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  • Articles  (616,962)
  • Elsevier  (415,309)
  • Springer  (173,527)
  • American Institute of Physics (AIP)  (26,481)
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  • 2000-2004  (616,962)
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  • 101
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We deepen the study of the so-called “silver channel” $\nu_e \to \nu_\tau$ [1] and of its relevance to solve some of the ambiguities that can arise in the simultaneous measurement of $(\theta_{13},\delta)$ at the Neutrino Factory by presenting in full detail the characteristics of the considered OPERA-like detector and the experimental treatment of the different backgrounds and signals. Furthermore, we perform a detailed study of the systematic errors associated both with the OPERA-like and the magnetized-iron detectors and their effects on the sensitivity. Finally, we also apply a refined statistical analysis of the simulated events based on the frequentist approach.
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  • 102
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    The European physical journal 33 (2004), S. 511-521 
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    Topics: Physics
    Notes: Abstract. The rates of inclusive photo- and electroproduction of the $\eta_c$ meson: $\gamma(^*) + p \to \eta_c + X$ are calculated in the triple Regge region, integrated over the diffractive mass X. For the Regge exchanges we use the hard pomeron and odderon, both being calculated in the framework of perturbative QCD. The integrated cross section depends upon the coupling of the BFKL pomeron to two C = -1 odderons, and it is found to be of the order of 60 pb for photoproduction and 1.5 pb at Q 2 = 25 GeV2.
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  • 103
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    The European physical journal 33 (2004), S. 543-553 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. We determine the relative pion mass shift $M_\pi(L)/M_\pi-1$ due to the finite spatial extent L of the box by means of two-flavor chiral perturbation theory and the one-particle Lüscher formula. We use as input the expression for the infinite volume $\pi \pi$ forward scattering amplitude up to next-to-next-to-leading order and can therefore control the convergence of the chiral series. A comparison to the full leading order chiral expression for the pion mass in finite volume allows us to check the size of subleading terms in the large-L expansion.
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  • 104
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    The European physical journal 33 (2004), S. 495-503 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Charm mesons produced in nucleus-nucleus collisions are expected to be less attenuated (quenched) by the medium than hadrons containing only light quarks, since radiative energy loss of heavy quarks should be reduced by the ‘dead-cone’ effect. We start from a published energy-loss model to derive the quenching for D mesons at the LHC, introducing an approximation of the dead-cone effect and employing a Glauber-based description of the geometry of central Pb-Pb collisions to estimate the in-medium path lengths of c quarks. We show that the exclusive reconstruction of ${\rm D}^0\to{\rm K\pi}^ + $ decays in ALICE allows to measure the nuclear modification factor of the D mesons transverse momentum distribution and the D/charged hadrons ratio and, thus, to investigate the energy loss of c quarks.
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  • 105
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    The European physical journal 34 (2004), S. 33-40 
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  • 106
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    The European physical journal 34 (2004), S. 25-31 
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  • 107
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    The European physical journal 34 (2004), S. 57-60 
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    Topics: Physics
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  • 108
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    The European physical journal 34 (2004), S. 371-376 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. A very economic model of generating small neutrino masses is the Zee model. This model has been studied extensively in the literature with most of the studies concentrated on the simplest version of the model, where all diagonal entries in the mass matrix are zero. SNO, and KamLAND data disfavor this simple version, but only when one also combines information from atmospheric and K2K data can one rule out this model with a high confidence level. We show that the simplest version of the Zee model is ruled out at $3\sigma$ level. The original Zee model, however, contains more than enough freedom to satisfy constraints from the data. We propose a new form of mass matrix by a naturalness consideration. This new form of the mass matrix is consistent with all experimental data. It predicts that $m_{\nu_3} = 0$ , and $\tan^2\theta_{\mathrm {{solar}}}$ increases and $\sin^2\theta_{\mathrm {{atm}}}$ decreases with |V e3|. For $\tan^2\theta_{\mathrm {{solar}}}$ and $\sin^2\theta_{\mathrm {{atm}}}$ to be in their $1\sigma$ allowed regions, |V e3| is sizeable but can be set below the 90% C.L. upper bound.
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  • 109
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    The European physical journal 34 (2004), S. 277-284 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. We present a next-to-leading order calculation of the cross section for the leptoproduction of large- $E_{\bot}$ hadrons and we compare our predictions with H1 data on the forward production of ${\rm\pi}^0$ . We find large higher order corrections and an important sensitivity to the renormalization and factorization scales. These large corrections are shown to arise in part from BFKL-like diagrams at the lowest order.
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  • 110
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. We analyze the pion electromagnetic, charged-current, and $\pi\gamma$ transition form factors at timelike momentum transfers q, $q^2 = s\le 1.4$ GeV2, using a dispersion approach. We discuss in detail the propagator matrix of the photon-vector meson system and define certain reduced amplitudes, or vertex functions, describing the coupling of this system to final states. We then apply the derived analytic expressions to the analysis of the recent $e^ + e^-\to \pi^ + \pi^-$ , $\tau^-\to \pi^-\pi^0\nu_\tau$ , and $e^ + e^-\to \pi^0\gamma$ data. We find the reduced amplitudes for the coupling of the photon and vector mesons to two pseudoscalars to be constant, independent of s, in the range considered, indicating a “freezing” of the amplitudes for $s\le 1$ GeV. The fit to the form factor data leads to the following values of the Breit-Wigner resonance masses $m_{\rho^-} = 775.3\pm 0.8$ MeV, $m_{\rho^0} = 773.8\pm 0.6$ MeV and $m_\omega = 782.43\pm 0.05$ MeV, where the errors are only statistical.
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  • 111
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    The European physical journal 33 (2004), S. 477-493 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. Dijet production in deep inelastic ep scattering is investigated in the region of low values of the Bjorken-variable x (10-4 〈 x 〈 10-2) and low photon virtualities Q 2 (5 〈 Q 2 〈 100 GeV2). The measured dijet cross sections are compared with perturbative QCD calculations in next-to-leading order. For most dijet variables studied, these calculations can provide a reasonable description of the data over the full phase space region covered, including the region of very low x. However, large discrepancies at low x and low Q 2 are observed for events with small separation in azimuth between the two highest transverse momentum jets. This region of phase space is described better by predictions based on the CCFM evolution equation, which incorporates k t factorized unintegrated parton distributions. A reasonable description can be also obtained using the Color Dipole Model or models incorporating virtual photon structure.
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  • 112
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    The European physical journal 33 (2004), S. 523-536 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Various rescattering sources are analyzed in the context of the SU(3) flavor symmetry. In particular, the possibility to account for intermediate charm at the hadronic level in B to PP is thoroughly investigated. Then, the rescattering sources are compared in light of recent decay measurements of B to two charmless pseudoscalars, with emphasis on the size of strong phases and on patterns of direct CP-asymmetries.
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  • 113
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    The European physical journal 33 (2004), S. 537-542 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. We have constructed the bag model having a central constant color field. The motion of the quark is studied in this bag and the Dirac equation is solved for it. The energy spectrum found has a branching due to the interaction of the quarks with the color background. It is pointed out that this model can be applied for taking into account, in the mass spectrum of the hadrons, the coupling of the constituent quarks with the gluon condensation as the interaction with the color background.
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  • 114
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    The European physical journal 33 (2004), S. 561-590 
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    Topics: Physics
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  • 115
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    The European physical journal 34 (2004), S. 419-427 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. We derive the Feynman rules of the standard model in the axial gauge. After this we prove that the fields $\phi_W$ and $\phi_Z$ do not correspond to physical particles. As a consequence, these fields cannot appear as incoming or outgoing lines in Feynman graphs. We then calculate the contribution of these fields in the case of a particular decay mode of the top quark.
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  • 116
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    The European physical journal 34 (2004), S. 439-445 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. Finite temperature Euclidean SU(2) lattice gauge fields close to the deconfinement phase transition are subjected to cooling. We find relatively stable or absolutely stable configurations with an action below the one-instanton action $S_{\mathrm {{inst}}} = 2\pi^2$ both in the deconfinement and the confinement phases. In this paper we attempt to interpret these lowest action configurations. Their action is purely magnetic and amounts to $S/S_{\mathrm {{inst}}} \approx N_{\mathrm {t}}/N_{\mathrm {s}}$ , where N t (N s) is the timelike (spacelike) lattice size, while the topological charge vanishes. In the confined phase part of the corresponding lattice configurations turns out to be absolutely stable with respect to the cooling process in which case Abelian projection reveals a homogeneous, purely Abelian magnetic field closed over the “boundary” in one of the spatial directions. Referring to the dyonic structure established for the confinement phase near T c and based on the observation made for this phase that such events below the instanton action S inst emerge from dyon-antidyon annihilation, the question of the stability (metastability) is discussed for both phases. The hypothetically different dyonic structure of the deconfinement phase, inaccessible by cooling, could explain the metastability.
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  • 117
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    The European physical journal 35 (2004), S. 53-65 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. We present a detailed numerical study of the K e3 decays to ${\cal O}(p^6, (m_d-m_u)p^2, e^2 p^2)$ in chiral perturbation theory with virtual photons and leptons. We describe the extraction of the CKM matrix element |V us | from the experimental K e3 decay parameters. We propose a consistency check of the K + e3 and K 0 e3 data that is largely insensitive to the dominating theoretical uncertainties, in particular the contributions of ${\cal O}(p^6)$ . Our analysis is highly relevant in view of the recent high statistics measurement of the K + e3 branching ratio by E865 at Brookhaven which does not indicate any significant deviation from CKM unitarity but rather a discrepancy with the present K 0 e3 data.
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  • 118
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    The European physical journal 35 (2004), S. 67-98 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. A second workshop on small-x physics, within the Small-x Collaboration, was held in Lund in June 2002 with the aim of over-viewing recent theoretical progress in this area and summarizing the experimental status.
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  • 119
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    The European physical journal 35 (2004), S. 1-20 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Approximately 438 pb-1 of e + e- data from the OPAL detector, taken with the LEP collider running at centre-of-mass energies of 192-209 GeV, are analyzed to search for evidence of chargino pair production, ${\mathrm{e}}^ + {\mathrm{e}}^-\to\tilde\chi^ + _1\tilde\chi^-_1$ , or neutralino associated production, ${\mathrm{e}}^ + {\mathrm{e}}^-\to\tilde\chi^0_2\tilde\chi^0_1$ . Limits are set at the 95% confidence level on the product of the cross-section for the process ${\mathrm{e}}^ + {\mathrm{e}}^-\to\tilde\chi^ + _1\tilde\chi^-_1$ and its branching ratios to topologies containing jets and missing energy, or jets with a lepton and missing energy, and on the product of the cross-section for ${\mathrm{e}}^ + {\mathrm{e}}^-\to\tilde\chi^0_2\tilde\chi^0_1$ and its branching ratio to jets. R-parity conservation is assumed throughout this paper. When these results are interpreted in the context of the Constrained Minimal Supersymmetric Standard Model, limits are also set on the masses of the $\tilde\chi^{\pm}_1, \tilde\chi^0_1$ and $\tilde\chi^0_2$ , and regions of the parameter space of the model are ruled out. Nearly model-independent limits are also set at the 95% confidence level on $\sigma({\mathrm{e}}^ + {\mathrm{e}}^-\to\tilde\chi^ + _1\tilde\chi^-_1)$ with the assumption that each chargino decays via a W boson, and on $\sigma({\mathrm{e}}^ + {\mathrm{e}}^-\to\tilde\chi^0_2\tilde\chi^0_1)$ with the $\tilde\chi^0_2$ assumed to decay via a Z0.
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  • 120
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    The European physical journal 35 (2004), S. 195-196 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. The experiment CPLEAR at CERN has measured an asymmetry between the transition rates of the antikaon to kaon process, and its reverse, kaon to antikaon. The present note shows, based on a criterion by Wolfenstein, that this observation constitutes direct evidence for time-reversal violation. Experiments at FNAL (KTEV) and CERN (NA48) have measured a T-odd asymmetry in the K L decay. Based on an analysis by Sehgal and van Leusen, it is demonstrated that this asymmetry is well described by a (hypothetical) kaon time evolution, which is time-reversal invariant.
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  • 121
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    The European physical journal 35 (2004), S. 221-222 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. In 1997 Diakonov, Petrov, and Polyakov, calculated the width of the exotic baryon that they called $\Theta^{ + }$ . The prediction, $\Gamma(\Theta^{ + })\lesssim 15$ MeV, has received considerable attention, especially in light of the narrowness of the experimentally reported $\Theta^{ + }$ resonance. However, there is an arithmetic error in their work: when corrected, the width estimate quoted in that paper should have been $\lesssim 30$ MeV.
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  • 122
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    The European physical journal 34 (2004), S. 367-369 
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    Topics: Physics
    Notes: Abstract. Dilepton production in heavy ion collisions in the intermediate mass region (IMR) has consistently shown an excess over theoretical estimates. An attempt to understand this discrepancy between the observed dilepton pairs and the theoretical estimate is made here through the production of the $\eta_c$ meson and estimates obtained by NRQCD calculations. We find that $\eta_c$ production offers a satisfactory quantitative picture for explaining the discrepancy.
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  • 123
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    The European physical journal 34 (2004), S. 393-398 
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    Topics: Physics
    Notes: Abstract. We introduce a master action in non-commutative space, out of which we obtain the action of the non-commutative Maxwell-Chern-Simons theory. Then, we look for the corresponding dual theory at both first and second order in the non-commutative parameter. At the first order, the dual theory happens to be, precisely, the action obtained from the usual commutative self-dual model by generalizing the Chern-Simons term to its non-commutative version, including a cubic term. Since this resulting theory is also equivalent to the non-commutative massive Thirring model in the large fermion mass limit, we remove, as a byproduct, the obstacles arising in the generalization to non-commutative space, and to the first non-trivial order in the non-commutative parameter, of the bosonization in three dimensions. Then, performing calculations at the second order in the non-commutative parameter, we explicitly compute a new dual theory which differs from the non-commutative self-dual model and, further, differs also from other previous results and involves a very simple expression in terms of ordinary fields. In addition, a remarkable feature of our results is that the dual theory is local, unlike what happens in the non-Abelian, but commutative case. We also conclude that the generalization to non-commutative space of bosonization in three dimensions is possible only when considering the first non-trivial corrections over ordinary space.
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  • 124
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    The European physical journal 36 (2004), S. 523-527 
    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. Two cosmological models with non-phantom matter having the same expansion of the universe as phantom cosmologies are constructed. The first model is characterized by the evolving gravitational “constant” G and a dark energy component with a non-conserved energy-momentum tensor. The second model includes two interacting components, the dark energy component and the matter component. Closed form solutions are obtained for the constant values of model parameters and constraints on the parameters of each model from cosmological observations are outlined. For both models it is explicitly shown how the components of each model produce the expansion of the universe characteristic of phantom cosmologies, despite the absence of phantom energy. These findings stress the interpretation of phantom energy as an effective description of the more complex dynamics of non-phantom matter.
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  • 125
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    The European physical journal 36 (2004), S. 413-423 
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    Topics: Physics
    Notes: Abstract. The cross section for anti-deuteron photoproduction is measured at HERA at a mean centre-of-mass energy of $W_{\gamma p} = 200$ GeV in the range 0.2 〈 p T /M 〈 0.7 and |y| 〈 0.4, where M, p T and y are the mass, transverse momentum and rapidity of the anti-deuteron in the HERA laboratory frame, respectively. The numbers of anti-deuterons per event are found to be similar in photoproduction to those in central proton-proton collisions at the CERN ISR but much lower than those in central Au-Au collisions at RHIC. The coalescence parameter B 2, which characterizes the likelihood of anti-deuteron production, is measured in photoproduction to be $0.010 \pm 0.002 \pm 0.001$ , which is much higher than in Au-Au collisions at a similar nucleon-nucleon centre-of-mass energy. No significant production of particles heavier than deuterons is observed and upper limits are set on the photoproduction cross sections for such particles.
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  • 126
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    The European physical journal 36 (2004), S. 503-507 
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    Topics: Physics
    Notes: Abstract. We study the possibility of observing an “invisible” Higgs boson in central exclusive diffractive production at the LHC. We evaluate the cross section using, as a simple example, the standard model with a heavy fourth generation, where the invisible decay mode $H \to \nu_4 \bar{\nu}_4$ dominates, with the heavy neutrino mass $M(\nu_4) \simeq 50$ GeV. We discuss the possible requirements on trigger conditions and the background processes.
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  • 127
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    The European physical journal 36 (2004), S. 515-522 
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    Topics: Physics
    Notes: Abstract. We consider the process $e^ + e^-\to\tilde{\chi}^ + _i\tilde{\chi}^-_j$ at a linear collider with transverse $e^{\pm}$ beam polarization. We investigate the influence of the CP phases on azimuthal asymmetries in $e^ + e^-\to\tilde{\chi}^ + _i\tilde{\chi}^-_j$ with subsequent two-body decays $\tilde{\chi}^-_j\to \tilde{\nu}_{\ell}\ell^-$ and $\tilde{\chi}^-_j\to W^-\tilde{\chi}^0_1$ . We show that triple product correlations involving the transverse $e^{\pm}$ beam polarization vanish if at least one subsequent chargino decay is not observed. We derive this result within the minimal supersymmetric standard model (MSSM) with complex parameters; however, it holds also in the general MSSM with SUSY flavor violation.
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  • 128
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    The European physical journal 36 (2004), S. 471-482 
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    Notes: Abstract. We show that configuration space techniques can be used to efficiently calculate the complete Laurent series $\varepsilon$ -expansion of sunrise-type diagrams to any loop order in D-dimensional space-time for any external momentum and for arbitrary mass configurations. For negative powers of $\varepsilon$ the results are obtained in analytical form. For positive powers of $\varepsilon$ including the finite $\varepsilon^0$ contribution the result is obtained numerically in terms of low-dimensional integrals. We present general features of the calculation and provide exemplary results up to five-loop order which are compared to available results in the literature.
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  • 129
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    The European physical journal 37 (2004), S. 307-313 
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    Notes: Abstract. We give the results for all the one-loop propagators, including finite parts, in the Coulomb gauge. In the finite parts we find new non-rational functions in addition to the single logarithms of the Feynman gauge. Of course, the two gauges must agree for any gauge invariant function.
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    The European physical journal 37 (2004), S. 293-298 
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    Notes: Abstract. Theoretically there are two approaches to predict single spin azimuthal asymmetries. One is to take transverse momenta of the partons into account by using transverse momentum dependent parton distributions, while another is to take asymmetries as twist-3 effects. The non-perturbative effects in these approaches are parameterized with different matrix elements, and predictions can be different. Recently, gauge invariant definitions of transverse momentum dependent parton distributions were derived. With these definitions it can be shown that there are relations between non-perturbative matrix elements in these two approaches. These relations may enable us to unify two approaches and to have unique predictions for single spin azimuthal asymmetries. In this letter we derive these relations by using time-reversal symmetry and show that even with these relations the single spin azimuthal asymmetry in a Drell-Yan process is predicted differently in different approaches.
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  • 131
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    Notes: Abstract. New accurate results of the neutron-proton spin-dependent total cross section difference $\Delta\sigma_{\mathrm L}(np)$ at the neutron beam kinetic energies 1.39, 1.69, 1.89 and 1.99 GeV are presented. Measurements were carried out in 2001 at the Synchrophasotron of the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research. A quasi-monochromatic neutron beam was produced by break-up of extracted polarized deuterons. The deuteron (and hence neutron) polarization direction was flipped every accelerator burst. The vertical neutron polarization direction was rotated onto the neutron beam direction and longitudinally (L) polarized neutrons were transmitted through a large proton L-polarized target. The target polarization vector was inverted after 1-2 days of measurements. The data were recorded for four different combinations of the beam and target parallel and antiparallel polarization directions at each energy. A fast decrease of $\Delta\sigma_{\mathrm L}(np)$ with increasing energy above 1.1 GeV was confirmed. The structure in the $\Delta\sigma_{\mathrm L}(np)$ energy dependence around 1.8 GeV, first observed from our previous data, seems to be well pronounced. The new results are also compared with model predictions and with phase shift analysis fits. The $\Delta\sigma_{\mathrm L}$ quantities for isosinglet state I = 0, deduced from the measured $\Delta\sigma_{\mathrm L}(np)$ values and the known $\Delta\sigma_{\mathrm L}(pp)$ data, are also given. The results were completed by the measurements of unpolarized total cross sections $\sigma_{0\mathrm{tot}}(np)$ at 1.3, 1.4 and 1.5 GeV and $\sigma_{0\mathrm{tot}}(n$ C) at 1.4 and 1.5 GeV. These data were obtained using the same apparatus and high intensity unpolarized deuteron beams were extracted either from the Synchrophasotron, or from the Nuclotron.
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  • 132
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    Notes: Abstract. The possibility to observe the medium-modified fragmentation of hard b quarks tagged by a leading muon in ultrarelativistic heavy ion collisions is analyzed. We have found that reasonable statistics, $\sim 10^4$ events per 1 month of LHC run with lead beams, can be expected for the realistic geometrical acceptance and kinematic cuts. The numerical estimates on the effect of the medium-induced softening b-jet fragmentation function are given.
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    The European physical journal 37 (2004), S. 379-389 
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    Notes: Abstract. We present explicit formulae for q-exponentials on quantum spaces which could be of particular importance in physics, i.e. the q-deformed Minkowski space and the q-deformed Euclidean space with two, three or four dimensions. Furthermore, these formulae can be viewed as 2-, 3- or 4-dimensional analogues of the well-known q-exponential function.
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    The European physical journal 37 (2004), S. 299-305 
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    Notes: Abstract. The longitudinal structure function in deep-inelastic scattering is one of the observables from which the gluon distribution can be unfolded. Consequently, this observable can be used to constrain the QCD dynamics at small x. In this work we compare the predictions of distinct QCD models with the recent experimental results for F L(x,Q 2) at small x and low Q 2 obtained by the H1 Collaboration. We focus mainly on the color dipole approach, selecting those models which include saturation effects. Such models are suitable at this kinematical region and also resum a wide class of higher-twist contributions to the observables. Therefore, we investigate the influence of these corrections to F L in the present region of interest.
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    The European physical journal 37 (2004), S. 323-333 
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    Notes: Abstract. Under the assumption that both light and heavy quarkonia populate approximately linear Regge trajectories with the requirements of additivity of intercepts and inverse slopes, the masses of different meson multiplets are estimated. The predictions derived from the quasi-linear Regge trajectories are in reasonable agreement with those given by many other references.
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    The European physical journal 37 (2004), S. 285-292 
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    Notes: Abstract. We perform a novel type of analysis of diffractive deep-inelastic scattering data, in which the input parton distributions of the pomeron are parameterised using the perturbative QCD expressions. In particular, we treat individually the components of the pomeron of different size. We are able to describe simultaneously both the recent ZEUS and H1 diffractive data. In addition to the usual two-gluon model for the perturbative pomeron, we allow for the possibility that it may be made from two sea quarks.
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    The European physical journal 38 (2004), S. 379-388 
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    Notes: Abstract. In the non-symmetric gravitational theory (NGT) the space-time metric $g_{\mu\nu}$ departs from the flat-space Minkowski form $\eta_{\mu\nu}$ in such a way that it is no longer symmetric, i.e. $g_{\mu\nu} \ne g_{\nu\mu}$ . We find that in the most conservative such scenario coupled to quantum field theory, which we call minimally non-symmetric quantum field theory (MNQFT), there are experimentally measurable consequences similar to those from non-commutative quantum field theory (NCQFT). This can be expected from the Seiberg-Witten map which has recently been interpreted as equating gauge theories on non-commutative space-times with those in a field-dependent gravitational background. In particular, in scattering processes such as the pair annihilation $e^ + e^- \to \gamma \gamma$ , both theories make the same striking prediction that the azimuthal cross section oscillates in $\phi$ . However the predicted number of oscillations differs in the two theories: MNQFT predicts between one and four, whereas NCQFT has no such restriction.
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    The European physical journal 38 (2004), S. 297-307 
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    Notes: Abstract. We calculate higher order corrections to the resolved component of the electroproduction cross section of large- $E_{\bot}$ hadrons. The parton distributions in the virtual photon are studied in detail and a NLO parametrization of the latter is proposed. The contribution of the resolved component to the forward production of large- $E_{\bot}$ hadrons is calculated and its connection with the BFKL cross section is discussed.
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    The European physical journal 38 (2004), S. 283-295 
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    Notes: Abstract. Double-lepton polarization asymmetries in $\Lambda_b \rightarrow \Lambda \ell^ + \ell^-$ decay are calculated using a general, model independent form of the effective Hamiltonian. The sensitivities of these asymmetries to the new Wilson coefficients are studied in detail. Furthermore, the correlations between averaged double-lepton polarization asymmetry and branching ratio are analyzed. It is shown that there exist certain regions of the new Wilson coefficients where new physics can be established by measuring the double-lepton polarization asymmetries only.
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    The European physical journal 38 (2004), S. 367-371 
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    Notes: Abstract. We develop a 5D mechanism, inspired by Campbell’s theorem, to explain the (neutral scalar field governed) evolution of the universe from an initially inflationary expansion that has a change of phase towards a decelerated expansion and thereafter evolves towards the present day observed accelerated (quintessential) expansion.
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    The European physical journal 38 (2004), S. 359-366 
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    Notes: Abstract. We study the μ problem and radiative electroweak symmetry breaking in an extended gauge mediation supersymmetry breaking model, in which the messenger fields are assumed to couple to the different singlet fields due to the discrete symmetry. Since the spectrum of superpartners is modified, the constraint from the μ problem can be relaxed in comparison with the ordinary GMSB at least from the viewpoint of radiative symmetry breaking. We study the consistency of the values of μ and $B_\mu$ with radiative electroweak symmetry breaking and also the mass spectrum of the superpartners.
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    The European physical journal 38 (2004), S. 267-276 
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    Notes: Abstract. The uncertainties in estimating the hadronic production of the B c meson are studied in the framework of the complete $\alpha_{\mathrm {s}}^4$ approach of perturbative QCD and the gluon-gluon fusion mechanism. Quantitative comparisons of the production at TEVATRON and LHC are made. Considering the detectors at TEVATRON and LHC, we have also estimated the production with proper kinematic cuts. Based on the results, we conclude that the experimental studies of the B c meson at the two colliders will be complementary and mutually stimulative. We find that as the CM energy is increasing from RUN-I to RUN-II at TEVATRON, the production cross section increases by about $20\%$ .
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    The European physical journal 38 (2004), S. 319-328 
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    Notes: Abstract. We calculate the nuclear cross section for vector meson exclusive photoproduction within the QCD color dipole picture and in the Regge approach. For the former approach, we have considered the phenomenological saturation model, whereas for the latter we use a model based on the dipole pomeron framework. Theoretical estimates for scattering on both light and heavy nuclei are given over a large range of energy.
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    The European physical journal 38 (2004), S. 349-357 
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    Notes: Abstract. The Higgs sector of the minimal nonlinear supersymmetric SU(5) model contains three mass parameters. Although these mass parameters are essentially free at the electroweak scale, they might have particular values if they evolve from a particular constraint at the GUT scale through the RG equations. By assuming a number of simple constraints on these mass parameters at the GUT scale, we obtain their values at the electroweak scale through the RG equations in order to investigate the phenomenological implications. Some of them are found to be consistent with the present experimental data.
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    The European physical journal 38 (2004), S. 329-334 
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    Notes: Abstract. We reconsider the volume source technique for the determination of flavor singlet quantities on the lattice. We point out a difficulty arising in the case of fermions in real representations of the gauge group and propose an improved version of the method (IVST) based on random gauge transformations of the background configuration. We compare the performance of IVST with the method based on stochastic estimators (SET). We consider the case of the N = 1 supersymmetric Yang-Mills theory, where just one fermionic flavor is present, the gluino in the adjoint representation, and only flavor singlet states are possible. This work is part of an inclusive analysis of the spectrum of the lightest particles of the theory, based on the simulation of the model on a $16^3\cdot32$ lattice with dynamical gluinos in the Wilson scheme.
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    The European physical journal 39 (2004), S. 347-357 
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    Notes: Abstract. The five different CP conserving amplitudes for the decays $K\to3\pi$ are calculated using Chiral Perturbation Theory. The calculation is made to next-to-leading order and includes full isospin breaking. The squared amplitudes are compared with the corresponding ones in the isospin limit to estimate the size of the isospin breaking effects. In this paper we add the radiative corrections to the earlier calculated m u -m d and local electromagnetic effects. We find corrections of order 5-10 percent.
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    The European physical journal 39 (2004), S. 389-395 
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    Notes: Abstract. We present the non-Abelian gaugings of supermembranes for general isometries for compactifications from eleven-dimensions, starting with an Abelian case as a guide. We introduce a super Killing vector in eleven-dimensional superspace for a non-Abelian group G associated with the compact space B for a general compactification, and couple it to a non-Abelian gauge field on the world-volume. As a technical tool, we use teleparallel superspace with no manifest local Lorentz covariance. Interestingly, the coupling constant is quantized for the non-Abelian group G, due to its non-trivial mapping $\pi_3(G)$ .
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    The European physical journal 39 (2004), S. 253-292 
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    Notes: Abstract. The determination of the centre-of-mass energies for all LEP 2 running is presented. Accurate knowledge of these energies is of primary importance to set the absolute energy scale for the measurement of the W boson mass. The beam energy between 80 and 104 GeV is derived from continuous measurements of the magnetic bending field by 16 NMR probes situated in a number of the LEP dipoles. The relationship between the fields measured by the probes and the beam energy is defined in the NMR model, which is calibrated against precise measurements of the average beam energy between 41 and 61 GeV made using the resonant depolarisation technique. The validity of the NMR model is verified by three independent methods: the flux-loop, which is sensitive to the bending field of all the dipoles of LEP; the spectrometer, which determines the energy through measurements of the deflection of the beam in a magnet of known integrated field; and an analysis of the variation of the synchrotron tune with the total RF voltage. To obtain the centre-of-mass energies, corrections are then applied to account for sources of bending field external to the dipoles, and variations in the local beam energy at each interaction point. The relative error on the centre-of-mass energy determination for the majority of LEP 2 running is 1.2 x 10-4, which is sufficiently precise so as not to introduce a dominant uncertainty on the W mass measurement.
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    The European physical journal 39 (2004), S. 155-168 
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    Notes: Abstract. Using bosonization approach, we derive an effective low-energy theory for XXZ-symmetric spin-1/2 zigzag ladders and discuss its phase diagram by a variational approach. A spin nematic phase emerges in a wide part of the phase diagram, either critical or massive. Possible crossovers between the spontaneously dimerized and spin nematic phases are discussed, and the topological excitations in all phases identified.
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    The European physical journal 39 (2004), S. 145-148 
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    Notes: Abstract. The substitution of 1%-Ce4 + for La3 + in LaCoO3 is found to change the sign of the Seebeck coefficient at room temperature. This demonstrates that not only holes but also electrons can be created in LaCoO3. The result is compatible with the Heikes formula for doping levels close to the “pure” trivalent Co3 + state. Nonetheless, the physical properties such as magnetic susceptibility, magnetization, thermal conductivity and resistivity are found to be asymmetric for hole and electron-doped LaCoO3. Such a different behaviour is ascribed to the very different spin-states of Co4 + (low-spin, t 2g 5 e g 0) and Co2 + (high-spin, t 2g 5 e g 2).
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    The European physical journal 41 (2004), S. 259-277 
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    Notes: Abstract. This paper shows in detail the application of a new stochastic approach for the characterization of surface height profiles, which is based on the theory of Markov processes. With this analysis we achieve a characterization of the scale dependent complexity of surface roughness by means of a Fokker-Planck or Langevin equation, providing the complete stochastic information of multiscale joint probabilities. The method is applied to several surfaces with different properties, for the purpose of showing the utility of this method in more detail. In particular we show evidence of the Markov properties, and we estimate the parameters of the Fokker-Planck equation by pure, parameter-free data analysis. The resulting Fokker-Planck equations are verified by numerical reconstruction of the conditional probability density functions. The results are compared with those from the analysis of multi-affine and extended multi-affine scaling properties which is often used for surface topographies. The different surface structures analysed here show in detail the advantages and disadvantages of these methods.
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    The European physical journal 39 (2004), S. 283-286 
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    Notes: Abstract. Density-functional theory (DFT) with generalized gradient approximation (GGA) is applied to study the electronic structure and the magnetic properties of ferromagnet [Cu( $\mu $ -C4H2O4)(NH3)2] n (H2O) m . The density of states, the electronic band structure and the spin magnetic moment are calculated. The calculations reveal that the compound has a stable half-metal-ferromagnetic ground state, and that there exists a dominant ferromagnetic interaction arising from the alkoxo-bridged dimeric part of the compound. The spin magnetic moment 1.0 $\mu_{B}$ per molecule mainly comes from the Cu ion with little contribution from O, N, C anion.
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    The European physical journal 41 (2004), S. 557-560 
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    Notes: Abstract. We discuss the proper definition of the spin current operator in Heisenberg magnets subject to inhomogeneous magnetic fields. We argue that only the component of the naive “current operator” $J_{ij}{\vec S}_i\times{\vec S}_j$ in the plane spanned by the local order parameters $\langle{\vec S}_i\rangle$ and $\langle{\vec S}_j\rangle$ is related to real transport of magnetization. Within a mean field approximation or in the classical ground state the spin current therefore vanishes. Thus, finite spin currents are a direct manifestation of quantum correlations in the system.
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    The European physical journal 41 (2004), S. 569-573 
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    Notes: Abstract. We present a dynamical model describing a predictable human behavior like the tuning process between singers. The purpose, inspired in physiological and behavioral grounds of human beings, is sensitive to all Fourier spectrum of each sound emitted and it contemplates an asymmetric coupling between individuals. We have recorded several tuning exercises and we have confronted the experimental evidence with the results of the model finding a very well agreement between calculated and experimental sonograms.
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    The European physical journal 41 (2004), S. 535-548 
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    Notes: Abstract. The thermal fluctuations that exist at very low temperature in disordered systems are often attributed to the existence of some two-level excitations. In this paper, we revisit this question via the explicit studies of the following 1D models (i) a particle in 1D random potentials (ii) the random field Ising chain with continuous disorder distribution. In both cases, we define precisely the ‘two-level’ excitations and their statistical properties, and we show that their contributions to various observables are in full agreement at low temperature with the the rigorous results obtained independently. The statistical properties of these two-level excitations moreover yield simple identities at order T in temperature for some generating functions of thermal cumulants. For the random-field Ising chain, in the regime where the Imry-Ma length is large, we obtain that the specific heat is dominated by small non-universal excitations, that depend on the details of the disorder distribution, whereas the magnetic susceptibility and the Edwards-Anderson order parameter are dominated by universal large excitations, whose statistical properties only depend on the variance of the initial disorder via the Imry-Ma length.
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    The European physical journal 42 (2004), S. 11-16 
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    Notes: Abstract. The basic properties of infrared laser radiation odd harmonic generation due to electron-charged impurity collisions in degenerate semiconductors are investigated. It is found that in the case of relatively weak fields, the electron Fermi distribution is the cause of an anomalous suppression of harmonic radiation. In the case of strong fields, the effect of the selective suppression of single harmonics is established.
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    The European physical journal 42 (2004), S. 3-10 
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    Notes: Abstract. A vortex line passes through as many pinning centers as possible on its way from one extremety of the superconductor to the other at the expense of increasing its self-energy. In the framework of the Ginzburg-Landau theory we study the relative growth in length, with respect to the straight line, of a vortex near a zigzag of defects. The defects are insulating pinning spheres that form a three-dimensional cubic array embedded in the superconductor. We determine the depinning transition beyond which the vortex line no longer follows the critical zigzag path of defects.
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    The European physical journal 42 (2004), S. 187-191 
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    Notes: Abstract. The temperature and voltage dependence of spin transport is theoretically investigated in a new type of magnetic tunnel junction, which consists of two ferromagnetic outer electrodes separated by a ferromagnetic barrier and a nonmagnetic (NM) metallic spacer. The effect of spin fluctuation in magnetic barrier, which plays an important role at finite temperature, is included by taking the mean-field approximation. It is found that, the tunnel magnetoresistance (TMR) and the electron-spin polarization depend strongly on the temperature and the applied voltage. The TMR and spin polarization at different temperatures show an oscillatory behavior as a function of the NM spacer thickness. Also, the amplitude of these oscillations is regularly reduced when the temperature increases. The maximum TMR value, varies approximately from 270 $\%$ in reverse bias (at T = 0 K) to 25 $\%$ in forward bias (at $T\geq T_C$ ).
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    The European physical journal 42 (2004), S. 157-163 
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    Notes: Abstract. In a polymer chain, an extra electron or hole distorts the chain to form a charged polaron, which is the charge carrier being responsible for conductivity. When an intermediate-strength electric field is applied, the polaron will be accelerated for a short time and then move at a constant velocity. The dynamical process of polaron in a polymer chain with impurities is simulated within a non-adiabatic evolution method, in which the electron wave function is described by the time-dependent Schrödinger equation while the polymer lattice is treated classically by a Newtonian equation of motion. We have considered two kinds of dynamical processes, one is the field-induced depinning of a charged polaron, which is initially bound by an attractive impurity; and the other is the scattering of a polaron from an impurity. In the former process, the charged polaron will depart from the attractive impurity only for the applied field with strength over a threshold, otherwise, the polaron will oscillate around the impurity. In the latter process, the charged polaron moves through the impurity in the presence of an electric field while it will be bounced back for a repulsive impurity or trapped to oscillate around an attractive impurity in the case that the applied electric field is weak and just be present for the polaron acceleration.
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    The European physical journal 42 (2004), S. 181-186 
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    Notes: Abstract. A design for omnidirectional asymmetrical high reflectors for optical telecommunication wavelengths is described. Asymmetry was introduced by applying a power law, so that the coordinates y of the transformed object were determined through the coordinates x of the quarter-wave stack air/H(LH)15/air in accordance with the following rule y = x 1 + k . Here k is the coefficient defining the asymmetry degree. It is shown that a high-reflection band at any incident angle for both polarizations, i.e., an omnidirectional high reflection band of 0.74 $\mu $ m for optical telecommunication wavelengths 0.85 and 1.3 $\mu $ m is found for the transformed system: air/Te(SiO2/Te)15/air corresponding to the optimized k value 0.24.
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    Notes: Abstract. We have investigated the magnetic ordering of Nd2-x Ce x CuO4 for x = 0, 0.09, 0.13, 0.15 and 0.18 by neutron diffraction at low temperatures down to 33 mK and under magnetic field up to 5 tesla applied along [1,-1,0] crystallographic direction. At zero applied magnetic field Cu magnetic sublattice orders at $T_{N} \approx 250$ , 210, 130 and 105 K for x = 0, 0.09, 0.13, 0.15, respectively. No long range magnetic order of the Cu could be detected for x = 0.18. The magnetic order of Nd was found in all samples, with a gradual increase of the polarized magnetic moment with decreasing temperature, saturating around 1 K. Hyperfine induced nuclear polarization of the Nd nuclear spin has been observed below about 400 mK for samples with x = 0, 0.13, 0.15 and 0.18. Field variation of the intensities of the principal and superstructure reflections of Nd2-x Ce x CuO4 at millikelvin temperatures shows a field-induced second-order double-k to single-k phase transition at H c = 0.75 and 0.56 tesla for samples with x = 0 and 0.15, respectively at T = 50 mK. We have also investigated the polarization of the Nd electronic sublattice due to the field of the Cu sublattice by the element specific X-ray resonant magnetic scattering investigation with synchrotron radiation.
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    The European physical journal 38 (2004), S. 99-102 
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    Notes: Abstract. We derive the exact bifurcation diagram of the Duffing oscillator with parametric noise thanks to the analytical study of the associated Lyapunov exponent. When the fixed point is unstable for the underlying deterministic dynamics, we show that the system undergoes a noise-induced reentrant transition in a given range of parameters. The fixed point is stabilised when the amplitude of the noise belongs to a well-defined interval. Noisy oscillations are found outside that range, i.e., for both weaker and stronger noise.
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    The European physical journal 38 (2004), S. 37-41 
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    Notes: Abstract. We investigate the phonon thermal conductivity $\kappa_{\mathrm{ph}}$ of doped $\rm La_2CuO_4$ based on out-of-plane thermal conductivity measurements. When room temperature is approached the temperature dependence of $\kappa_{\mathrm{ph}}$ strongly deviates from the T -1-decrease which is usually expected for heat transport by acoustic phonons. Instead, $\kappa_{\mathrm{ph}}$ decreases much weaker or even increases with rising temperature. Simple arguments suggest that such unusual temperature dependencies of $\kappa_{\mathrm{ph}}$ are caused by heat transport via dispersive optical phonons.
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    The European physical journal 38 (2004), S. 25-35 
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    Notes: Abstract. Two-level electron-phonon systems with reflection symmetry linearly coupled to one or two phonon modes (exciton and E $\otimes(b_1 + b_2)$ Jahn-Teller model) exhibit strong enhancement of quantum fluctuations of the phonon coordinates and momenta due to the complex interplay of quantum fluctuations and nonlinearities inherent to the models. We show that for the complex correlated quantum fluctuations of the anisotropic two-level systems the Shannon entropies of phonon coordinate and momentum and their sum yield their proper global description. On the other hand, the variance measures of the Heisenberg uncertainties suffer from several shortcomings to provide proper description of the fluctuations. Wave functions, related entropies and variances were determined by direct numerical simulations. Illustrative variational calculations were performed to demonstrate the effect on an analytically tractable exciton model.
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    Notes: Abstract. X-Ray Magnetic Circular Dichroism experiments have been conducted on a vanadium inorganic salt and a vanadium enamino-ketone complex. Measurements at the K edge of oxygen and nitrogen reveal the amount of magnetic moment transferred in the 2p orbitals of the ligand atoms from the magnetic V ion. Measurements at the L edge of vanadium show that the orbital moment is small and that J = L + S, contrary to the expected J = L-S coupling for a 3d metal with less than five d-electrons. This surprising inobservance of Hund’s third rule emphasizes the need for more detailed studies and calculations on such hybrid molecules.
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    The European physical journal 39 (2004), S. 207-218 
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    Notes: Abstract. The alloy Ca2-x Sr x RuO4 exhibits a complex phase diagram with peculiar magnetic metallic phases. In this paper some aspects of this alloy are discussed based on a mean field theory for an effective Kugel-Khomskii model of localized orbital and spin degrees of freedom. This model results from an orbital selective Mott transition which in the three-band system localized two orbitals while leaving the third one itinerant. Special attention is given to the region around a structure quantum phase transition at $ x \approx 0.5 $ where the crystal lattice changes from tetragonal to orthorhombic symmetry while leaving the system metallic. This transition yields, a change from ferromagnetic to antiferromagnetic spin correlations. The complete mean field phase diagram for this transition is given including orbital and spin order. The anisotropy of spin susceptibility, a consequence of spin-orbit coupling and orbital correlation, is a tell-tale sign of one of these phases. In the predominantly antiferromagnetic phase we describe a metamagnetic transition in a magnetic field and show that coupling of the itinerant band to the localized degrees of freedom yields an anomalous longitudinal magnetoresistance transition. Both phenomena are connected with the evolution of the ferromagnetic and antiferromagnetic domains in the external magnetic field and agree qualitatively with the experimental findings.
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    The European physical journal 39 (2004), S. 235-240 
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    Notes: Abstract. A phenomenological approach was applied to the dynamics of the intrinsic electric conductivity of dielectrics in an electric field in order to analyze its contribution to dielectric losses. The proposed differential equation contains only two parameters - the effective time $\tau_{F}$ of conductivity decay in an electric field, and $\tau_{R}$ , the time describing the recovery rate of the conductivity after switching off the field. The proposed approach predicts a linear dependence of specific conductivity of dielectrics on the sample thickness, as experimentally confirmed by Du Pont [1] for Teflon FEP. The field and time (or frequency) dependences of intrinsic conductivity and related dependences of dielectric losses were calculated, analyzed and illustrated with the published experimental data. The results show that the discussed contribution in dielectric losses is characterized by two hyperbolas (instead of one) while the distance between the branches depends on the intensity of applied electric field.
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    The European physical journal 39 (2004), S. 249-260 
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    Notes: Abstract. The aim of this paper is to explain the non monotonic temperature dependence of the self-consistent superconducting gap of ferromagnet/superconductor/ferromagnet (F/S/F) trilayers with weak ferromagnets in the parallel alignment (equivalent to F/S bilayers). We show that this is due to Andreev bound states that compete with the formation of a minigap. Using a recursive algorithm we discuss in detail the roles of various parameters (thicknesses of the superconductor and ferromagnets, relative spin orientation of the ferromagnets, exchange field, temperature, disorder, interface transparencies).
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  • 169
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    Notes: Abstract. By combining X-ray diffraction under grazing incidence (GIXD) and scanning tunneling microscopy (STM) measurements, we have determined the structure of 4-n-octyl-4’-cyanobiphenyl (8CB) molecules adsorbed on MoS2, under the thick organic film. The commensurability of the adsorbed network and the unit cell structure have been determined, revealing a complex 2D structure. This structure is characterized by straight ribbons with two types of ribbons, alternatively stacked. In one type, molecules are equally spaced, as they are paired in the other type. Considering the energetics of adsorption with a model of single ribbon, we recover the two observed ribbon structures. The alternate stacking of the ribbons appears as a consequence of the connection between the commensurabilities in the two main crystallographic directions. Moreover, we have found a particularly high value for the molecule-substrate potential corrugations, indicating that the dipole moment of 8CB molecules could play a fundamental role in the molecule-substrate interactions.
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    The European physical journal 41 (2004), S. 307-312 
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    Notes: Abstract. The response of a metamaterial, consisting of a 3D lattice of lossy capacitively loaded metallic loops is studied theoretically when it is inserted into a homogeneous harmonically varying magnetic field. The current distribution is found by taking into account the magnetic coupling between any pair of loops in the approximation of no retardation. It is shown that in a frequency range above its resonant frequency the metamaterial behaves as a diamagnet expelling the applied magnetic field. As the resonant frequency is approached the magnetic field is shown to be expelled not only from the volume of the metamaterial but from a larger zone which in the vicinity of the resonant frequency takes the form of a sphere. In the lossless case the radius of this exclusion sphere tends to infinity. In the presence of losses the maximum radius is limited by the quality factor of the individual elements. The response of a single element is shown to be analogous to that of a sphere of magnetic material, an analogy that leads to an alternative definition of effective permeability.
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  • 171
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    Notes: Abstract. Ab initio calculations allow to distinguish boron atoms in BO3 and BO4 complexes in lithium borates. On this basis an effective potential model for single crystals of Li2O-B2O3 is suggested. Empirical parameters of the interaction potentials are optimized in order to reproduce the experimental data of lithium tetraborate. The optimized parameters are applied to calculations of the structures of the anhydrous borate single crystals Li3BO3, LiBO2, Li2B4O7, Li3B7O12 and LiB3O5. The range of applicability of the potential model is increased by introducing a dependence of the effective oxygen charges on the Li content. In this way good agreement with experimental data is obtained for calculated structural and elastic properties.
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  • 172
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    Notes: Abstract. The microwave dielectric properties of ZnAl2O4 spinels were investigated and their properties were tailored by adding different mole fractions of TiO2. The samples were synthesized using the mixed oxide route. The phase purity and crystal structure were identified using X-ray diffraction technique. The sintered specimens were characterized in the microwave frequency range (3-13 GHz). The ZnAl2O4 ceramics exhibited interesting dielectric properties (dielectric constant ( $\varepsilon_{r}) = 8.5$ , unloaded quality factor (Q u ) = 4590 at 12.27 GHz and temperature coefficient of resonant frequency ( $\tau_{f}) = -79$ ppm/ $^{\circ}$ C). Addition of TiO2 into the spinel improved its properties and the $\tau_{f}$ approached zero for 0.83ZnAl2O4-0.17TiO2. This temperature compensated composition has excellent microwave dielectric properties ( $\varepsilon _{r} = 12.67$ , Q u = 9950 at 10.075 GHz) which can be exploited for microwave substrate applications.
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  • 173
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    Notes: Abstract. We report on field-induced variations of the microwave surface resistance at 9.6 GHz of Ba0.6K0.4BiO3 crystals. Energy losses have been investigated as a function of the static magnetic field in the range of temperatures 4.2 K $\div T_c$ . By analyzing the experimental results in the framework of the Coffey and Clem model we determine the temperature dependence of the first-penetration field, upper critical field and depinning frequency. The results show that the pinning energy of this bismuthate superconductor is weaker than those of cuprates.
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    The European physical journal 41 (2004), S. 325-332 
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    Notes: Abstract. The increasing interest in photonics in the field of communication has led to intense research work on silicon based nanostructures showing efficient photoluminescence. The present paper reports photoluminescence measurements obtained at room temperature in silicon-rich-silica-silica multilayers grown by reactive magnetron sputtering. The silicon nanograin size is controlled via the silicon layer thickness which can be monitored with high accuracy. We aim to develop a comprehensive understanding of the combined roles played by the quantum confinement effect through the silicon grain size and the existence of an interfacial region between the grain and the surrounding silica matrix. Two bands of photoluminescence are displayed in the 600 nm-900 nm range and correspond to the bands previously observed at 2 K. Their origin is demonstrated through a model based on the solution of the Schrödinger equation of the exciton wavefunction in a one-dimension geometry corresponding to the growth direction of the multilayers. The silicon layer as well as the Si-SiO2 interface thicknesses are the key parameters of the photoluminescence features.
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    The European physical journal 41 (2004), S. 319-323 
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    Notes: Abstract. A hexagonal ordered structure of magnetic columns, which results from an agglomeration of magnetic particles, is obtained in a magnetic fluid film when a magnetic field is applied perpendicularly to the film surface. The evolution of the initially ordered structure in the magnetic fluid film during the heating and cooling process is investigated under a given magnetic field. For the heating process, the columns remain unchanged until the temperature exceeds a critical temperature. As the temperature is further increased, column particles start to disperse into the liquid carrier. As a result, portions of columns disappear. As the temperature continue to rise, the ordered structure changes to a disordered column state, or even a monodispersed state. On the other hand, when the temperature is lowered, the magnetic particles in the carrier condense out of solution and finally an ordered structure of columns is achieved. However, this structural evolution during a thermal cycle is irreversible.
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    The European physical journal 41 (2004), S. 333-336 
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    Notes: Abstract. In a connected graph, nodes can be characterised locally (with their degree k) or globally (e.g. with their average length path $\xi$ to other nodes). Here we investigate how $\xi$ depends on k. The numerical algorithm based on the construction of the distance matrix is applied to random graphs and the growing networks: the scale-free ones and the exponential ones. The results are relevant for search strategies in different networks.
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    The European physical journal 41 (2004), S. 337-343 
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    Notes: Abstract. A delayed differential equation modelling a single neuron with inertial term subject to time delay is considered in this paper. Hopf bifurcation is studied by using the normal form theory of retarded functional differential equations. When adopting a nonmonotonic activation function, chaotic behavior is observed. Phase plots, waveform plots, and power spectra are presented to confirm the chaoticity.
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    The European physical journal 41 (2004), S. 345-363 
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    Notes: Abstract. This paper proposes a reformulation and extension of the concept of Extended Self-Similarity. In support of this new hypothesis, we discuss an analysis of the probability density function (pdf) of turbulent velocity increments based on the class of normal inverse Gaussian distributions. It allows for a parsimonious description of velocity increments that covers the whole range of amplitudes and all accessible scales from the finest resolution up to the integral scale. The analysis is performed for three different data sets obtained from a wind tunnel experiment, a free-jet experiment and an atmospheric boundary layer experiment with Taylor-Reynolds numbers $R_{\lambda} = 80,190,17000$ , respectively. The application of a time change in terms of the scale parameter $\delta$ of the normal inverse Gaussian distribution reveals some universal features that are inherent to the pdf of all three data sets.
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    The European physical journal 41 (2004), S. 413-420 
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    Notes: Abstract. We study the relaxation of ferroelastic domain walls in the vicinity of a free surface, by means of a nonlinear continuum elastic model treated with finite elements on an adaptive grid. Domain walls bend towards the free surface, as a consequence of the interplay of the energy per unit length of the domain wall and the long-range elastic strains which are generated by deviations from the prescribed compatible orientation. We also analyze the order parameter on the free surface. For walls orthogonal to the free surface we find, in accordance with previous studies, a double-peak structure. For different angles the picture is more complex, and in some cases only one small peak survives.
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    The European physical journal 41 (2004), S. 421-431 
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    Notes: Abstract. In this paper, we study numerically the influence of aggressive driving on the properties of the stochastic Nagel-Schreckenberg model, such as the traffic flow and the probability of car accidents. Hence, we find that these properties depend enormously on both the density $\rho $ and the fraction f of aggressive drivers. In addition, by studying the spatio-temporal organization of the vehicles, we show that at very low density, the traffic state transits from “ordinary” free traffic to “queueing” phase when we increase the fraction f. At relatively high density, the transition from congested traffic to queueing phase may also occur.
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    The European physical journal 39 (2004), S. 287-294 
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    Notes: Abstract. We give a multiresolution partition of pure point parts of diffraction patterns of one-dimensional aperiodic sets. When an aperiodic set is related to the Golden Ratio, denoted by $\tau$ , it is well known that the pure point part of its diffractive measure is supported by the extension ring of $\tau$ , denoted by $\mathbb{Z}[\tau]$ . The partition we give is based on the formalism of the so called $\tau$ -integers, denoted by $\mathbb{Z}_\tau$ . The set of $\tau$ -integers is a selfsimilar set obeying $\mathbb{Z}_\tau/\tau^{j-1}\subset\mathbb{Z}_\tau/\tau^j \subset \mathbb{Z}_\tau/\tau^{j + 1} \subset\mathbb{Z}[\tau]$ , $j\in\mathbb{Z}$ . The pure point spectrum is then partitioned with respect to this “Russian doll” like sequence of subsets $\mathbb{Z}_\tau/\tau^j$ . Thus we deduce the partition of the pure point part of the diffractive measure of aperiodic sets.
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    The European physical journal 39 (2004), S. 309-311 
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    Notes: Abstract. We investigate transport properties of electrons in a one-dimensional (1D) disordered system consisting of a host chain attached with specific impurities. Every impurity, labelled by j and possessing site energy $\epsilon_j$ , is side-coupled to two adjacent sites of the host chain with hopping integral t 1j and changesthe original nearest-neighbor (NN) hopping to t 2j . We show that if $t_{2j} = -\epsilon_j/2$ and $t_{1j} = \sqrt{t_0^2 - (\epsilon_j/2)^2}$ for all impurities, with t 0 being the NN hopping of the host chain, the states in the whole band are extended, even though $\epsilon_j$ ’s and positions of impurities are random. The phases of these states, however, are spatially random, corresponding to finite free path and infinite localization length in such a 1D system.
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  • 183
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    Notes: Abstract. The feasibility of three-dimensional (3-D) photonic crystals made using textile technology was investigated. Three different textures consisting of the cotton-yarn and TiO2 dispersed resin; a crossed linear-yarn laminated fabric, a multi layered woven fabric, and a 3-D woven fabric, were fabricated. The microwave attenuation of the transmission amplitude through these photonic crystals was measured. The straight cotton-yarn as well as the wavy cotton-yarn/TiO2 dispersed resin photonic crystals exhibited band gaps in the 6 to 15 GHz range. Thus, we could fabricate successfully 3-D photonic crystals using textile technology.
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  • 184
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    Notes: Abstract. The Nambu spinor Green’s function approach is applied to studying the proximity effect in ferromagnet/d-wave superconductor (FM/d-wave SC) junctions. It is found that the magnitude of the proximity effect depends to a great extent on the orientation of the SC crystal with respect to the interface normal. On the FM side, near the interface there are two different types of density of states (DOS) with superconducting features. On the SC side, the DOS near the interface is spin dependent, indicating a local coexistence of weak ferromagnetism and d-wave superconductivity.
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    The European physical journal 39 (2004), S. 385-396 
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    Notes: Abstract. Adiabatic pumping of electrons induced by surface acoustic waves (SAWs) in a ballistic quasi-1D quantum channel is considered using an exactly solvable tight-binding model for non-interacting electrons. The single-electron degrees of freedom, responsible for acoustoelectric current quantization, are related to the transmission resonances. We study the influence of experimentally controllable parameters (SAW power, gate voltage, source-drain bias, amplitude and phase of a secondary SAW beam) on the plateau-like structure of the acoustoelectric current. The results are consistent with existing experimental observations.
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    The European physical journal 39 (2004), S. 409-413 
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    Notes: Abstract. This paper presents a possible explanation for some of the empirical properties of asset returns within a heterogeneous-agents framework. The model turns out, even if we assume the input fundamental value follows an simple Gaussian distribution lacking both fat tails and volatility dependence, these features can show up in the time series of asset returns. In this model, the profit comparison and switching between heterogeneous play key roles, which build a connection between endogenous market and the emergence of stylized facts.
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    The European physical journal 39 (2004), S. 397-408 
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    Notes: Abstract. The optimal-velocity model, as proposed by Bando et al. [1], shows unrealistic values of the acceleration for various optimal-velocity functions [2,3]. We discuss different approaches of how to correct this problem. Multiple look-ahead (many-neighbour interaction) models are the most promising candidates in reducing accelerations and decelerations to realistic values. We focus on two such models and, in particular, their linear stability and how these affect the vehicle dynamics and wave solutions. As found earlier [4], multiple look-ahead models reproduce many real flow features, and our results further support the necessity of this ansatz. However, the problem of non-locality arises when they are transformed into the corresponding continuum model. We discuss three methods of how to interpret many-neighbour interaction in macroscopic models.
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    The European physical journal 42 (2004), S. 17-30 
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    Notes: Abstract. We use Wegner’s flow equation method to investigate the infinite-U periodic Anderson model. We show that this method poses a new approach to the description of heavy fermion behaviour. Within this scheme we derive an effective Hamiltonian in which the c and f degrees of freedom are decoupled. By evaluating one-particle energies as well as correlation functions we find an electronic structure which comprises two gapped quasiparticle bands. We also address the lattice Kondo temperature, which shows a typical exponential dependence on the hybridisation energy. This energy scale exhibits a significant decrease compared to that of the single impurity Anderson model.
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    The European physical journal 42 (2004), S. 63-83 
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    Notes: Abstract. We first show that, for problems dealing with trions, it is totally hopeless to use the standard many-body description in terms of electrons and holes and its associated Feynman diagrams. We then show how, by using a description as electrons interacting with excitons, we can obtain the trion absorption through far simpler electron-exciton diagrams. These diagrams are indeed novel because, for excitons being not exact bosons, standard procedures designed to deal with interacting true fermions or true bosons cannot be used. A new many-body formalism is in fact necessary to establish the validity of these electron-exciton diagrams. It relies on the “commutation technique” we recently developed to treat interaction with composite bosons. This technique generates a scattering associated to Coulomb processes between electrons and excitons, without electron exchange, and a “scattering” associated to electron exchange inside the electron-exciton pairs, without Coulomb process -- this Pauli scattering being the original part of our new many-body theory.
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  • 190
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    Notes: Abstract. The crystal structure, magnetization and electrical transport depending on the temperature and magnetic field for the doped stoichiometric ${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}_{1-x}^{3 + } {\rm Mn}_x^{4 + } {\rm O}_3^{2-} $ as well as anion-deficient ${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}^{3 + }{\rm O}_{3-x/2}^{2-} $ ( $0\le x \le 0.30$ ) ortomanganite systems have been experimentally studied. It is established that the stochiometric samples in the region of the $0 \le x \le 0.125$ are an ${\rm O}'$ -orthorhombic perovskites whereas in the $0.175 \le x \le 0.30$ - a rhombohedric. For the anion-deficient system the symmetry type of the unit cell is similar to the stoichiometric one. As a doping level increases the samples in the ground state undergo a number of the magnetic transitions. It is assumed that the samples with the large amount of oxygen vacancies are a cluster spin glasses ( $0.175 〈 x \le 0.30$ ) and temperature of the magnetic moment freezing is ~40 K. All the anion-deficient samples are semiconductors and show considerable magnetoresistance over a wide temperature range with a peak for the x = 0.175 only. Concentration dependences of the spontaneous magnetization and magnetic ordering temperature for the anion-deficient ${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}^{3 + }{\rm O}_{3-x/2}^{2-} $ system have been established by the magnetic measurements and compared with those for the stoichiometric ${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}_{1-x}^{3 + } {\rm Mn}_x^{4 + } {\rm O}_3^{2-} $ one. The magnetic propeprties of the anion-deficient samples may be interpreted on the base of the superexchange interaction and phase separation (chemical disorder) models.
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    The European physical journal 37 (2004), S. 479-487 
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    Notes: Abstract. Magnetooptical properties of the materials with periodically modulated dielectric constant - photonic crystals (or band-gap materials) have been examined with relation to their possible applications for the control of electromagnetic radiation in the integrated optics devices. For this investigation we propose the original theoretical approach based on the perturbation theory. Magnetooptical Faraday and Voigt effects have been studied near extremum points of photonic bands where their significant enhancement takes place. On the grounds of the elaborated theory some experimental results are discussed. Experimentally obtained Faraday rotation angle frequency dependence shows good agreement with our theoretical predictions.
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    The European physical journal 37 (2004), S. 473-478 
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    Notes: Abstract. Several intramolecular junctions (IMJs) connecting two semiconductor single-wall carbon nanotubes (SWNTs) have been realized by using the layer-divided technique and introducing the pentagon-heptagon topological defects. The atomic structure of each IMJ is optimized with a combination of density-functional theory (DFT) and the universal force field (UFF) method, based upon which a $\pi $ -orbital tight-binding calculation is performed on its electronic properties. Obtained results indicate that different topological defects and their distributions on the interfaces of the IMJs have decisive effects on the electronic properties of the IMJs. The specific geometrical defects control the localized defect states chiefly, while the diameters of the SWNTs on both sides are also related to them. The influence on the experimental observation brought by the choice of the scanning line is also presented by comparing the scanning results performed on the defect side with those on the defect-free side. A new IMJ structure has been found, and it probably reflects the real atomic structures of the semiconductor-semiconductor (S-S) IMJ [Phys. Rev. Lett. 90, 216107 (2003)].
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    The European physical journal 37 (2004), S. 499-506 
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    Notes: Abstract. We consider, in the frame of the long-wavelength Heisenberg model, the effect of a pinning field on the spin wave band gaps and transmission spectra of one-dimensional comb-like structures. Using a Green’s function method, we obtained closed-form expressions for the band structure and the transmission coefficients for an arbitrary value of the number N of sites (N‘of resonators) in the comb-like structure. We report the opening-up of stop bands inside the pass-bands due to the effect of the pinning field at the ends of the resonators of the comb. These structures, composed of one-dimensional ferromagnetic materials, may exhibit large gaps where the propagation of spin waves is forbidden. The width and frequency position of these gaps depends on the strength of the pinning field.
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    The European physical journal 37 (2004), S. 507-514 
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    Notes: Abstract. Aeolian sand dunes originate from wind flow and sand bed interactions. According to wind properties and sand availability, they can adopt different shapes, ranging from huge motion-less star dunes to small and mobile barchan dunes. The latter are crescentic and emerge under a unidirectional wind, with a low sand supply. Here, a 3d model for barchan based on existing 2d model is proposed. After describing the intrinsic issues of 3d modeling, we show that the deflection of particules in reptation due to the shape of the dune leads to a lateral sand flux deflection, which takes the mathematical form of a non-linear diffusive process. This simple and physically meaningful coupling method is used to understand the shape of barchan dunes.
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    Notes: Abstract. We present a study of the transport of a Brownian particle moving in a periodic symmetric potential in the presence of asymmetric unbiased fluctuations. The particle is considered to move in a medium with periodic space dependent friction. By tuning the parameters of the system, the direction of the current exhibits reversals, both as a function of temperature as well as the amplitude of rocking force. We found that the mutual interplay between the opposite driving factors is the necessary term for current reversals.
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    The European physical journal 37 (2004), S. 515-522 
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    Notes: Abstract. In this paper we consider a type-I superconducting film modeled by the Ginzburg-Landau model, confined between two parallel planes a distance L apart from one another. Our approach is based on the Gaussian effective potential in the transverse unitarity gauge, which allows to treat gauge contributions in a compact form. Using techniques from dimensional and $ \zeta $ -function regularizations, modified by the confinement conditions, we investigate the critical temperature as a function of the film thickness L. The contributions from the scalar self-interaction and from the gauge fluctuations are clearly identified. The model suggests the existence of a minimal critical thickness below which superconductivity is suppressed. A comparison with present experimental observations is done.
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    The European physical journal 37 (2004), S. 527-533 
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    Notes: Abstract. Using a variational procedure based on Lee-Low-Pines and Huybrechts canonical transformations, we study the stability region of two-dimensional bipolarons confined in a parabolic quantum dot, subject to a uniform magnetic field. In the framework of our approach, we calculate the ground-state energy for two-dimensional magnetobipolarons, together with the free polaron ground-state energy, by performing a self consistent calculation. We then obtain the binding energy for two-dimensional magnetobipolarons, in the usual way, to explore the properties of bipolaron formation in two-dimensional quantum dot structures. The stability region is found to be very sensitive to the confinement length of the parabolic potential and to the magnetic field strength, as well as to the material parameters $\alpha $ and $\eta $ . The stability region is also found to be remarkably enhanced by increasing the degree of spatial confinement and magnetic field. Our results are both in qualitative and quantitative agreement with those found in the literature.
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Cu2Te2O5X2, with X = Br and Cl, are spin-tetrahedral systems displaying magnetic ordering at low temperatures. We have performed optical reflectivity measurements over a broad spectral range as a function of temperature and magnetic field. We have identified the resonance frequencies of the infrared optically active phonon modes and estimated the value of the electronic gap in both tellurate compounds. No variation of the spectra has been observed while crossing the magnetic ordering transition temperature or by applying a magnetic field. The implications of these findings are discussed in relation to the nature of the phase transition.
    Type of Medium: Electronic Resource
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  • 199
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 42 (2004), S. 435-440 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. In this work we present a study of the properties of defective nanostructures. The material chosen to this purpose, i.e. SnO2, has practical applications and many of them rely on the spontaneous formation of vacancies. Therefore, crystalline grains with shape and size comparable to the experimental ones have been considered. According to the bulk properties, the grains lattice has the rutile structure and may also include vacancy defects. The calculations describe the effects of the structural grain parameters, i.e. size and shape, as well as of the defect type, on the grain cohesion and are based on a Tight Binding method. The comparison with Density Functional calculations, also carried out in the course of this study, illustrates the limits of both methods when used for these complex structures.
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  • 200
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We examine the light-induced charge transport properties of a series of chromium-doped $\rm {Sr}_{0.61}\rm {Ba}_{0.39}\rm {Nb}_2\rm {O}_6$ single crystals by measurements of the optical absorption and the electric conductivity. By comparing the wavelength dependence of the specific photoconductivity and the optical absorption we show that both effects stem from the same center. The intensity dependence of the photoconductivity shows the applicability of a one-center charge transport model for high doping concentrations, while for low doping concentrations a more sophisticated model is needed. The validity of a one-center model is exemplarily verified for a crystal doped with 0.51 mol % Cr over a wide intensity range using a holographic method. The product of mobility and recombination time of photoexcited electrons is deduced from the specific photoconductivity.
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