摘要:

The influence of the exchange of heat between a gas flowing through a tube and the outside atmosphere on the pressure in the gas stream is usually overlooked. Theoretical investigations show, however, that this influence is marked in the case of large stream velocities, approximating the velocity of sound. In addition, the theory permits us to state that the heat exchange is possible only when the stream velocity is maintained beyond certain limits. For stream velocities within these limits, heat exchange is not possible.The conclusion is reached that the velocity of flow in the tube, if the tube is heated or cooled, shows a natural and permanent tendency to reach the velocity of sound, after which the heat exchange is no longer possible.Finally, this theoretical investigation shows that the present view that the heat conductance coefficient increases continually with the stream velocity is wrong. This coefficient will be equal to zero when the stream velocity reaches the velocity of sound. This means that it will reach a certain maximum value corresponding to a value of stream velocity which is not exactly known but which will be less than that of sound.

ISSN:1923-4287    

DOI:10.1139/cjr45a-001

出版商:NRC Research Press    

年代:1945

数据来源: NRC

摘要:

The resonance energyErand the absorption coefficient for self-indicationKrwere measured for the neutron capture processes leading to the formation of the radioactive isotopes Mn56, Ga70, Ga72, and Pd109. For Mn, in addition the level width Γ was measured. The values found are the following: For Mn56,Er = 17 e.v.,Kr = 1.3 cm.2per gm., and Γ = 1.67 e.v. For Ga70,Er = 100 e.v. andKr = 3.9 cm.2per gm. referred to the absorbing isotope. For Ga72,Er = 50 e.v. andKr = 8.2 cm.2per gm. referred to the absorbing isotope. For Pd109,Er = 22 e.v. andKr = 37 cm.2per gm. referred to the absorbing isotope.Part of the measurements were performed employing simultaneously boron and the element itself as absorbers. For all the activities investigated, filtering through boron did not appreciably affect the absorption coefficient for self-indication, and, reciprocally, filtering through the element itself did not affect the absorption coefficient in boron. These facts are a good indication that most of the activity induced by non-thermal neutrons is due to one resonance level.In the case of Mn, the measured level width led to an approximate agreement between the measured absorption coefficient in the thermal region and the one calculated from the one-level formula.

ISSN:1923-4287    

DOI:10.1139/cjr45a-002

出版商:NRC Research Press    

年代:1945

数据来源: NRC

摘要:

In this communication there is described the effect of increasing the stimulated area of the central or foveal part of the retina upon the critical frequency of flicker. In order to do this, the vision of one eye—the right—was directed through a long black tube at a screen of constant brightness, the different areas stimulated being obtained and measured by using holes of various diameters in black paper placed over the far end of the tube. Between this end of the tube and the screen was a rotating sectored disk with which the fusion frequency was obtained and measured.It was found that the graph obtained by plotting the measurements has three breaks in it which correspond to the five central retinal zones delineated by histologists It was also found that the fusion frequencies are proportional to the logarithms of the diameters (or areas) of the retinal zones; or primarily, to the number of cones stimulated.A similar set of measurements was made on the periphery of the retina which showed both similarities to and differences from the central or foveal effects.

ISSN:1923-4287    

DOI:10.1139/cjr45a-003

出版商:NRC Research Press    

年代:1945

数据来源: NRC