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  • MDPI AG  (13)
  • 1
    Online Resource
    Online Resource
    Bibliometric Analysis of the Permafrost Research: Developments, Impacts, and Trends
    MDPI AG ; 2022
    In:  Remote Sensing Vol. 15, No. 1 ( 2022-12-31), p. 234-
    Details
    In: Remote Sensing, MDPI AG, Vol. 15, No. 1 ( 2022-12-31), p. 234-
    Abstract: Permafrost is a significant part of the cryosphere, which has gained increasing attention from scientists, policy-makers, and the general public due to global warming, environmental degradation, water shortages, and intense human activities. Although many permafrost research review articles have been published, these studies were predominantly limited to either one subject or one field, while systematic studies about permafrost based on bibliometric analysis methods remain limited. We aim to fill this gap by conducting a bibliometric analysis of 13,697 articles in the field of permafrost research from 1942 to 2021, collected from the Web of Science core collection database. The results indicate that permafrost research is a typically multi-author, multi-country, and multi-institution cooperative field, involved in many research fields. The cumulative number of publications has presented an exponential increase over the past 80 years, with an average annual growth rate of 10.40%. Since 2000, China has seen a rapid growth in the number of publications per year, surpassing the USA in 2016 and leading in the years since then. In addition, the authors from China have great contributions in publications, and there is good room for permafrost development in the future according to the authors’ M-index ranking. After the analysis of authors’ keywords, we found that, compared to the conventional methods, machine learning and interferometric synthetic aperture radar (InSAR) are new technological approaches introduced in recent years, and the Qinghai–Tibet Plateau has become a popular study area. The results presented here can help related researchers, scholars, and students in the field to better understand the past developments, current status, and future trends of permafrost research. Furthermore, this paper presents and expands the general process of the bibliometric method used in permafrost studies, which can provide researchers with new inspirations and improve discipline research approach.
    Type of Medium: Online Resource
    ISSN: 2072-4292
    URL: Article
    DOI: 10.3390/rs15010234
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2513863-7
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  • 2
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    Nanobubble Technology Enhanced Ozonation Process for Ammonia Removal
    MDPI AG ; 2022
    In:  Water Vol. 14, No. 12 ( 2022-06-10), p. 1865-
    Details
    In: Water, MDPI AG, Vol. 14, No. 12 ( 2022-06-10), p. 1865-
    Abstract: Ozone (O3) has been widely used for water and wastewater treatment due to its strong oxidation ability, however, the utilization efficiency of O3 is constrained by its low solubility and short half-life during the treatment process. Thereby, an integrated approach using novel nanobubble technology and ozone oxidation method was studied in order to enhance the ozonization of ammonia. Artificial wastewater (AW) with an initial concentration of 1600 mg/L ammonia was used in this study. In the ozone-nanobubble treatment group, the concentration of nano-sized bubbles was 2.2 × 107 particles/mL, and the bubbles with 〈 200 nm diameter were 14 times higher than those in the ozone-macrobubble treatment control group. Ozone aeration was operated for 5 min in both nanobubble treatment and control groups, however, the sampling and measurement were conducted for 30 min to compare the utilization of O3 for ammonia oxidation. H+ was the by-product of the ammonia ozonation process, thus the pH decreased from 8 to 7 and 7.5 in nanobubble treatment and control groups, respectively, after 30 min of operation. The fast removal of ammonia was observed in both systems in the first 10 min, where the concentration of ammonia decreased from 1600 mg/L to 835 and 1110 mg/L in nanobubble treatment and control groups, respectively. In the nanobubble treatment group, ammonia concentrations kept the fast-decreasing trend and reached the final removal performance of 82.5% at the end of the experiment, which was significantly higher than that (44.2%) in the control group. Moreover, the first-order kinetic model could be used to describe the removal processes and revealed a significantly higher kinetic rate constant (0.064 min−1) compared with that (0.017 min−1) in the control group. With these results, our study highlights the viability of the proposed integrated approach to enhance the ozonation of a high level of ammonia in contaminated water.
    Type of Medium: Online Resource
    ISSN: 2073-4441
    URL: Article
    DOI: 10.3390/w14121865
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2521238-2
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  • 3
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    Recent Advances in Copper-Doped Titanium Implants
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 7 ( 2022-03-22), p. 2342-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 7 ( 2022-03-22), p. 2342-
    Abstract: Titanium (Ti) and its alloys have been extensively used as implant materials in clinical practice due to their high corrosion resistance, light weight and excellent biocompatibility. However, the insufficient intrinsic osteogenic capacity of Ti and its alloys impedes bone repair and regeneration, and implant-related infection or inflammation remains the leading cause of implant failure. Bacterial infections or inflammatory diseases constitute severe threats to human health. The physicochemical properties of the material are critical to the success of clinical procedures, and the doping of Cu into Ti implants has been confirmed to be capable of enhancing the bone repair/regeneration, angiogenesis and antibacterial capability. This review outlines the recent advances in the design and preparation of Cu-doped Ti and Ti alloy implants, with a special focus on various methods, including plasma immersion implantation, magnetron sputtering, galvanic deposition, microarc oxidation and sol-gel synthesis. More importantly, the antibacterial and mechanical properties as well as the corrosion resistance and biocompatibility of Cu-doped Ti implants from different methods are systematically reviewed, and their prospects and limitations are also discussed.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15072342
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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  • 4
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    Nonlinear Energy Harvesting by Piezoelectric Bionic ‘M’ Shape Generating Beam Featured in Reducing Stress Concentration
    MDPI AG ; 2023
    In:  Micromachines Vol. 14, No. 5 ( 2023-05-06), p. 1007-
    Details
    In: Micromachines, MDPI AG, Vol. 14, No. 5 ( 2023-05-06), p. 1007-
    Abstract: Inspired by the flapping wings of seagulls during flight, a new low-cost, magnet-free, bistable piezoelectric energy harvester is proposed to obtain energy from low-frequency vibration and convert it into electrical energy and reduce fatigue damage caused by stress concentration. In order to optimize the power generation efficiency of this energy harvesting, finite element analysis and experimental tests were carried out. The results of finite element analysis and experimental results are in good agreement, and the superior performance in improving stress concentration of the energy harvester compared to the previous parabolic (bow-shaped) one using bistable technology was quantitatively analyzed using finite element simulation, with a maximum stress reduction of 32.34%. The experimental results showed that under optimal operating conditions, the maximum open-circuit voltage of the harvester was 11.5 V, and the maximum output power was 73 μW. These results indicate that this is a promising strategy, which provides a reference for collecting vibrational energy in low-frequency environments.
    Type of Medium: Online Resource
    ISSN: 2072-666X
    URL: Article
    DOI: 10.3390/mi14051007
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2620864-7
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  • 5
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    Structural Responses of a Supertall Building Subjected to a Severe Typhoon at Landfall
    MDPI AG ; 2020
    In:  Applied Sciences Vol. 10, No. 8 ( 2020-04-24), p. 2965-
    Details
    In: Applied Sciences, MDPI AG, Vol. 10, No. 8 ( 2020-04-24), p. 2965-
    Abstract: Typhoon Mangkhut (1822) was one of the strongest tropical cyclones that ever impacted the south coast of China in past decades. During the passage of this typhoon, the structural health monitoring (SHM) system installed on a 303 m high building in this region worked effectively, and high-quality field measurements at nine height levels of the building were collected successfully, which provides a valuable opportunity to explore the dynamic properties of the building and the associated wind effects. In this study, the typhoon wind characteristics are presented first based on in-situ measurements at two sites. Acceleration responses of the building is then investigated, and the building’s serviceability is assessed against several comfort criteria. This study further focuses on the identification of modal parameters (i.e., natural frequency, damping ratio, and modal shape) via two methods: stochastic subspace identification (SSI) method and a method based on combined use of spectral analysis and random decrement technique (RDT). The good agreement between the two results demonstrates the effectiveness and the accuracy of the adopted methods. The obtained results are further compared with the stipulations in several technical codes as well as simulation results via finite element method to examine their performances in this real case. The amplitude dependence of natural frequencies and damping ratios of the studied building are also stressed.
    Type of Medium: Online Resource
    ISSN: 2076-3417
    URL: Article
    DOI: 10.3390/app10082965
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2704225-X
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  • 6
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    Surface Engineering of WO3/BiVO4 to Boost Solar Water-Splitting
    MDPI AG ; 2020
    In:  Catalysts Vol. 10, No. 5 ( 2020-05-18), p. 556-
    Details
    In: Catalysts, MDPI AG, Vol. 10, No. 5 ( 2020-05-18), p. 556-
    Abstract: Single-phase photoanodes often suffer inferior charge transport, which can be mitigated by constructing efficient heterojunctions. Thus, we have fabricated a fluorine-doped tin oxide (FTO)/WO3/BiVO4 heterojunction using hydrothermal and spin-coating methods. Surface engineering was exploited to further accelerate the reaction kinetics, which was achieved via post-modification with NaOH solution. This treatment alters the surface chemical state of the BiVO4 nanoparticles, leading to enhanced charge transport and surface water oxidation processes. As a result, the optimized sample can produce a photocurrent more than two times that of WO3. The simple post-treatment provides a viable and cost-effective strategy for promoting the photoelectric properties of photoanodes.
    Type of Medium: Online Resource
    ISSN: 2073-4344
    URL: Article
    DOI: 10.3390/catal10050556
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2662126-5
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  • 7
    Online Resource
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    UAV’s Status Is Worth Considering: A Fusion Representations Matching Method for Geo-Localization
    MDPI AG ; 2023
    In:  Sensors Vol. 23, No. 2 ( 2023-01-08), p. 720-
    Details
    In: Sensors, MDPI AG, Vol. 23, No. 2 ( 2023-01-08), p. 720-
    Abstract: Visual geo-localization plays a crucial role in positioning and navigation for unmanned aerial vehicles, whose goal is to match the same geographic target from different views. This is a challenging task due to the drastic variations in different viewpoints and appearances. Previous methods have been focused on mining features inside the images. However, they underestimated the influence of external elements and the interaction of various representations. Inspired by multimodal and bilinear pooling, we proposed a pioneering feature fusion network (MBF) to address these inherent differences between drone and satellite views. We observe that UAV’s status, such as flight height, leads to changes in the size of image field of view. In addition, local parts of the target scene act a role of importance in extracting discriminative features. Therefore, we present two approaches to exploit those priors. The first module is to add status information to network by transforming them into word embeddings. Note that they concatenate with image embeddings in Transformer block to learn status-aware features. Then, global and local part feature maps from the same viewpoint are correlated and reinforced by hierarchical bilinear pooling (HBP) to improve the robustness of feature representation. By the above approaches, we achieve more discriminative deep representations facilitating the geo-localization more effectively. Our experiments on existing benchmark datasets show significant performance boosting, reaching the new state-of-the-art result. Remarkably, the recall@1 accuracy achieves 89.05% in drone localization task and 93.15% in drone navigation task in University-1652, and shows strong robustness at different flight heights in the SUES-200 dataset.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s23020720
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2052857-7
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  • 8
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    Numerical Analysis on Gas Production Efficiency from Hydrate Deposits by Thermal Stimulation: Application to the Shenhu Area, South China Sea
    MDPI AG ; 2011
    In:  Energies Vol. 4, No. 2 ( 2011-02-14), p. 294-313
    Details
    In: Energies, MDPI AG, Vol. 4, No. 2 ( 2011-02-14), p. 294-313
    Type of Medium: Online Resource
    ISSN: 1996-1073
    URL: Article
    DOI: 10.3390/en4020294
    Language: English
    Publisher: MDPI AG
    Publication Date: 2011
    detail.hit.zdb_id: 2437446-5
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  • 9
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    Modeling Ozone Source Apportionment and Performing Sensitivity Analysis in Summer on the North China Plain
    MDPI AG ; 2020
    In:  Atmosphere Vol. 11, No. 9 ( 2020-09-17), p. 992-
    Details
    In: Atmosphere, MDPI AG, Vol. 11, No. 9 ( 2020-09-17), p. 992-
    Abstract: In recent years, air quality issues due to fine particulate matter have been sufficiently treated. However, ozone (O3) has now become the primary pollutant in summer on the North China Plain (NCP). In this study, a three-dimensional chemical transport model (the Nested Air Quality Prediction Model System, NAQPMS) coupled with an online source apportionment module was applied to investigate the sources of O3 pollution over the NCP. Generally, the NAQPMS adequately captured the observed spatiotemporal features of O3 during the period of July 1st to August 31st in 2017 on the NCP. The results of the source apportionment indicated that the contributions of local emissions and transport from the NCP accounted for the largest proportion of O3, with magnitudes of 25% and 39%, respectively. Compared with those in the average monthly results, the local contribution and regional transport during O3 episodes on the NCP increased by 7% and 10%, respectively. Based on sensitivity tests, two thresholds of the sensitivity indicator P(H2O2)/P(HNO3) were detected, at 0.08 and 0.2. Ozone formation in the urban sites of Beijing, Tianjin, and the southern part of Hebei Province was controlled by VOCs, while the other sites were mainly controlled by NOX. Biogenic emissions contributed approximately 18% to O3 formation in July in the southwestern part of Hebei Province.
    Type of Medium: Online Resource
    ISSN: 2073-4433
    URL: Article
    DOI: 10.3390/atmos11090992
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2605928-9
    SSG: 23
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  • 10
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    Effects of Organic Fertilization Rates on Surface Water Nitrogen and Phosphorus Concentrations in Paddy Fields
    MDPI AG ; 2022
    In:  Agriculture Vol. 12, No. 9 ( 2022-09-14), p. 1466-
    Details
    In: Agriculture, MDPI AG, Vol. 12, No. 9 ( 2022-09-14), p. 1466-
    Abstract: Inappropriate organic fertilizer application may cause serious environmental risks, especially nitrogen (N) and phosphorus (P) losses. To achieve a win–win for high yield and environmental protection in organic agriculture, it was essential to demonstrate the relationship between the organic fertilizer input, rice yields, and risks of N and P losses. Based on a rice and green manure cropping rotation field experiment in the Yangtze River Delta of China, the effects of organic fertilization rates on the dynamics of surface water N and P concentrations and rice grain yields were determined. The results showed that the N (total N, ammonium-nitrogen, nitrate-nitrogen) and P (total P and dissolved P) concentrations in surface water immediately and greatly reached the highest values 1 day after basal fertilization and topdressing fertilization. Then, the N and P concentrations sharply decreased and were maintained at a relatively low level. The initial 3 and 7 days after organic fertilization were the high-risk periods for controlling N and P runoff losses. The surface water N and P concentrations had a positive correlation with the organic fertilization rate in high-risk periods. Besides, the effects of organic fertilization on surface water P concentrations existed longer than those of N concentrations. The rice grain yields increased with the increase in organic fertilization rates, but high organic fertilizer input ( 〉 225 kg N per hectare) did not increase the grain yield. Meanwhile, the high organic fertilizer input had the highest risks for N and P losses. Therefore, in organic rice farming, organic fertilization rates with 150~200 kg N per hectare are the optimal organic fertilizer input, with relatively high grain yields and low N and P losses.
    Type of Medium: Online Resource
    ISSN: 2077-0472
    URL: Article
    DOI: 10.3390/agriculture12091466
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2651678-0
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