1,671 research outputs found

    Absence of localization in a disordered one-dimensional ring threaded by an Aharonov-Bohm flux

    Full text link
    Absence of localization is demonstrated analytically to leading order in weak disorder in a one-dimensional Anderson model of a ring threaded by an Aharonov-Bohm (A-B) flux. The result follows from adapting an earlier perturbation treatment of disorder in a superconducting ring subjected to an imaginary vector potential proportional to a depinning field for flux lines bound to random columnar defects parallel to the axis of the ring. The absence of localization in the ring threaded by an A-B flux for sufficiently weak disorder is compatible with large free electron type persistent current obtained in recent studies of the above model

    Integration of Host Plant Resistance and Insecticides in the Control of \u3ci\u3eNephotettix virescens\u3c/i\u3e (Homoptera: Cicadelli-dae), a Vector of Rice Tungro Virus

    Get PDF
    Combined effects of levels of vector resistance and insecticide application in control of rice tungro virus (RTV) were determined in three field tests. Cultivar “IR28,” with high levels of resistance to the vector, Nephotettix virescens (Distant), had low RTV infection in all treatments including the untreated check. In moderately resistant “IR36,” RTV decreased with an increase in level of insecticide but did not decrease to a level equaling the untreated “IR28.” The N. virescens-susceptible cultivar “IR22” had extremely high levels of RTV infection at all insecticide levels. Economic analysis indicated that gross profit and net gain were highest in the N. virescens-resistant “IR28,” intermediate in moderately resistant “IR36,” and lowest in susceptible “IR22.

    Influence of external magnetic fields on growth of alloy nanoclusters

    Full text link
    Kinetic Monte Carlo simulations are performed to study the influence of external magnetic fields on the growth of magnetic fcc binary alloy nanoclusters with perpendicular magnetic anisotropy. The underlying kinetic model is designed to describe essential structural and magnetic properties of CoPt_3-type clusters grown on a weakly interacting substrate through molecular beam epitaxy. The results suggest that perpendicular magnetic anisotropy can be enhanced when the field is applied during growth. For equilibrium bulk systems a significant shift of the onset temperature for L1_2 ordering is found, in agreement with predictions from Landau theory. Stronger field induced effects can be expected for magnetic fcc-alloys undergoing L1_0 ordering.Comment: 10 pages, 3 figure

    Management of the Rice Tungro Virus Vector \u3ci\u3eNephotettix virescens\u3c/i\u3e (Homoptera: Cicadellidae) with Controlled-Release Formulations of Carbofuran

    Get PDF
    Field trials were conducted in lowland flooded rice in the Philippines to evaluate a number of carbofuran controlled-release formulations in comparison with commercial formulations. The test formulations were based on a biodegradable matrix of pine kraft lignin and were used as granules of different sizes and also in the form of small strips. The release rates were assessed under field conditions by bioassaying rice plants in the field, using adult rice green leafhopper, Nephotettix virescens Distant. The lignin formulations with a high level of active ingredient (15–45% by weight) gave as good or better control than the commercial 3% granules in tests based on three application techniques: broadcast into the floodwater, soil incorporation, and root zone injection. The improvements in control levels of green leafhoppers were most marked with soil incorporation and root zone application. The best lignin-based formulation reduced levels of tungro virus infection from 23% for a conventional flowable carbofuran formulation to 1.0% at an application rate of 0.5 kg (AI)/ha. At the same rate, the grain yield was increased from 3.56 t/ha to 5.5 t/ha, using the controlled-released formulation

    Evaluation of two observational methods to assess the numbers of nesting puffins (Fratercula arctica)

    Get PDF
    Accurate monitoring of population numbers is essential for conservation. Large numbers, dense flora, camouflage or inaccessible landscapes make counting individuals difficult or near impossible. This study compared two population count methods for puffins nesting in on steep cliffs. To estimate numbers in a colony, Apparently Occupied Burrows (AOB) are counted by the observation of adult birds returning with fish in their beaks and disappearing into the burrows (Joint Nature Conservation Committee, 2015). This study compared continuous counts via binoculars with the count obtained via a time-laps camera (one photo every 10 seconds) to help future estimates to be more accurate and provide a scientific method for the national census. The study was carried out on Lundy Island (51N, 04W) in the Bristol Channel, UK. Total counts of puffins present in the observation area were done at the beginning of each session, and then again every 30 minutes, both via binoculars and from still photos. The total camera bird count ranged from two to 39, for the live observation from zero to 45. The count of the AOBs via the photos ranged from five to 19, for the live count from one to 15. The camera count of the AOBs was always higher than the count via binoculars, by an average factor of 1.75. The difference between the two observers was smaller than the difference between the camera count and the observers. The differences in bird numbers between all three counts were significant. The observers’ bird counts did not show a trend to over- or underestimate total numbers. Both observational techniques were affected by weather conditions and visibility. Counting occupied nest sites by camera is more accurate than by live observation via binoculars. For overall numbers of birds the trend was inconclusive

    Enhanced Transmission Through Disordered Potential Barrier

    Full text link
    Effect of weak disorder on tunneling through a potential barrier is studied analytically. A diagrammatic approach based on the specific behavior of subbarrier wave functions is developed. The problem is shown to be equivalent to that of tunneling through rectangular barriers with Gaussian distributed heights. The distribution function for the transmission coefficient TT is derived, and statistical moments \left are calculated. The surprising result is that in average disorder increases both tunneling conductance and resistance.Comment: 10 pages, REVTeX 3.0, 2 figures available upon reques

    Exact transmission moments in one-dimensional weak localization and single-parameter scaling

    Full text link
    We obtain for the first time the expressions for the mean and the variance of the transmission coefficient for an Anderson chain in the weak localization regime, using exact expansions of the complex transmission- and reflection coefficients to fourth order in the weakly disordered site energies. These results confirm the validity of single-parameter scaling theory in a domain where the higher transmission cumulants may be neglected. We compare our results with earlier results for transmission cumulants in the weak localization domain based on the phase randomization hypothesis

    Theory of Second and Higher Order Stochastic Processes

    Full text link
    This paper presents a general approach to linear stochastic processes driven by various random noises. Mathematically, such processes are described by linear stochastic differential equations of arbitrary order (the simplest non-trivial example is x¨=R(t)\ddot x = R(t), where R(t)R(t) is not a Gaussian white noise). The stochastic process is discretized into nn time-steps, all possible realizations are summed up and the continuum limit is taken. This procedure often yields closed form formulas for the joint probability distributions. Completely worked out examples include all Gaussian random forces and a large class of Markovian (non-Gaussian) forces. This approach is also useful for deriving Fokker-Planck equations for the probability distribution functions. This is worked out for Gaussian noises and for the Markovian dichotomous noise.Comment: 35 pages, PlainTex, accepted for publication in Phys Rev. E

    Wireless internet architecture and testbed for wineglass

    Get PDF
    One of the most challenging issues in the area of mobile communication is the deployment of IPbased wireless multimedia networks in public and business environments. The public branch may involve public mobile networks, like UMTS as 3G system, while the business branch introduces local radio access networks by means of W-LANs. Conventional mobile networks realise mobile specific functionality, e.g. mobility management or authentication and accounting, by implementing appropriate mechanisms in specific switching nodes (e.g. SGSN in GPRS). In order to exploit the full potential of IP networking solutions a replacement of these mechanisms by IP-based solutions might be appropriate. In addition current and innovative future services in mobile environments require at least soft-guaranteed, differentiated QoS. Therefore the WINE GLASS project investigates and implements enhanced IP-based techniques supporting mobility and QoS in a wireless Internet architecture. As a means to verify the applicability of the implemented solutions, location-aware services deploying both IP-mobility and QoS mechanisms will be implemented and demonstratedPeer ReviewedPostprint (published version
    corecore