The angular momentum transport by unstable toroidal magnetic fields

We demonstrate with a nonlinear MHD code that angular momentum can be transported due to the magnetic instability of toroidal fields under the influence of differential rotation, and that the resulting effective viscosity may be high enough to explain the almost rigid-body rotation observed in radiative stellar cores. Only stationary current-free fields and only those combinations of rotation rates and magnetic field amplitudes which provide maximal numerical values of the viscosity are considered. We find that the dimensionless ratio of the effective over molecular viscosity, $\nu_T/\nu$;, linearly grows with the Reynolds number of the rotating fluid multiplied with the square-root of the magnetic Prandtl number - which is of order unity for the considered red sub-giant KIC 7341231. For the considered interval of magnetic Reynolds numbers - which is restricted by numerical constraints of the nonlinear MHD code - there is a remarkable influence of the magnetic Prandtl number on the relative importance of the contributions of the Reynolds stress and the Maxwell stress to the total viscosity, which is magnetically dominated only for Pm $\gtrsim$ 0.5. We also find that the magnetized plasma behaves as a non-Newtonian fluid, i.e. the resulting effective viscosity depends on the shear in the rotation law. The decay time of the differential rotation thus depends on its shear and becomes longer and longer during the spin-down of a stellar core.Comment: Revised version. 7 pages, 9 figures; accepted for publication in A&

Lithium abundance and 6Li/7Li ratio in the active giant HD123351 I. A comparative analysis of 3D and 1D NLTE line-profile fits

Current three-dimensional (3D) hydrodynamical model atmospheres together with NLTE spectrum synthesis, permit to derive reliable atomic and isotopic chemical abundances from high-resolution stellar spectra. Not much is known about the presence of the fragile 6Li isotope in evolved solar-metallicity RGB stars, not to mention its production in magnetically active targets like HD123351. From fits of the observed CFHT spectrum with synthetic line profiles based on 1D and 3D model atmospheres, we seek to estimate the abundance of the 6Li isotope and to place constraints on its origin. We derive A(Li) and the 6Li/7Li isotopic ratio by fitting different synthetic spectra to the Li-line region of a high-resolution CFHT spectrum (R=120 000, S/R=400). The synthetic spectra are computed with four different line lists, using in parallel 3D hydrodynamical CO5BOLD and 1D LHD model atmospheres and treating the line formation of the lithium components in non-LTE (NLTE). We find A(Li)=1.69+/-0.11 dex and 6Li/7Li=8.0+/-4.4 % in 3D-NLTE, using the line list of Mel\'endez et al. (2012), updated with new atomic data for V I, which results in the best fit of the lithium line profile of HD123351. Two other line lists lead to similar results but with inferior fit qualities. Our 2-sigma detection of the 6Li isotope is the result of a careful statistical analysis and the visual inspection of each achieved fit. Since the presence of a significant amount of 6Li in the atmosphere of a cool evolved star is not expected in the framework of standard stellar evolution theory, non-standard, external lithium production mechanisms, possibly related to stellar activity or a recent accretion of rocky material, need to be invoked to explain the detection of 6Li in HD123351.Comment: 16 pages, 11 figures. Accepted for publication in A&

Intermittent Sea Level Acceleration

Using instrumental observations from the Permanent Service for Mean Sea Level (PSMSL), we provide a new assessment of the global sea{level acceleration for the last 2 centuries (1820-2010). Our results, obtained by a stack of tide gauge time series, con firm the existence of a global sea level acceleration (GSLA) and, coherently with independent assessments so far, they point to a value close to 0:01 mm/yr2. However, di fferently from previous studies, we discuss how change points or abrupt inflections in individual sea level time series have contributed to the GSLA. Our analysis, based on methods borrowed from econometrics, suggests the existence of two distinct driving mechanisms for the GSLA, both involving a minority of tide gauges globally. The first effectively implies a gradual increase in the rate of sea level rise at individual tide gauges, while the second is manifest through a sequence of catastrophic variations of the sea level trend. These occurred intermittently since the end of the 19th century and became more frequent during the last four decades

Ice melting and earthquake suppression in Greenland

It has been suggested that the Greenland ice sheet is the cause of earthquake suppression in the region. With few exceptions, the observed seismicity extends only along the continental margins of Greenland, which almost coincide with the ice sheet margin. This pattern has been put forward as further validation of the earthquake suppression hypothesis. In this review, new evidence in terms of ice melting, post-glacial rebound and earthquake occurrence is gathered and discussed to re-evaluate the connection between ice mass unloading and earthquake suppression. In Greenland, the spatiotemporal distribution of earthquakes indicates that seismicity is mainly con- fined to regions where the thick layer of ice is absent and where significant ice melting is presently occurring. A clear correlation between seismic activity and ice melting in Greenland is not found. However, earthquake locations and corresponding depth distributions suggest two distinct governing mechanisms: post-glacial rebound promotes moderate-size crustal earthquakes at Greenland’s regional scale, while current ice melting promotes shallow low magnitude seismicity locall

Modelling the contribution of metacognitions and expectancies to problematic smartphone use

Abstract Background and aims In the current study we have sought to clarify the contribution of metacognitions concerning smartphone use relative to smartphone use expectancies in the relationship between well-established predisposing psychological factors and problematic smartphone use (PSU). We tested a model where psychological distress, impulsivity, and proneness to boredom predict metacognitions about smartphone use and smartphone use expectancies, which in turn predict PSU. Methods A sample of 535 participants (F = 71.2%; mean age = 27.38 ± 9.05 years) was recruited. Results The model accounted for 64% of the PSU variance and showed good fit indices (χ 2 = 16.01, df = 13, P = 0.24; RMSEA [90%CI] = 0.02 [0–0.05], CFI = 0.99; SRMR = 0.03). We found that: (i) when it comes to psychological distress and boredom proneness, negative metacognitions, and both positive and negative expectancies play a mediating role in the association with PSU, with negative metacognitions showing a dominant role; (ii) there is no overlap between positive expectancies and positive metacognitions, especially when it comes to smartphone use as a means for socializing; (iii) impulsivity did not show a significant effect on PSU Direct effects of the predictors on PSU were not found. Discussion and conclusions The current study found additional support for applying metacognitive theory to the understanding of PSU and highlight the dominant role of negative metacognitions about smartphone in predicting PSU

Using the Post—Widder formula to compute the Earth's viscoelastic Love numbers

The post-glacial or post-seismic relaxation of a Maxwell viscoelastic earth, 1-D or slightly laterally heterogeneous, can be calculated in a normal-mode approach, based on an application of the propagator technique. This semi-analytical approach, widely documented in the literature, allows to compute the response of an earth model whose rheological parameters vary quite strongly with depth, at least as accurately and efficiently as by 1-D numerical integration (Runge-Kutta). Its main drawback resides in the need to identify the roots of a secular polynomial, introduced after reformulating the problem in the Laplace domain, and required to transform the solution back to the time domain. Root finding becomes increasingly difficult, and ultimately unaffordable, as the complexity of rheological profiles grows: the secular polynomial gradually gets more ill behaved, and a larger number of more and more closely spaced roots is to be found. Here, we apply the propagator method to solve the Earth's viscoelastic momentum equation, like in the above-mentioned normal-mode framework, but bypass root finding, using, instead, the Post-Widder formula to transform the solution, found again in the Laplace domain, back to the time domain. We test our method against earlier normal-mode results, and prove its effectiveness in modelling the relaxation of earth models with extremely complex rheological profile

Modelling Online Gaming Metacognitions: The Role of Time Spent Gaming in Predicting Problematic Internet Use

© 2020, The Author(s). In recent years there have been growing concerns about problematic Internet use (PIU) as potential mental health problem. Among the many activities available on the Internet, the time spent gaming appears one of the most frequent risk factors in developing PIU. The aim of the current study was to model the relationship between negative affect, metacognitions about online gaming, frequency of online gaming and PIU. A total of 326 Italian gamers (mean age = 27 years, SD = 5.65 years; 93.3% males) participated in the study. The pattern of relationships specified by the theoretical model was examined through path analysis. Results showed that negative affect was directly associated with all other variables. Specifically, positive, strong and direct associations were found between negative affect and both positive and negative metacognitions about online gaming. Moreover, negative metacognitions about online gaming were strongly linked to PIU. Overall, the theoretical model was supported showing that metacognitions about online gaming may play a role in the association between time spent on online gaming to a broader pattern of PIU. Results are discussed within the context of the metacognitive model of psychopathology and clinical implications based on this model are outlined

Creep, Relaxation and Viscosity Properties for Basic Fractional Models in Rheology

The purpose of this paper is twofold: from one side we provide a general survey to the viscoelastic models constructed via fractional calculus and from the other side we intend to analyze the basic fractional models as far as their creep, relaxation and viscosity properties are considered. The basic models are those that generalize via derivatives of fractional order the classical mechanical models characterized by two, three and four parameters, that we refer to as Kelvin-Voigt, Maxwell, Zener, anti-Zener and Burgers. For each fractional model we provide plots of the creep compliance, relaxation modulus and effective viscosity in non dimensional form in terms of a suitable time scale for different values of the order of fractional derivative. We also discuss the role of the order of fractional derivative in modifying the properties of the classical models.Comment: 41 pages, 8 figure

Shallow upper mantle rheology and secular ice sheet fluctuations

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Clinical case seminar - Hypogonadotropic hypogonadism as a presenting feature of late-onset X-linked adrenal hypoplasia congenita

Mutations in the orphan nuclear receptor DAX-1 cause X-linked adrenal hypoplasia congenita. Affected boys usually present with primary adrenal failure in early infancy or childhood. Impaired sexual development because of hypogonadotropic hypogonadism becomes apparent at the time of puberty. We report adult-onset adrenal hypoplasia congenita in a patient who presented with hypogonadism at 28 yr of age. Although he had no clinical evidence of adrenal dysfunction, compensated primary adrenal failure was diagnosed by biochemical testing. Semen analysis showed azoospermia, and he did not achieve fertility after 8 months of treatment with gonadotropins. A novel Y380D DAX-1 missense mutation, which causes partial loss of function in transient gene expression assays, was found in this patient. This case demonstrates that partial loss-of-function mutations in DAX1 can present with hypogonadotropic hypogonadism and covert adrenal failure in adulthood. Further, an important role for DAX-1 in spermatogenesis in humans is confirmed, supporting findings in the Dax1 (Ahch) knockout mouse