Metallicity of high stellar mass galaxies with signs of merger events

We focus on an analysis of galaxies of high stellar mass and low metallicity. We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high resolution imaging and both spectroscopic and photometric information available in the SDSS database. For each galaxy in our sample, we conducted a systematic morphological analysis by visual inspection of MGC images using their luminosity contours. The galaxies are classified as either disturbed or undisturbed objects. We divide the sample into three metallicity regions, within wich we compare the properties of disturbed and undisturbed objects. We find that the fraction of galaxies that are strongly disturbed, indicative of being merger remnants, is higher when lower metallicity objects are considered. The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed galaxies (for high, medium, and low metallicity, respectively). Moreover, the ratio of the disturbed to undisturbed relative distributions of the population age indicator, Dn(4000), in the low metallicity bin, indicates that the disturbed objects have substantially younger stellar populations than their undisturbed counterparts. In addition, we find that an analysis of colour distributions provides similar results, showing that low metallicity galaxies with a disturbed morphology are bluer than those that are undisturbed. The bluer colours and younger populations of the low metallicity, morphologically disturbed objects suggest that they have experienced a recent merger with an associated enhanced star formation rate. [abridged]Comment: Astronomy & Astrophysics, in pres

Polynomial Relations in the Centre of U_q(sl(N))

When the parameter of deformation q is a m-th root of unity, the centre of U_q(sl(N))$ contains, besides the usual q-deformed Casimirs, a set of new generators, which are basically the m-th powers of all the Cartan generators of U_q(sl(N)). All these central elements are however not independent. In this letter, generalising the well-known case of U_q(sl(2)), we explicitly write polynomial relations satisfied by the generators of the centre. Application to the parametrization of irreducible representations and to fusion rules are sketched.Comment: 8 pages, minor TeXnical revision to allow automatic TeXin

Bromophenyl functionalization of carbon nanotubes : an ab initio study

We study the thermodynamics of bromophenyl functionalization of carbon nanotubes with respect to diameter and metallic/insulating character using density-functional theory (DFT). On one hand, we show that the activation energy for the grafting of a bromophenyl molecule onto a semiconducting zigzag nanotube ranges from 0.73 eV to 0.76 eV without any clear trend with respect to diameter within numerical accuracy. On the other hand, the binding energy of a single bromophenyl molecule shows a clear diameter dependence and ranges from 1.51 eV for a (8,0) zigzag nanotube to 0.83 eV for a (20,0) zigzag nanotube. This is in part explained by the transition from sp2 to sp3 bonding occurring to a carbon atom of a nanotube when a phenyl is grafted to it and the fact that smaller nanotubes are closer to a sp3 hybridization than larger ones due to increased curvature. Since a second bromophenyl unit can attach without energy barrier next to an isolated grafted unit, they are assumed to exist in pairs. The para configuration is found to be favored for the pairs and their binding energy decreases with increasing diameter, ranging from 4.34 eV for a (7,0) nanotube to 2.27 eV for a (29,0) nanotube. An analytic form for this radius dependence is derived using a tight binding hamiltonian and first order perturbation theory. The 1/R^2 dependance obtained (where R is the nanotube radius) is verified by our DFT results within numerical accuracy. Finally, metallic nanotubes are found to be more reactive than semiconducting nanotubes, a feature that can be explained by a non-zero density of states at the Fermi level for metallic nanotubes.Comment: 7 pages, 5 figures and 3 table

Electrical transport and low-temperature scanning tunneling microscopy of microsoldered graphene

Using the recently developed technique of microsoldering, we perform a systematic transport study of the influence of PMMA on graphene flakes revealing a doping effect of up to 3.8x10^12 1/cm^2, but a negligible influence on mobility and gate voltage induced hysteresis. Moreover, we show that the microsoldered graphene is free of contamination and exhibits a very similar intrinsic rippling as has been found for lithographically contacted flakes. Finally, we demonstrate a current induced closing of the previously found phonon gap appearing in scanning tunneling spectroscopy experiments, strongly non-linear features at higher bias probably caused by vibrations of the flake and a B-field induced double peak attributed to the 0.Landau level of graphene.Comment: 8 pages, 3 figure

A Semi-classical calculus of correlations

The method of passive imaging in seismology has been developped recently in order to image the earth crust from recordings of the seismic noise. This method is founded on the computation of correlations of the seismic noise. In this paper, we give an explicit formula for this correlation in the "semi-classical" regime. In order to do that, we define the power spectrum of a random field as the ensemble average of its Wigner measure, this allows phase-space computations: the pseudo-differential calculus and the ray theory. This way, we get a formula for the correlation of the seismic noise in the semi-classcial regime with a source noise which can be localized and non homogeneous. After that, we show how the use of surface guided waves allows to image the earth crust.Comment: To appear in a special issue "Imaging and Monitoring with Seismic Noise" of the series "Comptes Rendus G\'eosciences", from the French "Acad\'emie des sciences

On arithmetic detection of grey pulses with application to Hawking radiation

Micron-sized black holes do not necessarily have a constant horizon temperature distribution. The black hole remote-sensing problem means to find out the `surface' temperature distribution of a small black hole from the spectral measurement of its (Hawking) grey pulse. This problem has been previously considered by Rosu, who used Chen's modified Moebius inverse transform. Here, we hint on a Ramanujan generalization of Chen's modified Moebius inverse transform that may be considered as a special wavelet processing of the remote-sensed grey signal coming from a black hole or any other distant grey sourceComment: 5 pages, published versio

The Mauritian Truth and Justice Commission: legitimacy, political negotiation and the consequences of slavery

We examine the origins, processes and outcomes of the Mauritian Truth and Justice Commission’s (MTJC), examination of slavery, indentured labour and their contemporary effects. It has not been considered a success by any commentator. We therefore ask how far James L. Gibson’s application of legitimacy theory to ‘Truth Commissions’ has purchase in this context and whether it was cynically motivated. We use MTJC documentation, extensive interviews and newspaper reports to show that Gibson’s theory provides insight into MTJC outcomes while demonstrating that politico-economic power structures were crucial. Conversely, the MTJC does not sit easily in Van Zyl’s ‘cynical operation’ category

Searching for Hyperbolicity

This is an expository paper, based on by a talk given at the AWM Research Symposium 2017. It is intended as a gentle introduction to geometric group theory with a focus on the notion of hyperbolicity, a theme that has inspired the field from its inception to current-day research

Non-degenerate, three-wave mixing with the Josephson ring modulator

The Josephson ring modulator (JRM) is a device, based on Josephson tunnel junctions, capable of performing non-degenerate mixing in the microwave regime without losses. The generic scattering matrix of the device is calculated by solving coupled quantum Langevin equations. Its form shows that the device can achieve quantum-limited noise performance both as an amplifier and a mixer. Fundamental limitations on simultaneous optimization of performance metrics like gain, bandwidth and dynamic range (including the effect of pump depletion) are discussed. We also present three possible integrations of the JRM as the active medium in a different electromagnetic environment. The resulting circuits, named Josephson parametric converters (JPC), are discussed in detail, and experimental data on their dynamic range are found to be in good agreement with theoretical predictions. We also discuss future prospects and requisite optimization of JPC as a preamplifier for qubit readout applications.Comment: 21 pages, 16 figures, 4 table

Ising metamagnets in thin film geometry: equilibrium properties

Artificial antiferromagnets and synthetic metamagnets have attracted much attention recently due to their potential for many different applications. Under some simplifying assumptions these systems can be modeled by thin Ising metamagnetic films. In this paper we study, using both the Wang/Landau scheme and importance sampling Monte Carlo simulations, the equilibrium properties of these films. On the one hand we discuss the microcanonical density of states and its prominent features. On the other we analyze canonically various global and layer quantities. We obtain the phase diagram of thin Ising metamagnets as a function of temperature and external magnetic field. Whereas the phase diagram of the bulk system only exhibits one phase transition between the antiferromagnetic and paramagnetic phases, the phase diagram of thin Ising metamagnets includes an additional intermediate phase where one of the surface layers has aligned itself with the direction of the applied magnetic field. This additional phase transition is discontinuous and ends in a critical end point. Consequently, it is possible to gradually go from the antiferromagnetic phase to the intermediate phase without passing through a phase transition.Comment: 8 figures, accepted for publication in Physical Review