Influence of smoke suppressant on the smoke inhibition effect and properties of different types of asphalt

The current understanding of the influence of smoke suppressants on the smoke inhibition effect and working performance of different types of asphalt is limited. In this study, portable gas detector (PGD) tests were used to investigate the influence of the smoke suppressant on different types of asphalt and the smoke purification effect. Subsequently, gas chromatography-mass spectrometry (GC-MS) was used to analyze the influence of the smoke suppressant on the volatile organic compounds (VOCs) in different types of asphalt fume, so as to compare and verify the PGD tests results. Finally, scanning electron microscopy and energy dispersive spectrometry were used to observe and analyze the influence of the smoke suppressant on the microstructure and element composition of different types of asphalt. The results show that the smoke suppressant can purify various harmful gases volatilized from different types of asphalt, but the effect and the optimal dosage of smoke suppressant are slightly different. The purification rate of the smoke suppressant for SO2 or H2S in the fumes of various asphalts can reach >70% and the NO and VOC purification rates can reach >40%. The influence of the smoke suppressant on the VOC purification rate of different asphalts detected through the GC-MS and PGD tests is similar. The smoke suppressant has little effect on the asphalt surface microstructure and on the changes in the element content in asphalt, indicating that it has no effect on the main properties of the asphalt itself. This study is helpful to further understand the relationship between smoke suppressants and the smoke inhibition effect and the working performance of different types of asphalt. Additionally, it provides basis and guidance for the development of low-smoke asphalt with a better emission reduction effect, which has a certain guiding and application significance

Active Reconfigurable Intelligent Surface Enhanced Internet of Medical Things

The incredible potentiality of reconfigurable intelligent surface (RIS) in addressing power supply and obstacle environment of Internet of Medical Things (IoMT) has been capturing our interest. Considering the nettlesome “double-fading” effect introduced by passive RIS, we investigate an active RIS-enhanced IoMT system in this paper, where the wireless power transfer (WPT) from power station (PS) to IoMT devices and the wireless information transfer (WIT) from IoMT devices to the access point (AP) are both implemented with the assistance of active RIS. Aiming to maximize the sum throughput of the considered IoMT system, a joint design of time schedules and reflecting coefficient matrices of the active RIS is proposed. Trapped by the non-convex and obstinate optimization problem, we explore the semi-definite programming (SDP) relaxation and successive convex approximation (SCA) techniques based on alternating optimization (AO) algorithm. Simulation results verify our solution approach to the intractable optimization problem and showcase the boosted spectrum and energy efficiency of the active RIS-enhanced IoMT system

Active RIS-assisted secure transmission for cognitive satellite terrestrial networks

This correspondence develops a physical-layer security scheme for a cognitive-satellite terrestrial network, where the satellite and base station (BS) share the spectrum resource, and multiple eavesdroppers attempt to intercept the private signal from the BS to the mobile user. Different from the commonly used passive reconfigurable intelligent surface (RIS), the active RIS, whose reflecting elements can control both the amplitude and phase of the incident signal, is deployed to cooperatively enhance the secure transmission from the BS to the mobile user, and suppress the interference imposed to the earth station. We attempt to maximize the achievable secrecy rate subject to the transmit power constraint and the interference threshold. To address the above non-convex problem, we propose an effective alternating optimization scheme to jointly optimize the beamformer and artificial noise at the BS, and the reflecting coefficient at the RIS. Simulation results indicate that the impact of the “double fading” can be effectively relieved by using active RIS, thus leading to an apparently enhanced secrecy performance gain compared to those with the passive RIS and no RIS designs

Study on Mechanics-Based Cracking Resistance of Semiflexible Pavement Materials

Semiflexible mixture is a composite paving material combining the advantages of both asphalt and cement concrete materials. It consists of matrix asphalt skeleton and cement mortar. Due to the different volume characters between asphalt structure and cement mortar, stress concentration always happens in this semiflexible mixture, leading to internal cracking. The objective of this study is to alleviate the internal cracking concern of the semiflexible mixture by adjusting the material components. To this end, optimal material design and numerical simulation have been conducted. Matrix asphalt structures with four different air voids were incorporated with different dosages of cement mortar. The contraction strain and expansion strain of cement mortar as well as the indirect tensile strength of matrix asphalt structure were measured. The results were input into ABAQUS for numerical simulation. The results indicated that (1) the internal stress in this semiflexible mixture is mainly determined by the contraction of cement mortar, rather than expansion; (2) larger air void of matrix asphalt structure and less volumetric variation of cement mortar reduce the internal stress; (3) once the air void of matrix asphalt structure is decided, both maximum contraction and expansion deformations of cement mortar should meet specific requirement to ensure less internal cracking. This is a practical-ready paper that provides reference for the anticracking design of semiflexible pavement

Recycled asphalt mixture's discrete element model-based composite structure and mesoscale-mechanical properties

To investigate the composite structure and mesoscale-mechanical properties of recycled asphalt mixture, this paper has established discrete element models of recycled asphalt mixture with distinct characteristics of new aggregates, recycled asphalt pavement, new asphalt, and old asphalt according to the coarse aggregate contour characteristic parameters obtained by three-dimensional scanning. The composite skeleton and micro-crack development characteristics of recycled asphalt mixture were also studied. Finally, a method for determining the recycled asphalt pavement content was proposed considering the balance between rutting and crack resistance. The results show that the recycled asphalt pavement content has a negligible impact on the number of contact points of the composite skeleton, and this component primarily impacts the interfacial mechanical properties and contact of asphalt mortar. When the recycled asphalt pavement contents were 0 %, 15 %, 30 %, 45 %, and 60 %, the bottom stresses of the rutting specimens were approximately 0.6, 0.55, 0.5, 0.48, and 0.44 times of the bearing plate stress, respectively. In the composite skeleton, there were compressive, tensile, and tensile–compressive stresses at the contact point of coarse aggregates, the proportions of which were generally 70–80 %, 15–20 %, and 5–10 %, respectively. Shear cracks mainly occurred in the recycled asphalt pavement contact interface area, while tensile cracks occurred at the aggregate–aggregate contact interface, as well as in the asphalt mortar. The number of shear cracks was 50–80 % that of the tensile cracks. The maximum micro-crack length is 8–12 mm, and its minimum length is approximately 0.3 mm with micro-crack generally in the asphalt mortar. The results can provide a reference for the recycled asphalt mixture design to improve road performance

A New Method for Designing Dense Skeleton Asphalt Mixture Based on Meso Parameter

At present, research on the internal structures of asphalt mixtures has mostly focused on the statistical analysis of their mesostructural components such as aggregates, voids, and asphalt mortars, in addition to the verification of the mechanical behaviour of the mixture through simulations. Furthermore, the capacity of the research has not risen to a level where a design method to guide the design and optimisation of the asphalt mixture gradation has been formulated. After an in-depth analysis of the existing evaluation parameters and standards for the asphalt mixture skeleton, this study proposes a new method for precise designing a dense skeleton asphalt mixture (DSAM) based on meso parameter. The results indicate that the application of digital image processing (DIP) techniques to adjust the gradation increases the average coordination number (n¯c) and reduces the ratio of the quantity of coarse aggregate without contact point to the total quantity of coarse aggregate (C value). This can effectively improve the meso parameters of the mixture so that the quality of the main skeleton is significantly enhanced; the process also has higher precision and demands less test work. VCAmix(IMAGE) ≤ VCADRC and n¯c>1.6 while C < 20% can be used as qualitative and quantitative evaluation criterion for forming better main skeleton structure of coarse aggregate. The new method of designing a DSAM based on meso parameter is intuitive and convenient, which considerably reduces the blindness and tediousness in the design of the asphalt mixture gradation. The engineering example also proves that the asphalt mixture has an excellent pavement performance and verifies the feasibility of the proposed design method

The combined effect of MTHFR C677T and A1298C polymorphisms on the risk of digestive system cancer among a hypertensive population

Abstract Background and purpose The enzyme methylenetetrahydrofolate reductase (MTHFR) plays a crucial role in directing folate species towards nucleotide synthesis or DNA methylation. The MTHFR polymorphisms C677T and A1298C have been linked to cancer susceptibility, but the evidence supporting this association has been equivocal. To investigate the individual and joint associations between MTHFR C677T, A1298C, and digestive system cancer in a Chinese hypertensive population, we conducted a population-based case–control study involving 751 digestive system cancer cases and one-to-one matched controls from the China H-type Hypertension Registry Study (CHHRS). Methods We utilized the conditional logistic regression model to evaluate multivariate odds ratios (ORs) and 95% confidence intervals (CIs) of digestive system cancer. Results The analysis revealed a significantly lower risk of digestive system cancer in individuals with the CT genotype (adjusted OR: 0.71; 95% CI 0.52, 0.97; P = 0.034) and TT genotype (adjusted OR: 0.57; 95% CI 0.40, 0.82; P = 0.003; P for trend = 0.003) compared to those with the 677CC genotype. Although A1298C did not show a measurable association with digestive system cancer risk, further stratification of 677CT genotype carriers by A1298C homozygotes (AA) and heterozygotes (AC) revealed a distinct trend within these subgroups. Conclusion These findings indicate a potential protective effect against digestive system cancer associated with the T allele of MTHFR C677T. Moreover, we observed that the presence of different combinations of MTHFR polymorphisms may contribute to varying susceptibilities to digestive system cancer