Photometric and Astrometric Calibration of the JWST Instrument Complement

In preparation for James Webb Space Telescope (JWST), a set of cross calibration programs with HST and Spitzer for suitable primary photometric standards and astrometric fields were developed. NICMOS/HST and IRAC/Spitzer photometry observations of new solar analog standards in NGC 6791 and Melotte 66 were executed. These new photometric standards will provide ~ 5% photometric precision at V~19 from the near-IR to the mid-IR wavelength range for efficient on-orbit calibration and measuring of photometric stability of the JWST complement. For the astrometric calibration, a field in the LMC has been selected. This field falls within the JWST continuous viewing zone, within 5 degrees from the ecliptic poles, and has the stellar density necessary to achieve accuracies better than 1 mas with HST/ACS. These independent observations will play a key role in meeting the mission requirements and will allow a fast commissioning of the observatory.Comment: 9 pages, 3 figures; to appear in The Future of Photometric, spectrophotometric, and Polarimetric Standardization, ed. C. Sterken, AS

A Positive Test for Fermi-Dirac Distributions of Quark-Partons

By describing a large class of deep inelastic processes with standard parameterization for the different parton species, we check the characteristic relationship dictated by Pauli principle: broader shapes for higher first moments. Indeed, the ratios between the second and the first moment and the one between the third and the second moment for the valence partons is an increasing function of the first moment and agrees quantitatively with the values found with Fermi-Dirac distributions.Comment: 15 pages LaTeX, 2 eps figures. Final version, to appear in Mod. Phys. Lett.

Magnetoasymmetric transport in a mesoscopic interferometer: From the weak to the strong coupling regime

The microreversibility principle implies that the conductance of a two-terminal Aharonov-Bohm interferometer is an even function of the applied magnetic flux. Away from linear response, however, this symmetry is not fulfilled and the conductance phase of the interferometer when a quantum dot is inserted in one of its arms can be a continuous function of the bias voltage. Such magnetoasymmetries have been investigated in related mesoscopic systems and arise as a consequence of the asymetric response of the internal potential of the conductor out of equilibrium. Here we discuss magnetoasymmetries in quantum-dot Aharonov-Bohm interferometers when strong electron-electron interactions are taken into account beyond the mean-field approach. We find that at very low temperatures the asymmetric element of the differential conductance shows an abrupt change for voltages around the Fermi level. At higher temperatures we recover a smooth variation of the magnetoasymmetry as a function of the bias. We illustrate our results with the aid of the electron occupation at the dot, demonstrating that its nonequilibrium component is an asymmetric function of the flux even to lowest order in voltage. We also calculate the magnetoasymmetry of the current-current correlations (the noise) and find that it is given, to a good extent, by the magnetoasymmetry of the weakly nonlinear conductance term. Therefore, both magnetoasymmetries (noise and conductance) are related to each other via a higher-order fluctuation-dissipation relation. This result appears to be true even in the low temperature regime, where Kondo physics and many-body effects dominate the transport properties.Comment: 17 pages, 9 figure

Analysis of Balmer Profiles of early type stars

The spectral energy distribution (SED) of recent star formation regions is dominated by the more massive and early stars (O and B types). These stars show large and very significant absorption features, the most prominent being the recombination lines of H, HeI and HeII. In particular, the shape of their profiles are very dependent on the luminosity of the star. We have explored the potential use of high resolution profiles to discriminate between different luminosity classes and spectral types, by using profiles of the He and Balmer lines. We have calculated growth curves for each of the lines and their dependence on gravity and effective temperature. We show some of these theoretical growth curves and our preliminary conclusions are analyzed and discussed.Comment: 1 pag, Contribution to the conference "Cosmic Evolution and Galaxy Formation: Structure, Interactions and Feedback", Nov. 1999 (Puebla, Mexico), to be published in ASP. Conf. Series, Eds. J. Franco, E. Terlevich. O. Lopez-Cruz, I. Aretxag

Quatre dies de congrés a València : el "XII Congreso Nacional de Geografía"

Le XII Congrès National de Géographie, organisé par l'AGE et l'Université de Valence, s'est tenu à Valence dans les derniers jours du mois de mai de 1991. Il y a eu quatre séances scientifiques, sur des sujets de géographie urbaine, géographie rurale, changements dans l'environnement et risques naturels. La dichotomie entre géographie physique et géographie humaine a plané sur tous les débats et une table ronde lui a été consacrée. De même, la thématique de l'environnement a domine sur tout autre sujet au cours des débats. Une visite à l'Albufera et quatre excursions dans le Pays Valencien ont complété les séances.At the end of May 1991 it was held in Valencia the 12th National Geographical Congress organized by the AGE (Association of Spanish Geographers) and by the University of Valencia. Four sessions were developed: Urban Geography, Rural Geography, Geographical Implications of Environmental Change, and Uncertainty and Natural Hazards. One of the pervasive issues in the Congress was the eternal dichotomy between Physical and Human Geography, selected for a panel discussion. Environmental issues fared high in sessions and debates. A visit to the Albufera and four field trips in the Valencia area completed the sessions held in the Facultat de Geografia i Historia of the University of Valencia.Se celebró en Valencia, a finales de mayo de 1991, el XII Congreso Nacional de Geografia organizado por la AGE y la Universidad de Valencia. Se desarrollaron cuatro ponencias: una sobre geografia urbana, otra sobre geografia rural, y las otras dos sobre «Cambio ambiental y repercusiones geográficas» e «incertidumbre y riesgos naturales», más cercanas a la geografia física. Pero, de hecho, una de las cuestiones permanentemente flotantes en las sesiones congresuales fue la eterna dicotomia entre geografia física y humana, y asi se explicitó en una mesa redonda dedicada al tema. La temática medioambiental dominó sobre las otras a lo largo de los debates. Una visita a la Albufera y cuatro excursiones por el País Valenciano completaron las sesiones desarrolladas en la Facultad de Geografia e Historia de la Universidad de Valencia.Va celebrar-se a València, a finals de maig de 1991, el XII Congrés Nacional de Geografia organitzat per l'AGE i la Universitat de València. Es van desenvolupar quatre ponúncies: una sobre geografia urbana, una altra sobre geografia rural i dues més sobre «Canvi ambiental i repercussions geogràfiques» i «Incertesa i riscos naturals», més properes a la geografia física. De fet, pero, una de les qüestions permanentment flotants en les sessions coneressuals va ser l'eterna "dicotomia entre geografia física i humana, i així es va explicitar en una taula rodona dedicada al tema. La temàtica del medi ambient va dominar sobre les altres al llarg dels debats. Una visita a l'Albufera i quatre excursions pel País València van completar les sessions desenvolupades a la Facultat de Geografia i Història de la Universitat de València