Transmission Dynamics of an SIS Model with Age Structure on Heterogeneous Networks

Infection age is often an important factor in epidemic dynamics. In order to realistically analyze the spreading mechanism and dynamical behavior of epidemic diseases, in this paper, a generalized disease transmission model of SIS type with age-dependent infection and birth and death on a heterogeneous network is discussed. The model allows the infection and recovery rates to vary and depend on the age of infection, the time since an individual becomes infected. We address uniform persistence and find that the model has the sharp threshold property, that is, for the basic reproduction number less than one, the disease-free equilibrium is globally asymptotically stable, while for the basic reproduction number is above one, a Lyapunov functional is used to show that the endemic equilibrium is globally stable. Finally, some numerical simulations are carried out to illustrate and complement the main results. The disease dynamics rely not only on the network structure, but also on an age-dependent factor (for some key functions concerned in the model).     

E-cadherin与卵巢癌侵袭、转移关系的研究进展

卵巢癌被认为是预后最差的妇科恶性肿瘤之一.侵袭和转移是恶性肿瘤细胞的重要生物学特征之一.研究表明,E-cadherin与人体肿瘤的侵袭和转移密切相关.本文就E-cadherin与卵巢肿瘤侵袭、转移的关系研究进展作一综述.     

General Relationship of Global Topology,Local Dynamics,and Directionality in Large-Scale Brain Networks

The balance of global integration and functional specialization is a critical feature of efficient brain networks, but the relationship of global topology, local node dynamics and information flow across networks has yet to be identified. One critical step in elucidating this relationship is the identification of governing principles underlying the directionality of interactions between nodes. Here, we demonstrate such principles through analytical solutions based on the phase lead/lag relationships of general oscillator models in networks. We confirm analytical results with computational simulations using general model networks and anatomical brain networks, as well as high-density electroencephalography collected from humans in the conscious and anesthetized states. Analytical, computational, and empirical results demonstrate that network nodes with more connections (i.e., higher degrees) have larger amplitudes and are directional targets (phase lag) rather than sources (phase lead). The relationship of node degree and directionality therefore appears to be a fundamental property of networks, with direct applicability to brain function. These results provide a foundation for a principled understanding of information transfer across networks and also demonstrate that changes in directionality patterns across states of human consciousness are driven by alterations of brain network topology.     

Generalised Sandpile Dynamics on Artificial and Real-World Directed Networks

The main finding of this paper is a novel avalanche-size exponent τ ≈ 1.87 when the generalised sandpile dynamics evolves on the real-world Japanese inter-firm network. The topology of this network is non-layered and directed, displaying the typical bow tie structure found in real-world directed networks, with cycles and triangles. We show that one can move from a strictly layered regular lattice to a more fluid structure of the inter-firm network in a few simple steps. Relaxing the regular lattice structure by introducing an interlayer distribution for the interactions, forces the scaling exponent of the avalanche-size probability density function τ out of the two-dimensional directed sandpile universality class τ = 4/3, into the mean field universality class τ = 3/2. Numerical investigation shows that these two classes are the only that exist on the directed sandpile, regardless of the underlying topology, as long as it is strictly layered. Randomly adding a small proportion of links connecting non adjacent layers in an otherwise layered network takes the system out of the mean field regime to produce non-trivial avalanche-size probability density function. Although these do not display proper scaling, they closely reproduce the behaviour observed on the Japanese inter-firm network.     

产甲烷常温古细菌和嗜热古细菌代谢网络拓扑结构与功能间的关联性研究

根据从KEGG数据库获得的产甲烷的常温古细菌Methanosarcina acetivorans(MAC)和嗜热古细菌Methanopyrus kandleri(MKA)的代谢网络,通过不同的网络属性特征的比较,发现常温古细菌MAC的代谢网络比嗜热古细菌MKA有更长的平均路径长度,更大的直径,这表明常温古细菌MAC的总体结构是相对低密度、松散的网络结构.同时为了从系统水平上分析这些特征蕴含的功能意义,采用了Grivan和Newman提出的模块算法(简称GN算法)分析这两个生物体的功能模块,并将所得的结果与KEGG数据库中的途径信息进行比较研究,发现大部分模块对应2~4个KEGG途径,表明这些网络模块均具有一定功能意义.     

Relationship Between Competence for Transfection and for Transformation

Deoxyribonucleic acid (DNA) extracted from phage SPP1 is highly infectious on Bacillus subtilis competent cells; the efficiency of infection is 5 x 10(3) to 6 x 10(3) phage equivalents per plaque-forming unit. This DNA was used to study the relationship between competence for transfection and for transformation. The experiments were concerned with the frequency of infection and transformation in mutants exhibiting different levels of competence, the effect of periodate on competence for infection and for transformation, the competition between phage and bacterial DNA, the transformation of cells preinfected with phage DNA, and the infection of cells pretreated with bacterial DNA. The data show that B. subtilis cells competent for transformation are also competent for transfection and vice versa; transfection with phage DNA represents, therefore, a simple way to measure the total number of competent cells in a culture. The fraction of competent cells, determined by SPP1 DNA infection, varied from 10(-2) to 7 x 10(-2).     

Occupancy Modeling for Improved Accuracy and Understanding of Pathogen Prevalence and Dynamics

Most pathogen detection tests are imperfect, with a sensitivity < 100%, thereby resulting in the potential for a false negative, where a pathogen is present but not detected. False negatives in a sample inflate the number of non-detections, negatively biasing estimates of pathogen prevalence. Histological examination of tissues as a diagnostic test can be advantageous as multiple pathogens can be examined and providing important information on associated pathological changes to the host. However, it is usually less sensitive than molecular or microbiological tests for specific pathogens. Our study objectives were to 1) develop a hierarchical occupancy model to examine pathogen prevalence in spring Chinook salmon Oncorhynchus tshawytscha and their distribution among host tissues 2) use the model to estimate pathogen-specific test sensitivities and infection rates, and 3) illustrate the effect of using replicate within host sampling on sample sizes required to detect a pathogen. We examined histological sections of replicate tissue samples from spring Chinook salmon O. tshawytscha collected after spawning for common pathogens seen in this population: Apophallus/echinostome metacercariae, Parvicapsula minibicornis, Nanophyetus salmincola/ metacercariae, and Renibacterium salmoninarum. A hierarchical occupancy model was developed to estimate pathogen and tissue-specific test sensitivities and unbiased estimation of host- and organ-level infection rates. Model estimated sensitivities and host- and organ-level infections rates varied among pathogens and model estimated infection rate was higher than prevalence unadjusted for test sensitivity, confirming that prevalence unadjusted for test sensitivity was negatively biased. The modeling approach provided an analytical approach for using hierarchically structured pathogen detection data from lower sensitivity diagnostic tests, such as histology, to obtain unbiased pathogen prevalence estimates with associated uncertainties. Accounting for test sensitivity using within host replicate samples also required fewer individual fish to be sampled. This approach is useful for evaluating pathogen or microbe community dynamics when test sensitivity is <100%.     

Effect of Control Strategies on Prevalence,Incidence and Re-infection of Clonorchiasis in Endemic Areas of China

Background

A pilot clonorchiasis control project was implemented to evaluate the efficacies of various chemotherapy strategies on prevalence, incidence and re-infection in Heilongjiang Province, China.

Methods and Findings

Seven intervention groups (14,139 residents, about 2000 in each group) in heavily or moderately endemic areas were subjected to repeated praziquantel administration from 2001 to 2004. In the selective chemotherapy groups, residents were examined for fecal eggs, and those who tested positive were treated with three doses of 25 mg/kg praziquantel at 5-hour-intervals in one day. However, all residents were treated in the mass chemotherapy groups. In heavily endemic areas, two mass treatments of all residents in 2001 and 2003 reduced the prevalence from 69.5% to 18.8%, while four annual mass treatments reduced the prevalence from 48.0% in 2001 to 8.4% in 2004. Selective annual treatments for egg-positive subjects reduced the egg-positive rates from 54.9% in 2001 to 15.0% in 2004 or from 73.2% in 2001 to 12.3% in 2004. Selective treatments every 6 months significantly reduced the prevalence from 59.5% in 2001 to 7.5% in 2004. All of the repeated treatments reduced EPG (eggs per gram of feces) significantly. The annual mass treatment and selective treatment every 6 months produced lower prevalence and re-infection rates and higher egg reduction rate than annual selective treatments did. In the moderate endemic areas, egg positive rates were 24.8% and 29.7% in 2001 but were 1.9% and 1.3% after 2 or 3 selective treatments. The prevalence, incidence, re-infection rates in a moderately endemic area were significantly lower than those of heavy endemic areas.

Conclusions

Repeated mass treatment or selective treatment with praziquantel every 6 to 12 months is highly effective for clonorchiasis control in heavily endemic areas. In contrast, one or two selective treatments with health education is effective in moderately endemic areas.     

生产力与生物多样性之间的相互关系研究概述

生态系统生产力与生物多样性是人们普遍关心的二个中心问题。文章论述二者的相互关系及进行研究的主要内容,评述已有研究的几种假说,指出在进行生态学比较时,应该考虑生产力的因素相似而多样性不同的生态系统系列,才能客观地分析其原因。     

Relationship Between mRNA Stability and Length: An Old Question with a New Twist

The half-life of individual mRNA plays a central role in controlling the level of gene expression. However, the determinants of mRNA stability have not yet been well defined. Most previous studies suggest that mRNA length does not affect its stability. Here, we show significant negative correlations between mRNA length and stability in human and Escherichia coli, but not in Saccharomyces cerevisiae or Bacillus subtilis. This finding suggests the possibility that endonucleolytic attacks by RNA endonuclease and/or mechanical damage may strongly influence mRNA stability in both prokaryotes and eukaryotes.     

Interaction Between Cryopreservation, Rewarming Rate and Seed Humidification on the Germination of Two Spanish Endemic Species

The effects of humidification, storage in liquid nitrogen (1or 30 d) and rewarming rate on seed germination were studiedin two Spanish endemics. Humidification resulted in higher germinationpercentages only in the species with hard covers, especiallyin slowly rewarmed seeds. In an experiment lasting 21 weeks,seeds stored in liquid nitrogen were removed for 10 min eachweek to mimic the withdrawal of samples from a seed bank; thishad no effect on germination.Copyright 1998 Annals of BotanyCompany Centaurea hyssopifolia,Limonium dichotomum, cryopreservation, cypsela, endemics, germination, humidification, seeds.     

Selenium Level Surveillance for the Year 2007 of Keshan Disease in Endemic Areas and Analysis on Surveillance Results Between 2003 and 2007

Selenium deficiency is widely accepted as a fundamental cause of Keshan disease (KD). In the present study, the selenium levels of hair and food samples of KD in some endemic areas were measured; the prevalence and incidence of KD for the year 2007 in these areas were surveyed. The results for KD surveillance from 2003 to 2007 were analyzed. The selenium level was measured fluorometrically. In 2007, a total of 19,280 residents were surveyed in 15 provinces. The prevalence and incidence of KD were 3.0% and 4.9‰, respectively. In KD and control subjects, the mean levels of hair selenium were respectively 0.3223 mg/kg and 0.4466 mg/kg. The mean level of staple food selenium was 0.0227?±?0.0144 mg/kg. During the 5 years, the selenium content in hair was always kept at a normal level within inhabitants of KD-endemic areas, but that in staple food was always kept at a lower level. These results indicate that the pathogenic factor has not been drastically eliminated even with the increasing selenium level of internal environment and is still continually damaging public health of KD in endemic areas. Since KD is still a serious threat to public health in its endemic areas, it is of great importance to pay attention to the prevention and control of this disease.     

Lake Characteristics,Population Properties and Invasion History Determine Impact of Invasive Bivalves on Lake Nutrient Dynamics

Ecosystems - Invasive species can have large impacts on ecosystems, including the cycling and distribution of nutrients. To determine the whole-ecosystem effects of invasive zebra mussels on lake...     

生物多样性与生态系统功能关系研究进展

生物多样性和生态系统功能关系的研究,是生态学和环境学的一个中心论题。围绕这一主题,首先介绍了生物多样性及生态系统功能的含义;其次,一方面历史地回顾了生物多样性与生态系统功能关系的研究,另一方面结合近20年间的研究及实验,分别从多样性与生产力、多样性与稳定性、多样性与生态系统可持续性3个方面系统地阐述了二者关系研究的主要论点;最后,对其今后面临的挑战及发展趋势进行了展望。     

小麦残茬落叶的分解与土壤因子间动态关系的研究

东北高寒地区的黑钙土土质优良肥沃 ,适合小麦、大豆和玉米等种植。近年来 ,由于人们只重视无机化肥的使用 ,忽视了地力培育 ,大量秸秆被移出田外 ,造成土壤有机质含量降低 ,土壤板结 ,使原本高产的农田逐渐变成中低产田 ,甚至有的已成为撂荒地。因此 ,研究当前农田土壤对枯枝落叶的分解现状 ,对于认识现有耕种条件下 ,农田土壤亚系统的物质转化和能量流动具有实际意义。1　研究地区和研究方法1 .1　自然概况该研究是在黑龙江省克山师专农场进行的。地理位置位于东经 1 2 5°8′～ 1 2 6°8′,北纬 47°50′～ 48°33′。年均气温 1 .3℃ ,1…     

脑肠肽Ghrelin-GHSR信号系统与肿瘤的关系

脑肠肽Ghrelin是一种含有28个氨基酸的生长激素释放肽,为生长激素促分泌素受体(growth hormone secretagogue recep-tor,GHSR)的内源性配体。Ghrelin及其功能性受体GHSR-1a广泛分布于中枢和外周组织。此外,在多种肿瘤组织和癌细胞中发现有Ghrelin及其功能性受体GHSR-1a的表达。我们的前期工作和目前的研究发现Ghrelin可与经典的功能性受体GHSR-1a或新型受体结合,通过激活多条信号转导通路,对肿瘤的生物学行为发挥重要的调控作用。因此,脑肠肽Ghrelin-GHSR信号系统可为肿瘤的临床诊断和预后评估发挥重要作用,并为肿瘤的分子治疗提供新靶点。     

Snakes on the Balearic Islands: An Invasion Tale with Implications for Native Biodiversity Conservation

Biological invasions are a major conservation threat for biodiversity worldwide. Islands are particularly vulnerable to invasive species, especially Mediterranean islands which have suffered human pressure since ancient times. In the Balearic archipelago, reptiles represent an outstanding case with more alien than native species. Moreover, in the last decade a new wave of alien snakes landed in the main islands of the archipelago, some of which were originally snake-free. The identification of the origin and colonization pathways of alien species, as well as the prediction of their expansion, is crucial to develop effective conservation strategies. In this study, we used molecular markers to assess the allochthonous status and the putative origin of the four introduced snake species (Hemorrhois hippocrepis, Malpolon monspessulanus, Macroprotodon mauritanicus and Rhinechis scalaris) as well as ecological niche models to infer their patterns of invasion and expansion based on current and future habitat suitability. For most species, DNA sequence data suggested the Iberian Peninsula as the potential origin of the allochthonous populations, although the shallow phylogeographic structure of these species prevented the identification of a restricted source-area. For all of them, the ecological niche models showed a current low habitat suitability in the Balearic, which is however predicted to increase significantly in the next few decades under climate change scenarios. Evidence from direct observations and spatial distribution of the first-occurrence records of alien snakes (but also lizards and worm lizards) suggest the nursery trade, and in particular olive tree importation from Iberian Peninsula, as the main pathway of introduction of alien reptiles in the Balearic islands. This trend has been reported also for recent invasions in NE Spain, thus showing that olive trees transplantation may be an effective vector for bioinvasion across the Mediterranean. The combination of molecular and ecological tools used in this study reveals a promising approach for the understanding of the complex invasion process, hence guiding conservation management actions.