Depletion of chlorine into HCl ice in a protostellar core

The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances $<10^{-5}$ has not yet been well studied. Our aim here is to study the depletion of chlorine in the protostellar core, OMC-2 FIR 4. We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H$_{2}$ hyperfine collisional excitation rate coefficients. A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9e-11, a factor of only 0.001 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous foreground cloud, where we find no depletion of volatile chlorine. Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with an abundance of <1e-10 in most of the protostellar core. We find the 35Cl/37Cl ratio in OMC-2 FIR 4 to be 3.2\pm0.1, consistent with the solar system value.Comment: 13 pages, 12 figures, accepted for publication in A&

Improving evapotranspiration in a land surface model using biophysical variables derived from MSG/SEVIRI satellite

Monitoring evapotranspiration over land is highly dependent on the surface state and vegetation dynamics. Data from spaceborn platforms are desirable to complement estimations from land surface models. The success of daily evapotranspiration monitoring at continental scale relies on the availability, quality and continuity of such data. The biophysical variables derived from SEVIRI on board the geostationary satellite Meteosat Second Generation (MSG) and distributed by the Satellite Application Facility on Land surface Analysis (LSA-SAF) are particularly interesting for such applications, as they aimed at providing continuous and consistent daily time series in near-real time over Africa, Europe and South America. In this paper, we compare them to monthly vegetation parameters from a database commonly used in numerical weather predictions (ECOCLIMAP-I), showing the benefits of the new daily products in detecting the spatial and temporal (seasonal and inter-annual) variability of the vegetation, especially relevant over Africa. We propose a method to handle Leaf Area Index (LAI) and Fractional Vegetation Cover (FVC) products for evapotranspiration monitoring with a land surface model at 3&amp;ndash;5 km spatial resolution. The method is conceived to be applicable for near-real time processes at continental scale and relies on the use of a land cover map. We assess the impact of using LSA-SAF biophysical variables compared to ECOCLIMAP-I on evapotranspiration estimated by the land surface model H-TESSEL. Comparison with in-situ observations in Europe and Africa shows an improved estimation of the evapotranspiration, especially in semi-arid climates. Finally, the impact on the land surface modelled evapotranspiration is compared over a north–south transect with a large gradient of vegetation and climate in Western Africa using LSA-SAF radiation forcing derived from remote sensing. Differences are highlighted. An evaluation against remote sensing derived land surface temperature shows an improvement of the evapotranspiration simulations

Computing the zeros of the partial sums of the Riemann zeta function

In this paper, we introduce a formula for the exact number of zeros of every partial sum of the Riemann zeta function inside infinitely many rectangles of the critical strips where they are situated

Managing Congestion in Vehicular Networks Using Tabu Search

© 2018, Springer Nature Switzerland AG. In this era of communication, exponentially growing networks bring a lot of challenges to address for smoother network functionalities. Among them is efficiency in handling packet traffic to avoid and control congestion. A particular case is applicable to Vehicular Ad-hoc Networks, which are known with unbalanced resource utilisation, communication overheads, high transmission delay and least transmission capacity. This paper aims to minimise the delay and jitter for enhancing the Quality of Service (QoS) in Vehicular Adhoc Networks (VANET) using tabu search algorithm with multi-channel allocation capability. We proposed a scheme that prioritises each message considering the basis of message type or its substances, such as crisis, reference point, and administration oriented etc., and uses tabu search for scheduling the transmission of queued messages in order to enhance the efficiency, security, and durability of VANET. A comprehensive simulation is conducted to validate the proposed scheme and to evaluate the performances in comparison with other state-of-the-art approaches

Depletion of chlorine into HCl ice in a protostellar core: The CHESS spectral survey of OMC-2 FIR 4

Context. The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances <10^(-5) has not yet been well studied. Aims. Our aim here is to study the depletion of chlorine in the protostellar core, OMC-2 FIR 4. Methods. We observed transitions of HCl and H_2Cl^+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H_2 hyperfine collisional excitation rate coefficients. Results. A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9 × 10^(-11), a factor of only 10^(-3) that of volatile elemental chlorine. The H_2Cl^+ lines are detected in absorption and trace a tenuous foreground cloud, where we find no depletion of volatile chlorine. Conclusions. Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with an abundance of ≲10^(-10) in most of the protostellar core. We find the [^(35)Cl]/[^(37)Cl] ratio in OMC-2 FIR 4 to be 3.2 ± 0.1, consistent with the solar system value

Transient evolution of C-type shocks in dusty regions of varying density

Outflows of young stars drive shocks into dusty, molecular regions. Most models of such shocks assume that they are steady and propagating perpendicular to the magnetic field. Real shocks often violate both of these assumptions and the media through which they propagate are inhomogeneous. We use the code employed previously to produce the first time-dependent simulations of fast-mode, oblique C-type shocks interacting with density perturbations. We include a self-consistent calculation of the thermal and ionisation balances and a fluid treatment of grains. We identify features that develop when a multifluid shock encounters a density inhomogeneity to investigate whether any part of the precursor region ever behaves in a quasi-steady fashion. If it does the shock may be modelled approximately without solving the time-dependent hydromagnetic equations. Simulations were made for initially steady oblique C-type shocks encountering density inhomogeneities. For a semi-finite inhomogeneity with a density larger than the surrounding medium, a transmitted shock evolves from being J-type to a steady C-type shock on a timescale comparable to the ion-flow time through it. A sufficiently upstream part of the precursor of an evolving J-type shock is quasi-steady. The ion-flow timescale is also relevant for the evolution of a shock moving into a region of decreasing density. The models for shocks propagating into regions in which the density increases and then decreases to its initial value cannot be entirely described in terms of the results obtained for monotonically increasing and decreasing densities. For the latter model, the long-term evolution to a C-type shock cannot be approximated by quasi-steady models.Comment: 11 pages, 9 figure

Seeds of Life in Space (SOLIS): XI. First measurement of nitrogen fractionation in shocked clumps of the L1157 protostellar outflow

Context. The isotopic ratio of nitrogen presents a wide range of values in the Solar System: from 140 in meteorites and comets to 441 in the solar wind. In star-forming systems, we observe evena higher spread of ~150-1000. The origin of these differences is still unclear. Aims. Chemical reactions in the gas phase are one of the possible processes that could modify the 14N/15N ratio. We aim to investigate if and how the passage of a shock wave in the interstellar medium, which activates a rich chemistry, can affect the relative fraction of nitrogen isotopes. Theideal place for such a study is the chemically rich outflow powered by the L1157-mm protostar, where several shocked clumps are present. Methods. We present the first measurement of the 14N/15N ratio in the two shocked clumps, B1 and B0, of the protostellar outflow L1157. The measurement is derived from the interferometeric maps of the H13CN (1-0) and the HC15N (1-0) lines obtained with the NOrthern Extended Millimeter Array (NOEMA) interferometeras part of the Seeds of Life in Space (SOLIS) programme. Results. In B1, we find that the H13CN (1-0) and HC15N (1-0) emission traces the front of the clump, that is the apex of the shocked region, where the fast jet impacts the lower velocity medium with an averaged column density of N(H13CN) ~ 7 × 1012 cm-2 and N(HC15N) 2 × 1012 cm-2. In this region, the ratio H13CN (1-0)/HC15N (1-0) is almost uniform with an average value of ~5 ± 1. The same average value isalso measured in the smaller clump B0e. Assuming the standard 12C/13C = 68, we obtain 14N/15N = 340 ± 70. This ratio is similar to those usually found with the same species in prestellar cores and protostars. We analysed the prediction of a chemical shock model for several shock conditions and we found that the nitrogen and carbon fractionations do not vary much for the first period after the shock. The observed H13CN/HC15N can be reproduced by a non-dissociative, C-type shock with pre-shock density n(H) = 105 cm-3, shock velocity Vs between 20 and 40 km s-1, and cosmic-ray ionization rate of 3 × 10-16 s-1; this agrees with previous modelling of other chemical species in L1157-B1. Conclusions. Both observations and chemical models indicate that the rich chemistry activated by the shock propagation does not affect the nitrogen isotopic ratio, which remains similar to that measured in lower temperature gas in prestellar cores and protostellar envelopes

EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

The role of magnetic fields in the formation of high-mass stars is still under debate, and recent measurements of their orientation and strength by using polarized maser emissions are contributing new insights. Masers polarization, in particular of the 6.7-GHz methanol masers, are one of the best probes of the magnetic field morphologies around massive protostars. Determining the magnetic field morphology around an increasing number of massive protostars at milliarcsecond resolution by observing 6.7-GHz methanol masers is crucial to better understand the role of magnetic fields in massive star formation.The First EVN Group consists of 4 massive star-forming complexes: W51, W48, IRAS18556+0138, and W3(OH). These contain well-studied \hii ~regions from some of which molecular bipolar outflows were also detected (W51-e2, G35.20-0.74N). Nine of the European VLBI Network antennas were used to measure the linear polarization and Zeeman-splitting of the 6.7-GHz methanol masers in the star-forming regions of the First EVN Group. We detected a total of 154 CH3OH masers, one third of these towards W3(OH). Fractional linear polarization (1.2-11.5%) was detected towards 55 masers. The linear polarization vectors are well-ordered in all the massive star-forming regions. We measured significant Zeeman-splitting in 3 massive star-forming regions (W51, W48, and W3(OH)) revealing a range of separations -3.5 m/s<\Delta V_{z}<3.8 m/s with the smallest |\Delta V_{z}|=0.4m/s. We were also able to compare our magnetic field results with those obtained from submillimeter wavelength dust observation in W51 and show that the magnetic field at low and high resolutions are in perfect agreement.Comment: 15 pages, 11 figures, 5 tables, accepted by Astronomy & Astrophysic

European Sea Bass (Dicentrarchus labrax) immune status and disease resistance are impaired by arginine dietary supplementation

Infectious diseases and fish feeds management are probably the major expenses in the aquaculture business. Hence, it is a priority to define sustainable strategies which simultaneously avoid therapeutic procedures and reinforce fish immunity. Currently, one preferred approach is the use of immunostimulants which can be supplemented to the fish diets. Arginine is a versatile amino acid with important mechanisms closely related to the immune response. Aiming at finding out how arginine affects the innate immune status or improve disease resistance of European seabass (Dicentrarchus labrax) against vibriosis, fish were fed two arginine-supplemented diets (1% and 2% arginine supplementation). A third diet meeting arginine requirement level for seabass served as control diet. Following 15 or 29 days of feeding, fish were sampled for blood, spleen and gut to assess cell-mediated immune parameters and immune-related gene expression. At the same time, fish from each dietary group were challenged against Vibrio anguillarum and survival was monitored. Cell-mediated immune parameters such as the extracellular superoxide and nitric oxide decreased in fish fed arginine-supplemented diets. Interleukins and immune-cell marker transcripts were down-regulated by the highest supplementation level. Disease resistance data were in accordance with a generally depressed immune status, with increased susceptibility to vibriosis in fish fed arginine supplemented diets. Altogether, these results suggest a general inhibitory effect of arginine on the immune defences and disease resistance of European seabass. Still, further research will certainly clarify arginine immunomodulation pathways thereby allowing the validation of its potential as a prophylactic strategy.European Union's Seventh Framework Programme AQUAEXCEL (Aquaculture Infrastructures for Excellence in European Fish Research) [262336]; AQUAIMPROV [NORTE-07-0124-FEDER-000038]; North Portugal Regional Operational Programme (ON. 2 - O Novo Norte) , under the National Strategic Reference Framework, through the European Regional Development Fund; North Portugal Regional Operational Programme (ON. 2 - O Novo Norte), under the National Strategic Reference Framework through the COMPETE - Operational Competitiveness Programme; Fundacao para a Ciencia e Tecnologia; Fundacao para a Ciencia e Tecnologia [SFRH/BD/89457/2012, SFRH/BPD/77210/2011]; Generalitat Valenciana through the project REVIDPAQUA [ISIC/2012/003]; [PEst-C/MAR/LA0015/2013]; [UID/Multi/04423/2013]info:eu-repo/semantics/publishedVersio