Higher absorbed solar radiation partly offset the negative effects of water stress on the photosynthesis of Amazon forests during the 2015 drought

Amazon forests play an important role in the global carbon cycle and Earth\u27s climate. The vulnerability of Amazon forests to drought remains highly controversial. Here we examine the impacts of the 2015 drought on the photosynthesis of Amazon forests to understand how solar radiation and precipitation jointly control forest photosynthesis during the severe drought. We use a variety of gridded vegetation and climate datasets, including solar-induced chlorophyll fluorescence (SIF), photosynthetic active radiation (PAR), the fraction of absorbed PAR (APAR), leaf area index (LAI), precipitation, soil moisture, cloud cover, and vapor pressure deficit (VPD) in our analysis. Satellite-derived SIF observations provide a direct diagnosis of plant photosynthesis from space. The decomposition of SIF to SIF yield (SIFyield) and APAR (the product of PAR and fPAR) reveals the relative effects of precipitation and solar radiation on photosynthesis. We found that the drought significantly reduced SIFyield, the emitted SIF per photon absorbed. The higher APAR resulting from lower cloud cover and higher LAI partly offset the negative effects of water stress on the photosynthesis of Amazon forests, leading to a smaller reduction in SIF than in SIFyield and precipitation. We further found that SIFyield anomalies were more sensitive to precipitation and VPD anomalies in the southern regions of the Amazon than in the central and northern regions. Our findings shed light on the relative and combined effects of precipitation and solar radiation on photosynthesis, and can improve our understanding of the responses of Amazon forests to drought

Geodesic Distance Function Learning via Heat Flow on Vector Fields

Learning a distance function or metric on a given data manifold is of great importance in machine learning and pattern recognition. Many of the previous works first embed the manifold to Euclidean space and then learn the distance function. However, such a scheme might not faithfully preserve the distance function if the original manifold is not Euclidean. Note that the distance function on a manifold can always be well-defined. In this paper, we propose to learn the distance function directly on the manifold without embedding. We first provide a theoretical characterization of the distance function by its gradient field. Based on our theoretical analysis, we propose to first learn the gradient field of the distance function and then learn the distance function itself. Specifically, we set the gradient field of a local distance function as an initial vector field. Then we transport it to the whole manifold via heat flow on vector fields. Finally, the geodesic distance function can be obtained by requiring its gradient field to be close to the normalized vector field. Experimental results on both synthetic and real data demonstrate the effectiveness of our proposed algorithm

Study of a sociable molecule: Mapping the binding interfaces of the cell division regulator MipZ in Caulobacter crescentus

In most bacteria, cell division requires assembly of FtsZ, the tubulin homologue, into a ring-like structure, the so-called Z-ring. The Z-ring acts as a scaffold for the cell division machinery and marks the future division site. To precisely localize the Z-ring, bacteria have evolved different regulatory mechanisms. In the model organism Caulobacter crescentus, Z-ring positioning depends on a P-loop ATPase, MipZ. MipZ forms bipolar gradients within the cell and acts as an inhibitor of FtsZ polymerization, thereby restricting assembly of the Z-ring to the midcell region. Gradient formation is driven by the alternation of MipZ between a monomeric and dimeric state with distinct interaction patterns and diffusion rates. This alternation results in a dynamic localization cycle, in which MipZ continuously oscillates between non-specific chromosomal DNA and the polarly localized ParB protein. In this study, we investigated the function of MipZ by mapping its interaction interfaces with FtsZ, ParB and DNA. We systematically exchanged surface-exposed residues using alanine-scanning mutagenesis. Analyzing the subcellular distribution of the mutant proteins as well as their ability to support division site placement, we identified four clusters of residues that are important for MipZ activity. Two of them are likely responsible for contacting FtsZ and chromosomal DNA, respectively, whereas the other two appear to be involved in the interaction with ParB. Notably, the DNA-binding and FtsZ-binding interfaces of MipZ comprise residues from both monomeric subunits and are located on opposite sides of the dimer. This result is consistent with the previous finding that the regulatory effect of MipZ is specific for its dimeric form and that only the dimeric form contacts DNA and FtsZ. We also found that the DNA-binding region mainly consists of positively charged arginine and lysine residues. In vivo and in vitro studies showed that mutation of these residues impairs the DNA-binding activity of MipZ to different extents; moreover, mutation of R194 and R198 abolished the MipZ-DNA interaction. These results provide the first detailed analysis of the interaction determinants of MipZ and deepen our knowledge of the molecular mechanism underlying the function of this intriguing cell division regulator

Fabrication of B doped g-C3N4/TiO2 heterojunction for efficient photoelectrochemical water oxidation

With the development of clean and renewable energy, hydrogen produced via photoelectrochemical (PEC) water splitting has attracted considerable attention. However, to develop the photoanodes with stable and excellent PEC ability is still a big challenge. In our work, TiO2 nanorods decorated with boron doped g-C3N4 (BCN/TiO2) is fabricated via thermal polymerization method to improve the PEC performance. The BCN/TiO2 displays 4-fold increase of the photocurrent density (1.01 mA cm−2) at 1.23 V vs. RHE under irradiation (100 mW cm−2, AM 1.5 G). And the onset potential of BCN/TiO2 exhibits a negative shift with 100 mV. Attributed to the broad light absorption of BCN and hetero-junction forming between BCN and TiO2, the IPCE value is increased to 87.8% in 380 nm, and the charge separation and transfer efficiency are both increased. Doping metal-free inorganic material with heteroatoms is a simple and efficient strategy to increase the light absorption within visible light and charge transfer efficiency in PEC and photocatalytic applications

Exploring the dark matter inelastic frontier with 79.6 days of PandaX-II data

We report here the results of searching for inelastic scattering of dark matter (initial and final state dark matter particles differ by a small mass splitting) with nucleon with the first 79.6-day of PandaX-II data (Run 9). We set the upper limits for the spin independent WIMP-nucleon scattering cross section up to a mass splitting of 300 keV/c$^2$ at two benchmark dark matter masses of 1 and 10 TeV/c$^2$.Comment: 5 pages, 6 figure

Dark Matter Results From 54-Ton-Day Exposure of PandaX-II Experiment

We report a new search of weakly interacting massive particles (WIMPs) using the combined low background data sets in 2016 and 2017 from the PandaX-II experiment in China. The latest data set contains a new exposure of 77.1 live day, with the background reduced to a level of 0.8$\times10^{-3}$ evt/kg/day, improved by a factor of 2.5 in comparison to the previous run in 2016. No excess events were found above the expected background. With a total exposure of 5.4$\times10^4$ kg day, the most stringent upper limit on spin-independent WIMP-nucleon cross section was set for a WIMP with mass larger than 100 GeV/c$^2$, with the lowest exclusion at 8.6$\times10^{-47}$ cm$^2$ at 40 GeV/c$^2$.Comment: Supplementary materials at https://pandax.sjtu.edu.cn/articles/2nd/supplemental.pdf version 2 as accepted by PR

Positive Definiteness of High-Order Subdifferential and High-Order Optimality Conditions in Vector Optimization Problems

We obtain a new Taylor's formula in terms of the order subdifferential of a function from to . As its applications in optimization problems, we build order sufficient optimality conditions of this kind of functions and order necessary conditions for strongly -quasiconvex functions

Three-dimensional deep-water focusing waves by Irrotational Green–Naghdi equations

Nonlinear interactions and the superposition of various wave groups can generate rogue waves with extreme heights in oceans that significantly affects the ocean dynamics. A comprehensive understanding of these phenomena is essential for accurate wave-force analysis. This study introduces the Irrotational Green–Naghdi (IGN) deep-water equations designed to study, specifically, the propagation and generation of three-dimensional focused waves. The proposed equations employ finite-difference methods for spatial discretization on a Cartesian grid and use the Adams time-stepping scheme for temporal iterations. Discussion is provided on identifying the optimized value of the representative wavenumber. The proposed IGN equations are compared with focused wave experimental measurements and second-order wave theory results. These reveal that the selected representative wavenumber significantly affects the computational efficiency: an appropriate value enables rapid algorithm convergence with high accuracy, whereas unsuitable values yield slower convergence and reduced efficiency. The wave surface profiles generated by the IGN equations at the focal location exhibit excellent agreement with experimental data, both before and after the focus. In addition, the velocity field along the water depth at the focal time closely matches the experimental velocity field

Low-mass dark matter search results from full exposure of PandaX-I experiment

We report the results of a weakly-interacting massive particle (WIMP) dark matter search using the full 80.1\;live-day exposure of the first stage of the PandaX experiment (PandaX-I) located in the China Jin-Ping Underground Laboratory. The PandaX-I detector has been optimized for detecting low-mass WIMPs, achieving a photon detection efficiency of 9.6\%. With a fiducial liquid xenon target mass of 54.0\,kg, no significant excess event were found above the expected background. A profile likelihood analysis confirms our earlier finding that the PandaX-I data disfavor all positive low-mass WIMP signals reported in the literature under standard assumptions. A stringent bound on the low mass WIMP is set at WIMP mass below 10\,GeV/c$^2$, demonstrating that liquid xenon detectors can be competitive for low-mass WIMP searches.Comment: v3 as accepted by PRD. Minor update in the text in response to referee comments. Separating Fig. 11(a) and (b) into Fig. 11 and Fig. 12. Legend tweak in Fig. 9(b) and 9(c) as suggested by referee, as well as a missing legend for CRESST-II legend in Fig. 12 (now Fig. 13). Same version as submitted to PR