In the vadose zone, air–water interfaces play
an important
role in particle fate and transport, as particles can attach to the
air–water interfaces by action of capillary forces. This attachment
can either retard or enhance the movement of particles, depending
on whether the air–water interfaces are stationary or mobile.
Here we use three standard PTFE particles (sphere, circular cylinder,
and tent) and seven natural mineral particles (basalt, granite, hematite,
magnetite, mica, milky quartz, and clear quartz) to quantify the capillary
forces between an air–water interface and the different particles.
Capillary forces were determined experimentally using tensiometry,
and theoretically assuming volume-equivalent spherical, ellipsoidal,
and circular cylinder shapes. We experimentally distinguished between
the maximum capillary force and the snap-off force when the air–water
interface detaches from the particle. Theoretical and experimental
values of capillary forces were of similar order of magnitude. The
sphere gave the smallest theoretical capillary force, and the circular
cylinder had the largest force due to pinning of the air–water
interface. Pinning was less pronounced for natural particles when
compared to the circular cylinder. Ellipsoids gave the best agreement
with measured forces, suggesting that this shape can provide a reasonable
estimation of capillary forces for many natural particles.
Knowledge of mechanisms of infection in vulnerable populations is needed in order to prepare for future outbreaks. Here, using a unique dataset collected during a 2009 outbreak of influenza A(H1N1)pdm09 in a university town, we evaluated mechanisms of infection and identified that an epidemiological model containing partial protection of susceptibles best describes H1N1 dynamics in a rural university environment. We found that the protected group was over 14 times less susceptible to H1N1 infection than unprotected susceptibles. Our estimates show that the basic reproductive rate, R 0, was 5·96 (95% confidence interval 5·83-6·61), and, importantly, R 0 could be decreased to below 1 and similar epidemics could be avoided by increasing the proportion of the initial protected group. Moreover, several weeks into the epidemic, this protected group generated more new infections than the unprotected susceptible group, and thus, such protected groups should be taken into account while studying influenza epidemics in similar settings.
Data are rare on influenza outbreaks spreading through a workplace, but such transmission dynamics would be useful for comparison with the spread of the infection in other settings. We collected and compared infection data from two settings, a workplace and a university campus, during the 2009 pandemic influenza A(H1N1)pdm09 outbreak in a geographically contained community. Trajectories of infection were markedly alike in both settings. This suggests that transmission behaviour was similar in individuals in the two environments, despite the condition that individuals can leave the workplace setting in order to avoid transmission.
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