3,950 research outputs found
Using a quantum dot as a high-frequency shot noise detector
We present the experimental realization of a Quantum Dot (QD) operating as a
high-frequency noise detector. Current fluctuations produced in a nearby
Quantum Point Contact (QPC) ionize the QD and induce transport through excited
states. The resulting transient current through the QD represents our detector
signal. We investigate its dependence on the QPC transmission and voltage bias.
We observe and explain a quantum threshold feature and a saturation in the
detector signal. This experimental and theoretical study is relevant in
understanding the backaction of a QPC used as a charge detector.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Single-shot readout of electron spin states in a quantum dot using spin-dependent tunnel rates
We present a method for reading out the spin state of electrons in a quantum
dot that is robust against charge noise and can be used even when the electron
temperature exceeds the energy splitting between the states. The spin states
are first correlated to different charge states using a spin dependence of the
tunnel rates. A subsequent fast measurement of the charge on the dot then
reveals the original spin state. We experimentally demonstrate the method by
performing read-out of the two-electron spin states, achieving a single-shot
visibility of more than 80%. We find very long triplet-to-singlet relaxation
times (up to several milliseconds), with a strong dependence on in-plane
magnetic field.Comment: 4 pages, 4 figure
Control and Detection of Singlet-Triplet Mixing in a Random Nuclear Field
We observe mixing between two-electron singlet and triplet states in a double
quantum dot, caused by interactions with nuclear spins in the host
semiconductor. This mixing is suppressed by applying a small magnetic field, or
by increasing the interdot tunnel coupling and thereby the singlet-triplet
splitting. Electron transport involving transitions between triplets and
singlets in turn polarizes the nuclei, resulting in striking bistabilities. We
extract from the fluctuating nuclear field a limitation on the time-averaged
spin coherence time T2* of 25 ns. Control of the electron-nuclear interaction
will therefore be crucial for the coherent manipulation of individual electron
spins.Comment: 4 pages main text, 4 figure
Does virulence assessment of Vibrio anguillarum using sea bass (Dicentrarchus labrax) larvae correspond with genotypic and phenotypic characterization?
Background: Vibriosis is one of the most ubiquitous fish diseases caused by bacteria belonging to the genus Vibrio such as Vibrio (Listonella) anguillarum. Despite a lot of research efforts, the virulence factors and mechanism of V. anguillarum are still insufficiently known, in part because of the lack of standardized virulence assays.
Methodology/Principal Findings: We investigated and compared the virulence of 15 V. anguillarum strains obtained from different hosts or non-host niches using a standardized gnotobiotic bioassay with European sea bass (Dicentrarchus labrax L.) larvae as model hosts. In addition, to assess potential relationships between virulence and genotypic and phenotypic characteristics, the strains were characterized by random amplified polymorphic DNA (RAPD) and repetitive extragenic palindromic PCR (rep-PCR) analyses, as well as by phenotypic analyses using Biolog's Phenotype MicroArray (TM) technology and some virulence factor assays.
Conclusions/Significance: Virulence testing revealed ten virulent and five avirulent strains. While some relation could be established between serotype, genotype and phenotype, no relation was found between virulence and genotypic or phenotypic characteristics, illustrating the complexity of V. anguillarum virulence. Moreover, the standardized gnotobiotic system used in this study has proven its strength as a model to assess and compare the virulence of different V. anguillarum strains in vivo. In this way, the bioassay contributes to the study of mechanisms underlying virulence in V. anguillarum
Equipotential Surfaces and Lagrangian points in Non-synchronous, Eccentric Binary and Planetary Systems
We investigate the existence and properties of equipotential surfaces and
Lagrangian points in non-synchronous, eccentric binary star and planetary
systems under the assumption of quasi-static equilibrium. We adopt a binary
potential that accounts for non-synchronous rotation and eccentric orbits, and
calculate the positions of the Lagrangian points as functions of the mass
ratio, the degree of asynchronism, the orbital eccentricity, and the position
of the stars or planets in their relative orbit. We find that the geometry of
the equipotential surfaces may facilitate non-conservative mass transfer in
non-synchronous, eccentric binary star and planetary systems, especially if the
component stars or planets are rotating super-synchronously at the periastron
of their relative orbit. We also calculate the volume-equivalent radius of the
Roche lobe as a function of the four parameters mentioned above. Contrary to
common practice, we find that replacing the radius of a circular orbit in the
fitting formula of Eggleton (1983) with the instantaneous distance between the
components of eccentric binary or planetary systems does not always lead to a
good approximation to the volume-equivalent radius of the Roche-lobe. We
therefore provide generalized analytic fitting formulae for the
volume-equivalent Roche lobe radius appropriate for non-synchronous, eccentric
binary star and planetary systems. These formulae are accurate to better than
1% throughout the relevant 2-dimensional parameter space that covers a dynamic
range of 16 and 6 orders of magnitude in the two dimensions.Comment: 12 pages, 10 figures, 2 Tables, Accepted by the Astrophysical Journa
Concept of unbearable suffering in context of ungranted requests for euthanasia: qualitative interviews with patients and physicians
Objective To obtain in-depth information about the views of patients and physicians on suffering in patients who requested euthanasia in whom the request was not granted or granted but not performed
Semiconductor few-electron quantum dot operated as a bipolar spin filter
We study the spin states of a few-electron quantum dot defined in a
two-dimensional electron gas, by applying a large in-plane magnetic field. We
observe the Zeeman splitting of the two-electron spin triplet states. Also, the
one-electron Zeeman splitting is clearly resolved at both the zero-to-one and
the one-to-two electron transition. Since the spin of the electrons transmitted
through the dot is opposite at these two transitions, this device can be
employed as an electrically tunable, bipolar spin filter. Calculations and
measurements show that higher-order tunnel processes and spin-orbit interaction
have a negligible effect on the polarization.Comment: 4 pages, 3 figure
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Modelling flood damages under climate change conditions-a case study for Germany
The aim of the study is to analyze and discuss possible climate change impacts on flood damages in Germany. The study was initiated and supported by the German insurance sector whereby the main goal was to identify general climate-related trends in flood hazard and damages and to explore sensitivity of results to climate scenario uncertainty. The study makes use of climate scenarios regionalized for the main river basins in Germany. A hydrological model (SWIM) that had been calibrated and validated for the main river gauges, was applied to transform these scenarios into discharge for more than 5000 river reaches. Extreme value distribution has been fitted to the time series of river discharge to derive the flood frequency statistics. The hydrological results for each river reach have been linked using the flood statistics to related damage functions provided by the German Insurance Association, considering damages on buildings and small enterprises. The result is that, under the specific scenario conditions, a considerable increase in flood related losses can be expected in Germany in future, warmer, climate
Spin filling of a quantum dot derived from excited-state spectroscopy
We study the spin filling of a semiconductor quantum dot using excited-state
spectroscopy in a strong magnetic field. The field is oriented in the plane of
the two-dimensional electron gas in which the dot is electrostatically defined.
By combining the observation of Zeeman splitting with our knowledge of the
absolute number of electrons, we are able to determine the ground state spin
configuration for one to five electrons occupying the dot. For four electrons,
we find a ground state spin configuration with total spin S=1, in agreement
with Hund's first rule. The electron g-factor is observed to be independent of
magnetic field and electron number.Comment: 11 pages, 7 figures, submitted to New Journal of Physics, focus issue
on Solid State Quantum Informatio
Modeling and analysis of energy distribution networks using switched differential systems
It is a pleasure to dedicate this contribution to Prof. Arjan van der Schaft on the occasion of his 60th birthday. We study the dynamics of energy distribution networks consisting of switching power converters and multiple (dis-)connectable modules. We use parsimonious models that deal effectively with the variant complexity of the network and the inherent switching phenomena induced by power converters. We also present the solution to instability problems caused by devices with negative impedance characteristics such as constant power loads. Elements of the behavioral system theory such as linear differential behaviors and quadratic differential forms are crucial in our analysis
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