5,535 research outputs found
The Nambu-Jona Lasinio mechanism and the electroweak symmetry breaking in the Standard Model
This is a short report of the entire work developed during the study of the
possible realizations of the "Top Mode" Standard Model. Here it is examined the
breaking of internal symmetries from another point of view showing that is
possible to reproduce the gauged electroweak panorama of the traditional
Standard Model in a exhaustive and selfconsistent way. The result is reached
applying the main futures of the Nambu-Jona Lasinio (NJL) mechanism to an
electroweak invariant Lagrangian. In this context the use of functional
formalism for composite operators naturally leads to a different dynamical
approach. Meanwhile the Higgs mechanism acts on the Lagrangian form, a NJL like
model looks directly at the physics of the system showing the real dynamical
content hidden in the Green functions of the theory.Comment: 18 Pages, no figures, LaTex, corrected typos, references remove
Block Iterative Eigensolvers for Sequences of Correlated Eigenvalue Problems
In Density Functional Theory simulations based on the LAPW method, each
self-consistent field cycle comprises dozens of large dense generalized
eigenproblems. In contrast to real-space methods, eigenpairs solving for
problems at distinct cycles have either been believed to be independent or at
most very loosely connected. In a recent study [7], it was demonstrated that,
contrary to belief, successive eigenproblems in a sequence are strongly
correlated with one another. In particular, by monitoring the subspace angles
between eigenvectors of successive eigenproblems, it was shown that these
angles decrease noticeably after the first few iterations and become close to
collinear. This last result suggests that we can manipulate the eigenvectors,
solving for a specific eigenproblem in a sequence, as an approximate solution
for the following eigenproblem. In this work we present results that are in
line with this intuition. We provide numerical examples where opportunely
selected block iterative eigensolvers benefit from the reuse of eigenvectors by
achieving a substantial speed-up. The results presented will eventually open
the way to a widespread use of block iterative eigensolvers in ab initio
electronic structure codes based on the LAPW approach.Comment: 12 Pages, 5 figures. Accepted for publication on Computer Physics
Communication
Multiparametric Quantum Algebras and the Cosmological Constant
With a view towards applications for de Sitter, we construct the
multi-parametric -deformation of the so(5,\IC) algebra using the
Faddeev-Reshetikhin-Takhtadzhyan (FRT) formalism.Comment: v4: cosmetic changes from the published versio
Correlated dynamics of water and amphiphilic molecules in thin Newton black films
The dynamical properties of amphiphilics in Newton black films, as well as those of the water confined between the two charged hydrophilic surfaces, have been calculated via a series of molecular dynamic calculations in several films with different water content. A charged semi-flexible amphiphilic model and the TIP5P model of water are used in our simulations [J. Chem. Phys. 129, 164901 (2008)]. We calculate the diffusion coefficients, reorientational dynamics and the atomic density profile of water molecules as a function of the number of water molecules per amphiphilic (nw). We also analyse the reorientational motion of the amphiphilics and determine a strong correlation between the dynamics of water molecules and the translational and reorientational dynamics of the amphiphilics, as well as a correlation between the reorientational dynamics of the amphiphilics belonging to the upper and lower halves of the studied thin films.Fil: Di Napoli, Solange Mariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Gamba, Z.. Comisión Nacional de Energía Atómica; Argentin
The Trigger System of the ARGO-YBJ detector
The ARGO-YBJ experiment has been designed to detect air shower events over a
large size scale and with an energy threshold of a few hundreds GeV. The
building blocks of the ARGO-YBJ detector are single-gap Resistive Plate
Counters (RPCs). The trigger logic selects the events on the basis of their hit
multiplicity. Inclusive triggers as well as dedicated triggers for specific
physics channels or calibration purposes have been developed. This paper
describes the architecture and the main features of the trigger system.Comment: 4 pages, to be published in the Proceedings of the 28th International
Cosmic Ray Conference (Tsukuba, Japan 2003
Families and Social Media Use: The Role of Parents' Perceptions about Social Media Impact on Family Systems in the Relationship between Family Collective Efficacy and Open Communication
Communication through social media characterizes modern lifestyles and relationships, including family interactions. The present study aims at deepening the role that parents’ perceptions about social media effects on family systems can exert within their family functioning, specifically referring to the relationship between collective family efficacy and open communications within family systems with adolescents. A questionnaire to detect the openness of family communications, thecollectivefamilyefficacyandtheperceptionsabouttheimpactsofsocialmediaonfamilysystems wasadministeredto227Italianparentswhohadoneormoreteenagechildren,andwhouseFacebook and WhatsApp to communicate with them. From the results, these perceptions emerge as a mediator in the relationship between the collective family efficacy and the openness of communications, suggestingthatitisnotonlytheactualimpactofsocialmediaonfamilysystemsthatmattersbutalso parents’ perceptions about it and how much they feel able to manage their and their children’s social media use without damaging their family relationships. Thus, the need to foster parents’ positive perceptions about social media’s potential impact on their family relationships emerges. A strategy could be the promotion of knowledge on how to functionally use social media
An Optimized and Scalable Eigensolver for Sequences of Eigenvalue Problems
In many scientific applications the solution of non-linear differential
equations are obtained through the set-up and solution of a number of
successive eigenproblems. These eigenproblems can be regarded as a sequence
whenever the solution of one problem fosters the initialization of the next. In
addition, in some eigenproblem sequences there is a connection between the
solutions of adjacent eigenproblems. Whenever it is possible to unravel the
existence of such a connection, the eigenproblem sequence is said to be
correlated. When facing with a sequence of correlated eigenproblems the current
strategy amounts to solving each eigenproblem in isolation. We propose a
alternative approach which exploits such correlation through the use of an
eigensolver based on subspace iteration and accelerated with Chebyshev
polynomials (ChFSI). The resulting eigensolver is optimized by minimizing the
number of matrix-vector multiplications and parallelized using the Elemental
library framework. Numerical results show that ChFSI achieves excellent
scalability and is competitive with current dense linear algebra parallel
eigensolvers.Comment: 23 Pages, 6 figures. First revision of an invited submission to
special issue of Concurrency and Computation: Practice and Experienc
An Example of Symmetry Exploitation for Energy-related Eigencomputations
One of the most used approaches in simulating materials is the tight-binding
approximation. When using this method in a material simulation, it is necessary
to compute the eigenvalues and eigenvectors of the Hamiltonian describing the
system. In general, the system possesses few explicit symmetries. Due to them,
the problem has many degenerate eigenvalues. The ambiguity in choosing a
orthonormal basis of the invariant subspaces, associated with degenerate
eigenvalues, will result in eigenvectors which are not invariant under the
action of the symmetry operators in matrix form. A meaningful computation of
the eigenvectors needs to take those symmetries into account. A natural choice
is a set of eigenvectors, which simultaneously diagonalizes the Hamiltonian and
the symmetry matrices. This is possible because all the matrices commute with
each other. The simultaneous eigenvectors and the corresponding eigenvalues
will be in a parametrized form in terms of the lattice momentum components.
This functional dependence of the eigenvalues is the dispersion relation and
describes the band structure of a material. Therefore it is important to find
this functional dependence in any numerical computation related to material
properties.Comment: To appear in the proceedings of the 7th International Conference on
Computational Methods in Science and Engineering (ICCMSE '09
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Mean radiant temperature from global-scale numerical weather prediction models
In human biometeorology, the estimation of mean radiant temperature (MRT) is generally considered challenging. This work presents a general framework to compute the MRT at the global scale for a human subject placed in an outdoor environment and irradiated by solar and thermal radiation both directly and diffusely. The proposed framework requires as input radiation fluxes computed by numerical weather prediction (NWP) models and generates as output gridded globe-wide maps of MRT. It also considers changes in the Sun’s position affecting radiation components when these are stored by NWP models as an accumulated-over-time quantity. The applicability of the framework was demonstrated using NWP reanalysis radiation data from the European Centre for Medium-Range Weather Forecasts. Mapped distributions of MRT were correspondingly computed at the global scale. Comparison against measurements from radiation monitoring stations showed a good agreement with NWP-based MRT (coefficient of determination greater than 0.88; average bias equal to 0.42 °C) suggesting its potential as a proxy for observations in application studies
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