7 research outputs found
Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study
The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C2H5Br+ and C2H5I+) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-of-flight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spinâorbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spinâorbit resolved ab initio calculations of cuts through the potential energy surfaces (along the RCâBr/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C2H5Br+ cations undergo prompt CâBr bond fission to form predominantly C2H5+ + Br* products with a near-limiting âparallelâ recoil velocity distribution. The observed C2H3+ + H2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C2H5+ products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C2H5I+, along with an additional energetically accessible CâI bond fission channel to form C2H5 + I+ products. HX (X = Br, I) elimination from the highly internally excited C2H5X+ cation is deemed the most probable route to forming the C2H4+ fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor CâC bond fission process to form CH2X+ + CH3 products
Galaxy Zoo: The Environmental Dependence of Bars and Bulges in Disc Galaxies
We present an analysis of the environmental dependence of bars and bulges in
disc galaxies, using a volume-limited catalogue of 15810 galaxies at z<0.06
from the Sloan Digital Sky Survey with visual morphologies from the Galaxy Zoo
2 project. We find that the likelihood of having a bar, or bulge, in disc
galaxies increases when the galaxies have redder (optical) colours and larger
stellar masses, and observe a transition in the bar and bulge likelihoods, such
that massive disc galaxies are more likely to host bars and bulges. We use
galaxy clustering methods to demonstrate statistically significant
environmental correlations of barred, and bulge-dominated, galaxies, from
projected separations of 150 kpc/h to 3 Mpc/h. These environmental correlations
appear to be independent of each other: i.e., bulge-dominated disc galaxies
exhibit a significant bar-environment correlation, and barred disc galaxies
show a bulge-environment correlation. We demonstrate that approximately half
(50 +/- 10%) of the bar-environment correlation can be explained by the fact
that more massive dark matter haloes host redder disc galaxies, which are then
more likely to have bars. Likewise, we show that the environmental dependence
of stellar mass can only explain a small fraction (25 +/- 10%) of the
bar-environment correlation. Therefore, a significant fraction of our observed
environmental dependence of barred galaxies is not due to colour or stellar
mass dependences, and hence could be due to another galaxy property. Finally,
by analyzing the projected clustering of barred and unbarred disc galaxies with
halo occupation models, we argue that barred galaxies are in slightly
higher-mass haloes than unbarred ones, and some of them (approximately 25%) are
satellite galaxies in groups. We also discuss implications about the effects of
minor mergers and interactions on bar formation.Comment: 20 pages, 18 figures; references updated; published in MNRA
Validation of quantitative susceptibility mapping with Perls' iron staining for subcortical gray matter
Quantitative susceptibility mapping (QSM) measures bulk susceptibilities in the brain, which can arise from many sources. In iron-rich subcortical gray matter (GM), non-heme iron is a dominant susceptibility source. We evaluated the use of QSM for iron mapping in subcortical GM by direct comparison to tissue iron staining. We performed in situ or in vivo QSM at 4.7 T combined with Perls' ferric iron staining on the corresponding extracted subcortical GM regions. This histochemical process enabled examination of ferric iron in complete slices that could be related to susceptibility measurements. Correlation analyses were performed on an individual-by individual basis and high linear correlations between susceptibility and Perls' iron stain were found for the three multiple sclerosis (MS) subjects studied (R-2 = 0.75, 0.62, 0.86). In addition, high linear correlations between susceptibility and transverse relaxation rate (R2*) were found (R-2 = 0.88, 0.88, 0.87) which matched in vivo healthy subjects (R-2 = 0.87). This work validates the accuracy of QSM for brain iron mapping and also confirms ferric iron as the dominant susceptibility source in subcortical GM, by demonstrating high linear correlation of QSM to Perls' ferric iron staining. (C) 2014 Elsevier Inc. All rights reserved
Multimass Velocity-Map Imaging with the Pixel Imaging Mass Spectrometry (PImMS) Sensor: An Ultra-Fast Event-Triggered Camera for Particle Imaging
We present the first multimass velocity-map imaging data
acquired
using a new ultrafast camera designed for time-resolved particle imaging.
The PImMS (Pixel Imaging Mass Spectrometry) sensor allows particle
events to be imaged with time resolution as high as 25 ns over data
acquisition times of more than 100 ÎŒs. In photofragment imaging
studies, this allows velocity-map images to be acquired for multiple
fragment masses on each time-of-flight cycle. We describe the sensor
architecture and present bench-testing data and multimass velocity-map
images for photofragments formed in the UV photolysis of two test
molecules: Br<sub>2</sub> and <i>N</i>,<i>N</i>-dimethylformamide