On the kinetic modelling of reactive waves in the hydrodynamic limit

The present study deals with the extension of the exact and approximate models of the Boltzmann equation to a gas mixture of four constituents undergoing a reversible bimolecular reaction, and its application to wave propagation problems. The paper intends to highlight how Boltzmann type models, on the basis of a shared kinetic framework, can be adopted as the starting point for a consistent derivation of the reactive hydrodynamic equations, at both the Euler and Navier Stokes limit. At this scope, a proper mathematical procedure is applied to obtain an approximate solution to the model equations, which is necessary in order to derive the closed system of the governing equations in the above said hydrodynamic limits. Resorting to this unified kinetic approach which is presented in detail, one can recognize how the dynamics of rather different wave problems well known in literature, as the steady detonation wave and its linear stability, the sound wave propagation and the light scattering phenomena, match a satisfactory description with care for the chemical mechanism at the microscopic scale. The knowledge of the chemical process at this level permits to evaluate the influence of the chemical reaction on the fundamental aspects of the reacting gas system, reinforcing the proposed kinetic approach. Accordingly, some propagation wave problems, recently studied by the authors in this context, are in turn here reviewed at the end of focusing how their formulation and solution depend on the proposed hydrodynamic closure procedure.Fundação para a Ciência e a Tecnologia (FCT

Shape engineering driven by selective growth of SnO2 on doped Ga2O3 nanowires

Tailoring the shape of complex nanostructures requires control of the growth process. In this work, we report on the selective growth of nanostructured tin oxide on gallium oxide nanowires leading to the formation of SnO2/Ga2O3 complex nanostructures. Ga2O3 nanowires decorated with either crossing SnO2 nanowires or SnO2 particles have been obtained in a single step treatment, by thermal evaporation. The reason for this dual behavior is related to the growth direction of trunk Ga2O3 nanowires. Ga2O3 nanowires grown along the [001] direction favor the formation of crossing SnO2 nanowires. Alternatively, SnO2 forms rhombohedral particles on [110] Ga2O3 nanowires leading to skewer-like structures. These complex oxide structures were grown by a catalyst-free vapor-solid process. When pure Ga and tin oxide were used as source materials and compacted powders of Ga2O3 acted as substrates, [110] Ga2O3 nanowires grow preferentially. High-resolution transmission electron microscopy analysis reveals epitaxial relationship lattice matching between the Ga2O3 axis and SnO2 particles, forming skewer-like structures. The addition of chromium oxide to the source materials modifies the growth direction of the trunk Ga2O3 nanowires, growing along the [001], with crossing SnO2 wires. The SnO2/Ga2O3 junctions does not meet the lattice matching condition, forming a grain boundary. The electronic and optical properties have been studied by XPS and CL with high spatial resolution, enabling us to get both local chemical and electronic information of the surface in both type of structures. The results will allow tuning optical and electronic properties of oxide complex nanostructures locally as a function of the orientation. In particular, we report a dependence of the visible CL emission of SnO2 on its particular shape. Orange emission dominates in SnO2/Ga2O3 crossing wires while green-blue emission is observed in SnO2 particles attached to Ga2O3 trunks. The results show that the Ga2O3-SnO2 system appears to be a benchmark for shape engineering to get architectures involving nanowires via the control of the growth direction of the nanowires

Direct observation of tunnelled intergrowth in SnO2/Ga2O3 complex nanowires

beta-Ga_2O_3 intergrowths have been revealed in the SnO_2 rutile structure when SnO_2/Ga_2O_3 complex nanostructures are grown by thermal evaporation with a catalyst-free basis method. The structure is formed by a Ga_2O_3 nanowire trunk, around which a rutile SnO_2 particle is formed with [001] aligned to the [010] Ga_2O_3 trunk axis. Inside the SnO_2 particle, beta-Ga_2O_3 units occur separated periodically by hexagonal tunnels in the (210) rutile plane. Orange (620 nm) optical emission from tin oxide, with a narrow linewidth indicating localised electronic states, may be associated with this beta-Ga_2O_3 intergrowth

Phlebotominae (Diptera, Psychodidae) na Província Espeleológica do Vale do Ribeira - 1. Parque Estadual Intervales (PEI), estado de São Paulo, Brasil

The identification of the sandfly fauna and investigation of some ecological aspects of its populations in areas frequented by tourists of the PEI, an Atlantic forest reserve with many caves, were the objective of this study. Captures were undertaken monthly from January 2001 to December 2002, with automatic light traps installed in 13 ecotopes, including caves, forests, domiciliary and peridomiciliary environments, and by aspiration in armadillo burrows. Additionally, although not at regular intervals, Shannon traps were installed in forests and anthropic environments, aspirations were made on cave walls, among roots and fallen leaves, and some insects were captured while biting researchers. A total of 891 sandflies belonging to 21 species were captured. Six hundred specimens representing 19 species were captured with light traps, 215 in anthropic (2.24 insects/trap) and 385 in extra-domiciliary (1.46 insects/trap) environments. Brumptomyia troglodytes was the most abundant species (the Standardised Index of Species Abundance = 0.705). Pintomyia monticola predominated in the Shannon traps and showed anthropophilic and diurnal activity. Psathyromyia pascalei predominated in the aspirations; the largest number being in armadillo burrows. Eleven species were captured in caves; although some might be troglophiles, the majority used these ecotopes as resting places. Nyssomyia intermedia, Nyssomyia neivai and Migonemyia migonei, implicated in the transmission of cutaneous leishmaniasis in the Southeastern Brazilian region, were all found, though in such low densities as to suggest minimal risk of the disease in the PEI.A identificação da fauna flebotomínea e de alguns aspectos ecológicos de suas populações em áreas freqüentadas por turistas no PEI, situado em reserva de mata Atlântica, constituem-se nos objetivos deste estudo. As capturas foram mensais de janeiro/2001 a dezembro/2002, com armadilhas automáticas luminosas em 13 ecótopos, incluindo cavernas, matas e peridomicílio e aspiração em tocas de tatus. Sem intervalos regulares, foram realizadas capturas com armadilhas de Shannon na mata e ambientes antrópicos, aspiração em paredes de cavernas e entre raízes e folhedo e em membros da equipe quando picados por flebotomíneos. No total foram capturados 891 flebotomíneos pertencentes a 21 espécies. Com as armadilhas automáticas luminosas capturou-se 19 espécies e 600 espécimes, 215 em ambiente antrópico (2,24 insetos/armadilha) e 385 em ambiente natural (1,46 insetos/armadilha). Brumptomyia troglodytes foi a mais abundante, com o índice de abundância das espécies padronizado = 0,705. Pintomyia monticola predominou nas armadilhas de Shannon, mostrando-se antropofílica e com atividade hematofágica diurna e noturna. Psathyromyia pascalei predominou nas aspirações, com a maioria dos espécimes aspirados de tocas de tatu. Das 11 espécies capturadas em cavernas, embora algumas possam ser consideradas troglófilas, a maioria usa este ecótopo como local de abrigo. Nyssomyia intermedia, Nyssomyia neivai e Migonemyia migonei, implicados na transmissão da leishmaniose tegumentar na Região Sudeste do Brasil foram capturados, todavia em tão baixa densidade que sugere risco mínimo da doença no PEI.FAPESPIBAMA-S

Equilibrium and stability properties of detonation waves in the hydrodynamic limit of a kinetic model

A shock wave structure problem, like the one which can be formulated for the planar detonation wave, is analyzed here for a binary mixture of ideal gases undergoing the symmetric reaction A1+A1=A2+A2 . The problem is studied at the hydrodynamic Euler limit of a kinetic model of the reactive Boltzmann equation. The chemical rate law is deduced in this frame with a second-order reaction rate, in a hemical regime such that the gas flow is not far away from the chemical equilibrium. The caloric and the thermal equations of state for the specific internal energy and temperature are employed to close the system of balance laws. With respect to other approaches known in the kinetic literature for detonation problems with a reversible reaction, this paper aims to improve some aspects of the wave solution. Within the mathematical analysis of the detonation model, the equation of the equilibrium Hugoniot curve of the final states is explicitly derived for the first time and used to define the correct location of the equilibrium Chapman–Jouguet point in the Hugoniot diagram. The parametric space is widened to investigate the response of the detonation solution to the activation energy of the chemical reaction. Finally, the mathematical formulation of the linear stability problem is given for the wave detonation structure via a normal-mode approach, when bidimensional disturbances perturb the steady solution. The stability equations with their boundary conditions and the radiation condition of the considered model are explicitly derived for small transversal deviations of the shock wave location. The paper shows how a second-order chemical kinetics description, derived at the microscopic level, and an analytic deduction of the equilibrium Hugoniot curve, lead to an accurate picture of the steady detonation with reversible reaction, as well as to a proper bidimensional linear stability analysis.Brazilian Research Council (CNPq), by Italian Research Council GNFM-INdAM, and by the Research Centre of Mathematics of the University of Minho with the Portuguese Funds of FCT, project PEstOE/MAT/UI0013/2014

Hysteresis loops in CuO

Hysteresis loops at room temperature have been observed and investigated in nanostructures and nanoparticles ofCupric Oxide (CuO) with same average grain size. Morphological and structural properties of the studied sampleswere characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). Energy-dispersive X-rayspectroscopy (EDS) was employed to analyze the possible presence of impurities. Mean crystallite diameter sizeswere determined using Rietveld refinement analysis of the diffraction patterns. The results suggest that hysteresisloops morphology depend on the process to obtain each sample, which not only affect grain size, but also mayinduce anisotropic forms and residual microstrains.Lazos de histéresis a temperatura ambiente han sido observados y estudiados en nanoestructuras y nanopartículas de óxido cúprico (CuO) con el mismo tamaño promedio de cristalito. Las propiedades morfológicas y estructurales de las muestras fueron caracterizadas usando difracción de rayos X y microscopía electrónica de barrido (SEM). La presencia de impurezas ha sido descartada a partir de resultados de espectrometría de dispersión de energía de rayos X (EDS). El tamaño promedio de los cristalitos ha sido determinado usando el método de refinamiento de Rietveld de los patrones de difracción. Los resultados sugieren que las características de los lazos de histéresis dependen del proceso de obtención de las muestras, el que no sólo influye en el tamaño de grano sino también puede inducir formas y micro tensiones residuales anisotrópicas.Instituto de Física La PlataFacultad de IngenieríaConsejo Nacional de Investigaciones Científicas y Técnica

Hysteresis loops in CuO

Hysteresis loops at room temperature have been observed and investigated in nanostructures and nanoparticles ofCupric Oxide (CuO) with same average grain size. Morphological and structural properties of the studied sampleswere characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). Energy-dispersive X-rayspectroscopy (EDS) was employed to analyze the possible presence of impurities. Mean crystallite diameter sizeswere determined using Rietveld refinement analysis of the diffraction patterns. The results suggest that hysteresisloops morphology depend on the process to obtain each sample, which not only affect grain size, but also mayinduce anisotropic forms and residual microstrains.Lazos de histéresis a temperatura ambiente han sido observados y estudiados en nanoestructuras y nanopartículas de óxido cúprico (CuO) con el mismo tamaño promedio de cristalito. Las propiedades morfológicas y estructurales de las muestras fueron caracterizadas usando difracción de rayos X y microscopía electrónica de barrido (SEM). La presencia de impurezas ha sido descartada a partir de resultados de espectrometría de dispersión de energía de rayos X (EDS). El tamaño promedio de los cristalitos ha sido determinado usando el método de refinamiento de Rietveld de los patrones de difracción. Los resultados sugieren que las características de los lazos de histéresis dependen del proceso de obtención de las muestras, el que no sólo influye en el tamaño de grano sino también puede inducir formas y micro tensiones residuales anisotrópicas.Instituto de Física La PlataFacultad de IngenieríaConsejo Nacional de Investigaciones Científicas y Técnica

High-resolution, 3D radiative transfer modelling : IV. AGN-powered dust heating in NGC 1068

The star formation rate and the mass of interstellar medium (ISM) have a high predictive power for the future evolution of a galaxy. Nevertheless, deriving such properties is not straightforward. Dust emission, an important diagnostic of star formation and ISM mass throughout the Universe, can be powered by sources unrelated to ongoing star formation. In the framework of the DustPedia project we set out to disentangle the radiation of the ongoing star formation from that of the older stellar populations. This is done through detailed 3D radiative transfer simulations of face-on spiral galaxies. We take special care in modelling the morphological features present for each source of radiation. In this particular study, we focus on NGC 1068, which in addition contains an active galactic nucleus (AGN). The effect of diffuse dust heating by an AGN (beyond the torus) has so far only been investigated for quasars. This additional dust heating source further contaminates the broadband fluxes that are used by classic galaxy modelling tools to derive physical properties. We aim to fit a realistic model to the observations of NGC 1068 and quantify the contribution of the several dust-heating sources. Our model is able to reproduce the global spectral energy distribution of the galaxy. It matches the resolved optical and infrared images fairly well, but deviates in the UV and the submillimetre (submm). This is partly due to beam smearing effects, but also because the input dust distribution is not sufficiently peaked in the centre. We find that AGN contamination of the broadband fluxes has a strong dependency on wavelength. It peaks in the mid-infrared, drops in the far-infrared, and then rises again at submm wavelengths. We quantify the contribution of the dust-heating sources in each 3D dust cell and find a median value of 83% for the star formation component. The AGN contribution is measurable at the percentage level in the disc, but quickly increases in the inner few hundred parsecs, peaking above 90%. This is the first time the phenomenon of an AGN heating the diffuse dust beyond its torus is quantified in a nearby star-forming galaxy. NGC 1068 only contains a weak AGN, meaning this effect could be stronger in galaxies with a more luminous AGN. This could significantly impact the derived star formation rates and ISM masses for such systems

High-resolution, 3D radiative transfer modelling : V. A detailed model of the M 51 interacting pair

Context. Investigating the dust heating mechanisms in galaxies provides a deeper understanding of how the internal energy balance drives their evolution. Over the last decade radiative transfer simulations based on the Monte Carlo method have emphasised the role of the various stellar populations heating the diffuse dust. Beyond the expected heating through ongoing star formation, older stellar populations (>= 8 Gyr) and even active galactic nuclei can both contribute energy to the infrared emission of diffuse dust.Aims. In this particular study we examine how the radiation of an external heating source, such as the less massive galaxy NGC 5195 in the M 51 interacting system, could affect the heating of the diffuse dust of its parent galaxy NGC 5194, and vice versa. Our goal is to quantify the exchange of energy between the two galaxies by mapping the 3D distribution of their radiation field.Methods. We used SKIRT, a state-of-the-art 3D Monte Carlo radiative transfer code, to construct the 3D model of the radiation field of M 51, following the methodology defined in the DustPedia framework. In the interest of modelling, the assumed centre-to-centre distance separation between the two galaxies is similar to 10 kpc.Results. Our model is able to reproduce the global spectral energy distribution of the system, and it matches the resolved optical and infrared images fairly well. In total, 40.7% of the intrinsic stellar radiation of the combined system is absorbed by dust. Furthermore, we quantify the contribution of the various dust heating sources in the system, and find that the young stellar population of NGC 5194 is the predominant dust-heating agent, with a global heating fraction of 71.2%. Another 23% is provided by the older stellar population of the same galaxy, while the remaining 5.8% has its origin in NGC 5195. Locally, we find that the regions of NGC 5194 closer to NGC 5195 are significantly affected by the radiation field of the latter, with the absorbed energy fraction rising up to 38%. The contribution of NGC 5195 remains under the percentage level in the outskirts of the disc of NGC 5194. This is the first time that the heating of the diffuse dust by a companion galaxy is quantified in a nearby interacting system

Revealing the last 13,500 years of environmental history from the multiproxy record of a mountain lake (Lago Enol, northern Iberian Peninsula)

This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10933-009-9387-7.We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.The Spanish Inter-Ministry Commission of Science and Technology (CICYT), the Spanish National Parks agency, the European Commission, the Spanish Ministry of Science, and the European Social Fund