6,502 research outputs found
ROCOV scheme for Fault Detection and Location in HVDC sytems
A reliable DC fault protection system is essential
for the development of HVDC grids. Therefore, this paper deals
with the voltage derivative ROCOV scheme to locate and detect
DC faults. The algorithm is able to differentiate internal and
external faults considerably fast. The proposed algorithm is
analyzed in a HVDC grid with different fault case scenarios.
Finally, the ROCOV protection thresholds are discussed.The authors thank the support from the Spanish Ministry of
Economy, Industry and Competitiveness (project
ENE2016-79145-R AEI/FEDER, UE) and GISEL research
group IT1083-16), as well as from the University of the
Basque Country UPV/EHU (research group funding
PPG17/23)
Quantum Interference and Decoherence in Single-Molecule Junctions: How Vibrations Induce Electrical Current
Quantum interference effects and decoherence mechanisms in single-molecule
junctions are analyzed employing a nonequilibrium Green's function approach.
Electrons tunneling through quasi-degenerate states of a nanoscale molecular
junction exhibit interference effects. We show that electronic-vibrational
coupling, inherent to any molecular junction, strongly quenches such
interference effects. As a result, the electrical current can be significantly
larger than without electronic-vibrational coupling. The analysis reveals that
the quenching of quantum interference is particularly pronounced if the
junction is vibrationally highly excited, e.g. due to current-induced
nonequilibrium effects in the resonant transport regime.Comment: 11 pages, 4 figure
Detecting multiple chiral centers in chiral molecules with high harmonic generation
Characterizing chiral is highly important for applications in the pharmaceutical industry, as well as in the study of dynamical chemical and biological systems. However, this task has remained challenging, especially due to the ongoing increasing complexity and size of the molecular structure of drugs and active compounds. In particular, large molecules with many active chiral centers are today ubiquitous, but remain difficult to structurally analyze due to their high number of stereoisomers. Here we theoretically explore the sensitivity of high harmonic generation (HHG) to the chiral of molecules with a varying number of active chiral centers. We find that HHG driven by bi-chromatic non-collinear lasers is a sensitive probe for the stereo-configuration of a chiral molecule. We first show through calculations (from benchmark chiral molecules with up to three chiral centers) that the HHG spectrum is imprinted with information about the handedness of each chiral center in the driven molecule. Next, we show that using both classical- and deep-learning-based reconstruction algorithms, the composition of an unknown mixture of stereoisomers can be reconstructed with high fidelity by a single-shot HHG measurement. Our work illustrates how the combination of non-linear optics and machine learning might open routes for ultra-sensitive sensing in chiral systems
Switching the Conductance of a Molecular Junction using a Proton Transfer Reaction
A novel mechanism for switching a molecular junction based on a proton
transfer reaction triggered by an external electrostatic field is proposed. As
a specific example to demonstrate the feasibility of the mechanism, the
tautomers [2,5-(4-hydroxypyridine)] and {2,5-[4(1H)-pyridone]} are considered.
Employing a combination of first-principles electronic structure calculations
and Landauer transport theory, we show that both tautomers exhibit very
different conductance properties and realize the "on" and "off" states of a
molecular switch. Moreover, we provide a proof of principle that both forms can
be reversibly converted into each other using an external electrostatic field.Comment: 14 pages, 5 figure
Alternative strategies to reduce public deficits: the case of Spain
High government deficits are a matter of concern in many European countries. We examine the effects of several alternative
measures intended to reduce public deficits, distinguishing between those acting through either taxes or spending. Our analysis
is applied to the Spanish economy, using a computable general equilibrium mode
Comment on âOrigin of symmetry-forbidden high-order harmonic generation in the time-dependent Kohn-Sham formulationâ
In their recent paper [Phys. Rev. A 103, 043106 (2021)], Zang et al. theoretically investigated high harmonic generation (HHG) in benchmark two-electron systems that are inversion symmetric with time-dependent density functional theory (TDDFT) in the Kohn-Sham formulation. They found that the theory wrongly predicted the emission of symmetry-forbidden even harmonics and concluded that this error originates from an inherent problem of TDDFT that unphysically populates one- and two-electron excited states. They further claimed that this effect results in an incorrect HHG cutoff energy. We reproduced their main results, but found that the unphysical even harmonics that they observed originated from numerical errors introduced by the boundary conditions. We show that contrary to their claims, the HHG cutoff energy calculated within TDDFT agrees perfectly with the standard and well-established models of HHG
Controlling Physical Systems with Symmetries
Symmetry properties of the evolution equation and the state to be controlled
are shown to determine the basic features of the linear control of unstable
orbits. In particular, the selection of control parameters and their minimal
number are determined by the irreducible representations of the symmetry group
of the linearization about the orbit to be controlled. We use the general
results to demonstrate the effect of symmetry on the control of two sample
physical systems: a coupled map lattice and a particle in a symmetric
potential.Comment: 6 page
Mediating pathways in the socio-economic gradient of child development: Evidence from children 6-42 months in Bogota
Research has previously shown a gap of near 0.5 of a standard deviation (SD) in cognition and language development between the top and bottom household wealth quartile in children aged 6â42 months in a large representative sample of low- and middle-income families in Bogota, using the Bayley Scales of Infant and Toddler Development. The gaps in fine motor and socio-emotional development were about half that size. Developmental deficits increased with age. The current study explored the associations amongst child development, household socio-economic status (SES), and a set of potential mediating variablesâparental characteristics, child biomedical factors, and the quality of the home environmentâin this sample. We ran mediation tests to quantify the contribution of these variables to the SES gap, and explored the role of age as a moderator. Parental education, particularly maternal education, and the quality of the home environment mediated the SES gap in all outcomes examined. Height-for-age mediated a small amount of the deficit in language scales only. More educated mothers provided better home stimulation than less educated mothers and the home environment partly mediated the effect of maternal education. These results suggested that in interventions aimed at promoting child development, those focusing on the quality of the home environment should be effective
Energy transfer in porphyrin-functionalized graphene
We present a theoretical study on the moleculeâsubstrate interaction within the porphyrin-functionalized graphene. Recent experiments on porphyrin-functionalized carbon nanotubes have revealed an extremely efficient energy transfer from the adsorbed molecules to the carbon substrate. To investigate the energy transfer mechanism, we have characterized the hybrid structure within the density functional theory including the calculation of the molecular transition dipole moment, which allows us to determine the Förster coupling rate. We find a strongly pronounced Förster-induced energy transfer in the range of fsâ1 inline image confirming the experimental observations
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