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In this paper, the electrical tree growth characteristics of silicone rubber (SiR) are studied under impulse superimposed on DC voltage and a temperature gradient (TG) field. The temperature difference between high voltage (HV) and ground (GD) electrodes varies from -90 to 90 °C resulting in a TG field in the samples. The electrical tree morphology, length and accumulated damage are discussed. Experimental results show that with the increase of absolute value of TG, the electrical tree length and accumulated damage continue to increase, and the tree morphology turns from branch-like tree to bush-branch hybrid tree. The positive TG has a more obvious acceleration effect on the tree growth than does the negative TG. Under the TG, the temperature dependent carrier transport results in space charge accumulation and electric field distortion at low temperature side, which is the main reason for the different growth characteristics of electrical tree. Besides, the accumulated damage of DC superimposed with heteropolar impulse voltage is larger than that under DC superimposed with homopolar impulse voltage. It is concluded that the temperature gradient and impulse superimposed on DC voltage promote the electrical tree growth of HVDC cable accessories insulation.

In this paper, graphene/silicone rubber (SiR) nanocomposites with filler contents of 0.001–0.005 wt% are prepared to improve electrical tree inhibiting ability under different temperature gradients. The electrical treeing test is performed under three temperature gradients by controlling the temperature of high voltage and ground sides. Experimental results indicate that the SiR sample with 0.003 wt% graphene presents the best performance on electrical tree resistance. The tree length and accumulated damage are both reduced with the increase of graphene content from 0 to 0.003 wt%, but increased with the further increase of filler content from 0.003 to 0.005 wt%. The tree outline tends to be circular in neat SiR under negative temperature gradient, while it is triangular under positive temperature gradient. However, the effect of temperature gradient is weakened when graphene exists. Based on quantum dot models, the role of graphene quantum wells (QWs) in the regulation of charge transport and electrical tree resistance in SiR is revealed. This research provides an effective method to suppress electrical trees of SiR for cable accessories.

In this work, nano-titanium oxide (TiO 2 ) is encapsulated into boron nitride nanosheets (BNNS) by the calcination process to fabricate core-shell structured TiO 2 @BNNS nanofillers. The effects of TiO 2 @BNNS fillers on the DC conductivity, space charge and breakdown strength of polypropylene (PP) composites are investigated. Experimental results show that PP/TiO 2 @BNNS composites have a lower temperature-dependent conductivity with an activation energy of 0.64 eV, which is much lower than that of PP, 0.95 eV. The DC breakdown strength of PP/TiO 2 @BNNS samples is 22.2% higher than that of PP at 90 °C. The average space charge density and electric field distortion rate of PP/TiO 2 @BNNS are reduced by 6.6 C/m3 and 23.3%, respectively, compared with PP, under a polarization electric field of 40 kV/mm at 90 °C. It is proven that TiO 2 @BNNS nanofillers form numbers of electrical potential wells for charge carriers, thereby, inhibiting the hot electron transport and their damage to polymer molecules. This work provides an effective method to improve the dielectric performance of PP cable insulation.

In this paper, the effects of harmonic superimposed DC voltage on electrical tree growth characteristics in ethylene propylene diene monomer (EPDM) for HVDC cable accessories insulation are studied. Harmonic component with a frequency from 50 to 450 Hz is superimposed on DC voltage to analyze the mechanism of harmonic amplitude, order and voltage polarity on electrical tree growth. The results show that the electrical treeing process is promoted with an increase in harmonic amplitude and order, which brings a longer tree length and more accumulated damage to the insulation. Especially when the amplitude of harmonic component exceeds that of DC voltage, the electrical treeing processes are significantly deteriorated, resulting from the large amount of energy released by the recombination of hetero charges. The growth of electrical tree has an obvious polarity effect which tends to be branch-like tree under positive voltage and bush-like tree under negative voltage. The polarity effect may be caused by different propagation processes of electron avalanche under different voltage polarities. As harmonic order increases, the main channel of positive electrical tree is broadened, while the negative tree becomes denser with a lot of bifurcation. These results indicate that harmonic component accelerates the initiation and propagation of electrical tree by affecting the charge transport behavior under the superimposed electric field.

This paper focuses on the effects of hindered phenolic antioxidants AO300 and AO736 with similar molecular structure on the electrical properties of isotactic polypropylene (iPP). Experiments of conductivity, space charge distribution, and DC breakdown strength after the hetero-polarity DC prestress are performed. The experimental results show that these two antioxidants can increase the conductivity-temperature coefficient, reduce the accumulation of space charge and improve the DC breakdown strength after the hetero-polarity DC prestress of iPP. By calculating the molecular orbitals of these two antioxidants, it is found that the antioxidants introduce local states in the forbidden band of iPP matrix to capture high-energy charges. Besides, the bond dissociation energy (BDE) of the hydrogen-oxygen bond in AO736 is lower than that in AO300, representing a stronger ability of proton transfer, which scavenges the radicals, inhibits the growth of microvoids and prevents the process of breakdown. It is concluded that the improvement of space charge and breakdown properties is attributed to the coupling effects of deep trap sites and radicals scavenging introduced by antioxidant. This research shows that AO736 has potential applications in PP insulation.

The effects of control fields on the energy spectra and the number of created pairs and the information transmission by the Dirac vacuum modes are investigated by employing computational quantum field theory approach. It is found that the oscillation structures on the energy spectra are sensitive to the direction, the width, and the oscillation frequency of control fields. The pair yield can have obvious changes for a small frequency and a very large frequency. Moreover, the information encoded in the control fields, such as the field direction, the laser frequency and the time interval between two laser pulses, can also embodied by the vacuum modes in the change of pair-creation rate with time. These results not only can deepen our understanding of the control of pair creation and the information transmission, but also can provide a theoretical reference to the related experiments in the future., Comment: 17pages, 7 figures

OBJECTIVE: To explore the characteristics of gastric microbiota in children with and without (Helicobacter pylori, H. pylori) infection who had family history of H. pylori infection. METHODS: Mucosal biopsy samples of the gastric corpus and gastric antrum were collected during the gastroscope. And the gastric mucosa flora's information of the two groups of children were obtained after sample DNA extraction, PCR amplification of the 16S ribosomal DNA (rDNA) V3-V4 region, high-throughput sequencing and data processing. All the samples with family history of H. pylori infection were divided into two groups, the H. pylori infection group (n=18) and the H. pylori non-infection group (n=24). Then the α-, β-diversity and bacteria abundance of the gastric microbiota were compared between the H. pylori infection and non-infection groups at different taxonomic levels. The differential microbiota was found out by LEfSe analysis, and then the function of microbiota predicted using phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) method. RESULTS: There was statistically significant difference in α-diversity (P < 0.05) between the two groups, indicating that the H. pylori non-infection group had higher microbial richness than the H. pylori infection group. Moreover, the β-diversity was significantly different as well (P < 0.05), which meant that the microbiota composition of the two groups was different. At the phyla level, Proteobacteria, Firmicutes, Bacteroides, Actinobacteria, and Fusobacteria were dominant in the two groups. At the genus level, Bacteroides, Prevotella, Streptococcus, and Neisseria, etc. were dominant in the H. pylori non-infected group. Meanwhile, Helicobacter and Haemophilus etc. were dominant in the H. pylori infected group. LEfSe analysis showed that the relative abundance of Bacteroides etc. at the genus level in the H. pylori non-infected group was significantly higher than that in the H. pylori infected group. Functional prediction showed that Bacteroides were positively correlated with amino acid and vitamin metabolism, mitogen-activated protein kinase (MAPK), mammalian target of rapamycin (mTOR) signaling pathway and ansamycin synthesis pathway. CONCLUSION: The gastric microbiota between H. pylori positive and H. pylori negative in children with family history of H. pylori infection is significant different. Some gastric microbiota, such as Bacteroides, may have a potential relationship with H. pylori infection in children.

Domestic and foreign literatures related to the persistence of SARS-CoV-2 and the re-positive cases infected with SARS-CoV-2 were reviewed, and the characteristics and infectivity of the re-positive cases were analyzed to provide scientific evidence for the improvement of case management and the development of measures to stop the spread of SARS-CoV-2. Existing studies have shown that re-positive rate of SARS-CoV-2 ranged from 2.4% to 19.8%, the median of interval between re-positive detection and discharge was 4-15 days. Following the second course of the disease, the anti-SARS-CoV-2 IgM, IgG and IgA positive rates of the cases were 11.11%-86.08%, 52.00%-100.00% and 61.54%-100.00% respectively, the total antibody and neutralizing antibody positive rates were 98.72% and 88.46%. The viral load of the re-positive cases was lower than that in the initial infection. At least 3 380 re-positive cases have been reported globally. SARS-CoV-2 strains were isolated from the samples of 3 re-positive cases (1 immunodeficiency case and 2 cases with abnormal pulmonary imaging). There were close contacts that were infected by an asymptomatic case taking immunosuppressive agents. In conclusion, the infectivity of re-positive cases infected with SARS-CoV-2 is generally very low. Rare re-positive cases infected with SARS-CoV-2 might cause further transmission. The management approach for the re-positive cases can be based on the assessment of the individual transmission risk according to the pathogen detection results.针对国内外新型冠状病毒（新冠病毒）感染者排毒持久性以及复检核酸阳性者的相关研究文献进行综述，分析复检阳性者的特征与传染性，为完善病例管理与预防新冠病毒传播措施的制定提供科学依据。现有研究结果显示，新冠病毒复检阳性率范围在2.4%~19.8%之间，复检阳性时间中位数为出院后4~15 d。复检阳性后新冠病毒特异性IgM、IgG和IgA抗体血清阳性率分别为11.11%~86.08%、52.00%~100.00%、61.54%~100.00%；总抗体和中和抗体的血清阳性率分别为98.72%和88.46%。复检阳性后病毒载量低于初次感染时的病毒载量。目前，全球至少报告了3 380例复检阳性者，有3例复检阳性者（1例免疫缺陷病例和2例肺部影像学异常病例）的标本中分离到具有传染性的活病毒，有1例应用免疫抑制剂的无症状感染者引起密切接触者感染。复检阳性者具有传染性的风险总体很低，极个别复检阳性者不排除引起续发传播的可能。对于复检阳性者的管理时间和管理方式，可基于病原检测结果对个体传播风险评估后进行确定。.

Ischemic hepatitis is inflammation caused by necrosis of liver cells due to ischemia and hypoxia caused by low cardiac output or septic shock. It is often complicated by heart failure or severe septic shock. One of the pathogenesis of ischemic hepatitis is hepatocyte injury caused by ischemia and hypoxia, which results in damage-associated molecular patterns (DAMPs) release and binding to membrane receptors such as toll like receptors (TLRs) to cause inflammatory reactions.The other is when the ischemic liver is reperfused, hepatocyte mitochondrias will produce a large amount of ROS causing ischemia reperfusion injury. These two mechanisms and related molecular pathways are elaborated in this paper.缺血性肝炎是由于心脏的低排出量或感染性休克而导致的肝脏细胞因缺血缺氧而发生坏死所产生的炎症，其常并发于心力衰竭患者和重度呼吸道感染患者等。缺血性肝炎的发病机制一方面是由于缺血缺氧导致的肝细胞损伤，释放damage-associated molecular patterns（DAMPs），与细胞表面如Toll样受体等结合引起炎症反应；另一方面是由于当缺血的肝脏再次恢复血供时，肝细胞线粒体产生大量ROS，造成二次损伤，即缺血再灌注损伤。现对这两种机制及相关的分子通路进行阐述。.

The electrical-tree degradation inside XLPE cable is a serious threat to the cables under operation. In this paper, the DCIC (direct current integrated charge) method was employed to evaluate the electrical tree inside XLPE insulation. During the preparation of cable samples, the tree inception voltage of ~8 kV was tested. Then 1, 5 and 10 needle electrodes were inserted into cable samples for the tree generation. After the preparation of samples, AC voltage of 10 kV was applied onto the needle electrodes for electrical tree growth. The treeing time was set to 0, 20, 40 and 60 min for the DCIC test. During the DCIC test, a DC voltage of 2 kV was applied on the conductor, and the integral capacitor was connected between the copper shield of cable and ground. From the experiment result, it can be found that with the increase of treeing time, the charging coefficient increases obviously if there are 5 and 10 electrical trees in the cable, this is maybe caused by the occurrence of polarization. The conduction current coefficient changes obviously before and after needles insertion. The information in DCIC curve can be used to analyze electrical tree degradation and mechanical damage in cables at the same time. This nondestructive testing method proposed in this paper will improve the testing efficiency and speed.

The cross-linked polyethylene insulation of power cables under multiple stresses will age and deteriorate, and eventually cause insulation failure, which threatens the reliability of transmission lines. In this contribution, based on Direct Current Integrated Charge method, the performances of XLPE under thermal aging are investigated. The results show that the charge minimally injects into the unaged XLPE insulation, and the charge injected behavior intensifies with the thermal aging time. Thermal aging treatment results in greater relative permittivity, volumetric conductivity, and absorbed charge of XLPE insulation. The permittivity of the aged XLPE insulation gradually increases by 18.24%, whereas the conductivity rises by 14.48 times, and the absorption charge shoots up by 18.03 times. It is conducted that the enhancement in charge injection and the acceleration of charge accumulation reflects the cable insulation thermal aging intensified.

Seismic waves might be unavoidably triggered during underground energy and resource exploitation. Surface irregularities and subsurface cavities have significant effects on seismic wave propagation and cause amplification or reduction of ground motion. Hence, it is significant to address the scattering problem of SH waves induced by topography features and subsurface cavities in earthquake engineering. In this paper, based on the wave function expansion method coupling with the conjunction concept and the Graf’s addition formula, a series solution to this scattering problem of SH waves induced by a semi-cylindrical hill and a nearby cylindrical cavity in a homogeneous, isotropic, linear elastic half-space is derived. The displacement amplitudes on the hill surface and its environs are calculated, and compared with the results in the existing works to verify the validity of the deriving process. Then, parametric studies are performed to analyze the effects of the cavity (its location and size), and the characteristics of incident waves (the frequency and incident angle) on the seismic response of the semi-cylindrical hill. Finally, the seismic behavior of the cylindrical cavity near or away from the hill for different frequencies and incident angles is examined.

In condensed matter systems, chiral topological nodes are robust band crossing points in momentum space that carry nonzero Chern numbers. The chirality is manifested by the presence of surface Fermi arcs connecting the projections of nodes with opposite Chern numbers. In addition to the well-known Weyl nodes, theorists have proposed several other types of chiral topological nodes in condensed matter systems, but the direct experimental evidence of their existence is still lacking. Here, using angle-resolved photoemission spectroscopy, we reveal two types of new chiral nodes, namely the spin-1 nodes and charge-2 Dirac nodes, at the band crossing points near the Fermi level in CoSi, the projections of which on the (001) surface are connected by topologically protected surface Fermi arcs. As these chiral nodes in CoSi are enforced at the Brillouin zone (BZ) center and corner by the crystalline symmetries, the surface Fermi arcs connecting their projections form a non-contractible path traversing the entire (001) surface BZ, in sharp contrast to pairs of Weyl nodes with small separation. Our work marks the first experimental observation of chiral topological nodes beyond the Weyl nodes both in the bulk and on the surface in condensed matter systems.

来自免疫、儿童保健、消化4位不同专业的专家，对2019年“儿童过敏性疾病诊断和治疗专家共识”中食物过敏早期预防的几个热点问题进行讨论。食物过敏的免疫学机制是Th2细胞功能亢进，目前预防的趋势是以积极诱导免疫耐受的方法代替被动避免过敏原暴露。诱导免疫耐受的方法包括早期过敏原小剂量暴露、补充益生元，益生菌和共生元，补充免疫耐受性肽。.

As the progress of population aging in China, the proportion of elderly population is increasing. Both chronic diseases and infectious diseases can threaten the health of the elderly. There are many kinds of infectious diseases, including vaccine preventable infectious diseases affecting the health of adults, such as influenza, pneumococcal diseases and herpes zoster. In addition, the newly emerged COVID-19 has caused a pandemic in the world, resulting the highest proportion of deaths occurred in the elderly and posing a serious threat to the health of the elderly. This paper mainly summarizes the prevention and control of vaccine preventable diseases and COVID-19 to which the elderly are susceptible, analyzes the infectious disease problems affecting the health of elderly population, and recommends countermeasures for the prevention and control of these diseases in elderly population.随着我国逐步步入老龄社会，老年人群占比越来越大，其健康受到慢性病和传染病的双重威胁。传染病种类繁多，针对成年人的重要疫苗可预防传染病有流感、肺炎球菌性疾病和带状疱疹等，另外新发传染病新型冠状病毒肺炎造成了全世界的大流行，死亡人群中老年人占比最高，对老年人的健康造成重大威胁。本研究主要针对老年人群的疫苗可预防疾病和新型冠状病毒肺炎进行概述，总结老年人群所面临的部分传染病问题，并提出防控建议。.

COVID-19 is an emerging infectious disease caused by SARS-CoV-2. After the infection of the virus, the host immune system is stimulated to produce multifarious specific antibodies to decrease or eliminate effects of the pathogen. Study of the specific antibodies dynamic characteristics in patients with COVID-19 is very important for the understanding and diagnosis of the disease, research and development of vaccine, and planning of prevention and control strategy. This paper reviews and summarizes the domestic and oversea research on dynamic characteristics of specific antibodies of COVID-19 patients, including the antibody producing, duration and level, and its possible influencing factors in order to improve the understanding of the immunological characteristics of COVID-19.新型冠状病毒肺炎是由新型冠状病毒（新冠病毒）引起的新发传染病。新冠病毒侵入人体后，刺激免疫系统产生多种特异性抗体，来减弱或清除病原体对机体的影响。研究新冠病毒感染后人体内特异性抗体动态变化特征对于疾病认识、诊断、以及疫苗研究与防控策略制定具有重要意义。本文对国内外关于新冠病毒感染者不同类型特异性抗体产生和持续时间、抗体水平及其可能的影响因素等方面的相关研究进行归纳分析，从而增进对新冠病毒感染后机体免疫学特征的了解。.

The studies on infectiousness of person infected with SARS-CoV-2 at different stages of illness are an important basis for making effective prevention and control measures such as investigating the infectious source, determining the scope of close contacts and the timing of case isolation. This review discusses the infectiousness of cases infected with SARS-CoV-2 in the incubation period, symptomatic period and convalescent period by reviewing national and international literatures, technical and professional guidelines. Existing researches suggest that the infectious viruses could be isolated at the end of the incubation period as well as since illness onset, and viral load in upper respiratory tract swabs reached the peak on day 4-6 after illness onset and thereafter began to decline, implying the infectiousness was relatively strong at the end of incubation period and within one week after illness onset. Although there were a few cases who tested positive for SARS-CoV-2 after recovery, no evidence was found to indicate these cases can cause the transmission.新型冠状病毒（新冠病毒）感染不同阶段的传染性特征是调查病例感染来源、确定密切接触者范围和病例隔离时间等防控措施的重要基础。本文通过对国内外文献、技术报告与专业指南等资料进行综述，基于病原学和流行病学两个维度的研究结果，探讨新冠病毒感染者在潜伏期、临床症状期和恢复期阶段的传染性特征。现有研究提示，新冠病毒感染者在潜伏期末和发病期均可分离到具有感染性病毒，发病4~6d后在上呼吸道样本中病毒载量达到高峰，随后开始下降，提示在潜伏期末和发病1周内的传染性相对较强。个别病例在恢复期尽管可再次检出新冠病毒核酸，但未发现具有传染性的证据。.

嗅觉是人体的基本感觉之一，在人类生命活动中起着非常重要的作用。儿童嗅觉功能障碍与食欲、学习、情绪和免疫等因素密切相关，严重影响其身心健康。较成人而言，儿童群体的嗅觉功能障碍易被忽视，相关研究较缺乏。儿童通常不能主动或准确描述症状，因此加强对儿童嗅觉功能的检测具有重要意义。本文通过对现有儿童嗅觉心理物理测试方法及其临床应用情况进行综述，旨在为临床上儿童嗅觉功能测试方法的选择及相关研究提供参考。.

Here, a novel carrier fabricated by the interaction of negatively charged heparin and positively charged PEI and Ca