15 research outputs found
The Effect of Weak Cosmic-ray Heating Events on the Desorption of H2
No full textThe typical amount of molecular hydrogen (H-2) in interstellar ices is not known, but significant freeze-out of H-2 on dust grains is not expected. However, chemical models ubiquitously predict large amounts of H-2 freeze-out in dense cloud conditions, and specialized treatments are needed to control the H-2 population on grains. Here we present a numerical desorption model where the effect of weak heating events induced by cosmic rays (CRs) that heat grains to temperatures of a few tens of kelvin at high frequencies is included, improving upon earlier desorption models that only consider strong heating events (maximum grain temperature close to 100 K) that occur at a low frequency. A temperature of a few tens of kelvin is high enough to induce efficient desorption of H-2, but we find that even the weak heating events do not occur often enough to lead to significant H-2 desorption. Taking the weak heating events into account does affect the predicted abundances of other lightly bound species, but the effect is restricted to low column densities. We make here the canonical assumption that the grains are spherical with a radius of 0.1 mu m. It is conceivable that in the case of a grain size distribution, weak heating events could provide a boost to H-2 desorption coming off small grains, which are the most numerous. Further studies are still required to better quantify the role of CRs in the desorption of H-2 and other weakly bound species
Values for Sulfation of Diverse Phenolic Substrates by Human Catecholamine Sulfotransferase SULT1A3.
No full textA low cosmic-ray ionisation rate in the pre-stellar core Ophiuchus/H-MM1
No full textAims. We test the use of three common molecular ions, ortho-H2D+ (oH2D+), N2H+, and DCO+, as probes of the internal structure and kinematics of a dense, starless molecular cloud core.
Methods. The pre-stellar core H-MM1 in Ophiuchus was mapped in the oH2D+(110 − N2H+(4 − 3), and DCO+ (5 − 4) lines with the Large APEX sub-Millimeter Array (LAsMA) multi-beam receiver of the Atacama Pathfinder EXperiment (APEX) telescope. We also ran a series of chemistry models to predict the abundance distributions of the observed molecules, and to estimate the effect of the cosmic-ray ionisation rate on their abundances.
Results. The three line maps show different distributions. The oH2D+ map is extended and outlines the general structure of the core, N2H+ mainly shows the density maxima, and the DCO+ emission peaks are shifted towards one edge of the core where a region of enhanced desorption had previously been found. According to the chemical simulation, the fractional oH2D+ abundance remains relatively high in the centre of the core, and its column density correlates strongly with the cosmic-ray ionisation rate, ζH2. Simulated line maps constrain the cosmic-ray ionisation rate to be low, between 5 × 10−18 s−1 and 1 × 10−17 s−1 in the H-MM1 core. This estimate agrees with the gas temperature measured in the core.
Conclusions. The present observations show that very dense, cold gas in molecular clouds can be traced by mapping the ground-state line of oH2D+ and high-J transitions of DCO+ and N2H+, despite the severe depletion of the latter two molecules. Modelling line emission of oH2D+ provides a straightforward method of determining the cosmic-ray ionisation rate in dense clouds, where the primary ion, H3+, is not observable
ChemInform Abstract: Synthesis and Pharmacological Properties of 4(5)-(2-Ethyl-2,3-dihydro- 2-silainden-2-yl)imidazole, a Silicon Analogue of Atipamezole.
No full textExperimental febrile seizures are precipitated by a hyperthermia-induced respiratory alkalosis
No full textFebrile seizures are frequent during early childhood, and prolonged (complex) febrile seizures are associated with an increased susceptibility to temporal lobe epilepsy. The pathophysiological consequences of febrile seizures have been extensively studied in rat pups exposed to hyperthermia. The mechanisms that trigger these seizures are unknown, however. A rise in brain pH is known to enhance neuronal excitability. Here we show that hyperthermia causes respiratory alkalosis in the immature brain, with a threshold of 0.2-0.3 pH units for seizure induction. Suppressing alkalosis with 5% ambient CO2 abolished seizures within 20 s. CO2 also prevented two long-term effects of hyperthermic seizures in the hippocampus: the upregulation of the I(h) current and the upregulation of CB1 receptor expression. The effects of hyperthermia were closely mimicked by intraperitoneal injection of bicarbonate. Our work indicates a mechanism for triggering hyperthermic seizures and suggests new strategies in the research and therapy of fever-related epileptic syndromes
Physical exercise-induced hypoglycemia caused by failed silencing of monocarboxylate transporter 1 in pancreatic β cells
No full textDeuteration of ammonia in the starless core Ophiuchus/ H-MM1
No full textContext. Ammonia and its deuterated isotopologues probe physical conditions in dense molecular cloud cores. The time-dependence of deuterium fractionation and the relative abundances of different nuclear spin modifications are supposed to provide a means of determining the evolutionary stages of these objects. Aims. We aim to test the current understanding of spin-state chemistry of deuterated species by determining the abundances and spin ratios of NH2D, NHD2 and ND3 in a quiescent, dense cloud. Methods. Spectral lines of NH3, NH2D, NHD2, ND3 and N2D+ were observed towards a dense, starless core in Ophiuchus with the APEX, GBT and IRAM 30-m telescopes. The observations were interpreted using a gas-grain chemistry model combined with radiative transfer calculations. The chemistry model distinguishes between the different nuclear spin states of light hydrogen molecules, ammonia and their deuterated forms. Different desorption schemes can be considered. Results. High deuterium fractionation ratios with NH2D = NH3 similar to 0 : 4, NHD2 = NH2D similar to 0 : 2 and ND3 = NHD2 similar to 0 : 06 are found in the core. The observed ortho/para ratios of NH2D and NHD2 are close to the corresponding nuclear spin statistical weights. The chemistry model can approximately reproduce the observed abundances, but consistently predicts too low ortho/para-NH2D, and too large ortho/para-NHD2 ratios. The longevity of N2H+ and NH3 in dense gas, which is prerequisite to their strong deuteration, can be attributed to the chemical inertia of N-2 on grain surfaces. Conclusions. The discrepancies between the chemistry model and the observations are likely to be caused by the fact that the model assumes complete scrambling in principal gas-phase deuteration reactions of ammonia, which means that all the nuclei are mixed in reactive collisions. If, instead, these reactions occur through proton hop/hydrogen abstraction processes, statistical spin ratios are to be expected. The present results suggest that while the deuteration of ammonia changes with physical conditions and time, the nuclear spin ratios of ammonia isotopologues do not probe the evolutionary stage of a cloud.Peer reviewe
Effect of tungsten off-axis accumulation on neutral beam deposition in JET rotating plasmas
No full textEvidence for low field side accumulation of tungsten is often observed in bolometry and soft x-ray emissivities of highly rotating JET ITER-like wall (ILW) plasmas. Poloidal variation of the density of high-Z impurities, such as tungsten, in the core of NBI heated plasmas is expected from neoclassical theory due to charge displacement and parallel electric field generated by the centrifugal force. We calculate the poloidally asymmetric distribution of tungsten using fluid equations and a 1D transport simulation with the JETTO/SANCO code. Peaking of tungsten on the outboard side of the plasma is found and verified with soft x-ray and bolometry measurements. We then study the effect of a poloidally asymmetric tungsten distribution on the distribution of the NBI heat source by simulations with the Monte Carlo code ASCOT. The simulations show that the poloidally asymmetric tungsten profile redistributes the fast NBI ions radially through shifting their ionization profile and poloidally through enhanced pitch-angle scattering at high energy. The amplitude of the redistribution is in the order of 10% for the highest n(W)/n(e) ratios of similar to 10(-4) measured in recent JET H-mode plasmas. As a result of the scattering of the beam particles, the core heat deposition is changed less than 10%, which does not have a significant impact to the performance of JET plasmas. The modelling is in qualitative agreement with measurements by the vertical neutron camera that sees a broadening in the 2.5 MeV neutron profile when tungsten peaks on the outboard side of the plasma.</p
Massive clumps in W43-main: Structure formation in an extensively shocked molecular cloud
No full textAims. W43-main is a massive molecular complex undergoing starburst activities, located at the interaction of the Scutum arm and the Galactic bar. We aim to investigate the gas dynamics, in particular, the prevailing shock signatures from cloud to clump scales. We also look to assess the impact of shocks on the formation of dense gas and early-stage cores in OB cluster formation processes.
Methods. We carried out NOEMA and IRAM-30 m observations at 3 mm towards five molecular gas clumps in W43 main located within large-scale interacting gas components. We used CH3CCH and H2CS lines to trace the extended gas temperature and CH3OH lines to probe the volume density of the dense gas components (≳105 cm−3). We adopted multiple tracers that are sensitive to different gas density regimes to reflect the global gas motions. The density enhancements constrained by CH3OH and a population of NH2D cores are correlated (in the spatial and velocity domains) with SiO emission, which is a prominent indicator of shock processing in molecular clouds.
Results. The emission of SiO (2–1) is extensive across the region (~4 pc) and it is contained within a low-velocity regime, hinting at a large-scale origin for the shocks. Position-velocity maps of multiple tracers show systematic spatio-kinematic offsets supporting the cloud-cloud collision-merging scenario. We identified an additional extended velocity component in the CCH emission, which coincides with one of the velocity components of the larger scale 13CO (2−1) emission, likely representing an outer, less-dense gas layer in the cloud merging process. We find that the ‘V-shaped’, asymmetric SiO wings are tightly correlated with localised gas density enhancements, which is direct evidence of dense gas formation and accumulation in shocks. The dense gas that is formed in this way may facilitate the accretion of the embedded, massive pre-stellar and protostellar cores. We resolved two categories of NH2D cores: those exhibiting only subsonic to transonic velocity dispersions and those with an additional supersonic velocity dispersion. The centroid velocities of the latter cores are correlated with the shock front seen via SiO. The kinematics of the ~0.1 pc NH2D cores are heavily imprinted by shock activities and may represent a population of early-stage cores forming around the shock interface
The synergistic role of sulfuric acid, ammonia and organics in particle formation over an agricultural land
No full textAgriculture provides people with food, but poses environmental challenges. Via comprehensive observations on an agricultural land at Qvidja in Southern Finland, we were able to show that soil-emitted compounds (mainly ammonia and amines), together with available sulfuric acid, form new aerosol particles which then grow to climate-relevant sizes by the condensation of extremely low volatile organic compounds originating from a side production of photosynthesis (compounds emitted by ground and surrounding vegetation). We found that intensive local clustering events, with particle formation rates at 3 nm about 5-10 times higher than typical rates in boreal forest environments, occur on around 30% of all days. The requirements for these clustering events to occur were found to be clear sky, a low wind speed to accumulate the emissions from local agricultural land, particularly ammonia, the presence of low volatile organic compounds, and sufficient gaseous sulfuric acid. The local clustering will then contribute to regional new particle formation. Since the agricultural land is much more effective per surface area than the boreal forest in producing aerosol particles, these findings provide insight into the participation of agricultural lands in climatic cooling, counteracting the climatic warming effects of farming.Peer reviewe
