Evaluating Conformance to WCAG 2.0: Open Challenges

Web accessibility for people with disabilities is a highly visible area of work in the field of ICT accessibility, including many policy activities in several countries. The commonly accepted guidelines for web accessibility (WCAG 1.0) were published in 1999 and have been extensively used by designers, evaluators and legislators. A new version of these guidelines (WCAG 2.0) was published in 2008. In this paper we point out the main challenges that WCAG 2.0 raises for web accessibility evaluators: the concept of "accessibility supported technologies"; success criteria testability; technique and failure openness, and the aggregation of partial results. We conclude the paper with some recommendations for the future

Gravitational re-accumulation as the origin of most contact binaries and other small body shapes

Asteroids show a variety of shapes, ranging from roundish to elongated to binary systems and ‘contact binaries’ like (25143) Itokawa, the target of the Hayabusa mission (JAXA). These bodies spend most of their time within a collisional system, the asteroid belt, where impact processes are relatively frequent. Speculations on the origin of asteroid shapes invoke mechanisms such as collisions and spin-up effects. N-body numerical simulations of fragment evolution following catastrophic collisions have been recently carried out (Campo Bagatin et al., 2018). In this study the idea that the stochastic process of gravitational re-accumulation may be responsible for many observed asteroid shapes is introduced. Asteroid ‘contact binaries’ are shown to be regularly produced by the gravitational re-accumulation process following catastrophic impact. Similar processes may have occurred in the case of some comets and Trans-Neptunian Objects.ACB and PGB acknowledge funding from AYA2016-79500-R (2016–2018) grant by the Spanish Ministerio de Economía, Industria y Competitividad

Internal structure of asteroid gravitational aggregates

The internal structure of small asteroids is fundamentally unknown due to lack of direct measurements. The only clues on this topic come from theoretical considerations and from the comparison between measured bulk densities of asteroids and their corresponding analogue meteorite densities. The mass distribution and the void space between components in a gravitational aggregate determine the structure of such objects. In this paper we study numerically the dynamical and collisional evolution of the reaccumulation process of the fragments created in catastrophic collisions of asteroids in the 500 m to 10 km size range. An effort to consider irregularly shaped fragments is made by taking advantage of the results of laboratory experiments that provide relative mass distributions and aspect ratios for fragment shapes. We find that the processes that govern the final properties of the resulting aggregates are mainly stochastic, however interesting patterns can be identified. This study matches estimated macro-porosities of S-type asteroids and finds a loose linear relationship between macro-prorosity of asteroid aggregates and the mass ratio of the largest component to the whole aggregate (for both S and C-types). As for observed C-type asteroids, we conclude that their interiors should be more fragmented than in the case of S-type asteroids, explaining the difference in the estimated macro-porosity of real C asteroids with respect to S-types. We also find that slow rotators may be interpreted as a natural result in the process of gravitational reaccumulation.This work has been possible thanks to the grants AYA2008- 06202C0303 and AYA2011-30106-C02-02 by the extinct Spanish Ministerio de Ciencia e Innovación

Impact simulation in the gravity regime: Exploring the effects of parent body size and internal structure

In this work we extend the systematic investigation of impact outcomes of 100-km-diameter targets started by Durda et al. (2007) and Benavidez et al. (2012) to targets of D = 400 km using the same range of impact conditions and two internal structures: monolithic and rubble-pile. We performed a new set of simulations in the gravity regime for targets of 400 km in diameter using these same internal structures. This provides a large set of 600 simulations performed in a systematic way that permits a thorough analysis of the impact outcomes and evaluation of the main features of the size frequency distribution due mostly to self-gravity. In addition, we use the impact outcomes to attempt to constrain the impact conditions of the asteroid belt where known asteroid families with a large expected parent body were formed. We have found fairly good matches for the Eunomia and Hygiea families. In addition, we identified a potential acceptable match to the Vesta family from a monolithic parent body of 468 km. The impact conditions of the best matches suggest that these families were formed in a dynamically excited belt. The results also suggest that the parent body of the Eunomia family could be a monolithic body of 382 km diameter, while the one for Hygiea could have a rubble-pile internal structure of 416 km diameter.This work was partly supported by the Spanish Ministerio de Ciencia e Innovacion (now expired) grant AYA2011-30106-C02-02

Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL5

Trojan asteroids are small bodies orbiting around the L4 or L5 Lagrangian points of a Sun-planet system. Due to their peculiar orbits, they provide key constraints to the Solar System evolution models. Despite numerous dedicated observational efforts in the last decade, asteroid 2010 TK7 has been the only known Earth Trojan thus far. Here we confirm that the recently discovered 2020 XL5 is the second transient Earth Trojan known. To study its orbit, we used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories. Our study of its orbital stability shows that 2020 XL5 will remain in L4 for at least 4 000 years. With a photometric analysis we estimate its absolute magnitude to be Hr=18.58+0.16−0.15, and color indices suggestive of a C-complex taxonomy. Assuming an albedo of 0.06 ± 0.03, we obtain a diameter of 1.18 ± 0.08 km, larger than the first known Earth Trojan asteroid.The work of TS-R was carried out through grant APOSTD/2019/046 by Generalitat Valenciana (Spain). This work was (partially) funded by the Spanish MICIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” by the “European Union” through grant RTI2018-095076-B-C21, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ‘María de Maeztu’) through grant CEX2019-000918-M. P-YL acknowledges NEO-MAPP project under H2020-SPACE-2019 GA 870377. PGB, and ACB acknowledge funding from the Spanish MICINN project RTI2018-099464-B-I00. AA-C acknowledges support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). DO was supported by National Science Centre, Poland, grants numbers 2017/26/D/ST9/00240 and 2017/25/B/ST9/00740