Spectral estimation for locally stationary time series with missing observations

Time series arising in practice often have an inherently irregular sampling structure or missing values, that can arise for example due to a faulty measuring device or complex time-dependent nature. Spectral decomposition of time series is a traditionally useful tool for data variability analysis. However, existing methods for spectral estimation often assume a regularly-sampled time series, or require modifications to cope with irregular or ‘gappy’ data. Additionally, many techniques also assume that the time series are stationary, which in the majority of cases is demonstrably not appropriate. This article addresses the topic of spectral estimation of a non-stationary time series sampled with missing data. The time series is modelled as a locally stationary wavelet process in the sense introduced by Nason et al. (J. R. Stat. Soc. B 62(2):271–292, 2000) and its realization is assumed to feature missing observations. Our work proposes an estimator (the periodogram) for the process wavelet spectrum, which copes with the missing data whilst relaxing the strong assumption of stationarity. At the centre of our construction are second generation wavelets built by means of the lifting scheme (Sweldens, Wavelet Applications in Signal and Image Processing III, Proc. SPIE, vol. 2569, pp. 68–79, 1995), designed to cope with irregular data. We investigate the theoretical properties of our proposed periodogram, and show that it can be smoothed to produce a bias-corrected spectral estimate by adopting a penalized least squares criterion. We demonstrate our method with real data and simulated examples.     

From Play to Art—From Experience to Insight

This article investigates the role of play and playlike activities (imagination, art) in developing and using symbolic tools. We understand processes of development of symbolic tools as coordination between two types of relationships: the subject–object relationships and the subject–subject relationships. This coordination begins when a new, playlike frame of activity is introduced in the interaction. The imaginary frame of activity changes relationships between the participants. Furthermore, the imaginary activity frame may enter into interaction with the out-of-play activity frames (“reality” frames). Structures and relationships built within the imaginary frames are then used to shape the actual understanding of the world (subject–object relationship) as well as the interpersonal relationships and identities of the participants.

Introduction and further development of imaginary frames is a recursive process that takes place on different but related time scales: from microdevelopment through ontogenetic development to cultural development. Our project was designed to demonstrate some of the key moments that occur in the symbolic construction, in an “untangled” manner. To that effect, we designed a drama workshop to outline and illustrate processes that take place at the point of introduction of a new, imaginary frame and at the point when this imaginary frame begins to interact with the out-of-play frames. The aim of the workshop was to magnify each stage in construction of semiotic tools by “walking” professional researchers through a series of playlike activities.     

Revisiting the Association between Pornography Use and Risky Sexual Behaviors: The Role of Early Exposure to Pornography and Sexual Sensation Seeking

Among the suggested problems and harms associated with widespread pornography use among young people, risky sexual behaviors have been frequently mentioned. To further explore this public health concern, this article analyzed sexual sensation seeking (SSS) as a potential confounder of the association between pornography use and sexual risks using data collected in 2010 from a population-based sample of young Croatian adults aged 18 to 25 (n = 1,005). Significant, but small, correlations were found between the indicators of pornography use (age at first exposure, frequency of use in the past 12 months, and personal importance of pornography) and sexual risk taking. However, in a multivariate analysis, only age at first exposure to pornography remained a significant, albeit weak, predictor of sexual risk taking among both women and men. SSS, defined as the dispositional tendency toward the impulsive pursuit of sexual arousal and stimulation, neither confounded nor moderated this association. Overall, the findings do not support the notion that pornography use is substantially associated with sexual risk taking among young adults, but suggest that early exposure to sexually explicit material and high SSS are additive risk factors for sexual risk taking.     

Social stability challenged by Covid-19: Pandemics,inequality and policy responses

The public health measures implemented to limit the COVID-19 pandemic are likely to affect economic inequalities. In this paper we first provide a theoretical framework to analyse how income inequality contributes shaping the trade-off between economic lockdown and contagion. Our empirical analysis on EU countries shows that the lockdown is likely to significantly increase inequality and poverty and that the magnitude of the change is larger in more unequal countries. To avoid social collapse, countries must consider inequality as an additional source of fragility, while supranational, coordinated health and fiscal policies are needed in the interest of all European economies.