Extremal spectral properties of Otsuki tori

Otsuki tori form a countable family of immersed minimal two-dimensional tori in the unitary three-dimensional sphere. According to El Soufi-Ilias theorem, the metrics on the Otsuki tori are extremal for some unknown eigenvalues of the Laplace-Beltrami operator. Despite the fact that the Otsuki tori are defined in quite an implicit way, we find explicitly the numbers of the corresponding extremal eigenvalues. In particular we provide an extremal metric for the third eigenvalue of the torus.Comment: 14 pages, 1 figure. v.2: minor corrections v.3: references are updated. arXiv admin note: text overlap with arXiv:1009.028

Laplacian eigenvalues functionals and metric deformations on compact manifolds

In this paper, we investigate critical points of the Laplacian's eigenvalues considered as functionals on the space of Riemmannian metrics or a conformal class of metrics on a compact manifold. We obtain necessary and sufficient conditions for a metric to be a critical point of such a functional. We derive specific consequences concerning possible locally maximizing metrics. We also characterize critical metrics of the ratio of two consecutive eigenvalues

Verification of Kramers-Kronig relationship in porous materials having a rigid frame

The propagation of acoustic waves in porous materials having a rigid frame is well described by several models. A doubt about the causality of these models has been raised recently in the literature. A verification of the causality of these models is studied in this paper using the Kramers–Kronig dispersion relations adapted to the frequency power law dependence of the attenuation. It is shown that these models are causal in the high- and low-frequency range. A time domain wave equation and time-causal theory have been treated

No X-Rays or Radio from the Nearest Black Holes and Implications for Future Searches

Astrometry from the Gaia mission was recently used to discover the two nearest known stellar-mass black holes (BHs), Gaia BH1 and Gaia BH2. Both systems contain $\sim 1\,M_{\odot}$ stars in wide orbits ($a\approx$1.4 AU, 4.96 AU) around $\sim9\,M_{\odot}$ BHs. These objects are among the first stellar-mass BHs not discovered via X-rays or gravitational waves. The companion stars -- a solar-type main sequence star in Gaia BH1 and a low-luminosity red giant in Gaia BH2 -- are well within their Roche lobes. However, the BHs are still expected to accrete stellar winds, leading to potentially detectable X-ray or radio emission. Here, we report observations of both systems with the Chandra X-ray Observatory and radio observations with the Very Large Array (for Gaia BH1) and MeerKAT (for Gaia BH2). We did not detect either system, leading to X-ray upper limits of $L_X < 10^{29.4}$ and $L_X < 10^{30.1}\,\rm erg\,s^{-1}$ and radio upper limits of $L_r < 10^{25.2}$ and $L_r < 10^{25.9}\,\rm erg\,s^{-1}$. For Gaia BH2, the non-detection implies that the the accretion rate near the horizon is much lower than the Bondi rate, consistent with recent models for hot accretion flows. We discuss implications of these non-detections for broader BH searches, concluding that it is unlikely that isolated BHs will be detected via ISM accretion in the near future. We also calculate evolutionary models for the binaries' future evolution using Modules for Experiments in Stellar Astrophysics (MESA). We find that Gaia BH1 will be X-ray bright for 5--50 Myr when the star is a red giant, including 5 Myr of stable Roche lobe overflow. Since no symbiotic BH X-ray binaries are known, this implies either that fewer than $\sim 10^4$ Gaia BH1-like binaries exist in the Milky Way, or that they are common but have evaded detection, perhaps due to very long outburst recurrence timescales.Comment: Submitted to PAS

Analytical modeling of a coil in a ferromagnetic circuit including a superconductor pellet

PosterInternational audienceIn the design phase of the inductor required for the magnetization of High Temperature Superconductor (HTS) bulks, modeling and simulation are necessary for the design of this inductor. In this paper we have developed an analytical model to calculate the inductance for a coil of a ferromagnetic circuit with gap including a superconducting pellet. This model is based on the determination of the magnetic vector potential from solving the Laplace’s and Poisson’s equations in different regions of interest, using the separation of variables method in which the Cartesian coordinates are used. The boundary and continuity conditions between regions are considered to determine the global solution. This analytical resolution is carried out using a computation code developed under MATLAB. The results obtained are compared with those obtained by a numerical simulation based on the finite element method implemented under COMSOL. A remarkable concordance is observed between both approaches

Strengthening the impact of plant genetic resources through collaborative collection, conservation, characterisation, and evaluation: a tribute to the legacy of Dr Clive Francis

This paper is a tribute to the legacy of Dr Clive Francis, who directly and indirectly collected >14 000 accessions across 60 genera of pasture, forage, and crop species and their wild relatives around the Mediterranean basin, Eastern Africa, and Central and South Asia from 1973 to 2005. This was achieved by a collaborative approach that built strong interactions between disparate organisations (ICARDA, VIR, CLIMA, and Australian genebanks) based on germplasm exchange, conservation and documentation, capacity building, and joint collection. These activities greatly strengthened Australian pasture, forage, and crop genebanks, and led to widespread germplasm utilisation that has waned in the last 5 years, reflecting changing priorities among industry funding bodies and research providers. This situation must be reversed, given the pivotal role genetic resource collections must play to broaden the genetic and adaptive base of plant breeding, to meet the challenge of feeding an increasing population in a depleting resource base. Because the use of germplasm subsets that facilitate phenotyping will stimulate wider utilisation of genetic resources, we discuss the application of core collection and germplasm selection through habitat characterisation/filtering in Australian collections. Both are valid entry points into large collections, but the latter has the advantage of enabling both trait discovery and investigation of plant adaptation, and because it is based on a priori hypothesis testing, it increases understanding even when the trait of interest is not identified

R-parity violating resonant stop production at the Large Hadron Collider

We have investigated the resonant production of a stop at the Large Hadron Collider, driven by baryon number violating interactions in supersymmetry. We work in the framework of minimal supergravity models with the lightest neutralino being the lightest supersymmetric particle which decays within the detector. We look at various dilepton and trilepton final states, with or without b-tags. A detailed background simulation is performed, and all possible decay modes of the lighter stop are taken into account. We find that higher stop masses are sometimes easier to probe, through the decay of the stop into the third or fourth neutralino and their subsequent cascades. We also comment on the detectability of such signals during the 7 TeV run, where, as expected, only relatively light stops can be probed. Our conclusion is that the resonant process may be probed, at both 10 and 14 TeV, with the R-parity violating coupling {\lambda}"_{312} as low as 0.05, for a stop mass of about 1 TeV. The possibility of distinguishing between resonant stop production and pair-production is also discussed.Comment: 20 pages, 4 figures, 6 tables; Version accepted by JHE

Snowmass 2001: Jet Energy Flow Project

Conventional cone jet algorithms arose from heuristic considerations of LO hard scattering coupled to independent showering. These algorithms implicitly assume that the final states of individual events can be mapped onto a unique set of jets that are in turn associated with a unique set of underlying hard scattering partons. Thus each final state hadron is assigned to a unique underlying parton. The Jet Energy Flow (JEF) analysis described here does not make such assumptions. The final states of individual events are instead described in terms of flow distributions of hadronic energy. Quantities of physical interest are constructed from the energy flow distribution summed over all events. The resulting analysis is less sensitive to higher order perturbative corrections and the impact of showering and hadronization than the standard cone algorithms

First report of Cloeon vanharteni Gattolliat & Sartori, 2008 (Baetidae, Ephemeroptera) in the Maghreb

Cloeon vanharteni Gattolliat & Sartori, 2008 was newly discovered in the framework of our study of Ephemeroptera in the Draa basin, located in the southern region of the High Atlas in Morocco. This discovery is rather unexpected as the species was never reported outside the Arabian Peninsula and Levant; it is thus the first record for the Maghreb. The identification was based on morphological evidence and confirmed by the mitochondrial COI barcode