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Search Results: 1 - 10 of 43318 matches for " Xiaohong Xu "
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Asymptotic Properties of a Hepatitis B Virus Infection Model with Time Delay
Xiaohong Tian,Rui Xu
Discrete Dynamics in Nature and Society , 2010, DOI: 10.1155/2010/182340
Abstract: A hepatitis B virus infection model with time delay is discussed. By analyzing the corresponding characteristic equations, the local stability of each of the feasible equilibria of the model is studied. By using comparison arguments, it is proved that if the basic reproduction ratio is less than unity, the infection-free equilibrium is globally asymptotically stable. If the basic reproduction ratio is greater than unity, by means of an iteration technique, sufficient conditions are derived for the global asymptotic stability of the virus-infected equilibrium. Numerical simulations are carried out to illustrate the theoretical results. 1. Introduction Hepatitis B is a potentially life-threatening liver infection caused by the hepatitis B virus. It is a major global health problem and the most serious type of viral hepatitis. It can cause chronic liver disease and puts people at high risk of death from cirrhosis of the liver and liver cancer. Worldwide, estimated two billion people have been infected with the hepatitis B virus (HBV), and more than 350 million have chronic (long-term) liver infections. In the past decade, therapy for HBV has been revolutionized by the advent of drugs that directly block replication of the HBV genome. All these drugs (to date) are nucleoside or nucleotide analogues that selectively target the viral reverse transcriptase. The first successful drug, lamivudine, emerged from screening for inhibitors of the HBV reverse transcriptase and was introduced into clinical practice for the management of HBV infection. Recently, mathematical models have been used frequently to study the transmission dynamics of HBV (see, e.g., [1–15]). In [1], Anderson and May used a simple mathematical model to illustrate the effects of carriers on the transmission of HBV. In an effort to model HBV infection dynamics and its treatment with the reverse transcriptase inhibitor lamivudine, Nowak and Bangham [7] and Bonhoeffer et al. [2] proposed the following basic HBV infection model: where and are numbers of uninfected cells, infected cells, and free-virus cells, respectively. Uninfected cells are assumed to be produced at a constant rate , die at rate , and become infected at rate in which is the mass action rate constant describing the infection process. Infected cells are killed by immune cells at rate and produce free virus at rate , here is the so-called burst constant. Free-virus cells are cleared at rate . It is assumed that parameters are positive constants. In [4], by constructing novel Lyapunov functions, it was proven that if the basic
Stability Analysis of a Delayed SIR Epidemic Model with Stage Structure and Nonlinear Incidence
Xiaohong Tian,Rui Xu
Discrete Dynamics in Nature and Society , 2009, DOI: 10.1155/2009/979217
Abstract: We investigate the stability of an SIR epidemic model with stage structure and time delay. By analyzing the eigenvalues of the corresponding characteristic equation, the local stability of each feasible equilibrium of the model is established. By using comparison arguments, it is proved when the basic reproduction number is less than unity, the disease free equilibrium is globally asymptotically stable. When the basic reproduction number is greater than unity, sufficient conditions are derived for the global stability of an endemic equilibrium of the model. Numerical simulations are carried out to illustrate the theoretical results.
Global Stability of a Virus Infection Model with Time Delay and Absorption
Xiaohong Tian,Rui Xu
Discrete Dynamics in Nature and Society , 2011, DOI: 10.1155/2011/152415
Abstract: In this paper, a virus infection model with time delay and absorption is studied. By analyzing the corresponding characteristic equations, the local stability of each of feasible equilibria of the model is established. By using comparison arguments, it is shown that the infection free equilibrium is globally asymptotically stable when the basic reproduction ratio is less than unity. When the basic reproduction ratio is greater than unity, sufficient conditions are derived for the global stability of the virus-infected equilibrium. Numerical simulations are carried out to illustrate the theoretical results.
Significance Test and Genome Selection in Bayesian Shrinkage Analysis
Xiaohong Che,Shizhong Xu
International Journal of Plant Genomics , 2010, DOI: 10.1155/2010/893206
Abstract: Bayesian shrinkage analysis is the state-of-the-art method for whole genome analysis of quantitative traits. It can estimate the genetic effects for the entire genome using a dense marker map. The technique is now called genome selection. A nice property of the shrinkage analysis is that it can estimate effects of QTL as small as explaining 2% of the phenotypic variance in a typical sample size of 300–500 individuals. In most cases, QTL can be detected with simple visual inspection of the entire genome for the effect because the false positive rate is low. As a Bayesian method, no significance test is needed. However, it is still desirable to put some confidences on the estimated QTL effects. We proposed to use the permutation test to draw empirical thresholds to declare significance of QTL under a predetermined genome wide type I error. With the permutation test, Bayesian shrinkage analysis can be routinely used for QTL detection. 1. Introduction Interval mapping [1] and multiple interval mapping [2] are the most commonly used methods for QTL mapping. These methods are developed in the maximum likelihood framework, which has limitation in terms of handling large saturated models. Bayesian mapping [3–7] deals with large models more efficiently through the reversible jump Markov chain Monte Carlo (RJMCMC) [4], the shrinkage analysis [8, 9], or the stochastic search variable selection (SSVS) [10]. Shrinkage mapping and SSVS are more efficient in terms of whole genome evaluation because they are statistically easy to understand and also provide better chance to evaluate the entire genome. These two methods are related to the Lasso method for regression analysis [11]. Rather than deleting nonsignificant QTL explicitly from the model, these methods use a special algorithm to shrink estimated QTL effects to zero or close to zero. A QTL with zero estimated effect is treated the same as being excluded from the model. No statistical test is required because genome regions bearing no QTL often show no bumps (QTL effects) in the QTL effect profile (plot of QTL effects against genome location). The visual inspection on the QTL effect profile is not optimal because small QTL may come and go during the MCMC sampling process. It is desirable to provide some kind of statistical confidence on these small QTL. Permutation test [12] itself is not a method of QTL mapping; rather, it is a method to find the critical value used to declare the significance of QTL for any method of QTL mapping. It is very efficient in interval mapping under the maximum likelihood framework. A
Research of Anti-Cancer Components in Traditional Chinese Medicine on Hollow Fibre Cell Fishing and Hollow Fibre Liquid Phase Microextraction  [PDF]
Feixue Li, Xuan Chen, Yanli Xu, Xiaohong Bai
American Journal of Analytical Chemistry (AJAC) , 2016, DOI: 10.4236/ajac.2016.710063
Abstract: Hollow fibre cell fishing with HPLC (HFCF-HPLC) based on the human ovarian cancer cell line SKOV-3, human renal tubular cell line ACHN or hepatoma cell line HepG-2 was employed to screen active groups of coumarin and volatile oil in Radix angelicae sinensis, Radix angelicae dahuricae and Fructus citri sarcodactylis. Simultaneously, hollow fibre liquid phase microextraction with HPLC (HFLPME-HPLC) was conducted to enrich and determine the contents of active components in the same sample solution. Before application, for HFCF-HPLC, cells growth states and survival rates on the fibre, effect of ethanol concentration in the extract of samples on cell survival rates, non-specific binding between fibre active centres and the target components, positive and negative controls and repeatabilities were validated; for HFLPME, extraction solvent, sample phase pH, agitation speed, extraction time and sample phase volume were investigated. Many active components were screened from three medicines. Some of them, such as scoparone, psoralen, bergapten, oxypeucedanin, imperatorin, ligustilide, were identified by MS. The target fishing factors of active components and the cell apoptosis rates of three cells under the medicines effect were researched. The binding sites of active groups on HepG-2 cells were preliminarily determined. The results demonstrated that HFCF-HPLC, coupled with HFLPME-HPLC, is a simple and universal approach to find bioactive components at the cellular level, determine their content and research traditional Chinese medicines (TCMs) entirety effect of multi-component and multi-target. The approach may provide us a new and good solution to clarify the material basis of anti-cancer effect and conduct personalized quality control for the components associated with efficacy in TCMs.
Structure and magnetic properties of [FePt/Ag]10 multilayer films
Xiaohong Xu,Fang Wang,Haishun Wu
Chinese Science Bulletin , 2004, DOI: 10.1007/BF03183713
Abstract: [FePt/Ag]10 multilayers were deposited on glass substrates by magnetron sputtering. After being annealed at 550°C for 30 min, the coercivities of [FePt/Ag]10 multilayer films were observably improved. Magnetic properties of [FePt/Ag]10 multilayer films are influenced by the Ag content. The highest coercivity is obtained for those multilayer films that the Ag content is about 25%. The analysis for the remanence curves shows that the lower FePt layer thickness is favorable for decreasing the intergranular interaction. Result of XRD shows that a thick Ag layer can enhance the intensity of FePt(00l) peak. A magnetic activation volume of the order of 10 24 m3 is obtained by the measurement of magnetic viscosity, showing that it is promising to be ultrahigh density recording media.
Ab initio molecular orbital study of structure on aluminium borides A1Bn(n=1-5) series
Haishun Wu,Xiaohong Xu,Weiliang Zhou
Chinese Science Bulletin , 1997, DOI: 10.1007/BF02882544
Abstract:
(001)-oriented FePt/Ag composite films for perpendicular recording

Wenfeng LIU,Fang WANG,Xiaohong XU,

金属学报(英文版) , 2009,
Abstract: FePt/Ag thin films were deposited by magnetron sputtering onto 7059 glass substrates, then were annealed at 550 ℃ for 30 min. Nanostructured FePt/Ag films were successfully obtained with the magnetic easy axis of Ll_0 FePt perpendicular to the film plane. It was found that the development of (001) texture depended strongly on the thicknesses of FePt magnetic layer and Ag underlayer. The L10 ordered FePt(15 nm)/Ag(50 nm) with (001) orientation can be obtained. And the perpendicular coercivity of FePt(15 nm)/Ag(50 nm) film reached to 7.2×10~5 A/m, whereas the longitudinal one was only 3.2×10~4 A/m. The non-magnetic Ag underlayer can not only induce (001) orientation and ordering of FePt grains, but also reduce the intergrain interactions.
End-to-end delay in two hop relay MANETs with limited buffer
Jia Liu,Yang Xu,Xiaohong Jiang
Computer Science , 2015, DOI: 10.1109/CANDAR.2014.13
Abstract: Despite lots of literature has been dedicated to researching the delay performance in two-hop relay (2HR) mobile ad hoc networks (MANETs), however, they usually assume the buffer size of each node is infinite, so these studies are not applicable to and thus may not reflect the real delay performance of a practical MANET with limited buffer. To address this issue, in this paper we explore the packet end-to-end delay in a 2HR MANET, where each node is equipped with a bounded and shared relay-buffer for storing and forwarding packets of all other flows. The transmission range of each node can be adjusted and a group-based scheduling scheme is adopted to avoid interference between simultaneous transmissions, meanwhile a handshake mechanism is added to the 2HR routing algorithm to avoid packet loss. With the help of Markov Chain Theory and Queuing Theory, we develop a new framework to fully characterize the packet delivery processes, and obtain the relay-buffer blocking probability (RBP) under any given exogenous packet input rate. Based on the RBP, we can compute the packet queuing delay in its source node and delivery delay respectively, and further derive the end-to-end delay in such a MANET with limited buffer.
Growth Hormone Replacement Therapy in Adult Growth Hormone Deficiency and Risk of Cancer: A Meta-Analysis  [PDF]
Li Zeng, Xiaoxiao Song, Chenhong Lin, Jon Kee Ho, Pingxiang Yu, Sanjay Jaiswal, Xiaohong Xu
Open Journal of Endocrine and Metabolic Diseases (OJEMD) , 2017, DOI: 10.4236/ojemd.2017.79016
Abstract: The growth hormone (GH) replacement therapy in adult growth hormone deficiency (AGHD) is now well developed, nevertheless, the safety of GH replacement, especially the incidence of cancer in these patients remains to be further clarified. To summarize the evidence on the safety of using GH in AGHD, we conduct this meta-analysis to assess the relationship between the risk of cancer and GH replacement therapy. Randomized controlled trials and cohort studies involved in GH therapy for AGHD were selected. Meta-analysis was performed and risk ratio (RR) was pooled with 95% confidence interval (CI) to investigate the relationship between GH replacement and the risk of cancer. The result indicated that there was no evidence to draw a conclusion that GH replacement therapy will increase the risk of cancer (P = 0.001, RR = 0.77, 95% CI [0.65, 0.90]). Meanwhile, according to the calculated analysis, the replacement therapy might even reduce the risk of cancer. Furthermore, subgroup analysis demonstrated that there was no correlation between replacement therapy of GH and the risk of cancer both in prospective and retrospective cohort design research, and in prospective group, the risk of cancer even decreased (P = 0.0002, RR = 0.71, 95%CI [0.59, 0.85]). In conclusion, our study corroborates evidence from previous studies showing that GH replacement therapy in AGHD patients would not increase the risk of cancer; instead, it might be even decrease cancer risk. The results suggested that GH replacement therapy in AGHD patients was safe.
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