[en] As a kind of MR perfusion imaging methods, arterial spin labeling (ASL) takes water in arterial blood, which is freely diffusible, as an endogenous tracer. Through quantitatively measuring local relative blood flow, ASL can provide tangible proofs for diseases diagnosis. Not like dynamic susceptibility contrast enhanced MR perfusion, it does not need exogenous contrast agent. With the advantage of noninvasiveness, simplicity, relatively lower costs and repeatability, it has strong potential in clinical application. In this review we mainly focued on the principle, categories, clinical applications, and future prospects of ASL. (authors)

[en] This paper presents a study on the formation, microstructure and mechanical property of Cr₃C₂/Fe nanocomposites using selective laser melting (SLM). Scanning electron microscope (SEM), transmission electron microscope (TEM) and tensile tests were conducted to investigate the influence of Cr₃C₂ particulates on the microstructure and mechanical properties. It was found that the porosity decreased when volumetric energy density increased from 27 to 37 J/mm³, then rose to 55 J/mm³. The results showed that the Cr₃C₂ particulates decomposed completely during SLM process and interacted with Fe matrix to form (α-Fe, Cr) solid solution and M(Fe, Cr)₂₃C₆ carbides. In addition, due to the characteristic of rapid solidification, very fine grains were obtained throughout the composites. The tensile tests showed that the ultimate tensile strength could reach up to 1158 MPa.

[en] 4B8 beamline at Beijing Synchrotron Radiation Facility (BSRF) is based on the previous 3B1B beamline with some modification. This beamline will focus on the advancement of vacuum ultraviolet circular dichroism (CD) spectroscopy for studying secondary structure of proteins. Along with beamline moving, some measurements are taken to overcome the exposed problems in 3B1B, such as optical contamination, high stray light level

[en] The confinement losses in air-guiding photonic bandgap fibers (PBGFs) with air hole missing are studied with the full-vector finite-element method. It is confirmed that there are two loss peaks (1.555 and 1.598 μm) if there is a hole missing in the cladding far from the core. The closer to the core the hole missing is, the larger the confinement losses are, and even no mode could propagate in the core. The main power of the fundamental mode leaks from the core to the cladding defect. The quality of PBGFs can be improved through controlling the number and position of defects. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

[en] Great efforts have been made to control air pollution in China, and these have markedly changed air quality. Here, a detailed analysis of changes in air pollution in Nanjingbetween 2011 and 2017 based on hourly concentration measurements of six air pollutants is presented. The concentrations of most of these pollutants have decreased since 2013. This has resulted in the annual proportion of days meeting the new Chinese air quality standards increasing by 17.5%, as well as the proportion of days of severe or strong pollution decreasing by 8.0%. However, the ozone (O₃) concentration increased between 2011 and 2017, and the number of days that O₃ concentrations exceeded the Chinese standard dramatically increased from 8 days in 2011 to 60 days in 2017. Clearly, O₃ has replaced fine particulate matter (PM_2.5) as the most frequent dominant pollutant since 2016. Our results indicate that air pollution in Nanjing has evolved from being dominated by primary pollutants to being dominated by secondary pollutants, reflecting interaction of multiple emissions and chemical processes. Current policies and strategies need to be reassessed and modified to deal with interactions between emissions from different sources under variable meteorological conditions.

[en] Highlights: • The Er addition refines the grains and modifies the Si particles. • The uniformly distributed ZrB₂ nanoparticles can be obtained in the composites. • The tensile properties can be increased greatly with the 0.05.wt% Er addition. In this study, the effects of Er addition on the microstructure and properties of in situ nano A356-3 wt%ZrB₂ composites were investigated. The A356-3 wt%ZrB₂ composite was prepared by an in situ reaction between K₂ZrF₆ and KBF₄ salts, which were added in the proper stoichiometric ratio to form ZrB₂ in the A356.2 alloy melt at 1123 K(850 °C). The addition of Er could modify the coarse lamellar eutectic Si particles into fine fibrous particles and refine the second dendrite arm spacing (SDAS) of the grains simultaneously. Furthermore, the Er also influenced the distribution and size of the ZrB₂ particles by homogenizing the distribution of the nanoparticles and reducing their size. Tensile testing showed that the ultimate tensile strength (UTS), yield strength (YS) and elongation increased to 325 MPa, 250MPa and 13.65%, respectively, due to the homogeneous distribution of the nanoparticles, the refinement of the SDAS of the α-Al grains and the modification of the eutectic Si particles upon increasing the Er content to 0.05 wt% combined with T6 heat treatment.

[en] By using developed particle swarm optimization algorithm on crystal structural prediction, we have explored the possible crystal structures of B-C system. Their structures, stability, elastic properties, electronic structure, and chemical bonding have been investigated by first-principles calculations with density functional theory. The results show that all the predicted structures are mechanically and dynamically stable. An analysis of calculated enthalpy with pressure indicates that increasing of boron content will increase the stability of boron carbides under low pressure. Moreover, the boron carbides with rich carbon content become more stable under high pressure. The negative formation energy of predicted B₅C indicates its high stability. The density of states of B₅C show that it is p-type semiconducting. The calculated theoretical Vickers hardnesses of B-C exceed 40 GPa except B₄C, BC, and BC₄, indicating they are potential superhard materials. An analysis of Debye temperature and electronic localization function provides further understanding chemical and physical properties of boron carbide

[en] To study the influence of Acidithiobacillus ferrooxidans (At.f) mutated by X-ray on the biooxidation and bioleaching of refractory gold ores, X-ray was used to irradiate At.f strains at different doses, and more efficient strains were screened by microbiology methods and the measurement of relevant indicators. Compared with the original strain, the bioleaching ratio of iron by the mutants after irradiation at 450 Gy was 50.24%, namely 44% increased, and the bioleaching ratio of gold reached 86.68%-two folds than gold direct cyanidation leaching. It is proved that X-ray irradiation is an outstanding way to breed mutants of high bioleaching ratio of iron and gold strains of At.f. (authors)

[en] The temperature-dependent conductivity spectrum from 3×10² Hz to 1×10⁸ Hz in the ab-plane of a K_0.85Fe_1.66Se_2.0 single crystal is probed. The dc measurements indicate that the charge transport can be described well by the variable range hopping model. From the ac conductivity spectrum, clear evidence for small polaron tunnelling with an activation energy of about 155meV in ab-plane is revealed. With decreasing temperature, the real part of the dielectric spectrum shifts towards lower frequencies and also shows a wider distribution of the relaxation time. Below 140 K, the peak position of the dielectric loss spectra begins to deviate from thermal excitation behavior, reflecting the freezing of the phonon which assists the tunnelling

[en] MOF-derived zink and nitrogen co-doped porous carbon (ZNPC) was synthesized through the pyrolysis of MOF-5-NH₂ and used as a solid-phase microextraction (SPME) coating material. Coupled with gas chromatography-mass spectrometry (GC–MS), headspace SPME (HS-SPME) based on ZNPC was adopted for the determination of phenols in food samples. The co-existence of N and Zn in ZNPC endows the derived carbon superior hydrophilicity, which is highly beneficial for phenols capture. After optimizing the conditions of extraction and desorption, a sensitive analytical method was established with low limits of detections (LODs, 0.73–2.3 ng g⁻¹) and wide linear ranges (5–5000 ng g⁻¹). Both the intra-fiber repeatability (RSDs from 2.8–7.3%) and inter-fiber reproducibility (RSDs from 9.7–11.7%) were satisfactory. The established method was applied to phenol determination in beef jerky and duck neck with satisfactory recoveries of 81.2–120.4% and RSDs of 2.8–9.9%, which met well with the requirement of practical application. Graphical abstract: