59,903 research outputs found

    Protocyanobacteria: Oxygenic and Anoxygenic photosynthesis in mat-forming bacteria

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    The oldest record of life is preserved in prePhanerozoic stromatolites dated 3500 million years old and is most likely of filamentous mat-forming cyanobacteria. The sedimentary records of cyanobacterial mats in stromatolites are the most abundant record of life throughout the prePhanerozoic. Stromatolites persisted into the Phanerozoic Eon, yet they become much less pronounced relative to earlier ones. The abundance and persistence of cyanobacterial mats throughout most of geological time point to the evolutionary success of these kinds of microbial communities and their possible role in the evolution of the earth and atmosphere

    Configurations, and parallelograms associated to centers of mass

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    The purpose of this article is to \begin{enumerate} \item define M(t,k)M(t,k) the tt-fold center of mass arrangement for kk points in the plane, \item give elementary properties of M(t,k)M(t,k) and \item give consequences concerning the space M(2,k)M(2,k) of kk distinct points in the plane, no four of which are the vertices of a parallelogram. \end{enumerate} The main result proven in this article is that the classical unordered configuration of kk points in the plane is not a retract up to homotopy of the space of kk unordered distinct points in the plane, no four of which are the vertices of a parallelogram. The proof below is homotopy theoretic without an explicit computation of the homology of these spaces. In addition, a second, speculative part of this article arises from the failure of these methods in the case of odd primes pp. This failure gives rise to a candidate for the localization at odd primes pp of the double loop space of an odd sphere obtained from the pp-fold center of mass arrangement. Potential consequences are listed.Comment: 11 page

    The conductance of a multi-mode ballistic ring: beyond Landauer and Kubo

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    The Landauer conductance of a two terminal device equals to the number of open modes in the weak scattering limit. What is the corresponding result if we close the system into a ring? Is it still bounded by the number of open modes? Or is it unbounded as in the semi-classical (Drude) analysis? It turns out that the calculation of the mesoscopic conductance is similar to solving a percolation problem. The "percolation" is in energy space rather than in real space. The non-universal structures and the sparsity of the perturbation matrix cannot be ignored.Comment: 7 pages, 8 figures, with the correct version of Figs.6-

    The Continuity of Discontinuity: How Young Jews Are Connecting, Creating, and Organizing Their Own Jewish Lives

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    Based on case studies of four self-initiated ventures in Jewish self-organizing, explores their organizing principles, the limitations of and challenges for conventional institutions, and implications for engaging the new generation

    Beyond Distancing: Young Adult American Jews and Their Alienation from Israel

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    This research reports on a mounting body of evidence that has pointed to a growing distancing from Israel of American Jews, most pronounced among younger Jews, and explores critical questions behind their presumably diminished attachment to Israel