Deep unsupervised clustering with Gaussian mixture variational autoencoders

We study a variant of the variational autoencoder model with a Gaussian mixture as a prior distribution, with the goal of performing unsupervised clustering through deep generative models. We observe that the standard variational approach in these models is unsuited for unsupervised clustering, and mitigate this problem by leveraging a principled information-theoretic regularisation term known as consistency violation. Adding this term to the standard variational optimisation objective yields networks with both meaningful internal representations and well-defined clusters. We demonstrate the performance of this scheme on synthetic data, MNIST and SVHN, showing that the obtained clusters are distinct, interpretable and result in achieving higher performance on unsupervised clustering classification than previous approaches

Relapsing cytomegalovirus infection in solid organ transplant recipients

Efforts to prevent relapsed cytomegalovirus (CMV) disease among solid organ transplant (SOT) recipients present clinical challenges. Historically, SOT recipients treated with short courses of ganciclovir, without documented clearance of viremia, had relapse rates of 23–33%. Current treatment often includes much longer courses of valganciclovir, and persistence of viremia at the end of treatment is rare. We sought to determine the rate and risk factors for relapse under those treatment conditions. Records of 1760 SOT recipients from January 2003 to June 2007 were reviewed; 105 cases of CMV viremia were identified. Relapse occurred in 20/105 (19%); 50% had end-organ disease at the time of relapse. Most patients received approximately 3 months of valganciclovir. Clearance of viremia was documented in 19/20 patients with relapse. Multivariable analysis identified receipt of a thoracic organ and diabetes mellitus as risk factors for relapse. Despite long treatment courses with valganciclovir and documented clearance of viremia, CMV relapse remains common among SOT recipients. Better understanding of the epidemiology of CMV among SOT recipients and validation of risk factors for disease relapse should be the focus of future prospective trials. Such trials should include different treatment durations and extended monitoring for relapse.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73013/1/j.1399-3062.2009.00443.x.pd

SU(3) breaking in hyperon transition vector form factors

We present a calculation of the SU(3)-breaking corrections to the hyperon transition vector form factors to $\mathcal{O}(p^4)$ in heavy baryon chiral perturbation theory with finite-range regularisation. Both octet and decuplet degrees of freedom are included. We formulate a chiral expansion at the kinematic point $Q^2=-(M_{B_1}-M_{B_2})^2$, which can be conveniently accessed in lattice QCD. The two unknown low-energy constants at this point are constrained by lattice QCD simulation results for the $\Sigma^-\rightarrow n$ and $\Xi^0\rightarrow \Sigma^+$ transition form factors. Hence we determine lattice-informed values of $f_1$ at the physical point. This work constitutes progress towards the precise determination of $|V_{us}|$ from hyperon semileptonic decays

A Positioning Theory Analysis of Interaction Surrounding Design Failures in an Elementary Engineering Club

This qualitative study applies Positioning Theory to identify positions that mediate the experiences of design failure within the context of an afterschool engineering club (EC) with elementary students diverse in language, race, ethnicity, gender, and academic abilities. We ask: (1) What kinds of structural design failure and failure responses did participants in EC experience? and (2) What are students’ and teachers’ positions in relation to responses to design failure? Types of positions (e.g., builder, tinkerer, idea-elicitor, director, observer) were identified in relation to children’s and teachers’ actions and speech in response to structural design failure during EC. Participants included 12 third-grade students and four teachers involved in EC for eight weeks. Data sources include audio transcripts, video, and field notes. Twenty-four design failure episodes were identified and transcribed multimodally from video, followed by coding of episodes using a multimodal Positioning Theory analytical framework. Findings discuss the kinds of engineering design actions and associated positionings unfolding in response to failure as well as the positions mediating teacher and student responses to design. We highlight the importance of student and teacher mediation as well as how Positioning Theory can be used to expand our understanding of (re)positionings that can occur within responses to design failure. Specifically, elementary engineering curricular materials must create the context to support the range of positions taken up in response to design failure. This includes explicit modeling of discursive actions surrounding design failure, multiple opportunities for students to experience and respond to design failure with time to improve beyond the design–build–test model, and support for teachers to address the range of students’ responses to design failures knowledgeably and flexibly

Heavy-light decay constants from clover heavy quark action in QCD with two flavors of dynamical quarks

We present results on an analysis of the decay constants f_B and f_Bs with two flavours of sea quark. The calculation has been carried out on 3 different bare gauge couplings and 4 sea quark masses at each gauge coupling, with m_pi/m_rho ranging from 0.8 to 0.6. We employ the Fermilab formalism to perform calculations with heavy quarks whose mass is in the range of the b-quark. A detailed comparison with a quenched calculation using the same action is made to elucidate the effects due to the sea quarks.Comment: Contribution to Lattice 99 (Heavy Quarks). Latex file, uses espcrc2.sty and epsf.sty. 3 pages, 3 encapsulated postscript figure

The political and scientific challenges in evaluating compulsory drug treatment centers in Southeast Asia

BACKGROUND: In Vietnam, like many countries in Southeast Asia, the commonly used approach of center-based compulsory drug treatment (CCT) has been criticized on human rights ground. Meanwhile, community-based voluntary methadone maintenance treatment (MMT) has been implemented for nearly a decade with promising results. Reform-minded leaders have been seeking empirical evidence of the costs and effectiveness associated with these two main treatment modalities. Conducting evaluations of these treatments, especially where randomization is not ethical, presents challenges. The aim of this paper is to discuss political challenges and methodological issues when conducting cost-effectiveness studies within the context of a non-democratic Southeast Asian country. METHODS: A retrospective analysis of the political and scientific challenges that were experienced in the study design, sample size determination, government approval and ethics approvals, participant recruitment, data collection, and determination of sources, and quantification of cost and effectiveness data was undertaken. As a consequence of the non-randomized design, analysis of patient characteristics for both treatment types was undertaken to identify the magnitude of baseline group differences. Concordance between self-reported heroin use and urine drug testing was undertaken to determine the reliability of self-report data in a politically challenging environment. RESULTS: We demonstrate that conducting research around compulsory treatment in a non-democratic society is feasible, yet it is politically challenging and requires navigation between science and politics. We also demonstrate that engagement with the government decision makers in the research conception, implementation, and dissemination of the results increases the likelihood of research evidence being considered for change in a contentious drug policy area. CONCLUSIONS: Local empirical evidence on the comparative cost-effectiveness of CCT and MMT in a Southeast Asian setting is critical to consideration of more holistic, humane, and effective drug-dependence treatment approaches, but the garnering of such evidence is very challenging.Thu Vuong, Nhu Nguyen , Giang Le, Marian Shanahan, Robert Ali and Alison Ritte

A systematic review of modelling approaches in economic evaluations of health interventions for drug and alcohol problems

© 2016 Hoang et al. Background: The overarching goal of health policies is to maximize health and societal benefits. Economic evaluations can play a vital role in assessing whether or not such benefits occur. This paper reviews the application of modelling techniques in economic evaluations of drug and alcohol interventions with regard to (i) modelling paradigms themselves; (ii) perspectives of costs and benefits and (iii) time frame. Methods: Papers that use modelling approaches for economic evaluations of drug and alcohol interventions were identified by carrying out searches of major databases. Results: Thirty eight papers met the inclusion criteria. Overall, the cohort Markov models remain the most popular approach, followed by decision trees, Individual based model and System dynamics model (SD). Most of the papers adopted a long term time frame to reflect the long term costs and benefits of health interventions. However, it was fairly common among the reviewed papers to adopt a narrow perspective that only takes into account costs and benefits borne by the health care sector. Conclusions: This review paper informs policy makers about the availability of modelling techniques that can be used to enhance the quality of economic evaluations for drug and alcohol treatment interventions