Giant impact on early Ganymede and its subsequent reorientation

The origin and early evolution of the Jovian moon Ganymede, known to have an internal ocean, have garnered considerable interest in the field of origin of satellites and life. Ganymede has an ancient impact structure, called a furrow system. The furrow system is the largest impact structures in the outer solar system and the impact should have significantly affected Ganymede's early history; however, its impact is poorly understood. Here we show that mass redistribution induced by the furrow-forming impact caused a reorientation (true polar wander) of Ganymede. The center of the furrow system is located close to the tidal axis, indicating that the impact created a positive mass anomaly that reoriented the impact site toward the tidal axis. We found that an impactor with a radius of 150 km and an incidence angle between 60 degree and 90 degree can reproduce the current location of the furrow system. Furthermore, this ejecta model is adoptable in Pluto's reorientation. Although it is proposed that Pluto's reorientation indicates the presence of a global ocean, our model indicates that it occurs even if no ocean.Comment: manuscript before publicatio

Secondary cratering from Rheasilvia as the possible origin of Vesta's equatorial troughs

Asteroid 4 Vesta has a set of parallel troughs aligned with its equator. Although previous evaluations suggest that it is of shock fracturing tectonic origin, we propose that the equatorial troughs can be created by secondary cratering from the largest impact basin, Rheasilvia. We calculated the trajectories of ejecta particles from Rheasilvia by considering Vesta's rapid rotation. As a result, we found that secondary craters should be parallel to the latitude. In particular, if we assume that ejecta particles are launched at an initial launch velocity of approximately 350-380 m/s and a launch angle of 25 degree, the parallel equatorial troughs, the Divalia Fossae, can be suitably explained by secondary cratering. This model works well on objects, such as Haumea, Salacia, and Chariklo, but not on Mercury, the Moon, and regular satellites.Comment: 35 pages, 13 figures, 3 table

Subsynchronous Shaft Vibration in an Integrally Geared Expander-Compressor due to Vortex Flow in an Expander

Lectur

Dust release from cold ring particles as a mechanism of spoke formation in Saturn's rings

Spokes in Saturn's rings are radially-extended structures consisting of dust grains. Although spacecraft and space telescope observations have revealed various detailed features of the spokes and their time variation, their formation mechanism is still under debate. Previous models examined charging mechanisms to attempt at explaining dust release from cm-sized ring particles; however, the attempt has been unsuccessful, because the electrostatic force caused by such charging mechanisms is much weaker than the cohesive force acting on dust grains at ordinary conditions in the ring environment. Here we propose a novel model for the formation of the spokes, where the temperature dependence of cohesion plays an essential role. Ring particles with a temperature below 60K adsorb an O2 ring atmosphere, which facilitates release of dust grains from them by a reduction in the cohesive force between the grains and the particles on the morning ansa. Then, intense electrostatic forces sufficient to overcome the cohesive force are generated on the surface of ring particles and the released dust grains form the structure of spokes. Our model explains observational features of the spokes including their longitudinal location, lifetime, radial expansion velocity, and seasonality.Comment: 37 pages, 7 figure

Subsynchronous Shaft Vibration in an Integrally Geared Expander-Compressor due to Vortex Flow in an Expander

LecturesSubsynchronous shaft vibration was observed in an integrally geared expander-compressor when the machine was operated with a partial load in the course of plant start up. The root cause of the synchronous shaft vibration was identified, by means of CFD analysis, as the vortex flow which was generated in the downstream piping of the gas expander wheel. OEM installed an object, called “vortex breaker”, in the piping in order to eliminate the excitation force of the vortex flow, and as the result, the subsynchronous shaft vibration disappeared. This paper provides the detailed shaft vibration data, root cause analysis, countermeasure and the result from the countermeasure

Different effects of colloid and crystalloid solutions for fl uid resuscitation on hemodynamics and peripheral organ functions in acute hemorrhagic shock rats

Background: The impact of fl uid resuscitation on hemorrhagic shock may depend on the type of fl uids used. This study investigated the specifi c effects of fl uid resuscitation with colloids or crystalloids on the hemodynamics and peripheral organ functions, including mitochondrial activities, infl ammation, blood rheology, clotting and platelet functions.Methods: Hemorrhagic shock was induced in 48 anesthetized rats by blood withdrawal at 1 mL/kg/min. Withdrawal continued until mean arterial pressure (MAP) decreased to 30 mmHg and hypotension was maintained for 20 min. Rats received fl uid resuscitation with 6% hydroxyethyl starch 130/0.4 (HES, n = 12), 5% albumin (ALB, n = 12), normal saline (NS, n = 12) at 1 mL/kg/min or normal saline at 3 mL/kg/min (3-NS, n = 12). Changes investigated included hemodynamics, blood gas analysis, mitochondrial functions,cytokine concentrations, blood rheology, clotting and platelet functions after hemorrhage and fl uid resuscitation.Results: MAP in HES (55 ± 5 mmHg) and ALB (56 ± 12 mmHg) were signifi cantly higher than NS (23 ± 8 mmHg) and 3-NS (38± 5 mmHg) 45 min after resuscitation (P < 0.001). HES and ALB, but not NS signifi cantly attenuated mitochondrial dysfunction and infl ammatory responses. Colloids but not NS signifi cantly induced hemodilution and a consistent blood fl ow. Although there was no difference between HES and ALB, colloids interfered with clotting formation.Conclusion: Fluid resuscitation with colloids but not crystalloids preserved hemodynamics and peripheral organ function afterhemorrhagic shock. Although colloids modulated clotting formation via hemodilution, there was no difference between HES and ALB.departmental bulletin pape

土星系小型衛星に記録されたエンセラダスの火山活動

学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 杉田 精司, 神戸大学教授 荒川 政彦, 東京大学准教授 生駒 大洋, 東京大学准教授 関根 康人, 東京大学教授 栗田 敬University of Tokyo(東京大学

Subsynchronous Shaft Vibration in an Integrally Geared Expander-Compressor due to Vortex Flow in an Expander

LecturesSubsynchronous shaft vibration was observed in an integrally geared expander-compressor when the machine was operated with a partial load in the course of plant start up. The root cause of the synchronous shaft vibration was identified, by means of CFD analysis, as the vortex flow which was generated in the downstream piping of the gas expander wheel. OEM installed an object, called “vortex breaker”, in the piping in order to eliminate the excitation force of the vortex flow, and as the result, the subsynchronous shaft vibration disappeared. This paper provides the detailed shaft vibration data, root cause analysis, countermeasure and the result from the countermeasure