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http://hdl.handle.net/2117/3918
Sun, 05 Jul 2015 19:34:50 GMT
20150705T19:34:50Z
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Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació
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J2 effect and elliptic inclined periodic orbits in the collision threebody problem
http://hdl.handle.net/2117/21117
Title: J2 effect and elliptic inclined periodic orbits in the collision threebody problem
Authors: Barrabes, Esther; Cors Iglesias, Josep Maria; Pinyol, Conxita; Soler Villanueva, Jaume
Abstract: The existence of a new class of inclined periodic orbits of the collision restricted
three{body problem is shown. The symmetric periodic solutions found are perturbations of elliptic
kepler orbits and they exist only for special values of the inclination and are related to the motion
of a satellite around an oblate planet.
http://hdl.handle.net/2117/21117
Barrabes, Esther; Cors Iglesias, Josep Maria; Pinyol, Conxita; Soler Villanueva, Jaume
no
collision restricted threebody problem, periodic orbits, symmetric orbits, critical inclination, continuation method
The existence of a new class of inclined periodic orbits of the collision restricted
three{body problem is shown. The symmetric periodic solutions found are perturbations of elliptic
kepler orbits and they exist only for special values of the inclination and are related to the motion
of a satellite around an oblate planet.

Nonlinear equations for fractional Laplacians, I: Regularity, maximum principles, and Hamiltonian estimates
http://hdl.handle.net/2117/22391
Title: Nonlinear equations for fractional Laplacians, I: Regularity, maximum principles, and Hamiltonian estimates
Authors: Cabré Vilagut, Xavier; Sire, Yannick
Abstract: This is the first of two articles dealing with the equation ()sv = f (v) in Rn, with s ¿ (0,1), where ()s stands for the fractional Laplacian — the in¿nitesimal generator of a Lévy process. This equation can be realized as a local linear degenerate elliptic equation in Rn+1+ together with a nonlinear Neumann boundary condition on ¿Rn+1 + =Rn.
In this ¿rst article, we establish necessary conditions on the nonlinearity f to admit certain type of solutions, with special interest in bounded increasing solutions in all of R. These necessary conditions (which will be proven in a followup paper to be also suficient for the existence of a bounded increasing solution) are derived from an equality and an estimate involving a Hamiltonian — in the spirit of a result of Modica for the Laplacian. Our proofs are uniform ass ¿1, establishing in the limit the corresponding known results for the Laplacian.
In addition, we study regularity issues, as well as maximum and Harnack principles associated to the equation.
http://hdl.handle.net/2117/22391
Cabré Vilagut, Xavier; Sire, Yannick
no
This is the first of two articles dealing with the equation ()sv = f (v) in Rn, with s ¿ (0,1), where ()s stands for the fractional Laplacian — the in¿nitesimal generator of a Lévy process. This equation can be realized as a local linear degenerate elliptic equation in Rn+1+ together with a nonlinear Neumann boundary condition on ¿Rn+1 + =Rn.
In this ¿rst article, we establish necessary conditions on the nonlinearity f to admit certain type of solutions, with special interest in bounded increasing solutions in all of R. These necessary conditions (which will be proven in a followup paper to be also suficient for the existence of a bounded increasing solution) are derived from an equality and an estimate involving a Hamiltonian — in the spirit of a result of Modica for the Laplacian. Our proofs are uniform ass ¿1, establishing in the limit the corresponding known results for the Laplacian.
In addition, we study regularity issues, as well as maximum and Harnack principles associated to the equation.

Error assessment in structural transient dynamics
http://hdl.handle.net/2117/28506
Title: Error assessment in structural transient dynamics
Authors: Verdugo Rojano, Francesc; Parés Mariné, Núria; Díez, Pedro
Abstract: This paper presents in a unified framework the most representative stateoftheart techniques on a posteriori error assessment for second order hyperbolic problems, i.e., structural transient dynamics. For the sake of presentation, the error estimates are grouped in four types: recoverybased estimates, the dual weighted residual method, the constitutive relation error method and error estimates for timelinedependent quantities of interest. All these methodologies give a comprehensive overview on the available error assessment techniques in structural dynamics, both for energylike and goaloriented estimates.
Thu, 02 Jul 2015 10:30:38 GMT
http://hdl.handle.net/2117/28506
20150702T10:30:38Z
Verdugo Rojano, Francesc; Parés Mariné, Núria; Díez, Pedro
no
Elastodynamics, Transient dynamics, Goaloriented error assessment, Adjoint problem, Quantity of interest, Recovery estimates, Dual weighted residuals, Constitutive relation error, Timelinedependent quantity of interest, Finiteelement methods, Superconvergent patch recovery, Partialdifferential equations, Linearfunctional outputs, Timestepping procedure, Constitutive relation, Parabolicproblems, Local quantities, Waveequation, Exact bounds
This paper presents in a unified framework the most representative stateoftheart techniques on a posteriori error assessment for second order hyperbolic problems, i.e., structural transient dynamics. For the sake of presentation, the error estimates are grouped in four types: recoverybased estimates, the dual weighted residual method, the constitutive relation error method and error estimates for timelinedependent quantities of interest. All these methodologies give a comprehensive overview on the available error assessment techniques in structural dynamics, both for energylike and goaloriented estimates.

Nonisomorphic Hopf Galois structures with isomorphic underlying Hopf algebras
http://hdl.handle.net/2117/28490
Title: Nonisomorphic Hopf Galois structures with isomorphic underlying Hopf algebras
Authors: Crespo, Teresa; Río Doval, Ana; Vela del Olmo, Mª Montserrat
Abstract: We give a degree 8 nonnormal separable extension having two nonisomorphic Hopf Galois structures with isomorphic underlying Hopf algebras.
Wed, 01 Jul 2015 11:16:43 GMT
http://hdl.handle.net/2117/28490
20150701T11:16:43Z
Crespo, Teresa; Río Doval, Ana; Vela del Olmo, Mª Montserrat
no
Hopf algebra, Separable field extension, Galois theory, Hopf Galois structure
We give a degree 8 nonnormal separable extension having two nonisomorphic Hopf Galois structures with isomorphic underlying Hopf algebras.

Northsouth components of the annual asymmetry in the ionosphere
http://hdl.handle.net/2117/28489
Title: Northsouth components of the annual asymmetry in the ionosphere
Authors: Gulyaeva, Tamara L.; Arikan, Feza; Hernández Pajares, Manuel; Veselovsky, I.S.
Abstract: A retrospective study of the asymmetry in the ionosphere during the solstices is made using the different geospace parameters in the North and South magnetic hemispheres. Data of total electron content (TEC) and global electron content (GEC) produced from global ionospheric maps, GIMTEC for 19992013, the ionospheric electron content (IEC) measured by TOPEXJason 1 and 2 satellites for 20012012, the F2 layer critical frequency and peak height measured on board ISIS 1, ISIS 2, and IK19 satellites during 19691982, and the earthquakes M5+ occurrences for 19992013 are analyzed. Annual asymmetry is observed with GEC and IEC for the years of observation with asymmetry index, AI, showing January > July excess from 0.02 to 0.25. The coincident pattern of JanuarytoJuly asymmetry ratio of TEC and IEC colocated along the magnetic longitude sector of 270 degrees +/ 5 degrees E in the Pacific Ocean is obtained varying with local time and magnetic latitude. The sea/land differences in the F2 layer peak electron density, NmF2, and the peak height, h(m)F(2), gathered with topside sounding data exhibit tilted ionosphere along the seashores with denser electron population at greater peak heights over the sea. The topside peak electron density NmF2, TEC, IEC, and the hemisphere part of GEC are dominant in the South hemisphere which resembles the pattern for seismic activity with dominant earthquake occurrence in the South magnetic hemisphere. Though the study is made for the hemispheric and annual asymmetry during solstices in the ionosphere, the conclusions seem valid for other aspects of seismicionospheric associations with tectonic plate boundaries representing zones of enhanced risk for space weather.
Wed, 01 Jul 2015 11:09:52 GMT
http://hdl.handle.net/2117/28489
20150701T11:09:52Z
Gulyaeva, Tamara L.; Arikan, Feza; Hernández Pajares, Manuel; Veselovsky, I.S.
no
GLOBAL ELECTRONCONTENT, SOLARACTIVITY, EARTHQUAKE, TEC, ANOMALIES, MAPS, CALIBRATION, ATMOSPHERE, LATITUDES, SATELLITE
A retrospective study of the asymmetry in the ionosphere during the solstices is made using the different geospace parameters in the North and South magnetic hemispheres. Data of total electron content (TEC) and global electron content (GEC) produced from global ionospheric maps, GIMTEC for 19992013, the ionospheric electron content (IEC) measured by TOPEXJason 1 and 2 satellites for 20012012, the F2 layer critical frequency and peak height measured on board ISIS 1, ISIS 2, and IK19 satellites during 19691982, and the earthquakes M5+ occurrences for 19992013 are analyzed. Annual asymmetry is observed with GEC and IEC for the years of observation with asymmetry index, AI, showing January > July excess from 0.02 to 0.25. The coincident pattern of JanuarytoJuly asymmetry ratio of TEC and IEC colocated along the magnetic longitude sector of 270 degrees +/ 5 degrees E in the Pacific Ocean is obtained varying with local time and magnetic latitude. The sea/land differences in the F2 layer peak electron density, NmF2, and the peak height, h(m)F(2), gathered with topside sounding data exhibit tilted ionosphere along the seashores with denser electron population at greater peak heights over the sea. The topside peak electron density NmF2, TEC, IEC, and the hemisphere part of GEC are dominant in the South hemisphere which resembles the pattern for seismic activity with dominant earthquake occurrence in the South magnetic hemisphere. Though the study is made for the hemispheric and annual asymmetry during solstices in the ionosphere, the conclusions seem valid for other aspects of seismicionospheric associations with tectonic plate boundaries representing zones of enhanced risk for space weather.

Almost every tree with m edges decomposes K2m,2m
http://hdl.handle.net/2117/28488
Title: Almost every tree with m edges decomposes K2m,2m
Authors: Drmota, Michael; Lladó Sánchez, Ana M.
Abstract: We show that asymptotically almost surely a tree with m edges decomposes the complete bipartite graph K2m,2m, a result connected to a conjecture of Graham and Häggkvist. The result also implies that asymptotically almost surely a tree with m edges decomposes the complete graph with O(m2) edges. An ingredient of the proof consists in showing that the bipartition classes of the base tree of a random tree have roughly equal size. © Cambridge University Press 2013.
Wed, 01 Jul 2015 11:06:35 GMT
http://hdl.handle.net/2117/28488
20150701T11:06:35Z
Drmota, Michael; Lladó Sánchez, Ana M.
no
Bipartition, Complete bipartite graphs, Complete graphs, Equal sizes, Random tree
We show that asymptotically almost surely a tree with m edges decomposes the complete bipartite graph K2m,2m, a result connected to a conjecture of Graham and Häggkvist. The result also implies that asymptotically almost surely a tree with m edges decomposes the complete graph with O(m2) edges. An ingredient of the proof consists in showing that the bipartition classes of the base tree of a random tree have roughly equal size. © Cambridge University Press 2013.

Classification of numerical 3semigroups by means of Lshapes
http://hdl.handle.net/2117/28487
Title: Classification of numerical 3semigroups by means of Lshapes
Authors: Aguiló Gost, Francisco de Asis L.; Marijuan López, Carlos
Abstract: We recall Lshapes, which are minimal distance diagrams, related to weighted 2Cayley digraphs, and we give the number and the relation between minimal distance diagrams related to the same digraph. On the other hand, we consider some classes of numerical semigroups useful in the study of curve singularity. Then, we associate Lshapes to each numerical 3semigroup and we describe some main invariants of numerical 3semigroups in terms of their associated Lshapes. Finally, we give a characterization of the parameters of the Lshapes associated with a numerical 3semigroup in terms of its generators, and we use it to classify the numerical 3semigroups of interest in curve singularity.
Wed, 01 Jul 2015 11:02:05 GMT
http://hdl.handle.net/2117/28487
20150701T11:02:05Z
Aguiló Gost, Francisco de Asis L.; Marijuan López, Carlos
no
Numerical semigroup, Symmetric, Free, Curve plane semigroup, Cayley digraph, Lshape, Frobenius number, NETWORKS
We recall Lshapes, which are minimal distance diagrams, related to weighted 2Cayley digraphs, and we give the number and the relation between minimal distance diagrams related to the same digraph. On the other hand, we consider some classes of numerical semigroups useful in the study of curve singularity. Then, we associate Lshapes to each numerical 3semigroup and we describe some main invariants of numerical 3semigroups in terms of their associated Lshapes. Finally, we give a characterization of the parameters of the Lshapes associated with a numerical 3semigroup in terms of its generators, and we use it to classify the numerical 3semigroups of interest in curve singularity.

Distribution and mitigation of higherorder ionospheric effects on precise GNSS processing
http://hdl.handle.net/2117/28486
Title: Distribution and mitigation of higherorder ionospheric effects on precise GNSS processing
Authors: Hernández Pajares, Manuel; Aragon Angel, Maria Angeles; Defraigne, Pascale; Bergeot, Nicolas; Prieto Cerdeira, Roberto; García Rigo, Alberto
Abstract: Higherorder ionospheric effects (I2+) are one of the main limiting factors in very precise Global Navigation Satellite Systems (GNSS) processing, for applications where millimeter accuracy is demanded. This paper summarizes a comprehensive study of the I2+ effects in range and in GNSS precise products such as receiver position and clock, tropospheric delay, geocenter offset, and GNSS satellite position and clock. All the relevant higherorder contributions are considered: second and third orders, geometric bending, and slant total electron content (dSTEC) bending (i.e., the difference between the STEC for straight and bent paths). Using a realistic simulation with representative solar maximum conditions on GPS signals, both the effects and mitigation errors are analyzed. The usage of the combination of multifrequency L band observations has to be rejected due to its increased noise level. The results of the study show that the main two effects in range are the secondorder ionospheric and dSTEC terms, with peak values up to 2 cm. Their combined impacts on the precise GNSS satellite products affects the satellite Z coordinates (up to +1 cm) and satellite clocks (more than ±20 ps). Other precise products are affected at the millimeter level. After correction the impact on all the precise GNSS products is reduced below 5 mm. We finally show that the I2+ impact on a Precise Point Positioning (PPP) user is lower than the current uncertainties of the PPP solutions, after applying consistently the precise products (satellite orbits and clocks) obtained under I2+ correction
Wed, 01 Jul 2015 10:56:01 GMT
http://hdl.handle.net/2117/28486
20150701T10:56:01Z
Hernández Pajares, Manuel; Aragon Angel, Maria Angeles; Defraigne, Pascale; Bergeot, Nicolas; Prieto Cerdeira, Roberto; García Rigo, Alberto
no
higher order ionospheric effects, precise geodesy based on GNSS data, precise ionospheric modeling of GNSS observations
Higherorder ionospheric effects (I2+) are one of the main limiting factors in very precise Global Navigation Satellite Systems (GNSS) processing, for applications where millimeter accuracy is demanded. This paper summarizes a comprehensive study of the I2+ effects in range and in GNSS precise products such as receiver position and clock, tropospheric delay, geocenter offset, and GNSS satellite position and clock. All the relevant higherorder contributions are considered: second and third orders, geometric bending, and slant total electron content (dSTEC) bending (i.e., the difference between the STEC for straight and bent paths). Using a realistic simulation with representative solar maximum conditions on GPS signals, both the effects and mitigation errors are analyzed. The usage of the combination of multifrequency L band observations has to be rejected due to its increased noise level. The results of the study show that the main two effects in range are the secondorder ionospheric and dSTEC terms, with peak values up to 2 cm. Their combined impacts on the precise GNSS satellite products affects the satellite Z coordinates (up to +1 cm) and satellite clocks (more than ±20 ps). Other precise products are affected at the millimeter level. After correction the impact on all the precise GNSS products is reduced below 5 mm. We finally show that the I2+ impact on a Precise Point Positioning (PPP) user is lower than the current uncertainties of the PPP solutions, after applying consistently the precise products (satellite orbits and clocks) obtained under I2+ correction

Permutation 2groups I: structure and splitness
http://hdl.handle.net/2117/28484
Title: Permutation 2groups I: structure and splitness
Authors: Elgueta Montó, Josep
Abstract: By a 2group we mean a groupoid equipped with a weakened group structure. It is called split when it is equivalent to the semidirect product of a discrete 2group and a oneobject 2group. By a permutation 2group we mean the 2group Sym(G) of selfequivalences of a groupoid G and natural isomorphisms between them, with the product given by composition of selfequivalences. These generalize the symmetric groups Sn, n >= 1, obtained when G is a finite discrete groupoid.; After introducing the wreath 2product Sn (sic) G of the symmetric group Sn with an arbitrary 2group G, it is shown that for any (finite type) groupoid G the permutation 2group Sym(G) is equivalent to a product of wreath 2products of the form Sn (sic) Sym(G) for a group G thought of as a oneobject groupoid. This is next used to compute the homotopy invariants of Sym(G) which classify it up to equivalence. Using a previously shown splitness criterion for strict 2groups, it is then proved that Sym(G) can be nonsplit, and that the step from the trivial groupoid to an arbitrary oneobject groupoid is the only source of nonsplitness. Various examples of permutation 2groups are explicitly computed, in particular the permutation 2group of the underlying groupoid of a (finite type) 2group. It also follows from well known results about the symmetric groups that the permutation 2group of the groupoid of all finite sets and bijections between them is equivalent to the direct product 2group Z(2)[1] x Z(2)[0] where Z(2)[0] and Z(2)[1] stand for the group Z(2) thought of as a discrete and a oneobject 2group, respectively. (C) 2014 Elsevier Inc. All rights reserved.
Wed, 01 Jul 2015 10:49:52 GMT
http://hdl.handle.net/2117/28484
20150701T10:49:52Z
Elgueta Montó, Josep
no
Groupoid, Categorical group, Split 2group, Permutation 2group, ALGEBRAICGEOMETRY, HOMOTOPY TYPES, CATEGORIES, REPRESENTATION, GROUPOIDS
By a 2group we mean a groupoid equipped with a weakened group structure. It is called split when it is equivalent to the semidirect product of a discrete 2group and a oneobject 2group. By a permutation 2group we mean the 2group Sym(G) of selfequivalences of a groupoid G and natural isomorphisms between them, with the product given by composition of selfequivalences. These generalize the symmetric groups Sn, n >= 1, obtained when G is a finite discrete groupoid.; After introducing the wreath 2product Sn (sic) G of the symmetric group Sn with an arbitrary 2group G, it is shown that for any (finite type) groupoid G the permutation 2group Sym(G) is equivalent to a product of wreath 2products of the form Sn (sic) Sym(G) for a group G thought of as a oneobject groupoid. This is next used to compute the homotopy invariants of Sym(G) which classify it up to equivalence. Using a previously shown splitness criterion for strict 2groups, it is then proved that Sym(G) can be nonsplit, and that the step from the trivial groupoid to an arbitrary oneobject groupoid is the only source of nonsplitness. Various examples of permutation 2groups are explicitly computed, in particular the permutation 2group of the underlying groupoid of a (finite type) 2group. It also follows from well known results about the symmetric groups that the permutation 2group of the groupoid of all finite sets and bijections between them is equivalent to the direct product 2group Z(2)[1] x Z(2)[0] where Z(2)[0] and Z(2)[1] stand for the group Z(2) thought of as a discrete and a oneobject 2group, respectively. (C) 2014 Elsevier Inc. All rights reserved.

Conditions of consistency for multicomponent stellar systems. II. Is a pointaxial symmetric model suitable for the Galaxy?
http://hdl.handle.net/2117/28482
Title: Conditions of consistency for multicomponent stellar systems. II. Is a pointaxial symmetric model suitable for the Galaxy?
Authors: Cubarsí Morera, Rafael
Abstract: Under a common potential, a finite mixture of ellipsoidal velocity distributions satisfying the Boltzmann collisionless
equation provides a set of integrability conditions that may constrain the population kinematics. They are referred to as
conditions of consistency and were discussed in a previous paper on mixtures of axisymmetric populations. As a corollary,
these conditions are now extended to pointaxial symmetry, that is, point symmetry around the rotation axis or bisymmetry,
by determining which potentials are connected with a more flexible superposition of stellar populations. Under pointaxial
symmetry, the potential is still axisymmetric, but the velocity and mass distributions are not necessarily. A pointaxial stellar
system is, in a natural way, consistent with a flat velocity distribution of a disc population. Therefore, no additional integrability
conditions are required to solve the Boltzmann collisionless equation for such a population. For other populations, if the
potential is additively separable in cylindrical coordinates, the populations are not kinematically constrained, although under
pointaxial symmetry, the potential is reduced to the harmonic function, which, for the Galaxy, is proven to be nonrealistic.
In contrast, a nonseparable potential provides additional conditions of consistency. When mean velocities for the populations
are unconstrained, the potential becomes quasistationary, being a particular case of the axisymmetric model. Then, the radial
and vertical mean velocities of the populations can differ and produce an apparent vertex deviation of the whole velocity
distribution. However, single population velocity ellipsoids still have no vertex deviation in the Galactic plane and no tilt in
their intersection with a meridional Galactic plane. If the thick disc and halo ellipsoids actually have nonvanishing tilt, as the
surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data seem to show, the pointaxial model
is unable to fit the local velocity distribution. Conversely, the axisymmetric model is capable of making a better approach. If,
in the end, more accurate data confirm a negligible tilt of the populations, then the pointaxisymmetric model will be able to
describe nonaxisymmetric mass and velocity distributions, although in the Galactic plane the velocity distribution will still be
axisymmetric.
Wed, 01 Jul 2015 08:38:01 GMT
http://hdl.handle.net/2117/28482
20150701T08:38:01Z
Cubarsí Morera, Rafael
no
galaxies: kinematics and dynamics – Galaxy: solar neighbourhood – galaxies: statistics
Under a common potential, a finite mixture of ellipsoidal velocity distributions satisfying the Boltzmann collisionless
equation provides a set of integrability conditions that may constrain the population kinematics. They are referred to as
conditions of consistency and were discussed in a previous paper on mixtures of axisymmetric populations. As a corollary,
these conditions are now extended to pointaxial symmetry, that is, point symmetry around the rotation axis or bisymmetry,
by determining which potentials are connected with a more flexible superposition of stellar populations. Under pointaxial
symmetry, the potential is still axisymmetric, but the velocity and mass distributions are not necessarily. A pointaxial stellar
system is, in a natural way, consistent with a flat velocity distribution of a disc population. Therefore, no additional integrability
conditions are required to solve the Boltzmann collisionless equation for such a population. For other populations, if the
potential is additively separable in cylindrical coordinates, the populations are not kinematically constrained, although under
pointaxial symmetry, the potential is reduced to the harmonic function, which, for the Galaxy, is proven to be nonrealistic.
In contrast, a nonseparable potential provides additional conditions of consistency. When mean velocities for the populations
are unconstrained, the potential becomes quasistationary, being a particular case of the axisymmetric model. Then, the radial
and vertical mean velocities of the populations can differ and produce an apparent vertex deviation of the whole velocity
distribution. However, single population velocity ellipsoids still have no vertex deviation in the Galactic plane and no tilt in
their intersection with a meridional Galactic plane. If the thick disc and halo ellipsoids actually have nonvanishing tilt, as the
surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data seem to show, the pointaxial model
is unable to fit the local velocity distribution. Conversely, the axisymmetric model is capable of making a better approach. If,
in the end, more accurate data confirm a negligible tilt of the populations, then the pointaxisymmetric model will be able to
describe nonaxisymmetric mass and velocity distributions, although in the Galactic plane the velocity distribution will still be
axisymmetric.

A surface mesh smoothing and untangling method independent of the CAD parameterization
http://hdl.handle.net/2117/28479
Title: A surface mesh smoothing and untangling method independent of the CAD parameterization
Authors: Gargallo Peiró, Abel; Roca Navarro, Xevi; Sarrate Ramos, Josep
Abstract: A method to optimize triangular and quadrilateral meshes on parameterized surfaces is proposed. The optimization procedure relocates the nodes on the surface to improve the quality (smooth) and ensures that the elements are not inverted (untangle). We detail how to express any measure for planar elements in terms of the parametric coordinates of the nodes. The extended measures can be used to check the quality and validity of a surface mesh. Then, we detail how to optimize any Jacobianbased distortion measure to obtain smoothed and untangled meshes with the nodes on the surface. We prove that this method is independent of the surface parameterization. Thus, it can optimize meshes on CAD surfaces defined by lowquality parameterizations. The examples show that the method can optimize meshes composed by a large number of inverted elements. Finally, the method can be extended to obtain highorder meshes with the nodes on the CAD surfaces.
Wed, 01 Jul 2015 08:01:33 GMT
http://hdl.handle.net/2117/28479
20150701T08:01:33Z
Gargallo Peiró, Abel; Roca Navarro, Xevi; Sarrate Ramos, Josep
no
Mesh quality, Mesh optimization, Smoothing and untangling, CAD surfaces, QUALITY METRICS, INITIAL MESHES, OPTIMIZATION, IMPROVEMENT, TRIANGULATIONS
A method to optimize triangular and quadrilateral meshes on parameterized surfaces is proposed. The optimization procedure relocates the nodes on the surface to improve the quality (smooth) and ensures that the elements are not inverted (untangle). We detail how to express any measure for planar elements in terms of the parametric coordinates of the nodes. The extended measures can be used to check the quality and validity of a surface mesh. Then, we detail how to optimize any Jacobianbased distortion measure to obtain smoothed and untangled meshes with the nodes on the surface. We prove that this method is independent of the surface parameterization. Thus, it can optimize meshes on CAD surfaces defined by lowquality parameterizations. The examples show that the method can optimize meshes composed by a large number of inverted elements. Finally, the method can be extended to obtain highorder meshes with the nodes on the CAD surfaces.

A new continuousdiscontinuous damage model: cohesive cracks via an accurate energytransfer process
http://hdl.handle.net/2117/28470
Title: A new continuousdiscontinuous damage model: cohesive cracks via an accurate energytransfer process
Authors: Tamayo Mas, Elena; Rodríguez Ferran, Antonio
Abstract: A new continuousdiscontinuous strategy to describe failure of quasibrittle materials is presented. For the early stages of the failure process, a gradientenhanced model based on smoothed displacements is employed. As soon as the damage parameter exceeds a critical value Dcrit<1, a cohesive crack is introduced. A new criterion to estimate the energy not yet dissipated by the bulk when switching modelsfrom continuous to continuousdiscontinuousis proposed. Then, this energy is transferred to the cohesive crack thus ensuring that the continuous and the continuousdiscontinuous strategies are energetically equivalent. Compared to other existing techniques, this new strategy accounts for the different unloading branches of damage models and thus, a more accurate estimation of the energy that has to be transferred is obtained. The performance of this technique is illustrated with one and twodimensional examples.
Tue, 30 Jun 2015 11:50:18 GMT
http://hdl.handle.net/2117/28470
20150630T11:50:18Z
Tamayo Mas, Elena; Rodríguez Ferran, Antonio
no
Cohesive cracks, Continuousdiscontinuous strategy, Energy balance, Regularisation, Smoothed displacements
A new continuousdiscontinuous strategy to describe failure of quasibrittle materials is presented. For the early stages of the failure process, a gradientenhanced model based on smoothed displacements is employed. As soon as the damage parameter exceeds a critical value Dcrit<1, a cohesive crack is introduced. A new criterion to estimate the energy not yet dissipated by the bulk when switching modelsfrom continuous to continuousdiscontinuousis proposed. Then, this energy is transferred to the cohesive crack thus ensuring that the continuous and the continuousdiscontinuous strategies are energetically equivalent. Compared to other existing techniques, this new strategy accounts for the different unloading branches of damage models and thus, a more accurate estimation of the energy that has to be transferred is obtained. The performance of this technique is illustrated with one and twodimensional examples.

Conditions of consistency for multicomponent axisymmetric stellar systems. Is an axisymmetric model suitable yet?
http://hdl.handle.net/2117/28464
Title: Conditions of consistency for multicomponent axisymmetric stellar systems. Is an axisymmetric model suitable yet?
Authors: Cubarsí Morera, Rafael
Abstract: Solving the Boltzmann collisionless equatio n under the axisymmetric hypot hesis introduces serious lim itations on describing the kinematics of a single stellar system according to the local Galactic observables. Instead of relaxing the hypothesis of axisymmetry, one alternative is to assume a mixture model. For a finite mixture of ellipsoidal velocity distributions, the coexistence of several stellar populations sharing a co mmon potential introduces a set of conditions of consistency that m ay also constrain the population kinematics. For only a few potentials, the populations may have independent mean veloc ities and unconstrained velocity ellipsoids. In this paper, we determine which axisymmetric potentials are connect ed with a more flexible superposition of the stellar populations. The conditions of consistency are checked against recent results derived from kinematic surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data. Several key observables are used to determine whether the axisymmetric mixture model is able to account for the main features of the local velocity distribution, such as the vertex deviation associated with the second central moment µ ¿ , the population radial mean velocities, the radial gradient of the moment µ z , the tilt of the velocity ellipsoids, and the existence of stars with no net rotation. In addition, the mixture moments for an arbitrary number of populations are derived in terms of the onetoone mean velocity di ff erences in order to study whether a more populated mixture could add any new features to the velocity distribution that remain unnoticed in a twocomponent mixture. According to this analysis, the quasistationary potential is the only potential allowing arbitrary directions of the population mean velocities. Then, the apparent vertex deviation of the total velocity distribution is due to the di ff erence of the mean velocities of the populations whose velocity ellipsoids hav e no vertex deviation. For a nonseparable pot ential, the population v elocity ellipsoids have the same orientation and point towards the Galactic centre. For a potential separable in addition in cylindrical coordinates, the population velocity ellipsoids may ha ve arbitrary tilt.
Tue, 30 Jun 2015 08:51:39 GMT
http://hdl.handle.net/2117/28464
20150630T08:51:39Z
Cubarsí Morera, Rafael
no
galaxies: kinematics and dynamics  Galaxy: solar neighbourhood  galaxies: statistics
Solving the Boltzmann collisionless equatio n under the axisymmetric hypot hesis introduces serious lim itations on describing the kinematics of a single stellar system according to the local Galactic observables. Instead of relaxing the hypothesis of axisymmetry, one alternative is to assume a mixture model. For a finite mixture of ellipsoidal velocity distributions, the coexistence of several stellar populations sharing a co mmon potential introduces a set of conditions of consistency that m ay also constrain the population kinematics. For only a few potentials, the populations may have independent mean veloc ities and unconstrained velocity ellipsoids. In this paper, we determine which axisymmetric potentials are connect ed with a more flexible superposition of the stellar populations. The conditions of consistency are checked against recent results derived from kinematic surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data. Several key observables are used to determine whether the axisymmetric mixture model is able to account for the main features of the local velocity distribution, such as the vertex deviation associated with the second central moment µ ¿ , the population radial mean velocities, the radial gradient of the moment µ z , the tilt of the velocity ellipsoids, and the existence of stars with no net rotation. In addition, the mixture moments for an arbitrary number of populations are derived in terms of the onetoone mean velocity di ff erences in order to study whether a more populated mixture could add any new features to the velocity distribution that remain unnoticed in a twocomponent mixture. According to this analysis, the quasistationary potential is the only potential allowing arbitrary directions of the population mean velocities. Then, the apparent vertex deviation of the total velocity distribution is due to the di ff erence of the mean velocities of the populations whose velocity ellipsoids hav e no vertex deviation. For a nonseparable pot ential, the population v elocity ellipsoids have the same orientation and point towards the Galactic centre. For a potential separable in addition in cylindrical coordinates, the population velocity ellipsoids may ha ve arbitrary tilt.

On the natural stabilization of convection dominated problems using high order Bubnov–Galerkin finite elements
http://hdl.handle.net/2117/28463
Title: On the natural stabilization of convection dominated problems using high order Bubnov–Galerkin finite elements
Authors: Cai, Quanji; Kollmannsberger, Stefan; Sala Lardies, Esther; Huerta, Antonio; Rank, Ernst
Abstract: Inthecaseofdominatingconvection,standardBubnov–Galerkinfiniteelementsareknown to deliver oscillating discrete solutions for the convection–diffusion equation. This paper demonstrates that increasing the polynomial degree ( p extension) limits these artificial numerical oscillations. This is contrary to a widespread notion that an increase of the poly nomialdegreedestabilizesthediscretesolution. Thistreatisealsoprovidesexplicitexpres sionsastowhichpolynomialdegreeissufficientlyhightoobtainstablesolutionsforagiven P ´ eclet number at the nodes of a mesh.
Tue, 30 Jun 2015 08:42:53 GMT
http://hdl.handle.net/2117/28463
20150630T08:42:53Z
Cai, Quanji; Kollmannsberger, Stefan; Sala Lardies, Esther; Huerta, Antonio; Rank, Ernst
no
p FEM Convection–diffusion problems Singularperturbation problem with boundary laye
Inthecaseofdominatingconvection,standardBubnov–Galerkinfiniteelementsareknown to deliver oscillating discrete solutions for the convection–diffusion equation. This paper demonstrates that increasing the polynomial degree ( p extension) limits these artificial numerical oscillations. This is contrary to a widespread notion that an increase of the poly nomialdegreedestabilizesthediscretesolution. Thistreatisealsoprovidesexplicitexpres sionsastowhichpolynomialdegreeissufficientlyhightoobtainstablesolutionsforagiven P ´ eclet number at the nodes of a mesh.

GIMTEC adaptive ionospheric weather assessment and forecast system
http://hdl.handle.net/2117/28462
Title: GIMTEC adaptive ionospheric weather assessment and forecast system
Authors: Gulyaeva, Tamara L.; Arikan, Feza; Hernández Pajares, Manuel; Stanislawska, Iwona
Abstract: The Ionospheric Weather Assessment and Forecast (IWAF) system is a computer software package designed to assess and predict the worldwide representation of 3D electron density profiles from the Global Ionospheric Maps of Total Electron Content (GIMTEC). The unique system products include dailyhourly numerical global maps of the F2 layer critical frequency (foF2) and the peak height (hmF2) generated with the International Reference Ionosphere extended to the plasmasphere, IRIPlas, upgraded by importing the dailyhourly GIMTEC as a new model driving parameter. Since GIMTEC maps are provided with 1 or 2days latency, the global maps forecast for 1 day and 2 days ahead are derived using an harmonic analysis applied to the temporal changes of TEC, foF2 and hmF2 at 5112 grid points of a map encapsulated in IONEX format (87.5°:2.5°:87.5°N in latitude, 180°:5°:180°E in longitude). The system provides online the ionospheric disturbance warnings in the global Windex map establishing categories of the ionospheric weather from the quiet state (W=±1) to intense storm (W=±4) according to the thresholds set for instant TEC perturbations regarding quiet reference median for the preceding 7 days. The accuracy of IWAF system predictions of TEC, foF2 and hmF2 maps is superior to the standard persistence model with prediction equal to the most recent ‘true’ map. The paper presents outcomes of the new service expressed by the global ionospheric foF2, hmF2 and Windex maps demonstrating the process of origin and propagation of positive and negative ionosphere disturbances in space and time and their forecast under different scenarios.
Tue, 30 Jun 2015 08:28:00 GMT
http://hdl.handle.net/2117/28462
20150630T08:28:00Z
Gulyaeva, Tamara L.; Arikan, Feza; Hernández Pajares, Manuel; Stanislawska, Iwona
no
Crirical frequency, Global ionospheric map, Ionospheric weather, IRIPlas, Peak height, Total electron content
The Ionospheric Weather Assessment and Forecast (IWAF) system is a computer software package designed to assess and predict the worldwide representation of 3D electron density profiles from the Global Ionospheric Maps of Total Electron Content (GIMTEC). The unique system products include dailyhourly numerical global maps of the F2 layer critical frequency (foF2) and the peak height (hmF2) generated with the International Reference Ionosphere extended to the plasmasphere, IRIPlas, upgraded by importing the dailyhourly GIMTEC as a new model driving parameter. Since GIMTEC maps are provided with 1 or 2days latency, the global maps forecast for 1 day and 2 days ahead are derived using an harmonic analysis applied to the temporal changes of TEC, foF2 and hmF2 at 5112 grid points of a map encapsulated in IONEX format (87.5°:2.5°:87.5°N in latitude, 180°:5°:180°E in longitude). The system provides online the ionospheric disturbance warnings in the global Windex map establishing categories of the ionospheric weather from the quiet state (W=±1) to intense storm (W=±4) according to the thresholds set for instant TEC perturbations regarding quiet reference median for the preceding 7 days. The accuracy of IWAF system predictions of TEC, foF2 and hmF2 maps is superior to the standard persistence model with prediction equal to the most recent ‘true’ map. The paper presents outcomes of the new service expressed by the global ionospheric foF2, hmF2 and Windex maps demonstrating the process of origin and propagation of positive and negative ionosphere disturbances in space and time and their forecast under different scenarios.