Search results for "Faces"
showing 10 items of 3167 documents
A theory ofnonverticaltriplet energy transfer in terms of accurate potential energy surfaces: The transfer reaction from π,π* triplet donors to 1,3,5…
2004
Triplet energy transfer (TET) from aromatic donors to 1,3,5,7-cyclooctatetraene (COT) is an extreme case of "nonvertical" behavior, where the transfer rate for low-energy donors is considerably faster than that predicted for a thermally activated (Arrhenius) process. To explain the anomalous TET of COT and other molecules, a new theoretical model based on transition state theory for nonadiabatic processes is proposed here, which makes use of the adiabatic potential energy surfaces (PES) of reactants and products, as computed from high-level quantum mechanical methods, and a nonadiabatic transfer rate constant. It is shown that the rate of transfer depends on a geometrical distortion paramet…
O2 Diffusion in Amorphous SiO2 Nanoparticles Probed by Outgassing
2012
An experimental study of the O2 diffusion process in nanoparticles of amorphous SiO2 in the temperature range from 98 to 157 °C was carried out by Raman and photoluminescence techniques. We studied O2 diffusion in high purity silica nanoparticles with a mean diameter of 14, 20, and 40 nm detecting the outgassing of molecules trapped during the manufacturing. The kinetics of diffusion is well described for all the investigated nanoparticles by the Fick’s equation proving its applicability to nanoscale systems. The diffusion coefficient features an Arrhenius law temperature dependence in the explored temperature range, and the diffusion coefficient values are in good agreement with extrapolat…
Quasi-elastic Neutron Scattering Investigation of the Hydrogen Surface Self-Diffusion on Polymer Electrolyte Membrane Fuel Cell Catalyst Support
2008
International audience; Quasi-elastic neutron scattering (QENS) measurements have been performed to investigate the surface selfdiffusion of hydrogen molecules. A monolayer of molecular hydrogen was adsorbed on a carbon material commonly used in polymer electrolyte membrane fuel cells, called XC-72. QENS spectra were recorded at the time-of-flight spectrometer IN5 at Institut Laue-Langevin (ILL) in Grenoble at 40, 50, 60, and 70 K. By using the Chudley & Elliott model for jump diffusion, we found the diffusion coefficient at each temperature. The logarithm of the diffusion coefficient was plotted versus the inverse of the temperature to give the coefficient in the Arrhenius equation. From t…
Report of the COSPAR Mars special regions colloquium
2010
International audience; In this paper we present the findings of a COSPAR Mars Special Regions Colloquium held in Rome in 2007. We review and discuss the definition of Mars Special Regions, the physical parameters used to define Mars Special Regions, and physical features on Mars that can be interpreted as Mars Special Regions. We conclude that any region experiencing temperatures > -25 degrees C for a few hours a year and a water activity > 0.5 can potentially allow the replication of terrestrial microorganisms. Physical features on Mars that can be interpreted as meeting these conditions constitute a Mars Special Region. Based on current knowledge of the martian environment and the conser…
Interannual variability of Greenland winter precipitation sources: 2. Effects of North Atlantic Oscillation variability on stable isotopes in precipi…
2008
[1] A new Lagrangian moisture source diagnostic is applied to identify the atmospheric conditions relevant for the fractionation of stable water isotopes during evaporation over the ocean and subsequent transport to Greenland. Northern Hemisphere winter months with positive and negative North Atlantic Oscillation (NAO) index are studied on the basis of ERA-40 reanalysis data. Diagnosed moisture transport conditions are supplied to a Rayleigh-type isotope fractionation model to derive estimates for the isotopic composition of stable isotopes in winter precipitation on the Greenland plateau for the two NAO phases. Because of changes in atmospheric circulation, moisture source locations for pr…
Particle size distributions of currently used pesticides in a rural atmosphere of France
2013
This work presents first data on the particle size distributions of current-used pesticides in the atmosphere. Ambient air samples were collected using a cascade impactor distributed into four size fractions in a rural site of Centre Region (France). Most pesticides were accumulated in the fine (0.1-1 mu m) particle size fraction such as cyprodinil, pendimethalin, fenpropidin, fenpropimorph and spiroxamine. Other pesticides such as acetochlor and metolachlor presented a bimodal distribution with maximum concentrations in the ultrafine (0.03-0.1 mu m) coarse (1-10 mu m) and in the ultrafine fine size ranges, respectively. No pesticides were detected in the size fraction >10 mu m. (C) 2013 El…
Modeling the outdoor cooling impact of highly radiative “super cool” materials applied on roofs
2021
Abstract Highly reflective “cool materials” are commonly used to reduce temperatures in the urban environment. Recently developed “super cool” materials feature an even higher albedo and emissivity (both above 0.95) than traditional cool materials. To examine the impacts of super cool roofing materials on outdoor air temperature compared to traditional cool roofs and green roofs, we conduct a sensitivity study with the microclimate model ENVI-met. Simulated surface temperature of super cool roofs remained around 6 K below ambient air temperature during high solar irradiation, which is consistent with observations. Super cool roofs – with an averaged street-level air temperature cooling of a…
Vegetation fire emissions and their impact on air pollution and climate
2009
Gaseous and particulate emissions from vegetation fires substantially modify the atmospheric chemical composition, degrade air quality and can alter weather and climate. The impact of vegetation fire emissions on air pollution and climate has been recognised in the late 1970s. The application of satellite data for fire-related studies in the beginning of the 21th century represented a major break through in our understanding of the global importance of fires. Today the location and extent of vegetation fires, burned area and emissions released from fires are determined from satellite products even though many uncertainties persist. Numerous dedicated experimental and modeling studies contri…
Modeling impacts of super cool roofs on air temperature at pedestrian level in mesoscale and microscale climate models
2021
Abstract Passive daytime radiative cooling is gaining increasing relevance as recent studies report that newly developed materials with very high reflectivity and emissivity could be able to effectively reduce urban heat stress, when applied as roofing material (super cool roofs). A recent microscale sensitivity study with ENVI-met modeled the impact of super cool roofs with maximum air temperature reductions of around 0.85 K at pedestrian level for an idealized model area. To verify these findings in real urban structures featuring complex building morphologies and varying meteorological conditions, we conducted climate simulations for two contrasting cities: New York City, NY, and Phoenix…
How effective are the vegetated surfaces for the CO2 sequestration? Analyzing parameters and methods
2021
Human activities are severe sources of greenhouse gases and, particularly, of CO 2 . This trend, according with the highly demanding criteria released by the international institutions, must be suitably cut, in order of turning the pollutant emissions within limits that will guarantee a sustainable and environmentally safe development of the human species. Apart the measures that are since long time usually implemented in the technological systems, other interventions should be properly adopted in supporting the sustainability of the anthropic activities. These actions mainly apply to the so-called bioclimatic and passive measures and, particularly, could usefully refer to the plantation of…