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71.
AIM OF THE STUDY: Mechanical lever-out tests were performed in vitro to investigate the initial stability of press fit acetabular cups. METHOD: Five different uncemented, hemispherical press-fit cups were implanted in a standardized manner into Sawbones, Polyurethane foam blocks. Each cup was levered-out by using a 250 mm stainless steel rod, which was connected to the acetabular cup. Loads were then applied to the rod causing the cup to be diplaced. Lever-out forces were recorded by a computer. RESULTS: The results of the lever-out forces ranged between 39,2 and 50,8 Nm. The highest initial stability was achieved by two Titanium cups with a Titanium plasmaspray coating, a flattened pole and a sharp equatorial edge. According to our trials the equatorial rim of the polyurethane cavity is the crucial area for the implant's initial stabilty. There the highest amount of attrition was observed. CONCLUSION: To guarantee a high reproducibilty of the tests it is essential to pay particular attention to the quality of the polyurethane foam blocks, to the exactness of the reaming procedure and to a defined cup insertion. However as our trials were carried out under optimized labaratory conditions one must be careful not to over-interpret its results. Intraoperatively primary stability is also influenced by the quality of the bone. 相似文献
72.
73.
Biochemical and Cytochemical Evidence for the Polar Concentration of Periplasmic Enzymes in a “Minicell” Strain of Escherichia coli 下载免费PDF全文
A number of "surface" enzymes of Escherichia coli (i.e., among those selectively released by osmotic shock) all displayed higher specific activities in extracts of minicells than in extracts of typical rod forms; these enzymes included alkaline phosphatase, cyclic phosphodiesterase, acid hexose monophosphatase, 5'-nucleotidase, and ribonuclease I. In addition, alkaline phosphatase, cyclic phosphodiesterase, and acid hexose monophosphatase were cytochemically localized to regions of minicell periplasm that resembled reactive polar enlargements of the periplasm in rod forms. In contrast, a number of "internal" cytoplasmic enzymes (inorganic pyrophosphatase, beta-galactosidase, glutamine synthetase, polynucleotide phosphorylase, and ribonuclease II) showed elevated or similar specific activities in extracts of rod forms versus extracts of minicells. A specific heat-labile inhibitor for 5'-nucleotidase, known to occur in the cytoplasm, also showed no enrichment in minicells. These findings indicate that the "surface" enzymes are segregated in vivo into the terminal minicell buds, possibly because these enzymes are concentrated in the polar enlargements of the periplasm in typical rod forms. 相似文献
74.
A. Wetzel 《Zoomorphology》1927,9(5):719-737
Ohne Zusammenfassung 相似文献
75.
Abstract
Decomposition of standing litter of the emergent macrophyte Erianthus giganteus (plumegrass) was quantified in a small freshwater wetland in Alabama, USA. Living green shoots of E. giganteus were tagged and periodically retrieved for determination of leaf and culm mass loss, litter-associated fungal biomass (ergosterol),
and nitrogen and phosphorus concentrations. Laboratory studies were also conducted to examine the effects of plant litter
moisture content and temperature on rates of CO2 evolution from plant litter. Culm and leaf material lost 25 and 32% AFDM, respectively, during plant senescence and early
litter decay. Fungal biomass, as determined by ergosterol concentrations, increased significantly in both leaf and culm litter
during decomposition, with maximum biomass accounting for 3.7 and 6.7% of the total detrital weight in culm and leaf litter,
respectively. Spatial differences in fungal biomass were observed along the culm axis, with upper regions of the culm accumulating
significantly greater amounts of fungal mass than basal regions (p < 0.01, ANOVA). Rates of CO2 evolution from both leaf and culm litter increased rapidly after wetting (0 to 76 μg CO2−C g−1 AFDM h−1 within 5 min). In addition, rates of CO2 evolution from water saturated culms increased exponentially as the temperature was increased from 10 to 30°C. These results
provide evidence that considerable microbial colonization and mineralization of standing emergent macrophyte litter can occur
before collapse of senescent shoot material to the water and sediment surface.
Received: 5 December 1998; Accepted: 31 March 1999 相似文献
76.
77.
Patrick Martin Enrique Martinez-Ansemil Adrian Pinder Tarmo Timm Mark J. Wetzel 《Hydrobiologia》2008,606(1):117-127
One of the predicted consequences of climate change is an increase in the occurrence of extreme rainfall and a subsequent
increase in frequency of high flow events in rivers. High flow events have the potential to impact estuarine communities like
mussel assemblages due to decreased salinity and/or the transport of sediments, organic matter and nutrients from the terrestrial
environment to the estuary. The impact of two high flow events was investigated using mussels located within the Conwy estuary,
North Wales, using the ‘Beyond BACI’ approach. Three study sites were chosen, the potentially impacted site (Conwy) and two
control sites located outside the estuary. Sampling took place over 18 months with samples being collected before and after
each event. On each sampling occasion, the following data were collected: the total haemocyte count (THC) and condition index
(CI) of the mussels and the diversity (Hloge) of their associated macrofauna. A significant effect of the first event (22nd October 2004) was found on the CI of the Conwy
mussels, whereas a significant effect of the second event (10th October 2005) was found on mussel THC. No effect of either
event was found on the diversity of the associated fauna. The results of this study suggest that any increase in the number
or intensity of heavy precipitation or high flow events have potential implications for the health and resilience of estuarine
mussel populations.
Guest editors: J. Davenport, G. Burnell, T. Cross, M. Emmerson, R. McAllen, R. Ramsay & E. Rogan
Challenges to Marine Ecosystems 相似文献
78.
Patrick Winterhagen Cornelia Dubois Melanie Sinn Thierry Wetzel Götz M. Reustle 《Plant Physiology and Biochemistry》2009,47(8):739-742
RNA interference (RNAi) was established in Nicotiana benthamiana plants by introducing constructs containing a defective interfering (DI) sequence from Tomato bushy stunt virus (TBSV) in combination with a conserved sense-sequence from the target Grapevine fanleaf virus (GFLV). Silencing in plants was confirmed by Agrobacterium-mediated infiltration of a GFP-sensor containing the GFLV-derived target sequence. The transgene-induced RNAi led to silencing of the GFP-sensor and GFP fluorescence was absent post-infiltration. In plants without GFP fluorescence after infiltration with the GFP-sensor, siRNA specific to GFP and the target virus sequence could not be detected. In contrast, infiltrated leaves of wild type and transgenic plants showing GFP fluorescence after infiltration revealed accumulation of siRNA specific to the sequence of the sensor. Silencing could be inhibited by co-infiltration using a p19 silencing suppressor construct together with the GFP-sensor, which always resulted in bright GFP fluorescence. In parallel, virus resistance of transgenic Nicotiana benthamiana was investigated via challenge inoculation with GFLV. Our results indicate that efficient RNAi in transgenic plants does not necessarily lead to a detectable accumulation of siRNA. 相似文献
79.
Paul R. Wetzel Arnold G. van der Valk Susan Newman Carlos A. Coronado Tiffany G. Troxler-Gann Daniel L. Childers William H. Orem Fred H. Sklar 《Plant Ecology》2009,200(1):83-90
The biologically mediated transfer of nutrients from one part of a landscape to another may create nutrient gradients or subsidize
the productivity at specific locations. If limited, this focused redistribution of the nutrient may create non-random landscape
patterns that are unrelated to underlying environmental gradients. The Florida Everglades, USA, is a large freshwater wetland
that is patterned with tree islands, elevated areas that support woody vegetation. A survey of 12 tree islands found total
soil phosphorus levels 3–114 times greater on the island head than the surrounding marsh, indicating that the Florida Everglades
is not a homogeneous oligotrophic system. It was estimated that historically 67% of the phosphorus entering the central Everglades
was sequestered on tree islands, which are ~3.8% of the total land area. This internal redistribution of phosphorus onto tree
islands due to the establishment of trees may be one reason that marshes have remained oligotrophic and may explain the spatial
differentiation of the patterned Everglades landscape. 相似文献
80.