Abstract. Airborne bacteria are widespread as a major proportion of
bioaerosols, and their coexistence with dust particles enables both bacteria
and dust particles to be more active in ice cloud
formation and to be harmful to public health. However, the abundance and
viability of particle-attached and free-floating bacteria in dusty air have
not been quantitatively investigated. We researched this subject based on
the fact that airborne bacterial cells are approximately 1 µm or
smaller in aerodynamic diameter; therefore, particle-attached bacteria
should occur in aerosol samples of particles larger than 1 µm, and
free-floating bacteria should occur among particles smaller than 1 µm.
Our observations at a coastal site in Japan in spring, when the westerlies
frequently transported dust from the Asian continent, revealed that
particle-attached bacteria in dust episodes, at the concentration of 3.2±2.1×105 cells m−3 on average, occupied 72±9 % of the total bacteria. In contrast, the fraction was 56±17 % during nondusty periods, and the concentration was 1.1±0.7×105 cells m−3. The viability, defined as the ratio
of viable cells to total cells, of particle-attached bacteria was 69±19 % in dust episodes and 60±22 % during nondusty periods on
average, both of which were considerably lower than the viabilities of
free-floating bacteria (about 87 %) under either dusty or nondusty
conditions. The presented cases suggest that dust particles carried
substantial amounts of bacteria on their surfaces, more than half of which
were viable, and spread these bacteria through the atmosphere. This implies
that dust and bacteria have important roles as internally mixed assemblages
in cloud formation and in linking geographically isolated microbial
communities, as well as possibly having a synergistic impact on human health.
With the high-speed development of industrialization process and the Internet e-commerce in China, the number of the fast cargoes is increasing. The transportation demands of customer should be provided in a convenient and efficient way. However, compared to road and aviation, railway express freight network is lagging in China, the market share is relatively low, and the service is still in a low level. The operation scheme of railway express freight train can improve the railway efficiency. This paper studies the railway express freight train schemes on several related questions. They are as follows: (1) We analyze the factors of operating express freight train. (2) Based on the assumption of the shortest path for the flow of traffic, the operation scheme of express freight railways is optimized by establishing a multitarget model with making the largest railway revenue and the largest satisfaction of cargo owner. (3) The multitarget model is proposed to be converted into a single-target model. It is the case of carrying out the operation scheme in the four logistics node cities of the southwest China. The following conclusions are taken: (1) The choice method of the flow path is generally analyzed by heuristic method, which is more accurate. (2) We establish a multiobjective optimization model on the base of getting the maximum of transport revenue and satisfying the cargo owner’s demand.
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