Detection of rubella virus in fetal and placental tissues and in the throats of neonates after serologically confirmed rubella in pregnancy

From 35 therapeutic abortions performed because rubella had occurred at 2–19 weeks of pregnancy, 120 fetal organs, 12 specimens of mixed products of conception, and 15 placentae were tested for rubella virus. Virus was isolated from 10 out of 11 fetuses (91 per cent) from women infected at 2–8 weeks, from 5 out of 8 (63 per cent) infected at 9–10 weeks, and from 2 out of 16 (13 per cent) infected at 11–19 weeks. Hybridization tests for viral RNA on 39 fetal organs from eight cases revealed infection in four additional fetuses. Virus was isolated from only 3 out of 15 aborted placentae, but hybridization tests on six placentae revealed infection in three additional specimens. Hybridization was superior to virus isolation for detecting rubella infection in products of conception and is therefore potentially the better method for examining chorionic villus biopsies. Rubella virus was isolated from the throats of 4 out of 9 infants (44 per cent) infected during the first 12 weeks of gestation, but from none of 13 infected after 17 weeks. Infants in the latter group are unlikely to infect susceptible contacts.     

澳大利亚自然保护区系统与管理

澳大利亚是全球生物多样性最丰富的12个国家之一。于1879年4月26日建立的澳第一个国家公园是世界上第二个国家公园，澳保护区系统类型齐全，名称不一。大多数保护区由各州自行管理。     

Fluid mechanics of the mussel gill: The lateral cilia

Quantitative data on the water currents produced by the ciliary tracts of the gill filaments are needed to understand the fluid mechanics of suspension feeding in bivalves, as well as in other ciliary suspension feeders. This paper investigates the water currents produced by the bands of lateral cilia, as studied on isolated gill filaments, gill fragments, and intact gills of the mussel Mytilus edulis L with severed adductor muscles. The metachronally beating cilia produce oscillatory currents near the oscillating enveloping surface of the ciliary bands and rectilinear currents, the interfilamentary through-currents, farther from the surface. It is suggested that the oscillatory currents play an important role in the fluid mechanical capture of suspended particles. In the intact gill the interfilamentary currents pass the bands of lateral cilia at velocities that are two or more times higher than those generated by the bands of isolated filaments. The mussel gill is compared with an optimized peristaltic pump.     

Population differences in gonad and pyloric caeca cycles of the New Zealand seastarSclerasterias mollis (Echinodermata: Asteroidea)

Inshore and offshore populations ofSclerasterias mollis (Hutton, 1872) were sampled on the outer continental shelf off the Otago Peninsula, New Zealand, and their nutritional and reproductive cycles are described from 1985–1986. Histological changes in the gonads are generally typical of other asteroids. The gametogenic cycle takes 12 mo. The gonad and pyloric caeca indices in both females and males had an inverse relationship.S. mollis accumulates nutrients in the pyloric caeca during summer and early autumn. The gonads develop in the autumn and winter. Offshore seastars were much larger and had significantly higher gonad and pyloric caeca indices than inshore individuals. These differences in body sizes and organ indices arise from differences in food availability and/or population density.     

A hydromechanical principle for particle retention in Mytilus edulis and other ciliary suspension feeders

It is generally thought that the laterofrontal cirri of the bivalve gill act as filters that retain suspended particles in the through current and transfer the particles onto the frontal surface of the gill filaments. In Mytilus edulis calculations indicated that if water passed between the branching cilia of the cirri that are assumed to constitute the filter the pressure drop needed would amount to about 10 times the actual pressure drop across the whole gill. Thus, instead of acting as filters the laterofrontal cirri seem to move water. Presumably, the cirri together with the frontal cilia produce the water currents along the frontal surface of the gill filaments. Particle retention in the bivalve gill implies the transfer of suspended particles from the current of water about to enter an interfilamentar space into a neighbouring frontal surface current. The complex three-dimensional pattern of flow that arises where the 2 systems of current meet is characterized by steep velocity gradients. Particles that enter such steep, steady velocity gradients become exposed to transverse forces that cause the particles to migrate perpendicularly to the direction of flow. Whether particles enter the surface current, i.e. are retained, or they stay within the through current andescape, depends primarily upon particle size, and upon the steepness and height of the gradients within the boundary zone between the surface current and through current. Further studies are needed to evaluate the capacities and relative importance of this hydromechanical particle-trapping mechanism in suspension feeding bivalves. It is suggested that in downstream particle-retaining systems, e.g. on the tentacles of polychaetes and entoprocts, velocity gradients between through currents and surface currents also act as the particle-collecting mechanism.     

The taxation of nonreplenishable natural resources revisited

The theory of nonreplenishable resource extraction has been extended to allow for extraction costs which increase as deposits are increasingly depleted. In these cases, profit maximization may result in the cessation of extraction before reserves are totally exhausted. The effect of various taxation policies on optimal extraction patterns in these models are derived. With a few exceptions, the results are that the imposition of a tax will cause operators to extract at faster rates over shorter periods of time and to reduce the total amount of ore extracted. The analysis allows for an output price which increases over time.     

Changes in polybrominated diphenyl ether (PBDE) levels in cooked food

Food surveys for levels of toxic chemicals frequently report the levels on an uncooked basis. It is known that cooking may in some conditions decrease the amount of dioxins and related chemicals in food. Surveys of polybrominated diphenyl ether (PBDE) levels in food to date show data from uncooked food only. In this article, it was shown that broiling, with fat dripped from the foods reported here, ground beef, ground lamb, catfish, trout, and salmon, reduces the amount of PBDEs in these foods. This suggests that calculations of food intake need to take into consideration levels in the cooked food rather than in the uncooked food.