The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2's Small Carry-on Impactor. The impact ...produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. The ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. The crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. We discuss implications for Ryugu's surface age.
The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu's surface acquired ...with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Hayabusa2
is a sample return mission of JAXA launched on 3 December 2014.
Hayabusa2
is the successor of
Hayabusa
, which returned samples from the asteroid Itokawa to the Earth. Although the design ...of
Hayabusa2
follows that of
Hayabusa
, the former is equipped with some new components. The small carry-on impactor (SCI) is one of those components. The SCI is a compact kinetic impactor designed to remove the asteroid surface regolith locally and create an artificial crater. One of the most important scientific objectives of
Hayabusa2
is to investigate the chemical and physical properties of the internal materials and structures of the target body, asteroid Ryugu.
Hayabusa2
will attempt to observe the resultant crater with some scientific instruments and to get samples from around the crater. High kinetic energy is required to create a meaningful crater, however, the impact system design needs to fit within strict constraints. Complicated functions, such as a guidance and control system, are not permitted. A special type of shaped charge is used for the acceleration of the impactor of the SCI in order to make system simpler. Using this explosion technique makes it possible to accelerate the impactor very quickly and to hit the asteroid without a guidance system. However, the impact operation will be complicated because the explosive is very powerful and it scatters high-speed debris at the detonation. This paper describes an overview of the SCI system, the results of the development testing and an outline of the impact experiment of the
Hayabusa2
mission.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The reflectance spectra of the most abundant meteorites, ordinary chondrites, are different from those of the abundant S-type (mnemonic for siliceous) asteroids. This discrepancy has been thought to ...be due to space weathering, which is an alteration of the surfaces of airless bodies exposed to the space environment. Here we report evidence of space weathering on particles returned from the S-type asteroid 25143 Itokawa by the Hayabusa spacecraft. Surface modification was found in 5 out of 10 particles, which varies depending on mineral species. Sulfur-bearing Fe-rich nanoparticles exist in a thin (5 to 15 nanometers) surface layer on olivine, low-Ca pyroxene, and plagioclase, which is suggestive of vapor deposition. Sulfur-free Fe-rich nanoparticles exist deeper inside (<60 nanometers) ferromagnesian silicates. Their texture suggests formation by metamictization and in situ reduction of Fe2+.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The 405‐kyr eccentricity cycle is a consistent orbital parameter throughout the Phanerozoic that is associated with long‐term variations in global continental weathering. However, a lack of reliable ...geological evidence has hampered the understanding of the relation between the 405‐kyr eccentricity cycle and continental weathering during the Cretaceous. Os isotopic ratios (187Os/188Os) of the sedimentary record reflect the balance between radiogenic Os derived from continental weathering and Os derived from unradiogenic sources (e.g., hydrothermal activity, weathering of mafic rocks, and extraterrestrial sources). This ratio is therefore considered as a good proxy for the evaluation of short‐term changes in continental weathering patterns. To trace orbital‐paced continental weathering, this study reconstructs the marine Os isotopic records in upper Hauterivian to lower Barremian (Lower Cretaceous) carbonate rocks in central Italy, where previous studies have reported that variations in clay mineral composition are paced by the 405‐kyr cycle. Our new Os isotopic record documents periodic oscillations of 187Os/188Os between 0.7 and 0.9 that correspond to the 405‐kyr Earth's eccentricity cycle. Because the sedimentary interval with radiogenic 187Os/188Os values (∼0.9) corresponds to a time interval characterized by a humid climate in areas surrounding the Tethys, variations in the 187Os/188O values likely reflect cyclic changes in continental weathering caused by eccentricity‐paced intensification of monsoonal activity at low latitudes. This variation could have been further amplified by increased input of radiogenic Os from Paleozoic shale and Precambrian crust at higher latitudes that resulted from a latitudinal shift of the intertropical convergence zone.
Key Points
Hauterivian marine 187Os/188Os cyclically varied following the 405‐kyr eccentricity
405‐kyr eccentricity enhanced monsoon that intensified the continental weathering
187Os/188Os record does not support the massive volcanic event at the Faraoni Level
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The Small Carry-on Impactor (SCI) equipped on
Hayabusa2
was developed to produce an artificial impact crater on the primitive Near-Earth Asteroid (NEA) 162173 Ryugu (Ryugu) in order to explore the ...asteroid subsurface material unaffected by space weathering and thermal alteration by solar radiation. An exposed fresh surface by the impactor and/or the ejecta deposit excavated from the crater will be observed by remote sensing instruments, and a subsurface fresh sample of the asteroid will be collected there. The SCI impact experiment will be observed by a Deployable CAMera 3-D (DCAM3-D) at a distance of ∼1 km from the impact point, and the time evolution of the ejecta curtain will be observed by this camera to confirm the impact point on the asteroid surface. As a result of the observation of the ejecta curtain by DCAM3-D and the crater morphology by onboard cameras, the subsurface structure and the physical properties of the constituting materials will be derived from crater scaling laws. Moreover, the SCI experiment on Ryugu gives us a precious opportunity to clarify effects of microgravity on the cratering process and to validate numerical simulations and models of the cratering process.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Aim
To evaluate the efficacy of a prototype root canal dressing containing surface pre‐reacted glass–ionomer (S‐PRG) fillers on repairing induced periapical lesions in a rat model. Calcium hydroxide ...Ca(OH)2 was applied as a comparison in the healing process.
Methodology
The pulp chambers of the maxillary first molars in 64 male Wistar rats aged 16 weeks were opened to induce periapical lesions. After 28 days, the mesial canal of each tooth was prepared, irrigated with 2.5% sodium hypochlorite only (control group: irrigation) or followed by the respective dressing Ca(OH)2 group, irrigation + Ca(OH)2; S‐PRG group, irrigation + S‐PRG and restored with composite resin for 3 or 7 days (10/group). Four rats with healthy molars were used as blank controls. Descriptive analysis of the periapical radiographs, haematoxylin and eosin staining and immunohistochemical observation was performed 3 and 7 days after treatment. The periapical grey value, CD68 macrophages and osteoclasts (cathepsin‐K) were quantified and statistically analysed with Tukey’s honest significant difference test. A significant difference was achieved when P values were <0.05.
Results
S‐PRG and Ca(OH)2 dressings were associated with increased periapical grey values and inhibited osteoclast activity at 3 and 7 days; a significant difference in radiographic results and the number of osteoclasts was obtained at 3 and 7 days compared with the control group (P < 0.05). Reparative tissue was observed histologically in the space of the periapical resorbed necrotic area after S‐PRG and Ca(OH)2 treatment for 3 and 7 days. The number of macrophages was significantly decreased at 3 and 7 days in the S‐PRG and Ca(OH)2 specimens when compared with the controls (P < 0.05).
Conclusions
In a rat experimental model, the S‐PRG root canal dressing was comparable to Ca(OH)2 in promoting the healing of experimentally induced periapical lesions. S‐PRG paste has the potential to be used as an alternative intracanal dressing in teeth with apical periodontitis.
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BFBNIB, CMK, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A projectile accelerated by the Hayabusa2 Small Carry-on Impactor successfully produced an artificial impact crater with a final apparent diameter of 14.5 ± 0.8 m on the surface of the near-Earth ...asteroid 162173 Ryugu on April 5, 2019. At the time of cratering, Deployable Camera 3 took clear time-lapse images of the ejecta curtain, an assemblage of ejected particles forming a curtain-like structure emerging from the crater. Focusing on the optical depth of the ejecta curtain and comparing it with a theoretical model, we infer the size of the ejecta particles. As a result, the typical size of the ejecta particles is estimated to be several centimeters to decimeters, although it slightly depends on the assumed size distribution. Since the ejecta particles are expected to come from a depth down to ~1 m, our result suggests that the subsurface layer of Ryugu is composed of relatively small particles compared to the uppermost layer on which we observe many meter-sized boulders. Our result also suggests a deficit of particles of less than ~1 mm in the subsurface layer. These findings will play a key role in revealing the formation and surface evolution process of Ryugu and other small Solar System bodies.
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FMFMET, NUK, UL, UM, UPUK
This study aimed to use short-form visual analogue scale cochlear implantation questionnaires to evaluate subjective aspects at each out-patient visit. The correlation between subjective hearing ...tests using the short-form visual analogue scale and objective hearing outcomes was evaluated.
This study was conducted in a single centre. Cochlear implant users (
= 199) evaluated their hearing on a scale of 0 to 100 for the right, left and both ears. The Japanese speech perception test (CI-2004) Japanese monosyllable speech perception test (67-S) and cochlear implantation threshold were used for the objective cochlear implantation evaluation.
A significant correlation was found between the short-form visual analogue scale questionnaire and objective hearing outcome, for words (
= 0.64) and sentences (
= 0.62) in CI-2004 and 67-S (
= 0.56) tests. No significant correlation was found between the short-form visual analogue scale score and cochlear implantation threshold (
= -0.18).
Short-form visual analogue scale cochlear implantation questionnaires mean cochlear implant users spend less time answering subjective visual analogue scale questionnaires, and clinicians estimate a patient's cochlear implantation hearing and abnormality by chronological evaluation.
Background
Few studies have been conducted on patterns of recurrence after resection for distal cholangiocarcinoma (DCC). The aim of this study was to investigate the incidence and pattern of ...recurrence after resection of DCC, and to evaluate prognostic factors for time to recurrence and recurrence‐free survival (RFS).
Methods
Patients who underwent pancreatoduodenectomy with curative intent for DCC between 2001 and 2010 at one of 30 hospitals in Japan were reviewed retrospectively, with special attention to recurrence patterns. The Cox proportional hazards model was used for multivariable analysis.
Results
In the study interval, 389 patients underwent pancreatoduodenectomy for DCC with R0/M0 status. Recurrence developed in 213 patients (54·8 per cent). The estimated cumulative probability of recurrence was 54·3 per cent at 5 years. An initial locoregional recurrence occurred in 55 patients (14·1 per cent) and initial distant recurrence in 168 (43·2 per cent), most commonly in the liver. Isolated initial locoregional recurrence occurred in 45 patients (11·6 per cent). Independent prognostic factors for time to recurrence and RFS were perineural invasion (P = 0·001 and P = 0·009 respectively), pancreatic invasion (both P < 0·001) and lymph node metastasis (both P < 0·001). RFS worsened as the number of risk factors increased: the 5‐year RFS rate was 70·6 per cent for patients without any risk factors, 50·3 per cent for patients with one factor, 31·8 per cent for those with two factors, and 13·4 per cent when three factors were present.
Conclusion
More than half of patients with DCC experienced recurrence after R0 resection, usually within 5 years. Perineural invasion, pancreatic invasion and positive nodal involvement are risk factors for recurrence.
Adjuvant therapy warranted in selected patients
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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