4,375 research outputs found
Quantum Transport Through a Stretched Spin--1 Molecule
We analyze the electronic transport through a model spin-1 molecule as a
function of temperature, magnetic field and bias voltage. We consider the
effect of magnetic anisotropy, which can be generated experimentally by
stretching the molecule. In the experimentally relevant regime the conductance
of the unstretched molecule reaches the unitary limit of the underscreened
spin- 1 Kondo effect at low temperatures. The magnetic anisotropy generates an
antiferromagnetic coupling between the remaining spin 1/2 and a singular
density of quasiparticles, producing a second Kondo effect and a reduced
conductance. The results explain recent measurements in spin-1 molecules
[Science 328 1370 (2010)].Comment: 5 pages, 3 figures, minor changes, accepted for publication in EP
Thermopower of an SU(4) Kondo resonance under an SU(2) symmetry-breaking field
We calculate the thermopower of a quantum dot described by two doublets
hybridized with two degenerate bands of two conducting leads, conserving
orbital (band) and spin quantum numbers, as a function of the temperature
and a splitting of the quantum dot levels which breaks the SU(4)
symmetry. The splitting can be regarded as a Zeeman (spin) or valley (orbital)
splitting. We use the non-crossing approximation (NCA), the slave bosons in the
mean-field approximation (SBMFA) and also the numerical renormalization group
(NRG) for large . The model describes transport through clean C
nanotubes %with weak disorder and in Si fin-type field effect transistors,
under an applied magnetic field. The thermopower as a function of temperature
displays two dips that correspond to the energy scales given by the
Kondo temperature and and one peak when reaches the
charge-transfer energy. These features are much more pronounced than the
corresponding ones in the conductance, indicating that the thermopower is a
more sensitive probe of the electronic structure at intermediate or high
energies. At low temperatures () is a constant that
increases strongly near the degeneracy point . We find that the SBMFA
fails to provide an accurate description of the thermopower for large .
Instead, a combination of Fermi liquid relations with the quantum-dot
occupations calculated within the NCA gives reliable results for .Comment: 8 pages, 7 figure
Explaining Aviation Safety Incidents Using Deep Temporal Multiple Instance Learning
Although aviation accidents are rare, safety incidents occur more frequently
and require a careful analysis to detect and mitigate risks in a timely manner.
Analyzing safety incidents using operational data and producing event-based
explanations is invaluable to airline companies as well as to governing
organizations such as the Federal Aviation Administration (FAA) in the United
States. However, this task is challenging because of the complexity involved in
mining multi-dimensional heterogeneous time series data, the lack of
time-step-wise annotation of events in a flight, and the lack of scalable tools
to perform analysis over a large number of events. In this work, we propose a
precursor mining algorithm that identifies events in the multidimensional time
series that are correlated with the safety incident. Precursors are valuable to
systems health and safety monitoring and in explaining and forecasting safety
incidents. Current methods suffer from poor scalability to high dimensional
time series data and are inefficient in capturing temporal behavior. We propose
an approach by combining multiple-instance learning (MIL) and deep recurrent
neural networks (DRNN) to take advantage of MIL's ability to learn using weakly
supervised data and DRNN's ability to model temporal behavior. We describe the
algorithm, the data, the intuition behind taking a MIL approach, and a
comparative analysis of the proposed algorithm with baseline models. We also
discuss the application to a real-world aviation safety problem using data from
a commercial airline company and discuss the model's abilities and
shortcomings, with some final remarks about possible deployment directions
Evidence for Fixpoint Logic
For many modal logics, dedicated model checkers offer diagnostics (e.g., counterexamples) that help the user understand the result provided by the solver. Fixpoint logic offers a unifying framework in which such problems can be expressed and solved, but a drawback of this framework is that it lacks comprehensive diagnostics generation. We extend the framework with a notion of evidence, which can be specialized to obtain diagnostics for various model checking problems, behavioural equivalence and refinement checking problems. We demonstrate this by showing how our notion of evidence can be used to obtain diagnostics for the problem of deciding stuttering bisimilarity. Moreover, we show that our notion generalizes the existing notions of counterexample and witness for LTL and ACTL* model checking
A process algebra with global variables
In standard process algebra, parallel components do not share a common state
and communicate through synchronisation. The advantage of this type of
communication is that it facilitates compositional reasoning. For modelling and
analysing systems in which parallel components operate on shared memory,
however, the communication-through-synchronisation paradigm is sometimes less
convenient. In this paper we study a process algebra with a notion of global
variable. We also propose an extension of Hennessy-Milner logic with predicates
to test and set the values of the global variables, and prove correspondence
results between validity of formulas in the extended logic and stateless
bisimilarity and between validity of formulas in the extended logic without the
set operator and state-based bisimilarity. We shall also present a translation
from the process algebra with global variables to a fragment of mCRL2 that
preserves the validity of formulas in the extended Hennessy-Milner logic.Comment: In Proceedings EXPRESS/SOS 2020, arXiv:2008.1241
Parent-child interaction in Nigerian families: conversation analysis, context and culture
This paper uses a conversation analysis (CA) approach to explore parent child interaction (PCI) within Nigerian families. We illustrate how speech and language therapists (SLTs), by using CA, can tailor recommendations according to the interactional style of each individual family that are consonant with the familyās cultural beliefs. Three parent-child dyads were videoed playing and talking together in their home environments. The analysis uncovered a preference for instructional talk similar to that used in the classroom. Closer examination revealed that this was not inappropriate when considering the context of the activities and their perceived discourse role. Furthermore, this was not necessarily at the expense of responsivity or semantic contingency. The preference for instructional talk appeared to reflect deeply held cultural beliefs about the role of adults and children within the family and it is argued that the cultural paradigm is vitally important to consider when evaluating PCI. Given a potential risk that such young children may be vulnerable in terms of language difficulties, we offer an example of how PCI can be enhanced to encourage language development without disrupting the naturally occurring talk or the underlying purpose of the interaction
Photoinduced charge transport over branched conjugation pathways: donorāacceptor substituted 1,1-diphenylethene and 2,3-diphenylbutadiene
This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence (http://creativecommons.org/licenses/by-nc/3.0/)Photoinduced charge transport in 1,1-diphenylethene and 2,3-diphenylbutadiene functionalized with an electron donating dimethylamino group and an electron accepting cyano group is reported. UV-spectroscopy reveals that in these compounds, which incorporate a cross-conjugated spacer, a direct charge transfer transition is possible. It is shown by application of the generalized MullikenāHush approach that introduction of an additional branching point in the Ļ-electron spacer (i.e., when going from the 1,1-diphenylethene to the 2,3-diphenylbutadiene) leads to only a moderate reduction (68ā92%) of the electronic coupling between the ground and the charge separated state. The Ļ-electron system is however likely to be dominant in the photoinduced charge separation process
Towards Model Checking Executable UML Specifications in mCRL2
We describe a translation of a subset of executable UML (xUML) into the process algebraic specification language mCRL2. This subset includes class diagrams with class generalisations, and state machines with signal and change events. The choice of these xUML constructs is dictated by their use in the modelling of railway interlocking systems. The long-term goal is to verify safety properties of interlockings modelled in xUML using the mCRL2 and LTSmin toolsets. Initial verification of an interlocking toy example demonstrates that the safety properties of model instances depend crucially on the run-to-completion assumptions
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