8,086 research outputs found

    A heliospheric hybrid model: hydrodynamic plasma flow and kinetic cosmic ray transport

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    International audienceIn this paper we present a new five particle species hybrid model for calculating cosmic ray particle transport and acceleration in a dynamic heliospheric environment. In particular the effects of solar cycle related changes in the solar wind speed on the heliospheric geometry, solar wind flow and cosmic ray distribution are discussed, when a polar-ecliptic asymmetry at the inner boundary is modeled. It is shown that the disappearance of the fast solar wind over the solar poles toward solar maximum influences the geometry of the termination shock which is an important structure for cosmic ray acceleration. For solar maximum conditions, the shock radius is smaller in the polar regions and in the heliospheric tail compared to solar minimum. These changes influence cosmic ray transport and acceleration in these regions, especially for the polarity cycle where positive particles drift in along the heliospheric current sheet. For this polarity cycle, and for both the anomalous and galactic cosmic ray protons, an increase in particle intensities at the shock in the heliospheric tail is computed as the shock moves inward toward the Sun. For the heliospheric nose, it is also shown that both the plasma speed and cosmic ray intensities are relative insensitive to changes in the latitudinal profile of the solar wind speed. Therefore toward solar maximum conditions there is a decrease in the nose-tail asymmetry of the computed cosmic ray distribution compared to solar minimum conditions

    Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in Ce1x_{1-x}Lax_xNi9_9Ge4_4

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    We report specific heat and magneto-resistance studies on the compound Ce1x{}_{1-x}Lax{}_xNi9{}_9Ge4{}_4 for various concentrations over the entire stoichiometric range. Our data reveal single-ion scaling with Ce-concentration between x=0.1x = 0.1 and 0.95. Furthermore, CeNi9{}_9Ge4{}_4 turns out to have the largest ever recorded value of the electronic specific heat Δc/T\Delta c/T \approx 5.5 J K2mol1\rm K^{-2}mol^{-1} at T=0.08T=0.08 K which was found in Cerium f-electron lattice systems. In the doped samples Δc/T\Delta c/T increases logarithmically in the temperature range between 3 K and 50 mK typical for non-Fermi liquid (nFl) behavior, while ρ\rho exhibits a Kondo-like minimum around 30 K, followed by a single-ion local nFl behavior. In contrast to this, CeNi9{}_9Ge4{}_4 flattens out in Δc/T\Delta c/T below 300 mK and displays a pronounced maximum in the resistivity curve at 1.5 K indicating a coherent heavy fermion groundstate. These properties render the compound Ce1x{}_{1-x}Lax{}_xNi9{}_9Ge4{}_4 a unique system on the borderline between Fermi liquid and nFl physics.Comment: 2 pages, 3 figures, SCES0

    Virtual Compton scattering off the nucleon at low energies

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    We investigate the low-energy behavior of the four-point Green's function Γμν\Gamma^{\mu\nu} describing virtual Compton scattering off the nucleon. Using Lorentz invariance, gauge invariance, and crossing symmetry, we derive the leading terms of an expansion of the operator in the four-momenta qq and qq' of the initial and final photon, respectively. The model-independent result is expressed in terms of the electromagnetic form factors of the free nucleon, i.e., on-shell information which one obtains from electron-nucleon scattering experiments. Model-dependent terms appear in the operator at O(qαqβ)O(q_\alpha q'_\beta), whereas the orders O(qαqβ)O(q_\alpha q_\beta) and O(qαqβ)O(q'_\alpha q'_\beta) are contained in the low-energy theorem for Γμν\Gamma^{\mu\nu}, i.e., no new parameters appear. We discuss the leading terms of the matrix element and comment on the use of on-shell equivalent electromagnetic vertices in the calculation of ``Born terms'' for virtual Compton scattering.Comment: 26 pages, RevTex, to appear in Phys. Rev.

    Unusual Non-Fermi Liquid Behavior of Ce1x_{1-x}Lax_{x}Ni9_{9}Ge4_4 Analyzed in a Single Impurity Anderson Model with Crystal Field Effects

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    CeNi9_{9}Ge4_4 exhibits unusual non-Fermi liquid behavior with the largest ever recorded value of the electronic specific heat ΔC/T5.5\Delta C/T \cong 5.5 JK2^{-2}mol1^{-1} without showing any evidence of magnetic order. Specific heat measurements show that the logarithmic increase of the Sommerfeld coefficient flattens off below 200 mK. In marked contrast, the local susceptibility Δχ\Delta\chi levels off well above 200 mK and already becomes constant below 1 K. Furthermore, the entropy reaches 2RRln2 below 20 K corresponding to a four level system. An analysis of CC and χ\chi was performed in terms of an SU(N=4)SU(N=4) single impurity Anderson model with additional crystal electric field (CEF) splitting. Numerical renormalization group calculations point to a possible consistent description of the different low temperature scales in Δc\Delta c and Δχ\Delta \chi stemming from the interplay of Kondo effect and crystal field splitting.Comment: 2 pages, 2 figure

    Gauge symmetric delta(1232) couplings and the radiative muon capture in hydrogen

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    Using the difference between the gauge symmetric and standard pi-N-delta couplings, a contact pi-pi-N-N term, quadratic in the pi-N-delta coupling, is explicitly constructed. Besides, a contribution from the delta excitation mechanism to the photon spectrum for the radiative muon capture in hydrogen is derived from the gauge symmetric pi-N-delta and gamma-N-delta couplings. It is shown for the photon spectrum, studied recently experimentally, that the new spectrum is for the photon momentums k > 60 MeV by 4-10 % smaller than the one obtained from standardly used couplings with the on-shell deltas.Comment: 9 pages, 3 figure

    Thermoelectric properties of Zn_5Sb_4In_(2-δ)(δ=0.15)

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    The polymorphic intermetallic compound Zn_5Sb_4In_(2−δ) (δ = 0.15(3)) shows promising thermoelectric properties at low temperatures, approaching a figure of merit ZT of 0.3 at 300 K. However, thermopower and electrical resistivity changes discontinuously at around 220 K. Measurement of the specific heat locates the previously unknown temperature of the order-disorder phase transition at around 180 K. Investigation of the charge carrier concentration and mobility by Hall measurements and infrared reflection spectroscopy indicate a mixed conduction behavior and the activation of charge carriers at temperatures above 220 K. Zn_5Sb_4In_(2−δ) has a low thermal stability, and at temperatures above 470 K samples decompose into a mixture of Zn, InSb, and Zn_4Sb_3

    Pion electroproduction, PCAC, chiral Ward identities, and the axial form factor revisited

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    We re-investigate Adler's PCAC relation in the presence of an external electromagnetic field within the framework of QCD coupled to external fields. We discuss pion electroproduction within a tree-level approximation to chiral perturbation theory and explicitly verify a chiral Ward identity referred to as the Adler-Gilman relation. We critically examine soft-momentum techniques and point out how inadmissable approximations may lead to results incompatible with chiral symmetry. As a result we confirm that threshold pion electroproduction is indeed a tool to obtain information on the axial form factor of the nucleon.Comment: 33 pages, RevTex, 9 figure

    Nucleon-nucleon bremsstrahlung: An example of the impossibility of measuring off-shell amplitudes

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    For nearly fifty years theoretical and experimental efforts in nucleon-nucleon bremsstrahlung (NNγ\gamma) have been devoted to measuring off-shell amplitudes and distinguishing among various NN potentials on the basis of their off-shell behavior. New experiments are underway, designed specifically to attain kinematics further off shell than in the past, and thus to be more sensitive to the off-shell behavior. This letter shows that, contrary to these expectations, and due to the invariance of the S-matrix under transformations of the fields, the off-shell NN amplitude is as a matter of principle an unmeasurable quantity in NNγ\gamma.Comment: 9 pages, Latex, using RevTeX; Minor wording changes, title changed, version to be published in Phys. Rev. Letter

    Body and speech as expression of inner states

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    This article provides a sketch of the theoretical framework of German Expression Psychology (GEP) and discusses the forms and functions of bodily and verbal types of communication that express inner states. Starting with a brief historical overview, we discuss general concepts of the German Expression Psychology framework, in particular with respect to the definition of expression, the relationship between expression and its subject, and the perception of expression. Within each of these areas special attention is given to the face, body and voice as indicators of inner states. Following this general overview of German Expression Psychology, we focus on the contribution of three selected authors, namely, Philipp Lersch, Paul Leyhausen and Egon Brunswik, who have been particularly influential in the field of German Expression Psychology. For Lersch, we consider the co-existential relationship between affect and expression, the detailed anatomical description of expressions, as well as the analysis of dynamic aspects of expressions. Leyhausen added an ethological perspective on expressions and perceptions. Here, we focus on the developmental aspects of expression and impression formation, and differentiate between phylogenetic and ontogenetic aspects of expression. Brunswik’s Lens Model allows a separation between distal indicators on the part of the sender and proximal percepts on the part of the observer. Here, we discuss how such a model can be used to describe and analyze nonverbal communication on both the encoding and decoding side. Deriving from the presentation of all three authors, we outline the general relevance of German Expression Psychology for current research, specifically with respect to the definition and function of expressions and perceptions, and existing approaches to the study of verbal and nonverbal behavior
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