A structural approach including the behavior of collagen cross-links to model patient-specific human carotid arteries

The final publication is available at Springer via http://dx.doi.org/10.1007/s10439-014-0995-7The objective of this work is to develop a remodeling model for biological matter coupling two different processes in a 3D framework: reorientation of the preferential direction of a given fibered structure and reorientation of the fibrils or filaments that make up such a structure. This work uses the microsphere-based approach to take into account the micro mechanics involved in biological fibered structures regarding both their passive behavior and the reorientation of their micro constituents. Moreover, the macro behavior of the material as a whole is obtained by means of homogenizing the underlying micro response. We associate the orientation space of the integration directions to the physical space of micro-fibrils. To approximate the directional distribution of the fibrils within each fiber bundle, a Bingham probability orientation density function is introduced into the Helmholtz energy function. With all these assumptions, the problem is studied from an energetic point of view, describing the dissipation inherent to remodeling processes, and the evolution equations for both reorientations (change in preferential direction of the network and change in shape of the fibril distribution) re obtained. The model is included in a finite element code which allows computing different geometries and boundary value problems. This results in a complete methodology for characterizing the reorientation evolution of different fibered biological structures, such as cells. Our results show remodeling of fibered structures in two different scales, presenting a qualitatively good agreement with experimental findings in cell mechanics. Hierarchical structures align in the direction of the maximum principal direction of the considered stimulus and narrow in the perpendicular direction. The dissipation rates follows predictable trends although there are no experimental findings to date for comparison. The incorporation of metabolic processes and an insight into cell-oriented mechano-sensing processes can help to overcome the limitations involved.Peer ReviewedPostprint (author's final draft

The Black Box of Mutual Fund Fees

This paper re-examines the determinants of mutual fund fees paid by mutual fund shareholders for management costs and other expenses. There are two novelties with respect to previous studies. First, each type of fee is explained separately. Second, the paper employs a new dataset consisting of Spanish mutual funds, making it the second paper to study mutual fund fees outside the US market. Furthermore, the Spanish market has three interesting characteristics: (i) both distribution and management are highly dominated by banks and savings banks, which points towards potential conflicts of interest; (ii) Spanish mutual fund law imposes caps on all types of fees; and (iii) Spain ranks first in terms of average mutual fund fees among similar countries. We find significant differences in mutual fund fees not explained by the fund’s investment objective. For instance, management companies owned by banks and savings banks charge higher management fees and redemption fees to nonguaranteed funds. Also, investors in older non-guaranteed funds and non-guaranteed funds with a lower average investment are more likely to end up paying higher management fees. Moreover, there is clear evidence that some mutual funds enjoy better conditions from custodial institutions than others. In contrast to evidence from the US market, larger funds are not associated with lower fees, but with higher custody fees for guaranteed funds and higher redemption fees for both types of funds. Finally, fee-setting by mutual funds is not related to fund before-fee performance.mutual fund, fee caps, censored data

Gilles Deleuze i la història de la filosofia: una relació complexa explicada en termes formals (primera part)

Gilles Deleuze had based a significant part of his bibliographic production speaking about some of the occidental philosophy authors. From this singular historical pathway 'Deleuze check out the bibliography of important authors such as Hume, Bergson, Kant, Spinoza o Nietzsche', each person form its own philosophical system in which are mixed up elements coming from a tradition together with original new elements. In this case, we can analyze the principles that explain Deleuze's historiographic work, looking specifically at the innovative and experimental character of such work

Asymmetric quantum devices and heat transport

154 p.Motivada por el impacto tecnológico del diodo eléctrico, esta tesis se dedica a explorar la física y los posibles diseños de dispositivos que tienen una respuesta asimétrica a estímulos externos. Se estudian dispositivos diferentes. Uno de ellos es el diodo térmico, un dispositivo que, análogamente al diodo eléctrico, permite el flujo de corrientes de calor en una dirección pero se comporta como un aislante en la opuesta. Se exploran varios diseños basados en cadenas de iones y átomos para obtener un diodo térmico eficaz y factible. El segundo tipo de dispositivo se basa en un potencial cuántico en una dimensión que tenga coeficientes de transmisión y reflexión asimétricos para las partículas que inciden desde la izquierda y la derecha. Este tipo de dispositivo requiere hamiltonianos no hermíticos y no locales. Se propone una implementación de un hamiltoniano no local y no hermítico en una plataforma de óptica cuántica. Esta implementación cuántico-óptica da la asimetría de transmisión/reflexión coeficientes buscada.Motivated by the technological impact of the electric diode, this thesis is devoted to explore thephysics and possible designs of devices that have an asymmetric response to external inputs.Two different devices are studied. One of them is the thermal diode, a device that, analogouslyto the electric diode, allows heat currents to flow in one direction but behaves as an insulator inthe opposite one. Several designs based on chains of ions and atoms are explored to obtain a performant and feasible thermal diode. The second kind of device is based on a quantumpotential in 1 dimension that has asymmetric scattering coefficients for particles incident fromthe left and the right. This kind of device requires non-Hermitian and non-local hamiltonians. Animplementation of a non-local and non-Hermitian Hamiltonian is given in a quantum-opticalset-up. The quantum-optical implementation has asymmetric scattering coefficients

Visual Representation of Explainable Artificial Intelligence Methods: Design and Empirical Studies

Explainability is increasingly considered a critical component of artificial intelligence (AI) systems, especially in high-stake domains where AI systems’ decisions can significantly impact individuals. As a result, there has been a surge of interest in explainable artificial intelligence (XAI) to increase the transparency of AI systems by explaining their decisions to end-users. In particular, extensive research has focused on developing “local model-agnostic” explainable methods that generate explanations of individual predictions for any predictive model. While these explanations can support end-users in the use of AI systems through increased transparency, three significant challenges have hindered their design, implementation, and large-scale adoption in real applications. First, there is a lack of understanding of how end-users evaluate explanations. There are many critiques that explanations are based on researchers’ intuition instead of end-users’ needs. Furthermore, there is insufficient evidence on whether end-users understand these explanations or trust XAI systems. Second, it is unclear which effect explanations have on trust when they disclose different biases on AI systems’ decisions. Prior research investigating biased decisions has found conflicting evidence on explanations’ effects. Explanations can either increase trust through perceived transparency or decrease trust as end-users perceive the system as biased. Moreover, it is unclear how contingency factors influence these opposing effects. Third, most XAI methods deliver static explanations that offer end-users limited information, resulting in an insufficient understanding of how AI systems make decisions and, in turn, lower trust. Furthermore, research has found that end-users perceive static explanations as not transparent enough, as these do not allow them to investigate the factors that influence a given decision. This dissertation addresses these challenges across three studies by focusing on the overarching research question of how to design visual representations of local model-agnostic XAI methods to increase end-users’ understanding and trust. The first challenge is addressed through an iterative design process that refines the representations of explanations from four well-established model-agnostic XAI methods and a subsequent evaluation with end-users using eye-tracking technology and interviews. Afterward, a research study that takes a psychological contract violation (PCV) theory and social identity theory perspective to investigate the contingency factors of the opposing effects of explanations on end-users’ trust addresses the second challenge. Specifically, this study investigates how end-users evaluate explanations of a gender-biased AI system while controlling for their awareness of gender discrimination in society. Finally, the third challenge is addressed through a design science research project to design an interactive XAI system for end-users to increase their understanding and trust. This dissertation makes several contributions to the ongoing research on improving the transparency of AI systems by explicitly emphasizing the end-user perspective on XAI. First, it contributes to practice by providing insights that help to improve the design of explanations of AI systems’ decisions. Additionally, this dissertation provides significant theoretical contributions by contextualizing the PCV theory to gender-biased XAI systems and the contingency factors that determine whether end-users experience a PCV. Moreover, it provides insights into how end-users cognitively evaluate explanations and extends the current understanding of the impact of explanations on trust. Finally, this dissertation contributes to the design knowledge of XAI systems by proposing guidelines for designing interactive XAI systems that give end-users more control over the information they receive to help them better understand how AI systems make decisions

Asymmetric quantum devices and heat transport

154 p.Motivada por el impacto tecnológico del diodo eléctrico, esta tesis se dedica a explorar la física y los posibles diseños de dispositivos que tienen una respuesta asimétrica a estímulos externos. Se estudian dispositivos diferentes. Uno de ellos es el diodo térmico, un dispositivo que, análogamente al diodo eléctrico, permite el flujo de corrientes de calor en una dirección pero se comporta como un aislante en la opuesta. Se exploran varios diseños basados en cadenas de iones y átomos para obtener un diodo térmico eficaz y factible. El segundo tipo de dispositivo se basa en un potencial cuántico en una dimensión que tenga coeficientes de transmisión y reflexión asimétricos para las partículas que inciden desde la izquierda y la derecha. Este tipo de dispositivo requiere hamiltonianos no hermíticos y no locales. Se propone una implementación de un hamiltoniano no local y no hermítico en una plataforma de óptica cuántica. Esta implementación cuántico-óptica da la asimetría de transmisión/reflexión coeficientes buscada.Motivated by the technological impact of the electric diode, this thesis is devoted to explore thephysics and possible designs of devices that have an asymmetric response to external inputs.Two different devices are studied. One of them is the thermal diode, a device that, analogouslyto the electric diode, allows heat currents to flow in one direction but behaves as an insulator inthe opposite one. Several designs based on chains of ions and atoms are explored to obtain a performant and feasible thermal diode. The second kind of device is based on a quantumpotential in 1 dimension that has asymmetric scattering coefficients for particles incident fromthe left and the right. This kind of device requires non-Hermitian and non-local hamiltonians. Animplementation of a non-local and non-Hermitian Hamiltonian is given in a quantum-opticalset-up. The quantum-optical implementation has asymmetric scattering coefficients

Understanding the ex-ante cost of liquidity in the limit order book: A note

This paper estimates a new measure of liquidity costs in a market driven by orders. It represents thecost of simultaneously buying and selling a given amount of shares, and it is given by a single measure of ex-ante liquidity that aggregates all available information in the limit order book for a given number of shares. The cost of liquidity is an increasing function relating bid-ask spreads with the amounts available for trading. This measure completely characterizes the cost of liquidity of any given asset. It does not suffer from the usual ambiguities related to either the bid-ask spread or depth when they are considered separately. On the contrary, with a single measure, we are able to capture all dimensions of liquidity costs on ex-ante basis.liquidity cost, liquidity function, open limit order book, depth, bid ask spread

Asset pricing and systematic liquidity risk: an empirical investigation of the Spanish stock market

Systematic liquidity shocks should affect the optimal behavior of agents in financial markets. Indeed, fluctuations in various measures of liquidity are significantly correlated across common stocks. Accordingly, this paper empirically analyzes whether Spanish average returns vary cross-sectionally with betas estimated relative to two competing liquidity risk factors. The first one, proposed by Pastor and Stambaugh (2002), is associated with the strength of volume-related return reversals. Our marketwide liquidity factor is defined as the difference between returns highly sensitive to changes in the relative bid-ask spread and returns with low sensitivities to those changes. Our empirical results show that neither of these proxies for systematic liquidity risk seems to be priced in the Spanish stock market. Further international evidence is deserved.expected returns, systematic liquidity risk, order flow, bid ask spread

Designing Interactive Explainable AI Systems for Lay Users

Explainability considered a critical component of trustworthy artificial intelligence (AI) systems, has been proposed to address AI systems’ lack of transparency by revealing the reasons behind their decisions to lay users. However, most explainability methods developed so far provide static explanations that limit the information conveyed to lay users resulting in an insufficient understanding of how AI systems make decisions. To address this challenge and support the efforts to improve the transparency of AI systems, we conducted a design science research project to design an interactive explainable artificial intelligence (XAI) system to help lay users understand AI systems’ decisions. We relied on existing knowledge in the XAI literature to propose design principles and instantiate them in an initial prototype. We then conducted an evaluation of the prototype and interviews with lay users. Our research contributes design knowledge for interactive XAI systems and provides practical guidelines for practitioners