3,201 research outputs found
Partonic Energy Loss and the Drell-Yan Process
We examine the current status of the extraction of the rate of partonic
energy loss in nuclei from A dependent data. The advantages and difficulties of
using the Drell-Yan process to measure the energy loss of a parton traversing a
cold nuclear medium are discussed. The prospects of using relatively low energy
proton beams for a definitive measurement of partonic energy loss are
presented.Comment: 12 pages, 2 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
Transverse Spectra of Radiation Processes in Medium
We develop a formalism for evaluation of the transverse momentum dependence
of cross sections of the radiation processes in medium. The analysis is based
on the light-cone path integral approach to the induced radiation. The results
are applicable in both QED and QCD
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
Cytokine gene polymorphisms in preterm infants with necrotising enterocolitis: genetic association study
BACKGROUND The inflammatory cytokine cascade is implicated in the pathogenesis of necrotising enterocolitis (NEC). Genetic association studies of cytokine polymorphisms may help to detect molecular mechanisms that are causally related to the disease process. AIM To examine associations between the common genetic variants in candidate inflammatory cytokine genes and NEC in preterm infants. METHODS Multi-centre case-control and genetic association study. DNA samples were collected from 50 preterm infants with NEC and 50 controls matched for gestational age and ethnic group recruited to a multi-centre case-control study. Ten candidate single-nucleotide polymorphisms in cytokines previously associated with infectious or inflammatory diseases were genotyped. The findings were included in random-effects meta-analyses with data from previous genetic association studies. RESULTS All allele distributions were in Hardy-Weinberg equilibrium. None of the studied cytokine polymorphisms was significantly associated with NEC. Four previous genetic association studies of cytokine polymorphisms and NEC in preterm infants were found. Meta-analyses were possible for several single-nucleotide polymorphisms. These increased the precision of the estimates of effect size but did not reveal any significant associations. CONCLUSIONS The available data are not consistent with more than modest associations between these candidate cytokine variant alleles and NEC in preterm infants. Data from future association studies of these polymorphisms may be added to the meta-analyses to obtain more precise estimates of effects sizes.The study was funded by Tenovus (Scotland)
Photon Splitting in a Very Strong Magnetic Field
Photon splitting in a very strong magnetic field is analyzed for energy
. The amplitude obtained on the base of operator-diagram technique
is used. It is shown that in a magnetic field much higher than critical one the
splitting amplitude is independent on the field. Our calculation is in a good
agreement with previous results of Adler and in a strong contradiction with
recent paper of Mentzel et al.Comment: 5 pages,Revtex , 4 figure
Maximizing the Conditional Expected Reward for Reaching the Goal
The paper addresses the problem of computing maximal conditional expected
accumulated rewards until reaching a target state (briefly called maximal
conditional expectations) in finite-state Markov decision processes where the
condition is given as a reachability constraint. Conditional expectations of
this type can, e.g., stand for the maximal expected termination time of
probabilistic programs with non-determinism, under the condition that the
program eventually terminates, or for the worst-case expected penalty to be
paid, assuming that at least three deadlines are missed. The main results of
the paper are (i) a polynomial-time algorithm to check the finiteness of
maximal conditional expectations, (ii) PSPACE-completeness for the threshold
problem in acyclic Markov decision processes where the task is to check whether
the maximal conditional expectation exceeds a given threshold, (iii) a
pseudo-polynomial-time algorithm for the threshold problem in the general
(cyclic) case, and (iv) an exponential-time algorithm for computing the maximal
conditional expectation and an optimal scheduler.Comment: 103 pages, extended version with appendices of a paper accepted at
TACAS 201
Collinear Photon Emission from the Quark-Gluon Plasma: The Light-Cone Path Integral Formulation
We give a simple physical derivation of the photon emission rate from the
weakly coupled quark-gluon plasma connected with the collinear processes and . The analysis is based on the light-cone
path integral approach to the induced radiation. Our results agree with that by
Arnold, Moore and Yaffe obtained using the real-time thermal perturbation
theory. It is demonstrated that the solution of the AMY integral equation is
nothing but the time-integrated Green's function of the light-cone path
integral approach written in the momentum representation.Comment: 12 pages, 2 figure
Jet correlation measurement in heavy-ion collisions: from RHIC to LHC
We attempt to deduce simple options of `jet quenching' phenomena in heavy-ion
collisions at \snn=5.5 \tev at the LHC from the present knowledge of
leading-hadron suppression at RHIC energies. In light of the nuclear
modification factor for leading particles we introduce the nuclear modification
factor for jets, \RAA^{jet}, and for the longitudinal momenta of particles
along the jet axis, \RAA^{p_{\rm L}}.Comment: 9 pages, 7 figures, proceedings, MIT workshop on fluctuations and
correlations in relativistic nuclear collision
Radiative parton energy loss and jet quenching in high-energy heavy-ion collisions
We study within the light-cone path integral approach [3] the effect of the
induced gluon radiation on high-p_{T} hadrons in high-energy heavy-ion
collisions. The induced gluon spectrum is represented in a new form which is
convenient for numerical simulations. For the first time, computations are
performed with a realistic parametrization of the dipole cross section. The
results are in reasonable agreement with suppression of high-p_{T} hadrons in
Au+Au collisions at \sqrt{s}=200 GeV observed at RHIC.Comment: 12 pages, 3 epsi figures. Typos correcte
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