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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.
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.
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.
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.
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.
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.
Characterization of tempered exponential dichotomies
Luis Barreira,Joao Rijo,Claudia Valls 대한수학회 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.
Recent Clinical Results of Endoscopic Bariatric Therapies as an Obesity Intervention
Fateh Bazerbachi,Eric J. Vargas Valls,Barham K. Abu Dayyeh 대한소화기내시경학회 2017 Clinical Endoscopy Vol.50 No.1
Despite advances in lifestyle interventions, anti-obesity medications, and metabolic surgery, the issue of health burden due to obesity continues to evolve. Interest in endoscopic bariatric techniques has increased over the years, as they have been shown to be efficacious, reversible, relatively safe, and cost effective. Further, these techniques offer a therapeutic window for some patients who may otherwise be unable to undergo bariatric surgery. This article aims to review the literature on the safety and efficacy of currently offered endoscopic bariatric techniques, as well as those that are in the pipeline of end-development and regulatory approval.