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51.
52.
Four stages of a scientific discipline; four types of scientist 总被引:1,自引:0,他引:1
Alexander M. Shneider 《Trends in biochemical sciences》2009,34(5):217-223
53.
Alexander V. Kirdyanov Eugene A. Vaganov Malcolm K. Hughes 《Trees - Structure and Function》2007,21(1):37-44
We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology.
The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed
for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern
timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies
and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance
of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of
four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard
technique is correlated with temperature over a much longer period. For maximum density series from which the relationship
between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing
season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring
formation. 相似文献
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55.
A bacterial clone carrying sequences coding for elongation factor EF-1 alpha from Artemia 总被引:2,自引:0,他引:2
A bacterial cDNA clone was identified carrying one third of the nucleotides coding for elongation factor EF-1 alpha from the brine shrimp Artemia. The sequence of codons corresponds with the known sequence of amino acids of EF-1 alpha in the region involved. 相似文献
56.
Alexander Wiedenmann Peter Dimroth Christoph von Ballmoos 《Molecular microbiology》2009,72(2):479-490
F1 F0 ATP synthases use the electrochemical potential of H+ or Na+ across biological membranes to synthesize ATP by a rotary mechanism. In bacteria, the enzymes can act in reverse as ATP-driven ion pumps creating the indispensable membrane potential. Here, we demonstrate that the F0 parts of a Na+ - and H+ -dependent enzyme display major asymmetries with respect to their mode of operation, reflected by the requirement of ∼100 times higher Na+ or H+ concentrations for the synthesis compared with the hydrolysis of ATP. A similar asymmetry is observed during ion transport through isolated F0 parts, indicating different affinities for the binding sites in the a/c interface. Together with further data, we propose a model that provides a rationale for a differential usage of membrane potential and ion gradient during ATP synthesis as observed experimentally. The functional asymmetry might also reflect an important property of the ATP synthesis mechanism in vivo . In Escherichia coli , we observed respiratory chain-driven ATP production at pH 7–8, while P -site pH values < 6.5 were required for ATP synthesis in vitro . This discrepancy is discussed with respect to the hypothesis that during respiration lateral proton diffusion could lead to significant acidification at the membrane surface. 相似文献
57.
H. Wiksell V. Ekstrand C. Wadström G. Auer 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2009,25(3):128-132
A large and increasing number of women in the western world will at some point during their life be investigated morphologically for some type of breast lesion. Fine Needle Aspiration (FNA) is one morphological method which is considered to be the fastest, cheapest and the most patient-friendly approach. However, the frequency of conclusive samples using this method varies and is often too low, especially when performed by unexperienced operators. In this study we have developed and tested a new semi-automated instrument (“CytoTest”) designed for FNA which is intended to improve the efficacy of the technique by increasing the percentage of conclusive samples. A total of 443 consecutive aspiration procedures on palpable breast lesions were performed to compare this new “CytoTest” equipment with the standard protocol using the same type of needles. We conclude that by increasing the extent and frequency of the reciprocatory motions used by an experienced sampling operator as well as enhancing the ejection pressure, the cellular yield can be increased almost three folded compared to the standard protocol. For cases with high amounts of non-diagnostic material (such as blood or cystic fluid) which were discarded, up to four times more sample could be obtained. Furthermore, the frequency of sparse samples under 1 mg was halved with use of the “CytoTest”. 相似文献
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