DOI:10.1063/1.1707670

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

The phenomenon of bunching which takes place in a velocity modulated electron beam can be described in purely kinematical terms if space charge effects are negligible. However, the non‐uniform distribution of charge in the bunched beam gives rise to a field which opposes the bunching process so that the kinematic solution may be validly applied only for a limited length of drift space. An accurate solution of the bunching process requires the integration of the dynamical and field equations. These reduce to a linear homogeneous system under the assumption of ``small signal'' conditions. The device of a high frequency ``surface charge'' is employed in formulating the boundary conditions at the surface of the beam. In the non‐relativistic approximation the dynamical and field equations yield solutions which are classified as non‐solenoidal or solenoidal accordingly as the motion produces or does not produce a high frequency charge density within the beam. There exists a non‐solenoidal type of motion which generates no field outside the beam. The actual physical problem is solved by taking a suitable linear combination of both solutions. Under conditions met with in practice, a large part of the actual solution may be of the solenoidal type. The high frequency component of beam current appears as a sum of a volume current and a ``surface current,'' the latter term arising from the longitudinal motion of the high frequency ``surface charge.'' Again, under conditions met with in practice, a large part of the high frequency component of beam current may occur in the form of ``surface current.'' The theory contains three debunching wave numbers: one identical with that which occurs in Webster's debunching theory for a beam of unlimited cross section, and two which depend upon the transverse dimensions of the beam and drift tube, the current density, frequency, and beam velocity.

ISSN:0021-8979    

DOI:10.1063/1.1707671

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

The problem of the axi‐symmetrical vibrations of a shallow spherical shell is reduced to two simultaneous differential equations for the tangential and normal components of displacement. The solution of these equations is obtained in terms of Bessel functions. With this solution the third‐order determinant for the frequencies of a shell segment with clamped edge is given but not evaluated. Instead, an approximate value for the lowest frequency is calculated by means of the Rayleigh‐Ritz procedure [Eq. (40)]. It is found that very little curvature is needed to modify appreciably the corresponding flat‐plate frequency. The approximations which are made are those customary for shallow shells: (1) omission of the transverse shear term in the tangential force equilibrium equation, and (2) relations between couples and changes of curvatures as in the theory of flat plates.

ISSN:0021-8979    

DOI:10.1063/1.1707672

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

A first‐order differential equation for the voltage reflection coefficient of a non‐uniform line is obtained and it is shown how this equation may be used to calculate the resonant wave‐lengths of tapered lines.

ISSN:0021-8979    

DOI:10.1063/1.1707673

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

In this paper the resonant frequency of the nosed‐in cavity is studied as a function of the cavity dimensions. Maxwell's differential equations and boundary conditions are converted into an integral equation which is solved approximately by the Ritz variational method. The size and shape of the cavity are fixed by specification of the dimensions (cf. Fig. 1)r1andr2, the inner and outer radii; &egr;I, the post length and &egr;II, the gap space. If the cavity is to resonate to the wave‐length &lgr;, only three of its dimensions can be given independently; the fourth will be a function of the given three and the wave numberk=2&pgr;/&lgr;. For fixedr1/r2the dependence ofk&egr;Ionk&egr;IIis calculated with a precision of 1 percent.

ISSN:0021-8979    

DOI:10.1063/1.1707674

出版商:AIP    

年代:1946

数据来源: AIP

摘要:

A linear accelerator for charged particles, consisting of a number of cavity resonators placed end to end with the inside end plates removed, and thus forming a wave guide with two closed ends, is discussed. The shape of each section must be so chosen that the velocity of the particle will correspond to the phase velocity of the radiation of the cavity. In order to determine possible shapes for the cavity, the stationaryTM01modes between two parallel conducting planes are determined. In Part 1, excitation of a single mode is discussed, including the shape of the conducting surface that can be used to connect the planes and thus form a cavity. Three cases are considered—when the phase velocity in the cavity is greater than, equal to, and less than that of light. If only one mode is excited, and the phase velocity is not greater than that of light, then the radius of the cavity becomes infinite at the two plates. In Part 2, the simultaneous excitation of two modes is considered. The phase velocity of one mode is that of light; the other has a phase velocity 1/nthat of light, wherenis an odd integer. The cavity can be made finite by a suitable choice of the relative amplitude of the two modes, and the radius of one end of the cavity. This requires a rather elaborate discussion. This case is of particular interest for the acceleration of electrons. It is shown, furthermore, that only the first mode contributes to the acceleration of the electron. In Section 4, the application of the methods used in Part 3 to the case of an accelerator for heavy particles is touched upon.

ISSN:0021-8979    

DOI:10.1063/1.1707675

出版商:AIP    

年代:1946

数据来源: AIP