Experimental Studies of Prompt Fission Neutron Energy Spectra

AbstractPrompt fission neutron spectra were measured in the reactions 238U(n,f), 235U(n,f) and 237Np(n,f) at different incident neutron energies. The neutrons were detected using a coaxial doped p-terphenyl scintillation detector in coincidence with fission fragments and their time-of-flight was recorded. The properties of the neutron detector were determined and the results are presented in this work. A preliminary neutron detection efficiency was applied to data from the neutron-induced fission of 238U at En = 5.2 MeV, leading to encouraging results

Pareto, Lausanne et le canton de Vaud

Comment l’histoire locale peut-elle participer d’une histoire de la pensée économique focalisée sur la figure de Pareto ? Plus modestement, peut-on espérer clarifier la nature des rapports ayant uni Vilfredo Pareto à l’environnement politique de Lausanne ? La question s’avère épineuse, fidèle d’une certaine manière, aux difficultés à penser l’université dans ses rapports à la cité. Comme l’ont noté par ailleurs d’autres travaux, les sources d’information, pour construire un tel objet historiq..

Spectres en énergie des neutrons prompts de fission : optimisation du dispositif expérimental et application à l'²³⁸U

The nuclear fission is a complex phenomenon whose mechanisms are not fully understood. Within the framework of an international cooperation, the CEA/DAM/DIF is taking part in the study of prompt fission neutron energy spectra from fast neutron induced fission, focusing on the low energy domain of these spectra (<1 MeV). This PhD was dedicated to the optimization of the experimental setup. New fission detectors were developed. We report on their conception and their performances in terms of alpha-fission discrimination, timing resolution and distortion on the measured spectrum. In a second step, several neutron detectors were studied (neutron-gamma discrimination, detection efficiency), so as to optimize the detection of low energy neutrons (<1 MeV). In the present document, we report on the results of this comparative study. Finally, the optimized experimental setup was used to measure prompt fission neutron energy spectra for the fast-neutron induced fission of ²³⁸U. After detailing the data analysis method, the results are interpreted in terms of models and evaluations.La fission nucléaire est un phénomène complexe dont tous les mécanismes ne sont pas entièrement compris. Dans le cadre d'une coopération internationale, le CEA/DAM/DIF étudie les spectres en énergie des neutrons prompts émis lors de la fission induite par des neutrons rapides, et plus particulièrement la zone à basse énergie de ces spectres (<1 MeV). Ce travail de thèse a consisté à optimiser un dispositif expérimental de mesure de neutrons prompts de fission. Dans un premier temps, de nouveaux détecteurs de fission ont été développés. Nous en rapportons ici la conception et étudions leurs performances en termes de discrimination alpha-fission, de résolution en temps et de distorsion sur le spectre mesuré. Le second axe de développement abordé au cours de cette thèse est celui de la détection des neutrons. Plusieurs types de détecteurs ont été comparés (discrimination neutron-gamma, efficacité de détection), en vue d'optimiser la détection des neutrons de basse énergie (<1 MeV). Ce mémoire présente les résultats de ces études. Enfin, le dispositif expérimental ainsi optimisé est utilisé pour mesurer le spectre en énergie des neutrons prompts émis lors de la fission induite par neutrons de l' ²³⁸UU. Après avoir présenté la méthode utilisée pour l'analyse des données, les résultats obtenus sont interprétés en termes de modèles et d'évaluations

PR-Set7–dependent lysine methylation ensures genome replication and stability through S phase

PR-Set7/SET8 is a histone H4–lysine 20 methyltransferase required for normal cell proliferation. However, the exact functions of this enzyme remain to be determined. In this study, we show that human PR-Set7 functions during S phase to regulate cellular proliferation. PR-Set7 associates with replication foci and maintains the bulk of H4-K20 mono- and trimethylation. Consistent with a function in chromosome dynamics during S phase, inhibition of PR-Set7 methyltransferase activity by small hairpin RNA causes a replicative stress characterized by alterations in replication fork velocity and origin firing. This stress is accompanied by massive induction of DNA strand breaks followed by a robust DNA damage response. The DNA damage response includes the activation of ataxia telangiectasia mutated and ataxia telangiectasia related kinase–mediated pathways, which, in turn, leads to p53-mediated growth arrest to avoid aberrant chromosome behavior after improper DNA replication. Collectively, these data indicate that PR-Set7–dependent lysine methylation during S phase is an essential posttranslational mechanism that ensures genome replication and stability

Car Black Box System

This paper presents the concept of car black box vehicle safety system which would not only record the data, but also gives indication like engine overheating, alcohol consumption etc. In the case of an accident the message is sent through the GSM to prescribed mobile numbers. For the security purpose, the password is given to the black box to secure or prevent the recorded data. User enters the password for authentication of black box for accessing recorded data. Recorded data is used to find out the proper & actual reason behind an accident

The orthoptera in Lorraine (France). An ecological approach. (Insecta, Orthoptera)

A survey of the Orthoptera in Lorraine is presented: 60 species have been listed to date. A "reference list" is proposed, which gives, in addition to an up to date taxonomical list, the regional status of abundance for each species, as far as it can be outlined. The regional fauna is compared to those in neighbouring regions. Two examples of the use of Orthoptera in current Nature conservation and management are given. The conclusion deals with the importance of the Orthoptera as tool, but also as a goal, in Nature conservation.L'état provisoire de l'inventaire des Orthoptères de Lorraine est présenté. Il fait état de 60 espèces répertoriées jusqu'à présent. Une liste de référence est proposée, qui, en plus de la taxonomie, essaie de préciser le statut régional d'abondance de chaque espèce. Ce peuplement régional est comparé avec celui de régions voisines, pour lesquelles un travail analogue a été réalisé. L'utilisation des Orthoptères dans la gestion conservatoire des milieux naturels est illustrée par deux exemples: - les espèces déterminantes des Zones Naturelles d'Intérêt Ecologique Faunistique et Floristique - un aspect de la gestion d'une Réserve Naturelle de Lorraine par le biais des Orthoptères

DAFOE: A Platform for Building Ontologies from Texts

International audienceAlthough text-based ontology engineering gained much popularity in the last 10 years, very few ontology engineering platforms exploit the full potential of the connection between texts and ontologies. We propose DAFOE, a new platform for building ontologies with a terminological component using diff erent types of linguistic entries (text corpora, results of natural language processing tools, terminologies or thesauri). DAFOE supports knowledge structuring and conceptual modelling from these linguistic entries as well as ontology formalization. DAFOE outputs models with two main original features: an ontology articulated with a lexical component and a connection with the text or linguistic entry that motivated their defi nition

PR-SET7 and SUV4-20H regulate H4 lysine-20 methylation at imprinting control regions in the mouse

Imprinted genes are important in development and their allelic expression is mediated by imprinting control regions (ICRs). On their DNA-methylated allele, ICRs are marked by trimethylation at H3 Lys 9 (H3K9me3) and H4 Lys 20 (H4K20me3), similar to pericentric heterochromatin. Here, we investigate which histone methyltransferases control this methylation of histone at ICRs. We found that inactivation of SUV4-20H leads to the loss of H4K20me3 and increased levels of its substrate, H4K20me1. H4K20me1 is controlled by PR-SET7 and is detected on both parental alleles. The disruption of SUV4-20H or PR-SET7 does not affect methylation of DNA at ICRs but influences precipitation of H3K9me3, which is suggestive of a trans-histone change. Unlike at pericentric heterochromatin, however, H3K9me3 at ICRs does not depend on SUV39H. Our data show not only new similarities but also differences between ICRs and heterochromatin, both of which show constitutive maintenance of methylation of DNA in somatic cells