Classical and Quantum-like approaches to Charged-Particle Fluids in a Quadrupole

A classical description of the dynamics of a dissipative charged-particle fluid in a quadrupole-like device is developed. It is shown that the set of the classical fluid equations contains the same information as a complex function satisfying a Schrodinger-like equation in which Planck's constant is replaced by the time-varying emittance, which is related to the time-varying temperature of the fluid. The squared modulus and the gradient of the phase of this complex function are proportional to the fluid density and to the current velocity, respectively. Within this framework, the dynamics of an electron bunch in a storage ring in the presence of radiation damping and quantum-excitation is recovered. Furthermore, both standard and generalized (including dissipation) coherent states that may be associated with the classical particle fluids are fully described in terms of the above formalism.Comment: LaTex, to appear in Physica Script

Landau Damping and Coherent Structures in Narrow-Banded 1+1 Deep Water Gravity Waves

We study the nonlinear energy transfer around the peak of the spectrum of surface gravity waves by taking into account nonhomogeneous effects. In the narrow-banded approximation the kinetic equation resulting from a nonhomogeneous wave field is a Vlasov-Poisson type equation which includes at the same time the random version of the Benjamin-Feir instability and the Landau damping phenomenon. We analytically derive the values of the Phillips' constant $\alpha$ and the enhancement factor $\gamma$ for which the narrow-banded approximation of the JONSWAP spectrum is unstable. By performing numerical simulations of the nonlinear Schr\"{o}dinger equation we check the validity of the prediction of the related kinetic equation. We find that the effect of Landau damping is to suppress the formation of coherent structures. The problem of predicting freak waves is briefly discussed.Comment: 4 pages, 3 figure

Internal Space for the Noncommutative Geometry Standard Model and Strings

In this paper I discuss connections between the noncommutative geometry approach to the standard model on one side, and the internal space coming from strings on the other. The standard model in noncommutative geometry is described via the spectral action. I argue that an internal noncommutative manifold compactified at the renormalization scale, could give rise to the almost commutative geometry required by the spectral action. I then speculate how this could arise from the noncommutative geometry given by the vertex operators of a string theory.Comment: 1+22 pages. More typos and misprints correcte

Connection between jets, winds and accretion in T Tauri stars: the X-shooter view

We have analysed the [OI]6300 A line in a sample of 131 young stars with discs in the Lupus, Chamaeleon and signa Orionis star forming regions, observed with the X-shooter spectrograph at VLT. The stars have mass accretion rates spanning from 10^{-12} to 10^{-7} Mo/yr. The line profile was deconvolved into a low velocity component (LVC, 40 km/s ), originating from slow winds and high velocity jets, respectively. The LVC is by far the most frequent component, with a detection rate of 77%, while only 30% of sources have a HVC. The [OI]6300 luminosity of both the LVC and HVC, when detected, correlates with stellar and accretion parameters of the central sources (i.e. Lstar , Mstar , Lacc , Macc), with similar slopes for the two components. The line luminosity correlates better with the accretion luminosity than with the stellar luminosity or stellar mass. We suggest that accretion is the main drivers for the line excitation and that MHD disc-winds are at the origin of both components. In the sub-sample of Lupus sources observed with ALMA a relationship is found between the HVC peak velocity and the outer disc inclination angle, as expected if the HVC traces jets ejected perpendicularly to the disc plane. Mass loss rates measured from the HVC span from ~ 10^{-13} to ~10^{-7} Mo/yr. The corresponding Mloss/Macc ratio ranges from ~0.01 to ~0.5, with an average value of 0.07. However, considering the upper limits on the HVC, we infer a ratio < 0.03 in more than 40% of sources. We argue that most of these sources might lack the physical conditions needed for an efficient magneto-centrifugal acceleration in the star-disc interaction region. Systematic observations of populations of younger stars, that is, class 0/I, are needed to explore how the frequency and role of jets evolve during the pre-main sequence phase.Comment: 15 pages, 14 figures, Accepted for publication in A&

Globally stable tracking and estimation for single-phase electrical signals with DC-offset rejection

This work introduces a new algorithm, named Global Quadrature PLL (GQPLL) for tracking a sinusoidal signal and for estimating its frequency and amplitude. The proposed technique derives from the well-known PLL architecture based on Quadrature Signal Generation, that is widely used for tracking the fundamental of single-phase electrical signals. The proposed algorithm improves the existing quadrature-PLL solutions from two different perspectives. First, the cancellation of the DC-bias is embedded by construction. Moreover, a Lyapunov-based stability analysis guarantees the global convergence of the estimates for arbitrarily large adaptation gains, enabling fast adaptation transients. Simulations show that the proposed algorithm is able to deal with sudden variations of the fundamental frequency and of the DC-bias magnitude

Limit analysis assessment of experimental behavior of arches reinforced with GFRP materials

In this paper, a comparison between results furnished by a 3D FE upper bound limit analysis and experimental results for some reinforced masonry arches tested at the University of Minho (Portugal) is provided. While the delamination from arches support can be modelled only in an approximate way within limit analysis, the aim of the paper is to accurately reproduce the change in the failure mechanism observed in experimentation, due to the introduction of strengthening elements. Both experimental and numerical results showa clear change in the failure mechanism and in the corresponding ultimate peak load. A set of simulations is also performed on reinforced arches previously damaged, to investigate the role played by the reinforcement within a proper repairing procedure. Good correlation with experimental work and numerical simulations is achieved.info:eu-repo/semantics/publishedVersio

Numerical and experimental analysis of full scale arches reinforced with GFRP materials

In this contribution, original limit analysis numerical results are presented dealing with some reinforced masonry arches tested at the University of Minho-UMinho, PT. Twelve in-scale circular masonry arches were considered, reinforced in various ways at the intrados or at the extrados. GFRP reinforcements were applied either on undamaged or on previously damaged elements, in order to assess the role of external reinforcements even in repairing interventions. The experimental results were critically discussed at the light of limit analysis predictions, based on a 3D FE heterogeneous upper bound approach. Satisfactory agreement was found between experimental evidences and the numerical results, in terms of failure mechanisms and peak load.(undefined

Experimental and numerical FE analyses of curved masonry prisms and arches reinforced with FRP materials

An experimental and numerical study is presented herein, focusing on curved ma-sonry prisms and reinforced masonry arches with glass Fiber Reinforced Polymer (FRP). Both convex and concave configurations with a diverse curvature are considered for masonry prisms specimens. The experimental data are interpreted in the light of fully three-dimensional finite element simulations. Under the simplifying assumption of perfect adhesion, such advanced model allows to reconstruct local processes inside the masonry prisms, such as the damage distribution and the interface tractions. The effect of the geometrical curvature on the delamination response of the masonry prisms is comparatively assessed by means of ‘‘step-by-step’’ numerical predictions together with a ‘‘direct’’ lower bound limit analysis approach. To complement the experimental campaign, original limit analysis numerical re-sults are presented dealing with some reinforced masonry arches tested at the University of Minho-UMinho, PT. Twelve in-scale circular masonry arches were considered, reinforced in various ways at the intrados or at the extrados. GFRP reinforcements were applied either on undamaged or on previously damaged elements, in order to assess the role of external rein-forcements even in repairing interventions. The experimental results were critically discussed at the light of limit analysis predictions, based on a 3D FE heterogeneous upper bound ap-proach. The numerical results were able to reproduce failure mechanisms of reinforced ma-sonry arches while their peak loads were obtained within an acceptable margin. Due to the scatter of experimental test not all deformation was capture within the reinforced masonry arches numerical models

Assessment of curved FRP-reinforced masonry prisms : experiments and modeling

During the past decade, several approaches have been proposed to investigate the response of masonry structures strengthened by externally bonded Fiber Reinforced Polymer (FRP) reinforcements. Nowadays, regardless of the great efforts made, scarce information are available on the delamination behavior of reinforced curved substrates. An experimental and numerical study is presented herein, focusing on curved masonry prisms with a glass FRP strip. Both convex and concave configurations with a diverse curvature are considered for the specimens, constituted by four Portuguese bricks bonded by three joints of conventional mortar. The experimental data are interpreted in the light of fully threedimensional finite element simulations. Under the simplifying assumption of perfect adhesion, such advanced model allows to reconstruct local processes inside the masonry prisms, such as the damage distribution and the interface tractions, correlating them to the macroscopic response in terms of reaction force versus tangential slip. The effect of the geometrical curvature on the delamination response of the masonry prisms is critically and comparatively assessed by means of “step-by-step” numerical predictions together with a “direct” lower bound limit analysis approach. This topic is of paramount importance for structural engineering when dealing with masonry arches and double curvature structural elements.Ismael Basilio would like to express his gratitude to the CONACYT for the scholarship granted during his PhD, to the University of Minho for making possible the experimental campaign within its structural laboratory and the Danish Building Research during the FE models preparation

Sleep Regularity is Associated with Physical Activity and Sedentary Behavior in 13-17-Year-Old Adolescents

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