3,073 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
Chemical Equilibration in Hadronic Collisions
We study chemical equilibration in out-of-equilibrium Quark-Gluon Plasma
using the first principles method of QCD effective kinetic theory, accurate at
weak coupling. In longitudinally expanding systems--relevant for relativistic
nuclear collisions--we find that for realistic couplings chemical equilibration
takes place after hydrodynamization, but well before local thermalization. We
estimate that hadronic collisions with final state multiplicities
live long enough to reach approximate
chemical equilibrium, which is consistent with the saturation of strangeness
enhancement observed in proton-proton, proton-nucleus and nucleus-nucleus
collisions.Comment: 7 pages, 3 figures, see also our companion paper arXiv:1811.03068, v2
small changes, published versio
Medium-induced gluon radiation and jet quenching in heavy ion collisions
In this brief review, I summarize the new developments on the description of
gluon radiation by energetic quarks traversing a medium as well as the
observable consequences in high-energy heavy ion collisions. Information about
the initial state is essential for a reliable interpretation of the
experimental results and will also be reviewed. Comparison with experimental
data from RHIC and expectation for the future LHC will be given.Comment: 16 pages, 9 postscript figures. Invited brief review for Modern
Physics Letters
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
Limit Synchronization in Markov Decision Processes
Markov decision processes (MDP) are finite-state systems with both strategic
and probabilistic choices. After fixing a strategy, an MDP produces a sequence
of probability distributions over states. The sequence is eventually
synchronizing if the probability mass accumulates in a single state, possibly
in the limit. Precisely, for 0 <= p <= 1 the sequence is p-synchronizing if a
probability distribution in the sequence assigns probability at least p to some
state, and we distinguish three synchronization modes: (i) sure winning if
there exists a strategy that produces a 1-synchronizing sequence; (ii)
almost-sure winning if there exists a strategy that produces a sequence that
is, for all epsilon > 0, a (1-epsilon)-synchronizing sequence; (iii) limit-sure
winning if for all epsilon > 0, there exists a strategy that produces a
(1-epsilon)-synchronizing sequence.
We consider the problem of deciding whether an MDP is sure, almost-sure,
limit-sure winning, and we establish the decidability and optimal complexity
for all modes, as well as the memory requirements for winning strategies. Our
main contributions are as follows: (a) for each winning modes we present
characterizations that give a PSPACE complexity for the decision problems, and
we establish matching PSPACE lower bounds; (b) we show that for sure winning
strategies, exponential memory is sufficient and may be necessary, and that in
general infinite memory is necessary for almost-sure winning, and unbounded
memory is necessary for limit-sure winning; (c) along with our results, we
establish new complexity results for alternating finite automata over a
one-letter alphabet
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
Decays Z' -> \gamma\gamma\gamma{} and Z -> \gamma\gamma\gamma{} in the minimal 331 model
The possibility of a significant effect of exotic particles on the
Z'->\gamma\gamma\gamma{} and Z->\gamma\gamma\gamma{} decays is investigated in
the context of the minimal 331 model. This model, which is based in the
SU_C(3)xSU_L(3)xU_X(1) gauge group, predicts the existence of many exotic
charged particles that can significantly enhance the decay widths. It is found
that the standard model prediction for the Z->\gamma\gamma\gamma{} decay
remains essentially unchanged, as the new physics effects quickly decouples. On
the other hand, it is found that the contributions of the new exotic quarks and
gauge bosons predicted by this model lead to a branching fraction for the
Z'->\gamma\gamma\gamma{} decay of about 10^(-6), which is about three orders of
magnitude larger than that of the Z->\gamma\gamma\gamma{} decay.Comment: 20 pages and 20 figure
Quantitative multi-objective verification for probabilistic systems
We present a verification framework for analysing multiple quantitative objectives of systems that exhibit both nondeterministic and stochastic behaviour. These systems are modelled as probabilistic automata, enriched with cost or reward structures that capture, for example, energy usage or performance metrics. Quantitative properties of these models are expressed in a specification language that incorporates probabilistic safety and liveness properties, expected total cost or reward, and supports multiple objectives of these types. We propose and implement an efficient verification framework for such properties and then present two distinct applications of it: firstly, controller synthesis subject to multiple quantitative objectives; and, secondly, quantitative compositional verification. The practical applicability of both approaches is illustrated with experimental results from several large case studies
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
Multi-photon effects in energy losses spectra
Effect of radiation of many photons by a single electron traversing a target
is discussed. When the summary energy of emitted photons (the energy losses
spectrum) is measured only, the photon spectrum is distorted comparing with the
photon spectrum in one interaction. Influence of this effect is discussed for
the cases (1) bremsstrahlung (described by Bethe-Heitler formula), (2) the
strong Landau-Pomeranchuk-Migdal effect and (3) transition radiation.
Qualitative picture of the phenomenon is discussed in detail. Comparison with
the recent SLAC experiment in relatively thick target (2.7% of the radiation
length), where the effect of emission of many photons by a projectile is very
essential, shows perfect agreement of the theory and data.Comment: LaTeX2.09, 19 pages, 5 PostScript figure
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