Estimating the causal effect of a time-varying treatment on time-to-event using structural nested failure time models

In this paper we review an approach to estimating the causal effect of a time-varying treatment on time to some event of interest. This approach is designed for the situation where the treatment may have been repeatedly adapted to patient characteristics, which themselves may also be time-dependent. In this situation the effect of the treatment cannot simply be estimated by conditioning on the patient characteristics, as these may themselves be indicators of the treatment effect. This so-called time-dependent confounding is typical in observational studies. We discuss a new class of failure time models, structural nested failure time models, which can be used to estimate the causal effect of a time-varying treatment, and present methods for estimating and testing the parameters of these models

Living IoT: A Flying Wireless Platform on Live Insects

Sensor networks with devices capable of moving could enable applications ranging from precision irrigation to environmental sensing. Using mechanical drones to move sensors, however, severely limits operation time since flight time is limited by the energy density of current battery technology. We explore an alternative, biology-based solution: integrate sensing, computing and communication functionalities onto live flying insects to create a mobile IoT platform. Such an approach takes advantage of these tiny, highly efficient biological insects which are ubiquitous in many outdoor ecosystems, to essentially provide mobility for free. Doing so however requires addressing key technical challenges of power, size, weight and self-localization in order for the insects to perform location-dependent sensing operations as they carry our IoT payload through the environment. We develop and deploy our platform on bumblebees which includes backscatter communication, low-power self-localization hardware, sensors, and a power source. We show that our platform is capable of sensing, backscattering data at 1 kbps when the insects are back at the hive, and localizing itself up to distances of 80 m from the access points, all within a total weight budget of 102 mg.Comment: Co-primary authors: Vikram Iyer, Rajalakshmi Nandakumar, Anran Wang, In Proceedings of Mobicom. ACM, New York, NY, USA, 15 pages, 201

Prevalence and clinical features of patients with concurrent HBsAg and anti‐HBs: Evaluation of the hepatitis B research network cohort

The prevalence of concurrent HBsAg and anti‐HBs in plasma of persons with chronic hepatitis B virus (HBV) infection is variable and its clinical significance enigmatic. We examined the prevalence and clinical and virological features of concurrent HBsAg and anti‐HBs in children and adults with chronic HBV infection living in North America. A total of 1462 HBsAg positive participants in the Hepatitis B Research Network paediatric and adult cohorts were included (median age 41 (range 4‐80) years, 48% female, 11% white, 13% black, 73% Asians). Only 18 (1.2%) were found to be anti‐HBs positive (≥10 mIU/mL) at initial study evaluation. Distributions of sex, race, HBV genotype and ALT were similar between participants with and without concurrent anti‐HBs. Those who were anti‐HBs positive appeared to be older (median age 50 vs 41 years, P = .06), have lower platelet counts (median 197 vs 222 × 103/mm3, P = .07) and have higher prevalence of HBeAg (44% vs 26%, P = .10). They also had lower HBsAg levels (median 2.0 vs 3.5 log10 IU/mL, P = .02). Testing of follow‐up samples after a median of 4 years (range 1‐6) in 12 of the 18 participants with initial concurrent anti‐HBs showed anti‐HBs became undetectable in 6, decreased to <10 mIU/mL in 1 and remained positive in 5 participants. Two patients lost HBsAg during follow‐up. In conclusion, prevalence of concurrent HBsAg and anti‐HBs was low at 1.2%, with anti‐HBs disappearing in some during follow‐up, in this large cohort of racially diverse children and adults with chronic HBV infection living in North America. Presence of concurrent HBsAg and anti‐HBs did not identify a specific phenotype of chronic hepatitis B, nor did it appear to affect clinical outcomes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156489/3/jvh13312.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156489/2/jvh13312-sup-0001-FigS1-S3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156489/1/jvh13312_am.pd

Semiclassical theory of electron drag in strong magnetic fields

We present a semiclassical theory for electron drag between two parallel two-dimensional electron systems in a strong magnetic field, which provides a transparent picture of the most salient qualitative features of anomalous drag phenomena observed in recent experiments, especially the striking sign reversal of drag at mismatched densities. The sign of the drag is determined by the curvature of the effective dispersion relation obeyed by the drift motion of the electrons in a smooth disorder potential. Localization plays a role in explaining activated low temperature behavior, but is not crucial for anomalous drag per se.Comment: 10 page

Induction of protective immunity against larval Onchocerca volvulus in a mouse model.

BALB/cBYJ mice were immunized against larval Onchocerca volvulus by subcutaneous injection of normal, irradiated, or freeze-thaw-killed Onchocerca sp. larvae. The mice received challenge infections of O. volvulus third-stage larva (L3) contained in diffusion chambers implanted subcutaneously. At two-weeks postinfection, the diffusion chambers were removed and larval survival was assessed. When mice were immunized a single time with 35-krad-irradiated or normal O. volvulus L3, there was a significant reduction in the survival of challenge parasites. However, there was little or no reduction in challenge worm survival when mice were immunized a single time with freeze-thaw-killed O. volvulus L3 or fourth-stage larva (L4), or irradiated O. lienalis L3. When a second dose of freeze-thaw killed O. volvulus L3 or irradiated O. lienalis L3 was administered, there was a significant reduction in parasite survival in immunized mice. Immunization with O. volvulus L4 or a combination of L3 and L4 failed to confer protection. These results demonstrate that mice can be immunized against larval O. volvulus and that diffusion chambers are an efficient method for studying protective immunity to this parasite in a mouse model

Different but overlapping populations of Strongyloides stercoralis in dogs and humans-Dogs as a possible source for zoonotic strongyloidiasis

Strongyloidiasis is a much-neglected soil born helminthiasis caused by the nematode Strongyloides stercoralis. Human derived S. stercoralis can be maintained in dogs in the laboratory and this parasite has been reported to also occur in dogs in the wild. Some authors have considered strongyloidiasis a zoonotic disease while others have argued that the two hosts carry host specialized populations of S. stercoralis and that dogs play a minor role, if any, as a reservoir for zoonotic S. stercoralis infections of humans. We isolated S. stercoralis from humans and their dogs in rural villages in northern Cambodia, a region with a high incidence of strongyloidiasis, and compared the worms derived from these two host species using nuclear and mitochondrial DNA sequence polymorphisms. We found that in dogs there exist two populations of S. stercoralis, which are clearly separated from each other genetically based on the nuclear 18S rDNA, the mitochondrial cox1 locus and whole genome sequence. One population, to which the majority of the worms belong, appears to be restricted to dogs. The other population is indistinguishable from the population of S. stercoralis isolated from humans. Consistent with earlier studies, we found multiple sequence variants of the hypervariable region I of the 18 S rDNA in S. stercoralis from humans. However, comparison of mitochondrial sequences and whole genome analysis suggest that these different 18S variants do not represent multiple genetically isolated subpopulations among the worms isolated from humans. We also investigated the mode of reproduction of the free-living generations of laboratory and wild isolates of S. stercoralis. Contrary to earlier literature on S. stercoralis but similar to other species of Strongyloides, we found clear evidence of sexual reproduction. Overall, our results show that dogs carry two populations, possibly different species of Strongyloides. One population appears to be dog specific but the other one is shared with humans. This argues for the strong potential of dogs as reservoirs for zoonotic transmission of S. stercoralis to humans and suggests that in order to reduce the exposure of humans to infective S. stercoralis larvae, dogs should be treated for the infection along with their owners