Chemical tracers in proto-brown dwarfs: CO, ortho-H2_{2}CO, para-H2_{2}CO, HCO+^{+}, CS observations

We present a study of the CO isotopologues and the high-density tracers H$_{2}$CO, HCO$^{+}$, and CS in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30m telescope to observe the $^{12}$CO (2-1), $^{13}$CO (2-1), C$^{18}$O (2-1), C$^{17}$O (2-1), H$_{2}$CO (3-2), HCO$^{+}$ (3-2), and CS (5-4) lines in 7 proto-BDs. The hydrogen column density for the proto-BDs derived from the CO gas emission is $\sim$2-15 times lower than that derived from the dust continuum emission, indicating CO depletion from the gas-phase. The mean H$_{2}$CO ortho-to-para ratio is $\sim$3 for the proto-BDs and indicates gas-phase formation for H$_{2}$CO. We have investigated the correlations in the molecular abundances between the proto-BDs and protostars. Proto-BDs on average show a factor of $\sim$2 higher ortho-to-para H$_{2}$CO ratio than the protostars. Possible explanations include a difference in the H$_{2}$CO formation mechanism, spin-selective photo-dissociation, self-shielding effects, or different emitting regions for the ortho and para species. There is a tentative trend of a decline in the HCO$^{+}$ and H$_{2}$CO abundances with decreasing bolometric luminosity, while the CS and CO abundances show no particular difference between the proto-BDs and protostars. These trends reflect the scaled-down physical structures for the proto-BDs compared to protostars and differences in the peak emitting regions for these species. The C$^{17}$O isotopologue is detected in all of the proto-BDs as well as the more evolved Class Flat/Class II BDs in our sample, and can probe the quiescent gas at both early and late evolutionary stages.Comment: Accepted in MNRAS. arXiv admin note: text overlap with arXiv:1809.1016

Chemical tracers in proto-brown dwarfs: CN, HCN, and HNC observations

We present results from a study of nitrogen chemistry in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30 m telescope to observe the CN (2-1), HCN (3-2), and HNC (3-2) lines in 7 proto-BDs. All proto-BDs show a large CN/HCN abundance ratio of >20, and a HNC/HCN abundance ratio close to or larger than unity. The enhanced CN/HCN ratios can be explained by high UV flux originating from an active accretion zone in the proto-BDs. The larger than unity HNC/HCN ratio for the proto-BDs is likely caused by a combination of low temperature and high density. Both CN and HNC show a flat distribution with CO, indicating that these species can survive in regions where CO is depleted. We have investigated the correlations in the molecular abundances of these species for the proto-BDs with Class 0/I protostars. We find tentative trends of CN (HCN) abundances being about an order of magnitude higher (lower) in the proto-BDs compared to protostars. HNC for the proto-BDs shows a nearly constant abundance unlike the large spread of ~2 orders of magnitude seen for the protostars. Also notable is a rise in the HNC/HCN abundance ratio for the lowest luminosity objects, suggesting that this ratio is higher under low-temperature environments. None of the relatively evolved Class Flat/Class II brown dwarfs in our sample show emission in HNC. The HNC molecule can be considered as an efficient tracer to search and identify early stage sub-stellar mass objects.Comment: Accepted in MNRA

The welfare of small livestock producers in Vietnam under trade liberalisation-- Integration of trade and household models

Vietnam has negotiated a series of bilateral and multilateral trade agreements and has made significant steps in integrating into the world economy. This integration is likely to have both positive and negative effects on different stakeholders in the economy. This paper seeks to measure the effects on the welfare of Vietnam’s small livestock producers' by linking a household model and the GTAP trade model. A GTAP utility SplitCom is used to separate out pig and poultry prior to several trade liberalisation scenarios being run. A recursive household model with a two-stage LES-AIDS model on consumption side and Cobb-Douglas functions on production side are used. Impacts of likely changes in the prices of inputs and outputs arising from different trade scenarios on behavior and welfare of the farm household are presented.International Relations/Trade, Livestock Production/Industries,

FUV and X-ray irradiated protoplanetary disks: a grid of models I. The disk structure

Context. Planets are thought to eventually form from the mostly gaseous (~99% of the mass) disks around young stars. The density structure and chemical composition of protoplanetary disks are affected by the incident radiation field at optical, FUV, and X-ray wavelengths, as well as by the dust properties. Aims. The effect of FUV and X-rays on the disk structure and the gas chemical composition are investigated. This work forms the basis of a second paper, which discusses the impact on diagnostic lines of, e.g., C+, O, H2O, and Ne+ observed with facilities such as Spitzer and Herschel. Methods. A grid of 240 models is computed in which the X-ray and FUV luminosity, minimum grain size, dust size distribution, and surface density distribution are varied in a systematic way. The hydrostatic structure and the thermo-chemical structure are calculated using ProDiMo. Results. The abundance structure of neutral oxygen is stable to changes in the X-ray and FUV luminosity, and the emission lines will thus be useful tracers of the disk mass and temperature. The C+ abundance distribution is sensitive to both X-rays and FUV. The radial column density profile shows two peaks, one at the inner rim and a second one at a radius r=5-10 AU. Ne+ and other heavy elements have a very strong response to X-rays, and the column density in the inner disk increases by two orders of magnitude from the lowest (LX = 1e29 erg/s) to the highest considered X-ray flux (LX = 1e32 erg/s). FUV confines the Ne+ ionized region to areas closer to the star at low X-ray luminosities (LX = 1e29 erg/s). H2O abundances are enhanced by X-rays due to higher temperatures in the inner disk and higher ionization fractions in the outer disk. The line fluxes and profiles are affected by the effects on these species, thus providing diagnostic value in the study of FUV and X-ray irradiated disks around T Tauri stars. (abridged)Comment: 47 pages, accepted by Astronomy and Astrophysics, a high resolution version of the paper is located at http://www.astro.rug.nl/~meijerink/disk_paperI_xrays.pd

The effects of dust evolution on disks in the mid-IR

In this paper, we couple together the dust evolution code two-pop-py with the thermochemical disk modelling code ProDiMo. We create a series of thermochemical disk models that simulate the evolution of dust over time from 0.018 Myr to 10 Myr, including the radial drift, growth, and settling of dust grains. We examine the effects of this dust evolution on the mid-infrared gas emission, focussing on the mid-infrared spectral lines of C2H2, CO2, HCN, NH3, OH, and H2O that are readily observable with Spitzer and the upcoming E-ELT and JWST. The addition of dust evolution acts to increase line fluxes by reducing the population of small dust grains. We find that the spectral lines of all species except C2H2 respond strongly to dust evolution, with line fluxes increasing by more than an order of magnitude across the model series as the density of small dust grains decreases over time. The C2H2 line fluxes are extremely low due to a lack of abundance in the infrared line-emitting regions, despite C2H2 being commonly detected with Spitzer, suggesting that warm chemistry in the inner disk may need further investigation. Finally, we find that the CO2 flux densities increase more rapidly than the other species as the dust disk evolves. This suggests that the flux ratios of CO2 to other species may be lower in disks with less-evolved dust populations.Comment: 13 pages, 9 figures, accepted in A&

Impurity effect of Lambda hyperon on collective excitations of atomic nuclei

Taking the ground state rotational band in $^{24}$Mg as an example, we investigate the impurity effect of $\Lambda$ hyperon on collective excitations of atomic nuclei in the framework of non-relativistic energy density functional theory. To this end, we take into account correlations related to the restoration of broken symmetries and fluctuations of collective variables by solving the eigenvalue problem of a five-dimensional collective Hamiltonian for quadrupole vibrational and rotational degrees of freedom. The parameters of the collective Hamiltonian are determined with constrained mean-field calculations for triaxial shapes using the SGII Skyrme force. We compare the low-spin spectrum for $^{24}$Mg with the spectrum for the same nucleus inside $^{25}_{\Lambda}$Mg. It is found that the $\Lambda$ hyperon stretches the ground state band and reduces the $B(E2:2^+_1 \rightarrow 0^+_1)$ value by $\sim 9$, mainly by softening the potential energy surface towards the spherical shape, even though the shrinkage effect on the average proton radius is only $\sim0.5$.Comment: 16 pages, 5 figures, and 1 tabl

Water depletion in the disk atmosphere of Herbig AeBe stars

We present high resolution (R = 100,000) L-band spectroscopy of 11 Herbig AeBe stars with circumstellar disks. The observations were obtained with the VLT/CRIRES to detect hot water and hydroxyl radical emission lines previously detected in disks around T Tauri stars. OH emission lines are detected towards 4 disks. The OH P4.5 (1+,1-) doublet is spectrally resolved as well as the velocity profile of each component of the doublet. Its characteristic double-peak profile demonstrates that the gas is in Keplerian rotation and points to an emitting region extending out to ~ 15-30 AU. The OH, emission correlates with disk geometry as it is mostly detected towards flaring disks. None of the Herbig stars analyzed here show evidence of hot water vapor at a sensitivity similar to that of the OH lines. The non-detection of hot water vapor emission indicates that the atmosphere of disks around Herbig AeBe stars are depleted of water molecules. Assuming LTE and optically thin emission we derive a lower limit to the OH/H2O column density ratio > 1 - 25 in contrast to T Tauri disks for which the column density ratio is 0.3 -- 0.4.Comment: Accepted for publication in Ap

Liste complémentaire des poissons marins de Nha-trang

This commented inventory of 310 fishes of Nhatrang Bay (Vietnam) completed the previous list compiled by P. Chevey, P. Chabanaud, J. Durand et Quang

Comparative metagenomic analysis reveals mechanisms for stress response in hypoliths from extreme hyperarid deserts

Understanding microbial adaptation to environmental stressors is crucial for interpreting broader ecological patterns. In the most extreme hot and cold deserts, cryptic niche communities are thought to play key roles in ecosystem processes and represent excellent model systems for investigating microbial responses to environmental stressors. However, relatively little is known about the genetic diversity underlying such functional processes in climatically extreme desert systems. This study presents the first comparative metagenome analysis of cyanobacteria-dominated hypolithic communities in hot (Namib Desert, Namibia) and cold (Miers Valley, Antarctica) hyperarid deserts. The most abundant phyla in both hypolith metagenomes were Actinobacteria, Proteobacteria, Cyanobacteria and Bacteroidetes with Cyanobacteria dominating in Antarctic hypoliths. However, no significant differences between the twometagenomeswere identified. The Antarctic hypolithicmetagenome displayed a high number of sequences assigned to sigma factors, replication,recombination andrepair, translation, ribosomal structure,andbiogenesis. In contrast, theNamibDesert metagenome showed a high abundance of sequences assigned to carbohydrate transport and metabolism. Metagenome data analysis also revealed significantdivergence inthe geneticdeterminantsof aminoacidandnucleotidemetabolismbetween these two metagenomes and those of soil from other polar deserts, hot deserts, and non-desert soils. Our results suggest extensive niche differentiation in hypolithic microbial communities from these two extreme environments and a high genetic capacity for survival under environmental extremes.Fil: Le, Phuong Thi. University of Pretoria; Sudáfrica. Vlaams Instituut voor Biotechnologie; Bélgica. University of Ghent; BélgicaFil: Makhalanyane, Thulani P.. University of Pretoria; SudáfricaFil: Guerrero, Leandro Demián. University of Pretoria; Sudáfrica. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Vikram, Surendra. University of Pretoria; SudáfricaFil: Van De Peer, Yves. University of Pretoria; Sudáfrica. Vlaams Instituut voor Biotechnologie; Bélgica. University of Ghent; BélgicaFil: Cowan, Don A.. University of Pretoria; Sudáfric