Cambios florísticos en comunidades de malezas : un marco conceptual basado en reglas de ensamblaje

150-158Agriculture provides interesting situations to study ecological succession in weed communities. There is empirical evidence of floristic shifts in weed communities due to both environmental and technological changes, which have been interpreted in the light of succession theory. In turn, the assembly rules framework has proved to be useful to describe and predict patterns of change in communities. The aim of this paper is to present the application of an approach based on community assembly rules to study floristic changes in weed communities. Assembly rules are associated with specific factors that explain the patterns observed in a community. Assembly rules operate as a filter restricting the number of species of the regional pool that occur in local communities. The regional species pool is defined by means of a hierarchical classification as three nested spatial domains: geographic, landscape and habitat type. At large spatial scales (1000-10000 km 2), the species pool is determined by the factors regulating the rates of both speciation and extinction and plant migrations between distant regions. Landscape complexity effects are higher at regional level. While dispersion increases its influence in mosaics of patches (100 m 2-10 ha), habitat heterogeneity is more important in smaller patches (1-1000 m 2-1 ha). In small plots (<10 m 2), plant communities are modulated by biotic interactions, soil fertility, abiotic stress and microdisturbances. Species from the regional pool are filtering out by the limitations to dispersal within the region and the restrictions imposed by both the abiotic environment and biotic interaction at local scale. Community assembly rules provide a flexible framework for building descriptive models of successional trajectories in weed communities in response to changes in agricultural systems

Cambios florísticos en comunidades de malezas : un marco conceptual basado en reglas de ensamblaje

150-158Agriculture provides interesting situations to study ecological succession in weed communities. There is empirical evidence of floristic shifts in weed communities due to both environmental and technological changes, which have been interpreted in the light of succession theory. In turn, the assembly rules framework has proved to be useful to describe and predict patterns of change in communities. The aim of this paper is to present the application of an approach based on community assembly rules to study floristic changes in weed communities. Assembly rules are associated with specific factors that explain the patterns observed in a community. Assembly rules operate as a filter restricting the number of species of the regional pool that occur in local communities. The regional species pool is defined by means of a hierarchical classification as three nested spatial domains: geographic, landscape and habitat type. At large spatial scales (1000-10000 km 2), the species pool is determined by the factors regulating the rates of both speciation and extinction and plant migrations between distant regions. Landscape complexity effects are higher at regional level. While dispersion increases its influence in mosaics of patches (100 m 2-10 ha), habitat heterogeneity is more important in smaller patches (1-1000 m 2-1 ha). In small plots (<10 m 2), plant communities are modulated by biotic interactions, soil fertility, abiotic stress and microdisturbances. Species from the regional pool are filtering out by the limitations to dispersal within the region and the restrictions imposed by both the abiotic environment and biotic interaction at local scale. Community assembly rules provide a flexible framework for building descriptive models of successional trajectories in weed communities in response to changes in agricultural systems

Magnetic anisotropy of individual maghemite mesocrystals

Interest in creating magnetic metamaterials has led to methods for growing superstructures of magnetic nanoparticles. Mesoscopic crystals of maghemite (gamma-Fe2O3) nanoparticles can be arranged into highly ordered body-centered tetragonal lattices of up to a few micrometers. Although measurements on disordered ensembles have been carried out, determining the magnetic properties of individual mesoscopic crystals is challenging due to their small total magnetic moment. Here, we overcome these challenges by utilizing sensitive dynamic cantilever magnetometry to study individual micrometer-sized gamma-Fe2O3 mesocrystals. These measurements reveal an unambiguous cubic anisotropy, resulting from the crystalline anisotropy of the constituent maghemite nanoparticles and their alignment within the mesoscopic lattice. The signatures of anisotropy and its origins come to light because we combine the self-assembly of highly ordered mesocrystals with the ability to resolve their individual magnetism. This combination is promising for future studies of the magnetic anisotropy of other nanoparticles, which are too small to investigate individually

Implicitly Constrained Semi-Supervised Least Squares Classification

We introduce a novel semi-supervised version of the least squares classifier. This implicitly constrained least squares (ICLS) classifier minimizes the squared loss on the labeled data among the set of parameters implied by all possible labelings of the unlabeled data. Unlike other discriminative semi-supervised methods, our approach does not introduce explicit additional assumptions into the objective function, but leverages implicit assumptions already present in the choice of the supervised least squares classifier. We show this approach can be formulated as a quadratic programming problem and its solution can be found using a simple gradient descent procedure. We prove that, in a certain way, our method never leads to performance worse than the supervised classifier. Experimental results corroborate this theoretical result in the multidimensional case on benchmark datasets, also in terms of the error rate.Comment: 12 pages, 2 figures, 1 table. The Fourteenth International Symposium on Intelligent Data Analysis (2015), Saint-Etienne, Franc

Test of the Running of αs\alpha_s in τ\tau Decays

The $\tau$ decay rate into hadrons of invariant mass smaller than $\sqrt{s_0}\gg\Lambda_{\rm QCD}$ can be calculated in QCD assuming global quark--hadron duality. It is shown that this assumption holds for $s_0>0.7$~GeV$^2$. From measurements of the hadronic mass distribution, the running coupling constant $\alpha_s(s_0)$ is extracted in the range 0.7~GeV$^2<s_0<m_\tau^2$. At $s_0=m_\tau^2$, the result is $\alpha_s(m_\tau^2)=0.329\pm 0.030$. The running of $\alpha_s$ is in good agreement with the QCD prediction.Comment: 9 pages, 3 figures appended; shortened version with new figures, to appear in Physical Review Letters (April 1996

Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire

Soon after the first measurements of nuclear magnetic resonance (NMR) in a condensed matter system, Bloch predicted the presence of statistical fluctuations proportional to $1/\sqrt{N}$ in the polarization of an ensemble of $N$ spins. First observed by Sleator et al., so-called "spin noise" has recently emerged as a critical ingredient in nanometer-scale magnetic resonance imaging (nanoMRI). This prominence is a direct result of MRI resolution improving to better than 100 nm^3, a size-scale in which statistical spin fluctuations begin to dominate the polarization dynamics. We demonstrate a technique that creates spin order in nanometer-scale ensembles of nuclear spins by harnessing these fluctuations to produce polarizations both larger and narrower than the natural thermal distribution. We focus on ensembles containing ~10^6 phosphorus and hydrogen spins associated with single InP and GaP nanowires (NWs) and their hydrogen-containing adsorbate layers. We monitor, control, and capture fluctuations in the ensemble's spin polarization in real-time and store them for extended periods. This selective capture of large polarization fluctuations may provide a route for enhancing the weak magnetic signals produced by nanometer-scale volumes of nuclear spins. The scheme may also prove useful for initializing the nuclear hyperfine field of electron spin qubits in the solid-state.Comment: 18 pages, 5 figure

Testing QCD with Hypothetical Tau Leptons

We construct new tests of perturbative QCD by considering a hypothetical tau lepton of arbitrary mass, which decays hadronically through the electromagnetic current. We can explicitly compute its hadronic width ratio directly as an integral over the e^+ e^- annihilation cross section ratio, R_{e^+e^-}. Furthermore, we can design a set of commensurate scale relations and perturbative QCD tests by varying the weight function away from the form associated with the V-A decay of the physical tau. This method allows the wide range of the R_{e^+e^-} data to be used as a probe of perturbative QCD.Comment: 4 pages, 4 figure

The role of dose-dense (DD) adjuvant chemotherapy (CT) in HER2-positive (HER2+) early breast cancer (BC) patients (pts) before and after the introduction of trastuzumab (T): Exploratory analysis of the GIM2 trial

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Robustness and Generalization

We derive generalization bounds for learning algorithms based on their robustness: the property that if a testing sample is "similar" to a training sample, then the testing error is close to the training error. This provides a novel approach, different from the complexity or stability arguments, to study generalization of learning algorithms. We further show that a weak notion of robustness is both sufficient and necessary for generalizability, which implies that robustness is a fundamental property for learning algorithms to work

The Adler Function for Light Quarks in Analytic Perturbation Theory

The method of analytic perturbation theory, which avoids the problem of ghost-pole type singularities and gives a self-consistent description of both spacelike and timelike regions, is applied to describe the "light" Adler function corresponding to the non-strange vector channel of the inclusive decay of the $\tau$ lepton. The role of threshold effects is investigated. The behavior of the quark-antiquark system near threshold is described by using a new relativistic resummation factor. It is shown that the method proposed leads to good agreement with the ``experimental'' Adler function down to the lowest energy scale.Comment: 13 pages, one ps figure, REVTe