12,876 research outputs found

    Electrical connector pin with wiping action

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    Electrical connector pin with wiping action to assure reliable contac

    Pseudoknots in a Homopolymer

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    After a discussion of the definition and number of pseudoknots, we reconsider the self-attracting homopolymer paying particular attention to the scaling of the number of pseudoknots at different temperature regimes in two and three dimensions. Although the total number of pseudoknots is extensive at all temperatures, we find that the number of pseudoknots forming between the two halves of the chain diverges logarithmically at (in both dimensions) and below (in 2d only) the theta-temparature. We later introduce a simple model that is sensitive to pseudoknot formation during collapse. The resulting phase diagram involves swollen, branched and collapsed homopolymer phases with transitions between each pair.Comment: submitted to PR

    Boundary Spatiotemporal Correlations in a Self-Organized Critical Model of Punctuated Equilibrium

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    In a semi-infinite geometry, a 1D, M-component model of biological evolution realizes microscopically an inhomogeneous branching process for M→∞M \to \infty. This implies in particular a size distribution exponent τ′=7/4\tau'=7/4 for avalanches starting at a free end of the evolutionary chain. A bulk--like behavior with τ′=3/2\tau'=3/2 is restored if `conservative' boundary conditions strictly fix to its critical, bulk value the average number of species directly involved in an evolutionary avalanche by the mutating species located at the chain end. A two-site correlation function exponent τR′=4{\tau_R}'=4 is also calculated exactly in the `dissipative' case, when one of the points is at the border. These results, together with accurate numerical determinations of the time recurrence exponent τfirst′\tau_{first}', show also that, no matter whether dissipation is present or not, boundary avalanches have the same space and time fractal dimensions as in the bulk, and their distribution exponents obey the basic scaling laws holding there.Comment: 5 pages, 3 eps figure

    The acquisition of English L2 prosody by Italian native speakers: experimental data and pedagogical implications

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    This paper investigates Yes-No question intonation patterns in English L2, Italian L1, and English L1. The aim is to test the hypothesis that L2 learners may show different acquisition strategies for different dimensions of intonation, and particularly the phonological and phonetic components. The study analyses the nuclear intonation contours of 4 target English words and 4 comparable Italian words consisting of sonorant segments, stressed on the semi-final or final syllable, and occurring in Yes-No questions in sentence-final position (e.g., Will you attend the memorial?, Hai sentito la Melania?). The words were contained in mini-dialogues of question-answer pairs, and read 5 times by 4 Italian speakers (Padova area, North-East Italy) and 3 English female speakers (London area, UK). The results show that: 1) different intonation patterns may be used to realize the same grammatical function; 2) different developmental processes are at work, including transfer of L1 categories and the acquisition of L2 phonological categories. These results suggest that the phonetic dimension of L2 intonation may be more difficult to learn than the phonological one

    Strong gravitational field light deflection in binary systems containing a collapsed star

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    Large light deflection angles are produced in the strong gravitational field regions around neutron stars and black holes. In the case of binary systems, part of the photons emitted from the companion star towards the collapsed object are expected to be deflected in the direction of the earth. Based on a semi-classical approach we calculate the characteristic time delays and frequency shifts of these photons as a function of the binary orbital phase. The intensity of the strongly deflected light rays is reduced by many orders of magnitude, therefore making the observations of this phenomenon extremely difficult. Relativistic binary systems containing a radio pulsar and a collapsed object are the best available candidates for the detection of the strongly deflected photons. Based on the accurate knowledge of their orbital parameters, these systems allow to predict accurately the delays of the pulses along the highly deflected path, such that the sensitivity to very weak signals can be substantially improved through coherent summation over long time intervals. We discuss in detail the cases of PSR 1913+16 and PSR 1534+12 and find that the system geometry is far more promising for the latter. The observation of the highly deflected photons can provide a test of general relativity in an unprecedented strong field regime as well as a tight constraint on the radius of the collapsed object.Comment: 7 pages, uuencoded, gzip'ed, postscript file with figures included. Accepted for pubblication in MNRA

    Hybrid lattice Boltzmann model for binary fluid mixtures

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    A hybrid lattice Boltzmann method (LBM) for binary mixtures based on the free-energy approach is proposed. Non-ideal terms of the pressure tensor are included as a body force in the LBM kinetic equations, used to simulate the continuity and Navier-Stokes equations. The convection-diffusion equation is studied by finite difference methods. Differential operators are discretized in order to reduce the magnitude of spurious velocities. The algorithm has been shown to be stable and reproducing the correct equilibrium behavior in simple test configurations and to be Galilean invariant. Spurious velocities can be reduced of about an order of magnitude with respect to standard discretization procedure.Comment: Final version, to appear in Phys. Rev.
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