In order to investigate the self-healing capability of fibre reinforced cementitious composites (FRCC), mechanical properties and surface morphology of crack in FRCC were studied. Three types of FRCC specimens containing (1) polyethylene (PE) fibre, (2) steel cord (SC) fibre, and (3) hybrid fibres composite (both of PE and SC) were prepared. These specimens, in which cracks were introduced by tension test, were retained in water for 28 days. The self-healing capability of the specimens was investigated by means of microscope observation, water permeability test, tension test and backscattered electron image analysis. It was found that many very fine fibres of PE were bridging over the crack and crystallization products became easy to be attached to a large number of PE fibres. As a result, water permeability coefficient decreased and tensile strength was improved significantly. Therefore amount of the PE fibre per volume was indicated to have a great influence on self-healing. Furthermore, by means of backscattered electron image analysis, it was also shown that the difference of hydration degree in each FRCC has only little influence on the self-healing capability in case of the employed test series.

We report the discovery of a new ultra-faint dwarf satellite companion of the Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru Strategic Program. This new satellite, Virgo I, which is located in the constellation of Virgo, has been identified as a statistically significant (5.5σ) spatial overdensity of star-like objects with a well-defined main sequence and red giant branch in their color-magnitude diagram. The significance of this overdensity increases to 10.8σ when the relevant isochrone filter is adopted for the search. Based on the distribution of the stars around the likely main sequence turn-off at r ∼ 24 mag, the distance to Virgo I is estimated as 87 kpc, and its most likely absolute magnitude calculated from a Monte Carlo analysis is M V = −0.8 ± 0.9 mag. This stellar system has an extended spatial distribution with a half-light radius of 38 +12 −11 pc, which clearly distinguishes it from a globular cluster with comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites known and is located beyond the reach of the Sloan Digital Sky Survey. This demonstrates the power of this survey program to identify very faint dwarf satellites. This discovery of Virgo I is based only on about 100 square degrees of data, thus a large number of faint dwarf satellites are likely to exist in the outer halo of the Milky Way.

We present the results from a search for new Milky Way (MW) satellites from the first two years of data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) ∼ 300 deg 2 and report the discovery of a highly compelling ultra-faint dwarf galaxy candidate in Cetus. This is the second ultra-faint dwarf we have discovered after Virgo I reported in our previous paper. This satellite, Cetus III, has been identified as a statistically significant (10.7σ) spatial overdensity of star-like objects, which are selected from a relevant isochrone filter designed for a metal-poor and old stellar population. This stellar system is located at a heliocentric distance of 251 +24 −11 kpc with a most likely absolute magnitude of M V = −2.4 ± 0.6 mag estimated from a Monte Carlo analysis. Cetus III is extended with a half-light radius of r h = 90 +42 −17 pc, suggesting that this is a faint dwarf satellite in the MW located beyond the detection limit of the Sloan Digital Sky Survey. Further spectroscopic studies are needed to assess the nature of this stellar system. We also revisit and update the parameters for Virgo I finding M V = −0.33 +0.75 −0.87 mag and r h = 47 +19 −13 pc. Using simulations of Λ-dominated cold dark matter models, we predict that we should find one or two new MW satellites from ∼ 300 deg 2 HSC-SSP data, in rough agreement with the discovery rate so far. The further survey and completion of HSC-SSP over ∼ 1, 400 deg 2 will provide robust insights into the missing satellites problem.

We report on the discovery of a new Milky Way (MW) satellite in Boötes based on data from the on-going Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). This satellite, named Boötes IV, is the third ultra-faint dwarf that we have discovered in the HSC-SSP. We have identified a statistically significant (32.3σ) overdensity of stars having characteristics of a metalpoor, old stellar population. The distance to this stellar system is D ⊙ = 209 +20 −18 kpc with a V -band absolute magnitude of M V = −4.53 +0.23 −0.21 mag. Boötes IV has a half-light radius of r h = 462 +98 −84 pc and an ellipticity of 0.64 +0.05 −0.05 , which clearly suggests that this is a dwarf satellite galaxy. We also found another overdensity that appears to be a faint globular cluster with M V = −0.20 +0.59 −0.83 mag and r h = 5.9 +1.5 −1.3 pc located at D ⊙ = 46 +4 −4 kpc. Adopting the recent prediction for the total population of satellites in a MW-sized halo by Newton et al. (2018), which combined the characteristics of the observed satellites by the Sloan Digital Sky Survey and the Dark Energy Survey with the subhalos obtained in ΛCDM models, we estimate that there should be about two MW satellites at M V ≤ 0 in the ∼ 676 deg 2 covered by HSC-SSP, whereas that area includes six satellites (Sextans, Leo IV, Pegasus III, Cetus III, Virgo I and Boötes IV).Thus, the observed number of satellites is larger than the theoretical prediction. On the face of it, we have a problem of too many satellites, instead of the well-known missing satellites problem whereby the ΛCDM theory overpredicts the number of satellites in a MW-sized halo. This may imply that the models need more refinements for the assignment of subhalos to satellites such as considering those found by the current deeper survey. Statistically more robust constraints on this issue will be brought by further surveys of HSC-SSP over the planned ∼ 1, 400 deg 2 area.

Various types of fiber reinforced cementitious composites (FRCCs) were experimentally studied to evaluate their self-healing capabilities regarding their watertightness and mechanical properties. Cracks were induced in the FRCC specimens during a tensile loading test, and the specimens were then immersed in static water for self-healing. By water permeability and reloading tests, it was determined that the FRCCs containing synthetic fiber and cracks of width within a certain range (<0.1 mm) exhibited good self-healing capabilities regarding their watertightness. Particularly, the high polarity of the synthetic fiber (polyvinyl alcohol (PVA)) series and hybrid fiber reinforcing (polyethylene (PE) and steel code (SC)) series showed high recovery ratio. Moreover, these series also showed high potential of self-healing of mechanical properties. It was confirmed that recovery of mechanical property could be obtained only in case when crack width was sufficiently narrow, both the visible surface cracks and the very fine cracks around the bridging of the SC fibers. Recovery of the bond strength by filling of the very fine cracks around the bridging fibers enhanced the recovery of the mechanical property.