Faculty of Science
https://dspace.library.uvic.ca//handle/1828/64
Thu, 18 Oct 2018 21:12:31 GMT2018-10-18T21:12:31ZA reversible-jump Markov chain Monte Carlo algorithm for 1D inversion of magnetotelluric data
https://dspace.library.uvic.ca//handle/1828/10169
A reversible-jump Markov chain Monte Carlo algorithm for 1D inversion of magnetotelluric data
Mandolesi, Eric; Ogaya, Xenia; CampanyĆ , Joan; Agostinetti, Nicola Piana
This paper presents a new computer code developed to solve the 1D magnetotelluric (MT) inverse problem using a Bayesian trans-dimensional Markov chain Monte Carlo algorithm. MT data are sensitive to the depth-distribution of rock electric conductivity (or its reciprocal, resistivity). The solution provided is a probability distribution - the so-called posterior probability distribution (PPD) for the conductivity at depth, together with the PPD of the interface depths. The PPD is sampled via a reversible-jump Markov Chain Monte Carlo (rjMcMC) algorithm, using a modified Metropolis-Hastings (MH) rule to accept or discard candidate models along the chains. As the optimal parameterization for the inversion process is generally unknown a trans-dimensional approach is used to allow the dataset itself to indicate the most probable number of parameters needed to sample the PPD. The algorithm is tested against two simulated datasets and a set of MT data acquired in the Clare Basin (County Clare, Ireland). For the simulated datasets the correct number of conductive layers at depth and the associated electrical conductivity values is retrieved, together with reasonable estimates of the uncertainties on the investigated parameters. Results from the inversion of field measurements are compared with results obtained using a deterministic method and with well-log data from a nearby borehole. The PPD is in good agreement with the well-log data, showing as a main structure a high conductive layer associated with the Clare Shale formation.
In this study, we demonstrate that our new code go beyond algorithms developend using a linear inversion scheme, as it can be used: (1) to by-pass the subjective choices in the 1D parameterizations, i.e. the number of horizontal layers in the 1D parameterization, and (2) to estimate realistic uncertainties on the retrieved parameters. The algorithm is implemented using a simple MPI approach, where independent chains run on isolated CPU, to take full advantage of parallel computer architectures. In case of a large number of data, a master/slave appoach can be used, where the master CPU samples the parameter space and the slave CPUs compute forward solutions.
Mon, 01 Jan 2018 00:00:00 GMThttps://dspace.library.uvic.ca//handle/1828/101692018-01-01T00:00:00ZPhenol-selective mass spectrometric analysis of jet fuel
https://dspace.library.uvic.ca//handle/1828/10166
Phenol-selective mass spectrometric analysis of jet fuel
Zhu, Haoxuan; Janusson, Eric; Luo, Jingwei; Piers, James; Islam, Farhana; McGarvey, G. Bryce; Oliver, Allen G.; Granot, Ori; McIndoe, J. Scott
Bromobenzyl compounds react selectively with phenols via the Williamson ether synthesis. An imidazolium charge-tagged bromobenzyl compound can be used to reveal phenol impurities in jet fuel by analysis via electrospray ionization mass spectrometry. The complex matrix as revealed by Cold EI GC/MS analysis is reduced to a few simple sets of compounds in the charge-tagged ESI mass spectrum, primarily substituted phenols and thiols. Examination of jet fuels treated by different refinery methods reveals the efficacy of these approaches in removing these contaminants.
Fri, 01 Sep 2017 00:00:00 GMThttps://dspace.library.uvic.ca//handle/1828/101662017-09-01T00:00:00ZSolvent effects on surface activity of aggregate ions in electrospray ionization
https://dspace.library.uvic.ca//handle/1828/10165
Solvent effects on surface activity of aggregate ions in electrospray ionization
Pape, Jennifer; Vikse, Krista L.; Janusson, Eric; Taylor, Nichole; McIndoe, J. Scott
A principal feature of electrospray ionization (ESI) is the transfer of ions in solution into the gas-phase for analysis by mass spectrometry. The electrospray process is intricate and therefore each stage of the process must be well-characterized in order to optimize the quality of the data obtained. The surface activity of a given ion is a substantial factor in its likelihood of evaporating from droplets formed by the electrospray, and leads to a differential response of one ion over another. Consequently, investigation of the response of a variety of ions in multiple solvents lends insight toward both desolvation processes and the surface activity of the ions studied in the chosen solvent. In the present work, a cationic ionic liquid, butyl methylimidazolium (BMIM), was paired with a counterion and mixed in various solvents. Subsequently, BMIM paired with a different counterion was added to the solution and analyzed by ESI mass spectrometry to determine the relative response ratio between two observable aggregates. The findings assist in the elucidation of differential surface activity of chemically distinct ions in ESI, with respect to changes in solvent. Furthermore, the results obtained suggest acetonitrile is an optimal solvent for the analysis of ions of this type due to a reduction in differential effects, whereas other common ESI solvents prove to enhance the surface activity of specific aggregate ions.
Sat, 01 Nov 2014 00:00:00 GMThttps://dspace.library.uvic.ca//handle/1828/101652014-11-01T00:00:00ZMass transfer and convection effects in small-scale catalytic hydrogenation
https://dspace.library.uvic.ca//handle/1828/10164
Mass transfer and convection effects in small-scale catalytic hydrogenation
Luo, Jingwei; Wu, Yang; Zijlstra, Harmen S.; Harrington, David A.; McIndoe, J. Scott
Rhodium-catalyzed hydrogenation of alkynes was studied under conditions of low concentration of substrate and either one or two equivalents of hydrogen using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS). Four sample vials of the same volume but of different diameter enabled the investigation of the effects of surface area on reaction rates. Running the same experiments with stirring on or off allowed further details to emerge, notably the obvious effects of convection thanks to the localized sampling technique employed. Modelling of the system allowed for a better understanding of the relative importance of the various factors in play (reaction rate, surface area, mass transfer, convection). These factors should be carefully considered when studying or optimizing reactions involving narrow reaction flasks, especially when those flasks are unstirred.
Thu, 01 Jun 2017 00:00:00 GMThttps://dspace.library.uvic.ca//handle/1828/101642017-06-01T00:00:00Z