Lawrence Pratt - Academia.edu (original) (raw)

Papers by Lawrence Pratt

We simulated the interface between liquid water and a stationary phase of tethered n-C18 alkyl ch... more We simulated the interface between liquid water and a stationary phase of tethered n-C18 alkyl chains at a thermodynamic state of low pressure and water vapor-liquid coexistence. The interfacial water (oxygen atom) density profile so obtained is compared with a precisely defined proximal density of water molecules (oxygen atoms) conditional on the alkyl chain configurations. Though the conventional interfacial density profile takes a traditional monotonic form, the proximal radial distribution of oxygen atoms around a specific methyl (methylene) group closely resembles that for a solitary methane solute in liquid water. Moreover, this proximal radial distribution function is sufficient to accurately reconstruct the water oxygen density profile of the oil-water interface. These observations provide an alternative interpretation to collective drying or vaporization interpretations of commonly observed oil-water interfacial profiles for which water penetration into the interfacial region plays a role.

Fluid Phase Equilibria, 1998

Reported here are theoretical calculations on the trifluoromethanesulfonic (triflic) acid and wat... more Reported here are theoretical calculations on the trifluoromethanesulfonic (triflic) acid and water molecules, establishing molecular scale information necessary to molecular modeling of the structure, thermodynamics, and ionic transport of Nafion R membranes. The optimized geometry determined for the isolated triflic acid molecule, obtained from ab initio molecular orbital calculations, agrees with previous studies. In order to characterize side chain flexibility and accessibility of the acid proton, potential energy and free energy surfaces for rotation of both carbon-sulfur and sulfuroxygen(hydroxyl) bonds are presented. A continuum dielectric solvation model is used to obtain free energies of electrostatic interaction with the solvent. Electrostatic solvation is predicted to reduce the free energy barrier to rotation of the F3C-SO3 bond to about 2.7 kcal/mol. This electrostatic effect is associated with slight additional polarization of the CF bond in the eclipsed conformation. The energetic barrier to rotation of the acid hydroxyl group away from the sulfonic acid oxygen plane, out into the solvent is substantially flattened by electrostatic solvation effects. The maximum free energy change for those solvent accessible proton conformations is less than one kcal/mol. We carried out additional ab initio electronic structure calculations with a probe water molecule interacting with the triflic acid. The minimum energy structures found here for the triflic acid molecule with the probe water revise results reported previously. To investigate the reaction path for abstraction of a proton from triflic acid, we found minimum energy structures, energies, and free energies for: (a) a docked configuration of triflate anion and hydronium cation and (b) a transition state for proton interchange between triflic acid and a water molecule. Those configurations are structurally similar but energetically substantially different. The activation free energy for that proton interchange is predicted to be 4.7 kcal/mol above the reaction end-points.

Journal of the American Chemical Society, 2005

Journal of the American Chemical Society, 2000

The Journal of Physical Chemistry A, 2001

... 19) Rempe, SG; Pratt, LR; Hummer, G.; Kress, JD; Martin, RL; Redondo, A. J. Am. Chem. Soc.200... more ... 19) Rempe, SG; Pratt, LR; Hummer, G.; Kress, JD; Martin, RL; Redondo, A. J. Am. Chem. Soc.2000, 122, 966. ... Leoncio Garrido, Javier Pozuelo, Mar L pez-Gonz lez, Jianhua Fang and Evaristo Riande. Macromolecules 2009 42 (17), 6572-6580. ...

The International Food and Agribusiness Management Review

Latin America's coffee market continues in economic crisis. Sustainable coffee production and... more Latin America's coffee market continues in economic crisis. Sustainable coffee production and certification is one option for economic recuperation and social and environmental sustainability for the region's coffee producers. This paper explores four viable certification processes (Organic, Fair Trade, Rainforest Alliance, and Utz Kapeh) by first defining their requirements. Then, an assessment of microeconomic impacts is given, where the production processes of sustainable and conventional coffee are evaluated and compared. Finally, the paper presents their future relevance and entrepreneurial potential by considering long-term market perspectives. Information about sustainable production in Latin America was gathered through primary sources in interviews and markets analyses conducted by the CIMS Foundation.

This executive profile summarized here identifies the great environmental challenges of the Mesoa... more This executive profile summarized here identifies the great environmental challenges of the Mesoamerican region, highlights the achievements of the last decade, and points out the future course that will guide the region's environmental management advancements. There are three main issues addressed here: natural resources management, environmental impact of urban and industrial development and the relationship between the environment and competitiveness. This document was presented at the Environment Network of the Regional Policy Dialogue's 1st Hemispheric Meeting: Towards an Effective Environmental Management held on April 4th and 5th, 2002.

Journal of Organic Chemistry, 2007

Density functional theory was used to examine the solvation number and aggregation state of sever... more Density functional theory was used to examine the solvation number and aggregation state of several alkyllithium compounds in clusters with tetrahydrofuran molecules coordinated to each lithium atom. We then made the microsolvation approximation and approximated the bulk free energy of solvation by the free energy of clustering with solvent molecules in the gas phase. The trends in the computed results are in reasonable agreement with the available experimental data.

In order to alleviate the impacts of the low coffee prices in recent years, sustainable coffee pr... more In order to alleviate the impacts of the low coffee prices in recent years, sustainable coffee production and certification have been a logical strategy for many producers to: a) differentiate their product in the market place; and, b) shift their production cost structure away from more input intensive techniques. This paper explores the two most widely recognized certification schemes (organic and ''fairtrade'') to determine whether certification to these systems is actually benefiting producers. It then explores the principal differences in production costs and price premiums for the two systems and their effect on different categories of producers. Finally, it considers the dynamics of the conventional and sustainable coffee markets to assess the likely medium to long-term economic outlook for producers involved in the certification schemes. The research is based on a combination of published sources and detailed primary source data (interviews and surveys) gathered by the CIMS Foundation. D

ABSTRACT Trapping of tritium on polymers with specific functional groups was investigated as a me... more ABSTRACT Trapping of tritium on polymers with specific functional groups was investigated as a means of treating waste streams containing low levels of tritium. Chemical exchange of tritium with hydrogen on the functional group was used as the mechanism for trapping. The polymers tested include Aurorez polybenzimidazole resin beads, Chelex 100 resin beads, Duolite GT-73, microcrystalline cellulose, and polyethylenimine. The tests were performed under simulated operating conditions on water obtained from the Radioactive Liquid Waste Treatment Facility at Los Alamos National Laboratory, Tritiated water from the Tritium Systems Test Assembly is discharged to this plant. Polyethylenimine is a water-soluble polymer that was tested using a stirred membrane cell with an ultrafiltration membrane. All of the polymers except polyethylenimine took up tritium from the water. Polybenzimidazole demonstrated the highest tritium uptake. The results are explained on the basis of the type of functional group, hydrogen bonding, and rigidity of the molecular structure of the polymer. The theoretical calculations indicate that significant isotope discrimination requires high-frequency modes with hydrogen bonding contribution and support the experimental findings. Modeling suggested trends that may lead to structures that are more efficient in trapping tritium.

Description/Abstract In the course of the 3 years we have conducted calculations on molecular str... more Description/Abstract In the course of the 3 years we have conducted calculations on molecular structures containing actinides, lanthanides, and other heavy elements. Our calculations were done at the relativistically-correct, all-electron, 4-component calculations (DHF, MP2, and CCSD (T)), using density functional theory (DFT) with relativistic effective core potentials (RECPs), and various other methodologies. We studied the ground-and excited state structures, energetics, vibrational frequencies, and NMR, excitation and ...

... de lo anterior, de CLACDS y no necesariamente de los socios contribuyentes del proyecto. ... ... more ... de lo anterior, de CLACDS y no necesariamente de los socios contribuyentes del proyecto. ... zonas aledañas a los depósitos de desechos ya los cursos de agua afectados, fuera ... industria son a nivel de pequeños productores independientes que venden su cosecha a empresas ...

Medical Imaging 2011: Image Processing, 2011

Plexiform Neurofibroma (PN) is a major complication of NeuroFibromatosis-1 (NF1), a common geneti... more Plexiform Neurofibroma (PN) is a major complication of NeuroFibromatosis-1 (NF1), a common genetic disease that involving the nervous system. PNs are peripheral nerve sheath tumors extending along the length of the nerve in various parts of the body. Treatment decision is based on tumor volume assessment using MRI, which is currently time consuming and error prone, with limited semi-automatic segmentation support. We present in this paper a new method for the segmentation and tumor mass quantification of PN from STIR MRI scans. The method starts with a user-based delineation of the tumor area in a single slice and automatically detects the PN lesions in the entire image based on the tumor connectivity. Experimental results on seven datasets yield a mean volume overlap difference of 25% as compared to manual segmentation by expert radiologist with a mean computation and interaction time of 12 minutes vs. over an hour for manual annotation. Since the user interaction in the segmentation process is minimal, our method has the potential to successfully become part of the clinical workflow.