1,032 research outputs found

    Two-jet inclusive cross sections in heavy-ion collisions in the perturbative QCD

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    In the framework of perturbative QCD, double inclusive cross sections for high ptp_t parton production in nucleus-nucleus collisions are computed with multiple rescattering taken into account. The induced long-range correlations between numbers of jets at forward and backward rapidities are found to reach 10÷2010\div 20% for light nuclei at s=200\sqrt{s}=200 GeV/c and to be suppressed for heavy nuclei and LHC energies.Comment: 17 pages, 6 figures. V2: Major revision

    A search for ferromagnetism in transition-metal-doped piezoelectric ZnO

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    We present the results of a computational study of ZnO in the presence of Co and Mn substitutional impurities. The goal of our work is to identify potential ferromagnetic ground states within the (Zn,Co)O or (Zn,Mn)O material systems that are also good candidates for piezoelectricity. We find that, in contrast to previous results, robust ferromagnetism is not obtained by substitution of Co or Mn on the Zn site, unless additional carriers (holes) are also incorporated. We propose a practical scheme for achieving such pp-type doping in ZnO

    KamLAND, solar antineutrinos and the solar magnetic field

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    In this work the possibility of detecting solar electron antineutrinos produced by a solar core magnetic field from the KamLAND recent observations is investigated. We find a scaling of the antineutrino probability with respect to the magnetic field profile in the sense that the same probability function can be reproduced by any profile with a suitable peak field value. In this way the solar electron antineutrino spectrum can be unambiguosly predicted. We use this scaling and the negative results indicated by the KamLAND experiment to obtain upper bounds on the solar electron antineutrino flux. We get ϕνˉ<3.8×103ϕ(8B)\phi_{\bar\nu}<3.8\times 10^{-3}\phi(^8B) at 95% CL. For 90% CL this becomes ϕνˉ<3.4×103ϕ(8B)\phi_{\bar\nu}<3.4\times 10^{-3}\phi(^8B), an improvement by a factor of 3-5 with respect to existing bounds. These limits are independent of the detailed structure of the magnetic field in the solar interior. We also derive upper bounds on the peak field value which are uniquely determined for a fixed solar field profile. In the most efficient antineutrino producing case, we get (95% CL) an upper limit on the product of the neutrino magnetic moment by the solar field μB<2.8×1019\mu B< 2.8\times 10^{-19} MeV or B04.9×107GB_0 \leq 4.9 \times 10^7 G for μν=1012μB\mu_\nu=10^{-12}\mu_B.Comment: 15 pages. References corrected. Minor changes in the tex

    Thermal Casimir effect in ideal metal rectangular boxes

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    The thermal Casimir effect in ideal metal rectangular boxes is considered using the method of zeta functional regularization. The renormalization procedure is suggested which provides the finite expression for the Casimir free energy in any restricted quantization volume. This expression satisfies the classical limit at high temperature and leads to zero thermal Casimir force for systems with infinite characteristic dimensions. In the case of two parallel ideal metal planes the results, as derived previously using thermal quantum field theory in Matsubara formulation and other methods, are reproduced starting from the obtained expression. It is shown that for rectangular boxes the temperature-dependent contribution to the electromagnetic Casimir force can be both positive and negative depending on side lengths. The numerical computations of the scalar and electromagnetic Casimir free energy and force are performed for cubesComment: 10 pages, 4 figures, to appear in Europ. Phys. J.

    Vasorelaxant effect of a phenylethylamine analogue based on schwarzinicine A an alkaloid isolated from the leaves of Ficus schwarzii

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    N-Phenethyl-1-phenyl-pentan-3-amine (1) is a new compound synthesised as a simplified analogue of schwarzinicine A (2), a natural compound extracted from Ficus schwarzii. Compound 1 differs from compound 2 due to its structural simplification, featuring two phenyl rings without methoxy substitution, as opposed to compound 2, which possesses three 3,4-dimethoxy aromatic rings. Our previous research findings highlighted the calcium-inhibitory effects of compound 2, but the mechanism of action for compound 1 remains unexplored, serving as the primary focus of this study. Building upon our earlier research, this study aimed to elucidate compound 1's calcium-modulating potential by using rat-isolated aortae in an organ bath set-up and HEK cells expressing hTRPC channels with the fluorometric assay to measure calcium influx. Compound 1 elicited a vasorelaxation response (Emax 111.4%) similar to its parent compound 2 (Emax 123.1%), and inhibited hTRPC3-, hTRPC4-, hTRPC5-, and hTRPC6-mediated calcium influx into HEK cells with IC50 values of 6, 2, 2, 5 µM, respectively. Compound 1 has a similar pharmacological profile as its parent compound 2, whereby it exerts a vasorelaxant effect by attenuating calcium influx and inhibits multiple TRPC channels

    Agro-materials : a bibliographic review

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    Facing the problems of plastic recycling and fossil resources exhaustion, the use of biomass to conceive new materials appears like a reasonable solution. Two axes of research are nowadays developed : on the one hand the synthesis of biodegradable plastics, whichever the methods may be, on the other hand the utilization of raw biopolymers, which is the object of this paper. From this perspective, the “plastic” properties of natural polymers, the caracteristics of the different classes of polymers, the use of charge in vegetable matrix and the possible means of improving the durability of these agro-materials are reviewed

    Solar Neutrinos: What We Have Learned

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    The four operating solar neutrino experiments confirm the hypothesis that the energy source for solar luminosity is hydrogen fusion. However, the measured rate for each of the four solar neutrino experiments differs significantly (by factors of 2.0 to 3.5) from the corresponding theoretical prediction that is based upon the standard solar model and the simplest version of the standard electroweak theory. If standard electroweak theory is correct, the energy spectrum for \b8 neutrinos created in the solar interior must be the same (to one part in 10510^5) as the known laboratory \b8 neutrino energy spectrum. Direct comparison of the chlorine and the Kamiokande experiments, both sensitive to \b8 neutrinos, suggests that the discrepancy between theory and observations depends upon neutrino energy, in conflict with standard expectations. Monte Carlo studies with 1000 implementations of the standard solar model confirm that the chlorine and the Kamiokande experiments cannot be reconciled unless new weak interaction physics changes the shape of the \b8 neutrino energy spectrum. The results of the two gallium solar neutrino experiments strengthen the conclusion that new physics is required and help determine a relatively small allowed region for the MSW neutrino parameters.Comment: LaTeX file, 19 pages. For hardcopy with figures contact [email protected]. Institute for Advanced Study number AST 93/6

    Rare Charm Decays in the Standard Model and Beyond

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    We perform a comprehensive study of a number of rare charm decays, incorporating the first evaluation of the QCD corrections to the short distance contributions, as well as examining the long range effects. For processes mediated by the cu+c\to u\ell^+\ell^- transitions, we show that sensitivity to short distance physics exists in kinematic regions away from the vector meson resonances that dominate the total rate. In particular, we find that Dπ+D\to\pi\ell^+\ell^- and Dρ+D\to\rho\ell^+\ell^- are sensitive to non-universal soft-breaking effects in the Minimal Supersymmetric Standard Model with R-parity conservation. We separately study the sensitivity of these modes to R-parity violating effects and derive new bounds on R-parity violating couplings. We also obtain predictions for these decays within extensions of the Standard Model, including extensions of the Higgs, gauge and fermion sectors, as well as models of dynamical electroweak symmetry breaking.Comment: 45 pages, typos fixed, discussions adde

    D* Production in Deep Inelastic Scattering at HERA

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    This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel D+(D0Kπ+)π+D^{*+}\to (D^0 \to K^- \pi^+) \pi^+ (+ c.c.) has been used in the study. The e+pe^+p cross section for inclusive D^{*\pm} production with 5<Q2<100GeV25<Q^2<100 GeV^2 and y<0.7y<0.7 is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {1.3<pT(D±)<9.01.3<p_T(D^{*\pm})<9.0 GeV and η(D±)<1.5| \eta(D^{*\pm}) |<1.5}. Differential cross sections as functions of p_T(D^{*\pm}), η(D±),W\eta(D^{*\pm}), W and Q2Q^2 are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and η\eta(D^{*\pm}), the charm contribution F2ccˉ(x,Q2)F_2^{c\bar{c}}(x,Q^2) to the proton structure function is determined for Bjorken xx between 2 \cdot 104^{-4} and 5 \cdot 103^{-3}.Comment: 17 pages including 4 figure
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