Search results for "cycle"

Italian experiences in Life Cycle Assessment of olive oil: a survey and critical review

2010

Sequence stratigraphy of a mesozoic carbonate platform-to-basin system in Western sicily

2009

Abstract Sequence stratigraphic studies of the Triassic through Paleogene carbonate successions of platform, slope and basin in western Sicily (Palermo and Termini Imerese Mountains) have identified a sedimentary cyclicity mostly caused by relative oscillations of sea level. The stratigraphic successions of the Imerese and Panormide palaeogeographic domains of the southern Tethyan continental margin were studied with physical-stratigraphy and facies analysis to reconstruct the sedimentary evolution of this platform-to-basin system. The Imerese Basin is characterized by a carbonate and siliceous-calcareous succession, 1200–1400m thick, Late Triassic to Eocene in age. The strata display a typ…

A proof of bistability for the dual futile cycle

2014

Abstract The multiple futile cycle is an important building block in networks of chemical reactions arising in molecular biology. A typical process which it describes is the addition of n phosphate groups to a protein. It can be modelled by a system of ordinary differential equations depending on parameters. The special case n = 2 is called the dual futile cycle. The main result of this paper is a proof that there are parameter values for which the system of ODE describing the dual futile cycle has two distinct stable stationary solutions. The proof is based on bifurcation theory and geometric singular perturbation theory. An important entity built of three coupled multiple futile cycles is…

Multiple Canard Cycles in Generalized Liénard Equations

2001

AbstractThe paper treats multiple limit cycle bifurcations in singular perturbation problems of planar vector fields. The results deal with any number of parameters. Proofs are based on the techniques introduced in “Canard Cycles and Center Manifolds” (F. Dumortier and R. Roussarie, 1996, Mem. Amer. Math. Soc., 121). The presentation is limited to generalized Liénard equations εx+α(x, c)x+β(x, c)=0.

La gestion de l'hétérogénéité des publics d'élèves au collège

1997

International audience; Depuis l'instauration du collège unique, tous les élèves d'une classe d'âge sont supposés être scolarisés en premier cycle secondaire dans des contextes de scolarisation identiques. Le texte examine dans quelle mesure les collèges suivent ce principe ou bien constituent en leur sein des classes de niveau ; on conclut, sur la base d'observation de plus de 200 collèges qu'il y a des pratiques variées à cet égard mais qu'une proportion forte de collèges recourt clairement à ce mode de groupement ; on observe qu'il y a en fait davantage de variété produite par les collèges par la constitution de classes que les collèges n'en héritent de par la carte scolaire.Le texte exa…

Cyclicity of common slow–fast cycles

2011

Abstract We study the limit cycles of planar slow–fast vector fields, appearing near a given slow–fast cycle, formed by an arbitrary sequence of slow parts and fast parts, and where the slow parts can meet the fast parts in a nilpotent contact point of arbitrary order. Using the notion slow divergence integral, we delimit a large subclass of these slow–fast cycles out of which at most one limit cycle can perturb, and a smaller subclass out of which exactly one limit cycle will perturb. Though the focus lies on common slow–fast cycles, i.e. cycles with only attracting or only repelling slow parts, we present results that are valid for more general slow–fast cycles. We also provide examples o…

Tetraspanin CD151 Mediates Papillomavirus Type 16 Endocytosis

2013

ABSTRACT Human papillomavirus type 16 (HPV16) is the primary etiologic agent for cervical cancer. The infectious entry of HPV16 into cells occurs via a so-far poorly characterized clathrin- and caveolin-independent endocytic pathway, which involves tetraspanin proteins and actin. In this study, we investigated the specific role of the tetraspanin CD151 in the early steps of HPV16 infection. We show that surface-bound HPV16 moves together with CD151 within the plane of the membrane before they cointernalize into endosomes. Depletion of endogenous CD151 did not affect binding of viral particles to cells but resulted in reduction of HPV16 endocytosis. HPV16 uptake is dependent on the C-termina…

RNAi mediated acute depletion of Retinoblastoma protein (pRb) promotes aneuploidy in human primary cells via micronuclei formation

2009

BACKGROUND: Changes in chromosome number or structure as well as supernumerary centrosomes and multipolar mitoses are commonly observed in human tumors. Thus, centrosome amplification and mitotic checkpoint dysfunctions are believed possible causes of chromosomal instability. The Retinoblastoma tumor suppressor (RB) participates in the regulation of synchrony between DNA synthesis and centrosome duplication and it is involved in transcription regulation of some mitotic genes. Primary human fibroblasts were transfected transiently with short interfering RNA (siRNA) specific for human pRb to investigate the effects of pRb acute loss on chromosomal stability. RESULTS: Acutely pRb-depleted fibr…

Internalization of coxsackievirus A9 is mediated by {beta}2-microglobulin, dynamin, and Arf6 but not by caveolin-1 or clathrin.

2010

ABSTRACT Coxsackievirus A9 (CAV9) is a member of the human enterovirus B species within the Enterovirus genus of the family Picornaviridae . It has been shown to utilize αV integrins, particularly αVβ6, as its receptors. The endocytic pathway by which CAV9 enters human cells after the initial attachment to the cell surface has so far been unknown. Here, we present a systematic study concerning the internalization mechanism of CAV9 to A549 human lung carcinoma cells. The small interfering RNA (siRNA) silencing of integrin β6 subunit inhibited virus proliferation, confirming that αVβ6 mediates the CAV9 infection. However, siRNAs against integrin-linked signaling molecules, such as Src, Fyn, R…

Understanding the Experiences of Heavy Smokers after Exercise

2015

There is now strong evidence that exercise has an acute effect on the urge to smoke and the accompanying withdrawal symptoms. However, the perceptions by heavy smokers of exercise and its relationship to the urge to smoke have not been well documented. The aim of the present study is to understand the experiences of heavy smokers with regard to exercise and its effect on their urge to smoke. Five physically inactive, heavy smokers are asked to abstain from smoking the night before exercising on a cycle ergometer under two conditions (one at medium and one at vigorous intensity done a week apart). Semi-structured, in-depth interviews are conducted after the second exercise session. Thematic …