Ion–molecule reactions of CoAr₆⁺ with nitrogen oxides N₂O, NO, and NO₂: measuring absolute pressure by shock-freezing of the collision complex

A new method to determine the absolute pressure in an ultra-high vacuum apparatus is tested using ion molecule reactions with CoAr₆⁺. In a collision with a neutral reactant, the complex between Co⁺ and the collision partner is stabilized by evaporation of argon atoms. If CoAr₆⁺ reacts with collision rate, the absolute pressure can be determined by comparing the experimental collision rate with the collision rate calculated from average dipole orientation theory. The experimental results with N₂O, NO, and NO₂ indeed show that the collision complex is frozen out. Comparison of the rates of primary, secondary and tertiary reaction products, however, suggests that not all collisions of CoAr₆⁺ are reactive

Photodissociation and photochemistry of V⁺ (H₂O)n, n = 1–4, in the 360–680 nm region

The photodissociation and photochemistry of V⁺ (H₂O)n, n = 1–4, was studied in the 360–680 nm region in a Fourier transform ion cyclotron resonance mass spectrometer. The light of a high pressure mercury arc lamp was filtered with band pass filters, with center wavelengths from 360 to 680 nm in steps of 20 nm. The bandwidth of the filters, defined as full width at half maximum, was 10 nm. Photodissociation channels are loss of water molecules, as well as loss of atomic or molecular hydrogen, which may be accompanied by loss of water molecules. The most intense absorptions are red shifted with increasing hydration. Theoretical spectra are calculated with time dependent density functional theory. Calculations reproduce all features of the experimental spectra, including the red shift with increasing hydration shell and the overall pattern of strong and weak absorptions

Formation of (Xe2H)* centers in solid Xe via recombination: nonstationary luminescence and «internal electron emission»

The formation of excimers (Xe2H)* in solid Xe doped with molecular hydrogen under electron beam is studied using the original two-stage technique of nonstationary (NS) cathodoluminescence (CL) in combination with the current activation spectroscopy method — thermally stimulated exoelectron emission (TSEE). Charged species were generated using a high-density electron beam. The species produced were then probed with a lowdensity beam on gradual sample heating. The near UV emission of the (Xe2H)* was used to monitor the neutralization process. It is found that the temperature behavior of the NS CL band of (Xe2H)* clearly correlates with the yield of TSEE measured after identical pre-irradiation of the sample. The fingerprints of the thermally stimulated detrapping of electrons — «internal electron emission» in the spectrum of NS CL point to the essential role of neutralization reaction in the stability of the proton solvated by rare-gas atoms

Quantum Smoluchowski equation: Escape from a metastable state

We develop a quantum Smoluchowski equation in terms of a true probability distribution function to describe quantum Brownian motion in configuration space in large friction limit at arbitrary temperature and derive the rate of barrier crossing and tunneling within an unified scheme. The present treatment is independent of path integral formalism and is based on canonical quantization procedure.Comment: 10 pages, To appear in the Proceedings of Statphys - Kolkata I

Brain disconnectome mapping derived from white matter lesions and serum neurofilament light levels in multiple sclerosis: a longitudinal multicenter study

BACKGROUND AND OBJECTIVES: Connectivity-based approaches incorporating the distribution and magnitude of the extended brain network aberrations caused by lesions may offer higher sensitivity for axonal damage in patients with multiple sclerosis (MS) than conventional lesion characteristics. Using individual brain disconnectome mapping, we tested the longitudinal associations between putative imaging-based brain network aberrations and levels of serum neurofilament light chain (NfL) as a neuroaxonal injury biomarker. METHODS: MS patients (n = 312, mean age 42.9 years, 71 % female) and healthy controls (HC) (n = 59, mean age 39.9 years, 78 % female) were prospectively enrolled at four European MS centres, and reassessed after two years (MS, n = 242; HC, n = 30). Post-processing of 3 Tesla (3 T) MRI data was performed at one centre using a harmonized pipeline, and disconnectome maps were calculated using BCBtoolkit based on individual lesion maps. Global disconnectivity (GD) was defined as the average disconnectome probability in each patient's white matter. Serum NfL concentrations were measured by single molecule array (Simoa). Robust linear mixed models (rLMM) with GD or T2-lesion volume (T2LV) as dependent variables, patient as a random factor, serum NfL, age, sex, timepoint for visit, diagnosis, treatment, and center as fixed factors were run. RESULTS: rLMM revealed significant associations between GD and serum NfL (t = 2.94, p = 0.003), age (t = 4.21, p = 2.5 × 10(-5)), and longitudinal changes in NfL (t = -2.29, p = 0.02), but not for sex (t = 0.63, p = 0.53) or treatments (t = 0.80-0.83, p = 0.41-0.42). Voxel-wise analyses revealed significant associations between dysconnectivity in cerebellar and brainstem regions and serum NfL (t = 7.03, p < 0.001). DISCUSSION: In our prospective multi-site MS cohort, rLMMs demonstrated that the extent of global and regional brain disconnectivity is sensitive to a systemic biomarker of axonal damage, serum NfL, in patients with MS. These findings provide a neuroaxonal correlate of advanced disconnectome mapping and provide a platform for further investigations of the functional and potential clinical relevance of brain disconnectome mapping in patients with brain disorders

Brain disconnectome mapping and serum neurofilament light levels in multiple sclerosis

The pathophysiological mechanisms for classical plaque characteristics and their predictive value for clinical course and outcome in multiple sclerosis is unclear. Connectivity-based approaches incorporating the distribution and magnitude of the extended brain network aberrations caused by lesions may offer higher sensitivity for axonal damage. Using individual brain disconnectome mapping, we tested the longitudinal associations between putative brain network aberrations and levels of serum neurofilament light chain (sNfL) as a neuroaxonal injury biomarker. Multiple sclerosis patients (n = 328, mean age 42.9 years, 71 % female) were prospectively enrolled at four European multiple sclerosis centres, and reassessed after two years (n = 280). Post-processing of 3 Tesla (3T) MRI data was performed at one centre using a harmonized pipeline, and disconnectome maps were calculated using BCBtoolkit based on individual lesion maps. Global disconnectivity (GD) was defined as the average disconnectome probability in each patient′s white matter. Serum NfL concentrations were measured by single molecule array (Simoa). Robust linear mixed models (rLMM) with GD or T2-lesion volume (T2LV) as dependent variables, patient and centre as a random factor, sNfL, age, sex, timepoint for visit, diagnosis, and treatment as fixed factors were run. Robust LMM revealed significant associations between higher levels of GD and increased sNfL (t = 2.30, β = 0.03, p = 0.02), age (t = 5.01, β = 0.32, p < 5.5 x 10-7), and diagnosis progressive multiple sclerosis (PMS); t = 1.97, β = 1.06, p = 0.05), but not for sex (t = 0.78, p = 0.43), treatments (effective; t = 0.85, p = 0.39, highly-effective; t = 0.86, p = 0.39) or sNfL change between base line and two-year follow up (t = -1.65, p = 0.10). Voxel-wise analyses revealed distributed associations in cerebellar and brainstem regions. In our prospective multi-site multiple sclerosis cohort, rLMMs demonstrated that the extent of global brain disconnectivity is sensitive to a systemic biomarker of axonal damage, sNfL, in patients with multiple sclerosis. These findings provide a neuropathological correlate of advanced disconnectome mapping and provide a platform for further investigations of the functional and clinical relevance in patients with brain disorders

Measurement of the cross section for isolated-photon plus jet production in pp collisions at √s=13 TeV using the ATLAS detector

The dynamics of isolated-photon production in association with a jet in proton–proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fb−1. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti- algorithm with radius parameter and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements