3,151 research outputs found
Detection of arabis mosaic virus using the polymerase chain reaction (PCR)
A new method is described for detecting arabis mosaic virus (ArMV) in infected plants. Specific sequences of ArMV-RNA present in total nucleic acid extracts of infected Vitis vinifera or Chenopodium quinoa were initially reverse-transcribed into a complementary DNA (cDNA), then amplified by PCR using specific oligonucleotide-primers. Different primer combinations distinguished between an ArMV infection and an infection with grapevine fanleaf or raspberry ringspot virus. The amount of nucleic acids obtained from 5 mg grapevine leaves resp. 1 mg leaves of Ch. quinoa were sufficient for detecting ArMV
Amplification of different marker sequences for identification of Agrobacterium vitis strains
Research Not
Population dynamics of Agrobacterium vitis in two grapevine varieties during the vegetation period
In this work populations of Agrobacterium vitis were monitored within one year. Starting in the middle of May, the population density of A. vitis was screened every week in all parts of two-year-old Müller-Thurgau and Riesling grapevines which were freed from A. vitis by thermotherapy and inoculated with A. vitis NW90. Every week, 5 plants of the two varieties were examined for A. vitis in new shoots, around the inoculation site, in one- and two-year-old parts of the stem, in the rootstock and in the roots. Beyond the inoculation site the A. vitis population density was too low for statistical evaluation of population dynamics. At the inoculation site a seasonal course of the A. vitis population was found in both grapevine varieties. The A. vitis population density was highest at the end of May, but little later it dropped to a low level during the sommer months. A second maximum of population density was determined in October which reached nearly the same value as in spring. Population density of A. vitis correlated to physiological changes of the grapevine plant during the vegetation period. Though the population dynamics of A. vitis followed parallel courses in both grapevine varieties, differences in the population density and in the onset of the autumn increase were determined. This could be attributed to physiological differences of the two varieties. The migration of pathogenic bacteria from the inoculation site to the roots took at least 15 weeks
Crystallographically oriented magnetic ZnFe2O4 nanoparticles synthesized by Fe implantation into ZnO
In this paper, a correlation between structural and magnetic properties of Fe
implanted ZnO is presented. High fluence Fe^+ implantation into ZnO leads to
the formation of superparamagnetic alpha-Fe nanoparticles. High vacuum
annealing at 823 K results in the growth of alpha-Fe particles, but the
annealing at 1073 K oxidized the majority of the Fe nanoparticles. After a long
term annealing at 1073 K, crystallographically oriented ZnFe2O4 nanoparticles
were formed inside ZnO with the orientation relationship of
ZnFe2O4(111)[110]//ZnO(0001)[1120]. These ZnFe2O4 nanoparticles show a
hysteretic behavior upon magnetization reversal at 5 K.Comment: 21 pages, 7 figures, accepted by J. Phys. D: Appl. Phy
Crystalline Ni nanoparticles as the origin of ferromagnetism in Ni implanted ZnO crystals
We report the structural and magnetic properties of ZnO single crystals
implanted at 623 K with up to 10 at. % of Ni. As revealed by X-ray diffraction,
crystalline fcc-Ni nanoparticles were formed inside ZnO. The magnetic behavior
(magnetization with field reversal and with different temperature protocol) of
all samples is well explained by a magnetic Ni-nanoparticle system. Although
the formation of Ni:ZnO based diluted magnetic semiconductor cannot be ruled
out, the major contribution to the magnetic properties stems from crystalline
nanoparticles synthesized under these implantation conditions.Comment: 15 pages, 4 figures, to be published at J. Appl. Phy
Kinetic Ising model in an oscillating field: Finite-size scaling at the dynamic phase transition
We study hysteresis for a two-dimensional, spin-1/2, nearest-neighbor,
kinetic Ising ferromagnet in an oscillating field, using Monte Carlo
simulations. The period-averaged magnetization is the order parameter for a
proposed dynamic phase transition (DPT). To quantify the nature of this
transition, we present the first finite-size scaling study of the DPT for this
model. Evidence of a diverging correlation length is given, and we provide
estimates of the transition frequency and the critical indices ,
and .Comment: Accepted by Physical Review Letters. 9 page
Self-Assembly of Supramolecular Triblock Copolymer Complexes
Four different poly(tert-butoxystyrene)-b-polystyrene-b-poly(4-vinylpyridine) (PtBOS-b-PS-b-P4VP) linear triblock copolymers, with the P4VP weight fraction varying from 0.08 to 0.39, were synthesized via sequential anionic polymerization. The values of the unknown interaction parameters between styrene and tert-butoxystyrene and between tert-butoxystyrene and 4-vinylpyridine were determined from random copolymer blend miscibility studies and found to satisfy 0.031<χS,tBOS<0.034 and 0.39<χ4VP,tBOS<0.43, the latter being slightly larger than the known 0.30<χS,4VP≤0.35 value range. All triblock copolymers synthesized adopted a P4VP/PS core/shell cylindrical self-assembled morphology. From these four triblock copolymers supramolecular complexes were prepared by hydrogen bonding a stoichiometric amount of pentadecylphenol (PDP) to the P4VP blocks. Three of these complexes formed a triple lamellar ordered state with additional short length scale ordering inside the P4VP(PDP) layers. The self-assembled state of the supramolecular complex based on the triblock copolymer with the largest fraction of P4VP consisted of alternating layers of PtBOS and P4VP(PDP) layers with PS cylinders inside the latter layers. The difference in morphology between the triblock copolymers and the supramolecular complexes is due to two effects: (i) a change in effective composition and, (ii) a reduction in interfacial tension between the PS and P4VP containing domains. The small angle X-ray scattering patterns of the supramolecules systems are very temperature sensitive. A striking feature is the disappearance of the first order scattering peak of the triple lamellar state in certain temperature intervals, while the higher order peaks (including the third order) remain. This is argued to be due to the thermal sensitivity of the hydrogen bonding and thus directly related to the very nature of these systems.
Resonant inelastic x-ray scattering study of the electronic structure of CuO
A resonant inelastic x-ray scattering study of the electronic structure of
the semiconductor cuprous oxide, , is reported. When the incident
x-ray energy is tuned to the Cu K-absorption edge, large enhancements of the
spectral features corresponding to the electronic transitions between the
valence band and the conduction band are observed. A feature at 6.5 eV can be
well described by an interband transition from occupied states of mostly Cu 3d
charactor to unoccupied states with mixed 3d, 4s and 2p character. In addition,
an insulating band gap is observed, and the momentum dependence of the lower
bound is measured along the direction. This is found to be in good
agreement with the valence band dispersion measured with angle-resolved
photoemission spectroscopy.Comment: 7 pages, 6 figure
Random Field Models for Relaxor Ferroelectric Behavior
Heat bath Monte Carlo simulations have been used to study a four-state clock
model with a type of random field on simple cubic lattices. The model has the
standard nonrandom two-spin exchange term with coupling energy and a random
field which consists of adding an energy to one of the four spin states,
chosen randomly at each site. This Ashkin-Teller-like model does not separate;
the two random-field Ising model components are coupled. When , the
ground states of the model remain fully aligned. When , a
different type of ground state is found, in which the occupation of two of the
four spin states is close to 50%, and the other two are nearly absent. This
means that one of the Ising components is almost completely ordered, while the
other one has only short-range correlations. A large peak in the structure
factor appears at small for temperatures well above the transition
to long-range order, and the appearance of this peak is associated with slow,
"glassy" dynamics. The phase transition into the state where one Ising
component is long-range ordered appears to be first order, but the latent heat
is very small.Comment: 7 pages + 12 eps figures, to appear in Phys Rev
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