Descripción: We compute the order αs2 corrections to the one particle inclusive electroproduction cross section of hadrons with non vanishing transverse momentum. We compare our results with H1 data on forward production of π0, and conclude that the data is well described by the DGLAP approach. within the theoretical uncertainties. © 2005 American Institute of Physics.

Descripción: We consider the transverse-momentum (qT) distribution of Higgs bosons produced at hadron colliders. We use a formalism that uniformly treats both the small-qT and large-qT regions in QCD perturbation theory. At small qT (qT ≪ MH, MH being the mass of the Higgs boson), we implement an all-order resummation of logarithmically-enhanced contributions up to next-to-next-to-leading logarithmic accuracy. At large qT (qT ≳ MH), we use fixed-order perturbation theory up to next-to-leading order. The resummed and fixed-order approaches are consistently matched by avoiding double-counting in the intermediate-qT region. In this region, the introduction of unjustified higher-order terms is avoided by imposing unitarity constraints, so that the integral of the qT spectrum exactly reproduces the perturbative result for the total cross section up to next-to-next-to-leading order. Numerical results at the LHC are presented. These show that the main features of the qT distribution are quite stable with respect to perturbative QCD uncertainties. © 2003 Elsevier Science B.V. All rights reserved.

Descripción: We deal with randomness quantifiers and concentrate on their ability to discern the hallmark of chaos in time series used in connection with pseudo-random number generators (PRNGs). Workers in the field are motivated to use chaotic maps for generating PRNGs because of the simplicity of their implementation. Although there exist very efficient general-purpose benchmarks for testing PRNGs, we feel that the analysis provided here sheds additional didactic light on the importance of the main statistical characteristics of a chaotic map, namely (i) its invariant measure and (ii) the mixing constant. This is of help in answering two questions that arise in applications: (i) which is the best PRNG among the available ones? and (ii) if a given PRNG turns out not to be good enough and a randomization procedure must still be applied to it, which is the best applicable randomization procedure? Our answer provides a comparative analysis of several quantifiers advanced in the extant literature. © 2009 The Royal Society.

Descripción: Aims: To establish a reliable and rapid protocol to simultaneously obtain high quality DNA from an infected host plant and the infecting pathogen. To develop an accurate and sensitive low-cost assay for the quantification and in planta monitoring of Phytophthora infestans growth.Methods and Results: In this study, we describe a SYBR Green-based quantitative real-time PCR (qPCR) method for the quantification of P. infestans. The method is based on a simultaneous plant-pathogen DNA purification followed by a qPCR in which the relative quantification of pathogen and plant DNA is performed. Besides assuring an accurate quantification, the use of a plant gene provides a reliable indicator of sample quality, allowing the exclusion of inappropriate samples. By applying this methodology, we were able to detect P. infestans in potato leaf and tuber tissue before the first symptoms of the disease were observed and to monitor the in planta growth of the pathogen for 6 days.Conclusions: This is a reliable low-cost assay that provides rapid, accurate and sensitive quantification of the late blight pathogen, allowing the in planta monitoring of P. infestans growth.Significance and Impact of the Study: The quantitative nature of the assay described in this study may be useful in plant breeding programmes and basic research. The method is appropriate for the comparison of cultivars with different, and even subtle, degrees of pathogen resistance and in the screening of new anti-oomycete compounds. The method can be easily adapted to tomato and the model plant Nicotiana benthamiana. © No claim to Argentinean Government works. Letters in Applied Microbiology 51, 603-610 © 2010 The Society for Applied Microbiology.

Descripción: The retrograde transport of nerve growth factor (NGF) in neurite-like processes of living differentiated PC12 cells was studied using streptavidin-quantum dots (QDs) coupled to monobiotin-NGF. These reagents were active in differentiation, binding, internalization, and transport. Ten-35% of the QD-NGF-receptor complexes were mobile. Quantitative single particle tracking revealed a bidirectional step-like motion, requiring intact microtubules, with a net retrograde velocity of 0.054 ± 0.020 μm/s. Individual runs had a mean velocity of ∼0.15 μm/s at room temperature, and the run times were exponentially distributed. The photostability and brightness of QDs permit extended real-time analysis of individual QDbNGF- receptor complexes trafficking within neurites. © 2007 Federation of European Biochemical Societies.

Descripción: Simple cosmological models are used to show that gravitation can be quantized as an ordinary gauge system if the Hamilton-Jacobi equation for the model under consideration is separable. In this situation, a canonical transformation can be performed such that in terms of the new variables the model has a linear and homogeneous constraint, and therefore canonical gauges are admissible in the path integral. This has the additional practical advantage that gauge conditions that do not generate Gribov copies are then easy to choose. © 1998 American Institute of Physics.

Descripción: In the present paper, we are interested in natural quantum analogues of Richardson varieties in the type A grassmannians. To be more precise, the objects that we investigate are quantum analogues of the homogeneous coordinate rings of Richardson varieties which appear naturally in the theory of quantum groups. Our point of view, here, is geometric: we are interested in the regularity properties of these non-commutative varieties, such as their irreducibility, normality, Cohen-Macaulayness... in the spirit of non-commutative algebraic geometry. A major step in our approach is to show that these algebras have the structure of an algebra with a straightening law. From this, it follows that they degenerate to some quantum analogues of toric varieties. © 2012 Elsevier Inc.

Descripción: Irreversibility in quantum processes in the Bunimovich stadium and rectangular billiard in the presence of noise is studied. For this purpose, a novel method based on Loschmidt echo and quantum trajectories, as defined in the de Broglie-Bohm formulation, is used. Our results indicate that the dynamics along the diagonal of the billiard is most sensitive to noise when the wave packet (or alternatively the quantum trajectories) collide with the corners of the billiard. © 2005 American Institute of Physics.

Descripción: We study improper mixtures from a quantum logical and geometrical point of view. Taking into account the fact that improper mixtures do not admit an ignorance interpretation and must be considered as states in their own right, we do not follow the standard approach which considers improper mixtures as measures over the algebra of projections. Instead of it, we use the convex set of states in order to construct a new lattice whose atoms are all physical states: pure states and improper mixtures. This is done in order to overcome one of the problems which appear in the standard quantum logical formalism, namely, that for a subsystem of a larger system in an entangled state, the conjunction of all actual properties of the subsystem does not yield its actual state. In fact, its state is an improper mixture and cannot be represented in the von Neumann lattice as a minimal property which determines all other properties as is the case for pure states or classical systems. The new lattice also contains all propositions of the von Neumann lattice. We argue that this extension expresses in an algebraic form the fact that-alike the classical case-quantum interactions produce nontrivial correlations between the systems. Finally, we study the maps which can be defined between the extended lattice of a compound system and the lattices of its subsystems. © 2010 American Institute of Physics.

Descripción: Ring polymer molecular dynamics experiments have been carried out to examine effects derived from nuclear quantum fluctuations at ambient conditions on equilibrium and non-equilibrium dynamical characteristics of charge solvation by a popular simple, rigid, water model, SPC/E, and for a more recent, and flexible, q-TIP4P/F model, to examine the generality of conclusions. In particular, we have recorded the relaxation of the solvent energy gap following instantaneous, ±e charge jumps in an initially uncharged Lennard-Jones-like solute. In both charge cases, quantum effects are reflected in sharper decays at the initial stages of the relaxation, which produce up to a ∼20% reduction in the characteristic timescales describing the solvation processes. For anionic solvation, the magnitude of polarization fluctuations controlling the extent of the water proton localization in the first solvation shell is somewhat more marked than for cations, bringing the quantum solvation process closer to the classical case. Effects on the solvation response from the explicit incorporation of flexibility in the water Hamiltonian are also examined. Predictions from linear response theories for the overall relaxation profile and for the corresponding characteristic timescales are reasonably accurate for the solvation of cations, whereas we find that they are much less satisfactory for the anionic case. © 2013 AIP Publishing LLC.

Descripción: We analyze the possibility of finding almost hexagonal and quasicrystalline patterns, in finite square containers, as the result of the nonlinear interaction of four-dimensional and eight-dimensional representations of [Formula Presented]. We report the possibility of sustained oscillations between simple and nonsimple squares as the result of these interactions. © 1997 The American Physical Society.

Descripción: This work is devoted to the study of a quasilinear elliptic system of resonant type. We prove the existence of infinitely many solutions of a related nonlinear eigenvalue problem. Applying an abstract minimax theorem, we obtain a solution of the quasilinear system -Δ pu = F u(x,u,v), -Δ qv = F v(x,u,v), under conditions involving the first and the second eigenvalues. Copyright © 2002 Hindawi Publishing Corporation.

Descripción: We consider scalar and spinorial perturbations on a background described by a z = 3 three-dimensional Lifshitz black hole. We obtained the corresponding quasinormal modes which perfectly agree with the analytical result for the quasinormal frequency in the scalar case. The numerical results for the spinorial perturbations reinforce our conclusion on the stability of the model under these perturbations. We also calculate the area spectrum, which prove to be equally spaced, as an application of our results.

Descripción: A simple model that employs a periodic, planar array of parallel cylinders representing the nanotubes is presented. Using this method, the existence of several phase transitions in the film is demonstrated. These include both two-dimensional (2D) transitions and quasi-1D transitions.

Descripción: Along the eastern front of the Sierra de Velasco and at the southern end of the Sierra de Ambato, western Sierras Pampeanas, have been found new evidences of Quaternary tectonic activity near La Rioja city. Observed evidences correspond to different reactivated sections of the faults that bound the mountain fronts, as well as to structures affecting the Quaternary deposits on the piedmont. The bounding faults of the Sierra de Velasco Oriental-front exhibit a NNE trend and WNW dip, while structures at the southernmost Ambato range are characterized by NE trend and NW dip. The neotectonic faults of the El Carrizal block are the result of the interference of both structural trends, resulting in a sector with higher structural complexity. The here described deformation show the persistence of a compressive regime during the Quaternary, with eastern to southeastern verging reverse faults. It is considering that these faults are driving the current uplift of the mountain ranges and constitute potential earthquake sources.

Descripción: Fil:Van Zele, M.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Quintessence and k-essence have been proposed as candidates for the dark energy component of the universe that would be responsible of the currently observed accelerated expansion. In this Letter we investigate the degree of resemblance between those two theoretical setups, and find that every quintessence model can be viewed as a k-essence model generated by a kinetic linear function. In addition, we show the true effects of k-essence begin at second order in the expansion of the kinetic function in powers of the kinetic energy. © 2005 Elsevier B.V. All rights reserved.