African swine fever (ASF) is a highly lethal contagious disease of swine caused by African swine fever virus (ASFV). At present, it is listed as a notifiable disease reported to the World ...Organization for Animal Health (OIE) and a class one animal disease ruled by Chinese government. ASF has brought significant economic losses to the pig industry since its outbreak in China in August 2018. In this review, we recapitulated the epidemic situation of ASF in China as of July 2020 and analyzed the influencing factors during its transmission. Since the situation facing the prevention, control, and eradication of ASF in China is not optimistic, safe and effective vaccines are urgently needed. In light of the continuous development of ASF vaccines in the world, the current scenarios and evolving trends of ASF vaccines are emphatically analyzed in the latter part of the review. The latest research outcomes showed that attempts on ASF gene-deleted vaccines and virus-vectored vaccines have proven to provide complete homologous protection with promising efficacy. Moreover, gaps and future research directions of ASF vaccine are also discussed.
The carburizing and quenching process of 18CrNiMo7-6 steel was performed through simulation methods and experiments. The study was carried out to accurately predict the residual stress distribution ...of carburized samples after the quenching process. The stress and retained-austenite amount were measured via X-ray diffraction. Similarly, the carbon content was determined using a carbon sulfur analyzer, respectively. A detailed model with the coupling of thermal, metallic, and mechanical fields was built to predict the evolution of the stress field during the quenching process. The carburized “thoroughly” specimens at different carbon potentials were used to obtain the required mechanical property parameters and dilatometric parameters for FEM simulation. According to the results, the martensite transformation kinetic parameters α value of 18CrNiMo7-6 alloy steel should be 0.0202. With the increase of carbon content, the changing trend of the transformation plasticity coefficient K appeared as a 'tick' shape. A compressive residual stress field was generated at the carburized layer surface after the quenching process, and the maximum value of 340 MPa occurred at ~ 0.9 mm below the surface. The carbon profile and residual stress fields predicted from the FEM simulation corresponded closely to the experimentally determined results.
Seasonal thermal stratification has a significant impact on water quality. In this paper, the variation of vertical distribution of ammonia nitrogen in a source water reservoir was studied, on the ...base of field monitoring data. The dominant factor of the variation in ammonia nitrogen is the anaerobic environment caused by the seasonal thermal stratification, which leads to the degradation of nitrogen-containing organic compounds in the sediments. To determine the rates of ammonia accumulation, an in situ experimental chamber was used. The results showed that, before the formation of thermal stratification in the reservoir, sediments in the bottom of the water have a high tendency to release ammonia; the rates of ammonia accumulation in the overlying water are 40.31–111.41 mg·m−2·d−1. However, thermal stratification causes changes in the physical and chemical properties of the sediment and reduction in the degradability of the nitrogen-containing compound in the sediment. The rates of ammonia accumulation (39.44–44.65 mg·m−2·d−1) after thermal stratification are lower than before. Considering the water pollution hazards caused by seasonal thermal stratification, it is necessary to take corresponding emergency response measures to cope with the possibility of water pollution risk.
Thermal stratification has an important impact on the cycling of reservoir water quality. Uneven vertical distribution of water quality factors, such as dissolved oxygen and nutrients, occurs during ...seasonal stratification, which creates chemical stratification. Typically, thermocline and chemocline characteristics vary across different reservoirs. In this study, a field study was conducted in the Zhoucun Reservoir (ZCR), China, to investigate the variation in water quality during periods of thermal stratification. The results revealed the maximum water depth as 15 m at 122 mamsl, which is relatively shallow for stratified reservoirs. However, an extremely high thermocline strength index (TSI) was recorded, which indicates that the thermal stratification of ZCR water is very stable, contrary to our common understanding that stratification is more obvious at greater water depths. The chemical stratification strength index (IC-i) was compared with the TSI and the relative water column stability (RWCS). The TSI had a high correlation with IC-i, which explains the high stability of ZCR chemical stratification. Moreover, it highlights the suitability of TSI for characterising the chemical stability of reservoir stratification. Finally, this study also found that the formation and disappearance of thermal and chemical stratification in the ZCR were synchronous. As stratification directly influences a reservoir water quality regime, this study may be a helpful reference for optimising water quality management.
Display omitted
•The characteristics of thermal and chemical stratification in a source water reservoir were explored.•Thermocline strength index had better correlation with chemical stratification index (IC-i).•ZCR has higher chemical stratification stability, although it is shallower than other reservoirs.•The formation and disappearance of the thermal and chemical stratification in the ZCR are synchronous.
•A novel swine enteric alphacoronavirus (tentatively named SeACoV) was isolated from diarrheic piglets in southern China.•SeACoV is likely antigenetically distinct from PEDV, TGEV and PDCoV.•Genomic ...and phylogenetic analysis showed that SeACoV might have originated from the bat coronavirus HKU2.•The extreme amino-terminal domain of SeACoV spike glycoprotein had an extremely high variability compared to that of HKU2.•Experimental infection study showed that SeACoV is infectious and pathogenic in newborn piglets.
Outbreaks of diarrhea in newborn piglets without detection of transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV), have been recorded in a pig farm in southern China since February 2017. Isolation and propagation of the pathogen in cell culture resulted in discovery of a novel swine enteric alphacoronavirus (tentatively named SeACoV) related to the bat coronavirus HKU2 identified in the same region a decade ago. Specific fluorescence signal was detected in Vero cells infected with SeACoV by using a positive sow serum collected in the same farm, but not by using TGEV-, PEDV- or PDCoV-specific antibody. Electron microscopy observation demonstrated that the virus particle with surface projections was 100–120nm in diameter. Complete genomic sequencing and analyses of SeACoV indicated that the extreme amino-terminal domain of the SeACoV spike (S) glycoprotein structurally similar to the domain 0 of the alphacoronavirus NL63, whereas the rest part of S structurally resembles domains B to D of the betacoronavirus. The SeACoV-S domain 0 associated with enteric tropism had an extremely high variability, harboring 75-amino-acid (aa) substitutions and a 2-aa insertion, compared to that of HKU2, which is likely responsible for the extended host range or cross-species transmission. The isolated virus was infectious in pigs when inoculated orally into 3-day-old newborn piglets, leading to clinical signs of diarrhea and fecal virus shedding. These results confirmed that it is a novel swine enteric coronavirus representing the fifth porcine coronavirus.
•Carburizing improve the fatigue performance of notched specimens significantly.•The macro-plasticity has little effect on the fatigue performance.•Carburizing reduce the notch sensitivity of notched ...specimens.•The fatigue sources of the notched specimens are on the root surface of the notch.•During fatigue, carburized specimens retain a portion of stable retained austenite.
Since stress concentration is easily formed at the notch, improving the fatigue performance of notched parts is critical. The carburizing process is widely used to manufacture notched parts. In this research, the effects of carburizing process and notch stress concentration on fatigue performance were analyzed by bending fatigue tests. In addition, the microstructure and hardness evolution processes of the carburized notched 18CrNiMo7-6 specimens were observed quasi-in situ. The results showed that macro-plasticity has little effect on the bending fatigue performance of notched samples and that the improvement in fatigue performance is primarily attributable to the high hardness and residual compressive stress introduced by carburizing. The fatigue notch sensitivity is therefore reduced after carburizing. Compared to the uncarburized specimens, the fatigue limit of the carburized specimens is increased by up to 128%. With the increase of the effective hardening layer depth, the fatigue limit increases first and then decreases. Moreover, the brittle phase transformation product (twinning martensite) of metastable retained austenite is easy to produce stress concentration. Conversely, the 'film-like' retained austenite with an extremely high stability can effectively avoid the phase transformation products.
•Design a micromechanical resonator with inherent high-order nonlinearities.•Unveil the pseudo-linear behavior in resonators with high-order nonlinearities.•Frequency stabilization is achieved in the ...pseudo-linear region.•The tailored inherent high-order nonlinearities make the frequency stabilization scheme more robust.•Reveal the effect of parametric excitation on the suppression of phase noise.
Micromechanical oscillator sustains oscillation through a velocity-proportional feedback force. Stabilization of the oscillation frequency is typically achieved by increasing the amplitude of the resonator while remaining in its linear regime. However, nonlinear effects and parasitic cross-talk unavoidably emerge with the reduction of oscillator size, severely limiting its performance. To overcome these limitations, in this paper, a novel and robust frequency stabilization scheme that employs the interaction of intrinsic high-order nonlinearities in a parametrically driven arch beam resonator is proposed and verified. Firstly, a micromechanical resonator with intrinsic high-order nonlinearities is specifically designed. Upon parametrically driving the resonator into resonance at large vibrational amplitudes, the bending of the resonance curve changes direction. This mixed behavior forms a pseudo-linear region without the need for auxiliary electrostatic tuning, simplifying the circuits and enhancing the robustness of the system. Secondly, significant frequency stability enhancement is observed when driving the resonator into self-sustained parametric oscillation in the pseudo-linear regime where output frequency decouples from the amplitude noise. Besides, the phase noise suppression effect of the parametrically driven oscillator is experimentally demonstrated when compared with the conventional directly driven oscillator. Finally, a theoretical phase noise model is developed, which well reproduces the observed frequency stabilization in the pseudo-linear regime and phase noise suppression effect of parametric oscillations.
Display omitted
A porcine reproductive and respiratory syndrome virus (PRRSV) QY1 was serially passed on Marc-145 cells. Virulence of different intermediate derivatives of QY1 (P5, P60, P80, and P100) were ...determined. The study found that QY1 had been gradually attenuated during the in vitro process. Pathogenicity study showed that pigs inoculated with QY1 P100 and P80 did not develop any significant PRRS clinic symptoms. However, mild-to-moderate clinical signs and acute HP-PRRSV symptoms of infection were observed in pigs inoculated with QY1 P60 and P5, respectively. Furthermore, we determined the whole genome sequences of these four intermediate viruses. The results showed that after 100 passages, compared to QY1 P5, a total of 32 amino acid mutations were found. Moreover, there were one nucleotide deletion and a unique 34-amino acid deletion found at 5′UTR and in nsp2 gene during the attenuation process, respectively. Such deletions were genetically stable in vivo. Following PRRSV experimental challenge, pigs inoculated with a single dose of QY1 P100 developed no significant clinic symptoms and well tolerated lethal challenge, while QY1 P80 group still developed mild fever in the clinic trial after challenge. Thus, we concluded that QY1 P100 was a promising and highly attenuated PRRSV vaccine candidate.
Transparent exopolymer particles (TEP) have been described as a class of particulate acidic polysaccharides, which are commonly found in various surface waters. Due to their unique physicochemical ...characteristics, they have recently been receiving increasing attention on their effects in water treatment. Currently, TEP are commonly known as clear, gel-like polysaccharides. This review first introduced the definition of TEP in water treatment and the relationship between TEP and algal organic matter (AOM). Further, in the review, the authors attempt to offer a holistic view and critical analysis concerning the research on TEPs in source water reservoirs, water plants and membrane treatment processes. It was clearly demonstrated in this review that the formation of TEP in source water reservoirs is largely related to water quality and phytoplankton, and the seasonal water stratification may indirectly affect the formation of TEP. In the waterworks, the relationship between TEP and water treatment process is mutual and there is limited research on this relationship. Finally, the mechanism of TEP-induced membrane fouling and the effect of alleviating TEP-induced membrane fouling is discussed in this review. The TEP removed by ultrafiltration can be recombined after membrane, and the recombination mechanism may be an important way to reduce reverse osmosis membrane contamination.
PDF
