241 research outputs found
Crossing velocities for an annealed random walk in a random potential
We consider a random walk in an i.i.d. non-negative potential on the
d-dimensional integer lattice. The walk starts at the origin and is conditioned
to hit a remote location y on the lattice. We prove that the expected time
under the annealed path measure needed by the random walk to reach y grows only
linearly in the distance from y to the origin. In dimension one we show the
existence of the asymptotic positive speed.Comment: 29 page
Enhancements of gravity wave amplitudes at midlatitudes during sudden stratospheric warmings in 2008
Water vapor transport in the lower mesosphere of the subtropics: a trajectory analysis
The Institute of Applied Physics operates an airborne microwave radiometer AMSOS that measures the rotational transition line of water vapor at 183.3 GHz. Water vapor profiles are retrieved for the altitude range from 15 to 75 km along the flight track. We report on a water vapor enhancement in the lower mesosphere above India and the Arabian Sea. The measurements took place on our flight from Switzerland to Australia and back in November 2005 conducted during EC- project SCOUT-O3. We find an enhancement of up to 25% in the lower mesospheric H<sub>2</sub>O volume mixing ratio measured on the return flight one week after the outward flight. The origin of the air is traced back by means of a trajectory model in the lower mesosphere and wind fields from ECMWF. During the outward flight the air came from the Atlantic Ocean around 25 N and 40 W. On the return flight the air came from northern India and Nepal around 25 N and 90 E. Mesospheric H<sub>2</sub>O measurements from Aura/MLS confirm the transport processes of H<sub>2</sub>O derived by trajectory analysis of the AMSOS data. Thus the large variability of H<sub>2</sub>O VMR during our flight is explained by a change of the winds in the lower mesosphere. This study shows that trajectory analysis can be applied in the mesosphere and is a powerful tool to understand the large variability in mesospheric H<sub>2</sub>O
Variability in the Speed of the Brewer-Dobson Circulation as Observed by Aura/MLS
We use Aura/MLS stratospheric water vapour (H2O) measurements as tracer for dynamics and infer interannual variations in the speed of the Brewer-Dobson circulation (BDC) from 2004 to 2011. We correlate one-year time series of H2O in the lower stratosphere at two subsequent pressure levels (68 hPa, approx.18.8 km and 56 hPa, approx 19.9 km at the Equator) and determine the time lag for best correlation. The same calculation is made on the horizontal on the 100 hPa (approx 16.6 km) level by correlating the H2O time series at the Equator with the ones at 40 N and 40 S. From these lag coefficients we derive the vertical and horizontal speeds of the BDC in the tropics and extra-tropics, respectively. We observe a clear interannual variability of the vertical and horizontal branch. The variability reflects signatures of the Quasi Biennial Oscillation (QBO). Our measurements confirm the QBO meridional circulation anomalies and show that the speed variations in the two branches of the BDC are out of phase and fairly well anti-correlated. Maximum ascent rates are found during the QBO easterly phase. We also find that transport of H2O towards the Northern Hemisphere (NH) is on the average two times faster than to the Southern Hemisphere (SH) with a mean speed of 1.15m/s at 100 hPa. Furthermore, the speed towards the NH shows much more interannual variability with an amplitude of about 21% whilst the speed towards the SH varies by only 10 %. An amplitude of 21% is also observed in the variability of the ascent rate at the Equator which is on the average 0.2mm/s
Towards a Swiss National Research Infrastructure
In this position paper we describe the current status and plans for a Swiss
National Research Infrastructure. Swiss academic and research institutions are
very autonomous. While being loosely coupled, they do not rely on any
centralized management entities. Therefore, a coordinated national research
infrastructure can only be established by federating the various resources
available locally at the individual institutions. The Swiss Multi-Science
Computing Grid and the Swiss Academic Compute Cloud projects serve already a
large number of diverse user communities. These projects also allow us to test
the operational setup of such a heterogeneous federated infrastructure
Lyapunov exponents of Green's functions for random potentials tending to zero
We consider quenched and annealed Lyapunov exponents for the Green's function
of , where the potentials , are i.i.d.
nonnegative random variables and is a scalar. We present a
probabilistic proof that both Lyapunov exponents scale like as
tends to 0. Here the constant is the same for the quenched as for
the annealed exponent and is computed explicitly. This improves results
obtained previously by Wei-Min Wang. We also consider other ways to send the
potential to zero than multiplying it by a small number.Comment: 16 pages, 3 figures. 1 figure added, very minor corrections. To
appear in Probability Theory and Related Fields. The final publication is
available at http://www.springerlink.com, see
http://www.springerlink.com/content/p0873kv68315847x/?p=4106c52fc57743eba322052bb931e8ac&pi=21
The Arabidopsis Pep-PEPR system is induced by herbivore feeding and contributes to JA-mediated plant defence against herbivory
Dysfunction of the Pep-PEPR system and its interplay with JA signalling results in increased plant susceptibility towards herbivore attack indicating that endogenous signalling also contributes to herbivore defenc
Evolutionary divergence of the plant elicitor peptides (Peps) and their receptors: interfamily incompatibility of perception but compatibility of downstream signalling
Plant elicitor peptides (Peps) co-evolved with their receptors, resulting in interfamily incompatibility of Pep recognition. In contrast, operation of defence pathways by Pep receptors is conserved within the flowering plant
What makes a compost suppressive to soilborne pathogens?
Composts have been shown to suppress soilborne pathogens in numerous greenhouse and field experiments. However, the effectiveness of disease suppression is highly variable between composts, and we currently lack reliable indicators to select composts for plant protection. We hypothesize that disease suppression is a complex interplay between abiotic and biotic compost properties. Investigating the microbial communities may help to develop tools for predicting suppressive properties and producing composts with strong biocontrol activity.
In the first part of the project, 17 composts were assessed for disease suppression in a cress–Globisporangium ultimum (syn. Pythium ultimum) system and assessed for their physico-chemical properties. Their microbial communities were analyzed using an Illumina metabarcoding approach, which identified bacterial taxa that are indicative for disease suppression. This data set has now been extended by 30 additional composts and a cucumber–G. ultimum and a cucumber–Rhizoctonia solani test system, which revealed differences in disease suppression between pathogens and plant species. The microbial communities are currently assessed by SMRT cell long-read sequencing with the goal to get a high taxonomic resolution to accurately relate the sequencing data with isolates obtained from the composts. Our comprehensive data set provides new insights into the contribution of different abiotic and biotic factors to disease-suppressive activity of composts
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