Bond-forming reactions of N22+ with C2H4, C2H6, C3H4 and C3H6

Mass spectrometry, coupled with position-sensitive coincidence detection, has been used to investigate the reactions of N22+ with various small hydrocarbon molecules (C2H4, C2H6, C3H4, c-C3H6 and n-C3H6) at collision energies below 10 eV in the centre-of-mass frame. The reactivity, in each case, is dominated by electron transfer. However, in each collision system we also clearly identify products formed following the creation of new chemical bonds. These bond-forming reactions comprise two distinct classes: (i) hydride transfer reactions which initially form NnH+ (n = 1, 2) and (ii) N+ transfer reactions which form monocationic products with Csingle bondN bonds. These bond-forming reactions make a small (5–10%), but significant, contribution to the overall product ion yield in each collision system. The temporal and positional data recorded by our coincidence detection technique are used to construct scattering diagrams which reveal the mechanisms of the bond-forming reactions. For the hydride transfer process, the scattering diagrams reveal that H− is directly transferred from the hydrocarbon to N22+ at significant interspecies separations. For the hydride transfer reactions with C2H4, C2H6 and C3H4, we observe fragmentation of the nascent N2H+* to form NH+ + N. The N+ transfer reaction also proceeds by a direct mechanism: a single step involving N+/H exchange results in the formation of a singly-charged organic species containing a Csingle bondN bond which is detected in coincidence with H+. The two general classes of bond-forming reactivity we observe in the reactions of N22+ with organic molecules may be relevant in the chemistry of energised environments rich in molecular nitrogen and hydrocarbon species, such as the atmosphere of Titan

Sparse Bayesian mass mapping with uncertainties: peak statistics and feature locations

Weak lensing convergence maps – upon which higher order statistics can be calculated – can be recovered from observations of the shear field by solving the lensing inverse problem. For typical surveys this inverse problem is ill-posed (often seriously) leading to substantial uncertainty on the recovered convergence maps. In this paper we propose novel methods for quantifying the Bayesian uncertainty in the location of recovered features and the uncertainty in the cumulative peak statistic – the peak count as a function of signal-to-noise ratio (SNR). We adopt the sparse hierarchical Bayesian mass-mapping framework developed in previous work, which provides robust reconstructions and principled statistical interpretation of reconstructed convergence maps without the need to assume or impose Gaussianity. We demonstrate our uncertainty quantification techniques on both Bolshoi N-body (cluster scale) and Buzzard V-1.6 (large-scale structure) N-body simulations. For the first time, this methodology allows one to recover approximate Bayesian upper and lower limits on the cumulative peak statistic at well-defined confidence levels

Sparse Bayesian mass-mapping with uncertainties: Full sky observations on the celestial sphere

To date weak gravitational lensing surveys have typically been restricted to small fields of view, such that the flat-sky approximation has been sufficiently satisfied. However, with Stage IV surveys (e.g. LSST and Euclid) imminent, extending mass-mapping techniques to the sphere is a fundamental necessity. As such, we extend the sparse hierarchical Bayesian massmapping formalism presented in previous work to the spherical sky. For the first time, this allows us to construct maximum a posteriori spherical weak lensing dark-matter mass-maps, with principled Bayesian uncertainties, without imposing or assuming Gaussianty. We solve the spherical mass-mapping inverse problem in the analysis setting adopting a sparsity promoting Laplacetype wavelet prior, though this theoretical framework supports all log-concave posteriors. Our spherical mass-mapping formalism facilitates principled statistical interpretation of reconstructions. We apply our framework to convergence reconstruction on high resolution N-body simulations with pseudo-Euclid masking, polluted with a variety of realistic noise levels, and show a significant increase in reconstruction fidelity compared to standard approaches. Furthermore, we perform the largest joint reconstruction to date of the majority of publicly available shear observational data sets (combining DESY1, KiDS450, and CFHTLens) and find that our formalism recovers a convergence map with significantly enhanced small-scale detail. Within our Bayesian framework we validate, in a statistically rigorous manner, the community’s intuition regarding the need to smooth spherical Kaiser-Squires estimates to provide physically meaningful convergence maps. Such approaches cannot reveal the small-scale physical structures that we recover within our framework

Mapping dark matter on the celestial sphere with weak gravitational lensing

Convergence maps of the integrated matter distribution are a key science result from weak gravitational lensing surveys. To date, recovering convergence maps has been performed using a planar approximation of the celestial sphere. However, with the increasing area of sky covered by dark energy experiments, such as Euclid, the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST), and the Nancy Grace Roman Space Telescope, this assumption will no longer be valid. We recover convergence fields on the celestial sphere using an extension of the Kaiser–Squires estimator to the spherical setting. Through simulations, we study the error introduced by planar approximations. Moreover, we examine how best to recover convergence maps in the planar setting, considering a variety of different projections and defining the local rotations that are required when projecting spin fields such as cosmic shear. For the sky coverages typical of future surveys, errors introduced by projection effects can be of the order of tens of percent, exceeding 50 per cent in some cases. The stereographic projection, which is conformal and so preserves local angles, is the most effective planar projection. In any case, these errors can be avoided entirely by recovering convergence fields directly on the celestial sphere. We apply the spherical Kaiser–Squires mass-mapping method presented to the public Dark Energy Survey science verification data to recover convergence maps directly on the celestial sphere

Electron transfer and bond-forming reactions following collisions of I2+ with CO and CS2

Collisions between I2+ and CO have been investigated using time-of flight mass spectrometry at a range of centre-of-mass collision energies between 0.5 eV and 3.0 eV. Following I2+ + CO collisions we detect I+ + CO+ from a single-electron transfer reaction and IO+ + C+ from bond-forming reactivity. Reaction-window calculations, based on Landau-Zener theory, have been used to rationalise the electron transfer reactivity and computational chemistry has been used to explore the [I-CO] 2+ potential energy surface to account for the observation of IO+. In addition, collisions between I2+ and CS2 have been investigated over a range of centre-of-mass collision energies between 0.8 eV and 6.0 eV. Both single and double electron transfer reactions are observed in the I2+/CS2 collision system, an observation again rationalized by reaction-window theory. The monocations IS+ and IC+ are also detected following collisions of I2+ with CS2, and these ions are clearly products from a bond-forming reaction. We present a simple model based on the structure of the [I-CS2]2+ collision complex to rationalize the significantly larger yield of IS+ than IC+ in this bond-forming process

Efficient Generalized Spherical CNNs

Many problems across computer vision and the natural sciences require the analysis of spherical data, for which representations may be learned efficiently by encoding equivariance to rotational symmetries. We present a generalized spherical CNN framework that encompasses various existing approaches and allows them to be leveraged alongside each other. The only existing non-linear spherical CNN layer that is strictly equivariant has complexity OpC2L5q, where C is a measure of representational capacity and L the spherical harmonic bandlimit. Such a high computational cost often prohibits the use of strictly equivariant spherical CNNs. We develop two new strictly equivariant layers with reduced complexity OpCL4q and OpCL3 log Lq, making larger, more expressive models computationally feasible. Moreover, we adopt efficient sampling theory to achieve further computational savings. We show that these developments allow the construction of more expressive hybrid models that achieve state-of-the-art accuracy and parameter efficiency on spherical benchmark problems

Ice nucleation by fertile soil dusts: Relative importance of mineral and biogenic components

Agricultural dust emissions have been estimated to contribute around 20% to the global dust burden. In contrast to dusts from arid source regions, the ice-nucleating abilities of which have been relatively well studied, soil dusts from fertile sources often contain a substantial fraction of organic matter. Using an experimental methodology which is sensitive to a wide range of ice nucleation efficiencies, we have characterised the immersion mode ice-nucleating activities of dusts (d<11 μ m) extracted from fertile soils collected at four locations around England. By controlling droplet sizes, which ranged in volume from 10 to 10 L (concentration=0.02 to 0.1 wt% dust), we have been able to determine the ice nucleation behaviour of soil dust particles at temperatures ranging from 267K (-6°C) down to the homogeneous limit of freezing at about 237K (-36°C). At temperatures above 258K (-15°C) we find that the ice-nucleating activity of soil dusts is diminished by heat treatment or digestion with hydrogen peroxide, suggesting that a major fraction of the ice nuclei stems from biogenic components in the soil. However, below 258 K, we find that the ice active site densities tend towards those expected from the mineral components in the soils, suggesting that the inorganic fraction of soil dusts, in particular the K-feldspar fraction, becomes increasingly important in the initiation of the ice phase at lower temperatures. We conclude that dusts from agricultural activities could contribute significantly to atmospheric IN concentrations, if such dusts exhibit similar activities to those observed in the current laboratory study

Studies of the Precipitation Pattern of Paclitaxel in Intravenous Infusions and Rat Plasma Using Laser Nephelometry

Cremophor EL (CrEL) is commonly used to solubilize paclitaxel (Ptx); a widely established anticancer agent used against many types of cancer. Using laser-based microplate nephelometry, in this work we assessed the precipitation kinetics of Ptx in CrEL-containing formulations upon dilutions with different infusion media or upon introduction into rat plasma. The precipitation profile of Ptx was assessed for a Taxol-like formulation and compared with a preparation with reduced CrEL content. These two formulations were diluted at various ratios in compatible infusion media and with or without rat plasma. The percentages of Ptx precipitated in dilution media and protein-binding in plasma were quantified using HPLC. The findings of turbidity measurements were in good agreement with HPLC. Despite the presence of albumin, it was possible to assess turbidity within infusion solutions and predict Ptx precipitation. Upon addition to plasma, no precipitation in Taxol-like formulation occurred after 2 h. In contrast, precipitation occurred immediately in CrEL-reduced formulation. It is possible that the high percentage of protein-bound Ptx in plasma (98.5–99.2%) has inhibited drug precipitation. Turbidity measurements using laser nephelometry can provide a rapid screening tool when developing intravenous formulations for poorly soluble drugs, such as Ptx and assess its stability upon dilution in animal plasma