1,352 research outputs found
A calm and peaceful land
No full textUPEI 091; [sound recording] / P. Batchilder, M. Hennessey, C. Perry.; 2 sound cassettes (125 min.; Contents : Introductions (Grant & Robb) -- The Belfast riots (Batchilder) -- "The artist" (Hennessey) -- Rum running days (Perry).; Introduction : William Grant ; Andy Robb.; Recorded at the Confederation of the Arts Centre, 13 March 1977.; The Belfast riotsSource type: Electronic(1
Relaxation Paths from a Conical Intersection: The Mechanism of Product Formation in the Cyclohexadiene/Hexatriene Photochemical Interconversion
No full textAn algorithm for the computation of initial relaxation directions (IRD) from the tip of a conical intersection is discussed. The steepest descent paths that can be computed starting from these IRD provide a description of the ground state relaxation of the "cold" excited state species that occur in organic photochemistry where slow motion and/or thermal equilibration is possible (such as in cool jet, in matrices, and in solution). Under such conditions we show that the central conclusions drawn from a search for IRD and those obtained from semiclassical trajectory computations are the same. In this paper, IRD computations are used to investigate the mechanism of photoproduct formation and distribution in the photolysis of cyclohexadiene (CHD) and cZc-hexatriene (cZc-HT). A systematic search for the IRD in the region of the 2A1/1A1 conical intersection (see Celani, P.; Ottani, S.; Olivucci, M.; Bernardi, F.; Robb, M. A. J. Am. Chem. Soc. 1994, 116, 10141-10151) located on the 2A1 potential energy surface of these systems yields three relaxation paths. The first two paths, which start in the strict vicinity of the intersection, are nearly equivalent energetically and lead to production of CHD and cZc-HT, respectively. The third path, which begins at a much larger distance, lies higher in energy and ends at a methylenecyclopentene diradical (MCPD) minimum. Further, while the first two paths define directions that form a 60° angle with the excited state entry channel (i.e. the direction along where the conical intersection region is entered), the third path is orthogonal. It is shown that these findings are consistent with the experimental observations which show nearly equivalent quantum yields for CHD and cZc-HT and no production of MCPD. The results of the IRD computations have been validated by investigating the decay dynamics of trajectories starting from a "circle" of points around the conical intersection, with the initial kinetic energy distributed in randomly sampled vibrational modes. These computations have been carried out using a trajectory-surface-hopping (TSH) method and a hybrid molecular mechanics valence bond (MM-VB) force field to model the ab initio potentials
DFT Study of the Reactions between Singlet-Oxygen and a Carotenoid Model
No full textCarotenoids such as beta-carotene are one of the most efficient singlet-oxygen (O-1(2)) quenchers. They quench catalytically O-1(2) (a highly reactive and toxic form of oxygen) through an almost diffusion-controlled energy transfer process (physical pathway): O-1(2) + carotenoid --> O-3(2) + (3)carotenoid --> O-3(2) + carotenoid (+ heat) (eq 1). In contrast to physical quenching, less efficient but concomitant processes exist, involving real chemical reactions. For example. chemical oxidation reactions, which result in the destruction of carotenoids and thus in the loss of antioxidant protection, have been observed (chemical pathway): O-1(2) + carotenoid --> chemical pathway (eq 2). To obtain more detailed information about the reactions between carotenoids and singlet-oxygen, we have performed a DFT computational study of the reaction mechanisms involved in the attack of O-1(2) to the all-trans-decaottanonaene (P-9), a polyene with 9 conjugated double bonds, chosen as carotenoid model. We have found that, together with the main energy transfer pathway (eq 1) which is almost barrierless, there are secondary but concomitant reactions (eq 2) with low-energy barriers leading to biradical intermediates via direct addition of O-1(2) to P-9. These biradicals may give ring closure to form 1,2-addition dioxetane products whose decomposition leads to the observed carbonyl chain cleavage oxidation fragments. However, these biradicals seem to be also responsible, through an S-0 --> T-1 intersystem crossing, of an alternative chemically mediated catalytic quenching of the singlet-oxygen which is returned to its triplet deactivated ground state through a dissociation process on T-1
ESTIMATING PRODUCER'S SURPLUS WITH THE CENSORED REGRESSION MODEL: AN APPLICATION TO PRODUCERS AFFECTED BY COLUMBIA RIVER BASIN SALMON RECOVERY
No full textApplication of the tobit model to estimate economic welfare is transferred from the consumer side to the producer side. Supply functions are estimated for multioutput irrigators in the Pacific Northwest. Empirical procedures are then developed for computing expected producer's surplus from the output supply functions. Confidence intervals for the surplus measures are generated using the Krinsky-Robb method. An experiment predicts decreases in surplus given increases in water pumping cost. The experiment replicates possible increases in hydroelectric prices due to the salmon recovery program in the Columbia-Snake River Basin. Output substitution explains producers' ability to mitigate the effect of the price increases on producer's surplus.Resource /Energy Economics and Policy,
AUT824103_Supplemental_material_3 – Supplemental material for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies
No full textSupplemental material, AUT824103_Supplemental_material_3 for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies by Antonio Y Hardan, Robert L Hendren, Michael G Aman, Adelaide Robb, Raun D Melmed, Kristen A Andersen, Rachel Luchini, Rezwanur Rahman, Sanjida Ali, X Daniel Jia, Madhuja Mallick, Jordan E Lateiner, Robert H Palmer and Stephen M Graham in Autism</p
AUT824103_Supplemental_material_1 – Supplemental material for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies
No full textSupplemental material, AUT824103_Supplemental_material_1 for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies by Antonio Y Hardan, Robert L Hendren, Michael G Aman, Adelaide Robb, Raun D Melmed, Kristen A Andersen, Rachel Luchini, Rezwanur Rahman, Sanjida Ali, X Daniel Jia, Madhuja Mallick, Jordan E Lateiner, Robert H Palmer and Stephen M Graham in Autism</p
Pulmonary blood flow distribution has a hilar-to-peripheral gradient in awake, prone sheep
No full text Walther, Sten M., Karen B. Domino, Robb W. Glenny, Nayak L. Polissar, and Michael P. Hlastala. Pulmonary blood flow distribution has a hilar-to-peripheral gradient in awake, prone sheep. J. Appl. Physiol. 82(2): 678–685, 1997.—We examined the pulmonary blood flow distribution with intravenous fluorescent microspheres (15 μm) in nine prone, unanesthetized, lambs. Lungs flushed free of blood were air-dried at total lung capacity and sectioned into ∼2-cm3 pieces. The pieces were weighed, identified by lobe, and assigned spatial coordinates. Fluorescence was read on a spectrophotometer, and signals were corrected for piece weight and normalized to mean flow. Pulmonary blood flow heterogeneity was assessed by using the coefficient of variation of the flow data. The number of pieces (±SD) analyzed were 1,249 ± 150/animal. Heterogeneity of blood flow was 29.5 ± 6.5% (coefficient of variation = SD/mean). Pulmonary blood flow decreased with distance from hilus ( P < 0.002) but did not change significantly with vertical height. Distance from the hilus was the best predictor of pulmonary blood flow ( R 2 = 0.201) and, together with spatial coordinates and lobe, accounted for 33.7 ± 12.0% of blood flow variability. We conclude that pulmonary blood flow in the awake, prone sheep is distributed with a hilar-to-peripheral gradient but no significant vertical gradient. </jats:p
AUT824103_Lay_Abstract – Supplemental material for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies
No full textSupplemental material, AUT824103_Lay_Abstract for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies by Antonio Y Hardan, Robert L Hendren, Michael G Aman, Adelaide Robb, Raun D Melmed, Kristen A Andersen, Rachel Luchini, Rezwanur Rahman, Sanjida Ali, X Daniel Jia, Madhuja Mallick, Jordan E Lateiner, Robert H Palmer and Stephen M Graham in Autism</p
AUT824103_Supplemental_material_2 – Supplemental material for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies
No full textSupplemental material, AUT824103_Supplemental_material_2 for Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies by Antonio Y Hardan, Robert L Hendren, Michael G Aman, Adelaide Robb, Raun D Melmed, Kristen A Andersen, Rachel Luchini, Rezwanur Rahman, Sanjida Ali, X Daniel Jia, Madhuja Mallick, Jordan E Lateiner, Robert H Palmer and Stephen M Graham in Autism</p
Minimum Energy Paths in the Excited and Ground States of Short Protonated Schiff Bases and of the Analogous Polyenes: a CASSCF/PT2 Study
No full textA theoretical study of the minimum energy paths (MEP) for the first excited state S1 and for the ground state S0 of two short-chain protonated Schiff bases (the protonated s-cis 1-iminium-2-propene H2C=CH-CH=NH2+ and the protonated tZt 1-iminium-2,4-pentadiene H2C=CH-CH=CH-CH=NH2+) and of the two analogous polyenes (s-cis butadiene H2C=CH-CH=CH2 and tZt hexatriene H2C=CH-CH=CH-CH=CH2) is reported. The geometries have been optimized at the CAS-SCF level and the energetics have been refined via single-point computations at the multi-reference MP2 level. It is demonstrated that the photochemistry of the protonated Schiff bases and of the analogous polyenes is driven by two different S1 excited states, the spectroscopic 1B ionic state for the protonated Schiff bases and the covalent 2A1 excited state for the analogous polyenes. This difference induces different electronic and geometric featjres in the computed MEP and conical intersections which depend on the nature of the involved excited states. The conical intersections between S1/S0 in polyenes have a covalent tetraradicaloid nature and are characterized by the development of a typical (-CH-)3 'kink' in the carrion moiety, while the conical intersection points in the protonated Schiff bases have a twisted double bond. Thus in the protonated Schiff bases, the photoproducts arise only from isomerization processes, while in the analogous polyenes, the photoproducts arise from various types of recoupling schemes of the electrons of the quasi-tetraradical conical intersection point, leading to a more complex photoreactivity pattern. © 1998 Elsevier Science S.A. All rights reserved
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