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• A comprehensive review of the current research status of microchannel heat sinks was conducted from the perspectives of channel configuration, secondary structure, combined structure, and special cooling agents. • An analysis of the heat transfer and flow characteristics of various microchannel heat sinks was conducted. • A comparison of the advantages and disadvantages of various microchannel heat sinks was made. Enhanced heat transfer technology can be divided into active technology and passive technology based on whether external power is consumed. Due to the absence of external energy consumption, passive technology is more reliable than active cooling technology. Microchannel heat sink (MCHS) are widely used for heat dissipation in the field of microelectronics. In recent years, due to the continuous miniaturization of electronic chips and the high heat flux per unit area (about 300 W/cm2), the passive enhanced heat transfer technology of microchannel heat sinks has developed rapidly. This article provides a comprehensive review of passive enhanced heat transfer technology in MCHS. It introduces the influence of channel configuration, secondary structure, combined structure, and different heat transfer media on the heat transfer capacity and pressure drop of microchannel heat sinks. Finally, a summary is given based on the collected data. [ABSTRACT FROM AUTHOR]

Evolutionary convergence is one of the most striking examples of adaptation driven by natural selection. However, genomic evidence for convergent adaptation to extreme environments remains scarce. Here, we assembled reference genomes of two alpine plants, Saussurea obvallata (Asteraceae) and Rheum alexandrae (Polygonaceae), with 37,938 and 61,463 annotated protein‐coding genes. By integrating an additional five alpine genomes, we elucidated genomic convergence underlying high‐altitude adaptation in alpine plants. Our results detected convergent contractions of disease‐resistance genes in alpine genomes, which might be an energy‐saving strategy for surviving in hostile environments with only a few pathogens present. We identified signatures of positive selection on a set of genes involved in reproduction and respiration (e.g., MMD1, NBS1, and HPR), and revealed signatures of molecular convergence on genes involved in self‐incompatibility, cell wall modification, DNA repair and stress resistance, which may underlie adaptation to extreme cold, high ultraviolet radiation and hypoxia environments. Incorporating transcriptomic data, we further demonstrated that genes associated with cuticular wax and flavonoid biosynthetic pathways exhibit higher expression levels in leafy bracts, shedding light on the genetic mechanisms of the adaptive "greenhouse" morphology. Our integrative data provide novel insights into convergent evolution at a high‐taxonomic level, aiding in a deep understanding of genetic adaptation to complex environments. [ABSTRACT FROM AUTHOR]

Daytime HONO photolysis is an important source of atmospheric hydroxyl radicals (OH). Knowledge of HONO formation chemistry under typical haze conditions, however, is still limited. In the Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain in 2018, we investigated the wintertime HONO formation and its atmospheric implications at a rural site Gucheng. Three different episodes based on atmospheric aerosol loading levels were classified: clean periods (CPs), moderately polluted periods (MPPs) and severely polluted periods (SPPs). Correlation analysis revealed that HONO formation via heterogeneous conversion of N O 2 was more efficient on aerosol surfaces than on ground, highlighting the important role of aerosols in promoting HONO formation. Daytime HONO budget analysis indicated a large missing source (with an average production rate of 0.66 ± 0.26, 0.97 ± 0.47 and 1.45 ± 0.55 ppbV/hr for CPs, MPPs and SPPs, respectively), which strongly correlated with photo-enhanced reactions (N O 2 heterogeneous reaction and particulate nitrate photolysis). Average OH formation derived from HONO photolysis reached up to (0.92 ± 0.71), (1.75 ± 1.26) and (1.82 ± 1.47) ppbV/hr in CPs, MPPs and SPPs respectively, much higher than that from O 3 photolysis (i.e., (0.004 ± 0.004), (0.006 ± 0.007) and (0.0035 ± 0.0034) ppbV/hr). Such high OH production rates could markedly regulate the atmospheric oxidation capacity and hence promote the formation of secondary aerosols and pollutants. [ABSTRACT FROM AUTHOR]

In this study, the physical properties of refractory BC (rBC) including mass concentration, core size distribution and mixing state were in-situ characterized with a single particle soot photometer (SP2) at a polluted rural site in the North China Plain in November 2018. The average rBC mass concentration is 4.12 ± 2.47 μg m−3, accounting for 6.26% of PM 1 mass. Its diurnal variation shows that the rBC concentration is affected by both the local residential activities and the evolution of planetary boundary layer (PBL). And a broader rBC core mass size distribution (CMSD) can be observed in the afternoon. The CMSD show a primary mode with peak diameter (D m) of ~222 nm, and a small secondary mode with D m of ~687 nm. The average absolute coating thickness (ACT) of rBC particles is 50 nm and the bulk relative coating thickness (BRCT) is about 1.7, indicating a relatively high aging level of rBC. The correlation analysis between SP2-separated rBC and PMF-separated OA factors indicate that rBC with different core size (D c) and ACT may be originated from different sources. The rBC contributed by coal combustion is distributed throughout a large D c range (~70–500 nm). The rBC particles emitted by traffic sources have small core sizes and thin coating thickness (D c < 180 nm and ACT <50 nm); while the rBC particles emitted from biomass burning show a higher degree of aging (ACT >250 nm). In addition, the secondary mode of rBC particles are likely to be originated from coal combustion. • High concentration of rBC with relatively high aging level was observed in the North China Plain • The rBC core mass size distribution was bimodal distribution with a small secondary mode at ~687 nm • The secondary mode of rBC was likely to be contributed by coal combustion [ABSTRACT FROM AUTHOR]

Cloud condensation nuclei (CCN) play an important role in the formation and evolution of cloud droplets. However, the dataset of global CCN number concentration (N CCN) is still scarce due to the lack of direct CCN measurements, hindering an accurate evaluation of its climate effects. Alternative approaches to determine N CCN have thus been proposed to calculate N CCN based on measurements of other aerosol properties, such as particle number size distribution, bulk aerosol chemical composition and aerosol optical properties. To better understand the interaction between haze pollution and climate, we performed direct CCN measurements in the winter of 2018 at the Gucheng site, a typical polluted suburban site in North China Plain (NCP). The results show that the average CCN concentrations were 3.81 × 103 cm−3, 5.35 × 103 cm−3, 9.74 × 103 cm−3, 1.27 × 104 cm−3, 1.44 × 104 cm−3 at measured supersaturation levels of 0.114%, 0.148%, 0.273%, 0.492% and 0.864%, respectively. Based on these observational data, we have further investigated two methods of calculating N CCN from: (1) bulk aerosol chemical composition and particle number size distribution; (2) bulk aerosol chemical composition and aerosol optical properties. Our results showed that both methods could well reproduce the observed concentration (R 2 > 0.88) and variability of N CCN with a 9% to 23% difference in the mean value. Further error analysis shows that the estimated N CCN tends to be underestimated by about 20% during the daytime while overestimated by <10% at night compared with the measured N CCN. These results provide quantitative instructions for the N CCN prediction based on conventional aerosol measurements in the NCP. Unlabelled Image • Conventional measurements of PNSD and bulk aerosol chemical composition perform well in predicting N CCN • The estimation of N CCN based on conventional measurements of AOP can be applicable under SSs lower than 0.114% • Relative deviations between calculated and measured N CCN suggest significant diurnal variations of aerosol hygroscopicity. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols play an important role in modifying the PBL meteorology and severity of haze pollution through its radiative effect (Ding et al. 2016). The radiative effect of BC strongly depends on its mixing state or coating thickness, which is subject to the aging process in the atmosphere (Cheng et al. 2006, 2008). North China Plain (NCP) is one of the areas where both severe haze and high abundance of BC have been reported. By using a single particle soot photometer (SP2) and complimentary measurements, we investigated the aging of BC during several severe haze events in the North China Plain during our winter campaign in 2018. We calculated the size-resolved mixing state and aging rate of BC in the ambient air under different pollution levels. Our results show a fast aging of BC especially during the haze events with high concentrations of air pollutants and condensable vapors. The occurrence of fog episodes in the campaign enables us to analyze the BC-droplet interactions, especially the effect of aerosol size and coating thickness on its activation and removal, which is key for understanding the aerosol-cloud and aerosol fog interactions. Moreover, we find that most coated BC particles can be classified to a "core-shell" type while only a small fraction of BC-containing particles is in an "attached" type. It suggests that the traditional Core-Shell model should still be applicable for modeling the radiative properties of BC in the North China Plain. Based on the Mie model calculation, we determined their absorption enhancement factor of BC due to the aging process and discussed its implication to the formation of severe haze.References:Ding, A. J., Huang, X., Nie, W., Sun, J. N., Kerminen, V. M., Petaja, T., Su, H., Cheng, Y. F., Yang, X. Q., Wang, M. H., Chi, X. G., Wang, J. P., Virkkula, A., Guo, W. D., Yuan, J., Wang, S. Y., Zhang, R. J., Wu, Y. F., Song, Y., Zhu, T., Zilitinkevich, S., Kulmala, M., and Fu, C. B.: Enhanced haze pollution by black carbon in megacities in China, Geophys. Res. Lett., 43, 2873-2879, 10.1002/2016gl067745, 2016.Cheng, Y. F., Eichler, H., Wiedensohler, A., Heintzenberg, J., Zhang, Y. H., Hu, M., Herrmann, H., Zeng, L. M., Liu, S., Gnauk, T., Bruggemann, E., and He, L. Y.: Mixing state of elemental carbon and non-light-absorbing aerosol components derived from in situ particle optical properties at Xinken in Pearl River Delta of China, J. Geophys. Res.-Atmos., 111, 18, 10.1029/2005jd006929, 2006.Cheng, Y. F., Wiedensohler, A., Eichler, H., Su, H., Gnauk, T., Brueggemann, E., Herrmann, H., Heintzenberg, J., Slanina, J., Tuch, T., Hu, M., and Zhang, Y. H.: Aerosol optical properties and related chemical apportionment at Xinken in Pearl River Delta of China, Atmos. Environ., 42, 6351-6372, 10.1016/j.atmosenv.2008.02.034, 2008. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is the most important light-absorbing species in the atmosphere and has a strong positive direct radiative forcing. Recent studies found that BC-containing particles may also modify the structure of planetary boundary layer and thus enhance haze pollution, especially in densely populated areas, for instance, in China. It is however difficult to quantify these effects due to their complex mixing state, hygroscopicity and the high spatial variability of concentration. During an intensive field campaign conducted in the North China Plain in a cold season, the mass size distribution and mixing state of BC was measured with a single particle soot photometer (SP2). During a severe haze event, the BC mass concentration exceeded 15 ug m-3. Stemming from the strong aging process under high relative humidity condition, freshly emitted BC particle was observed to turn into internally mixing within a short time scale. To understand the variation of the hygroscopicity of BC during its aging process, the hygroscopic growth factor of BC-containing particles was measured with a combination of a hygroscopic tandem differential mobility analyzer and a SP2. The particle hygroscopic growth factor was found to be correlated with the volume fraction of BC. During haze events, a fraction of the more-hygroscopic mode particles was observed to contain BC cores; while a minor fraction of the hydrophobic mode particles contained no BC. [ABSTRACT FROM AUTHOR]