Evaluating Spatiotemporal Patterns and Integrated Driving Forces of Habitat Quality in the Northern Sand-Prevention Belt of China

Understanding habitat quality patterns and their drivers in arid zones is of fundamental importance to the sustainability maintenance of terrestrial ecosystems, but remains elusive. Here, we applied the InVEST model to investigate the spatiotemporal patterns of habitat quality in the northern sand-prevention belt (NSPB) across five time periods (2000, 2005, 2010, 2015, 2018), coupled with the structural equation model (SEM) and boosted regression tree (BRT) model to identify their integrated driving forces. The results exhibited that habitat quality in high-level zones expanded gradually from 2000 to 2018, while the middle- and low-level zones shrank. Climate, soil, topography, and human activities were significantly correlated with habitat quality, with mean annual temperature (MAT) and human activities being key contributing factors in the high-level and low-level zones, respectively, whereas the contribution of factors varied considerably in the middle-level zones. The interactions among climate, soil, topography, and human activities jointly drive habitat quality changes. Climate intensified the positive effects of soil on habitat quality, while the topographic and human activities mainly affected habitat quality indirectly through climate and soil. Our findings offer a scientific guidance for the restoration and sustainable management of desertification ecosystems in northern China.</p

Structural Optimization of Graphene Triangular Lattice Phononic Crystal Based on Dissipation Dilution Theory

Nanomechanical resonators offer brilliant mass and force sensitivity applied in many fields, owing to a low mass m and high-quality factor Q. However, in vibrating process, resonant energy is inevitably dissipated. Typically, quality factor does not surpass the inverse of the material loss angle &phi;. Recently, some exceptions emerged in the use of highly stressed silicon nitride material. As yet, it is interpreted that the pre-stress seems to &ldquo;dilute&rdquo; the intrinsic energy dissipation according to the Zener model. Is there any other material that could further break the 1/&phi; limit and achieve higher quality factors? In our previous research, through theoretical calculation and finite element simulation, we have proved that graphene&rsquo;s quality factor is two orders of magnitude larger than silicon nitride, on account of the extremely thin thickness of graphene. Based on this, we further optimize the structure of phononic crystals to achieve higher quality factors, in terms of duty cycle and cell size. Through simulation analysis, the quality factor could improve with a larger duty cycle and bigger cell size of triangular lattice phononic crystal. Unexpectedly, the Q amplification coefficient of the 3 &times; 5-cell structure, which is the least number to compose a phononic crystal with a central defect area, is the highest. In contrast, the minimal cell-number structure in hexagonal lattice could not achieve the brilliant dissipation dilution effect as well as the triangular one. Then we consider how overall size and stress influence quality factor and, furthermore, compare theoretical calculation and finite simulation. Lastly, we start from the primitive 3 &times; 5 cells, constantly adding cells to the periphery. Through simulation, to our surprise, the largest Q amplification coefficient does not belong to the largest structure, instead originating from the moderate one consisting of 7 &times; 13 cells

Response of <i>Ammodendron bifolium</i> Seedlings Inoculated with AMF to Drought Stress

Drought has become a serious environmental problem affecting people all around the world as a result of rising atmospheric pollution and global warming. Through symbiosis with Arbuscular mycorrhizal fungus (AMF), plants may mitigate the impacts of drought stress on growth and development as well as physiological metabolism. As a pioneer plant for windbreak and sand fixation, the symbiosis between AMF and Ammodendron bifolium can improve its drought resistance, which is of great significance for species protection and desertification control. In this study, A. bifolium seedlings were used as the test subject in a pot experiment with four drought stress gradients and two inoculation treatments to examine the effects of water treatment and AMF inoculation on the growth of the seedlings. The results showed that drought stress significantly inhibited the growth indexes of A. bifolium seedlings such as the height, basal diameter, blades number, and biomass, and that inoculation with AMF could promote the growth of A. bifolium seedlings and help mitigate the damage caused by drought stress. Drought stress increased the antioxidant enzyme activity and proline (Pro) accumulation in A. bifolium plants, and AMF inoculation induced higher antioxidant enzyme activity and lower malondialdehyde (MDA) and Pro contents in A. bifolium seedlings compared to non-AMF-inoculated plants. Drought stress harmed the chloroplast structure, reduced the chlorophyll concentration, and decreased the photosynthetic efficiency in A. bifolium seedlings. The ability of AMF-inoculated plants to withstand drought was enhanced by increased levels of photosynthetic pigments, higher photosynthetic activity, and increased photosynthetic product accumulation in the roots. These results suggest that AMF inoculation can alleviate drought-induced damage by promoting plant growth and improving plant antioxidant, osmoregulation, and photosynthetic capacity. In the context of increasing drought due to global warming, AMF inoculation can be an excellent way to enhance A. bifolium drought resistance

A Review on Optical Measurement Method of Chemical Oxygen Demand in Water Bodies

International audienceWater quality monitoring technology based on optical method is the trend for modern water environmental monitoring. Compared with the traditional monitoring methods, Spectroscopy is a more simple, a small amount of reagent consumption, good repeatability, high accuracy and rapid detection of significant advantages, which is very suitable for rapid and on-line monitoring determination of environment water samples COD. This paper summarized the status and research progress of optical methods for monitoring of COD in water. The basic principle of traditional analysis methods and optical methods for measuring COD in water were brief described, and compared to the characteristic of different waveband of the detection of COD. The principles and applications of spectroscopic methods commonly used spectral preprocessing methods and calibration methods were listed, and also introduced the progress of optical sensors. Finally, the future research focus and direction of spectroscopic methods were prospected

Large-Size Suspended Mono-Layer Graphene Film Transfer Based on the Inverted Floating Method

Suspended graphene can perfectly present the excellent material properties of graphene, which has a good application prospect in graphene sensors. The existing suspended graphene pressure sensor has several problems that need to be solved, one of which is the fabrication of a suspended sample. It is still very difficult to obtain large-size suspended graphene films with a high integrity that are defect-free. Based on the simulation and analysis of the kinetic process of the traditional suspended graphene release process, a novel setup for large-size suspended graphene release was designed based on the inverted floating method (IFM). The success rate of the single-layer suspended graphene with a diameter of 200 μm transferred on a stainless-steel substrate was close to 50%, which is greatly improved compared with the traditional impregnation method. The effects of the defects and burrs around the substrate cavity on the stress concentration of graphene transfer explain why the transfer success rate of large-size suspended graphene is not high. This research lays the foundation for providing large-size suspended graphene films in the area of graphene high-precision sensors