Cell Volume Regulation Studies with the Electron Microprobe

Lumbricals from the hind feet of young rats are dissected free, stretched to approximately 125% of resting length, and mounted on individual, simple plastic forms. After recovery in physiological saline, the isolated muscles are incubated for periods of 40 to 60 min. in one of a series of hypertonic bathing solutions. The composition of each bathing solution is identical, except for osmolality which is increased with lactose. At least one muscle from each animal is incubated in a control solution to serve as a control muscle for that particular set of 5 to 8 muscles. Mounted muscles are removed from the bathing solutions and quickly plunged into chilled liquid propane. Tissue is freeze-dried at low temperature, fixed with osmium tetroxide vapor, and embedded in brominated EPON 826. Dilution of the embedding medium by tissue solids, assessed by reduction of the embedding plastic Br Lα signal, is used to establish intracellular hydration; or conversely, intracellular solids fractions. The Br Lα signal is monitored along with S Kα, K Kα, Cl Kα, Na Kα, and the continuum region from 4.2 to 7.2 keV using a simultaneous ED-WD spectrometer electron probe microanalyzer. This provides sufficient information to present intracellular concentrations in units of mmol/kg wet weight, mmol/kg water, or mmol/kg dry weight. Cell volume change relative to a suitable control is determined from the ratio of sulfur signals from the experimental and control cells. The response of cells to hypertonic challenge is assessed by comparing actual cell volume change with the change expected of a simple osmotic bag. Simultaneously, the intracellular electrolyte data provides information on the mechanism of cellular response to osmotic shifts

Optically thick envelopes around ULXs powered by accreating neutron stars

Magnetized neutron stars power at least some ultra-luminous X-ray sources. The accretion flow in these cases is interrupted at the magnetospheric radius and then reaches the surface of a neutron star following magnetic field lines. Accreting matter moving along magnetic field lines forms the accretion envelope around the central object. We show that, in case of high mass accretion rates $\gtrsim 10^{19}\,{\rm g\,s^{-1}}$ the envelope becomes closed and optically thick, which influences the dynamics of the accretion flow and the observational manifestation of the neutron star hidden behind the envelope. Particularly, the optically thick accretion envelope results in a multi-color black-body spectrum originating from the magnetospheric surface. The spectrum and photon energy flux vary with the viewing angle, which gives rise to pulsations characterized by high pulsed fraction and typically smooth pulse profiles. The reprocessing of radiation due to interaction with the envelope leads to the disappearance of cyclotron scattering features from the spectrum. We speculate that the super-orbital variability of ultra-luminous X-ray sources powered by accreting neutron stars can be attributed to precession of the neutron star due to interaction of magnetic dipole with the accretion disc.Comment: 8 pages, 6 figures, accepted for publication in MNRA

The Doctor and Society

The doctor, no less than any other scientist, is a member of society. His situation, however, is unique, inasmuch as in an age of technocracy he must remain human. Despite the pressure of his own discipline he should be an educated person in the general meaning of the word. The necessary attributes of this state are outlined and an jdeal is formulated

The response of four strains of White Leghorn layers to two levels of dietary phosphorus

The purpose of this experiment was to determine the response of four high producing strains of Single Comb White Leghorn-type hens to dietary phosphorus levels of 0.4 and 0.6 percent as measured by shell quality, egg production, egg weight, feed consumption, body weight and mortality. This study was conducted for 11 — 28 day periods. Results were subjected to analysis of variance and when significance was determined (P ≤ 0.05) mean separation was performed using Duncan\u27s Multiple Range test. The results showed no significant relationship between dietary phosphorus level and egg production, egg weight, feed per hen, feed per dozen or mortality. Dietary phosphorus level had a significant effect on egg shell quality and body weight in that the lower phosphorus diet resulted in significantly improved egg specific gravity but reduced final body weight and body weight gain. Efes shell quality declined wdLth length of lay and responded to environ-mental temperature by improving during the final period which was much cooler than the previous periods. Significant differences between strains were observed for all parameters studied and a significant difference in strain response to the two diets was observed for egg production. One strain had significantly lower egg production on the 0.4 percent phosphorus diet whereas another strain improved egg production on the same diet. There appeared to be differences in strain response for mortality but these differences proved statistically nonsignificant