Hydromagnetic and gravitomagnetic crust-core coupling in a precessing neutron star

We consider two types of mechanical coupling between the crust and the core of a precessing neutron star. First, we find that a hydromagnetic (MHD) coupling between the crust and the core strongly modifies the star's precessional modes when $t_a\le\sim (T_s\times T_p)^{1/2}$; here $t_a$ is the Alfven crossing timescale, and $T_s$ and $T_p$ are the star's spin and precession periods, respectively. We argue that in a precessing pulsar PSR B1828-11 the restoring MHD stress prevents a free wobble of the crust relative to the non-precessing core. Instead, the crust and the proton-electron plasma in the core must precess in unison, and their combined ellipticity determines the period of precession. Link has recently shown that the neutron superfluid vortices in the core of PSR B1828-11 cannot be pinned to the plasma; he has also argued that this lack of pinning is expected if the proton Fermi liquid in the core is type-I superconductor. In this case, the neutron superfluid is dynamically decoupled from the precessing motion. The pulsar's precession decays due to the mutual friction between the neutron superfluid and the plasma in the core. The decay is expected to occur over tens to hundreds of precession periods and may be measurable over a human lifetime. Such a measurement would provide information about the strong n-p interaction in the neutron-star core. Second, we consider the effect of gravitomagnetic coupling between the neutron superfluid in the core and the rest of the star and show that this coupling changes the rate of precession by about 10%. The general formalism developed in this paper may be useful for other applications.Comment: 6 page

Long-Term evolution of Discs around Magnetic Stars

We investigate the evolution of a thin viscous disc surrounding magnetic star, including the spindown of the star by the magnetic torques it exerts on the disc. The transition from an accreting to a non-accreting state, and the change of the magnetic torque across the corotation radius are included in a generic way, the widths of the transition taken in the range suggested by numerical simulations. In addition to the standard accreting state, two more are found. An accreting state can develop into a 'dead' disc state, with inner edge well outside corotation. More often, a 'trapped' state develops, in which the inner disc edge stays close to corotation even at very low accretion rates. The long-term evolution of these two states is different. In the dead state the star spins down incompletely, retaining much of its initial spin. In the trapped state the star asymptotically can spin down to arbitarily low rates, its angular momentum transferred to the disc. We identify these outcomes with respectively the rapidly rotating and the very slowly rotating classes of Ap stars and magnetic white dwarfs.Comment: 14 pages, 8 figures. Accepted by MNRA

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

Accreting Pulsars: Mixing-up Accretion Phases in Transitional Systems

In the last 20 years our understanding of the millisecond pulsar (MSP) population changed dramatically. Thanks to RXTE, we discovered that neutron stars in LMXBs spins at 200-750 Hz frequencies, and indirectly confirmed the recycling scenario, according to which neutron stars are spun up to ms periods during the LMXB-phase. In the meantime, the continuous discovery of rotation-powered MSPs in binary systems in the radio and gamma-ray band (mainly with the Fermi LAT) allowed us to classify these sources into two "spiders" populations, depending on the mass of their companion stars: Black Widow, with very low-mass companion stars, and Redbacks, with larger companions possibly filling their Roche lobes but without accretion. It was soon regained that MSPs in short orbital period LMXBs are the progenitors of the spider populations of rotation-powered MSPs, although a direct link between accretion- and rotation-powered MSPs was still missing. In 2013 XMM-Newton spotted the X-ray outburst of a new accreting MSP (IGR J18245-2452) in a source that was previously classified as a radio MSP. Follow up observations of the source when it went back to X-ray quiescence showed that it was able to swing between accretion- to rotation-powered pulsations in a relatively short timescale (few days), promoting this source as the direct link between the LMXB and the radio MSP phases. Following discoveries showed that there exists a bunch of sources, which alternates X-ray activity phases, showing X-ray pulsations, to radio-loud phases, showing radio pulsations, establishing a new class of MSPs: the Transitional MSP. In this review we describe these exciting discoveries and the properties of accreting and transitional MSPs, highlighting what we know and what we have still to learn about in order to fully understand the (sometime puzzling) behavior of these systems and their evolutive connection (abridged)

Defining the Effect of the 16p11.2 Duplication on Cognition, Behavior, and Medical Comorbidities

IMPORTANCE: The 16p11.2 BP4-BP5 duplication is the copy number variant most frequently associated with autism spectrum disorder (ASD), schizophrenia, and comorbidities such as decreased body mass index (BMI). OBJECTIVES: To characterize the effects of the 16p11.2 duplication on cognitive, behavioral, medical, and anthropometric traits and to understand the specificity of these effects by systematically comparing results in duplication carriers and reciprocal deletion carriers, who are also at risk for ASD. DESIGN, SETTING, AND PARTICIPANTS: This international cohort study of 1006 study participants compared 270 duplication carriers with their 102 intrafamilial control individuals, 390 reciprocal deletion carriers, and 244 deletion controls from European and North American cohorts. Data were collected from August 1, 2010, to May 31, 2015 and analyzed from January 1 to August 14, 2015. Linear mixed models were used to estimate the effect of the duplication and deletion on clinical traits by comparison with noncarrier relatives. MAIN OUTCOMES AND MEASURES: Findings on the Full-Scale IQ (FSIQ), Nonverbal IQ, and Verbal IQ; the presence of ASD or other DSM-IV diagnoses; BMI; head circumference; and medical data. RESULTS: Among the 1006 study participants, the duplication was associated with a mean FSIQ score that was lower by 26.3 points between proband carriers and noncarrier relatives and a lower mean FSIQ score (16.2-11.4 points) in nonproband carriers. The mean overall effect of the deletion was similar (-22.1 points; P 100) compared with the deletion group (P < .001). Parental FSIQ predicted part of this variation (approximately 36.0% in hereditary probands). Although the frequency of ASD was similar in deletion and duplication proband carriers (16.0% and 20.0%, respectively), the FSIQ was significantly lower (by 26.3 points) in the duplication probands with ASD. There also were lower head circumference and BMI measurements among duplication carriers, which is consistent with the findings of previous studies. CONCLUSIONS AND RELEVANCE: The mean effect of the duplication on cognition is similar to that of the reciprocal deletion, but the variance in the duplication is significantly higher, with severe and mild subgroups not observed with the deletion. These results suggest that additional genetic and familial factors contribute to this variability. Additional studies will be necessary to characterize the predictors of cognitive deficits

Force Field Independent Metal Parameters Using a Nonbonded Dummy Model

The cationic dummy atom approach provides a powerful nonbonded description for a range of alkaline-earth and transition-metal centers, capturing both structural and electrostatic effects. In this work we refine existing literature parameters for octahedrally coordinated Mn2+, Zn2+, Mg2+, and Ca2+, as well as providing new parameters for Ni2+, Co2+, and Fe2+. In all the cases, we are able to reproduce both M2+-O distances and experimental solvation free energies, which has not been achieved to date for transition metals using any other model. The parameters have also been tested using two different water models and show consistent performance. Therefore, our parameters are easily transferable to any force field that describes nonbonded interactions using Coulomb and Lennard-Jones potentials. Finally, we demonstrate the stability of our parameters in both the human and Escherichia coli variants of the enzyme glyoxalase 1 as showcase systems, as both enzymes are active with a range of transition metals. The parameters presented in this work provide a valuable resource for the molecular simulation community, as they extend the range of metal ions that can be studied using classical approaches, while also providing a starting point for subsequent parametrization of new metal centers