19 research outputs found
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A crust and upper mantle model of Eurasia and North Africa for Pn travel time calculation
We develop a Regional Seismic Travel Time (RSTT) model and methods to account for the first-order effect of the three-dimensional crust and upper mantle on travel times. The model parameterization is a global tessellation of nodes with a velocity profile at each node. Interpolation of the velocity profiles generates a 3-dimensional crust and laterally variable upper mantle velocity. The upper mantle velocity profile at each node is represented as a linear velocity gradient, which enables travel time computation in approximately 1 millisecond. This computational speed allows the model to be used in routine analyses in operational monitoring systems. We refine the model using a tomographic formulation that adjusts the average crustal velocity, mantle velocity at the Moho, and the mantle velocity gradient at each node. While the RSTT model is inherently global and our ultimate goal is to produce a model that provides accurate travel time predictions over the globe, our first RSTT tomography effort covers Eurasia and North Africa, where we have compiled a data set of approximately 600,000 Pn arrivals that provide path coverage over this vast area. Ten percent of the tomography data are randomly selected and set aside for testing purposes. Travel time residual variance for the validation data is reduced by 32%. Based on a geographically distributed set of validation events with epicenter accuracy of 5 km or better, epicenter error using 16 Pn arrivals is reduced by 46% from 17.3 km (ak135 model) to 9.3 km after tomography. Relative to the ak135 model, the median uncertainty ellipse area is reduced by 68% from 3070 km{sup 2} to 994 km{sup 2}, and the number of ellipses with area less than 1000 km{sup 2}, which is the area allowed for onsite inspection under the Comprehensive Nuclear Test Ban Treaty, is increased from 0% to 51%
Controlling Solvation and Mass Transport Properties of Biobased Solvents through CO2 Expansion: A Physicochemical and Molecular Modeling Study
Gas-expanded liquids have been studied during past years; however, the physicochemical properties of some of these fluids still need to be characterized and understood. In particular, the study of properties concerning solvation and mass transport is key for industrial applications. This work presents the characterization of eight CO2-expanded biosourced solvents: organic carbonates (dimethyl, diethyl, ethylene, and propylene carbonates), anisole, veratrole, γ-valerolactone, and 2-methyltetrahydrofuran. Two approaches have been used: spectroscopic measurements and molecular modeling. Phase equilibrium was determined for each CO2/biosourced solvent system, and then the solvatochromic probe Nile Red was used to determine changes in dipolarity/polarizability (π* Kamlet–Taft parameter) by CO2 pressure. Molecular dynamics calculations were performed to determine the density and viscosity changes with CO2 pressure. It is shown in this study that the degree of modulation of dipolarity/polarizability parameter can go from that of pure solvent (around 0.4 for linear organic carbonates) to negative values, close to that of pure CO2 at the T and P used in this study. Concerning transport properties, such as density and viscosity, a great decrease in both these properties’ values was observed after swelling of the solvent by CO2, for instance, in linear organic carbonates where density can decrease to 50% the density of pure solvent; concerning viscosity a decrease of up to 90% was measured for these compounds. It was observed that the solubility of CO2 and then modulation of properties were higher in linear organic carbonates than in the cyclic ones. This study shows once more that CO2 has a great capacity to be used as a knob for triggering changes in the physicochemical properties of green biosourced solvents that can help to implement these solvents in industrial applications
Hydrogenation of Naturally-Derived Nepetalactone as a Topical Insect Repellent
Dihydronepetalactone
(DHN) is a safe and effective topical insect
repellent,,, comparable
in efficacy to that of <i>N</i>,<i>N</i>-diethyl-<i>m</i>-toluamide (DEET). The latter is the most commonly used
active ingredient, found in many commercial insect repellents for
a broad range of biting insects. DHN can be produced by hydrogenating
nepetalactone (NL), which is the primary ingredient of the essential
oil obtained from the renewably sourced catmint plant, <i>Nepeta
cataria</i>. Optimizing the hydrogenation reaction to produce
DHN from catmint oil is a key economic driver for the process. Prior
to the study described here, Six Sigma methodologies were used to
select palladium on carbon (5% Pd/C) as the catalyst of choice. The
hydrogenation step was studied as a function of critical process variables
and the composition of the oil. As described in this article, a robust,
two-step hydrogenation process was developed to maximize the yield
of the desired DHNs from treated catmint oil. It was observed that
the composition of the catmint oil, vis-à-vis, the relative
amounts of <i>trans–cis</i> and <i>cis–trans</i>-nepetalactone isomers, had a major impact on the activity and selectivity
of the catalyst. This study also focused on minimizing the formation
of a less desirable byproduct, puleganic acid. On the basis of the
process variables tested in this study, temperature was found to have
a strong effect on the activity and selectivity of the catalyst. Higher
pressure enhanced the activity of the catalyst but it did not significantly
impact the formation of undesired byproducts, such as puleganic and
nepetalic acids. Spiking experiments with suspected catalyst poisons,
such as dimethyl sulfide, dimethyl sulfoxide, nepetalic acid, and
puleganic acid were also performed to study catalyst deactivation.
Sulfur was identified as the main factor for the catalyst deactivation.
Possible reaction mechanisms for the formation of less desirable puleganic
and nepetalic acids have been suggested