Encontrado(s) 2243953 resultado(s)
Encontrada(s) 224396 página(s)
Encontrada(s) 224396 página(s)
- Pérez Vidal, Lluís
- Vinh, La The
- Quang, Phuong Xuan
- García Rigo, Alberto
- Rovira Garcia, Adrià
- Ibáñez Segura, Deimos
In GNSS, one of the main error sources of the Standard Positioning Service (SPS) is introduced by the ionosphere. Although this error can be cancelled by combining two signals at different frequencies, most of the single - frequency mass - market receivers do not benefit from this cancel l ation. For that reason, a set of parameter s is included in the navigation message in order to compute the ionospheric delay of any observation by the Klobuchar model. The Klobuchar model is a very simple model that is able to remove more than the 50% of the ionospheric delay. Recently, more accurate ionospheric models have been introduced such as Global Ionospheric Map (GIM) or the F ast P recise P oint P ositioning ( F PPP ) ionospheric model. In previous works, with data gathered in Europe, it was shown the advantage of the F PPP’s ionospheric model. In this work, we conduct experiments to compare the performance of different ionospheric modelling methods including: Klobuchar, GIM s and F PPP. Our preliminary results show how F PPP and GIM s lead to better positioning precisions compared to the Klobuchar model. However, since data is not wide enough to cover different ionospheric cond itions, more experiments will be carried out in our future work to validate the current result s ., Peer Reviewed
Ver en: http://hdl.handle.net/2117/22728
Hydro morphodynamic modelling in Mediterranean storms: errors and uncertainties under sharp gradients
- Sánchez-Arcilla Conejo, Agustín
- Gracia Garcia, Vicente
- García León, Manuel
This paper deals with the limits in hydrodynamic and morphodynamic predictions for semi-enclosed coastal domains subject to sharp gradients (in bathymetry, topography, sediment transport and coastal damages). It starts with an overview of wave prediction limits (based on satellite images and buoy records) in a restricted domain, namely the Mediterranean basin, followed by an in-depth analysis of the Catalan coast, one of its land boundaries. The morphodynamic modelling for such regions is next discussed, based on the impact of a characteristic storm. The driving wave and surge conditions produce a morphodynamic response that is validated against the pre- and post-storm emerged beach state, recovered from two lidar images. The quality of the fit is discussed in terms of the physical processes and the suitability of the employed modelling suite. From here an assessment of errors and uncertainties is presented, with the aim of establishing the prediction limits for flooding and erosion analyses, key elements for coastal engineering decisions.
Ver en: http://hdl.handle.net/2117/24744
- Bohigas Nadal, Oriol
Ver en: http://hdl.handle.net/2117/25953
Constraint algorithm for k-presymplectic Hamiltonian systems. Application to singular field theories
- Gràcia Sabaté, Francesc Xavier
- Martín Grillo, Rubén
- Román Roy, Narciso
The k-symplectic formulation of field theories is especially simple, since only tangent and cotangent bundles are needed in its description. Its defining elements show a close relationship with those in the symplectic formulation of mechanics. It will be shown that this relationship also stands in the presymplectic case. In a natural way, one can mimick the presymplectic constraint algorithm to obtain a constraint algorithm that can be applied to k-presymplectic field theory, and more particularly to the Lagrangian and Hamiltonian formulations of field theories defined by a singular Lagrangian, as well as to the unified Lagrangian-Hamiltonian formalism (Skinner--Rusk formalism) for k-presymplectic field theory. Two examples of application of the algorithm are also analyzed.
Ver en: http://hdl.handle.net/2117/2644
- Eisert, J.
- Friesdorf, M.
- Gogolin, Christian
How do closed quantum many-body systems driven out of equilibrium eventually achieve equilibration? And how do these systems thermalize, given that they comprise so many degrees of freedom? Progress in answering these—and related— questions has accelerated in recent years—a trend that can be partially attributed to success with experiments performing quantum simulations using ultracold atoms and trapped ions. Here we provide an overview of this progress, specifically in studies probing dynamical equilibration and thermalization of systems driven out of equilibrium by quenches, ramps and periodic driving. In doing so, we also address topics such as the eigenstate thermalization hypothesis, typicality, transport, many-body localization and universality near phase transitions, as well as future prospects for quantum simulation., Peer Reviewed
Ver en: http://hdl.handle.net/2117/26765
- Salvia Punsoda, Víctor
In this work we will try to break down the fundamentals of deep generative models for image generation. For the sake of simplicity and understanding we will be using the MNIST dataset, which can be easily trained and understood. The algorithms that we will be explaining and comparing are an autoregressive model, a flow-based model, a variational autoencoder, and a generative adversarial network. Within each of these categories, we have chosen simple algorithms for the sake of clarity as well. Keep in mind that this is a wide but introductory work to the area of image generation. However, these algorithms were certainly state-of the-art around 2016.
- Parasyris, Konstantinos
- Keller, Kai Rasmus
- Bautista Gomez, Leonardo Arturo
- Unsal, Osman Sabri
As we approach the era of exa-scale computing, fault tolerance is of growing importance. The increasing number of cores as well as the increased complexity of modern heterogenous systems result in substantial decrease of the expected mean time between failures. Among the different fault tolerance techniques, checkpoint/restart is vastly adopted in supercomputing systems. Although many supercomputers in the TOP 500 list use GPUs, only a few checkpoint restart mechanism support GPUs.In this paper, we extend an application level checkpoint library, called fault tolerance interface (FTI), to support multi-node/multi-GPU checkpoints. In contrast to previous work, our library includes a memory manager, which upon a checkpoint invocation tracks the actual location of the data to be stored and handles the data accordingly. We analyze the overhead of the checkpoint/restart procedure and we present a series of optimization steps to massively decrease the checkpoint and recovery time of our implementation. To further reduce the checkpoint time we present a differential checkpoint approach which writes only the updated data to the checkpoint file. Our approach is evaluated and, in the best case scenario, the execution time of a normal checkpoint is reduced by 15x in contrast with a non-optimized version, in the case of differential checkpoint the overhead can drop to 2.6% when checkpointing every 30s., The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the LEGaTO Project (www.legato-project.eu), grant agreement #780681., Peer Reviewed
- Cayuela Plaza, Maria
Els traumatismes cranioencefàlics són lesions físiques produïdes sobre laregió cranial o facial que alteren de manera temporal o permanent la funció cerebral. A partir d’ells, el sistema visual es veu alterat, provocant que la vida quotidiana de la gent que ha patit un traumatisme cranial es veu alterada, donant lloc a diversos signes i símptomes.L’objectiu principal d'aquest treball és adquirir, mitjançant la lectura crítica d’articles científics, entendre i ser crític amb allò que estem llegint, en aquest cas fer una lectura crítica que versa sobreles alteracions visuals després d’un traumatisme cranioencefàlic. Per aconseguir aquest objectiu hem dividit el treball en diferents parts. En primer lloc, descriurem amb detall les característiques d’un traumatisme cranioencefàlic, incloent-hi les causes etiològiques i com afecten. Seguidament parlarem de com fer una lectura crítica d’articles científics en ciències de la salut i elaborarem unaguiageneral que seràutilitzadaper la darrera part del treball.Per finalitzar, realitzaré la lectura crítica de tres articles relacionats amb les alteracions visuals després d’un traumatisme cranial adquirit, a partir d’estudis amb pacients que han patit una lesió cranial, per veure quines alteracions es donen en més freqüència i altres estudis comparant pacients amb traumatisme cranioencefàlic i un grup control
- Lletjós Pont, Nilo
This thesis aims to build an ERP selection approach for the implementation of ERP systems in small and medium enterprises (SMEs). Currently, the majority of local companies with few workers manage all their information manually through emails, spreadsheets and text documents – client’s details, projects status, employees’ payrolls, material planning, etc –. However, these companies are living a forced transition to adapt to automated processes – especially when working with larger enterprises which use different ERP systems –, as technologies are evolving, and more companies are using automated systems. Moreover, all companies are using web services to store all information and keep it accessible to employees, however, most of the times this function is not fully integrated, and issues are experienced when it comes to smaller enterprises.