32,215 research outputs found
High damage potential of seed-borne spot blotch in organically grown spring barley in Denmark
Spot blotch of barley (Bipolaris sorokiniana, perfect state: Cochliobolus sativus) occurs wherever barley is grown but is normally not considered a major problem in Danish barley production. It is therefore not included in routine disease surveys or official variety testing in Denmark. However, recommended seed contamination thresholds are 30% for spring barley and 15% for winter barley. Several spring barley varieties were grown under organic (no seed dressing, mechanical weeding) and conventional (seed dressing with fungicides, herbicide application) production conditions at three sites in Denmark in 2003. The harvested seeds were analysed for contamination levels of seed-borne B. sorokiniana using a blotter method. The percentage of seeds contaminated with B. sorokiniana ranged from about 5 to 95 % and was highly depending on the site, production system and variety. Contamination levels of organically cultivated plots were about twice as high as those of plots receiving conventional treatments. The germinating ability of seeds was highly affected by the level of B. sorokiniana contamination and declined drastically at contamination levels above 60%. This effect appeared to differ among varieties. The 1000-grain weight was not affected by the level of spot blotch contamination of seeds. The results indicate that the importance of spot blotch may be underrated, especially in organic barley production and that the role of varietal resistance should be investigated. More results are expected from ongoing seed analyses
High voltage breakdown initiated by particle impact
High voltage breakdown initiated by particle impact across electrode ga
Ionization from Fe atoms incident on various gas targets
Ionization from iron atoms incident on target gases of helium, neon, nitrogen, carbon dioxide, and ai
Structure, phase behavior and inhomogeneous fluid properties of binary dendrimer mixtures
The effective pair potentials between different kinds of dendrimers in
solution can be well approximated by appropriate Gaussian functions. We find
that in binary dendrimer mixtures the range and strength of the effective
interactions depend strongly upon the specific dendrimer architecture. We
consider two different types of dendrimer mixtures, employing the Gaussian
effective pair potentials, to determine the bulk fluid structure and phase
behavior. Using a simple mean field density functional theory (DFT) we find
good agreement between theory and simulation results for the bulk fluid
structure. Depending on the mixture, we find bulk fluid-fluid phase separation
(macro-phase separation) or micro-phase separation, i.e., a transition to a
state characterized by undamped periodic concentration fluctuations. We also
determine the inhomogeneous fluid structure for confinement in spherical
cavities. Again, we find good agreement between the DFT and simulation results.
For the dendrimer mixture exhibiting micro-phase separation, we observe rather
striking pattern formation under confinement.Comment: 8 pages, 10 figure
Gas-liquid critical parameters of asymmetric models of ionic fluids
The effects of size and charge asymmetry on the gas-liquid critical
parameters of a primitive model (PM) of ionic fluids are studied within the
framework of the statistical field theory based on the collective variables
method. Recently, this approach has enabled us to obtain the correct trends of
the both critical parameters of the equisize charge-asymmetric PM without
assuming ionic association. In this paper we focus on the general case of an
asymmetric PM characterized by the two parameters: hard-sphere diameter-,
and charge, , ratios of the
two ionic species. We derive an explicit expression for the chemical potential
conjugate to the order parameter which includes the effects of correlations up
to the third order. Based on this expression we consider the three versions of
PM: a monovalent size-asymmetric PM (, ), an equisize
charge-asymmetric PM (, ) and a size- and charge-asymmetric
PM (, ). Similar to simulations, our theory predicts that
the critical temperature and the critical density decrease with the increase of
size asymmetry. Regarding the effects of charge asymmetry, we obtain the
correct trend of the critical temperature with , while the trend of the
critical density obtained in this approximation is inconsistent with
simulations, as well as with our previous results found in the higher-order
approximation. We expect that the consideration of the higher-order
correlations will lead to the correct trend of the critical density with charge
asymmetry.Comment: 23 pages, 6 figure
A reduced coupled-mode description for the electron-ion energy relaxation in dense matter
We present a simplified model for the electron-ion energy relaxation in dense two-temperature systems that includes the effects of coupled collective modes. It also extends the standard Spitzer result to both degenerate and strongly coupled systems. Starting from the general coupled-mode description, we are able to solve analytically for the temperature relaxation time in warm dense matter and strongly coupled plasmas. This was achieved by decoupling the electron-ion dynamics and by representing the ion response in terms of the mode frequencies. The presented reduced model allows for a fast description of temperature equilibration within hydrodynamic simulations and an easy comparison for experimental investigations. For warm dense matter, both fluid and solid, the model gives a slower electron-ion equilibration than predicted by the classical Spitzer result
Ion structure in warm dense matter: benchmarking solutions of hypernetted-chain equations by first-principle simulations
We investigate the microscopic structure of strongly coupled ions in warm dense matter using ab initio simulations and hypernetted chain (HNC) equations. We demonstrate that an approximate treatment of quantum effects by weak pseudopotentials fails to describe the highly degenerate electrons in warm dense matter correctly. However, one-component HNC calculations for the ions agree well with first-principles simulations if a linearly screened Coulomb potential is used. These HNC results can be further improved by adding a short-range repulsion that accounts for bound electrons. Examples are given for recently studied light elements, lithium and beryllium, and for aluminum where the extra short-range repulsion is essential
Suppression of hole-hole scattering in GaAs/AlGaAs heterostructures under uniaxial compression
Resistance, magnetoresistance and their temperature dependencies have been
investigated in the 2D hole gas at a [001] p-GaAs/AlGaAs
heterointerface under [110] uniaxial compression. Analysis performed in the
frame of hole-hole scattering between carriers in the two spin splitted
subbands of the ground heavy hole state indicates, that h-h scattering is
strongly suppressed by uniaxial compression. The decay time of the
relative momentum reveals 4.5 times increase at a uniaxial compression of 1.3
kbar.Comment: 5 pages, 3 figures. submitted to Phys.Rev.
A repulsive reference potential reproducing the dynamics of a liquid with attractions
A well-known result of liquid state theory is that the structure of dense
fluids is mainly determined by repulsive forces. The WCA potential, which cuts
intermolecular potentials at their minima, is therefore often used as a
reference. However, this reference gives quite wrong results for the viscous
dynamics of the Kob-Andersen binary Lennard-Jones liquid [Berthier and Tarjus,
Phys. Rev. Lett. 103, 170601 (2009)]. We show that repulsive inverse-power law
potentials provide a useful reference for this liquid by reproducing its
structure, dynamics, and isochoric heat capacity
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