Mineralogical Variations within Two Widespread Holocene Tephra Layers from Cascade Range Volcanoes, U.S.A.

The heavy mineral content of volcanic ash from Mount Mazama (layer O) and Mount St. Helens (layer Yn) decreases downwind from each volcano. The transparent heavy mineral suite of layer O also varies downwind because of differences in specific gravity and shape of the grains, reflecting sorting processes during transportation in the atmosphere. In the first few tens of kilometers from the volcano some values strongly deviate from the general trend. This is attributed to exceptional turbulence at the time of eruptions in the vicinity of the vent.Le contenu en minéraux denses a été étudié dans des échantillons provenant de deux retombées volcaniques largement répandues sur le nord-ouest des États-Unis et sur le sud-ouest du Canada. L'une d'entre elles correspond à l'explosion du mont Mazama (Oregon) survenue il y a environ 6700 ans; elle est connue sous le nom de « couche O ». L'autre résulte d'une explosion du mont St. Helens qui a eu lieu il y a environ 3400 ans; elle est connue sous le nom de « couche Yn ». Dans chacun des deux lobes, le contenu en minéraux denses diminue avec la distance aux volcans respectifs, et des variations spatiales systématiques de l'association de minéraux denses transparents dans le lobe de la « couche O » ont été mises en évidence. Ces variations sont comparées à celles qui ont été observées dans les retombées récentes des volcans mont St. Helens (É.-U., 18 mai 1980) et El Chichôn (Mexique, mars-avril 1982). Elles sont expliquées par des processus de sélection qui ont lieu dans les nuages de poussières au cours du transport dans l'atmosphère.In Proben, die aus zwei ausgedehnten vulkanischen Niederschlàgen im Nord-Westen der U.S.A. und dem Sùd-Westen Kanadas stammen, wurde der Gehalt an dichten Mineralen studiert. Der eine Niederschlag entspricht dem Ausbruch des Mount Mazama (Oregon), der vor etwa 6700 Jahren stattgefunden hat; er ist unter der Bezeichnung "Schicht O" bekannt. Der andere entstammt einem Ausbruch des Mount St. Helens, der vor ungefàhr 3400 Jahren stattgefunden hat ; er ist unter der Bezeichnung "Schicht Yn" bekannt. In jedem der zwei Ausschnitte nimmt der Gehalt an dichten Mineralen ab, entsprechend zur Entfernung zum jeweiligen Vulkan, und im Ausschnitt der "Schicht O" konnten systematische ôrtliche Schwankungen in der Assoziation der transparenten dichten Minérale nachgewiesen werden. Dièse Schwankungen werden verglichen mit denen, die in den neueren Niederschlagen der Vulkane von Mount St. Helens (U.S.A., 18. Mai 1980) und El Chichôn (Mexiko, Màrz-April 1982) beobachtet wurden. Sie werden erklàrt durch Selektionsprozesse, die in den Staubwolken wàhrend des Transports in der Atmosphère stattgefunden haben

Discovery of the brightest T dwarf in the northern hemisphere

We report the discovery of a bright (H=12.77) brown dwarf designated SIMP J013656.5+093347. The discovery was made as part of a near-infrared proper motion survey, SIMP (Sondage Infrarouge de Mouvement Propre), which uses proper motion and near-infrared/optical photometry to identify brown dwarf candidates. A low resolution (lambda/dlambda~40) spectrum of this brown dwarf covering the 0.88-2.35 microns wavelength interval is presented. Analysis of the spectrum indicates a spectral type of T2.5+/-0.5. A photometric distance of 6.4+/-0.3 pc is estimated assuming it is a single object. Current observations rule out a binary of mass ratio ~1 and separation >5 AU. SIMP 0136 is the brightest T dwarf in the northern hemisphere and is surpassed only by Eps Indi Bab over the whole sky. It is thus an excellent candidate for detailed studies and should become a benchmark object for the early-T spectral class.Comment: 4 pages, 3 figures, To be published in November 1, 2006 issue of ApJL. Following IAU recommendation, the survey acronym (IBIS) was changed to SIM

Recoil velocity at 2PN order for spinning black hole binaries

We compute the flux of linear momentum carried by gravitational waves emitted from spinning binary black holes at 2PN order for generic orbits. In particular we provide explicit expressions of three new types of terms, namely next-to-leading order spin-orbit terms at 1.5 PN order, spin-orbit tail terms at 2PN order, and spin-spin terms at 2PN order. Restricting ourselves to quasi-circular orbits, we integrate the linear momentum flux over time to obtain the recoil velocity as function of orbital frequency. We find that in the so-called superkick configuration the higher-order spin corrections can increase the recoil velocity up to about a factor 3 with respect to the leading-order PN prediction. Furthermore, we provide expressions valid for generic orbits, and accurate at 2PN order, for the energy and angular momentum carried by gravitational waves emitted from spinning binary black holes. Specializing to quasi-circular orbits we compute the spin-spin terms at 2PN order in the expression for the evolution of the orbital frequency and found agreement with Mik\'oczi, Vas\'uth and Gergely. We also verified that in the limit of extreme mass ratio our expressions for the energy and angular momentum fluxes match the ones of Tagoshi, Shibata, Tanaka and Sasaki obtained in the context of black hole perturbation theory.Comment: 28 pages (PRD format), 1 figure, reference added, version published in PRD, except that the PRD version contains a sign error: the sign of the RHS of Eqs.(4.26) and (4.27) is wrong; it has been corrected in this replacemen

Irregular behaviour of class numbers and Euler-Kronecker constants of cyclotomic fields: the log log log devil at play

Kummer (1851) and, many years later, Ihara (2005) both posed conjectures on invariants related to the cyclotomic field $\mathbb Q(\zeta_q)$ with $q$ a prime. Kummer's conjecture concerns the asymptotic behaviour of the first factor of the class number of $\mathbb Q(\zeta_q)$ and Ihara's the positivity of the Euler-Kronecker constant of $\mathbb Q(\zeta_q)$ (the ratio of the constant and the residue of the Laurent series of the Dedekind zeta function $\zeta_{\mathbb Q(\zeta_q)}(s)$ at $s=1$). If certain standard conjectures in analytic number theory hold true, then one can show that both conjectures are true for a set of primes of natural density 1, but false in general. Responsible for this are irregularities in the distribution of the primes. With this survey we hope to convince the reader that the apparently dissimilar mathematical objects studied by Kummer and Ihara actually display a very similar behaviour.Comment: 20 pages, 1 figure, survey, to appear in `Irregularities in the Distribution of Prime Numbers - Research Inspired by Maier's Matrix Method', Eds. J. Pintz and M. Th. Rassia