945 resultados para Stochastic integrals


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El pressupòsit bàsic d'aquesta experiència és que el nou model d'Espai Europeu d’Educació Superior pretén un major equilibri entre l'aprenentatge de l'alumnat i l'ensenyament del professor, fent més èmfasi en el primer. En aquest context, hem desenvolupat una eina que denominem "mòduls integrals d’aprenentatge (MIAPS)". L'experiència s'ha desenvolupat en els estudis de criminologia que, com bé es sap, va néixer en la cruïlla entre el model actual i el model de Bolonya, d'imminent implantació. Atès que no tenia sentit implantar un estudi sobre la base d'un model que ja estava condemnat a desaparèixer, centrat fonamentalment en l'ensenyament d'un temari, i en el qual el crèdit es corresponia amb 10 hores de classe; vàrem adoptar per un sistema més pròxim al nou model, basat en les hores del treball de l'alumne (1 cr = 25h). En aquest context, varem considerar que el 50% de les hores de treball de l'alumne haurien de correspondre's amb hores de contacte amb el professor, de les quals, almenys el 30% haurien de ser sessions presencials i la resta de tutories. L'altre 50% haurien de correspondre a hores de treball autònom. És precisament dintre d'aquestes hores de treball autònom que desenvolupem els MIAPS. Amb la finalitat d'homogeneïtzar l'estudi, es va establir que cada MIAP hauria de comportar unes 6 hores de treball de l'alumne. Els MIAPS són concebuts com a espais que combinen informació i activitat. Des d'aquest punt de vista, cada MIAP integra una unitat temàtica. En ella es recull la informació bàsica del tema i conté els vincles necessaris per a fitar adequadament el tema. Però addicionalment, el MIAP incorpora una sèrie d'activitats que es consideren necessàries i adequades per a aconseguir els coneixements i desenvolupar les competències vinculades al MIAP. Així, per exemple, si es pretén que una persona conegui els plantejaments d'una determinada teoria criminològica, el MIAP, a més de recollir la informació bàsica, relaciona, mitjançant vincles, altra informació que serveix per a contextualitzar el tema i ampliar i aprofundir la informació. Però el MIAP no es limita a un document que només proporciona informació, sinó que és també un document d'activitats. Si entre les competències relacionades està el treball en grup i l'anàlisi i resolució de problemes; el MIAP hauria d’incorporar, per exemple, un cas pràctic que han de treballar en grups i resoldre els problemes plantejats. El MIAP permet incorporar exercicis d'avaluació o autoavaluació. Els MIAPS estan pensats com a eines (documents interactius) que permeten treballar i desenvolupar aquelles temàtiques o aspectes que, en principi, no són objecte de classes presencials. Deixant les sessions presencials per fer coses diferents a repetir “allò que el professor sap”, i que generalment es pot trobar escrit. Des d'aquest punt de vista, els MIAPS són documents "complexos", en el sentit que incorporen una sèrie de recursos que van des de la informació a activitats d'avaluació o autoavaluació, passant per activitats de recerca, treballs en grups, elaboració de mapes conceptuals, etc. Així mateix, els MIAPS incorporen mecanismes que serveixen per a fer el seguiment de l'alumnat en el seu procés d'aprenentatge. Un aspecte important que vull ressaltar és que, entre els exercicis que l’alumnat pot desenvolupar, està la possibilitat fer les aportacions als MIAPS, a partir del seu procés d'aprenentatge. Aquesta eina es combina perfectament amb una avaluació continuada i amb metodologies com el portafolio o l'e-portafolio. Cal advertir que els MIAPS no tenen relació amb el tradicional "apunts" de classe o amb una recopilació de materials de lectura, sinó que constituïxen uns veritables documents de treball. El suport dels MIAPS és virtual i l’alumnat accedeix de forma restringida mitjançant la seva clau

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Exam questions and solutions in PDF

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Exam questions and solutions in LaTex

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Exercises and solutions for a third year engineering maths course. Diagrams for the question are all together in the support.zip file, as .eps files

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Exercises, exams and solutions for a second year maths course.

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The purpose of this expository arti le is to present a self- ontained overview of some results on the hara terization of the optimal value fun tion of a sto hasti target problem as (dis ontinuous) vis osity solution of a ertain dynami programming PDE and its appli ation to the problem of hedging ontingent laims in the presen e of portfolio onstraints and large investors

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A driver controls a car by turning the steering wheel or by pressing on the accelerator or the brake. These actions are modelled by Gaussian processes, leading to a stochastic model for the motion of the car. The stochastic model is the basis of a new filter for tracking and predicting the motion of the car, using measurements obtained by fitting a rigid 3D model to a monocular sequence of video images. Experiments show that the filter easily outperforms traditional filters.

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We consider the approximation of some highly oscillatory weakly singular surface integrals, arising from boundary integral methods with smooth global basis functions for solving problems of high frequency acoustic scattering by three-dimensional convex obstacles, described globally in spherical coordinates. As the frequency of the incident wave increases, the performance of standard quadrature schemes deteriorates. Naive application of asymptotic schemes also fails due to the weak singularity. We propose here a new scheme based on a combination of an asymptotic approach and exact treatment of singularities in an appropriate coordinate system. For the case of a spherical scatterer we demonstrate via error analysis and numerical results that, provided the observation point is sufficiently far from the shadow boundary, a high level of accuracy can be achieved with a minimal computational cost.

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Satellite-based rainfall monitoring is widely used for climatological studies because of its full global coverage but it is also of great importance for operational purposes especially in areas such as Africa where there is a lack of ground-based rainfall data. Satellite rainfall estimates have enormous potential benefits as input to hydrological and agricultural models because of their real time availability, low cost and full spatial coverage. One issue that needs to be addressed is the uncertainty on these estimates. This is particularly important in assessing the likely errors on the output from non-linear models (rainfall-runoff or crop yield) which make use of the rainfall estimates, aggregated over an area, as input. Correct assessment of the uncertainty on the rainfall is non-trivial as it must take account of • the difference in spatial support of the satellite information and independent data used for calibration • uncertainties on the independent calibration data • the non-Gaussian distribution of rainfall amount • the spatial intermittency of rainfall • the spatial correlation of the rainfall field This paper describes a method for estimating the uncertainty on satellite-based rainfall values taking account of these factors. The method involves firstly a stochastic calibration which completely describes the probability of rainfall occurrence and the pdf of rainfall amount for a given satellite value, and secondly the generation of ensemble of rainfall fields based on the stochastic calibration but with the correct spatial correlation structure within each ensemble member. This is achieved by the use of geostatistical sequential simulation. The ensemble generated in this way may be used to estimate uncertainty at larger spatial scales. A case study of daily rainfall monitoring in the Gambia, west Africa for the purpose of crop yield forecasting is presented to illustrate the method.

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We discuss and test the potential usefulness of single-column models (SCMs) for the testing of stchastic physics schemes that have been proposed for use in general circulation models (GCMs). We argue that although single column tests cannot be definitive in exposing the full behaviour of a stochastic method in the full GCM, and although there are differences between SCM testing of deterministic and stochastic methods, nonetheless SCM testing remains a useful tool. It is necessary to consider an ensemble of SCM runs produced by the stochastic method. These can be usefully compared to deterministic ensembles describing initial condition uncertainty and also to combinations of these (with structural model changes) into poor man's ensembles. The proposed methodology is demonstrated using an SCM experiment recently developed by the GCSS community, simulating the transitions between active and suppressed periods of tropical convection.

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A stochastic parameterization scheme for deep convection is described, suitable for use in both climate and NWP models. Theoretical arguments and the results of cloud-resolving models, are discussed in order to motivate the form of the scheme. In the deterministic limit, it tends to a spectrum of entraining/detraining plumes and is similar to other current parameterizations. The stochastic variability describes the local fluctuations about a large-scale equilibrium state. Plumes are drawn at random from a probability distribution function (pdf) that defines the chance of finding a plume of given cloud-base mass flux within each model grid box. The normalization of the pdf is given by the ensemble-mean mass flux, and this is computed with a CAPE closure method. The characteristics of each plume produced are determined using an adaptation of the plume model from the Kain-Fritsch parameterization. Initial tests in the single column version of the Unified Model verify that the scheme is effective in producing the desired distributions of convective variability without adversely affecting the mean state.

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Finite computing resources limit the spatial resolution of state-of-the-art global climate simulations to hundreds of kilometres. In neither the atmosphere nor the ocean are small-scale processes such as convection, clouds and ocean eddies properly represented. Climate simulations are known to depend, sometimes quite strongly, on the resulting bulk-formula representation of unresolved processes. Stochastic physics schemes within weather and climate models have the potential to represent the dynamical effects of unresolved scales in ways which conventional bulk-formula representations are incapable of so doing. The application of stochastic physics to climate modelling is a rapidly advancing, important and innovative topic. The latest research findings are gathered together in the Theme Issue for which this paper serves as the introduction.