Reversible enhancement of the magnetism of ultrathin Co films by H adsorption

By means of ab initio calculations, we have investigated the effect of H adsorption in the structural, electronic and magnetic properties of ultrathin Co films on Ru(0001). Our calculations predict that H occupies hollow sites preserving the two-dimensional 3-fold symmetry. The formation of a complete H overlayer leads to a very stable surface with strong H-Co bonds. H tends to suppress surface features, in particular, the enhancement of the magnetic moments of the bare film. The H-induced effects are mostly confined to the Co atoms bonded to H, independent of the H coverage or of the thickness and the structure of the Co film. However, for partial H coverages a significant increase occurs in the magnetic moment for the surface Co atoms not bonded to H, leading to a net enhancement of surface magnetism.Comment: 6 pages, 4 figures, 3 table

A pilot search for mm-wavelength recombination lines from emerging ionized winds in pre-planetary nebulae candidates

We report the results from a pilot search for radio recombination line (RRL) emission at millimeter wavelengths in a small sample of pre-planetary nebulae (pPNe) and young PNe (yPNe) with emerging central ionized regions. Observations of the H30\alpha, H31a, H39a, H41a, H48b, H49b, H51b, and H55g lines at 1 and 3mm have been performed with the IRAM 30 m radio telescope. These lines are excellent probes of the dense inner (<~150 au) and heavily obscured regions of these objects, where the yet unknown agents for PN-shaping originate. We detected mm-RRLs in three objects: CRL 618, MWC 922, and M 2-9. For CRL 618, the only pPN with previous published detections of H41a, H35a, and H30a emission, we find significant changes in the line profiles indicating that current observations are probing regions of the ionized wind with larger expansion velocities and mass-loss rate than ~29 years ago. In the case of MWC 922, we observe a drastic transition from single-peaked profiles at 3mm to double-peaked profiles at 1mm, which is consistent with maser amplification of the highest frequency lines; the observed line profiles are compatible with rotation and expansion of the ionized gas, probably arranged in a disk+wind system around a ~5-10 Msun central mass. In M 2-9, the mm-RRL emission appears to be tracing a recent mass outburst by one of the stars of the central binary system. We present the results from non-LTE line and continuum radiative transfer models, which enables us to constrain the structure, kinematics, and physical conditions (electron temperature and density) of the ionized cores of our sample. (abridged). We deduce mass-loss rates of ~1e-6-1e-7 Msun/yr, which are significantly higher than the values adopted by stellar evolution models currently in use and would result in a transition from the asymptotic giant branch to the PN phase faster than hitherto assumed.Comment: Accepted by Astronomy and Astrophysics. 28 pages, including figure

INFLUENCE OF PREPARATION PROCESS ON PHYSICAL PROPERTIES AND DEVITRIFICATION OF Li2B2O4 (0,9) LiFe5O8 (0,1) GLASSES

Double roller quenching of Li2B2O4(0.9)-LiFe5O8(0.1) has been performed with various melt temperatures and roller speeds. The changes in physical properties or in the devitrification process of the amorphous samples are shown to be related to the LiFe5O8 content variations or to the Fe2+ appearance but not to structural changes of the amorphous state due to preparation processe

VIMOS-VLT spectroscopy of the giant Ly-alpha nebulae associated with three z~2.5 radio galaxies

The morphological and spectroscopic properties of the giant (>60 kpc) Ly-alpha nebulae associated with three radio galaxies at z~2.5 (MRC 1558-003, MRC 2025-218 and MRC 0140-257) have been investigated using integral field spectroscopic data obtained with VIMOS on VLT. The morphologies are varied. The nebula of one source has a centrally peaked, rounded appearance. In the other two objects, it consists of two spatial components. The three nebulae are aligned with the radio axis within <30 deg. The total Ly-alpha luminosities are in the range (0.3-3.4) x 1e44 erg s-1. The Ly-alpha spectral profile shows strong variation through the nebulae, with FWHM values in the range ~400-1500 km s-1 and velocity shifts V~120-600 km s-1. We present an infall model which can explain successfully most Ly-alpha morphological and spectroscopic properties of the nebula associated with MRC 1558-003. This adds further support to our previous conclusion that the _quiescent_ giant nebulae associated with this and other high redshift powerful radio galaxies are in infall. A problem for this model is the difficulty to reproduce the large Ly-alpha FWHM values. We have discovered a giant (~85 kpc) Ly-alpha nebula associated with the radio galaxy MRC 0140-257 at z=2.64. It shows strikingly relaxed kinematics (FWHM2) radio galaxies.Comment: 14 pages, 13 figures. Accepted for publication in MNRA

Investigating the effect of belowground microbial volatiles on plant nutrient status: perspective and limitations

Volatile organic compounds displayed biological activities on a wide range of organisms, including plants and microbes. Investigating their role in the plant-microbe interaction processes occurring in the soil is challenging. By simulating belowground communication conditions between plant and microbes, in this study, we aimed to investigate the effects of the volatiles emitted by Serratia plymuthica and Fusarium culmorum on the nutrient status of maize plants. Plants were grown in potting soil and exposed to volatiles emitted by microbes inoculated in Petri dishes at the bottom of a jar. Nutrients content of plant tissues as well as soil volatiles were analyzed by ICP-MS and GC-MS, respectively. Our results showed that volatiles emitted belowground by Serratia plymuthica and Fusarium culmorum, in monoculture or interaction, differentially impacted on the content of some nutrient in plants, indicating that microbial volatiles-emitted belowground can affect the nutritional status of plants from a distance

Kinorhynch diversity in the southern Gulf of Mexico and a description of Dracoderes chaac sp. nov.

Sediment collections from the southern Gulf of Mexico between the Texas—Mexico border and the Yucatán Peninsula have resulted in many new kinorhynch species distribution records and the finding and taxonomic description of a new species, Dracoderes chaac sp. nov. This study focused on the non—echinoderid members of the Phylum Kinorhyncha, many of which are rare or restricted to only a few locations. A total of 136 specimens were identified from 24 sediment stations, distributed among the following species: Antygomonas gwenae, Campyloderes vanhoeffeni, Centroderes readae, Condyloderes flosfimbriatus, Co. rohalorum, Cristaphyes panamensis, Dracoderes chaac sp. nov., Leiocanthus corrugatus, L. langi, L. quinquenudus, L. satanicus, Pycnophyes alexandroi, Semnoderes lusca, and Sphenoderes aspidochelone. Additional undescribed species in the genera Leiocanthus, Mixtophyes, and Paracentrophyes were recovered. Statistical analysis of the stations revealed a grouping of locations where the majority of the pycnophyid species were recovered. Some species (e.g., Ca. vanhoeffeni, S. aspidochelone) had an extensive distribution, while others were recorded from one or few locations only (e.g., A. gwenae, Co. rohalorum). Most of the species were reported from earlier collections in the northern Gulf of Mexico on the U.S. continental shelf, between 700–1100 km away

Voltage dip generator for testing wind turbines connected to electrical networks

This paper describes a new voltage dip generator that allows the shape of the time profile of the voltage generated to be configured. The use of this device as a tool to test the fault ride-through capability of wind turbines connected to the electricity grid can provide some remarkable benefits: First, this system offers the possibility of adapting the main features of the time–voltage profile generated (dip depth, dip duration, the ramp slope during the recovery process after clearing fault, etc.) to the specific requirements set forth by the grid operation codes, in accordance with different network electrical systems standards. Second, another remarkable ability of this system is to provide sinusoidal voltage and current wave forms during the overall testing process without the presence of harmonic components. This is made possible by the absence of electronic converters. Finally, the paper includes results and a discussion on the experimental data obtained with the use of a reduced size laboratory prototype that was constructed to validate the operating features of this new device