Is there an intrinsic limit to the charge-carrier-induced increase of the Curie temperature of EuO?

Rare earth doping is the key strategy to increase the Curie temperature (T(C)) of the ferromagnetic semiconductor EuO. The interplay between doping and charge carrier density (n), and the limit of the T(C) increase, however, are yet to be understood. We report measurements of n and T(C) of Gd-doped EuO over a wide range of doping levels. The results show a direct correlation between n and T(C), with both exhibiting a maximum at high doping. On average, less than 35% of the dopants act as donors, raising the question about the limit to increasing T(C).     

Parsimonious representation of nonlinear dynamical systems through manifold learning: A chemotaxis case study

Nonlinear manifold learning algorithms, such as diffusion maps, have been fruitfully applied in recent years to the analysis of large and complex data sets. However, such algorithms still encounter challenges when faced with real data. One such challenge is the existence of “repeated eigendirections,” which obscures the detection of the true dimensionality of the underlying manifold and arises when several embedding coordinates parametrize the same direction in the intrinsic geometry of the data set. We propose an algorithm, based on local linear regression, to automatically detect coordinates corresponding to repeated eigendirections. We construct a more parsimonious embedding using only the eigenvectors corresponding to unique eigendirections, and we show that this reduced diffusion maps embedding induces a metric which is equivalent to the standard diffusion distance. We first demonstrate the utility and flexibility of our approach on synthetic data sets. We then apply our algorithm to data collected from a stochastic model of cellular chemotaxis, where our approach for factoring out repeated eigendirections allows us to detect changes in dynamical behavior and the underlying intrinsic system dimensionality directly from data.     

Depth of focus extended microscope configuration for imaging of incorporated groups of molecules, DNA constructs and clusters inside bacterial cells

Imaging of small objects such as single molecules, DNA clusters and single bacterial cells is problematic not only due to the lateral resolution that is obtainable in currently existing microscopy but also, and as much fundamentally limiting, due to the lack of sufficient axial depth of focus to have the full object focused simultaneously. Extension in depth of focus is helpful also for single molecule steady state FRET measurements. In this technique it is crucial to obtain data from many well focused molecules, which are often located in different axial depths.In this paper we present the implementation of an all-optical and a real time technique of extension in the depth of focus that may be incorporated in any high NA microscope system and to be used for the above mentioned applications. We demonstrate experimentally how after the integration of special optical element in high NA 100× objective lens of a single molecule imaging microscope system, the depth of focus is significantly improved while maintaining the same lateral resolution in imaging applications of incorporated groups of molecules, DNA constructs and clusters inside bacterial cells.     

Size and branching effects on the fluorescence of benzylic dendrimers possessing one apigenin fluorophore at the core

Different generations of dendrimers incorporating one fluorescent core of apigenin and three Fréchet benzylic dendrons have been prepared. The chief geometric features of these dendrimers have been obtained by Molecular Dynamics simulations. These computational data suggest that the asphericities of dendrimers belonging to the third and fourth generations are considerably larger than those associated with lower radii of gyration. Fluorescence spectra of high generation dendrimers evolve along time and quantum yields show an appreciable lowering for the fourth generation dendrimer. All these data suggest aggregation phenomena and lower quantum yields for nonspheric dendrimers in solution.     

The effect of negatively charged metallic nanocatalysts on their reactions with alkyl radicals

Abstract

Stored electrons on Au and Ag nanoparticles (NPs) have been found to catalyze various reduction processes initiated by ionizing irradiation or light illumination in which the NPs act as “nano-electrodes”. In the present study, we explored the effect of charging colloidal gold and silver NPs on their reaction with methyl radicals, ·CH₃. The results show that charging the colloidal metal NPs by excess of electrons, (NP)^n?, affected their reaction mechanism with methyl radicals and resulted in different product composition in comparison to the analogous reactions with uncharged particles. These results should be considered in photo(electro)catalytic processes when alkyl radicals are formed near the catalyst surface.     

Modeling the Flow Pattern at the Fractured Granites in Porto Alegre, Brazil

The studied 25 by 30 km site of Porto Alegre Southern Brazil fractured granites, accounts for surface lineaments assumed to mimic its fractures. Observations address the lineaments spatial characteristics, significant deviations between stationary groundwater levels condensed at part of the domain while sparse at most of the area, and no pumping/injection rates. Fractured media feature, e.g., dead end pathways, lack of flow interconnections, and preferential infiltration paths. These characteristics are not in line with the implementation of continuum-based macroscopic balance equations. Subject to such data and the inherent features, the objective was to verify if with lumped parameter modeling (LPM) following a flow directed graph approach we can assess a groundwater flow pattern. We at first addressed the site lineaments layout for which the evaluation of the hydraulic heads revealed the existence of isolated lineament clusters, leading to flow or no-flow zones. Aiming at better spatial distribution of flow distributions and based on the site surface lineaments, we established a virtual fracture network (VFN) for which the domain was subdivided into representative elementary area (REA) cells. Each REA was chosen so that the ratio of all its lineament lengths over that of the cell area remained practically unchanged between two consecutive subdivisions. Within each REA, lineaments with similar geometrical characteristics were considered as segment groups. The VFN was established upon elongating segments that created intersection points with other stretched segments from cells at the circumference of a considered REA. The evaluated steady state hydraulic head was compared between two LPM solutions: (1) Referring to flow along the VFN branches between intersection points, and (2) Using a flux interconnected network (FIN) for which each REA was replaced by a pole communicating flow to other poles. Computation of the FIN approach was significantly less intense. Both of these approaches resolved with hydraulic head isolines consistently similar to those obtained by interpolation between the observed groundwater levels. One reported event of a Nitrate polluted well and its plausible contaminating source within the study domain, show that it is in line with the predicted resultant flow direction following the FIN map.     

The geometry of the asymptotics of polynomial maps

The aim of this paper is to develop a theory for the asymptotic behavior of polynomials and of polynomial maps overR and overC and to apply it to the Jacobian conjecture. This theory gives a unified frame for some results on polynomial maps that were not related before. A well known theorem of J. Hadamard gives a necessary and sufficient condition on a local diffeomorphismf: R ⁿ →R ⁿ to be a global diffeomorphism. In order to show thatf is a global diffeomorphism it suffices to exclude the existence of asymptotic values forf. The real Jacobian conjecture was shown to be false by S. Pinchuk. Our first application is to understand his construction within the general theory of asymptotic values of polynomial maps and prove that there is no such counterexample for the Jacobian conjecture overC. In a second application we reprove a theorem of Jeffrey Lang which gives an equivalent formulation of the Jacobian conjecture in terms of Newton polygons. This generalizes a result of Abhyankar. A third application is another equivalent formulation of the Jacobian conjecture in terms of finiteness of certain polynomial rings withinC[U, V]. The theory has a geometrical aspect: we define and develop the theory of etale exotic surfaces. The simplest such surface corresponds to Pinchuk's construction in the real case. In fact, we prove one more equivalent formulation of the Jacobian conjecture using etale exotic surfaces. We consider polynomial vector fields on etale exotic surfaces and explore their properties in relation to the Jacobian conjecture. In another application we give the structure of the real variety of the asymptotic values of a polynomial mapf: R ² →R ² .