Iterative Approximate Consensus in the presence of Byzantine Link Failures

This paper explores the problem of reaching approximate consensus in synchronous point-to-point networks, where each directed link of the underlying communication graph represents a communication channel between a pair of nodes. We adopt the transient Byzantine link failure model [15, 16], where an omniscient adversary controls a subset of the directed communication links, but the nodes are assumed to be fault-free. Recent work has addressed the problem of reaching approximate consen- sus in incomplete graphs with Byzantine nodes using a restricted class of iterative algorithms that maintain only a small amount of memory across iterations [22, 21, 23, 12]. However, to the best of our knowledge, we are the first to consider approximate consensus in the presence of Byzan- tine links. We extend our past work that provided exact characterization of graphs in which the iterative approximate consensus problem in the presence of Byzantine node failures is solvable [22, 21]. In particular, we prove a tight necessary and sufficient condition on the underlying com- munication graph for the existence of iterative approximate consensus algorithms under transient Byzantine link model. The condition answers (part of) the open problem stated in [16].Comment: arXiv admin note: text overlap with arXiv:1202.609

Long-Distance Signals Are Required for Morphogenesis of the Regenerating Xenopus Tadpole Tail, as Shown by Femtosecond-Laser Ablation

tadpoles has recently emerged as an important model for these studies; we explored the role of the spinal cord during tadpole tail regeneration.Using ultrafast lasers to ablate cells, and Geometric Morphometrics to quantitatively analyze regenerate morphology, we explored the influence of different cell populations. For at least twenty-four hours after amputation (hpa), laser-induced damage to the dorsal midline affected the morphology of the regenerated tail; damage induced 48 hpa or later did not. Targeting different positions along the anterior-posterior (AP) axis caused different shape changes in the regenerate. Interestingly, damaging two positions affected regenerate morphology in a qualitatively different way than did damaging either position alone. Quantitative comparison of regenerate shapes provided strong evidence against a gradient and for the existence of position-specific morphogenetic information along the entire AP axis.We infer that there is a conduit of morphology-influencing information that requires a continuous dorsal midline, particularly an undamaged spinal cord. Contrary to expectation, this information is not in a gradient and it is not localized to the regeneration bud. We present a model of morphogenetic information flow from tissue undamaged by amputation and conclude that studies of information coming from far outside the amputation plane and regeneration bud will be critical for understanding regeneration and for translating fundamental understanding into biomedical approaches

Usability of a barcode scanning system as a means of data entry on a PDA for self-report health outcome questionnaires: a pilot study in individuals over 60 years of age

BACKGROUND: Throughout the medical and paramedical professions, self-report health status questionnaires are used to gather patient-reported outcome measures. The objective of this pilot study was to evaluate in individuals over 60 years of age the usability of a PDA-based barcode scanning system with a text-to-speech synthesizer to collect data electronically from self-report health outcome questionnaires. METHODS: Usability of the system was tested on a sample of 24 community-living older adults (7 men, 17 women) ranging in age from 63 to 93 years. After receiving a brief demonstration on the use of the barcode scanner, participants were randomly assigned to complete two sets of 16 questions using the bar code wand scanner for one set and a pen for the other. Usability was assessed using directed interviews with a usability questionnaire and performance-based metrics (task times, errors, sources of errors). RESULTS: Overall, participants found barcode scanning easy to learn, easy to use, and pleasant. Participants were marginally faster in completing the 16 survey questions when using pen entry (20/24 participants). The mean response time with the barcode scanner was 31 seconds longer than traditional pen entry for a subset of 16 questions (p = 0.001). The responsiveness of the scanning system, expressed as first scan success rate, was less than perfect, with approximately one-third of first scans requiring a rescan to successfully capture the data entry. The responsiveness of the system can be explained by a combination of factors such as the location of the scanning errors, the type of barcode used as an answer field in the paper version, and the optical characteristics of the barcode scanner. CONCLUSION: The results presented in this study offer insights regarding the feasibility, usability and effectiveness of using a barcode scanner with older adults as an electronic data entry method on a PDA. While participants in this study found their experience with the barcode scanning system enjoyable and learned to become proficient in its use, the responsiveness of the system constitutes a barrier to wide-scale use of such a system. Optimizing the graphical presentation of the information on paper should significantly increase the system's responsiveness

Deterministic diffusion fiber tracking improved by quantitative anisotropy

Diffusion MRI tractography has emerged as a useful and popular tool for mapping connections between brain regions. In this study, we examined the performance of quantitative anisotropy (QA) in facilitating deterministic fiber tracking. Two phantom studies were conducted. The first phantom study examined the susceptibility of fractional anisotropy (FA), generalized factional anisotropy (GFA), and QA to various partial volume effects. The second phantom study examined the spatial resolution of the FA-aided, GFA-aided, and QA-aided tractographies. An in vivo study was conducted to track the arcuate fasciculus, and two neurosurgeons blind to the acquisition and analysis settings were invited to identify false tracks. The performance of QA in assisting fiber tracking was compared with FA, GFA, and anatomical information from T 1-weighted images. Our first phantom study showed that QA is less sensitive to the partial volume effects of crossing fibers and free water, suggesting that it is a robust index. The second phantom study showed that the QA-aided tractography has better resolution than the FA-aided and GFA-aided tractography. Our in vivo study further showed that the QA-aided tractography outperforms the FA-aided, GFA-aided, and anatomy-aided tractographies. In the shell scheme (HARDI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 30.7%, 32.6%, and 24.45% of the false tracks, respectively, while the QA-aided tractography has 16.2%. In the grid scheme (DSI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 12.3%, 9.0%, and 10.93% of the false tracks, respectively, while the QA-aided tractography has 4.43%. The QA-aided deterministic fiber tracking may assist fiber tracking studies and facilitate the advancement of human connectomics. © 2013 Yeh et al

Improving Fecal Occult Blood Testing Compliance Using a Mailed Educational Reminder

Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths in the United States. Randomized controlled trials have shown that annual screening fecal occult blood testing (FOBT) reduces CRC mortality and incidence. However, patient compliance with FOBT is low. To determine whether a mailed educational reminder increases FOBT card return rates and to examine predictors of FOBT compliance. Blinded, randomized, controlled trial at the Veteran Affairs Medical Center, San Diego, California. Seven hundred and seventy-five consecutive patients ≥50 years of age referred by their primary care physicians for FOBT. Patients were randomly assigned to the usual care group or the intervention group. Ten days after picking up the FOBT cards, a 1-page reminder with information related to CRC screening was mailed to the intervention group only. The primary outcome was proportion of returned FOBT cards after 6 months. Patient demographic, clinical characteristics and prior FOBT completed were collected for multivariate regression analysis. At 6 months after card distribution, 64.6% of patients in the intervention group returned cards compared with 48.4% in the control group (P < 0.001). Patients who received a mailed reminder (OR 2.02; 95% CI: 1.48–2.74) or have a prior history of returning the FOBT cards (OR 1.87; 95% CI: 1.29–2.70) were more likely to return the FOBT cards. Patients with current or recent illicit drug use were less likely to return the FOBT cards (OR 0.26; 95% CI: 0.13–0.50). A simple mailed educational reminder significantly increases compliance with FOBT for CRC screening

Exposure to arsenic in drinking water is associated with increased prevalence of diabetes: a cross-sectional study in the Zimapán and Lagunera regions in Mexico

<p>Abstract</p> <p>Background</p> <p>Human exposures to inorganic arsenic (iAs) have been linked to an increased risk of diabetes mellitus. Recent laboratory studies showed that methylated trivalent metabolites of iAs may play key roles in the diabetogenic effects of iAs. Our study examined associations between chronic exposure to iAs in drinking water, metabolism of iAs, and prevalence of diabetes in arsenicosis-endemic areas of Mexico.</p> <p>Methods</p> <p>We used fasting blood glucose (FBG), fasting plasma insulin (FPI), oral glucose tolerance test (OGTT), glycated hemoglobin (HbA1c), and insulin resistance (HOMA-IR) to characterize diabetic individuals. Arsenic levels in drinking water and urine were determined to estimate exposure to iAs. Urinary concentrations of iAs and its trivalent and pentavalent methylated metabolites were measured to assess iAs metabolism. Associations between diabetes and iAs exposure or urinary metabolites of iAs were estimated by logistic regression with adjustment for age, sex, hypertension and obesity.</p> <p>Results</p> <p>The prevalence of diabetes was positively associated with iAs in drinking water (OR 1.13 per 10 ppb, p < 0.01) and with the concentration of dimethylarsinite (DMAs^III) in urine (OR 1.24 per inter-quartile range, p = 0.05). Notably, FPI and HOMA-IR were negatively associated with iAs exposure (β -2.08 and -1.64, respectively, p < 0.01), suggesting that the mechanisms of iAs-induced diabetes differ from those underlying type-2 diabetes, which is typically characterized by insulin resistance.</p> <p>Conclusions</p> <p>Our study confirms a previously reported, but frequently questioned, association between exposure to iAs and diabetes, and is the first to link the risk of diabetes to the production of one of the most toxic metabolites of iAs, DMAs^III.</p