Enhanced cosmic-ray flux toward zeta Persei inferred from laboratory study of H3+ - e- recombination rate

The H3+ molecular ion plays a fundamental role in interstellar chemistry, as it initiates a network of chemical reactions that produce many interstellar molecules. In dense clouds, the H3+ abundance is understood using a simple chemical model, from which observations of H3+ yield valuable estimates of cloud path length, density, and temperature. On the other hand, observations of diffuse clouds have suggested that H3+ is considerably more abundant than expected from the chemical models. However, diffuse cloud models have been hampered by the uncertain values of three key parameters: the rate of H3+ destruction by electrons, the electron fraction, and the cosmic-ray ionisation rate. Here we report a direct experimental measurement of the H3+ destruction rate under nearly interstellar conditions. We also report the observation of H3+ in a diffuse cloud (towards zeta Persei) where the electron fraction is already known. Taken together, these results allow us to derive the value of the third uncertain model parameter: we find that the cosmic-ray ionisation rate in this sightline is forty times faster than previously assumed. If such a high cosmic-ray flux is indeed ubiquitous in diffuse clouds, the discrepancy between chemical models and the previous observations of H3+ can be resolved.Comment: 6 pages, Nature, in pres

An analysis-ready and quality controlled resource for pediatric brain white-matter research

We created a set of resources to enable research based on openly-available diffusion MRI (dMRI) data from the Healthy Brain Network (HBN) study. First, we curated the HBN dMRI data (N = 2747) into the Brain Imaging Data Structure and preprocessed it according to best-practices, including denoising and correcting for motion effects, susceptibility-related distortions, and eddy currents. Preprocessed, analysis-ready data was made openly available. Data quality plays a key role in the analysis of dMRI. To optimize QC and scale it to this large dataset, we trained a neural network through the combination of a small data subset scored by experts and a larger set scored by community scientists. The network performs QC highly concordant with that of experts on a held out set (ROC-AUC = 0.947). A further analysis of the neural network demonstrates that it relies on image features with relevance to QC. Altogether, this work both delivers resources to advance transdiagnostic research in brain connectivity and pediatric mental health, and establishes a novel paradigm for automated QC of large datasets. BárbaraAvelar-Pereira 9 , EthanRoy2 , Valerie J.Sydnor3,4,5, JasonD.Yeatman1,2, The Fibr Community Science Consortium*, TheodoreD.Satterthwaite3,4,5,88 & Ariel Roke

Absorption cross section measurements of oxygen in the wavelength region 195-241 nm of the Herzberg continuum

The continuum cross section of oxygen at 296-300 K has been measured with a resolution of 0.13 nm throughout the wavelength region 205-241 nm with oxygen pressures from 5 to 760 torr and optical path lengths from 13.3 and 133m. The three processes contributing to the observed cross section are absorption into two kinds of continua, viz. the Herzberg continua of O 2 and a pressure-dependent continuum involving two molecules of O 2, and Rayleigh scattering. Extrapolation of the observed cross section to zero pressure yields the continuum cross section of O 2, from which the calculated Rayleigh scattering is subtracted to give the Herzberg continuum absorption cross section of O 2. Our previous continuum cross sections [Cheung et al. (1984) Can. J. Phys. 62, 1752], obtained from studies at high resolution (0.0013 nm) between the Schumann-Runge absorption lines in the region 194-204 nm, are here adjusted for Schumann-Runge line-wing contributions. These adjusted cross sections are compared with those calculated from computed Franck-Condon densities and a transition moment extrapolated from that calculated from our more accurate cross section measurements at longer wavelengths. Our calculated cross section in the region 195-237 nm is similar in shape to that calculated by Saxon and Slanger [J. geophys. Res., 91, 9877] from the transition moments computed ab initio by Klotz and Peyerimhoff [Molec. Phys., 57, 573]. Our values of the Herzberg continuum cross section of oxygen, tabulated at 1 nm intervals in the region 195-241 nm, increase from 6.3 × 10 -24 cm 2 at 195 nm to a maximum of 6.6 × 10 -24 cm 2 at 201 nm and then decrease to 0.85 × 10 24 cm 2 at 241 nm. Our results agree with those in the region 205-225 nm covered by the most recent previous laboratory study [Johnston et al. (1984) J. geophys. Res. 89, 11661] and are consistent with values in the region 200-220 nm spanned collectively by three in situ stratospheric studies [Frederick and Mentall (1982) Geophys. Res. Lett. 9, 461; Herman and Mentall (1982) J. geophys. Res. 87, 8967; Anderson and Hall (1983) J. geophys. Res. 88, 6801]. The larger Herzberg continuum cross sections found in another in situ stratospheric study [Pirre et al. (1984) Geophys. Res. Lett. 11, 1199] are in definite disagreement with our laboratory values, certainly in the region 205-214 nm. Our Herzberg continuum cross sections in the region 195-241 nm are significantly lower than those previously used in many photochemical stratospheric modelling calculations. Acceptance of our cross sections in such models will affect markedly the calculated altitude profiles of ozone, nitrous oxide, chlorofluorocarbons, and other trace stratospheric species. © 1986.link_to_subscribed_fulltex

Improved absorption cross-sections of oxygen in the wavelength region 205-240 nm of the Herzberg continuum

The laboratory values of the Herzberg continuum absorption cross-section of oxygen at room temperature from Cheung et al. (1986, Planet. Space Sci. 34, 1007), Jenouvrier et al. (1986a, Planet. Space Sci. 34, 253) and Jenouvrier et al. (1986, J. quant. Spectrosc. radiat. Transfer 36, 349) have been compared and re-analyzed. There is no discrepancy between the absolute values of these two sets of independent measurements. These values have been combined together in a linear least-squares fit to obtain improved values of the Herzberg continuum cross-section of oxygen at room temperature throughout the wavelength region 205-240 nm. Agreement with in situ and other laboratory measurements is discussed. © 1988.link_to_subscribed_fulltex

The ionospheric oxygen green airglow: Electron temperature dependence and aeronomical implications.

The laboratory measurement of processes involved in terrestrial airglows is essential in developing diagnostic tools of the dynamics and photochemistry of the upper atmosphere. Dissociative electron recombination of O 2+ in the ionospheric F-region is expected to produce both O( 1D) and O( 1S) which are the sources of the 630.0 nm red airglow and the 557.7 nm green airglow lines, respectively. We present both theoretical and experimental evidence, the latter from a heavy ion storage ring technique, that the O( 1S) quantum yield from O 2+ (v = 0) is a strong function of the electron temperature due to a molecular resonance phenomenon. At present the O 2+ (v = O) theoretical and laboratory recombination data cannot explain rocket observations of the ionospheric green and red airglows [Takahashi et al. 1990; Sobral et al. 1992]