11,696 research outputs found
Seed conservation in ex situ genebanks - genetic studies on longevity in barley
Recognizing the danger due to a permanent risk of loss of the genetic variability of cultivated plants and their wild relatives in response to changing environmental conditions and cultural practices, plant ex situ genebank collections were created since the beginning of the last century. World-wide more than 6 million accessions have been accumulated of which more than 90% are stored as seeds. Research on seed longevity was performed in barley maintained for up to 34 years in the seed store of the German ex situ genebank of the Leibniz-Institute of Plant Genetics and Crop Plant Research in Gatersleben. A high intraspecific variation was detected in those natural aged accessions. In addition three doubled haploid barley mapping populations being artificial aged were investigated to study the inheritance of seed longevity. Quantitative trait locus (QTL) mapping was based on a transcript map. Major QTLs were identified on chromosomes 2H, 5H (two) and 7H explaining a phenotypic variation of up to 54%. A sequence homology search was performed to derive the putative function of the genes linked to the QTLs
How ripples turn into dots: modeling ion-beam erosion under oblique incidence
Pattern formation on semiconductor surfaces induced by low energetic ion-beam
erosion under normal and oblique incidence is theoretically investigated using
a continuum model in form of a stochastic, nonlocal, anisotropic
Kuramoto-Sivashinsky equation. Depending on the size of the parameters this
model exhibits hexagonally ordered dot, ripple, less regular and even rather
smooth patterns. We investigate the transitional behavior between such states
and suggest how transitions can be experimentally detected.Comment: 11 pages, 4 figures, submitted for publication, revised versio
Moments of nonclassicality quasiprobabilities
A method is introduced for the verification of nonclassicality in terms of
moments of nonclassicality quasiprobability distributions. The latter are
easily obtained from experimental data and will be denoted as nonclassicality
moments. Their relation to normally-ordered moments is derived, which enables
us to verify nonclassicality by using well established criteria. Alternatively,
nonclassicality criteria are directly formulated in terms of nonclassicality
moments. The latter converge in proper limits to the usually used criteria, as
is illustrated for squeezing and sub-Poissonian photon statistics. Our theory
also yields expectation values of any observable in terms of nonclassicality
moments.Comment: 6 pages, 3 figure
Illumination in symbiotic binary stars: Non-LTE photoionization models. II. Wind case
We describe a non-LTE photoionization code to calculate the wind structure
and emergent spectrum of a red giant wind illuminated by the hot component of a
symbiotic binary system. We consider spherically symmetric winds with several
different velocity and temperature laws and derive predicted line fluxes as a
function of the red giant mass loss rate, \mdot. Our models generally match
observations of the symbiotic stars EG And and AG Peg for \mdot about 10^{-8}
\msunyr to 10^{-7} \msunyr. The optically thick cross- section of the red giant
wind as viewed from the hot component is a crucial parameter in these models.
Winds with cross-sections of 2--3 red giant radii reproduce the observed
fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models
favor winds with acceleration regions that either lie far from the red giant
photosphere or extend for 2--3 red giant radii.Comment: 51 pages, LaTeX including three tables, requires 15 Encapsulated
Postscript figures, to appear in Ap
Origin of non-exponential relaxation in a crystalline ionic conductor: a multi-dimensional 109Ag NMR study
The origin of the non-exponential relaxation of silver ions in the
crystalline ion conductor Ag7P3S11 is analyzed by comparing appropriate
two-time and three-time 109Ag NMR correlation functions. The non-exponentiality
is due to a rate distribution, i.e., dynamic heterogeneities, rather than to an
intrinsic non-exponentiality. Thus, the data give no evidence for the relevance
of correlated back-and-forth jumps on the timescale of the silver relaxation.Comment: 4 pages, 3 figure
Multipartite minimum uncertainty products
In our previous work we have found a lower bound for the multipartite
uncertainty product of the position and momentum observables over all separable
states. In this work we are trying to minimize this uncertainty product over a
broader class of states to find the fundamental limits imposed by nature on the
observable quantites. We show that it is necessary to consider pure states only
and find the infimum of the uncertainty product over a special class of pure
states (states with spherically symmetric wave functions). It is shown that
this infimum is not attained. We also explicitly construct a parametrized
family of states that approaches the infimum by varying the parameter. Since
the constructed states beat the lower bound for separable states, they are
entangled. We thus show that there is a gap that separates the values of a
simple measurable quantity for separable states from entangled ones and we also
try to find the size of this gap.Comment: 18 pages, 5 figure
Dynamical control of two-level system's decay and long time freezing
We investigate with exact numerical calculation coherent control of a
two-level quantum system's decay by subjecting the two-level system to many
periodic ideal phase modulation pulses. For three spectrum intensities
(Gaussian, Lorentzian, and exponential), we find both suppression and
acceleration of the decay of the two-level system, depending on difference
between the spectrum peak position and the eigen frequency of the two-level
system. Most interestingly, the decay of the two-level system freezes after
many control pulses if the pulse delay is short. The decay freezing value is
half of the decay in the first pulse delay.Comment: 6 pages, 6 figures, published in Phys. Rev.
Quantum homodyne tomography with a priori constraints
I present a novel algorithm for reconstructing the Wigner function from
homodyne statistics. The proposed method, based on maximum-likelihood
estimation, is capable of compensating for detection losses in a numerically
stable way.Comment: 4 pages, REVTeX, 2 figure
Operational Theory of Homodyne Detection
We discuss a balanced homodyne detection scheme with imperfect detectors in
the framework of the operational approach to quantum measurement. We show that
a realistic homodyne measurement is described by a family of operational
observables that depends on the experimental setup, rather than a single field
quadrature operator. We find an explicit form of this family, which fully
characterizes the experimental device and is independent of a specific state of
the measured system. We also derive operational homodyne observables for the
setup with a random phase, which has been recently applied in an ultrafast
measurement of the photon statistics of a pulsed diode laser. The operational
formulation directly gives the relation between the detected noise and the
intrinsic quantum fluctuations of the measured field. We demonstrate this on
two examples: the operational uncertainty relation for the field quadratures,
and the homodyne detection of suppressed fluctuations in photon statistics.Comment: 7 pages, REVTe
Homodyne detection for measuring internal quantum correlations of optical pulses
A new method is described for determining the quantum correlations at
different times in optical pulses by using balanced homodyne detection. The
signal pulse and sequences of ultrashort test pulses are superimposed, where
for chosen distances between the test pulses their relative phases and
intensities are varied from measurement to measurement. The correlation
statistics of the signal pulse is obtained from the time-integrated difference
photocurrents measured.Comment: 7 pages, A4.sty include
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