2024年12月25日 星期三 新京报
Guar gum, a plant colloid, costs less than agar and is better suited for growing thermophilic bacteria, but is also more difficult to handle, being more viscous and less transparent. The bacterial polysaccharide xanthan is cheaper as well but forms weaker jellies that, as with carrageenan, might result in puncturing its surface. Other colloids, like alginate (from brown seaweed) and gellan gum (from a bacterium), don’t set solely based on temperature and require additives for gelation. These additives might interfere with microbial growth and make the preparation of those jellies less handy than agar plates.
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NASA's decision to bring the crew home one month early, on Jan. 15, marked the agency's first controlled medical evacuation from the station in its 25 years of continuous operations. The incident highlighted the limits of treating complex health problems 250 miles away from Earth.
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