Development and multicenter performance evaluation of fully automated SARS-CoV-2 IgM and IgG immunoassays.

Objectives: The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly spread globally. The laboratory diagnosis of SARS-CoV-2 infection has relied on nucleic acid testing; however, it has some limitations, such as low throughput and high rates of false negatives. Tests of higher sensitivity are needed to effectively identify infected patients. Methods: This study has developed fully automated chemiluminescent immunoassays to determine IgM and IgG antibodies to SARS-CoV-2 in human serum. The assay performance has been evaluated at 10 hospitals. Clinical specificity was evaluated by measuring 972 hospitalized patients and 586 donors of a normal population. Clinical sensitivity was assessed on 513 confirmed cases of SARS-CoV-2 by RT-PCR. Results: The assays demonstrated satisfied assay precision with coefficient of variation of less than 4.45%. Inactivation of specimen did not affect assay measurement. SARS-CoV-2 IgM showed clinical specificity of 97.33 and 99.49% for hospitalized patients and the normal population respectively, and SARS-CoV-2 IgG showed clinical specificity of 97.43 and 99.15% respectively. SARS-CoV-2 IgM showed clinical sensitivity of 82.54, 92.93, and 84.62% before 7 days, 7-14 days, and after 14 days respectively, since onset of symptoms, and SARS-CoV-2 IgG showed clinical sensitivity of 80.95, 97.98, and 99.15% respectively at the same time points above. Conclusions: We have developed fully automated immunoassays for detecting SARS-CoV-2 IgM and IgG antibodies in human serum. The assays demonstrated high clinical specificity and sensitivity, and add great value to nucleic acid testing in fighting against the global pandemic of the SARS-CoV-2 infection.

The Influence of Presentation Frames of Visualization Information for Safety on Situational Awareness under a Three-Level User-Interface Design.

To explore the influence of the construction and presentation frames of visualization information for safety (VIS) on people's situation awareness (SA), we designed a three-level user interface (UI) of VIS based on the three-stage SA theory, including perception (SA1), comprehension (SA2), and projection (SA3). Then, 166 subjects were recruited and divided into three groups to participate in the experiment, in which SA was measured by the situation-present-assessment method (SPAM) and situation-awareness-rating technique (SART), and eye-movement data were recorded. The results show that the level-3 UI design could effectively improve the subjects' SA levels. Although the increase in VIS displayed caused by the higher UI level led to a decrease in the perception-stage score of SA, the level-3 UI fully considered the three stages of human information processing, and helped improve the SA of the subjects; the overall SA score measured using the SART method was not significant, but the result was consistent with the SPAM. There was a framing effect on the presentation of VIS, and subjects perceived different degrees of risk under different presentation frames; that is, less risk under the positive frame, more risk under the negative frame, and a higher level of SA under the positive frame compared with the negative frame. To some extent, the nearest-neighbor-index (NNI) algorithm could be utilized to quantify subjects' eye-tracking fixation mode. While the frames were guided by the high-level interface and the positive presentation frame, the distribution of the subjects' gaze points was more discrete; they could grasp the relevant information more comprehensively and had a relatively high level of SA. To some extent, this study can provide a reference for the design and optimization of the VIS presentation interface.

Investigation of the Suppression of Methane Explosions by N2/CO2 Mixtures in Different Proportions.

To characterize the inerting effect of N2/CO2 mixtures containing various proportions on methane-air explosions, a series of experiments were conducted in a 20 L spherical vessel under the normal temperature (25 °C) and normal pressure (101 kPa). Six concentrations (10, 12, 14, 16, 18, and 20%) of N2/CO2 mixtures were selected to analyze the suppression of methane explosion by N2/CO2 mixtures. The results indicated that the maximum explosion pressure (p max) of methane explosions was 0.501 MPa (17% N2 + 3% CO2), 0.487 MPa (14% N2 + 6% CO2), 0.477 MPa (10% N2 + 10% CO2), 0.461 MPa (6% N2 + 14% CO2), and 0.442 MPa (3% N2 + 17% CO2) in the presence of the same N2/CO2 concentration, and similar decreases in the rate of pressure rise, flame propagation velocity, and production of free radicals were observed. Therefore, with the increase of CO2 concentration in the gas mixture, the inerting effect of N2/CO2 was enhanced. Meanwhile, the whole process of the methane combustion reaction was affected by N2/CO2 inerting, which was mainly attributed to heat absorption and dilution of the N2/CO2 mixture. N2/CO2 with a greater inerting effect leads to lower production of free radicals under the same explosion energy and a lower combustion reaction rate at the same flame propagation velocity. The findings of the current research provide references for the design of safe and reliable industrial processes and the mitigation of methane explosions.

Human reliability assessment of intelligent coal mine hoist system based on Bayesian network.

The human reliability of intelligent coal mine hoist operation system is affected by many factors, in order to reduce the occurrence of human error in the hoist system and improve the reliability of the system. The characteristics of phased-mission task operation of hoists is combined, the phase dependence of human cognitive errors is considered and, a new human reliability evaluation method is proposed with the help of Bayesian network (BN) model in this paper. Firstly, the phase dependence of human cognitive errors was analyzed based on the cognitive behavior model. Then the human error analysis in the hoist system was carried out, and several main performance shaping factors are selected. Secondly, BN was used to build the human reliability model of the hoist system at each stage. Finally, it is found that the phase dependence of cognitive errors has a negative impact on the human reliability of the hoist system through the case analysis. At the same time, several main performance shaping factors (PSFs)were quantitatively analyzed by using the reverse reasoning ability of BN, which proves the effectiveness of the proposed method, and provides a scientific and reasonable theoretical basis for the development of effective human error prevention measures for the operation of intelligent coal mine hoists.

Chemical kinetic behaviors at the chain initiation stage of CH4/H2/air mixture.

To intensively investigate chemical kinetic behaviors at the initial stage of CH4/H2/air mixture thoroughly, the density functional theory (CAMB3LYP/6-31 G) and a detailed mechanism (GRI-Mech3.0) were used to obtain kinetic and thermodynamic parameters. The reaction paths during the explosion process were analyzed, and the reaction rates of elementary reactions were compared with different ratios of CH4/H2/air mixture. The key reactions at the initiation stage of CH4/H2/air mixture explosion were determined, and their configurations were optimized. The reaction mechanism, reaction channel and configuration parameters of key reactions were obtained, which was verified by the intrinsic reaction coordinate (IRC) theory. Results show that H2 addition increases the laminar burning velocity, while it shortens the ignition delay time of H2/CH4/air mixture. The addition of hydrogen greatly accelerated the explosion reaction from sample 1 to sample 4. Moreover, CH4 still plays a key role at the chain initiation stage in H2/CH4/air mixture system; the addition of H2 would not compete with CH4 for triggering the explosion reaction, nor will it suppress the explosion of CH4. H2 could not replace or take precedence over the chain branching reactant (CH2O) of CH4 explosion to react with O2. Besides, H2 takes precedence over CH4 in the process of chain transfer after the chain reaction beginning, although CH4 has a distinct advantage in the chain initiation stage. The present results can provide theoretical guidance for the prevention and control of gas explosion, which may effectively reduce the explosion hazards.

Effects of N2 and CO2 dilution on the explosion behavior of liquefied petroleum gas (LPG)-air mixtures.

The present work aims to provide theoretical support to prevent LPG explosion accidents and reduce its hazardous effect. The explosion of LPG-air mixtures (4.0 % - 9.0 % in volume) under N2 and CO2 dilution (0.0%-30.0% in volume) was experimentally investigated by using a 20-L vessel at ambient temperature and pressure. The parameters of the maximum explosion pressure (pmax), time to reach the maximum explosion pressure (tc), maximum rate of the pressure rise ((dp/dt)max), time to reach the maximum rate of the pressure rise (tb), and average velocity of flame propagation (v) were investigated. In addition, the inerting efficiencies of N2 and CO2 were compared and analyzed. The results show that there exists a cubic function relation among pmax, (dp/dt)maxx, tc, tb and LPG volume fraction during the LPG explosion process. At the volume fraction of LPG was 5.7 %, all parameters reached peak values. The addition of N2 and CO2 effectively suppressed the explosion of LPG, reduced pmax, (dp/dt)max, and v and extended tc and tb. At a low LPG volume fraction, the inerting efficiency of CO2 was higher than that of N2. At a high LPG volume fraction, the inerting efficiency of N2 was higher than that of CO2.

SARS-CoV-2-specific immune response in COVID-19 convalescent individuals.

We collected blood from coronavirus disease 2019 (COVID-19) convalescent individuals and investigated SARS-CoV-2-specific humoral and cellular immunity in these discharged patients. Follow-up analysis in a cohort of 171 patients at 4-11 months after the onset revealed high levels of IgG antibodies. A total of 78.1% (164/210) of the specimens tested positive for neutralizing antibody (NAb). SARS-CoV-2 antigen peptide pools-stimulated-IL-2 and -IFN-γ response can distinguish COVID-19 convalescent individuals from healthy donors. Interestingly, NAb survival was significantly affected by the antigen peptide pools-stimulated-IL-2 response, -IL-8 response, and -IFN-γ response. The antigen peptide pools-activated CD8+ T cell counts were correlated with NAb. The antigen peptide pools-activated natural killer (NK) cell counts in convalescent individuals were correlated with NAb and disease severity. Our data suggested that the development of NAb is associated with the activation of T cells and NK cells. Our work provides a basis for further analysis of the protective immunity to SARS-CoV-2 and for understanding the pathogenesis of COVID-19. It also has implications for the development of an effective vaccine for SARS-CoV-2 infection.