259 research outputs found
Two distinct AFLP types in three populations of marram grass (Ammophila arenaria in Wales)
The genetic structure of marram grass populations at coastal and inland locations, 200 m apart, was investigated at three sites by means of amplified fragment length polymorphism (AFLP) DNA markers. We expected a genetic differentiation between coastal and inland populations and more genetic variation in the coastal areas as a result of different events of colonization by different plant materials. An assignment test showed that the sampled Ammophila arenaria could be assigned to two groups based on AFLP data. The spatial distribution of the two AFLP types of A. arenaria varied with sampling location. In two of the three locations, mainly one type (1) was found in the newly formed dunes. This type did also occur further landward, but the second type (2) was preferentially found in inland populations. Genetic diversity was very low and of similar value in both coastal and inland populations. For each site, outlier loci with respect to FST value were identified, which may be indicative of different selection pressures in coastal compared with inland clusters. However, no identical outlier loci were found at all three sites. Possible explanations for the observed difference in distribution of type 1 and 2 populations between coastal and inland sites are discusse
Bodemweerbaarheid als alternatief voor chemie
Bodems die planten beschermen tegen bodemziekten en -plagen? Ze bestaan. De kunst is om dit verschijnsel in alle bodems op te roepen. Stap voor stap ontrafelen onderzoekers van Wageningen UR het mechanisme en ontwikkelen ze praktische toepassingen
Interaction Effects on Number Fluctuations in a Bose-Einstein Condensate of Light
We investigate the effect of interactions on condensate-number fluctuations
in Bose-Einstein condensates. For a contact interaction we variationally obtain
the equilibrium probability distribution for the number of particles in the
condensate. To facilitate comparison with experiment, we also calculate the
zero-time delay autocorrelation function for different strengths
of the interaction. Finally, we focus on the case of a condensate of photons
and discuss possible mechanisms for the interaction.Comment: 13 pages, version 3, 4 figure
Phase diffusion in a Bose-Einstein condensate of light
We study phase diffusion in a Bose-Einstein condensate of light in a
dye-filled optical microcavity, i.e., the spreading of the probability
distribution for the condensate phase. To observe this phenomenon, we propose
an interference experiment between the condensed photons and an external laser.
We determine the average interference patterns, considering quantum and thermal
fluctuations as well as dissipative effects due to the dye. Moreover, we show
that a representative outcome of individual measurements can be obtained from a
stochastic equation for the global phase of the condensate
Theory for Bose-Einstein condensation of light in nano-fabricated semiconductor microcavities
We construct a theory for Bose-Einstein condensation of light in
nano-fabricated semiconductor microcavities. We model the semiconductor by one
conduction and one valence band which consist of electrons and holes that
interact via a Coulomb interaction. Moreover, we incorporate screening effects
by using a contact interaction with the scattering length for a Yukawa
potential and describe in this manner the crossover from exciton gas to
electron-hole plasma as we increase the excitation level of the semiconductor.
We then show that the dynamics of the light in the microcavities is damped due
to the coupling to the semiconductor. Furthermore, we demonstrate that on the
electron-hole plasma side of the crossover, which is relevant for the
Bose-Einstein condensation of light, this damping can be described by a single
dimensionless damping parameter that depends on the external pumping.
Hereafter, we propose to probe the superfluidity of light in these
nano-fabricated semiconductor microcavities by making use of the differences in
the response in the normal or superfluid phase to a sudden rotation of the
trap. In particular, we determine frequencies and damping of the scissors modes
that are excited in this manner. Moreover, we show that a distinct signature of
the dynamical Casimir effect can be observed in the density-density
correlations of the excited light fluid
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