Search results for "VARIATION"
showing 10 items of 2124 documents
A non-linear optimization procedure to estimate distances and instantaneous substitution rate matrices under the GTR model.
2006
Abstract Motivation: The general-time-reversible (GTR) model is one of the most popular models of nucleotide substitution because it constitutes a good trade-off between mathematical tractability and biological reality. However, when it is applied for inferring evolutionary distances and/or instantaneous rate matrices, the GTR model seems more prone to inapplicability than more restrictive time-reversible models. Although it has been previously noted that the causes for intractability are caused by the impossibility of computing the logarithm of a matrix characterised by negative eigenvalues, the issue has not been investigated further. Results: Here, we formally characterize the mathematic…
Malliavin smoothness on the Lévy space with Hölder continuous or BV functionals
2020
Abstract We consider Malliavin smoothness of random variables f ( X 1 ) , where X is a pure jump Levy process and the function f is either bounded and Holder continuous or of bounded variation. We show that Malliavin differentiability and fractional differentiability of f ( X 1 ) depend both on the regularity of f and the Blumenthal–Getoor index of the Levy measure.
Hard-Core Thinnings of Germ‒Grain Models with Power-Law Grain Sizes
2013
Random sets with long-range dependence can be generated using a Boolean model with power-law grain sizes. We study thinnings of such Boolean models which have the hard-core property that no grains overlap in the resulting germ‒grain model. A fundamental question is whether long-range dependence is preserved under such thinnings. To answer this question, we study four natural thinnings of a Poisson germ‒grain model where the grains are spheres with a regularly varying size distribution. We show that a thinning which favors large grains preserves the slow correlation decay of the original model, whereas a thinning which favors small grains does not. Our most interesting finding concerns the c…
M-Centrality: identifying key nodes based on global position and local degree variation
2023
Identifying influential nodes in a network is a major issue due to the great deal of applications concerned, such as disease spreading and rumor dynamics. That is why, a plethora of centrality measures has emerged over the years in order to rank nodes according to their topological importance in the network. Local metrics such as degree centrality make use of a very limited information and are easy to compute. Global metrics such as betweenness centrality exploit the information of the whole network structure at the cost of a very high computational complexity. Recent works have shown that combining multiple metrics is a promising strategy to quantify the node's influential ability. Our wor…
Deducing self-interaction in eye movement data using sequential spatial point processes
2016
Eye movement data are outputs of an analyser tracking the gaze when a person is inspecting a scene. These kind of data are of increasing importance in scientific research as well as in applications, e.g. in marketing and man-machine interface planning. Thus the new areas of application call for advanced analysis tools. Our research objective is to suggest statistical modelling of eye movement sequences using sequential spatial point processes, which decomposes the variation in data into structural components having interpretation. We consider three elements of an eye movement sequence: heterogeneity of the target space, contextuality between subsequent movements, and time-dependent behaviou…
INTRA- AND INTERSPECIFIC VARIATION IN INTERNAL STRUCTURES OF THE GENUSSTENOSARINA(BRACHIOPODA, TEREBRATULIDA) USING LANDMARKS
2001
Abstract Although a number of brachiopod genera have been defined mainly from their internal structures, the fixity of those structures has rarely been investigated. Variability of the rather simple loops of two New Caledonian species of the Recent genus Stenosarina (Terebratulida), one species having a variant with endemic morphology, provides insight into the relationship between the two species. Procrustes methods based on landmarks are used. Intra-population variability is found to be of the same order of magnitude as inter-population variability. Moreover, the morphological distance between the endemic variant and the other specimens is greater than the distance between the two species…
Detoxication of carcinogenic fjord-region diol epoxides of polycyclic aromatic hydrocarbons by glutathione transferase P1-1 variants and glutathione.
1998
AbstractEpidemiological studies suggest that individuals differing in the expression of allelic variants of the human glutathione transferase (GST) Pi gene differ in susceptibility to chemical carcinogens such as polycyclic aromatic hydrocarbons (PAH). This study reports the catalytic efficiencies (kcat/Km) of two naturally occurring variants, GSTP1-1/I-105 and GSTP1-1/V-105, towards a series of fjord-region diol epoxides representing potent biologically active PAH metabolites, and two GSTP1-1 mutants with Ala105 and Trp105 in the active site. The results indicate that individuals who are homozygous for the allele encoding GSTP1-1/V-105 might be more susceptible to PAH carcinogenesis due to…
Reliability of physical functioning measures in ambulatory subjects with MS.
2005
Background and Purpose. One of the primary reasons for measuring outcomes during rehabilitation is to determine the effect of physiotherapy. Repeated measurement situations are susceptible to several sources of error, including inconsistencies caused by the subject, the procedure, the instrument and the examiner. Therefore, the reliability of the measures needs to be examined. Method. The present study used a repeated-measures design. Two studies were undertaken to examine the test–retest and inter-rater reliability for physical functioning measures. The interval between the measurements was one week. The sample consisted of 19 ambulatory subjects with mutliple sclerosis (MS) in the test–re…
In viaggio con Stravinsky, gli ultimi anni di tournée e le "Choral-Variationen" sul canto natalizio Vom Himme hoch..." (1955-56)
2022
The text takes up in organic form the speeches held on June 3, 2021 as part of the conference "Stravinsky in/and Italy. Day dedicated to the memory of Igor Stravinsky in the fiftieth anniversary of his death (1971-2021)" and the subsequent round table. The first paragraphs have the character of a reconstruction of the life of Igor Stravinsky ‘as an old man’, dealing above all with the theme of the trips to Italy made by the Maestro together with his wife Vera de Bosset, the conductor Robert Craft. The second part of the text is about the "Choral-Variationen on the Christmas carol “Vom Himmel hoch...”, written in 1955-56 to be performed with the Canticum Sacrum in the St. Mark’s Basilica in …
The Structural Variety and Metabolism of Proteins
1994
Individual eukaryote cells contain in the order of 104 different proteins, and each animal species contains an even greater number due to differences between the tissues of an individual and between the individuals themselves; furthermore, the protein spectrum changes during the course of development. The number of different proteins to be found in extant organisms may be as high as 1012. The description of this variety, its origin and biological significance is the most extensive theme in comparative biochemistry. This chapter will concern itself with the possibilities for structural variation and the general metabolism of proteins; further chapters will deal with comparative studies of in…