6,010 research outputs found
Nectria galligena as the cause of a collar rot disease in organically grown Topaz apple trees
Symptoms resembling collar rot were detected in organically managed Topaz trees aged 3-10 years, occur-ring one to several years after planting of the orchard. Trees were killed within the same growing season in which symptoms were first observed. The disease commonly progressed as a complete covered canker at the base of the tree trunk. Isolation attempts were negative for Phytophthora and other Oomycetes, but con-sistently yielded Nectria galligena. The possibility of latent (endophytic) infections of N. galligena as the cause of delayed collar rot symptoms is briefly discussed
Diplodia seriata, cause of black fruit rot in organically grown apples in Holland, Belgium and Northern Germany
A fruit rot resembling Gloeosporium infections but appearing on fruits prior to harvest was
noticed in organic apple orchards in Holland, Belgium and Northern Germany in 2007.
Infections were most commonly observed on âElstarâ, but other cultivars were also
affected. Fruit colonisation progressed in two steps, whereby a latent stage of sunken
black lesions in immature fruits gave rise to a rapidly spreading firm brown rot upon fruit
ripening. Isolation experiments from both stages consistently yielded a single species of
fungus identified as Diplodia seriata, formerly known under the teleomorph name
Botryosphaeria obtusa. Lesions of D. seriata were also seen on leaves as necrotic light
brown spots surrounded by a purple halo, and occasionally on small twigs as cankers.
Fruit mummies on apple twigs were heavily colonised by D. seriata and are thus likely to
carry inoculum for fruit infections during late summer or in the following growing season
Konzept zur Reduktion der Regenfleckenkrankheit - Ermittlung von Parametern zur Biologie der Erreger unter westeuropĂ€ischen Klimabedingungen als Grundlage fĂŒr die Weiterentwicklung eines Prognosemodells
Ziel des dreijĂ€hrigen Projekts war es, SchlĂŒsselparameter der bisher unter europĂ€ischen Bedingungen nur wenig erforschten Regenfleckenkrankheit (RFK) zu erarbeiten. In den Regionen Altes Land und Bodensee dominierte in allen drei Versuchsjahren (2007 â 2009) ein und derselbe RFK-Erreger, Peltaster sp.. Weitere RFK-Erreger sowie der Erreger der Fliegenschmutzkrankheit (FSK), Schizothyrium pomi, kamen nur sporadisch vor und sind wahrscheinlich fĂŒr die BekĂ€mpfung der Symptome derzeit ohne Bedeutung. In beiden Regionen ist die RFK fast ausschlieĂlich auf ökologisch bewirtschaftete Anlagen beschrĂ€nkt. Eine Besiedlung von Obstanlagen durch RFK-Erreger findet zunĂ€chst von auĂen statt, kann dann aber in den darauf folgenden Jahren durch endogenes Inokulum getragen werden. Fruchtmumien spielen eine Rolle als endogene Infektionsquellen. Umfangreiche Versuche zur PrĂ€zisierung der Infektionsbedingungen haben ergeben, dass eine Besiedlung der jungen FrĂŒchte bereits zum sehr frĂŒhen Zeitpunkt (T-Stadium, BBCH 74) und danach wĂ€hrend des gesamten weiteren Saisonverlaufs erfolgen kann. Die StĂ€rke der SymptomausprĂ€gung zur Ernte ist in erster Linie davon abhĂ€ngig, wie lange die FrĂŒchte den natĂŒrlichen Infektionsbedingungen ausgesetzt waren. Je spĂ€ter in der Saison Infektionen stattfinden, desto weniger Zeit haben die RFK-Pilze fĂŒr die Besiedlung und Ausbreitung auf der Frucht, so dass spĂ€te Infektionen i.d.R. nicht mehr zu starken Befallsgraden fĂŒhren. Zur AusprĂ€gung von RFK-Symptomen ist Blattfeuchte, auch in Form von Taubildung, ausreichend, jedoch wird die Symptomausbildung mit zunehmenden Niederschlagsmengen deutlich beschleunigt. Sind erste RFK-Symptome in einer Anlage sichtbar, verkĂŒrzt sich die zur Inkubation notwendige kumulative BlattnĂ€ssedauer von etwa 250 auf unter 150 Stunden. Die RFK-Erreger scheinen eine mehrwöchige Trockenphase unbeschadet ĂŒberdauern zu können. Apfelsorten zeigen deutliche Unterschiede in der AusprĂ€gung der RFK-Symptome. Die Ursachen hierfĂŒr mĂŒssen in weiteren Untersuchungen geklĂ€rt werden
Reaction dynamics in Pb+Pb at the CERN/SPS: from partonic degrees of freedom to freeze-out
We analyze the reaction dynamics of central Pb+Pb collisions at 160
GeV/nucleon. First we estimate the energy density pile-up at mid-rapidity and
calculate its excitation function: The energy density is decomposed into
hadronic and partonic contributions. A detailed analysis of the collision
dynamics in the framework of a microscopic transport model shows the importance
of partonic degrees of freedom and rescattering of leading (di)quarks in the
early phase of the reaction for E > 30 GeV/nucleon. The energy density reaches
up to 4 GeV/fm^3, 95% of which are contained in partonic degrees of freedom. It
is shown that cells of hadronic matter, after the early reaction phase, can be
viewed as nearly chemically equilibrated. This matter never exceeds energy
densities of 0.4 GeV/fm^3, i.e. a density above which the notion of separated
hadrons loses its meaning. The final reaction stage is analyzed in terms of
hadron ratios, freeze-out distributions and a source analysis for final state
pions.Comment: 10 pages, 7 figures, Proceedings of the Erice School on Nuclear
Physics in Erice, Sicily, Italy, September 17 -25 1998; to be published in
Progress in Particle and Nuclear Physics Vol. 4
Phase chaos in the anisotropic complex Ginzburg-Landau Equation
Of the various interesting solutions found in the two-dimensional complex
Ginzburg-Landau equation for anisotropic systems, the phase-chaotic states show
particularly novel features. They exist in a broader parameter range than in
the isotropic case, and often even broader than in one dimension. They
typically represent the global attractor of the system. There exist two
variants of phase chaos: a quasi-one dimensional and a two-dimensional
solution. The transition to defect chaos is of intermittent type.Comment: 4 pages RevTeX, 5 figures, little changes in figures and references,
typos removed, accepted as Rapid Commun. in Phys. Rev.
Topological Lensing in Spherical Spaces
This article gives the construction and complete classification of all
three-dimensional spherical manifolds, and orders them by decreasing volume, in
the context of multiconnected universe models with positive spatial curvature.
It discusses which spherical topologies are likely to be detectable by
crystallographic methods using three-dimensional catalogs of cosmic objects.
The expected form of the pair separation histogram is predicted (including the
location and height of the spikes) and is compared to computer simulations,
showing that this method is stable with respect to observational uncertainties
and is well suited for detecting spherical topologies.Comment: 32 pages, 26 figure
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Search for anomalous t t-bar production in the highly-boosted all-hadronic final state
A search is presented for a massive particle, generically referred to as a
Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are
sufficiently massive to produce highly Lorentz-boosted top quarks, which yield
collimated decay products that are partially or fully merged into single jets.
The analysis uses new methods to analyze jet substructure, providing
suppression of the non-top multijet backgrounds. The analysis is based on a
data sample of proton-proton collisions at a center-of-mass energy of 7 TeV,
corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits
in the range of 1 pb are set on the product of the production cross section and
branching fraction for a topcolor Z' modeled for several widths, as well as for
a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any
enhancement in t t-bar production beyond expectations of the standard model for
t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version
includes a minor typo correction that will be submitted as an erratu
- âŠ