368,505 research outputs found
Cooperative Interval Games Arising from Airport Situations with Interval Data
No full textThis paper deals with the research area of cooperative interval games arising from airport situations with interval data. We also extend to airport interval games some results from classical theory.cooperative interval games;concave games;airport games;cost games;interval data
Geoadditive hazard regression for interval censored survival times
No full textThe Cox proportional hazards model is the most commonly used method when analyzing the impact of covariates on continuous survival times. In its classical form, the Cox model was introduced in the setting of right-censored observations. However, in practice other sampling schemes are frequently encountered and therefore extensions allowing for interval and left censoring or left truncation are clearly desired. Furthermore, many applications require a more flexible modeling of covariate information than the usual linear predictor. For example, effects of continuous covariates are likely to be of nonlinear form or spatial information is to be included appropriately. Further extensions should allow for time-varying effects of covariates or covariates that are themselves time-varying. Such models relax the assumption of proportional hazards. We propose a regression model for the hazard rate that combines and extends the above-mentioned features on the basis of a unifying Bayesian model formulation. Nonlinear and time-varying effects as well as the baseline hazard rate are modeled by penalized splines. Spatial effects can be included based on either Markov random fields or stationary Gaussian random fields. The model allows for arbitrary combinations of left, right and interval censoring as well as left truncation. Estimation is based on a reparameterisation of the model as a variance components mixed model. The variance parameters corresponding to inverse smoothing parameters can then be estimated based on an approximate marginal likelihood approach. As an application we present an analysis on childhood mortality in Nigeria, where the interval censoring framework also allows to deal with the problem of heaped survival times caused by memory effects. In a simulation study we investigate the effect of ignoring the impact of interval censored observations
Specification and Prototyping of Structured Multimedia Documents using Interval Temporal Logic
No full textThis paper explores a formalism for describing a wide class of multimedia document constraints. The formalism is based on an interval temporal logic. We describe the requirements on temporal logic specification that arise from the multimedia documents application area. In particular, we highlight a canonical document example. Then we present the temporal logic formalism that we use. This formalism extends existing interval temporal logic with a number of new features: actions, framing of actions, past operators, a projection-like operator called filter and a new handling of interval length. A model theory and satisfaction relation is defined for the notation and a specification of the canonical example is presented
Genetic association study of QT interval highlights role for calcium signaling pathways in myocardial repolarization.
No full textThe QT interval, an electrocardiographic measure reflecting myocardial repolarization, is a heritable trait. QT prolongation is a risk factor for ventricular arrhythmias and sudden cardiac death (SCD) and could indicate the presence of the potentially lethal mendelian long-QT syndrome (LQTS). Using a genome-wide association and replication study in up to 100,000 individuals, we identified 35 common variant loci associated with QT interval that collectively explain ∼8-10% of QT-interval variation and highlight the importance of calcium regulation in myocardial repolarization. Rare variant analysis of 6 new QT interval-associated loci in 298 unrelated probands with LQTS identified coding variants not found in controls but of uncertain causality and therefore requiring validation. Several newly identified loci encode proteins that physically interact with other recognized repolarization proteins. Our integration of common variant association, expression and orthogonal protein-protein interaction screens provides new insights into cardiac electrophysiology and identifies new candidate genes for ventricular arrhythmias, LQTS and SCD
Solving the linear interval tolerance problem for weight initialization of neural networks
No full textDetermining good initial conditions for an algorithm used to train a neural network is considered a parameter estimation problem dealing with uncertainty about the initial weights. Interval Analysis approaches model uncertainty in parameter estimation problems using intervals and formulating tolerance problems. Solving a tolerance problem is defining lower and upper bounds of the intervals so that the system functionality is guaranteed within predefined limits. The aim of this paper is to show how the problem of determining the initial weight intervals of a neural network can be defined in terms of solving a linear interval tolerance problem. The proposed Linear Interval Tolerance Approach copes with uncertainty about the initial weights without any previous knowledge or specific assumptions on the input data as required by approaches such as fuzzy sets or rough sets. The proposed method is tested on a number of well known benchmarks for neural networks trained with the back-propagation family of algorithms. Its efficiency is evaluated with regards to standard performance measures and the results obtained are compared against results of a number of well known and established initialization
methods. These results provide credible evidence that the proposed method outperforms classical weight initialization methods
Novel genes for QTc interval. How much heritability is explained, and how much is left to find?
No full textThe corrected QT (QTc) interval is a complex quantitative trait, believed to be influenced by several genetic and environmental factors. It is a strong prognostic indicator of cardiovascular mortality in patients with and without cardiac disease. More than 700 mutations have been described in 12 genes (LQT1-LQT12) involved in congenital long QT syndrome. However, the heritability (genetic contribution) of QTc interval in the general population cannot be adequately explained by these long QT syndrome genes. In order to further investigate the genetic architecture underlying QTc interval in the general population, genome-wide association studies, in which up to one million single nucleotide polymorphisms are assayed in thousands of individuals, are now being employed and have already led to the discovery of variants in seven novel loci and five loci that are known to cause congenital long or short QT syndrome. Here we show that a combined risk score using 11 of these loci explains about 10% of the heritability of QTc. Additional discovery of both common and rare variants will yield further etiological insight and accelerate clinical applications
Genome-Wide Association Studies of the PR Interval in African Americans
No full textThe PR interval on the electrocardiogram reflects atrial and atrioventricular nodal conduction time. The PR interval is heritable, provides important information about arrhythmia risk, and has been suggested to differ among human races. Genome-wide association (GWA) studies have identified common genetic determinants of the PR interval in individuals of European and Asian ancestry, but there is a general paucity of GWA studies in individuals of African ancestry. We performed GWA studies in African American individuals from four cohorts (n = 6,247) to identify genetic variants associated with PR interval duration. Genotyping was performed using the Affymetrix 6.0 microarray. Imputation was performed for 2.8 million single nucleotide polymorphisms (SNPs) using combined YRI and CEU HapMap phase II panels. We observed a strong signal (rs3922844) within the gene encoding the cardiac sodium channel (SCN5A) with genome-wide significant association (p 10(-8)) in two of the four cohorts and in the meta-analysis. The signal explained 2% of PR interval variability in African Americans (beta = 5.1 msec per minor allele, 95% CI = 4.1-6.1, p = 3 x 10(-23)). This SNP was also associated with PR interval (beta = 2.4 msec per minor allele, 95% CI = 1.8-3.0, p = 3 x 10(-16)) in individuals of European ancestry (n = 14,042), but with a smaller effect size (p for heterogeneity < 0.001) and variability explained (0.5%). Further meta-analysis of the four cohorts identified genome-wide significant associations with SNPs in SCN10A (rs6798015), MEIS1 (rs10865355), and TBX5 (rs7312625) that were highly correlated with SNPs identified in European and Asian GWA studies. African ancestry was associated with increased PR duration (13.3 msec, p = 0.009) in one but not the other three cohorts. Our findings demonstrate the relevance of common variants to African Americans at four loci previously associated with PR interval in European and Asian samples and identify an association signal at one of these loci that is more strongly associated with PR interval in African Americans than in Europeans
A least squares approach to Principal Component Analysis for interval valued data
No full textPrincipal Component Analysis (PCA) is a well known technique the aim of which is to synthesize huge amounts of numerical data by means of a low number of unobserved variables, called components. In this paper, an extension of PCA to deal with interval valued data is proposed. The method, called Midpoint Radius Principal Component Analysis (MR-PCA) recovers the underlying structure of interval valued data by using both the midpoints (or centers) and the radii (a measure of the interval width) information. In order to analyze how MR-PCA works, the results of a simulation study and two applications on chemical data are proposed.Principal Component Analysis, Least squares approach, Interval valued data, Chemical data
The Study of Interval between Onset of the Clinical Symptoms and Streptokinase Receiving in Patients with Acute Myocardial Infarction
No full textBackground & Objectives: Myocardial infarction is one of the most common causes of mortality throughout the world. Utilization of thrombolytic drugs at the first hours upon MI leads to decrease in the rate of mortality. Streptokinase (SK) is commonly used because of its cost and availability. The golden time for maximum effect of SK appeared to be first hours after MI. The drug efficiency diminishes after 3 hours and it will be ineffective after 12 hours.
This study was aimed to investigate interval between onset of the clinical symptoms and streptokinase receiving in patients with acute myocardial infarction admitted for drug reception.
Methods: This cross-sectional study was conducted in 150 patients with STEMI (ST elevation Myocardial Infarction) who were attended to emergency room of Imam Khomeini hospital and fulfilled a questionnaire containing the data about age, sex, educational level, onset of symptoms, referring time to emergency room, SK utilization, past medical history of cardiac diseases, type and location of AMI, contraindications and side effects of SK.
Results: In 111 men (74%) and 39 women (26%), the mean for interval between onset of symptoms and drug injection was 8 hour and 27 minutes ± 8 hour and 18 minutes .Only 41% of patients received streptokinase in less than 3 hours after chest pain. The main reasons for delaying in drug consumption were delayed decision to come to hospital in 61% of persons, long distance to hospital for 22% of individuals, delayed admission tor CCU for 13% of cases and delay in physician diagnosis for 0.043% of patients. To have a male sex and residency in city where the hospital was establilished were associated with less-delayed treatment start. However, the educational level, age and history of MI were not correlated with onset of treatment.
Conclusions: Our results clearly show that the majority of patients receipt streptokinase more than 3 hours after chest pain. With considering the factors associated with delay to receive SK, teaching the patients with ischemic heart disease and giving information about golden time for thrombolytic therapy and its effect in prognosis as well as extending cardiac disease treatment centers in suburbs are recommended
A semi-Markov model for stroke with piecewise-constant hazards in the presence of left, right and interval censoring.
No full textThis paper presents a parametric method of fitting semi-Markov models with piecewise-constant hazards in the presence of left, right and interval censoring. We investigate transition intensities in a three-state illness-death model with no recovery. We relax the Markov assumption by adjusting the intensity for the transition from state 2 (illness) to state 3 (death) for the time spent in state 2 through a time-varying covariate. This involves the exact time of the transition from state 1 (healthy) to state 2. When the data are subject to left or interval censoring, this time is unknown. In the estimation of the likelihood, we take into account interval censoring by integrating out all possible times for the transition from state 1 to state 2. For left censoring, we use an Expectation-Maximisation inspired algorithm. A simulation study reflects the performance of the method. The proposed combination of statistical procedures provides great flexibility. We illustrate the method in an application by using data on stroke onset for the older population from the UK Medical Research Council Cognitive Function and Ageing Study
- …
