How do nitrogen-limited alpine coniferous forests acquire nitrogen?A rhizosphere perspective

Background:Alpine coniferous forest ecosystems dominated by ectomycorrhizal(ECM)tree species are generally characterized by low soil nitrogen(N)availability but stabilized plant productivity.Thus,elucidating potential mechanisms by which plants maintain efficient N acquisition is crucial for formulating optimized management practices in these ecosystems.Methods:We summarize empirical studies conducted at a long-term field monitoring station in the alpine coniferous forests on the eastern Tibetan Plateau,China.We propose a root-soil interaction-based framework encompassing key components including soil N supply,microbial N transformation,and root N uptake in the rhizosphere.Results:We highlight that,(i)a considerable size of soil dissolved organic N pool mitigates plant dependence on inorganic N supply;(ii)ectomycorrhizal roots regulate soil N transformations through both rhizosphere and hyphosphere effects,providing a driving force for scavenging soil N;(iii)a complementary pattern of plant uptake of different soil N forms via root-and mycorrhizal mycelium-pathways enables efficient N acquisitions in response to changing soil N availability.Conclusions:Multiple rhizosphere processes abovementioned collaboratively contribute to efficient plant N acquisition in alpine coniferous forests.Finally,we identify several research outlooks and directions to improve the understanding and prediction of ecosystem functions in alpine coniferous forests under on-going global changes.

Influencing factors and optimization on mechanical performance of solid waste-derived rapid repair mortar

There is a great demand for high performance rapid repair mortar(RRM)because of the wide use of cement concrete.Solid-waste-based sulfoaluminate cement(WSAC)is very suitable as a green cementitious material for repair materials because of its characteristics of high early-age strength and short setting time.However,the influence and optimization of various factors of WSAC-based RRM,such as water-to-RRM ratio,binder-to-sand ratio and additives,as well as the further solid waste replacement of aggregate,remain to be studied.This paper comprehensively studied the influence of the above factors on the performance of WSAC-based RRM and obtained a green high-performance RRM by optimizing these factors.The experimental results showed that the early and late strength of the obtained RRM is excellent,and the setting time and fluidity are appropriate,which reflected good mechanical properties and construction performance.Ordinary Portland cement(OPC)doping could not improve RRM strength.It was feasible to prepare RRM with gold tailing sand replacing part of the quartz sand.This paper provides data and a theoretical basis for the preparation of high-performance RRM based on solid waste,expanding the high value utilization of solid waste,which is conducive to the development of a low carbon society.

In-orbit performance of LE onboard Insight-HXMT in the first 5 years

Purpose The low-energy X-ray telescope(LE)is a main instrument of the Insight-HXMT mission and consists of 96 swept charge devices covering the 1–10 keV energy band.The energy gain and resolution are continuously calibrated by analyzing Cassiopeia A(Cas A)and blank sky data,while the effective areas are also calibrated with the observations of the Crab Nebula.In this paper,we present the evolution of the in-orbit performances of LE in the first 5 years since launch.Methods The Insight-HXMT data analysis software package(HXMTDAS)is utilized to extract the spectra of Cas A,blank sky,and Crab Nebula using different good time interval selections.We fit a model with a power-law continuum and several Gaussian lines to different ranges of Cas A and blank sky spectra to get peak energies of their lines through xspec.After updating the energy gain calibration in CALibration DataBase(CALDB),we rerun the Cas A data to obtain the energy resolution.An empirical function is used to modify the simulated effective areas so that the background-subtracted spectrum of the Crab Nebula can best match the standard model of the Crab Nebula.Results The energy gain,resolution,and effective areas are calibrated every month.The corresponding calibration results are duly updated in CALDB,which can be downloaded and used for the analysis of Insight-HXMT data.Simultaneous observations with NuSTAR and NICER can also be used to verify our derived results.Conclusion LE is a well-calibrated X-ray telescope working in 1–10 keV band.The uncertainty of LE gain is less than 20eV in 2–9 keV band,and the uncertainty of LE resolution is less than 15eV.The systematic errors of LE,compared to the model of the Crab Nebula,are lower than 1.5%in 1–10 keV.

Insight-HXMT observations of the first binary neutron star merger GW170817

Finding the electromagnetic(EM) counterpart of binary compact star merger, especially the binary neutron star(BNS) merger,is critically important for gravitational wave(GW) astronomy, cosmology and fundamental physics. On Aug. 17, 2017,Advanced LIGO and Fermi/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart,GRB 170817 A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope(HE) onboard Insight-HXMT(Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart(SSS17 a/AT2017 gfo) with very large collection area(~1000 cm^2) and microsecond time resolution in 0.2-5 MeV. In addition,Insight-HXMT quickly implemented a Target of Opportunity(ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight-HXMT did not detect any significant high energy(0.2-5 MeV) radiation from GW170817, its observation helped to confirm the unexpected weak and soft nature of GRB 170817 A. Meanwhile,Insight-HXMT/HE provides one of the most stringent constraints(~10^(-7) to 10^(-6) erg/cm^2/s) for both GRB170817 A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.

Overview to the Hard X-ray Modulation Telescope (Insight-HXMT) Satellite

As China’s first X-ray astronomical satellite, the Hard X-ray Modulation Telescope (HXMT), which was dubbed as Insight-HXMT after the launch on June 15, 2017, is a wide-band(1-250 ke V) slat-collimator-based X-ray astronomy satellite with the capability of all-sky monitoring in 0.2-3 Me V. It was designed to perform pointing, scanning and gamma-ray burst(GRB)observations and, based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed.Here we give an overview of the mission and its progresses, including payload, core sciences, ground calibration/facility, ground segment, data archive, software, in-orbit performance, calibration, background model, observations and some preliminary results.

The enhanced X-ray Timing and Polarimetry mission—eXTP

In this paper we present the enhanced X-ray Timing and Polarimetry mission—eXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring effects of QED, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, eXTP will be a very powerful observatory for astrophysics that will provide observations of unprecedented quality on a variety of galactic and extragalactic objects. In particular, its wide field monitoring capabilities will be highly instrumental to detect the electro-magnetic counterparts of gravitational wave sources.The paper provides a detailed description of:(1) the technological and technical aspects, and the expected performance of the instruments of the scientific payload;(2) the elements and functions of the mission, from the spacecraft to the ground segment.

The Low Energy X-ray telescope (LE) onboard the Insight-HXMT astronomy satellite

The Low Energy X-ray telescope(LE) is one of the three main instruments of the Insight-Hard X-ray Modulation Telescope(Insight-HXMT). It is equipped with Swept Charge Device(SCD) sensor arrays with a total geometrical area of 384 cm^2 and an energy band from 0.7 to 13 ke V. In order to evaluate the particle induced X-ray background and the cosmic X-ray background simultaneously, LE adopts collimators to define four types of Field Of Views(FOVs), i.e., 1.6°×6°, 4°×6°, 50°-60°×2°-6 oand the blocked ones which block the X-ray by an aluminum cover. LE is constituted of three detector boxes(LEDs) and an electric control box(LEB) and achieves a good energy resolution of 140 e V@5.9 ke V, an excellent time resolution of 0.98 ms, as well as an extremely low pileup(<1%@18000 cts/s). Detailed performance tests and calibration on the ground have been performed,including energy-channel relation, energy response, detection efficiency and time response.