Collège de France

About: Collège de France is a education organization based out in Paris, France. It is known for research contribution in the topics: Population & Receptor. The organization has 6541 authors who have published 11983 publications receiving 648742 citations. The organization is also known as: College de France.

Temporal and spectral gamma-ray properties of Mkn 421 above 250 GeV from CAT observations between 1996 and 2000

Abstract: The -ray emission above 250 GeV from the BL Lac object Markarian 421 was observed by the CAT Cherenkov imaging telescope between December, 1996, and June, 2000. In 1998, the source produced a series of small flares, making it the second extragalactic source detected by CAT. The time-averaged dierential spectrum has been measured from 0: 3t o 5 TeV, which is welltted with ap ower law: dE E 2:880:12 stat 0:06 syst TeV . In 2000, the source showed an unprecedented activity, with variability time-scales as short as one hour, as for instance observed during the night between 4 and 5 February. The 2000 time-averaged spectrum measured is compatible with that of 1998, but some indication of a spectral curvature is found between 0:3 and 5 TeV. The possibility of TeV spectral hardening during flares is also discussed, and the results are compared to those obtained on the other TeV BL Lac, Markarian 501.

Gap Junction Communication

Abstract: Gap junction channels provide an intercellular pathway for direct cytoplasm-to-cytoplasm exchanges of ions and small molecules (<1.8 kDa). These channels are widely expressed in the central nervous system, especially in neurons (electrical synapses) and in glial cells (astrocytic networks). Connexins, their molecular constituents, belong to a multigenic family and at least eight of them have being detected in the brain. Their functional and molecular properties set the rules for an intercellular ‘language’ based on electrical and metabolic coupling. Several signaling molecules have been identified to cross these junctional channels and to contribute to important brain functions, such as information processing and ionic and metabolic homeostasis.

RXRalpha-null F9 embryonal carcinoma cells are resistant to the differentiation, anti-proliferative and apoptotic effects of retinoids.

Abstract: The F9 murine embryonal carcinoma (EC) cell line, a well established model system for the study of retinoic acid (RA)-induced differentiation, differentiates into cells resembling three types of extra-embryonic endoderm (primitive, parietal and visceral), depending on the culture conditions and RA concentration used. A number of previously identified genes are differentially expressed during this process and serve as markers for the different endodermal cell types. Differentiation is also accompanied by a decreased rate of proliferation and an apoptotic response. Using homologous recombination, we have disrupted both alleles of the retinoid X receptor (RXR) alpha gene in F9 cells to investigate its role in mediating these responses. The loss of RXRalpha expression impaired the morphological differentiation of F9 EC cells into primitive and parietal endoderm, but has little effect on visceral endodermal differentiation. Concomitantly the inducibility of most primitive and parietal endoderm differentiation-specific genes was impaired, while several genes upregulated during visceral endodermal differentiation were induced normally. We also demonstrate that RXRalpha is required for both the anti-proliferative and apoptotic responses in RA-treated F9 cells. Additionally, we provide further evidence that retinoic acid receptor (RAR)-RXR heterodimers are the functional units transducing the effects of retinoids in F9 cells.

From atoms to crystals: a mathematical journey

Abstract: We present an overview of some works on the models of computational quantum chemistry. We examine issues such as the existence of ground states (both for the electronic structure and the configuration of nuclei), the foundations of the models of the crystalline phase, and the macroscopic limits. We emphasize the connections between the physical modelling, the numerical concerns and the mathematical analysis of the problems. 1. Outline This article presents an expository review of some collective work by a group of researchers (X. Blanc, E. Cancès, I. Catto, M. Esteban, E. Séré) to which we belong on the mathematical aspects of the models used for the simulation of matter at the microscopic scale. The relation of these models to models for the continuum description of matter at the macroscopic scale will also be examined. The mathematical material reported on here covers almost two decades, starting in the late 1980s with our contribution to a general endeavour (mainly initiated by E.H. Lieb, B. Simon, W. Thirring) to put the models of quantum chemistry on a sound mathematical basis (see Sections 3 to 5). It continues in the 1990s with our work on the thermodynamic limit of molecular models in order to establish and/or justify models for the crystal phase (see Section 6). The most recent step (in fact hardly addressed here, only outlined in Section 7, and postponed until future publications) is the definition of the energy of general infinite microscopic sets of particles and the passage to the macroscale with the tentative definition of the density of mechanical energy on the basis of models at the atomistic scale. The program described above is ambitious. However, we are in a position where on the one hand some building blocks of the whole program are indeed known from the mathematical standpoint for most of the models used in practice, and on the other hand where we are able to accomplish all the steps for some models, rather academic in nature but nevertheless illustrative and of some physical relevance. Therefore, we believe that this is the proper time for such a survey article. Enough convincing arguments are available to prove that it is indeed possible to analyze models of microscopic matter and to determine the macroscopic limit, on a mathematical ground, provided one restricts one’s ambition. A large body Received by the editors November 20, 2004. 2000 Mathematics Subject Classification. Primary 35Bxx, 35Jxx, 35Pxx, 49Kxx, 81Q05, 81Q10, 82Bxx. This article is an extended version by the two authors of notes based upon a series of lectures given by PLL at Collège de France during the fall semester of the academic year 2003/04. c ©2005 American Mathematical Society Reverts to public domain 28 years from publication