Large-scale and diffuse population flow amplifies the localized COVID-19 outbreak into a widespread pandemic. Network analysis provides a new methodology to uncover the topology and evolution of the ...population flow and understand its influence on the early dynamics of COVID-19 transmission. In this paper, we simulated 42 transmission scenarios to show the distribution of the COVID-19 outbreak across China. We predicted some original (Guangzhou, Shanghai, Shenzhen) had higher total aggregate population outflows than Wuhan, indicating larger spread scopes and faster growth rates of COVID-19 outbreak. We built an importation risk model to identify some major cities (Dongguan and Foshan) with the highest total importation risk values and the highest standard deviations, indicating the core transmission chains (Dongguan-Shenzhen, Foshan-Guangzhou). We built the population flow networks to analyze their Spatio-temporal characteristics and identify the influential sub-groups and spreaders. By removing different influential spreaders, we identified Guangzhou can most influence the network's topological characteristics, and some major cities' degree centrality was significantly decreased. Our findings quantified the effectiveness of travel restrictions on delaying the epidemic growth and limiting the spread scope of COVID-19 in China, which helped better derive the geographical COVID-19 transmission related to population flow networks' structural features.
•42 transmission scenarios were simulated to test contribution of different original epicenters to seeding COVID-19 in China.•An importation risk model was built to test contribution of population flow among multiple epicenters to spreading COVID-19.•A population flow network was built to capture evolution of COVID-19 transmission and identify influential spreaders.•This paper quantified the effectiveness of travel restrictions on reducing the numbers of confirmed COVID-19 cases in China.
Fetal electrocardiograms (FECGs) provide important clinical information for early diagnosis and intervention. However, FECG signals are extremely weak and are greatly influenced by noises. FECG ...signal extraction and detection are still challenging. In this work, we combined the fast independent component analysis (FastICA) algorithm with singular value decomposition (SVD) to extract FECG signals. The improved wavelet mode maximum method was applied to detect QRS waves and ST segments of FECG signals. We used the abdominal and direct fetal ECG database (ADFECGDB) and the Cardiology Challenge Database (PhysioNet2013) to verify the proposed algorithm. The signal-to-noise ratio of the best channel signal reached 45.028 dB and the issue of missing waveforms was addressed. The sensitivity, positive predictive value and F1 score of fetal QRS wave detection were 96.90%, 98.23%, and 95.24%, respectively. The proposed algorithm may be used as a new method for FECG signal extraction and detection.
•Spray falling film of oily wastewater over a horizontal tube was investigated.•VOF model was used to simulate the gas-liquid falling film flow.•The non-uniform film flow, temperature and thickness ...distributions were analyzed.•The non-uniform heat transfer properties were quantitatively investigated.•The effects of oil content, spray density and tube diameter were studied.
Recently, the spray heat exchanger became an important technology in a sewage source heat pump (SSHP) to recover thermal energy from oily wastewater. Hence, it's necessary to study the heat transfer properties and its enhancements. In this paper, a numerical model with VOF method was established to study the oily wastewater spray falling film over a horizontal tube. The flow field, falling film distribution and temperature distribution and heat transfer coefficient were investigated, and the non-uniformity of flow, temperature and heat transfer were further analyzed. Regions of low level film thickness were found around tube suggesting the non-uniform axial and circumferential distribution, corresponding to low film temperature regions. The non-uniformity of heat transfer coefficient at different circumferential angles was evaluated showing severe non-uniformity in impingement and departure regions due to the intense impinging of falling wastewater at the top and instability of dropping flow at the bottom. Thereafter, the influence of oil content, spray density and tube diameter were studied. The increase in oil content led the flow pattern changed from sheet flow to column-sheet flow due to increase in viscosity, resulting to non-uniformity increase from 0.15 to 0.19. Compared to tube diameter of 25.4 mm, the 12.7 mm tube accelerated flow downstream, therefore, the non-uniformity at the top was weakened to 0.13 and the downstream non-uniformity was strengthened to 0.19. The higher spray density of 0.262 kg/m∙s reduced the negative effect of viscosity, enhanced the flow velocity and weakened the non-uniformity at the top. However, the increase in flow velocity raised the flow instability in downstream suggesting higher non-uniformity.
Fetal electrocardiogram (ECG) signals provide important clinical information for early diagnosis and intervention of fetal abnormalities. In this paper, we propose a new method for fetal ECG signal ...extraction and analysis. Firstly, an improved fast independent component analysis method and singular value decomposition algorithm are combined to extract high-quality fetal ECG signals and solve the waveform missing problem. Secondly, a novel convolutional neural network model is applied to identify the QRS complex waves of fetal ECG signals and effectively solve the waveform overlap problem. Finally, high quality extraction of fetal ECG signals and intelligent recognition of fetal QRS complex waves are achieved. The method proposed in this paper was validated with the data from the PhysioNet computing in cardiology challenge 2013 database of the Complex Physiological Signals Research Resource Network. The results show that the average sensitivity and positive prediction values of the extraction algorithm are 98.
•Spray falling film of oily wastewater over a horizontal tube was investigated.•VOF model was used to simulate the gas-liquid falling film flow.•The unsteady film and tube temperature distributions ...were analyzed.•The unsteady heat transfer properties were investigated.•The effects of oil content, spray density and tube diameter were studied.
The oil exploit in late-period oilfield usually produce large amount of oily wastewater at moderate and high temperature, the thermal energy of which can be recuperated through a sewage source heat pump (SSHP). Among different kinds of heat recovery facility in SSHP, the spray heat exchanger is a better choice to recover energy from the oily wastewater due to its advantages of simple structure, high heat transfer efficiency and anti-blocking ability. However, the spray falling heat transfer was an unsteady procedure, and the complex properties of oil-water mixer will lead to different heat transfer and flow characteristics in the heat exchanger, which also affect the unsteady heat transfer. Hence, in this paper, a numerical model with VOF method was established to study the unsteady heat transfer properties of oily wastewater spray falling film on a horizontal tube, and the effects of different oil contents, spray densities and tube diameters on the unsteady properties of heat transfer coefficient. The results show that the film temperature and tube temperature were continuously varying with time, and the slight variation in upper part and greater variation in lower part of the tube were observed. A further understanding on the flow field of liquid on the tube revealed the unsteady heat transfer was due to the falling flow instability. Thereafter, the influences of oil content, tube diameter and spray density on the unsteady heat transfer were analyzed. It was found that the decrease in oil content, increase in tube diameter will reduce the fluctuation intensity of heat transfer properties.
•Spray falling film of oily wastewater over a horizontal tube was investigated.•VOF model was used to track the gas-liquid interface of falling film flow.•The effect of different glycerin content on ...heat transfer was investigated.•The effects of spray parameters and tube parameters were studied.•The temperature distribution inside the liquid film was analyzed.
Sewage heat exchanger is the key equipment of oily sewage source heat pump system, which has great influence on its performance. Among many kinds of heat exchangers, the spray heat exchanger has the advantages of simple structure, high heat transfer efficiency, good operability and anti-blocking ability. Therefore, it can be used in a sewage source heat pump to recover energy from the oily wastewater. However, the heat transfer and flow characteristics of oily wastewater spraying in the heat exchanger are different from the ordinary sewage heat pump system. Hence, it’s necessary to investigate the heat transfer of oily wastewater spray falling film on horizontal tube for better application. In this paper, a three-dimensional numerical model was established for a spraying heat exchanger in the oily sewage source heat pump system, and a mixture of water and glycerin was used to simulate the oily wastewater. The VOF model was used to track the liquid-gas interface of oily wastewater spray falling film over a horizontal tube in the heat exchanger, and the effects of different glycerin content, heat flux, spray density, tube diameter, liquid distributor height and spray temperature on the heat transfer coefficient were investigated. To further understand the mechanism of heat transfer inside the film, the temperature distribution inside the liquid film was obtained and analyzed. The results show that: (1) the heat transfer characteristic can be divided into three regions around the tube; (2) the local heat transfer coefficient decreased with increase of glycerin content in the thermal developing region; (3) the local heat transfer coefficient increased with the increase of the spray density and spray temperature, decreased with the increase of the tube diameter and was little affected by heat flux in the thermal developing region, and the increase in the liquid distributor height caused increase of local heat transfer coefficient in the upper part of the tube.
In the sewage source heat pump (SSHP) system, which is used to recover the low-level thermal energy in oily sewage, the sewage heat exchanger is an important equipment to determine the heat exchange ...efficiency of the system. In this paper, an oily sewage source heat pump (OSHP) system experimental setup with a spray-type sewage heat exchanger as the evaporator was established. The effects of oil content, spray density and spray temperature on the flow patterns between horizontal tubes and heat flux of tube were investigated and analyzed. It was found that the critical spray density for transformation from droplet flow to column flow was increased to 0.109 kg m
−1
s
−1
for oily sewage, which was much higher than 0.082 kg m
−1
s
−1
of pure water for pure water, indicating that a much higher spray density was needed to maintain a higher heat transfer for oily sewage. With the increase in spray temperature of oily sewage, the critical spray density of flow pattern transformation from droplet flow to column flow was decreased from 0.137 kg m
−1
s
−1
at 46 °C to 0.082 kg m
−1
s
−1
at 65 °C. Besides, oily sewage had obvious lower heat flux than pure water, and the difference was enlarged with the increase in spray density. New heat transfer correlations obtained depending on Re and Pr numbers were proposed, showing more accurate predictions than previously reported models. Corresponding to the falling film flow pattern, a clear dividing between 0.055 and 0.082 kg m
−1
s
−1
for pure water and between 0.082 and 0.109 kg m
−1
s
−1
for oily sewage, for the tube surface temperature distribution for droplet flow and column flow was observed, indicating the significantly high heat transfer for column flow pattern compared with droplet flow.
The purpose of this study is to uncover and optimize the structure and performance of the collaborative network that emerged in response to COVID-19 in Hubei Province, China. This study reconstructed ...the Hubei Public Health Emergency Response Network as the actual collaborative network and built COVID-19 Collaborative Emergency Network as a planned task-oriented collaborative network. Based on the data sets of the inter-organizational collaboration collected from the content analysis, this study explored the core tasks of the participating actors and their relationships during the COVID-19 emergency response, and built six sub-networks to accomplish six core tasks. Network analysis was used with the Pajek software to compare the structural characteristics and performance of the planned network with the actual one and six sub-networks, and identified the central actors, key bridges, and brokers in networks and sub-networks separately. Findings suggested that COVID-19 Collaborative Emergency Network had a more tightly, central, and connective structure than Hubei Public Health Emergency Response Network, because it had more participating actors (i.e., databases and AI systems), more powerful and strong collaborative relationships with research institutions and non-profit organizations. With practical-based recommendations for inter-organizational collaboration, this study concluded that COVID-19 Collaborative Emergency Network could significantly enhance the local capacity of Hubei Province for emergency collaboration, which provided insights for building and optimizing COVID-19 collaborative networks in other provinces of China, even other countries.
Various low ratios of triplet iridium complexes (0, 0.5, 1, 1.5, 2.5, and 5 mol%) are conjugated to the backbone of the famous champion donor polymer PTB7. At the same conditions, the power ...conversion efficiency for polymer containing 1% of Ir increases by 45%, 39%, and 31% in three batches of devices compared with control Ir‐free PTB7.
Early Carboniferous Luzhai Formation developed continuous and thick shales, which is a critical succession for hydrocarbon exploration and production in southern China. However, no high-resolution ...stratigraphic sequence framework or cyclostratigraphic studies on early Carboniferous (Tournaisian Stage) are available for this organic-rich shale formation. In this research, Milankovitch cycle evidence has been reported in two boreholes of Luzhai Formation in Guizhong Depression. Natural gamma-ray logging data allowed the establishment of a ∼5.9-Myr floating astronomical timescale (FATS) based on stable long eccentricity (405-kyr) cycles in Luzhai Formation. We anchored FATS to Devonian and Carboniferous boundary age (359.3 ± 0.4 Ma), and an absolute timescale for intervals of 359.3 to 353.4 Ma was developed. Correlation coefficient (COCO), evolutionary COCO, and evolutionary TimeOpt method (eTimeOpt) were employed for quantitatively fit observed stratigraphic cycles to astronomical cycles for providing possible range of sedimentation rates. Sedimentary noise model was adopted for detecting orbital forcing-controlled high-resolution sea-level changes which were correlated to ∼1.2-Myr obliquity amplitude modulation (AM) cycles. Sedimentary noise models (autocorrelation coefficient analysis, ρ1, and dynamic noise after orbital tuning analysis, DYNOT) revealed a correlation between obliquity AM cycle (∼1.2-Myr) and sea level changes in early Carboniferous Luzhai Formation. The ∼1.2-Myr obliquity AM was the main driver of third-order sequence development, the 3rd-order sequence boundaries were related to maximum values of DYNOT median curve and minima values of ∼1.2-Myr amplitude modulation (AM) curve.
•A new Floating ATS for the first time to calibrate the Tournaisian depositional sequences.•The deposition of Luzhai Formation shale in Early Carboniferous lasted ∼5.9-Myr.•Third-order sequences and sea-level change can be generated by cyclostratigraphic research.•∼1.2-Myr obliquity amplitude modulation dominated sea-level changes.
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