5,754 research outputs found
On the Lyapunov Matrix of Linear Delay Difference Equations in Continuous Time
The fundamental matrix and the delay Lyapunov matrix of linear delay
difference equations are introduced. Some properties of the Lyapunov matrix,
and the jump discontinuities of its derivative are proven, leading to its
construction in the case of single delay or commensurate delays. An
approximation is proposed for the non-commensurate case
Parafermionic character formulae
We study various aspects of parafermionic theories such as the precise field
content, a description of a basis of states (that is, the counting of
independent states in a freely generated highest-weight module) and the
explicit expression of the parafermionic singular vectors in completely
irreducible modules. This analysis culminates in the presentation of new
character formulae for the parafermionic primary fields. These characters
provide novel field theoretical expressions for \su(2) string functions.Comment: Harvmac (b mode : 37 p
GeoCLEF 2006: the CLEF 2006 Ccross-language geographic information retrieval track overview
After being a pilot track in 2005, GeoCLEF advanced to be a regular track within CLEF 2006. The
purpose of GeoCLEF is to test and evaluate cross-language geographic information retrieval (GIR): retrieval for
topics with a geographic specification. For GeoCLEF 2006, twenty-five search topics were defined by the
organizing groups for searching English, German, Portuguese and Spanish document collections. Topics were
translated into English, German, Portuguese, Spanish and Japanese. Several topics in 2006 were significantly
more geographically challenging than in 2005. Seventeen groups submitted 149 runs (up from eleven groups and
117 runs in GeoCLEF 2005). The groups used a variety of approaches, including geographic bounding boxes,
named entity extraction and external knowledge bases (geographic thesauri and ontologies and gazetteers)
Sensorless variable speed single-phase induction motor drive system based on direct rotor flux orientation
The single-phase induction motor (SPIM) is one of the electrical machines more used in the World, and can be found in several fractional and sub-fractional horsepower applications in houses, offices, shoppings, farms, and industries. The introduction of more sophisticated applications has required the use of variable speed drives for SPIM, where the adoption of sensorless techniques is the more reasonable option for speed control due to the low cost of this electrical machine. A proposal for sensorless variable speed SPIM drive based on direct rotor field orientation techniques is presented in this paper. None transformation is used in order to eliminate the asymmetry of the stator windings of the SPIM. The rotor speed is estimated from an flux observer, which is based on two independent linear feedback control systems. The speed and flux estimatives are used in two control loop based on PID regulators, which determine the voltages to be applied to the SPIM windings by a three-legs VSI inverter. Using computer simulations, two situations are considered in order to demonstrate the satisfactory performance of the proposed sensorless speed control for SPIM drives: variations on rotor speed reference and the application of mechanical load
Character decomposition of Potts model partition functions. I. Cyclic geometry
We study the Potts model (defined geometrically in the cluster picture) on
finite two-dimensional lattices of size L x N, with boundary conditions that
are free in the L-direction and periodic in the N-direction. The decomposition
of the partition function in terms of the characters K\_{1+2l} (with
l=0,1,...,L) has previously been studied using various approaches (quantum
groups, combinatorics, transfer matrices). We first show that the K\_{1+2l}
thus defined actually coincide, and can be written as traces of suitable
transfer matrices in the cluster picture. We then proceed to similarly
decompose constrained partition functions in which exactly j clusters are
non-contractible with respect to the periodic lattice direction, and a
partition function with fixed transverse boundary conditions.Comment: 21 pages, 4 figure
Singular Vectors and Conservation Laws of Quantum KdV type equations
We give a direct proof of the relation between vacuum singular vectors and
conservation laws for the quantum KdV equation or equivalently for
-perturbed conformal field theories. For each degree at which a
classical conservation law exists, we find a quantum conserved quantity for a
specific value of the central charge. Various generalizations (
supersymmetric, Boussinesq) of this result are presented.Comment: 9 page
Intermolecular interactions, spectroscopic and theoretical investigation of 4-aminoacetophenone
The molecular structure of 4-aminoacetophenone (PAAP) was determined by DFT calculations using different basis sets. The structural parameters, electronic properties and vibrational wavenumbrers of the optimized geometry have been determined. The vibrational wave-numbers of the fundamental modes of the title compound have been precisely assigned and analyzed and the theoretical results are com-pared with the experimental vibrations observing a very good correlation. TD-DFT approach was applied to assign the electronic transitions ob-served in the experimental UV-vis spectrum. The molecular electrostatic potential map was used to identify the possible electrophilic and nucleophilic sites. Natural bond orbital (NBO) analysis and atoms in molecules (AIM) approach are applied in order to quantify the relative strength of hydrogen bonding interactions and to account their effect on the stabilities of molecular arrangements. In addition, a detailed exploration of the intermolecular interactions that stabilizes the crystal packing has been performed by using the Hirshfeld surface analysis.Fil: Rocha, Mariana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Tucumán. Instituto de QuĂmica del Noroeste. Universidad Nacional de Tucumán. Facultad de BioquĂmica, QuĂmica y Farmacia. Instituto de QuĂmica del Noroeste; ArgentinaFil: Di Santo, Alfredo Alejandro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Tucumán. Instituto de QuĂmica del Noroeste. Universidad Nacional de Tucumán. Facultad de BioquĂmica, QuĂmica y Farmacia. Instituto de QuĂmica del Noroeste; ArgentinaFil: Ben Altabef, Aida. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Tucumán. Instituto de QuĂmica del Noroeste. Universidad Nacional de Tucumán. Facultad de BioquĂmica, QuĂmica y Farmacia. Instituto de QuĂmica del Noroeste; ArgentinaFil: Gil, Diego Mauricio. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Tucumán. Instituto de QuĂmica del Noroeste. Universidad Nacional de Tucumán. Facultad de BioquĂmica, QuĂmica y Farmacia. Instituto de QuĂmica del Noroeste; Argentin
Coulomb-gas approach for boundary conformal field theory
We present a construction of boundary states based on the Coulomb-gas
formalism of Dotsenko and Fateev. It is shown that Neumann-like coherent states
on the charged bosonic Fock space provide a set of boundary states with
consistent modular properties. Such coherent states are characterised by the
boundary charges, which are related to the number of bulk screening operators
through the charge neutrality condition. We illustrate this using the Ising
model as an example, and show that all of its known consistent boundary states
are reproduced in our formalism. This method applies to minimal conformal
theories and provides an unified computational tool for studying boundary
states of such theories.Comment: 10 pages, 1 figure, revtex. Minor corrections, references added. To
appear in Nuclear Physics
Tuning of electron transport through a moebius strip: shot noise
We explore electron transport through a moebius strip attached to two
metallic electrodes by the use of Green's function technique. A parametric
approach is used based on the tight-binding model to characterize the electron
transport through such a bridge system and it is observed that the transport
properties are significantly affected by (a) the transverse hopping strength
between the two channels and (b) the strip-to-electrode coupling strength. In
this context we also describe the noise power of the current fluctuations that
provides a key information about the electron correlation which is obtained by
calculating the Fano factor (). The knowledge of this current fluctuations
gives important ideas for fabrication of efficient electronic devices.Comment: 9 pages, 8 figure
Proximal changes in signal transduction that modify CD8+ T cell responsiveness in vivo
The antigen dose conditions the functional properties of CD8+ T cells generated after priming.
At relatively low antigen doses, efficient memory T cells may be generated, while high
antigen doses lead to tolerance. To determine the mechanisms leading to such different
functional outcomes, we compared the proximal TCR signal transduction of naive cells, to
that of memory or high-dose tolerant cells generated in vivo. In vivo activation led to the constitutive
phosphorylation of CD3 4 , recruiting Zap70, in both memory and tolerant cells. In tolerant
cells, these phenomena were much more marked, the CD3 4 and ´ chains no longer
associated, and the Src kinases p56Lck and p59Fyn were inactive. Therefore, when the antigen
load overcomes the capacities of immune control, a new mechanism intervenes to block
signal transduction: the recruitment of Zap70 to CD3 4 becomes excessive, leading to TCR
complex destabilization, Src kinase dysfunction, and signal arrest
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