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See detailPhase field simulation of early-age fracture in cement-based materials (Top 10%)
Nguyen, Thanh-Tung; Waldmann, Danièle UL; Bui, Tinh Quoc

in International Journal of Solids and Structures (in press)

In this paper, a new computational approach, which is based on a multi-physics coupling of the chemo-thermo-mechanical process, is developed for modeling failure mechanism in cement-based materials at ... [more ▼]

In this paper, a new computational approach, which is based on a multi-physics coupling of the chemo-thermo-mechanical process, is developed for modeling failure mechanism in cement-based materials at early-age hydration. A new constitutive law describing mechanical behavior of young concrete is thus derived, taking into account the effects of several factors including thermal expansion, shrinkage, damage, and both basic and transient thermal creeps. A strongly coupled model describing the interaction between fracture and multi-physics problems of cement hydration is obtained. The present phase field model in terms of smeared crack approach is highly suitable for simulating crack, especially when considering the unilateral contact conditions at crack surfaces. The capability of the proposed model in modeling complex crack initiation and propagation under arbitrary boundary conditions is highlighted. Fracture phenomena at both macroscopic and mesoscopic scales are considered and analyzed. The effects of creep and microstructural heterogeneity in different length scale are investigated, showing the great potential of the developed approach. [less ▲]

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See detailDomain-specific views on aging and preparation for age-related changes – Development and validation of three brief scales.
Kornadt, Anna Elena UL; Hess, Thomas M; Rothermund, Klaus

in Journals of Gerontology. Series B, Psychological Sciences and Social Sciences (in press)

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See detailMachine learning in nanoscience: big data at small scales
Brown, Keith A.; Brittman, Sarah; Maccaferri, Nicolò UL et al

in Nano Letters (in press)

Recent advances in machine learning (ML) offer new tools to extract new insights from large data sets and to acquire small data sets more effectively. Researchers in nanoscience are experimenting with ... [more ▼]

Recent advances in machine learning (ML) offer new tools to extract new insights from large data sets and to acquire small data sets more effectively. Researchers in nanoscience are experimenting with these tools to tackle challenges in many fields. In addition to ML’s advancement of nanoscience, nanoscience provides the foundation for neuromorphic computing hardware to expand the implementation of ML algorithms. In this mini-review, which is not able to be comprehensive, we highlight some recent efforts to connect the ML and nanoscience communities focusing on three types of interaction: (1) using ML to analyze and extract new information from large nanoscience data sets, (2) applying ML to accelerate materials discovery, including the use of active learning to guide experimental design, and (3) the nanoscience of memristive devices to realize hardware tailored for ML. We conclude with a discussion of challenges and opportunities for future interactions between nanoscience and ML researchers. [less ▲]

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See detailThe Uniqueness of Subjective Ageing. Convergent and Discriminant Validity
Spuling, Svenja M.; Klusmann, Verena; Bowen, Catherine E. et al

in European Journal of Ageing (in press)

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See detailNanoscale magnetophotonics
Maccaferri, Nicolò UL; Zubritskaya, Irina; Razdolski, Ilya et al

in Journal of Applied Physics (in press)

This Perspective surveys the state-of-the-art and future prospects of science and technology employing the nanoconfined light (nanophotonics and nanoplasmonics) in combination with magnetism. We denote ... [more ▼]

This Perspective surveys the state-of-the-art and future prospects of science and technology employing the nanoconfined light (nanophotonics and nanoplasmonics) in combination with magnetism. We denote this field broadly as nanoscale magnetophotonics. We include a general introduction to the field and describe the emerging magneto-optical effects in magnetoplasmonic and magnetophotonic nanostructures supporting localized plasmons. Special attention is given to magnetoplasmonic crystals with transverse magnetization and the associated nanophotonic nonreciprocal effects, and to magneto-optical effects in nanostructure’s periodic arrays. We also give an overview of the applications of these systems in biological and chemical sensing, as well as in light polarization and phase control. We further review the area of nonlinear magnetophotonics, the semiconductor spin-plasmonics, and the general principles and applications of optomagnetism and nano-optical ultrafast control of magnetism and spintronics. [less ▲]

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See detailA short Survey on the Cyber Security in Control Systems
Bezzaoucha, Souad UL; Voos, Holger UL

Scientific Conference (2020, July)

In the present survey paper, we give a short, yet exhaustive state-of-the-art about the cyber-security applied to control systems, especially the event-based strategy. Indeed, in the past few years, due ... [more ▼]

In the present survey paper, we give a short, yet exhaustive state-of-the-art about the cyber-security applied to control systems, especially the event-based strategy. Indeed, in the past few years, due to a highest degree of connectivity in modern systems, new related control-specific cyber-physical systems security challengesarise and novel approaches integrating the cyber aspect are developed.Our goal in this paper is then to provide an overview of attack-modeling and security analysis approaches in recent works thatexplore networked control systems subject to cyber-attacks attacks. To this end, we look at the control, estimation, and modeling problems. [less ▲]

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See detailConstcamer Paintings as Epistemic Images: Early Modern Theaters of Wisdom
Koeleman, Floor UL

Scientific Conference (2020, April)

This paper argues, against existing literature, that 17th-cent. constcamer paintings were objects to think with, functioning as the two-dimensional space of artificial memory. In turn, these artworks ... [more ▼]

This paper argues, against existing literature, that 17th-cent. constcamer paintings were objects to think with, functioning as the two-dimensional space of artificial memory. In turn, these artworks complicate conventional definitions of epistemic images more broadly. I focus on an analysis of constcamer paintings accounting for the reception of the ancients and the mnemonic and propaedeutic role of images, entailing concepts such as wonder or thauma (from Greek θεάομαι), the drive to gather knowledge, memory as the locus of this ‘collection’, and recollecting as the intellectual process of interaction with memorized knowledge. The term inventor, referring to the creator of a given collection, is derived from the rhetorical technique for the retrieval of information. The theatre or ‘place for viewing’ provided the physical context for the collected wisdom. Inventors of constcamer paintings – often artists themselves – vitally participated in knowledge formation contributing to contemporary intellectual debates. [less ▲]

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See detailMetamorphic Security Testing for Web Systems
Mai, Xuan Phu UL; Pastore, Fabrizio UL; Goknil, Arda et al

in IEEE International Conference on Software Testing, Verification and Validation (ICST) 2020 (2020, March)

Security testing verifies that the data and the resources of software systems are protected from attackers. Unfortunately, it suffers from the oracle problem, which refers to the challenge, given an input ... [more ▼]

Security testing verifies that the data and the resources of software systems are protected from attackers. Unfortunately, it suffers from the oracle problem, which refers to the challenge, given an input for a system, of distinguishing correct from incorrect behavior. In many situations where potential vulnerabilities are tested, a test oracle may not exist, or it might be impractical due to the many inputs for which specific oracles have to be defined. In this paper, we propose a metamorphic testing approach that alleviates the oracle problem in security testing. It enables engineers to specify metamorphic relations (MRs) that capture security properties of the system. Such MRs are then used to automate testing and detect vulnerabilities. We provide a catalog of 22 system-agnostic MRs to automate security testing in Web systems. Our approach targets 39% of the OWASP security testing activities not automated by state-of-the-art techniques. It automatically detected 10 out of 12 vulnerabilities affecting two widely used systems, one commercial and the other open source (Jenkins). [less ▲]

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See detailSuicide Prevention: Using the Number of Health Complaints as an Indirect Alternative for Screening Suicidal Adolescents
Heinz, Andreas UL; Catunda, Carolina UL; van Duin, Claire UL et al

in Journal of Affective Disorders (2020), 260

Background: Suicide is the second leading cause of death in adolescents. Screening for persons at risk usually includes asking about suicidal ideation, which is considered inappropriate in some societies ... [more ▼]

Background: Suicide is the second leading cause of death in adolescents. Screening for persons at risk usually includes asking about suicidal ideation, which is considered inappropriate in some societies and situations. To avoid directly addressing suicide, this paper investigates whether the Health Behaviour in School-aged Children Symptom Checklist (HBSC-SCL), a validated non-clinical measure of eight subjective health complaints (e.g. headache, feeling low), could be used as a tool for screening suicidal ideation and behavior in adolescents. Methods: 5262 secondary school students aged 12-18 answered the Luxembourgish HBSC 2014 survey, including the HBSC-SCL items and suicidal ideation and behavior questions. Results: Each HBSC-SCL item correlates with suicidal ideation and behavior. A sum score was calculated ranging from zero to eight health complaints to predict respondents who considered suicide (area under the ROC curve = .770). The ideal cut-off for screening students who consider suicide is three or more health complaints: sensitivity is 66.3%, specificity is 75.9% and positive predictive value is 32.9%. Limitations: One limitation is HBSC-SCL's low positive predictive value. This is a general problem of screening rare events: the lower the prevalence, the lower the positive predictive value. Sensitivity and specificity could be improved by taking age-, gender- and country-specific cut-off values, but such refinements would make the score calculation more complicated. Conclusions: The HBSC-SCL is short, easy to use, with satisfactory screening properties. The checklist can be used when suicide cannot be addressed directly, and also in a more general context, e.g. by school nurses when screening adolescents. [less ▲]

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See detailModel Uncertainty and Pricing Performance in Option Valuation
Bams, Dennis; Blanchard, Gildas; Lehnert, Thorsten UL

in The Journal of Derivatives (2020), 27(3), 31-49

The objective of this paper is to evaluate option pricing model performance at the cross sectional level. For this purpose, we propose a statistical framework, in which we in particular account for the ... [more ▼]

The objective of this paper is to evaluate option pricing model performance at the cross sectional level. For this purpose, we propose a statistical framework, in which we in particular account for the uncertainty associated with the reported pricing performance. Instead of a single figure, we determine an entire probability distribution function for the loss function that is used to measure option pricing model performance. This methodology enables us to visualize the effect of parameter uncertainty on the reported pricing performance. Using a data driven approach, we confirm previous evidence that standard volatility models with clustering and leverage effects are sufficient for the option pricing purpose. In addition, we demonstrate that there is short-term persistence but long-term heterogeneity in cross-sectional option pricing information. This finding has two important implications. First, it justifies the practitioner’s routine to refrain from time series approaches, and instead estimate option pricing models on a cross-section by cross-section basis. Second, the long term heterogeneity in option prices pinpoints the importance of measuring, comparing and testing option pricing model for each cross-section separately. To our knowledge no statistical testing framework has been applied to a single cross-section of option prices before. We propose a methodology that addresses this need. The proposed framework can be applied to a broad set of models and data. In the empirical part of the paper, we show by means of example, an application that uses a discrete time volatility model on S&P 500 index options. [less ▲]

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See detailThe joint role of impulsivity and distorted cognitions in recreational and problem gambling: A cluster analytic approach.
Devos, Mr Gaetan; Clark, Luke; Bowden-Jones, Henrietta et al

in Journal of affective disorders (2020), 260

BACKGROUND AND AIMS: The Pathways Model (Blaszczynski & Nower, 2002) posits that problem gambling is a heterogeneous disorder with distinct subgroups (behaviorally conditioned gamblers, emotionally ... [more ▼]

BACKGROUND AND AIMS: The Pathways Model (Blaszczynski & Nower, 2002) posits that problem gambling is a heterogeneous disorder with distinct subgroups (behaviorally conditioned gamblers, emotionally vulnerable gamblers, and antisocial-impulsivist gamblers). Impulsivity traits and gambling-related cognitions are recognized as two key psychological factors in the onset and maintenance of problem gambling. To date, these constructs have been explored separately, and their joint role in determining problem gambling subtypes has received little attention. The goal of our study was to identify subgroups of gamblers based on impulsivity traits and gambling-related cognitions, and to determine whether this approach is consistent with the Pathways model. METHODS: Gamblers from the community (N=709) and treatment-seeking pathological gamblers (N=122) completed questionnaires measuring gambling habits, disordered gambling symptoms, gambling-related cognitions, and impulsivity traits. RESULTS: Cluster analyses revealed that three clusters globally aligned with the pathways proposed by Blaszczynski & Nower (2002). Two other clusters emerged: (1) impulsive gamblers without cognitive-related cognitions; and (2) gamblers without impulsivity or gambling-related cognitions. Gamblers with both heightened impulsive traits and gambling-related cognitions had more severe problem gambling symptoms. CONCLUSION: We successfully identified, based on an a priori theoretical framework, different subtypes of gamblers that varied in terms of problem gambling symptoms and clinical status. The diversity of the cluster profiles supports the development of personalized prevention strategies and psychological interventions. [less ▲]

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See detailChapter 16 - Cognitive factors associated with gaming disorder
Billieux, Joël UL; Potenza, Marc N.; Maurage, Pierre et al

in Verdejo-Garcia, Antonio (Ed.) Cognition and Addiction (2020)

There is substantial clinical and public health evidence that video gaming, particularly online gaming, can become excessive and lead to psychological distress and functional impairment. This has led to ... [more ▼]

There is substantial clinical and public health evidence that video gaming, particularly online gaming, can become excessive and lead to psychological distress and functional impairment. This has led to the inclusion of gaming disorder as an official mental condition in the International Classification of Diseases, 11th Edition (ICD-11; World Health Organization, 2019). Psychological models recognize the importance of cognitive factors to explain the initiation, development, and maintenance of problematic gaming behaviors. This chapter will summarize some of the known cognitive factors associated with problem gaming and gaming disorder. These cognitions will be divided into two broad categories: (1) cognitive deficits (e.g., impaired executive functioning, hazardous decision-making, or deliberative processes) and (2) cognitive biases (e.g., attentional biases, cognitive distortions, dysfunctional cognitions). This chapter will review and synthesize available research findings and highlight their clinical implications for gaming disorder. The limitations of the research base are considered and some potential avenues for future research are proposed. [less ▲]

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See detailToo good to be cautious: High implicit self-esteem predicts self-reported dangerous mobile phone use
Lannoy, Séverine; Chatard, Armand; Selimbegovic, Leila et al

in Computers in Human Behavior (2020), 103

Mobile phone use and misuse have become a pressing challenge in today's society. Dangerous mobile phone use, such as the use of a mobile phone while driving, is widely practiced, though banned in several ... [more ▼]

Mobile phone use and misuse have become a pressing challenge in today's society. Dangerous mobile phone use, such as the use of a mobile phone while driving, is widely practiced, though banned in several jurisdictions. Research aiming at unfolding the psychological predictors of dangerous mobile phone use have so far been scarce. Especially, researchers have never taken the role of self-esteem into account, which is unfortunate given prior research linking self-esteem to addictive mobile phone use. In the present study, we evaluated the associations between both explicit and implicit self-esteem and dangerous mobile phone use, with a particular focus on phoning while driving. To do so, we assessed implicit self-esteem among 95 participants (89 females) via the Implicit Association Test and explicit self-esteem via a self-reported measure. Problematic mobile phone use and demographic data were assessed with self-reported measures. Implicit self-esteem predicted dangerous mobile phone use, even after we controlled for demographic data and mobile phone dependence. Explicit self-esteem, however, was related to neither dependence nor dangerous use of the mobile phone, thereby supporting the importance of distinguishing between explicit and implicit self-esteem. Our results set the scene for new research avenues regarding mobile phone use while driving. [less ▲]

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See detailAdversarial Embedding: A robust and elusive Steganography and Watermarking technique
Ghamizi, Salah UL; Cordy, Maxime UL; Papadakis, Mike UL et al

Scientific Conference (2020)

We propose adversarial embedding, a new steganography and watermarking technique that embeds secret information within images. The key idea of our method is to use deep neural networks for image ... [more ▼]

We propose adversarial embedding, a new steganography and watermarking technique that embeds secret information within images. The key idea of our method is to use deep neural networks for image classification and adversarial attacks to embed secret information within images. Thus, we use the attacks to embed an encoding of the message within images and the related deep neural network outputs to extract it. The key properties of adversarial attacks (invisible perturbations, nontransferability, resilience to tampering) offer guarantees regarding the confidentiality and the integrity of the hidden messages. We empirically evaluate adversarial embedding using more than 100 models and 1,000 messages. Our results confirm that our embedding passes unnoticed by both humans and steganalysis methods, while at the same time impedes illicit retrieval of the message (less than 13% recovery rate when the interceptor has some knowledge about our model), and is resilient to soft and (to some extent) aggressive image tampering (up to 100% recovery rate under jpeg compression). We further develop our method by proposing a new type of adversarial attack which improves the embedding density (amount of hidden information) of our method to up to 10 bits per pixel. [less ▲]

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See detailBorders and border experiences
Wille, Christian UL; Nienaber, Birte UL

in Wille, Christian; Nienaber, Birte (Eds.) Border Experiences in Europe. Everyday Life - Working Life - Communication - Languages (2020)

The idea of a “Europe without borders” has been contested for the last decade and is increasingly overshadowed by rebordering phenomena. This development has sparked debates within border studies on how ... [more ▼]

The idea of a “Europe without borders” has been contested for the last decade and is increasingly overshadowed by rebordering phenomena. This development has sparked debates within border studies on how borders should be thought of and investigated. The introductory article deals with this and reconstructs the formation and differentiation of the bordering approach. Furthermore, the concept of border experiences is determined as an investigative perspective that is interested in everyday cultural arenas of bordering processes. It puts the agency of ‘border(lands) residents’ in the center and provides insights into everyday cultural border (re)productions.With this in mind, we will present the book articles in the final section. [less ▲]

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See detailBorder Experiences in Europe. Everyday Life - Working Life - Communication - Languages
Wille, Christian UL; Nienaber, Birte UL

Book published by Nomos (2020)

For a decade now, borders in Europe have been back on the political agenda. Border research has responded and is breaking new ground in thinking about and exploring borders. This book follows this ... [more ▼]

For a decade now, borders in Europe have been back on the political agenda. Border research has responded and is breaking new ground in thinking about and exploring borders. This book follows this development and strengthens a perspective that is interested in life realities and that focuses on everyday cultural experiences of borders. The authors reconstruct such experiences in the context of different forms of migration and mobility as well as language contact situations and are sensitive to the freedom of the participants. In this way, they empirically identify everyday cultural usage or appropriation strategies of borders as vastly different experiences of borders. The readers of this volume will gain insights into current developments in border research and life realities in Europe where borders are (made) relevant. With contributions by Christian Wille, Birte Nienaber, Carsten Yndigegn, Isabelle Pigeron-Piroth, Rachid Belkacem, Ursula Roos, Elisabeth Boesen, Ariela House, Ignacy Jóźwiak, Corinne Martin, Erika Kalocsányiová, Xosé-Afonso Álvarez, Konstanze Jungbluth, Florian Dost, Nicole Richter, Dominik Gerst [less ▲]

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See detailExperimental and analytical analysis of the load-bearing capacity Pu of improved dry-stacked masonry
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL

in Journal of Building Engineering (2020), 27

Dry-Stacked Masonry (DSM) as structural load-bearing element is still unexploited because of many factors including the early face-shell cracking, the impacts of the block imperfections on the wall load ... [more ▼]

Dry-Stacked Masonry (DSM) as structural load-bearing element is still unexploited because of many factors including the early face-shell cracking, the impacts of the block imperfections on the wall load-bearing capacity (Pu) and the lack of design code safely predicting Pu. Through experimental tests, this paper investigates a strategy for improving Pu of DSM by placing an additional horizontal contact layer on the top face of raw DSM blocks. The effect of four mixtures used to improve the raw DSM blocks has been investigated. Further, a mathematical model predicting Pu is proposed which takes into account the effects of the block imperfections. In the course of the investigation, 20 DSM wallets and 25 DSM prisms built with raw and improved DSM blocks were tested to failure under axial compression. In the former, the face-shell cracking load (Pcrack) and the load-bearing capacity (Pu) were recorded, while in the latter, the actual contact area was recorded in hundred full bed-joints using Prescale Fujifilm strips. The results showed that a contact layer of well-defined properties increased the actual contact area from 23% to 55% and improved Pu by 31,9%. The mathematical model for the raw DSM blocks predicts Pu with a mean accuracy of 93% and a standard deviation of 12% where the standards EN 1996-1-1 for mortared masonry exhibited a mean accuracy of 137% and a standard deviation of about 29%. Concerning the improved DSM blocks, the proposed model predicts Pu with a mean accuracy of 106% and a standard deviation of 10%, whereas the standards EN 1996-1-1 presents a mean accuracy of 124% and a standard deviation of 9%. [less ▲]

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See detailOvercome of bed-joint imperfections and improvement of actual contact in dry-stacked masonry
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL

in Construction and Building Materials (2020)

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed ... [more ▼]

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed-joint imperfections as well as by height differences between different masonry blocks leading both to high stress concentration. This paper concentrates on the first type on imperfections. Through experimental tests, it analyses the influence of bed-joint roughness on the load bearing capacity and investigates a strategy to improve the load-bearing capacity of DSM by placing an additional horizontal layer on the top face of raw masonry blocks. First, different contact layers using conventional and auxetic materials were applied. Then 20 dry-stacked masonry prisms built with raw and improved masonry blocks were tested under axial compressive load until failure. Prescale Fujifilm strips were used to measure the actual contact in the bed-joints. Experimental tests show that the use of a contact layer with well-defined material properties enables firstly to increase the actual contact area in the bed-joints from 23% to 98% of the nominal contact area and secondly to increase the load-bearing capacity by 14 to 97%. In addition, the contact layer with an auxetic material shows a significant capacity in altering the lateral expansion in the block units. The outcomes show that although the bed joint roughness influences the stress distribution in a dry-stacked masonry block, a contact layer with well-defined material properties enables to overcome the roughness induced by the bed-joint imperfections. [less ▲]

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See detailWhy is the Market Skewness-Return Relationship Negative?
Lehnert, Thorsten UL

Scientific Conference (2019, December 13)

The observed negative relationship between market skewness and excess return or the negative price of market skewness risk in the cross-section of stock returns is somewhat counterintuitive when we ... [more ▼]

The observed negative relationship between market skewness and excess return or the negative price of market skewness risk in the cross-section of stock returns is somewhat counterintuitive when we consider the usual interpretation of e.g. option-implied skewness as an indicator of jump risk or downside risk. One possible explanation for this inconsistency is that there are factors affecting option-implied market skewness other than jump risk in the stock market. In this paper, I find that price pressure associated with “crowded trades” of mutual funds is an important endogenous factor. Given that retail investors are prone to herding, the directional trading of mutual funds is correlated, and their collective actions can generate short-term price pressure on aggregate stock prices. Short sellers systematically exploit these patterns not only in the equity lending market, but also in the options market. In line with this economic channel, I find that firstly, the significant negative relationship between market skewness and returns becomes insignificant, once I control for price pressure. Secondly, the negative relationship is only present for the “bad” downside component of risk-neutral skewness, associated with out-of-the-money put options. For the “good” upside component of risk-neutral skewness, associated with out-of-the-money call options, the relationship is always positive. Thirdly, price pressure affects the skewness-return relationship, which can be clearly distinguished from the impact of flows on the volatility-return relationship in terms of the leverage effect. [less ▲]

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