a b s t r a c tIt has been recently shown that a macroscopic fundamental diagram (MFD) linking spacemean network flow, density and speed exists in the urban transportation networks under some conditions. An MFD is further well defined if the network is homogeneous with links of similar properties. This collective behavior concept can also be utilized to introduce simple control strategies to improve mobility in homogeneous city centers without the need for details in individual links. However many real urban transportation networks are heterogeneous with different levels of congestion. In order to study the existence of MFD and the feasibility of simple control strategies to improve network performance in heterogeneously congested networks, this paper focuses on the clustering of transportation networks based on the spatial features of congestion during a specific time period. Insights are provided on how to extend this framework in the dynamic case. The objectives of partitioning are to obtain (i) small variance of link densities within a cluster which increases the network flow for the same average density and (ii) spatial compactness of each cluster which makes feasible the application of perimeter control strategies. Therefore, a partitioning mechanism which consists of three consecutive algorithms, is designed to minimize the variance of link densities while maintaining the spatial compactness of the clusters. Firstly, an over segmenting of the network is provided by a sophisticated algorithm (Normalized Cut). Secondly, a merging algorithm is developed based on initial segmenting and a rough partitioning of the network is obtained. Finally, a boundary adjustment algorithm is designed to further improve the quality of partitioning by decreasing the variance of link densities while keeping the spatial compactness of the clusters. In addition, both density variance and shape smoothness metrics are introduced to identify the desired number of clusters and evaluate the partitioning results. These results show that both the objectives of small variance and spatial compactness can be achieved with this partitioning mechanism. A simulation in a real urban transportation network further demonstrates the superiority of the proposed method in effectiveness and robustness compared with other clustering algorithms.

Research on congestion propagation in large urban city networks has been mainly based on microsimulations of link-level traffic dynamics. However, both the unpredictability of travel behaviors and high complexity of accurate physical modeling remain challenging and simulation results may be far time consuming and not realistic. The main purpose of this paper is to reveal the hidden information during the process of congestion formation by exploring empirical data from large-scale urban networks. Specifically, we aim at studying the spatiotemporal relation of congested links, observing congestion propagation from an macroscopic perspective, and finally identifying critical congestion regimes to aid the design of peripheral control strategies. To achieve these goals, we use maximum connected component of congested links to capture congestion propagation in the city by utilizing a large dataset of 20,000 taxis with GPS data from Shenzhen of China. We present the empirical macroscopic fundamental diagrams of congested regions observed in propagation and quantify the critical congestion regimes. The findings show that the proposed methodology can effectively distinguish the congestion pockets from the rest of the network and efficiently track the congestion evolution in linear time .3

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Printed circuit heat exchanger (PCHE) is a promising regenerative device in the sCO2 power cycle, with the advantages of a large specific surface area and compact structure. Its tiny and complex flow channel structure brings enhanced heat transfer performance, while increasing pressure drop losses. It is, thus, important to balance heat transfer and flow resistance performances with the consideration of sCO2 as the working agent. Herein, three-dimensional models are built with a full consideration of fluid flow and heat transfer fields. A trapezoidal channel is developed and its thermal–hydraulic performances are compared with the straight, the S-shape, and the zigzag structures. Nusselt numbers and the Fanning friction factors are analyzed with respect to the changes in Reynolds numbers and structure geometric parameters. A sandwiched structure that couples two hot channels with one cold channel is further designed to match the heat transfer capacity and the velocity of sCO2 flows between different sides. Through this novel design, we can reduce the pressure drop by 75% and increase the regenerative efficiency by 5%. This work can serve as a solid reference for the design and applications of PCHEs.

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Peach (Prunus persica (L.) Batsch) is one of the most popular fruits grown in Northern China. In July 2021, a fruit rot outbreak on the peach cultivar “Yonglian Sweet” occurred after unusual rains in Baoding, Hebei Province, China. Sixty peach trees from three orchards were assessed, and a 30% disease incidence was estimated. The disease initiated as a small concave spot on the fruit surface expanding circularly rotting the fruit (3-5 cm deep) with the appearance of grayish-white mycelia (Figure S1A). The infected fruit did not disintegrate but turned light brown. To identify the pathogen, 20 infected fruits were collected, and fruit tissues from lesion margins were inoculated on the potato dextrose agar (PDA) medium. A total of 15 fungal pure cultures with highly similar morphological characteristics were obtained by the hyphal-tipping method. The fungal culture formed smooth-edged colonies of extensive, dense, wooly aerial mycelium, with color changing from sienna to luteous, and to grayish-white along the radius of colonies (Figure S1B) Chlamydospores were extensive and developed micro-sclerotia after 20 d of growth. The conidiophore produced three branches in a “broom” shape, with the primary branch ranging 7.5-25.0 μm in length, the secondary branch 5.5-15.5 μm, and the tertiary branch 10-12.5 μm (N = 30). The top of the tertiary branch tapered and produced conidia. Conidia were colorless and culm-like, 40.0-57.5 μm long and 3.8-6.25 μm wide (N = 30). Hyphae occasionally produced spherical chlamydospores with a diameter of around 7.5 μm (N = 30). Conidia germinated after 12 h in moist conditions, and germ tubes originated from multiple points on the conidia. Based on these morphological features, the isolated fungus was identified as Calonectria spp. (Lombard et al. 2010). Six loci, including ITS, act, cmdA, his3, tef1, and tub2, were amplified and sequenced for molecular identification of an isolate F099 using primers listed in Table S1. The obtained ITS (528 bp, GenBank accession no. OL635556), act (263 bp, OL694221), cmdA (470 bp, OL694222), his3 (432 bp, OL694223), tef1 (487 bp, OL694224), and tub2 (535 bp, OL694225) sequences showed 100% similarity to the ex-type strain of Calonectria canadiana, CMW 23673 (accession nos. MT359667, MT334976, MT335206, MT335446, MT412737, and MT412958, respectively; Figure S1D) (Kang et al. 2001, Lechat et al. 2010, Liu et al. 2020). The isolate F099 of C. canadiana was further subjected to pathogenicity tests. Koch’s postulates were performed by placing three mycelial disks (ten-day old, 5 mm) with conidia on the sterile needle-acupunctured surface of healthy fruits of the peach cultivar “Yonglian Sweet” (N= 10). Mock inoculations with sterile PDA disks were served as a control. All the inoculated fruits were kept in a moist chamber (25℃, 16-h light and 8-h dark period). The inoculation assay was repeated twice. Rotting symptoms developed on all the inoculated fruits about 5 days post-inoculation (dpi) and grayish-white mycelia appeared around ten days post inoculation while mock inoculated fruits did not show any rotting. The pathogen of interest was re-isolated from the inoculated fruits and validated as C. canadiana by ITS and tef1 sequences. All above evidence collectively indicates that the fungal pathogen causing the peach fruit rot is C. canadiana. The new host plant and new geographic distribution reported here will inform future management of this fungal species.