3,049 research outputs found
Non-interacting electrons and the metal-insulator transition in 2D with correlated impurities
While standard scaling arguments show that a system of non-interacting
electrons in two dimensions and in the presence of uncorrelated disorder is
insulating, in this work we discuss the case where inter-impurity correlations
are included. We find that for point-like impurities and an infinite
inter-impurity correlation length a mobility edge exists in 2D even if the
individual impurity potentials are random. In the uncorrelated system we
recover the scaling results, while in the intermediate regime for length scales
comparable to the correlation length, the system behaves like a metal but with
increasing fluctuations, before strong localization eventually takes over for
length scales much larger than the correlation length. In the intermediate
regime, the relevant length scale is not given by the elastic scattering length
but by the inter-impurity correlation length, with important consequences for
high mobility systems.Comment: 4 page
Analyzing WLCG File Transfer Errors Through Machine Learning: An Automatic Pipeline to Support Post-mortem Distributed Data Management
The increasingly growing scale of modern computing infrastructures solicits more ingenious and automatic solutions to their management. Our work focuses on file transfer failures within the Worldwide Large Hadron Collider Computing Grid and proposes a pipeline to support distributed data management operations by suggesting potential issues to investigate. Specifically, we adopt an unsupervised learning approach leveraging Natural Language Processing and Machine Learning tools to automatically parse error messages and group similar failures. The results are presented in the form of a summary table containing the most common textual patterns and time evolution charts. This approach has two main advantages. First, the joint elaboration of the error string and the transfer’s source/destination enables more informative and compact trouble- shooting, as opposed to inspecting each site and checking unique messages separately. As a by-product, this also reduces the number of errors to check by some orders of magnitude (from unique error strings to unique categories or patterns). Second, the time evolution plots allow operators to immediately filter out secondary issues (e.g. transient or in resolution) and focus on the most serious problems first (e.g. escalating failures). As a preliminary assessment, we compare our results with the Global Grid User Support ticketing system, showing that most of our suggestions are indeed real issues (direct association), while being able to cover 89% of reported incidents (inverse relationship)
Correlations, inhomogeneous screening, and suppression of spin-splitting in quantum wires at strong magnetic fields
A self-consistent treatment of exchange and correlation interactions in a
quantum wire (QW) subject to a strong perpendicular magnetic field is presented
using a modified local-density approximation (MLDA). The influence of many-body
interactions on the spin-splitting between the two lowest Landau levels (LLs)
is calculated within the screened Hartree-Fock approximation (SHFA), for
filling factor \nu=1, and the strong spatial dependence of the screening
properties of electrons is taken into account. In comparison with the
Hartree-Fock result, the spatial behavior of the occupied LL in a QW is
strongly modified when correlations are included. Correlations caused by
screening at the edges strongly suppress the exchange splitting and smoothen
the energy dispersion at the edges. The theory accounts well for the
experimentally observed strong suppression of the spin-splitting pertinent to
the \nu=1 quantum Hall effect (QHE) state as well as the destruction of this
state in long, quasi-ballistic GaAlAs/GaAs QWs.Comment: Text 23 pages in Latex/Revtex/preprint format, 6 Postscript figures,
submitted to Physical Review
Anomalous Rashba spin splitting in two-dimensional hole systems
It has long been assumed that the inversion asymmetry-induced Rashba spin
splitting in two-dimensional (2D) systems at zero magnetic field is
proportional to the electric field that characterizes the inversion asymmetry
of the confining potential. Here we demonstrate, both theoretically and
experimentally, that 2D heavy hole systems in accumulation layer-like single
heterostructures show the opposite behavior, i.e., a decreasing, but nonzero
electric field results in an increasing Rashba coefficient.Comment: 4 pages, 3 figure
Spin-orbit terms in multi-subband electron systems: A bridge between bulk and two-dimensional Hamiltonians
We analyze the spin-orbit terms in multi-subband quasi-two-dimensional
electron systems, and how they descend from the bulk Hamiltonian of the
conduction band. Measurements of spin-orbit terms in one subband alone are
shown to give incomplete information on the spin-orbit Hamiltonian of the
system. They should be complemented by measurements of inter-subband spin-orbit
matrix elements. Tuning electron energy levels with a quantizing magnetic field
is proposed as an experimental approach to this problem.Comment: Typos noticed in the published version have been corrected and
several references added. Published in the special issue of Semiconductors in
memory of V.I. Pere
Multi-phonon Raman scattering in semiconductor nanocrystals: importance of non-adiabatic transitions
Multi-phonon Raman scattering in semiconductor nanocrystals is treated taking
into account both adiabatic and non-adiabatic phonon-assisted optical
transitions. Because phonons of various symmetries are involved in scattering
processes, there is a considerable enhancement of intensities of multi-phonon
peaks in nanocrystal Raman spectra. Cases of strong and weak band mixing are
considered in detail. In the first case, fundamental scattering takes place via
internal electron-hole states and is participated by s- and d-phonons, while in
the second case, when the intensity of the one-phonon Raman peak is strongly
influenced by the interaction of an electron and of a hole with interface
imperfections (e. g., with trapped charge), p-phonons are most active.
Calculations of Raman scattering spectra for CdSe and PbS nanocrystals give a
good quantitative agreement with recent experimental results.Comment: 16 pages, 2 figures, E-mail addresses: [email protected],
[email protected], [email protected], accepted for publication in
Physical Review
Landau level mixing and spin degeneracy in the quantum Hall effect
We study dynamics of electrons in a magnetic field using a network model with
two channels per link with random mixing in a random intrachannel potential;
the channels represent either two Landau levels or two spin states. We consider
channel mixing as function of the energy separation of the two extended states
and show that its effect changes from repulsion to attraction as the energy
separation increases. For two Landau levels this leads to level floating at low
magnetic fields while for Zeeman split spin states we predict level attraction
at high magnetic fields, accounting for ESR data. We also study random mixing
of two degenerate channels, while the intrachannel potential is periodic
(non-random). We find a single extended state with a localization exponent
for real scattering at nodes; the general case has also a
single extended state, though the localized nature of nearby states sets in at
unusually large scales.Comment: 18 pages, 11 tex-files and 1 ps-file of figure
Avaluació de l’estat sanitari del gènere Turdus Linnaeus 1758 a Mallorca: una proposta de col·laboració entre la caça, l’administració i l’acadèmia
[cat] Els tords són unes de les espècies cinegètiques que tenen un major interès per als caçadors de Mallorca. Per a la seva caça s’empren diferents modalitats, si bé la caça amb coll permet la realització d’un seguiment dels exemplars amb una major selecció sense afectar a altres espècies. El seguiment de les espècies cinegètiques és un assumpte clau per a poder gestionar les poblacions hivernants de manera adequada, i més encara quan els individus que es cacen son consumits per la població local. En aquest sentit l’aparició al 2018 d’exemplars de tords amb presència del paràsit Morishitium polonicum remarca la necessitat de realitzar un seguiment de l’estat sanitari de les diferents espècies del gènere Turdus. Per la qual cosa en el present manuscrit es proposa una col·laboració entre les societats de caçadors, l’administració responsable de la gestió de caça a l’illa de Mallorca i la Universitat de les Illes Balears, com a institució científica.[eng] True thrushes are the group of hunting species with greater appreciation among the hunters of Mallorca island. For hunting them, several techniques are used, but nevertheless the use of nets within the autochthonous technique named coll allows to carry out a monitoring of the individuals with major selection, thus not affecting other species of birds. The monitoring of hunting species is a key issue to manage winter populations in a proper way, and even more when the hunted specimens are eaten by native population. In this regard, the record of the occurrence of the parasite Morishitium polonicum highlights the need of a monitoring of the health status of different species of the genus Turdus. Therefore, in the present manuscript it is proposed an agreement among the hunter societies, the responsible administration for management of hunting activity at Mallorca island and the University of the Balearic Islands, as a scientific institution
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
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