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"Du, Z."
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Disorder-induced nonlinear Hall effect with time-reversal symmetry
The nonlinear Hall effect has opened the door towards deeper understanding of topological states of matter. Disorder plays indispensable roles in various linear Hall effects, such as the localization in the quantized Hall effects and the extrinsic mechanisms of the anomalous, spin, and valley Hall effects. Unlike in the linear Hall effects, disorder enters the nonlinear Hall effect even in the leading order. Here, we derive the formulas of the nonlinear Hall conductivity in the presence of disorder scattering. We apply the formulas to calculate the nonlinear Hall response of the tilted 2D Dirac model, which is the symmetry-allowed minimal model for the nonlinear Hall effect and can serve as a building block in realistic band structures. More importantly, we construct the general scaling law of the nonlinear Hall effect, which may help in experiments to distinguish disorder-induced contributions to the nonlinear Hall effect in the future.
Disorder may play a dominant role in determining the nonlinear Hall effect in a topological material. Here, Du et al. derive formulas of the nonlinear Hall conductivity and construct the general scaling law of the nonlinear Hall effect in a tilted two dimensional Dirac model.
Journal Article
Quantum theory of the nonlinear Hall effect
The nonlinear Hall effect is an unconventional response, in which a voltage can be driven by two perpendicular currents in the Hall-bar measurement. Unprecedented in the family of the Hall effects, it can survive time-reversal symmetry but is sensitive to the breaking of discrete and crystal symmetries. It is a quantum transport phenomenon that has deep connection with the Berry curvature. However, a full quantum description is still absent. Here we construct a quantum theory of the nonlinear Hall effect by using the diagrammatic technique. Quite different from nonlinear optics, nearly all the diagrams account for the disorder effects, which play decisive role in the electronic transport. After including the disorder contributions in terms of the Feynman diagrams, the total nonlinear Hall conductivity is enhanced but its sign remains unchanged for the 2D tilted Dirac model, compared to the one with only the Berry curvature contribution. We discuss the symmetry of the nonlinear conductivity tensor and predict a pure disorder-induced nonlinear Hall effect for point groups
C
3
,
C
3
h
,
C
3
v
,
D
3
h
,
D
3
in 2D, and
T
,
T
d
,
C
3
h
,
D
3
h
in 3D. This work will be helpful for explorations of the topological physics beyond the linear regime.
The nonlinear Hall effect is a quantum phenomenon, in which two perpendicular currents induce a Hall voltage; however, previous theories for this effect has remained at the semi classical level. Here, the authors develop a full quantum theory of the nonlinear Hall effect by using the diagrammatic technique.
Journal Article
Nonlinear Hall effects
The Hall effects comprise one of the oldest but most vital fields in condensed matter physics, and they persistently inspire new findings, such as quantum Hall effects and topological phases of matter. The recently discovered nonlinear Hall effect is a new member of the family of Hall effects. It is characterized as a transverse Hall voltage in response to two longitudinal currents in the Hall measurement, but it does not require time-reversal symmetry to be broken. It has deep connections to symmetry and topology and, thus, opens new avenues by which to probe the spectral, symmetry and topological properties of emergent quantum materials and phases of matter. In this Perspective, we present an overview of the recent progress regarding the nonlinear Hall effect. We discuss the open problems, the prospects of the use of the nonlinear Hall effect in spectroscopic and device applications, and generalizations to other nonlinear transport effects.The recent measurement of a nonlinear Hall effect has provided a new way to probe the spectral, symmetry and topological properties of quantum materials. This Perspective discusses the open questions around this new effect and potential applications.
Journal Article
Biomass burning contribution to Beijing aerosol
Biomass burning, the largest global source of elemental carbon (EC) and primary organic carbon (OC), is strongly associated with many subjects of great scientific concern, such as secondary organic aerosol and brown carbon which exert important effects on the environment and on climate in particular. This study investigated the relationships between levoglucosan and other biomass burning tracers (i.e., water soluble potassium and mannosan) based on both ambient samples collected in Beijing and source samples. Compared with North America and Europe, Beijing was characterized by high ambient levoglucosan concentrations and low winter to summer ratios of levoglucosan, indicating significant impact of biomass burning activities throughout the year in Beijing. Comparison of levoglucosan and water soluble potassium (K+) levels suggested that it was acceptable to use K+ as a biomass burning tracer during summer in Beijing, while the contribution of fireworks to K+ could be significant during winter. Moreover, the levoglucosan to K+ ratio was found to be lower during the typical summer period (0.21 ± 0.16) compared with the typical winter period (0.51 ± 0.15). Levoglucosan correlated strongly with mannosan (R2 = 0.97) throughout the winter and the levoglucosan to mannosan ratio averaged 9.49 ± 1.63, whereas levoglucosan and mannosan exhibited relatively weak correlation (R2 = 0.73) during the typical summer period when the levoglucosan to mannosan ratio averaged 12.65 ± 3.38. Results from positive matrix factorization (PMF) model analysis showed that about 50% of the OC and EC in Beijing were associated with biomass burning processes. In addition, a new source identification method was developed based on the comparison of the levoglucosan to K+ ratio and the levoglucosan to mannosan ratio among different types of biomass. Using this method, the major source of biomass burning aerosol in Beijing was suggested to be the combustion of crop residuals, while the contribution from softwood burning was also non-negligible, especially in winter.
Journal Article
Tumor-suppressive function of long noncoding RNA MALAT1 in glioma cells by downregulation of MMP2 and inactivation of ERK/MAPK signaling
Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a type of long noncoding RNA. It is associated with metastasis and is a favorable prognostic factor for lung cancer. Recent studies have shown that MALAT1 plays an important role in other malignancies. But, little is known about the role of MALAT1 in glioma. In this study, quantitative reverse transcription PCR (qRT-PCR) was used to demonstrate that the expression of MALAT1 was lower than that in normal brain tissues. Stable RNA interference-mediated knockdown of MALAT1 in human glioma cell lines (U87 and U251) significantly promoted the invasion and proliferation of the glioma cells by
in vitro
assays. Conversely, overexpression of MALAT1 caused significant reduction in cell proliferation and invasion
in vitro
, and tumorigenicity in both subcutaneous and intracranial human glioma xenograft models. Furthermore, MALAT1-mediated tumor suppression in glioma cells may be via reduction of extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling activity and expression of matrix metalloproteinase 2 (MMP2). In conclusion, overall data demonstrated the tumor-suppressive role of MALAT1 in glioma by attenuating ERK/MAPK-mediated growth and MMP2-mediated invasiveness.
Journal Article
Environmental impacts of nitrogen emissions in China and the role of policies in emission reduction
Atmospheric reactive nitrogen (N r ) has been a cause of serious environmental pollution in China. Historically, China used too little N r in its agriculture to feed its population. However, with the rapid increase in N fertilizer use for food production and fossil fuel consumption for energy supply over the last four decades, increasing gaseous N r species (e.g. NH 3 and NO x ) have been emitted to the atmosphere and then deposited as wet and dry deposition, with adverse impacts on air, water and soil quality as well as plant biodiversity and human health. This paper reviews the issues associated with this in a holistic way. The emissions, deposition, impacts, actions and regulations for the mitigation of atmospheric N r are discussed systematically. Both NH 3 and NO x make major contributions to environmental pollution but especially to the formation of secondary fine particulate matter (PM 2.5 ), which impacts human health and light scattering (haze). In addition, atmospheric deposition of NH 3 and NO x causes adverse impacts on terrestrial and aquatic ecosystems due to acidification and eutrophication. Regulations and practices introduced by China that meet the urgent need to reduce N r emissions are explained and resulting effects on emissions are discussed. Recommendations for improving future N management for achieving ‘win-win’ outcomes for Chinese agricultural production and food supply, and human and environmental health, are described. This article is part of a discussion meeting issue ‘Air quality, past present and future’.
Journal Article
Mass absorption efficiency of elemental carbon and water-soluble organic carbon in Beijing, China
The mass absorption efficiency (MAE) of elemental carbon (EC) in Beijing was quantified using a thermal-optical carbon analyzer. The MAE measured at 632 nm was 8.45±1.71 and 9.41±1.92 m2 g−1 during winter and summer respectively. The daily variation of MAE was found to coincide with the abundance of organic carbon (OC), especially the OC to EC ratio, perhaps due to the enhancement by coating with organic aerosol (especially secondary organic aerosol, SOA) or the artifacts resulting from the redistribution of liquid-like organic particles during the filter-based absorption measurements. Using a converting approach that accounts for the discrepancy caused by measurements methods of both light absorption and EC concentration, previously published MAE values were converted to the equivalent-MAE, which is the estimated value if using the same measurement methods as used in this study. The equivalent-MAE was found to be much lower in the regions heavily impacted by biomass burning (e.g., below 2.7 m2 g−1 for two Indian cities). Results from source samples (including diesel exhaust samples and biomass smoke samples) also demonstrated that emissions from biomass burning would decrease the MAE of EC. Moreover, optical properties of water-soluble organic carbon (WSOC) in Beijing were presented. Light absorption by WSOC exhibited strong wavelength (λ) dependence such that absorption varied approximately as λ−7, which was characteristic of the brown carbon spectra. The MAE of WSOC (measured at 365 nm) was 1.79±0.24 and 0.71±0.20 m2 g−1 during winter and summer respectively. The large discrepancy between the MAE of WSOC during winter and summer was attributed to the difference in the precursors of SOA such that anthropogenic volatile organic compounds (AVOCs) should be more important as the precursors of SOA in winter. The MAE of WSOC in Beijing was much higher than results from the southeastern United States which were obtained using the same method as used in this study, perhaps due to the stronger emissions of biomass burning in China.
Journal Article
The solar cycle: predicting the peak of solar cycle 25
Motivated by a successful prediction on the peak of solar cycle 24 (81.7, comparable to the observed 81.9, Du in Astrophys. Space Sci. 338:9, 2012), based on the logarithmic relationship between the maximum amplitude (Rm) of a solar cycle and the preceding minimum aa geomagnetic index (aamin), we perform a prediction on the peak of the upcoming cycle 25 using the sunspot number of the new version instead. If the suggested error in aa (3 nT) before 1957 is corrected, the correlation between lnRm and lnaamin (r=0.92) is stronger than that not corrected (r=0.86). Based on this relationship, the peak value of cycle 25 is predicted to be Rm(25)≃151.1±16.9, about 30% stronger than cycle 24. Employing the ‘Waldmeier effect’ that the rise time of a cycle is well anti-correlated to its amplitude, we estimated the rise time, Ta(25)=4.3±0.2±0.6, and the peak time of cycle 25, 2024.1±0.8 (years), which is during April 2023 and November 2024.
Journal Article
RN1, a novel galectin-3 inhibitor, inhibits pancreatic cancer cell growth in vitro and in vivo via blocking galectin-3 associated signaling pathways
Galectin-3 (Gal-3) has been implicated in pancreatic ductal adenocarcinoma (PDAC), and its candidacy as a therapeutic target has been evaluated. Gal-3 is widely upregulated in tumors, and its expression is associated with the development and malignancy of PDAC. In the present study, we demonstrate that a polysaccharide, RN1, purified from the flower of
Panax notoginseng
binds to Gal-3 and suppresses its expression. In addition, RN1 markedly inhibits PDAC cells growth
in vitro
,
in vivo
and in patient-derived xenografts. Mechanistically, RN1 binds to epidermal growth factor receptor (EGFR) and Gal-3, thereby disrupting the interaction between Gal-3 and EGFR and downregulating extracellular-related kinase (ERK) phosphorylation and the transcription factor of Gal-3, Runx1 expression. Inhibiting the expression of Runx1 by RN1, suppresses Gal-3 expression and inactivates Gal-3-associated signaling pathways, including the EGFR/ERK/Runx1, BMP/smad/Id-3 and integrin/FAK/JNK signaling pathways. In addition, RN1 can also bind to bone morphogenetic protein receptors (BMPR1A and BMPR2) and block the interaction between Gal-3 and the BMPRs. Thus, our results suggest that a novel Gal-3 inhibitor RN1 may be a potential candidate for human PDAC treatment via multiple targets and multiple signaling pathways.
Journal Article