Using Read-k Inequalities to Analyze a Distributed MIS Algorithm

Until recently, the fastest distributed MIS algorithm, even for simple graphs, e.g., unoriented trees has been the simple randomized algorithm discovered the 80s. This algorithm (commonly called Luby's algorithm) computes an MIS in $O(\log n)$ rounds (with high probability). This situation changed when Lenzen and Wattenhofer (PODC 2011) presented a randomized $O(\sqrt{\log n}\cdot \log\log n)$-round MIS algorithm for unoriented trees. This algorithm was improved by Barenboim et al. (FOCS 2012), resulting in an $O(\sqrt{\log n \cdot \log\log n})$-round MIS algorithm. The analyses of these tree MIS algorithms depends on "near independence" of probabilistic events, a feature of the tree structure of the network. In their paper, Lenzen and Wattenhofer hope that their algorithm and analysis could be extended to graphs with bounded arboricity. We show how to do this. By using a new tail inequality for read-k families of random variables due to Gavinsky et al. (Random Struct Algorithms, 2015), we show how to deal with dependencies induced by the recent tree MIS algorithms when they are executed on bounded arboricity graphs. Specifically, we analyze a version of the tree MIS algorithm of Barenboim et al. and show that it runs in O(\mbox{poly}(\alpha) \cdot \sqrt{\log n \cdot \log\log n}) rounds in the $\mathcal{CONGEST}$ model for graphs with arboricity $\alpha$. While the main thrust of this paper is the new probabilistic analysis via read-$k$ inequalities, for small values of $\alpha$, this algorithm is faster than the bounded arboricity MIS algorithm of Barenboim et al. We also note that recently (SODA 2016), Gaffari presented a novel MIS algorithm for general graphs that runs in $O(\log \Delta) + 2^{O(\sqrt{\log\log n})}$ rounds; a corollary of this algorithm is an $O(\log \alpha + \sqrt{\log n})$-round MIS algorithm on arboricity-$\alpha$ graphs.Comment: To appear in PODC 2016 as a brief announcemen

The Complexity of Symmetry Breaking in Massive Graphs

The goal of this paper is to understand the complexity of symmetry breaking problems, specifically maximal independent set (MIS) and the closely related beta-ruling set problem, in two computational models suited for large-scale graph processing, namely the k-machine model and the graph streaming model. We present a number of results. For MIS in the k-machine model, we improve the O~(m/k^2 + Delta/k)-round upper bound of Klauck et al. (SODA 2015) by presenting an O~(m/k^2)-round algorithm. We also present an Omega~(n/k^2) round lower bound for MIS, the first lower bound for a symmetry breaking problem in the k-machine model. For beta-ruling sets, we use hierarchical sampling to obtain more efficient algorithms in the k-machine model and also in the graph streaming model. More specifically, we obtain a k-machine algorithm that runs in O~(beta n Delta^{1/beta}/k^2) rounds and, by using a similar hierarchical sampling technique, we obtain one-pass algorithms for both insertion-only and insertion-deletion streams that use O(beta * n^{1+1/2^{beta-1}}) space. The latter result establishes a clear separation between MIS, which is known to require Omega(n^2) space (Cormode et al., ICALP 2019), and beta-ruling sets, even for beta = 2. Finally, we present an even faster 2-ruling set algorithm in the k-machine model, one that runs in O~(n/k^{2-epsilon} + k^{1-epsilon}) rounds for any epsilon, 0 <=epsilon <=1. For a wide range of values of k this round complexity simplifies to O~(n/k^2) rounds, which we conjecture is optimal. Our results use a variety of techniques. For our upper bounds, we prove and use simulation theorems for beeping algorithms, hierarchical sampling, and L_0-sampling, whereas for our lower bounds we use information-theoretic arguments and reductions to 2-party communication complexity problems

Symmetry Breaking in the Congest Model:Time- and Message-Efficient Algorithms for Ruling Sets

We study local symmetry breaking problems in the CONGEST model, focusing on ruling set problems, which generalize the fundamental Maximal Independent Set (MIS) problem. A $\beta$-ruling set is an independent set such that every node in the graph is at most $\beta$ hops from a node in the independent set. Our work is motivated by the following central question: can we break the $\Theta(\log n)$ time complexity barrier and the $\Theta(m)$ message complexity barrier in the CONGEST model for MIS or closely-related symmetry breaking problems? We present the following results: - Time Complexity: We show that we can break the $O(\log n)$ "barrier" for 2- and 3-ruling sets. We compute 3-ruling sets in $O\left(\frac{\log n}{\log \log n}\right)$ rounds with high probability (whp). More generally we show that 2-ruling sets can be computed in $O\left(\log \Delta \cdot (\log n)^{1/2 + \varepsilon} + \frac{\log n}{\log\log n}\right)$ rounds for any $\varepsilon > 0$, which is $o(\log n)$ for a wide range of $\Delta$ values (e.g., $\Delta = 2^{(\log n)^{1/2-\varepsilon}}$). These are the first 2- and 3-ruling set algorithms to improve over the $O(\log n)$-round complexity of Luby's algorithm in the CONGEST model. - Message Complexity: We show an $\Omega(n^2)$ lower bound on the message complexity of computing an MIS (i.e., 1-ruling set) which holds also for randomized algorithms and present a contrast to this by showing a randomized algorithm for 2-ruling sets that, whp, uses only $O(n \log^2 n)$ messages and runs in $O(\Delta \log n)$ rounds. This is the first message-efficient algorithm known for ruling sets, which has message complexity nearly linear in $n$ (which is optimal up to a polylogarithmic factor)

Patterns of coronary artery vessel disease on diagnostic angiography in a south asian population

Objective: The objective was to establish patterns of diseased vessels amongst the study population.Methodology: This retrospective descriptive study analyzed the data of 396 patients who underwent diagnostic angiographies at a large tertiary care public hospital in Islamabad, from January-2018 till October 2018. All data was coded and recorded in SPSS and was quantitatively run to find percentages and tests of significance were done.Results: We found that single vessel disease was the most common at 31.6%, and that the left anterior descending was the most commonly involved vessel with the most significant coronary artery disease, 86.6% and 71.4% respectively. Conclusion: Hypertension and diabetes has a great burden on our South Asian population and contribution to the development of coronary artery disease. Severe disease present in one vessel should alert physicians to the possibility of multi-vessel involvement and multi vessel progression in the disease progress.&nbsp; Delineation of the vessel involvement pattern in South Asians forms the basis for formulating local guidelines and strategies for tackling coronary artery disease.Keywords: Angiography, CAD, patterns

Enhancement of Solar PV Hosting Capacity in a Remote Industrial Microgrid: A Methodical Techno-Economic Approach

To meet the zero-carbon electricity generation target as part of the sustainable development goals (SDG7), remote industrial microgrids worldwide are considering the uptake of more and more renewable energy resources, especially solar PV systems. Estimating the grid PV hosting capacity plays an essential role in designing and planning such microgrids. PV hosting capacity assessment determines the maximum PV capacity suitable for the grid and the appropriate electrical location for PV placement. This research reveals that conventional static criteria to assess the PV hosting capacity fail to ensure the grid&rsquo;s operational robustness. It hence demands a reduction in the theoretical hosting capacity estimation to ensure grid compatible post-fault voltage and frequency recovery. Energy storage technologies, particularly fast-responsive batteries, can potentially prevent such undesirable scenarios; nevertheless, careful integration is required to ensure an affordable cost of energy. This study proposes a novel methodical techno-economic approach for an off-grid remote industrial microgrid to enhance the PV hosting capacity by integrating battery energy storage considering grid disturbance and recovery scenarios. The method has been validated in an industrial microgrid with a 2.6 MW peak demand in a ready-made garment (RMG) factory having a distinctive demand pattern and unique constraints in remote Bangladesh. According to the analysis, integrating 2.5 MW of PV capacity and a 1.2 MVA battery bank to offset existing diesel and grid consumption would result in an energy cost of BDT 14.60 per kWh (USD 0.1719 per kWh). For high PV penetration scenarios, the application of this method offers higher system robustness, and the financial analysis indicates that the industries would not only benefit from positive environmental impact but also make an economic profit

Association between proton pump inhibitor therapy and clostridium difficile infection: a contemporary systematic review and meta-analysis.

Abstract Introduction Emerging epidemiological evidence suggests that proton pump inhibitor (PPI) acid-suppression therapy is associated with an increased risk of Clostridium difficile infection (CDI). Methods Ovid MEDLINE, EMBASE, ISI Web of Science, and Scopus were searched from 1990 to January 2012 for analytical studies that reported an adjusted effect estimate of the association between PPI use and CDI. We performed random-effect meta-analyses. We used the GRADE framework to interpret the findings. Results We identified 47 eligible citations (37 case-control and 14 cohort studies) with corresponding 51 effect estimates. The pooled OR was 1.65, 95% CI (1.47, 1.85), I2 = 89.9%, with evidence of publication bias suggested by a contour funnel plot. A novel regression based method was used to adjust for publication bias and resulted in an adjusted pooled OR of 1.51 (95% CI, 1.26–1.83). In a speculative analysis that assumes that this association is based on causality, and based on published baseline CDI incidence, the risk of CDI would be very low in the general population taking PPIs with an estimated NNH of 3925 at 1 year. Conclusions In this rigorously conducted systemic review and meta-analysis, we found very low quality evidence (GRADE class) for an association between PPI use and CDI that does not support a cause-effect relationship

The prevalence of developmental dysplasia of the hip in idiopathic clubfoot: a systematic review and meta-analysis.

Purpose Developmental dysplasia of the hip (DDH) and idiopathic clubfoot are both common paediatric orthopaedic conditions. There is conflicting evidence in the literature as to whether the prevalence of DDH is higher in children with idiopathic clubfoot. The aim of our study was to systematically review the literature and determine the prevalence of DDH in idiopathic clubfoot. Methods We searched several databases from 1946 to 2014 for observational studies that reported the prevalence of DDH in idiopathic clubfoot. We performed a meta-analysis using random effects model to pool the prevalence of DDH in idiopathic clubfoot. We also investigated the imaging modality utilised to diagnose and treat DDH in idiopathic clubfoot. Descriptive, quantitative and qualitative data were extracted. Results Twelve studies (ten case series, one retrospective cohort and one retrospective case–control) were eligible for the meta-analysis, with a total of 2,549 children with idiopathic clubfoot including 83 with DDH. The pooled prevalence estimate of DDH in children with idiopathic clubfoot was 4.1 % (95 % CI, 2.1–7.7 %). There was a substantial amount of between study heterogeneity (I 2 = 87.1 %, p < 0.001) due to variability between studies rather than chance variability. Sensitivity analyses showed that the pooled prevalence estimate was 3.5 % (95 % CI, 1.1–10.8 %) and 3.8 % (95 % CI, 1.0–13.7 %) for studies utilising ultrasound as the imaging modality of diagnosis and treatment with a Pavlik harness respectively. Conclusions The overall pooled prevalence of DDH in idiopathic clubfoot is similar to the normal population. The cumulative evidence at present does not indicate an association between DDH and idiopathic clubfoot. Therefore, we do not recommend routine screening for DDH in children with idiopathic clubfoot. However, future retrospective and/or prospective cohort studies of better quality will be able to answer this question with more certainty

Avascular Necrosis and time to surgery for unstable slipped capital femoral epiphysis: a systematic review and meta-analysis

Background: Avascular necrosis (AVN) is a well-known complication of unstable slipped capital femoral epiphysis (SCFE) and its cause is multifactorial. Higher AVN rates have been reported with surgery undertaken between 24 hours to 7 days from the onset of symptoms. The current evidence regarding time to surgery and AVN rate remains unclear. The aim of our study was to investigate the rate of AVN and time to surgery in unstable SCFE. Methods: A literature search of several databases was conducted. Eligibility criteria included all studies that reported AVN rates and time to surgery in unstable SCFE patients. We performed a meta-analysis using a random-effects model to pool the rate of AVN in unstable SCFE using different time to surgery subgroups (≤24 h, 24 h - 7 d and >7 d). Descriptive, quantitative and qualitative data were extracted. Results: Twelve studies matched our eligibility criteria. In total, there were 434 unstable SCFE of which 244 underwent closed reduction (CR). The pooled AVN rates were 24% [95% CI: 16%-35%] and 29% [95% CI: 16%-45%] for the total and CR groups, respectively. The highest AVN rates were with surgery between 24 hours to 7 days, 42% and 54% for the total and CR groups, respectively. The lowest rates of AVN were with time to surgery ≤24 hours (22% and 21% respectively) and >7 days (18% and 29% respectively). These differences were not statistically significant. There was significant subgroup heterogeneity which was highest in the 24 hours - 7 days subgroup and lowest in the >7 days subgroup. Conclusions: The cumulative evidence was not conclusive for an association between AVN rate and time to surgery. The overall AVN rates were lower in unstable SCFE patients who had surgery ≤24 hours and >7 days. However, treatment techniques were very variable and there was significant heterogeneity in the included studies. Multi-centre prospective studies are required with well-defined time to surgery outcomes. Level of Evidence: Level III/IV

Constrained Optimization-Based Extreme Learning Machines with Bagging for Freezing of Gait Detection

The Internet-of-Things (IoT) is a paradigm shift from slow and manual approaches to fast and automated systems. It has been deployed for various use-cases and applications in recent times. There are many aspects of IoT that can be used for the assistance of elderly individuals. In this paper, we detect the presence or absence of freezing of gait in patients suffering from Parkinson&rsquo;s disease (PD) by using the data from body-mounted acceleration sensors placed on the legs and hips of the patients. For accurate detection and estimation, constrained optimization-based extreme learning machines (C-ELM) have been utilized. Moreover, in order to enhance the accuracy even further, C-ELM with bagging (C-ELMBG) has been proposed, which uses the characteristics of least squares support vector machines. The experiments have been carried out on the publicly available Daphnet freezing of gait dataset to verify the feasibility of C-ELM and C-ELMBG. The simulation results show an accuracy above 90% for both methods. A detailed comparison with other state-of-the-art statistical learning algorithms such as linear discriminate analysis, classification and regression trees, random forest and state vector machines is also presented where C-ELM and C-ELMBG show better performance in all aspects, including accuracy, sensitivity, and specificity