摘要:

A concentric cylinder rotational plastometer which automatically plots the shear strainvstime curve for each of a number of shear stresses is described. The flow behavior of molten polyethylene resins, measured with this instrument from 130°C to 210°C, is discussed. It is shown that, at each shear stress, the shear strainvstime curve for these resins is describable in terms of a viscosity, an elastic shear strain and a retardation time. As the shear stress is raised both the viscosity and retardation time decrease, while the elastic shear strain increases. The shear stress dependency of the viscosity and elastic shear strain are shown to be related and in a manner which suggests that the viscosity change is the result of an entropy effect.

ISSN:0021-8979    

DOI:10.1063/1.1721826

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The complexities of the internal friction and dynamic modulus of metals in the cold‐worked condition may be understood reasonably well by separation of the phenomena into the following three distinct effects: (1) the ``nonlinear'' effect, characterized by strong amplitude dependence, frequency independence, and its disappearance after severe deformation; (2) the Ko¨ster effect, which shows rapid recovery after deformation, at temperatures well below the recrystallization temperature; (3) the ``viscosity'' effect, characterized by strong frequency and temperature dependence. The origin of each of these effects is briefly discussed from the point of view of dislocation theory.

ISSN:0021-8979    

DOI:10.1063/1.1721827

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The rheological properties of concentrated suspensions of sized glass spheres in an equal‐density medium has been investigated with the rotational viscosimeter. It has been found that the variation of fluidity with rate of shear can be expressed satisfactorily by a form of an expression suggested by Reiner relating the fluidity to the shearing stress, the fluidity at rest, and the fluidity at infinite shearing stress. It is also shown that values of the apparent fluidity are influenced by the time of shearing, the aging of the suspensions, and temperature effect attributed to the work of shearing.The viscosity of suspensions of sized spheres at concentrations as great as 55 volume percent solids may be satisfactorily represented by either the relation of Mooney or of Maron, Madow, and Krieger; the identity of their relations is also shown. The constants for the equation relating viscosity and concentration are shown to be in satisfactory agreement with those predicted by Mooney. Constants for the viscosity‐concentration equation are also given for several examples of experimental work selected from the literature; the form of equation proposed by Mooney relating viscosity and concentration is generally useful though the constants may not agree with the predicted values.It has been found that the apparent fluidity of the glass bead suspensions decreases with an increase in particle diameter when the suspending fluid is zinc bromide in aqueous glycerol though the viscosity is independent of particle diameter when the suspending fluid is the nonaqueous mixture of ethylene tetrabromide and diethylene glycol.The viscosity of a bimodal system of glass beads was shown to decrease very significantly as the bulk density was increased by packing progressively smaller spheres into the interstices of the larger spheres of the bimodal system, in qualitative agreement with a relation proposed by Mooney.

ISSN:0021-8979    

DOI:10.1063/1.1721828

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

It is known that many physical systems, both time and space dependent, are described by difference‐differential equations. Although the exact solutions to such equations are known to be unique, their determination usually involves a segmented type of solution that is very laborious to obtain. An approximate method of determining any number of roots is described. This approximate procedure allows forward gain and delay to be freely chosen and gives immediately the maximum stable value of forward gain. In many cases, especially where an optimum value of damping constant or forward gain is to be found, it appears that this approximate procedure is more easily applied than any previously described method.

ISSN:0021-8979    

DOI:10.1063/1.1721829

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The authors investigate the transient response of ap‐njunction in a circuit where the applied voltage is suddenly switched from the forward to the reversed direction. The behavior is studied as a function of the circuit resistance. The solution of the appropriate diffusion equation is carried out for a time‐dependent boundary condition, resulting in an integrodifferential equation. Analytical and numerical results for the current and the junction voltage as a function of time are then obtained by suitable approximations for the ``recovery'' and reverse periods. The ``recovery'' or reversal timetfis the time required for the junction voltage to become negative and is given byerftf&tgr;=11+(If/Ir),where &tgr; is the lifetime of holes,Ifis the forward current, andIrthe initial reverse current, which is limited by the external resistance.

ISSN:0021-8979    

DOI:10.1063/1.1721830

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The natural, undamped modes of propagation in a concentric line having a circular outer conductor and a tape‐helix inner conductor are investigated. The investigation is primarily concerned with a study of the propagation characteristics of the modes and, by making suitable approximations, closed expressions for the propagation factors of a few of the lower modes are obtained. Numerical results are then presented for a system having typical geometrical parameters, and generalizations of a qualitative nature are indicated. In the course of the work, the natural‐mode field expressions are derived.

ISSN:0021-8979    

DOI:10.1063/1.1721831

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

By using a new theorem concerning noise in electron streams together with work by D. A. Watkins, an expression for the minimum noise figure of a traveling‐wave tube with a uniform helix is deduced. For reasonable values of tube parameters this minimum lies around 6 db.

ISSN:0021-8979    

DOI:10.1063/1.1721832

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A small amplitude high‐frequency voltage has been superposed on a large amplitude low‐frequency sweeping voltage to study the dielectric behavior of barium titanate single crystals while traversing the hysteresis loop. The output of a capacitance bridge (filtered to pass only the high‐frequency component) is displayed on an oscilloscope as a function of either the applied sweeping voltage, the polarization, or the current to the sample. As a result, the bridge can be balanced for any portion of the sweeping voltage cycle desired. The dielectric constant and loss obtained in this manner have been studied as a function of measuring frequency, of sweeping frequency, of sweeping voltage and of rate of switching polarization (current). The measuring frequency and the switching current are shown to be the significant variables. The frequency dependence of the dielectric constant and loss can be described by a relaxation type of spectrum with a relaxation time of 5.5 microseconds.

ISSN:0021-8979    

DOI:10.1063/1.1721833

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The time‐dependent diffusion equation is solved using transformation calculus to obtain the solute concentration in a solvent after a segregating liquid‐solid interface is passed through the material. The results are presented in graphical and tabular form for typical experimental conditions and compared with previously published findings.

ISSN:0021-8979    

DOI:10.1063/1.1721834

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

This paper presents a general mathematical technique for studying the response and stability of linear time‐varying circuits that contain parameters whose magnitudes vary in a periodic manner with the time. The method presented reduces the solution of the circuit differential equation to that of computing powers of matrices. For purposes of illustration, the method is used to determine the response of an electric circuit consisting of a constant resistance and inductance in series with a periodically varying capacitance. The cases of square‐wave and saw‐tooth‐wave variations of the variable parameter are considered in detail.

ISSN:0021-8979    

DOI:10.1063/1.1721835

出版商:AIP    

年代:1954

数据来源: AIP