Computer simulations of dynamical properties of fluids: atomistic-continuum hybrid methods

Computational methods for the calculation of dynamical properties of fluids might consider the system as a continuum or as an assembly of molecules. Molecular dynamics (MD) simulation includes molecular resolution, whereas computational fluid dynamics (CFD) considers the fluid as a continuum. This work provides a review of hybrid methods MD/CFD recently proposed in the literature. Theoretical foundations, basic approaches of computational methods, and dynamical properties typically calculated by MD and CFD are first presented in order to appreciate the similarities and differences between these two methods. Then, methods for coupling MD and CFD, and applications of hybrid simulations MD/CFD, are presented.FAPESPCNP

The Spread of Opinions and Proportional Voting

Election results are determined by numerous social factors that affect the formation of opinion of the voters, including the network of interactions between them and the dynamics of opinion influence. In this work we study the result of proportional elections using an opinion dynamics model similar to simple opinion spreading over a complex network. Erdos-Renyi, Barabasi-Albert, regular lattices and randomly augmented lattices are considered as models of the underlying social networks. The model reproduces the power law behavior of number of candidates with a given number of votes found in real elections with the correct slope, a cutoff for larger number of votes and a plateau for small number of votes. It is found that the small world property of the underlying network is fundamental for the emergence of the power law regime.Comment: 10 pages, 7 figure

Theoretical Investigations of the Herbicide Glyphosate Adsorption on the B12N12 Nanocluster

Nowadays is emergent the development of new materials which can be used in the adsorption process to remove herbicide glyphosate from the aquatic environment. Therefore, density functional theory (DFT) calculations were performed to study the adsorption process of the glyphosate on the B12N12 nanocage in aqueous media. The optimized structures of adsorbed glyphosate do not affect the nanocage structure indicating its structural stability. The chemisorption of this herbicide is an exothermic process with −43.89 kcal.mol-1. The most stable complex displayed an adsorption energy and ∆G values of −53.97 and −40.79 kcal.mol-1, respectively. The HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies are located in the glyphosate implying that this herbicide can be removed by chemical reaction. Our results show that the B12N12 nanocluster can be a suitable new nanomaterial to remove the glyphosate from wastewater. DOI: http://dx.doi.org/10.17807/orbital.v9i3.99

Automatic Network Fingerprinting through Single-Node Motifs

Complex networks have been characterised by their specific connectivity patterns (network motifs), but their building blocks can also be identified and described by node-motifs---a combination of local network features. One technique to identify single node-motifs has been presented by Costa et al. (L. D. F. Costa, F. A. Rodrigues, C. C. Hilgetag, and M. Kaiser, Europhys. Lett., 87, 1, 2009). Here, we first suggest improvements to the method including how its parameters can be determined automatically. Such automatic routines make high-throughput studies of many networks feasible. Second, the new routines are validated in different network-series. Third, we provide an example of how the method can be used to analyse network time-series. In conclusion, we provide a robust method for systematically discovering and classifying characteristic nodes of a network. In contrast to classical motif analysis, our approach can identify individual components (here: nodes) that are specific to a network. Such special nodes, as hubs before, might be found to play critical roles in real-world networks.Comment: 16 pages (4 figures) plus supporting information 8 pages (5 figures

INTEGRATING THE BeppoSAX GAMMA-RAY BURST MONITOR INTO THE THIRD INTERPLANETARY NETWORK

We have added the BeppoSAX Gamma-Ray Burst Monitor to the third Interplanetary Network (IPN3) of burst detectors. We analyze 16 bursts whose positions are known to good accuracy from mea- surements at other wavelengths. We show that there is excellent agreement between the Ulysses/ BeppoSAX triangulation annuli and the known positions of these events and that these annuli can in many cases provide useful constraints on the positions of bursts detected by the BeppoSAX Wide-Field Camera and Narrow-Field Instruments. Subject heading: gamma rays: burst

A Comparative Study of the X-Ray Afterglow Properties of Optically Bright and Dark Gamma-Ray Bursts

We have examined the complete set of X-ray afterglow observations of dark and optically bright gamma-ray bursts (GRBs) performed by BeppoSAX through 2001 February. X-ray afterglows are detected in ~90% of the cases. We do not find significant differences in the X-ray spectral shape, in particular no increased X-ray absorption in GRBs without optical transient (dark GRBs) compared to GRBs with optical transient (OTGRBs). Rather, we find that the 1.6-10 keV flux of OTGRBs is on average about 5 times larger than that of the dark GRBs. A Kolmogorov-Smirnov test shows that this difference is significant at 99.8% probability. Under the assumption that dark and OTGRBs have similar spectra, this could suggest that the first are uncaught in the optical band because they are just faint sources. In order to test this hypothesis, we have determined the optical-to-X-ray flux ratios of the sample. OTGRBs show a remarkably narrow distribution of flux ratios, which corresponds to an average optical-to-X-ray spectral index = 0.794 ? 0.054. We find that, while 75% of dark GRBs have flux ratio upper limits still consistent with those of OT GRBs, the remaining 25% are 4-10 times weaker in optical than in X-rays. The significance of this result is ?2.6 ?. If this subpopulation of dark GRBs were constituted by objects assimilable to OTGRBs, they should have shown optical fluxes higher than upper limits actually found. We discuss the possible causes of their behavior, including a possible occurrence in high-density clouds or origin at very high redshift and a connection with ancient, Population III stars

The modulation of the symbiont/host interaction between wolbachia pipientis and aedes fluviatilis embryos by glycogen metabolism

Wolbachia pipientis, a maternally transmitted bacterium that colonizes arthropods, may affect the general aspects of insect physiology, particularly reproduction. Wolbachia is a natural endosymbiont of Aedes fluviatilis, whose effects in embryogenesis and reproduction have not been addressed so far. In this context, we investigated the correlation between glucose metabolism and morphological alterations during A. fluviatilis embryo development in Wolbachia-positive (W+) and Wolbachia-negative (W2) mosquito strains. While both strains do not display significant morphological and larval hatching differences, larger differences were observed in hexokinase activity and glycogen contents during early and mid-stages of embryogenesis, respectively. To investigate if glycogen would be required for parasite-host interaction, we reduced Glycogen Synthase Kinase-3 (GSK-3) levels in adult females and their eggs by RNAi. GSK-3 knock-down leads to embryonic lethality, lower levels of glycogen and total protein and Wolbachia reduction. Therefore, our results suggest that the relationship between A. fluviatilis and Wolbachia may be modulated by glycogen metabolism