4,407 research outputs found
Collective dipole excitations in sodium clusters
Some properties of small and medium sodium clusters are described within the
RPA approach using a projected spherical single particle basis. The oscillator
strengths calculated with a Schiff-like dipole transition operator and folded
with Lorentzian functions are used to calculate the photoabsorbtion cross
section spectra. The results are further employed to establish the dependence
of the plasmon frequency on the number of cluster components. Static electric
polarizabilities of the clusters excited in a RPA dipole state are also
calculated.
Comparison of our results with the corresponding experimental data show an
overall good agreement.Comment: 23 pages, 5 figure
Regularization of geodesics in static spherically symmetric Kerr-Schild spacetimes
Spanish Relativity Meeting: "Almost 100 years after Einstein's revolution". University of Valencia, 1st-5th of September 2014We describe a method to analyze causal geodesics in static and spherically symmetric spacetimes of Kerr-Schild form which, in particular, allows for a detailed study of the geodesics in the vicinity of the central singularity by means of a regularization procedure based on a generalization of the McGehee regularization for the motion of Newtonian point particles moving in a power-law potential. The McGehee regularization was used by Belbruno and Pretorius [1] to perform a dynamical system regularization of the central singularity of the motion of massless test particles in the Schwarzschild spacetime. Our generalization allows us to consider causal (timelike or null) geodesics in any static and spherically symmetric spacetime of Kerr-Schild form. As an example, we apply these results to causal geodesics in the Schwarzschild and Reissner-Nordstrom spacetimes
Canonical non-symmetrical correspondence analysis: an alternative in constrained ordination
Canonical non-symmetrical correspondence analysis is developed as an alternative method for constrained ordination, relating external information (e.g., environmental variables) with ecological data, considering species abundance as dependant on sites. Ordination axes are restricted to be linear
combinations of the environmental variables, based on the information of the most abundant species. This extension and its associated unconstrained ordination method are terms of a global model that permits an empirical evaluation of the impact that the environmental variables have on the community
composition. Scores, contributions, qualities of representation, interpretation of dispersion graphs and an application to real vegetation data are presented.Peer Reviewe
Deformations of Multiparameter Quantum gl(N)
Multiparameter quantum gl(N) is not a rigid structure. This paper defines an
essential deformation as one that cannot be interpreted in terms of a
similarity transformation, nor as a perturbation of the parameters. All the
equivalence classes of first order essential deformations are found, as well as
a class of exact deformations. This work provides quantization of all the
classical Lie bialgebra structures (constant r-matrices) found by Belavin and
Drinfeld for sl(n). A special case, that requires the Hecke parameter to be a
cubic root of unity, stands out.Comment: 15 pages. Plain Te
Canonical non-symmetrical correspondence analysis: an alternative in constrained ordination
Canonical non-symmetrical correspondence analysis is developed as an alternative method for constrained ordination, relating external information (e.g., environmental variables) with ecological data, considering species abundance as dependant on sites. Ordination axes are restricted to be linear
combinations of the environmental variables, based on the information of the most abundant species. This extension and its associated unconstrained ordination method are terms of a global model that permits an empirical evaluation of the impact that the environmental variables have on the community
composition. Scores, contributions, qualities of representation, interpretation of dispersion graphs and an application to real vegetation data are presented.Peer Reviewe
Data Analysis with Intersection Graphs
AbstractThis paper presents a new framework for multivariate data analysis, based on graph theory, using intersection graphs [1]. We have named this approach DAIG – Data Analysis with Intersection Graphs. This new framework represents data vectors as paths on a graph, which has a number of advantages over the classical table representation of data. To do so, each node represents an atom of information, i.e. a pair of a variable and a value, associated with the set of observations for which that pair occurs. An edge exists between a pair of nodes whenever the intersection of their respective sets is not empty. We show that this representation of data as an intersection graph allows an easy and intuitive geometric interpretation of data observations, groups of observations, and results of multivariate data analysis techniques such as biplots, principal components, cluster analysis, or multidimensional scaling. These will appear as paths on the graph, relating variables, values and observations. This approach allows for a compact and memory efficient representation of data that contains many missing values or multi-valued attributes. The basic principles and advantages of this approach are presented with an example of its application to a simple toy problem. The main features of this methodology are illustrated with the aid software specifically developed for this purpose
Exploring New Lagrangian Cyclers to Enhance Science: Communications with CubeSat Technology
This paper discusses the opportunities that abound by using the CubeSat technology to travel to and communicate with the International Space Station, explore space, monitor space weather, monitor space debris and perhaps travel to Mars
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