5,092 research outputs found
Resonant tunneling in a Luttinger liquid for arbitrary barrier transmission
A numerically exact dynamical quantum Monte Carlo approach has been developed
and applied to transport through a double barrier in a Luttinger liquid with
arbitrary transmission. For strong transmission, we find broad Fabry-Perot
Coulomb blockade peaks, with a lineshape parametrized by a single parameter,
but at sufficiently low temperatures, non-Lorentzian universal lineshapes
characteristic of coherent resonant tunneling emerge, even for strong
interactions. For weak transmission, our data supports the recently proposed
correlated sequential tunneling picture and is consistent with experimental
results on intrinsic nanotube dots.Comment: 4 pages, 4 figure
Tuning nonlinearity, dynamic range, and frequency of nanomechanical resonators
We explore an electrostatic mechanism for tuning the nonlinearity of nanomechanical resonators and increasing their dynamic range for sensor applications. We also demonstrate tuning the resonant frequency of resonators both upward and downward. A theoretical model is developed that qualitatively explains the experimental results and serves as a simple guide for design of tunable nanomechanical devices
Dynamic range of nanotube- and nanowire-based electromechanical systems
Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest due to their expected high sensitivity. However, a strongly nonlinear response combined with a high thermomechanical noise level limits the useful linear dynamic range of this type of device. We derive the equations governing this behavior and find a strong dependence [[proportional]dsqrt((d/L)[sup 5])] of the dynamic range on aspect ratio
Disease suppressive soilless culture systems; characterisation of its microflora
The trend in glasshouse horticulture has always been to start culture systems as aseptic as possible. However, several root diseases still cause problems under these conditions. The present paper shows the importance of the microflora to suppress Pythium aphanidermatum, a fungal root pathogen which is a serious threat in cucumber. Introduced single antagonists as well as the indigenous microflora suppressed pythium root and crown rot. Pseudomonas fluorescens, Streptomyces griseoviridis, Pythium oligandrum, and 2 isolates of Trichoderma harzianum reduced the disease occurrence by 60 ␘r more in several, but not all, of the experiments. The indigenous microflora showed a very constant disease suppression of 50 to 100 &Eth;This was tested in experiments where P. aphanidermatum was added to sterilised and non-sterilised rockwool, and to sterilised rockwool that had been recolonised with the original microflora. Suppressiveness correlated with the number of filamentous actinomycetes present in the nutrient solution in the rockwool slabs. If a beneficial microflora is present in the cropping system, it should not be disturbed or eradicated by treatments such as disinfection of the recirculated nutrient solution. Therefore, the effects of different disinfection procedures on the composition of the microflora were compared. Numbers of filamentous actinomycetes in the nutrient solution in the tank after the disinfection treatment were highest without disinfection, intermediate after slow filtration, and lowest after UV treatment. Numbers of actinomycetes in the slabs, i.e. around the roots, were not distinctly different between the treatments. The implication of potential shifts in the microbial populations due to certain treatments for the disease development is not known. Increased knowledge on the beneficial microflora and the treatments that influence the composition of such a microflora, will stimulate the exploitation of microbially balanced and optimised soilless culture systems
Study of the Growth of Entropy Modes in MSSM Flat Directions Decay: Constraints on the Parameter Space
We study how the resonant decay of moduli fields arising in the Minimal
Supersymmetric Standard Model (MSSM) could affect large scale curvature
perturbations in the early universe. It has been known for some time that the
presence of entropy perturbations in a multi-component system can act as seeds
for the curvature perturbations on all scales. These entropy perturbations
could be amplified exponentially if one of the moduli decays via stochastic
resonance, affecting the curvature power spectrum in the process. By imposing
the COBE normalization on this power spectrum, one could put constraints on the
masses and couplings of the underlying particle physics model without having to
rely on collider experiments. We discuss in detail the case of the MSSM but
this method could be applied to other theories beyond the Standard Model.Comment: 6 pages, 1 figure, revtex4, comments added in section II, 1 reference
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Measuring final-year dental students’ ability to remove teeth independently using independence ratios
Background. Universities are obliged to ensure that dental graduates possess the necessary skills to render safe and effective treatment. Empirical evidence regarding the development of safe and effective independent practice at undergraduate level is unfortunately lacking.
Objectives. To measure final-year students’ abilities to correctly perform exodontia (tooth removal/extraction) skills independently, based on the applied postgraduate progressive independence theory.
Methods. Fourteen clinical teachers systematically assessed 13 263 tooth extractions completed by final-year dental students (2014 - 2016). An independence ratio (extractions performed without assistance/total number of extractions) was used as the key performance indicator to provide feedback on the ability to complete procedures independently over time. A customised index was used for controlling the level of difficulty.
Results. Final-year students (n=146) achieved independence ratios ranging between 90% and 94% (standard deviation 3.3%) by the end of their clinical training. Logical gradients of increased independence were illustrated with time, as well as variable performance among students. The level of difficulty index scores remained similar within cohorts per year of study. Acceptable assessment differences existed between clinical teachers, which could largely be explained by complex operational circumstances.
Conclusions. As far as we are aware, this is the first study that quantified progressive independence in exodontia for undergraduate students. The measure was sensitive enough to show logical independence gradients and variance among students. Final-year students demonstrated that they could remove >8/10 teeth independently by the time of their graduation. The measure shows promise as a proxy of competence for skills that are often practised. It is recommended that factors that influence these measurements be examined in more detail
Muon Pair Production by Electron-Photon Scatterings
The cross section for muon pair productions by electrons scattering over
photons, , is calculated analytically in the leading order. It is
pointed out that for the center-of-mass energy range, ,
the cross section for is less than b. The differential
energy spectrum for either of the resulting muons is given for the purpose of
high-energy neutrino astronomy. An implication of our result for a recent
suggestion concerning the high-energy cosmic neutrino generation through this
muon pair is discussed.Comment: a comment added, to appear in Phys. Rev. D, Rapid Communicatio
Flexibilisering gebruiksnormen : verkenning perspectieven voor de akkerbouw
Vanuit het Masterplan Mineralenmanagement wil men weten welke mogelijkheden er zijn om binnen milieurandvoorwaarden te komen tot systemen van flexibilisering van gebruiksnormen waarbij rekening wordt gehouden met de perceels- en bedrijfskenmerken van de ondernemer. Door PPO, NMI en DLV-Plant is in opdracht van Productschap Akkerbouw een studie uitgevoerd naar de perspectieven voor verdere differentiatie van het gebruiksnormenstelsel. Voor zowel stikstof als fosfaat is eerst nagegaan op basis van welke elementen verdere differentiatie van het huidige stelsel mogelijk is
Basins of attraction of a nonlinear nanomechanical resonator
We present an experiment that systematically probes the basins of attraction
of two fixed points of a nonlinear nanomechanical resonator and maps them out
with high resolution. We observe a separatrix which progressively alters shape
for varying drive strength and changes the relative areas of the two basins of
attraction. The observed separatrix is blurred due to ambient fluctuations,
including residual noise in the drive system, which cause uncertainty in the
preparation of an initial state close to the separatrix. We find a good
agreement between the experimentally mapped and theoretically calculated basins
of attraction
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