摘要:

The readjustment of the mean exit pressure to its steady‐flow equilibrium level, following the arrival of a shock wave at an open end of a duct, has been investigated. For a cylindrical duct in which the gas is initially at rest, a solution based on acoustic theory was obtained in the form of a Fourier integral. The nature of this solution was established as a series of damped harmonic oscillations superposed on an exponential pressure decay. The actual pressure decay curve was obtained by numerical integrations. The same problem was also attacked experimentally using a shock tube of 3.23 inches i.d. From pressure records taken some distance from the open end, the ``effective'' exit pressure was derived.It was found that the exit pressure deviates appreciably from its steady‐flow equilibrium value during a time in which a sound wave could travel about three duct diameters. Satisfactory agreement between theory and experiment was observed for shock pressure ratios up to about 1.9 (in air) although, near this limit, significant deviations owing to wall friction were observed toward the end of the pressure decay region. For still stronger shocks, the influence of the decay time on the phenomena inside the duct becomes unimportant while friction effects dominate. The possible significance of the lag in the establishment of steady‐flow boundary conditions in practical applications is discussed, in particular, for cases where the acceleration of the gas by the reflected expansion wave may be of importance.

ISSN:0021-8979    

DOI:10.1063/1.1722149

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The magnetic domain structure of polycrystalline grain‐oriented 3¼% silicon steel has been investigated by the magnetic‐powder‐pattern technique and the orientation of individual grains determined by the etchpit optical‐goniometer technique. A semiquantitative relationship has been found between the domain patterns and crystalline orientation. The observed powder patterns can be grouped into five types, depending upon the angle, &phgr;, between the rolling plane and the <100> direction lying closest to the rolling plane. When the rolling direction is known and &phgr; is <10°, semiquantitative grain‐by‐grain orientation information can be obtained solely from the domain patterns.The behavior of two of the types of patterns in an applied magnetic field is shown, and on the basis of this behavior, a three‐dimensional domain configuration is proposed for one of the less complicated surface patterns.

ISSN:0021-8979    

DOI:10.1063/1.1722150

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Water superheated to the limit in an open tube develops aninternalnegative pressurePn(tending to tear the molecules apart) equal to the saturation vapor at that temperature, less one atmosphere. Kendrick, Gilbert, and Wisner heated water in an open thin‐walled capillary U‐tube to 270°C for 5 sec before it exploded (Pn=53 atmos). Using their method, the writer heated three tubes to 264°, 266°, and 267°C for 5 sec or more before explosion occurred (Pn=48 to 51 atmos). The cohesive strength of water is thus sufficient to withstand aninternalnegative pressure of over 51 atmos at 267°C. At this temperature an additional negative pressure (appliedexternallythrough centrifugal force) would rupture the water column. It has been predicted from van der Waals' equation that theexternalnegative pressure which the system could withstand would vanish at 273°C, in fair agreement with experiment.

ISSN:0021-8979    

DOI:10.1063/1.1722122

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The DuBridge variation of the Fowler theory of photoelectric emission was utilized to determine the work function of the borides of La, Pr, and Nd. The work functions of LaB6, PrB6, and NdB6were found to be 2.74 ev, 3.12 ev, and 4.57 ev, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1722123

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The role of space charge as a factor influencing the potentials and potential gradients in a mass spectrometer ion source of the electron bombardment type is calculated. Planar equipotential surfaces are assumed, and the analysis then becomes that of a plane parallel positive ion diode. The ``cathode'' of the ion diode may be either emission‐limited or space‐charged‐limited. The analysis considers the charge of the electrons in the ionizing sheet and the charge of the positive ions in the diode.At a critical gas pressure the influences of the positive and negative charges on the potential of the ionizing region are equal and opposite, for small ionizing current. This concept leads to a pressure normalization in terms of the critical pressure. For a given source geometry and electron bombarding energy one can construct universal curves which give the potentials and the potential gradients as a function of the normalized gas pressure and the ratio of the ionizing electron current density to the repeller voltage. Experimental data are in agreement with the predictions of the theory.

ISSN:0021-8979    

DOI:10.1063/1.1722124

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The results of a measurement of the slowing down distribution in water of neutrons from a point fission source to indium resonance energy, 1.458 ev, are given. The second, fourth, sixth, and eighth moments of the measured distribution are calculated and have the values,r¯2=184.7 cm2,r¯4=1.222×105 cm4,r¯6=2.27×108 cm6, andr¯8=8.6×1011 cm8.

ISSN:0021-8979    

DOI:10.1063/1.1722125

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The mean square slowing down length,r¯2, has been measured for two aluminum light water mixtures, the aluminum‐to‐water volume ratios being 1:1 and 1:2 by volume. The values ofr¯2obtained are 460.7 cm2and 297.4 cm2, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1722126

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Metal semiconductor contacts of a number of different metals were made onn‐ andp‐type germanium using jet etching and plating techniques. Current voltage curves taken on 12 of these metals on 5 ohm‐cmn‐type germanium showed rectification which follows the diode equationJ=J0(eqV/kT−1). No correlation was found between the reverse saturation current densities of these diodes and such properties of the metals as work function, electromotive force, etc. For those metal contacts possessing the lowest saturation current densities, calculations indicated the current crossing the contact was to a large percent hole current and that the magnitude of the hole current was controlled primarily by the geometry of the diode. All metals plated on 5 ohm‐cmp‐type germanium produced ohmic contacts of resistivity comparable to the spreading resistance expected for the diode geometry used.For indium diodes, a study of rectificationversusresistivity indicated that the barrier produced on bothn‐ andp‐type germanium with plated contacts is one to electron flow rather than hole flow. When the assumption of only hole current crossing the barrier was made, it was shown that the I–V curves calculated from the diode theory, for different resistivities of germanium, were in qualitative agreement with the measured curves. Curves of zero voltage conductanceversustemperature for different resistivities of germanium were also found to be in good agreement with those calculated on the assumption of all hole current.

ISSN:0021-8979    

DOI:10.1063/1.1722127

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Self‐sustained ion and electron plasma oscillations have been observed simultaneously in an ion neutralized electron beam traveling in a transverse magnetic field. The observed frequencies of oscillation agree with the Langmuir‐Tonks theory for plasma oscillations. Electron plasma oscillations occur when the electron plasma frequency equals the gyro frequency of a circular orbit in the magnetic field.

ISSN:0021-8979    

DOI:10.1063/1.1722128

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The ac power flow in an electron beam moving in weak electric fields is given a precise definition. Since it is a quantity quadratic in the applied field strength its evaluation requires the quadratic perturbation theory of the beam to be worked out. Quadratic expressions in the first‐order variables of the beam and circuit may also be written down which have the dimensions of power and are shown to satisfy a conservation theorem. The relations between the exact quantities of the nonlinear theory and the constructs from linear theory are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722129

出版商:AIP    

年代:1955

数据来源: AIP