We present the results of low- and high-resolution spectroscopic and multicolour photometric observations of two early-type emission-line stars, AS 78 and MWC 657. They were identified by Dong & Hu ...(1991) with the IRAS sources 03549+5602 and 22407+6008, respectively, among many other sources displaying a very strong infrared excess, $V-25 \ge$ 8 mag AS 78 is recognized as a photometric variable for the first time. A large near-IR excess radiation is detected in AS 78 and confirmed by new, higher-quality, data for MWC 657. Significant variations in the Balmer line profiles are detected for both objects. Modelling of the Balmer line profiles of AS 78 obtained in 1994 yields the following parameters of the star and its wind: $T_{\rm eff} \sim$ $17\, 000$ K, log Lbol/$L_{\odot} \sim$ 4.0, $\dot M$ ~ 10-6 $M_{\odot}$ yr-1. The photometric and new spectroscopic data indicate that the star's Teff increases with time, while the stellar wind changes its structure. Distances towards both objects are estimated on the basis of their radial velocities and the galactic rotation curve. Consideration of different options about the nature and evolutionary state of both objects leads us to suggest that they are binary systems containing a B-type intermediate-luminosity star and a gaseous disk around the less luminous component.
The method of ultrathin sections of unsquashed salivary gland polytene chromosomes of Ch. thummi was applied to their ultrastrual mapping. There was a good agreement between electron micrographs and ...Hägele's light microscopic map (1970) with respect to the pattern and number of bands. 94% of bands were identified in larval and prepupal chromosomes. In Ch. thummi, band thickness varied from 0.05-0.5 mum. Most characteristic were 0.2-0.3 mum bands. Morphologically, bands were classified as: continuous (frequently with holes and gaps), discrete, dotted and continuous-discrete, discrete-dotted. Band morphology is related to band size, such that smaller bands, as a rule, were also dotted. Bands beginning to puff likewise became dotted. Interbands in unsquashed chromosome sections were from 0.05-0.15 mum. The smallest interbands contained only fibrils, in the larger interbands few granules could be observed. This makes interbands distinguishable from a typical puff with many such granules.
Isolation of a fraction enriched with centrioles from bovine spleen cells is described. The method involves preparation of a nuclear-centriolar complex and detachment of centrioles from the complex ...by mechanical treatment in a homogenizer. Purification of centrioles was achieved by centrifugation through a sucrose concentration gradient after treatment by ultrasound, DNase I and Triton X-100. The resulting centrioles retain their in situ ultrastructure.
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