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  • MDPI AG  (8)
  • 1
    Online Resource
    Online Resource
    Experimental Study on Fire Suppression of the Outdoor Oil-Immersed Transformer by High-Pressure Water Mist System
    MDPI AG ; 2023
    In:  Fire Vol. 6, No. 6 ( 2023-06-15), p. 238-
    Details
    In: Fire, MDPI AG, Vol. 6, No. 6 ( 2023-06-15), p. 238-
    Abstract: Fire accidents due to oil-immersed transformers seriously threaten the safe operation of power systems. In this paper, the similarity principle was used to design a high-pressure water mist fire-extinguishing test platform for a small-scale transformer fire, and the design method achieved a good fire extinguishing effect. The results indicate that a deflagration phenomenon, lasting about 2–4 s, could be observed after activating the high-pressure water mist system; the flame temperature rose rapidly at first, then dropped sharply, and finally cooled to the indoor temperature. The nozzle’s flow rate in this system has a significant impact on the fire extinguishing time. Meanwhile, the adjustment of the upper nozzle height also influenced the fire suppression effectiveness of the system, where a height of 1800 mm achieved the best performance compared to the others. In addition, the ambient wind speed is a very unfavorable factor for transformer fire suppression, where the fire extinguishing efficiency decreases rapidly with the increase in wind speed. Therefore, under low wind speed conditions, the high-pressure water mist system has great advantages in the fire suppression of outdoor oil-immersed transformers, and the above research results can provide a reference for the optimization design of this system.
    Type of Medium: Online Resource
    ISSN: 2571-6255
    URL: Article
    DOI: 10.3390/fire6060238
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2924038-4
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  • 2
    Online Resource
    Online Resource
    High-Precision CO2 Column Length Analysis on the Basis of a 1.57-μm Dual-Wavelength IPDA Lidar
    MDPI AG ; 2020
    In:  Sensors Vol. 20, No. 20 ( 2020-10-17), p. 5887-
    Details
    In: Sensors, MDPI AG, Vol. 20, No. 20 ( 2020-10-17), p. 5887-
    Abstract: For high-precision measurements of the CO2 column concentration in the atmosphere with airborne integrated path differential absorption (IPDA) Lidar, the exact distance of the Lidar beam to the scattering surface, that is, the length of the column, must be measured accurately. For the high-precision inversion of the column length, we propose a set of methods on the basis of the actual conditions, including autocorrelation detection, adaptive filtering, Gaussian decomposition, and optimized Levenberg–Marquardt fitting based on the generalized Gaussian distribution. Then, based on the information of a pair of laser pulses, we use the direct adjustment method of unequal precision to eliminate the error in the distance measurement. Further, the effect of atmospheric delay on distance measurements is considered, leading to further correction of the inversion results. At last, an airborne experiment was carried out in a sea area near Qinhuangdao, China on 14 March 2019. The results showed that the ranging accuracy can reach 0.9066 m, which achieved an excellent ranging accuracy on 1.57-μm IPDA Lidar and met the requirement for high-precision CO2 column length inversion.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s20205887
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2052857-7
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  • 3
    Online Resource
    Online Resource
    Estimation of Earth Rotation Parameters and Prediction of Polar Motion Using Hybrid CNN–LSTM Model
    MDPI AG ; 2023
    In:  Remote Sensing Vol. 15, No. 2 ( 2023-01-10), p. 427-
    Details
    In: Remote Sensing, MDPI AG, Vol. 15, No. 2 ( 2023-01-10), p. 427-
    Abstract: The Earth rotation parameters (ERPs), including polar motion (PMX and PMY) and universal time (UT1-UTC), play a central role in functions such as monitoring the Earth’s rotation and high-precision navigation and positioning. Variations in ERPs reflect not only the overall state of movement of the Earth, but also the interactions among the atmosphere, ocean, and land on the spatial and temporal scales. In this paper, we estimated ERP series based on very long baseline interferometry (VLBI) observations between 2011–2020. The results show that the average root mean square errors (RMSEs) are 0.187 mas for PMX, 0.205 mas for PMY, and 0.022 ms for UT1-UTC. Furthermore, to explore the high-frequency variations in more detail, we analyzed the polar motion time series spectrum based on fast Fourier transform (FFT), and our findings show that the Chandler motion was approximately 426 days and that the annual motion was about 360 days. In addition, the results also validate the presence of a weaker retrograde oscillation with an amplitude of about 3.5 mas. This paper proposes a hybrid prediction model that combines convolutional neural network (CNN) and long short-term memory (LSTM) neural network: the CNN–LSTM model. The advantages can be attributed to the CNN’s ability to extract and optimize features related to polar motion series, and the LSTM’s ability to make medium- to long-term predictions based on historical time series. Compared with Bulletin A, the prediction accuracies of PMX and PMY are improved by 42% and 13%, respectively. Notably, the hybrid CNN–LSTM model can effectively improve the accuracy of medium- and long-term polar motion prediction.
    Type of Medium: Online Resource
    ISSN: 2072-4292
    URL: Article
    DOI: 10.3390/rs15020427
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2513863-7
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  • 4
    Online Resource
    Online Resource
    Metabolic Effects of Selective Deletion of Group VIA Phospholipase A2 from Macrophages or Pancreatic Islet Beta-Cells
    MDPI AG ; 2020
    In:  Biomolecules Vol. 10, No. 10 ( 2020-10-17), p. 1455-
    Details
    In: Biomolecules, MDPI AG, Vol. 10, No. 10 ( 2020-10-17), p. 1455-
    Abstract: To examine the role of group VIA phospholipase A2 (iPLA2β) in specific cell lineages in insulin secretion and insulin action, we prepared mice with a selective iPLA2β deficiency in cells of myelomonocytic lineage, including macrophages (MØ-iPLA2β-KO), or in insulin-secreting β-cells (β-Cell-iPLA2β-KO), respectively. MØ-iPLA2β-KO mice exhibited normal glucose tolerance when fed standard chow and better glucose tolerance than floxed-iPLA2β control mice after consuming a high-fat diet (HFD). MØ-iPLA2β-KO mice exhibited normal glucose-stimulated insulin secretion (GSIS) in vivo and from isolated islets ex vivo compared to controls. Male MØ-iPLA2β-KO mice exhibited enhanced insulin responsivity vs. controls after a prolonged HFD. In contrast, β-cell-iPLA2β-KO mice exhibited impaired glucose tolerance when fed standard chow, and glucose tolerance deteriorated further when introduced to a HFD. β-Cell-iPLA2β-KO mice exhibited impaired GSIS in vivo and from isolated islets ex vivo vs. controls. β-Cell-iPLA2β-KO mice also exhibited an enhanced insulin responsivity compared to controls. These findings suggest that MØ iPLA2β participates in HFD-induced deterioration in glucose tolerance and that this mainly reflects an effect on insulin responsivity rather than on insulin secretion. In contrast, β-cell iPLA2β plays a role in GSIS and also appears to confer some protection against deterioration in β-cell functions induced by a HFD.
    Type of Medium: Online Resource
    ISSN: 2218-273X
    URL: Article
    DOI: 10.3390/biom10101455
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2701262-1
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  • 5
    Online Resource
    Online Resource
    Study on the Location Determination of Building Fire Points Based on Acoustic CT Temperature Measurement
    MDPI AG ; 2023
    In:  Fire Vol. 6, No. 9 ( 2023-09-09), p. 353-
    Details
    In: Fire, MDPI AG, Vol. 6, No. 9 ( 2023-09-09), p. 353-
    Abstract: Rapid perception of the location of the fire point is crucial to building fire emergency response in the process of building fire emergency response, which can help firefighters direct fire-fighting operations, effectively control fire sources, and provide strong evidence for the analysis and investigation of fire causes. This paper uses acoustic CT temperature measurement technology to determine the fire source location of a building fire and verifies its validity and applicability as follows: we construct various fire point numerical models based on the fire dynamics simulator (FDS) and obtain temperature data at different times; neural network means were used to obtain the time-of-flight (TOF) of an acoustic wave traveling; the large ill-conditioned matrix equation of acoustic flight under different meshing schemes was constructed and solved based on the simultaneous algebraic reconstruction technique (SART) and least squares QR-decomposition (LSQR), and then reconstruction temperature data under each scheme were obtained. Through the error analysis, the reconstruction effect of each reconstruction scheme is evaluated, and then the applicability of the location coordinate determination of the fire point is analyzed. The results show that the determination of the fire location under the conditions of various fire points in the building space can be realized by acoustic CT temperature measurement technology.
    Type of Medium: Online Resource
    ISSN: 2571-6255
    URL: Article
    DOI: 10.3390/fire6090353
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2924038-4
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  • 6
    Online Resource
    Online Resource
    Modeling Occupant Window Behavior in Hospitals—A Case Study in a Maternity Hospital in Beijing, China
    MDPI AG ; 2023
    In:  Sustainability Vol. 15, No. 11 ( 2023-05-25), p. 8606-
    Details
    In: Sustainability, MDPI AG, Vol. 15, No. 11 ( 2023-05-25), p. 8606-
    Abstract: Nowadays, relevant data collected from hospital buildings remain insufficient because hospital buildings often have stricter environmental requirements resulting in more limited data access than other building types. Additionally, existing window-opening behavior models were mostly developed and validated using data measured from the experimental building itself. Hence, their accuracy is only assessed by the algorithm’s evaluation index, which limits the model’s applicability, given that it is not tested by the actual cases nor cross-verified with other buildings. Based on the aforementioned issues, this study analyzes the window-opening behavior of doctors and patients in spring in a maternity hospital in Beijing and develops behavioral models using logistic regression. The results show that the room often has opened windows in spring when the outdoor temperature exceeds 20 °C. Moreover, the ward windows’ use frequency is more than 10 times higher than those of doctors’ office. The window-opening behavior in wards is more susceptible to the influence of outdoor temperature, while in the doctors’ office, more attention is paid to indoor air quality. Finally, by embedding the logistic regression model of each room into the EnergyPlus software to simulate the CO2 concentration of the room, it was found that the model has better applicability than the fixed schedule model. However, by performing cross-validation with different building types, it was found that, due to the particularity of doctors’ offices, the models developed for other building types cannot accurately reproduce the window-opening behavior of doctors. Therefore, more data are still needed to better understand window usage in hospital buildings and support the future building performance simulations of hospital buildings.
    Type of Medium: Online Resource
    ISSN: 2071-1050
    URL: Article
    DOI: 10.3390/su15118606
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2518383-7
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  • 7
    Online Resource
    Online Resource
    Study on Group Movement Characteristics in Stairwell of High-Rise Buildings
    MDPI AG ; 2022
    In:  Buildings Vol. 13, No. 1 ( 2022-12-29), p. 83-
    Details
    In: Buildings, MDPI AG, Vol. 13, No. 1 ( 2022-12-29), p. 83-
    Abstract: In order to cope with limited land availability and the increasing urban population, more high-rise buildings are being built throughout cities, but this has also led to new challenges in the emergency evacuation of people. Therefore, we conducted an evacuation experiment of a group of people in the stairwells of high-rise buildings to explore the movement law of groups in stairwells. The experiment had 18 scenes, including the evacuation movement of an independent group and the crowd evacuation movement of different groups. Analyzing the independent groups’ movement showed that regardless of the type of group, the average speed of the crowd was more than 1.2 m/s, which was longer than that of previous studies. The more constraints in the evacuation process, the smaller the speed difference between males and females. Group cohesion was mostly concentrated at about 1 s. Moreover, group velocity and cohesion were found to have no significant correlation in stairwell movement. Analyzing the crowd evacuation time of eight different scenes showed that it took longer for crowds bearing weight to evacuate than those not bearing weight. According to the spatiotemporal evolution of crowd evacuation in stairwells, the crowd moves intermittently in the evacuation process, especially in the early and middle stages of evacuation, and the influence of group factors on this process was not obvious. Regardless of the kind of scene or stairwell, the number of pedestrians generally first increased and then decreased to a significantly low value, and the number of pedestrians reached about 30 in the scenario of people without any load. Additionally, the speed of the pedestrians entering the stairwell in the back of the group was not faster than that of the pedestrians in the front, which showed that pedestrians rarely engaged in overtaking behavior. The research results of this paper not only enrich evacuation research but also provide support for the design of high-rise stairs.
    Type of Medium: Online Resource
    ISSN: 2075-5309
    URL: Article
    DOI: 10.3390/buildings13010083
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2661539-3
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  • 8
    Online Resource
    Online Resource
    Designing a Mixed Texture in Mg/Mg Laminated Composite via Bimetal Co-Extrusion to Ameliorate the Mechanical Anisotropy
    MDPI AG ; 2022
    In:  Metals Vol. 12, No. 4 ( 2022-04-07), p. 637-
    Details
    In: Metals, MDPI AG, Vol. 12, No. 4 ( 2022-04-07), p. 637-
    Abstract: Room-temperature (RT) mechanical anisotropy limits the broad applications of wrought magnesium (Mg) alloys. To weaken the anisotropy, here, we proposed a design idea to create a mixed texture. In the present study, we successfully fabricated the Mg-3Y/Mg-5Li (W3/L5, wt.%) laminated composite, having a mixed texture with a closely orthotropic shape, consisting of an ED-split component in the W3 layer and a TD-split in the L5 layer, via bimetal co-extrusion (ED and TD represent the extrusion and transverse directions, respectively). The mechanical results show that the W3/L5 laminated composite demonstrates a better isotropy at RT, indicating that forming a mixed texture is an effective method to reduce the anisotropy of wrought Mg alloys by bimetal co-extrusion. However, extremely poor interface shear strength, induced by rich O element voids on the interface, triggered poor interface bonding, leading to worse ultimate strength and elongation -to-failure. In future works, controlling co-extrusion parameters or implementing a suitable heat-treatment after extrusion will be necessary to further ameliorate the mechanical properties of the Mg/Mg laminated composites with mixed texture.
    Type of Medium: Online Resource
    ISSN: 2075-4701
    URL: Article
    DOI: 10.3390/met12040637
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2662252-X
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