267 research outputs found

    HF radar for port management: case study in the Port of Rotterdam

    Get PDF
    The phased array HF ocean radar installed at the Port of Rotterdam gives good quality near real-time information on surface currents for port management. This paper examines the potential to infer current profiles from HF radar and wind station data using prior knowledge of the site. It is shown that tidal currents follow a logarithmic boundary layer profile, and the wind-driven currents have an approximately exponential profile. These two models are combined to estimate the current profiles

    In situ XPS investigation of Pt(Sn)/Mg(Al)O catalysts during ethane dehydrogenation experiments

    Get PDF
    Calcined hydrotalcite with or without added metal (Mg(Al)O, Pt/Mg(Al)O and Pt,Sn/Mg(Al)O) have been investigated with in situ X-ray Photoelectron Spectroscopy (XPS) during ethane dehydrogenation experiments. The temperature in the analysis chamber was 450oC and the gas pressure was in the range 0.3 – 1 mbar. Depth profiling of calcined hydrotalcite and platinum catalysts under reaction, oxidation and in hydrogen-water mixture was performed by varying the photon energy, covering an analysis depth of 10-21 Å. It was observed that the Mg/Al ratio in the Mg(Al)O crystallites does not vary significantly in the analysis depth range studied. This result indicates that Mg and Al are homogeneously distributed in the Mg(Al)O crystallites. Catalytic tests have shown that the initial activity of a Pt,Sn/Mg(Al)O catalyst increases during an activation period consisting of several cycles of reduction - dehydrogenation - oxidation. The Sn/Mg ratio in a Pt,Sn/Mg(Al)O catalyst was followed during several such cycles, and was found to increase during the activation period, probably due to a process where tin spreads over the carrier material and covers an increasing fraction of the Mg(Al)O surface. The results further indicate that spreading of tin occurs under reduction conditions. A PtSn2 alloy was studied separately. The surface of the alloy was enriched in Sn during reduction and reaction conditions at 450°C. Binding energies were determined and indicated that Sn on the particle surface is predominantly in an oxidized state under reaction conditions, while Pt and a fraction of Sn is present as a reduced Pt-Sn alloy

    Nonlinear corrections to the DGLAP equations in view of the HERA data

    Get PDF
    The effects of the first nonlinear corrections to the DGLAP evolution equations are studied by using the recent HERA data for the structure function F2(x,Q2)F_2(x,Q^2) of the free proton and the parton distributions from CTEQ5L and CTEQ6L as a baseline. By requiring a good fit to the H1 data, we determine initial parton distributions at Q02=1.4Q_0^2=1.4 GeV2^2 for the nonlinear scale evolution. We show that the nonlinear corrections improve the agreement with the F2(x,Q2)F_2(x,Q^2) data in the region of x3105x\sim 3\cdot 10^{-5} and Q21.5Q^2\sim 1.5 GeV2^2 without paying the price of obtaining a worse agreement at larger values of xx and Q2Q^2. For the gluon distribution the nonlinear effects are found to play an increasingly important role at x\lsim 10^{-3} and Q^2\lsim10 GeV2^2, but rapidly vanish at larger values of xx and Q2Q^2. Consequently, contrary to CTEQ6L, the obtained gluon distribution at Q2=1.4Q^2=1.4 GeV2^2 shows a power-like growth at small xx. Relative to the CTEQ6L gluons, an enhancement up to a factor 6\sim6 at x=105x=10^{-5}, Q02=1.4Q_0^2=1.4 GeV2^2 reduces to a negligible difference at Q^2\gsim 10 GeV2^2.Comment: 13 pages, 5 eps-figures; revision: references added, Fig. 3 revise

    Fractal Inspired Models of Quark and Gluon Distributions and Longitudinal Structure Function FL(x, Q2) at small x

    Full text link
    In recent years, Fractal Inspired Models of quark and gluon densities at small x have been proposed. In this paper, we investigate longitudinal structure function F-L (x, Q2) within this approach. We make predictions using the QCD based approximate relation between the longitudinal structure function and the gluon density. As the Altarelli-Martinelli equation for the longitudinal structure function cannot be applied to Model I due to the presence of a singularity in the Bjorken x-space we consider Model II only. The qualitative feature of the prediction of Model II is found to be compatible with the QCD expectation.Comment: 11 pages, 4 figures, Accepted for publication on 10-07-2010 in Indian Journal of Physic

    Nanoscale inclusions in the phonon glass thermoelectric material

    Get PDF
    We have investigated the thermoelectric material Zn 4 Sb 3 using transmission electron microscopy (TEM). Nanoscale inclusions with a diameter of about 10 nm were observed, constituting on the order of 1% by volume of the material. Studies using energy filtered imaging, electron diffraction, and high-angle annular dark-field STEM indicate that the inclusions consist of Zn. These inclusions are expected to scatter the medium and long-wavelength phonons effectively, thus contributing to phonon glass behavior which results in the exceptionally low thermal conductivity for this thermoelectric material

    Measurement of the proton and deuteron structure functions, F2p and F2d, and of the ratio sigma(L)/sigma(T)

    Get PDF
    The muon-proton and muon-deuteron inclusive deep inelastic scattering cross sections were measured in the kinematic range 0.002 < x < 0.60 and 0.5 < Q2 < 75 GeV2 at incident muon energies of 90, 120, 200 and 280 GeV. These results are based on the full data set collected by the New Muon Collaboration, including the data taken with a small angle trigger. The extracted values of the structure functions F2p and F2d are in good agreement with those from other experiments. The data cover a sufficient range of y to allow the determination of the ratio of the longitudinally to transversely polarised virtual photon absorption cross sections, R= sigma(L)/sigma(T), for 0.002 < x < 0.12 . The values of R are compatible with a perturbative QCD prediction; they agree with earlier measurements and extend to smaller x.Comment: In this replacement the erroneously quoted R values in tables 3-6 for x>0.12, and R1990 values in tables 5-6 for all x, have been corrected, and the cross sections in tables 3-4 have been adapted. Everything else, including the structure functions F2, remained unchanged. 22 pages, LateX, including figures, with two .sty files, and three separate f2tab.tex files for the F2-tables. Accepted for publication in Nucl.Phys.B 199

    Measurement of the diffractive structure function in deep inelastic scattering at HERA

    Full text link
    This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in epep interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of \xpom, the momentum fraction lost by the proton, of β\beta, the momentum fraction of the struck quark with respect to \xpom, and of Q2Q^2. The \xpom dependence is consistent with the form \xpoma where a = 1.30 ± 0.08 (stat)  0.14+ 0.08 (sys)a~=~1.30~\pm~0.08~(stat)~^{+~0.08}_{-~0.14}~(sys) in all bins of β\beta and Q2Q^2. In the measured Q2Q^2 range, the diffractive structure function approximately scales with Q2Q^2 at fixed β\beta. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil
    corecore