Estimating seasonal variations in cloud droplet number concentration over the boreal forest from satellite observations

Seasonal variations in cloud droplet number concentration (NCD) in low-level stratiform clouds over the boreal forest are estimated from MODIS observations of cloud optical and microphysical properties, using a sub-adiabatic cloud model to interpret vertical profiles of cloud properties. An uncertainty analysis of the cloud model is included to reveal the main sensitivities of the cloud model. We compared the seasonal cycle in NCD, obtained using 9 yr of satellite data, to surface concentrations of potential cloud activating aerosols, measured at the SMEAR II station at Hyytiälä in Finland. The results show that NCD and cloud condensation nuclei (CCN) concentrations have no clear correlation at seasonal time scale. The fraction of aerosols that actually activate as cloud droplet decreases sharply with increasing aerosol concentrations. Furthermore, information on the stability of the atmosphere shows that low NCD is linked to stable atmospheric conditions. Combining these findings leads to the conclusion that cloud droplet activation for the studied clouds over the boreal forest is limited by convection. Our results suggest that it is important to take the strength of convection into account when studying the influence of aerosols from the boreal forest on cloud formation, although they do not rule out the possibility that aerosols from the boreal forest affect other types of clouds with a closer coupling to the surfac

Simulation of radiation-induced structural transformation in amorphous metals

Molecular-dynamics simulations investigating the radiation-induced structural transformations in metallic glasses are reported. We have studied three models of an equilibrium simple glass, possessing a pronounced icosahedral local order. Two of these are monatomic and one represents the amorphous Ni-P alloy. A detailed analysis of the evolution of the structural damage induced by irradiation is presented. In all the systems, a persistent residual reduction in icosahedral order is observed. An important finding of this study is that the metallic glasses are able to sustain a considerable increase in the number of vacancies which arises as a result of the irradiation-induced structural transformationPeer reviewe

Quasigraphite: Density functional theory based predictions of a structure and its properties

Based on density-functional calculations, we propose a carbon-based nanostructure which we call quasigraphite phase. The quasigraphite phase resembles carbon nanotubes welded into planes, which are arranged similar to layers in graphite. It demonstrates a strong stability with respect to temperatures and external strain. The elastic and electronic properties of the proposed structure are discussed.Peer reviewe

Impact of broad-spectrum anthelmintic treatment in the summer on the weight gain of reindeer calves

The results indicate that broad-spectrum helminth control may increase summer growth of reindeer calves at least when heavily parasitized. The significant weight gain caused by the treatment was, however, relatively small. On natural reindeer pastures with seasonal migration the parasite infection pressure is possibly considerably lower than in this trial

Ab initio study of point defects in CdF2

The plane-wave pseudopotential method is used to study point defects in CdF2. We present comprehensive results for the native defects as well as for dominant impurities. In addition to Fi, VCd and OF were found to be easily formed compensating acceptors. For In and Ga impurities the experimentally observed large Stokes shift could not be established, and the results rule out symmetric atomic relaxation as the mechanism leading to the bistable behavior. The limitations of the present approach utilizing density-functional theory and the local-density approximation in the case of ionic materials are addressed.Peer reviewe

Molecular ordering of precursor films during spreading of tiny liquid droplets

In this work we address a novel feature of spreading dynamics of tiny liquid droplets on solid surfaces, namely the case where the ends of the molecules feel different interactions to the surface. We consider a simple model of dimers and short chain--like molecules which cannot form chemical bonds with the surface. We study the spreading dynamics by Molecular Dynamics techniques. In particular, we examine the microscopic structure of the time--dependent precursor film and find that in some cases it can exhibit a high degree of local order. This order persists even for flexible chains. Our results suggest the possibility of extracting information about molecular interactions from the structure of the precursor film.Comment: 4 pages, revtex, no figures, complete file available from ftp://rock.helsinki.fi/pub/preprints/tft/ or at http://www.physics.helsinki.fi/tft/tft_preprints.html (to appear in Phys. Rev. E Rapid Comm.