No abstract

Working memory capacity (WMC) and fluid intelligence (Gf) are highly correlated, but what accounts for this relationship remains elusive. Process-overlap theory (POT) proposes that the positive manifold is mainly caused by the overlap of domain-general executive processes which are involved in a battery of mental tests. Thus, executive processes are proposed to explain the relationship between WMC and Gf. The current study aims to (1) achieve a relatively purified representation of the core executive processes including shifting and inhibition by a novel approach combining experimental manipulations and fixed-links modeling, and (2) to explore whether these executive processes account for the overlap between WMC and Gf. To these ends, we reanalyzed data of 215 university students who completed measures of WMC, Gf, and executive processes. Results showed that the model with a common factor, as well as shifting and inhibition factors, provided the best fit to the data of the executive function (EF) task. These components explained around 88% of the variance shared by WMC and Gf. However, it was the common EF factor, rather than inhibition and shifting, that played a major part in explaining the common variance. These results do not support POT as underlying the relationship between WMC and Gf.

No abstract

This large-scale pre-registered study examined the development of working memory and inhibitory control in a sample of 144 children aged between 3 and 6 years. Two paradigms – one a version of a spatial conflict task, the other a combined continuous performance test and go/no-go task – were adapted to allow the orthogonal manipulation of working memory and inhibitory demands. This allowed for the simultaneous measurement of these functions within each paradigm, removing concerns of task-specific variance and testing an interactive model of executive function that assumes that working memory and inhibition compete for a shared pool of executive resources. In addition, latent working memory and inhibition variables extracted from the tasks were correlated with parental reports of participants’ temperament, including effortful control. The novel experimental tasks successfully and reliably captured developmental and individual differences in working memory and inhibitory control. However, these factors did not interact with one another in an over-additive fashion or correlate meaningfully with parental ratings of effortful control. These findings support the separability of executive functions in this age range while raising important questions about how best to measure the development of executive control among young children.

The single-layered molybdenum disulfide (<inline-formula><tex-math id="M6">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M6.png"/></alternatives></inline-formula>) is a two-dimensional nanomaterial with wide potential applications due to its excellent electrical and frictional properties. However, there have been few investigations of its mechanical properties up to now, and researchers have not paid attention to its nonlinear mechanical properties under the multi-fields co-existing environment. The present paper proposed a nonlinear plate theory to model the effect of finite temperatures on the single-layered <inline-formula><tex-math id="M7">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M7.png"/></alternatives></inline-formula>. It is similar to the classical plate theory that both the in-plane stretching deformation and the out-of-plane bending deformation are taken into account in the new theory. However, the new theory consists of two independent in-plane mechanical parameters and two independent out-of-plane mechanical parameters. Neither of the two out-of-plane mechanical parameters in the new theory, which describe the resistance of <inline-formula><tex-math id="M8">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M8.png"/></alternatives></inline-formula> to the bending and the twisting, depends on the structure’s thickness. This reasonably avoids the Yakobson paradox: uncertainty stemming from the thickness of the single-layered two-dimensional structures will lead to the uncertainty of the structure’s out-of-plane stiffness. The new nonlinear plate equations are then solved approximately through the Galerkin method for the thermoelastic mechanical problems of the graphene and <inline-formula><tex-math id="M9">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M9.png"/></alternatives></inline-formula>. The approximate analytic solutions clearly reveal the effects of temperature and structure stiffness on the deformations. Through comparing the results of two materials under combined temperature and load, it is found, for the immovable boundaries, that (1) the thermal stress, which is induced by the finite temperature, reduces the stiffness of <inline-formula><tex-math id="M10">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M10.png"/></alternatives></inline-formula>, but increases the stiffness of graphene; (2) the significant difference between two materials is that the graphene’s in-plane stiffness is greater than the <inline-formula><tex-math id="M11">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M11.png"/></alternatives></inline-formula>’s, but the graphene’s out-of-plane stiffness is less than the <inline-formula><tex-math id="M12">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M12.png"/></alternatives></inline-formula>’s. Because the <inline-formula><tex-math id="M13">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M13.png"/></alternatives></inline-formula>’s bending stiffness is much greater than graphene’s, the graphene’s deformation is greater than MoS₂’s with a small load. However, the graphene’s deformation is less than the <inline-formula><tex-math id="M14">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M14.png"/></alternatives></inline-formula>’s with a large load since the graphene’s in-plane stretching stiffness is greater than the MoS₂’s. The present research shows that the applied axial force and ambient temperature can conveniently control the mechanical properties of single-layered two-dimensional nanostructures. The new theory provides the basis for the intensive research of the thermoelastic mechanical problems of <inline-formula><tex-math id="M15">\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M15.png"/></alternatives></inline-formula>, and one can easily apply the theory to other single-layered two-dimensional nanostructures.