Two defects in the surface oxide layer of ultrafine Si particles, temporarily named an EXL center and an EXH center, were investigated by electron spin resonance (ESR). The Si particles were prepared by a conventional gas evaporation method. The specimens were exposed to air at room temperature to oxidize the surfaces. After the heat treatment in vacuum at 600 and 1000 °C, the ESR signal of the EXL and EXH center appeared, respectively, and after successive annealing in O2 gas at that temperature, the signal disappeared completely. The ESR signals of the defects have different microwave power saturabilities. The EXL center and the EXH center are different defects though they have the same g value. The relationship between ESR signals and infrared spectra was studied. The EXL center was found to be a defect related to the Si–OH structure.
From December 26, 2020 to February 28, 2021, quantitative antigen test (Ag test) of SARS-CoV-2 was conducted by using a nasopharyngeal swab for 990 patients aged from 0 to 99 years old (average age; 63.1 +/-22.5 years old, male: 537, female: 463), who presented at least one of the following symptoms, such as fever, respiratory symptoms, and taste disorder. In 578 patients, Ag test and PCR test were conducted at the same time and these patients were analyzed. In 74 patients with Ag > = 1.0, 44 patients were PCR positive (positive ratio = 0.59). In 43 patients with Ag > = 10.0, 41 patients were PCR positive (positive ratio = 0.95), and all of 42 patients with Ag > = 100.0 were PCR positive. In 504 patients with Ag < 1.0, only five patients were PCR positive (positive ratio = 0.01). In 31 patients with 10 > Ag > = 1.0, three patients were PCR positive (positive ratio = 0.10). All eight patients presented a typical pneumonia, and five patients had a history of close contact with COVID-19 patients within 14 days. With an appropriate cut off value, Ag test is concluded to have enough sensitivity and specificity. Considering the advantage of handiness, rapidness, high-throughput and economy over PCR test, Ag test seems useful diagnostic method for COVID-19 in the pandemic situation.
Silver (Ag) was evaporated in argon (Ar) and xenon (Xe) gases at various pressures in the low-gravity environment aboard the space shuttle. Four glass bulbs with filament tips coated with 50 mg of silver were filled with
Ar gas of 6.7 Pa (A) or 40 Pa (B) or Xe gas of 0.67 Pa (C) or 1.33 Pa (D) and ignited one by one in the low
gravitational field of space. The evaporation temperatures were maintained at 1150°C at which smoke plumes
were barely detectable in all cases in the ground experiment. A ball of smoke particles appeared to grow around
the evaporation source instead of rising as it would under earth gravity conditions. No smoke was observed in
(A), but it was observed in (B) and (C) and bursts of smoke extended in various directions from the smoke ball
in the case of (D). The experiment suggested that vapor could be confined locally around the source with high
pressure and temperature by the surrounding gas in the low gravity. This suggestion cannot be derived from any
conventional model of evaporation in the gas.
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