Landscape Fragmentation as a Risk Factor for Buruli Ulcer Disease in Ghana

Land cover and its change have been linked to Buruli ulcer (BU), a rapidly emerging tropical disease. However, it is unknown whether landscape structure affects the disease prevalence. To examine the association between landscape pattern and BU presence, we obtained land cover information for 20 villages in southwestern Ghana from high resolution satellite images, and analyzed the landscape pattern surrounding each village. Eight landscape metrics indicated that landscape patterns between BU case and reference villages were different (P < 0.05) at the broad spatial extent examined (4 km). The logistic regression models showed that landscape fragmentation and diversity indices were positively associated with BU presence in a village. Specifically, for each increase in patch density and edge density by 100 units, the likelihood of BU presence in a village increased 2.51 (95% confidence interval [CI] = 1.36–4.61) and 4.18 (95% CI = 1.63–10.76) times, respectively. The results suggest that increased landscape fragmentation may pose a risk to the emergence of BU

Two-to-one resonant multi-modal dynamics of horizontal/inclined cables. Part II : internal resonance activation, reduced-order models and nonlinear normal modes

Resonant multi-modal dynamics due to planar 2:1 internal resonances in the nonlinear, finite-amplitude, free vibrations of horizontal/inclined cables are parametrically investigated based on the second-order multiple scales solution in Part I [1]. The already validated kinematically non-condensed cable model accounts for the effects of both non-linear dynamic extensibility and system asymmetry due to inclined sagged configurations. Actual activation of 2:1 resonances is discussed, enlightening on a remarkable qualitative difference of horizontal/inclined cables as regards non-linear orthogonality properties of normal modes. Based on the analysis of modal contribution and solution convergence of various resonant cables, hints are obtained on proper reduced-order model selections from the asymptotic solution accounting for higher-order effects of quadratic nonlinearities. The dependence of resonant dynamics on coupled vibration amplitudes, and the significant effects of cable sag, inclination and extensibility on system non-linear behavior are highlighted, along with meaningful contributions of longitudinal dynamics. The spatio-temporal variation of non-linear dynamic configurations and dynamic tensions associated with 2:1 resonant non-linear normal modes is illustrated. Overall, the analytical predictions are validated by finite difference-based numerical investigations of the original partial-differential equations of motion

Réglage de la pénétration capillaire dans les milieux poreux: combinaison des effets géométriques et d'évaporation

International audienceCapillary penetration of liquids in porous media is of great importance in many applications and the ability to tune such penetration processes is increasingly sought after. In general, liquid penetration can be retarded or restricted by the evaporation of volatile liquid at the surface of the porous media. Moreover, when capillary penetration occurs in a porous layer with non-uniform cross section, the penetration process can be accelerated or impeded by adjusting the section geometry. In this work, on the basis of Darcy's Law and mass conservation, a theoretical model of capillary penetration combining evaporation effects in two-dimensional homogeneous porous media of varying cross-section is developed and further examined by numerical simulations. The effects of sample geometry and liquid evaporation on capillary penetration are quantitatively analyzed. Results show that the penetration velocity is sensitive to the geometry of the porous layer, and can be tuned by varying the evaporation rate for a given geometry. Under given evaporation conditions, penetration is restricted to a limited region with a predictable boundary. Furthermore, we find that the inhibition of liquid penetration by evaporation can be offset by varying the geometry of the porous layer. In addition, the theoretical model is further extended to model the capillary flow in three-dimensional porous media, and the interplay of geometry and evaporation during the capillary flow process in 3D conditions is also investigated. The results obtained can be used for facilitating the design of porous structures, achieving tunable capillary penetration for practical applications in various fields.La pénétration capillaire de liquides dans des milieux poreux revêt une grande importance dans de nombreuses applications et la capacité de réglage de tels processus de pénétration est de plus en plus recherchée. En général, la pénétration de liquide peut être retardée ou limitée par l'évaporation de liquide volatil à la surface du support poreux. De plus, lorsque la pénétration capillaire se produit dans une couche poreuse de section transversale non uniforme, le processus de pénétration peut être accéléré ou empêché en ajustant la géométrie de la section. Dans ce travail, sur la base de la loi de Darcy et de la conservation de masse, un modèle théorique de pénétration capillaire combinant les effets d'évaporation dans des milieux poreux homogènes à deux dimensions de sections différentes est développé et examiné plus en détail par des simulations numériques. Les effets de la géométrie de l'échantillon et de l'évaporation du liquide sur la pénétration capillaire sont analysés de manière quantitative. Les résultats montrent que la vitesse de pénétration est sensible à la géométrie de la couche poreuse et peut être ajustée en faisant varier le taux d'évaporation pour une géométrie donnée. Dans des conditions d'évaporation données, la pénétration est limitée à une région limitée avec une limite prévisible. En outre, nous trouvons que l'inhibition de la pénétration du liquide par évaporation peut être compensée en faisant varier la géométrie de la couche poreuse. En outre, le modèle théorique est élargi pour modéliser l'écoulement capillaire dans des milieux poreux tridimensionnels, et les interactions entre la géométrie et l'évaporation pendant le processus d'écoulement capillaire dans des conditions 3D sont également étudiées. Les résultats obtenus peuvent être utilisés pour faciliter la conception de structures poreuses, en réalisant une pénétration capillaire ajustable pour des applications pratiques dans divers domaines

Two-to-one resonant multi-modal dynamics of horizontal/inclined cables. Part I : theoretical formulation and model validation

This paper is first of the two papers dealingwith analytical investigation of resonant multimodal dynamics due to 2:1 internal resonances in the finite-amplitude free vibrations of horizontal/inclined cables. Part I deals with theoretical formulation and validation of the general cable model. Approximate nonlinear partial differential equations of 3-D coupled motion of small sagged cables - which account for both spatio-temporal variation of nonlinear dynamic tension and system asymmetry due to inclined sagged configurations - are presented. A multidimensional Galerkin expansion of the solution ofnonplanar/planar motion is performed, yielding a complete set of system quadratic/cubic coefficients. With the aim of parametrically studying the behavior of horizontal/inclined cables in Part II [25], a second-order asymptotic analysis under planar 2:1 resonance is accomplished by the method of multiple scales. On accounting for higher-order effectsof quadratic/cubic nonlinearities, approximate closed form solutions of nonlinear amplitudes, frequencies and dynamic configurations of resonant nonlinear normal modes reveal the dependence of cable response on resonant/nonresonant modal contributions. Depending on simplifying kinematic modeling and assigned system parameters, approximate horizontal/inclined cable models are thoroughly validated by numerically evaluating statics and non-planar/planar linear/non-linear dynamics against those of the exact model. Moreover, the modal coupling role and contribution of system longitudinal dynamics are discussed for horizontal cables, showing some meaningful effects due to kinematic condensation

"quasi-particles" in bosonization theory of interacting fermion liquids at arbitrary dimensions

Within bosonization theory we introduce in this paper a new definition of "quasi-particles" for interacting fermions at arbitrary space dimenions. In dimensions higher than one we show that the constructed quasi-particles are consistent with quasi-particle descriptions in Landau Fermi liquid theory whereas in one-dimension the quasi-particles" are non-perturbative objects (spinons and holons) obeying fractional statistics. The more general situation of Fermi liquids with singular Landau interaction is discussed.Comment: 10 page

Conditions for Successful Extended Inflation

We investigate, in a model-independent way, the conditions required to obtain a satisfactory model of extended inflation in which inflation is brought to an end by a first-order phase transition. The constraints are that the correct present strength of the gravitational coupling is obtained, that the present theory of gravity is satisfactorily close to general relativity, that the perturbation spectra from inflation are compatible with large scale structure observations and that the bubble spectrum produced at the phase transition doesn't conflict with the observed level of microwave background anisotropies. We demonstrate that these constraints can be summarized in terms of the behaviour in the conformally related Einstein frame, and can be compactly illustrated graphically. We confirm the failure of existing models including the original extended inflation model, and construct models, albeit rather contrived ones, which satisfy all existing constraints.Comment: 8 pages RevTeX file with one figure incorporated (uses RevTeX and epsf). Also available by e-mailing ARL, or by WWW at http://star-www.maps.susx.ac.uk/papers/infcos_papers.html; Revised to include extra references, results unchanged, to appear Phys Rev

Quasiparticle Interactions in Fractional Quantum Hall Systems: Justification of Different Hierarchy Schemes

The pseudopotentials describing the interactions of quasiparticles in fractional quantum Hall (FQH) states are studied. Rules for the identification of incompressible quantum fluid ground states are found, based upon the form of the pseudopotentials. States belonging to the Jain sequence nu=n/(1+2pn), where n and p are integers, appear to be the only incompressible states in the thermodynamic limit, although other FQH hierarchy states occur for finite size systems. This explains the success of the composite Fermion picture.Comment: RevTeX, 10 pages, 7 EPS figures, submitted fo Phys.Rev.

Mixed States of Composite Fermions Carrying Two and Four Vortices

There now exists preliminary experimental evidence for some fractions, such as $\nu$ = 4/11 and 5/13, that do not belong to any of the sequences $\nu=n/(2pn\pm 1)$, $p$ and $n$ being integers. We propose that these states are mixed states of composite fermions of different flavors, for example, composite fermions carrying two and four vortices. We also obtain an estimate of the lowest-excitation dispersion curve as well as the transport gap; the gaps for 4/11 are smaller than those for 1/3 by approximately a factor of 50.Comment: Accepted for PRB rapid communication (scheduled to appear in Nov 15, 2000 issue

North American Influence on Tropospheric Ozone and the Effects of Recent Emission Reductions: Constraints from ICARTT Observations

We use observations from the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign over eastern North America in summer 2004, interpreted with a global 3‐D model of tropospheric chemistry (GEOS‐Chem), to improve and update estimates of North American influence on global tropospheric ozone and the effect of recent U.S. anthropogenic reductions on surface ozone pollution. We find that the 50% decrease in U.S. stationary NOx sources since 1999 has decreased mean U.S. boundary layer ozone concentrations by 6–8 ppbv in the southeast and 4–6 ppbv in the Midwest. The observed dO3/dCO molar enhancement ratio in the U.S. boundary layer during ICARTT was 0.46 mol mol−1, larger than the range of 0.3–0.4 from studies in the early 1990s, possibly reflecting the decrease in the NOx/CO emission ratio as well as an increase in the ozone production efficiency per unit NOx. North American NOx emissions during summer 2004 as constrained by the ICARTT observations (0.72 Tg N fossil fuel, 0.11 Tg N biomass burning, 0.28 Tg N lightning for 1 July to 15 August) enhanced the hemispheric tropospheric ozone burden by 12.4%, with comparable contributions from fossil fuel and lightning (5–6%), but only 1% from biomass burning emissions despite 2004 being a record fire year over Alaska and western Canada.Earth and Planetary Science

Biogenic Versus Anthropogenic Sources of CO in the United States

Aircraft observations of carbon monoxide (CO) from the ICARTT campaign over the eastern United States in summer 2004 (July 1–August 15), interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem), show that the national anthropogenic emission inventory from the U.S. Environmental Protection Agency (93 Tg CO y−1) is too high by 60% in summer. Our best estimate of the CO anthropogenic source for the ICARTT period is 6.4 Tg CO, including 4.6 Tg from direct emission and 1.8 Tg CO from oxidation of anthropogenic volatile organic compounds (VOCs). The biogenic CO source for the same period from the oxidation of isoprene and other biogenic VOCs is 8.3 Tg CO, and is independently constrained by ICARTT observations of formaldehyde (HCHO). Anthropogenic emissions of CO in the U.S. have decreased to the point that they are now lower than the biogenic source in summer.Earth and Planetary SciencesEngineering and Applied Science