209 research outputs found
Evidence for a rapid decrease in Pluto's atmospheric pressure revealed by a stellar occultation in 2019
We report observations of a stellar occultation by Pluto on 2019 July 17. A
single-chord high-speed (time resolution s) photometry dataset was
obtained with a CMOS camera mounted on the Tohoku University 60 cm telescope
(Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an
existing Pluto's atmospheric model. We find the lowest pressure value at a
reference radius of among those reported after 2012,
indicating a possible rapid (approximately of the previous
value) pressure drop between 2016 (the latest reported estimate) and 2019.
However, this drop is detected at a level only and still requires
confirmation from future observations. If real, this trend is opposite to the
monotonic increase of Pluto's atmospheric pressure reported by previous
studies. The observed decrease trend is possibly caused by ongoing
condensation processes in the Sputnik Planitia glacier associated with an
orbitally driven decline of solar insolation, as predicted by previous
theoretical models. However, the observed amplitude of the pressure decrease is
larger than the model predictions.Comment: 7 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Thermo-Mechanical Strength Parameters of Single Crystal Rare-Earth High Tc Bulk Superconductors
Studies on the Thermo-Mechanical Strength Characteristics of Single Crystal RE High Tc Bulk Superconductors
Studies on the Mechanical Properties and Fracture Mechanisms of Single Crystal RE High Tc Bulk Superconductors
Vertical emissivity profiles of Jupiter's northern H-3(+) and H-2 infrared auroras observed by Subaru/IRCS
We resolved the vertical emissivity profiles of H-3(+) overtone, H-3(+) hot overtone, and H-2 emission lines of the Jovian northern auroras in K band obtained in December 2011 observed by the IR Camera and Spectrograph of the Subaru 8.2m telescope with the adaptive optics system (AO188). The spatial resolution achieved was similar to 0.2 arcsec, corresponding to similar to 600 km at Jupiter. We derived the vertical emissivity profiles at three polar regions close to the Jovian limb. The H-3(+) overtone and H-3(+) hot overtone lines had similar peak altitudes of 700-900 km and 680-950 km above the 1 bar level, which were 100-300 km and 150-420 km lower, respectively, than the model values. On the contrary, the H-2 peak emission altitude was high, 590-720 km above the 1 bar level. It was consistent with the value expected for precipitation of similar to 1 keV electron, which favors a higher-altitude emissivity profile. We concluded that the lower peak altitudes of H-3(+) overtone and hot overtone lines were caused by the nonlocal thermodynamic equilibrium effect stronger than the model assumption. We could reproduce the observational emissivity profiles from the model by including this effect. It has been proposed that neutral H-2 and ionized H-3(+) emissions can have different source altitudes because of their different morphologies and velocities; however, our observed results with a general circulation model show that the peak emission altitudes of H-3(+) and H-2 can be similar even with different velocities
Spatial evolution of frictional heating and the predicted thermospheric wind effects in the vicinity of an auroral arc measured with the Sondrestrom incoherent-scatter radar and the Reimei satellite
Axial Tensile Strain/Transverse Compressive Stress Characteristics in High Strength Nb_3Sn Superconducting Wires(High Field Superconductors)
In order to improve the strain/stress characteristics of the critical current I_c, the availability of Nb matrix as well as the external CuNb reinforcing stabilizer to bronze processed Nb_3Sn multifilamentary superconducting wires has been examined up to the magnetic field of 14T and at a temperature of 4.2K. Although the axial tensile strain sensitivity of I_c does not change, the strain for peak I_c as well as the reversible strain limit increase in the wire with CuNb reinforcing stabilizer. Furthermore, the transverse compressive stress sensitivity of I_c decreases and the reversible stress limit increases. Although critical current density is not high, the Nb matrix Nb_3Sn wire shows higher tolerance to stress/strain. Correlation between axial strain effect and transverse compressive stress effect is briefly discussed
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