Regular Disk Research Articles

A model for symbiotic star Z Andromedae

An analysis of the results of observations of the symbiotic star Z And has shown that no definite model can be derived at present on their basis. If the hot component is essentially an accreting white dwarf with a hydrogen-burning shell source, then the gas envelope must be optically thin for Lc-emission and itsTe must be in the neighborhood of 2.6×104K. And if the hot component is a Main-Sequence star with an accretion disk around it, then it is classified with red dwarfs. The electron temperature of the gas envelope must be 1.5×104K. The luminosity of the hot component at the minimum of its visual brightness is only a few times lower than its Eddington limit. Therefore, as the accretion rate goes up, the initial increase in its brightness (ΔU≲1m.5), unaccompanied by any perceptible changes in the spectrum of Z And, will be followed by disintegration of the regular disk and flare of the star in the visible range. In the same model, partial eclipses of the hot source must occur. They seem to be observable on the star's light curve in theU band. Substitution of a solar-type star for the first-named component in the binary ‘red dwarf + red giant’ system will lead to a significant decrease in the excitation of the combination spectrum.

Computer simulation of hard-disc packings with spherical boundary conditions

Random packings of hard discs are generated on the surface of a sphere by a “successive compression” technique. Since the discs follow the curvature of the sphere their shape is similar to that of watch glasses. The disordering influence of curvature prohibits hexagonal packings. Increasing the number of discs (N) means that the particles shrink compared with the supporting sphere. Accordingly, the effect of curvature decreases. The random dense-packing fraction ηRDP(N) obtained in the compression runs is seen to increase with increasing N. The calculations result in a limiting packing fraction ηRDP(N→∞) between 0.866 and 0.874 with an average contact number between 3 and 4. This may be compared with η= 0.907 and contact number 6 for (Euclidean) hexagonal packing. The possibility of regular disc packings on the surface of a sphere is also considered.

The Slotted Conical Disk Spring

The slotted conical disk spring is a modification of the regular conical disk spring or Belleville spring inasmuch as it has regularly arranged slots extending from the inside diameter. A single disk of the slotted type undergoes a larger deflection at a smaller load than a regular disk spring of comparable dimensions, thereby combining some of the advantages of the disk spring and the cantilever type spring in a single unit. It is used, where stacking is undesirable, a relatively large outside diameter is tolerable, and a regressive load-deflection-diagram is desired, like in clutch applications. The theory presented here allows the design of slotted disk springs without the lengthy trial and error procedure that has been used so far. Experiments show the validity of the new theory.

Bro, en senglacial boplads på Fyn

Bro, en senglacial boplads på Fyn

OBSERVATIONS ON THE DETERMINATION OF ANTIBIOTICS IN MILK

A so-called “2 hour” test for the detection of penicillin in milk showed no advantage over the regular disc assay procedure. Sensitivity of the latter test was increased by (1) reducing to 4 ml. the volume of seeded agar per plate, (2) refrigerating “planted” plates for 2–6 hours, (3) avoiding overnight incubation at 37°C, and (4) using the larger (0.5 in.) paper discs.Dornbush's disc assay procedure using B. cereus for detecting aureomycin was. also found to be less sensitive than claimed. Zones of inhibition were less sharply defined than with penicillin. A spore suspension was successfully substituted for a broth culture here.The methylene blue reduction type of test showed good sensitivity in detecting aureomycin. B. cereus was more sensitive than B mesentericus, and broth cultures more than spore suspensions.

Effect of Particle Size on the Diffraction Image in Microscopy with Narrow-Coned, Axial Illumination

The distribution of energy density is derived for the diffraction image produced by an Airy type objective of a single, uniform, opaque or transmitting particle located in a uniform, transmitting surround and illuminated by a narrow cone of axial illumination. It is shown that for a large class of particles the diffraction image can have an irregular variation in energy density in addition to a regular variation and that these variations are in accord with experiments performed with opaque particles. The irregular variation can appear as a secondary Airy disk located well within the regular Airy disk. The development of the diffraction image with increasing radii of disk-shaped particles is described. The equations which govern this development are adapted to the determination of the radius of the particle from linear or photometric measurements upon the diffraction image. The smallest measurable radii are restricted by practical limits rather than by physical limits as in the resolution of two particles. The practical limit is about 0.6 Airy unit for the linear measurements but may fall below 0.3 Airy unit with photometric measurements.