4,506 research outputs found
Bound states of in nuclei
We study the binding energy and the width of the in nuclei,
associated to the and components. The first one leads to
negligible contributions while the second one leads to a sizeable attraction,
enough to bind the in nuclei. Pauli blocking and binding effects on
the decay reduce considerably the decay width in nuclei and
medium effects associated to the component also lead to a very small
width, as a consequence of which one finds separation between the bound levels
considerably larger than the width of the states.Comment: Presentation in the 10th International Baryon Conference BARYON0
Topological Structure of Dense Hadronic Matter
We present a summary of work done on dense hadronic matter, based on the
Skyrme model, which provides a unified approach to high density, valid in the
large limit. In our picture, dense hadronic matter is described by the
{\em classical} soliton configuration with minimum energy for the given baryon
number density. By incorporating the meson fluctuations on such ground state we
obtain an effective Lagrangian for meson dynamics in a dense medium. Our
starting point has been the Skyrme model defined in terms of pions, thereafter
we have extended and improved the model by incorporating other degrees of
freedom such as dilaton, kaons and vector mesons.Comment: 13 pages, 8 figures, Talk given at the KIAS-APCTP Symposium in
Astro-Hadron Physics "Compact Stars: Quest for New States of Dense Matter",
November 10-14, 2003, Seoul, Korea, published by World Scientific. Based on
talk by B.-Y. Par
No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2
The gas cloud G2 falling toward Sagittarius A* (Sgr A*), the supermassive
black hole at the center of the Milky Way, is supposed to provide valuable
information on the physics of accretion flows and the environment of the black
hole. We observed Sgr A* with four European stations of the Global Millimeter
Very Long Baseline Interferometry Array (GMVA) at 86 GHz on 1 October 2013 when
parts of G2 had already passed the pericenter. We searched for possible
transient asymmetric structure -- such as jets or winds from hot accretion
flows -- around Sgr A* caused by accretion of material from G2. The
interferometric closure phases remained zero within errors during the
observation time. We thus conclude that Sgr A* did not show significant
asymmetric (in the observer frame) outflows in late 2013. Using simulations, we
constrain the size of the outflows that we could have missed to ~2.5 mas along
the major axis, ~0.4 mas along the minor axis of the beam, corresponding to
approximately 232 and 35 Schwarzschild radii, respectively; we thus probe
spatial scales on which the jets of radio galaxies are suspected to convert
magnetic into kinetic energy. As probably less than 0.2 Jy of the flux from Sgr
A* can be attributed to accretion from G2, one finds an effective accretion
rate eta*Mdot < 1.5*10^9 kg/s ~ 7.7*10^-9 Mearth/yr for material from G2.
Exploiting the kinetic jet power--accretion power relation of radio galaxies,
one finds that the rate of accretion of matter that ends up in jets is limited
to Mdot < 10^17 kg/s ~ 0.5 Mearth/yr, less than about 20% of the mass of G2.
Accordingly, G2 appears to be largely stable against loss of angular momentum
and subsequent (partial) accretion at least on time scales < 1 year.Comment: 5 pages, 2 figures, 1 table; A&A Letter, in press (submitted 2015
February 26; accepted 2015 March 31
Monte Carlo simulation of nonlinear Couette flow in a dilute gas
The Direct Simulation Monte Carlo method is applied to solve the Boltzmann
equation in the steady planar Couette flow for Maxwell molecules and hard
spheres. Nonequilibrium boundary conditions based on the solution of the
Bhatnagar-Gross-Krook (BGK) model for the Couette flow are employed to diminish
the influence of finite-size effects. Non-Newtonian properties are
characterized by five independent generalized transport coefficients: a
viscosity function, a thermal conductivity function, two viscometric functions,
and a cross coefficient measuring the heat flux orthogonal to the thermal
gradient. These coefficients depend nonlinearly on the shear rate. The
simulation results are compared with theoretical predictions given by the Grad
method and the BGK and the ellipsoidal statistical (ES) models. It is found
that the kinetic models present a good agreement with the simulation,
especially in the case of the ES model, while the Grad method is only
qualitatively reliable for the momentum transport. In addition, the velocity
distribution function is also measured and compared with the BGK and ES
distributions.Comment: 25 pages (including 15 figures); minor changes; revised version
accepted for publication in Physics of Fluid
Recommended from our members
Symposium: Dynamic Decisions, Conflict Resolution, and Real-Time Diagnosis in Complex Domains
Strongly Coupled QED
A short review of some of the most relevant contributions to non-perturbative
QED is done. Since a Gaussian behaviour of QED \`a la has been
ruled out by the numerical data, I analyse the other two most reliable
scenarios, i.e. triviality \`a la Nambu-Jona Lasinio and non-Gaussian critical
behaviour. I give a suggestive theoretical argument against a Gaussian
behaviour of QED \`a la Nambu-Jona Lasinio, and show how the numerical data for
the susceptibility at the critical point of QED support this result.Comment: Plenary talk given at the International Symposium on Lattice Field
Theory, 4-8 June 1996, St. Louis, Missouri, USA, 19 pages, latex, three
Postscript figures and two table
New Technology, New Rules for Journalism and a New World of Engagement
UID/CCI/04667/2016The ways in which people learn, communicate and engage in discussion have changed profoundly during the past decade. As Jenkins related in her book, The Convergence Crisis: An Impending Paradigm Shift in Advertising, Millenials do not want to be told the whole story. Rather, they want someone to begin a conversation that will engage others to become participants in the development of that story (2015). Technology now allows that to happen, sometimes with unintended and/or ill consequences, but technology also generates a dynamic potential to create international and interactive discourse aimed at addressing shared global challenges.publishersversionpublishe
âiCub, clean the table!â A robot learning from demonstration approach using Deep Neural Networks
Autonomous service robots have become a key research topic in robotics, particularly for household chores.
A typical home scenario is highly unconstrained and a service robot needs to adapt constantly to new situations. In this paper, we address the problem of autonomous cleaning tasks in uncontrolled environments. In our approach, a human instructor uses kinestethic demonstrations to teach a robot how to perform different cleaning tasks on a table. Then, we use Task Parametrized Gaussian Mixture Models (TP-GMMs) to encode the demonstrations variability, while providing appropriate generalization abilities. TP-GMMs extend Gaussian Mixture Models with an auxiliary set of reference frames, in order to extrapolate the demonstrations to different task parameters such as movement locations, amplitude or orientations. However, the reference frames (that parametrize TP-GMMs) can be very difficult to extract in practice, as it may require segmenting the cluttered images of the working table-top. Instead, in this work the reference frames are automatically extracted from robot camera images, using a deep neural network that was trained during human demonstrations of a cleaning task. This approach has two main benefits: (i) it takes the human completely out of the loop while performing complex cleaning tasks; and (ii) the network is able to identify the specific task to be performed directly from image data, thus also enabling automatic task selection from a set of previously demonstrated tasks. The system was implemented on the iCub humanoid robot. During the tests, the robot was able to successfully clean a table with two different types of dirt (wiping a markerâs scribble or sweeping clusters of lentils).info:eu-repo/semantics/publishedVersio
Unified Approach to Dense Matter
We apply the Skyrme model to dense hadronic matter, which provides a unified
approach to high density, valid in the large Nc limit. In our picture, dense
hadronic matter is described by the classical soliton configuration with
minimum energy for the given baryon number density. By incorporating the meson
fluctuations on such ground state we obtain an effective Lagrangian for meson
dynamics in a dense medium. Our starting point has been the Skyrme model
defined in terms of pions, thereafter we have extended and improved the model
by incorporating other degrees of freedom such as dilaton, kaons and vector
mesons.Comment: 6 pages, 4 figures, a talk given at the international conference QCD
DOWN UNDER, March 10 - 19, Adelaide, Australi
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