That is, the amount of debris... Currently in orbit has reached a threshold where it will continually collide with itself, further increasing the population of orbital debris.
Some bioluminescent bacteria, for example, light up when their population exceeds a threshold size (Journal of Bacteriology, vol 104, p 313).
例如有些生物发光菌当他们的数量超过某个界限值就会发光。
3
Most studies could not quantify disease frequency in the general population as they are hospital-based and confounded by variations in threshold and the rate of hospitalization.