1,088 research outputs found
On the Angular Dependence of the Radiative Gluon Spectrum
The induced momentum spectrum of soft gluons radiated from a high energy
quark produced in and propagating through a QCD medium is reexamined in the
BDMPS formalism. A mistake in our published work (Physical Review C60 (1999)
064902) is corrected. The correct dependence of the fractional induced loss
as a universal function of the variable
where is the size of the medium and
the transport coefficient is presented. We add the proof that the
radiated gluon momentum spectrum derived in our formalism is equivalent with
the one derived in the Zakharov-Wiedemann approach.Comment: LaTex, 5 pages, 1 figur
Laser-dressed vacuum polarization in a Coulomb field
We investigate quantum electrodynamic effects under the influence of an
external, time-dependent electromagnetic field, which mediates dynamic
modifications of the radiative corrections. Specifically, we consider the
quantum electrodynamic vacuum-polarization tensor under the influence of two
external background fields: a strong laser field and a nuclear Coulomb field.
We calculate the charge and current densities induced by a nuclear Coulomb
field in the presence of a laser field. We find the corresponding induced
scalar and vector potentials. The induced potential, in first-order
perturbation theory, leads to a correction to atomic energy levels. The
external laser field breaks the rotational symmetry of the system.
Consequently, the induced charge density is not spherically symmetric, and the
energy correction therefore leads to a "polarized Lamb shift." In particular,
the laser generates an additional potential with a quadrupole moment. The
corresponding laser-dressed vacuum-polarization potential behaves like 1/r**3
at large distances, unlike the Uehling potential that vanishes exponentially
for large r. Our investigation might be useful for other situations where
quantum field theoretic phenomena are subjected to external fields of a rather
involved structure.Comment: 13 pages, RevTe
Religious Construction of Coherence in Life Narratives
International audienceDuring the last decade the concepts of meaning and meaning-making have received widespread attention in psychology of religion rekindling interest in narrative, especially in life narratives and in the sense-making processes talking place by constructing coherence in life narratives. Habermas and Bluck (2000) coined the term autobiographical reasoning to denote a process of self-reflecting thinking that implies the life story as relevant frame of reference and produces coherence (e.g. thematic and causal-motivational coherence) in life narratives. This paper investigates how communication about religion in life narratives can enhance the construction of coherence in life narratives. First, religions may be understood as global belief systems that enable people to derive meaning from them in constructing a coherent life story. Second, especially relating religious or spiritual conversion implies enhanced autobiographical reasoning in order to position one's own life story in the context of one or more global belief systems and to articulate the change adequately. This autobiographical reasoning implies the construction of multiple coherences ( in particular thematic and causal-motivational coherence), sometimes accompanied by a meta-communication about the coherent composition of the "fabula" about the "sjuzet"
Non-Abelian Energy Loss at Finite Opacity
A systematic expansion in opacity, , is used to clarify the
non-linear behavior of induced gluon radiation in quark-gluon plasmas. The
inclusive differential gluon distribution is calculated up to second order in
opacity and compared to the zeroth order (factorization) limit. The opacity
expansion makes it possible to take finite kinematic constraints into account
that suppress jet quenching in nuclear collisions below RHIC (
AGeV) energies.Comment: 4 pages (revtex) with 3 eps figures, submitted to PR
Potential of different composts to improve soil fertility
Composts can influence soil fertility and plant health. These influences can be positive or negative, depending of the quality of the composts. Some practitioners already make use of the positive effects on plant health. For example, they use composts to protect their plants against soil borne diseases in substrate, or to detoxify and reactivate soil after steaming. In order to estimate the potential of Swiss composts to influence
soil fertility and plant health positively, we analyzed one hundred composts representative of the different composting systems and qualities available on the market.
The organic substance and the nutrient content of the composts varied greatly between the composts; the materials of origin were the major factor influencing these values. The respiration rate and enzyme activities also varied greatly, particularly in the youngest composts. These differences become smaller when the composts become more mature. Maturity, the degradation stage of the organic matter, depended not only on the age of the compost, but also on the management of the process. The N-mineralization potential from compost added to soil showed that a high proportion of young composts immobilized the nitrogen in the soil. This problem was hardly correlated with the materials of origin, but with the management of the first stage of the composting
process. Especially composts which had become too dry in this period lost their ammonia-nitrogen, and hence immobilized nitrogen in the soil. Also composts with a low NO3/NH4 ratio, as a rough indicator for an immature compost, immobilized nitrogen in the soil. By contrast, the phytotoxicity of the composts varied very much also in matured composts, showing that the storage of the compost plays a decisive role. While the
majority of compost protected cucumber plants against Pythium ultimum, only a few composts suppressed Rhizoctonia solani in basil. With respect to disease suppression, the management of the maturation process seems to play a major role.
In conclusion, big differences in compost quality and of their impact on soil fertility and on plant health were observed. The management of the composting process seems to influence the quality of the composts to a higher extent than the materials of origin or the composting system. More attention should be paid to biological quality of composts, in order to produce composts with more beneficial effects on crops
Parton energy loss due to synchrotron-like gluon emission
We develop a quasiclassical theory of the synchrotron-like gluon radiation.
Our calculations show that the parton energy loss due to the synchrotron gluon
emission may be important in the jet quenching phenomenon if the plasma
instabilities generate a sufficiently strong chromomagnetic field. Our gluon
spectrum disagrees with that obtained by Shuryak and Zahed within the
Schwinger's proper time method.Comment: 11 pages, 3 eps figure
The role of finite kinematic bounds in the induced gluon emission from fast quarks in a finite size quark-gluon plasma
We study the influence of finite kinematic boundaries on the induced gluon
radiation from a fast quark in a finite size quark-gluon plasma. The
calculations are carried out for fixed and running coupling constant. We find
that for running coupling constant the kinematic correction to the radiative
energy loss is small for quark energy larger than about 5 GeV. Our results
differ both analytically and numerically from that obtained by the GLV group
[6]. The effect of the kinematic cut-offs is considerably smaller than reported
in [6].Comment: 11 pages, 4 figure
Experimental investigations of synchrotron radiation at the onset of the quantum regime
The classical description of synchrotron radiation fails at large Lorentz
factors, , for relativistic electrons crossing strong transverse
magnetic fields . In the rest frame of the electron this field is comparable
to the so-called critical field T. For quantum corrections are essential for the description of
synchrotron radiation to conserve energy. With electrons of energies 10-150 GeV
penetrating a germanium single crystal along the axis, we have
experimentally investigated the transition from the regime where classical
synchrotron radiation is an adequate description, to the regime where the
emission drastically changes character; not only in magnitude, but also in
spectral shape. The spectrum can only be described by quantum synchrotron
radiation formulas. Apart from being a test of strong-field quantum
electrodynamics, the experimental results are also relevant for the design of
future linear colliders where beamstrahlung - a closely related process - may
limit the achievable luminosity.Comment: 11 pages, 18 figures, submitted to PR
Towards an analysis of shear suspension flows using radial basis functions
In this paper, radial basis functions are utilised for numerical prediction of the bulk properties of
particulate suspensions under simple shear conditions. The
suspending fluid is Newtonian and the suspended particles are rigid. Results obtained are compared well with those based on finite elements in the literature
QCD motivated approach to soft interactions at high energies: nucleus-nucleus and hadron-nucleus collisions
In this paper we consider nucleus-nucleus and hadron-nucleus reactions in the
kinematic region: g A^{1/3} G_{3\pom} \exp\Lb \Delta Y\Rb \approx 1
G^2_{3\pom} \exp\Lb \Delta Y\Rb \approx 1 , where G_{3\pom} is the triple
Pomeron coupling, is the vertex of Pomeron nucleon interaction, and 1 +
\Delta_{\pom} denotes the Pomeron intercept. We find that in this kinematic
region the traditional Glauber-Gribov eikonal approach is inadequate. We show
that it is necesssary to take into account inelastic Glauber corrections, which
can not be expressed in terms of the nucleon-nucleon scattering amplitudes. In
the wide range of energies where \alpha'_\pom Y
\ll R^2_A,the scattering amplitude for the nucleus-nucleus interaction, does
not depend on the details of the nucleon-nucleon interaction at high energy. In
the formalism we present, the only (correlated) parameters that are required to
describe the data are \Delta_{\pom}, G_{3\pom} and . These parameters
were taken from our description of the nucleon-nucleon data at high energies
\cite{GLMM}.The predicted nucleus modification factor is compared with RHIC
Au-Au data at Estimates for LHC energies are presented and
discusssed.Comment: 18pp. 14 fugure
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