Relevance Of Dispersion Research Articles

Relevance of Dispersion and the Electronic Spin in the DFT + U Approach for the Description of Pristine and Defective TiO2 Anatase.

A density functional theory + U systematic theoretical study was performed on the geometry, electronic structure, and energies of properties relevant for the chemical reactivity of TiO2 anatase. The effects of D3(BJ) dispersion correction and the Hubbard U value over the energies corresponding to the TiO2/Ti2O3 reduction reaction, the oxygen vacancy formation, and transition-metal doping were analyzed to attain an accurate and well-balanced description of these properties. It is suggested to fit the Hubbard correction for the metal dopant atom by taking as reference the observed low spin–high spin (HS) energy difference for the metal atom. PBEsol-D3 calculations revealed a distinct electronic ground state for the yttrium-doped TiO2 anatase surface depending upon the type of doping and interstitial or substitutional defects. Based on the calculations, it was found that a HS state explains the observed ferromagnetism in cobalt-substituted TiO2 anatase. The results presented herein might be relevant for further catalytic studies on TiO2 anatase using a large surface model that would be worthwhile for heterogeneous catalysis simulations.

TiO2-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

TiO2-supported heteropoly acids are very active catalysts for DME production from methanol. Due to the interaction with the support, the most active catalysts are obtained when a monolayer of HPA is deposited on the support.

Threshold dynamics in a time-delayed epidemic model with dispersal

The global dynamics of a time-delayed model with population dispersal between two patches is investigated. For a general class of birth functions, persistence theory is applied to prove that a disease is persistent when the basic reproduction number is greater than one. It is also shown that the disease will die out if the basic reproduction number is less than one, provided that the initial size of the infected population is relatively small. Numerical simulations are presented using some typical birth functions from biological literature to illustrate the main ideas and the relevance of dispersal.

Relaxed molecular clock provides evidence for long-distance dispersal of Nothofagus (southern beech).

Nothofagus (southern beech), with an 80-million-year-old fossil record, has become iconic as a plant genus whose ancient Gondwanan relationships reach back into the Cretaceous era. Closely associated with Wegener's theory of “Kontinentaldrift”, Nothofagus has been regarded as the “key genus in plant biogeography”. This paradigm has the New Zealand species as passengers on a Moa's Ark that rafted away from other landmasses following the breakup of Gondwana. An alternative explanation for the current transoceanic distribution of species seems almost inconceivable given that Nothofagus seeds are generally thought to be poorly suited for dispersal across large distances or oceans. Here we test the Moa's Ark hypothesis using relaxed molecular clock methods in the analysis of a 7.2-kb fragment of the chloroplast genome. Our analyses provide the first unequivocal molecular clock evidence that, whilst some Nothofagus transoceanic distributions are consistent with vicariance, trans-Tasman Sea distributions can only be explained by long-distance dispersal. Thus, our analyses support the interpretation of an absence of Lophozonia and Fuscospora pollen types in the New Zealand Cretaceous fossil record as evidence for Tertiary dispersals of Nothofagus to New Zealand. Our findings contradict those from recent cladistic analyses of biogeographic data that have concluded transoceanic Nothofagus distributions can only be explained by vicariance events and subsequent extinction. They indicate that the biogeographic history of Nothofagus is more complex than envisaged under opposing polarised views expressed in the ongoing controversy over the relevance of dispersal and vicariance for explaining plant biodiversity. They provide motivation and justification for developing more complex hypotheses that seek to explain the origins of Southern Hemisphere biota.

Paleozoic Brachiopod Biogeography

Over two hundred years ago the Swedish scientist Carl Linnæus (1781), in an analysis of the biogeographic patterns of living organisms, suggested that all species originated in Paradise. Although there has been considerable progress in the understanding of biogeographical patterns during the intervening two centuries, modern debate has focused on the general applicability of the concept of faunal realms together with the relevance of dispersal, panbiogeographic, and vicariance models (Nelson and Platnick, 1981). To date, studies of Paleozoic brachiopod biogeography have no strong theoretical base; rather the various numerical techniques available, including both cladistic and phenetic methodologies, have helped organize the growing amount of distributional data into recognizable and useful structures.

Is fire a selective force of seed size in pine species?

Abstract Fire is selectively shaping most of the traits of plants growing in fire-prone environments. However, seed size and other features related to seed production have not been studied in the light of the evolutionary role of fire. Our research tests the hypothesis that larger seeds have a higher chance of surviving wildfires and produce more vigorous seedlings with a lower death rate. To test this hypothesis the germination and early seedling growth of five Spanish pine species were studied. Weight, length and width of all seeds were measured. The biomass (fresh and dry weight) and length (root and total) of subsequent seedlings were also measured after 30 d from emergence. Seeds were submitted to elevated temperatures for periods in which the chance of survival was 50 % (calculated by means of a logistic model for each pine species). The differences observed among species suggests that fire may be adaptively shaping seed size in pines with larger seeds ( Pinus canariensis and P. pinaster ), because larger seeds are more likely to survive after heat shocks. Furthermore, in P. canariensis , seedlings after heat treatment are even larger than those submitted to control. In P. halepensis , despite being well adapted to fire, our results indicated no relationships between fire and seed characteristics. Finally, although heat treatment has a general adverse effect on seedling growth in the case of the two subalpine pines, we have detected a positive relationship between seed size and seedling growth but only in the largest seeds. This might also suggest the relevance of fire as a selective force for these pines which is outperformed by the relevance of dispersal and emergence time as adaptive traits in the post-fire scenario.

Modelling in-sewer changes in wastewater quality under aerobic conditions

In the present paper a model for the simulation of in-sewer transformation processes occurring during the transport of wastewater under aerobic conditions is presented. The basic approach is to use a detailed description of the transport processes to separate the effect of advection-dispersion in the variations of concentration (of a certain pollutant in a certain pipe length) from those due to transformation processes. The focus is on dry weather flow and free surface flows. Processes such as reaeration, heterotrophic growth and decay, hydrolysis, ammonification and biofilm consumption of substrate and oxygen are considered. Transformation processes are modelled using a similar approach to that of the IAWQ Activated sludge model n°1. Results of tracer experiments are presented showing the relevance of dispersion in pipe flow. The results of sensitivity analysis on the model parameters are presented. The model results are especially sensitive to variations in yield and maximum growth rate for heterotrophs. Thus, these parameters should be determined experimentally for a given system. Less precise estimates for the other parameters have less impact on the model results. This aspect is especially relevant due to the lack of established methods for the estimation of these parameters for sewer systems modelling.

Optical bistability in dispersive and absorptive media

The relevance of dispersion in optical bistability is outlined. The results are compared with those for absorptive bistability, and a connection with experiments is discussed.