5,391 research outputs found
A Change of Variables to the Dual and Factorization of Composite Anomalous Jacobians
Changes of variables giving the dual model are constructed explicitly for
sigma-models without isotropy. In particular, the jacobian is calculated to
give the known results. The global aspects of the abelian case as well as some
of those of the cases where the isometry group is simply connected are
considered.
Considering the anomalous case, we infer by a consistency argument that the
`multiplicative anomaly' should be replaceable by adequate rules for
factorization of composite jacobians. These rules are then generalized in a
simple way for composite jacobians defined in spaces of different types.
Implimentation of these rules then gives specific formulas for the anomally for
semisimple algebras and also for solvable ones.Comment: 15 pages, no figures, Latex file, A treatment of the global aspects
of the abelian and of semisimple duality groups are added. General formulas
for the mixed anomaly are derive
Hydrodynamics in 1+1 dimensions with gravitational anomalies
The constraints imposed on hydrodynamics by the structure of gauge and
gravitational anomalies are studied in two dimensions. By explicit integration
of the consistent gravitational anomaly, we derive the equilibrium partition
function at second derivative order. This partition function is then used to
compute the parity-violating part of the covariant energy-momentum tensor and
the transport coefficients.Comment: 9 pages, JHEP format.v2; added comments and references, matching
published versio
Calidad de la Tithonia diversifolia en una zona del Valle del Cauto
13 páginas, 5 tablas.This experiment was carried out with the objective of determining the nutritive value of Tithonia diversifolia to different bud ages during the two periods of the year. A 0.5 ha field was used, where a standardization cut at 15 cm high from the soil was applied at the beginning of each period. The ages taken into consideration were 60, 120 and 180 days, and the elements evaluated were the RP, the fibrous fractioning, the dry matter In vitro digestibility, the wall cell digestibility and the tanins. To this purpose, a random- block design with three treatments and four repetitions was used through the application of a double classification analysis, and the average results were compared by means of the multiple ranges Duncan test. The statistical program utilized was Statiics version 6.0 for Windows. In the chapter that deals with the analysis of the results, it is evident that the dry matter, NDF, ADF, ADL, Hemicellulous, TF, TCT, CTAF and FTC increased their content (29. 47 %, 50. 51 %, 32. 12 %, 32. 12 %, 18. 39 %, 6.47, 13. 11, 10. 12, and 2. 99 g/kg respectively) at the age of 180 days, whereas the raw protein, the cellulous, the cell content, the In vitro digestibility and the wall cell digestibility decreased with their highest value (28.95, 21.08, 56.34, 78.59 y 76.61 %) at the age of 60 days. As a conclusion, age had a marked effect on the behavior of the evaluated elements, which was stronger during the rainy season, decreasing the nutritive quality.Trabajo realizado con financiación del Programa de Cooperación Interuniversitaria e Investigación Científica de la Agencia Española de Cooperación Internacional para el Desarrollo (Proyecto AECID A/023167/09).Peer Reviewe
An Introduction to T-Duality in String Theory
In these lectures a general introduction to T-duality is given. In the
abelian case the approaches of Buscher, and Ro\u{c}ek and Verlinde are
reviewed. Buscher's prescription for the dilaton transformation is recovered
from a careful definition of the gauge integration measure. It is also shown
how duality can be understood as a quite simple canonical transformation. Some
aspects of non-abelian duality are also discussed, in particular what is known
on relation to canonical transformations. Some implications of the existence of
duality on the cosmological constant and the definition of distance in String
Theory are also suggested.Comment: Latex file (1 figure), dina4p macro inserte
Temperature dependence of the anomalous effective action of fermions in two and four dimensions
The temperature dependence of the anomalous sector of the effective action of
fermions coupled to external gauge and pseudo-scalar fields is computed at
leading order in an expansion in the number of Lorentz indices in two and four
dimensions. The calculation preserves chiral symmetry and confirms that a
temperature dependence is compatible with axial anomaly saturation. The result
checks soft-pions theorems at zero temperature as well as recent results in the
literature for the pionic decay amplitude into static photons in the chirally
symmetric phase. The case of chiral fermions is also considered.Comment: RevTex, 19 pages, no figures. References adde
A two-step learning approach for solving full and almost full cold start problems in dyadic prediction
Dyadic prediction methods operate on pairs of objects (dyads), aiming to
infer labels for out-of-sample dyads. We consider the full and almost full cold
start problem in dyadic prediction, a setting that occurs when both objects in
an out-of-sample dyad have not been observed during training, or if one of them
has been observed, but very few times. A popular approach for addressing this
problem is to train a model that makes predictions based on a pairwise feature
representation of the dyads, or, in case of kernel methods, based on a tensor
product pairwise kernel. As an alternative to such a kernel approach, we
introduce a novel two-step learning algorithm that borrows ideas from the
fields of pairwise learning and spectral filtering. We show theoretically that
the two-step method is very closely related to the tensor product kernel
approach, and experimentally that it yields a slightly better predictive
performance. Moreover, unlike existing tensor product kernel methods, the
two-step method allows closed-form solutions for training and parameter
selection via cross-validation estimates both in the full and almost full cold
start settings, making the approach much more efficient and straightforward to
implement
Degenerate Stars and Gravitational Collapse in AdS/CFT
We construct composite CFT operators from a large number of fermionic primary
fields corresponding to states that are holographically dual to a zero
temperature Fermi gas in AdS space. We identify a large N regime in which the
fermions behave as free particles. In the hydrodynamic limit the Fermi gas
forms a degenerate star with a radius determined by the Fermi level, and a mass
and angular momentum that exactly matches the boundary calculations. Next we
consider an interacting regime, and calculate the effect of the gravitational
back-reaction on the radius and the mass of the star using the
Tolman-Oppenheimer-Volkoff equations. Ignoring other interactions, we determine
the "Chandrasekhar limit" beyond which the degenerate star (presumably)
undergoes gravitational collapse towards a black hole. This is interpreted on
the boundary as a high density phase transition from a cold baryonic phase to a
hot deconfined phase.Comment: 75 page
Palladium‐Catalyzed Cross‐Dehydrogenative Coupling of <i>o</i>‐Xylene: Evidence of a New Rate‐Limiting Step in the Search for Industrially Relevant Conditions
An efficient cross‐dehydrogenative coupling of o‐xylene under neat conditions, which brings important industrial benefits towards the synthesis of a monomer used in polyimide resins, is reported. The catalyst based on the combination of Pd/N ligand/carboxylate=1:1:2 does not require a Cu cocatalyst and proceeds at 11 bar of O2 pressure. Evaluation of the deuterium kinetic isotope effect (KIE) provides evidence for three different rate‐determining steps, which depend on the reaction conditions (medium, temperature). Under the reported neat conditions, the dissociation of a carboxylate‐bridged dimer to generate a more reactive monometallic Pd species is proposed to be the rate‐limiting step
Analysis of both the envelope sequence and the complete genome of a HIV-1 subtype f cluster of rapid expansion in Galicia: coreceptor use prediction and phylogeny
La epidemia por VIH-1 en España, al igual que en el resto de Europa occidental, está dominada por el subtipo B. Sin embargo, recientemente se ha descrito la rápida expansión de un cluster de subsubtipo F1 entre hombres que tienen relaciones sexuales con hombres en Galicia. Los objetivos de este trabajo son analizar la secuencia de la envoltura de los virus del mencionado cluster para predicción de utilización de correceptores y presencia de aminoácidos característicos, así como caracterizar secuencias de genomas completos, determinando las relaciones filogenéticas con virus de subtipo F de otros países. Los análisis filogenéticos permitieron determinar relaciones del cluster F con virus de Brasil, Suiza, Bélgica, Francia y Gran Bretaña. Por otra parte, se han encontrado posiciones características del cluster en la región V3, diferentes de otras cepas F1, así como en otras regiones de la envoltura. Aparte, se han identificado mutaciones características asociadas a tropismo X4. El cluster de VIH-1 de subtipo F recientemente expandido en Galicia procede de una variante ampliamente diseminada en Europa occidental. Los virus de dicho cluster presentan aminoácidos característicos en la envoltura, identificándose en algunos de ellos mutaciones asociadas a tropismo X4, de potencial relevancia biológicaThe HIV-1 epidemic in Spain, as in the rest of Western Europe, is dominated by subtype B. However, it has recently been reported that a subsubtype F1 cluster has rapidly expanded among men who have sex with men in Galicia. The objectives of this work are to analyze the virus envelope sequence of the aforementioned cluster to predict the use of coreceptors and to examine the presence of characteristic amino acids, as well as to characterize full-length genome sequences, determining the phylogenetic relations with subtype F viruses from other countries. The phylogenetic analyses allowed to determine the relation of the Galician F cluster with viruses from Brazil, Switzerland, Belgium, France and Great Britain. On the other hand, characteristic amino acid residues were found in the V3 loop of viruses of the cluster, differing from other F1 strains, as well as in other regions of the envelope. Additionally, characteristic mutations associated with X4 tropism were identified. The HIV-1 subtype F cluster recently expanded in Galicia derives from a variant widely disseminated in Western Europe. The viruses of the mentioned cluster show characteristic amino acids in the envelope, with mutations associated with X4 tropism having been identified in some of them, which are of potential biological relevance
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