中国牡竹属的研究(之一)

本文着重探讨了有关本属的概念、与邻近属之间的关系、属下分类系统以及本属在竹亚科中的系统位置。基于形态学的分析、比较,特别是数量分类学的验证,笔者支持广义牡竹属的概念,即赞成“甜竹属Sinocalamus McClure emend keng f.”应为牡竹属的异名。本文建立了牡竹属—新亚属,即龙竹亚属 Dendrocalamus subgen.Sinocalamus(McClure)Hsueh et D.Z.Li,stat.nov.;四个新组,即椅子竹组 Sect Bambusoidetes Hsueh et D.Z.Li,Sect.nov.;龙竹组 Sect.Draconicalamus Hsueh et D.Z.Li,sect.nov.;麻竹组 Sect.Sinocalamus(McCl.)Hsueh et D.Z.Li,sect.nov.;碟环慈竹组 Sect.Patellares Hsueh et D.Z.Li,sect.nov.。本文记载了牡竹属植物10新种、1新变种和3新变型;报道了6种牡竹属植物为中国分布新记录,3种云南分布新记录;证实我国并无 Dendrocal-amus strictus(Roxb.)Nees 的天然分布。至此,中国牡竹属已知有29种2变种4变型(不含原变种及原变型)。本文对牡竹属的区系特征也做了初步分析。     

Pathological changes in the mammary gland and biochemical changes in milk of the goat following oral dosing with leaf of the Avocado (Persea americana)

Two varieties of avocado leaves (Persea americana var Guatemalan and var Mexican) were administered to lactating goats. The Mexican variety was without effect. The Guatemalan variety in doses exceeding 20 g fresh leaf per kg bodyweight, produced damage to the mammary gland with decreased milk production. The lesions were characterised by oedema and reddening, with clots in the large ducts. Microscopically, there was widespread degeneration and necrosis of the secretory epithelium, the necrotic cells sloughing into the lumen. There was no significant cellular inflammatory response. Concentrations of antitrypsin in the milk, indicating changes in vascular permeability, increased rapidly 15 h after a single high dose, coinciding with palpable oedema. Concentrations of NAGase, indicating cell damage, increased after 24 h. Goats given multiple doses followed a similar pattern but the initial response was delayed. The toxic principle, and its mode of action in selectively damaging mammary secretory cells, remains to be determined.     

Infection of pigs with transmissible gastroenteritis virus from contaminated carcases

Sixteen 6-month-old pigs were exposed to transmissible gastroenteritis (TGE) virus by placing them in close contact with piglets infected at 1 week of age. Fourteen of the older pigs were slaughtered between 1 and 5 d after exposure to infection and their carcases dressed in simulated abattoir conditions. Samples of muscle, bone marrow and carcase lymph nodes were stored at -25 degrees C for at least 30 d and then homogenised and fed to groups of 1-week-old and 3-week-old pigs. Four of 12 one-week-old pigs died and TGE virus was isolated from intestinal contents of one of these. All pigs of both age groups developed neutralising antibody to TGE virus over the ensuing 4 w. The results indicate that carcases from pigs infected with TGE virus can represent a source of infection for susceptible pigs given access to them.     

A neoproterozoic snowball earth

Negative carbon isotope anomalies in carbonate rocks bracketing Neoproterozoic glacial deposits in Namibia, combined with estimates of thermal subsidence history, suggest that biological productivity in the surface ocean collapsed for millions of years. This collapse can be explained by a global glaciation (that is, a snowball Earth), which ended abruptly when subaerial volcanic outgassing raised atmospheric carbon dioxide to about 350 times the modern level. The rapid termination would have resulted in a warming of the snowball Earth to extreme greenhouse conditions. The transfer of atmospheric carbon dioxide to the ocean would result in the rapid precipitation of calcium carbonate in warm surface waters, producing the cap carbonate rocks observed globally.     

Polyolefin spheres from metallocenes supported on noninteracting polystyrene

To obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of alpha-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40 degreesC affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time.     

Photometry and spectroscopy of the GRB 970508 optical counterpart

An optical transient within the error box of the gamma ray burst GRB 970508 was imaged 4 hours after the event. It displayed a strong ultraviolet excess, and reached maximum brightness 2 days later. The optical spectra did not show any emission lines, and no variations on time scales of minutes were observed for 1 hour during the decline phase. According to the fireball and afterglow models, the intensity should rise monotonically before the observed optical maximum, but the data indicate that another physical mechanism may be responsible for the constant phase seen during the first hours after the burst.