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In positron emission tomography (PET), the original points of emission are unknown, and the scanners record pairs of photons emitting from those origins and creating lines of response (LORs) in random directions. This presents a latent variable problem, since at least one dimension of relevant information is lost. This can be solved by a statistical approach to image reconstruction—modeling the image as a Gaussian mixture model (GMM). This allows us to obtain a high-quality continuous model that is not computationally demanding and does not require postprocessing. In this paper, we propose a novel method of GMM estimation in the PET setting, directly from lines of response. This approach utilizes some well-known and convenient properties of the Gaussian distribution and the fact that the random slopes of the lines are independent from the points of origin. The expectation–maximization (EM) algorithm that is most commonly used to estimate GMMs in the traditional setting here is adapted to lower-dimensional data. The proposed estimation method is unbiased, and simulations and experiments show that accurate reconstruction on synthetic data is possible from relatively small samples. [ABSTRACT FROM AUTHOR]

Using a Bayesian statistical approach, this study aimed to provide a robust assessment of associations between religiosity and personal faith, timing of sexual initiation and sexual risk taking in young people. To produce posterior probability distribution of the estimation of associations, this study combined two population-based surveys of emerging Croatian adults and meta-analytical estimates pertaining to international studies published between 2000 and 2020. Regardless of the prior used, age at sexual debut was delayed by both religiosity (correlations ranged from 0.10 to 0.13) and personal faith (r = 0.09–0.13). Apart from delaying sexual debut, the findings suggest a very limited role of religiosity and personal faith in the protection of sexual and reproductive health among young people. [ABSTRACT FROM AUTHOR]

An image or volume of interest in positron emission tomography (PET) is reconstructed from gamma rays emitted from a radioactive tracer, which are then captured and used to estimate the tracer's location. The image or volume of interest is reconstructed by estimating the pixel or voxel values on a grid determined by the scanner. Such an approach is usually associated with limited resolution of the reconstruction, high computational complexity due to slow convergence and noisy results. This paper presents a novel method of PET image reconstruction using the underlying assumption that the originals of interest can be modelled using Gaussian mixture models. Parameters are estimated from one-dimensional projections using an iterative algorithm resembling the expectation-maximization algorithm. This presents a complex computational problem which is resolved by a novel approach that utilizes L 1 minimization. [ABSTRACT FROM AUTHOR]

An image or volume of interest in positron emission tomography (PET) is reconstructed from gamma rays emitted from a radioactive tracer, which are then captured and used to estimate the tracer's location. The image or volume of interest is reconstructed by estimating the pixel or voxel values on a grid determined by the scanner. Such an approach is usually associated with limited resolution of the reconstruction, high computational complexity due to slow convergence and noisy results. This paper presents a novel method of PET image reconstruction using the underlying assumption that the originals of interest can be modelled using Gaussian mixture models. Parameters are estimated from one-dimensional projections using an iterative algorithm resembling the expectation-maximization algorithm. This presents a complex computational problem which is resolved by a novel approach that utilizes L 1 minimization. [ABSTRACT FROM AUTHOR]

Despite increasing concerns that pornography decreases adolescents' well-being, existing empirical support for this position is largely limited to cross-sectional studies. To explore possible links between adolescent pornography use and psychological well-being more systematically, this study focused on parallel dynamics in pornography use, self-esteem and symptoms of depression and anxiety. A sample of 775 female and 514 male Croatian high school students (Mage at baseline 15.9 years, SD 0.52) from 14 larger secondary schools, who were surveyed 6 times at approximately 5-month intervals, was used for the analyses. The longitudinal data were analyzed using latent growth curve and latent class growth modeling. We observed no significant correspondence between growth in pornography use and changes in the two indicators of psychological well-being over time in either female or male participants. However, a significant negative association was found between female adolescents' pornography use and psychological well-being at baseline. Controlling for group-specific trajectories of pornography use (i.e., latent classes) confirmed the robustness of findings in the both female and male samples. This study's findings do not corroborate the notion that pornography use in middle to late adolescence contributes to adverse psychological well-being, but do not rule out such a link during an earlier developmental phase—particularly in female adolescents. The findings have ramifications for educational and adolescent health specialists, but also for concerned parents. [ABSTRACT FROM AUTHOR]

The rising prevalence of (online) pornography use among, mostly male, adolescents revived social concerns regarding possible effects of pornography use on sexual aggressiveness. Given the paucity of longitudinal explorations of this link, this study focused on the following two research questions: (Q1) Is pornography use during middle to late adolescence related to male adolescents' self-reported sexual aggressiveness; and (Q2) can personality traits and characteristics that have been associated with sexual aggression account for this presumed link? Using data from a six-wave panel sample of 594 male Croatian high-school sophomore students (Mage at baseline  = 15.8 years, SD = 0.52), latent class and latent growth curve modeling were employed to answer these questions. There was a significant baseline difference in the frequency of pornography use between participants who reported no or marginal levels of sexual aggressiveness during the period under observation (20 months) and their peers who reported substantial sexual aggressiveness, with the former reporting significantly lower initial levels of pornography use compared to the latter. Controlling for personality characteristics did not cancel this association. In addition, bullying and reported peer pressure significantly predicted initial levels of pornography use, but not its subsequent change. With the controls omitted from the analysis, a slight average increase in pornography use was observed among adolescents who reported no or lowest levels of sexual aggressiveness. In contrast, pornography use decreased somewhat among their peers who reported moderate sexual aggressiveness. Insights from this study can contribute to school-based sexual violence prevention programs, as well as inform recently proposed pornography literacy programs which aim to assist adolescents in navigating the increasingly sexually explicit online environment. [ABSTRACT FROM AUTHOR]

Findings since 2000 about the association between the frequency of religious service attendance (formal religiosity) and sexual risk taking in adolescents and emerging adults were explored. A systematic literature search (April 2020) focused on articles with data on religiosity and age at sexual debut, number of sexual partners, condom use at most recent sexual intercourse, and consistent condom use. A total of 27 studies with 37,430 participants (M age = 18.4, range: 12–25, 43.5% male) were included. In random-effects meta-analysis, the link between formal religiosity and sexual risk taking was significant only for age at sexual debut (r = 0.09, 95% CI = 0.05, 0.13) and the number of sexual partners (r = −0.14, 95% CI = −0.19, −0.09). Weak associations between the constructs of interest indicate that formal religiosity is not sufficient to protect young people's sexual health. [ABSTRACT FROM AUTHOR]

Investors' decisions on capital markets depend on their anticipation and preferences about risk, and volatility is one of the most common measures of risk. This paper proposes a method of estimating the market price of volatility risk by incorporating both conditional heteroscedasticity and nonlinear effects in market returns, while accounting for asymmetric shocks. We develop a model that allows dynamic risk premiums for the underlying asset and for the volatility of the asset under the physical measure. Specifically, a nonlinear in mean time series model combining the asymmetric autoregressive conditional heteroscedastic model with leverage (NGARCH) is adapted for modeling return dynamics. The local risk-neutral valuation relationship is used to model investors' preferences of volatility risk. The transition probabilities governing the evolution of the price of the underlying asset are adjusted for investors' attitude towards risk, presenting the asset returns as a function of the risk premium. Numerical studies on asset return data show the significance of market shocks and levels of asymmetry in pricing the volatility risk. Estimated premiums could be used in option pricing models, turning options markets into volatility trading markets, and in measuring reactions to market shocks. [ABSTRACT FROM AUTHOR]

Background Research suggests a general link between sexual boredom and sexual desire, but its understanding is currently very limited. Aim To identify distinct (latent) groups of women and men in long-term relationships based on their reported levels of sexual boredom and sexual desire. Methods Latent profile analysis (LPA) was conducted in an online sample of 1223 Portuguese participants aged 18 and 66 years (mean ± SD, 32.75 ± 6.11), using indicators of sexual boredom and partner-related, attractive other–related, and solitary sexual desire to categorize participants. Multinomial logistic regression analysis was carried out to explore predictors and correlates of the latent profiles. Outcomes Sexual boredom was assessed by the Sexual Boredom Scale, while sexual desire was measured with the Sexual Desire Inventory. Results As compared with women, men reported higher levels of sexual boredom and sexual desire. LPA indicated 3 profiles in women and 2 profiles in men. Among women, P1 was characterized by above-average sexual boredom, below-average partner- and attractive other–related sexual desire, and very low solitary sexual desire; P2 by below-average sexual boredom, attractive other–related sexual desire, and solitary sexual desire and above-average partner-related sexual desire; and P3 by above-average sexual boredom, attractive other–related sexual desire, and solitary sexual desire and below-average partner-related sexual desire. In men, P1 was characterized by high sexual boredom, above-average partner-related sexual desire, and high attractive other–related and solitary sexual desire and P2 by below-average sexual boredom and above-average partner-related, attractive other–related, and solitary sexual desire. The latent profiles did not differ according to relationship duration. Overall, the sole consistent correlate of the latent categorization was sexual satisfaction. Clinical Implications In women, above-average levels of sexual boredom were linked to below-average levels of partner-related desire, which suggests likely benefits of helping the couple to minimize or cope better with their sexual routines. In men, participants in the 2 profiles did not differ in partner-related sexual desire, suggesting that clinical interventions dealing with male sexual boredom should investigate factors beyond the current relationship. Strengths and Limitations This study explored different facets of sexual desire and used LPA, rendering advantages over previous research. The male sample has lower statistical power than the female sample. Conclusion Patterns of sexual boredom and sexual desire among individuals in long-term monogamous relationships are distinct and consistently related to sexual satisfaction in women and men and to relationship satisfaction among only women, which have important clinical ramifications. [ABSTRACT FROM AUTHOR]

Although there is some evidence that religious faith may offer protection against sexual risk taking in adolescence and emerging adulthood, no attempts have been made to systematically quantify the association. Using data from studies conducted in the 2000–2020 period, this meta-analysis aimed to estimate the link between religious faith and four sexual risk-taking behaviors in samples of adolescents and emerging adults. Five different search systems were used to conduct a systematic literature search in April 2020. Studies that contained quantitative data on religious faith and at least one indicator of sexual risk taking (age at sexual debut, number of sexual partners, condom use at most recent sexual intercourse, and consistent condom use) were searched for. In total, 35 articles published in peer-reviewed journals, in English, were identified. Random-effects meta-analytic approach was used to assess target associations among 41,758 adolescents and emerging adults (M age = 18.9 years, 37% male). To estimate the effect across the four risk indicators, we employed robust variance estimation (RVE) method. We found small associations between religious faith on the one hand and age at sexual debut (r = 0.08, 95% CI = 0.03, 0.12) and the number of sexual partners on the other hand (r = −0.15, 95% CI = −0.21, −0.09). No association with condom use was observed. With all studies included, the overall effect size was 0.11 (95% CI = 0.06, 0.16), indicating a small (protective) role of religious faith in young people's sexual risk taking. Considering the limited role of religious faith in young people's sexual and reproductive health, comprehensive sexuality education remains essential for risk-reduction, even among more religious young people. • Higher levels of religious faith were associated with later sexual debut. • Higher levels of faith were related to lower reported number of sexual partners. • Both effects were small in size (r = 0.08; r = −0.15). • There is a lack of recent studies on religious faith and condom use. • Young people's sexual and reproductive health seems only marginally linked to faith. [ABSTRACT FROM AUTHOR]

• Block-based sparse polynomial approximation from compressed sensing measurements. • Spline-like model provides a desired level of smoothness. • Spline-like model avoids blocking artifacts and mitigates Runge phenomenon. • Experiments were conducted on real compressive imaging measurements. This paper introduces a novel spline-like parametric model for an image representation obtained directly from compressive imaging (CI) measurements. As a representation basis we use Chebyshev polynomials. To avoid common problem of blocking artifacts in block-based reconstruction algorithms, a desired number of derivatives are equated on the block boundaries in a spline-like fashion. This introduces a new set of constraints that fits into CI setup. Unlike splines, the proposed system of equations is underdetermined to provide a necessary degree of freedom for achieving sparsity by solving an ℓ 1 optimization problem. Recovered coefficients of the parametric model can be further used for image processing where operations can be elegantly defined and calculated. This offers a new framework for acquisition and processing of analog signals without converting them into samples. Experiments on real measurements show that our model achieves sparse representation without visible blocking artifacts from a reduced set of CI measurements. [ABSTRACT FROM AUTHOR]