The response tensor for a highly relativistic magnetized thermal plasma

The transverse part of the linear response tensor is evaluated for a highly relativistic thermal electron gas, starting from Trubnikov's response tensor for an arbitrary temperature. Three contributions to the response tensor are important. The diagonal components are dominated by an unmagnetized term, which gives the familiar dispersion k2=w2p0, where wp0 is the proper plasma frequency. The difference between the diagonal components is larger in magnitude than the off-diagonal components, implying that the natural modes are nearly linearly polarized. This leads to a generalized form of Faraday rotation in which linear polarization is partially converted into circular polarization at a rate per unit path length ∝λ3 (λ=wavelength).

Glomerular capillary permeability in developing canines

The changes in glomerular permeability that occur during development were assessed in 1- and 6-wk-old canines by analyzing dextran-sieving curves obtained in six animals at each age. The fractional clearance of the smallest dextran molecules (18 A) was 0.97 +/- 0.02 (+/- SE) in both 1- and 6-wk-old animals, and it became progressively less at larger molecular sizes. The sieving curves were consistent with an isosporous model of a glomerular capillary. When axial changes in protein concentration were included in the mathematical model, the apparent pore radius was 62.7 +/- 1.7 and 61.7 +/- 1.69 A in 1- and 6-wk-old puppies, respectively (P greater than 0.7). The effects of developmental changes in hydrostatic pressure and renal blood flow were balanced by the increases in serum protein concentration and filtration fraction leaving the fractional clearances of macromolecules unchanged. In contrast, the total cross-sectional pore area per unit path length (Aw/delta x) increased during this 6-wk period by approximately 7.5-fold (from 1.39 +/- 0.2 to 10.55 +/- 3.0 10(-5) cm, P less than 0.0001), and the ultrafiltration coefficient rose from 0.012 +/- 0.002 to 0.093 +/- 0.012 ml X s-1 X mmHg-1 (P less than 0.0001). The findings reveal constancy of pore size and an increase in total pore area as a function of age. Analysis by classical pore theory yielded similar findings. We conclude that the predominant factor determining the rise in glomerular filtration rate during development is the large increment in Aw/delta x, which in turn is due to increases in the surface area and pore density of the glomerular capillaries.

The dielectric breakdown of low density gases I. Theoretical

Although the Townsend theory of dielectric breakdown of gases is generally accepted, it is also realized that it does not apply at low gas density. This embraces the range of gas density between a true gas breakdown and vacuum breakdown. Under such conditions, the concept of an average number of collisions per unit path length, fundamental in the Townsend theory, can not be applied. A review of previous theoretical work covering this region is given and it is shown that it is essential to calculate the number of ionizing collisions made by an electron moving from the cathode to the anode before any model of breakdown can be developed. A method of making such a calculation using Monte Carlo computer techniques is described with special reference to mercury vapour. This gas shows are-entrant from of Paschen curve, similar to that exhibited by helium . It is shown that the theory developed for pre-breakdown current growth can explain why some gases exhibit the re­mentrant form and others do not. However, complete verification is not possible because of lack of experimental data.

RADIATION FROM A LINE SOURCE IN A UNIAXIALLY ANISOTROPIC PLASMA

Two problems of radiation in a magnetized, incompressible plasma are investigated. The radiation characteristics of a line source of magnetic current are studied for the case in which the external magnetic field is infinite and oriented in a direction perpendicular to that of the source. The second problem that is treated is the radiation from a uniformly moving line charge. Two cases are considered, namely: (1) when the motion of the line charge is parallel and (2) when it is perpendicular to the direction of the external magnetic field. In each case it is found that there is a Cerenkov-type radiation for frequencies less than the plasma frequency. The frequency and the angular spectrum, as well as the total energy radiated per unit path length, are determined for both cases.

Diffusion Barriers in the Squid Nerve Fiber

The squid nerve barriers are formed by (a) the axolemma (membrane of the axon proper), a membrane 80 Å thick perforated by cylindrical pores 4.0 to 4.5 Å radius, and (b) the Schwann layer, constituted of numerous cells forming a layer one cell thick, crossed by 60 Å wide slit channels. If a molecule present in the axoplasm has to reach the extraneural space, it has to pass (a) the pores, and (b) the channels, in series, and the diffusion rate will depend on the effective diffusion areas per unit path length, Apd/Δx for the axolemma, and Acd/Δx for the Schwann layer. By addition, And/Δx, the transneural effective area for diffusion per unit path length is obtained. The diffusion rates of C14-ethylene glycol (2.2 Å radius), and C14-glycerol (2.8 Å radius) were measured. The diffusion rate of H3-labeled water (1.5 Å radius) has been previously determined. The results expressed in terms of And/Δx (mean values ± SD, referred to 1 cm2 of nerve surface) are 5.3 ± 1.4 cm for water, 2.5 ± 0.4 cm for ethylene glycol, and 0.29 ± 0.03 cm for glycerol. Theoretical values for And/Δx of 2.5 and 0.83 cm for ethylene glycol and glycerol have been calculated. The agreement between the theoretical values for And/Δx and the experimental ones supports the diffusion barrier model described above.