When plastics enter the environment, they are exposed to abiotic and biotic impacts, resulting in degradation and the formation of micro- and nanoplastic. Microplastic is ubiquitous in every ...environmental compartment. Nevertheless, the underlying degradation processes are not yet fully understood. Here, we studied the abiotic degradation of commonly used semi-crystalline, low-density polyethylene (LDPE) in a long-term accelerated weathering experiment combining several macro- and microscopic methods. Based on our observations, the degradation of LDPE proceeds in three stages. Initially, LDPE objects are prone to abrasion, followed by a period of surface cracking. A large number of secondary particles with a high degree of crystallinity are formed, with sizes down to the nanometer scale. These particles consist of highly polar oligomers leading to agglomeration in the final stage. We therefore suppose that weathered microplastic and nanoplastic particles will attach to colloidal environmental matter. This offers an explanation for the absence of free nanoplastic particles in natural samples.
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•Knowledge on environmental degradation from macro- to microplastic is lacking.•Long-term, accelerated laboratory weathering of semi-crystalline LDPE•Combining a multitude of analytical methods on a macro- and microscopic scale•Development of a three-stage degradation model for semi-crystalline polymers•Nanoplastic particles visualized, strongly adhering to microplastic particles
To formulate the daily generation scheduling of a wind-solar-hydro complementary system (WSHCS), the hourly forecasts of the reservoir inflow, wind speed, and sunlight intensity within a day and ...their longer prediction can be used to assess the benefit of the day-ahead and remaining stages, respectively. Thus, the current two-stage model coupling these forecasts can efficiently maximize the total benefits of day-ahead and remaining stages. However, the two-stage model does not consider the significant difference between non-adjustable and adjustable periods for hydropower. Namely, the hydro unit commitment should be decided in the current stage (non-adjustable period), and it can be adjusted in the coming stage (adjustable period). To address this issue, a three-stage model, including the day-ahead non-adjustable stage, the day-ahead adjustable stage, and the remaining period stage, is proposed to formulate a daily generation scheduling of the WSHCS. The Guandi wind-solar-hydro hybrid power plant on China's Yalong River is selected as a case study. Results show that compared with the two-stage model, the proposed three-stage operation model can increase the average energy production of the WSHCS by 2.23 GWh for typical days, and the average power curtailment rate reduces by 0.26%. A three-layer nested approach can simplify from 576 to 26 decision variables for the high-dimensional three-stage model, and improve the computational efficiency. Thus, the proposed method could guide the daily generation scheduling of a WSHCS.
•A model coupling current non-adjustable, coming adjustable and remaining stages is proposed.•A benefit-risk indicators system considering three-stage is established.•A three-layer nested approach is used to solve the high-dimension model.•The proposed model provides guidance for daily generation scheduling.
•Propose a three-stage resilient enhancement approach under hurricanes.•Coordinate MEGs with fault isolation and the forced cut-off of wind power.•Establish the step function of wind power ...cut-off.•Introduce auxiliary variables indicating faulted, energized, and outage zones.•Establish a stochastic model solved by the modified progressive hedging algorithm.
Mobile emergency generators (MEGs) have been widely used to enhance the resilience of distribution systems. However, the traditional two-stage MEG dispatch strategies focus on only the prepositioning and reallocation before and after hurricanes, neglecting the resilient operation during hurricanes. Therefore, this paper proposes a novel three-stage MEG dispatch model to enhance the resilience of distribution systems. To improve the survivability of distribution systems during hurricanes, the fault isolation operations by remote-controlled switches (RCSs) and forced cut-off of wind power are coordinated with MEG dispatch, which is prepositioned as a preparedness measure before hurricanes. Based on the realization of fault scenarios during hurricanes, MEG reallocation and fault isolation by manual switches (MSs) are conducted to boost the restoration of the distribution system after hurricanes. Considering the uncertainties of wind power cut-off and line faults, the proposed method is incorporated into a stochastic dispatch model, which takes the conditional value-at-risk (CVaR) as an objective function to improve robustness in extreme cases. In addition, the computational burden with multiple scenarios is reduced by the modified progressive hedging algorithm (PHA). Finally, the proposed method is validated on a modified IEEE 33-bus distribution system. Simulation results show that the survivability and restoration of the distribution system can be enhanced by the proposed approach.
A 3‐stage model is used to evaluate the results of an experimental campaign, previously carried out with the aim of studying the deflection of reinforced concrete structures made with reinforced ...concrete (RC) and fiber‐reinforced concrete (R/FRC). In particular, 12 four‐point bending tests were performed on beams, whose cross‐sections were obtained by combining four effective ratios of the tensile reinforcement (i.e., 0.73%, 1.7%, 3%, and 6.3%), two concrete covers (i.e., 32 mm and 82 mm), and three amounts of steel fibers (0, 0.5%, and 1.0% in volume) recycled from end‐of‐life tyres. In reinforced beams with low reinforcement ratios, there is a reduction in deflections and the load at yielding of steel increases with the content of fibers. On the contrary, the mechanical behavior of R/FRC and RC beams does not substantially differ in presence of a high effective reinforcement ratio. These experimental observations are in accordance with the results of the three‐stage model, introduced herein to predict the possible variation of the load‐deflection curves. For a given deflection, the model provides a possible range of applied loads, whose upper bound is related to the situation of incipient cracking (i.e., the maximum tension stiffening effects), whereas the lower bound concerns a fully cracked beam (i.e., the minimum tension stiffening effects). Regardless of the content of fibers, the difference between the upper and lower bounds vanishes in highly reinforced concrete beams.
In this paper, two types of parameters representing tabletability and compactibility profiles of a series of α-lactose monohydrate powders, ranging in particle size from approximately 3.5 to 203 µm, ...are derived and compared. By approximating the tabletability profiles using a three-stage model and the compactibility profiles using the Ryshkewitch-Duckworth equation, two compaction rate parameters and two compaction endpoint parameters were derived. The original median particle diameter had generally a strong effect on the tablet tensile strength and hence the tabletability and compactibility profiles. The experimental profiles were well approximated by the models used, and the compaction parameters were regarded as representative of the experimental profiles. The compaction endpoint parameters increased with decreased particle size and were controlled by the same structural feature as the compacts. The tabletability rate parameter also increased with decreased particle size and correlated well with the tabletability endpoint parameter. The compactibility rate parameter tended to increase with decreased particle size, but the effect was limited; moreover, no general correlation was obtained with the compactibility endpoint parameter. It is concluded that compactibility and tabletability parameters collectively provide a concentrated description of the compaction properties of a powder.
A free trial of an information technology service (ITS) provides users an opportunity to obtain direct usage experience without purchase commitment, which can significantly reduce their uncertainty ...about the utility and quality of the ITS and promote their intention of final purchasing. Previous studies of user behavior in a free trial of ITS have mainly focused on either the adoption intention in the pre-trial stage or purchase intention in the post-trial stage. There is a lack of study investigating the trial stage that facilitates the transition and connection between these two separately studied stages. In this study, we view free trial as a motivated learning process and propose a Three-Stage Model (TSM) based on the learning motivation theory and reference-dependent theory to investigate users’ free trial behavior dynamics in moving from motivation to trial, making efforts to gain trial experience, and finally making a further purchase decision after the trial. We collected 377 users’ free trial experience to test our TSM using partial least squares-based structural equation modeling. Our results indicate that the perceived trial benefit and social influence strongly motivate user’s willingness to trial and that the utility experience and flow experience gained through trial effort leads to a willingness to accept and ultimately affect user’s willingness to pay through the mediation effect of expected additional value and price justification. Our study contributes to the theory that explains the dynamics of user decision-making behavior in the context of a free trial of ITS.
Due to the increased frequency of extreme weather events and the implementation of the China's dual-carbon target, thermal power companies have been under pressure to construct green infrastructure ...and to actively pursue low-carbon transformation in response to stricter environmental regulations. This research thus selects 30 listed thermal power enterprises in China as study objects and assesses their green investment efficiency in the low-carbon transition process using three-stage DEA evaluation model with environmental regulation as an exogenous variable. Based on this, a benchmark regression model is used to corroborate the relationship between environmental regulation and green investment. Simultaneously, we carry out analysis to compare the correlation between thermal power firms' green investment efficiency and their focus on green investments. The results show in terms of total efficiency that environmental regulation significantly improves the total efficiency of 80% of thermal power enterprises compared to the absence of this exogenous variable. With the addition of environmental regulation, firms' total efficiency declines gradually in general from 2018 to 2022, with the mean value of efficiency falling by 0.068. In terms of stage-specific efficiency, the efficiency of the green investment stage of the majority of firms is between 0.3 and 0.6, which is much lower than that of the operational stage and the market performance stage. In terms of sub-indicator efficiency, both green investment efficiency and social donation efficiency among thermal power enterprises show obvious polarization, with 30% of them having an efficiency of 1 and 30% less than 0.1. In terms of green investment focus, thermal power unit renovation has a more obvious role in boosting the green investment efficiency of thermal power enterprises than do wind power and photovoltaic projects. Therefore, both governmental departments and thermal power enterprises need to take active measures in order to achieve green transformation from the perspective of green investment efficiency. Through the segmentation of important projects of green investment, this paper provides a reasonable investment direction reference for the sustainable transformation of China's thermal power industry. It also provides a rich and novel theoretical basis for the Chinese government to further improve the relevant environmental protection laws and regulations of thermal power industry.
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