191 research outputs found
Numerical test of the damping time of layer-by-layer growth on stochastic models
We perform Monte Carlo simulations on stochastic models such as the
Wolf-Villain (WV) model and the Family model in a modified version to measure
mean separation between islands in submonolayer regime and damping time
of layer-by-layer growth oscillations on one dimension. The
stochastic models are modified, allowing diffusion within interval upon
deposited. It is found numerically that the mean separation and the damping
time depend on the diffusion interval , leading to that the damping time is
related to the mean separation as for the WV model
and for the Family model. The numerical results are in
excellent agreement with recent theoretical predictions.Comment: 4 pages, source LaTeX file and 5 PS figure
The effect of monomer evaporation on a simple model of submonolayer growth
We present a model for thin film growth by particle deposition that takes
into account the possible evaporation of the particles deposited on the
surface. Our model focuses on the formation of two-dimensional structures. We
find that the presence of evaporation can dramatically affect the growth
kinetics of the film, and can give rise to regimes characterized by different
``growth'' exponents and island size distributions. Our results are obtained by
extensive computer simulations as well as through a simple scaling approach and
the analysis of rate equations describing the system. We carefully discuss the
relationship of our model with previous studies by Venables and Stoyanov of the
same physical situation, and we show that our analysis is more general.Comment: 41 pages including figures, Revtex, to be published in Physical
Review
The Impact of Immigrant Entrepreneurs’ Social Capital Related Motivations
The immigrant entrepreneurship literature indicates that immigrant entrepreneurs reap numerous benefits from their co-ethnic communities’ social capital. These benefits, however, often come at a price because scholars note the potential for this community social capital to impose limitations on the entrepreneurs. While the literature largely focuses on the benefits of social capital, there is no research on what motivates the immigrant entrepreneurs to engage with their co-ethnic community in terms of contributing to, and utilizing, their co-ethnic communities’ social capital, and the consequences these may have on their enterprises. Addressing this gap in the literature is important in the development of successful immigrant enterprises. Thus, based on a model posited by Portes and Sensenbrenner (1993), we suggest that immigrant entrepreneurs’ motivations will influence their use of, and contributions to, co-ethnic community social capital, impacting, in turn, business success. We contribute to both the immigrant entrepreneurship and social capital research through exploring how entrepreneurs’ motives, with respect to their co-ethnic communities’ social capital, influence business success
Plastic Hotspot Mapping in Urban Water Systems
Reducing plastic pollution in rivers, lakes, and oceans is beneficial to aquatic animals and human livelihood. To achieve this, reliable observations of the abundance, spatiotemporal variation, and composition of plastics in aquatic ecosystems are crucial. Current efforts mainly focus on collecting data on the open ocean, on beaches and coastlines, and in river systems. Urban areas are the main source of plastic leakage into the natural environment, yet data on plastic pollution in urban water systems are scarce. In this paper, we present a simple method for plastic hotspot mapping in urban water systems. Through visual observations, macroplastic abundance and polymer categories are determined. Due to its simplicity, this method is suitable for citizen science data collection. A first application in the Dutch cities of Leiden and Wageningen showed similar mean plastic densities (111–133 items/km canal) and composition (75–80% soft plastics), but different spatial distributions. These observations emphasize the importance of long-term data collection to further understand and quantify spatiotemporal variations of plastics in urban water systems. In turn, this will support improved estimates of the contribution of urban areas to the plastic pollution of rivers and oceans.Industrial EcologyEnvironmental Biolog
Геохимические особенности антропогенных карбонатных отложений на территории Республики Башкортостан
Геохимические особенности антропогенных карбонатных отложений на территории Республики Башкортостан.Geochemical features of anthropogenic carbonate deposits on the territory of the Republic of Bashkortostan
Macrofossil evidence for a rapid and severe Cretaceous–Paleogene mass extinction in Antarctica
Debate continues about the nature of the Cretaceous–Paleogene (K–Pg) mass extinction event. An abrupt crisis triggered by a bolide impact contrasts with ideas of a more gradual extinction involving flood volcanism or climatic changes. Evidence from high latitudes has also been used to suggest that the severity of the extinction decreased from low latitudes towards the poles. Here we present a record of the K–Pg extinction based on extensive assemblages of marine macrofossils (primarily new data from benthic molluscs) from a highly expanded Cretaceous–Paleogene succession: the López de Bertodano Formation of Seymour Island, Antarctica. We show that the extinction was rapid and severe in Antarctica, with no significant biotic decline during the latest Cretaceous, contrary to previous studies. These data are consistent with a catastrophic driver for the extinction, such as bolide impact, rather than a significant contribution from Deccan Traps volcanism during the late Maastrichtian
Growth of nanostructures by cluster deposition : a review
This paper presents a comprehensive analysis of simple models useful to
analyze the growth of nanostructures obtained by cluster deposition. After
detailing the potential interest of nanostructures, I extensively study the
first stages of growth (the submonolayer regime) by kinetic Monte-Carlo
simulations. These simulations are performed in a wide variety of experimental
situations : complete condensation, growth with reevaporation, nucleation on
defects, total or null cluster-cluster coalescence... The main scope of the
paper is to help experimentalists analyzing their data to deduce which of those
processes are important and to quantify them. A software including all these
simulation programs is available at no cost on request to the author. I
carefully discuss experiments of growth from cluster beams and show how the
mobility of the clusters on the surface can be measured : surprisingly high
values are found. An important issue for future technological applications of
cluster deposition is the relation between the size of the incident clusters
and the size of the islands obtained on the substrate. An approximate formula
which gives the ratio of the two sizes as a function of the melting temperature
of the material deposited is given. Finally, I study the atomic mechanisms
which can explain the diffusion of the clusters on a substrate and the result
of their mutual interaction (simple juxtaposition, partial or total
coalescence...)Comment: To be published Rev Mod Phys, Oct 99, RevTeX, 37 figure
Initial stages of Cu epitaxy on Ni(100): Postnucleation and a well-defined transition in critical island size
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