5,361 research outputs found
Bohr's 1913 molecular model revisited
It is generally believed that the old quantum theory, as presented by Niels
Bohr in 1913, fails when applied to few electron systems, such as the H2
molecule. Here we find new solutions within the Bohr theory that describe the
potential energy curve for the lowest singlet and triplet states of H2 about as
well as the early wave mechanical treatment of Heitler and London. We also
develop a new interpolation scheme which substantially improves the agreement
with the exact ground state potential curve of H2 and provides a good
description of more complicated molecules such as LiH, Li2, BeH and He2.Comment: 6 pages, 9 figure
The Marine Living Resources of the Southern Ocean
The author suggests that the abundance of marine life in Antarctica presents ample opportunity both for scientific study and for exploitation. The author provides a survey of the distinct ecological system of the Southern Ocean through his discussion of the main marine species-from the simple organisms involved in primary production to the large marine mammals which have been subject to exploitation in the past. His primary emphasis is on krill, the small, shrimp-like crustacean which serves as the pivotal link in the Antarctic food chain. The abundance of krill, its high nutritive value and its ease of harvesting are factors which the author perceives as according krill significant potential for exploitation. At the same time, he identifies economic and technical obstacles which must be overcome if commercial krill harvesting is to develop
Pathogenicity of anti-ADAMTS13 autoantibodies in acquired thrombotic thrombocytopenic purpura.
BACKGROUND: Acquired thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease in which anti-ADAMTS13 autoantibodies cause severe enzyme deficiency. ADAMTS13 deficiency causes the loss of regulation of von Willebrand factor multimeric size and platelet-tethering function, which results in the formation of disseminated microvascular platelet microthrombi. Precisely how anti-ADAMTS13 autoantibodies, or antibody subsets, cause ADAMTS13 deficiency (ADAMTS13 activity generally <Â 10%) has not been formally investigated. METHODS: We analysed 92 acquired TTP episodes at presentation, through treatment and remission/relapse using epitope mapping and functional analyses to understand the pathogenic mechanisms of anti-ADAMTS13 IgG. RESULTS: 89/92 of TTP episodes had IgG recognising the ADAMTS13 N-terminal domains. The central spacer domain was the only N-terminal antigenic target detected. 38/92 TTP episodes had autoantibodies recognising the N-terminal domains alone; 54/92 TTP episodes also had antibodies against the ADAMTS13 C-terminal domains (TSP2-8 and/or CUB domains). Changes in autoantibody specificity were detected in 9/16 patients at relapse, suggesting a continued development of the disease. Functional analyses on IgG from 43 patients revealed inhibitory IgG were limited to anti-spacer domain antibodies. However, 15/43 patients had autoantibodies with no detectable inhibitory action and as many as 32/43 patients had autoantibodies with inhibitory function that was insufficient to account for the severe deficiency state, suggesting that in many patients there is an alternative pathogenic mechanism. We therefore analysed plasma ADAMTS13 antigen levels in 91 acquired TTP presentation samples. We demonstrated markedly reduced ADAMTS13 antigen levels in all presentation samples, median 6% normal (range 0-47%), with 84/91 patients having <Â 25% ADAMTS13 antigen. ADAMTS13 antigen in the lowest quartile at first presentation was associated with increased mortality (odds ratio 5.7). CONCLUSIONS: Anti-spacer domain autoantibodies are the major inhibitory antibodies in acquired TTP. However, depletion of ADAMTS13 antigen (rather than enzyme inhibition) is a dominant pathogenic mechanism. ADAMTS13 antigen levels at presentation have prognostic significance. Taken together, our results provide new insights into the pathophysiology of acquired TTP
The Effect of Material Variability on the Deflection of Bamboo Fly Rods
This study tested and compared the theoretical effect of variability in modulus of elasticity versus rod taper in the “action” of bamboo fly fishing rods. Action is a rod’s tendency to flex in specific areas when loaded and the extent to which it deforms in that area. MATLAB functions were scripted to plot the large deflection of bamboo fly rods in order to model the action of a rod given various properties. The bamboo fly rod was considered to be a cantilever beam with a point load acting on the end, and large deflection considerations had to be made. Materials testing was performed on bamboo to obtain an expected distribution of modulus of elasticity values to be used within the function. Various rod taper dimensions were retrieved from David Ray’s Taper Library and used in the deflection function. This study observed strictly the static deflection of bamboo fly rods in the considerations of material variability’s effect on fly rod action. Material variability in bamboo was found to have a significant impact on the action of a fly rod with respect to taper
The Marine Living Resources of the Southern Ocean
The author suggests that the abundance of marine life in Antarctica presents ample opportunity both for scientific study and for exploitation. The author provides a survey of the distinct ecological system of the Southern Ocean through his discussion of the main marine species-from the simple organisms involved in primary production to the large marine mammals which have been subject to exploitation in the past. His primary emphasis is on krill, the small, shrimp-like crustacean which serves as the pivotal link in the Antarctic food chain. The abundance of krill, its high nutritive value and its ease of harvesting are factors which the author perceives as according krill significant potential for exploitation. At the same time, he identifies economic and technical obstacles which must be overcome if commercial krill harvesting is to develop
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