Speaking and singing are activities linked to increased aerosol particle emissions from the respiratory system, dependent on the utilized vocal intensity. As a result, these activities have experienced considerable restrictions in enclosed spaces since the onset of the COVID-19 pandemic due to the risk of infection from the SARS-CoV-2 virus, transmitted by virus-carrying aerosols. These constraints have affected public education and extracurricular activities for children as well, from in-person music instruction to children’s choirs. However, existing risk assessments for children have been based on emission measurements of adults. To address this, we measured the particle emission rates of 15 pre-adolescent children, all eight to ten years old, with a laser particle counter for the test conditions: breathing at rest, speaking, singing and shouting. Compared with values taken from 15 adults, emission rates for breathing, speaking and singing were significantly lower for children. Particle emission rates were reduced by a factor of 4.3 across all conditions, whereas emitted particle volume rates were reduced by a factor of 4.8. These data can supplement SARS-CoV-2 risk management scenarios for various school and extracurricular settings. 相似文献
The use of user-interface design knowledge such as general guidelines and environment-specific style guides can be valuable, and is increasingly required in professional user-interface design. However, conventional guidelines and style guides (
and
) in the form of documents are consistently found hard to use. We have earlier demonstrated knowledge-based critiquing to be a technically feasible way of delivering relevant
and
knowledge. The purpose of this study was to investigate the need and acceptability of such techniques for professional user-interface designers.
An experiment was carried out where four professional designers developed user-interface prototypes to a functional specification. The designs were evaluated using our
and
-based critiquing system, which identified a total of 17 deviations from style-guide requirements or design recommendations. Interviews were conducted with the designers to find the reasons for the deviations and to identify important requirements for a critiquing design-support tool. The deviation analysis points to an existing need for better ways of accessing
and
knowledge. The interviews indicate that the designers would find a critiquing tool valuable, provided that it leaves them in control of their work and indicates the severity of the detected deviations. 相似文献
Fracture features, residual stresses, and zirconia transformation are studied in indentation strength specimens of alumina-Y2O3-stabilized zirconia (3% mol of Y2O3, 3YTZP) ceramics in order to analyze the extension of the indentation damage in the bulk of the specimens. Two compositions, 5 vol% 3YTZP (A5) and 40 vol% 3YTZP (A40), have been prepared by stacking tape-casted tapes and sintering. After indentation with loads ranging from 50 to 300 N, samples were fractured in four-point bending and the fracture surfaces were characterized by scanning electron microscopy. Raman and piezospectroscopic techniques were used to determine the monoclinic zirconia fraction and the residual stresses through the fracture surfaces. In the A5 composition, the indentation damage morphology was clearly half-penny, whereas the A40 composition presented Palmqvist crack formation. Zirconia transformation was only observed in the plastically deformed zones underneath the imprints whereas there were significant residual compressive stresses outside the plastic zones due to the indentation damage. The intensity of this residual compressive field was dependent on the level of zirconia transformation due to indentation damage because zirconia transformation induced tensile stress fields superimposed on the compressive stresses. 相似文献
Injection of brine with lower salinity than the connate brine has proven to give a moderate increase in oil recovery in sandstones. Recent research has shown that this process will significantly benefit from introducing surfactant optimised for low salinity environment.The mechanisms underlying increased recovery by low salinity brine injection are not yet fully understood. However, research to date suggests that they are related to complex crude oil/brine/rock interactions. With this in mind, the present paper investigates primarily how the extent of oil recovery from Berea sandstones subjected to long term exposure of crude oil is influenced by (1) low salinity water injection and (2) combined process low salinity water injection with surfactant flooding.Core displacement tests were conducted on four Berea cores (30 cm), two in a natural state and two that had been subject to extensive crude oil ageing at high temperature. Results obtained from different flooding steps are discussed in terms of oil recovery and effluent properties including turbidity, pH- and ion analysis (Na+, Mg2+, Ca2+). The results effectively illustrate that oil recoveries from the aged cores are higher during both low salinity water injection and low salinity water injection combined with surfactant flooding. An assessment of how tertiary oil recovery in aged and unaged cores varies with surfactant concentration is also presented.Effluent ion analysis from low salinity water floods showed that Mg2+ ions were strongly retained in the aged core while Ca2+ ions were being produced from both aged and unaged cores. The latter was attributed mainly to calcite dissolution. Results obtained from pressure profiles, effluent ion analysis and turbidity tests suggest higher production and elution of fine particles from the unaged core. 相似文献
In ferritic steels a propagating cleavage microcrack changes its propagation direction as it advances from grain to grain.
This is due to differences in the orientation of the cleavage planes of two neighboring grains. In order to reach a cleavage
plane in a new grain, a microcrack must first penetrate the grain boundary. Grain boundaries therefore act as natural barriers
in cleavage fracture. The influence of a grain boundary and the associated misorientation in cleavage planes on crack arrest
is here examined using a 3D finite element model with axisymmetric periodicity, representing two grains whose cleavage planes
are tilted and twisted relative to each other. The temperature dependent mechanical properties of ferrite are modeled using
a temperature dependent viscoplastic response. The development of the crack front as the microcrack penetrates through a grain
boundary is here presented. The influence of the twist misorientation on the critical grain size, defined as the largest grain
size that can arrest a rapidly propagating microcrack, is examined in a temperature range corresponding to the ductile to
brittle transition (DBT) region. It is shown that when both tilt and twist misorientation are present, the influence of tilt
and twist, respectively, on crack growth resistance can be decoupled. 相似文献