1,048 research outputs found
Shape computations without compositions
Parametric CAD supports design explorations through generative methods which compose and transform geometric elements. This paper argues that elementary shape computations do not always correspond to valid compositional shape structures. In many design cases generative rules correspond to compositional structures, but for relatively simple shapes and rules it is not always possible to assign a corresponding compositional structure of parts which account for all operations of the computation. This problem is brought into strong relief when design processes generate multiple compositions according to purpose, such as product structure, assembly, manufacture, etc. Is it possible to specify shape computations which generate just these compositions of parts or are there additional emergent shapes and features? In parallel, combining two compositions would require the associated combined computations to yield a valid composition. Simple examples are presented which throw light on the issues in integrating different product descriptions (i.e. compositions) within parametric CAD
Pilot3 D5.1 - Verification and validation plan
This deliverable provides the methodological framework which will enable the execution of the verification and validation activities. The actions defined within framework plan will support the incremental development of the prototype based on the principle of Agile paradigm. The verification defines all activities that will ensure the thorough test of different prototype versions, while validation will assess the functioning hypotheses addressing the operational benefits of the tool. The validation campaign will be done primarily through the interaction with the internal and external experts to capture their feedback.
The deliverable presents the five-level hierarchy approach on the definition of experiments (scenario and case studies) that ensures the flexibility and tractability in their selection through different versions of prototype development.
The deliverable also details the organisation and schedule of the internal and external meetings, workshops and dedicated activities along with the specification of the questionnaires, flow-type diagrams and other instruments which aims to facilitate the validation assessments
On gonihedric loops and quantum gravity
We present an analysis of the gonihedric loop model, a reformulation of the
two dimensional gonihedric spin model, using two different techniques. First,
the usual regular lattice statistical physics problem is mapped onto a height
model and studied analytically. Second, the gravitational version of this loop
model is studied via matrix models techniques. Both methods lead to the
conclusion that the model has for all values of the parameters
of the model. In this way it is possible to understand the absence of a
continuous transition
Optimización robusta en aplicaciones aeronáuticas con la combinación de cálculo estocástico y algoritmos evolutivos
ResumenLas incertidumbres son un problema cotidiano en la ingeniería aeroespacial y en sus aplicaciones. Los métodos de optimización robusta utilizan, normalmente, y para asegurar la robustez de las soluciones, la generación aleatoria de los valores con incertidumbres así como criterios de selección multi-punto para la determinación del óptimo. Desde un punto de vista computacional, la aplicación a problemas de fluido-dinámica (CFD) o interacción fluido-estructura (FSI) puede ser extremadamente cara. Este trabajo presenta el acoplamiento entre el cálculo estocástico y los algoritmos evolutivos para la definición de un procedimiento de optimización robusta. Se propone, en primer lugar, una metodología para el cálculo estocástico, que a continuación se aplica a la solución de problemas de optimización. Estos métodos propuestos se han aplicado a dos tipos de problemas; un problema de CFD y otro de FSI orientados a la reducción de la resistencia aerodinámica y del fenómeno de estabilidad estructural conocido por «flutter», respectivamente.AbstractUncertainties are a daily issue to deal with in aerospace engineering and applications. Robust optimization methods commonly use a random generation of the inputs and take advantage of multi-point criteria to look for robust solutions accounting with uncertainty definition. From the computational point of view, the application to coupled problems, like fluid-dynamics (CFD) or fluid-structure interaction (FSI), can be extremely expensive. This work presents a coupling between stochastic analysis techniques and evolutionary optimization algorithms for the definition of a stochastic robust optimization procedure. At first, a stochastic procedure is proposed to be applied into optimization problems. The proposed method has been applied to both CFD and FSI problems for the reduction of drag and flutter, respectively
Stationary axisymmetric exteriors for perturbations of isolated bodies in general relativity, to second order
Perturbed stationary axisymmetric isolated bodies, e.g. stars, represented by
a matter-filled interior and an asymptotically flat vacuum exterior joined at a
surface where the Darmois matching conditions are satisfied, are considered.
The initial state is assumed to be static. The perturbations of the matching
conditions are derived and used as boundary conditions for the perturbed Ernst
equations in the exterior region. The perturbations are calculated to second
order. The boundary conditions are overdetermined: necessary and sufficient
conditions for their compatibility are derived. The special case of
perturbations of spherical bodies is given in detail.Comment: RevTeX; 32 pp. Accepted by Phys. Rev. D. Added references and extra
comments in introductio
The Mean Metal-line Absorption Spectrum of DLAs in BOSS
We study the mean absorption spectrum of the Damped Lyman alpha population at
by stacking normalized, rest-frame shifted spectra of DLAs from the DR12 of BOSS/SDSS-III. We measure the equivalent widths
of 50 individual metal absorption lines in 5 intervals of DLA hydrogen column
density, 5 intervals of DLA redshift, and overall mean equivalent widths for an
additional 13 absorption features from groups of strongly blended lines. The
mean equivalent width of low-ionization lines increases with ,
whereas for high-ionization lines the increase is much weaker. The mean metal
line equivalent widths decrease by a factor from to
, with small or no differences between low- and high-ionization
species. We develop a theoretical model, inspired by the presence of multiple
absorption components observed in high-resolution spectra, to infer mean metal
column densities from the equivalent widths of partially saturated metal lines.
We apply this model to 14 low-ionization species and to AlIII, SIII, SiIII,
CIV, SiIV, NV and OVI. We use an approximate derivation for separating the
equivalent width contributions of several lines to blended absorption features,
and infer mean equivalent widths and column densities from lines of the
additional species NI, ZnII, CII, FeIII, and SIV. Several of these mean
column densities of metal lines in DLAs are obtained for the first time; their
values generally agree with measurements of individual DLAs from
high-resolution, high signal-to-noise ratio spectra when they are available.Comment: Resubmitted after referee revision. Added evolution of metal-line
equivalent widths with redshift (Section 5). Added assessment of result
dependencies on sample and methodology. Comparison of relative abundances of
DLAs vs Milky Way ISM and halo (Figure 16). Publicly available videos of
composite quasar and DLA spectra realizations here:
https://github.com/lluism
Pilot3 D2.1 - Trade-off report on multi criteria decision making techniques
This deliverable describes the decision making approach that will be followed in Pilot3.
It presents a domain-driven analysis of the characteristics of Pilot3 objective function and optimisation framework. This has been done considering inputs from deliverable D1.1 - Technical Resources and Problem definition, from interaction with the Topic Manager, but most importantly from a dedicated Advisory Board workshop and follow-up consultation. The Advisory Board is formed by relevant stakeholders including airlines, flight operation experts, pilots, and other relevant ATM experts.
A review of the different multi-criteria decision making techniques available in the literature is presented. Considering the domain-driven characteristics of Pilot3 and inputs on how the tool could be used by airlines and crew. Then, the most suitable methods for multi-criteria optimisation are selected for each of the phases of the optimisation framework
Analysis of uncertainty and variability in finite element computational models for biomedical engineering: characterization and propagation
Computational modeling has become a powerful tool in biomedical engineering thanks to its potential to simulate coupled systems. However, real parameters are usually not accurately known, and variability is inherent in living organisms. To cope with this, probabilistic tools, statistical analysis and stochastic approaches have been used. This article aims to review the analysis of uncertainty and variability in the context of finite element modeling in biomedical engineering. Characterization techniques and propagation methods are presented, as well as examples of their applications in biomedical finite element simulations. Uncertainty propagation methods, both non-intrusive and intrusive, are described. Finally, pros and cons of the different approaches and their use in the scientific community are presented. This leads us to identify future directions for research and methodological development of uncertainty modeling in biomedical engineering
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