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Despite extensive experimental and theoretical studies, the atomistic mechanisms responsible for dielectric breakdown (BD) in amorphous (a)-SiO2 are still poorly understood. A number of qualitative physical models and mathematical formulations have been proposed over the years to explain experimentally observable statistical trends. However, these models do not provide clear insight into the physical origins of the BD process. Here, we investigate the physical mechanisms responsible for dielectric breakdown in a-SiO2 using a multi-scale approach where the energetic parameters derived from a microscopic mechanism are used to predict the macroscopic degradation parameters of BD, i.e., time-dependent dielectric breakdown (TDDB) statistics, and its voltage dependence. Using this modeling framework, we demonstrate that trapping of two electrons at intrinsic structural precursors in a-SiO2 is responsible for a significant reduction of the activation energy for Si-O bond breaking. This results in a lower barrier for the formation of O vacancies and allows us to explain quantitatively the TDDB data reported in the literature for relatively thin (3-9 nm) a-SiO2 oxide films. [ABSTRACT FROM AUTHOR]

The prevalence of Clonorchis sinensis infection in freshwater fishes was surveyed in Heilongjiang Province, northeastern China, between August 2011 and September 2013. Thirteen species of freshwater fish (n = 3221) and one species of shrimp (n = 93) were collected from Songhua river, Nenjiang river and other lakes or ponds in 37 sites of 15 representative cities in Heilongjiang Province. They were individually examined by digestion technique, and the C. sinensis metacercariae were identified morphologically followed by confirmation using sequences of the second internal transcribed spacer of ribosomal DNA. Ten of the 13 examined species of freshwater fishes were infected with C. sinensis metacercariae, while all shrimps were negative. The overall prevalence of C. sinensis infection in 3221 examined freshwater fishes was 19.96%, with 42.57% (272/639) in Pseudorasbora parva, 22.55% (83/368) in Hemicculter leuciclus, 20.44% (121/592) in Carassius auratus, 17.71% (68/384) in Saurogobio dabryi, 10.85% (23/212) in Rhodeus ocellatus, 10.54% (48/455) in Phoxinus lagowskii, 8.20% (21/256) in Perccottus glehnii, 6.25% (5/80) in Misgurnus anguillicaudatus, 4.55% (1/22) in Xenocypris davidi, and 1.49% (1/67) in Cyprinus carpio. The average infection intensity in P. parva was 103.3 encysted metacercariae per gram of fish meat in Zhaoyuan city. The average prevalence of C. sinensis infection in Songhua river, Nenjiang river and lakes or ponds were 31.96% (503/1574), 11.30% (102/903) and 7.93% (59/744), respectively. The prevalence of C. sinensis infection in Zhaoyuan city (43.68%) was the highest among all sampling locations. These results revealed a high-prevalence of C. sinensis infection in freshwater fishes in Heilongjiang Province, northeastern China, posing significant public health concern. [ABSTRACT FROM AUTHOR]

Hand, foot, and mouth disease (HFMD) is a common childhood infectious disease caused by various enteroviruses. China has the most significant number of reported cases and deaths of HFMD over the globe. Understanding the epidemic laws of HFMD can provide a scientific basis for designing prevention and control measures. The dynamic transmission models focus on the transmission mechanism of infectious diseases. They can simulate the actual situation to study the epidemic rules of diseases by adding, deleting, and subdividing compartments. More researchers have paid attention to dynamic models because of their high flexibility. To carry out the dynamic model of the HFMD research more effectively, a comprehensive understanding of related research progress in this field is deeply needed. In this paper, based on various researchers' different research purposes of dynamic models, the research progress was classified and summarized, providing meaningful guidance for model construction methods and future research directions and references for dynamic modeling of other models of infectious diseases. It was found that most studies used the SIR dynamic model or its extended model (such as the SEIR model), and few studies contained a complex factor compartment. Some important epidemiological parameters (such as R 0 ) were obtained by studying the HFMD cases in a specific region, simulating different intervention scenarios to evaluate the effect of measures, or revealing the future trend by model prediction. However, there is no dynamic model simultaneously considering age structure, population moving, seasonality and periodicity, and vaccination.

This study examined sequence variability in internal transcribed spacers (ITS) of nuclear ribosomal DNA among Syphacia obvelata and Aspiculuris tetraptera isolates from laboratory mice from different geographical locations in China. ITS1, 5.8S and ITS2 rDNA were amplified separately from adult S. obvelata and A. tetraptera individuals by polymerase chain reaction (PCR), and the amplicons were subjected to sequencing from both directions. The lengths of the sequences of ITS1, 5.8S and ITS2 rDNA from both nematodes were 314 bp and 456 bp, 157 bp, and 273 bp and 419 bp, respectively. The intraspecific sequence variations in S. obvelata ITS1 were 0-0.3%. For A. tetraptera they were 0-0.7% in ITS1 and 0-1.0% in ITS2. However, the interspecific sequence differences among members of the infraorder Oxyuridomorpha were significantly higher, being 54.0-65.5% for ITS1 and 55.3-64.1% for ITS2. Phylogenetic analysis based on the combined partial sequences of ITS1 and ITS2 using three inference methods - Bayesian inference, maximum likelihood and maximum parsimony - revealed that all the S. obvelata and A. tetraptera samples formed independent monophyletic groups. Syphacia obvelata was closer to Syphacia muris than to A. tetraptera, consistent with morphological classification. These results demonstrate that ITS1 and ITS2 rDNA sequences are useful markers for population genetic studies of oxyurid nematodes.