6,034 research outputs found
Polarized Proton Pionic Capture in Deuterium as a Probe of 3N Dynamics
The proton analyzing power Ay in pion production reaction pd --> pi0 3He has
been calculated including one- and two-body meson production mechanisms with a
proper treatment of the three-nucleon dynamics and an accurate solution of the
3N bound-state problem for phenomenological two-nucleon potentials. In the
region around the Delta resonance, the structure of the analyzing power can be
understood once interference effects among amplitudes describing intermediate
Delta N formation in different orbital states are considered along with the
additional interference with the S-wave pion production amplitudes. Then, the
inclusion of three-nucleon dynamics in the initial state produces the structure
of the analyzing power that has been observed experimentally.Comment: 9 pages, 5 figure
Dark MaGICC: the effect of Dark Energy on galaxy formation. Cosmology does matter
We present the Dark MaGICC project, which aims to investigate the effect of
Dark Energy (DE) modeling on galaxy formation via hydrodynamical cosmological
simulations. Dark MaGICC includes four dynamical Dark Energy scenarios with
time varying equations of state, one with a self-interacting Ratra-Peebles
model. In each scenario we simulate three galaxies with high resolution using
smoothed particle hydrodynamics (SPH). The baryonic physics model is the same
used in the Making Galaxies in a Cosmological Context (MaGICC) project, and we
varied only the background cosmology. We find that the Dark Energy
parameterization has a surprisingly important impact on galaxy evolution and on
structural properties of galaxies at z=0, in striking contrast with predictions
from pure Nbody simulations. The different background evolutions can (depending
on the behavior of the DE equation of state) either enhance or quench star
formation with respect to a LCDM model, at a level similar to the variation of
the stellar feedback parameterization, with strong effects on the final galaxy
rotation curves. While overall stellar feedback is still the driving force in
shaping galaxies, we show that the effect of the Dark Energy parameterization
plays a larger role than previously thought, especially at lower redshifts. For
this reason, the influence of Dark Energy parametrization on galaxy formation
must be taken into account, especially in the era of precision cosmology.Comment: 11 pages, 13 figure
Pose consensus based on dual quaternion algebra with application to decentralized formation control of mobile manipulators
This paper presents a solution based on dual quaternion algebra to the
general problem of pose (i.e., position and orientation) consensus for systems
composed of multiple rigid-bodies. The dual quaternion algebra is used to model
the agents' poses and also in the distributed control laws, making the proposed
technique easily applicable to time-varying formation control of general
robotic systems. The proposed pose consensus protocol has guaranteed
convergence when the interaction among the agents is represented by directed
graphs with directed spanning trees, which is a more general result when
compared to the literature on formation control. In order to illustrate the
proposed pose consensus protocol and its extension to the problem of formation
control, we present a numerical simulation with a large number of free-flying
agents and also an application of cooperative manipulation by using real mobile
manipulators
Folds and Buckles at the Nanoscale: Experimental and Theoretical Investigation of the Bending Properties of Graphene Membranes
The elastic properties of graphene crystals have been extensively investigated, revealing unique properties in the linear and nonlinear regimes, when the membranes are under either stretching or bending loading conditions. Nevertheless less knowledge has been developed so far on folded graphene membranes and ribbons. It has been recently suggested that fold-induced curvatures, without in-plane strain, can affect the local chemical reactivity, the mechanical properties, and the electron transfer in graphene membranes. This intriguing perspective envisages a materials-by-design approach through the engineering of folding and bending to develop enhanced nano-resonators or nano-electro-mechanical devices. Here we present a novel methodology to investigate the mechanical properties of folded and wrinkled graphene crystals, combining transmission electron microscopy mapping of 3D curvatures and theoretical modeling based on continuum elasticity theory and tight-binding atomistic simulations
Thermodynamical properties of hairy black holes in n spacetimes dimensions
The issue concerning the existence of exact black hole solutions in presence
of non vanishing cosmological constant and scalar fields is reconsidered. With
regard to this, in investigating no-hair theorem violations, exact solutions of
gravity having as a source an interacting and conformally coupled scalar field
are revisited in arbitrary dimensional non asymptotically flat space-times. New
and known hairy black hole solutions are discussed. The thermodynamical
properties associated with these solutions are investigated and the invariance
of the black hole entropy with respect to different conformal frames is proven.Comment: Latex document, 23 pages, references added to section [1] and [3],
typos correcte
Bifactor analysis and construct validity of the five facet mindfulness questionnaire (FFMQ) in non-clinical Spanish samples
The objective of the present study was to examine the dimensionality, reliability, and construct validity of the Five Facet Mindfulness Questionnaire (FFMQ) in three Spanish samples using structural equation modeling (SEM). Pooling the FFMQ data from 3 Spanish samples (n = 1191), we estimated the fit of two competing models (correlated five-factor vs. bifactor) via confirmatory factor analysis. The factorial invariance of the best fitting model across meditative practice was also addressed. The pattern of relationships between the FFMQ latent dimensions and anxiety, depression, and distress was analyzed using SEM. FFMQ reliability was examined by computing the omega and omega hierarchical coefficients. The bifactor model, which accounted for the covariance among FFMQ items with regard to one general factor (mindfulness) and five orthogonal factors (observing, describing, acting with awareness, non-judgment, and non-reactivity), fit the FFMQ structure better than the correlated five-factor model. The relationships between the latent variables and their manifest indicators were not invariant across the meditative experience. Observing items had significant loadings on the general mindfulness factor, but only in the meditator sub-sample. The SEM analysis revealed significant links between mindfulness and symptoms of depression and stress. When the general factor was partialled out, the acting with awareness facet did not show adequate reliability. The FFMQ shows a robust bifactor structure among Spanish individuals. Nevertheless, the Observing subscale does not seem to be adequate for assessing mindfulness in individuals without meditative experience
A New Look at the Tetraquarks and Baryons in the Diquark Model
We analyze the hidden charm -wave tetraquarks in the diquark model, using
an effective Hamiltonian incorporating the dominant spin-spin, spin-orbit and
tensor interactions. We compare with other -wave system such as -wave
charmonia and the newly discovered baryons, analysed recently in
this framework. Given the uncertain experimental situation on the states,
we allow for different spectra and discuss the related parameters in the
diquark model. In addition to the presently observed ones, we expect many more
states in the supermultiplet of diquarkonia, whose quantum
numbers and masses are worked out, using the parameters from the currently
preferred -states pattern. The existence of these new resonances would be a
decisive footprint of the underlying diquark dynamics.Comment: Revised and extended to accommodate referee comments. Added a table
and references. Accepted for publication in the EPJ
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