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Hydrogen energy has been under close scrutiny by countries around the world. At present, the main technologies for utilizing hydrogen energy in transport power systems are hydrogen internal combustion engine (HICE) and proton exchange membrane fuel cell (PEMFC). Since both of them generate a large amount of waste heat, and waste heat recovery technology is one of the most promising means of utilizing waste heat to improve efficiency, this paper makes a comprehensive comparison of the two technologies in composite waste heat recovery (WHR) system in terms of modeled maximum efficiency, full operating condition efficiency and future predicted maximum efficiency. Based on the thermal efficiency analysis, the advantages, disadvantages, and development prospects of the two technologies in composite the WHR system are reevaluated. The results demonstrate that the efficiency of the HICE and PEMFC can be improved by 6.83% and 2.81%, with the use of WHR system, respectively. Under the full range of operating conditions, the HICE-WHR composite system has obvious efficiency advantage in middle-high load working condition, but PEMFC-WHR composite system has obvious efficiency advantage in low load working condition. Both of them will be very competitive and potential technology routes of hydrogen energy utilization for land transportation. [ABSTRACT FROM AUTHOR]

It is of great practical significance to utilize the agricultural carbon emission reduction effect of the policy of re-designation of counties as cities or city districts (RCCD) to achieve agricultural high-quality development. This paper uses panel data of 39 cities in the Yangtze River Delta region in China from 2010 to 2022, and adopts a staggered difference-in-difference model and a panel threshold model to identify the causal impact of the policy of RCCD on agricultural carbon emissions (ACE). We show that: (1) Overall, the policy of RCCD exerts a tangible dampening effect on ACE, with cities in the experimental group exhibiting a significant reduction of 0.069 in agricultural carbon emissions compared to the control group post-implementation of the policy. (2) A dual-threshold effect of environmental regulation emerges in the context of the policy of RCCD, wherein the impact on ACE varies depending on the level of environmental regulation. (3) The policy of RCCD exerts a notable inhibitory influence on urban ACE in cities with high urbanization levels, underdeveloped regions and central regions. (4) Agricultural green technology progress plays the mediating role in the relationship between the policy of RCCD and ACE. (5) The suppressive effect of the policy of RCCD on ACE is characterized by a delayed and enduring influence. Our study has both theoretical and practical implications for accelerating agricultural high-quality development. [ABSTRACT FROM AUTHOR]

This study provides a method for the rapid, non-destructive testing of the internal quality of Korla fragrant pears. The dielectric constant (ε′) and dielectric loss factor (ε″) of pear samples were tested at 100 frequency points (range = 0.1–26.5 GHz) using a vector network analyzer and coaxial probe. The variations in the dielectric parameters of fragrant pears were analyzed. The linear relationships between the dielectric parameters and internal quality were explored. Internal quality prediction models for Korla fragrant pears were built using partial least squares regression (PLSR), support vector regression (SVR) and particle swarm optimization–least squares support vector regression (PSO-LSSVR). The optimal model was then determined. There was a weak correlation between the dielectric parameters and soluble solid content (SSC) under a single frequency. The model based on PLSR and using ε′ as a variable predicted hardness the best, while the model based on PLSR using ε″ as a variable predicted SSC the best. Its R and MSE values were 0.77 and 0.073 in hardness prediction, respectively, and 0.91 and 0.087 in SSC prediction. This study provides a new method for the non-destructive online testing of the internal quality of Korla fragrant pears. [ABSTRACT FROM AUTHOR]

Ultrathin inorganic nanowires are an emerging class of building blocks for creating functional materials and devices, but there remains challenging to fine‐tune the structure and property of the nanowires at the molecular level. Here, this work shows that ultrathin polymer‐grafted gold nanowires (PG‐AuNWs) can exhibit bottlebrush polymer‐like physical behaviors and macroscopic properties. The hybrid PG‐AuNWs in solutions show polymer‐like viscoelasticity which can be finely regulated by controlling the structural parameters (e.g., length of the AuNWs, molecular weight of grafted polymers) of the PG‐AuNWs, the environmental conditions (e.g., temperature, solvent compositions), and the aging time. Furthermore, this work unravels at the molecular level that the conformational properties (e.g., contour length, persistence length, and mean‐squared radius of gyration) of the PG‐AuNWs can be correlated to their structural parameters following similar power‐law relations as molecular bottlebrush polymers. This work bridges the fundamental gap between polymer‐like inorganic nanowires and bottlebrush polymers, thus accelerating the development of new nanowire‐based functional hybrid materials and devices. [ABSTRACT FROM AUTHOR]

Detection of combustion instability is crucial for the safety and reliability of gas turbines. In this paper, the recurrence quantification analysis (RQA) and multi-fractal analysis (MFA) methods are applied to investigate the transition process from combustion noise to combustion instability in an industrial-scale combustor. Based on the dynamic pressure (DP) obtained from high pressure and high temperature tests, a novel method is proposed to construct early detection indicators (EDI) of combustion instability. The method is mainly based on the three-dimensional map of the recurrence rate, Hurst exponent, and root mean square ratio. A regression method and SVM are applied to define the classification boundary. For three test cases, the results showed that the proposed EDI can effectively detect the onset of combustion instability. Compared to the conventional method based on the root mean square levels of dynamic pressure, the EDI has capability to forecast the onset of combustion instability approximately a few hundred milliseconds in advance. [ABSTRACT FROM AUTHOR]