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141.
S. Angel I. M. Levinger Mazal Amosi 《Cellular and molecular life sciences : CMLS》1976,32(8):1042-1043
Summary It was found that most feather follicles possess more than a single muscle system but only single nerve endings were observed in a feather follicle. It seems that muscles exist which antagonize each other. Anastomoses of nerves orginating from different sources and flowing of mixed nerves into the feather follicle could explain the antagonistic action of the muscles on the feather follicle.Partially supported by a grant from the Israel Egg and Poultry Board. 相似文献
142.
New spectrophotometry of SS433 shows that the variable-wavelength emission features discovered by Margon et al. are due to the simultaneous presence of material having a substantial redshift and a substantial blueshift. A magnetic interpretation for the features is also ruled out by polarimetric measurements. Implications for dynamical models are discussed. 相似文献
143.
Functional data sets appear in many areas of science. Although each data point may be seen as a large finite-dimensional vector
it is preferable to think of them as functions, and many classical multivariate techniques have been generalized for this
kind of data. A widely used technique for dealing with functional data is to choose a finite-dimensional basis and find the
best projection of each curve onto this basis. Therefore, given a functional basis, an approach for doing curve clustering
relies on applying the k-means methodology to the fitted basis coefficients corresponding to all the curves in the data set.
Unfortunately, a serious drawback follows from the lack of robustness of k-means. Trimmed k-means clustering (Cuesta-Albertos,
Gordaliza, and Matran 1997) provides a robust alternative to the use of k-means and, consequently, it may be successfully
used in this functional framework. The proposed approach will be exemplified by considering cubic B-splines bases, but other
bases can be applied analogously depending on the application at hand. 相似文献
144.
We propose and discuss improved Bayes rules to discriminate between two populations using ordered predictors. To address the
problem we propose an alternative formulation using a latent space that allows to introduce the information about the order
in the theoretical rules. The rules are first defined when the marginal densities are fully known and then under normality
when the parameters are unknown and training samples are available. Several numerical examples and simulations in the paper
illustrate the methodology and show that the new rules handle the information appropriately. We compare the new rules with
the classical Bayes and Fisher rules in these examples and we show that the misclassification probability is smaller for the
new rules. The method is also applied to data from a diabetes study where we again show that the new rules improve over the
usual Fisher rule.
Research partially supported by Spanish DGES and by PAPIJCL. The authors thank the editor and an anonymous reviewer for their
detailed reading that resulted in this much improved version of the paper. 相似文献
145.
146.
Extinction risk from climate change 总被引:20,自引:0,他引:20
Thomas CD Cameron A Green RE Bakkenes M Beaumont LJ Collingham YC Erasmus BF De Siqueira MF Grainger A Hannah L Hughes L Huntley B Van Jaarsveld AS Midgley GF Miles L Ortega-Huerta MA Peterson AT Phillips OL Williams SE 《Nature》2004,427(6970):145-148
Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration. 相似文献
147.
Notch activity acts as a sensor for extracellular calcium during vertebrate left-right determination
Raya A Kawakami Y Rodríguez-Esteban C Ibañes M Rasskin-Gutman D Rodríguez-León J Büscher D Feijó JA Izpisúa Belmonte JC 《Nature》2004,427(6970):121-128
During vertebrate embryo development, the breaking of the initial bilateral symmetry is translated into asymmetric gene expression around the node and/or in the lateral plate mesoderm. The earliest conserved feature of this asymmetric gene expression cascade is the left-sided expression of Nodal, which depends on the activity of the Notch signalling pathway. Here we present a mathematical model describing the dynamics of the Notch signalling pathway during chick embryo gastrulation, which reveals a complex and highly robust genetic network that locally activates Notch on the left side of Hensen's node. We identify the source of the asymmetric activation of Notch as a transient accumulation of extracellular calcium, which in turn depends on left-right differences in H+/K+-ATPase activity. Our results uncover a mechanism by which the Notch signalling pathway translates asymmetry in epigenetic factors into asymmetric gene expression around the node. 相似文献
148.
Detection of large-scale variation in the human genome 总被引:26,自引:0,他引:26
Iafrate AJ Feuk L Rivera MN Listewnik ML Donahoe PK Qi Y Scherer SW Lee C 《Nature genetics》2004,36(9):949-951
We identified 255 loci across the human genome that contain genomic imbalances among unrelated individuals. Twenty-four variants are present in > 10% of the individuals that we examined. Half of these regions overlap with genes, and many coincide with segmental duplications or gaps in the human genome assembly. This previously unappreciated heterogeneity may underlie certain human phenotypic variation and susceptibility to disease and argues for a more dynamic human genome structure. 相似文献
149.
Zenz R Eferl R Kenner L Florin L Hummerich L Mehic D Scheuch H Angel P Tschachler E Wagner EF 《Nature》2005,437(7057):369-375
Psoriasis is a frequent, inflammatory disease of skin and joints with considerable morbidity. Here we report that in psoriatic lesions, epidermal keratinocytes have decreased expression of JunB, a gene localized in the psoriasis susceptibility region PSORS6. Likewise, inducible epidermal deletion of JunB and its functional companion c-Jun in adult mice leads (within two weeks) to a phenotype resembling the histological and molecular hallmarks of psoriasis, including arthritic lesions. In contrast to the skin phenotype, the development of arthritic lesions requires T and B cells and signalling through tumour necrosis factor receptor 1 (TNFR1). Prior to the disease onset, two chemotactic proteins (S100A8 and S100A9) previously mapped to the psoriasis susceptibility region PSORS4, are strongly induced in mutant keratinocytes in vivo and in vitro. We propose that the abrogation of JunB/activator protein 1 (AP-1) in keratinocytes triggers chemokine/cytokine expression, which recruits neutrophils and macrophages to the epidermis thereby contributing to the phenotypic changes observed in psoriasis. Thus, these data support the hypothesis that epidermal alterations are sufficient to initiate both skin lesions and arthritis in psoriasis. 相似文献
150.
本书总结了作者在流体力学、磁流体力学、经典热力学和天体物理方面的研究成果。全书分为14章,三大部分,第一部分含第1-3章,理论基础如运动与变形几何学、雷诺输运定律、哈密尔顿原理及分析力学等相关基础知识。第二部分含第4-10,12-13章,着重介绍哈密尔顿原理在理想流体、势流、粘性流体、 相似文献