Nine human remains were recovered from Shiraho-Saonetabaru Cave on Ishigaki Island, Okinawa Prefecture, Japan, between 2007 and 2009. Six of the nine samples produced well-preserved biogenic collagen, which was submitted to radiocarbon dating by accelerator mass spectrometry. Three human samples (Nos. 2, 4, and 8) from the fossil chamber were dated to between 16 and 20 ka BP, and can clearly be assigned to the Late Pleistocene. One animal bone from the same chamber which was treated and measured for radiocarbon independently was also of great antiquity (c. 12 ka BP). These dates are the first concrete evidence of human occupation on the Ryukyu Islands during the Pleistocene, based on the direct radiocarbon dates of human remains. It is expected that more human remains and archaeological objects of the Pleistocene will be recovered from Shiraho-Saonetabaru Cave and the surrounding region by future intensive collaborations between anthropologists, archaeologists, and speleologists.
The objective of this study is to obtain an enhanced understanding of the effect of split injection on mixture formation and combustion processes of diesel spray. A two-dimensional (2D) piston cavity of the same shape as that used in a small-bore diesel engine was employed to form the impinging spray flame. The fuel was injected into a high pressure, high temperature constant volume vessel through a single-hole nozzle with a hole diameter of 0.11 mm. The injection process comprised a pre-injection followed by the main injection. The main injection was carried out either as a single injection of injection pressure 100 MPa (Pre + S100), or by two types of split injection of injection pressure 160 MPa. The latter two types were defined by mass fraction ratios 1:1 and 3:1 (Pre + D160_1-1, Pre + D160_3-1). In order to observe the spray mixture formation process, the tracer laser absorption scattering (LAS) techique was adopted. Tracer LAS fuel with 97.5 vol% of n-tridecane and 2.5 vol% of 1-methylnaphthalene (a-MN) was employed. The spatial distributions of the vapor and liquid phases and the spray mixture formation characteristics in the 2D piston cavity for the three injection strategies were investigated. The diesel spray combustion and soot formation processes were studied using a highspeed video camera. The flame structure and soot formation process were examined using two-color pyrometry. The experimental results revealed that the split-injection vapor distribution was significantly more homogeneous than that of the single injection. The main injection fuel caught up with the pre-injection fuel and provided the spray tip with substantial additional momentum, enabling it to advance further. A high soot concentration and low temperatures appeared near the cavity wall region under the three injection strategies. The soot reduction rate for split injection was higher than that for single injection. The second main injection caught up with the previous injection's flame, which deteriorated the combustion and resulted in higher soot generation. The effect of split injection on the process of soot evolution finished at the same time as that of single injection.
Second harmonic plasma breakdown using electron cyclotron (EC) waves has been studied experimentally in the helical-heliotron device Heliotron J. The magnetic field and the injected EC beam parameters such as power, polarization and injection angle are scanned. The experimental results show that the plasma starts up around the crossing point between the injected EC beam and the resonance layer. The initial plasma moves as the crossing point is shifted. The breakdown is earliest when the beam crosses the resonant layer around the magnetic axis with the X-mode polarization. These results indicate that the single pass absorption has the dominant role on the breakdown rather than the multi-reflection absorption, although the linear absorption is quite low. The bumpiness component in the magnetic field spectrum is also scanned from negative to positive values with the resonance located on-axis. The breakdown is most delayed when the bumpiness component is zero, suggesting that the confinement of accelerated electrons is important.
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