No description available.

No description available.

The centromere is the site of kinetochore assembly that ensures proper chromosome segregation. Active centromeres are formed at chromosomal locations that do not appear to share homology between different species; this and other analyses has lead to the conclusion that centromeres are epigenetically determined. In all organisms, centromere location is specified by the assembly of unusual nucleosomes containing the histone H3 variant CENP-A in place of H3. However, an apparent paradox is that CENP-A in most organisms generally occurs on certain preferred sequences. The analyses presented focuses on the influence of DNA sequence on the selection of the locus where CENP-A chromatin are formed and whether there are any particular DNA features that promote CENP-ACnp1 assembly at centromeres in Schizosaccharomyces pombe. S. pombe provides an excellent model to study the structure and function of a complex eukaryotic centromere as it possesses epigenetically regulated centromeres that are structurally related to those of metazoa. Furthermore, plasmid-based circular minichromosomes provide a useful tool for studying these centromeres and the inactivation of minichromosome centromeres does not affect cell viability. The main aim of this study was to identify those features that enable centromeric sequences to assemble CENP-A chromatin. Manipulated circular minichromosomes were utilised to investigate the minimal central core sequence requirement for establishment of CENP-ACnp1 chromatin. These analyses showed that a minimal 2kb region from the central core of cen2 could form a functional centromere. A second aim was to analyse the DNA sequence requirements for centromere function on this minimal 2 kb region. To facilitate this, the endogenous central core region of endogenous cen2 was replaced with the central core region of cen1. This modified strain allows the structural and biological properties associated with plasmid borne central core 2 sequences to be analysed. Transcription of central domain sequences has been proposed to play a role in CENP-A establishment and/or maintenance. To explore the contribution of transcription potential promoters were mapped within the minimal 2 kb sequence and their regulatory elements investigated. Mutation of the minimal DNA element impedes its ability to assemble CENP-A chromatin. Therefore the primary DNA sequence of fission yeast centromeres is important for establishing functional centromeres and thus centromere location not entirely epigenetically regulated. It remains to be determined if the characteristics associated with theses sequences, and their mode of action, are conserved at other centromeres.

Foram medidos os \"yields\" de eletrofissão do 236 ANTPOT u e 238 ANTPOT u na faixa de 5 a 30 MeV, bem como as distribuições angulares dos fragmentos de eletrofissão, utilizando o feixe de elétrons do Acelerador Linear do Instituto de Física da Universidade de São Paulo. É apresentado um formalismo para análise das distribuições angulares dos fragmentos de foto e eletrofissão, a partir do qual é estudada a competição entre os canais de quadrupolo na fotofissão do 238 ANTPOT u. Desenvolveu-se um novo método de análise para a obtenção de contribuições multipolares , diferentes de El, no processo da fotofissão, que permite obter o \"yield\" integrado dos multipolos adicionais a partir da análise simultânea da foto e eletrofissão, mais o formalismo dos fótons virtuais em DWBA. Através do \"unfolding\" das secções de choque dos multipolos adicionais foram obtidas ressonâncias gigantes de E2 para 236 ANTPOT u e 238 ANTPOT. U, com picos em (10,7 ± 0,2) MeV e (9,9 ± 0,2) MeV, e larguras de (7,8 ± 0,2) MeV e (8,7 ± 0,2) MeV, respectivamente . As posições das ressonâncias E2 estão em razoável acordo com as previsões de Bohr e Mottelson: Ep = 60. A POT -1/3 MeV. As larguras são compatíveis com um possível \"splitting\" triplo das ressonâncias. Foram mostradas evidências quanto a uma mistura de Ml na faixa 6-7 MeV. / Measurements of electrofission yields of 236u and 238u were perfomed in the energy range of 5 to 30 MeV, as well as angular distribution of electrofission fragments using the electron beam of the Linear Accelerator of the Physics Institute of the University of São Paulo. A formalism for the analysis of angular distribution of photo and electrofission fragments is presented, from which a competition between the quadrupole channels in the photo fission of 238u is studied. A new method of analysis to obtain the multipole contribution, other than El, in the process of photofission was developed, which allows the obtainment of the integrated yield on the additional multipoles, from the simultaneous analysis of photo and electrofission using the formalism of virtual photons in OWBA. Through the unfolding of the additional multipoles cross sections the E2 giant resonances were obtained for the 236u and 238u, presenting peaks at (10.7 ± 0.2) MeV and (9.9 ± 0.2) MeV, and widths of (7.8 ± 0.2) MeV and (8.7±0.2) MeV, respectively. The positions of these E2 resonances are in reasonable agreement with the predictions of Bohr and Mottelson: Ep = 60 A -1/3 MeV. The width are compatible with a possible triple splitting of the resonances. Evidences of a Ml mixture were shown in the energy range of 6 to 7 MeV.

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Bien que découverte il y a 75 ans, la fission nucléaire fait toujours l'objet de recherches. En effet, la compréhension de ce phénomène présente encore des difficultés théoriques dues à sa complexité. Cela nécessite une bonne compréhension de la structure du noyau de l'atome ainsi qu'une description détaillée du mécanisme pilotant l'évolution du système fissionnant.Un nouveau modèle statistique, appelé SPY (Scission Point Yields), a été développé pour déterminer les caractéristiques des fragments (rendements de fission, énergie cinétique, énergie d¹excitation). Ce modèle est basé sur le modèle de Wilkins développé en 1976. Il consiste en une description statistique du processus de fission au point de scission où les fragments sont complètement définis. L'une des principales avancées du modèle SPY est l'introduction de la description microscopique de la structure nucléaire dans le calcul de l'énergie du système à la scission.Il permet d'étudier la relation entre les propriétés des fragments et leur structure nucléaire. Avec le modèle SPY, il est possible de calculer les propriétés des fragments et d'identifier les tendances globales pour environ 3000 noyaux fissionnants de Z=70 à Z=109, de la drip line neutron jusqu'à la drip line proton.Après une présentation générale de la version de référence du modèle SPY, les résultats obtenus pour la fission thermique de l'uranium 235 et la fission spontanée du californium 252 sont comparés aux données expérimentales. Une étude systématique sur l'ensemble des noyaux actuellement synthétisés est également menée avant d'étendre cette étude bien au-delà de la zone des noyaux synthétisables. Deux développements seront ensuite détaillés. Le premier concerne la manière de calculer l'énergie d'interaction coulombienne entre les deux fragments. Les distributions de charges issues de calculs microscopiques seront introduites afin d'améliorer le calcul de l'énergie d'interaction coulombienne. La possibilité de redéfinir le point de scission du système grâce à ces distributions de charge sera également discuté.Le deuxième développement porte sur le lien entre la modélisation du noyau et les observables associées aux fragments de fission. D'une part, différents modèles du noyau pour le calcul de l'énergie individuelle des fragments, tel que le modèle de la goutte liquide, seront envisagés et l'impact du choix de la modélisation du noyau sera étudiée.D'autre part, l'impact de la prise en compte de la structure nucléaire des fragments dans le calcul des densités d'états sur les observables sera étudié. / Although discovered 75 years ago, nuclear fission is still under investigation. Indeed, the understanding of this phenomenon still presents theoretical difficulties due to its complexity. This requires a good understanding of the structure of atomic nucleus and at the same time a detailed description of the mechanisms driving the evolution of a fissioning system.A new statistical scission point model named SPY (Scission Point Yields) is developped to model the fission mechanism and determine nascent fragments characteristics (yields, kinetic energy, excitation energy). This model is based on the Wilkins model developed in 1976. It consists in a statistical description of the fission process at the scission point where fragments are completely defined and well separated. One of the main advance brought by SPY model is the introduction of microscopic description of the nuclear structure in the calculation of the energy of the system at scission. Therefore, this model can be regarded as a theoretical laboratory for fission modeling since it allows to study the relationship between fission fragments properties and their nuclear structure.With SPY, we were able to calculate the properties of fragments and to identify global trends for about 3000 fissioning nuclei from Z=70 to Z=109 and from proton drip line to neutron drip line.After a general presentation of SPY model, results for thermal fission of uranium 235 and spontaneous fission of 252 californium are compared with experimental data. A systematic study over all currently synthesized nuclei is also done before extending this study beyond the synthesizable nuclei area. Finally the main developments of the model performed will be detailed.The first one is related to calcultation of the Coulomb interaction energy between the two fragments. The charge distributions from microscopic calculations are introduced to improve the calculation of the energy of Coulomb interaction. The ability to redefine the scission point of the system thanks to these distributions will also be discussed. The second development concerns the relationship between nucleus modeling and observables related to fission fragments. On the one hand, different models of the nucleus to calculate the individual energy of the fragments, such as liquid drop model, will be considered and the impact of the choice of the nucleus modeling will be studied. On the other hand, the impact of the inclusion of the nuclear structure of the fragments in the calculation of states densities on observable will be studied.

No description available.

Abstract Formosan macaque (Macaca cyclopis) is the endemic and threatening species of Taiwan, but information regarding their social behaviors is rare. Troop fission of macaque¡¦s social behaviors was the rarely and accidental behavior. Two fission of Formosan macaques troops, from B0 and C0, at Mt. Longevity of Taiwan were the objects in this study. Field study was concentrated from November 1999 when fission occurred till May 2000. The records included the troop¡¦s composition changes and interactions of troops after fission, and using these records to infer the reason of troop fission in Formosan macaques. The focal sampling method and scan sampling method were used to collect individuals¡¦ behaviors¡Bsocial behaviors and habitat utilization of four troops¡]main troop B, branch troop Ba, main troop C and branch troop Ca¡^ after fission. Troop B and Ba remained separately six months after fission. But two months after fission, a fusion occurred between troop Ca and troop C. In the phenomenon of fission, the individuals who left the original troop and emigrated to the branch troop were all the subordinate or periphery individuals in the original troops. When they emigrated to the branch troops, their ranks were higher than that of the original troops. Adult females initiated the troop fission, and the other individuals joined later. Compared with the adult male, the composition of troop adult females were much stable and were the nucleus of branch troops. Only the adult sex ratios of troop Ca was lower than that of the original troop. Females delivered infants in branch troops were pregnant before troop fission. These two cases indicated that: fission occurred in Formosan macaque was not due to increasing mating partners or chances, but because of some adult females¡¦ fitness lost in their original troop. After fission, the branch troops, Ba and Ca, were 1/4 ~ 1/5 troop size to the main troop. When main troop B met the branch troop Ba, the behaviors of main troop B indicated troop B was dominant to the branch troop Ba. The main troop B and branch troop Ba had a significant difference in home range using ¡]£q2 = 49.195, d.f.= 14, p< 0.05¡^. The branch troop Ba¡¦ home range was larger than that of the main troop B or of the original troop B0. The difference of night resting-sites between the main troop B and the branch troop Ba was not significant¡]£q2 = 11.6, d.f.= 13, p> 0.598¡^.

The gap between processor speed and memory access performance increases continuingly. In order to improve performance degradation due to memory accesses, we can reduce memory block accesses by improving data locality. In this research, we focus on optimizing data locality in loops. We adopt an iterative greedy algorithm. It iteratively perform loop fission and loop fusion by moving strongly-connected components among loops subject to data dependence constraints. It evaluates data locality change of each move and decide if accept such move. Subsequently loops can be improved gradually forward optimal result.

Thèse de doctorat : Mécanique et énergétique : INPL : 2008. / Titre provenant de l'écran-titre.