590 research outputs found
IrF4: From Tetrahedral Compass Model to Topological Semimetal
The intersection of topology, symmetry, and magnetism yields a rich structure
of possible phases. In this work, we study theoretically the consequences of
magnetism on IrF4, which was recently identified as a possible candidate
topological nodal chain semimetal in the absence of magnetic order. We show
that the spin-orbital nature of the Ir moments gives rise to strongly
anisotropic magnetic couplings resembling a tetrahedral compass model on a
diamond lattice. The predicted magnetic ground state preserves key symmetries
protecting the nodal lines, such that they persist into the ordered phase at
the mean-field level. The consequences for other symmetry reductions are also
discussed
APPLICABILITY OF A FULL BODY INERTIAL MEASUREMENT SYSTEM FOR KINEMATIC ANALYSIS OF THE DISCUS THROW
The aim of the study was the application of a full body inertial measurement system (IMS) for a kinematic analysis of the discus throw and the evaluation of its applicability. For this purpose, one male sports student performed three discus throws equipped with the IMS. All trials were additionally filmed by high-speed video. The results indicate that perfor-mance-relevant information can be obtained regarding the temporal coordination of the body segments and body joint angles. Limitations exist for the accurate detection of the last foot contact related instant and the discus release instant by solely using the IMS data
A coproduct structure on the formal affine Demazure algebra
In the present paper we generalize the coproduct structure on nil Hecke rings
introduced and studied by Kostant-Kumar to the context of an arbitrary
algebraic oriented cohomology theory and its associated formal group law. We
then construct an algebraic model of the T-equivariant oriented cohomology of
the variety of complete flags.Comment: 28 pages; minor revision of the previous versio
On Coupling FCA and MDL in Pattern Mining
International audiencePattern Mining is a well-studied field in Data Mining and Machine Learning. The modern methods are based on dynamically updating models, among which MDL-based ones ensure high-quality pattern sets. Formal concepts also characterize patterns in a condensed form. In this paper we study MDL-based algorithm called Krimp in FCA settings and propose a modified version that benefits from FCA and relies on probabilistic assumptions that underlie MDL. We provide an experimental proof that the proposed approach improves quality of pattern sets generated by Krimp
Partial orders and logical concept analysis to explore patterns extracted by data mining
International audienceData mining techniques are used in order to discover emerging knowledge (patterns) in databases. The problem of such techniques is that there are, in general, too many resulting patterns for a user to explore them all by hand. Some methods try to reduce the number of patterns without a priori pruning. The number of patterns remains, nevertheless, high. Other approaches, based on a total ranking, propose to show to the user the top-k patterns with respect to a measure. Those methods do not take into account the user's knowledge and the dependencies that exist between patterns. In this paper, we propose a new way for the user to explore extracted patterns. The method is based on navigation in a partial order over the set of all patterns in the Logical Concept Analysis framework. It accommodates several kinds of patterns and the dependencies between patterns are taken into account thanks to partial orders. It allows the user to use his/her background knowledge to navigate through the partial order, without a priori pruning. We illustrate how our method can be applied on two different tasks (software engineering and natural language processing) and two different kinds of patterns (association rules and sequential patterns)
Empirical comparison of high gradient achievement for different metals in DC and pulsed mode
For the SwissFEL project, an advanced high gradient low emittance gun is
under development. Reliable operation with an electric field, preferably above
125 MV/m at a 4 mm gap, in the presence of an UV laser beam, has to be achieved
in a diode configuration in order to minimize the emittance dilution due to
space charge effects. In the first phase, a DC breakdown test stand was used to
test different metals with different preparation methods at voltages up to 100
kV. In addition high gradient stability tests were also carried out over
several days in order to prove reliable spark-free operation with a minimum
dark current. In the second phase, electrodes with selected materials were
installed in the 250 ns FWHM, 500 kV electron gun and tested for high gradient
breakdown and for quantum efficiency using an ultra-violet laser.Comment: 25 pages, 13 figures, 5 tables. Follow up from FEL 2008 conference
(Geyongju Korea 2008) New Title in JVST A (2010) : Vacuum breakdown limit and
quantum efficiency obtained for various technical metals using DC and pulsed
voltage source
Theory of Concepts
UID/FIL/00183/2013authorsversionpublishe
AQFT from n-functorial QFT
There are essentially two different approaches to the axiomatization of
quantum field theory (QFT): algebraic QFT, going back to Haag and Kastler, and
functorial QFT, going back to Atiyah and Segal. More recently, based on ideas
by Baez and Dolan, the latter is being refined to "extended" functorial QFT by
Freed, Hopkins, Lurie and others. The first approach uses local nets of
operator algebras which assign to each patch an algebra "of observables", the
latter uses n-functors which assign to each patch a "propagator of states".
In this note we present an observation about how these two axiom systems are
naturally related: we demonstrate under mild assumptions that every
2-dimensional extended Minkowskian QFT 2-functor ("parallel surface transport")
naturally yields a local net. This is obtained by postcomposing the propagation
2-functor with an operation that mimics the passage from the Schroedinger
picture to the Heisenberg picture in quantum mechanics.
The argument has a straightforward generalization to general
pseudo-Riemannian structure and higher dimensions.Comment: 39 pages; further examples added: Hopf spin chains and asymptotic
inclusion of subfactors; references adde
Constraint Programming for Multi-criteria Conceptual Clustering
International audienceA conceptual clustering is a set of formal concepts (i.e., closed itemsets) that defines a partition of a set of transactions. Finding a conceptual clustering is an N P-complete problem for which Constraint Programming (CP) and Integer Linear Programming (ILP) approaches have been recently proposed. We introduce new CP models to solve this problem: a pure CP model that uses set constraints, and an hybrid model that uses a data mining tool to extract formal concepts in a preprocessing step and then uses CP to select a subset of formal concepts that defines a partition. We compare our new models with recent CP and ILP approaches on classical machine learning instances. We also introduce a new set of instances coming from a real application case, which aims at extracting setting concepts from an Enterprise Resource Planning (ERP) software. We consider two classic criteria to optimize, i.e., the frequency and the size. We show that these criteria lead to extreme solutions with either very few small formal concepts or many large formal concepts, and that compromise clusterings may be obtained by computing the Pareto front of non dominated clusterings
Human cyclin T1 expression ameliorates a T-cell-specific transcriptional limitation for HIV in transgenic rats, but is not sufficient for a spreading infection of prototypic R5 HIV-1 strains ex vivo
<p>Abstract</p> <p>Background</p> <p>Cells derived from native rodents have limits at distinct steps of HIV replication. Rat primary CD4 T-cells, but not macrophages, display a profound transcriptional deficit that is ameliorated by transient trans-complementation with the human Tat-interacting protein Cyclin T1 (hCycT1).</p> <p>Results</p> <p>Here, we generated transgenic rats that selectively express hCycT1 in CD4 T-cells and macrophages. hCycT1 expression in rat T-cells boosted early HIV gene expression to levels approaching those in infected primary human T-cells. hCycT1 expression was necessary, but not sufficient, to enhance HIV transcription in T-cells from individual transgenic animals, indicating that endogenous cellular factors are critical co-regulators of HIV gene expression in rats. T-cells from hCD4/hCCR5/hCycT1-transgenic rats did not support productive infection of prototypic wild-type R5 HIV-1 strains <it>ex vivo</it>, suggesting one or more significant limitation in the late phase of the replication cycle in this primary rodent cell type. Remarkably, we identify a replication-competent HIV-1 GFP reporter strain (R7/3 YU-2 Env) that displays characteristics of a spreading, primarily cell-to-cell-mediated infection in primary T-cells from hCD4/hCCR5-transgenic rats. Moreover, the replication of this recombinant HIV-1 strain was significantly enhanced by hCycT1 transgenesis. The viral determinants of this so far unique replicative ability are currently unknown.</p> <p>Conclusion</p> <p>Thus, hCycT1 expression is beneficial to <it>de novo </it>HIV infection in a transgenic rat model, but additional genetic manipulations of the host or virus are required to achieve full permissivity.</p
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