Articles de revistahttp://hdl.handle.net/2117/35652024-03-28T16:38:24Z2024-03-28T16:38:24ZStructural stability of planar bimodal linear systemsFerrer Llop, JosepPeña Carrera, MartaSusín Sánchez, Antoniohttp://hdl.handle.net/2117/262262020-07-23T20:28:40Z2015-02-05T10:53:33ZStructural stability of planar bimodal linear systems
Ferrer Llop, Josep; Peña Carrera, Marta; Susín Sánchez, Antonio
Structural stability ensures that the qualitative behavior of a system is preserved under small perturbations. We study it for planar bimodal linear dynamical systems, that is, systems consisting of two linear dynamics acting on each side of a given hyperplane and assuming continuity along the separating hyperplane. We describe which one of these systems is structurally stable when (real) spiral does not appear and when it does we give necessary and sufficient conditions concerning finite periodic orbits and saddle connections. In particular, we study the finite periodic orbits and the homoclinic orbits in the saddle/spiral case.
2015-02-05T10:53:33ZFerrer Llop, JosepPeña Carrera, MartaSusín Sánchez, AntonioStructural stability ensures that the qualitative behavior of a system is preserved under small perturbations. We study it for planar bimodal linear dynamical systems, that is, systems consisting of two linear dynamics acting on each side of a given hyperplane and assuming continuity along the separating hyperplane. We describe which one of these systems is structurally stable when (real) spiral does not appear and when it does we give necessary and sufficient conditions concerning finite periodic orbits and saddle connections. In particular, we study the finite periodic orbits and the homoclinic orbits in the saddle/spiral case.Robust treatment of degenerate elements in interactive corotational FEM simulationsCivit Flores, OscarSusín Sánchez, Antoniohttp://hdl.handle.net/2117/247352020-07-23T22:21:21Z2014-11-17T11:06:59ZRobust treatment of degenerate elements in interactive corotational FEM simulations
Civit Flores, Oscar; Susín Sánchez, Antonio
We address the problem of robust and efficient treatment of element collapse and inversion in corotational FEM simulations of deformable objects in two and three dimensions, and show that existing degeneration treatment methods have previously unreported flaws that seriously threaten robustness and physical plausibility in interactive applications. We propose a new method that avoids such flaws, yields faster and smoother degeneration recovery and extends the range of well-behaved degenerate configurations without adding significant complexity or computational cost to standard explicit and quasi-implicit solvers.
2014-11-17T11:06:59ZCivit Flores, OscarSusín Sánchez, AntonioWe address the problem of robust and efficient treatment of element collapse and inversion in corotational FEM simulations of deformable objects in two and three dimensions, and show that existing degeneration treatment methods have previously unreported flaws that seriously threaten robustness and physical plausibility in interactive applications. We propose a new method that avoids such flaws, yields faster and smoother degeneration recovery and extends the range of well-behaved degenerate configurations without adding significant complexity or computational cost to standard explicit and quasi-implicit solvers.Anisomorphic ray-casting manipulation for interacting with 2D GUIsAndújar Gran, Carlos AntonioArgelaguet Sanz, Fernandohttp://hdl.handle.net/2117/239942020-07-23T22:37:57Z2014-09-08T07:53:18ZAnisomorphic ray-casting manipulation for interacting with 2D GUIs
Andújar Gran, Carlos Antonio; Argelaguet Sanz, Fernando
The accommodation of conventional 2D GUIs with virtual environments (VEs) can greatly enhance the possibilities of many VE applications. In this paper we present a variation of the well-known ray-casting technique for fast and accurate selection of 2D widgets over a virtual window immersed into a 3D world. The main idea is to provide a new interaction mode where hand rotations are scaled down so that the ray is constrained to intersect the active virtual window. This is accomplished by changing the control–display ratio between the orientation of the user’s hand and the ray used for selection. Our technique uses a curved representation of the ray providing visual feedback of the orientation of both the input device and the selection ray. We have implemented this technique and evaluated its effectiveness in terms of performance and user preference. Our experiments on a four-sided CAVE indicate that the proposed technique
can increase the speed and accuracy of component selection in 2D GUIs immersed into 3D worlds.
2014-09-08T07:53:18ZAndújar Gran, Carlos AntonioArgelaguet Sanz, FernandoThe accommodation of conventional 2D GUIs with virtual environments (VEs) can greatly enhance the possibilities of many VE applications. In this paper we present a variation of the well-known ray-casting technique for fast and accurate selection of 2D widgets over a virtual window immersed into a 3D world. The main idea is to provide a new interaction mode where hand rotations are scaled down so that the ray is constrained to intersect the active virtual window. This is accomplished by changing the control–display ratio between the orientation of the user’s hand and the ray used for selection. Our technique uses a curved representation of the ray providing visual feedback of the orientation of both the input device and the selection ray. We have implemented this technique and evaluated its effectiveness in terms of performance and user preference. Our experiments on a four-sided CAVE indicate that the proposed technique
can increase the speed and accuracy of component selection in 2D GUIs immersed into 3D worlds.Contenido colónico fisiológico medido por resonancia magnéticaBendezú, ÁlvaroMerino, XaviAccarino Garaventa, Anna MaríaMonclús Lahoya, EvaNavazo Álvaro, IsabelAzpiroz Vidaur, Fernandohttp://hdl.handle.net/2117/233582021-05-20T04:15:47Z2014-07-01T10:28:44ZContenido colónico fisiológico medido por resonancia magnética
Bendezú, Álvaro; Merino, Xavi; Accarino Garaventa, Anna María; Monclús Lahoya, Eva; Navazo Álvaro, Isabel; Azpiroz Vidaur, Fernando
2014-07-01T10:28:44ZBendezú, ÁlvaroMerino, XaviAccarino Garaventa, Anna MaríaMonclús Lahoya, EvaNavazo Álvaro, IsabelAzpiroz Vidaur, FernandoInteractive visualization of medical volume models in mobile devicesCampoalegre, LázaroBrunet Crosa, PereNavazo Álvaro, Isabelhttp://hdl.handle.net/2117/233182021-11-14T07:22:33Z2014-06-27T09:38:21ZInteractive visualization of medical volume models in mobile devices
Campoalegre, Lázaro; Brunet Crosa, Pere; Navazo Álvaro, Isabel
Interactive visualization of volume models in standard mobile devices is a challenging present problem with increasing interest from new application fields like telemedicine. The complexity of present volume models in medical applications is continuously increasing, therefore increasing the gap between the available models and the rendering capabilities in low-end mobile clients. New and efficient rendering algorithms and interaction paradigms are required for these small platforms. In this paper, we propose a transfer function-aware compression and interaction scheme, for client-server architectures with visualization on standard mobile devices. The scheme is block-based, supporting adaptive ray-casting in the client. Our two-level ray-casting allows focusing on small details on targeted regions while keeping bounded memory requirements in the GPU of the client. Our approach includes a transfer function-aware compression scheme based on a local wavelet transformation, together with a bricking scheme that supports interactive inspection and levels of detail in the mobile device client. We also use a quantization technique that takes into account a perceptive metrics of the visual error. Our results show that we can have full interaction with high compression rates and with transmitted model sizes that can be of the order of a single photographic image.
2014-06-27T09:38:21ZCampoalegre, LázaroBrunet Crosa, PereNavazo Álvaro, IsabelInteractive visualization of volume models in standard mobile devices is a challenging present problem with increasing interest from new application fields like telemedicine. The complexity of present volume models in medical applications is continuously increasing, therefore increasing the gap between the available models and the rendering capabilities in low-end mobile clients. New and efficient rendering algorithms and interaction paradigms are required for these small platforms. In this paper, we propose a transfer function-aware compression and interaction scheme, for client-server architectures with visualization on standard mobile devices. The scheme is block-based, supporting adaptive ray-casting in the client. Our two-level ray-casting allows focusing on small details on targeted regions while keeping bounded memory requirements in the GPU of the client. Our approach includes a transfer function-aware compression scheme based on a local wavelet transformation, together with a bricking scheme that supports interactive inspection and levels of detail in the mobile device client. We also use a quantization technique that takes into account a perceptive metrics of the visual error. Our results show that we can have full interaction with high compression rates and with transmitted model sizes that can be of the order of a single photographic image.Adaptive cross-sections of anatomical modelsDíaz Iriberri, JoséMonclús Lahoya, EvaNavazo Álvaro, IsabelVázquez Alcocer, Pere Pauhttp://hdl.handle.net/2117/195912021-05-20T12:14:31Z2013-06-20T13:14:58ZAdaptive cross-sections of anatomical models
Díaz Iriberri, José; Monclús Lahoya, Eva; Navazo Álvaro, Isabel; Vázquez Alcocer, Pere Pau
Medical illustrations have been used for a long time for teaching and communicating information for diagnosis or surgery planning. Illustrative visualization systems create methods and tools that adapt traditional illustration techniques to enhance the result of renderings. Clipping the volume is a popular operation in volume rendering for inspecting the inner parts, though it may remove some information of the context that is worth preserving. In this paper we present a new editing technique based on the use of clipping planes, direct structure extrusion, and illustrative methods, which preserves the context by adapting the extruded region to the structures of interest of the volumetric model. We will show that users may interactively modify the clipping plane and edit the structures to highlight, in order to easily create the desired result. Our approach works with segmented volume models and non-segmented ones. In the last case, a local segmentation is performed on-the-fly. We will demonstrate the efficiency and utility of our method.
2013-06-20T13:14:58ZDíaz Iriberri, JoséMonclús Lahoya, EvaNavazo Álvaro, IsabelVázquez Alcocer, Pere PauMedical illustrations have been used for a long time for teaching and communicating information for diagnosis or surgery planning. Illustrative visualization systems create methods and tools that adapt traditional illustration techniques to enhance the result of renderings. Clipping the volume is a popular operation in volume rendering for inspecting the inner parts, though it may remove some information of the context that is worth preserving. In this paper we present a new editing technique based on the use of clipping planes, direct structure extrusion, and illustrative methods, which preserves the context by adapting the extruded region to the structures of interest of the volumetric model. We will show that users may interactively modify the clipping plane and edit the structures to highlight, in order to easily create the desired result. Our approach works with segmented volume models and non-segmented ones. In the last case, a local segmentation is performed on-the-fly. We will demonstrate the efficiency and utility of our method.Mechanisms of abdominal distension in severe intestinal dysmotility: abdomino-thoracic response to gut retentionBarba, ElisabethQuiroga, SantiAccarino, AnnaMonclús Lahoya, EvaMalagelada, CBurri, ENavazo Álvaro, IsabelMalagelada, JAzpiroz, Fernandohttp://hdl.handle.net/2117/195792021-05-20T08:51:35Z2013-06-19T12:35:59ZMechanisms of abdominal distension in severe intestinal dysmotility: abdomino-thoracic response to gut retention
Barba, Elisabeth; Quiroga, Santi; Accarino, Anna; Monclús Lahoya, Eva; Malagelada, C; Burri, E; Navazo Álvaro, Isabel; Malagelada, J; Azpiroz, Fernando
BACKGROUND: We previously showed that abdominal distension in patients with functional gut disorders is due to a paradoxical diaphragmatic contraction without major increment in intraabdominal volume. Our aim was to characterize the pattern of gas retention and the abdomino-thoracic mechanics associated with abdominal distension in patients with intestinal dysmotility.
METHODS: In 15 patients with manometrically proven intestinal dysmotility, two abdominal CT scans were performed: one during basal conditions and other during an episode of severe abdominal distension. In 15 gender- and age-matched healthy controls, a basal scan was performed.
KEY RESULTS: In basal conditions, patients exhibited more abdominal gas than healthy subjects, particularly in the small bowel, and the volume significantly increased during an episode of distension. During episodes of abdominal distension, the increase in abdominal content was associated with increased girth and antero-posterior abdominal diameter, as well as a cephalic displacement of the diaphragm, which reduced the height of the lung. The consequent reduction in the air volume of the lung was attenuated by an increase in the antero-posterior diameter of the chest.
CONCLUSIONS & INFERENCES: Abdominal distension in patients with severe intestinal dysfunction is related to marked pooling of gut contents, particularly in the small bowel. This increase in content is accommodated within the abdominal cavity by a global and coordinated abdomino-phreno-thoracic response, involving an accommodative ascent of the diaphragm and a compensatory expansion of the chest wall.
2013-06-19T12:35:59ZBarba, ElisabethQuiroga, SantiAccarino, AnnaMonclús Lahoya, EvaMalagelada, CBurri, ENavazo Álvaro, IsabelMalagelada, JAzpiroz, FernandoBACKGROUND: We previously showed that abdominal distension in patients with functional gut disorders is due to a paradoxical diaphragmatic contraction without major increment in intraabdominal volume. Our aim was to characterize the pattern of gas retention and the abdomino-thoracic mechanics associated with abdominal distension in patients with intestinal dysmotility.
METHODS: In 15 patients with manometrically proven intestinal dysmotility, two abdominal CT scans were performed: one during basal conditions and other during an episode of severe abdominal distension. In 15 gender- and age-matched healthy controls, a basal scan was performed.
KEY RESULTS: In basal conditions, patients exhibited more abdominal gas than healthy subjects, particularly in the small bowel, and the volume significantly increased during an episode of distension. During episodes of abdominal distension, the increase in abdominal content was associated with increased girth and antero-posterior abdominal diameter, as well as a cephalic displacement of the diaphragm, which reduced the height of the lung. The consequent reduction in the air volume of the lung was attenuated by an increase in the antero-posterior diameter of the chest.
CONCLUSIONS & INFERENCES: Abdominal distension in patients with severe intestinal dysfunction is related to marked pooling of gut contents, particularly in the small bowel. This increase in content is accommodated within the abdominal cavity by a global and coordinated abdomino-phreno-thoracic response, involving an accommodative ascent of the diaphragm and a compensatory expansion of the chest wall.The ViRVIG instituteAndújar Gran, Carlos AntonioNavazo Álvaro, IsabelVázquez Alcocer, Pere PauPatow, Gustavo ArielPueyo Sandez, Francesc Xavierhttp://hdl.handle.net/2117/180162021-05-21T02:32:13Z2013-02-28T11:07:58ZThe ViRVIG institute
Andújar Gran, Carlos Antonio; Navazo Álvaro, Isabel; Vázquez Alcocer, Pere Pau; Patow, Gustavo Ariel; Pueyo Sandez, Francesc Xavier
In this paper we present the ViRVIG Institute, a recently created institution that joins two well-known research groups: MOVING in Barcelona, and GGG in Girona. Our
main research topics are Virtual Reality devices and interaction techniques, complex data models, realistic materials and lighting, geometry processing, and medical image visualization. We briefly introduce the history of both research groups and present some representative projects. Finally, we sketch our lines for future research.
2013-02-28T11:07:58ZAndújar Gran, Carlos AntonioNavazo Álvaro, IsabelVázquez Alcocer, Pere PauPatow, Gustavo ArielPueyo Sandez, Francesc XavierIn this paper we present the ViRVIG Institute, a recently created institution that joins two well-known research groups: MOVING in Barcelona, and GGG in Girona. Our
main research topics are Virtual Reality devices and interaction techniques, complex data models, realistic materials and lighting, geometry processing, and medical image visualization. We briefly introduce the history of both research groups and present some representative projects. Finally, we sketch our lines for future research.Avatar locomotion in crowd simulationPelechano Gómez, NúriaSpanlang, BernhardBeacco Porres, Alejandrohttp://hdl.handle.net/2117/169052023-01-08T06:46:28Z2012-11-13T10:51:14ZAvatar locomotion in crowd simulation
Pelechano Gómez, Núria; Spanlang, Bernhard; Beacco Porres, Alejandro
This paper presents an Animation Planning Mediator (APM) designed to synthesize animations efficiently for virtual characters in real time crowd simulation. From a set of animation clips, the APM selects the most appropriate and modifies the skeletal configuration of each character to satisfy desired constraints (e.g. eliminating foot-sliding or restricting upper body torsion), while still providing natural looking animations. We use a hardware accelerated character animation library to blend animations increasing the number of possible locomotion types. The APM allows the crowd simulation module to maintain control of path planning, collision avoidance and response. A key advantage of our approach is that the APM can be integrated with any crowd simulator working in continuous space. We show visual results achieved in real time for several hundreds of agents, as well as the quantitative ac-curacy.
2012-11-13T10:51:14ZPelechano Gómez, NúriaSpanlang, BernhardBeacco Porres, AlejandroThis paper presents an Animation Planning Mediator (APM) designed to synthesize animations efficiently for virtual characters in real time crowd simulation. From a set of animation clips, the APM selects the most appropriate and modifies the skeletal configuration of each character to satisfy desired constraints (e.g. eliminating foot-sliding or restricting upper body torsion), while still providing natural looking animations. We use a hardware accelerated character animation library to blend animations increasing the number of possible locomotion types. The APM allows the crowd simulation module to maintain control of path planning, collision avoidance and response. A key advantage of our approach is that the APM can be integrated with any crowd simulator working in continuous space. We show visual results achieved in real time for several hundreds of agents, as well as the quantitative ac-curacy.Efficient rendering of animated characters through optimized per-joint impostorsBeacco Porres, AlejandroAndújar Gran, Carlos AntonioPelechano Gómez, NúriaSpanlang, Bernhardhttp://hdl.handle.net/2117/163902023-01-08T01:36:00Z2012-08-27T16:35:45ZEfficient rendering of animated characters through optimized per-joint impostors
Beacco Porres, Alejandro; Andújar Gran, Carlos Antonio; Pelechano Gómez, Núria; Spanlang, Bernhard
In this paper, we present a new impostor-based representation for 3D animated characters supporting real-time rendering
of thousands of agents. We maximize rendering performance by using a collection of pre-computed impostors sampled
from a discrete set of view directions. Our approach differs from previous work on view-dependent impostors in that we
use per-joint rather than per-character impostors. Our characters are animated by applying the joint rotations directly to the
impostors, instead of choosing a single impostor for the whole character from a set of pre-defined poses. This offers more
flexibility in terms of animation clips, as our representation supports any arbitrary pose, and thus, the agent behavior is not
constrained to a small collection of pre-defined clips. Because our impostors are intended to be valid for any pose, a key
issue is to define a proper boundary for each impostor to minimize image artifacts while animating the agents. We pose
this problem as a variational optimization problem and provide an efficient algorithm for computing a discrete solution as
a pre-process. To the best of our knowledge, this is the first time a crowd rendering algorithm encompassing image-based
performance, small graphics processing unit footprint, and animation independence is proposed.
2012-08-27T16:35:45ZBeacco Porres, AlejandroAndújar Gran, Carlos AntonioPelechano Gómez, NúriaSpanlang, BernhardIn this paper, we present a new impostor-based representation for 3D animated characters supporting real-time rendering
of thousands of agents. We maximize rendering performance by using a collection of pre-computed impostors sampled
from a discrete set of view directions. Our approach differs from previous work on view-dependent impostors in that we
use per-joint rather than per-character impostors. Our characters are animated by applying the joint rotations directly to the
impostors, instead of choosing a single impostor for the whole character from a set of pre-defined poses. This offers more
flexibility in terms of animation clips, as our representation supports any arbitrary pose, and thus, the agent behavior is not
constrained to a small collection of pre-defined clips. Because our impostors are intended to be valid for any pose, a key
issue is to define a proper boundary for each impostor to minimize image artifacts while animating the agents. We pose
this problem as a variational optimization problem and provide an efficient algorithm for computing a discrete solution as
a pre-process. To the best of our knowledge, this is the first time a crowd rendering algorithm encompassing image-based
performance, small graphics processing unit footprint, and animation independence is proposed.