319 research outputs found
Exceeding the threshold value for Trioza apicalis Förster 1848 in carrot fields did not cause damage as revealed during monitoring in Germany from 2017–2020
The carrot psyllid Trioza apicalis Förster 1848 is a carrot pest in Europe that can cause serious damages in case of massive occurrence. Damages up to a total loss of yield have been reported from Scandinavian countries but also from Switzerland. The action threshold to control the pest with chemical pesticides is 0.2 T. apicalis per day and trap caught by sticky traps. We investigated the number of T. apicalis with sticky traps on carrot fields of the study regions Lüneburg/Uelzen and Hameln/Bad Pyrmont in Germany, during the period 2017–2020. The number of T. apicalis caught was generally very low in both study regions. On several fields in successive weeks almost no individuals were found in the study region Hameln/Bad Pyrmont. In Lüneburg/Uelzen was at least one field each year where the number of carrot psyllid was clearly higher than in all other fields and exceeded the threshold level. Surprisingly on carrot fields in close proximity to carrot fields from the previous year, the T. apicalis numbers were only slightly increased. Nonetheless, no loss of yield was reported for any of the fields in the four years of the study, although the generally defined threshold has been exceeded on many of the investigated carrot fields.Bundesanstalt für Landwirtschaft und Ernährung
http://dx.doi.org/10.13039/501100010771Bundesanstalt für Landwirtschaft und Ernährung (DE)Julius Kühn-Institut (JKI), Bundesforschungsinstitut für Kulturpflanzen (4250)Peer Reviewe
Exceeding the threshold value for Trioza apicalis Förster 1848 in carrot fields did not cause damage as revealed during monitoring in Germany from 2017–2020
The carrot psyllid Trioza apicalis Förster 1848 is a carrot pest in Europe that can cause serious damages in case of massive occurrence. Damages up to a total loss of yield have been reported from Scandinavian countries but also from Switzerland. The action threshold to control the pest with chemical pesticides is 0.2 T. apicalis per day and trap caught by sticky traps. We investigated the number of T. apicalis with sticky traps on carrot fields of the study regions Lüneburg/Uelzen and Hameln/Bad Pyrmont in Germany, during the period 2017–2020. The number of T. apicalis caught was generally very low in both study regions. On several fields in successive weeks almost no individuals were found in the study region Hameln/Bad Pyrmont. In Lüneburg/Uelzen was at least one field each year where the number of carrot psyllid was clearly higher than in all other fields and exceeded the threshold level. Surprisingly on carrot fields in close proximity to carrot fields from the previous year, the T. apicalis numbers were only slightly increased. Nonetheless, no loss of yield was reported for any of the fields in the four years of the study, although the generally defined threshold has been exceeded on many of the investigated carrot fields
Light-Induced Metastable Magnetic Texture Uncovered by in situ Lorentz Microscopy
Magnetic topological defects, such as vortices and Skyrmions, can be stabilized as equilibrium structures in nanoscale geometries and by tailored intrinsic magnetic interactions. Here, employing rapid quench conditions, we report the observation of a light-induced metastable magnetic texture, which consists of a dense nanoscale network of vortices and antivortices. Our results demonstrate the emergence of ordering mechanisms in quenched optically driven systems, which may give a general access to novel magnetic structures on nanometer length scales
Observation of Collective Excitations of the Dilute 2D Electron System
We report inelastic light scattering measurements of dispersive spin and
charge density excitations in dilute 2D electron systems reaching densities
less than 10^{10} cm^{-2}. In the quantum Hall state at nu=2, roton critical
points in the spin inter--Landau level mode show a pronounced softening as r_s
is increased. Instead of a soft mode instability predicted by Hartree--Fock
calculations for r_s ~ 3.3, we find evidence of multiple rotons in the
dispersion of the softening spin excitations. Extrapolation of the data
indicates the possibility of an instability for r_s >~ 11.Comment: Submitted to Physical Review Letter
The giant planet orbiting the cataclysmic binary DP Leonis
Planets orbiting post-common envelope binaries provide fundamental
information on planet formation and evolution, especially for the yet nearly
unexplored class of circumbinary planets. We searched for such planets in \odp,
an eclipsing short-period binary, which shows long-term eclipse-time
variations. Using published, reanalysed, and new mid-eclipse times of the white
dwarf in DP\,Leo, obtained between 1979 and 2010, we find agreement with the
light-travel-time effect produced by a third body in an elliptical orbit. In
particular, the measured binary period in 2009/2010 and the implied radial
velocity coincide with the values predicted for the motion of the binary and
the third body around the common center of mass. The orbital period, semi-major
axis, and eccentricity of the third body are P_c = 28.0 +/- 2.0 yrs, a_c = 8.2
+/- 0.4 AU, and e_c = 0.39 +/- 0.13. Its mass of M_c sin(i_c) = 6.1 +/- 0.5 M_J
qualifies it as a giant planet. It formed either as a first generation object
in a protoplanetary disk around the original binary or as a second generation
object in a disk formed in the common envelope shed by the progenitor of the
white dwarf. Even a third generation origin in matter lost from the present
accreting binary can not be entirely excluded. We searched for, but found no
evidence for a fourth body.Comment: Accepted by A&
Plasma dispersion of multisubband electron systems over liquid helium
Density-density response functions are evaluated for nondegenerate
multisubband electron systems in the random-phase approximation for arbitrary
wave number and subband index. We consider both quasi-two-dimensional and
quasi-one- dimensional systems for electrons confined to the surface of liquid
helium. The dispersion relations of longitudinal intrasubband and transverse
intersubband modes are calculated at low temperatures and for long wavelengths.
We discuss the effects of screening and two-subband occupancy on the plasmon
spectrum. The characteristic absorption edge of the intersubband modes is
shifted relatively to the single-particle intersubband separation and the
depolarization shift correction can be significant at high electron densities
Nano-structured magnetic metamaterial with enhanced nonlinear properties
Nano-structuring can significantly modify the properties of materials. We demonstrate that size-dependent modification of the spin-wave spectra in magnetic nano-particles can affect not only linear, but also nonlinear magnetic response. The discretization of the spectrum removes the frequency degeneracy between the main excitation mode of a nano-particle and the higher spin-wave modes, having the lowest magnetic damping, and reduces the strength of multi-magnon relaxation processes. This reduction of magnon-magnon relaxation for the main excitation mode leads to a dramatic increase of its lifetime and amplitude, resulting in the intensification of all the nonlinear processes involving this mode. We demonstrate this experimentally on a two-dimensional array of permalloy nano-dots for the example of parametric generation of a sub-harmonic of an external microwave signal. The characteristic lifetime of this sub-harmonic is increased by two orders of magnitude compared to the case of a continuous magnetic film, where magnon-magnon relaxation limits the lifetime
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