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21.
PHILIPPE PONCET FRANCOIS TROCHU JEAN DANSEREAU 《Computer methods in biomechanics and biomedical engineering》2013,16(4):295-308
In spinal deformation studies, three-dimensional reconstruction of the spine is frequently represented as a curve in space fitted to the vertebral centroids. Conventional interpolation techniques such as splines. Bezier and the least squares method are limited since they cannot describe precisely the great variety of spinal morphologies. This article presents a more general technique called dual kriging, which includes two mathematical constituents (drift and covariance) to adjust the interpolated functions to spinal deformity better. The cross-validation technique was used to compare the parametric representations of spinal curves with different combinations of drift and covariance functions. Model validation was performed from a series of analytic curves reflecting typical scoliotic spines. Calculation of geometric torsion, a sensitive parameter, was done to evaluate the accuracy of the kriging models. The best model showed an absolute mean difference of 1.2 x 10~5 (±7·1 × l()~ 5) mm?1 between the analytical and estimated geometric torsions compared to 5·25 × 10~ (±3.7 × 310~2) mm* 1 for the commonly used least-squares Fourier series method, a significant improvement in spinal torsion evaluation. 相似文献
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FRANCOIS J. MEUNIER 《Zoologica scripta》1980,9(1-4):307-317
The scaly part of the posttemporal bone and the lateral-line scales have the same structure as other scales. However, the lateral line with its bony canal induces some local transformations in both structures. The posttemporal bone can be interpreted as a lateral-line scale whose "dermo"-component is extensively developed. With its composite structure, both osseous and scaly, the posttemporal bone affords an instance peculiarly well suited for studying the relationships between isopedine and bone. The observations demonstrate that isopedine whose superposed collagen layers make a double-twisted plywood, is a specialized structure which evolved from a bony tissue. The fibrous basal plate of a Latimeria scale is homologous to the osseous basal plate of a cosmoid scale. 相似文献
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Double-nesting behaviour, a rare breeding system in which females lay in two nests, one incubated by herself and the other one by her mate, could be considered an intermediate stage in the evolutionary trend from biparental to uniparental care of single clutches. We examined the occurrence and success of double-nesting behaviour in Red-legged Partridges Alectoris rufa in Central Spain. Clutch size and hatching success were recorded, as well as the variation in these between years and between incubating sexes. Participation in incubation was higher for females (94.76%) than males (41.0%), and the proportion of incubating males varied markedly between years, with no incubating males in one dry year and approximately 50% of males incubating in other years. There was significant variation among years and between sexes in laying date, clutch size and hatching success. Clutch size decreased with later laying date in males and females. The probability of clutch loss to predation differed between sexes, being much higher for nests incubated by females. Our results suggest that both rainfall and predation influence the occurrence and success of double-nesting. 相似文献
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GERARD PRENSIER JEAN‐FRANCOIS DUBREMETZ JOSEPH SCHREVEL 《The Journal of eukaryotic microbiology》2008,55(6):541-553
ABSTRACT. The coelomic gregarine Diplauxis hatti exhibits a unique adaptation of its life cycle to its polychaete host Perinereis cultrifera. Experimental and ultrastructural observations on natural populations from the English Channel showed that release of parasite spores is concomitant with the polychaete spawning. As the development of P. cultrifera is direct, the notochete larva ingest parts of the jelly coat covered with numerous sporocysts of D. hatti during hatching. Transepithelial migration of the sporozoites takes place in the gut of three‐ or four‐segment notochete larvae and syzygies of about 20 μm are observed in the coelom. Growth of these young syzygies is slow: after 18–24 mo they reach only 60–70 μm. They exhibit active pendular movements. In the English Channel, female and male gametogenesis of P. cultrifera begins at 19 mo and 2 yr, respectively; the somatic transformations (epitoky) in the last 4 mo of their 3‐year life. During epitoky, the syzygies undergo an impressive growth and reach 700–800 μm within a few weeks. A shift from pendular to active peristaltic motility is observed when the syzygies reach 200–250 μm. When gamogony occurs, syncytial nuclear divisions are initiated and cellularization produces hundred to thousands of male and female gametes of similar size. The male gametes exhibit a flagellum with 3+0 axoneme. The mixing of the gametes (“danse des gametes”) and fertilization are observed during 4–5 h. Zygotes differentiate sporoblasts with eight sporozoites. The sporozoites exhibit the canonical structure of Apicomplexa, a polarized cell with micronemes and rhoptries. 相似文献
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FRANCOIS MOUGEOT MARK MOSELEY FIONA LECKIE JESUS MARTINEZ-PADILLA ALLEN MILLER MAT POUNDS R. JUSTIN IRVINE 《The Journal of wildlife management》2008,72(2):468-472
ABSTRACT Ticks are important arthropod vectors of diseases of human, livestock, and wildlife hosts. In the United Kingdom, the sheep tick (Ixodes ricinus) is increasingly recognized as a main limiting factor of red grouse (Lagopus lagopus) populations, a game bird of high economic value. We evaluated the effectiveness of a new practical technique that could help managers reduce negative impacts of ticks on young grouse. In a replicated field experiment, we treated breeding females with leg bands impregnated with permethrin, a slow-releasing potent acaracide. We found that treatment reduced tick burdens on young chicks. Because this treatment is easily applied, it offers a new practical management tool to tackle problems caused by ticks in game bird populations. 相似文献
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Pollen production and spontaneous polyploidization in diploid populations of Anthoxanthum alpinum 总被引:1,自引:0,他引:1
FRANCOIS BRETAGNOLLE 《Biological journal of the Linnean Society. Linnean Society of London》2001,72(2):241-247
The most common form of polyploidization is that which occurs via the fertilization of unreduced 2 n gametes, i.e. gametes that possess the somatic chromosome number of the species. However, very few data are available concerning the frequency of spontaneous polyploidization in diploid plant populations. In this study we have quantified both the frequency of In pollen production and the frequency of polyploid seed production in diploid populations of the grass Anthoxanthum alpinum. More than 6000 seeds from four different populations collected during two years of study were screened for ploidy using a flow cytometer. In parallel, the frequency both of plants with large pollen (LP) and of LP production on these plants was quantified in two populations. No tetraploid seeds were detected, although in each population a few triploid seeds were regularly produced at a frequency of two triploid seeds per thousand. The frequency of LP producers was similar in the four populations, as was the frequency of LP production. The frequency of LP was ten times that of triploid seeds. These finding suggest that the 'triploid block' is not enough to prevent the regular occurrence of triploids in diploid populations of this species. The role played by the hypothesized 'triploid bridge' in the genesis of autotetraploids is discussed in the light of these results. 相似文献
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