摘要:

Sound waves passing through arcs in air are photographed with a rotating mirror camera, whereby the sound velocity in the arc core is determined. From the observed sound velocity the arc temperature may be calculated by a method previously described. The arcs measured by this method, together with the sound velocities and corresponding temperatures, are:Cored carbon1.85×105 cm sec.−15500∘KNaCl cored C1.574740Al cored C2.146160W cored C2.176220W 6 mm electrodes2.045950W 9.5 mm electrodes2.276440W&sngbnd;Fe2.136150Fe&sngbnd;Fe welding arc2.086020The experimental error corresponds to ±100° at 5500°K. The experimental requirements of the sound source are discussed in detail. The gas temperature across the arc core is found to be constant within the error of observation. For most of the arcs studied the current density and electric gradients have also been measured, so that the data may be used as a test of the thermal ionization theory. The ``effective ionization potential (I.P.)'' of the arc gas is in all cases above the I.P. of the metallic vapor and below that of nitrogen. For the W arcs the effective I.P. is 15 volts, midway between the first I.P. of O2and N2. For the arcs other than tungsten, this quantity is lowered appreciably by electrode vapor. A small partial pressure of Na lowers the arc temperature by approximately 1500°. The temperature of a welding arc between a coated iron welding rod and a steel plate is measured to be 6000°, from which the dissociation of the arc atmosphere is found to be 81 percent. This high degree of dissociation points to the importance of the dissociation‐diffusion‐recombination process for heat transfer in welding arcs and explains the recently reported negative results of attempts to arc weld in pure argon.

ISSN:0021-8979    

DOI:10.1063/1.1745272

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

The shot effect of secondary electron currents from plates of triode tubes was measured at 105cycles. Calculations of the electronic charge from shot effects of temperature‐limited primary currents, to check the method, agreed with Millikan's value within 1 percent. Measurements were made on five tubes having different secondary emissivities. The average number of secondaries per primary electron, &ohgr;, ranged from1to4.5.The variation of &ohgr; with energy of the primaries is shown to agree qualitatively with existing theory. In every case the shot effects of both grid and plate currents were measured. Campbell's general expressions for the shot effect of secondary emission plate currents were extended to grid currents. From the observed differences between grid and plate shot effects it is concluded that secondary emission and primary impact are simultaneous within 10−6second or less. The large shot effects found at high values of &ohgr; are correlated with the fluctuations of &ohgr; from one impact to another. A qualitative analysis of secondary emission processes shows that, from these data, information can be obtained as to the number of reflected primary electrons and the number of primaries which emit no secondaries. The results obtained are in reasonable agreement with data obtained by other methods.

ISSN:0021-8979    

DOI:10.1063/1.1745273

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

Measurements have been made of the equilibrium permeabilities of softwoods to air of different relative vapor pressures. Transverse sections less than the average fiber length in thickness, in which the open cavities account for practically all of the permeability, show practically no change in permeability with changes in the equilibrium relative vapor pressure. Sections thicker than the maximum fiber length, the permeabilities of which are dependent upon the size of the pit openings, show an increase in permeability with a decrease in equilibrium relative vapor pressure. When the square root of the permeability is plotted against the moisture content of the wood in equilibrium with the various relative vapor pressures of air, practically a linear relationship is obtained from 0 to 20 percent moisture content. At higher moisture contents the permeabilities are considerably less than the linear relationship calls for. This is due to films of water forming across the capillaries. Higher pressures than those used are required to overcome the effect of the surface tension of the water in these capillaries. A new means of determining the distribution of size of openings in a porous membrane based on these findings is given.

ISSN:0021-8979    

DOI:10.1063/1.1745274

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

In previous papers we studied the effects of forces, produced by metabolism, on the mechanical stability of the metabolizing system. In this paper various other effects of those forces are discussed. First of all it is shown that, whenever those forces are of such a nature as to make the system unstable and cause its eventual division, their effect is also that of increasing the size of the system. This reminds of the relation between rate of growth and division in living cells. Further the effects of those forces on molecules and colloidal particles, present in the system, but not directly participating in metabolism, are studied. It is shown that those forces produce a nonhomogeneous distribution of those molecules and particles, and thus alter the structure and the physical constants of the system. For single molecules the effect is negligible; but for colloidal particles of a size above 10−5cm it may be very large and may produce a concentration of those particles at the surface of the system, altering thus the permeability of the latter. Those effects are present only as long as the system metabolizes. This may have a bearing on the sudden change of permeability of living cells after death. Since, under the influence of those forces the permeability of a system becomes a function of the intensity of the metabolizing processes, the fundamental equations describing such systems are much more complicated than those studied hitherto. One particularly interesting feature is that those equations now possess in general not one, butseveral stable solutions,so that the specification of all the parameters, which determine the external conditions, does not determine the configuration of the system in a unique way. As shown previously, such a situation leads to various hysteresis phenomena. One type of such a hysteresis, particularly interesting from the point of view of possible biological applications, is illustrated on a numerical example. It consists in an irreversible transition of the system from a state of slower growth and greater stability into a state of more rapid growth and lesser stability, under the influence of certain reversible changes in the environment of the system.

ISSN:0021-8979    

DOI:10.1063/1.1745275

出版商:AIP    

年代:1935

数据来源: AIP