8,095 research outputs found
A heliospheric hybrid model: hydrodynamic plasma flow and kinetic cosmic ray transport
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 CeLaNiGe
We report specific heat and magneto-resistance studies on the compound
CeLaNiGe for various concentrations over the entire
stoichiometric range. Our data reveal single-ion scaling with Ce-concentration
between and 0.95. Furthermore, CeNiGe turns out to have
the largest ever recorded value of the electronic specific heat 5.5 J at K which was found in Cerium
f-electron lattice systems. In the doped samples increases
logarithmically in the temperature range between 3 K and 50 mK typical for
non-Fermi liquid (nFl) behavior, while exhibits a Kondo-like minimum
around 30 K, followed by a single-ion local nFl behavior. In contrast to this,
CeNiGe flattens out in 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
CeLaNiGe 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
We investigate the low-energy behavior of the four-point Green's function
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 and
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 ,
whereas the orders and are
contained in the low-energy theorem for , 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 CeLaNiGe Analyzed in a Single Impurity Anderson Model with Crystal Field Effects
CeNiGe exhibits unusual non-Fermi liquid behavior with the largest
ever recorded value of the electronic specific heat
JKmol 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 levels off well above 200 mK and already becomes
constant below 1 K. Furthermore, the entropy reaches 2ln2 below 20 K
corresponding to a four level system. An analysis of and was
performed in terms of an 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 and 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
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
Pion electroproduction, PCAC, chiral Ward identities, and the axial form factor revisited
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
For nearly fifty years theoretical and experimental efforts in
nucleon-nucleon bremsstrahlung (NN) 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 NN.Comment: 9 pages, Latex, using RevTeX; Minor wording changes, title changed,
version to be published in Phys. Rev. Letter
Thermoelectric properties of Zn_5Sb_4In_(2-δ)(δ=0.15)
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
Body and speech as expression of inner states
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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