Estimation of Conditional Power for Cluster-Randomized Trials with Interval-Censored Endpoints

Cluster-randomized trials (CRTs) of infectious disease preventions often yield correlated, interval-censored data: dependencies may exist between observations from the same cluster, and event occurrence may be assessed only at intermittent clinic visits. This data structure must be accounted for when conducting interim monitoring and futility assessment for CRTs. In this article, we propose a flexible framework for conditional power estimation when outcomes are correlated and interval-censored. Under the assumption that the survival times follow a shared frailty model, we first characterize the correspondence between the marginal and cluster-conditional survival functions, and then use this relationship to semiparametrically estimate the cluster-specific survival distributions from the available interim data. We incorporate assumptions about changes to the event process over the remainder of the trial---as well as estimates of the dependency among observations in the same cluster---to extend these survival curves through the end of the study. Based on these projected survival functions we generate correlated interval-censored observations, and then calculate the conditional power as the proportion of times (across multiple full-data generation steps) that the null hypothesis of no treatment effect is rejected. We evaluate the performance of the proposed method through extensive simulation studies, and illustrate its use on a large cluster-randomized HIV prevention trial

Transcranial Doppler Directed Dextran Therapy in the Prevention of Carotid Thrombosis: Three Hour Monitoring is as Effective as Six Hours

AbstractBackgroundsix hours» monitoring by transcranial Doppler (TCD) has been successful in directing Dextran therapy in patients at high risk of thrombotic stroke after carotid endarterectomy (CEA).Objectivesis 3 h of routine monitoring as effective as 6 h in the prevention of early postoperative thrombotic stroke?Designprospective, consecutive study in all patients with an accessible cranial window.Methodsone hundred and sixty-six patients undergoing CEA underwent 3 h of postoperative monitoring by TCD. Any patient with >25 emboli detected in any 10 min period or those with emboli that distorted the arterial waveform were commenced on an incremental infusion of dextran 40.Resultsthe majority of patients destined to embolise will do so within the first 2 postoperative hours. Dextran therapy was instituted in nine patients (5%) and rapidly controlled this phase of embolisation although the dose had to be increased in three (33%). No patient suffered a postoperative carotid thrombosis but one suffered a minor stroke on day 5 and was found to have profuse embolisation on TCD; high dose dextran therapy was again instituted, the embolus count rate fell rapidly and he made a good recovery thereafter. Overall, the death and disabling stroke rate was 1.2% and the death/any stroke rate was 2.4%.Conclusionthree hours of postoperative TCD monitoring is as effective as 6 h in the prevention of postoperative carotid thrombosis

Assortative social mixing and sex disparities in tuberculosis burden

Globally, men have higher tuberculosis (TB) burden but the mechanisms underlying this sex disparity are not fully understood. Recent surveys of social mixing patterns have established moderate preferential within-sex mixing in many settings. This assortative mixing could amplify differences from other causes. We explored the impact of assortative mixing and factors differentially affecting disease progression and detection using a sex-stratified deterministic TB transmission model. We explored the influence of assortativity at disease-free and endemic equilibria, finding stronger effects during invasion and on increasing male:female prevalence (M:F) ratios than overall prevalence. Variance-based sensitivity analysis of endemic equilibria identified differential progression as the most important driver of M:F ratio uncertainty. We fitted our model to prevalence and notification data in exemplar settings within a fully Bayesian framework. For our high M:F setting, random mixing reduced equilibrium M:F ratios by 12% (95% CrI 0–30%). Equalizing male case detection there led to a 20% (95% CrI 11–31%) reduction in M:F ratio over 10 years—insufficient to eliminate sex disparities. However, this potentially achievable improvement was associated with a meaningful 8% (95% CrI 4–14%) reduction in total TB prevalence over this time frame

Pulsed Power Accelerators at CEM-UT

An overview of four accelerator programs utilizing pulsed power is presented. The goals of each project, a description of the power supplies and launchers utilized and test results from each program are provided. The four projects presented illustrate a variety of uses for electromagnetic (EM) launchers and the potential advantages and disadvantages of four different launcher systems. Included in the paper are micrometeorite impact studies of 50 to 500 μm diameter glass beads accelerated up to 11 km/s with plasma armatures and 2.5- kg solid armature packages launched at 2.6 km/s (a record 8.1 MJ of muzzle energy). A compact rep-rateable augmented rail launcher and compulsator system weighing less than 1,100 kg is also described. Finally a skid mounted rep-rateable launcher system capable of providing 9 MJ of muzzle energy is discussed.Center for Electromechanic

Nonlinear hyperbolic systems: Non-degenerate flux, inner speed variation, and graph solutions

We study the Cauchy problem for general, nonlinear, strictly hyperbolic systems of partial differential equations in one space variable. First, we re-visit the construction of the solution to the Riemann problem and introduce the notion of a nondegenerate (ND) system. This is the optimal condition guaranteeing, as we show it, that the Riemann problem can be solved with finitely many waves, only; we establish that the ND condition is generic in the sense of Baire (for the Whitney topology), so that any system can be approached by a ND system. Second, we introduce the concept of inner speed variation and we derive new interaction estimates on wave speeds. Third, we design a wave front tracking scheme and establish its strong convergence to the entropy solution of the Cauchy problem; this provides a new existence proof as well as an approximation algorithm. As an application, we investigate the time-regularity of the graph solutions $(X,U)$ introduced by the second author, and propose a geometric version of our scheme; in turn, the spatial component $X$ of a graph solution can be chosen to be continuous in both time and space, while its component $U$ is continuous in space and has bounded variation in time.Comment: 74 page

Light-Weight Containment for High Energy, Rotating Machines

Developed a lightweight containment system for high-speed composite rotors. The containment device, consisting of a rotatable, composite structure, has been demonstrated to contain the high-energy release from a rotor burst event and is applicable to composite rotors for pulsed power applications. The most important aspect of this design is that the free-floating containment structure dissipates the major loads (radial, torque, and axial) encountered during the burst event, greatly reducing the loads that pass through the stator structure to its attachments. The design results in significant system-level weight savings for the entire rotating machine when compared to a system with an all-metallic containment. Of equal interest to the containment design, the experimental design and instrumentation was very challenging and resulted in significant lessons learned. This paper describes the containment system design, rotor burst test setup, instrumentation for measuring loads induced by the burst event, and a detailed explanation of the successful containment test results and conclusions.Center for Electromechanic

Progress on a gas-accepting ion source for continuous-flow accelerator mass spectrometry

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 259 (2007): 83-87, doi:10.1016/j.nimb.2007.01.189.A gas-accepting microwave-plasma ion source is being developed for continuous-flow Accelerator Mass Spectrometry (AMS). Characteristics of the ion source will be presented. Schemes for connecting a gas or liquid chromatograph to the ion source will also be discussed

Cutoff for the Ising model on the lattice

Introduced in 1963, Glauber dynamics is one of the most practiced and extensively studied methods for sampling the Ising model on lattices. It is well known that at high temperatures, the time it takes this chain to mix in $L^1$ on a system of size $n$ is $O(\log n)$. Whether in this regime there is cutoff, i.e. a sharp transition in the $L^1$-convergence to equilibrium, is a fundamental open problem: If so, as conjectured by Peres, it would imply that mixing occurs abruptly at $(c+o(1))\log n$ for some fixed $c>0$, thus providing a rigorous stopping rule for this MCMC sampler. However, obtaining the precise asymptotics of the mixing and proving cutoff can be extremely challenging even for fairly simple Markov chains. Already for the one-dimensional Ising model, showing cutoff is a longstanding open problem. We settle the above by establishing cutoff and its location at the high temperature regime of the Ising model on the lattice with periodic boundary conditions. Our results hold for any dimension and at any temperature where there is strong spatial mixing: For $\Z^2$ this carries all the way to the critical temperature. Specifically, for fixed $d\geq 1$, the continuous-time Glauber dynamics for the Ising model on $(\Z/n\Z)^d$ with periodic boundary conditions has cutoff at $(d/2\lambda_\infty)\log n$, where $\lambda_\infty$ is the spectral gap of the dynamics on the infinite-volume lattice. To our knowledge, this is the first time where cutoff is shown for a Markov chain where even understanding its stationary distribution is limited. The proof hinges on a new technique for translating $L^1$ to $L^2$ mixing which enables the application of log-Sobolev inequalities. The technique is general and carries to other monotone and anti-monotone spin-systems.Comment: 34 pages, 3 figure

Active Magnetic Bearings for Energy Storage Systems for Combat Vehicles

Advanced energy storage systems for electric guns and other pulsed weapons on combat vehicles present significant challenges for rotor bearing design, Active magnetic bearings (AMBs) present one emerging bearing option with major advantages in terms of lifetime and rotational speed, and also favorably integrate into high-speed flywheel systems. The Department of Defense Combat Hybrid Power Systems (CHPS) program serves as a case study for magnetic bearing applications on combat vehicles. The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed active magnetic bearing actuators for use in a 5 MW flywheel alternator with a 318 kg (700 lb), 20000 rpm rotor. To minimize CHPS flywheel size and mass, a topology was chosen in which the rotating portion of the flywheel is located outside the stationary components. Accordingly, magnetic bearing actuators are required which share this configuration. Because of inherent low loss and nearly linear force characteristics, UT-CEM has designed and analyzed permanent magnet bias bearing actuators for this application. To verify actuator performance, a nonrotating bearing test fixture was designed and built which permits measurement of static and dynamic force. An AMB control system was designed to provide robust, efficient magnetic levitation of the CHPS rotor over a wide range of operating speeds and disturbance inputs, while minimizing the occurrence of backup bearing touchdowns. This paper discusses bearing system requirements, actuator and controller design, and predicted performance; it also compares theoretical vs. measured actuator characteristicsCenter for Electromechanic

Transmission modeling to infer tuberculosis incidence prevalence and mortality in settings with generalized HIV epidemics

Tuberculosis (TB) killed more people globally than any other single pathogen over the past decade. Where surveillance is weak, estimating TB burden estimates uses modeling. In many African countries, increases in HIV prevalence and antiretroviral therapy have driven dynamic TB epidemics, complicating estimation of burden, trends, and potential intervention impact. We therefore develop a novel age-structured TB transmission model incorporating evolving demographic, HIV and antiretroviral therapy effects, and calibrate to TB prevalence and notification data from 12 African countries. We use Bayesian methods to include uncertainty for all TB model parameters, and estimate age-specific annual risks of TB infection, finding up to 16.0%/year in adults, and the proportion of TB incidence from recent (re)infection, finding a mean across countries of 34%. Rapid reduction of the unacceptably high burden of TB in high HIV prevalence settings will require interventions addressing progression as well as transmission