Using mesoporous carbon to pack polyethylene glycol as a shape-stabilized phase change material with excellent energy storage capacity and thermal conductivity

A novel shape-stabilized phase change material was successfully prepared using polyethylene glycol (PEG) as PCM and mesoporous carbon FDU-15 as support via the melting impregnation method. The structural and thermal properties of materials were measured by TEM, SEM, XRD, FT-IR, nitrogen adsorption-desorption isotherms and DSC, respectively. The maximum loading of PEG/FDU-15 reaches up to 75 wt%, and the corresponding crystallization ratio is 71%, which is superior to other mesoporous-based composite phase change materials. Molecular dynamic (MD) analysis showed that some PEG adhered to the pore wall with an amorphous structure which failed to crystallize, ultimately resulting in a gap between the measured latent heat and the theoretical value. It was interesting that the filling of PEG could stimulate the frequency shift of atomic vibration in FDU-15, which then just fell in the dominant vibrational zone of PEG, despite the suppressed atomic vibration of PEG after compounding. Accordingly, the thermal conductivity of the composite is more than 60% higher compared to pure PEG, which relates to the reinforced matching of the atomic vibration between the skeleton and PCM material. FDU-15 was applied to pack PCM for the first time and delivered a better thermal performance compared with other mesopore-based composite PCMs

Thermal properties of PEG/MOF-5 regularized nanoporous composite phase change materials: A molecular dynamics simulation

In this paper, a metal-organic framework MOF-5 loaded polyethylene glycol (PEG) nanowire was used to form composite phase change material PEG/MOF-5. The molecular dynamics method was used to simulate the thermal conductivity, melting point and latent heat by G-K function and pseudo-supercritical path method, respectively. The results show that the pores of MOF-5 promote the increase of the angle of the PEG main chain and the extension of the helical segment. Therefore, the thermal conductivity of the composite (0.60 W/m·K) is 17.6% and 100% higher than that of the PEG nanowire (0.51 W/m∙K) and the skeleton (about 0.3 W/m∙K), respectively. At the same time, MOF-5 can improve the crystallinity of the PEG to a certain extent. The predicted latent heat of PEG/MOF-5 composite material is as high as 78.4 kJ/kg with a mass filling rate of 50%. This paper explores the mechanism from a microscopic perspective in order to provide models and data for the thermal design of such materials

A review of phase change heat transfer in shape-stabilized phase change materials (ss-PCMs) based on porous supports for thermal energy storage

Latent heat thermal energy storage (LHTES) uses phase change materials (PCMs) to store and release heat, and can effectively address the mismatch between energy supply and demand. However, it suffers from low thermal conductivity and the leakage problem. One of the solutions is integrating porous supports and PCMs to fabricate shape-stabilized phase change materials (ss-PCMs). The phase change heat transfer in porous ss-PCMs is of fundamental importance for determining thermal-fluidic behaviours and evaluating LHTES system performance. This paper reviews the recent experimental and numerical investigations on phase change heat transfer in porous ss-PCMs. Materials, methods, apparatuses and significant outcomes are included in the section of experimental studies and it is found that paraffin and metal foam are the most used PCM and porous support respectively in the current researches. Numerical advances are reviewed from the aspect of different simulation methods. Compared to representative elementary volume (REV)-scale simulation, the pore-scale simulation can provide extra flow and heat transfer characteristics in pores, exhibiting great potential for the simulation of mesoporous, microporous and hierarchical porous materials. Moreover, there exists a research gap between phase change heat transfer and material preparation. Finally, this review outlooks the future research topics of phase change heat transfer in porous ss-PCMs

Spatio-Temporal Dynamic and Structural Characteristics of Land Use/Cover Change Based on a Complex Network: A Case Study of the Middle Reaches of Yangtze River Urban Agglomeration

Due to the rapid urbanization and industrialization, urban agglomeration has become the area with the most drastic and concentrated land use change. The research on the evolution law and structural characteristics of urban agglomeration land use system is of great significance for the sustainable development. Taking the middle reaches of the Yangtze River urban agglomeration (MRYRUA) of China as the study area, we analyzed the phasic changes from 1980 to 2018 in land use/cover in the MRYRUA as well as the spatial differences between the three core regions. Furthermore, the transfer matrix of land use/cover change (LUCC) was converted to network, with land use types as nodes and conversion relationships between different land types as network connecting lines. Complex network indexes such as centrality, diffusion, and dominant flow were applied to identify the major changes in land use types, key change paths, and transformation patterns. The results show that: (1) in the past 40 years, the building land area in the MRYRUA has increased significantly, while the area of crop land and forest has, and still is, decreasing at an accelerated rate; (2) in terms of the scale, structure, and spatial distribution of land use transfer, there are distinct differences among the three core regions. The Wuhan metropolitan area has the largest intensity of land use transfer and the most drastic structural adjustment; (3) in all four periods, the land use transition network, crop land, and water bodies are the key land use types. Over time, the influence of building land and forest in the land use transition network has increased; and (4) the first transfer direction of each land use type was stable during different periods, such as the transfer of crop land to water bodies and building land, the transfer of water bodies to crop land, and the mutual transformations among crop land and forest, indicating a stable transfer pattern in the MRYRUA

Spatio-Temporal Dynamic and Structural Characteristics of Land Use/Cover Change Based on a Complex Network: A Case Study of the Middle Reaches of Yangtze River Urban Agglomeration

Due to the rapid urbanization and industrialization, urban agglomeration has become the area with the most drastic and concentrated land use change. The research on the evolution law and structural characteristics of urban agglomeration land use system is of great significance for the sustainable development. Taking the middle reaches of the Yangtze River urban agglomeration (MRYRUA) of China as the study area, we analyzed the phasic changes from 1980 to 2018 in land use/cover in the MRYRUA as well as the spatial differences between the three core regions. Furthermore, the transfer matrix of land use/cover change (LUCC) was converted to network, with land use types as nodes and conversion relationships between different land types as network connecting lines. Complex network indexes such as centrality, diffusion, and dominant flow were applied to identify the major changes in land use types, key change paths, and transformation patterns. The results show that: (1) in the past 40 years, the building land area in the MRYRUA has increased significantly, while the area of crop land and forest has, and still is, decreasing at an accelerated rate; (2) in terms of the scale, structure, and spatial distribution of land use transfer, there are distinct differences among the three core regions. The Wuhan metropolitan area has the largest intensity of land use transfer and the most drastic structural adjustment; (3) in all four periods, the land use transition network, crop land, and water bodies are the key land use types. Over time, the influence of building land and forest in the land use transition network has increased; and (4) the first transfer direction of each land use type was stable during different periods, such as the transfer of crop land to water bodies and building land, the transfer of water bodies to crop land, and the mutual transformations among crop land and forest, indicating a stable transfer pattern in the MRYRUA

Abnormal meiosis in an intersectional allotriploid of Populus L. and segregation of ploidy levels in 2x × 3x progeny.

Triploid plants are usually highly aborted owing to unbalanced meiotic chromosome segregation, but limited viable gametes can participate in the transition to different ploidy levels. In this study, numerous meiotic abnormalities were found with high frequency in an intersectional allotriploid poplar (Populus alba × P. berolinensis 'Yinzhong'), including univalents, precocious chromosome migration, lagging chromosomes, chromosome bridges, micronuclei, and precocious cytokinesis, indicating high genetic imbalance in this allotriploid. Some micronuclei trigger mini-spindle formation in metaphase II and participate in cytokinesis to form polyads with microcytes. Unbalanced chromosome segregation and chromosome elimination resulted in the formation of microspores with aneuploid chromosome sets. Fusion of sister nuclei occurs in microsporocytes with precocious cytokinesis, which could form second meiotic division restitution (SDR)-type gametes. However, SDR-type gametes likely contain incomplete chromosome sets due to unbalanced segregation of homologous chromosomes during the first meiotic division in triploids. Misorientation of spindles during the second meiotic division, such as fused and tripolar spindles with low frequency, could result in the formation of first meiotic division restitution (FDR)-type unreduced gametes, which most likely contain three complete chromosome sets. Although 'Yinzhong' yields 88.7% stainable pollen grains with wide diameter variation from 23.9 to 61.3 μm, the pollen viability is poor (2.78% ± 0.38). A cross of 'Yinzhong' pollen with a diploid female clone produced progeny with extensive segregation of ploidy levels, including 29 diploids, 18 triploids, 4 tetraploids, and 48 aneuploids, suggesting the formation of viable aneuploidy and unreduced pollen in 'Yinzhong'. Individuals with different chromosome compositions are potential to analyze chromosomal function and to integrate the chromosomal dosage variation into breeding programs of Populus

Efficient Quantum Simulation of an Anti-P-Pseudo-Hermitian Two-Level System

Besides Hermitian systems, quantum simulation has become a strong tool to investigate non-Hermitian systems, such as PT-symmetric, anti-PT-symmetric, and pseudo-Hermitian systems. In this work, we theoretically investigate quantum simulation of an anti-P-pseudo-Hermitian two-level system in different dimensional Hilbert spaces. In an arbitrary phase, we find that six dimensions are the minimum to construct the anti-P-pseudo-Hermitian two-level subsystem, and it has a higher success probability than using eight dimensions. We find that the dimensions can be reduced further to four or two when the system is in the anti-PT-symmetric or Hermitian phase, respectively. Both qubit-qudit hybrid and pure-qubit systems are able to realize the simulation, enabling experimental implementations in the near future