18,654 research outputs found

    Visible and ultraviolet reflectance and luminescence from various Saudi Arabian and Indiana limestone rocks

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    Visible and ultraviolet reflectance and luminescence for natural limeston

    Scale-free networks with tunable degree distribution exponents

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    We propose and study a model of scale-free growing networks that gives a degree distribution dominated by a power-law behavior with a model-dependent, hence tunable, exponent. The model represents a hybrid of the growing networks based on popularity-driven and fitness-driven preferential attachments. As the network grows, a newly added node establishes mm new links to existing nodes with a probability pp based on popularity of the existing nodes and a probability 1āˆ’p1-p based on fitness of the existing nodes. An explicit form of the degree distribution P(p,k)P(p,k) is derived within a mean field approach. For reasonably large kk, P(p,k)āˆ¼kāˆ’Ī³(p)F(k,p)P(p,k) \sim k^{-\gamma(p)}{\cal F}(k,p), where the function F{\cal F} is dominated by the behavior of 1/lnā”(k/m)1/\ln(k/m) for small values of pp and becomes kk-independent as pā†’1p \to 1, and Ī³(p)\gamma(p) is a model-dependent exponent. The degree distribution and the exponent Ī³(p)\gamma(p) are found to be in good agreement with results obtained by extensive numerical simulations.Comment: 12 pages, 2 figures, submitted to PR

    SURE Impact? An Empirical Investigation of Moral Hazard and Adverse Selection Behavior

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    The Supplemental Revenue Assistance Payments (SURE) program, enacted under the 2008 Farm Bill, is intended to provide indemnity payments to producers whose crop losses exceed 50% of their historical average yields. However, indemnification does not require that the farm is located in a region designated a disaster relief area -- a provision that can create significant moral hazard incentives. This study is the first to perform an empirical analysis of possible moral hazard behavior in corn, soybean, and wheat markets in response to the SURE program. Results suggest that an increase in crop insurance demand after the enactment of SURE may be due to the program's moral hazard incentives.Agricultural and Food Policy, Farm Management,

    A measurement of the cosmic ray elements C to Fe in the two energy intervals 0.5-2.0 GeV/n and 20-60 GeV/n

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    The study of the cosmic ray abundances beyond 20 GeV/n provides additional information on the propagation and containment of the cosmic rays in the galaxy. Since the average amount of interstellar material traversed by cosmic rays decreases as its energy increases, the source composition undergoes less distortion in this higher energy region. However, data over a wide energy range is necessary to study propagation parameters. Some measurements of some of the primary cosmic ray abundance ratios at both low (near 2 GeV/n) and high (above 20 GeV/n) energy are given and compared to the predictions of the leaky box mode. In particular, the integrated values (above 23.7 GeV/n) for the more abundant cosmic ray elements in the interval C through Fe and the differential flux for carbon, oxygen, and the Ne, Mg, Si group are presented. Limited statistics prevented the inclusion of the odd Z elements

    Unified description of bulk and interface-enhanced spin pumping

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    The dynamics of non-equilibrium spin accumulation generated in metals or semiconductors by rf magnetic field pumping is treated within a diffusive picture. The dc spin accumulation produced in a uniform system by a rotating applied magnetic field or by a precessing magnetization of a weak ferromagnet is in general given by a (small) fraction of hbar omega, where omega is the rotation or precession frequency. With the addition of a neighboring, field-free region and allowing for the diffusion of spins, the spin accumulation is dramatically enhanced at the interface, saturating at the universal value hbar omega in the limit of long spin relaxation time. This effect can be maximized when the system dimensions are of the order of sqrt(2pi D omega), where D is the diffusion constant. We compare our results to the interface spin pumping theory of A. Brataas et al. [Phys. Rev. B 66, 060404(R) (2002)]

    Secondary electron background produced by heavy nuclei in a multiwire proportional counter hodoscope

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    The secondary electron background produced by heavy nuclei in a multiwire proportional counter hodoscope is calculated using both a simplified and a more complete Monte Carlo model. These results are compared with experimental data from a small multiwire proportional counter hodoscope operated in a 530 MeV/nucleon accelerator beam of nitrogen nuclei. Estimates of the secondary electron background produced by heavy relativistic nuclei are presented along with the detailed results from calculations of energy deposition in the hodoscope counter cells

    Instability of scale-free networks under node-breaking avalanches

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    The instability introduced in a large scale-free network by the triggering of node-breaking avalanches is analyzed using the fiber-bundle model as conceptual framework. We found, by measuring the size of the giant component, the avalanche size distribution and other quantities, the existence of an abrupt transition. This test of strength for complex networks like Internet is more stringent than others recently considered like the random removal of nodes, analyzed within the framework of percolation theory. Finally, we discuss the possible implications of our results and their relevance in forecasting cascading failures in scale-free networks.Comment: 4 pages, 4 figures, final version to be published in Europhys. Let
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