Local orientational ordering in fluids of spherical molecules with dipolar-like anisotropic adhesion

We discuss some interesting physical features stemming from our previous analytical study of a simple model of a fluid with dipolar-like interactions of very short range in addition to the usual isotropic Baxter potential for adhesive spheres. While the isotropic part is found to rule the global structural and thermodynamical equilibrium properties of the fluid, the weaker anisotropic part gives rise to an interesting short-range local ordering of nearly spherical condensation clusters, containing short portions of chains having nose-to-tail parallel alignment which runs antiparallel to adjacent similar chains.Comment: 13 pages and 6 figure

Diffusion and Trapping on a one-dimensional lattice

The properties of a particle diffusing on a one-dimensional lattice where at each site a random barrier and a random trap act simultaneously on the particle are investigated by numerical and analytical techniques. The combined effect of disorder and traps yields a decreasing survival probability with broad distribution (log-normal). Exact enumerations, effective-medium approximation and spectral analysis are employed. This one-dimensional model shows rather rich behaviours which were previously believed to exist only in higher dimensionality. The possibility of a trapping-dominated super universal class is suggested.Comment: 20 pages, Revtex 3.0, 13 figures in compressed format using uufiles command, to appear in Phys. Rev. E, for an hard copy or problems e-mail to: [email protected]

Structure and phase behavior of colloidal dumbbells with tunable attractive interactions

We investigate thermodynamic and structural properties of colloidal dumbbells in the framework provided by the Reference Interaction Site Model (RISM) theory of molecular fluids and Monte Carlo simulations. We consider two different models: in the first one we set identical square-well attractions on the two tangent spheres composing the molecule (SW-SW model); in the second scheme, one of square-well interactions is switched off (HS-SW model). Appreciable differences emerge between the physical properties of the two models. Specifically, the $k \to 0$ behavior of SW-SW structure factors $S(k)$ points to the presence of a gas-liquid coexistence, as confirmed by subsequent fluid phase equilibria calculations. Conversely, the HS-SW $S(k)$ develops a low-$k$ peak, signaling the presence of aggregates; such a process destabilizes the gas-liquid phase separation, promoting at low temperatures the formation of a cluster phase, whose structure depends on the system density. We further investigate such differences by studying the phase behavior of a series of intermediate models, obtained from the original SW-SW by progressively reducing the depth of one square-well interaction. RISM structural predictions positively reproduce the simulation data, including the rise of $S(k \to 0$) in the SW-SW model and the low-$k$ peak in the HS-SW structure factor. As for the phase behavior, RISM agrees with Monte Carlo simulations in predicting a gas-liquid coexistence for the SW-SW model (though the critical parameters appears overestimated by the theory) and its progressive disappearance moving toward the HS-SW model.Comment: 12 pages, 13 figures, 1 table, 78 reference

Correspondence of Electroencephalography and Near-Infrared Spectroscopy Sensitivities to the Cerebral Cortex using a High-Density Layout

This study investigates the correspondence of the cortical sensitivity of electroencephalography (EEG) and near-infrared spectroscopy (NIRS). EEG forward model sensitivity to the cerebral cortex was calculated for 329 EEG electrodes following the 10-5 EEG positioning system using a segmented structural magnetic resonance imaging scan of a human subject. NIRS forward model sensitivity was calculated for the same subject using 156 NIRS source-detector pairs selected from 32 source and 32 detector optodes positioned on the scalp using a subset of the 10-5 EEG positioning system. Sensitivity correlations between colocalized NIRS source-detector pair groups and EEG channels yielded R=0.46±0.08 . Groups of NIRS source-detector pairs with maximum correlations to EEG electrode sensitivities are tabulated. The mean correlation between the point spread functions for EEG and NIRS regions of interest (ROI) was R=0.43±0.07 . Spherical ROIs with radii of 26 mm yielded the maximum correlation between EEG and NIRS averaged across all cortical mesh nodes. These sensitivity correlations between EEG and NIRS should be taken into account when designing multimodal studies of neurovascular coupling and when using NIRS as a statistical prior for EEG source localization

Correlation of vulnerability and damage between artistic assets and structural elements: The DataBAES archive for the conservation planning of CH masonry buildings in seismic areas

Historical buildings in seismic hazard-prone regions need specific measures in safety protection, largely due to the presence of artistic assets and/or decorations, both movable (e.g., statues, pinnacles, etc.) and unmovable (e.g., frescoes, valuable plasters or wall paintings, mosaics, and stuccoes). A correlation of damage between structural systems and artworks is fundamental for defining limit states, which can identify the proper conditions for interventions. Nevertheless, several vulnerability aspects can be identified before a seismic event occurs, the study of which can provide the basic dataset for setting up preventive measures in conservation programs. In this paper, the vulnerability and damage conditions related to structural elements (SE) and unmovable artistic assets (AA) belonging to historical masonry buildings are analysed. Optimized survey forms for the onsite detection of either intrinsic (e.g., compositional) defects or deterioration phenomena for both materials and structure are proposed, and results are provided in a web data system (called DataBAES). This enables us to compare the current levels of vulnerability and damage of AA and SE on a scale of five increasing grades. This procedure has been validated on a series of buildings struck by earthquakes in Italy and can be used for correlations of the seismic behaviour of SE and AA in predictive analyses

Phase diagram and structural properties of a simple model for one-patch particles

We study the thermodynamic and structural properties of a simple, one-patch fluid model using the reference hypernetted-chain (RHNC) integral equation and specialized Monte Carlo simulations. In this model, the interacting particles are hard spheres, each of which carries a single identical, arbitrarily-oriented, attractive circular patch on its surface; two spheres attract via a simple square-well potential only if the two patches on the spheres face each other within a specific angular range dictated by the size of the patch. For a ratio of attractive to repulsive surface of 0.8, we construct the RHNC fluid-fluid separation curve and compare with that obtained by Gibbs ensemble and grand canonical Monte Carlo simulations. We find that RHNC provides a quick and highly reliable estimate for the position of the fluid-fluid critical line. In addition, it gives a detailed (though approximate) description of all structural properties and their dependence on patch size.Comment: 27 pages, 10 figures, J. Chem. Phys. in pres

Phase diagrams of Janus fluids with up-down constrained orientations

A class of binary mixtures of Janus fluids formed by colloidal spheres with the hydrophobic hemispheres constrained to point either up or down are studied by means of Gibbs ensemble Monte Carlo simulations and simple analytical approximations. These fluids can be experimentally realized by the application of an external static electrical field. The gas-liquid and demixing phase transitions in five specific models with different patch-patch affinities are analyzed. It is found that a gas-liquid transition is present in all the models, even if only one of the four possible patch-patch interactions is attractive. Moreover, provided the attraction between like particles is stronger than between unlike particles, the system demixes into two subsystems with different composition at sufficiently low temperatures and high densities.Comment: 10 pages, 6 figure

Preliminary study on mini-modus device designed to oxygenate bottom anoxic waters without perturbing polluted sediments

The Tangential Guanabara Bay Aeration and Recovery (TAGUBAR) project derives its origins from a Brazilian government decision to tackle the planning and management challenges related to the restoration of some degraded aquatic ecosystems such as Guanabara Bay (state of Rio de Janeiro), Vitória Bay, and Espírito Santo Bay (state of Espírito Santo). This was performed by using the successful outcomes of a previous Ministry of Foreign Affairs and Directorate General for Cooperation and Development (i.e., Direttore Generale alla Cooperazione allo Sviluppo, MFA– DGCS) cooperation program. The general objective of the program was to contribute to the economic and social development of the population living around Guanabara, Vitória, and Espírito Santo Bays, while promoting the conservation of their natural resources. This objective was supposed to be achieved by investing money to consolidate the local authorities’ ability to plan and implement a reconditioning program within a systemic management framework in severely polluted ecosystems such as Guanabara Bay, where sediments are highly contaminated. Sediments normally represent the final fate for most contaminants. Therefore, it would be highly undesirable to perturb them, if one wishes to avoid contaminant recycling. In this context, we explored a bench-scale novel technology, called the module for the decontamination of units of sediment (MODUS), which produces an oxygenated water flow directed parallel to the sediment floor that is aimed to create “tangential aeration” of the bottom water column. The purpose of this is to avoid perturbing the top sediment layer, as a flow directed toward the bottom sediment would most probably resuspend this layer. Three kinds of tests were performed to characterize a bench-scale version of MODUS (referred to as “mini-MODUS”) behavior: turbulence–sediment resuspension tests, hydrodynamic tests, and oxygenation–aeration tests. In order to understand the functioning of the mini-MODUS, we needed to eliminate as many variables as possible. Therefore, we chose a static version of the module (i.e., no speed for the mini-MODUS as well as no water current with respect to the bottom sediment and no flume setting), leaving dynamic studies for a future paper. The turbulence tests showed that the water enters and exits the mini-MODUS mouths without resuspending the sediment surface at all, even if the sediment is very soft. Water flow was only localized very close to both mouth openings. Hydrodynamic tests showed an interesting behavior. An increase of low air flows produced a sharp linear increase of the water flow. However, a plateau was quickly reached and then no further increase of water flow was observed, implying that for a certain specific geometry of the equipment and for the given experimental conditions, an increase in the air flow does not produce any reduction of the residence time within the aeration reactor. Oxygenation–aeration tests explored three parameters that were deemed to be most important for our study: the oxygen global transfer coefficient, KLa; the oxygenation capacity, OC; and the oxygenation efficiency, OE%. An air flow increase causes an increase of both KLa and OC, while OE% decreases (no plateau was observed for KLa and OC). The better air flow would be a compromise between high KLa and OC, with no disadvantageous OE%, a compromise that will be the topic of the next paper

Diffusion on non exactly decimable tree-like fractals

We calculate the spectral dimension of a wide class of tree-like fractals by solving the random walk problem through a new analytical technique, based on invariance under generalized cutting-decimation transformations. These fractals are generalizations of the NTD lattices and they are characterized by non integer spectral dimension equal or greater then 2, non anomalous diffusion laws, dynamical dimension splitting and absence of phase transitions for spin models.Comment: 5 pages Latex, 3 figures (figures are poscript files