176 research outputs found
Adoption of European Union´s Law in Hungary, in the Area of Product Adequacy
The EU measures to introduce the internal market came into force on December
31st, 1992. The Council of the European Community produced a Directive, which
describes harmonization of rules issued by the Member Countries concerning
machines. The European Union is an important economic partner of Hungary. We
analyzed the situation concerning machines before the Hungarian connection to
European Community
Singularity theory of Weyl-point creation and annihilation
Weyl points (WP) are robust spectral degeneracies, which can not be split by
small perturbations, as they are protected by their non-zero topological
charge. For larger perturbations, WPs can disappear via pairwise annihilation,
where two oppositely charged WPs merge, and the resulting neutral degeneracy
disappears. The neutral degeneracy is unstable, meaning that it requires the
fine-tuning of the perturbation. Fine-tuning of more than one parameter can
lead to more exotic WP mergers. In this work, we reveal and analyze a
fundamental connection of the WP mergers and singularity theory: phase boundary
points of Weyl phase diagrams, i.e., control parameter values where Weyl point
mergers happen, can be classified according to singularity classes of maps
between manifolds of equal dimension. We demonstrate this connection on a
Weyl--Josephson circuit where the merger of 4 WPs draw a swallowtail
singularity, and in a random BdG Hamiltonian which reveal a rich pattern of
fold lines and cusp points. Our results predict universal geometrical features
of Weyl phase diagrams, and generalize naturally to creation and annihilation
of Weyl points in electronic (phononic, magnonic, photonic, etc) band-structure
models, where Weyl phase transitions can be triggered by control parameters
such as mechanical strain.Comment: 11 pages, 3 figures, 2 table
Angular dependence of core hole screening in LiCoO2: A DFT+U calculation of the oxygen and cobalt K-edge x-ray absorption spectra
Angular dependent core-hole screening effects have been found in the cobalt
K-edge x-ray absorption spectrum of LiCoO2, using high-resolution data and
parameter-free GGA+U calculations. The Co 1s core-hole on the absorber causes
strong local attraction. The core-hole screening on the nearest neighbours
cobalt induces a 2 eV shift in the density of states with respect to the
on-site 1s-3d transitions, as detected in the Co K pre-edge spectrum. Our DFT+U
calculations reveal that the off-site screening is different in the
out-of-plane direction, where a 3 eV shift is visible in both calculations and
experiment. The detailed analysis of the inclusion of the core-hole potential
and the Hubbard parameter U shows that the core-hole is essential for the
off-site screening, while U improves the description of the angular dependent
screening effects. In the case of oxygen K-edge, both the core-hole potential
and the Hubbard parameter improve the relative positions of the spectral
features
Weyl points in ball-and-spring mechanical systems
Degeneracy points of parameter-dependent Hermitian matrices play a
fundamental role in quantum physics, as illustrated by the concept of Berry
phase in quantum dynamics, the Weyl semimetals in condensed-matter physics, and
the robust ground-state degeneracies in topologically ordered quantum systems.
Here, we construct simple ball-and-spring mechanical systems, whose
eigenfrequency degeneracies mimic the behaviour of degeneracy points of
electronic band structures. These classical-mechanical arrangements can be
viewed as de-quantized versions of Weyl Josephson circuits, i.e.,
superconducting nanostructures proposed recently to mimic band structure
effects of Weyl semimetals. In the mechanical setups we study, we identify
degeneracy patterns beyond simple Weyl points, including the chirality flip
effect and a quadratic degeneracy point. Our theoretical work is a step toward
simple and illustrative table-top experiments exploring topological and
differential geometrical aspects of physics.Comment: Main text: 10 pages, 3 figures. Appendix: 6 pages, 1 figur
Observation of spin-orbit coupling induced Weyl points and topologically protected Kondo effect in a two-electron double quantum dot
Recent years have brought an explosion of activities in the research of
topological aspects of condensed-matter systems. Topologically non-trivial
phases of matter are typically accompanied by protected surface states or
exotic degenerate excitations such as Majorana end states or Haldane's
localized spinons. Topologically protected degeneracies can, however, also
appear in the bulk. An intriguing example is provided by Weyl semimetals, where
topologically protected electronic band degeneracies and exotic surface states
emerge even in the absence of interactions. Here we demonstrate experimentally
and theoretically that Weyl degeneracies appear naturally in an interacting
quantum dot system, for specific values of the external magnetic field. These
magnetic Weyl points are robust against spin-orbit coupling unavoidably present
in most quantum dot devices. Our transport experiments through an InAs double
dot device placed in magnetic field reveal the presence of a pair of Weyl
points, exhibiting a robust ground state degeneracy and a corresponding
protected Kondo effect.Comment: 6 pages, 3 figures. Supplementary Information can be downloaded as an
ancillary pdf fil
Автоматизация процесса выбора лекарственных препаратов на основе экспертных знаний
Материалы XX Междунар. науч.-техн. конф. студентов, аспирантов и молодых ученых, Гомель, 23–24 апр. 2020 г
Metagenomic analysis reveals mixed Mycobacterium tuberculosis infection in a 18th century Hungarian midwife
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