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Abstract Boron carbide (B 4 C) is an important type of neutron radiation shielding material with relatively high efficiency due to the high content of 10B element. Incorporation of B 4 C particles into polymer to prepare high-performance neutron radiation shielding material has become more and more important for the safe operation of nuclear power in the defense industry and nuclear power plant. The polyimide/B 4 C composite films with different micro-sized B 4 C contents were successfully prepared by in-situ polymerization. Silane coupling agent KH550 was employed to functionalize B 4 C particles to improve the dispersion of B 4 C particles in the polyimide matrix with strengthened interfacial interaction. As shown that the micro-sized B 4 C functional particles can be well dispersed in the BPDA/ODA polyimide matrix. With the B 4 C content increase, thermal stability of the polyimide/B 4 C composite films can be significantly improved, even mechanical properties partly declined. Meanwhile, the polyimide/B 4 C composite films exhibit good thermal neutron radiation shielding properties. The neutron permeability I/I 0 changes exponentially with the change of B 4 C content. When the B 4 C content is increased to 30 wt%, the polyimide/B 4 C composite films show optimum properties combination with thermal decomposition temperature (T d 10) of 622 °C, neutron permeability (I/I 0) of 0.24 (800 μm in thickness), and tensile strength of 406 MPa. The composite thus shows great potential for use in applications which require materials with high thermal stability and neutron radiation shielding ability, such as fusion reactor system and nuclear waste disposal. [ABSTRACT FROM AUTHOR]

The establishment, reproduction, dispersal, and distribution of alien plants are affected by various factors during the transition from being newly introduced in a habitat to being invasive. In the agro-pastoral ecotone of northern China, comprising farmlands and natural grasslands, the biological characteristics of alien plant species were the key intrinsic factors (propagation characteristics and competitive ability), followed by such extrinsic factors as human interference and environmental heterogeneity. Among biological characteristics, the life form may be an important and useful indicator of the invasive ability of a species, and the risk of invasion is greater from alien species that are poisonous, inedible, and have traits that facilitate wide dispersal. Farmlands may serve as initial shelters for alien species, from which they spread into neighbouring habitats, whereas natural grassland may act as a barrier to plant invasions. Management practices detrimental to grasslands, including overgrazing, reclamation, and road construction, often facilitate the invasions; therefore, counter measures such as reseeding and a ban on grazing need special attention. Environmental factors including precipitation, nutrients, prevailing winds, fires, and topography may be other factors that promote or block the process of invasion. In studying ways of preventing or controlling such invasions, alien plants with short life cycle, prolific seed production, and strong competitiveness, deserve particular attention and so do human activities that may damage the environment and fragile habitats. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) shows great bioenergy potential and provides multiple ecological services. However, its severe seed shedding causes biomass waste and seed diffusion risk. Questions arise as to the production performance of switchgrass after panicle removal (PR), which remains unknown. We revealed switchgrass growth responses to PR and illustrated physiological reasons. Compared to the untreated switchgrass, PR significantly stimulated stem elongation (32.13%) and increased tiller number (39.70%), as well as aboveground biomass (24.69%). Importantly, PR significantly increased contents of nonstructural carbohydrates (NSCs) in the stem, which was directly beneficial to the ethanol conversion, and in the rhizome and root. The chlorophyll contents, net photosynthetic efficiency, and photochemical quantum efficiencies of flag leaf increased significantly. PR switchgrass allocated more assimilates into the stem, root, rhizome, and NSCs. Activities of phosphoenolpyruvate carboxylase, ribulose-1, 5-diphosphate carboxylase, sucrose phosphate synthase (SPS) in flag leaf and adenosine diphosphate glucose pyrophosphorylase (AGPase) and SPS in the stem and rhizome all increased significantly. In contrast, activities of the AGPase in flag leaf and sheath decreased significantly. Contents of zeatin nucleoside, gibberellins, and indoleacetic acid in flag leaf, stem, and rhizome all increased. Abscisic acid contents in flag leaf and stem decreased significantly while increased significantly in the rhizome. In conclusion, growth-promoting hormones delayed plant senescence, enhanced leaf photosynthesis, and enhanced vegetative growth through regulating assimilates-metabolism-related enzymes, which increased biomass accumulation in PR switchgrass. This work provided new insights for yield and digestibility improvement in switchgrass through field management practices, hormones regulation, or genetic modification strategies. [Display omitted] • Panicle removal (PR) retarded plant senescence in switchgrass. • PR increased biomass dry weights of switchgrass. • PR increased contents of nonstructural carbohydrates in stem, root and rhizome. • AGPase and SPS facilitated storage and transport of C assimilates in PR switchgrass. • Growth promoting hormones played critical roles in delaying plant senescence. [ABSTRACT FROM AUTHOR]

In this work, two Nb(Ta)TiZr medium-entropy alloy (MEA) coatings were fabricated successfully on a commercially pure Zr sheet by pulsed laser cladding. Their phase constitutions, microstructural characteristics, chemical compositions and grain orientations were well characterized and analyzed by using X-ray diffraction (XRD), electron channeling contrast (ECC) imaging, energy dispersive spectrometry (EDS) and electron backscatter diffraction (EBSD) techniques, with hardness and wear resistance measured and correlated with the microstructural characteristics as well. Results show that irregular-shaped bulk grains (BCC solid-solution phase) are formed in the two Nb(Ta)TiZr MEA coatings (cladding zones), both of which have a thickness of ∼800 μm with good metallurgical bonding to the substrate. After adding Ta, grains in the MEA coating are slightly refined. The phase constitutions in both the coatings agree with calculations based on several theoretical parameters. Hardness tests show that the NbTiZr and the NbTaTiZr coatings have hardnesses of 360 ± 18 HV and 430 ± 28 HV, respectively, ∼1.8 times and ∼2.2 times that of the substrate (196 ± 4 HV). This can be ascribed to combined effects of grain refinement strengthening, solid solution strengthening with denser low angle boundaries in the MEA coatings. Specific wear rates of the NbTiZr and the NbTaTiZr coatings are only ∼17% and ∼6% of that of the substrate, respectively, indicating markedly improved wear resistance. This is demonstrated to be closely related to complete oxide films easily formed on the coatings with oxidation and abrasive wear mechanisms. • Two Nb(Ta)TiZr MEA coatings were prepared on a pure Zr sheet by pulsed laser cladding. • The MEA coatings have a thickness of ∼800 μm and consist of irregular-shaped BCC phase. • Hardness and wear resistance of both MEA coatings are greatly improved compared to the substrate. • Their superior properties are related to grain refinement, solid solution and denser low angle boundaries. [ABSTRACT FROM AUTHOR]

In the research of wide-range light-absorbing coordination polymers, to enhance intermolecular or intramolecular charge transfer (CT) and decrease the electron transition excitation energy, a dedicatedly designed novel pyridine diketopyrrolopyrrole (DPP) ligand with strong electron-withdrawing unit were introduced into the Zn, Cu and 1,4-benzenedicarboxylic acid (BDC) based coordination frameworks and porous coordination polymers DPP-Zn(BDC) and DPP-Cu(BDC) were obtained, respectively. By comparing study with physically-mixed samples DPP + Zn(BDC) and DPP + Cu(BDC), a fresh light-absorbing peak around 720 nm is observed and makes the samples exhibit a wide-range absorption in the range of 200–1400 nm and gives another experimental evidence for the research of charge transfer effect in naphthalenediimide-based metal-organic framework Zn 2 (NDC) 2 (DPNI) (J. Phys. Chem. Lett. 2013, 4, 453–458). The tremendous red-shift of absorbing onset wavelength could be ascribed to the enhanced intermolecular or intramolecular CT due to electron-withdrawing DPP ligands. At the mean time slow-photon effect is also discussed. The materials have been also characterized through powder XRD, FT-IR, SEM, XPS, solution-state spectra techniques and etc. This study underscores the importance of analyzing the extended structure for interpreting photophysical data based on the potential factors: CT, slow photon, or J-coupling. Moreover the research work might inspire the construction of light-responsive coordination polymers or metal-organic frameworks (MOFs) for charge or electron transfer. [ABSTRACT FROM AUTHOR]

Novel microencapsulated phase change materials (MEPCMs) with high encapsulation capacity and enhanced leakage-prevention performance were prepared by in situ polymerization. For these MEPCMs, paraffin and melamine-formaldehyde resin (MF) are respectively used as core and shell, and graphene oxide (GO) nanosheets, which can be seen as extra protective screen, are situated at the interface between the core and the shell. Effects of GO on morphology, microstructure and properties of MEPCMs were characterized by scanning electronic microscopy (SEM), laser diffraction particle analyzer, atomic force microscopy (AFM), Fourier transformation infrared spectroscopy (FTIR), X-ray diffractometry (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and paraffin leakage rate test. The results show that the fabricated MEPCMs with GO nanosheets have gradual increasing average diameters from 6.32 to 15.89 μm with an increase content of GO, while the size of MEPCMs without GO is 5.63 μm. When the time of leakage rate test is 50 h, the MEPCMs prepared with 0.5 mg/mL GO aqueous dispersion have considerably high encapsulation ratio of 93.9 wt.%, and the leakage rate is reduced by 93.1% compared with those without GO. The high encapsulation capacity and enhanced leakage-prevention performance might be highly attractive for the application of MEPCMs. [ABSTRACT FROM AUTHOR]

Switchgrass ( Panicum virgatum L.) has been developed into a major herbaceous bioenergy crop for the production of cellulosic biofuels in North America and many counties in European. As cultivar selection has a major impact on the ultimate biomass productivity, we evaluated the adaptability and yield potential of 12 switchgrass cultivars including both upland and lowland ecotypes from 2010 to 2013 in the Beijing region, Northern China. Plant height was measured after anthesis, but phytomer number and tiller density were investigated at harvest. One single autumn harvest was carried out each year and biomass yields were determined. It was found that the lowland cultivars ‘Alamo’, ‘Kanlow’ and ‘NewYork’ produced the most biomass for their better performances in number of phytomers per tiller and mass per phytomer, though upland cultivars had higher tiller density. ‘Cave-in-rock’ and ‘Trailblazer’ had better biomass production among the upland cultivars and they were also recommended for planting together with lowland ones for their excellent cold tolerance in this region. [ABSTRACT FROM AUTHOR]