ABSTRACT
Terrestrial planets covered globally with thick oceans (termed ocean planets) in the habitable zone were previously inferred to have extremely hot climates in most cases. This is because H2O ...high-pressure (HP) ice on the seafloor prevents chemical weathering and, thus, removal of atmospheric CO2. Previous studies, however, ignored melting of the HP ice and horizontal variation in heat flux from oceanic crusts. Here, we examine whether high heat fluxes near the mid-ocean ridge melt the HP ice and thereby remove atmospheric CO2. We develop integrated climate models of an Earth-size ocean planet with plate tectonics for different ocean masses, which include the effects of HP ice melting, seafloor weathering, and the carbonate–silicate geochemical carbon cycle. We find that the heat flux near the mid-ocean ridge is high enough to melt the ice, enabling seafloor weathering. In contrast to the previous theoretical prediction, we show that climates of terrestrial planets with massive oceans lapse into extremely cold ones (or snowball states) with CO2-poor atmospheres. Such extremely cold climates are achieved mainly because the HP ice melting fixes seafloor temperature at the melting temperature, thereby keeping a high weathering flux regardless of surface temperature. We estimate that ocean planets with oceans several tens of the Earth’s ocean mass no longer maintain temperate climates. These results suggest that terrestrial planets with extremely cold climates exist even in the habitable zone beyond the Solar system, given the frequency of water-rich planets predicted by planet formation theories.
Poor oral health and hygiene are increasingly recognized as major risk factors for pneumonia among the elderly. To identify modifiable oral health–related risk factors, we prospectively investigated ...associations between a constellation of oral health behaviors and incident pneumonia in the community-living very elderly (i.e., 85 years of age or older). At baseline, 524 randomly selected seniors (228 men and 296 women; mean age, 87.8 years) were examined for oral health status and oral hygiene behaviors as well as medical assessment, including blood chemistry analysis, and followed up annually until first hospitalization for or death from pneumonia. During a 3-year follow-up period, 48 events associated with pneumonia (20 deaths and 28 acute hospitalizations) were identified. Among 453 denture wearers, 186 (40.8%) who wore their dentures during sleep were at higher risk for pneumonia than those who removed their dentures at night (log rank P = 0.021). In a multivariate Cox model, both perceived swallowing difficulties and overnight denture wearing were independently associated with an approximately 2.3-fold higher risk of the incidence of pneumonia (for perceived swallowing difficulties, hazard ratio HR, 2.31; and 95% confidence interval CI, 1.11–4.82; and for denture wearing during sleep, HR, 2.38; and 95% CI, 1.25–4.56), which was comparable with the HR attributable to cognitive impairment (HR, 2.15; 95% CI, 1.06–4.34), history of stroke (HR, 2.46; 95% CI, 1.13–5.35), and respiratory disease (HR, 2.25; 95% CI, 1.20–4.23). In addition, those who wore dentures during sleep were more likely to have tongue and denture plaque, gum inflammation, positive culture for Candida albicans, and higher levels of circulating interleukin-6 as compared with their counterparts. This study provided empirical evidence that denture wearing during sleep is associated not only with oral inflammatory and microbial burden but also with incident pneumonia, suggesting potential implications of oral hygiene programs for pneumonia prevention in the community.
Deep low‐frequency earthquakes (DLFEs) are ubiquitous seismic activities in the deep parts of volcanoes. Owing to the low signal‐to‐noise ratio, the seismic activities of DLFEs have not been ...characterized in detail; particularly, the linkage between DLFEs and shallow volcanic activity has not been understood sufficiently. In this study, numerous DLFEs have been successfully detected beneath the Hakone volcano, central Japan, by cross‐correlating a template to the continuous seismic signals. The resulting seismic catalog reveals that DLFEs are activated prior to notable earthquake swarms in the shallow part of a volcano and to the crustal expansion caused by a pressure source at a depth of 7 km. Results indicate that the activation of DLFEs reflects the feeding of magmatic fluid from depth. The subsequent increment in the magmatic‐fluid pressure triggers shallow volcanic activities.
Plain Language Summary
Deep low‐frequency earthquakes (DLFEs) are ubiquitous seismic activities in the deep parts of volcanoes. This deep seismicity provides potentially useful information for assessing volcanic hazards or forecasting eruptions because DLFE is thought to be related to deep magmatism. However, owing to its low signal‐to‐noise ratio, such seismic activity has not been characterized in detail; therefore, its linkage to shallow volcanic activity remains unclear. We studied the DLFEs beneath Hakone, which is an active volcano in central Japan, using the matched‐filter technique. We uncovered numerous DLFEs from seismic records spanning 17 years. We observed a statistically well‐supported correlation between the DLFE and shallow‐earthquake swarms/volcanic crustal deformation. Results revealed a recurring pattern of initially deep low‐frequency seismicity, followed by expansion of the volcanic edifice and increasing shallow‐earthquake swarms. This sequence reflects the migration of magmatic‐fluid pressure leading to volcanic events at the surface. These findings not only help scientific enquiry but also will be useful in mitigation of volcanic hazards because DLFE activation is the precursor of shallow volcanic events.
Key Points
Numerous deep low‐frequency earthquakes are detected beneath the Hakone volcano, central Japan, using the matched‐filter technique
Deep low‐frequency earthquakes occur before the volcanic edifice expands, and the shallow swarm activity increases
Activation of deep low‐frequency earthquakes may reflect feeding in the magmatic fluid below Hakone
High strength steel and aluminium alloy sheets were joined by mechanical clinching with dies for control of metal flow. Since the sheets undergo plastic deformation for the joining during the ...mechanical clinching, the high strength steel sheets tend to fracture due to the small ductility. For the upper high strength steel sheet, fracture was caused by the concentration of deformation around the corner of the punch, and cracks were caused by the tensile stress generated in the bulged bottom into the groove of the die for the lower high strength steel sheet. To prevent these defects, metal flow of the sheets was controlled by optimising a shape of the die. For the upper high strength steel sheets, the depth of the die was decreased to prevent the concentration of deformation around the corner of the punch. On the other hand, the groove of the die was eliminated to reduce the tensile stress for the lower high strength steel sheets. The sheets below SPFC780 and SPFC980 were successively joined with the aluminium alloy sheet for the upper and lower high strength steel sheets, respectively.
Multiple steel and aluminium alloy sheets were joined by self-pierce riveting. Self-pierce riveting is attractive for joining multiple and dissimilar sheets, because joining of individual interfaces ...is not necessary unlike the conventional joining processes, i.e. sheets except for a lower sheet are merely pieced with a rivet shirt. The steel sheets ranged from mild steel to ultra-high strength one having 980MPa in tensile strength, and the joinability for three steel and aluminium alloy sheets for various combinations was examined from both experiments and finite element simulation. The joinability was improved by setting a softer sheet uppermost due to smooth piercing. In addition, the joining range for self-piece riveting of three high strength steel and aluminium alloy sheets was extended by optimising a shape of the die, and the ultra-high strength steel, mild steel and aluminium alloy sheets were successfully joined.
Recognizing the critical need for standardization in strain imaging, in 2010, the European Association of Echocardiography (now the European Association of Cardiovascular Imaging, EACVI) and the ...American Society of Echocardiography (ASE) invited technical representatives from all interested vendors to participate in a concerted effort to reduce intervendor variability of strain measurement. As an initial product of the work of the EACVI/ASE/Industry initiative to standardize deformation imaging, we prepared this technical document which is intended to provide definitions, names, abbreviations, formulas, and procedures for calculation of physical quantities derived from speckle tracking echocardiography and thus create a common standard.
The static and fatigue strengths of mechanically clinched and self-pierce riveted joints in aluminium alloy sheets were compared with those of a resistance spot welded joint. Both static and fatigue ...strengths of the joint for the self-pierce riveting were the highest. Although the static strength for the mechanical clinching was about half for the resistance spot welding, the fatigue strength was almost similar. The mechanism of superiority of fatigue strength for the mechanical clinching and self-pierce riveting and was examined from finite element simulation of elastic loading of the joints. In the resistance spot welding, the stress concentrates at the edge of the weld nugget due to the complete bonding, whereas the concentration of stress is relaxed by the slight slip at the interface between the sheets for the mechanical clinching and self-pierce riveting. In addition, the yield stresses for the mechanical clinching and self-pierce riveting are increased by the work-hardening undergone during the joining processes, whereas the yield stress for the resistance spot welding is reversely decreased by the annealing in the welding. It was found that the mechanical clinching and self-pierce riveting have superior fatigue strength.
PDF
