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  • MDPI AG  (13)
  • Han, Yuan  (13)
  • 1
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    Online Resource
    Acoustic Performance Study of Fiber-Optic Acoustic Sensors Based on Fabry–Pérot Etalons with Different Q Factors
    MDPI AG ; 2022
    In:  Micromachines Vol. 13, No. 1 ( 2022-01-12), p. 118-
    Details
    In: Micromachines, MDPI AG, Vol. 13, No. 1 ( 2022-01-12), p. 118-
    Abstract: The ideal development direction of the fiber-optic acoustic sensor (FOAS) is toward broadband, a high sensitivity and a large dynamic range. In order to further promote the acoustic detection potential of the Fabry–Pérot etalon (FPE)-based FOAS, it is of great significance to study the acoustic performance of the FOAS with the quality (Q) factor of FPE as the research objective. This is because the Q factor represents the storage capability and loss characteristic of the FPE. The three FOASs with different Q factors all achieve a broadband response from 20 Hz to 70 kHz with a flatness of ±2 dB, which is consistent with the theory that the frequency response of the FOAS is not affected by the Q factor. Moreover, the sensitivity of the FOAS is proportional to the Q factor. When the Q factor is 1.04×106, the sensitivity of the FOAS is as high as 526.8 mV/Pa. Meanwhile, the minimum detectable sound pressure of 347.33 μPa/Hz1/2  is achieved. Furthermore, with a Q factor of 0.27×106, the maximum detectable sound pressure and dynamic range are 152.32 dB and 107.2 dB, respectively, which is greatly improved compared with two other FOASs. Separately, the FOASs with different Q factors exhibit an excellent acoustic performance in weak sound detection and high sound pressure detection. Therefore, different acoustic detection requirements can be met by selecting the appropriate Q factor, which further broadens the application range and detection potential of FOASs.
    Type of Medium: Online Resource
    ISSN: 2072-666X
    URL: Article
    DOI: 10.3390/mi13010118
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2620864-7
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  • 2
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    Acoustic Sensing Performance Investigation Based on Grooves Etched in the Ring Resonators
    MDPI AG ; 2023
    In:  Micromachines Vol. 14, No. 3 ( 2023-02-22), p. 512-
    Details
    In: Micromachines, MDPI AG, Vol. 14, No. 3 ( 2023-02-22), p. 512-
    Abstract: Acoustic detection based on optical technology has moved in the direction of high sensitivity and resolution. In this study, an optical waveguide acoustic sensor based on a ring resonator with the evanescent field is proposed. Grooves are introduced into the ring resonators as a direct sensitive structure to excite the evanescent field. A series of resonators with diverse grooves are fabricated for a comparative analysis of acoustic performance. The acoustic parameters of bandwidth, sensitivity, and signal-to-noise ratio (SNR) vary with different grooves indicated by the Q-factor. The results show that the ring resonators with variable-sized grooves exhibit excellent capability of acoustics detection. A maximum frequency of 160 kHz and a high sensitivity of 60.075 mV/Pa is achieved, with the minimum detectable sound pressure being 131.34 µPa/Hz1/2. Furthermore, the resonators with high Q-factors represent a remarkable sound resolution reaching 0.2 Hz. This work is of great significance for optimizing acoustic sensors and broadening the application range.
    Type of Medium: Online Resource
    ISSN: 2072-666X
    URL: Article
    DOI: 10.3390/mi14030512
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 3
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    Study on the Rate of the Removal of Nano-Crystalline Diamond—Coated Materials by Femtosecond Laser Etching
    MDPI AG ; 2023
    In:  Applied Sciences Vol. 13, No. 17 ( 2023-08-31), p. 9864-
    Details
    In: Applied Sciences, MDPI AG, Vol. 13, No. 17 ( 2023-08-31), p. 9864-
    Abstract: The rate of the removal of materials coated with nano−crystalline diamonds by femtosecond laser etching was examined by adjusting the repetition rate of the femtosecond laser, the energy−flux density of the concentrated spot, and the scanning speed. The observational results of the white-light interferometer and the numerical fitting approach were used to develop the removal rate function model of the nano-crystalline diamond-covered material etched by the femtosecond laser. The findings demonstrated that the rate of material removal was not greatly affected by the repetition frequency and that the amount of laser energy accumulated over time on the coated surface is steady. The processing outcomes under different laser scanning speeds are different, and the material removal rate tends to increase and then decrease with an increase in scanning speed. The greater the energy−flux density of the focused spot, the greater the etching intensity, and the greater the material removal rate. With an increase in scanning speed, the rate at which the material is removed often rises initially before falling.
    Type of Medium: Online Resource
    ISSN: 2076-3417
    URL: Article
    DOI: 10.3390/app13179864
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2704225-X
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  • 4
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    Evaluation of Light Pollution in Global Protected Areas from 1992 to 2018
    MDPI AG ; 2021
    In:  Remote Sensing Vol. 13, No. 9 ( 2021-05-09), p. 1849-
    Details
    In: Remote Sensing, MDPI AG, Vol. 13, No. 9 ( 2021-05-09), p. 1849-
    Abstract: Light pollution, a phenomenon in which artificial nighttime light (NTL) changes the form of brightness and darkness in natural areas such as protected areas (PAs), has become a global concern due to its threat to global biodiversity. With ongoing global urbanization and climate change, the light pollution status in global PAs deserves attention for mitigation and adaptation. In this study, we developed a framework to evaluate the light pollution status in global PAs, using the global NTL time series data. First, we classified global PAs (30,624) into three pollution categories: non-polluted (5974), continuously polluted (8141), and discontinuously polluted (16,509), according to the time of occurrence of lit pixels in/around PAs from 1992 to 2018. Then, we explored the NTL intensity (e.g., digital numbers) and its trend in those polluted PAs and identified those hotspots of PAs at the global scale with consideration of global urbanization. Our study shows that global light pollution is mainly distributed within the range of 30°N and 60°N, including Europe, north America, and East Asia. Although the temporal trend of NTL intensity in global PAs is increasing, Japan and the United States of America (USA) have opposite trends due to the implementation of well-planned ecological conservation policies and declining population growth. For most polluted PAs, the lit pixels are close to their boundaries (i.e., less than 10 km), and the NTL in/around these lit areas has become stronger over the past decades. The identified hotspots of PAs (e.g., Europe, the USA, and East Asia) help support decisions on global biodiversity conservation, particularly with global urbanization and climate change.
    Type of Medium: Online Resource
    ISSN: 2072-4292
    URL: Article
    DOI: 10.3390/rs13091849
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 5
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    Tectono-Magmatic Significance of the Lower Devonian Mafic Intrusions in the East Kunlun Orogenic Belt: Keys for the Evolution of Proto-Tethys
    MDPI AG ; 2023
    In:  Minerals Vol. 13, No. 4 ( 2023-03-28), p. 478-
    Details
    In: Minerals, MDPI AG, Vol. 13, No. 4 ( 2023-03-28), p. 478-
    Abstract: Studies on post-collisional magmatic rocks can provide key clues to researching the crust–mantle interactions and the tectonic evolution of collisional orogenic belts. This study investigated a suite of newly discovered mafic intrusions in the middle of the East Kunlun orogenic belt through integrated analysis of petrology, petrography, and zircon U–Pb dating. The data could offer new insights into the generation of the Proto-Tethyan tectonic evolution. The result shows that these mafic intrusions are mainly gabbro and diabase, formed in the Early Devonian, with zircon U–Pb ages of 408.9 ± 2.0 Ma for gabbro and 411.1 ± 3.1 Ma for diabase. It consists of plagioclase, pyroxene, and dark minerals, and a small number of calcite and chlorite. Diabase has a small amount of amygdale. Their Na2O + K2O contents range from 3.47 wt.% to 5.45 wt.%, with Na2O/K2O ratios from 1.39 to 3.09, suggesting that they are calc–alkaline rocks. These rocks have an Fe2O3ᵀ content of 7.68 wt.%–11.59 wt.% and Mg# of 50.58–59.48, belonging to the iron-rich and magnesium-poor type. The chondrite-normalized rare earth elements show similar patterns that are characterized by enrichment of light rare earth elements, with (La/Yb)N of 3.27–6.75 and no significant europium anomaly, indicating the rocks are homogenous. The studied rocks are characterized by low contents of compatible elements Cr and Ni, enrichment of large-ion lithophile elements such as Rb, U, Sr, and Nd, and high-field-strength elements such as Nb, Ta, Zr, Hf, and Th. The mafic magma originated from the partial melting of the enriched mantle and was assimilated and mixed with crust materials during the process of migration. Based on the regional tectonic evolution, we interpret that the Proto-Tethys Ocean had closed in the Early Devonian, and that the East Kunlun region was in a post-collisional extensional tectonic setting.
    Type of Medium: Online Resource
    ISSN: 2075-163X
    URL: Article
    DOI: 10.3390/min13040478
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2655947-X
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  • 6
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    Petrogenesis and Geochronology of the Shazuoquan Ophiolite, Beishan Orogenic Belt: Constraints on the Evolution of the Beishan Ocean
    MDPI AG ; 2023
    In:  Minerals Vol. 13, No. 8 ( 2023-08-11), p. 1067-
    Details
    In: Minerals, MDPI AG, Vol. 13, No. 8 ( 2023-08-11), p. 1067-
    Abstract: The ophiolites in the Beishan Orogenic Belt provide important information about the evolution of the Beishan Ocean in the Paleozoic Era. We studied ophiolite petrology, geochemistry and isotopic chronology. The Shazouquan ophiolites consist of dunites, wehrlites, gabbros and anorthosites. Ophiolitic mélange belts are composed of matrixes and blocks, and different rocks are fault-bounded. Dunites and wehrlites are high in Mg#, Cr# and MgO, low in TiO2, relatively depleted in large-ion lithophile elements (Ti and P) and enriched in high-strength elements (U, Zr and Hf). They have a total REE of 1.25 × 10–6−5.39 × 10−6 and δEu of 1.12–3.54, which are similar to those of SSZ-type ophiolites, indicating that their parent magma source region may be a weakly depleted mantle source region. The anorthosite and gabbro are high in Al2O3, MgO and Mg#, low in TiO2, enriched in large-ion lithophile elements (Rb and Sr), and depleted in high-strength elements (Nb, Ta and Ti), but enriched in Zr and Hf. They have similar geochemical signatures to those of arc magmatic rocks. They are derived from the mantle peridotite formed against the tectonic background of subduction and modified by the fluid materials in the subduction zone. We collected anorthosite and gabbro, which were produced as ophiolite for U-Pb dating. The anorthosite yields a zircon U-Pb, aged 394 ± 11 Ma (MSWD = 0.84), and a gabbro zircon U-Pb, aged 466 ± 12 Ma (MSWD = 3.2), indicating that the Shazouquan ophiolite was formed in the Middle Ordovician–Early Devonian eras. Combining the above evidence, we conclude that the Beishan Ocean was in a subduction tectonic background from the Middle Ordovician to Early Devonian periods.
    Type of Medium: Online Resource
    ISSN: 2075-163X
    URL: Article
    DOI: 10.3390/min13081067
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 7
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    A Predictive Model of Major Postoperative Respiratory Adverse Events in Pediatric Patients Undergoing Rigid Bronchoscopy for Exploration and Foreign Body Removal
    MDPI AG ; 2023
    In:  Journal of Clinical Medicine Vol. 12, No. 17 ( 2023-08-25), p. 5552-
    Details
    In: Journal of Clinical Medicine, MDPI AG, Vol. 12, No. 17 ( 2023-08-25), p. 5552-
    Abstract: Background: No nomogram has been established to predict the incidence of major postoperative respiratory adverse events (mPRAEs) in children undergoing rigid bronchoscopy for airway foreign bodies (AFB) removal and exploration of the airway, though some studies have confirmed the risk factors. Methods: 1214 pediatric patients (≤3 years old) undergoing rigid bronchoscopy for AFB from June 2014 to December 2020 were enrolled in this study. The primary outcome was the occurrence of mPRAEs, including laryngospasm and bronchospasm. Following that, a nomogram prediction model for the mPRAEs was developed. Results: The incidence of mPRAEs was 84 (6.9%) among 1214 subjects. American Society of Anesthesiologists physical status (ASA-PS), intraoperative desaturation (SpO2 〈 90%), procedural duration and ventilatory approach were all independent risk factors of mPRAEs. The area under the receiver operating characteristic curve (AUC) value of the nomogram for predicting mPRAEs was 0.815 (95% CI: 0.770–0.861), and the average AUC for ten-fold cross-validation was 0.799. These nomograms were well calibrated by Hosmer-Lemshow (p = 0.607). Decision curve analysis showed that the nomogram prediction model is effective in clinical settings. Conclusions: Combining ASA-PS, intraoperative desaturation, procedural duration, and ventilatory approach, the nomogram model is adequate for predicting the risk of developing mPRAEs, followed by rigid bronchoscopy for AFB removal and exploration.
    Type of Medium: Online Resource
    ISSN: 2077-0383
    URL: Article
    DOI: 10.3390/jcm12175552
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2662592-1
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  • 8
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    Evaluation of Linear Kernel-Driven BRDF Models over Snow-Free Rugged Terrain
    MDPI AG ; 2023
    In:  Remote Sensing Vol. 15, No. 3 ( 2023-01-30), p. 786-
    Details
    In: Remote Sensing, MDPI AG, Vol. 15, No. 3 ( 2023-01-30), p. 786-
    Abstract: Semi-empirical kernel-driven models have been widely used to characterize anisotropic reflectance due to their simple form and physically meaningful approximation. Recently, several kernel-driven models have been coupled with topographic effects to improve the fitting of bidirectional reflectance over rugged terrains. However, extensive evaluations of the various models’ performances are required before their subsequent application in remote sensing. Three typical kernel-driven BRDF models over snow-free rugged terrains such as the RTLSR, TCKD, and the KDST-adjusted TCKD (KDST-TCKD) were investigated in this paper using simulated and observed BRFs. Against simulated data, the fitting error (NIR/Red RMSE) of the RTLSR gradually increases from 0.0358/0.0342 to 0.0471/0.0516 with mean slopes (α) increases from 9.13° to 33.40°. However, the TCKD and KDST-TCKD models perform an overall better fitting accuracy: the fitting errors of TCKD gradually decreased from 0.0366/0.0337 to 0.0252/0.0292, and the best fit from the KDST-TCDK model with NIR/Red RMSE decreased from 0.0192/0.0269 to 0.0169/0.0180. When compared to the sandbox data (α from 8.4° to 30.36°), the NIR/Red RMSE of the RTLSR model ranges from 0.0147/0.0085 to 0.0346/0.0165, for the TCKD model from 0.0144/0.0086 to 0.0298/0.0154, and for the KDST-TCKD model from 0.0137/0.0082 to 0.0234/0.0149. Using MODIS data, the TCKD and KDST-TCKD models show more significant improvements compared to the RTLSR model in rugged terrains. Their RMSE differences are within 0.003 over a relatively flat terrain (α 〈 10°). When α is large (20°–30° and 〉 30°), the RMSE of the TCKD model has a decrease of around 0.01 compared to that of the RTLSR; for KDST-TCKD, it is approximately 0.02, and can even reach 0.0334 in the savannas. Therefore, the TCKD and KDST-TCKD models have an overall better performance than the RTLSR model in rugged terrains, especially in the case of large mean slopes. Among them, the KDST-TCKD model performs the best due to its consideration of topographic effects, geotropic growth, and component spectra.
    Type of Medium: Online Resource
    ISSN: 2072-4292
    URL: Article
    DOI: 10.3390/rs15030786
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 9
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    An Empirical Mode Decomposition for Establishing Spatiotemporal Air Quality Trends in Shandong Province, China
    MDPI AG ; 2021
    In:  Sustainability Vol. 13, No. 22 ( 2021-11-22), p. 12901-
    Details
    In: Sustainability, MDPI AG, Vol. 13, No. 22 ( 2021-11-22), p. 12901-
    Abstract: Air pollution is a serious problem in China, and the government has taken a series of steps to solve it. However, it is still u2nclear how the situation has improved after years of atmospheric pollution control. Shandong Province, which has the second largest population and the highest coal consumption in China, was chosen to analyze the spatiotemporal air quality trends. We obtained daily air quality index (AQI) values from 91 stations in the province from 1 January 2014, to 31 December 2019, based on an adaptive data analysis method, empirical mode decomposition (EMD). The distribution of AQI in Shandong Province was heterogeneous at both spatial and temporal scales. All the stations could be divided into four clusters whose AQI trends decreased from 75 to 53, 95 to 68, 128 to 82, and 148 to 82, respectively. The overall trend of pollution became more serious from east to west in the province. The AQI is the largest in winter, followed by spring and autumn, and the smallest index occurs in summer. There are four types of annual trends of the AQI of each city. The overall downward trend indicates that the air quality of each city was improving annually.
    Type of Medium: Online Resource
    ISSN: 2071-1050
    URL: Article
    DOI: 10.3390/su132212901
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2518383-7
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  • 10
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    Application of AHP to Road Selection
    MDPI AG ; 2020
    In:  ISPRS International Journal of Geo-Information Vol. 9, No. 2 ( 2020-02-01), p. 86-
    Details
    In: ISPRS International Journal of Geo-Information, MDPI AG, Vol. 9, No. 2 ( 2020-02-01), p. 86-
    Abstract: The analytic hierarchy process (AHP), a decision-making method, allows the relative prioritization and assessment of alternatives under multiple criteria contexts. This method is also well suited for road selection. The method for road selection based on AHP involves four steps: (i) Points of Interest (POIs), the point-like representations of the facilities and habitations in maps, are used to describe and build the contextual characteristic indicator of roads; (ii) form an AHP model of roads with topological, geometrical, and contextual characteristic indicators to calculate their importance; (iii) select roads based on their importance and the adaptive thresholds of their constituent density partitions; and (iv) maintain the global connectivity of the selected network. The generalized result at a scale of 1:200,000 by AHP-based methods better preserved the structure of the original road network compared with other methods. Our method also gives preference to roads with relatively significant contextual characteristics without interfering with the structure of the road network. Furthermore, the result of our method largely agrees with that of the manual method.
    Type of Medium: Online Resource
    ISSN: 2220-9964
    URL: Article
    DOI: 10.3390/ijgi9020086
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2655790-3
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