No abstract

Infectious respiratory diseases such as the current COVID-19 have caused public health crises and interfered with social activity. Given the complexity of these novel infectious diseases, their dynamic nature, along with rapid changes in social and occupational environments, technology, and means of interpersonal interaction, respiratory protective devices (RPDs) play a crucial role in controlling infection, particularly for viruses like SARS-CoV-2 that have a high transmission rate, strong viability, multiple infection routes and mechanisms, and emerging new variants that could reduce the efficacy of existing vaccines. Evidence of asymptomatic and pre-symptomatic transmissions further highlights the importance of a universal adoption of RPDs. RPDs have substantially improved over the past 100 years due to advances in technology, materials, and medical knowledge. However, several issues still need to be addressed such as engineering performance, comfort, testing standards, compliance monitoring, and regulations, especially considering the recent emergence of pathogens with novel transmission characteristics. In this review, we summarize existing knowledge and understanding on respiratory infectious diseases and their protection, discuss the emerging issues that influence the resulting protective and comfort performance of the RPDs, and provide insights in the identified knowledge gaps and future directions with diverse perspectives.

In order to address the influence of aging on the performance degradation of SBS-modified asphalt, a composite modification of SBS-modified asphalt by nano-zinc oxide (nano-ZnO) and Trinidad Lake asphalt (TLA) was proposed. Several tests were conducted after adding nano-ZnO and TLA to SBS-modified asphalt, including a rotary film oven test (RTFOT), ultraviolet aging (UV), and the pressure aging vessel test (PAV). The conventional physical index, rheological index, and four-component content of SBS-modified asphalt before and after three aging modes were tested, and the characteristic functional groups in SBS-modified asphalt were tracked and analyzed by Fourier transform infrared spectroscopy (FTIR). The results show that the effects of aging on the rheological properties of SBS-modified asphalt are clearly reduced by adding different proportions of nano-ZnO and TLA in the process of thermal oxygen aging and the ultraviolet aging test, and the antiaging ability of SBS-modified asphalt is clearly improved. To improve the conventional performance and rheological properties of SBS-modified asphalt, an incorporation ratio of 3% nano-ZnO + 25% TLA was proposed. At the same time, the increased rate of heavy components and the change index of the colloidal instability index in the SBS-modified asphalt under the blending ratio were significantly lower than the blank SBS-modified asphalt samples in the same aging mode. FTIR spectra also showed that SBS-modified asphalt performance deterioration were mainly caused by long-term aging and ultraviolet aging. The addition of nano-ZnO and TLA effectively reduced the increase of carbonyl groups and the breakage of the C=C double bond in butadiene and synergistically improved the comprehensive aging resistance of SBS-modified asphalt. Therefore, the use of this modification is an effective method to solve the aging problem of SBS-modified asphalt.

In order to study the influence of different thickness ratios on the mechanical properties of rock-concrete composite, a 50 mm diameter split Hopkinson pressure bar device (SHPB) was used to conduct impact loading tests on ϕ 50 mm × 50 mm cylindrical composite with sandstone thickness of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 mm. The results show that with the increase of the proportion of rock in the composite, the dynamic compressive strength increases gradually, and the dynamic elastic modulus increases linearly. When the rock thickness increases, the average strain rate decreases and the peak strain decreases. In dynamic loading combination behind the rock specimen with concrete cushion, absorb energy decrease with the increase of rock accounted concrete; when the rock is 25 mm, total absorption energy reached its lowest point; when the thickness of the rock is greater than the thickness of concrete, concrete and adjacent parts of rock joint cushion absorb the energy into a rising trend. With the increase of the proportion of rock, the degree of fragmentation of the composite specimens decreases gradually, and the fragments are mostly concrete with smaller particle size, which is correlated with the dynamic compressive strength. The rock-concrete interface is a weak surface relative to the materials on both sides.

With the gradual deepening of mine excavation depth, the strong disturbance of deep strata becomes more and more obvious. Rock’s failure under blasting mainly depends on its dynamic tensile strength. The changes in rock’s dynamic properties are obviously affected by temperature and water. In order to study the dynamic tensile properties of annular sandstone specimens under the influence of temperature and water, deep sandstone was drilled, followed by water bath tests at eight temperatures (25~95°C). It can be seen from the analysis of test results that the mass and volume growth rates of the annular and the intact sandstone specimens first increased and then decreased, while the density growth rate first decreased and then increased. The mass and volume growth rates of the annular sandstone specimens were smaller, but the density growth rate was larger. Because of the increase in water temperature, the dynamic compressive strength first increased and then decreased. The dynamic tensile strength of the annular sandstone specimen was lower. The average strain rate and peak strain also showed a quadratic function relationship of first decreasing and then increasing with the increase in water temperature. The average strain rate of the annular sandstone specimen was smaller, but the peak value changed greatly. The Brazilian disc validity condition is applicable to two failure conditions of sandstone specimens. Through XRD and SEM analysis, we found that the changes in the dynamic properties of sandstone specimens were not due to their own material composition, but to the damage to their structure caused by the temperature–water coupling effect.