2,558 research outputs found
Hyperbolic Topological Invariants and the Black Hole Geometry
We discuss the isometry group structure of three-dimensional black holes and
Chern-Simons invariants. Aspects of the holographic principle relevant to black
hole geometry are analyzed.Comment: 11 pages, AMSTeX, Contribution to the Fifth Alexander Friedmann
International Seminar on Gravitation and Cosmolog
Analytical device model for graphene bilayer field-effect transistors using weak nonlocality approximation
We develop an analytical device model for graphene bilayer field-effect
transistors (GBL-FETs) with the back and top gates. The model is based on the
Boltzmann equation for the electron transport and the Poisson equation in the
weak nonlocality approximation for the potential in the GBL-FET channel. The
potential distributions in the GBL-FET channel are found analytically. The
source-drain current in GBL-FETs and their transconductance are expressed in
terms of the geometrical parameters and applied voltages by analytical formulas
in the most important limiting cases. These formulas explicitly account for the
short-gate effect and the effect of drain-induced barrier lowering. The
parameters characterizing the strength of these effects are derived. It is
shown that the GBL-FET transconductance exhibits a pronounced maximum as a
function of the top-gate voltage swing. The interplay of the short-gate effect
and the electron collisions results in a nonmonotonic dependence of the
transconductance on the top-gate length.Comment: 12 pages, 7 figure
Fuzzy interpretation for temporal-difference learning in anomaly detection problems
Nowadays, information control systems based on databases develop dynamically worldwide. These systems are extensively implemented
into dispatching control systems for railways, intrusion detection systems for computer security and other domains centered on big data
analysis. Here, one of the main tasks is the detection and prediction of temporal anomalies, which could be a signal leading to significant (and often critical) actionable information. This paper proposes the new anomaly prevent detection technique, which allows for determining the predictive temporal structures. Presented approach is based on a hybridization of stochastic Markov reward model by using fuzzy production rules, which allow to correct Markov information based on expert knowledge about the process dynamics as well as Markov’s intuition about the probable anomaly occurring. The paper provides experiments showing the efficacy of detection and prediction. In addition, the analogy between new framework and temporal-difference learning for sequence anomaly detection is graphically illustrated.Web of Science64363262
Anisotropic Topological Hall Effect with Real and Momentum Space Berry Curvature in the Antiskrymion Hosting Heusler Compound MnPtSn
The topological Hall effect (THE) is one of the key signatures of
topologically non-trivial magnetic spin textures, wherein electrons feel an
additional transverse voltage to the applied current. The magnitude of THE is
often small compared to the anomalous Hall effect. Here, we find a large THE of
0.9 cm that is of the same order of the anomalous Hall effect in the
single crystalline antiskyrmion hosting Heusler compound MnPtSn, a
non-centrosymmetric tetragonal compound. The THE is highly anisotropic and
survives in the whole temperature range where the spin structure is noncoplanar
(<170 K). The THE is zero above the spin reorientation transition temperature
of 170 K, where the magnetization will have a collinear and ferromagnetic
alignment. The large value of the THE entails a significant contribution from
the momentum space Berry curvature along with real space Berry curvature, which
has never been observed earlier
Modifications of gravity via differential transformations of field variables
We discuss field theories appearing as a result of applying field
transformations with derivatives (differential field transformations, DFT) to a
known theory. We begin with some simple examples of DFTs to see the basic
properties of the procedure. In this process the dynamics of the theory might
either change or conserve. After that we concentrate on the theories of gravity
which appear as a result of various DFT applied to general relativity, namely
the mimetic gravity and Regge-Teitelboim embedding theory. We review main
results related to the extension of dynamics in these theories, as well as the
possibility to write down the action of a theory after DFT as the action of the
original theory before DFT plus an additional term. Such a term usually
contains some constraints with Lagrange multipliers and can be interpreted as
an action of additional matter, which might be of use in cosmological
applications, e.g. for the explanation of the effects of dark matter.Comment: 18 page
Robust metastable skyrmions with tunable size in the chiral magnet FePtMoN
Synthesis of new materials that can host magnetic skyrmions and their
thorough experimental and theoretical characterization are essential for future
technological applications. The -Mn-type compound FePtMoN is one
such novel material that belongs to the chiral space group , where the
antisymmetric Dzyaloshinkii-Moriya interaction is allowed due to the absence of
inversion symmetry. We report the results of small-angle neutron scattering
(SANS) measurements of FePtMoN and demonstrate that its magnetic ground
state is a long-period spin helix with a Curie temperature of 222~K. The
magnetic field-induced redistribution of the SANS intensity showed that the
helical structure transforms to a lattice of skyrmions at 13~mT at
temperatures just below . Our key observation is that the skyrmion
state in FePtMoN is robust against field cooling down to the lowest
temperatures. Moreover, once the metastable state is prepared by field cooling,
the skyrmion lattice exists even in zero field. Furthermore, we show that the
skyrmion size in FePtMoN exhibits high sensitivity to the sample
temperature and can be continuously tuned between 120 and 210~nm. This offers
new prospects in the control of topological properties of chiral magnets.Comment: 6 pages, 4 figure
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