1,089 research outputs found
Effect of bicarbonate on uptake and translocation of 59Fe in two grapevine rootstocks differing in their resistance to Fe deficiency chlorosis
In order to study the effect of high bicarbonate concentration in the root medium on root FeIII reduction, Fe uptake and its translocation to the leaves, two rootstocks (Vitis riparia Michx., susceptible, and 41 B (Vitis vinifera L. cv. Chasselas x Vitis berlandieri Planch.), resistant to Fe deficiency chlorosis) were pre-cultivated in nutrient solutions with high and low Fe supply. After three weeks of preculture at low Fe, chlorosis symptoms occurred in both, Fe-resistant and Fe-susceptible genotypes. The FeIII reducing capacity by roots was enhanced at Fe deficiency in both genotypes, which was consistent with the increase of subsequent root uptake and translocation rates of 59Fe. In the presence of bicarbonate in the solutions the FeIII reducing capacity, 59Fe uptake and translocation rate decreased in both genotypes precultured with low re supply. The 59Fe uptake and translocation rate, however, were significantly higher in the Fe chlorosis-resistant rootstock 41 B. These results clearly indicate that bicarbonate-induced Fe chlorosis in grapevine rootstocks is obviously caused by an inhibition of Fe uptake and translocation due to an inhibition of FeIII reduction by root cells. The fact that these processes were less inhibited in the chlorosis-resistant rootstock hints to genotypical differences in Fe acquisition by roots at high bicarbonate levels. These differences might be used in breeding programs to identify Fe chlorosis-resistant rootstocks
Vacuum-ultraviolet frequency-modulation spectroscopy
Frequency-modulation (FM) spectroscopy has been extended to the
vacuum-ultraviolet (VUV) range of the electromagnetic spectrum. Coherent VUV
laser radiation is produced by resonance-enhanced sum-frequency mixing
() in Kr and Xe using two
near-Fourier-transform-limited laser pulses of frequencies
and . Sidebands generated in the output of the second laser ()
using an electro-optical modulator operating at the frequency
are directly transfered to the VUV and used to record FM
spectra. Demodulation is demonstrated both at and
. The main advantages of the method are that its
sensitivity is not reduced by pulse-to-pulse fluctuations of the VUV laser
intensity, compared to VUV absorption spectroscopy is its background-free
nature, the fact that its implementation using table-top laser equipment is
straightforward and that it can be used to record VUV absorption spectra of
cold samples in skimmed supersonic beams simultaneously with
laser-induced-fluorescence and photoionization spectra. To illustrate these
advantages we present VUV FM spectra of Ar, Kr, and N in selected regions
between 105000cm and 122000cm.Comment: 23 pages, 10 figure
Imaging electric fields in the vicinity of cryogenic surfaces using Rydberg atoms
The ability to characterize static and time-dependent electric fields in situ
is an important prerequisite for quantum-optics experiments with atoms close to
surfaces. Especially in experiments which aim at coupling Rydberg atoms to the
near field of superconducting circuits, the identification and subsequent
elimination of sources of stray fields is crucial. We present a technique that
allows the determination of stray-electric-field distributions
at distances of less than from (cryogenic) surfaces using
coherent Rydberg-Stark spectroscopy in a pulsed supersonic beam of metastable
helium atoms. We demonstrate the
capabilities of this technique by characterizing the electric stray field
emanating from a structured superconducting surface. Exploiting coherent
population transfer with microwave radiation from a coplanar waveguide, the
same technique allows the characterization of the microwave-field distribution
above the surface.Comment: 6 pages, 4 figure
Measuring the dispersive frequency shift of a rectangular microwave cavity induced by an ensemble of Rydberg atoms
In recent years the interest in studying interactions of Rydberg atoms or
ensembles thereof with optical and microwave frequency fields has steadily
increased, both in the context of basic research and for potential applications
in quantum information processing. We present measurements of the dispersive
interaction between an ensemble of helium atoms in the 37s Rydberg state and a
single resonator mode by extracting the amplitude and phase change of a weak
microwave probe tone transmitted through the cavity. The results are in
quantitative agreement with predictions made on the basis of the dispersive
Tavis-Cummings Hamiltonian. We study this system with the goal of realizing a
hybrid between superconducting circuits and Rydberg atoms. We measure maximal
collective coupling strengths of 1 MHz, corresponding to 3*10^3 Rydberg atoms
coupled to the cavity. As expected, the dispersive shift is found to be
inversely proportional to the atom-cavity detuning and proportional to the
number of Rydberg atoms. This possibility of measuring the number of Rydberg
atoms in a nondestructive manner is relevant for quantitatively evaluating
scattering cross sections in experiments with Rydberg atoms
Aseptic dual culture of grape (Vitis spp.) and grape phylloxera (Daktulosphaira vitifoliae FITCH)
An aseptic dual culture of grape phylloxera (Daktulosphaira vitifoliae FITCH) and grape vine (Vitis spp.) was developed. This method permits continuous observation of phylloxera feeding and the whole plant response on a dynamic basis. The plant/parasite interaction of three testplants (V. vinifera L., var. Riesling, SO 4 (V. berlandieri PLANCH. X V. riparia L.) and V. riparia, var. Gloire de Montpellier) are demonstrated by observing post-infectious reactions of the host- and population dynamics of the parasite. Different stages of phylloxera could be observed including nymphs, winged phylloxera (alatae) and sexual male phylloxera. Several potential applications for this aseptic dual culture are demonstrated
Spectra of Harmonium in a magnetic field using an initial value representation of the semiclassical propagator
For two Coulombically interacting electrons in a quantum dot with harmonic
confinement and a constant magnetic field, we show that time-dependent
semiclassical calculations using the Herman-Kluk initial value representation
of the propagator lead to eigenvalues of the same accuracy as WKB calculations
with Langer correction. The latter are restricted to integrable systems,
however, whereas the time-dependent initial value approach allows for
applications to high-dimensional, possibly chaotic dynamics and is extendable
to arbitrary shapes of the potential.Comment: 11 pages, 1 figur
Observation of enhanced rate coefficients in the H + H H + H reaction at low collision energies
The energy dependence of the rate coefficient of the H reaction has been measured in the range of
collision energies between K and
mK. A clear deviation of the rate coefficient from the value expected on the
basis of the classical Langevin-capture behavior has been observed at collision
energies below K, which is attributed to the joint
effects of the ion-quadrupole and Coriolis interactions in collisions involving
ortho-H molecules in the rotational level, which make up 75% of the
population of the neutral H molecules in the experiments. The experimental
results are compared to very recent predictions by Dashevskaya, Litvin, Nikitin
and Troe (J. Chem. Phys., in press), with which they are in agreement.Comment: 14 pages, 3 figure
Effect of soil fertilization on the incidence of berry shrivel and the quality of resulting wine
Berry shrivel is becoming an increasing concern for winegrowers all over the world. Until today, no single factor causing this physiological disorder has been determined. Studies concerning berry shrivel conducted in Austria have shown that an unbalanced ratio of K and Mg in the soil is a likely factor contributing to the disorder. The aims of the present study were to establish a better understanding of the causes and consequences of berry shrivel and observe the effects of K and Mg fertilization via the soil on the incidence of berry shrivel, the mineral composition of affected berries and the resulting wine quality. A two-year fertilization trial was conducted on two sites located within southern Germany with the varieties 'Zweigelt' and 'Pinot Blanc'. Different amounts of K and Mg were applied each year at both locations in order to generate different ratios of K and Mg in the soil. Before harvest, the incidences of berry shrivel of the different treatments were determined. In addition, macronutrients including K, Mg and Ca that were translocated in healthy berries and berries affected by berry shrivel were determined at harvest. To compare the quality of wine influenced by berry shrivel, different wines were produced consisting of shrivelled berries, berries affected by bunch stem necrosis and healthy berries. In the soil fertilization trials, no significant differences in the incidences of berry shrivel were observed in relation to the soil fertilization. Major differences were found in the wine qualities of the different wines. Wines produced from healthy berries were always rated as the best wines, whereas wines produced from shrivelled berries were always rated as the lowest quality. The low quality parameters found in the must did not improve in the wine making process. Wines produced from berries affected by bunch stem necrosis were rated better than berry-shrivel-wines, however, rated less than the wine produced from healthy berries. The determinations of macronutrients’ level in the berries showed significant differences regarding the concentration of Ca. In the variety 'Zweigelt' in 2009, an average of 36 mg∙L-1 of Ca were found in healthy berries and 107 mg∙L-1 in berries affected by berry shrivel. In 'Pinot Blanc' in 2010, the average of Ca in healthy berries was 46 mg∙L-1 and 70 mg∙L-1 in berries affected by berry shrivel. No significant differences were found for K and Mg in the berries.
Supercurrent-phase relationship of a Nb/InAs(2DES)/Nb Josephson junction in overlapping geometry
Superconductor/normal conductor/superconductor (SNS) Josephson junctions with
highly transparent interfaces are predicted to show significant deviations from
sinusoidal supercurrent-phase relationships (CPR) at low temperatures. We
investigate experimentally the CPR of a ballistic Nb/InAs(2DES)/Nb junction in
the temperature range from 1.3 K to 9 K using a modified Rifkin-Deaver method.
The CPR is obtained from the inductance of the phase-biased junction. Transport
measurements complement the investigation. At low temperatures, substantial
deviations of the CPR from conventional tunnel-junction behavior have been
observed. A theoretical model yielding good agreement to the data is presented.Comment: RevTex4, 4 pages including 3 figure
Collective shuttling of attracting particles in asymmetric narrow channels
The rectification of a single file of attracting particles subjected to a low
frequency ac drive is proposed as a working mechanism for particle shuttling in
an asymmetric narrow channel. Increasing the particle attraction results in the
file condensing, as signalled by the dramatic enhancement of the net particle
current. Magnitude and direction of the current become extremely sensitive to
the actual size of the condensate, which can then be made to shuttle between
two docking stations, transporting particles in one direction, with an
efficiency much larger than conventional diffusive models predict
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