18,445 research outputs found

    A Novel Approach to Discontinuous Bond Percolation Transition

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    We introduce a bond percolation procedure on a DD-dimensional lattice where two neighbouring sites are connected by NN channels, each operated by valves at both ends. Out of a total of NN, randomly chosen nn valves are open at every site. A bond is said to connect two sites if there is at least one channel between them, which has open valves at both ends. We show analytically that in all spatial dimensions, this system undergoes a discontinuous percolation transition in the NN\to \infty limit when γ=lnnlnN\gamma =\frac{\ln n}{\ln N} crosses a threshold. It must be emphasized that, in contrast to the ordinary percolation models, here the transition occurs even in one dimensional systems, albeit discontinuously. We also show that a special kind of discontinuous percolation occurs only in one dimension when NN depends on the system size.Comment: 6 pages, 6 eps figure

    GRB011211: An alternative interpretation of the optical and X-ray spectra in terms of blueshifts

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    The redshifts of the gamma ray burst (GRB) GRB 011211 has been determined as 2.14 from several absorption lines seen in the spectrum of its optical afterglow. The spectrum of its X-ray afterglow exhibited several emission lines,and their identification led to a mean redshift 1.862. A supernova model has been proposed based on the redshift of the GRB as 2.141. It is shown here that the redshift interpretation cannot explain the observed spectra, as some serious inconsistencies exist in the process of redshift determinations in spectra of both optical and X-ray afterglows. In view of that, an alternative interpretation of the spectra is presented in terms of blueshifts. Ejection mechanism is proposed as a possible scenario to explain the blueshifted spectrum.Comment: 26 pages, one table; in Canadian Journal of Physics, June 200

    Impact of Rural Employment Guarantee Schemes on Seasonal Labor Markets: Optimum Compensation and Workers' Welfare

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    The recent enactment of the National Rural Employment Guarantee Act in India has been widely hailed a policy that provides a safety net for the rural poor with the potential to boost rural income, stabilize agricultural production and reduce rural-urban migration. This paper, models the impact of such employment guarantee schemes in the context of an agrarian economy characterized by lean season involuntary unemployment as a consequence of tied-labor contracts. Specifically, we examine labor and output market responses to a productive rural Employment Guarantee Scheme (EGS) and determine the optimal compensation to public work employees consistent with the objectives of (i) productive efficiency in agriculture and (ii) welfare maximization of the laborers. Our framework provides a theoretical framework for the evaluation of a number of (sometimes) conflicting observations and empirical results on the impact of an EGS on agricultural wages, employment and output, and underscores the importance of the relative productivity of workers in the EGS program vis-à-vis their counterparts engaged in agricultural production in determining the success of these programs.labor contracts, rural unemployment, employment guarantee schemes, public input, optimal wage

    Local asymptotic minimax risk bounds in a locally asymptotically mixture of normal experiments under asymmetric loss

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    Local asymptotic minimax risk bounds in a locally asymptotically mixture of normal family of distributions have been investigated under asymmetric loss functions and the asymptotic distribution of the optimal estimator that attains the bound has been obtained.Comment: Published at http://dx.doi.org/10.1214/074921706000000527 in the IMS Lecture Notes--Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

    The dynamo effect - A dynamic renormalisation group approach

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    The Dynamo effect is used to describe the generation of magnetic fields in astrophysical objects. However, no rigorous derivation of the dynamo equation is available. We justify the form of the equation using an Operator Product Expansion (OPE) of the relevant fields. We also calculate the coefficients of the OPE series using a dynamic renormalisation group approach and discuss the time evolution of the initial conditions on the initial seed magnetic field.Comment: submitted to EP

    Universal properties of three-dimensional magnetohydrodynamic turbulence: Do Alfv\'en waves matter?

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    We analyse the effects of the propagating Alfv\'en waves, arising due to non-zero mean magnetic fields, on the nonequilibrium steady states of three-dimensional (3d) homogeneous Magnetohydrodynamic (MHD) turbulence. In particular, the effects of Alfv\'en waves on the universal properties of 3dMHD turbulence are studied in a one-loop self-consistent mode-coupling approach. We calculate the kinetic- and magnetic energy-spectra. We find that {\em even} in the presence of a mean magnetic field the energy spectra are Kolmogorov-like, i.e., scale as k5/3k^{-5/3} in the inertial range where k\bf k is a Fourier wavevector belonging to the inertial range. We also elucidate the multiscaling of the structure functions in a log-normal model by evaluating the relevant intermittency exponents, and our results suggest that the multiscaling deviations from the simple Kolmogorov scaling of the structure functions decrease with increasing strength of the mean magnetic field. Our results compare favourably with many existing numerical and observational results.Comment: To appear in JSTAT (2005