摘要:

Silver iodide particles have been found to serve as nuclei for the formation of ice crystals in super‐cooled water and in water vapor super‐saturated with respect to ice. It is believed that silver iodide serves as a very effective nucleus because it very closely resembles ice in crystal structure. Both dimensions of the unit cell of ice and silver iodide are the same to within approximately one percent. The maximum temperature at which the silver iodide particles serve as nuclei is approximately −4°C for particles one micron in diameter, and −8°C for particles 100 Angstrom units in diameter. A silver iodide smoke generator has been constructed which consumes 1 mg of silver iodide per second and produces 1013effective nuclei per second.

ISSN:0021-8979    

DOI:10.1063/1.1697813

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

An equation for waves in elastic tubes is developed and applied to cylindrical tubes with Hookian and with elastomeric walls. The former application yields the Moens‐Korteweg formula, which has been found inadequate. The latter application leads to a rather complicated equation for the pulse‐wave velocity.Values of pulse‐wave velocities are computed for the thoracic aorta by means of the foregoing equation, and the results are compared with measured mean velocities for the entire aorta. Graphs and tables are given, so that a graphical analysis of this velocity equation can be applied to any large artery; and the method is illustrated by computing the pulse‐wave velocity in the left common carotid. The relationl÷∫0lds/v, for the mean velocity over a tube of lengthl, is shown to be valid for the aorta and large arteries.

ISSN:0021-8979    

DOI:10.1063/1.1697814

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

An electronic synthesizer is described for determination of atomic positions in crystals. The synthesizer sums the two‐dimensional Fourier series representing planar, centro‐symmetric projections of electron densities in a crystal unit cell; and the projection is presented by a television scan on the screen of a cathode ray oscilloscope. The specific advantage of the device is the immediate observability of effects on the projection of alterations in signs of one or any number of Fourier coefficients.

ISSN:0021-8979    

DOI:10.1063/1.1697815

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

Fixed and variable length re‐entrant resonant cavities designed for the measurement of dielectric constant and dissipation factor are described. These cavities operate in the frequency decade of 108to 109cycles per second, a region avoided by many experimenters because the frequency is too high for the application of circuit techniques and not high enough for the convenient use of coaxial lines or wave guides. The theoretical considerations in the design of these cavities are presented. The well‐known susceptance variation method, widely used in the frequency range of 104to 108cycles per second, was extended to apply to these cavities; it yields a rapid measuring technique and very simple expressions for calculating the values of the dielectric properties. The performance of this apparatus is discussed and the results of the measurements of a few typical dielectrics are given.

ISSN:0021-8979    

DOI:10.1063/1.1697816

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

A variable capacitor is described for measuring (1) small displacements, (2) small volume changes, and (3) pressure differences. The capacitor consists of a deflectable diaphragm and a fixed electrode. The diaphragm is metallic, plane‐parallel, clamped at the edges, and at ground potential; the electrode, at an a.c. potential, has a plane surface parallel to the undeflected plate across an air gap. For use in displacement measurements, the diaphragm's center is deflected by a point contact from a mechanical link to the observed system, or by a uniform pressure load from a fluid link to the system. The fluid link is used also when measuring volume changes and pressure differences. The plate deflection results in a change in the air gap, and thus generates a capacitance signal. This signal is measured by electrical methods.A theoretical analysis of this variable capacitor is presented; sensitivity and alinearity factors for the three uses of the device are derived. The experimental performance shows reasonably satisfactory agreement with the derived theory. The displacement of the plate's center was measured with an interferometric method, using a yellow He line as a standard of reference; the applied pressure, with a liquid manometer; and the capacitance signal, with a standard capacitor substitution procedure. The gauge can be used so as to give quantitative electrical indications of displacement, volume change, or pressure difference; or can be used as a null indicator device in which an unknown pressure is balanced against a known one on opposite sides of the diaphragm. In order to achieve large volume an displacement sensitivities, small air gaps (5.10–4cm) are employed. Details of a construction method to assure small values are presented.

ISSN:0021-8979    

DOI:10.1063/1.1697817

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

Methods of measuring effective conductivities at microwave frequencies are described. These consist of either measuring the transmission loss in a long waveguide, or in measuring theQ's of resonant cavities. Both methods have been applied to measurements at 1.25 cm. Results for a number of metals are presented. Deviations from d.c. conductivity are thought to be due to surface roughness.

ISSN:0021-8979    

DOI:10.1063/1.1697818

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

In this paper are presented the approximate formulas for the components of radiation vectors of a short‐circuited circular loop with non‐uniform current distribution. The formulas are valid for the ratio of loop perimeter to wavelength of the order of 0.5 or less, and assume the current distribution of the hyperbolic cosine form. These formulas lead to the radiation intensity formula from which the expressions for the horizontal and vertical field patterns are derived. The latter formulas are further simplified assuming that the attenuation constant is much smaller than the phase constant. From the expression for horizontal field pattern, it follows that the pattern is symmetrical about the loop axis of symmetry. Moreover, this horizontal pattern exhibits a directional effect with maximum field in the direction of the feeder end of the loop. This directional effect is a function of loop dimensions. The theoretical horizontal pattern agrees very closely with the experimental one. From the expression for vertical field pattern, it follows that the non‐uniform current distribution produces a pattern intermediate between that for horizontal dipole and horizontal small loop with uniform current distribution. The field intensity in the zenithal direction is again a function of loop dimensions. Using the expression for radiation intensity, formulas for a radius of equivalent circular horizontal field pattern, power gain, average power gain, and radiation resistance are derived. It is shown that the average power gain is essentially a function of loop radius and decreases with the increase of the latter. Finally, the approximate expression for the attenuation constant of the transmission line equivalent to the loop is derived.

ISSN:0021-8979    

DOI:10.1063/1.1697819

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

Dynamic shortening of one‐half inch long copper cylinders is achieved by striking them with a hardened steel projectile at high velocities. The average strain rate was about 1200 per second. Energy per unit volume absorbed by the copper is plotted against strain. A true stress‐logarithmic strain curve is computed. This curve is compared with a similar curve derived from high speed tests on copper in tension.

ISSN:0021-8979    

DOI:10.1063/1.1697820

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

Field components for a transverse magnetic wave in a wave guide with two coaxial dielectrics are computed. A typical example is given to show the calculation of guide dimensions to reduce phase velocity to a preassigned value.

ISSN:0021-8979    

DOI:10.1063/1.1697821

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

The Fourier transform method of determining the response of a linear system to an arbitrary input signal often has its practical usefulness impaired because of difficulties in evaluating the necessary integrals. One possibility of overcoming these difficulties lies in the application of graphical methods to the transformations. Three such graphical procedures are described, all based upon fundamental properties of the transforms. Each method involves an analysis of the curves of the function to be transformed as a sum of curves of simpler functions whose transforms are known. The methods are useful in cases where the problem is too complicated for a simple analytic solution, or where part of the necessary data is available only in the form of a curve obtained, say, from experimental measurements of transmission characteristics or wave shapes. The accuracy of the methods is restricted only by that of the graphical plotting and curve fitting. If only approximate results are required, they may be obtained relatively quickly by these methods.

ISSN:0021-8979    

DOI:10.1063/1.1697822

出版商:AIP    

年代:1947

数据来源: AIP