Volatility Transmission and Correlation Analysis between the USA and Asia: The Impact of the Global Financial Crisis

NATALIA VALLS,HELENA CHULIA 연세대학교 동서문제연구원 2012 Global economic review Vol.41 No.2

This paper examines volatility transmission and conditional correlations behaviour between the US and the Asian stock markets considering the effect of the Global Financial crisis. One Asian mature market and 10 emerging markets are included in the sample. To carry out the analysis, we use a multivariate asymmetric GARCH model. Results show that there exists volatility transmission between the US and the Asian markets. Moreover, it is found that, after the crisis, volatility transmission patterns have barely changed. Finally, results suggest that the lower the country‘s level of development, the lower the correlation with the USA.

The realm of the ultra-low surface brightness universe

David Valls-Gabaud 한국천문학회 2017 天文學會報 Vol.42 No.1

Vertically-Aligned ZnO/InxSy Core-Shell Nanorods for High Efficient Dye-Sensitized Solar Cells

Irene Gonzalez-Valls,Belen Ballesteros,Mónica Lira-Cantu 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.7

Innovative vertically aligned ZnO/InxSy nanorod (NR) electrodes were prepared by successive ion layer adsorption and reaction (SILAR) technique. The InxSy shell layer was deposited on top of ZnO NR electrodes of two different lengths, ~ 1.6 µm and ~ 3.2 µm. Two sulfur contents on the InxSy shell layer with different layer thicknesses were analyzed. These electrodes were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), Energy-dispersive x-ray spectroscopy (EDS), Infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) and then applied in dye-sensitized solar cells (DSC). Power conversion efficiency of 2.32% was observed when a low-sulfur content InxSy shell layer was applied in comparison to the stoichiometric In2S3 shell layer (0.21%) or the bare ZnO NRs (0.87%). In the case of low sulfur content, a shell layer of In(OH)xSy or/and In(OH)3 is formed as observed by the presence of –OH observed by FTIR analyses. The presence of higher amounts of hydroxide groups modifies the bandgap and work function of the InxSy shell and facilitates dye adsorption, increasing the final solar cell performance.

Efficiency of stiffening plates in fabricated concrete-filled tubes under monotonic compression

Albert Albareda-Valls,Jordi Maristany Carreras 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.4

Concrete-filled tubes (CFT), formed by an outer steel tube filled with plain or reinforced concrete inside, have been increasingly used these recent decades as columns or beam-columns, especially for tall buildings in seismic areas due to their excellent structural response. This improved behavior is derived from the effect of confinement provided by the tube, since the compressive strength of concrete increases when being subjected to hydrostatic pressure. In circular CFTs under compression, the whole tube is uniformly tensioned due to the radial expansion of concrete. Contrarily, in rectangular and square-shaped CFTs, the lateral flanges become subjected to in-plane bending derived from this volumetric expansion, and this fact implies a reduction of the confinement effect of the core. This study presents a numerical analysis of different configurations of CFT stub columns with inner stiffening plates, limited to the study of the influence of these plates on the compressive behavior without eccentricity. The final purpose is to evaluate the efficiency in terms of strength and ductility of introducing stiffeners into circular and square CFT sections under large deformation axial loading.

PARAMETER DEPENDENCE OF SMOOTH STABLE MANIFOLDS

Barreira, Luis,Valls, Claudia Korean Mathematical Society 2019 대한수학회지 Vol.56 No.3

We establish the existence of $C^1$ stable invariant manifolds for differential equations $u^{\prime}=A(t)u+f(t,u,{\lambda})$ obtained from sufficiently small $C^1$ perturbations of a nonuniform exponential dichotomy. Since any linear equation with nonzero Lyapunov exponents has a nonuniform exponential dichotomy, this is a very general assumption. We also establish the $C^1$ dependence of the stable manifolds on the parameter ${\lambda}$. We emphasize that our results are optimal, in the sense that the invariant manifolds are as regular as the vector field. We use the fiber contraction principle to establish the smoothness of the invariant manifolds. In addition, we can also consider linear perturbations, and thus our results can be readily applied to the robustness problem of nonuniform exponential dichotomies.

Parameter dependence of smooth stable manifolds

Luis Barreira,Claudia Valls 대한수학회 2019 대한수학회지 Vol.56 No.3

We establish the existence of $C^1$ stable invariant manifolds for differential equations $u'=A(t)u+f(t,u,\lambda)$ obtained from sufficiently small $C^1$ perturbations of a \emph{nonuniform} exponential dichotomy. Since any linear equation with nonzero Lyapunov exponents has a nonuniform exponential dichotomy, this is a very general assumption. We also establish the $C^1$ dependence of the stable manifolds on the parameter $\lambda$. We emphasize that our results are optimal, in the sense that the invariant manifolds are as regular as the vector field. We use the fiber contraction principle to establish the smoothness of the invariant manifolds. In addition, we can also consider linear perturbations, and thus our results can be readily applied to the robustness problem of nonuniform exponential dichotomies.

해상 부유체 동적 거동 해석을 위한 ALE 알고리듬이 적용된 ODDLS 기법 기반의 전산유체해석 코드 개발

이준호(Junho Lee),Aleix Valls,Julio Garcia-Espinosa 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11

CHARACTERIZATION OF TEMPERED EXPONENTIAL DICHOTOMIES

Barreira, Luis,Rijo, Joao,Valls, Claudia Korean Mathematical Society 2020 대한수학회지 Vol.57 No.1

For a nonautonomous dynamics defined by a sequence of bounded linear operators on a Banach space, we give a characterization of the existence of an exponential dichotomy with respect to a sequence of norms in terms of the invertibility of a certain linear operator between general admissible spaces. This notion of an exponential dichotomy contains as very special cases the notions of uniform, nonuniform and tempered exponential dichotomies. As applications, we detail the consequences of our results for the class of tempered exponential dichotomies, which are ubiquitous in the context of ergodic theory, and we show that the notion of an exponential dichotomy under sufficiently small parameterized perturbations persists and that their stable and unstable spaces are as regular as the perturbation.

Adaptive Motion Planning in Bin-Picking with Object Uncertainties

Thomas Fridolin Iversen,Lars-Peter Ellekilde,Jaime Valls Miro 제어로봇시스템학회 2017 제어로봇시스템학회 국제학술대회 논문집 Vol.2017 No.10

Doing motion planning for bin-picking with object uncertainties requires either a re-grasp of picked objects or an online sensor system. Using the latter is advantageous in terms of computational time, as no time is wasted doing an extra pick and place action. It does, however, put extra requirements on the motion planner, as the target position may change on-the-fly. This paper solves that problem by using a state adjusting Partial Observable Markov Decision Process, where the state space is modified between runs, to better fit earlier solved problems. The approach relies on a set of waypoints, containing information about which parts of the state space may contain feasible solutions. Waypoints are pushed around the state space by observing which states in the neighborhood lead to successfully solved problems. Two bin-picking scenarios are modeled with the proposed method. One scenario in which the system receives an object pose update while moving towards the place position. Another where the update includes the object type being grasped out of a fixed number of options, each class to be deposited in a different place. When an online POMDP solver is utilized, the state adjusting POMDP is improving performance by up to 28% on execution times compared to a not adjusted POMDP.

A methodology to derive global maps of leaf traits using remote sensing and climate data

Moreno-Martí,nez, Á,lvaro,Camps-Valls, Gustau,Kattge, Jens,Robinson, Nathaniel,Reichstein, Markus,van Bodegom, Peter,Kramer, Koen,Cornelissen, J. Hans C.,Reich, Peter,Bahn, Michael,Niineme Elsevier 2018 Remote sensing of environment Vol.218 No.-

<P><B>Abstract</B></P> <P>This paper introduces a modular processing chain to derive global high-resolution maps of leaf traits. In particular, we present global maps at 500 m resolution of specific leaf area, leaf dry matter content, leaf nitrogen and phosphorus content per dry mass, and leaf nitrogen/phosphorus ratio. The processing chain exploits machine learning techniques along with optical remote sensing data (MODIS/Landsat) and climate data for gap filling and up-scaling of in-situ measured leaf traits. The chain first uses random forests regression with surrogates to fill gaps in the database (> 45<I>%</I> of missing entries) and maximizes the global representativeness of the trait dataset. Plant species are then aggregated to Plant Functional Types (PFTs). Next, the spatial abundance of PFTs at MODIS resolution (500 m) is calculated using Landsat data (30 m). Based on these PFT abundances, representative trait values are calculated for MODIS pixels with nearby trait data. Finally, different regression algorithms are applied to globally predict trait estimates from these MODIS pixels using remote sensing and climate data. The methods were compared in terms of precision, robustness and efficiency. The best model (random forests regression) shows good precision (normalized RMSE≤ 20<I>%</I>) and goodness of fit (averaged Pearson's correlation R = 0.78) in any considered trait. Along with the estimated global maps of leaf traits, we provide associated uncertainty estimates derived from the regression models. The process chain is modular, and can easily accommodate new traits, data streams (traits databases and remote sensing data), and methods. The machine learning techniques applied allow attribution of information gain to data input and thus provide the opportunity to understand trait-environment relationships at the plant and ecosystem scales. The new data products – the gap-filled trait matrix, a global map of PFT abundance per MODIS gridcells and the high-resolution global leaf trait maps – are complementary to existing large-scale observations of the land surface and we therefore anticipate substantial contributions to advances in quantifying, understanding and prediction of the Earth system.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Presented a modular process chain for plant trait mapping including local effects </LI> <LI> High-resolution global maps of leaf traits by fusing measured trait data, LANDSAT and MODIS </LI> <LI> Scope for testing and parameterizing trait-enabled Earth System models </LI> <LI> Implications for land management and Earth system science applications </LI> </UL> </P>