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Analyses of dental function are an essential component of the study of human evolution. However, with few exceptions, they have utilized the traditional analogizing method of comparative anatomy, and have assumed rather than demonstrated that proposed adaptive characters confer a performance benefit. Since food reduction is a mechanical process, it is appropriate to measure performance using mechanical parameters, specifically the ability of a given morphology to induce failure in food particle by either of the two major regimes: crush and shear, corresponding to simple stresses (tensile and compressive) and shear stress, respectively. We apply finite elements stress analysis to model the relationship between the angulation of the intercuspal occlusal surfaces in a “puncture crushing” mode of mastication. On the basis of morphological data acquired from sectioned great ape molars, we have predicted the nature, magnitude and distribution of stress in a standard food particle by models representing each morphotype. Results indicate that the blunt-cusped molars ofHomo, the gradually-sloping supporting (buccal) cusps but high-angled guiding (lingual) cusps of the lower molars ofPan, and the high angled occlusal surfaces ofGorillaare all more likely to fracture small food particles by shear, while the gradually sloping occlusal surfaces ofPongomolars are more likely to break them down by “crush”. Mechanisms of food failure induced by molars ofPanandHomowill vary according to the orientation of the tooth–food contacting surfaces, which in turn will vary according to the size of the food particle. These genera may be able to break food down either by shear or by “crush”. 相似文献
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三棱栎群落的区系成分初步研究 总被引:7,自引:3,他引:4
根据三棱区栎群落的野外调查结果,分析了该落的区系成分。热带及亚热带区系成分占很大的比重(占总种数90.25%),其中印度-马来西亚成分占有绝对优势(占41.46%),滇、顷、老、泰、越周边地区的区系成分次之(共占29.27%),与热带非洲有微弱联系,但与热带大洋洲与美洲并无联系。这就在该群落区系成分分析的基础上有力地支持Kevin C.Nixon和William L.Crepet的论点:三棱栎的独 相似文献
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Durosinmi M. A. Ojo J. O. Oluwole A. F. Ononye A. F. Akanle O. A. Spyrou N. M. 《Biological trace element research》1994,(1):357-361
The concentrations of a number of elements are determined in the plasma and erythrocytes of 21 Nigerians (11 females, 10 males)
with symptomatic affective disorders (11 depressives, 10 manics) and in 40 normal controls using proton-induced X-ray emission
(PIXE) analysis. The study shows that there is significant elevation of plasma K and Zn, as well as the erythrocyte S in the
patients relative to the controls. The plasma and erythrocyte Cu, and the erythrocyte P, Ca, Fe, and Zn are significantly
lower in the patients compared to the controls. However, the plasma levels of Ca, S, Fe, and Br are similar in both the patients
and the controls. Similarly, the concentrations of K, Br, and Rb show no significant difference in the erythrocytes of patients
and controls. 相似文献
77.
Study of trace elements in blood of cancer patients by proton-induced X-ray emission (PIXE) analysis
Durosinmi M. A. Ojo J. O. Oluwole A. F. Akanle O. A. Spyrou N. M. 《Biological trace element research》1994,(1):351-355
Proton-induced X-ray emission (PIXE) analysis was employed to determine the concentrations of six elements in the plasma and
erythrocytes of 18 cancer subjects (15 males and 3 females) with neoplastic disorders and in 70 controls (35 males and 35
females). It was found that the concentrations of Br, K, and Zn were significantly elevated in the erythrocytes of the cancer
subjects compared to the controls, whereas the concentration of Fe was significantly depressed, but with no difference observed
in the concentration of Ca. In the plasma, the concentrations of Br, Cu, Ca, and K were significantly elevated, whereas the
concentrations of Fe and Zn were found to be significantly depressed compared to the controls. 相似文献
78.
A. Teplyakov G. Obmolova K. S. Wilson K. Ishii H. Kaji T. Samejima I. Kuranova 《Protein science : a publication of the Protein Society》1994,3(7):1098-1107
The 3-dimensional structure of inorganic pyrophosphatase from Thermus thermophilus (T-PPase) has been determined by X-ray diffraction at 2.0 A resolution and refined to R = 15.3%. The structure consists of an antiparallel closed beta-sheet and 2 alpha-helices and resembles that of the yeast enzyme in spite of the large difference in size (174 and 286 residues, respectively), little sequence similarity beyond the active center (about 20%), and different oligomeric organization (hexameric and dimeric, respectively). The similarity of the polypeptide folding in the 2 PPases provides a very strong argument in favor of an evolutionary relationship between the yeast and bacterial enzymes. The same Greek-key topology of the 5-stranded beta-barrel was found in the OB-fold proteins, the bacteriophage gene-5 DNA-binding protein, toxic-shock syndrome toxin-1, and the major cold-shock protein of Bacillus subtilis. Moreover, all known nucleotide-binding sites in these proteins are located on the same side of the beta-barrel as the active center in T-PPase. Analysis of the active center of T-PPase revealed 17 residues of potential functional importance, 16 of which are strictly conserved in all sequences of soluble PPases. Their possible role in the catalytic mechanism is discussed on the basis of the present crystal structure and with respect to site-directed mutagenesis studies on the Escherichia coli enzyme. The observed oligomeric organization of T-PPase allows us to suggest a possible mechanism for the allosteric regulation of hexameric PPases. 相似文献
79.
The inorganic contents of bone, brain, erythrocyte, heart, kidney cortex, kidney medulla, liver, lung, muscle and plasma from spontaneously hypertensive rats were compared with those of the same tissues from healthy Sprague-Dawley rats. A general inductively coupled plasma-mass spectrometry method developed for multi-element determinations of most of the elements present in biological tissues was used. Variations were found not only for major elements, as expected, but also for many trace elements in several tissues. 相似文献
80.