A rod fastened rotor (RFR), which contains serial disks, rods (or a rod), and a torque tube, is the main form of heavy duty gas turbines and light duty aero engines. The roughness of the interface is ...the main parameter affecting the bending stiffness of RFR, and the jumpiness of the disks is the intuitive representation of the unbalance of the rotor. In this paper, a multi-optimization algorithm, NSGA-Ⅱ, was used to improve the vibration behavior of the RFR-bearing system. First, the quantitative relation between the bending stiffness of the rotor and the roughness of the interface was set up by combining the Persson contact theory and the Greenwood–Williamson model, and the nondimensional bending stiffness (NS) was proposed as the optimization objective of roughness. Then, the optimization objective of the jumpiness of the disk, (A + B), was rendered based on the minimum unbalance force. Finally, the multi-optimization on the roughness and jumpiness of the RFR was carried out, and the vibration behavior was improved greatly. In addition, this multi-optimization method was applied to a practical RFR, and the experimental results showed that the vibration amplitude was reduced by about 82%. The work in this paper can provide the guidance for vibration reduction of the rotor system.
Municipal solid waste and cement manufacture are two sources of environmental justice issues in urban and suburban areas. Waste utilization is an attractive alternative to disposal for eliminating ...environmental injustice, reducing potential hazards, and improving urban sustainability. The re-use and recycling of municipal solid waste incineration (MSWI) ash in the construction industry has drawn significant attention. Incorporating MSWI ash in cement and concrete production is a potential path that mitigates the environmental justice issues in waste management and the construction industry. This paper presents a critical overview of the pretreatment methods that optimize MSWI ash utilization in cement/concrete and the influences of MSWI ash on the performance of cement/concrete. This review aims to elucidate the potential advantages and limitations associated with the use of MSWI ash for producing cement clinker, alternative binder (e.g., alkali-activated material), cement substitutes, and aggregates. A brief overview of the generation and characteristics of MSWI ash is reported, accompanied by identifying opportunities for the use of MSWI ash-incorporated products in industrial-scale applications and recognizing associated environmental justice implications.
Abstract
The art design of interactive device is based on Arduino, an open-source technology and Processing, a programming language, whose application enriches the interactivity and expansibility of ...the device, and improves its visual effect and experience. With the rapid development of social economy, urban noise pollution has become increasingly severe, which has been yet to arouse enough public attention. Therefore, the research enables people to more intuitively experience the impact of urban noise through the interactive device, and realizes the interaction between the device and people through the communication between Arduino and Processing, so that people can deeply understand the severity and danger of urban noise pollution, thus calling for public’s higher awareness of noise prevention.
Polyethylene terephthalate (PET) is selectively depolymerized by a carbon‐supported single‐site molybdenum‐dioxo catalyst to terephthalic acid (PTA) and ethylene. The solventless reactions are most ...efficient under 1 atmosphere of H2. The catalyst exhibits high stability and can be recycled multiple times without loss of activity. Waste beverage bottle PET or a PET + polypropylene (PP) mixture (simulating the bottle + cap) proceeds at 260 °C with complete PET deconstruction and quantitative PTA isolation. Mechanistic studies with a model diester, 1,2‐ethanediol dibenzoate, suggest the reaction proceeds by initial retro‐hydroalkoxylation/β‐C−O scission and subsequent hydrogenolysis of the vinyl benzoate intermediate.
A carbon‐supported single‐site molybdenum‐dioxo catalyst, C/MoO2, catalyzes the hydrogenolytic deconstruction of polyethylene terephthalate (PET) to its monomers, terephthalic acid and ethylene, under 1 atm of H2. C/MoO2 can be recycled multiple times without loss of activity. Mechanistic studies suggest an initial β‐scission step, followed by hydrogenolysis of a vinyl benzoate intermediate.
To arrest the growth of global environmental issues, curbing the greenhouse gas emissions and primary energy consumption in concrete production is among the efficacious strategies. Cement production ...being the most energy- and emission-intensive activity in concrete manufacture, the partial replacement of cement clinker with supplementary cementitious materials (SCMs), which require less intensive processing, is the effective approach. Due to the unbalanced source distribution of commonly-used SCMs, e.g. fly ash (FA) and ground granulated blast furnace slag (GGBFS), this study analyzed the substitution of Portland cement (PC) in mortar and concrete mixes with up to 40% of the highly-reactive pozzolanic diatomaceous earth (DE) with abundant deposit in western United States and many other countries, aiming to provide an alternative SCM with local availability in many regions of limited FA and GGBFS supply. The influence of DE on the density, compressive strength, workability, soundness, and environmental impacts of the production of a mix was studied at different substitution levels in binary, ternary, and quaternary systems. DE-containing mixes showed improved strength development and early properties suitable for general applications. The approach of life-cycle assessment quantified the influence of DE on environmental impacts from material production, processing, and transportation in mortar or concrete manufacture. Substitution of PC with DE at 30 wt% resulted in over ∼30% lower global warming potential and energy use as well as appreciably reduction in air pollutant emissions. The use of DE as SCMs in concrete is promising, worth the consideration regarding availability and cost.
•The replacement of cement by diatomite and limestone in concrete is up to 40%.•28-day strength of green concrete is increased by 40% with the use of diatomite.•CO2 emission, energy use, and air pollutants in concrete production are reduced.•The intensity of global warming potential of green concrete is 50% lower.
The lack of quantitative risk assessment of airborne transmission of COVID-19 under practical settings leads to large uncertainties and inconsistencies in our preventive measures. Combining in situ ...measurements and computational fluid dynamics simulations, we quantify the exhaled particles from normal respiratory behaviors and their transport under elevator, small classroom, and supermarket settings to evaluate the risk of inhaling potentially virus-containing particles. Our results show that the design of ventilation is critical for reducing the risk of particle encounters. Inappropriate design can significantly limit the efficiency of particle removal, create local hot spots with orders of magnitude higher risks, and enhance particle deposition causing surface contamination. Additionally, our measurements reveal the presence of a substantial fraction of faceted particles from normal breathing and its strong correlation with breathing depth.
•Provide in situ characterization of particle generation through normal breathing.•Reveal presence of droplet and crystalline particles generated through breathing.•Risk assessment of airborne transmission of infectious diseases through virus-containing particles.•Inappropriate ventilation enhances the risk of airborne disease transmission.
•Different types of strength of MPC with or without fly ash were studied.•The effects of fly ash on various types of strength were compared and analyzed.•Relationship among axial tensile, splitting ...and compressive strength was analyzed.•The fracture characteristics of different MPC were studied.
The mechanical properties and fracture toughness of magnesium phosphate cement (MPC) were studied in this paper. The results show that the strengths (compressive, flexural, axial tensile and splitting strengths) of MPC increased rapidly over curing ages and then increasing rates slowed down. The compressive strength increased with the addition of fly ash, while the tensile strength decreased. For both the specimens with and without the addition of fly ash, the axial tensile strength was lower than the splitting strength. The axial tensile strength of MPC without fly ash was 1/13–1/10 of compressive strength and the axial tensile strength of MPC with fly ash is 1/17–1/14 of compressive strength. The ratio decreased over time. The load–deflection curve showed the failure mode of MPC is brittle failure. The fracture energy increased over time, while the value was relatively small. The failure load and the corresponding mid-span deflection of MPC decreased in presence of fly ash, which results in the further decrease of fracture energy of MPC.
To evaluate the effect of telephone instructions on the quality of bowel preparation in patients undergoing colonoscopy. Online English databases (PubMed, Web of Science, Cochrane Library, and ...Embase) were screened for randomized controlled trials on telephone instructions regarding bowel preparation for colonoscopy from inception to April 15, 2022. After data extraction, the Review Manager software was used for meta-analysis. Nine randomized controlled trials with 3,836 patients were included in the meta-analysis. The rate of adequate bowel preparation was significantly higher in the telephone group than in the control group. The pooled relative risk (RR) was 1.17 (95% confidence interval CI: 1.05-1.30, P < 0.01). The pooled mean difference (MD) for the Boston Bowel Preparation Scale score was 1.32 (95% CI: 0.15-2.49, P < 0.05), and that for the Ottawa Bowel Preparation Scale score was -1.93 (95% CI: -2.35 to -1.51, P < 0.01). The polyp detection rate was significantly higher in the telephone group than in the control group (RR = 1.58, 95% CI: 1.23-2.04, P < 0.01), whereas no significant difference was noted in the adenoma detection rate between the groups (RR = 1.37, 95% CI: 0.97-1.94, P = 0.08). Telephone instructions for patients undergoing colonoscopy significantly improved the quality of bowel preparation and increased polyp detection rate.
Nano/micro-indentation has been extensively used to examine elastic properties and creep of cement-based materials. However, there have been inconsistencies in the measured elastic moduli and debate ...on the creep mechanism of calcium (alumino) silicate hydrates (C-(A-)S-H). To bring new insights, we examined the deviatoric stress-induced preferred orientation of calcium aluminosilicate hydrate (C-A-S-H), portlandite, and ettringite compacts, using synchrotron-based X-ray diffraction. Intense preferred orientations were observed in C-A-S-H compacts, and the c-axis of unit cells is highly aligned with the compression direction; weaker c-axis related fiber-type texture formed in portlandite and ettringite. Higher humidity, greater compacting pressure, and/or increased duration of the pressure intensified the C-A-S-H preferred orientation, which is facilitated by gel-pore water lubrication. This pressure-induced time-dependent preferential re-orientation of crystallites can contribute to the creep of cement-based materials, and it may cause overrepresentation of the soft c-axis of C-(A-)S-H unit-cell in nanoindentation experiments and underestimation of Young's modulus.
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