The B-ring's surface mass density from hidden density waves: Less than meets the eye?

Saturn's B ring is the most opaque ring in our solar system, but many of its fundamental parameters, including its total mass, are not well constrained. Spiral density waves generated by mean-motion resonances with Saturn's moons provide some of the best constraints on the rings' mass density, but detecting and quantifying such waves in the B ring has been challenging because of this ring's high opacity and abundant fine-scale structure. Using a wavelet-based analyses of 17 occultations of the star gamma Crucis observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we are able to examine five density waves in the B ring. Two of these waves are generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances at 96,427 km and 101,311 km from Saturn's center, respectively. Both of these waves can be detected in individual occultation profiles, but the multi-profile wavelet analysis reveals unexpected variations in the pattern speed of the Janus 2:1 wave that might arise from the periodic changes in Janus' orbit. The other three wave signatures are associated with the Janus 3:2, Enceladus 3:1 and Pandora 3:2 Inner Lindblad Resonances at 115,959 km, 115,207 km and 108,546 km. These waves are not visible in individual profiles, but structures with the correct pattern speeds can be detected in appropriately phase-corrected average wavelets. Estimates of the ring's surface mass density derived from these five waves fall between 40 and 140 g/cm^2, even though the ring's optical depth in these regions ranges from 1.5 to almost 5. This suggests that the total mass of the B ring is most likely between one-third and two-thirds the mass of Saturn's moon Mimas.Comment: 40 Pages, 21 Figures, Accepted for publication in Icarus, a few typos fixe

A Tidally-Disrupted Asteroid Around the White Dwarf G29-38

The infrared excess around the white dwarf G29-38 can be explained by emission from an opaque flat ring of dust with an inner radius 0.14 of the radius of the Sun and an outer radius approximately equal to the Sun's. This ring lies within the Roche region of the white dwarf where an asteroid could have been tidally destroyed, producing a system reminiscent of Saturn's rings. Accretion onto the white dwarf from this circumstellar dust can explain the observed calcium abundance in the atmosphere of G29-38. Either as a bombardment by a series of asteroids or because of one large disruption, the total amount of matter accreted onto the white dwarf may have been comparable to the total mass of asteroids in the Solar System, or, equivalently, about 1% of the mass in the asteroid belt around the main sequence star zeta Lep.Comment: ApJ Letters, in pres

Alcohol and healthy ageing: a challenge for alcohol policy

Objectives: This paper presents findings of a qualitative study of older people's use of alcohol during retirement and identifies ways that an improved understanding of older people's drinking can inform policy approaches to alcohol and active and healthy ageing. Study design: Qualitative semi-structured interviews conducted with a self-selecting sample of retired people. Methods: Participants were recruited from three geographical locations in the West of Scotland. A quota sampling design was used to ensure a broad spread of participants in terms of socio-economic position, age and gender. In total 40 participants were interviewed and the data analysed thematically using Braun and Clarke's (2006) approach. Results: Amongst those who used alcohol, it was most often framed in terms of pleasure, relaxation, socialising and as a way to mark the passage of time. Alcohol was often associated with social occasions and interactions both in private and in public spaces. There were also many examples of the use of imposed routines to limit alcohol use and of a decreasing volume of alcohol being consumed as participants aged. This suggests that older people are often active in constructing what they regard as ‘healthier’ routines around alcohol use. However, processes and circumstances associated with ageing can lead to risk of social isolation and/or increased alcohol consumption. Such processes include retirement from paid work and other ‘biographical disruptions’ such as caring for a partner, bereavement and/or loss of social networks. Conclusions: These findings highlight processes that can result in changes in drinking habits and routines. Whilst these processes can be associated with a reduction or cessation of alcohol use as people age, they can also be associated with increased risk of harmful alcohol consumption. Fractured or disrupted routines, particularly those associated with bereavement or the burden of caring responsibilities, through increasing the risk of loneliness and isolation, can construct increased risk of harmful alcohol consumption. These findings reframe the pathway of risk between ageing and alcohol-related harm by highlighting the vulnerability to harmful drinking practices brought by fracture or sudden change of routine. The findings point to a role for public health in supporting the reconstruction of routines that provide structure and meaning and can be used to actively manage the benefits and harms associated with drinking

You Said You Would! The Predictability of Other's Behavior From Their Intentions Determines Predictive Biases in Action Perception.

The perception of an action is shifted farther along the observed trajectory if the observer has prior knowledge of the actor's intention. This intention-action prediction effect is explained by predictive perception models, wherein sensory input is interpreted in light of expectancies. This study altered the precision of the prediction by varying the predictability of the action from the intention, to increase/decrease the predictive perceptual bias. Participants heard an actor state an intention ("I'll take it"/"I'll leave it") before the actor reached or withdrew from an object, thus confirming or contradicting the intention. The intention was predictive of the action (75% congruency) for one group and counterpredictive (25%) for another. The action disappeared midmovement and participants estimated the disappearance position. The intention-action prediction effect was greater if the intention was predictive than if counterpredictive. However, participants needed to explicitly know the predictability rates (Experiments 1 and 3). No group differences emerged when both groups believed the intention was nonpredictive (Experiment 2a), nor when a nonpredictive intention was believed to be (counter)predictive (Experiment 2b). The perception of others behavior is determined by its predictability from their intentions, and the precision of our social predictions is adapted to individual differences in behavior. (PsycINFO Database Recor