1,876 research outputs found
Potential environmental impact of tidal energy extraction in the Pentland Firth at large spatial scales : results of a biogeochemical model
A model study was carried out of the potential large-scale (> 100 km) effects of marine renewable tidal energy generation in the Pentland Firth, using the 3-D hydrodynamics–biogeochemistry model GETM-ERSEM-BFM. A realistic 800 MW scenario and a high-impact scenario with massive expansion of tidal energy extraction to 8 GW scenario were considered. The realistic 800 MW scenario suggested minor effects on the tides, and undetectable effects on the biogeochemistry. The massive-expansion 8 GW scenario suggested effects would be observed over hundreds of kilometres away with changes of up to 10 % in tidal and ecosystem variables, in particular in a broad area in the vicinity of the Wash. There, waters became less turbid, and primary production increased with associated increases in faunal ecosystem variables. Moreover, a one-off increase in carbon storage in the sea bed was detected. Although these first results suggest positive environmental effects, further investigation is recommended of (i) the residual circulation in the vicinity of the Pentland Firth and effects on larval dispersal using a higher-resolution model and (ii) ecosystem effects with (future) state-of-the-art models if energy extraction substantially beyond 1 GW is planned
Separating spin and charge transport in single wall carbon nanotubes
We demonstrate spin injection and detection in single wall carbon nanotubes
using a 4-terminal, non-local geometry. This measurement geometry completely
separates the charge and spin circuits. Hence all spurious magnetoresistance
effects are eliminated and the measured signal is due to spin accumulation
only. Combining our results with a theoretical model, we deduce a spin
polarization at the contacts of approximately 25 %. We show that the
magnetoresistance changes measured in the conventional two-terminal geometry
are dominated by effects not related to spin accumulation.Comment: Number of pages: 11 Number of figures:
The Magneto-coulomb effect in spin valve devices
We discuss the influence of the magneto-coulomb effect (MCE) on the
magnetoconductance of spin valve devices. We show that MCE can induce
magnetoconductances of several per cents or more, dependent on the strength of
the coulomb blockade. Furthermore, the MCE-induced magnetoconductance changes
sign as a function of gate voltage. We emphasize the importance of separating
conductance changes induced by MCE from those due to spin accumulation in spin
valve devices.Comment: This paper includes 3 figure
Bistable hysteresis and resistance switching in hydrogen gold junctions
Current-voltage characteristics of H2-Au molecular junctions exhibit
intriguing steps around a characteristic voltage of 40 mV. Surprisingly, we
find that a hysteresis is connected to these steps with a typical time scale >
10 ms. This time constant scales linearly with the power dissipated in the
junction beyond an ofset power P_s = IV_s. We propose that the hysteresis is
related to vibrational heating of both the molecule in the junction and a set
of surrounding hydrogen molecules. Remarkably, we can engineer our junctions
such that the hysteresis' characteristic time becomes >days. We demonstrate
that reliable switchable devices can be built from such junctions.Comment: Submitted to Phys. Rev. Let
Modelling survival and connectivity of Mnemiopsis leidyi in the south-western North Sea and Scheldt estuaries
Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a high-resolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here
Opportunities and limitations of transition voltage spectroscopy: a theoretical analysis
In molecular charge transport, transition voltage spectroscopy (TVS) holds
the promise that molecular energy levels can be explored at bias voltages lower
than required for resonant tunneling. We investigate the theoretical basis of
this novel tool, using a generic model. In particular, we study the length
dependence of the conducting frontier orbital and of the 'transition voltage'
as a function of length. We show that this dependence is influenced by the
amount of screening of the electrons in the molecule, which determines the
voltage drop to be located at the contacts or across the entire molecule. We
observe that the transition voltage depends significantly on the length, but
that the ratio between the transition voltage and the conducting frontier
orbital is approximately constant only in strongly screening (conjugated)
molecules. Uncertainty about the screening within a molecule thus limits the
predictive power of TVS. We furthermore argue that the relative length
independence of the transition voltage for non-conjugated chains is due to
strong localization of the frontier orbitals on the end groups ensuring binding
of the rods to the metallic contacts. Finally, we investigate the
characteristics of TVS in asymmetric molecular junctions. If a single level
dominates the transport properties, TVS can provide a good estimate for both
the level position and the degree of junction asymmetry. If more levels are
involved the applicability of TVS becomes limited.Comment: 8 pages, 12 figure
Bulk and Surface Nucleation Processes in Ag2S Conductance Switches
We studied metallic Ag formation inside and on the surface of Ag2S thin
films, induced by the electric field created with a STM tip. Two clear regimes
were observed: cluster formation on the surface at low bias voltages, and full
conductance switching at higher bias voltages (V > 70mV). The bias voltage at
which this transition is observed is in agreement with the known threshold
voltage for conductance switching at room temperature. We propose a model for
the cluster formation at low bias voltage. Scaling of the measured data with
the proposed model indicates that the process takes place near steady state,
but depends on the STM tip geometry. The growth of the clusters is confirmed by
tip retraction measurements and topography scans. This study provides improved
understanding of the physical mechanisms that drive conductance switching in
solid electrolyte memristive devices.Comment: In press for PR
Graph Analysis of EEG Functional Connectivity Networks During a Letter-Speech Sound Binding Task in Adult Dyslexics
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