Hybrid model for vascular tree structures

This paper proposes a new representation scheme of the cerebral blood vessels. This model provides information on the semantics of the vascular structure: the topological relationships between vessels and the labeling of vascular accidents such as aneurysms and stenoses. In addition, the model keeps information of the inner surface geometry as well as of the vascular map volume properties, i.e. the tissue density, the blood flow velocity and the vessel wall elasticity. The model can be constructed automatically in a pre-process from a set of segmented MRA images. Its memory requirements are optimized on the basis of the sparseness of the vascular structure. It allows fast queries and efficient traversals and navigations. The visualizations of the vessel surface can be performed at different levels of detail. The direct rendering of the volume is fast because the model provides a natural way to skip over empty data. The paper analyzes the memory requirements of the model along with the costs of the most important operations on it.Postprint (published version

FASTM: a log-based hardware transactional memory with fast abort recovery

Version management, one of the key design dimensions of Hardware Transactional Memory (HTM) systems, defines where and how transactional modifications are stored. Current HTM systems use either eager or lazy version management. Eager systems that keep new values in-place while they hold old values in a software log, suffer long delays when aborts are frequent because the pre-transactional state is recovered by software. Lazy systems that buffer new values in specialized hardware offer complex and inefficient solutions to handle hardware overflows, which are common in applications with coarse-grain transactions. In this paper, we present FASTM, an eager log-based HTM that takes advantage of the processor’s cache hierarchy to provide fast abort recovery. FASTM uses a novel coherence protocol to buffer the transactional modifications in the first level cache and to keep the non-speculative values in the higher levels of the memory hierarchy. This mechanism allows fast abort recovery of transactions that do not overflow the first level cache resources. Contrary to lazy HTM systems, committing transactions do not have to perform any actions in order to make their results visible to the rest of the system. FASTM keeps the pre-transactional state in a software-managed log as well, which permits the eviction of speculative values and enables transparent execution even in the case of cache overflow. This approach simplifies eviction policies without degrading performance, because it only falls back to a software abort recovery for transactions whose modified state has overflowed the cache. Simulation results show that FASTM achieves a speed-up of 43% compared to LogTM-SE, improving the scalability of applications with coarse-grain transactions and obtaining similar performance to an ideal eager HTM with zero-cost abort recovery.Peer ReviewedPostprint (published version

La Congestió viària i la mobilitat sostenible

El paradigma de la sostenibilitat, introduït recentment al marc legal català (Llei d'urbanisme 1/2005, Llei de la mobilitat 9/2003), obliga a redefinir objectius i metodologies en la planificació territorial, en general, i en la planificació de la mobilitat, en particular. En aquest sentit, l'article pretén aportar elements per tal d'abordar el fenomen de la congestió viària sota aquest nou prisma, justificant la necessitat de frenar la construcció de nova xarxa viària i posant l'èmfasi en la gestió de la demanda i en estratègies que minimitzin la inducció de nou trànsit de vehicles privats.El paradigma de la sostenibilidad, introducido recientemente en el marco legal catalán (Ley de urbanismo 1/2005, Ley de la movilidad 9/2003), obliga a redefinir objetivos y metodologías en la planificación territorial, en general, y en la planificación de la movilidad, en particular. En este sentido, el artículo pretende aportar elementos para abordar el fenómeno de la congestión vial bajo este nuevo prisma, justificando la necesidad de frenar la construcción de nueva red vial y poniendo el énfasis en la gestión de la demanda y en estrategias que minimicen la inducción de nuevo tráfico de vehículos privados.The sustainable paradigm, introduced recently into the legal Catalan system (Law of urban planning 1/2005, Law of mobility 9/2003), forces to redefine objectives and methodologies in territorial planning and more also in mobility planning. In this sense this paper brings new elements in order to face the road congestion phenomenon. We justify the need to stop the expansion of new road networks and support the management of the demand fostering strategies that diminish the stimulation of more traffic of private vehicles

Enabling collaboration in virtual reality navigators

In this paper we characterize a feature superset for Collaborative Virtual Reality Environments (CVRE), and derive a component framework to transform stand-alone VR navigators into full-fledged multithreaded collaborative environments. The contributions of our approach rely on a cost-effective and extensible technique for loading software components into separate POSIX threads for rendering, user interaction and network communications, and adding a top layer for managing session collaboration. The framework recasts a VR navigator under a distributed peer-to-peer topology for scene and object sharing, using callback hooks for broadcasting remote events and multicamera perspective sharing with avatar interaction. We validate the framework by applying it to our own ALICE VR Navigator. Experimental results show that our approach has good performance in the collaborative inspection of complex models.Postprint (published version

Geometric transformations in octrees using shears

Existent algorithms to perform geometric transformations on octrees can be classified in two families: inverse transformation and address computation ones. Those in the inverse transformation family essentially resample the target octree from the source one, and are able to cope with all the affine transformations. Those in the address computation family only deal with translations, but are commonly accepted as faster than the former ones for they do no intersection tests, but directly calculate the transformed address of each black node in the source tree. This work introduces a new translation algorithm that shows to perform better than previous one when very small displacements are involved. This property is particularly useful in applications such as simulation, robotics or computer animation.Postprint (published version

La ecuación hipergeométrica de Gauss

En este trabajo se estudiarán las ecuaciones diferenciales lineales de orden superior a 1 con coeficientes holomorfos en la esfera de Riemann, en especial la ecuación hipergeométrica de Gauss. En la primera parte se compararán los teoremas de existencia y unicidad para ecuaciones diferenciales no lineales y ecuaciones diferenciales lineales donde los coeficientes son funciones holomorfas, abordando también la prolongación analítica de las soluciones a lo largo de curvas y el teorema de monodromía. En la segunda parte clasificaremos las singularidades de las ecuaciones diferenciales lineales en singularidades de primer y segundo tipo, regulares e irregulares; y se hará un estudio más exhaustivo de las ecuaciones de orden 2 con coeficientes funciones racionales. En la tercera parte se estudiará como caso particular la ecuación hipergeométrica de Gauss y finalmente se darán aplicaciones prácticas de las ecuaciones diferenciales lineales, así como ideas sobre su implementación computacional.Grado en Matemática

The influence of Mediterranean riparian zones on stream nitrogen dynamics: A catchment approach.

[cat] Durant l'última dècada, les activitats antropogèniques han doblat el nitrogen disponible, provocant nombrosos problemes ambientals. En un context de conca, els boscos de ribera tenen la capacitat de reduir els excessos de nitrogen que els hi arriben dels ecosistemes terrestres adjacents i, per tant, poden ser fonamentals per determinar la concentració de nitrogen al riu i l'exportació d'aquest nutrient aigües avall. L'objectiu d'aquesta tesi és analitzar la influència dels boscos de ribera sobre els recursos hídrics i la dinàmica del nitrogen en una conca mediterrània. Durant l'estudi, els sòls de ribera exhibiren unes taxes netes de mineralització i nitrificació clarament superiors als boscos de capçalera (alzinar i fageda), les quals foren atribuïdes als estocs de fullaraca i a l'alta humitat dels sòls riparians. A més, els sòls de ribera foren importants fonts de nitrat al riu, especialment quan les altes temperatures o les fortes precipitacions provocaren pics d'activitat microbiana que contribuïren > 25% en termes anuals. Hidrològicament parlant, la vegetació ripariana tingué un paper clau sobre els recursos hídrics de la conca, perquè regulà el cabal fluvial a diferents escales temporals, i promogué la pèrdua d'aigua del riu cap a la ribera en el fons de vall. Tanmateix, la ribera no retingué nitrogen durant el període de retenció hidràulica, així com tampoc durant la resta de l'any. Per contra, el baix cabal i les altes temperatures incentivaren la nitrificació a la llera del riu durant l'estiu. A més, durant la primavera, l'augment de llum previ al desenvolupament de la capçada de ribera afavorí la producció primària bruta en el riu, la qual provocà clares fluctuacions diàries en les concentracions de nitrat i reduí un 10% les exportacions d'aquest nutrient aigües avall. Conjuntament, els resultats d'aquesta tesi no només qüestionen la idea que les zones de ribera són filtres naturals de nitrogen en regions mediterrànies, sinó que manifesten la importància d'una visió integradora de tots els components del paisatge per tal per tal d'avançar en el nostre coneixement sobre la hidrologia i la biogeoquímica a escala de conca.[eng] Riparian areas are recognized to be natural filters of nitrogen (N) because they can substantially diminish the N delivery from terrestrial to aquatic ecosystems. However, understanding the influence of riparian zones on regulating N export from catchments is still challenging, mainly because stream water chemistry integrates biogeochemical processes co-occurring within upland, riparian, and fluvial ecosystems. The present dissertation aims to explore the influence of Mediterranean riparian zones on regulating both stream hydrology and catchment N exports, by combining empirical and modelling approaches at different temporal and spatial scales. Findings obtained from plot experiments show that the studied Mediterranean riparian soils acted as hot spots of soil microbial N supply within the catchment because they exhibited considerably higher net N mineralization (NNM) and net nitrification (NN) rates than upland oak and beech soils. This difference was attributed to larger stocks of N-rich leaf litter and permanent moist conditions in the riparian soils. Furthermore, soil microbial processes in the riparian site showed a distinct climatic sensitivity than in upland sites, which ultimately led to different temporal patterns of soil N cycling. Soil moisture was the major driver of NNM and NN in upland forests, while both temperature and precipitation shaped soil N dynamics in the riparian zone. Therefore, both upland and riparian soils exhibited pulses of NNM and NN following spring rewetting events, though summer temperatures only stimulate microbial activity at the riparian site. Riparian microbial pulses contributed > 25% to annual rates of NNM and NN; and coincided with increases in stream N loads. These results suggest that Mediterranean riparian soils may become important sources of nitrate (NO3-) to streams under future warming scenarios. Additionally, findings obtained from catchment-scale studies show that our Mediterranean riparian zone exerted a strong control on stream hydrology during the vegetative period. Riparian evapotranspiration (ET) influenced the temporal pattern of stream discharge and riparian groundwater elevation across daily and seasonal scales. Further, the influence of riparian ET on stream hydrology increased from headwaters to the valley bottom, where stream hydrological retention was prominent. Nonetheless, such stream hydrological retention wasn’t accompanied by a decrease in catchment N exports, likely because low flow conditions, relatively warm conditions, and large stocks of N-rich leaf litter within the streambed enhanced in-stream NO3- release in summer. Conversely, in-stream photoautotrophic NO3- uptake was the major controlling factor of stream N dynamics in spring, when high light inputs favored gross primary productivity (GPP) prior to riparian canopy closure. As it occurred for summer nitrification, the influence of GPP on stream N dynamics increased along the stream continuum. At the valley bottom, in-stream photoautotrophic activity drop midday stream N concentration by 13% and reduced catchment NO3 exports by 10%. Finally, during the dormant period, we found minimal evidences of either NO3 uptake or release in the riparian zone. Mass balance calculations at the whole-reach scale showed that both riparian groundwater inputs and in-stream processes contributed to longitudinal changes in stream NO3 concentrations, and thus, both sources of variation were necessary to understand stream water chemistry along the stream. Together, these results suggest that the high bioreactivity of streams ecosystems can influence stream N dynamics at the catchment scale, and even screen the potential buffer capacity of riparian zones as observed for this Mediterranean catchment. Overall, findings gathered in the present dissertation question the idea that Mediterranean riparian zones are efficient N buffers, and stress that an integrated view of upland, riparian, and stream ecosystems is essential for advancing our understanding of catchment hydrology and biogeochemistry

El maltrato en las organizaciones

La mayoría de las personas pasa gran parte de su vida en los lugares de trabajo. Mientras trabajan, viven. Lo que ocurre en esos lugares, tiene gran influencia en la calidad de vida. Por las estructuras formales propias de las organizaciones, unas personas están expuestas a la autoridad de otros. Cuando el que tiene autoridad maltrata a quienes están a su cargo, maltrata a una parte de la sociedad. Ello es porque no solo afecta a quienes lo sufren directamente, sino también a sus familias y a los clientes, usuarios, o público que se relaciona con las organizaciones. Si existe maltrato, es una situación que se debe conocer y se debe mejorar. Se sugiere implementar soluciones por la vía institucional o por la vía personal.Most people spend great part of their Eves in their working places. While working, they live. What happens in those places, greatly influences the quality of their lives. Because of the formal structures which are typical of these organizations, some people are exposed to other people's authority When the one who has authority ill-treats those under him/her, part of the society b being ill-treated as well. This is so because the ill-treatment affects not only those employees directly involved in the situation, but also their families and the customers, users or general public related to the organization if there is ill-treatment in the organization, that situation should be acknowledged and improved. The implementation of solutions through personal or institutional means is suggested.Fil: Navazo de Grant, Rosa María. Universidad Nacional de Cuyo. Facultad de Ciencias Económica