We have developed a microfabricated fluorescence-activated cell sorter system using a thermoreversible gelation polymer (TGP) as a switching valve. The glass sorter chip has Y-shaped microchannels with one inlet and two outlets. A biological specimen containing fluorescently labeled cells is mixed with a solution containing a thermoreversible sol-gel polymer. The mixed solution is then introduced into the sorter chip through the inlet. The sol-gel transformation was locally induced by site-directed infrared laser irradiation to plug one of the outlets. The fluorescently labeled target cells were detected with sensitive fluorescence microscopy. In the absence of a fluorescence signal, the collection channel is plugged through laser irradiation of the TGP and the specimens are directed to the waste channel. Upon detection of a fluorescence signal from the target cells, the laser beam is then used to plug the waste channel, allowing the fluorescent cells to be channeled into the collection reservoir. The response time of the sol-gel transformation was 3 ms, and a flow switching time of 120 ms was achieved. Using this system, we have demonstrated the sorting of fluorescent microspheres and Escherichia coli cells expressing fluorescent proteins. These cells were found to be viable after extraction from the sorting system, indicating no damage to the cells.
Influence of hot top and mould design on the formation of central porosities and loose structure in heavy forging ingot was analysed by using finite element method. The results of the analysis were compared with those of sectioning investigation of 100 and 135 t ingots and the influence of mould and hot top design on the internal defects has been made clear quantitatively. The result shows that the geometry of hot top and mould design plays most important role in the manufacture of sound heavy ingots. The central porosities and loose structure are liable to increase when the rate of vertical solidification at the centerline of ingot exceeds the value of about 10 mm/ min, and the defects are strengthened at the area where the rate of solidification is accelerated. For 0.25%C-3.5%Ni-Cr-Mo-V steel ingot, "A" segregation begins to form when the rate of transverse (horizontal) solidification decreases to the value of about 0.8 mm/min.
Deep levels are found in n-type silicon that is annealed in N2 and quenched to room temperature. The energy level and capture cross section of the deep levels are estimated to be about E c-0.42 eV and of the order of 10-17 cm2, respectively. The charge state of the deep levels is determined to be acceptor type by measuring the temperature dependence of the Schottky junction capacitance made in the specimen with the deep levels. The depth profile of the deep level density is found to correspond to that of the complementary error function, and the diffusion coefficient calculated from the profile is in good agreement with that of nitrogen in silicon. It is assumed that generation of deep levels is due to the formation of nitrogen-vacancy complexes, because quenching to room temperature and several hours' storage after quenching are required to form the deep levels. In order to confirm this assumption, we attempted to control the deep level density by changing the vacancy concentration. Oxidation of the specimen surface and formation of oxygen precipitates in silicon are known to decrease the vacancy concentration, since they supply excess interstitials from the oxide and silicon interface. Experimental results clearly show that the deep level density observed in these specimens is very low.
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