Museums, conversations, and learning

In this study, 178 groups of visitors were interviewed and recorded during their visits to museums. Three clusters of elements were shown to influence learning: the identity of the visitors, their response to the learning environment, and their explanatory engagement during the visit. A structural equation model using these variables fit well. Further examination revealed that not all conversational behavior was supportive of learning; some actions, such as making frequent personal connections, were detrimental to learning; additionally, silent contemplation was modestly associated with learning. This paper discusses these findings through the experiences of four couples whose outcome measures placed them at the extreme high or low end of the learning distribution

The material role of digital media in connecting with, within, and beyond museums

The connective potentials of digital media have been positioned as a key part of a contemporary museum visitor experience. Using a sociology of translation, we construct a network of visitor experiences using data from a digital media engagement project at a large and multi-sited museum in the United Kingdom. These experiences relate to (dis)connections with the museum, museum objects, and other visitors. Through this analysis we disclose the often contradictory roles of the non-human, including and going beyond the digital, as contributors to the success and failure of attempts to change museum visitor experiences through engagement activities rooted in narratives of participation and connectivity

Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar Planets

Since the 1980's it has been becoming increasingly clear that the Solar System's irregular satellites are collisionally evolved. We derive a general model for the collisional evolution of an irregular satellite swarm and apply it to the Solar System and extrasolar planets. Our model reproduces the Solar System's complement of observed irregulars well, and suggests that the competition between grain-grain collisions and Poynting-Robertson (PR) drag helps set the fate of the dust. Because swarm collision rates decrease over time the main dust sink can change with time, and may help unravel the accretion history of synchronously rotating regular satellites that show brightness asymmetries. Some level of dust must be present on AU scales around the Solar System's giant planets, which we predict may be at detectable levels. We also predict whether dust produced by extrasolar circumplanetary swarms can be detected. The coronagraphic instruments on JWST will have the ability to detect the dust generated by these swarms, which are most detectable around planets that orbit at tens of AU from the youngest stars. Because the collisional decay of swarms is relatively insensitive to planet mass, swarms can be much brighter than their host planets and allow discovery of Neptune-mass planets that would otherwise remain invisible. This dust may have already been detected. The observations of the planet Fomalhaut b can be explained as scattered light from dust produced by the collisional decay of an irregular satellite swarm around a 10 Earth-mass planet. Such a swarm comprises about 5 Lunar masses worth of irregular satellites. Finally, we consider what happens if Fomalhaut b passes through Fomalhaut's main debris ring, which allows the circumplanetary swarm to be replenished through collisions with ring planetesimals. (abridged)Comment: accepted to MNRA

Are debris disks self-stirred?

This paper considers the evidence that debris disks are self-stirred by the formation of Plutos. A model for the dust produced during self-stirring is applied to statistics for A stars. As there is no significant difference between excesses of A-stars <50Myr old, we focus on reproducing the broad trends, the "rise and fall" of the fraction of stars with excesses. Using a population model, we find that the statistics and trends can be reproduced with a self-stirring model of planetesimal belts with radii distributed between 15-120AU. Disks must have this 15AU minimum radius to show a peak in disk fraction, rather than a monotonic decline. Populations of extended disks with fixed inner and/or outer radii fail to fit the statistics, due mainly to the slow 70um evolution as stirring moves further out in the disk. This conclusion, that debris disks are narrow belts, is independent of the significance of 24um trends for young A-stars. We show that the statistics can also be reproduced with a model in which disks are stirred by secular perturbations from a nearby eccentric planet. Detailed imaging is therefore the best way to characterise the stirring mechanism. From a more detailed look at beta Pictoris Moving Group and TW Hydrae Association A-stars we find that the disk around beta Pictoris is likely the result of secular stirring by the proposed planet at ~10AU; the structure of the HR 4796A disk also points to sculpting by a planet. The two other stars with disks, HR 7012 and eta Tel, possess transient hot dust, though the outer eta Tel disk is consistent with a self-stirred origin. Planet formation provides a natural explanation for the belt-like nature of debris disks, with inner regions cleared by planets that may also stir the disk, and the outer edges set by where planetesimals can form. [abridged]Comment: Accepted to MNRA

Extreme debris disk variability : exploring the diverse outcomes of large asteroid impacts during the era of terrestrial planet formation

The most dramatic phases of terrestrial planet formation are thought to be oligarchic and chaotic growth, on timescales of up to 100─200 Myr, when violent impacts occur between large planetesimals of sizes up to protoplanets. Such events are marked by the production of large amounts of debris, as has been observed in some exceptionally bright and young debris disks (termed extreme debris disks). Here we report five years of Spitzer measurements of such systems around two young solar-type stars: ID8 and P1121. The short-term (weekly to monthly) and long-term (yearly) disk variability is consistent with the aftermaths of large impacts involving large asteroid-sized bodies. We demonstrate that an impact-produced clump of optically thick dust, under the influence of the dynamical and viewing geometry effects, can produce short-term modulation in the disk light curves. The long-term disk flux variation is related to the collisional evolution within the impact-produced fragments once released into a circumstellar orbit. The time-variable behavior observed in the P1121 system is consistent with a hypervelocity impact prior to 2012 that produced vapor condensates as the dominant impact product. Two distinct short-term modulations in the ID8 system suggest two violent impacts at different times and locations. Its long-term variation is consistent with the collisional evolution of two different populations of impact-produced debris dominated by either vapor condensates or escaping boulders. The bright, variable emission from the dust produced in large impacts from extreme debris disks provides a unique opportunity to study violent events during the era of terrestrial planet formation

Dusty Planetary Systems

Extensive photometric stellar surveys show that many main sequence stars show emission at infrared and longer wavelengths that is in excess of the stellar photosphere; this emission is thought to arise from circumstellar dust. The presence of dust disks is confirmed by spatially resolved imaging at infrared to millimeter wavelengths (tracing the dust thermal emission), and at optical to near infrared wavelengths (tracing the dust scattered light). Because the expected lifetime of these dust particles is much shorter than the age of the stars (>10 Myr), it is inferred that this solid material not primordial, i.e. the remaining from the placental cloud of gas and dust where the star was born, but instead is replenished by dust-producing planetesimals. These planetesimals are analogous to the asteroids, comets and Kuiper Belt objects (KBOs) in our Solar system that produce the interplanetary dust that gives rise to the zodiacal light (tracing the inner component of the Solar system debris disk). The presence of these "debris disks" around stars with a wide range of masses, luminosities, and metallicities, with and without binary companions, is evidence that planetesimal formation is a robust process that can take place under a wide range of conditions. This chapter is divided in two parts. Part I discusses how the study of the Solar system debris disk and the study of debris disks around other stars can help us learn about the formation, evolution and diversity of planetary systems by shedding light on the frequency and timing of planetesimal formation, the location and physical properties of the planetesimals, the presence of long-period planets, and the dynamical and collisional evolution of the system. Part II reviews the physical processes that affect dust particles in the gas-free environment of a debris disk and their effect on the dust particle size and spatial distribution.Comment: 68 pages, 25 figures. To be published in "Solar and Planetary Systems" (P. Kalas and L. French, Eds.), Volume 3 of the series "Planets, Stars and Stellar Systems" (T.D. Oswalt, Editor-in-chief), Springer 201

Percutaneous versus surgical strategy for tracheostomy: protocol for a systematic review and meta-analysis of perioperative and postoperative complications

Background: Tracheostomy is one of the most frequently performed procedures in intensive care medicine. The two main approaches to form a tracheostoma are the open surgical tracheotomy (ST) and the interventional strategy of percutaneous dilatational tracheotomy (PDT). It is particularly important to the critically ill patients that both procedures are performed with high success rates and low complication frequencies. Therefore, the aim of this systematic review is to summarize and analyze existing and relevant evidence for peri- and postoperative parameters of safety. Methods/design: A systematic literature search will be conducted in The Cochrane Library, MEDLINE, LILACS, and Embase to identify all randomized controlled trials (RCTs) comparing peri- and postoperative complications between the two strategies and to define the strategy with the lower risk of potentially life-threatening events. A priori defined data will be extracted from included studies, and methodological quality will be assessed according to the recommendations of the Cochrane Collaboration. Discussion: The findings of this systematic review with proportional meta-analysis will help to identify the strategy with the lowest frequency of potentially life-threatening events. This may influence daily practice, and the data may be implemented in treatment guidelines or serve as the basis for planning further randomized controlled trials. Considering the critical health of these patients, they will particularly benefit from evidence-based treatment. Systematic review registration: PROSPERO CRD4201502196