We experimentally demonstrate that the flow rate of granular material through an aperture is controlled by the exit velocity imposed to the particles and not by the pressure at the base, contrary to what is often assumed in previous works. This result is achieved by studying the discharge process of a dense packing of monosized disks through an orifice. The flow is driven by a conveyor belt. This two-dimensional horizontal setup allows to uncouple pressure and velocity and, therefore, to independently control the velocity at which the disks escape the horizontal silo and the pressure in the vicinity of the aperture. The flow rate is found to be directly proportional to the belt velocity, independent of the amount of disks in the container and, thus, independent of the pressure in the outlet region. In addition, this specific experimental configuration makes it possible to get information on the system dynamics from a single image of the disks that rest on the conveyor belt after the discharge.

We simultaneously measure the flow rate and the normal force on the base, near the outlet, during the discharge through an orifice of a dense packing of monosized disks driven by a conveyor belt. We find that the normal force on the base decreases even when a constant flow rate is measured. In addition, we show, by changing the mass of the disks, that pressure can be changed while the flow rate remains constant. Conversely, we are able, by changing the belt velocity, to set different flow rates for the same pressure. The experiment confirms that, contrary to what has been implicitly assumed in numerous works, the flow rate through an aperture is not controlled by the pressure in the outlet region.

Anthropogenic changes affect biological communities of host and vectors driving arbovirus activity. In general, urban and agricultural ecosystems harbor less avian and mosquito diversity than native ecosystems and are dominated by few species. Human activities have led to the emergence / re-emergence of different infectious pathogens particularly arboviruses representing a threat to both public health and biodiversity. Saint Louis encephalitis (SLEV) and West Nile viruses (WNV) are transmitted by Culex spp. mosquitoes as main vectors and several bird species as hosts. With the aim to study the exposure of free-ranging bird communities to SLEV and WNV in Pampean agroecosystems as well as to evaluate the environmental/ biological factors potentially associated we collected and bleed free ranging birds in 12 sites. Serum samples were analyzed by Plaque Reduction Neutralization Test (PRNT) for both viruses. Generalized Linear Mixed Models (GLMM) were performed to analyze the association between environmental / biological variables from each sampled site and avian exposition. A total of 1019 birds were sampled during 2017 - 2019. Overall, we found SLEV NTAb in 60 out of 1019 samples (5.8%) while WNV seroprevalence was 2.1% (21/1019). SLEV and WNV seroprevalence were different among the sampled sites. Agricultural area was positively associated with the SLEV-WNV infection risk for an avian host. Forested area also had a strong association but in a negative way. Our results suggest that open agricultural area increase the infection risk of free ranging birds to SLEV and WNV while forested area diminishes the infection risk maybe through a dilution effect of vector and host communities.