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A Nationwide Nitrogen Deposition Monitoring Network (NNDMN) containing 43 monitoring sites was established in China to measure gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− in air and/or precipitation from 2010 to 2014. Wet/bulk deposition fluxes of Nr species were collected by precipitation gauge method and measured by continuous-flow analyzer; dry deposition fluxes were estimated using airborne concentration measurements and inferential models. Our observations reveal large spatial variations of atmospheric Nr concentrations and dry and wet/bulk Nr deposition. On a national basis, the annual average concentrations (1.3–47.0 μg N m−3) and dry plus wet/bulk deposition fluxes (2.9–83.3 kg N ha−1 yr−1) of inorganic Nr species are ranked by land use as urban > rural > background sites and by regions as north China > southeast China > southwest China > northeast China > northwest China > Tibetan Plateau, reflecting the impact of anthropogenic Nr emission. Average dry and wet/bulk N deposition fluxes were 20.6 ± 11.2 (mean ± standard deviation) and 19.3 ± 9.2 kg N ha−1 yr−1 across China, with reduced N deposition dominating both dry and wet/bulk deposition. Our results suggest atmospheric dry N deposition is equally important to wet/bulk N deposition at the national scale. Therefore, both deposition forms should be included when considering the impacts of N deposition on environment and ecosystem health.

Merons which are topologically equivalent to one-half of skyrmions can exist only in pairs or groups in two-dimensional (2D) ferromagnetic (FM) systems. The recent discovery of meron lattice in chiral magnet Co 8 Zn 9 Mn 3 raises the immediate challenging question that whether a single meron pair, which is the most fundamental topological structure in any 2D meron systems, can be created and stabilized in a continuous FM film? Utilizing winding number conservation, we develop a new method to create and stabilize a single pair of merons in a continuous Py film by local vortex imprinting from a Co disk. By observing the created meron pair directly within a magnetic field, we determine its topological structure unambiguously and explore the topological effect in its creation and annihilation processes. Our work opens a pathway towards developing and controlling topological structures in general magnetic systems without the restriction of perpendicular anisotropy and Dzyaloshinskii–Moriya interaction. A meron is one half of a skyrmion but whether a single meron pair can be created and stabilized remains a challenging question. Here, Gao et al. develop a method to create and stabilize individual pairs of merons in a continuous Py film by local vortex imprinting from Co disks.

Flexoelectricity refers to electric polarization generated by heterogeneous mechanical strains, namely strain gradients, in materials of arbitrary crystal symmetries. Despite more than 50 years of work on this effect, an accurate identification of its coupling strength remains an experimental challenge for most materials, which impedes its wide recognition. Here, we show the presence of flexoelectricity in the recently discovered polar vortices in PbTiO 3 /SrTiO 3 superlattices based on a combination of machine-learning analysis of the atomic-scale electron microscopy imaging data and phenomenological phase-field modeling. By scrutinizing the influence of flexocoupling on the global vortex structure, we match theory and experiment using computer vision methodologies to determine the flexoelectric coefficients for PbTiO 3 and SrTiO 3 . Our findings highlight the inherent, nontrivial role of flexoelectricity in the generation of emergent complex polarization morphologies and demonstrate a viable approach to delineating this effect, conducive to the deeper exploration of both topics. Flexoelectric coupling between strain gradients and polarization influences the physics of ferroelectric devices but it is difficult to directly probe its effects. Here, Li et al. use principal component analysis to compare STEM images with phase-field modeling and extract the flexoelectric contributions.

An overview of Sun–Sky Radiometer Observation Network (SONET) measurements in China is presented. Based on observations at 16 distributed SONET sites in China, atmospheric aerosol parameters are acquired via standardization processes of operational measurement, maintenance, calibration, inversion, and quality control implemented since 2010. A climatology study is performed focusing on total columnar atmospheric aerosol characteristics, including optical (aerosol optical depth, ÅngstrÖm exponent, fine-mode fraction, single-scattering albedo), physical (volume particle size distribution), chemical composition (black carbon; brown carbon; fine-mode scattering component, coarse-mode component; and aerosol water), and radiative properties (aerosol radiative forcing and efficiency). Data analyses show that aerosol optical depth is low in the west but high in the east of China. Aerosol composition also shows significant spatial and temporal variations, leading to noticeable diversities in optical and physical property patterns. In west and north China, aerosols are generally affected by dust particles, while monsoon climate and human activities impose remarkable influences on aerosols in east and south China. Aerosols in China exhibit strong light-scattering capability and result in significant radiative cooling effects.

The major goal of breast cancer prevention is to reduce the incidence of ductal carcinoma in situ (DCIS), an early stage of breast cancer. However, the biology behind DCIS formation is not well understood. It is suspected that cancer stem cells (CSCs) are already programmed in pre-malignant DCIS lesions and that these tumor-initiating cells may determine the phenotype of DCIS. MicroRNA (miRNA) profiling of paired DCIS tumors revealed that loss of miR-140 is a hallmark of DCIS lesions. Previously, we have found that miR-140 regulates CSCs in luminal subtype invasive ductal carcinoma. Here, we find that miR-140 has a critical role in regulating stem cell signaling in normal breast epithelium and in DCIS. miRNA profiling of normal mammary stem cells and cancer stem-like cells from DCIS tumors revealed that miR-140 is significantly downregulated in cancer stem-like cells compared with normal stem cells, linking miR-140 and dysregulated stem cell circuitry. Furthermore, we found that SOX9 and ALDH1, the most significantly activated stem-cell factors in DCIS stem-like cells, are direct targets of miR-140. Currently, targeted therapies (tamoxifen) are only able to reduce DCIS risk in patients with estrogen receptor α (ERα)-positive disease. We examined a model of ERα-negative/basal-like DCIS and found that restoration of miR-140 via a genetic approach or with the dietary compound sulforaphane decreased SOX9 and ALDH1, and reduced tumor growth in vivo . These results support that a miR-140/ALDH1/SOX9 axis is critical to basal CSC self-renewal and tumor formation in vivo , suggesting that the miR-140 pathway may be a promising target for preventative strategies in patients with basal-like DCIS.

Telomerase activation through induction of telomerase reverse transcriptase (hTERT) contributes to malignant transformation by stabilizing telomeres. Clinical studies demonstrate that higher hTERT expression is associated with cancer progression and poor outcomes, but the underlying mechanism is unclear. Because epithelial–mesenchymal transition (EMT) and cancer stem cells (CSCs) are key factors in cancer metastasis and relapse, and hTERT has been shown to exhibit multiple biological activities independently of its telomere-lengthening function, we address a potential role of hTERT in EMT and CSCs using gastric cancer (GC) as a model. hTERT overexpression promotes, whereas its inhibition suppresses, EMT and stemness of GC cells, respectively. Transforming growth factor (TGF)-β1 and β-catenin-mediated EMT was abolished by small interfering RNA depletion of hTERT expression. hTERT interacts with β-catenin, enhances its nuclear localization and transcriptional activity, and occupies the β-catenin target vimentin promoter. All these hTERT effects were independent of its telomere-lengthening function or telomerase activity. hTERT and EMT marker expression correlates positively in GC samples. Mouse experiments demonstrate the in vivo stimulation of hTERT on cancer cell colonization. Collectively, hTERT stimulates EMT and induces stemness of cancer cells, thereby promoting cancer metastasis and recurrence. Thus, targeting hTERT may prevent cancer progression by inhibiting EMT and CSCs.

Al–Nb–B master alloy has been regarded as a promising grain refiner that can reduce grain size of hypoeutectic Al–Si casting alloys. However, its grain refinement performance remains to be improved. In this work, the grain refinement efficacy of Al–Nb–B master alloy is significantly enhanced by modifying the Nb/B ratio through thermodynamic calculation. An Al–Nb–B master alloy with optimum Nb/B ratio of ~ 10:1 provides a fully equiaxed structure across the sections of the Al–10Si and commercial Al–9Si–0.08Ti alloys with an average grain size below 220 μm. The phenomenon is attributed to the existence of NbAl3 and the higher number density of NbB2 at the Nb/B ratio of ~ 10:1, which offers sufficient active nucleating sites to promote the formation of smaller grains. Moreover, the segregation behavior of Si atoms and interfacial energies after doping Si are investigated by first-principles calculations, and the results reveal that Si tends to segregate to the NbAl3/α-Al interface, whereas grain refining potency of NbAl3 for Al remains unchanged. This study has implications for strategic design of Al–Si cast alloy with fine and equiaxed grain structure inoculated by grain refiner.

Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three-dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe 5 , adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit. There is a long-standing experimental effort to observe field-induced correlated states in three-dimensional materials. Here, the authors observe an unconventional Hall response in the quantum limit of the bulk semimetal HfTe 5 with a plateau-like feature in the Hall conductivity.

Ambient volatile organic compounds (VOCs) were measured using an online system, gas chromatography–mass spectrometry/flame ionization detector (GC-MS/FID), in Beijing, China, before, during, and after Asia-Pacific Economic Cooperation (APEC) China 2014, when stringent air quality control measures were implemented. Positive matrix factorization (PMF) was applied to identify the major VOC contributing sources and their temporal variations. The secondary organic aerosols potential (SOAP) approach was used to estimate variations of precursor source contributions to SOA formation. The average VOC mixing ratios during the three periods were 86.17, 48.28, and 72.97 ppbv, respectively. The mixing ratios of total VOC during the control period were reduced by 44 %, and the mixing ratios of acetonitrile, halocarbons, oxygenated VOCs (OVOCs), aromatics, acetylene, alkanes, and alkenes decreased by approximately 65, 62, 54, 53, 37, 36, and 23 %, respectively. The mixing ratios of all measured VOC species decreased during control, and the most affected species were chlorinated VOCs (chloroethane, 1,1-dichloroethylene, chlorobenzene). PMF analysis indicated eight major sources of ambient VOCs, and emissions from target control sources were clearly reduced during the control period. Compared with the values before control, contributions of vehicular exhaust were most reduced, followed by industrial manufacturing and solvent utilization. Reductions of these three sources were responsible for 50, 26, and 16 % of the reductions in ambient VOCs. Contributions of evaporated or liquid gasoline and industrial chemical feedstock were slightly reduced, and contributions of secondary and long-lived species were relatively stable. Due to central heating, emissions from fuel combustion kept on increasing during the whole campaign; because of weak control of liquid petroleum gas (LPG), the highest emissions of LPG occurred in the control period. Vehicle-related sources were the most important precursor sources likely responsible for the reduction in SOA formation during this campaign.

The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. The question currently surrounding this topic is: whether and how could THz antiferromagnetic magnons mediate a GHz spin current? This mismatch of frequencies becomes particularly critical for the case of coherent ac spin current, raising the fundamental question of whether a GHz ac spin current can ever keep its coherence inside an antiferromagnetic insulator and so drive the spin precession of another ferromagnet layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe 75 Co 25 /MgO(001) heterostructures, here we demonstrate that a coherent GHz ac spin current pumped by the Py ferromagnetic resonance can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the Fe 75 Co 25 layer. Further measurement results favor thermal magnons rather than evanescent spin waves as the mediator of the coherent ac spin current in CoO. The mechanism underpinning the frequency mismatch between THz magnons and the GHz spin currents observed in antiferromagnetic insulators remains unknown. Here, the authors demonstrate that, in a Py/Ag/CoO/Ag/Fe 75 Co 25 /MgO(001) heterostructure, a GHz spin current transmits coherently across the antiferromagnetic CoO insulating layer to drive a coherent spin precession of the ferromagnetic Fe 75 Co 25 layer.