We describe a recently completed network of densitometric tree-ring time series representing various aspects of tree-growth for up to 200 years at 69 sites spread across the northern North American conifer zone from Yukon to Labrador. Duplicate cores, from 12 to 15 trees per site, provide time series for a suite of growth parameters including earlywood (spring), latewood (summer) and total (annual) ring widths and mean earlywood, mean latewood, minimum and maximum ring density. These data form the basis for extensive analyses of intra- and inter-site parameter comparisons and regional climate/tree-growth comparisons. Five large-scale regional chronologies do not suggest that any anomalous growth increases have occurred in recent decades, at least on these regional scales, despite the observed changes in atmospheric composition and climate. 相似文献
The effective management of salmonid fisheries requires that the factors influencing variation in the abundance of stream populations are understood. The use of habitat models to explain the spatial component of population variance offers potential for management, but has not previously been set in the context of long term variation in population abundance because of the lack of suitable data sets. This paper examines contributions of spatial and temporal factors lo fish density variance using a 10-year data set from five tributaries of the River Conwy, North Wales. Recently developed habitat models were applied to the data to test their ability to explain nominal spatial variance. Spatial variance accounted for between 21 and 62% of the overall variance of salmonid abundance, and habitat models explained up to 95% of the spatial variance component. Synchrony in population variation amongst sites within and between tributaries is described, and some of the factors that may influence this are discussed. 相似文献
Abstract— Primary cultures of bovine brain capillary endo-thelial cells (BCEC), possessing tight junctions and high levels of γ-glutamyl transpeptidase, were used as an in vitro model for the blood-brain barrier. The interaction of acetylated low density lipoprotein (AcLDL) with BCEC was studied to characterize the scavenger receptor on these cells. A saturable high affinity binding site was found with a dissociation constant of AcLDL of 5.4 μg/ml (3.1 n M ) and a maximal binding ranging from 284 to 626 ng of AcLDL/mg of cell protein for eight primary cultures, and independent of the presence of calcium. Cell association was coupled to degradation, and both could be effectively competed for by polyinosinic acid and AcLDL but not by low density lipoprotein or by high density lipoprotein. Prolonged incubation showed an accumulation of the ligand in the cells. The rate of degradation of AcLDL was ∼ 10–20-fold lower in BCEC than that of peripheral endothelial cells. No evidence for lysosomal degradation could be obtained. Binding of 1,1'-dioctadecyl-3,3,3,3'-tetramethylindocar-boxyamine perchlorate-labeled AcLDL by BCEC was observed, which could be competed for by an excess of un-labeled AcLDL and polyinosinic acid. We have shown that in vitro BCEC possesses specific binding sites for AcLDL, whereas these cells show a relatively low degradative capacity. 相似文献
Reduction in nutrient loss during dialysis cultivation of Escherichia coli on a glycerol medium was investigated. A dialysis reactor with an inner fermentation and an outer dialysis chamber was used. Aerobic condition was maintained by limiting the glycerol feed rate to an optimum value which was estimated from the oxygen requirements for glycerol oxidation and oxygen transfer capacity of the reactor. High reduction in nutrient loss was achieved by using water as the dialyzing fluid. However, osmotic movement of water from the dialysis to the fermentation chamber was observed, and the final cell concentration was low. With a nutrient-split feeding strategy (feeding glycerol directly to the fermentation chamber and dialyzing with salt solution), glycerol loss was small, there was no osmotic flux of water to the fermentation chamber, and the cell concentration was high. Both glycerol and salt loss could be avoided, and a cell concentration of 170 g/L was obtained when the dialysis process was substituted by addition of XAD adsorbents to the dialysis chamber. Application of this nutrient-split feeding strategy to cell cultivation in a stirred tank reactor, coupled with dialysis in external dialyzer modules, resulted in low cell concentrations. (c) 1993 Wiley & Sons, Inc. 相似文献
To determine the potential for adaptation to a local biotic environment, we examined the magnitude and nature of genetic variation in response to neighboring plants within a natural population of the native California annual, Nemophila menziesii. A total of 22 plants from a natural population were crossed in three reciprocal factorials. The progeny were grown in a greenhouse in nine treatments that varied in conspecific density and in the density of a naturally co-occurring grass species, Bromus diandrus. Increasing the density of each species significantly reduced individual survival, fruit number, and dry weight. Among survivors, we found small to moderate heritability of dry weight within treatments. Additive genetic correlations (rA) of dry weight between competitive regimes were generally large and positive. In no case were they significantly different from 1, as expected under the null hypothesis that the relative performance of the genotypes under consideration is the same in all environments. On the basis of these results, we cannot conclude that the structure of genetic covariation within this population would promote genetic differentiation in response to locally varying conditions of density of these two species. Aspects of the experiment that may have compromised our ability to detect rA differing from 1 are discussed. 相似文献
Human plasmain vitro inhibits the growth of coagulase negative staphylococci,S. epidermidis, which may be pathogenic in the immunocompromised host. To determine the antimicrobial components, serum was fractionated by column chromatography, which revealed that elution areas where lipoproteins can be yielded had high antimicrobial activity againstS. epidermidis. Therefore, lipoprotein fractions, including very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL), were separated by ultracentrifugation and incubated withS. epidermidis. All 3 lipoprotein fractions suppressed bacterial growth within the first 3 h but VLDL enhanced bacterial growth after 9 h of incubation compared with the control. HDL, however, inhibited bacterial growth throughout 21 h of incubation.To confirm these results, serum from healthy volunteers was separated by ion exchange column chromatography and again by HPLC to purify the antimicrobial fraction. In the protein analysis with gradient polyacrylamide-SDS gel, apolipoprotein Al (apo Al), which is a major apolipoprotein of HDL, was detected in the antimicrobial fraction. Therefore, this fraction was loaded onto an immunoaffinity column coupled with the anti-apo Al monoclonal antibody (Mab). Unbound fraction had no antimicrobial activity, but anti-S. epidermidis activity was recovered from the bound fraction which consisted mainly of apo Al, All and apo C in protein composition.These results indicated that the antimicrobial activity was associated with the apo Al-containing lipoprotein particles (HDL). This property of HDL may directly affect bacterial growth and promote the self-defense mechanisms of normal and immunocompromised individuals. 相似文献
1. 1. The influence of ethnic differences is discussed with reference to the following issues.
2. 2. It has been found that total numbers of active sweat glands increase in tropical populations compared with people from northern latitudes.
3. 3. It has also been observed that the active sweat glands of Eskimos are fewer than those of Caucasians.
4. 4. The rate of the evaporated sweat loss was calculated by measuring body weight loss and it was found that the evaporated sweat loss of Caucasians is larger than that of Japanese in the same climate.
5. 5. Meteorological factors might have been responsible for the smaller loss in Japanese compared with that of Japanese-Americans.
6. 6. Under the same experimental conditions, it was observed that there were little or no differences between the Caucasians and Negros.
Light traps equipped with light emitting diodes (LEDs) have been applied to manage some phototactic insect pests. The diamondback moth, Plutella xylostella, is a cosmopolitan insect pest to be seriously harmful to many cruciferous plants. The present research focused on evaluating the phototactic behavior responses of the moths to several wavelengths and photon flux densities of LED lights under laboratory and field conditions. The results from the laboratory showed that the highest phototactic behavior responses of P. xylostella moths were recorded for UV (380 nm) LED light under 1.5 µmol m−2 s−1 and 2.5 µmol m−2 s−1. The moths were more attracted to light traps equipped with 4 LEDs and 6 LEDs of 380 nm, respectively, between 20:00 and 22:00 than the other groups and night times in the field. The finding from the field was consistent with the results from the laboratory. We found that the 380 nm LED light results in the strongest attraction rate of the moths by 92.4 % and the moths caught in light trap with the UV LEDs was 1.62 times more than that with a black light. These data clearly demonstrate that P. xylostella moths have a high sensitivity to 380 nm, therefore, a 380 nm LED light trap could be useful for monitoring and controlling the moths. 相似文献