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Since its invention, plastic has brought great changes to our daily life. It is considered as one of the most basic materials for the development of modern society. Most of the plastic produced are used for packaging and disposable products. Due to the high disposable rate and mismanagement, a large amount of plastic debris enters the marine environment. Potentially lasting several hundred years in the environment, the large plastic debris can be continuously broken into microplastics which are smaller than 5 mm under the action of ultraviolet light, heat, wind, tide, wave and bacteria etc. Therefore, the amount of microplastics will keep rising in the ocean. Microplastics is considered as a new emerging pollutant and has become a global concern. Understanding the degradation process of plastic in the environment is important for evaluating the contribution of plastic debris as one microplastics source. In this work, polyethylene film from 6 kinds of packaging bags commonly used in our daily life, i.e., food packing bag, garbage bag, thick film, and express packing bag, were selected to carry out photodegradation experiment under ultraviolet radiation in the laboratory. Properties of plastic films were investigated by tensile tests, infra-red spectrometry and scanning electron microscope at various time intervals. The results showed that the elongation-at-break of six kinds of polyethylene film decreased with increasing of UV exposure time. While Young’s modulus showed a trend of increase-decrease with increasing exposure time in general. The yield strength showed a general increasing-decreasing or decreasing trend with increasing exposure time. PE films from food packing bag and degradable garbage bag became brittle and tended to break into microplasics after 36 h under UV irradiation of 160 W/m2. However, the retained elongation-at-break of PE film from express packing bag was up to 76% after 180 h UV irradiation. Chain scission and structure changes occurred during photodegradation process. FT-IR spectra indicated that difference existed in photodegraded process among PE films from six kinds of plastic bags. Ether group existed in FT-IR spectra of PE film from food packing bag, while ketone, ester, carboxylic acid, and vinyl group appeared in the spectra of thick film and express packing bag. Carbonyl index, crystallinity index and vinyl index of films from food packing bag, thick film and express packing bag increased at various degrees with prolongation of exposure time. The microstructure at tensile fracture surface became smoother after photodegradation, showing appearance of small fragments. This indicated that the intermolecular force decreased significantly, which was consistent with the trend of mechanical properties. The plastic packing bags commonly used in our daily life tend to become brittle and fragment into small pieces under ultraviolet radiation and become one source of microplastics in environment. These results can provide basic data and theoretical support for study of environmental behavior processes of plastic debris and source of microplastics, assessment of environmental risk, etc.

Background The virological or clinical relapse is common in chronic hepatitis B (CHB) patients after stopping long-term nucleos(t)ide analogue (NA) therapy. Soluble growth stimulation expressed gene 2 (sST2), one of the Toll-like/interleukin-1 receptor members, is involved in a variety of inflammatory processes and immune responses. However, the expression and function of serum sST2 in CHB patients after stopping NA treatment remains unknown. Methods A total of 91 non-cirrhotic Asian patients with CHB who discontinued NA therapy according to international guidelines were prospectively followed up to 240 weeks. All patients were divided into clinical relapse group and non-clinical relapse (including sustained virological response and only virological relapse) group according HBV DNA and ALT levels. The serum levels of sST2 of all participants were determined by ELISA and compared between each two groups. Results Clinical relapse occurred in 26 patients and virological relapse occurred in 57 patients. We found that there was a positive correlation between sST2 expression and HBsAg, ALT, HBV DNA, and anti-HBc levels in CHB patients after discontinuation of NA treatment. Levels of serum sST2 in clinical relapse patients showed a rising trend and most patients showed peak sST2 levels at the point of clinical relapse. Moreover, the sST2 levels of clinical relapse group at week 12, week 24 and week 48 were relatively higher than non-clinical relapse group. However, the level of sST2 at the end of treatment was not an effective biological marker for the early prediction of clinical relapse after discontinuation of long-term NA therapy. Conclusions In conclusion, we found that an increase in sST2 in clinical relapse patients might be associated with an inflammation-related immune response after discontinuation of NA treatment. Trial registration The trial was retrospectively registered at Chinese Clinical Trial Registry: ChiCTR-OOC-17013970. Registration date: December 15, 2017.

Coronaviruses (CoVs) are nonsegmented, single-stranded, positive-sense RNA viruses highly pathogenic to humans. Some CoVs are known to cause respiratory and intestinal diseases, posing a threat to the global public health. Against this backdrop, it is of critical importance to develop safe and effective vaccines against these CoVs. This review discusses human vaccine candidates in any stage of development and explores the viral characteristics, molecular epidemiology, and immunology associated with CoV vaccine development. At present, there are many obstacles and challenges to vaccine research and development, including the lack of knowledge about virus transmission, pathogenesis, and immune response, absence of the most appropriate animal models.

Hepatitis B virus-associated (HBV(+)) hepatocellular carcinoma (HCC) accounts for a large proportion of liver cancer with poor clinical outcomes and treatment options. However, the underly...

In this paper, a bi-stable nonlinear energy sink (BNES) with buckled beam is developed to suppress the vibration of unbalanced rotor system. The structure of the BNES is developed. The specific structures and working principles of the buckled beam are introduced. Based on these, the dynamic equations of the rotor-BNES system are established. Then, the transient and steady state responses of the rotor-BNES system are numerically studied and compared with the linear visco-elastic damper. In addition, the vibration suppression ability and frequency suppression range of the BNES are analyzed. Finally, experiments are carried out and compared with the simulations to confirm the vibration suppression effectiveness of the BNES. The numerical and experimental results show that the designed BNES has a strong vibration suppression effect on the rotor system and can withstand a wide range of energy.

This paper uses the theories of phonemics, phonology and mathematical statistics to concrete research and analysis the tones of 20 dialect points of 7 dialect areas in modern Chinese dialects. Through the research some resulted have gained that: 1) the phonetic system of southern dialect is complex than the north dialect and retains more ancient phonetic ingredients; 2) The tone category number of south dialect is more than the north dialect, the tones of Chinese dialect toward the simplification trend of development; 3) The development of north dialect is faster than south dialect; 4) the tone pitch is the most unstable part of the phonetic system. The research of this article research basically reflects the dialect characteristics of each dialect area and the distribution patterns of tone pitch and tone category in each dialect points. This paper provides objective data, theoretical basis and certain reference value for the whole further research of modern Chinese dialect phonemic system.