Effects of electromagnetic waves on the electrical properties of contacts between grains

A DC electrical current is injected through a chain of metallic beads. The electrical resistances of each bead-bead contacts are measured. At low current, the distribution of these resistances is large and log-normal. At high enough current, the resistance distribution becomes sharp and Gaussian due to the creation of microweldings between some beads. The action of nearby electromagnetic waves (sparks) on the electrical conductivity of the chain is also studied. The spark effect is to lower the resistance values of the more resistive contacts, the best conductive ones remaining unaffected by the spark production. The spark is able to induce through the chain a current enough to create microweldings between some beads. This explains why the electrical resistance of a granular medium is so sensitive to the electromagnetic waves produced in its vicinity.Comment: 4 pages, 5 figure

Oxydation en voie humide de la pollution organique aqueuse par le peroxyde d'hydrogène Procédé « Wet Peroxide Oxidation » (WPO®) Étude de nouveaux catalyseurs

Les effluents aqueux pollués par des matières organiques provenant d'industries chimiques présentent souvent une faible biodégradabilité. Dans certains domaines de concentration (DCO = 0,5 - 15 g/l), le procédé WPO® développé au laboratoire se substitue avantageusement à l'incinération pour traiter ce type d'effluents. La réaction, qui met en œuvre le réactif de Fenton à température élevée, conduit parfois à la formation de quantités importantes d'acides carboxyliques légers. Nous avons donc développé des systèmes catalytiques originaux remplaçant les sels de fer et conduisant à une oxydation totale des acides carboxyliques. Le système le plus efficace constitué de sels de fer, de cuivre et de manganèse permet d'obtenir, en 1 h à 100 °C, l'oxydation totale d'un mélange synthétique de ces acides (COT = 5 g/l) avec 1,5 fois la quantité de peroxyde théoriquement nécessaire à l'oxydation. Le catalyseur précipité et séparé en fin de traitement peut être recyclé et conserve la môme activité. Les unités industrielles permettant d'effectuer le traitement WPO® avec les nouveaux catalyseurs, recyclés ou non, seront similaires à celle déjà réalisée pour le traitement de « points noirs » industriels.There is an important concern about the problems occuring with wastes elimination, specially the industrial liquid wastes. Te face the problem of organic aqueous wastes coming front various branches of industry, the WPO® (wet peroxide oxidation) process was developed at the laboratory. In the WAO process (wet air oxidation), which uses gaseous oxygen, the limiting step is usually oxygen transfer. In this new process, this problem is suppressed by using a liquid oxidising agent (hydrogen peroxide). This process is adapted from the classical Fenton's reaction and iron salts are used as the catalyst in order to promote the formation of •OH radicles which are the main active species. But the reaction is carried out at about 120 °C; so, a very significant TOC (total organic carton) removal efficiency is obtained (60 to 90 %) in comparison with the low efficiency of the classical Fenton's reagent (typically 25 % at room temperature).Significant amounts of free fatty acids are formed during the reaction. They are namely oxalic, malonic, succinic and acetic acids, which are common by products obtained during audition of most industrial organic pollutants. In order to comply with the regulations requirements, it was necessary to improve the efficiency of the original process. It was also very important to obtain an efficient elimination at a temperature not greater than 100 °C in order to avoid to pressurize the treatment reactor. This could be obtained by using new catalysts which are described in this paper.Because of the related field, precious metals like Pt and potentially toxic ones like Cr were not considered. One needs a treatment process as cheap and as reliable as possible. So, only Fe, Cu, Co, Ni and Mn were used as salts in order to test their calalytic activity in the treatment by hydrogen peroxide of a synthetical mixture of oxalic, malonic, succinic and acetic acids (O, M, S, A). The experimental device is a stirred tank reactor where the organics and the catalyst are batch loaded. It is continuously fed, for 1 hour, with hydrogen peroxide. The total amount injected is 1.5 the stoechiometric amount. In table 1, it can be seen that any metal has a satisfactory activity when used alone (TOC removal efficiency cannot exceed 22 %). In table 2, it is clear that, in soma cases, the association of two or three metals with each other can lead to very important synergetic effects. When using a mixture of Fe, Cu and Mn, the removal efficiency can increase to 91 %. This Fe/Cu/Mn catalyst is studied with further details in table 4. It appears to have its best efficiency at about 100 °C because of a parasitic decomposition of the peroxide at higher temperatures. For an organic mixture coutaining 5 g TOC/l, 100 ppm of each metal is a convenient concentration. This new catalyst still needs an acidic pH, from 3 to about 5, but the dependency is not so strict than with Fe alone (original process) which needs a value from 3 to 3.5. In addition, it was observed that the treatment time could be easily reduced (down to 45 minutes) as well as the amount of peroxide injected.Very similar results have been obtained with synthetic solutions of pollutants and with real industrial ones, thus establishing the ability of the Fe/Cu/Mn mixture to catalyse the oxidation of a large variety of species and not only carboxilic acids. The difference between the efficiency of this new catalyst and the conventional one is shown in table 5. Figures 1 and 2 are related to an Industrial WPO® unit which is commonly used with the conventional catalyst (Fe). It has been possible to improve its efficiency by using the new one without any significant modification. The Fe/Cu/Mn catalyst can be easily separated alter reaction (coprecipitation effect). Thus, the treated water meets the regulation requirements and the recovered catalyst can be easily resolubilized and recycled

Resolving galaxies in time and space: II: Uncertainties in the spectral synthesis of datacubes

In a companion paper we have presented many products derived from the application of the spectral synthesis code STARLIGHT to datacubes from the CALIFA survey, including 2D maps of stellar population properties and 1D averages in the temporal and spatial dimensions. Here we evaluate the uncertainties in these products. Uncertainties due to noise and spectral shape calibration errors and to the synthesis method are investigated by means of a suite of simulations based on 1638 CALIFA spectra for NGC 2916, with perturbations amplitudes gauged in terms of the expected errors. A separate study was conducted to assess uncertainties related to the choice of evolutionary synthesis models. We compare results obtained with the Bruzual & Charlot models, a preliminary update of them, and a combination of spectra derived from the Granada and MILES models. About 100k CALIFA spectra are used in this comparison. Noise and shape-related errors at the level expected for CALIFA propagate to 0.10-0.15 dex uncertainties in stellar masses, mean ages and metallicities. Uncertainties in A_V increase from 0.06 mag in the case of random noise to 0.16 mag for shape errors. Higher order products such as SFHs are more uncertain, but still relatively stable. Due to the large number statistics of datacubes, spatial averaging reduces uncertainties while preserving information on the history and structure of stellar populations. Radial profiles of global properties, as well as SFHs averaged over different regions are much more stable than for individual spaxels. Uncertainties related to the choice of base models are larger than those associated with data and method. Differences in mean age, mass and metallicity are ~ 0.15 to 0.25 dex, and 0.1 mag in A_V. Spectral residuals are ~ 1% on average, but with systematic features of up to 4%. The origin of these features is discussed. (Abridged)Comment: A&A, accepte

The Fornax Deep Survey with VST. II. Fornax A: a two-phase assembly caught on act

As part of the Fornax Deep Survey with the ESO VLT Survey Telescope, we present new $g$ and $r$ bands mosaics of the SW group of the Fornax cluster. It covers an area of $3 \times 2$ square degrees around the central galaxy NGC1316. The deep photometry, the high spatial resolution of OmegaCam and the large covered area allow us to study the galaxy structure, to trace stellar halo formation and look at the galaxy environment. We map the surface brightness profile out to 33arcmin ($\sim 200$kpc $\sim15R_e$) from the galaxy centre, down to $\mu_g \sim 31$ mag arcsec$^{-2}$ and $\mu_r \sim 29$ mag arcsec$^{-2}$. This allow us to estimate the scales of the main components dominating the light distribution, which are the central spheroid, inside 5.5 arcmin ($\sim33$ kpc), and the outer stellar envelope. Data analysis suggests that we are catching in act the second phase of the mass assembly in this galaxy, since the accretion of smaller satellites is going on in both components. The outer envelope of NGC1316 still hosts the remnants of the accreted satellite galaxies that are forming the stellar halo. We discuss the possible formation scenarios for NGC1316, by comparing the observed properties (morphology, colors, gas content, kinematics and dynamics) with predictions from cosmological simulations of galaxy formation. We find that {\it i)} the central spheroid could result from at least one merging event, it could be a pre-existing early-type disk galaxy with a lower mass companion, and {\it ii)} the stellar envelope comes from the gradual accretion of small satellites.Comment: Accepeted for publication in Ap

NMR Experiments on a Three-Dimensional Vibrofluidized Granular Medium

A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient (PFG) NMR coupled with one-dimensional magnetic resonance imaging (MRI). The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers N_ell <= 4 was sufficiently low to achieve a nearly time-independent granular fluid. Using NMR, the vertical profiles of density and granular temperature were directly measured, along with the distributions of vertical and horizontal grain velocities. The velocity distributions showed modest deviations from Maxwell-Boltzmann statistics, except for the vertical velocity distribution near the sample bottom which was highly skewed and non-Gaussian. Data taken for three values of N_ell and two dimensionless accelerations Gamma=15,18 were fit to a hydrodynamic theory, which successfully models the density and temperature profiles including a temperature inversion near the free upper surface.Comment: 14 pages, 15 figure

Welcome to the Twilight Zone: The Mid-Infrared Properties of Poststarburst Galaxies

We investigate the optical and Wide-field Survey Explorer (WISE) colors of "E+A" identified post-starburst galaxies, including a deep analysis on 190 post-starbursts detected in the 2{\mu}m All Sky Survey Extended Source Catalog. The post-starburst galaxies appear in both the optical green valley and the WISE Infrared Transition Zone (IRTZ). Furthermore, we find that post-starbursts occupy a distinct region [3.4]-[4.6] vs. [4.6]-[12] WISE colors, enabling the identification of this class of transitioning galaxies through the use of broad-band photometric criteria alone. We have investigated possible causes for the WISE colors of post-starbursts by constructing a composite spectral energy distribution (SED), finding that mid-infrared (4-12{\mu}m) properties of post-starbursts are consistent with either 11.3{\mu}m polycyclic aromatic hydrocarbon emission, or Thermally Pulsating Asymptotic Giant Branch (TP-AGB) and post-AGB stars. The composite SED of extended post- starburst galaxies with 22{\mu}m emission detected with signal to noise >3 requires a hot dust component to produce their observed rising mid-infrared SED between 12 and 22{\mu}m. The composite SED of WISE 22{\mu}m non-detections (S/N<3), created by stacking 22{\mu}m images, is also flat, requiring a hot dust component. The most likely source of this mid-infrared emission of these E+A galaxies is a buried active galactic nucleus. The inferred upper limit to the Eddington ratios of post-starbursts are 1e-2 to 1e-4, with an average of 1e-3. This suggests that AGNs are not radiatively dominant in these systems. This could mean that including selections able to identify active galactic nuclei as part of a search for transitioning and post-starburst galaxies would create a more complete census of the transition pathways taken as a galaxy quenches its star formation.Comment: 13 pages, 11 figures, accepted for publication in the Astrophysical Journa

Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs

We present improved atmospheric parameters of nearby white dwarfs lying within 20 pc of the Sun. The aim of the current study is to obtain the best statistical model of the least-biased sample of the white dwarf population. A homogeneous analysis of the local population is performed combining detailed spectroscopic and photometric analyses based on improved model atmosphere calculations for various spectral types including DA, DB, DC, DQ, and DZ stars. The spectroscopic technique is applied to all stars in our sample for which optical spectra are available. Photometric energy distributions, when available, are also combined to trigonometric parallax measurements to derive effective temperatures, stellar radii, as well as atmospheric compositions. A revised catalog of white dwarfs in the solar neighborhood is presented. We provide, for the first time, a comprehensive analysis of the mass distribution and the chemical distribution of white dwarf stars in a volume-limited sample.Comment: 104 pages, 22 figures, 2 tables, accepted for publication in the Astrophysical Journal Supplemen