Mixed-effects Models with Skewed Distributions for Time-varying Decay Rate in HIV Dynamics

After initiation of treatment, HIV viral load has multiphasic changes, which indicates that the viral decay rate is a time-varying process. Mixed-effects models with different time-varying decay rate functions have been proposed in literature. However, there are two unresolved critical issues: (i) it is not clear which model is more appropriate for practical use, and (ii) the model random errors are commonly assumed to follow a normal distribution, which may be unrealistic and can obscure important features of within- and among-subject variations. Because asymmetry of HIV viral load data is still noticeable even after transformation, it is important to use a more general distribution family that enables the unrealistic normal assumption to be relaxed. We developed skew-elliptical (SE) Bayesian mixed-effects models by considering the model random errors to have an SE distribution. We compared the performance among five SE models that have different time-varying decay rate functions. For each model, we also contrasted the performance under different model random error assumptions such as normal, Student-t, skew-normal, or skew-t distribution. Two AIDS clinical trial datasets were used to illustrate the proposed models and methods. The results indicate that the model with a time-varying viral decay rate that has two exponential components is preferred. Among the four distribution assumptions, the skew-t and skew-normal models provided better fitting to the data than normal or Student-t model, suggesting that it is important to assume a model with a skewed distribution in order to achieve reasonable results when the data exhibit skewness.     

病毒式营销在企业中的应用研究

病毒式营销开始步入主流营销手段的行列。病毒式营销相比于传统的营销方式具有传播速度快、成本低廉、传播的爆发性、信息病毒的变异和衰减等特点。进行有效的病毒式营销必须充分认识其成功的关键因素,掌握实施病毒式营销的传播媒介,遵照病毒式营销的步骤和流程。同时,实施病毒式营销应注意其适用性、病毒的生命周期以及信息病毒的创新性和真实性等问题。     

A three-state continuous time Markov chain model for HIV disease burden

Plasma HIV viral load (VL) is the clinical indicator used to evaluate disease burden for HIV-infected patients. We developed a covariate-adjusted, three-state, homogenous continuous time Markov chain model for HIV/AIDS disease burden among subgroups. We defined Detectable and Undetectable HIV VL levels as two transient states and Death as the third absorbing state. We implemented the exact maximum likelihood method to estimate the parameters with related asymptotic distribution to conduct hypothesis testing. We evaluated the proposed model using HIV-infected individuals from South Carolina (SC) HIV surveillance data. Using the developed model, we estimated and compared the transition hazards, transition probabilities, and the state-specific duration for HIV-infected individuals. We examined gender, race/ethnicity, age, CD4 count, place of residence, and antiretroviral treatment regimen prescribed at the beginning of the study period. We found that patients with a higher CD4 count, increased age, heterosexual orientation, white, and single tablet regimen users were associated with reduced risk of transitioning to a Detectable VL from an Undetectable VL, whereas shorter time since diagnosis, being male, and injection drug use increased the risk of the same transition.     

The Globality of Whiteness in Post-Racial Visual Culture

This essay examines the spatial contours of post-racial visual culture. It argues that the ‘post-racial’ names the conditions under which racism operates flexibly within and beyond the logics of the colour line, while routinely disavowing its properly racial character through the symbolic deployment of multicultural humanitarianism. Even as it works through the figure of the ‘post-racial’ to bracket an engagement with the racialized rationale for the ‘nongeneralizability of human value’, the current US racial order has renovated the social structures that shore up whiteness as the privileged form humanity takes. The essay's point of departure is the iconic HOPE poster, produced by Shepard Fairey in 2008. It locates the poster's public display within a visual field subjected to neoliberal processes central to the constitution of a post-racial whiteness. It identifies two key moments in these processes. The first moment abstracts historical practices of materialist antiracism, such that racism becomes visualized as a manifestly individual subjective affair. In the second moment, post-racial visual culture repackages the visual logic of racial reference by displacing anti-black racism into morally benevolent categories suitable for humanitarian intervention, whose additional dematerialization is propped up by its migration to a digital terrain. To make this argument, the essay first offers a genealogy of the HOPE poster as it emerges from street art practices of commodity activism that obscure the structures of racial capitalism. It then treats the poster's central role in the ‘KONY 2012’ campaign, which redeployed this abstraction to recode the power of sight as a privileged form of US humanitarian violence. It concludes by considering the refusals by activists in the Occupy Wall Street movement to countenance a revised HOPE poster, even as the post-racial figure of ‘the protestor’ was lauded in corporate media.     

慢性乙型病毒性肝炎的科学治疗与预防

乙肝在我国广泛流行,严重危害人民的健康,给病人、家庭、社会造成沉重的经济负担和巨大的精神压力,给社会发展带来不容忽视的影响。针对公众对于乙肝的恐慌心理和治疗、预防乙肝的模糊认识,文章介绍了慢性乙型病毒性肝炎(乙肝)的感染机理、乙肝病毒的传播途径和预防方法、乙肝病人的临床诊断和治疗原则。在此基础上介绍了病程进展和相关表现症状,明确了乙肝治疗的总体目标,传递了科学的治疗与预防知识,提出了预防控制乙肝宣传教育的知识要点。     

Two-step and likelihood methods for HIV viral dynamic models with covariate measurement errors and missing data

HIV viral dynamic models have received much attention in the literature. Long-term viral dynamics may be modelled by semiparametric nonlinear mixed-effect models, which incorporate large variation between subjects and autocorrelation within subjects and are flexible in modelling complex viral load trajectories. Time-dependent covariates may be introduced in the dynamic models to partially explain the between-individual variations. In the presence of measurement errors and missing data in time-dependent covariates, we show that the commonly used two-step method may give approximately unbiased estimates but may under-estimate standard errors. We propose a two-stage bootstrap method to adjust the standard errors in the two-step method and a likelihood method.     

病毒式营销的运用

病毒式营销是一种信息传递战略,能通过用户的口碑宣传网络,使信息像病毒一样迅速地传向成千上万的受众。网络时代,病毒式营销的成功例子很多,如Hotmail和QQ。本文将重点讨论病毒式营销运用中的病毒传播媒介和病毒传播策略,并简单归纳运用中应注意的问题。     

VIRALITY 2.0

Media virality is a current fetish object in a number of overlapping contexts including marketing, IT design and academia. The desirability of media ‘going viral’ is confirmed by efforts now undertaken to categorize viral success through a range of typologies and metrics, conceived in order to predict and achieve virality. A recent online ad campaign, staged as a ‘how to make a viral video’, signals the complexity of the concept of manufactured virality. This article takes as a point of departure a moment of conceptual slippage in the commercial to argue that the current discourse of media virality has paradoxically expelled its own progenitor, the virus. Contrary to Henry Jenkins's claim that the discourse of virality is ‘a kind of smallpox-soaked blanket theory of media circulation’, I argue that as transmission has been rebranded as ‘sharing’, questions of personal and moral responsibility attendant to transmission and infection have been erased in favour of a bland ideology of interactivity. The concept of ‘virality 2.0’ is proposed to account for this double movement: that the discourse of digital virality has relegated viruses to the past, while structurally exploiting their dynamic of circulation. Moreover, virality 2.0 reinscribes viral subject positions with normative values drawn from this same cultural past. The argument is supported by three main claims. First, behaviour deemed risky and marginal within a heteronormative discourse of promiscuity has been reappropriated as ‘sharing’ and ‘leadership’. Second, practices of digital media transmission may be as much about systemic functionality as active and engaged participation. And third, post-viral media virality works to stabilise and fetishise the active ‘sharing subject’ in neoliberal and heteronormative terms, at the expense of other practices and pleasures.     

A Bayesian approach for estimating antiviral efficacy in HIV dynamic models

The study of HIV dynamics is one of the most important developments in recent AIDS research. It has led to a new understanding of the pathogenesis of HIV infection. Although important findings in HIV dynamics have been published in prestigious scientific journals, the statistical methods for parameter estimation and model-fitting used in those papers appear surprisingly crude and have not been studied in more detail. For example, the unidentifiable parameters were simply imputed by mean estimates from previous studies, and important pharmacological/clinical factors were not considered in the modelling. In this paper, a viral dynamic model is developed to evaluate the effect of pharmacokinetic variation, drug resistance and adherence on antiviral responses. In the context of this model, we investigate a Bayesian modelling approach under a non-linear mixed-effects (NLME) model framework. In particular, our modelling strategy allows us to estimate time-varying antiviral efficacy of a regimen during the whole course of a treatment period by incorporating the information of drug exposure and drug susceptibility. Both simulated and real clinical data examples are given to illustrate the proposed approach. The Bayesian approach has great potential to be used in many aspects of viral dynamics modelling since it allow us to fit complex dynamic models and identify all the model parameters. Our results suggest that Bayesian approach for estimating parameters in HIV dynamic models is flexible and powerful.     

突发事件舆论中的情绪极性与传染模式：社会网络分析视角

互联网在公共领域的渗透日渐深入，局部或者单一的突发事件由于社交媒体的介入往往会延伸至公共空间，成为公众广泛关注、参与的公共议题。社交媒体用户的情绪积累与传染可能左右网络舆情的走向。判断社交媒体舆论中的情绪类型，分析情绪传播特征继而验证影响情绪传染的因素变得十分重要。以“昆山反杀案”为切入口，运用情绪挖掘与社会网络分析方法，对突发事件舆论中的网络情绪进行粗、细粒度识别和网络模体、级联深度分析。研究发现，在微博场域中，“昆山反杀案”舆论的情绪化倾向明显，情绪分布以“好”的情绪最为显著；情绪传染路径以广播式传播为主，情绪传染呈现明显趋同性特征。事件发展态势与情绪极性均为情绪传染的相关因素，而随着级联深度的增加和讨论的深入，情绪逐渐趋于理性，显示了微博舆论场的“自我净化”功能。