Departament de Matemàtiques
http://hdl.handle.net/2117/3917
Wed, 21 Feb 2018 01:25:48 GMT2018-02-21T01:25:48ZImplementing data-dependent triangulations with higher order delaunay triangulations
http://hdl.handle.net/2117/114278
Implementing data-dependent triangulations with higher order delaunay triangulations
Rodríguez, Natalia; Silveira, Rodrigo Ignacio
The Delaunay triangulation is the standard choice for building triangulated irregular networks (TINs) to represent terrain surfaces. However, the Delaunay triangulation is based only on the 2D coordinates of the data points, ignoring their elevation. This can affect the quality of the approximating surface. In fact, it has long been recognized that sometimes it may be beneficial to use other, non-Delaunay, criteria that take elevation into account to build TINs. Data-dependent triangulations were introduced decades ago to address this exact issue. However, data-dependent trianguations are rarely used in practice, mostly because the optimization of data-dependent criteria often results in triangulations with many slivers (i.e., thin and elongated triangles), which can cause several types of problems. More recently, in the field of computational geometry, higher order Delaunay triangulations (HODTs) were introduced, trying to tackle both issues at the same time—data-dependent criteria and good triangle shape—by combining data-dependent criteria with a relaxation of the Delaunay criterion. In this paper, we present the first extensive experimental study on the practical use of HODTs, as a tool to build data-dependent TINs. We present experiments with two USGS 30m digital elevation models that show that the use of HODTs can give significant improvements over the Delaunay triangulation for the criteria previously identified as most important for data-dependent triangulations, often with only a minor increase in running times. The triangulations produced have measure values comparable to those obtained with pure data-dependent approaches, without compromising the shape of the triangles, and can be computed much faster.
Tue, 20 Feb 2018 11:07:48 GMThttp://hdl.handle.net/2117/1142782018-02-20T11:07:48ZRodríguez, NataliaSilveira, Rodrigo IgnacioThe Delaunay triangulation is the standard choice for building triangulated irregular networks (TINs) to represent terrain surfaces. However, the Delaunay triangulation is based only on the 2D coordinates of the data points, ignoring their elevation. This can affect the quality of the approximating surface. In fact, it has long been recognized that sometimes it may be beneficial to use other, non-Delaunay, criteria that take elevation into account to build TINs. Data-dependent triangulations were introduced decades ago to address this exact issue. However, data-dependent trianguations are rarely used in practice, mostly because the optimization of data-dependent criteria often results in triangulations with many slivers (i.e., thin and elongated triangles), which can cause several types of problems. More recently, in the field of computational geometry, higher order Delaunay triangulations (HODTs) were introduced, trying to tackle both issues at the same time—data-dependent criteria and good triangle shape—by combining data-dependent criteria with a relaxation of the Delaunay criterion. In this paper, we present the first extensive experimental study on the practical use of HODTs, as a tool to build data-dependent TINs. We present experiments with two USGS 30m digital elevation models that show that the use of HODTs can give significant improvements over the Delaunay triangulation for the criteria previously identified as most important for data-dependent triangulations, often with only a minor increase in running times. The triangulations produced have measure values comparable to those obtained with pure data-dependent approaches, without compromising the shape of the triangles, and can be computed much faster.Qualitative properties in strain gradient thermoelasticity with microtemperatures
http://hdl.handle.net/2117/114271
Qualitative properties in strain gradient thermoelasticity with microtemperatures
Iesan, Dorin; Quintanilla de Latorre, Ramón
This paper is devoted to the strain gradient theory of thermoelastic aterials whose microelements possess microtemperatures. The work is motivated by an increasing use of materials which possess thermal variation at a microstructure level. In the first part of this paper we deduce the system of basic equations of the linear theory and formulate the boundary-initial-value problem. We establish existence, uniqueness, and continuous dependence results by the means of semigroup theory. Then, we study the one-dimensional problem and establish the analyticity of solutions. Exponential stability and impossibility of localization are consequences of this result. In the case of the anti-plane problem we derive uniqueness and instability results without assuming the positivity of the mechanical energy. Finally, we study equilibrium theory and investigate the effects of a concentrated heat source in an unbounded body
Tue, 20 Feb 2018 09:23:05 GMThttp://hdl.handle.net/2117/1142712018-02-20T09:23:05ZIesan, DorinQuintanilla de Latorre, RamónThis paper is devoted to the strain gradient theory of thermoelastic aterials whose microelements possess microtemperatures. The work is motivated by an increasing use of materials which possess thermal variation at a microstructure level. In the first part of this paper we deduce the system of basic equations of the linear theory and formulate the boundary-initial-value problem. We establish existence, uniqueness, and continuous dependence results by the means of semigroup theory. Then, we study the one-dimensional problem and establish the analyticity of solutions. Exponential stability and impossibility of localization are consequences of this result. In the case of the anti-plane problem we derive uniqueness and instability results without assuming the positivity of the mechanical energy. Finally, we study equilibrium theory and investigate the effects of a concentrated heat source in an unbounded bodyOn the existence and uniqueness in phase-lag thermoelasticity
http://hdl.handle.net/2117/114238
On the existence and uniqueness in phase-lag thermoelasticity
Magaña Nieto, Antonio; Quintanilla de Latorre, Ramón
This paper is devoted to analyze the phaselag thermoelasticity problem. We study two different cases and we prove, for each one of them, that the
solutions of the problem are determined by a quasicontractive semigroup. As a consequence, existence, uniqueness and continuous dependence of the solutions are obtained
Mon, 19 Feb 2018 13:26:46 GMThttp://hdl.handle.net/2117/1142382018-02-19T13:26:46ZMagaña Nieto, AntonioQuintanilla de Latorre, RamónThis paper is devoted to analyze the phaselag thermoelasticity problem. We study two different cases and we prove, for each one of them, that the
solutions of the problem are determined by a quasicontractive semigroup. As a consequence, existence, uniqueness and continuous dependence of the solutions are obtainedOn the Sato-Tate conjecture for non-generic abelian surfaces
http://hdl.handle.net/2117/114198
On the Sato-Tate conjecture for non-generic abelian surfaces
Johansson, Christian; Fite Naya, Francesc
We prove many non-generic cases of the Sato-Tate conjecture for abelian surfaces as formulated by Fité, Kedlaya, Rotger and Sutherland, using the potential automorphy theorems of Barnet-Lamb, Gee, Geraghty and Taylor.
Fri, 16 Feb 2018 13:27:14 GMThttp://hdl.handle.net/2117/1141982018-02-16T13:27:14ZJohansson, ChristianFite Naya, FrancescWe prove many non-generic cases of the Sato-Tate conjecture for abelian surfaces as formulated by Fité, Kedlaya, Rotger and Sutherland, using the potential automorphy theorems of Barnet-Lamb, Gee, Geraghty and Taylor.Seducir matematicamente?
http://hdl.handle.net/2117/114188
Seducir matematicamente?
Gómez Urgellés, Joan Vicenç
Fri, 16 Feb 2018 12:08:30 GMThttp://hdl.handle.net/2117/1141882018-02-16T12:08:30ZGómez Urgellés, Joan VicençGPS differential code biases determination: methodology and analysis
http://hdl.handle.net/2117/114184
GPS differential code biases determination: methodology and analysis
Sanz Subirana, Jaume; Juan Zornoza, José Miguel; Rovira Garcia, Adrià; González Casado, Guillermo
We address two main problems related to the receiver and satellite differential code biases (DCBs) determination. The first issue concerns the drifts and jumps experienced by the DCB determinations of the International GNSS Service (IGS) due to satellite constellation changes. A new alignment algorithm is introduced to remove these nonphysical effects, which is applicable in real time. The full-time series of 18 years of Global Positioning System (GPS) satellite DCBs, computed by IGS, are realigned using the proposed algorithm. The second problem concerns the assessment of the DCBs accuracy. The short- and long-term receiver and satellite DCB performances for the different Ionospheric Associate Analysis Centers (IAACs) are discussed. The results are compared with the determinations computed with the two-layer Fast Precise Point Positioning (Fast-PPP) ionospheric model, to assess how the geometric description of the ionosphere affects the DCB determination and to illustrate how the errors in the ionospheric model are transferred to the DCB estimates. Two different determinations of DCBs are considered: the values provided by the different IAACs and the values estimated using their pre-computed Global Ionospheric Maps (GIMs). The second determination provides a better characterization of DCBs accuracy, as it is confirmed when analyzing the DCB variations associated with the GPS Block-IIA satellites under eclipse conditions, observed mainly in the Fast-PPP DCB determinations. This study concludes that the accuracy of the IGS IAACs receiver DCBs is approximately 0.3–0.5 and 0.2 ns for the Fast-PPP. In the case of the satellite DCBs, these values are about 0.12–0.20 ns for IAACs and 0.07 ns for Fast-PPP.
The final publication is available at Springer via http://dx.doi.org/10.1007/s10291-017-0634-5
Fri, 16 Feb 2018 11:10:58 GMThttp://hdl.handle.net/2117/1141842018-02-16T11:10:58ZSanz Subirana, JaumeJuan Zornoza, José MiguelRovira Garcia, AdriàGonzález Casado, GuillermoWe address two main problems related to the receiver and satellite differential code biases (DCBs) determination. The first issue concerns the drifts and jumps experienced by the DCB determinations of the International GNSS Service (IGS) due to satellite constellation changes. A new alignment algorithm is introduced to remove these nonphysical effects, which is applicable in real time. The full-time series of 18 years of Global Positioning System (GPS) satellite DCBs, computed by IGS, are realigned using the proposed algorithm. The second problem concerns the assessment of the DCBs accuracy. The short- and long-term receiver and satellite DCB performances for the different Ionospheric Associate Analysis Centers (IAACs) are discussed. The results are compared with the determinations computed with the two-layer Fast Precise Point Positioning (Fast-PPP) ionospheric model, to assess how the geometric description of the ionosphere affects the DCB determination and to illustrate how the errors in the ionospheric model are transferred to the DCB estimates. Two different determinations of DCBs are considered: the values provided by the different IAACs and the values estimated using their pre-computed Global Ionospheric Maps (GIMs). The second determination provides a better characterization of DCBs accuracy, as it is confirmed when analyzing the DCB variations associated with the GPS Block-IIA satellites under eclipse conditions, observed mainly in the Fast-PPP DCB determinations. This study concludes that the accuracy of the IGS IAACs receiver DCBs is approximately 0.3–0.5 and 0.2 ns for the Fast-PPP. In the case of the satellite DCBs, these values are about 0.12–0.20 ns for IAACs and 0.07 ns for Fast-PPP.Eccentricity samples: implications on the potential and the velocity distribution
http://hdl.handle.net/2117/114123
Eccentricity samples: implications on the potential and the velocity distribution
Cubarsí Morera, Rafael; Stojanovic, Milan; Ninkovic, Slobodan
Planar and vertical epicycle frequencies and local angular velocity are related to the derivatives up to the second order of the local potential and can be used to test the shape of the potential from stellar disc samples. These samples show a more complex velocity distribution than halo stars and should provide a more realistic test. We assume an axisymmetric potential allowing a mixture of independent ellipsoidal velocity distributions, of separable or Staeckel form in cylindrical or spherical coordinates. We prove that values of local constants are not consistent with a potential separable in addition in cylindrical coordinates and with a spherically symmetric potential. The simplest potential that fits the local constants is used to show that the harmonical and non-harmonical terms of the potential are equally important. The same analysis is used to estimate the local constants. Two families of nested subsamples selected for decreasing planar and vertical eccentricities are used to borne out the relation between the mean squared planar and vertical eccentricities and the velocity dispersions of the subsamples. According to the first-order epicycle model, the radial and vertical velocity components provide accurate information on the planar and vertical epicycle frequencies. However, it is impossible to account for the asymmetric drift which introduces a systematic bias in estimation of the third constant. Under a more general model, when the asymmetric drift is taken into account, the rotation velocity dispersions together with their asymmetric drift provide the correct fit for the local angular velocity. The consistency of the results shows that this new method based on the distribution of eccentricities is worth using for kinematic stellar samples.
Wed, 14 Feb 2018 13:39:04 GMThttp://hdl.handle.net/2117/1141232018-02-14T13:39:04ZCubarsí Morera, RafaelStojanovic, MilanNinkovic, SlobodanPlanar and vertical epicycle frequencies and local angular velocity are related to the derivatives up to the second order of the local potential and can be used to test the shape of the potential from stellar disc samples. These samples show a more complex velocity distribution than halo stars and should provide a more realistic test. We assume an axisymmetric potential allowing a mixture of independent ellipsoidal velocity distributions, of separable or Staeckel form in cylindrical or spherical coordinates. We prove that values of local constants are not consistent with a potential separable in addition in cylindrical coordinates and with a spherically symmetric potential. The simplest potential that fits the local constants is used to show that the harmonical and non-harmonical terms of the potential are equally important. The same analysis is used to estimate the local constants. Two families of nested subsamples selected for decreasing planar and vertical eccentricities are used to borne out the relation between the mean squared planar and vertical eccentricities and the velocity dispersions of the subsamples. According to the first-order epicycle model, the radial and vertical velocity components provide accurate information on the planar and vertical epicycle frequencies. However, it is impossible to account for the asymmetric drift which introduces a systematic bias in estimation of the third constant. Under a more general model, when the asymmetric drift is taken into account, the rotation velocity dispersions together with their asymmetric drift provide the correct fit for the local angular velocity. The consistency of the results shows that this new method based on the distribution of eccentricities is worth using for kinematic stellar samples.Revisiting Kneser’s theorem for field extensions
http://hdl.handle.net/2117/114080
Revisiting Kneser’s theorem for field extensions
Bachoc, Christine; Serra Albó, Oriol; Zemor, Gilles
A Theorem of Hou, Leung and Xiang generalised Kneser’s addition Theorem to field extensions. This theorem was known to be valid only in separable extensions, and it was a conjecture of Hou that it should be valid for all extensions. We give an alternative proof of the theorem that also holds in the non-separable case, thus solving Hou’s conjecture. This result is a consequence of a strengthening of Hou et al.’s theorem that is inspired by an addition theorem of Balandraud and is obtained by combinatorial methods transposed and adapted to the extension field setting.
Tue, 13 Feb 2018 14:33:26 GMThttp://hdl.handle.net/2117/1140802018-02-13T14:33:26ZBachoc, ChristineSerra Albó, OriolZemor, GillesA Theorem of Hou, Leung and Xiang generalised Kneser’s addition Theorem to field extensions. This theorem was known to be valid only in separable extensions, and it was a conjecture of Hou that it should be valid for all extensions. We give an alternative proof of the theorem that also holds in the non-separable case, thus solving Hou’s conjecture. This result is a consequence of a strengthening of Hou et al.’s theorem that is inspired by an addition theorem of Balandraud and is obtained by combinatorial methods transposed and adapted to the extension field setting.Report on the EGNSS competition after Y2
http://hdl.handle.net/2117/114076
Report on the EGNSS competition after Y2
Sanz Subirana, Jaume; Juan Zornoza, José Miguel; Alonso Alonso, María Teresa; Povero, Gabriella
Tue, 13 Feb 2018 12:40:33 GMThttp://hdl.handle.net/2117/1140762018-02-13T12:40:33ZSanz Subirana, JaumeJuan Zornoza, José MiguelAlonso Alonso, María TeresaPovero, GabriellaDigital image analysis of yeast single cells growing in two different oxygen concentrations to analyze the population growth and to assist individual-based modeling
http://hdl.handle.net/2117/114065
Digital image analysis of yeast single cells growing in two different oxygen concentrations to analyze the population growth and to assist individual-based modeling
Ginovart Gisbert, Marta; Carbó Moliner, Rosa; Blanco Abellán, Mónica; Portell Canal, Xavier
Nowadays control of the growth of Saccharomyces to obtain biomass or cellular
wall components is crucial for specific industrial applications. The general aim of this
contribution is to deal with experimental data obtained from yeast cells and from
yeast cultures to attempt the integration of the two levels of information, individual and population, to progress in the control of yeast biotechnological processes by means of the overall analysis of this set of experimental data, and to assist in the improvement of an individual-based model, namely, INDISIM-Saccha
Mon, 12 Feb 2018 17:23:51 GMThttp://hdl.handle.net/2117/1140652018-02-12T17:23:51ZGinovart Gisbert, MartaCarbó Moliner, RosaBlanco Abellán, MónicaPortell Canal, XavierNowadays control of the growth of Saccharomyces to obtain biomass or cellular
wall components is crucial for specific industrial applications. The general aim of this
contribution is to deal with experimental data obtained from yeast cells and from
yeast cultures to attempt the integration of the two levels of information, individual and population, to progress in the control of yeast biotechnological processes by means of the overall analysis of this set of experimental data, and to assist in the improvement of an individual-based model, namely, INDISIM-Saccha