5,421 research outputs found

    Measurement of the Proton Structure Function F2F_2 and the Extraction of the Gluon Density at Small xx

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    In the following article we describe our measurement of the proton structure function F2F_2 and of the gluon momentum density xgxg in epep collisions with the ZEUS detector at HERA in 1993. The results for F2F_2 confirm our measurement from the previous year but with much higher statistics and show a strong rise towards small xx. The gluon momentum density xgxg is measured for the first time in a range from 4‚čÖ10‚ąí4<x<10‚ąí2 4 \cdot 10^{-4} < x < 10^{-2} at a value of Q2=20Q^2 = 20~GeV2^2.Comment: 7 pages uuencode-gzipped postscript. LaTeX and individual figures can be found on http://ppewww.ph.gla.ac.uk/preprints/95/01/fleck.shtm

    Tungsten wire-reinforced superalloys for 1093 C (2000 F) turbine blade applications

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    Various combinations of fiber and matrix materials were fabricated and evaluated for the purpose of selecting a specific combination that exhibited the best overall properties for a turbine blade application. A total of seven matrix alloys, including Hastelloy X, Nimonic 80A, Inconel 600, Inconel 625, IN-102, FeCrA1Y, were investigated reinforced with either 218CS tungsten, or W-Hf-C fibers. Based on preliminary screening studies, FeCrA1Y, Inconel 600 and Inconel 625 matrix composites systems were selected for extended thermal cycle tests and for property evaluations which included stress rupture, impact, and oxidation resistance. Of those investigated, the FeCrA1Y matrix composite system exhibited the best overall properties required for a turbine blade application. The W-Hf-C/FeCrA1Y system was selected for further property evaluation. Tensile strength values of up to 724 MPa (105,000 psi) were obtained for this material at 982 C and 607 MPa at 1093 C

    Prospective Analysis Spin- and CP-sensitive Variables in H -> ZZ -> l_1 l_1 l_2 l_2 with Atlas

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    A possibility to prove spin and CP-eigenvalue of a Standard Model (SM) Higgs boson is presented. We exploit angular correlations in the subsequent decay H -> ZZ -> 4l (muons or electrons) for Higgs masses above 200 GeV. We compare the angular distributions of the leptons originating from the SM Higgs with those resulting from decays of hypothetical particles with differing quantum numbers. We restrict our analysis to the use of the Atlas-detector which is one of two multi-purpose detectors at the upcoming 14 TeV proton-proton-collider (LHC) at CERN. By applying a fast simulation of the Atlas detector it can be shown that these correlations will be measured sufficiently well that consistency with the spin-CP hypothesis 0+ of the Standard Model can be verified and the 0- and 1+- can be ruled out with an integrated luminosity of 100 fb^-1.Comment: 25 pages, 9 figures Version 2: Minor changes made as requested by Atlas referee and Springer editor. Added a chapter where background subtraction is detaile

    Spectra of Doubly Heavy Quark Baryons

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    Baryons containing two heavy quarks are treated in the Born-Oppenheimer approximation. Schr\"odinger equation for two center Coulomb plus harmonic oscillator potential is solved by the method of ethalon equation at large intercenter separations. Asymptotical expansions for energy term and wave function are obtained in the analytical form. Using those formulas, the energy spectra of doubly heavy baryons with various quark compositions are calculated analytically.Comment: 19 pages, latex2e, published at PRC61(2000)04520

    One-dimensional metallic behavior of the stripe phase in La2‚ąíx_{2-x}Srx_xCuO4_4

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    Using an exact diagonalization method within the dynamical mean-field theory we study stripe phases in the two-dimensional Hubbard model. We find a crossover at doping őī‚ČÉ0.05\delta\simeq 0.05 from diagonal stripes to vertical site-centered stripes with populated domain walls, stable in a broad range of doping, 0.05<őī<0.170.05<\delta<0.17. The calculated chemical potential shift ‚ąĚ‚ąíőī2\propto -\delta^2 and the doping dependence of the magnetic incommensurability are in quantitative agreement with the experimental results for doped La2‚ąíx_{2-x}Srx_xCuO4_4. The electronic structure shows one-dimensional metallic behavior along the domain walls, and explains the suppression of spectral weight along the Brillouin zone diagonal.Comment: 4 pages, 4 figure

    Gehalte an Makro- und Mikroelementen sowie Zuckern in Möhren aus der biologisch-dynamischen und konventionellen landwirtschaftlichen Praxis

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    Mit dem Ziel, die Marktsituation f√ľr den Konsumenten hinsichtlich der Produktqualit√§t zu beschreiben, wurden Proben von Speisem√∂hren des Anbaujahres 1996 aus der biologisch-dynamischen (n=57) und konventionellen (n=18) Praxis gesammelt. Ermittelt wurden unter Anderem: - Makroelemente: P, K, Na, Cl, Mg, S - Mikroelemente: Fe, B, Zn, Mn, Cu, Pb - Zucker: D-Glu, D-Fru, Sa

    Carbon sequestration in Mediterranean ecosystems: critical aspects related to plant respiration, wildfires and nitrogen budget

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    La producci√≥ prim√†ria neta (NPP) de la biosfera est√† limitada pels baixos nivells actuals de CO2 atmosf√®ric (Ca). Per conseq√ľent, l'augment de Ca degut a l'activitat humana, considerat la causa principal del canvi clim√†tic, s'hauria de traduir en un augment de la NPP i, per tant, en un augment del segrestament de Ca a la biomassa. Els augments de NPP i del segrestament de Ca ja s√≥n detectables en boscos boreals i tropicals. L'augment de Ca produeix tamb√© una disminuci√≥ de la respiraci√≥ vegetal ?un 17 % de mitjana?, fet que podria provocar que el segrestament de Ca fos m√©s gran que no s'havia previst. Aquests resultats han fet que alguns autors ofereixin visions for√ßa optimistes sobre la capacitat dels ecosistemes terrestres per compensar l'exc√©s de Ca. No obstant aix√≤, l'augment de Ca no es tradueix nom√©s en un augment de la NPP (diferent per a cada esp√®cie), sin√≥ tamb√© en canvis en la morfologia de la planta (tamb√© diferents per a cada esp√®cie), que comportaran canvis en els patrons d'ocupaci√≥ de l'espai, que fan dif√≠cil predir en quin sentit canviar√† la NPP a llarg termini en l'ecosistema sencer. No √©s gens clar que aquestes previsions optimistes siguin aplicables als ecosistemes terrestres mediterranis, en els quals la sequera ?principal factor limitant de la NPP? s'espera que s'agreugi en un futur, com a conseq√ľ√®ncia del canvi clim√†tic. L'agreujament de la sequera es pot traduir en un augment del risc d'incendi, fet que pot conduir els ecosistemes mediterranis a una situaci√≥ de gran inestabilitat, en cas que la periodicitat i la intensitat dels focs superin llur capacitat de recuperaci√≥ (per germinaci√≥ o rebrot). L'incendi implica p√®rdues importants de N i P per volatilitzaci√≥; tamb√© provoca un fort augment de la disponibilitat de nutrients (sobretot N) i, doncs, un augment de la fertilitat del s√≤l. Moltes esp√®cies mediterr√†nies, i en concret l'alzina (Quercus ilex), tenen una gran capacitat d'acumular N en √≤rgans basals, probablement per facilitar un rebrot r√†pNet primary production (NPP) in the biosphere is limited by the current low atmospheric CO2 concentration (Ca). Hence, the increase in Ca due to anthropogenic activities, which is thought to be the main cause of climate change, is expected to result in an increase in NPP, and therefore in an increased Ca sequestration in the biomass. Increases in NPP and Ca sequestration in the biota are already detectable in boreal and tropical forests. Increased Ca results in a decrease in plant respiration ?on average, about 17%?, and therefore the increase in Ca sequestration could be higher than previously assumed. This has led some authors to publish highly optimistic views about the capacity of terrestrial ecosystems to compensate for the excess of Ca. Nevertheless, increased Ca results not only in an increase in NPP (different for every plant species), but also in changes in plant morphology (also different for every plant species); these will result in changes in the patterns of space occupation by plants, which make it difficult to predict how the NPP will change in the long term, at a whole-ecosystem level. It is not clear that such optimistic views can be applied to Mediterranean terrestrial ecosystems, in which drought ?the main constraint for NPP? is expected to increase in the future as a result of climate change. Increased drought is expected to lead to a greater risk of wildfires, which can generate a highly unstable situation in the ecosystem if the periodicity and intensity of fire events surpasses its capacity to recover (either by resprouting or seeding). Wildfires cause significant losses of N and P by volatilization. They also result in a strong increase in the availability of nutrients (mainly N), and hence an increase in soil fertility

    Quantum Dot Potentials: Symanzik Scaling, Resurgent Expansions and Quantum Dynamics

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    This article is concerned with a special class of the ``double-well-like'' potentials that occur naturally in the analysis of finite quantum systems. Special attention is paid, in particular, to the so-called Fokker-Planck potential, which has a particular property: the perturbation series for the ground-state energy vanishes to all orders in the coupling parameter, but the actual ground-state energy is positive and dominated by instanton configurations of the form exp(-a/g), where a is the instanton action. The instanton effects are most naturally taken into account within the modified Bohr-Sommerfeld quantization conditions whose expansion leads to the generalized perturbative expansions (so-called resurgent expansions) for the energy values of the Fokker-Planck potential. Until now, these resurgent expansions have been mainly applied for small values of coupling parameter g, while much less attention has been paid to the strong-coupling regime. In this contribution, we compare the energy values, obtained by directly resumming generalized Bohr-Sommerfeld quantization conditions, to the strong-coupling expansion, for which we determine the first few expansion coefficients in powers of g^(-2/3). Detailed calculations are performed for a wide range of coupling parameters g and indicate a considerable overlap between the regions of validity of the weak-coupling resurgent series and of the strong-coupling expansion. Apart from the analysis of the energy spectrum of the Fokker-Planck Hamiltonian, we also briefly discuss the computation of its eigenfunctions. These eigenfunctions may be utilized for the numerical integration of the (single-particle) time-dependent Schroedinger equation and, hence, for studying the dynamical evolution of the wavepackets in the double-well-like potentials.Comment: 13 pages; RevTe

    Spectroscopy of doubly charmed baryons: őěcc+\Xi_{cc}^{+} and őěcc++\Xi_{cc}^{++}

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    Using the quark-diquark approximation in the framework of Buchm\" uller-Tye potential model, we investigate the spectroscopy of doubly charmed baryons: őěcc++\Xi_{cc}^{++} and őěcc+\Xi_{cc}^{+}. Our results include the masses, parameters of radial wave functions of states with the different excitations of both diquark and light quark-diquark system. We calculate the values of fine and hyperfine splittings of these levels and discuss some new features, connected to the identity of heavy quarks, in the dynamics of hadronic and radiative transitions between the states of these baryons.Comment: 10 pages, Latex file, 1 fig, corrected some typo

    Field theoretic description of charge regulation interaction

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    In order to find the exact form of the electrostatic interaction between two proteins with dissociable charge groups in aqueous solution, we have studied a model system composed of two macroscopic surfaces with charge dissociation sites immersed in a counterion-only ionic solution. Field-theoretic representation of the grand canonical partition function is derived and evaluated within the mean-field approximation, giving the Poisson-Boltzmann theory with the Ninham-Parsegian boundary condition. Gaussian fluctuations around the mean-field are then analyzed in the lowest order correction that we calculate analytically and exactly, using the path integral representation for the partition function of a harmonic oscillator with time-dependent frequency. The first order (one loop) free energy correction gives the interaction free energy that reduces to the zero-frequency van der Waals form in the appropriate limit but in general gives rise to a mono-polar fluctuation term due to charge fluctuation at the dissociation sites. Our formulation opens up the possibility to investigate the Kirkwood-Shumaker interaction in more general contexts where their original derivation fails.Comment: 12 pages, 9 figures, submitted to EPJ
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