University of Patras

About: University of Patras is a education organization based out in Pátrai, Greece. It is known for research contribution in the topics: Population & Catalysis. The organization has 13372 authors who have published 31263 publications receiving 677159 citations. The organization is also known as: Panepistímio Patrón.

CCN activity and droplet growth kinetics of fresh and aged monoterpene secondary organic aerosol

Abstract: The ability of secondary organic aerosol (SOA) produced from the ozonolysis of α-pinene and monoterpene mixtures (α-pinene, β-pinene, limonene and 3-carene) to become cloud droplets was investigated. A static CCN counter and a Scanning Mobility CCN Analyser (a Scanning Mobility Particle Sizer coupled with a Continuous Flow counter) were used for the CCN measurements. Consistent with previous studies monoterpene SOA is quite active and would likely be a good source of cloud condensation nuclei (CCN) in the atmosphere. A decrease in CCN activation diameter for α-pinene SOA of approximately 3 nm hr −1 was observed as the aerosol continued to react with oxidants. Hydroxyl radicals further oxidize the SOA particles thereby enhancing the particle CCN activity with time. The initial concentrations of ozone and monoterpene precursor (for concentrations lower than 40 ppb) do not appear to affect the activity of the resulting SOA. Kohler Theory Analysis (KTA) is used to infer the molar mass of the SOA sampled online and offline from atomized filter samples. The estimated average molar mass of online SOA was determined to be 180±55 g mol −1 (consistent with existing SOA speciation studies) assuming complete solubility. KTA suggests that the aged aerosol (both from α-pinene and the mixed monoterpene oxidation) is primarily water-soluble (around 65%). CCN activity measurements of the SOA mixed with (NH 4 ) 2 SO 4 suggest that the organic can depress surface tension by as much as 10 N m −1 (with respect to pure water). The droplet growth kinetics of SOA samples are similar to (NH 4 ) 2 SO 4 , except at low supersaturation, where SOA tends to grow more slowly. The CCN activation diameter of α-pinene and mixed monoterpene SOA can be modelled to within 10–15% of experiments by a simple implementation of Kohler theory, assuming complete dissolution of the particles, no dissociation into ions, a molecular weight of 180 g mol −1 , a density of 1.5 g cm −3 , and the surface tension of water.

Electromagnetically induced transparency and slow light in an array of metallic nanoparticles

Abstract: We present a classical analog of electromagnetically induced transparency occurring when light is absorbed by a two-dimensional lattice of metallic spheres mounted on an asymmetric dielectric waveguide. The transparency is manifested as a spectral hole within the surface-plasmon absorption peak of the metallic spheres and is a result of destructive interference of the waveguide modes with incident radiation. The presence of transparency windows is accompanied by slow light effect wherein the group velocity is reduced by a factor of 6000. At the same time, the minimum length for storing a bit of information is of the order of 100 nm. The proposed setup is a much easier means to achieve transparency and slow light compared to existing atomic, solid-state, and photonic systems and allows for the realization of ultracompact optical delay lines and buffers.

A Preliminary Synthesis of Modeled Climate Change Impacts on U.S. Regional Ozone Concentrations

Abstract: This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the differe...

Atomistic Molecular Dynamics Simulation of Polydisperse Linear Polyethylene Melts

Abstract: Well-relaxed atomistic configurations of polydisperse, linear polyethylene (PE) melts, obtained with the end-bridging Monte Carlo algorithm, have been subjected to detailed molecular dynamics simulations in both the canonical (NVE) and microcanonical (NVT) ensembles. Three different systems have been investigated, characterized by mean molecular lengths C24, C78, and C156, and by the same polydispersity index I of about 1.09. Results are presented for the static and (mainly) dynamic properties of these melts at P = 1 atm and T = 450 K. The diffusion coefficient D, determined for various chain lengths, N, is in very good agreement with experimentally measured values. The friction coefficient ζD is extracted from D by invoking the Rouse model; it is seen to increase from a relatively small value characteristic of short alkanes to a chain-length-independent plateau, reached in a region of N = 60−80. The friction coefficient ζτ is also obtained by analyzing the decay of the time autocorrelation function for t...