How perilous are broad-scale correlations with environmental variables?

Many studies correlate geographic variation of biotic variables (e.g., species ranges, species richness, etc.) with variation in environmental variables (climate, topography, history). Often, the resulting correlations are interpreted as evidence of causal links. However, both the dependent and independent variables in these analyses are strongly spatially structured. Several studies have suggested that spatially structured variables may be significantly correlated with one another despite the absence of a causal link between them. In this study we ask: if two variables are spatially structured, but causally unrelated, how strong is the expected correlation between them? As a specific example, we consider the correlations between broad-scale variation in gamma species richness and climatic variables. Are these correlations likely to be statistical artefacts? To answer these questions, we randomly generated pseudo-climatic variables that have the same range and spatial autocorrelation as temperature and precipitation in the Americas. We related mammal and bird species richness both to the real and the pseudo-climatic variables. We also observed the correlations among pseudo-climate simulations. Correlations among randomly generated, spatially unstructured, variables are very small. In contrast, the median correlations between spatially structured variables are near r2=0.1 – 0.3, and the 95% confidence limits extend to r2=0.6 – 0.7. Viewing this as a null expectation, given spatially structured variables, it is worth nothing that published richness–climate correlations are typically marginally stronger than these values. However, many other published richness–environment correlations would fail this test. Tests of the “predictive ability” of a correlation cannot reliably distinguish correlations due to spatial structure from causal relationships. Our results suggest a three-part update of Tobler’s “First Law of Geography”: #1) Everything in geography that is spatially structured will be collinear. #2) Near things are more related than distant things. #3) The more strongly spatially structured two variables are, the stronger the collinearity between them will be

Obtaining the Full Unitarity Triangle from B -> pi K Decays

We present a method of obtaining the entire unitarity triangle from measurements of B -> pi K decay rates alone. Electroweak penguin amplitudes are included, and are related to tree operators. Discrete ambiguities are removed by comparing solutions with independent experimental data. The theoretical uncertainty in this method is rather small, in the range 5--10%.Comment: 4 pages, RevTeX, no figures. Clarifying remarks and references adde

Synthesis process of nanowired Al/CuO thermite.

Al/CuO nanothermites were fabricated by thermal oxidation of copper layer at 4501C for 5 hand by aluminum thermal evaporation: thermal evaporation allows producing thin layer less than 2 mminsize. The copper has been deposited by electroplating or thermal evaporation depending on the required thickness. The obtained diameter of Al/CuO nanowiresis 150–250nm. Al/CuO nanowires composite were characterized by scanning electronmicroscopy (SEM), X-raydiffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Two distinct exothermicreactions occurred at 515 and 6671C and total energy release of this thermite is 10kJ/cm

Numerical simulation of a turbulent channel flow with an acoustic liner

International audienceNumerical simulations of a compressible turbulent channel flow with an acoustic impedance boundary condition are performed to assess how the flow is modified compared with a channel flow with rigid walls. When the liner resonance frequency is not too large and the resistance sufficiently small, turbulent statistics deviate from those obtained with rigid walls and surface waves are found traveling along the liner surface. For small resonance frequencies these waves are two-dimensional, they have a large wavelength compared to the turbulent structures and modulate these structures. As a result, they transport momentum toward the impedance wall, causing a drag increase. When the resonance frequency increases, the waves along the liner surface progressively lose their spanwise coherence while their streamwise wavelength decreases to get close to the flow typical length scales, which may also result in a drag increase when the resistance is sufficiently small. In the cases in which the surface waves are two-dimensional, a connection is established between them and the unstable modes computed by using a linear stability analysis. Given the streamwise periodicity of the channel, a temporal stability analysis is performed rather than a spatial analysis, the latter being more frequently encountered in acoustic mode computations. This temporal analysis shows that the unstable mode in the vicinity of an acoustic liner arises from the A-branch of wall modes

Methods for Measuring New-Physics Parameters in B Decays

Recently, it was argued that new-physics (NP) effects in B decays can be approximately parametrized in terms of a few quantities. As a result, CP violation in the $B$ system allows one not only to detect the presence of new physics (NP), but also to measure its parameters. This will allow a partial identification of the NP, before its production at high-energy colliders. In this paper, we examine three methods for measuring NP parameters. The first uses a technique involving both \btos and \btod penguin B decays. Depending on which pair of decays is used, the theoretical error is in the range 5--15%. The second involves a comparison of $B\to \pi K$ and $B\to\pi\pi$ decays. Although the theoretical error is large (\gsim 25%), the method can be performed now, with presently-available data. The third is via a time-dependent angular analysis of \bvv decays. In this case, there is no theoretical error, but the technique is experimentally challenging, and the method applies only to those NP models whose weak phase is universal to all NP operators. A reliable identification of the NP will involve the measurement of the NP parameters in many different ways, and with as many B decay modes as possible, so that it will be important to use all of these methods.Comment: 33 pages, latex, no figures. Appendix added. Analysis and conclusions unchange

Exploitation du monde animal sur le versant nord des Pyrénées au Tardiglaciaire

International audienceLes changements climatiques survenus entre la fin du Tardiglaciaire et le début du Postglaciaire ont modifié de manière considérable l'environnement dans lequel vivaient les populations préhistoriques. Dans le Sud de la France, les grandes étendues steppiques dans lesquelles évoluaient de larges troupeaux d'Ongulés sont peu à peu remplacées par des forêts. Ces écosystèmes cloisonnés abritent une biomasse de grands Herbivores plus faible que les grandes plaines. Par ailleurs, l'augmentation des températures s'accompagne d'un accroissement de la saison végétative des plantes qui, dès lors, sont susceptibles d'être plus intensément exploitées par les groupes humains. Ainsi, du point de vue des ressources alimentaires, le réchauffement postglaciaire aurait eu pour conséquence un élargissement de la diète au profit des petites espèces animales et des végétaux. Pourtant, dans le Nord et l'Est de la France, les travaux de A. Bridault (1993; 1997) ont montré que, pour les grands mammifères, les spectres fauniques n'étaient pas plus diversifiés au Mésolithique qu'au Magdalénien. Ses résultats sur la petite faune réfutent également l'hypothèse d'un élargissement systématique de la diète au profit des petites espèces animales à partir du Mésolithique. De telles études montrent la nécessité de tester, dans le sud de la France, la validité de cette hypothèse. Par une analyse critique des données taphonomiques et archéozoologiques disponibles, nous essaierons de voir si, sur le versant nord des Pyrénées, le réchauffement est, effectivement, à l'origine de l'apparition de nouvelles stratégies alimentaires fondées sur une diversification des ressources, stratégies nouvelles en rupture avec les économies de chasse paléolithiques dépendantes du grand gibier )Les changements climatiques survenus entre la fin du Tardiglaciaire et le début du Postglaciaire ont modifié de manière considérable l'environnement dans lequel vivaient les populations préhistoriques. Dans le Sud de la France, les grandes étendues steppiques dans lesquelles évoluaient de larges troupeaux d'Ongulés sont peu à peu remplacées par des forêts. Ces écosystèmes cloisonnés abritent une biomasse de grands Herbivores plus faible que les grandes plaines. Par ailleurs, l'augmentation des températures s'accompagne d'un accroissement de la saison végétative des plantes qui, dès lors, sont susceptibles d'être plus intensément exploitées par les groupes humains. Ainsi, du point de vue des ressources alimentaires, le réchauffement postglaciaire aurait eu pour conséquence un élargissement de la diète au profit des petites espèces animales et des végétaux. Pourtant, dans le Nord et l'Est de la France, les travaux de A. Bridault (1993; 1997) ont montré que, pour les grands mammifères, les spectres fauniques n'étaient pas plus diversifiés au Mésolithique qu'au Magdalénien. Ses résultats sur la petite faune réfutent également l'hypothèse d'un élargissement systématique de la diète au profit des petites espèces animales à partir du Mésolithique. De telles études montrent la nécessité de tester, dans le sud de la France, la validité de cette hypothèse. Par une analyse critique des données taphonomiques et archéozoologiques disponibles, nous essaierons de voir si, sur le versant nord des Pyrénées, le réchauffement est, effectivement, à l'origine de l'apparition de nouvelles stratégies alimentaires fondées sur une diversification des ressources, stratégies nouvelles en rupture avec les économies de chasse paléolithiques dépendantes du grand gibier (Barbaza, 1999). Bibliographie Barbaza M. (1999) Les civilisations postglaciaires - La vie dans la grande forêt tempérée. Histoire de la France préhistorique. Maison des Roches, Paris, 126 p. Bridault A. (1993) Les économies de chasse épipaléolithiques et mésolithiques dans le nord de la France, Thèse de doctorat, Université Paris X, 552. Bridault A. (1997) Chasseurs, ressources animales et milieux dans le nord de la France de la fin du Paléolithique à la fin du Mésolithique : problématique et état de la recherche. In Le Tardiglaciaire en Europe du Nord-Ouest, J.-P. Fagnart et A. Thévenin (ed.), pp. 165-176. Paris : CTHS

On-surface synthesis of functional organic nanostructures

The improvement of electronic device efficiency is currently based on the miniaturization of existing electronic devices. The manufacturing costs of reducing the size of semiconductor based circuits below 10 nm is unfeasible for companies. To overcome this limitation, other materials are currently being developed to fabricate equivalent electronic circuits with smaller dimensions. In this context, on-surface synthesis (OSS) is a bottom-up manufacturing technique based on the reaction of molecules to achieve a well-defined organic structure. The atomic precision of OSS allows to create functional organic molecules for molecular electronic devices. Scanning probe microscopy techniques are the most common microscopy techniques used to analyze on-surface synthesized structures. In this thesis, we present the synthesis by OSS and characterization by scanning tunneling microscopy (STM) and spectroscopy (STS) techniques of functional nanostructures. The synthesized manganese phthalocyanine (MnPc) includes in the phthalocyanine ring four diarylethylene moieties (DAE). The DAE moiety is an optically active group. This organo-metallic complex with optically active groups and the Mn in its structure could work as a magneto-optical transducer. We have successfully induced reversible switches with the STM tip between the assigned open and closed configurations of the DAE moiety. The other organic structures synthesized by OSS studied in this thesis are chiral graphene nanoribbons (ch-GNRs) on Ag(001). Combining STM and STS techniques we have studied the evolution of the electronic structure of ch-GNRs depending on their width and length. Furthermore, when the ch-GNRs are relocated on top of MgO monoloayers grown on the same Ag(001) substrate by means of atomic manipulation, a combination of charge transfer and electronic localization gives rise to a critical discretization of the extended edge states. This causes unprecedented long life times of the ribbon’s electronic states and spin splitting of the frontier orbitals ascribed to electron-electron correlations. Finally, we have evaluated the suitability of the ch-GNR/MgO monolayer/Ag(001) system as a molecular spin polarized transistor.<br /