A Semiparametric Marginalized Model for Longitudinal Data with Informative Dropout
Directory of Open Access Journals (Sweden)
Mengling Liu
2012-01-01
Full Text Available We propose a marginalized joint-modeling approach for marginal inference on the association between longitudinal responses and covariates when longitudinal measurements are subject to informative dropouts. The proposed model is motivated by the idea of linking longitudinal responses and dropout times by latent variables while focusing on marginal inferences. We develop a simple inference procedure based on a series of estimating equations, and the resulting estimators are consistent and asymptotically normal with a sandwich-type covariance matrix ready to be estimated by the usual plug-in rule. The performance of our approach is evaluated through simulations and illustrated with a renal disease data application.
Performance of nonlinear mixed effects models in the presence of informative dropout.
Björnsson, Marcus A; Friberg, Lena E; Simonsson, Ulrika S H
2015-01-01
Informative dropout can lead to bias in statistical analyses if not handled appropriately. The objective of this simulation study was to investigate the performance of nonlinear mixed effects models with regard to bias and precision, with and without handling informative dropout. An efficacy variable and dropout depending on that efficacy variable were simulated and model parameters were reestimated, with or without including a dropout model. The Laplace and FOCE-I estimation methods in NONMEM 7, and the stochastic simulations and estimations (SSE) functionality in PsN, were used in the analysis. For the base scenario, bias was low, less than 5% for all fixed effects parameters, when a dropout model was used in the estimations. When a dropout model was not included, bias increased up to 8% for the Laplace method and up to 21% if the FOCE-I estimation method was applied. The bias increased with decreasing number of observations per subject, increasing placebo effect and increasing dropout rate, but was relatively unaffected by the number of subjects in the study. This study illustrates that ignoring informative dropout can lead to biased parameters in nonlinear mixed effects modeling, but even in cases with few observations or high dropout rate, the bias is relatively low and only translates into small effects on predictions of the underlying effect variable. A dropout model is, however, crucial in the presence of informative dropout in order to make realistic simulations of trial outcomes.
Ye, Cheng; Biswas, Gautam
2014-01-01
Our project is motivated by the early dropout and low completion rate problem in MOOCs. We have extended traditional features for MOOC analysis with richer and higher granularity information to make more accurate predictions of dropout and performance. The results show that finer-grained temporal information increases the predictive power in the…
Chan, Jennifer S K
2016-05-01
Dropouts are common in longitudinal study. If the dropout probability depends on the missing observations at or after dropout, this type of dropout is called informative (or nonignorable) dropout (ID). Failure to accommodate such dropout mechanism into the model will bias the parameter estimates. We propose a conditional autoregressive model for longitudinal binary data with an ID model such that the probabilities of positive outcomes as well as the drop-out indicator in each occasion are logit linear in some covariates and outcomes. This model adopting a marginal model for outcomes and a conditional model for dropouts is called a selection model. To allow for the heterogeneity and clustering effects, the outcome model is extended to incorporate mixture and random effects. Lastly, the model is further extended to a novel model that models the outcome and dropout jointly such that their dependency is formulated through an odds ratio function. Parameters are estimated by a Bayesian approach implemented using the user-friendly Bayesian software WinBUGS. A methadone clinic dataset is analyzed to illustrate the proposed models. Result shows that the treatment time effect is still significant but weaker after allowing for an ID process in the data. Finally the effect of drop-out on parameter estimates is evaluated through simulation studies. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Directory of Open Access Journals (Sweden)
Renata Maria Abrantes Baracho
2016-04-01
Full Text Available This research addresses the use of information management processes in order to extract student dropout indicators in distance mode courses. Distance education in Brazil aims to facilitate access to information. The MEC (Ministry of Education announced, in the second semester of 2013, that the main obstacles faced by institutions offering courses in this mode were students dropping out and the resistance of both educators and students to this mode. The research used a mixed methodology, qualitative and quantitative, to obtain student dropout indicators. The factors found and validated in this research were: the lack of interest from students, insufficient training in the use of the virtual learning environment for students, structural problems in the schools that were chosen to offer the course, students without e-mail, incoherent answers to activities to the course, lack of knowledge on the part of the student when using the computer tool. The scenario considered was a course offered in distance mode called Aluno Integrado (Integrated Student
Directory of Open Access Journals (Sweden)
Zhaojun Yang
2011-01-01
Full Text Available We study the question what value an agent in a generalized Black-Scholes model with partial information attributes to the complementary information. To do this, we study the utility maximization problems from terminal wealth for the two cases partial information and full information. We assume that the drift term of the risky asset is a dynamic process of general linear type and that the two levels of observation correspond to whether this drift term is observable or not. Applying methods from stochastic filtering theory we derive an analytical tractable formula for the value of information in the case of logarithmic utility. For the case of constant relative risk aversion (CRRA we derive a semianalytical formula, which uses as an input the numerical solution of a system of ODEs. For both cases we present a comparative analysis.
Shen, Xu; Tian, Xinmei; Liu, Tongliang; Xu, Fang; Tao, Dacheng
2017-10-03
Dropout has been proven to be an effective algorithm for training robust deep networks because of its ability to prevent overfitting by avoiding the co-adaptation of feature detectors. Current explanations of dropout include bagging, naive Bayes, regularization, and sex in evolution. According to the activation patterns of neurons in the human brain, when faced with different situations, the firing rates of neurons are random and continuous, not binary as current dropout does. Inspired by this phenomenon, we extend the traditional binary dropout to continuous dropout. On the one hand, continuous dropout is considerably closer to the activation characteristics of neurons in the human brain than traditional binary dropout. On the other hand, we demonstrate that continuous dropout has the property of avoiding the co-adaptation of feature detectors, which suggests that we can extract more independent feature detectors for model averaging in the test stage. We introduce the proposed continuous dropout to a feedforward neural network and comprehensively compare it with binary dropout, adaptive dropout, and DropConnect on Modified National Institute of Standards and Technology, Canadian Institute for Advanced Research-10, Street View House Numbers, NORB, and ImageNet large scale visual recognition competition-12. Thorough experiments demonstrate that our method performs better in preventing the co-adaptation of feature detectors and improves test performance.
Distributed synthesis in continuous time
DEFF Research Database (Denmark)
Hermanns, Holger; Krčál, Jan; Vester, Steen
2016-01-01
We introduce a formalism modelling communication of distributed agents strictly in continuous-time. Within this framework, we study the problem of synthesising local strategies for individual agents such that a specified set of goal states is reached, or reached with at least a given probability....... The flow of time is modelled explicitly based on continuous-time randomness, with two natural implications: First, the non-determinism stemming from interleaving disappears. Second, when we restrict to a subclass of non-urgent models, the quantitative value problem for two players can be solved in EXPTIME....... Indeed, the explicit continuous time enables players to communicate their states by delaying synchronisation (which is unrestricted for non-urgent models). In general, the problems are undecidable already for two players in the quantitative case and three players in the qualitative case. The qualitative...
Sullivan, Amanda L.; Sadeh, Shanna
2016-01-01
For the past 30 years, the dropout rate for students with emotional disturbance has hovered around 50%, a rate substantially higher than the dropout rate for students with other disabilities and the general population. This systematic review evaluated the literature published between 1990 and 2013 on the effectiveness of dropout prevention and…
Chemical Continuous Time Random Walks
Aquino, T.; Dentz, M.
2017-12-01
Traditional methods for modeling solute transport through heterogeneous media employ Eulerian schemes to solve for solute concentration. More recently, Lagrangian methods have removed the need for spatial discretization through the use of Monte Carlo implementations of Langevin equations for solute particle motions. While there have been recent advances in modeling chemically reactive transport with recourse to Lagrangian methods, these remain less developed than their Eulerian counterparts, and many open problems such as efficient convergence and reconstruction of the concentration field remain. We explore a different avenue and consider the question: In heterogeneous chemically reactive systems, is it possible to describe the evolution of macroscopic reactant concentrations without explicitly resolving the spatial transport? Traditional Kinetic Monte Carlo methods, such as the Gillespie algorithm, model chemical reactions as random walks in particle number space, without the introduction of spatial coordinates. The inter-reaction times are exponentially distributed under the assumption that the system is well mixed. In real systems, transport limitations lead to incomplete mixing and decreased reaction efficiency. We introduce an arbitrary inter-reaction time distribution, which may account for the impact of incomplete mixing. This process defines an inhomogeneous continuous time random walk in particle number space, from which we derive a generalized chemical Master equation and formulate a generalized Gillespie algorithm. We then determine the modified chemical rate laws for different inter-reaction time distributions. We trace Michaelis-Menten-type kinetics back to finite-mean delay times, and predict time-nonlocal macroscopic reaction kinetics as a consequence of broadly distributed delays. Non-Markovian kinetics exhibit weak ergodicity breaking and show key features of reactions under local non-equilibrium.
High School Dropout and Teen Childbearing
Marcotte, Dave E.
2013-01-01
Understanding the relationship between high school dropout and teen childbearing is complicated because both are affected by a variety of difficult to control factors. In this paper, I use panel data on aggregate dropout and fertility rates by age for all fifty states to develop insight by instrumenting for dropout using information on state…
Maeda, Shin-ichi
2014-01-01
Dropout is one of the key techniques to prevent the learning from overfitting. It is explained that dropout works as a kind of modified L2 regularization. Here, we shed light on the dropout from Bayesian standpoint. Bayesian interpretation enables us to optimize the dropout rate, which is beneficial for learning of weight parameters and prediction after learning. The experiment result also encourages the optimization of the dropout.
Parameter Estimation in Continuous Time Domain
Directory of Open Access Journals (Sweden)
Gabriela M. ATANASIU
2016-12-01
Full Text Available This paper will aim to presents the applications of a continuous-time parameter estimation method for estimating structural parameters of a real bridge structure. For the purpose of illustrating this method two case studies of a bridge pile located in a highly seismic risk area are considered, for which the structural parameters for the mass, damping and stiffness are estimated. The estimation process is followed by the validation of the analytical results and comparison with them to the measurement data. Further benefits and applications for the continuous-time parameter estimation method in civil engineering are presented in the final part of this paper.
Dropout Phenomena at Universities
DEFF Research Database (Denmark)
Larsen, Michael Søgaard; Kornbeck, Kasper Pihl; Kristensen, Rune
Dropout from university studies comprises a number of complex phenomena with serious complex consequences and profound political attention. Further analysis of the field is, therefore, warranted. Such an analysis is offered here as a systematic review which gives answers based on the best possible...... such dropout phenomena occur at universities? What can be done by the universities to prevent or reduce such dropout phenomena?...
a Continuous-Time Positive Linear System
Directory of Open Access Journals (Sweden)
Kyungsup Kim
2013-01-01
Full Text Available This paper discusses a computational method to construct positive realizations with sparse matrices for continuous-time positive linear systems with multiple complex poles. To construct a positive realization of a continuous-time system, we use a Markov sequence similar to the impulse response sequence that is used in the discrete-time case. The existence of the proposed positive realization can be analyzed with the concept of a polyhedral convex cone. We provide a constructive algorithm to compute positive realizations with sparse matrices of some positive systems under certain conditions. A sufficient condition for the existence of a positive realization, under which the proposed constructive algorithm works well, is analyzed.
Continuous Time Structural Equation Modeling with R Package ctsem
Directory of Open Access Journals (Sweden)
Charles C. Driver
2017-04-01
Full Text Available We introduce ctsem, an R package for continuous time structural equation modeling of panel (N > 1 and time series (N = 1 data, using full information maximum likelihood. Most dynamic models (e.g., cross-lagged panel models in the social and behavioural sciences are discrete time models. An assumption of discrete time models is that time intervals between measurements are equal, and that all subjects were assessed at the same intervals. Violations of this assumption are often ignored due to the difficulty of accounting for varying time intervals, therefore parameter estimates can be biased and the time course of effects becomes ambiguous. By using stochastic differential equations to estimate an underlying continuous process, continuous time models allow for any pattern of measurement occasions. By interfacing to OpenMx, ctsem combines the flexible specification of structural equation models with the enhanced data gathering opportunities and improved estimation of continuous time models. ctsem can estimate relationships over time for multiple latent processes, measured by multiple noisy indicators with varying time intervals between observations. Within and between effects are estimated simultaneously by modeling both observed covariates and unobserved heterogeneity. Exogenous shocks with different shapes, group differences, higher order diffusion effects and oscillating processes can all be simply modeled. We first introduce and define continuous time models, then show how to specify and estimate a range of continuous time models using ctsem.
Path probabilities of continuous time random walks
International Nuclear Information System (INIS)
Eule, Stephan; Friedrich, Rudolf
2014-01-01
Employing the path integral formulation of a broad class of anomalous diffusion processes, we derive the exact relations for the path probability densities of these processes. In particular, we obtain a closed analytical solution for the path probability distribution of a Continuous Time Random Walk (CTRW) process. This solution is given in terms of its waiting time distribution and short time propagator of the corresponding random walk as a solution of a Dyson equation. Applying our analytical solution we derive generalized Feynman–Kac formulae. (paper)
Stochastic volatility of volatility in continuous time
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole; Veraart, Almut
This paper introduces the concept of stochastic volatility of volatility in continuous time and, hence, extends standard stochastic volatility (SV) models to allow for an additional source of randomness associated with greater variability in the data. We discuss how stochastic volatility...... of volatility can be defined both non-parametrically, where we link it to the quadratic variation of the stochastic variance process, and parametrically, where we propose two new SV models which allow for stochastic volatility of volatility. In addition, we show that volatility of volatility can be estimated...
Heterogeneous continuous-time random walks
Grebenkov, Denis S.; Tupikina, Liubov
2018-01-01
We introduce a heterogeneous continuous-time random walk (HCTRW) model as a versatile analytical formalism for studying and modeling diffusion processes in heterogeneous structures, such as porous or disordered media, multiscale or crowded environments, weighted graphs or networks. We derive the exact form of the propagator and investigate the effects of spatiotemporal heterogeneities onto the diffusive dynamics via the spectral properties of the generalized transition matrix. In particular, we show how the distribution of first-passage times changes due to local and global heterogeneities of the medium. The HCTRW formalism offers a unified mathematical language to address various diffusion-reaction problems, with numerous applications in material sciences, physics, chemistry, biology, and social sciences.
Expectation propagation for continuous time stochastic processes
International Nuclear Information System (INIS)
Cseke, Botond; Schnoerr, David; Sanguinetti, Guido; Opper, Manfred
2016-01-01
We consider the inverse problem of reconstructing the posterior measure over the trajectories of a diffusion process from discrete time observations and continuous time constraints. We cast the problem in a Bayesian framework and derive approximations to the posterior distributions of single time marginals using variational approximate inference, giving rise to an expectation propagation type algorithm. For non-linear diffusion processes, this is achieved by leveraging moment closure approximations. We then show how the approximation can be extended to a wide class of discrete-state Markov jump processes by making use of the chemical Langevin equation. Our empirical results show that the proposed method is computationally efficient and provides good approximations for these classes of inverse problems. (paper)
Interaction-aided continuous time quantum search
International Nuclear Information System (INIS)
Bae, Joonwoo; Kwon, Younghun; Baek, Inchan; Yoon, Dalsun
2005-01-01
The continuous quantum search algorithm (based on the Farhi-Gutmann Hamiltonian evolution) is known to be analogous to the Grover (or discrete time quantum) algorithm. Any errors introduced in Grover algorithm are fatal to its success. In the same way the Farhi-Gutmann Hamiltonian algorithm has a severe difficulty when the Hamiltonian is perturbed. In this letter we will show that the interaction term in quantum search Hamiltonian (actually which is in the generalized quantum search Hamiltonian) can save the perturbed Farhi-Gutmann Hamiltonian that should otherwise fail. We note that this fact is quite remarkable since it implies that introduction of interaction can be a way to correct some errors on the continuous time quantum search
The Dropout Learning Algorithm
Baldi, Pierre; Sadowski, Peter
2014-01-01
Dropout is a recently introduced algorithm for training neural network by randomly dropping units during training to prevent their co-adaptation. A mathematical analysis of some of the static and dynamic properties of dropout is provided using Bernoulli gating variables, general enough to accommodate dropout on units or connections, and with variable rates. The framework allows a complete analysis of the ensemble averaging properties of dropout in linear networks, which is useful to understand the non-linear case. The ensemble averaging properties of dropout in non-linear logistic networks result from three fundamental equations: (1) the approximation of the expectations of logistic functions by normalized geometric means, for which bounds and estimates are derived; (2) the algebraic equality between normalized geometric means of logistic functions with the logistic of the means, which mathematically characterizes logistic functions; and (3) the linearity of the means with respect to sums, as well as products of independent variables. The results are also extended to other classes of transfer functions, including rectified linear functions. Approximation errors tend to cancel each other and do not accumulate. Dropout can also be connected to stochastic neurons and used to predict firing rates, and to backpropagation by viewing the backward propagation as ensemble averaging in a dropout linear network. Moreover, the convergence properties of dropout can be understood in terms of stochastic gradient descent. Finally, for the regularization properties of dropout, the expectation of the dropout gradient is the gradient of the corresponding approximation ensemble, regularized by an adaptive weight decay term with a propensity for self-consistent variance minimization and sparse representations. PMID:24771879
School Dropouts in Perspective.
Sherraden, Michael W.
1986-01-01
Discusses aspects of the school dropout problem: figures and trends, related youth problems (unemployment, crime and vandalism, drug and alcohol abuse, political alienation, teen pregnancy and childbirth, homicide and suicide), and suggestions for solving the problem. (CT)
Poernomo, Alvin; Kang, Dae-Ki
2018-08-01
Training a deep neural network with a large number of parameters often leads to overfitting problem. Recently, Dropout has been introduced as a simple, yet effective regularization approach to combat overfitting in such models. Although Dropout has shown remarkable results on many deep neural network cases, its actual effect on CNN has not been thoroughly explored. Moreover, training a Dropout model will significantly increase the training time as it takes longer time to converge than a non-Dropout model with the same architecture. To deal with these issues, we address Biased Dropout and Crossmap Dropout, two novel approaches of Dropout extension based on the behavior of hidden units in CNN model. Biased Dropout divides the hidden units in a certain layer into two groups based on their magnitude and applies different Dropout rate to each group appropriately. Hidden units with higher activation value, which give more contributions to the network final performance, will be retained by a lower Dropout rate, while units with lower activation value will be exposed to a higher Dropout rate to compensate the previous part. The second approach is Crossmap Dropout, which is an extension of the regular Dropout in convolution layer. Each feature map in a convolution layer has a strong correlation between each other, particularly in every identical pixel location in each feature map. Crossmap Dropout tries to maintain this important correlation yet at the same time break the correlation between each adjacent pixel with respect to all feature maps by applying the same Dropout mask to all feature maps, so that all pixels or units in equivalent positions in each feature map will be either dropped or active during training. Our experiment with various benchmark datasets shows that our approaches provide better generalization than the regular Dropout. Moreover, our Biased Dropout takes faster time to converge during training phase, suggesting that assigning noise appropriately in
[Dropout behavior during inpatient psychotherapy ].
Martens, Ute; Rempel, Irene; Zipfel, Stephan; Enck, Paul; Teufel, Martin
2014-01-01
Dropouts result in far-reaching consequences for the individual patient, fellow patients, therapists, and the clinic. This study was aimed at early identification of patients with a dropout risk. Data from patients of the Department of Psychosomatic Medicine and Psychotherapy of the Medical University Clinic of Tübingen (Germany) were analyzed retrospectively in a case-control study (matched). Differences in the results of various questionnaires (SCL-90-R, IIP-D, SF-36) regarding reasons for dropout and sociodemographic data were analyzed. A total of 59 dropouts, 50 females and 9 males, were included. They were split into 28 early dropouts and 31 late dropouts. The data were compared between early and late dropouts and control group. Early dropouts were significantly younger than late dropouts; they tended to live with their parents or on their own, and suffered more frequently from eating disorders. Late dropouts lived together with partners and suffered from somatoform disorders more frequently than early dropouts. The reasons given for dropout did not differ between the groups. No differences between dropouts and the controls were found with respect to psychopathology (SCL- 90-R) and quality of life (SF-36). Late dropouts did show significantly lower scores on the scale "autocracy/dominance" than the controls (IIP). Therapy dropout is a multifactorial occurrence. It is generally not predictable, though it may be predicted with different instruments on the basis of a diagnosis, especially with respect to interpersonal behavior patterns. In further studies, targeted interventions should be developed and tested which enable procedures to minimize the risk of dropout and to achieve complete treatment according to patients' intentions.
Accounting for dropout reason in longitudinal studies with nonignorable dropout.
Moore, Camille M; MaWhinney, Samantha; Forster, Jeri E; Carlson, Nichole E; Allshouse, Amanda; Wang, Xinshuo; Routy, Jean-Pierre; Conway, Brian; Connick, Elizabeth
2017-08-01
Dropout is a common problem in longitudinal cohort studies and clinical trials, often raising concerns of nonignorable dropout. Selection, frailty, and mixture models have been proposed to account for potentially nonignorable missingness by relating the longitudinal outcome to time of dropout. In addition, many longitudinal studies encounter multiple types of missing data or reasons for dropout, such as loss to follow-up, disease progression, treatment modifications and death. When clinically distinct dropout reasons are present, it may be preferable to control for both dropout reason and time to gain additional clinical insights. This may be especially interesting when the dropout reason and dropout times differ by the primary exposure variable. We extend a semi-parametric varying-coefficient method for nonignorable dropout to accommodate dropout reason. We apply our method to untreated HIV-infected subjects recruited to the Acute Infection and Early Disease Research Program HIV cohort and compare longitudinal CD4 + T cell count in injection drug users to nonusers with two dropout reasons: anti-retroviral treatment initiation and loss to follow-up.
Continuous-time quantum walks on star graphs
International Nuclear Information System (INIS)
Salimi, S.
2009-01-01
In this paper, we investigate continuous-time quantum walk on star graphs. It is shown that quantum central limit theorem for a continuous-time quantum walk on star graphs for N-fold star power graph, which are invariant under the quantum component of adjacency matrix, converges to continuous-time quantum walk on K 2 graphs (complete graph with two vertices) and the probability of observing walk tends to the uniform distribution.
Czech Academy of Sciences Publication Activity Database
Slovák, Dalibor
2014-01-01
Roč. 2, č. 1 (2014), s. 31-33 ISSN 1805-8698 Grant - others:SVV(CZ) 260034 Institutional support: RVO:67985807 Keywords : drop-out * peak height * DNA interpretation Subject RIV: IN - Informatics, Computer Science http://www.ijbh.org/ijbh2014-1.pdf
Linardon, Jake; Hindle, Annemarie; Brennan, Leah
2018-05-01
Cognitive-behavioral therapy (CBT) is efficacious for a range of eating disorder presentations, yet premature dropout is one factor that might limit CBTs effectiveness. Improved understanding of dropout from CBT for eating disorders is important. This meta-analysis aimed to study dropout from CBT for eating disorders in randomized controlled trials (RCTs), by (a) identifying the types of dropout definitions applied, (b) providing estimates of dropout, (c) comparing dropout rates from CBT to non-CBT interventions for eating disorders, and (d) testing moderators of dropout. RCTs of CBT for eating disorders that reported rates of dropout were searched. Ninety-nine RCTs (131 CBT conditions) were included. Dropout definitions varied widely across studies. The overall dropout estimate was 24% (95% CI = 22-27%). Diagnostic type, type of dropout definition, baseline symptom severity, study quality, and sample age did not moderate this estimate. Dropout was highest among studies that delivered internet-based CBT and was lowest in studies that delivered transdiagnostic enhanced CBT. There was some evidence that longer treatment protocols were associated with lower dropout. No significant differences in dropout rates were observed between CBT and non-CBT interventions for all eating disorder subtypes. Present study dropout estimates are hampered by the use of disparate dropout definitions applied. This meta-analysis highlights the urgency for RCTs to utilize a standardized dropout definition and to report as much information on patient dropout as possible, so that strategies designed to minimize dropout can be developed, and factors predictive of CBT dropout can be more easily identified. © 2018 Wiley Periodicals, Inc.
Coaction versus reciprocity in continuous-time models of cooperation.
van Doorn, G Sander; Riebli, Thomas; Taborsky, Michael
2014-09-07
Cooperating animals frequently show closely coordinated behaviours organized by a continuous flow of information between interacting partners. Such real-time coaction is not captured by the iterated prisoner's dilemma and other discrete-time reciprocal cooperation games, which inherently feature a delay in information exchange. Here, we study the evolution of cooperation when individuals can dynamically respond to each other's actions. We develop continuous-time analogues of iterated-game models and describe their dynamics in terms of two variables, the propensity of individuals to initiate cooperation (altruism) and their tendency to mirror their partner's actions (coordination). These components of cooperation stabilize at an evolutionary equilibrium or show oscillations, depending on the chosen payoff parameters. Unlike reciprocal altruism, cooperation by coaction does not require that those willing to initiate cooperation pay in advance for uncertain future benefits. Correspondingly, we show that introducing a delay to information transfer between players is equivalent to increasing the cost of cooperation. Cooperative coaction can therefore evolve much more easily than reciprocal cooperation. When delays entirely prevent coordination, we recover results from the discrete-time alternating prisoner's dilemma, indicating that coaction and reciprocity are connected by a continuum of opportunities for real-time information exchange. Copyright © 2014 Elsevier Ltd. All rights reserved.
A continuous-time control model on production planning network ...
African Journals Online (AJOL)
A continuous-time control model on production planning network. DEA Omorogbe, MIU Okunsebor. Abstract. In this paper, we give a slightly detailed review of Graves and Hollywood model on constant inventory tactical planning model for a job shop. The limitations of this model are pointed out and a continuous time ...
Continuous Time Modeling of the Cross-Lagged Panel Design
Oud, J.H.L.
2002-01-01
Since Newton (1642-1727) continuous time modeling by means of differential equations is the standard approach of dynamic phenomena in natural science. It is argued that most processes in behavioral science also unfold in continuous time and should be analyzed accordingly. After dealing with the
Elliott, Thomas J.; Gu, Mile
2018-03-01
Continuous-time stochastic processes pervade everyday experience, and the simulation of models of these processes is of great utility. Classical models of systems operating in continuous-time must typically track an unbounded amount of information about past behaviour, even for relatively simple models, enforcing limits on precision due to the finite memory of the machine. However, quantum machines can require less information about the past than even their optimal classical counterparts to simulate the future of discrete-time processes, and we demonstrate that this advantage extends to the continuous-time regime. Moreover, we show that this reduction in the memory requirement can be unboundedly large, allowing for arbitrary precision even with a finite quantum memory. We provide a systematic method for finding superior quantum constructions, and a protocol for analogue simulation of continuous-time renewal processes with a quantum machine.
Dropout in vocational education
DEFF Research Database (Denmark)
Jørgensen, Christian Helms
For the last ten years drop out of vocational education has increased strongly in Denmark. Only half of the students, who take up a vocational programme on upper secondary level, complete it. Like in other European countries the low completion rates has caused considerable alarm on the political...... level (Lamb and Markussen 2011). Continuing high dropout rates will make it very hard for the government to reach its target for educational completion, and the government has launched a series of measures to increase retention including the obligation for all colleges to make plans for retention...... and monitor the progress in achieving the goals. The questions addressed in this paper are why and how dropout in VET takes place. The objective is to provide more detailed and qualified knowledge of the complex processes of dropping out....
Integral-Value Models for Outcomes over Continuous Time
DEFF Research Database (Denmark)
Harvey, Charles M.; Østerdal, Lars Peter
Models of preferences between outcomes over continuous time are important for individual, corporate, and social decision making, e.g., medical treatment, infrastructure development, and environmental regulation. This paper presents a foundation for such models. It shows that conditions on prefere...... on preferences between real- or vector-valued outcomes over continuous time are satisfied if and only if the preferences are represented by a value function having an integral form......Models of preferences between outcomes over continuous time are important for individual, corporate, and social decision making, e.g., medical treatment, infrastructure development, and environmental regulation. This paper presents a foundation for such models. It shows that conditions...
Continuous-time Markov decision processes theory and applications
Guo, Xianping
2009-01-01
This volume provides the first book entirely devoted to recent developments on the theory and applications of continuous-time Markov decision processes (MDPs). The MDPs presented here include most of the cases that arise in applications.
Continuous-time quantum random walks require discrete space
International Nuclear Information System (INIS)
Manouchehri, K; Wang, J B
2007-01-01
Quantum random walks are shown to have non-intuitive dynamics which makes them an attractive area of study for devising quantum algorithms for long-standing open problems as well as those arising in the field of quantum computing. In the case of continuous-time quantum random walks, such peculiar dynamics can arise from simple evolution operators closely resembling the quantum free-wave propagator. We investigate the divergence of quantum walk dynamics from the free-wave evolution and show that, in order for continuous-time quantum walks to display their characteristic propagation, the state space must be discrete. This behavior rules out many continuous quantum systems as possible candidates for implementing continuous-time quantum random walks
Continuous-time quantum random walks require discrete space
Manouchehri, K.; Wang, J. B.
2007-11-01
Quantum random walks are shown to have non-intuitive dynamics which makes them an attractive area of study for devising quantum algorithms for long-standing open problems as well as those arising in the field of quantum computing. In the case of continuous-time quantum random walks, such peculiar dynamics can arise from simple evolution operators closely resembling the quantum free-wave propagator. We investigate the divergence of quantum walk dynamics from the free-wave evolution and show that, in order for continuous-time quantum walks to display their characteristic propagation, the state space must be discrete. This behavior rules out many continuous quantum systems as possible candidates for implementing continuous-time quantum random walks.
On Transaction-Cost Models in Continuous-Time Markets
Directory of Open Access Journals (Sweden)
Thomas Poufinas
2015-04-01
Full Text Available Transaction-cost models in continuous-time markets are considered. Given that investors decide to buy or sell at certain time instants, we study the existence of trading strategies that reach a certain final wealth level in continuous-time markets, under the assumption that transaction costs, built in certain recommended ways, have to be paid. Markets prove to behave in manners that resemble those of complete ones for a wide variety of transaction-cost types. The results are important, but not exclusively, for the pricing of options with transaction costs.
Pseudo-Hermitian continuous-time quantum walks
Energy Technology Data Exchange (ETDEWEB)
Salimi, S; Sorouri, A, E-mail: shsalimi@uok.ac.i, E-mail: a.sorouri@uok.ac.i [Department of Physics, University of Kurdistan, PO Box 66177-15175, Sanandaj (Iran, Islamic Republic of)
2010-07-09
In this paper we present a model exhibiting a new type of continuous-time quantum walk (as a quantum-mechanical transport process) on networks, which is described by a non-Hermitian Hamiltonian possessing a real spectrum. We call it pseudo-Hermitian continuous-time quantum walk. We introduce a method to obtain the probability distribution of walk on any vertex and then study a specific system. We observe that the probability distribution on certain vertices increases compared to that of the Hermitian case. This formalism makes the transport process faster and can be useful for search algorithms.
Stability of continuous-time quantum filters with measurement imperfections
Amini, H.; Pellegrini, C.; Rouchon, P.
2014-07-01
The fidelity between the state of a continuously observed quantum system and the state of its associated quantum filter, is shown to be always a submartingale. The observed system is assumed to be governed by a continuous-time Stochastic Master Equation (SME), driven simultaneously by Wiener and Poisson processes and that takes into account incompleteness and errors in measurements. This stability result is the continuous-time counterpart of a similar stability result already established for discrete-time quantum systems and where the measurement imperfections are modelled by a left stochastic matrix.
A continuous time formulation of the Regge calculus
International Nuclear Information System (INIS)
Brewin, Leo
1988-01-01
A complete continuous time formulation of the Regge calculus is presented by developing the associated continuous time Regge action. It is shown that the time constraint is, by way of the Bianchi identities conserved by the evolution equations. This analysis leads to an explicit first integral for each of the evolution equations. The dynamical equations of the theory are therefore reduced to a set of first-order differential equations. In this formalism the time constraints reduce to a simple sum of the integration constants. This result is unique to the Regge calculus-there does not appear to be a complete set of first integrals available for the vacuum Einstein equations. (author)
Application of continuous-time random walk to statistical arbitrage
Directory of Open Access Journals (Sweden)
Sergey Osmekhin
2015-01-01
Full Text Available An analytical statistical arbitrage strategy is proposed, where the distribution of the spread is modelled as a continuous-time random walk. Optimal boundaries, computed as a function of the mean and variance of the firstpassage time ofthe spread,maximises an objective function. The predictability of the trading strategy is analysed and contrasted for two forms of continuous-time random walk processes. We found that the waiting-time distribution has a significant impact on the prediction of the expected profit for intraday trading
Student engagement and its relationship with early high school dropout.
Archambault, Isabelle; Janosz, Michel; Fallu, Jean-Sébastien; Pagani, Linda S
2009-06-01
Although the concept of school engagement figures prominently in most school dropout theories, there has been little empirical research conducted on its nature and course and, more importantly, the association with dropout. Information on the natural development of school engagement would greatly benefit those interested in preventing student alienation during adolescence. Using a longitudinal sample of 11,827 French-Canadian high school students, we tested behavioral, affective, cognitive indices of engagement both separately and as a global construct. We then assessed their contribution as prospective predictors of school dropout using factor analysis and structural equation modeling. Global engagement reliably predicted school dropout. Among its three specific dimensions, only behavioral engagement made a significant contribution in the prediction equation. Our findings confirm the robustness of the overall multidimensional construct of school engagement, which reflects both cognitive and psychosocial characteristics, and underscore the importance attributed to basic participation and compliance issues in reliably estimating risk of not completing basic schooling during adolescence.
Incomplete Continuous-time Securities Markets with Stochastic Income Volatility
DEFF Research Database (Denmark)
Christensen, Peter Ove; Larsen, Kasper
2014-01-01
We derive closed-form solutions for the equilibrium interest rate and market price of risk processes in an incomplete continuous-time market with uncertainty generated by Brownian motions. The economy has a finite number of heterogeneous exponential utility investors, who receive partially...
Continuous time modeling of panel data by means of SEM
Oud, J.H.L.; Delsing, M.J.M.H.; Montfort, C.A.G.M.; Oud, J.H.L.; Satorra, A.
2010-01-01
After a brief history of continuous time modeling and its implementation in panel analysis by means of structural equation modeling (SEM), the problems of discrete time modeling are discussed in detail. This is done by means of the popular cross-lagged panel design. Next, the exact discrete model
Identification of continuous-time systems from samples of input ...
Indian Academy of Sciences (India)
Abstract. This paper presents an introductory survey of the methods that have been developed for identification of continuous-time systems from samples of input±output data. The two basic approaches may be described as (i) the indirect method, where first a discrete-time model is estimated from the sampled data and then ...
Incomplete Continuous-Time Securities Markets with Stochastic Income Volatility
DEFF Research Database (Denmark)
Christensen, Peter Ove; Larsen, Kasper
In an incomplete continuous-time securities market governed by Brownian motions, we derive closed-form solutions for the equilibrium risk-free rate and equity premium processes. The economy has a finite number of heterogeneous exponential utility investors, who receive partially unspanned income ...
The deviation matrix of a continuous-time Markov chain
Coolen-Schrijner, P.; van Doorn, E.A.
2001-01-01
The deviation matrix of an ergodic, continuous-time Markov chain with transition probability matrix $P(.)$ and ergodic matrix $\\Pi$ is the matrix $D \\equiv \\int_0^{\\infty} (P(t)-\\Pi)dt$. We give conditions for $D$ to exist and discuss properties and a representation of $D$. The deviation matrix of a
The deviation matrix of a continuous-time Markov chain
Coolen-Schrijner, Pauline; van Doorn, Erik A.
2002-01-01
he deviation matrix of an ergodic, continuous-time Markov chain with transition probability matrix $P(.)$ and ergodic matrix $\\Pi$ is the matrix $D \\equiv \\int_0^{\\infty} (P(t)-\\Pi)dt$. We give conditions for $D$ to exist and discuss properties and a representation of $D$. The deviation matrix of a
Model checking conditional CSL for continuous-time Markov chains
DEFF Research Database (Denmark)
Gao, Yang; Xu, Ming; Zhan, Naijun
2013-01-01
In this paper, we consider the model-checking problem of continuous-time Markov chains (CTMCs) with respect to conditional logic. To the end, we extend Continuous Stochastic Logic introduced in Aziz et al. (2000) [1] to Conditional Continuous Stochastic Logic (CCSL) by introducing a conditional...
Noise Simulation of Continuous-Time ΣΔ Modulators
International Nuclear Information System (INIS)
Arias, J.; Quintanilla, L.; Bisbal, D.; San Pablo, J.; Enriquez, L.; Vicente, J.; Barbolla, J.
2005-01-01
In this work, an approach for the simulation of the effect of noise sources in the performance of continuous-time ΔΣ modulators is presented. Electrical noise including thermal noise, 1/f noise and clock jitter are included in a simulation program and their impact on the system performance is analyzed
A mean-variance frontier in discrete and continuous time
Bekker, Paul A.
2004-01-01
The paper presents a mean-variance frontier based on dynamic frictionless investment strategies in continuous time. The result applies to a finite number of risky assets whose price process is given by multivariate geometric Brownian motion with deterministically varying coefficients. The derivation
Stability and the structure of continuous-time economic models
Nieuwenhuis, H.J.; Schoonbeek, L.
In this paper we investigate the relationship between the stability of macroeconomic, or macroeconometric, continuous-time models and the structure of the matrices appearing in these models. In particular, we concentrate on dominant-diagonal structures. We derive general stability results for models
Yalowitz, Jeffrey S.; Schroer, Michael A.; Dickson, John E., Jr.
1992-01-01
This final report describes work performed by SRS Technologies for the NASA Marshall Space Flight Center under Contract NAS8-39077, entitled 'Integrated Receiver-Decoder Dropout Study'. The purpose of the study was to determine causes of signal fading effects on ultra-high-frequency (UHF) range safety transmissions to the Space Shuttle during flyout. Of particular interest were deep fades observed at the External Tank (ET) Integrated Receiver-Decoder (IRD) during the flyout interval between solid rocket booster separation and ET separation. Analytical and simulation methods were employed in this study to assess observations captured in flight telemetry data records. Conclusions based on the study are presented in this report, and recommendations are given for future experimental validation of the results.
Efficient batchwise dropout training using submatrices
Graham, Ben; Reizenstein, Jeremy; Robinson, Leigh
2015-01-01
Dropout is a popular technique for regularizing artificial neural networks. Dropout networks are generally trained by minibatch gradient descent with a dropout mask turning off some of the units---a different pattern of dropout is applied to every sample in the minibatch. We explore a very simple alternative to the dropout mask. Instead of masking dropped out units by setting them to zero, we perform matrix multiplication using a submatrix of the weight matrix---unneeded hidden units are neve...
From discrete-time models to continuous-time, asynchronous modeling of financial markets
Boer, Katalin; Kaymak, Uzay; Spiering, Jaap
2007-01-01
Most agent-based simulation models of financial markets are discrete-time in nature. In this paper, we investigate to what degree such models are extensible to continuous-time, asynchronous modeling of financial markets. We study the behavior of a learning market maker in a market with information
A stochastic surplus production model in continuous time
DEFF Research Database (Denmark)
Pedersen, Martin Wæver; Berg, Casper Willestofte
2017-01-01
surplus production model in continuous time (SPiCT), which in addition to stock dynamics also models the dynamics of the fisheries. This enables error in the catch process to be reflected in the uncertainty of estimated model parameters and management quantities. Benefits of the continuous-time state......Surplus production modelling has a long history as a method for managing data-limited fish stocks. Recent advancements have cast surplus production models as state-space models that separate random variability of stock dynamics from error in observed indices of biomass. We present a stochastic......-space model formulation include the ability to provide estimates of exploitable biomass and fishing mortality at any point in time from data sampled at arbitrary and possibly irregular intervals. We show in a simulation that the ability to analyse subannual data can increase the effective sample size...
A mean-variance frontier in discrete and continuous time
Bekker, Paul A.
2004-01-01
The paper presents a mean-variance frontier based on dynamic frictionless investment strategies in continuous time. The result applies to a finite number of risky assets whose price process is given by multivariate geometric Brownian motion with deterministically varying coefficients. The derivation is based on the solution for the frontier in discrete time. Using the same multiperiod framework as Li and Ng (2000), I provide an alternative derivation and an alternative formulation of the solu...
Continuous Time Portfolio Selection under Conditional Capital at Risk
Directory of Open Access Journals (Sweden)
Gordana Dmitrasinovic-Vidovic
2010-01-01
Full Text Available Portfolio optimization with respect to different risk measures is of interest to both practitioners and academics. For there to be a well-defined optimal portfolio, it is important that the risk measure be coherent and quasiconvex with respect to the proportion invested in risky assets. In this paper we investigate one such measure—conditional capital at risk—and find the optimal strategies under this measure, in the Black-Scholes continuous time setting, with time dependent coefficients.
Continuous-Time Symmetric Hopfield Nets are Computationally Universal
Czech Academy of Sciences Publication Activity Database
Šíma, Jiří; Orponen, P.
2003-01-01
Roč. 15, č. 3 (2003), s. 693-733 ISSN 0899-7667 R&D Projects: GA AV ČR IAB2030007; GA ČR GA201/02/1456 Institutional research plan: AV0Z1030915 Keywords : continuous-time Hopfield network * Liapunov function * analog computation * computational power * Turing universality Subject RIV: BA - General Mathematics Impact factor: 2.747, year: 2003
Parallel algorithms for simulating continuous time Markov chains
Nicol, David M.; Heidelberger, Philip
1992-01-01
We have previously shown that the mathematical technique of uniformization can serve as the basis of synchronization for the parallel simulation of continuous-time Markov chains. This paper reviews the basic method and compares five different methods based on uniformization, evaluating their strengths and weaknesses as a function of problem characteristics. The methods vary in their use of optimism, logical aggregation, communication management, and adaptivity. Performance evaluation is conducted on the Intel Touchstone Delta multiprocessor, using up to 256 processors.
Estimation of Continuous Time Models in Economics: an Overview
Clifford R. Wymer
2009-01-01
The dynamics of economic behaviour is often developed in theory as a continuous time system. Rigorous estimation and testing of such systems, and the analysis of some aspects of their properties, is of particular importance in distinguishing between competing hypotheses and the resulting models. The consequences for the international economy during the past eighteen months of failures in the financial sector, and particularly the banking sector, make it essential that the dynamics of financia...
Dynamical continuous time random Lévy flights
Liu, Jian; Chen, Xiaosong
2016-03-01
The Lévy flights' diffusive behavior is studied within the framework of the dynamical continuous time random walk (DCTRW) method, while the nonlinear friction is introduced in each step. Through the DCTRW method, Lévy random walker in each step flies by obeying the Newton's Second Law while the nonlinear friction f(v) = - γ0v - γ2v3 being considered instead of Stokes friction. It is shown that after introducing the nonlinear friction, the superdiffusive Lévy flights converges, behaves localization phenomenon with long time limit, but for the Lévy index μ = 2 case, it is still Brownian motion.
Martingale Regressions for a Continuous Time Model of Exchange Rates
Guo, Zi-Yi
2017-01-01
One of the daunting problems in international finance is the weak explanatory power of existing theories of the nominal exchange rates, the so-called “foreign exchange rate determination puzzle”. We propose a continuous-time model to study the impact of order flow on foreign exchange rates. The model is estimated by a newly developed econometric tool based on a time-change sampling from calendar to volatility time. The estimation results indicate that the effect of order flow on exchange rate...
Recommender engine for continuous-time quantum Monte Carlo methods
Huang, Li; Yang, Yi-feng; Wang, Lei
2017-03-01
Recommender systems play an essential role in the modern business world. They recommend favorable items such as books, movies, and search queries to users based on their past preferences. Applying similar ideas and techniques to Monte Carlo simulations of physical systems boosts their efficiency without sacrificing accuracy. Exploiting the quantum to classical mapping inherent in the continuous-time quantum Monte Carlo methods, we construct a classical molecular gas model to reproduce the quantum distributions. We then utilize powerful molecular simulation techniques to propose efficient quantum Monte Carlo updates. The recommender engine approach provides a general way to speed up the quantum impurity solvers.
Continuous-time quantum walks on multilayer dendrimer networks
Galiceanu, Mircea; Strunz, Walter T.
2016-08-01
We consider continuous-time quantum walks (CTQWs) on multilayer dendrimer networks (MDs) and their application to quantum transport. A detailed study of properties of CTQWs is presented and transport efficiency is determined in terms of the exact and average return probabilities. The latter depends only on the eigenvalues of the connectivity matrix, which even for very large structures allows a complete analytical solution for this particular choice of network. In the case of MDs we observe an interplay between strong localization effects, due to the dendrimer topology, and good efficiency from the linear segments. We show that quantum transport is enhanced by interconnecting more layers of dendrimers.
Price discovery in a continuous-time setting
DEFF Research Database (Denmark)
Dias, Gustavo Fruet; Fernandes, Marcelo; Scherrer, Cristina
We formulate a continuous-time price discovery model in which the price discovery measure varies (stochastically) at daily frequency. We estimate daily measures of price discovery using a kernel-based OLS estimator instead of running separate daily VECM regressions as standard in the literature. We...... show that our estimator is not only consistent, but also outperforms the standard daily VECM in finite samples. We illustrate our theoretical findings by studying the price discovery process of 10 actively traded stocks in the U.S. from 2007 to 2013....
Coupled continuous time-random walks in quenched random environment
Magdziarz, M.; Szczotka, W.
2018-02-01
We introduce a coupled continuous-time random walk with coupling which is characteristic for Lévy walks. Additionally we assume that the walker moves in a quenched random environment, i.e. the site disorder at each lattice point is fixed in time. We analyze the scaling limit of such a random walk. We show that for large times the behaviour of the analyzed process is exactly the same as in the case of uncoupled quenched trap model for Lévy flights.
Discrete and continuous time dynamic mean-variance analysis
Reiss, Ariane
1999-01-01
Contrary to static mean-variance analysis, very few papers have dealt with dynamic mean-variance analysis. Here, the mean-variance efficient self-financing portfolio strategy is derived for n risky assets in discrete and continuous time. In the discrete setting, the resulting portfolio is mean-variance efficient in a dynamic sense. It is shown that the optimal strategy for n risky assets may be dominated if the expected terminal wealth is constrained to exactly attain a certain goal instead o...
Discrete time and continuous time dynamic mean-variance analysis
Reiss, Ariane
1999-01-01
Contrary to static mean-variance analysis, very few papers have dealt with dynamic mean-variance analysis. Here, the mean-variance efficient self-financing portfolio strategy is derived for n risky assets in discrete and continuous time. In the discrete setting, the resulting portfolio is mean-variance efficient in a dynamic sense. It is shown that the optimal strategy for n risky assets may be dominated if the expected terminal wealth is constrained to exactly attain a certain goal instead o...
Continuous-time quantum Monte Carlo impurity solvers
Gull, Emanuel; Werner, Philipp; Fuchs, Sebastian; Surer, Brigitte; Pruschke, Thomas; Troyer, Matthias
2011-04-01
Continuous-time quantum Monte Carlo impurity solvers are algorithms that sample the partition function of an impurity model using diagrammatic Monte Carlo techniques. The present paper describes codes that implement the interaction expansion algorithm originally developed by Rubtsov, Savkin, and Lichtenstein, as well as the hybridization expansion method developed by Werner, Millis, Troyer, et al. These impurity solvers are part of the ALPS-DMFT application package and are accompanied by an implementation of dynamical mean-field self-consistency equations for (single orbital single site) dynamical mean-field problems with arbitrary densities of states. Program summaryProgram title: dmft Catalogue identifier: AEIL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIL_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: ALPS LIBRARY LICENSE version 1.1 No. of lines in distributed program, including test data, etc.: 899 806 No. of bytes in distributed program, including test data, etc.: 32 153 916 Distribution format: tar.gz Programming language: C++ Operating system: The ALPS libraries have been tested on the following platforms and compilers: Linux with GNU Compiler Collection (g++ version 3.1 and higher), and Intel C++ Compiler (icc version 7.0 and higher) MacOS X with GNU Compiler (g++ Apple-version 3.1, 3.3 and 4.0) IBM AIX with Visual Age C++ (xlC version 6.0) and GNU (g++ version 3.1 and higher) compilers Compaq Tru64 UNIX with Compq C++ Compiler (cxx) SGI IRIX with MIPSpro C++ Compiler (CC) HP-UX with HP C++ Compiler (aCC) Windows with Cygwin or coLinux platforms and GNU Compiler Collection (g++ version 3.1 and higher) RAM: 10 MB-1 GB Classification: 7.3 External routines: ALPS [1], BLAS/LAPACK, HDF5 Nature of problem: (See [2].) Quantum impurity models describe an atom or molecule embedded in a host material with which it can exchange electrons. They are basic to nanoscience as
Correlated continuous time random walk and option pricing
Lv, Longjin; Xiao, Jianbin; Fan, Liangzhong; Ren, Fuyao
2016-04-01
In this paper, we study a correlated continuous time random walk (CCTRW) with averaged waiting time, whose probability density function (PDF) is proved to follow stretched Gaussian distribution. Then, we apply this process into option pricing problem. Supposing the price of the underlying is driven by this CCTRW, we find this model captures the subdiffusive characteristic of financial markets. By using the mean self-financing hedging strategy, we obtain the closed-form pricing formulas for a European option with and without transaction costs, respectively. At last, comparing the obtained model with the classical Black-Scholes model, we find the price obtained in this paper is higher than that obtained from the Black-Scholes model. A empirical analysis is also introduced to confirm the obtained results can fit the real data well.
Nonequilibrium thermodynamic potentials for continuous-time Markov chains.
Verley, Gatien
2016-01-01
We connect the rare fluctuations of an equilibrium (EQ) process and the typical fluctuations of a nonequilibrium (NE) stationary process. In the framework of large deviation theory, this observation allows us to introduce NE thermodynamic potentials. For continuous-time Markov chains, we identify the relevant pairs of conjugated variables and propose two NE ensembles: one with fixed dynamics and fluctuating time-averaged variables, and another with fixed time-averaged variables, but a fluctuating dynamics. Accordingly, we show that NE processes are equivalent to conditioned EQ processes ensuring that NE potentials are Legendre dual. We find a variational principle satisfied by the NE potentials that reach their maximum in the NE stationary state and whose first derivatives produce the NE equations of state and second derivatives produce the NE Maxwell relations generalizing the Onsager reciprocity relations.
Language Emptiness of Continuous-Time Parametric Timed Automata
DEFF Research Database (Denmark)
Benes, Nikola; Bezdek, Peter; Larsen, Kim Guldstrand
2015-01-01
Parametric timed automata extend the standard timed automata with the possibility to use parameters in the clock guards. In general, if the parameters are real-valued, the problem of language emptiness of such automata is undecidable even for various restricted subclasses. We thus focus on the case...... where parameters are assumed to be integer-valued, while the time still remains continuous. On the one hand, we show that the problem remains undecidable for parametric timed automata with three clocks and one parameter. On the other hand, for the case with arbitrary many clocks where only one......-time semantics only. To the best of our knowledge, this is the first positive result in the case of continuous-time and unbounded integer parameters, except for the rather simple case of single-clock automata....
A Continuous-Time Model for Valuing Foreign Exchange Options
Directory of Open Access Journals (Sweden)
James J. Kung
2013-01-01
Full Text Available This paper makes use of stochastic calculus to develop a continuous-time model for valuing European options on foreign exchange (FX when both domestic and foreign spot rates follow a generalized Wiener process. Using the dollar/euro exchange rate as input for parameter estimation and employing our FX option model as a yardstick, we find that the traditional Garman-Kohlhagen FX option model, which assumes constant spot rates, values incorrectly calls and puts for different values of the ratio of exchange rate to exercise price. Specifically, it undervalues calls when the ratio is between 0.70 and 1.08, and it overvalues calls when the ratio is between 1.18 and 1.30, whereas it overvalues puts when the ratio is between 0.70 and 0.82, and it undervalues puts when the ratio is between 0.86 and 1.30.
Evidence on Dropout Phenomena at Universities
DEFF Research Database (Denmark)
Larsen, Malene Rode; Sommersel, Hanna Bjørnøy; Larsen, Michael Søgaard
This publication is an excerpt from the full technical report ‘Dropout Phenomena at Universities: What is Dropout? Why does Dropout Occur? What Can be Done by the Universities to Prevent or Reduce it? A systematic review’, which was completed in April 2013. The purpose of this excerpt is to present...... the knowledge we have on dropout phenomena at European universities in a short, precise and comprehensible form to allow readers to orient themselves on the subject in a more readable manner....
San Diego's High School Dropout Crisis
Wilson, James C.
2012-01-01
This article highlights San Diego's dropout problem and how much it's costing the city and the state. Most San Diegans do not realize the enormous impact high school dropouts on their city. The California Dropout Research Project, located at the University of California at Santa Barbara, has estimated the lifetime cost of one class or cohort of…
Primary Education and Dropout in Nepal
Devkota, Shree Prasad; Bagale, Shiba
2015-01-01
This article tries to highlight the dropout rate of primary education of Nepal. The main essence of the article is to explore the situation of dropout of primary education. There are several programs and policies to reduce the dropout, out of the school children and so on but still there are several issues that are left behind. Educational budget…
Dropout during a driving simulator study: A survival analysis.
Matas, Nicole A; Nettelbeck, Ted; Burns, Nicholas R
2015-12-01
Simulator sickness is the occurrence of motion-sickness like symptoms that can occur during use of simulators and virtual reality technologies. This study investigated individual factors that contributed to simulator sickness and dropout while using a desktop driving simulator. Eighty-eight older adult drivers (mean age 72.82±5.42years) attempted a practice drive and two test drives. Participants also completed a battery of cognitive and visual assessments, provided information on their health and driving habits, and reported their experience of simulator sickness symptoms throughout the study. Fifty-two participants dropped out before completing the driving tasks. A time-dependent Cox Proportional Hazards model showed that female gender (HR=2.02), prior motion sickness history (HR=2.22), and Mini-SSQ score (HR=1.55) were associated with dropout. There were no differences between dropouts and completers on any of the cognitive abilities tests. Older adults are a high-risk group for simulator sickness. Within this group, female gender and prior motion sickness history are related to simulator dropout. Higher reported experience of symptoms of simulator sickness increased rates of dropout. The results highlight the importance of screening and monitoring of participants in driving simulation studies. Older adults, females, and those with a prior history of motion sickness may be especially at risk. Copyright © 2015 Elsevier Ltd and National Safety Council. All rights reserved.
Kolamunnage-Dona, Ruwanthi; Powell, Colin; Williamson, Paula Ruth
2016-04-28
Clinical trials with longitudinally measured outcomes are often plagued by missing data due to patients withdrawing or dropping out from the trial before completing the measurement schedule. The reasons for dropout are sometimes clearly known and recorded during the trial, but in many instances these reasons are unknown or unclear. Often such reasons for dropout are non-ignorable. However, the standard methods for analysing longitudinal outcome data assume that missingness is non-informative and ignore the reasons for dropout, which could result in a biased comparison between the treatment groups. In this article, as a post hoc analysis, we explore the impact of informative dropout due to competing reasons on the evaluation of treatment effect in the MAGNETIC trial, the largest randomised placebo-controlled study to date comparing the addition of nebulised magnesium sulphate to standard treatment in acute severe asthma in children. We jointly model longitudinal outcome and informative dropout process to incorporate the information regarding the reasons for dropout by treatment group. The effect of nebulised magnesium sulphate compared with standard treatment is evaluated more accurately using a joint longitudinal-competing risk model by taking account of such complexities. The corresponding estimates indicate that the rate of dropout due to good prognosis is about twice as high in the magnesium group compared with standard treatment. We emphasise the importance of identifying reasons for dropout and undertaking an appropriate statistical analysis accounting for such dropout. The joint modelling approach accounting for competing reasons for dropout is proposed as a general approach for evaluating the sensitivity of conclusions to assumptions regarding missing data in clinical trials with longitudinal outcomes. EudraCT number 2007-006227-12 . Registration date 18 Mar 2008.
Szafranski, Derek D; Snead, Alexandra; Allan, Nicholas P; Gros, Daniel F; Killeen, Therese; Flanagan, Julianne; Pericot-Valverde, Irene; Back, Sudie E
2017-10-01
High rates of comorbid posttraumatic stress disorder (PTSD) and substance use disorders (SUD) have been noted in veteran populations. Fortunately, there are a number of evidence-based psychotherapies designed to address comorbid PTSD and SUD. However, treatments targeting PTSD and SUD simultaneously often report high dropout rates. To date, only one study has examined predictors of dropout from PTSD/SUD treatment. To address this gap in the literature, this study aimed to 1) examine when in the course of treatment dropout occurred, and 2) identify predictors of dropout from a concurrent treatment for PTSD and SUD. Participants were 51 male and female veterans diagnosed with current PTSD and SUD. All participants completed at least one session of a cognitive-behavioral treatment (COPE) designed to simultaneously address PTSD and SUD symptoms. Of the 51 participants, 22 (43.1%) dropped out of treatment prior to completing the full 12 session COPE protocol. Results indicated that the majority of dropout (55%) occurred after session 6, with the largest amount of dropout occurring between sessions 9 and 10. Results also indicated a marginally significant relationship between greater baseline PTSD symptom severity and premature dropout. These findings highlight inconsistencies related to timing and predictors of dropout, as well as the dearth of information noted about treatment dropout within PTSD and SUD literature. Suggestions for procedural changes, such as implementing continual symptom assessments during treatment and increasing dialog between provider and patient about dropout were made with the hopes of increasing consistency of findings and eventually reducing treatment dropout. Published by Elsevier Ltd.
Continuous time quantum random walks in free space
Eichelkraut, Toni; Vetter, Christian; Perez-Leija, Armando; Christodoulides, Demetrios; Szameit, Alexander
2014-05-01
We show theoretically and experimentally that two-dimensional continuous time coherent random walks are possible in free space, that is, in the absence of any external potential, by properly tailoring the associated initial wave function. These effects are experimentally demonstrated using classical paraxial light. Evidently, the usage of classical beams to explore the dynamics of point-like quantum particles is possible since both phenomena are mathematically equivalent. This in turn makes our approach suitable for the realization of random walks using different quantum particles, including electrons and photons. To study the spatial evolution of a wavefunction theoretically, we consider the one-dimensional paraxial wave equation (i∂z +1/2 ∂x2) Ψ = 0 . Starting with the initially localized wavefunction Ψ (x , 0) = exp [ -x2 / 2σ2 ] J0 (αx) , one can show that the evolution of such Gaussian-apodized Bessel envelopes within a region of validity resembles the probability pattern of a quantum walker traversing a uniform lattice. In order to generate the desired input-field in our experimental setting we shape the amplitude and phase of a collimated light beam originating from a classical HeNe-Laser (633 nm) utilizing a spatial light modulator.
Chaos and unpredictability in evolution of cooperation in continuous time
You, Taekho; Kwon, Minji; Jo, Hang-Hyun; Jung, Woo-Sung; Baek, Seung Ki
2017-12-01
Cooperators benefit others with paying costs. Evolution of cooperation crucially depends on the cost-benefit ratio of cooperation, denoted as c . In this work, we investigate the infinitely repeated prisoner's dilemma for various values of c with four of the representative memory-one strategies, i.e., unconditional cooperation, unconditional defection, tit-for-tat, and win-stay-lose-shift. We consider replicator dynamics which deterministically describes how the fraction of each strategy evolves over time in an infinite-sized well-mixed population in the presence of implementation error and mutation among the four strategies. Our finding is that this three-dimensional continuous-time dynamics exhibits chaos through a bifurcation sequence similar to that of a logistic map as c varies. If mutation occurs with rate μ ≪1 , the position of the bifurcation sequence on the c axis is numerically found to scale as μ0.1, and such sensitivity to μ suggests that mutation may have nonperturbative effects on evolutionary paths. It demonstrates how the microscopic randomness of the mutation process can be amplified to macroscopic unpredictability by evolutionary dynamics.
Anomalous transport in turbulent plasmas and continuous time random walks
International Nuclear Information System (INIS)
Balescu, R.
1995-01-01
The possibility of a model of anomalous transport problems in a turbulent plasma by a purely stochastic process is investigated. The theory of continuous time random walks (CTRW's) is briefly reviewed. It is shown that a particular class, called the standard long tail CTRW's is of special interest for the description of subdiffusive transport. Its evolution is described by a non-Markovian diffusion equation that is constructed in such a way as to yield exact values for all the moments of the density profile. The concept of a CTRW model is compared to an exact solution of a simple test problem: transport of charged particles in a fluctuating magnetic field in the limit of infinite perpendicular correlation length. Although the well-known behavior of the mean square displacement proportional to t 1/2 is easily recovered, the exact density profile cannot be modeled by a CTRW. However, the quasilinear approximation of the kinetic equation has the form of a non-Markovian diffusion equation and can thus be generated by a CTRW
Stochastic calculus for uncoupled continuous-time random walks.
Germano, Guido; Politi, Mauro; Scalas, Enrico; Schilling, René L
2009-06-01
The continuous-time random walk (CTRW) is a pure-jump stochastic process with several applications not only in physics but also in insurance, finance, and economics. A definition is given for a class of stochastic integrals driven by a CTRW, which includes the Itō and Stratonovich cases. An uncoupled CTRW with zero-mean jumps is a martingale. It is proved that, as a consequence of the martingale transform theorem, if the CTRW is a martingale, the Itō integral is a martingale too. It is shown how the definition of the stochastic integrals can be used to easily compute them by Monte Carlo simulation. The relations between a CTRW, its quadratic variation, its Stratonovich integral, and its Itō integral are highlighted by numerical calculations when the jumps in space of the CTRW have a symmetric Lévy alpha -stable distribution and its waiting times have a one-parameter Mittag-Leffler distribution. Remarkably, these distributions have fat tails and an unbounded quadratic variation. In the diffusive limit of vanishing scale parameters, the probability density of this kind of CTRW satisfies the space-time fractional diffusion equation (FDE) or more in general the fractional Fokker-Planck equation, which generalizes the standard diffusion equation, solved by the probability density of the Wiener process, and thus provides a phenomenologic model of anomalous diffusion. We also provide an analytic expression for the quadratic variation of the stochastic process described by the FDE and check it by Monte Carlo.
Inverse Ising problem in continuous time: A latent variable approach
Donner, Christian; Opper, Manfred
2017-12-01
We consider the inverse Ising problem: the inference of network couplings from observed spin trajectories for a model with continuous time Glauber dynamics. By introducing two sets of auxiliary latent random variables we render the likelihood into a form which allows for simple iterative inference algorithms with analytical updates. The variables are (1) Poisson variables to linearize an exponential term which is typical for point process likelihoods and (2) Pólya-Gamma variables, which make the likelihood quadratic in the coupling parameters. Using the augmented likelihood, we derive an expectation-maximization (EM) algorithm to obtain the maximum likelihood estimate of network parameters. Using a third set of latent variables we extend the EM algorithm to sparse couplings via L1 regularization. Finally, we develop an efficient approximate Bayesian inference algorithm using a variational approach. We demonstrate the performance of our algorithms on data simulated from an Ising model. For data which are simulated from a more biologically plausible network with spiking neurons, we show that the Ising model captures well the low order statistics of the data and how the Ising couplings are related to the underlying synaptic structure of the simulated network.
A continuous-time neural model for sequential action.
Kachergis, George; Wyatte, Dean; O'Reilly, Randall C; de Kleijn, Roy; Hommel, Bernhard
2014-11-05
Action selection, planning and execution are continuous processes that evolve over time, responding to perceptual feedback as well as evolving top-down constraints. Existing models of routine sequential action (e.g. coffee- or pancake-making) generally fall into one of two classes: hierarchical models that include hand-built task representations, or heterarchical models that must learn to represent hierarchy via temporal context, but thus far lack goal-orientedness. We present a biologically motivated model of the latter class that, because it is situated in the Leabra neural architecture, affords an opportunity to include both unsupervised and goal-directed learning mechanisms. Moreover, we embed this neurocomputational model in the theoretical framework of the theory of event coding (TEC), which posits that actions and perceptions share a common representation with bidirectional associations between the two. Thus, in this view, not only does perception select actions (along with task context), but actions are also used to generate perceptions (i.e. intended effects). We propose a neural model that implements TEC to carry out sequential action control in hierarchically structured tasks such as coffee-making. Unlike traditional feedforward discrete-time neural network models, which use static percepts to generate static outputs, our biological model accepts continuous-time inputs and likewise generates non-stationary outputs, making short-timescale dynamic predictions. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
Continuous-time quantum algorithms for unstructured problems
International Nuclear Information System (INIS)
Hen, Itay
2014-01-01
We consider a family of unstructured optimization problems, for which we propose a method for constructing analogue, continuous-time (not necessarily adiabatic) quantum algorithms that are faster than their classical counterparts. In this family of problems, which we refer to as ‘scrambled input’ problems, one has to find a minimum-cost configuration of a given integer-valued n-bit black-box function whose input values have been scrambled in some unknown way. Special cases within this set of problems are Grover’s search problem of finding a marked item in an unstructured database, certain random energy models, and the functions of the Deutsch–Josza problem. We consider a couple of examples in detail. In the first, we provide an O(1) deterministic analogue quantum algorithm to solve the seminal problem of Deutsch and Josza, in which one has to determine whether an n-bit boolean function is constant (gives 0 on all inputs or 1 on all inputs) or balanced (returns 0 on half the input states and 1 on the other half). We also study one variant of the random energy model, and show that, as one might expect, its minimum energy configuration can be found quadratically faster with a quantum adiabatic algorithm than with classical algorithms. (paper)
Quantum trajectories and measurements in continuous time. The diffusive case
International Nuclear Information System (INIS)
Barchielli, Alberto; Gregoratti, Matteo
2009-01-01
continuous time for quantum systems. The two-level atom is again used to introduce and study an example of feedback based on the observed output. (orig.)
Echocardiography as an indication of continuous-time cardiac quiescence
Wick, C. A.; Auffermann, W. F.; Shah, A. J.; Inan, O. T.; Bhatti, P. T.; Tridandapani, S.
2016-07-01
Cardiac computed tomography (CT) angiography using prospective gating requires that data be acquired during intervals of minimal cardiac motion to obtain diagnostic images of the coronary vessels free of motion artifacts. This work is intended to assess B-mode echocardiography as a continuous-time indication of these quiescent periods to determine if echocardiography can be used as a cost-efficient, non-ionizing modality to develop new prospective gating techniques for cardiac CT. These new prospective gating approaches will not be based on echocardiography itself but on CT-compatible modalities derived from the mechanics of the heart (e.g. seismocardiography and impedance cardiography), unlike the current standard electrocardiogram. To this end, echocardiography and retrospectively-gated CT data were obtained from ten patients with varied cardiac conditions. CT reconstructions were made throughout the cardiac cycle. Motion of the interventricular septum (IVS) was calculated from both echocardiography and CT reconstructions using correlation-based, deviation techniques. The IVS was chosen because it (1) is visible in echocardiography images, whereas the coronary vessels generally are not, and (2) has been shown to be a suitable indicator of cardiac quiescence. Quiescent phases were calculated as the minima of IVS motion and CT volumes were reconstructed for these phases. The diagnostic quality of the CT reconstructions from phases calculated from echocardiography and CT data was graded on a four-point Likert scale by a board-certified radiologist fellowship-trained in cardiothoracic radiology. Using a Wilcoxon signed-rank test, no significant difference in the diagnostic quality of the coronary vessels was found between CT volumes reconstructed from echocardiography- and CT-selected phases. Additionally, there was a correlation of 0.956 between the echocardiography- and CT-selected phases. This initial work suggests that B-mode echocardiography can be used as a
Generalization bounds of ERM-based learning processes for continuous-time Markov chains.
Zhang, Chao; Tao, Dacheng
2012-12-01
Many existing results on statistical learning theory are based on the assumption that samples are independently and identically distributed (i.i.d.). However, the assumption of i.i.d. samples is not suitable for practical application to problems in which samples are time dependent. In this paper, we are mainly concerned with the empirical risk minimization (ERM) based learning process for time-dependent samples drawn from a continuous-time Markov chain. This learning process covers many kinds of practical applications, e.g., the prediction for a time series and the estimation of channel state information. Thus, it is significant to study its theoretical properties including the generalization bound, the asymptotic convergence, and the rate of convergence. It is noteworthy that, since samples are time dependent in this learning process, the concerns of this paper cannot (at least straightforwardly) be addressed by existing methods developed under the sample i.i.d. assumption. We first develop a deviation inequality for a sequence of time-dependent samples drawn from a continuous-time Markov chain and present a symmetrization inequality for such a sequence. By using the resultant deviation inequality and symmetrization inequality, we then obtain the generalization bounds of the ERM-based learning process for time-dependent samples drawn from a continuous-time Markov chain. Finally, based on the resultant generalization bounds, we analyze the asymptotic convergence and the rate of convergence of the learning process.
Work environment and school dropout
DEFF Research Database (Denmark)
Hansen, Claus D.; Andersen, Johan Hviid; Lund, Thomas
Aim The aim of this presentation is to examine the possible impact of work environment (and especially psychosocial work environment) on school dropout. The questions raised are: to what extent do psychosocial work environment and especially the social relations between young apprentices...... and their colleagues and managers play a role in dropping out of upper secondary education? Methods A cohort of 3058 adolescents born in 1989 and a cohort of approximately 2000 young adults born in 1983 are used to examine the associations between work environment and subsequent dropout in upper secondary educational...... indicated that ‘being treated badly by superior’ was part of the reason for doing so. Further analyses show that reporting repetitive and monotonous work tasks increases the risk of dropping out (OR: 1.74) and that reporting bad working climate at ones work place increases the risk of considering...
On the Inductive Bias of Dropout
Helmbold, David P.; Long, Philip M.
2014-01-01
Dropout is a simple but effective technique for learning in neural networks and other settings. A sound theoretical understanding of dropout is needed to determine when dropout should be applied and how to use it most effectively. In this paper we continue the exploration of dropout as a regularizer pioneered by Wager, et.al. We focus on linear classification where a convex proxy to the misclassification loss (i.e. the logistic loss used in logistic regression) is minimized. We show: (a) when...
Zvoch, Keith
2006-01-01
Data from a large school district in the southwestern United States were analyzed to investigate relations between student and school characteristics and high school freshman dropout patterns. Application of a multilevel logistic regression model to student dropout data revealed evidence of school-to-school differences in student dropout rates and…
Drop-out probabilities of IrisPlex SNP alleles
DEFF Research Database (Denmark)
Andersen, Jeppe Dyrberg; Tvedebrink, Torben; Mogensen, Helle Smidt
2013-01-01
In certain crime cases, information about a perpetrator's phenotype, including eye colour, may be a valuable tool if no DNA profile of any suspect or individual in the DNA database matches the DNA profile found at the crime scene. Often, the available DNA material is sparse and allelic drop-out...... of true alleles is possible. As part of the validation of the IrisPlex assay in our ISO17025 accredited, forensic genetic laboratory, we estimated the probability of drop-out of specific SNP alleles using 29 and 30 PCR cycles and 25, 50 and 100 Single Base Extension (SBE) cycles. We observed no drop-out...... when the amount of DNA was greater than 125 pg for 29 cycles of PCR and greater than 62 pg for 30 cycles of PCR. With the use of a logistic regression model, we estimated the allele specific probability of drop-out in heterozygote systems based on the signal strength of the observed allele...
Factors associated with dropout in medical education: a literature review
DEFF Research Database (Denmark)
O'Neill, Lotte; Wallstedt, Birgitta; Eika, Berit
2011-01-01
Medical school dropout may have negative consequences for society, patients, the profession, schools and dropouts. To our knowledge, the literature dealing with dropout from medical school has never been systematically and critically appraised.......Medical school dropout may have negative consequences for society, patients, the profession, schools and dropouts. To our knowledge, the literature dealing with dropout from medical school has never been systematically and critically appraised....
Detectability of Granger causality for subsampled continuous-time neurophysiological processes.
Barnett, Lionel; Seth, Anil K
2017-01-01
Granger causality is well established within the neurosciences for inference of directed functional connectivity from neurophysiological data. These data usually consist of time series which subsample a continuous-time biophysiological process. While it is well known that subsampling can lead to imputation of spurious causal connections where none exist, less is known about the effects of subsampling on the ability to reliably detect causal connections which do exist. We present a theoretical analysis of the effects of subsampling on Granger-causal inference. Neurophysiological processes typically feature signal propagation delays on multiple time scales; accordingly, we base our analysis on a distributed-lag, continuous-time stochastic model, and consider Granger causality in continuous time at finite prediction horizons. Via exact analytical solutions, we identify relationships among sampling frequency, underlying causal time scales and detectability of causalities. We reveal complex interactions between the time scale(s) of neural signal propagation and sampling frequency. We demonstrate that detectability decays exponentially as the sample time interval increases beyond causal delay times, identify detectability "black spots" and "sweet spots", and show that downsampling may potentially improve detectability. We also demonstrate that the invariance of Granger causality under causal, invertible filtering fails at finite prediction horizons, with particular implications for inference of Granger causality from fMRI data. Our analysis emphasises that sampling rates for causal analysis of neurophysiological time series should be informed by domain-specific time scales, and that state-space modelling should be preferred to purely autoregressive modelling. On the basis of a very general model that captures the structure of neurophysiological processes, we are able to help identify confounds, and offer practical insights, for successful detection of causal connectivity
Predictors of school dropout among adolescents in Puerto Rico.
Calderón, José M; Robles, Rafaela R; Reyes, Juan C; Matos, Tomás D; Negrón, Juan L; Cruz, Miguel A
2009-12-01
This research aims to understand the circumstances associated with school dropout in a cohort of Puerto Rican adolescents. The study collected data from adolescents and their parents. Information related to school dropout among adolescents was obtained from the second year follow-up data from the longitudinal study funded by NIDA "Risky Families Embedded in Risky Environments" (Grant No. R01 DA 15301). Data was collected employing a self-administered and a face-to-face interview protocol. Prediction of school dropout was assessed throughout adolescent characteristics, family background, school experiences and behaviors. During the second follow-up, two years after the baseline assessment, approximately 6.2% of the adolescents reported dropping out from school. Logistic regression analysis indicates that older adolescents (OR = 6.6, 1.37-31.67), whose mother used drugs during pregnancy (OR = 4.9, 1.31-17.91), who reported high rates of absenteeism (OR = 4.8, 1.63-14.13), high school grade retention (OR = 3.7, 1.14-12.05), and attended school where teachers were attacked or wounded by students (O R =7.0, 1.44-34.17) were more likely to dropout of school. : These findings emphasize the need to further understand the effects of different elements of adolescents' environment such as family and school. It has been posited that dropping out of school is a process whose characteristics can be detected long before it occurs. The fact that students who dropout are more likely to report skip classes and grade retention can be relevant elements in prevention and early intervention for teachers and other school personnel.
Factors predicting dropout in student nursing assistants
DEFF Research Database (Denmark)
Svensson, Annemarie Lyng; Strøyer, Jesper; Ebbehøj, Niels Erik
2008-01-01
BACKGROUND: The dropout rate among student nursing assistants (NAs) in Danish health and social care education is high at >20%. AIMS: To explore if recent low back pain (LBP) history is a predictor of dropout among NA students, taking into account conventional risk factors for LBP, general health...
Predicting secondary school dropout among South African ...
African Journals Online (AJOL)
... not living with one's mother, smoking cigarettes in the past month, and lower levels of leisure-related intrinsic motivation significantly predicted dropout. Results support comprehensive prevention programmes that target risk behaviour and leisure. Keywords: adolescence; leisure motivation; school dropout; substance use ...
West Virginia Dropout Study, 1985-86.
West Virginia State Dept. of Education, Charleston. Div. of General and Special Educational Development.
Reported in this document are dropout statistics from the State of West Virginia for the school year 1985-86. This annual survey of the 55 county school systems has been conducted since the 1968-69 school year. Topics surveyed include Education Consolidation and Improvement Act (ECIA) status, exit interviews, grade at exit, month dropout left…
When and Why Dropouts Leave High School
Stearns, Elizabeth; Glennie, Elizabeth J.
2006-01-01
Teens may leave school because of academic failure, disciplinary problems, or employment opportunities. In this article, the authors test whether the reasons dropouts leave school differ by grade level and age. We compare dropout rates and reasons across grade levels and ages for all high school students, ethnic groups, and gender groups. Across…
Parents and the School Dropout Problem.
Ferguson, Earl E.; Killingsworth, Jerry
1987-01-01
The school dropout problem is discussed, with suggestions for parents on ensuring that their children do not become part of the dropout population, including; monitoring children's school attendance patterns; making sure children understand how important school and attendance is; maintaining close contact with teachers; and helping children…
University Drop-Out: An Italian Experience
Belloc, Filippo; Maruotti, Antonello; Petrella, Lea
2010-01-01
University students' drop-out is a crucial issue for the universities' efficiency evaluation and funding. In this paper, we analyze the drop-out rate of the Economics and Business faculty of Sapienza University of Rome. We use administrative data on 9,725 undergraduates students enrolled in three-years bachelor programs from 2001 to 2007 and…
Valued Youth Anthology: Articles on Dropout Prevention.
Intercultural Development Research Association, San Antonio, TX.
This document contains, in chronological order, all articles related to dropouts that have appeared in the Intercultural Development Research Association (IDRA) Newsletter from 1986 to 1989. The articles are: (1) "The Prevention and Recovery of Dropouts: An Action Agenda" (Robledo); (2) "Coca Cola Valued Youth Partnership Program Results of Second…
Revisiting Primary School Dropout in Rural Cambodia
No, Fata; Sam, Chanphirun; Hirakawa, Yukiko
2012-01-01
Previous studies on school dropout in Cambodia often used data from subjects after they already dropped out or statistics from education-related institutions. Using data from children in two rural provinces before they dropped out, this study examines four main factors in order to identify their influence on primary school dropout in Cambodia.…
Child Psychotherapy Dropout: An Empirical Research Review
Deakin, Elisabeth; Gastaud, Marina; Nunes, Maria Lucia Tiellet
2012-01-01
This study aims to discuss the most recent data about child psychotherapy dropout, especially child psychoanalytical psychotherapy. The authors also try to offer some possible alternatives to prevent such a phenomenon. The definition of "child psychotherapy dropout" is extensively discussed. The goal has been to attempt to create a standardised…
Patterns, Consequences, and Possible Causes of Dropout in Upper Secondary Education in Mexico
Directory of Open Access Journals (Sweden)
Raja Bentaouet Kattan
2015-01-01
Full Text Available The present study provides a detailed analysis of upper secondary education dropout patterns in Mexico, exploring its consequences and possible causes. To perform the analysis we combine different databases and statistical methods ranging from the use of surveys with information on specific individuals to data aggregated at the municipal and state level. The main value added is the simultaneous analysis of the influence of individual-family, community, and macroaggregate factors, on school dropout in the country.
Relay selection in cooperative communication systems over continuous time-varying fading channel
Directory of Open Access Journals (Sweden)
Ke Geng
2017-02-01
Full Text Available In this paper, we study relay selection under outdated channel state information (CSI in a decode-and-forward (DF cooperative system. Unlike previous researches on cooperative communication under outdated CSI, we consider that the channel varies continuously over time, i.e., the channel not only changes between relay selection and data transmission but also changes during data transmission. Thus the level of accuracy of the CSI used in relay selection degrades with data transmission. We first evaluate the packet error rate (PER of the cooperative system under continuous time-varying fading channel, and find that the PER performance deteriorates more seriously under continuous time-varying fading channel than when the channel is assumed to be constant during data transmission. Then, we propose a repeated relay selection (RRS strategy to improve the PER performance, in which the forwarded data is divided into multiple segments and relay is reselected before the transmission of each segment based on the updated CSI. Finally, we propose a combined relay selection (CRS strategy which takes advantage of three different relay selection strategies to further mitigate the impact of outdated CSI.
Factors predicting dropout in student nursing assistants.
Svensson, Annemarie Lyng; Strøyer, Jesper; Ebbehøj, Niels Erik; Mortensen, Ole Steen
2008-12-01
The dropout rate among student nursing assistants (NAs) in Danish health and social care education is high at >20%. To explore if recent low back pain (LBP) history is a predictor of dropout among NA students, taking into account conventional risk factors for LBP, general health and physical fitness. Prospective study with 14-month follow-up (the duration of the education) in two schools of health and social care in the Region of Copenhagen, Denmark. Participants completed a comprehensive questionnaire, and their physical fitness (balance, back extension endurance, back flexion endurance and sagittal flexibility) was assessed at baseline. Dropout was defined as failure to complete NA education. A total of 790 subjects, 87% of those invited, completed the questionnaire; 612 subjects also completed the physical tests and were included in the present study and 500 (83%) were women. Recent LBP was not an independent predictor of school dropout. However, only among women who had LBP were other factors (a history of previous exposure to heavy physical workload, a low mental health score and failure to pass the back extension endurance test) associated with risk of dropout, OR (95% CI)=2.5 (1.2-5.3). Among men, only low height was significantly associated with dropout risk. A recent LBP history was not an independent single predictor of dropout from NA education but was a risk factor in combination with other factors.
Directory of Open Access Journals (Sweden)
Julie C.S. Boiché
2009-03-01
Full Text Available The purpose of this study was to investigate a large number of determinants of sport dropout among French adolescents, in order to reveal proximal and distal factors of dropout. 261 current and 106 dropout athletes (M = 14.6 participated to the study. The data were collected by a questionnaire assessing demographic information, athletes' perceptions on their experience, their parents, teammates and coach. t-tests revealed that current and former athletes were distinct on numerous variables. A discriminant function analysis showed three proximal predictors of sport dropout (perceived value of the activity, satisfaction, parents' investment. Subsequent regression analyses showed that perceived value was positively predicted by perceived competence, the value of the activity for teammates, coach's investment, and negatively by conflicts of interest and goal conflict with teammates; satisfaction was positively predicted by the coach's mastery climate, but negatively predicted by conflicts of interest and goal conflict with teammates and with the coach; parents investment was negatively predicted by the goal conflicts with them. This study permitted to discriminate between proximal and more distal psychological antecedents of the dropout behaviour. It brings information relative to the possible targets of interventions aiming at preventing dropout from organized sport
A District View: Dropouts and the Differentiated Diploma
Holden, E. Todd
2012-01-01
More students are deciding to dropout of school prior to graduation. As a result the dropout rate has become a hot topic in education across the United States. The average high school dropout salary is approximately 50% less than the salary of a high school graduate. The social factors are another reason the dropout rate needs to be a high…
Stabilization of Continuous-Time Random Switching Systems via a Fault-Tolerant Controller
Directory of Open Access Journals (Sweden)
Guoliang Wang
2017-01-01
Full Text Available This paper focuses on the stabilization problem of continuous-time random switching systems via exploiting a fault-tolerant controller, where the dwell time of each subsystem consists of a fixed part and random part. It is known from the traditional design methods that the computational complexity of LMIs related to the quantity of fault combination is very large; particularly system dimension or amount of subsystems is large. In order to reduce the number of the used fault combinations, new sufficient LMI conditions for designing such a controller are established by a robust approach, which are fault-free and could be solved directly. Moreover, the fault-tolerant stabilization realized by a mode-independent controller is considered and suitably applied to a practical case without mode information. Finally, a numerical example is used to demonstrate the effectiveness and superiority of the proposed methods.
Examining the Factors Affecting Student Dropout
Directory of Open Access Journals (Sweden)
Fethi Ahmet INAN
2006-07-01
Full Text Available This study examined the factors affecting student dropouts in an online certificate program. In this research, a combination of quantitative and qualitative methods was used. Online Course Dropout Survey was developed and used to determine which factors affect student attrition from the program. The dropout survey was sent by e-mail to 98 students who had dropped the program. Twenty-six students returned the survey. The findings show that the most important factor affecting student retention is finding sufficient time to study. Having personal problems and affordability of the program took second and third place.
Data-driven system to predict academic grades and dropout
Rovira, Sergi; Puertas, Eloi
2017-01-01
Nowadays, the role of a tutor is more important than ever to prevent students dropout and improve their academic performance. This work proposes a data-driven system to extract relevant information hidden in the student academic data and, thus, help tutors to offer their pupils a more proactive personal guidance. In particular, our system, based on machine learning techniques, makes predictions of dropout intention and courses grades of students, as well as personalized course recommendations. Moreover, we present different visualizations which help in the interpretation of the results. In the experimental validation, we show that the system obtains promising results with data from the degree studies in Law, Computer Science and Mathematics of the Universitat de Barcelona. PMID:28196078
A continuous-time/discrete-time mixed audio-band sigma delta ADC
International Nuclear Information System (INIS)
Liu Yan; Hua Siliang; Wang Donghui; Hou Chaohuan
2011-01-01
This paper introduces a mixed continuous-time/discrete-time, single-loop, fourth-order, 4-bit audio-band sigma delta ADC that combines the benefits of continuous-time and discrete-time circuits, while mitigating the challenges associated with continuous-time design. Measurement results show that the peak SNR of this ADC reaches 100 dB and the total power consumption is less than 30 mW. (semiconductor integrated circuits)
Fully on-chip switched capacitor NMOS low dropout voltage regulator
Camacho, D; Camacho, Daniel; Moreira, Paulo
2010-01-01
This paper presents a 1.5 V 50 mA low dropout voltage (LDO) regulator using an NMOS transistor as the output pass element. Continuous time,operation of the LDO is achieved using a new switched floating capacitor scheme that raises the gate voltage of the pass element. The regulator has a 0.2 V dropout at a 50 mA load and is stable for a wide load current range with loading capacitances up to 50 pF. The output variation when a full load step is applied is 300 mV and the recovery time is below 0.3 mu s. it is designed in a 0.13 mu m CMOS process with an area of 0.008 mm(2) and its operation does not require any external component.
Is obesity associated with school dropout? Key developmental and ethnic differences
Lanza, H. Isabella; Huang, David Y.C.
2015-01-01
Background We aimed to expand the literature on child obesity and school outcomes by examining associations between obesity and high school dropout, including the role of obesity onset and duration as well as ethnicity. Methods Data on 5066 children obtained between 1986 and 2010 from the child cohort of the 1979 National Longitudinal Study of Youth (NLSY79) were analyzed. Group-based trajectory analysis identified obesity trajectories from 6-18 years. School completion information from age 14 into young adulthood was used to calculate school dropout. Chi-square and pairwise comparison tests were used to identify significant associations between obesity trajectories and school dropout. Results Adolescents belonging to an increasing trajectory (adolescent-onset obesity) had a higher likelihood of dropping out of high school compared to those belonging to chronic, decreasing (childhood-only obesity), and non-obese trajectories. This association was particularly salient among white adolescents. Conclusions Obesity onset during early adolescence increased risk of high school dropout. White adolescents were particularly vulnerable. Given that early adolescence is marked by significant biological and social changes, future research should seek to identify the underlying processes linking adolescent-obesity and school dropout to decrease school dropout risk among this vulnerable population. PMID:26331748
Dropout of Children from schools in Nepal
Wagle, Dhirendra
2012-01-01
Nepal, a developing country of the south-asian region has bigger problem of children not completing the full cycle of basic education. In other words, large number of children dropout of schools, especially in the primary and secondary level of schooling. Especially, the situation is worse for those of the backward and socially disadvantaged populations and of the rural and the remote areas. Being in this frame, this study focused on the reasons of dropout of children from schools and the pos...
Towards dropout training for convolutional neural networks.
Wu, Haibing; Gu, Xiaodong
2015-11-01
Recently, dropout has seen increasing use in deep learning. For deep convolutional neural networks, dropout is known to work well in fully-connected layers. However, its effect in convolutional and pooling layers is still not clear. This paper demonstrates that max-pooling dropout is equivalent to randomly picking activation based on a multinomial distribution at training time. In light of this insight, we advocate employing our proposed probabilistic weighted pooling, instead of commonly used max-pooling, to act as model averaging at test time. Empirical evidence validates the superiority of probabilistic weighted pooling. We also empirically show that the effect of convolutional dropout is not trivial, despite the dramatically reduced possibility of over-fitting due to the convolutional architecture. Elaborately designing dropout training simultaneously in max-pooling and fully-connected layers, we achieve state-of-the-art performance on MNIST, and very competitive results on CIFAR-10 and CIFAR-100, relative to other approaches without data augmentation. Finally, we compare max-pooling dropout and stochastic pooling, both of which introduce stochasticity based on multinomial distributions at pooling stage. Copyright © 2015 Elsevier Ltd. All rights reserved.
Accurate Lithium-ion battery parameter estimation with continuous-time system identification methods
International Nuclear Information System (INIS)
Xia, Bing; Zhao, Xin; Callafon, Raymond de; Garnier, Hugues; Nguyen, Truong; Mi, Chris
2016-01-01
Highlights: • Continuous-time system identification is applied in Lithium-ion battery modeling. • Continuous-time and discrete-time identification methods are compared in detail. • The instrumental variable method is employed to further improve the estimation. • Simulations and experiments validate the advantages of continuous-time methods. - Abstract: The modeling of Lithium-ion batteries usually utilizes discrete-time system identification methods to estimate parameters of discrete models. However, in real applications, there is a fundamental limitation of the discrete-time methods in dealing with sensitivity when the system is stiff and the storage resolutions are limited. To overcome this problem, this paper adopts direct continuous-time system identification methods to estimate the parameters of equivalent circuit models for Lithium-ion batteries. Compared with discrete-time system identification methods, the continuous-time system identification methods provide more accurate estimates to both fast and slow dynamics in battery systems and are less sensitive to disturbances. A case of a 2"n"d-order equivalent circuit model is studied which shows that the continuous-time estimates are more robust to high sampling rates, measurement noises and rounding errors. In addition, the estimation by the conventional continuous-time least squares method is further improved in the case of noisy output measurement by introducing the instrumental variable method. Simulation and experiment results validate the analysis and demonstrate the advantages of the continuous-time system identification methods in battery applications.
Integrating Continuous-Time and Discrete-Event Concepts in Process Modelling, Simulation and Control
Beek, van D.A.; Gordijn, S.H.F.; Rooda, J.E.; Ertas, A.
1995-01-01
Currently, modelling of systems in the process industry requires the use of different specification languages for the specification of the discrete-event and continuous-time subsystems. In this way, models are restricted to individual subsystems of either a continuous-time or discrete-event nature.
Risk Psychosocial Factors to School Dropout and Early Teenage Pregnancy
Directory of Open Access Journals (Sweden)
Fabián Antonio Dávila Ramírez
2016-01-01
Full Text Available To explore the frequency and weight that psychosocial risk factors predispose to outcomes of early pregnancy and scholar dropout, a descriptive review was conducted. Materials and Methods: A search and review of the results reported by observational studies in the PubMed database indexed from July 27, 2010 until July 25, 2013 was performed, restricting the search to studies in humans, Spanish or English written, not made in countries in Africa or Asia. Search was widened to LILACS database for the years 2006 to 2013 for Latinamerican countries. For inclusion, all case-control studies comparing different types of interventions and psychosocial risk factors in adolescents were eligible. Results: The review suggests violence experienced during adolescence, sexual abuse, belonging to a low socioeconomic status, low self-esteem, eating behavior disorders, smoking, alcoholism and drug addiction, mental disorders, early initiation of sex, poor family ties, lack of access to information, and resources for family planning as main psychosocial factors related to early pregnancy and scholar dropout in adolescents. Conclusions: Both risk factors associated with pregnancy and scholar dropout were described, and interventions targeting the described risk factors could potentially contribute to the reduction of these outcomes were described.
Dropouts and Budgets: A Test of a Dropout Reduction Model among Students in Israeli Higher Education
Bar-Am, Ran; Arar, Osama
2017-01-01
This article deals with the problem of student dropout during the first year in a higher education institution. To date, no model on a budget has been developed and tested to prevent dropout among Engineering Students. This case study was conducted among first-year students taking evening classes in two practical engineering colleges in Israel.…
Predicting Psychotherapy Dropouts: A Multilevel Approach.
Kegel, Alexander F; Flückiger, Christoph
2015-01-01
The role of therapeutic processes in predicting premature termination of psychotherapy has been a particular focus of recent research. The purpose of this study was to contrast outpatients who completed therapy and those who dropped out with respect to their self-reported in-session experiences of self-esteem, mastery, clarification and the therapeutic alliance. The 296 patients with mixed disorders were treated with an integrative form of cognitive-behavioural therapy without pre-determined time limit (M = 20.2 sessions). Multilevel analyses indicated that patients who did not completetreatment reported, on average, lower levels of self-esteem, mastery and clarification and lower ratings of their therapeutic alliance in treatment in contrast to patients who completed therapy. Patient-reported change in self-esteem experiences over the course of treatment turned out to be the strongest predictor of dropout from psychotherapy or successful completion. When dropout occurred before the average treatment length was reached, patients reported fewer clarifying experiences as early as the first session and their ratings of the therapeutic alliance were characterized by an absence of positive development. Both of these aspects seem to be involved in patients' decisions to leave treatment early. The findings underscore the importance of the therapeutic process in understanding the mechanisms behind treatment dropout. Analyses data from 296 patients at a private outpatient clinic in a routine practice setting (CBT). Completer/dropout definition: presence or absence of measurement battery at post-assessment. Focuses on change in therapy processes by investigating post-session reports. Finds that positive changes in self-esteem experiences is the most robust predictor of dropout, followed by ratings of clarification experiences and the global alliance. In line with recent dropout research, these process indicators might help to detect therapeutic situations that are
International Nuclear Information System (INIS)
Liang Jinling; Cao Jinde
2004-01-01
First, convergence of continuous-time Bidirectional Associative Memory (BAM) neural networks are studied. By using Lyapunov functionals and some analysis technique, the delay-independent sufficient conditions are obtained for the networks to converge exponentially toward the equilibrium associated with the constant input sources. Second, discrete-time analogues of the continuous-time BAM networks are formulated and studied. It is shown that the convergence characteristics of the continuous-time systems are preserved by the discrete-time analogues without any restriction imposed on the uniform discretionary step size. An illustrative example is given to demonstrate the effectiveness of the obtained results
The reasons of dropout of sport in Hong Kong school athletes
Hassan, Abdul-Rahman; Lam, Michael Huen Sum; Ku, Susanna; Li, William Ho Cheung; Lee, Ka Yiu; Ho, Eva; Flint, Stuart W.; Wong, Anthony Siu Wo
2017-01-01
Dropout of sport is an issue in sport and public health domains. The aim of this study was to identify the potential dropout reasons of school athletes and to examine if their perception of dropout was affected by the previous dropout experience. There were 50 subjects who were divided into two groups based on their previous dropout experience (Dropout Group=22, No Dropout Group=28). They filled a questionnaire about potential dropout reasons of the current sport. Coach and teammates were two...
The influence of different curriculum designs on students' dropout rate: a case study.
Vergel, John; Quintero, Gustavo A; Isaza-Restrepo, Andrés; Ortiz-Fonseca, Martha; Latorre-Santos, Catalina; Pardo-Oviedo, Juan Mauricio
2018-12-01
The relationship between students' withdrawal and educational variables has generated a considerable number of publications. As the explosion of information in sciences and integration theories led to creating different curriculum designs, it has been assumed that differences among designs explain academic success and, therefore, students' retention. However, little attention has been given to examine explicitly how diverse designs influence dropout rates in practice, which questions if decisions to reform curricula are sufficiently informed. This article describes our curriculum reform, which exposes our former and current curriculum designs as having had dissimilar dropout percentages. Furthermore, we aimed to explore the influence of different curriculum designs on students' dropout rates. The conclusion is that dropout variations may be explained not only because of the curriculum design itself, but also because of the power relationship changes between teachers and students that brought out the design change. Consequently, more research is needed to fully understand the political implications of different curriculum designs and their influence on dropout rates.
The influence of different curriculum designs on students’ dropout rate: a case study
Vergel, John; Quintero, Gustavo A.; Isaza-Restrepo, Andrés; Ortiz-Fonseca, Martha; Latorre-Santos, Catalina; Pardo-Oviedo, Juan Mauricio
2018-01-01
ABSTRACT The relationship between students’ withdrawal and educational variables has generated a considerable number of publications. As the explosion of information in sciences and integration theories led to creating different curriculum designs, it has been assumed that differences among designs explain academic success and, therefore, students’ retention. However, little attention has been given to examine explicitly how diverse designs influence dropout rates in practice, which questions if decisions to reform curricula are sufficiently informed. This article describes our curriculum reform, which exposes our former and current curriculum designs as having had dissimilar dropout percentages. Furthermore, we aimed to explore the influence of different curriculum designs on students’ dropout rates. The conclusion is that dropout variations may be explained not only because of the curriculum design itself, but also because of the power relationship changes between teachers and students that brought out the design change. Consequently, more research is needed to fully understand the political implications of different curriculum designs and their influence on dropout rates. PMID:29392996
CMOS continuous-time adaptive equalizers for high-speed serial links
Gimeno Gasca, Cecilia; Aldea Chagoyen, Concepción
2015-01-01
This book introduces readers to the design of adaptive equalization solutions integrated in standard CMOS technology for high-speed serial links. Since continuous-time equalizers offer various advantages as an alternative to discrete-time equalizers at multi-gigabit rates, this book provides a detailed description of continuous-time adaptive equalizers design - both at transistor and system levels-, their main characteristics and performances. The authors begin with a complete review and analysis of the state of the art of equalizers for wireline applications, describing why they are necessary, their types, and their main applications. Next, theoretical fundamentals of continuous-time adaptive equalizers are explored. Then, new structures are proposed to implement the different building blocks of the adaptive equalizer: line equalizer, loop-filters, power comparator, etc. The authors demonstrate the design of a complete low-power, low-voltage, high-speed, continuous-time adaptive equalizer. Finally, a cost-...
International Nuclear Information System (INIS)
Huo Haifeng; Li Wantong
2009-01-01
This paper is concerned with the global stability characteristics of a system of equations modelling the dynamics of continuous-time bidirectional associative memory neural networks with impulses. Sufficient conditions which guarantee the existence of a unique equilibrium and its exponential stability of the networks are obtained. For the goal of computation, discrete-time analogues of the corresponding continuous-time bidirectional associative memory neural networks with impulses are also formulated and studied. Our results show that the above continuous-time and discrete-time systems with impulses preserve the dynamics of the networks without impulses when we make some modifications and impose some additional conditions on the systems, the convergence characteristics dynamics of the networks are preserved by both continuous-time and discrete-time systems with some restriction imposed on the impulse effect.
Comolli, Alessandro; Hakoun, Vivien; Dentz, Marco
2017-04-01
Achieving the understanding of the process of solute transport in heterogeneous porous media is of crucial importance for several environmental and social purposes, ranging from aquifers contamination and remediation, to risk assessment in nuclear waste repositories. The complexity of this aim is mainly ascribable to the heterogeneity of natural media, which can be observed at all the scales of interest, from pore scale to catchment scale. In fact, the intrinsic heterogeneity of porous media is responsible for the arising of the well-known non-Fickian footprints of transport, including heavy-tailed breakthrough curves, non-Gaussian spatial density profiles and the non-linear growth of the mean squared displacement. Several studies investigated the processes through which heterogeneity impacts the transport properties, which include local modifications to the advective-dispersive motion of solutes, mass exchanges between some mobile and immobile phases (e.g. sorption/desorption reactions or diffusion into solid matrix) and spatial correlation of the flow field. In the last decades, the continuous time random walk (CTRW) model has often been used to describe solute transport in heterogenous conditions and to quantify the impact of point heterogeneity, spatial correlation and mass transfer on the average transport properties [1]. Open issues regarding this approach are the possibility to relate measurable properties of the medium to the parameters of the model, as well as its capability to provide predictive information. In a recent work [2] the authors have shed new light on understanding the relationship between Lagrangian and Eulerian dynamics as well as on their evolution from arbitrary initial conditions. On the basis of these results, we derive a CTRW model for the description of Darcy-scale transport in d-dimensional media characterized by spatially random permeability fields. The CTRW approach models particle velocities as a spatial Markov process, which is
Continuous time Boolean modeling for biological signaling: application of Gillespie algorithm.
Stoll, Gautier; Viara, Eric; Barillot, Emmanuel; Calzone, Laurence
2012-08-29
Mathematical modeling is used as a Systems Biology tool to answer biological questions, and more precisely, to validate a network that describes biological observations and predict the effect of perturbations. This article presents an algorithm for modeling biological networks in a discrete framework with continuous time. There exist two major types of mathematical modeling approaches: (1) quantitative modeling, representing various chemical species concentrations by real numbers, mainly based on differential equations and chemical kinetics formalism; (2) and qualitative modeling, representing chemical species concentrations or activities by a finite set of discrete values. Both approaches answer particular (and often different) biological questions. Qualitative modeling approach permits a simple and less detailed description of the biological systems, efficiently describes stable state identification but remains inconvenient in describing the transient kinetics leading to these states. In this context, time is represented by discrete steps. Quantitative modeling, on the other hand, can describe more accurately the dynamical behavior of biological processes as it follows the evolution of concentration or activities of chemical species as a function of time, but requires an important amount of information on the parameters difficult to find in the literature. Here, we propose a modeling framework based on a qualitative approach that is intrinsically continuous in time. The algorithm presented in this article fills the gap between qualitative and quantitative modeling. It is based on continuous time Markov process applied on a Boolean state space. In order to describe the temporal evolution of the biological process we wish to model, we explicitly specify the transition rates for each node. For that purpose, we built a language that can be seen as a generalization of Boolean equations. Mathematically, this approach can be translated in a set of ordinary differential
A joint logistic regression and covariate-adjusted continuous-time Markov chain model.
Rubin, Maria Laura; Chan, Wenyaw; Yamal, Jose-Miguel; Robertson, Claudia Sue
2017-12-10
The use of longitudinal measurements to predict a categorical outcome is an increasingly common goal in research studies. Joint models are commonly used to describe two or more models simultaneously by considering the correlated nature of their outcomes and the random error present in the longitudinal measurements. However, there is limited research on joint models with longitudinal predictors and categorical cross-sectional outcomes. Perhaps the most challenging task is how to model the longitudinal predictor process such that it represents the true biological mechanism that dictates the association with the categorical response. We propose a joint logistic regression and Markov chain model to describe a binary cross-sectional response, where the unobserved transition rates of a two-state continuous-time Markov chain are included as covariates. We use the method of maximum likelihood to estimate the parameters of our model. In a simulation study, coverage probabilities of about 95%, standard deviations close to standard errors, and low biases for the parameter values show that our estimation method is adequate. We apply the proposed joint model to a dataset of patients with traumatic brain injury to describe and predict a 6-month outcome based on physiological data collected post-injury and admission characteristics. Our analysis indicates that the information provided by physiological changes over time may help improve prediction of long-term functional status of these severely ill subjects. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.
Lv, Yongfeng; Na, Jing; Yang, Qinmin; Wu, Xing; Guo, Yu
2016-01-01
An online adaptive optimal control is proposed for continuous-time nonlinear systems with completely unknown dynamics, which is achieved by developing a novel identifier-critic-based approximate dynamic programming algorithm with a dual neural network (NN) approximation structure. First, an adaptive NN identifier is designed to obviate the requirement of complete knowledge of system dynamics, and a critic NN is employed to approximate the optimal value function. Then, the optimal control law is computed based on the information from the identifier NN and the critic NN, so that the actor NN is not needed. In particular, a novel adaptive law design method with the parameter estimation error is proposed to online update the weights of both identifier NN and critic NN simultaneously, which converge to small neighbourhoods around their ideal values. The closed-loop system stability and the convergence to small vicinity around the optimal solution are all proved by means of the Lyapunov theory. The proposed adaptation algorithm is also improved to achieve finite-time convergence of the NN weights. Finally, simulation results are provided to exemplify the efficacy of the proposed methods.
A policy iteration approach to online optimal control of continuous-time constrained-input systems.
Modares, Hamidreza; Naghibi Sistani, Mohammad-Bagher; Lewis, Frank L
2013-09-01
This paper is an effort towards developing an online learning algorithm to find the optimal control solution for continuous-time (CT) systems subject to input constraints. The proposed method is based on the policy iteration (PI) technique which has recently evolved as a major technique for solving optimal control problems. Although a number of online PI algorithms have been developed for CT systems, none of them take into account the input constraints caused by actuator saturation. In practice, however, ignoring these constraints leads to performance degradation or even system instability. In this paper, to deal with the input constraints, a suitable nonquadratic functional is employed to encode the constraints into the optimization formulation. Then, the proposed PI algorithm is implemented on an actor-critic structure to solve the Hamilton-Jacobi-Bellman (HJB) equation associated with this nonquadratic cost functional in an online fashion. That is, two coupled neural network (NN) approximators, namely an actor and a critic are tuned online and simultaneously for approximating the associated HJB solution and computing the optimal control policy. The critic is used to evaluate the cost associated with the current policy, while the actor is used to find an improved policy based on information provided by the critic. Convergence to a close approximation of the HJB solution as well as stability of the proposed feedback control law are shown. Simulation results of the proposed method on a nonlinear CT system illustrate the effectiveness of the proposed approach. Copyright © 2013 ISA. All rights reserved.
Elastic LiDAR Fusion: Dense Map-Centric Continuous-Time SLAM
Park, Chanoh; Moghadam, Peyman; Kim, Soohwan; Elfes, Alberto; Fookes, Clinton; Sridharan, Sridha
2017-01-01
The concept of continuous-time trajectory representation has brought increased accuracy and efficiency to multi-modal sensor fusion in modern SLAM. However, regardless of these advantages, its offline property caused by the requirement of global batch optimization is critically hindering its relevance for real-time and life-long applications. In this paper, we present a dense map-centric SLAM method based on a continuous-time trajectory to cope with this problem. The proposed system locally f...
Early dropout predictive factors in obesity treatment.
Michelini, Ilaria; Falchi, Anna Giulia; Muggia, Chiara; Grecchi, Ilaria; Montagna, Elisabetta; De Silvestri, Annalisa; Tinelli, Carmine
2014-02-01
Diet attrition and failure of long term treatment are very frequent in obese patients. This study aimed to identify pre-treatment variables determining dropout and to customise the characteristics of those most likely to abandon the program before treatment, thus making it possible to modify the therapy to increase compliance. A total of 146 outpatients were consecutively enrolled; 73 patients followed a prescriptive diet while 73 followed a novel brief group Cognitive Behavioural Treatment (CBT) in addition to prescriptive diet. The two interventions lasted for six months. Anthropometric, demographic, psychological parameters and feeding behaviour were assessed, the last two with the Italian instrument VCAO Ansisa; than, a semi-structured interview was performed on motivation to lose weight. To identify the baseline dropout risk factors among these parameters, univariate and multivariate logistic models were used. Comparison of the results in the two different treatments showed a higher attrition rate in CBT group, despite no statistically significant difference between the two treatment arms (P = 0.127). Dropout patients did not differ significantly from those who did not dropout with regards to sex, age, Body Mass Index (BMI), history of cycling, education, work and marriage. Regardless of weight loss, the most important factor that determines the dropout appears to be a high level of stress revealed by General Health Questionnaire-28 items (GHQ-28) score within VCAO test. The identification of hindering factors during the assessment is fundamental to reduce the dropout risk. For subjects at risk, it would be useful to dedicate a stress management program before beginning a dietary restriction.
The Causes of Dropout in Rural Primary Schools in Malawi
谷口, 京子
2017-01-01
High dropout rates is a critical issue in most of developing countries. Malawi follows this trend of student nonpersistence; in 2013, the primary school dropout rate was approximately 12.2%.This study aims to find the causes of dropout in rural Malawian primary schools. There are two features: data were collected through survival analysis, which has been used to study dropout in developed countries; a multilevel logistic regression was used to classify individual, family, teacher and school f...
Directory of Open Access Journals (Sweden)
Robert M Dorazio
Full Text Available Several spatial capture-recapture (SCR models have been developed to estimate animal abundance by analyzing the detections of individuals in a spatial array of traps. Most of these models do not use the actual dates and times of detection, even though this information is readily available when using continuous-time recorders, such as microphones or motion-activated cameras. Instead most SCR models either partition the period of trap operation into a set of subjectively chosen discrete intervals and ignore multiple detections of the same individual within each interval, or they simply use the frequency of detections during the period of trap operation and ignore the observed times of detection. Both practices make inefficient use of potentially important information in the data.We developed a hierarchical SCR model to estimate the spatial distribution and abundance of animals detected with continuous-time recorders. Our model includes two kinds of point processes: a spatial process to specify the distribution of latent activity centers of individuals within the region of sampling and a temporal process to specify temporal patterns in the detections of individuals. We illustrated this SCR model by analyzing spatial and temporal patterns evident in the camera-trap detections of tigers living in and around the Nagarahole Tiger Reserve in India. We also conducted a simulation study to examine the performance of our model when analyzing data sets of greater complexity than the tiger data.Our approach provides three important benefits: First, it exploits all of the information in SCR data obtained using continuous-time recorders. Second, it is sufficiently versatile to allow the effects of both space use and behavior of animals to be specified as functions of covariates that vary over space and time. Third, it allows both the spatial distribution and abundance of individuals to be estimated, effectively providing a species distribution model, even in
Family Influences on Dropout Behavior in One California High School.
Rumberger, Russell W.; And Others
1990-01-01
Investigated how family processes influence high school student dropout behavior. Used a sample of 114 dropouts from 1 California high school, 48 of whom were matched to similarly profiled continuing students. Identified factors that explain students' dropout decisions: permissive parenting, negative parental reactions to grades, excessive…
Adjustment of High School Dropouts in Closed Religious Communities
Itzhaki, Yael; Itzhaky, Haya; Yablon, Yaacov B.
2018-01-01
Background: While extensive research has been done on high-school dropouts' adjustment, there is little data on dropouts from closed religious communities. Objective: This study examines the contribution of personal and social resources to the adjustment of high school dropouts in Ultraorthodox Jewish communities in Israel. Method: Using a…
Comparing Dropouts and Persistence in E-Learning Courses
Levy, Yair
2007-01-01
Several studies have been conducted related to dropouts from on-campus and distance education courses. However, no clear definition of dropout from academic courses was provided. Consequently, this study proposes a clear and precise definition of dropout from academic courses in the context of e-learning courses. Additionally, it is documented in…
Exploratory Study for Continuous-time Parameter Estimation of Ankle Dynamics
Kukreja, Sunil L.; Boyle, Richard D.
2014-01-01
Recently, a parallel pathway model to describe ankle dynamics was proposed. This model provides a relationship between ankle angle and net ankle torque as the sum of a linear and nonlinear contribution. A technique to identify parameters of this model in discrete-time has been developed. However, these parameters are a nonlinear combination of the continuous-time physiology, making insight into the underlying physiology impossible. The stable and accurate estimation of continuous-time parameters is critical for accurate disease modeling, clinical diagnosis, robotic control strategies, development of optimal exercise protocols for longterm space exploration, sports medicine, etc. This paper explores the development of a system identification technique to estimate the continuous-time parameters of ankle dynamics. The effectiveness of this approach is assessed via simulation of a continuous-time model of ankle dynamics with typical parameters found in clinical studies. The results show that although this technique improves estimates, it does not provide robust estimates of continuous-time parameters of ankle dynamics. Due to this we conclude that alternative modeling strategies and more advanced estimation techniques be considered for future work.
Socioeconomic differences in school dropout among young adults: the role of social relations.
Winding, Trine Nøhr; Andersen, Johan Hviid
2015-10-15
School dropout in adolescence is an important social determinant of health inequality in a lifetime perspective. It is commonly accepted that parental background factors are associated with later dropout, but to what extent social relations mediate this association is not yet fully understood. To investigate the effect of social relations on the association between parental socioeconomic position and school dropout in the Danish youth cohort Vestliv. This prospective study used data from questionnaires in 2004 and 2007 and register data in 2004 and 2010. The study population consisted of 3,054 persons born in 1989. Information on dropout was dichotomised into those who had completed a secondary education/were still attending one and those who had dropped out/had never attended a secondary education. Logistic regression analyses were used to investigate associations between parental socioeconomic position and dropout at age 21, taking into account effects of social relations at age 15 and 18. A large proportion of young people were having problems with social relations at age 15 and 18. In general, social relations were strongly related to not completing a secondary education, especially among girls. For instance, 18-year-old girls finding family conflicts difficult to handle had a 2.6-fold increased risk of not completing a secondary education. Young people from low socioeconomic position families had approximately a 3-fold higher risk of not completing a secondary education compared to young people from high position families, and the estimates did not change greatly after adjustment for social relations with family or friends. Poor relations with teachers and classmates at age 18 explained a substantial part of the association between income and dropout among both girls and boys. The study confirmed a social gradient in completion of secondary education. Despite the fact that poor social relations at age 15 and 18 were related to dropout at age 21, social
Directory of Open Access Journals (Sweden)
Wen-Min Zhou
2013-01-01
Full Text Available This paper is concerned with the consensus problem of general linear discrete-time multiagent systems (MASs with random packet dropout that happens during information exchange between agents. The packet dropout phenomenon is characterized as being a Bernoulli random process. A distributed consensus protocol with weighted graph is proposed to address the packet dropout phenomenon. Through introducing a new disagreement vector, a new framework is established to solve the consensus problem. Based on the control theory, the perturbation argument, and the matrix theory, the necessary and sufficient condition for MASs to reach mean-square consensus is derived in terms of stability of an array of low-dimensional matrices. Moreover, mean-square consensusable conditions with regard to network topology and agent dynamic structure are also provided. Finally, the effectiveness of the theoretical results is demonstrated through an illustrative example.
Cheng, X. Y.; Wang, H. B.; Jia, Y. L.; Dong, YH
2018-05-01
In this paper, an open-closed-loop iterative learning control (ILC) algorithm is constructed for a class of nonlinear systems subjecting to random data dropouts. The ILC algorithm is implemented by a networked control system (NCS), where only the off-line data is transmitted by network while the real-time data is delivered in the point-to-point way. Thus, there are two controllers rather than one in the control system, which makes better use of the saved and current information and thereby improves the performance achieved by open-loop control alone. During the transfer of off-line data between the nonlinear plant and the remote controller data dropout occurs randomly and the data dropout rate is modeled as a binary Bernoulli random variable. Both measurement and control data dropouts are taken into consideration simultaneously. The convergence criterion is derived based on rigorous analysis. Finally, the simulation results verify the effectiveness of the proposed method.
Causes of Student Absenteeism and School Dropouts
Sahin, Seyma; Arseven, Zeynep; Kiliç, Abdurrahman
2016-01-01
The aim of the study is to investigate the causes of student absenteeism and school dropouts at primary, secondary and high school level in Düzce Province and to develop suggestions for solving these problems. A "case study" design, which is one of the qualitative research approaches, was used in this study. The study group consisted of…
Parental Background and University Dropout in Italy
Aina, Carmen
2013-01-01
Using longitudinal data drawn from the European Community Household Panel, this paper examines Italian university entry and dropout rates in the context of specific parental and family characteristics. We are interested in the effects of the household's cultural and financial conditions on shaping investment in tertiary education and its failure,…
Psychological and Educational Variables in University Dropout
Bethencourt, Jose Tomas; Cabrera, Lidia; Hernandez, Juan Andres; Alvarez-Perez, Pedro; Gonzalez-Afonso, Miriam
2008-01-01
Introduction: The purpose of this research is to demonstrate that on the perceptions of university students, the student variables are seen as most important than the context variables to dropout their university studies. Method: The used methodology was cross-sectional or of cut, of retrospective type. 558 undergraduates were interviewed by…
GOAL Academy: Giving Dropouts a Second Chance
Dicksteen, Lisa Napell
2012-01-01
The U.S. Department of Education's (ED) National Center for Education Statistics defines dropouts as "16- through 21-year-olds who are not enrolled in school and have not earned a high school credential (either a diploma or an equivalency credential such as a General Education Development (GED) certificate)." According to the feds, the…
Reinforcement learning using a continuous time actor-critic framework with spiking neurons.
Directory of Open Access Journals (Sweden)
Nicolas Frémaux
2013-04-01
Full Text Available Animals repeat rewarded behaviors, but the physiological basis of reward-based learning has only been partially elucidated. On one hand, experimental evidence shows that the neuromodulator dopamine carries information about rewards and affects synaptic plasticity. On the other hand, the theory of reinforcement learning provides a framework for reward-based learning. Recent models of reward-modulated spike-timing-dependent plasticity have made first steps towards bridging the gap between the two approaches, but faced two problems. First, reinforcement learning is typically formulated in a discrete framework, ill-adapted to the description of natural situations. Second, biologically plausible models of reward-modulated spike-timing-dependent plasticity require precise calculation of the reward prediction error, yet it remains to be shown how this can be computed by neurons. Here we propose a solution to these problems by extending the continuous temporal difference (TD learning of Doya (2000 to the case of spiking neurons in an actor-critic network operating in continuous time, and with continuous state and action representations. In our model, the critic learns to predict expected future rewards in real time. Its activity, together with actual rewards, conditions the delivery of a neuromodulatory TD signal to itself and to the actor, which is responsible for action choice. In simulations, we show that such an architecture can solve a Morris water-maze-like navigation task, in a number of trials consistent with reported animal performance. We also use our model to solve the acrobot and the cartpole problems, two complex motor control tasks. Our model provides a plausible way of computing reward prediction error in the brain. Moreover, the analytically derived learning rule is consistent with experimental evidence for dopamine-modulated spike-timing-dependent plasticity.
Robust model predictive control for constrained continuous-time nonlinear systems
Sun, Tairen; Pan, Yongping; Zhang, Jun; Yu, Haoyong
2018-02-01
In this paper, a robust model predictive control (MPC) is designed for a class of constrained continuous-time nonlinear systems with bounded additive disturbances. The robust MPC consists of a nonlinear feedback control and a continuous-time model-based dual-mode MPC. The nonlinear feedback control guarantees the actual trajectory being contained in a tube centred at the nominal trajectory. The dual-mode MPC is designed to ensure asymptotic convergence of the nominal trajectory to zero. This paper extends current results on discrete-time model-based tube MPC and linear system model-based tube MPC to continuous-time nonlinear model-based tube MPC. The feasibility and robustness of the proposed robust MPC have been demonstrated by theoretical analysis and applications to a cart-damper springer system and a one-link robot manipulator.
International Nuclear Information System (INIS)
Wang Shen-Quan; Feng Jian; Zhao Qing
2012-01-01
In this paper, the problem of delay-distribution-dependent stability is investigated for continuous-time recurrent neural networks (CRNNs) with stochastic delay. Different from the common assumptions on time delays, it is assumed that the probability distribution of the delay taking values in some intervals is known a priori. By making full use of the information concerning the probability distribution of the delay and by using a tighter bounding technique (the reciprocally convex combination method), less conservative asymptotic mean-square stable sufficient conditions are derived in terms of linear matrix inequalities (LMIs). Two numerical examples show that our results are better than the existing ones. (general)
Optimization of Modulator and Circuits for Low Power Continuous-Time Delta-Sigma ADC
DEFF Research Database (Denmark)
Marker-Villumsen, Niels; Bruun, Erik
2014-01-01
This paper presents a new optimization method for achieving a minimum current consumption in a continuous-time Delta-Sigma analog-to-digital converter (ADC). The method is applied to a continuous-time modulator realised with active-RC integrators and with a folded-cascode operational transconduc...... levels are swept. Based on the results of the circuit analysis, for each modulator combination the summed current consumption of the 1st integrator and quantizer of the ADC is determined. By also sweeping the partitioning of the noise power for the different circuit parts, the optimum modulator...
STATISTICAL ANALYSIS OF NOTATIONAL AFL DATA USING CONTINUOUS TIME MARKOV CHAINS
Directory of Open Access Journals (Sweden)
Denny Meyer
2006-12-01
Full Text Available Animal biologists commonly use continuous time Markov chain models to describe patterns of animal behaviour. In this paper we consider the use of these models for describing AFL football. In particular we test the assumptions for continuous time Markov chain models (CTMCs, with time, distance and speed values associated with each transition. Using a simple event categorisation it is found that a semi-Markov chain model is appropriate for this data. This validates the use of Markov Chains for future studies in which the outcomes of AFL matches are simulated
Predicting Dropout Student: An Application of Data Mining Methods in an Online Education Program
Yukselturk, Erman; Ozekes, Serhat; Turel, Yalin Kilic
2014-01-01
This study examined the prediction of dropouts through data mining approaches in an online program. The subject of the study was selected from a total of 189 students who registered to the online Information Technologies Certificate Program in 2007-2009. The data was collected through online questionnaires (Demographic Survey, Online Technologies…
Valued Youth Partnerships: Programs in Caring. Cross-Age Tutoring Dropout Prevention Strategies.
Intercultural Development Research Association, San Antonio, TX.
This booklet provides information about the Valued Youth Partnership (VYP) program for dropout prevention. Begun in 1984 with the support of the Coca-Cola Company and the collaboration of the Intercultural Development Research Association, the VYP program is being implemented in the Edgewood and South San Antonio school districts in San Antonio,…
Development of a Program to Reduce Dropout Rates of Pregnant and Parenting Teens.
Pollack, Andrew M.
1987-01-01
Describes a program to reduce the dropout rate for pregnant and parenting teens at York Vocational-Technical School (Pennsylvania) for the second semester of 1985-86. One successful feature was a "caring class" providing information about pregnancy, childcare, nutrition, and other subjects. The program retained most of its enrollees. Includes 1…
Predicting dropout in adolescents receiving therapy for depression.
O'Keeffe, Sally; Martin, Peter; Goodyer, Ian M; Wilkinson, Paul; Consortium, Impact; Midgley, Nick
2017-10-30
Therapy dropout is a common occurrence, especially in adolescence. This study investigated whether dropout could be predicted from a range of child, family, and treatment factors in a sample of adolescents receiving therapy for depression. This study draws on data from 406 participants of the IMPACT study, a randomized controlled trial, investigating three types of therapy in the treatment of adolescent depression. Logistic regression was used to estimate the effects of predictors on the odds of dropout. Few pre-treatment predictors of dropout were found, with the only significant predictors being older age, antisocial behaviour, and lower scores of verbal intelligence. Missed sessions and poorer therapeutic alliance early in treatment also predicted dropout. Most child and family factors investigated were not significantly associated with dropout. There may be little about depressed adolescents' presentation prior to therapy starting that indicates their risk of dropout. However, within-treatment factors indicated that warning signs of dropout may be identifiable during the initial phase of therapy. Identifying and targeting early treatment indicators of dropout may provide possibilities for improving engagement. Clinical and methodological significance of this article: In the literature, a great deal of attention has been paid to child and family factors that predict therapy dropout, yet in this study, few pre-treatment characteristics were predictive of dropout. However, findings revealed possible warning signs of dropout in the early part of treatment, as poor therapeutic alliance and missed sessions were both found to be predictive of dropout. These findings call for therapists to be aware of such warning signs and clinical guidelines for managing cases at risk of dropout are warranted.
Relative entropy and waiting time for continuous-time Markov processes
Chazottes, J.R.; Giardinà, C.; Redig, F.H.J.
2006-01-01
For discrete-time stochastic processes, there is a close connection between return (resp. waiting) times and entropy (resp. relative entropy). Such a connection cannot be straightforwardly extended to the continuous-time setting. Contrarily to the discrete-time case one needs a reference measure on
Wang, Jun; Liang, Jin-Rong; Lv, Long-Jin; Qiu, Wei-Yuan; Ren, Fu-Yao
2012-02-01
In this paper, we study the problem of continuous time option pricing with transaction costs by using the homogeneous subdiffusive fractional Brownian motion (HFBM) Z(t)=X(Sα(t)), 0transaction costs of replicating strategies. We also give the total transaction costs.
From Discrete-Time Models to Continuous-Time, Asynchronous Models of Financial Markets
K. Boer-Sorban (Katalin); U. Kaymak (Uzay); J. Spiering (Jaap)
2006-01-01
textabstractMost agent-based simulation models of financial markets are discrete-time in nature. In this paper, we investigate to what degree such models are extensible to continuous-time, asynchronous modelling of financial markets. We study the behaviour of a learning market maker in a market with
A sixth-order continuous-time bandpass sigma-delta modulator for digital radio IF
Engelen, van J.A.E.P.; Plassche, van de R.J.; Stikvoort, E.F.; Venes, A.G.W.
1999-01-01
This paper presents a sixth-order continuous-time bandpass sigma-delta modulator (SDM) for analog-to-digital conversion of intermediate-frequency signals. An important aspect in the design of this SDM is the stability analysis using the describing function method. The key to the analysis is the
Stylised facts of financial time series and hidden Markov models in continuous time
DEFF Research Database (Denmark)
Nystrup, Peter; Madsen, Henrik; Lindström, Erik
2015-01-01
presents an extension to continuous time where it is possible to increase the number of states with a linear rather than quadratic growth in the number of parameters. The possibility of increasing the number of states leads to a better fit to both the distributional and temporal properties of daily returns....
Computing continuous-time Markov chains as transformers of unbounded observables
DEFF Research Database (Denmark)
Danos, Vincent; Heindel, Tobias; Garnier, Ilias
2017-01-01
The paper studies continuous-time Markov chains (CTMCs) as transformers of real-valued functions on their state space, considered as generalised predicates and called observables. Markov chains are assumed to take values in a countable state space S; observables f: S → ℝ may be unbounded...
Delsing, M.J.M.H.; Oud, J.H.L.; Bruyn, E.E.J. De
2005-01-01
In family research, bidirectional influences between the family and the individual are usually analyzed in discrete time. Results from discrete time analysis, however, have been shown to be highly dependent on the length of the observation interval. Continuous time analysis using stochastic
Measurement of average continuous-time structure of a bond and ...
African Journals Online (AJOL)
The expected continuous-time structure of a bond and bond's interest rate risk in an investment settings was studied. We determined the expected number of years an investor or manager will wait until the stock comes to maturity. The expected principal amount to be paid back per stock at time 't' was determined, while ...
Lyapunov stability robust analysis and robustness design for linear continuous-time systems
Luo, J.S.; Johnson, A.; Bosch, van den P.P.J.
1995-01-01
The linear continuous-time systems to be discussed are described by state space models with structured time-varying uncertainties. First, the explicit maximal perturbation bound for maintaining quadratic Lyapunov stability of the closed-loop systems is presented. Then, a robust design method is
Continuous-time random walk as a guide to fractional Schroedinger equation
International Nuclear Information System (INIS)
Lenzi, E. K.; Ribeiro, H. V.; Mukai, H.; Mendes, R. S.
2010-01-01
We argue that the continuous-time random walk approach may be a useful guide to extend the Schroedinger equation in order to incorporate nonlocal effects, avoiding the inconsistencies raised by Jeng et al. [J. Math. Phys. 51, 062102 (2010)]. As an application, we work out a free particle in a half space, obtaining the time dependent solution by considering an arbitrary initial condition.
Predictors of dropout in the German disease management program for type 2 diabetes.
Fullerton, Birgit; Erler, Antje; Pöhlmann, Boris; Gerlach, Ferdinand M
2012-01-10
To improve and assess the effectiveness of disease management programs (DMPs), it is critical to understand how many people drop out of disease management programs and why. We used routine data provided by a statutory health insurance fund from the regions North Rhine, North Wurttemberg and Hesse. As part of the German DMP for type 2 diabetes, the insurance fund received regular documentation of all members participating in the program. We followed 10,989 patients who enrolled in the DMP between July 2004 and December 2005 until the end of 2007 to study how many patients dropped out of the program. Dropout was defined based on the discontinuation of program documentation on a particular patient, excluding situations in which the patient died or left the insurance fund. Predictors of dropout, assessed at the time of program enrolment, were explored using logistic regression analysis. 5.5% of the patients dropped out of the disease management program within the observation period. Predictors of dropout at the time of enrolment were: region; retirement status; the number of secondary diseases; presence of a disabling secondary disease; doctor's recommendations to stop smoking or to seek nutritional counselling; and the completion and outcome of the routine foot and eye exams. Different trends of dropout were observed among retired and employed patients: retired patients of old age, who possibly drop out of the program due to other health care priorities and employed people of younger age who have not yet developed many secondary diseases, but were recommended to change their lifestyle. Overall, dropout rates for the German disease management programs for type 2 diabetes were low compared to other studies. Factors assessed at the time of program enrolment were predictive of later dropout and should be further studied to provide information for future program improvements.
Determinants of High-School Dropout: A Longitudinal Study in a Deprived Area of Japan.
Tabuchi, Takahiro; Fujihara, Sho; Shinozaki, Tomohiro; Fukuhara, Hiroyuki
2018-05-19
Our objective in this study was to find determinants of high-school dropout in a deprived area of Japan using longitudinal data, including socio-demographic and junior high school-period information. We followed 695 students who graduated the junior high school located in a deprived area of Japan between 2002 and 2010 for 3 years after graduation (614 students: follow-up rate, 88.3%). Multivariable log-binomial regression models were used to calculate the prevalence ratios (PRs) for high-school dropout, using multiple imputation (MI) to account for non-response at follow-up. The MI model estimated that 18.7% of students dropped out of high school in approximately 3 years. In the covariates-adjusted model, three factors were significantly associated with high-school dropout: ≥10 days of tardy arrival in junior high school (PR 6.44; 95% confidence interval [CI], 1.69-24.6 for "10-29 days of tardy arrival" and PR 8.01; 95% CI, 2.05-31.3 for "≥30 days of tardy arrival" compared with "0 day of tardy arrival"), daily smoking (PR 2.01; 95% CI, 1.41-2.86) and severe problems, such as abuse and neglect (PR 1.66; 95% CI, 1.16-2.39). Among students with ≥30 days of tardy arrival in addition to daily smoking or experience of severe problems, ≥50% high-school dropout rates were observed. Three determinants of high-school dropout were found: smoking, tardy arrival, and experience of severe problems. These factors were correlated and should be treated as warning signs of complex behavioral and academic problems. Parents, educators, and policy makers should work together to implement effective strategies to prevent school dropout.
van Rosmalen, Joost; Toy, Mehlika; O'Mahony, James F
2013-08-01
Markov models are a simple and powerful tool for analyzing the health and economic effects of health care interventions. These models are usually evaluated in discrete time using cohort analysis. The use of discrete time assumes that changes in health states occur only at the end of a cycle period. Discrete-time Markov models only approximate the process of disease progression, as clinical events typically occur in continuous time. The approximation can yield biased cost-effectiveness estimates for Markov models with long cycle periods and if no half-cycle correction is made. The purpose of this article is to present an overview of methods for evaluating Markov models in continuous time. These methods use mathematical results from stochastic process theory and control theory. The methods are illustrated using an applied example on the cost-effectiveness of antiviral therapy for chronic hepatitis B. The main result is a mathematical solution for the expected time spent in each state in a continuous-time Markov model. It is shown how this solution can account for age-dependent transition rates and discounting of costs and health effects, and how the concept of tunnel states can be used to account for transition rates that depend on the time spent in a state. The applied example shows that the continuous-time model yields more accurate results than the discrete-time model but does not require much computation time and is easily implemented. In conclusion, continuous-time Markov models are a feasible alternative to cohort analysis and can offer several theoretical and practical advantages.
Rohden, Adriane Isabel; Benchaya, Mariana Canellas; Camargo, Roger Santos; Moreira, Taís de Campos; Barros, Helena M T; Ferigolo, Maristela
2017-05-01
Depression currently affects 350 million people, and its prevalence among adolescents is 4% to 8%. Adolescents who abandon antidepressant treatment or drop out of clinical trials are less likely to recover or experience a remission of symptoms because they are not being followed up by a medical team. The objective of this study was to analyze the dropout rates of randomized clinical trials of depressed adolescents receiving treatment with antidepressant drugs and the factors associated with nonadherence by summarizing this information in a systematic review and meta-analysis. Articles were retrieved from MEDLINE, EMBASE, Cochrane, Clinical Trial, PsycINFO, and Web of Science using the MeSH terms "depressive disorder," "randomized trials," and "adolescents." The evaluation of study quality was performed by using the Cochrane Handbook for Systematic Reviews of Interventions and the Jadad scale. The final sample included 50 articles, of which 44 presented dropout rates. The overall dropout prevalence was 23% (95% CI, 20-27; P dropout prevalence, respectively (33% [95% CI, 27-39], 45% [95% CI, 31-64], and 15% [95% CI, 13-17]). The adverse effects most associated with dropout were attempted suicide followed by mania, skin rash, and headache. Problems relating to clinical trials and family arbitration were also related with dropout. Serotonin/norepinephrine reuptake inhibitor treatment, adolescent age >16 years, and receiving medication were the only factors demonstrating a higher association with dropout rates. Selective serotonin reuptake inhibitors were linked to the lowest prevalence, probably due to fewer perceived problems with related adverse effects and higher efficacy in adolescents. Cognitive-behavioral therapy combined with pharmacotherapy produced a lower nonadherence prevalence; this approach can be an alternative to avoid dropouts and relapse. Prospero identifier: CRD42014013475. Copyright © 2017 Elsevier HS Journals, Inc. All rights reserved.
Esch, Pascale; Bocquet, Valéry; Pull, Charles; Couffignal, Sophie; Graas, Marc; Lair, Marie-Lise; Lehnert, Torsten; Fond-Harmant, Laurence; Ansseau, Marc
2011-07-13
In Luxembourg, the extensive phenomenon of school dropout is a prime policy concern in the light of individual, social and economic consequences. Although the authorities report an overall decrease of the national dropout rate, the proportion of early school leavers who remain without any specific occupation is still alarming. Therefore, this study intends a shift of focus from system-inherent to individual factors, including mental health and family correlates, to provide a more comprehensive analysis of the dropout phenomenon. The objectives of this study are to investigate the type and prevalence of psychiatric disorders among school dropouts and to compare the findings with those by a matched control group of regularly enrolled students. Furthermore, family variables and socioeconomic status will be analysed, as they are factors likely to interfere with both educational attainment and mental health. A trained psychologist will use structured interviews and self-report forms to investigate for mental health issues, information on schooling, socioeconomic situation and family life. Controls will be matched for gender, age, school type and educational grade. As school dropouts face a serious risk of long term professional and social marginalization, there is an evident need for action. Identifying psychosocial risk and protective factors of school dropout will deliver solid insight on how to conceive public health strategies for young people who may need a more customized support to carry out their academic potential. ClinicalTrials.gov Identifier: NCT01354236.
Institute of Scientific and Technical Information of China (English)
LIAO Baochao; LIU Qun; ZHANG Kui; Abdul BASET; Aamir Mahmood MEMON; Khadim Hussain MEMON; HAN Yanan
2016-01-01
A continuous time delay-difference model (CTDDM) has been established that considers continuous time delays of biological processes.The southern Atlantic albacore (Thunnus alalunga) stock is the one of the commercially important tuna population in the marine world.The age structured production model (ASPM) and the surplus production model (SPM) have already been used to assess the albacore stock.However,the ASPM requires detailed biological information and the SPM lacks the biological realism.In this study,we focus on applying a CTDDM to the southern Atlantic albacore (T.alalunga) species,which provides an alternative method to assess this fishery.It is the first time that CTDDM has been provided for assessing the Atlantic albacore (T.alalunga) fishery.CTDDM obtained the 80％ confidence interval of MSY (maximum sustainable yield) of(21510 t,23118 t).The catch in 2011 (24100 t) is higher than the MSY values and the relative fishing mortality ratio (F2011/FMSY) is higher than 1.0.The results of CTDDM were analyzed to verify the proposed methodology and provide reference information for the sustainable management of the southern Atlantic albacore stock.The CTDDM treats the recruitment,the growth,and the mortality rates as all varying continuously over time and fills gaps between ASPM and SPM in this stock assessment.
Why Wait? Early Determinants of School Dropout in Preventive Pediatric Primary Care.
Directory of Open Access Journals (Sweden)
Marie-José Theunissen
Full Text Available To answer the question of what bio-psychosocial determinants in infancy, early and middle childhood, and adolescence predict school drop-out in young adulthood, we approached the complex process towards school dropout as a multidimensional, life-course phenomenon. The aim is to find signs of heightened risks of school dropout as early as possible which will eventually help public health workers in reducing these risks.In a case-control design, we used data from both the Preventive Pediatric Primary Care (PPPC files (that contain information from birth onwards and additional questionnaires filled out by 529 youngsters, aged 18-23 years, and living in the South-east of the Netherlands. We first conducted univariate logistic regression analyses with school-dropout as the dependent variable. Backward and forward stepwise analyses with the significant variables were done with variables pertaining to the 0 to 4 year period. Remaining significant variables were forced into the next model and subsequently variables pertaining to respectively the 4 to 8, 8 to 12 and 12 to 16 year period were introduced in a stepwise analysis. All analyses were cross-validated in an exploratory and confirmatory random half of the sample.One parent families and families with a non-Western background less often attended the health examinations of the PPPC and such less attendance was related to school dropout. The birth of a sibling (OR 0.63, 95% CI 0.43-0.93 in infancy and self-efficacy (OR 0.53, 95% CI 0.38-0.74 in adolescence decreased the odds of school dropout; externalizing behavior (OR 2.81, 95% CI 1.53-5.14 in middle childhood and (sickness absence (OR 5.62, 95% CI 2.18-14.52 in adolescence increased the risks.To prevent school dropout, PPPC professionals should not wait until imminent dropout, but should identify and tackle risk factors as early as possible and actively approach youngsters who withdraw from public health care.
Why Wait? Early Determinants of School Dropout in Preventive Pediatric Primary Care
Theunissen, Marie-José; Bosma, Hans; Verdonk, Petra; Feron, Frans
2015-01-01
Background To answer the question of what bio-psychosocial determinants in infancy, early and middle childhood, and adolescence predict school drop-out in young adulthood, we approached the complex process towards school dropout as a multidimensional, life-course phenomenon. The aim is to find signs of heightened risks of school dropout as early as possible which will eventually help public health workers in reducing these risks. Methods In a case-control design, we used data from both the Preventive Pediatric Primary Care (PPPC) files (that contain information from birth onwards) and additional questionnaires filled out by 529 youngsters, aged 18–23 years, and living in the South-east of the Netherlands. We first conducted univariate logistic regression analyses with school-dropout as the dependent variable. Backward and forward stepwise analyses with the significant variables were done with variables pertaining to the 0 to 4 year period. Remaining significant variables were forced into the next model and subsequently variables pertaining to respectively the 4 to 8, 8 to 12 and 12 to 16 year period were introduced in a stepwise analysis. All analyses were cross-validated in an exploratory and confirmatory random half of the sample. Results One parent families and families with a non-Western background less often attended the health examinations of the PPPC and such less attendance was related to school dropout. The birth of a sibling (OR 0.63, 95% CI 0.43–0.93) in infancy and self-efficacy (OR 0.53, 95% CI 0.38–0.74) in adolescence decreased the odds of school dropout; externalizing behavior (OR 2.81, 95% CI 1.53–5.14) in middle childhood and (sickness) absence (OR 5.62, 95% CI 2.18–14.52) in adolescence increased the risks. Conclusion To prevent school dropout, PPPC professionals should not wait until imminent dropout, but should identify and tackle risk factors as early as possible and actively approach youngsters who withdraw from public health care
Why Wait? Early Determinants of School Dropout in Preventive Pediatric Primary Care.
Theunissen, Marie-José; Bosma, Hans; Verdonk, Petra; Feron, Frans
2015-01-01
To answer the question of what bio-psychosocial determinants in infancy, early and middle childhood, and adolescence predict school drop-out in young adulthood, we approached the complex process towards school dropout as a multidimensional, life-course phenomenon. The aim is to find signs of heightened risks of school dropout as early as possible which will eventually help public health workers in reducing these risks. In a case-control design, we used data from both the Preventive Pediatric Primary Care (PPPC) files (that contain information from birth onwards) and additional questionnaires filled out by 529 youngsters, aged 18-23 years, and living in the South-east of the Netherlands. We first conducted univariate logistic regression analyses with school-dropout as the dependent variable. Backward and forward stepwise analyses with the significant variables were done with variables pertaining to the 0 to 4 year period. Remaining significant variables were forced into the next model and subsequently variables pertaining to respectively the 4 to 8, 8 to 12 and 12 to 16 year period were introduced in a stepwise analysis. All analyses were cross-validated in an exploratory and confirmatory random half of the sample. One parent families and families with a non-Western background less often attended the health examinations of the PPPC and such less attendance was related to school dropout. The birth of a sibling (OR 0.63, 95% CI 0.43-0.93) in infancy and self-efficacy (OR 0.53, 95% CI 0.38-0.74) in adolescence decreased the odds of school dropout; externalizing behavior (OR 2.81, 95% CI 1.53-5.14) in middle childhood and (sickness) absence (OR 5.62, 95% CI 2.18-14.52) in adolescence increased the risks. To prevent school dropout, PPPC professionals should not wait until imminent dropout, but should identify and tackle risk factors as early as possible and actively approach youngsters who withdraw from public health care.
Identifying potential dropouts from college physics classes
Wollman, Warren; Lawrenz, Frances
Hudson and Rottman (1981) established that mathematics ability is probably a secondary factor influencing dropout from college physics courses. Other factors remain to be found for predicting who will drop out or at least have difficulty with the course. When mathematics ability is coupled with general indicators of performance (total GPA and ACT natural science), prediction of performance for those who complete the course is substantially improved. Moreover, discriminant analyses reveal who will have at least some difficulty, but not who will drop out. The problem of isolating specific weaknesses of students who have difficulty persists. Physics achievement appears to depend on mathematics ability only to the extent that students possess the ability to utilize mathematics knowledge for solving physics problems. Identification of the specific aspects of this ability as well as the specific deficiencies leading to dropout should be the object of future research. For the present, interviews might be more revealing than group testing methods.
Directory of Open Access Journals (Sweden)
van der Beek Allard J
2009-12-01
Full Text Available Abstract Background Non-response and drop-out are problems that are commonly encountered in health promotion trials. Understanding the health-related characteristics of non-participants and drop-outs and the reasons for non-participation and drop-out may be beneficial for future intervention trials. Methods Male construction workers with an elevated risk of cardiovascular disease (CVD were invited to participate in a lifestyle intervention study. In order to investigate the associations between participation and CVD risk factors, and drop-out and CVD risk factors, crude and multiple logistic regression analyses were performed. The reasons for non-participation and drop-out were assessed qualitatively. Results 20% of the workers who were invited decided to participate; 8.6% of the participants dropped out before the first follow-up measurement. The main reasons for non-participation were 'no interest', 'current (para-medical treatment', and 'feeling healthy', and for drop-out they were 'lack of motivation', 'current (para-medical treatment', and 'disappointment'. Participants were 4.2 years older, had a higher blood pressure, higher total cholesterol, and lower HDL cholesterol than non-participants, and were more likely to report 'tiredness and/or stress' and 'chest pain and/or shortness of breath'. After adjusting for age, most risk factors were not significantly associated with participation. Drop-outs were 4.6 years younger than those who completed the study. The prevalence of smoking was higher among non-participants and drop-outs. Conclusion Participants had a worse CVD risk profile than non-participants, mainly because of the difference in age. Non-participants and drop-outs were younger and more likely to be smokers. The main reasons for non-participation and drop-out were health-related. Investigators in the field of health promotion should be encouraged to share comparable information. Trial registration Current Controlled Trials ISRCTN
Continuous-Time Classical and Quantum Random Walk on Direct Product of Cayley Graphs
International Nuclear Information System (INIS)
Salimi, S.; Jafarizadeh, M. A.
2009-01-01
In this paper we define direct product of graphs and give a recipe for obtaining probability of observing particle on vertices in the continuous-time classical and quantum random walk. In the recipe, the probability of observing particle on direct product of graph is obtained by multiplication of probability on the corresponding to sub-graphs, where this method is useful to determining probability of walk on complicated graphs. Using this method, we calculate the probability of continuous-time classical and quantum random walks on many of finite direct product Cayley graphs (complete cycle, complete K n , charter and n-cube). Also, we inquire that the classical state the stationary uniform distribution is reached as t → ∞ but for quantum state is not always satisfied. (general)
System Level Design of a Continuous-Time Delta-Sigma Modulator for Portable Ultrasound Scanners
DEFF Research Database (Denmark)
Llimos Muntal, Pere; Færch, Kjartan; Jørgensen, Ivan Harald Holger
2015-01-01
In this paper the system level design of a continuous-time ∆Σ modulator for portable ultrasound scanners is presented. The overall required signal-to-noise ratio (SNR) is derived to be 42 dB and the sampling frequency used is 320 MHz for an oversampling ratio of 16. In order to match these requir......, based on high-level VerilogA simulations, the performance of the ∆Σ modulator versus various block performance parameters is presented as trade-off curves. Based on these results, the block specifications are derived.......In this paper the system level design of a continuous-time ∆Σ modulator for portable ultrasound scanners is presented. The overall required signal-to-noise ratio (SNR) is derived to be 42 dB and the sampling frequency used is 320 MHz for an oversampling ratio of 16. In order to match...
Anticontrol of chaos in continuous-time systems via time-delay feedback.
Wang, Xiao Fan; Chen, Guanrong; Yu, Xinghuo
2000-12-01
In this paper, a systematic design approach based on time-delay feedback is developed for anticontrol of chaos in a continuous-time system. This anticontrol method can drive a finite-dimensional, continuous-time, autonomous system from nonchaotic to chaotic, and can also enhance the existing chaos of an originally chaotic system. Asymptotic analysis is used to establish an approximate relationship between a time-delay differential equation and a discrete map. Anticontrol of chaos is then accomplished based on this relationship and the differential-geometry control theory. Several examples are given to verify the effectiveness of the methodology and to illustrate the systematic design procedure. (c) 2000 American Institute of Physics.
The continuous time random walk, still trendy: fifty-year history, state of art and outlook
Kutner, Ryszard; Masoliver, Jaume
2017-03-01
In this article we demonstrate the very inspiring role of the continuous-time random walk (CTRW) formalism, the numerous modifications permitted by its flexibility, its various applications, and the promising perspectives in the various fields of knowledge. A short review of significant achievements and possibilities is given. However, this review is still far from completeness. We focused on a pivotal role of CTRWs mainly in anomalous stochastic processes discovered in physics and beyond. This article plays the role of an extended announcement of the Eur. Phys. J. B Special Issue [open-calls-for-papers/123-epj-b/1090-ctrw-50-years-on">http://epjb.epj.org/open-calls-for-papers/123-epj-b/1090-ctrw-50-years-on] containing articles which show incredible possibilities of the CTRWs. Contribution to the Topical Issue "Continuous Time Random Walk Still Trendy: Fifty-year History, Current State and Outlook", edited by Ryszard Kutner and Jaume Masoliver.
Continuous time sigma delta ADC design and non-idealities analysis
International Nuclear Information System (INIS)
Yuan Jun; Chen Zhenhai; Yang Yintang; Zhang Zhaofeng; Wu Jun; Wang Chao; Qian Wenrong
2011-01-01
A wide bandwidth continuous time sigma delta ADC is implemented in 130 nm CMOS. A detailed non-idealities analysis (excess loop delay, clock jitter, finite gain and GBW, comparator offset and DAC mismatch) is performed developed in Matlab/Simulink. This design is targeted for wide bandwidth applications such as video or wireless base-stations. Athird-order continuous time sigma delta modulator comprises a third-order RC operational-amplifier-based loop filter and 3-bit internal quantizer operated at 512 MHz clock frequency. The sigma delta ADC achieves 60 dB SNR and 59.3 dB SNDR over a 16-MHz signal band at an OSR of 16. The power consumption of the CT sigma delta modulator is 22 mW from the 1.2-V supply. (semiconductor integrated circuits)
Fermion bag approach to Hamiltonian lattice field theories in continuous time
Huffman, Emilie; Chandrasekharan, Shailesh
2017-12-01
We extend the idea of fermion bags to Hamiltonian lattice field theories in the continuous time formulation. Using a class of models we argue that the temperature is a parameter that splits the fermion dynamics into small spatial regions that can be used to identify fermion bags. Using this idea we construct a continuous time quantum Monte Carlo algorithm and compute critical exponents in the 3 d Ising Gross-Neveu universality class using a single flavor of massless Hamiltonian staggered fermions. We find η =0.54 (6 ) and ν =0.88 (2 ) using lattices up to N =2304 sites. We argue that even sizes up to N =10 ,000 sites should be accessible with supercomputers available today.
Continuous-Time Random Walk with multi-step memory: an application to market dynamics
Gubiec, Tomasz; Kutner, Ryszard
2017-11-01
An extended version of the Continuous-Time Random Walk (CTRW) model with memory is herein developed. This memory involves the dependence between arbitrary number of successive jumps of the process while waiting times between jumps are considered as i.i.d. random variables. This dependence was established analyzing empirical histograms for the stochastic process of a single share price on a market within the high frequency time scale. Then, it was justified theoretically by considering bid-ask bounce mechanism containing some delay characteristic for any double-auction market. Our model appeared exactly analytically solvable. Therefore, it enables a direct comparison of its predictions with their empirical counterparts, for instance, with empirical velocity autocorrelation function. Thus, the present research significantly extends capabilities of the CTRW formalism. Contribution to the Topical Issue "Continuous Time Random Walk Still Trendy: Fifty-year History, Current State and Outlook", edited by Ryszard Kutner and Jaume Masoliver.
Summary statistics for end-point conditioned continuous-time Markov chains
DEFF Research Database (Denmark)
Hobolth, Asger; Jensen, Jens Ledet
Continuous-time Markov chains are a widely used modelling tool. Applications include DNA sequence evolution, ion channel gating behavior and mathematical finance. We consider the problem of calculating properties of summary statistics (e.g. mean time spent in a state, mean number of jumps between...... two states and the distribution of the total number of jumps) for discretely observed continuous time Markov chains. Three alternative methods for calculating properties of summary statistics are described and the pros and cons of the methods are discussed. The methods are based on (i) an eigenvalue...... decomposition of the rate matrix, (ii) the uniformization method, and (iii) integrals of matrix exponentials. In particular we develop a framework that allows for analyses of rather general summary statistics using the uniformization method....
Selected determinants may account for dropout risks among medical students
DEFF Research Database (Denmark)
Mørcke, Anne Mette; O'Neill, Lotte; Kjeldsen, Inge Trads
2012-01-01
INTRODUCTION: The dropout level from the Danish medical schools is high, but we have only little insight into this problem. The purpose of this study was to qualify the ongoing discussions concerning dropout. MATERIAL AND METHODS: In this retrospective cohort study, relevant variables were...... extracted from the established database of Aarhus University for the 639 students initiating medicine studies between 1 January 1999 and 31December 2000. A multivariate pre-admission and post-admission model was examined. RESULTS: Of the 639 medical students, 20% dropped out. Most students dropped out...... during their first year. The type of admission exam was a strong predictor of dropout in the pre-admission model, whereas previous higher education protected against dropout. Obtaining leave was a very strong predictor of dropout in the post-admission model, whereas high grades protected against dropout...
Mean-variance Optimal Reinsurance-investment Strategy in Continuous Time
Directory of Open Access Journals (Sweden)
Daheng Peng
2017-10-01
Full Text Available In this paper, Lagrange method is used to solve the continuous-time mean-variance reinsurance-investment problem. Proportional reinsurance, multiple risky assets and risk-free asset are considered synthetically in the optimal strategy for insurers. By solving the backward stochastic differential equation for the Lagrange multiplier, we get the mean-variance optimal reinsurance-investment strategy and its effective frontier in explicit forms.
Continuous time Boolean modeling for biological signaling: application of Gillespie algorithm.
Stoll, Gautier; Viara, Eric; Barillot, Emmanuel; Calzone, Laurence
2012-01-01
Abstract Mathematical modeling is used as a Systems Biology tool to answer biological questions, and more precisely, to validate a network that describes biological observations and predict the effect of perturbations. This article presents an algorithm for modeling biological networks in a discrete framework with continuous time. Background There exist two major types of mathematical modeling approaches: (1) quantitative modeling, representing various chemical species concentrations by real...
On properties of continuous-time random walks with non-Poissonian jump-times
International Nuclear Information System (INIS)
Villarroel, Javier; Montero, Miquel
2009-01-01
The usual development of the continuous-time random walk (CTRW) proceeds by assuming that the present is one of the jumping times. Under this restrictive assumption integral equations for the propagator and mean escape times have been derived. We generalize these results to the case when the present is an arbitrary time by recourse to renewal theory. The case of Erlang distributed times is analyzed in detail. Several concrete examples are considered.
Time inconsistency and reputation in monetary policy: a strategic model in continuous time
Li, Jingyuan; Tian, Guoqiang
2005-01-01
This article develops a model to examine the equilibrium behavior of the time inconsistency problem in a continuous time economy with stochastic and endogenized dis- tortion. First, the authors introduce the notion of sequentially rational equilibrium, and show that the time inconsistency problem may be solved with trigger reputation strategies for stochastic setting. The conditions for the existence of sequentially rational equilibrium are provided. Then, the concept of sequen...
Global dissipativity of continuous-time recurrent neural networks with time delay
International Nuclear Information System (INIS)
Liao Xiaoxin; Wang Jun
2003-01-01
This paper addresses the global dissipativity of a general class of continuous-time recurrent neural networks. First, the concepts of global dissipation and global exponential dissipation are defined and elaborated. Next, the sets of global dissipativity and global exponentially dissipativity are characterized using the parameters of recurrent neural network models. In particular, it is shown that the Hopfield network and cellular neural networks with or without time delays are dissipative systems
Directory of Open Access Journals (Sweden)
Y. Saiki
2007-09-01
Full Text Available An infinite number of unstable periodic orbits (UPOs are embedded in a chaotic system which models some complex phenomenon. Several algorithms which extract UPOs numerically from continuous-time chaotic systems have been proposed. In this article the damped Newton-Raphson-Mees algorithm is reviewed, and some important techniques and remarks concerning the practical numerical computations are exemplified by employing the Lorenz system.
A continuous time model of the bandwagon effect in collective action
Arieh Gavious; Shlomo Mizrahi
2001-01-01
The paper offers a complex and systematic model of the bandwagon effect in collective action using continuous time equations. The model treats the bandwagon effect as a process influenced by ratio between the mobilization efforts of social activists and the resources invested by the government to counteract this activity. The complex modeling approach makes it possible to identify the conditions for specific types of the bandwagon effect, and determines the scope of that effect. Relying on ce...
A comparison of numerical methods for the solution of continuous-time DSGE models
DEFF Research Database (Denmark)
Parra-Alvarez, Juan Carlos
This paper evaluates the accuracy of a set of techniques that approximate the solution of continuous-time DSGE models. Using the neoclassical growth model I compare linear-quadratic, perturbation and projection methods. All techniques are applied to the HJB equation and the optimality conditions...... parameters of the model and suggest the use of projection methods when a high degree of accuracy is required....
Directory of Open Access Journals (Sweden)
Hajnalka Péics
2016-08-01
Full Text Available The asymptotic behavior of solutions of the system of difference equations with continuous time and lag function between two known real functions is studied. The cases when the lag function is between two linear delay functions, between two power delay functions and between two constant delay functions are observed and illustrated by examples. The asymptotic estimates of solutions of the considered system are obtained.
Wang, Xinghu; Hong, Yiguang; Yi, Peng; Ji, Haibo; Kang, Yu
2017-05-24
In this paper, a distributed optimization problem is studied for continuous-time multiagent systems with unknown-frequency disturbances. A distributed gradient-based control is proposed for the agents to achieve the optimal consensus with estimating unknown frequencies and rejecting the bounded disturbance in the semi-global sense. Based on convex optimization analysis and adaptive internal model approach, the exact optimization solution can be obtained for the multiagent system disturbed by exogenous disturbances with uncertain parameters.
Physical time scale in kinetic Monte Carlo simulations of continuous-time Markov chains.
Serebrinsky, Santiago A
2011-03-01
We rigorously establish a physical time scale for a general class of kinetic Monte Carlo algorithms for the simulation of continuous-time Markov chains. This class of algorithms encompasses rejection-free (or BKL) and rejection (or "standard") algorithms. For rejection algorithms, it was formerly considered that the availability of a physical time scale (instead of Monte Carlo steps) was empirical, at best. Use of Monte Carlo steps as a time unit now becomes completely unnecessary.
Correlated continuous-time random walks—scaling limits and Langevin picture
International Nuclear Information System (INIS)
Magdziarz, Marcin; Metzler, Ralf; Szczotka, Wladyslaw; Zebrowski, Piotr
2012-01-01
In this paper we analyze correlated continuous-time random walks introduced recently by Tejedor and Metzler (2010 J. Phys. A: Math. Theor. 43 082002). We obtain the Langevin equations associated with this process and the corresponding scaling limits of their solutions. We prove that the limit processes are self-similar and display anomalous dynamics. Moreover, we extend the model to include external forces. Our results are confirmed by Monte Carlo simulations
Stability Tests of Positive Fractional Continuous-time Linear Systems with Delays
Directory of Open Access Journals (Sweden)
Tadeusz Kaczorek
2013-06-01
Full Text Available Necessary and sufficient conditions for the asymptotic stability of positive fractional continuous-time linear systems with many delays are established. It is shown that: 1 the asymptotic stability of the positive fractional system is independent of their delays, 2 the checking of the asymptotic stability of the positive fractional systems with delays can be reduced to checking of the asymptotic stability of positive standard linear systems without delays.
Global stabilization of linear continuous time-varying systems with bounded controls
International Nuclear Information System (INIS)
Phat, V.N.
2004-08-01
This paper deals with the problem of global stabilization of a class of linear continuous time-varying systems with bounded controls. Based on the controllability of the nominal system, a sufficient condition for the global stabilizability is proposed without solving any Riccati differential equation. Moreover, we give sufficient conditions for the robust stabilizability of perturbation/uncertain linear time-varying systems with bounded controls. (author)
Mean-variance Optimal Reinsurance-investment Strategy in Continuous Time
Daheng Peng; Fang Zhang
2017-01-01
In this paper, Lagrange method is used to solve the continuous-time mean-variance reinsurance-investment problem. Proportional reinsurance, multiple risky assets and risk-free asset are considered synthetically in the optimal strategy for insurers. By solving the backward stochastic differential equation for the Lagrange multiplier, we get the mean-variance optimal reinsurance-investment strategy and its effective frontier in explicit forms.
Continuous-Time Mean-Variance Portfolio Selection under the CEV Process
Ma, Hui-qiang
2014-01-01
We consider a continuous-time mean-variance portfolio selection model when stock price follows the constant elasticity of variance (CEV) process. The aim of this paper is to derive an optimal portfolio strategy and the efficient frontier. The mean-variance portfolio selection problem is formulated as a linearly constrained convex program problem. By employing the Lagrange multiplier method and stochastic optimal control theory, we obtain the optimal portfolio strategy and mean-variance effici...
Directory of Open Access Journals (Sweden)
Hamidreza Mostafaei
2013-01-01
Full Text Available In this study, it has been attempted to select the best continuous- time stochastic model, in order to describe and forecast the oil price of Russia, by information and statistics about oil price that has been available for oil price in the past. For this purpose, method of The Maximum Likelihood Estimation is implemented for estimation of the parameters of continuous-time stochastic processes. The result of unit root test with a structural break, reveals that time series of the crude oil price is a stationary series. The simulation of continuous-time stochastic processes and the mean square error between the simulated prices and the market ones shows that the Geometric Brownian Motion is the best model for the Russian crude oil price.
Investigation of continuous-time quantum walk via modules of Bose-Mesner and Terwilliger algebras
International Nuclear Information System (INIS)
Jafarizadeh, M A; Salimi, S
2006-01-01
The continuous-time quantum walk on the underlying graphs of association schemes has been studied, via the algebraic combinatorics structures of association schemes, namely semi-simple modules of their Bose-Mesner and Terwilliger algebras. It is shown that the Terwilliger algebra stratifies the graph into a (d + 1) disjoint union of strata which is different from the stratification based on distance, except for distance regular graphs. In underlying graphs of association schemes, the probability amplitudes and average probabilities are given in terms of dual eigenvalues of association schemes, such that the amplitudes of observing the continuous-time quantum walk on all sites belonging to a given stratum are the same, therefore there are at most (d + 1) different observing probabilities. The importance of association scheme in continuous-time quantum walk is shown by some worked out examples such as arbitrary finite group association schemes followed by symmetric S n , Dihedral D 2m and cyclic groups. At the end it is shown that the highest irreducible representations of Terwilliger algebras pave the way to use the spectral distributions method of Jafarizadeh and Salimi (2005 Preprint quant-ph/0510174) in studying quantum walk on some rather important graphs called distance regular graphs
A new continuous-time formulation for scheduling crude oil operations
International Nuclear Information System (INIS)
Reddy, P. Chandra Prakash; Karimi, I.A.; Srinivasan, R.
2004-01-01
In today's competitive business climate characterized by uncertain oil markets, responding effectively and speedily to market forces, while maintaining reliable operations, is crucial to a refinery's bottom line. Optimal crude oil scheduling enables cost reduction by using cheaper crudes intelligently, minimizing crude changeovers, and avoiding ship demurrage. So far, only discrete-time formulations have stood up to the challenge of this important, nonlinear problem. A continuous-time formulation would portend numerous advantages, however, existing work in this area has just begun to scratch the surface. In this paper, we present the first complete continuous-time mixed integer linear programming (MILP) formulation for the short-term scheduling of operations in a refinery that receives crude from very large crude carriers via a high-volume single buoy mooring pipeline. This novel formulation accounts for real-world operational practices. We use an iterative algorithm to eliminate the crude composition discrepancy that has proven to be the Achilles heel for existing formulations. While it does not guarantee global optimality, the algorithm needs only MILP solutions and obtains excellent maximum-profit schedules for industrial problems with up to 7 days of scheduling horizon. We also report the first comparison of discrete- vs. continuous-time formulations for this complex problem. (Author)
Optimal control of nonlinear continuous-time systems in strict-feedback form.
Zargarzadeh, Hassan; Dierks, Travis; Jagannathan, Sarangapani
2015-10-01
This paper proposes a novel optimal tracking control scheme for nonlinear continuous-time systems in strict-feedback form with uncertain dynamics. The optimal tracking problem is transformed into an equivalent optimal regulation problem through a feedforward adaptive control input that is generated by modifying the standard backstepping technique. Subsequently, a neural network-based optimal control scheme is introduced to estimate the cost, or value function, over an infinite horizon for the resulting nonlinear continuous-time systems in affine form when the internal dynamics are unknown. The estimated cost function is then used to obtain the optimal feedback control input; therefore, the overall optimal control input for the nonlinear continuous-time system in strict-feedback form includes the feedforward plus the optimal feedback terms. It is shown that the estimated cost function minimizes the Hamilton-Jacobi-Bellman estimation error in a forward-in-time manner without using any value or policy iterations. Finally, optimal output feedback control is introduced through the design of a suitable observer. Lyapunov theory is utilized to show the overall stability of the proposed schemes without requiring an initial admissible controller. Simulation examples are provided to validate the theoretical results.
Simulating continuous-time Hamiltonian dynamics by way of a discrete-time quantum walk
International Nuclear Information System (INIS)
Schmitz, A.T.; Schwalm, W.A.
2016-01-01
Much effort has been made to connect the continuous-time and discrete-time quantum walks. We present a method for making that connection for a general graph Hamiltonian on a bigraph. Furthermore, such a scheme may be adapted for simulating discretized quantum models on a quantum computer. A coin operator is found for the discrete-time quantum walk which exhibits the same dynamics as the continuous-time evolution. Given the spectral decomposition of the graph Hamiltonian and certain restrictions, the discrete-time evolution is solved for explicitly and understood at or near important values of the parameters. Finally, this scheme is connected to past results for the 1D chain. - Highlights: • A discrete-time quantum walk is purposed which approximates a continuous-time quantum walk. • The purposed quantum walk could be used to simulate Hamiltonian dynamics on a quantum computer. • Given the spectra decomposition of the Hamiltonian, the quantum walk is solved explicitly. • The method is demonstrated and connected to previous work done on the 1D chain.
A New Continuous-Time Equality-Constrained Optimization to Avoid Singularity.
Quan, Quan; Cai, Kai-Yuan
2016-02-01
In equality-constrained optimization, a standard regularity assumption is often associated with feasible point methods, namely, that the gradients of constraints are linearly independent. In practice, the regularity assumption may be violated. In order to avoid such a singularity, a new projection matrix is proposed based on which a feasible point method to continuous-time, equality-constrained optimization is developed. First, the equality constraint is transformed into a continuous-time dynamical system with solutions that always satisfy the equality constraint. Second, a new projection matrix without singularity is proposed to realize the transformation. An update (or say a controller) is subsequently designed to decrease the objective function along the solutions of the transformed continuous-time dynamical system. The invariance principle is then applied to analyze the behavior of the solution. Furthermore, the proposed method is modified to address cases in which solutions do not satisfy the equality constraint. Finally, the proposed optimization approach is applied to three examples to demonstrate its effectiveness.
Understanding Catalan University Dropout from a Comparative Approach
Rodríguez-Gómez, David; Feixas, Mònica; Gairín, Joaquín; Muñoz, José Luís
2012-01-01
Last decade yielded important research to understand the extent to which university dropout is having relevant consequences for higher education. The dropout rate has also been quantified and used as an indicator of performance (Dearing, 1996; Bricall, 2000; Rauret & Grifol, 2001; OECD, 2008; Mandelson, 2009). The aim of this paper is to offer an extensive perspective on how university dropout is being studied and faced in several contexts (America, Europe and, more concretely, Spain and Cata...
Allelic drop-out probabilities estimated by logistic regression
DEFF Research Database (Denmark)
Tvedebrink, Torben; Eriksen, Poul Svante; Asplund, Maria
2012-01-01
We discuss the model for estimating drop-out probabilities presented by Tvedebrink et al. [7] and the concerns, that have been raised. The criticism of the model has demonstrated that the model is not perfect. However, the model is very useful for advanced forensic genetic work, where allelic drop-out...... is occurring. With this discussion, we hope to improve the drop-out model, so that it can be used for practical forensic genetics and stimulate further discussions. We discuss how to estimate drop-out probabilities when using a varying number of PCR cycles and other experimental conditions....
Energy Technology Data Exchange (ETDEWEB)
Weberg, Micah J. [PhD Candidate in Space Science, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2134A Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States); Lepri, Susan T. [Associate Professor, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2429 Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States); Zurbuchen, Thomas H., E-mail: mjweberg@umich.edu, E-mail: slepri@umich.edu, E-mail: thomasz@umich.edu [Professor, Space Science and Aerospace Engineering, Associate Dean for Entrepreneurship Senior Counselor of Entrepreneurship Education, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2431 Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States)
2015-03-10
The elemental abundances of heavy ions (masses larger than He) in the solar wind provide information about physical processes occurring in the corona. Additionally, the charge state distributions of these heavy ions are sensitive to the temperature profiles of their respective source regions in the corona. Heavy ion dropouts are a relatively new class of solar wind events identified by both elemental and ionic charge state distributions. We have shown that their origins lie in large, closed coronal loops where processes such as gravitational settling dominate and can cause a mass-dependent fractionation pattern. In this study we consider and attempt to answer three fundamental questions concerning heavy ion dropouts: (1) 'where are the source loops located in the large-scale corona?'; (2) 'how does the interplay between coronal processes influence the end elemental abundances?'; and (3) 'what are the most probable release mechanisms'? We begin by analyzing the temporal and spatial variability of heavy ion dropouts and their correlation with heliospheric plasma and magnetic structures. Next we investigate the ordering of the elements inside dropouts with respect to mass, ionic charge state, and first ionization potential. Finally, we discuss these results in the context of the prevailing solar wind theories and the processes they posit that may be responsible for the release of coronal plasma into interplanetary space.
International Nuclear Information System (INIS)
Weberg, Micah J.; Lepri, Susan T.; Zurbuchen, Thomas H.
2015-01-01
The elemental abundances of heavy ions (masses larger than He) in the solar wind provide information about physical processes occurring in the corona. Additionally, the charge state distributions of these heavy ions are sensitive to the temperature profiles of their respective source regions in the corona. Heavy ion dropouts are a relatively new class of solar wind events identified by both elemental and ionic charge state distributions. We have shown that their origins lie in large, closed coronal loops where processes such as gravitational settling dominate and can cause a mass-dependent fractionation pattern. In this study we consider and attempt to answer three fundamental questions concerning heavy ion dropouts: (1) 'where are the source loops located in the large-scale corona?'; (2) 'how does the interplay between coronal processes influence the end elemental abundances?'; and (3) 'what are the most probable release mechanisms'? We begin by analyzing the temporal and spatial variability of heavy ion dropouts and their correlation with heliospheric plasma and magnetic structures. Next we investigate the ordering of the elements inside dropouts with respect to mass, ionic charge state, and first ionization potential. Finally, we discuss these results in the context of the prevailing solar wind theories and the processes they posit that may be responsible for the release of coronal plasma into interplanetary space
Drop-out from a psychodynamic group psychotherapy outpatient unit.
Jensen, Hans Henrik; Mortensen, Erik Lykke; Lotz, Martin
2014-11-01
BACKGROUND. Drop-out from psychotherapy is common and represents a considerable problem in clinical practice and research. Aim. To explore pre-treatment predictors of early and late drop-out from psychodynamic group therapy in a public outpatient unit for non-psychotic disorders in Denmark. Methods. Naturalistic design including 329 patients, the majority with mood, neurotic and personality disorders referred to 39-session group therapy. Predictors were socio-demographic and clinical variables, self-reported symptoms (Symptom Check List-90-Revised) and personality style (Millon Clinical Multiaxial Inventory-II). Drop-out was classified into early and late premature termination excluding patients who dropped out for external reasons. Results. Drop-out comprised 20.6% (68 patients) of the sample. Logistic regression revealed social functioning, vocational training, alcohol problems and antisocial behavior to be related to drop-out. However, early drop-outs had prominent agoraphobic symptoms, lower interpersonal sensitivity and compulsive personality features, and late drop-outs cognitive and somatic anxiety symptoms and antisocial personality features. Clinical and psychological variables accounted for the major part of variance in predictions of drop-out, which ranged from 15.6% to 19.5% (Nagelkerke Pseudo R-Square). Conclusion. Social functioning was consistently associated with drop-out, but personality characteristics and anxiety symptoms differentiated between early and late drop-out. Failure to discriminate between stages of premature termination may explain some of the inconsistencies in the drop-out literature. Clinical implications. Before selection of patients to time-limited psychodynamic groups, self-reported symptoms should be thoroughly considered. Patients with agoraphobic symptoms should be offered alternative treatment. Awareness of and motivation to work with interpersonal issues may be essential for compliance with group therapy.
Fall, Anna-Maria; Roberts, Greg
2012-01-01
Research suggests that contextual, self-system, and school engagement variables influence dropping out from school. However, it is not clear how different types of contextual and self-system variables interact to affect students' engagement or contribute to decisions to dropout from high school. The self-system model of motivational development…
Numerical solution of continuous-time DSGE models under Poisson uncertainty
DEFF Research Database (Denmark)
Posch, Olaf; Trimborn, Timo
We propose a simple and powerful method for determining the transition process in continuous-time DSGE models under Poisson uncertainty numerically. The idea is to transform the system of stochastic differential equations into a system of functional differential equations of the retarded type. We...... classes of models. We illustrate the algorithm simulating both the stochastic neoclassical growth model and the Lucas model under Poisson uncertainty which is motivated by the Barro-Rietz rare disaster hypothesis. We find that, even for non-linear policy functions, the maximum (absolute) error is very...
On the rate of convergence in von Neumann's ergodic theorem with continuous time
International Nuclear Information System (INIS)
Kachurovskii, A G; Reshetenko, Anna V
2010-01-01
The rate of convergence in von Neumann's mean ergodic theorem is studied for continuous time. The condition that the rate of convergence of the ergodic averages be of power-law type is shown to be equivalent to requiring that the spectral measure of the corresponding dynamical system have a power-type singularity at 0. This forces the estimates for the convergence rate in the above ergodic theorem to be necessarily spectral. All the results obtained have obvious exact analogues for wide-sense stationary processes. Bibliography: 7 titles.
Continuous-Time Mean-Variance Portfolio Selection with Random Horizon
International Nuclear Information System (INIS)
Yu, Zhiyong
2013-01-01
This paper examines the continuous-time mean-variance optimal portfolio selection problem with random market parameters and random time horizon. Treating this problem as a linearly constrained stochastic linear-quadratic optimal control problem, I explicitly derive the efficient portfolios and efficient frontier in closed forms based on the solutions of two backward stochastic differential equations. Some related issues such as a minimum variance portfolio and a mutual fund theorem are also addressed. All the results are markedly different from those in the problem with deterministic exit time. A key part of my analysis involves proving the global solvability of a stochastic Riccati equation, which is interesting in its own right
Continuous-Time Mean-Variance Portfolio Selection with Random Horizon
Energy Technology Data Exchange (ETDEWEB)
Yu, Zhiyong, E-mail: yuzhiyong@sdu.edu.cn [Shandong University, School of Mathematics (China)
2013-12-15
This paper examines the continuous-time mean-variance optimal portfolio selection problem with random market parameters and random time horizon. Treating this problem as a linearly constrained stochastic linear-quadratic optimal control problem, I explicitly derive the efficient portfolios and efficient frontier in closed forms based on the solutions of two backward stochastic differential equations. Some related issues such as a minimum variance portfolio and a mutual fund theorem are also addressed. All the results are markedly different from those in the problem with deterministic exit time. A key part of my analysis involves proving the global solvability of a stochastic Riccati equation, which is interesting in its own right.
Finite-Time Stability and Controller Design of Continuous-Time Polynomial Fuzzy Systems
Directory of Open Access Journals (Sweden)
Xiaoxing Chen
2017-01-01
Full Text Available Finite-time stability and stabilization problem is first investigated for continuous-time polynomial fuzzy systems. The concept of finite-time stability and stabilization is given for polynomial fuzzy systems based on the idea of classical references. A sum-of-squares- (SOS- based approach is used to obtain the finite-time stability and stabilization conditions, which include some classical results as special cases. The proposed conditions can be solved with the help of powerful Matlab toolbox SOSTOOLS and a semidefinite-program (SDP solver. Finally, two numerical examples and one practical example are employed to illustrate the validity and effectiveness of the provided conditions.
Continuous time modelling of dynamical spatial lattice data observed at sparsely distributed times
DEFF Research Database (Denmark)
Rasmussen, Jakob Gulddahl; Møller, Jesper
2007-01-01
Summary. We consider statistical and computational aspects of simulation-based Bayesian inference for a spatial-temporal model based on a multivariate point process which is only observed at sparsely distributed times. The point processes are indexed by the sites of a spatial lattice......, and they exhibit spatial interaction. For specificity we consider a particular dynamical spatial lattice data set which has previously been analysed by a discrete time model involving unknown normalizing constants. We discuss the advantages and disadvantages of using continuous time processes compared...... with discrete time processes in the setting of the present paper as well as other spatial-temporal situations....
A 10 MHz Bandwidth Continuous-Time Delta-Sigma Modulator for Portable Ultrasound Scanners
DEFF Research Database (Denmark)
Llimos Muntal, Pere; Jørgensen, Ivan Harald Holger; Bruun, Erik
2016-01-01
comparator and a pull-down clocked latch. The feedback signal is generated with voltage DACs based on transmission gates. Using this implementation, a small and low-power solution required for portable ultrasound scanner applications is achieved. The modulator has a bandwidth of 10 MHz with an oversampling......A fourth-order 1-bit continuous-time delta-sigma modulator designed in a 65 nm process for portable ultrasound scanners is presented in this paper. The loop filter consists of RCintegrators, with programmable capacitor arrays and resistors, and the quantizer is implemented with a high-speed clocked...
A Continuous-Time Agency Model of Optimal Contracting and Capital Structure
Peter M. DeMarzo; Yuliy Sannikov
2004-01-01
We consider a principal-agent model in which the agent needs to raise capital from the principal to finance a project. Our model is based on DeMarzo and Fishman (2003), except that the agent's cash flows are given by a Brownian motion with drift in continuous time. The difficulty in writing an appropriate financial contract in this setting is that the agent can conceal and divert cash flows for his own consumption rather than pay back the principal. Alternatively, the agent may reduce the mea...
Finite-Time H∞ Filtering for Linear Continuous Time-Varying Systems with Uncertain Observations
Directory of Open Access Journals (Sweden)
Huihong Zhao
2012-01-01
Full Text Available This paper is concerned with the finite-time H∞ filtering problem for linear continuous time-varying systems with uncertain observations and ℒ2-norm bounded noise. The design of finite-time H∞ filter is equivalent to the problem that a certain indefinite quadratic form has a minimum and the filter is such that the minimum is positive. The quadratic form is related to a Krein state-space model according to the Krein space linear estimation theory. By using the projection theory in Krein space, the finite-time H∞ filtering problem is solved. A numerical example is given to illustrate the performance of the H∞ filter.
Forecasting the Global Mean Sea Level, a Continuous-Time State-Space Approach
DEFF Research Database (Denmark)
Boldrini, Lorenzo
In this paper we propose a continuous-time, Gaussian, linear, state-space system to model the relation between global mean sea level (GMSL) and the global mean temperature (GMT), with the aim of making long-term projections for the GMSL. We provide a justification for the model specification based......) and the temperature reconstruction from Hansen et al. (2010). We compare the forecasting performance of the proposed specification to the procedures developed in Rahmstorf (2007b) and Vermeer and Rahmstorf (2009). Finally, we compute projections for the sea-level rise conditional on the 21st century SRES temperature...
An Equivalent LMI Representation of Bounded Real Lemma for Continuous-Time Systems
Directory of Open Access Journals (Sweden)
Xie Wei
2008-01-01
Full Text Available Abstract An equivalent linear matrix inequality (LMI representation of bounded real lemma (BRL for linear continuous-time systems is introduced. As to LTI system including polytopic-type uncertainties, by using a parameter-dependent Lyapunov function, there are several LMIs-based formulations for the analysis and synthesis of performance. All of these representations only provide us with different sufficient conditions. Compared with previous methods, this new representation proposed here provides us the possibility to obtain better results. Finally, some numerical examples are illustrated to show the effectiveness of proposed method.
Kaiser, Kathryn A; Affuso, Olivia; Desmond, Renee; Allison, David B
Understanding participant demographic characteristics that inform the optimal design of obesity RCTs have been examined in few studies. The objective of this study was to investigate the association of individual participant characteristics and dropout rates (DORs) in obesity randomized controlled trials (RCT) by pooling data from several publicly available datasets for analyses. We comprehensively characterize DORs and patterns in obesity RCTs at the individual study level, and describe how such rates and patterns vary as a function of individual-level characteristics. We obtained and analyzed nine publicly-available, obesity RCT datasets that examined weight loss or weight gain prevention as a primary or secondary endpoint. Four risk factors for dropout were examined by Cox proportional hazards including sex, age, baseline BMI, and race/ethnicity. The individual study data were pooled in the final analyses with a random effect for study, and HR and 95% CIs were computed. Results of the multivariate analysis indicated that the risk of dropout was significantly higher for females compared to males (HR= 1.24, 95% CI = 1.05, 1.46). Hispanics and Non-Hispanic blacks had a significantly higher dropout rate compared to non-Hispanic whites (HR= 1.62, 95% CI = 1.37, 1.91; HR= 1.22, 95% CI = 1.11, 1.35, respectively). There was a significantly increased risk of dropout associated with advancing age (HR= 1.02, 95% CI = 1.01, 1.02) and increasing BMI (HR= 1.03, 95% CI = 1.03, 1.04). As more studies may focus on special populations, researchers designing obesity RCTs may wish to oversample in certain demographic groups if attempting to match comparison groups based on generalized estimates of expected dropout rates, or otherwise adjust a priori power estimates. Understanding true reasons for dropout may require additional methods of data gathering not generally employed in obesity RCTs, e.g. time on treatment.
Ultra-Low-Dropout Linear Regulator
Thornton, Trevor; Lepkowski, William; Wilk, Seth
2011-01-01
A radiation-tolerant, ultra-low-dropout linear regulator can operate between -150 and 150 C. Prototype components were demonstrated to be performing well after a total ionizing dose of 1 Mrad (Si). Unlike existing components, the linear regulator developed during this activity is unconditionally stable over all operating regimes without the need for an external compensation capacitor. The absence of an external capacitor reduces overall system mass/volume, increases reliability, and lowers cost. Linear regulators generate a precisely controlled voltage for electronic circuits regardless of fluctuations in the load current that the circuit draws from the regulator.
Desrosiers, Lyne; Saint-Jean, Micheline; Breton, Jean-Jacques
2015-06-01
The aim of this study was to gain a broader appreciation of processes involved in treatment dropout in adolescents with borderline personality disorder (BPD). A constructivist grounded theory was chosen using a multiple-case research design with three embedded levels of analysis (adolescent, parent, and care setting). Theoretical sampling and the different stages of analysis specific to grounded theory were performed according to the iterative process of constant comparative analysis. Twelve cases were examined (nine dropouts among adolescents with BPD and for the purpose of falsification, one dropout of suicidal adolescent without BPD and two completed treatments among adolescents with BPD). To document the cases, three groups of informants were recruited (adolescents, parents, and therapists involved in the treatment) and 34 interviews were conducted. Psychological characteristics, perception of mental illness and mental health care, and help-seeking context were the specific treatment dropout vulnerabilities identified in adolescents with BPD and in their parents. However, their disengagement became an issue only when care-setting response--including mitigation of accessibility problems, adaptation of services to needs of adolescents with BPD, preparation for treatment, and concern for clinicians' disposition to treat--was ill-suited to these treatment dropout vulnerabilities. Treatment planning proves to be a key milestone to properly engage adolescents with BPD and their parent. Systematic assessment of treatment dropout vulnerabilities before the intervention plan is laid out could foster better-suited responses of the care setting thus decreasing the incidence of treatment discontinuation in adolescents with BPD. Treatment dropout vulnerabilities specific to adolescents with BPD and their parents can be detected before the beginning of treatment. Premature treatment termination may be prevented if the care setting considers these vulnerabilities at treatment
Continuous-time digital front-ends for multistandard wireless transmission
Nuyts, Pieter A J; Dehaene, Wim
2014-01-01
This book describes the design of fully digital multistandard transmitter front-ends which can directly drive one or more switching power amplifiers, thus eliminating all other analog components. After reviewing different architectures, the authors focus on polar architectures using pulse width modulation (PWM), which are entirely based on unclocked delay lines and other continuous-time digital hardware. As a result, readers are enabled to shift accuracy concerns from the voltage domain to the time domain, to coincide with submicron CMOS technology scaling. The authors present different architectural options and compare them, based on their effect on the signal and spectrum quality. Next, a high-level theoretical analysis of two different PWM-based architectures – baseband PWM and RF PWM – is made. On the circuit level, traditional digital components and design techniques are revisited from the point of view of continuous-time digital circuits. Important design criteria are identified and diff...
Voelkle, Manuel C; Oud, Johan H L
2013-02-01
When designing longitudinal studies, researchers often aim at equal intervals. In practice, however, this goal is hardly ever met, with different time intervals between assessment waves and different time intervals between individuals being more the rule than the exception. One of the reasons for the introduction of continuous time models by means of structural equation modelling has been to deal with irregularly spaced assessment waves (e.g., Oud & Delsing, 2010). In the present paper we extend the approach to individually varying time intervals for oscillating and non-oscillating processes. In addition, we show not only that equal intervals are unnecessary but also that it can be advantageous to use unequal sampling intervals, in particular when the sampling rate is low. Two examples are provided to support our arguments. In the first example we compare a continuous time model of a bivariate coupled process with varying time intervals to a standard discrete time model to illustrate the importance of accounting for the exact time intervals. In the second example the effect of different sampling intervals on estimating a damped linear oscillator is investigated by means of a Monte Carlo simulation. We conclude that it is important to account for individually varying time intervals, and encourage researchers to conceive of longitudinal studies with different time intervals within and between individuals as an opportunity rather than a problem. © 2012 The British Psychological Society.
Gatto, Riccardo
2017-12-01
This article considers the random walk over Rp, with p ≥ 2, where a given particle starts at the origin and moves stepwise with uniformly distributed step directions and step lengths following a common distribution. Step directions and step lengths are independent. The case where the number of steps of the particle is fixed and the more general case where it follows an independent continuous time inhomogeneous counting process are considered. Saddlepoint approximations to the distribution of the distance from the position of the particle to the origin are provided. Despite the p-dimensional nature of the random walk, the computations of the saddlepoint approximations are one-dimensional and thus simple. Explicit formulae are derived with dimension p = 3: for uniformly and exponentially distributed step lengths, for fixed and for Poisson distributed number of steps. In these situations, the high accuracy of the saddlepoint approximations is illustrated by numerical comparisons with Monte Carlo simulation. Contribution to the "Topical Issue: Continuous Time Random Walk Still Trendy: Fifty-year History, Current State and Outlook", edited by Ryszard Kutner and Jaume Masoliver.
Research-Based Strategies and Best Practices for Dropout Prevention
Smink, Jay
2009-01-01
The National Dropout Prevention Center (NDPC) at Clemson University has been at the forefront of identifying model dropout prevention programs and promoting the use of best practices to increase the graduation rates in schools since 1986. The structure for these varied interventions and solutions takes the form of effective strategies, model…
Characteristics of Early Community College Dropouts. CCRC Analytics
Crosta, Peter M.
2013-01-01
For colleges to develop effective dropout prevention strategies, it is necessary to have a clear picture of who these early dropouts are. This report identifies distinguishing characteristics of this group by analyzing six years of transcript data on 14,429 first-time college students who in 2005 and 2006 enrolled at one of five community colleges…
Student Drop-Out from German Higher Education Institutions
Heublein, Ulrich
2014-01-01
28% of students of any one year currently give up their studies in bachelor degree programmes at German higher education institutions. Drop-out is to be understood as the definite termination in the higher education system without obtaining an academic degree. The drop-out rate is thereby calculated with the help of statistical estimation…
Dropout from exercise programs for seniors: A prospective cohort study
Stiggelbout, M.; Hopman-Rock, M.; Tak, E.; Lechner, L.; Mechelen, W. van
2005-01-01
This study examines dropout incidence, moment of dropout, and switching behavior in organized exercise programs for seniors in the Netherlands, as determined in a prospective cohort study (with baseline measurements at the start of the exercise program and follow-up after 6 months; N = 1,725,
Socioeconomic differences in school dropout among young adults
DEFF Research Database (Denmark)
Winding, Trine Nøhr; Andersen, Johan Hviid
2015-01-01
Background School dropout in adolescence is an important social determinant of health inequality in a lifetime perspective. It is commonly accepted that parental background factors are associated with later dropout, but to what extent social relations mediate this association is not yet fully...
Aggressive Students and High School Dropout: An Event History Analysis
Orozco, Steven R.
2016-01-01
Aggressive students often struggle in multiple domains of their school functioning and are at increased risk for high school dropout. Research has identified a variety of warning flags which are strong predictors of high school dropout. While it is known that aggressive students exhibit many of these warning flags, there is little research which…
Comparison of Urban and Rural Dropout Rates of Distance Students
de Hart, K. L.; Venter J. M. P.
2013-01-01
South Africa has one of the highest university dropout rates in the world. As a country, it also has a history of forced location and the withholding of resources, including quality education, from certain rural areas. This study investigates, the effect of urbanization (of the area in which a student resides) on the dropout rate of distance…
Dropout and completion in higher education in Europe: main report
Vossensteyn, Johan J.; Kottmann, Andrea; Jongbloed, Benjamin W.A.; Kaiser, Franciscus; Cremonini, Leon; Stensaker, Bjorn; Hovdhaugen, Elisabeth; Wollscheid, Sabine
2015-01-01
Improving completion and reducing dropout in higher education are key concerns for higher education in Europe. This study on dropout and completion in higher education in Europe demonstrates that national governments and higher education institutions use three different study success objectives:
Understanding Catalan University Dropout from a Cross-National Approach
Rodríguez-Gómez, David; Feixas, Mònica; Gairín, Joaquín; Muñoz, José Luís
2015-01-01
The dropout rate is an indicator of complex analysis and there is no consensus on its significance. Universities lack systematized, univocal methods for collecting student dropout data, making measurement problematic. In consequence, the formulas applied to analyze this phenomenon differ between countries and it is therefore an immense challenge…
Psychological Treatment as Part of Dropout Prevention: An Israeli Program
Schwartz, Hava; Hain, Rebecca
2014-01-01
This article reports on the integration of psychotherapy in a comprehensive dropout prevention program developed at the Dean of Students' office of Ben-Gurion University of the Negev in Israel. The program's psychologists conducted psychotherapy with a subset of dropout prevention program participants who had reacted with emotional turmoil to the…
Electron Dropout Echoes Induced by Interplanetary Shock: A Statistical Study
Liu, Z.; Zong, Q.; Hao, Y.; Zhou, X.; Ma, X.; Liu, Y.
2017-12-01
"Electron dropout echo" as indicated by repeated moderate dropout and recovery signatures of the flux of energetic electron in the out radiation belt region has been investigated systematically. The electron dropout and its echoes are usually found for higher energy (> 300 keV) channels fluxes, whereas the flux enhancements are obvious for lower energy electrons simultaneously after the interplanetary shock arrives at the Earth's geosynchronous orbit. 104 dropout echo events have been found from 215 interplanetary shock events from 1998 to 2007 based on LANL satellite data. In analogy to substorm injections, these 104 events could be naturally divided into two categories: dispersionless (49 events) or dispersive (55 events) according to the energy dispersion of the initial dropout. It is found that locations of dispersionless events are distributed mainly in the duskside magnetosphere. Further, the obtained locations derived from dispersive events with the time-of-flight technique of the initial dropout regions are mainly located at the duskside as well. Statistical studies have shown that the effect of shock normal, interplanetary magnetic field Bz and solar wind dynamic pressure may be insignificant to these electron dropout events. We suggest that the electric field impulse induced by the IP shock produces a more pronounced inward migration of electrons at the dusk side, resulting in the observed dusk-side moderate dropout of electron flux and its consequent echoes.
Diplomas Count 2013: Second Chances--Turning Dropouts into Graduates
Education Week, 2013
2013-01-01
The 2013 edition of "Diplomas Count," entitled "Second Chances: Turning Dropouts into Graduates," examines dropout recovery and innovative strategies for returning to the educational fold the 1 million students who leave school without a diploma each year. "Education Week's" journalists investigate interventions that…
School Dropout Indicators, Trends, and Interventions for School Counselors
Dockery, Donna J.
2012-01-01
School counselors are expected to develop programs that promote academic success for all students, including those at risk for dropping out of school. Knowledge of key indicators of potential dropouts and current trends in dropout prevention research may assist school counselors in better understanding this complex issue. Implementing recommended…
ACRES At-Risk Task Force: Dropout Survey.
Bull, Kay S.; And Others
This paper describes a study by the American Council on Rural Special Education (ACRES) to determine its membership's opinions on priorities and expertise regarding the dropout problem. ACRES members, primarily rural special-education teachers, parents, and collateral service workers, were surveyed about the dropout problem and what research they…
University Students’ Tendencies Toward and Reasons Behind Dropout
Directory of Open Access Journals (Sweden)
Hüseyin ŞİMŞEK
2013-04-01
Full Text Available In this research conducted to investigate university students’ tendencies toward and reasons behind dropout, it was found that university students had a high level of tendency towards dropout (45%. This indicated that one out of two students wanted to drop out of school at least once for a reason. As a result, their tendencies toward dropout was due to personal factors as well as those related to family, friends, and school. The personal factors affecting tendency toward dropout were gender, academic performance, school attendance, out-of-school work, boredom at school, and discipline penalty. According to the results, the factors related to school were faculty type, level of satisfaction with administrative and teaching staff as well as with social activities, level of difficulty in the department, and willingness to choose faculty. Furthermore, in this study, a positive relationship was found between dropout tendency and possession of close friends who dropped out of school.
Parenting practices and school dropout: a longitudinal study.
Blondal, Kristjana S; Adalbjarnardottir, Sigrun
2009-01-01
Adolescents' perceptions of parenting style and parental involvement in their education were examined longitudinally and related to school dropout among Icelandic youth (N = 427). Results indicated that adolescents who, at age 14, characterized their parents as authoritative (showing acceptance and supervision) were more likely to have completed upper secondary school by age 22 than adolescents from non-authoritative families, controlling for adolescents' gender, socioeconomic status (SES), temperament, and parental involvement. Parenting style seems to more strongly predict school dropout than parental involvement. Further, parenting style may moderate the relationship between parental involvement and dropout, but not in all groups; only in authoritative families does parental involvement decrease the likelihood of school dropout. Furthermore, even after controlling for previous academic achievement, adolescents from authoritative families were less likely to drop out than adolescents from authoritarian and neglectful families. These findings emphasize the importance of encouraging quality parent-child relationships in order to reduce the likelihood of school dropout.
Gueorguieva, Ralitza; Rosenheck, Robert; Lin, Haiqun
2011-01-01
Summary The ‘Clinical antipsychotic trials in intervention effectiveness’ study, was designed to evaluate whether there were significant differences between several antipsychotic medications in effectiveness, tolerability, cost and quality of life of subjects with schizophrenia. Overall, 74 % of patients discontinued the study medication for various reasons before the end of 18 months in phase I of the study. When such a large percentage of study participants fail to complete the study schedule, it is not clear whether the apparent profile in effectiveness reflects genuine changes over time or is influenced by selection bias, with participants with worse (or better) outcome values being more likely to drop out or to discontinue. To assess the effect of dropouts for different reasons on inferences, we construct a joint model for the longitudinal outcome and cause-specific dropouts that allows for interval-censored dropout times. Incorporating the information regarding the cause of dropout improves inferences and provides better understanding of the association between cause-specific dropout and the outcome process. We use simulations to demonstrate the advantages of the joint modelling approach in terms of bias and efficiency. PMID:22468033
Balfanz, Robert; Legters, Nettie
2004-01-01
The purpose of this report was to locate the dropout crisis- to determine its scale and scope by identifying the number of high schools with severe dropout problems, detailing the states, cities, and locales where they are concentrated, and establishing who attends them. For this analysis of high schools across the country, two cut-points were…
Continuous time random walk: Galilei invariance and relation for the nth moment
International Nuclear Information System (INIS)
Fa, Kwok Sau
2011-01-01
We consider a decoupled continuous time random walk model with a generic waiting time probability density function (PDF). For the force-free case we derive an integro-differential diffusion equation which is related to the Galilei invariance for the probability density. We also derive a general relation which connects the nth moment in the presence of any external force to the second moment without external force, i.e. it is valid for any waiting time PDF. This general relation includes the generalized second Einstein relation, which connects the first moment in the presence of any external force to the second moment without any external force. These expressions for the first two moments are verified by using several kinds of the waiting time PDF. Moreover, we present new anomalous diffusion behaviours for a waiting time PDF given by a product of power-law and exponential function.
Stochastic Games for Continuous-Time Jump Processes Under Finite-Horizon Payoff Criterion
Energy Technology Data Exchange (ETDEWEB)
Wei, Qingda, E-mail: weiqd@hqu.edu.cn [Huaqiao University, School of Economics and Finance (China); Chen, Xian, E-mail: chenxian@amss.ac.cn [Peking University, School of Mathematical Sciences (China)
2016-10-15
In this paper we study two-person nonzero-sum games for continuous-time jump processes with the randomized history-dependent strategies under the finite-horizon payoff criterion. The state space is countable, and the transition rates and payoff functions are allowed to be unbounded from above and from below. Under the suitable conditions, we introduce a new topology for the set of all randomized Markov multi-strategies and establish its compactness and metrizability. Then by constructing the approximating sequences of the transition rates and payoff functions, we show that the optimal value function for each player is a unique solution to the corresponding optimality equation and obtain the existence of a randomized Markov Nash equilibrium. Furthermore, we illustrate the applications of our main results with a controlled birth and death system.
Mixed-integrator-based bi-quad cell for designing a continuous time filter
International Nuclear Information System (INIS)
Chen Yong; Zhou Yumei
2010-01-01
A new mixed-integrator-based bi-quad cell is proposed. An alternative synthesis mechanism of complex poles is proposed compared with source-follower-based bi-quad cells which is designed applying the positive feedback technique. Using the negative feedback technique to combine different integrators, the proposed bi-quad cell synthesizes complex poles for designing a continuous time filter. It exhibits various advantages including compact topology, high gain, no parasitic pole, no CMFB circuit, and high capability. The fourth-order Butterworth lowpass filter using the proposed cells has been fabricated in 0.18 μm CMOS technology. The active area occupied by the filter with test buffer is only 200 x 170 μm 2 . The proposed filter consumes a low power of 201 μW and achieves a 68.5 dB dynamic range. (semiconductor integrated circuits)
New readout integrated circuit using continuous time fixed pattern noise correction
Dupont, Bertrand; Chammings, G.; Rapellin, G.; Mandier, C.; Tchagaspanian, M.; Dupont, Benoit; Peizerat, A.; Yon, J. J.
2008-04-01
LETI has been involved in IRFPA development since 1978; the design department (LETI/DCIS) has focused its work on new ROIC architecture since many years. The trend is to integrate advanced functions into the CMOS design to achieve cost efficient sensors production. Thermal imaging market is today more and more demanding of systems with instant ON capability and low power consumption. The purpose of this paper is to present the latest developments of fixed pattern noise continuous time correction. Several architectures are proposed, some are based on hardwired digital processing and some are purely analog. Both are using scene based algorithms. Moreover a new method is proposed for simultaneous correction of pixel offsets and sensitivities. In this scope, a new architecture of readout integrated circuit has been implemented; this architecture is developed with 0.18μm CMOS technology. The specification and the application of the ROIC are discussed in details.
A toolbox for safety instrumented system evaluation based on improved continuous-time Markov chain
Wardana, Awang N. I.; Kurniady, Rahman; Pambudi, Galih; Purnama, Jaka; Suryopratomo, Kutut
2017-08-01
Safety instrumented system (SIS) is designed to restore a plant into a safe condition when pre-hazardous event is occur. It has a vital role especially in process industries. A SIS shall be meet with safety requirement specifications. To confirm it, SIS shall be evaluated. Typically, the evaluation is calculated by hand. This paper presents a toolbox for SIS evaluation. It is developed based on improved continuous-time Markov chain. The toolbox supports to detailed approach of evaluation. This paper also illustrates an industrial application of the toolbox to evaluate arch burner safety system of primary reformer. The results of the case study demonstrates that the toolbox can be used to evaluate industrial SIS in detail and to plan the maintenance strategy.
An Expectation Maximization Algorithm to Model Failure Times by Continuous-Time Markov Chains
Directory of Open Access Journals (Sweden)
Qihong Duan
2010-01-01
Full Text Available In many applications, the failure rate function may present a bathtub shape curve. In this paper, an expectation maximization algorithm is proposed to construct a suitable continuous-time Markov chain which models the failure time data by the first time reaching the absorbing state. Assume that a system is described by methods of supplementary variables, the device of stage, and so on. Given a data set, the maximum likelihood estimators of the initial distribution and the infinitesimal transition rates of the Markov chain can be obtained by our novel algorithm. Suppose that there are m transient states in the system and that there are n failure time data. The devised algorithm only needs to compute the exponential of m×m upper triangular matrices for O(nm2 times in each iteration. Finally, the algorithm is applied to two real data sets, which indicates the practicality and efficiency of our algorithm.
Impulsive Control for Continuous-Time Markov Decision Processes: A Linear Programming Approach
Energy Technology Data Exchange (ETDEWEB)
Dufour, F., E-mail: dufour@math.u-bordeaux1.fr [Bordeaux INP, IMB, UMR CNRS 5251 (France); Piunovskiy, A. B., E-mail: piunov@liv.ac.uk [University of Liverpool, Department of Mathematical Sciences (United Kingdom)
2016-08-15
In this paper, we investigate an optimization problem for continuous-time Markov decision processes with both impulsive and continuous controls. We consider the so-called constrained problem where the objective of the controller is to minimize a total expected discounted optimality criterion associated with a cost rate function while keeping other performance criteria of the same form, but associated with different cost rate functions, below some given bounds. Our model allows multiple impulses at the same time moment. The main objective of this work is to study the associated linear program defined on a space of measures including the occupation measures of the controlled process and to provide sufficient conditions to ensure the existence of an optimal control.
Donier, J.; Bouchaud, J.-P.
2016-12-01
In standard Walrasian auctions, the price of a good is defined as the point where the supply and demand curves intersect. Since both curves are generically regular, the response to small perturbations is linearly small. However, a crucial ingredient is absent of the theory, namely transactions themselves. What happens after they occur? To answer the question, we develop a dynamic theory for supply and demand based on agents with heterogeneous beliefs. When the inter-auction time is infinitely long, the Walrasian mechanism is recovered. When transactions are allowed to happen in continuous time, a peculiar property emerges: close to the price, supply and demand vanish quadratically, which we empirically confirm on the Bitcoin. This explains why price impact in financial markets is universally observed to behave as the square root of the excess volume. The consequences are important, as they imply that the very fact of clearing the market makes prices hypersensitive to small fluctuations.
Offset-Free Direct Power Control of DFIG Under Continuous-Time Model Predictive Control
DEFF Research Database (Denmark)
Errouissi, Rachid; Al-Durra, Ahmed; Muyeen, S.M.
2017-01-01
This paper presents a robust continuous-time model predictive direct power control for doubly fed induction generator (DFIG). The proposed approach uses Taylor series expansion to predict the stator current in the synchronous reference frame over a finite time horizon. The predicted stator current...... is directly used to compute the required rotor voltage in order to minimize the difference between the actual stator currents and their references over the predictive time. However, as the proposed strategy is sensitive to parameter variations and external disturbances, a disturbance observer is embedded...... into the control loop to remove the steady-state error of the stator current. It turns out that the steady-state and the transient performances can be identified by simple design parameters. In this paper, the reference of the stator current is directly calculated from the desired stator active and reactive powers...
A Random Parameter Model for Continuous-Time Mean-Variance Asset-Liability Management
Directory of Open Access Journals (Sweden)
Hui-qiang Ma
2015-01-01
Full Text Available We consider a continuous-time mean-variance asset-liability management problem in a market with random market parameters; that is, interest rate, appreciation rates, and volatility rates are considered to be stochastic processes. By using the theories of stochastic linear-quadratic (LQ optimal control and backward stochastic differential equations (BSDEs, we tackle this problem and derive optimal investment strategies as well as the mean-variance efficient frontier analytically in terms of the solution of BSDEs. We find that the efficient frontier is still a parabola in a market with random parameters. Comparing with the existing results, we also find that the liability does not affect the feasibility of the mean-variance portfolio selection problem. However, in an incomplete market with random parameters, the liability can not be fully hedged.
Continuous-Time Mean-Variance Portfolio Selection under the CEV Process
Directory of Open Access Journals (Sweden)
Hui-qiang Ma
2014-01-01
Full Text Available We consider a continuous-time mean-variance portfolio selection model when stock price follows the constant elasticity of variance (CEV process. The aim of this paper is to derive an optimal portfolio strategy and the efficient frontier. The mean-variance portfolio selection problem is formulated as a linearly constrained convex program problem. By employing the Lagrange multiplier method and stochastic optimal control theory, we obtain the optimal portfolio strategy and mean-variance efficient frontier analytically. The results show that the mean-variance efficient frontier is still a parabola in the mean-variance plane, and the optimal strategies depend not only on the total wealth but also on the stock price. Moreover, some numerical examples are given to analyze the sensitivity of the efficient frontier with respect to the elasticity parameter and to illustrate the results presented in this paper. The numerical results show that the price of risk decreases as the elasticity coefficient increases.
An approach to the drone fleet survivability assessment based on a stochastic continues-time model
Kharchenko, Vyacheslav; Fesenko, Herman; Doukas, Nikos
2017-09-01
An approach and the algorithm to the drone fleet survivability assessment based on a stochastic continues-time model are proposed. The input data are the number of the drones, the drone fleet redundancy coefficient, the drone stability and restoration rate, the limit deviation from the norms of the drone fleet recovery, the drone fleet operational availability coefficient, the probability of the drone failure-free operation, time needed for performing the required tasks by the drone fleet. The ways for improving the recoverable drone fleet survivability taking into account amazing factors of system accident are suggested. Dependencies of the drone fleet survivability rate both on the drone stability and the number of the drones are analysed.
Stochastic Games for Continuous-Time Jump Processes Under Finite-Horizon Payoff Criterion
International Nuclear Information System (INIS)
Wei, Qingda; Chen, Xian
2016-01-01
In this paper we study two-person nonzero-sum games for continuous-time jump processes with the randomized history-dependent strategies under the finite-horizon payoff criterion. The state space is countable, and the transition rates and payoff functions are allowed to be unbounded from above and from below. Under the suitable conditions, we introduce a new topology for the set of all randomized Markov multi-strategies and establish its compactness and metrizability. Then by constructing the approximating sequences of the transition rates and payoff functions, we show that the optimal value function for each player is a unique solution to the corresponding optimality equation and obtain the existence of a randomized Markov Nash equilibrium. Furthermore, we illustrate the applications of our main results with a controlled birth and death system.
Continuous-time random walks with reset events. Historical background and new perspectives
Montero, Miquel; Masó-Puigdellosas, Axel; Villarroel, Javier
2017-09-01
In this paper, we consider a stochastic process that may experience random reset events which relocate the system to its starting position. We focus our attention on a one-dimensional, monotonic continuous-time random walk with a constant drift: the process moves in a fixed direction between the reset events, either by the effect of the random jumps, or by the action of a deterministic bias. However, the orientation of its motion is randomly determined after each restart. As a result of these alternating dynamics, interesting properties do emerge. General formulas for the propagator as well as for two extreme statistics, the survival probability and the mean first-passage time, are also derived. The rigor of these analytical results is verified by numerical estimations, for particular but illuminating examples.
Continuous-Time Mean-Variance Portfolio Selection: A Stochastic LQ Framework
International Nuclear Information System (INIS)
Zhou, X.Y.; Li, D.
2000-01-01
This paper is concerned with a continuous-time mean-variance portfolio selection model that is formulated as a bicriteria optimization problem. The objective is to maximize the expected terminal return and minimize the variance of the terminal wealth. By putting weights on the two criteria one obtains a single objective stochastic control problem which is however not in the standard form due to the variance term involved. It is shown that this nonstandard problem can be 'embedded' into a class of auxiliary stochastic linear-quadratic (LQ) problems. The stochastic LQ control model proves to be an appropriate and effective framework to study the mean-variance problem in light of the recent development on general stochastic LQ problems with indefinite control weighting matrices. This gives rise to the efficient frontier in a closed form for the original portfolio selection problem
Esfandiari, Kasra; Abdollahi, Farzaneh; Talebi, Heidar Ali
2017-09-01
In this paper, an identifier-critic structure is introduced to find an online near-optimal controller for continuous-time nonaffine nonlinear systems having saturated control signal. By employing two Neural Networks (NNs), the solution of Hamilton-Jacobi-Bellman (HJB) equation associated with the cost function is derived without requiring a priori knowledge about system dynamics. Weights of the identifier and critic NNs are tuned online and simultaneously such that unknown terms are approximated accurately and the control signal is kept between the saturation bounds. The convergence of NNs' weights, identification error, and system states is guaranteed using Lyapunov's direct method. Finally, simulation results are performed on two nonlinear systems to confirm the effectiveness of the proposed control strategy. Copyright © 2017 Elsevier Ltd. All rights reserved.
Yang, Xiong; Liu, Derong; Wang, Ding
2014-03-01
In this paper, an adaptive reinforcement learning-based solution is developed for the infinite-horizon optimal control problem of constrained-input continuous-time nonlinear systems in the presence of nonlinearities with unknown structures. Two different types of neural networks (NNs) are employed to approximate the Hamilton-Jacobi-Bellman equation. That is, an recurrent NN is constructed to identify the unknown dynamical system, and two feedforward NNs are used as the actor and the critic to approximate the optimal control and the optimal cost, respectively. Based on this framework, the action NN and the critic NN are tuned simultaneously, without the requirement for the knowledge of system drift dynamics. Moreover, by using Lyapunov's direct method, the weights of the action NN and the critic NN are guaranteed to be uniformly ultimately bounded, while keeping the closed-loop system stable. To demonstrate the effectiveness of the present approach, simulation results are illustrated.
DEFF Research Database (Denmark)
Tataru, Paula Cristina; Hobolth, Asger
2011-01-01
past evolutionary events (exact times and types of changes) are unaccessible and the past must be inferred from DNA sequence data observed in the present. RESULTS: We describe and implement three algorithms for computing linear combinations of expected values of the sufficient statistics, conditioned......BACKGROUND: Continuous time Markov chains (CTMCs) is a widely used model for describing the evolution of DNA sequences on the nucleotide, amino acid or codon level. The sufficient statistics for CTMCs are the time spent in a state and the number of changes between any two states. In applications...... of the algorithms is available at www.birc.au.dk/~paula/. CONCLUSIONS: We use two different models to analyze the accuracy and eight experiments to investigate the speed of the three algorithms. We find that they have similar accuracy and that EXPM is the slowest method. Furthermore we find that UNI is usually...
Fitting timeseries by continuous-time Markov chains: A quadratic programming approach
International Nuclear Information System (INIS)
Crommelin, D.T.; Vanden-Eijnden, E.
2006-01-01
Construction of stochastic models that describe the effective dynamics of observables of interest is an useful instrument in various fields of application, such as physics, climate science, and finance. We present a new technique for the construction of such models. From the timeseries of an observable, we construct a discrete-in-time Markov chain and calculate the eigenspectrum of its transition probability (or stochastic) matrix. As a next step we aim to find the generator of a continuous-time Markov chain whose eigenspectrum resembles the observed eigenspectrum as closely as possible, using an appropriate norm. The generator is found by solving a minimization problem: the norm is chosen such that the object function is quadratic and convex, so that the minimization problem can be solved using quadratic programming techniques. The technique is illustrated on various toy problems as well as on datasets stemming from simulations of molecular dynamics and of atmospheric flows
Impact of Dupoto-e-Maa education project on dropout rate and academic performance
Directory of Open Access Journals (Sweden)
James B. Ouda
2016-09-01
Conclusion: The study recommended that there is need to increase the number of non-governmental organisations modelled around the Dupoto-e-Maa education project so as to reduce dropout rate and improve pupil academic performance. The findings could also inform government policy in terms of recruitment and placement of teachers in schools in arid and semi-arid lands. Project funding could be increased to improve visibility and sustainability of project activities.
Anomalous dispersion in correlated porous media: a coupled continuous time random walk approach
Comolli, Alessandro; Dentz, Marco
2017-09-01
We study the causes of anomalous dispersion in Darcy-scale porous media characterized by spatially heterogeneous hydraulic properties. Spatial variability in hydraulic conductivity leads to spatial variability in the flow properties through Darcy's law and thus impacts on solute and particle transport. We consider purely advective transport in heterogeneity scenarios characterized by broad distributions of heterogeneity length scales and point values. Particle transport is characterized in terms of the stochastic properties of equidistantly sampled Lagrangian velocities, which are determined by the flow and conductivity statistics. The persistence length scales of flow and transport velocities are imprinted in the spatial disorder and reflect the distribution of heterogeneity length scales. Particle transitions over the velocity length scales are kinematically coupled with the transition time through velocity. We show that the average particle motion follows a coupled continuous time random walk (CTRW), which is fully parameterized by the distribution of flow velocities and the medium geometry in terms of the heterogeneity length scales. The coupled CTRW provides a systematic framework for the investigation of the origins of anomalous dispersion in terms of heterogeneity correlation and the distribution of conductivity point values. We derive analytical expressions for the asymptotic scaling of the moments of the spatial particle distribution and first arrival time distribution (FATD), and perform numerical particle tracking simulations of the coupled CTRW to capture the full average transport behavior. Broad distributions of heterogeneity point values and lengths scales may lead to very similar dispersion behaviors in terms of the spatial variance. Their mechanisms, however are very different, which manifests in the distributions of particle positions and arrival times, which plays a central role for the prediction of the fate of dissolved substances in
Estimating the continuous-time dynamics of energy and fat metabolism in mice.
Guo, Juen; Hall, Kevin D
2009-09-01
The mouse has become the most popular organism for investigating molecular mechanisms of body weight regulation. But understanding the physiological context by which a molecule exerts its effect on body weight requires knowledge of energy intake, energy expenditure, and fuel selection. Furthermore, measurements of these variables made at an isolated time point cannot explain why body weight has its present value since body weight is determined by the past history of energy and macronutrient imbalance. While food intake and body weight changes can be frequently measured over several weeks (the relevant time scale for mice), correspondingly frequent measurements of energy expenditure and fuel selection are not currently feasible. To address this issue, we developed a mathematical method based on the law of energy conservation that uses the measured time course of body weight and food intake to estimate the underlying continuous-time dynamics of energy output and net fat oxidation. We applied our methodology to male C57BL/6 mice consuming various ad libitum diets during weight gain and loss over several weeks and present the first continuous-time estimates of energy output and net fat oxidation rates underlying the observed body composition changes. We show that transient energy and fat imbalances in the first several days following a diet switch can account for a significant fraction of the total body weight change. We also discovered a time-invariant curve relating body fat and fat-free masses in male C57BL/6 mice, and the shape of this curve determines how diet, fuel selection, and body composition are interrelated.
Modeling commodity salam contract between two parties for discrete and continuous time series
Hisham, Azie Farhani Badrol; Jaffar, Maheran Mohd
2017-08-01
In order for Islamic finance to remain competitive as the conventional, there needs a new development of Islamic compliance product such as Islamic derivative that can be used to manage the risk. However, under syariah principles and regulations, all financial instruments must not be conflicting with five syariah elements which are riba (interest paid), rishwah (corruption), gharar (uncertainty or unnecessary risk), maysir (speculation or gambling) and jahl (taking advantage of the counterparty's ignorance). This study has proposed a traditional Islamic contract namely salam that can be built as an Islamic derivative product. Although a lot of studies has been done on discussing and proposing the implementation of salam contract as the Islamic product however they are more into qualitative and law issues. Since there is lack of quantitative study of salam contract being developed, this study introduces mathematical models that can value the appropriate salam price for a commodity salam contract between two parties. In modeling the commodity salam contract, this study has modified the existing conventional derivative model and come out with some adjustments to comply with syariah rules and regulations. The cost of carry model has been chosen as the foundation to develop the commodity salam model between two parties for discrete and continuous time series. However, the conventional time value of money results from the concept of interest that is prohibited in Islam. Therefore, this study has adopted the idea of Islamic time value of money which is known as the positive time preference, in modeling the commodity salam contract between two parties for discrete and continuous time series.
Chen, Xiaofeng; Song, Qiankun; Li, Zhongshan; Zhao, Zhenjiang; Liu, Yurong
2018-07-01
This paper addresses the problem of stability for continuous-time and discrete-time quaternion-valued neural networks (QVNNs) with linear threshold neurons. Applying the semidiscretization technique to the continuous-time QVNNs, the discrete-time analogs are obtained, which preserve the dynamical characteristics of their continuous-time counterparts. Via the plural decomposition method of quaternion, homeomorphic mapping theorem, as well as Lyapunov theorem, some sufficient conditions on the existence, uniqueness, and global asymptotical stability of the equilibrium point are derived for the continuous-time QVNNs and their discrete-time analogs, respectively. Furthermore, a uniform sufficient condition on the existence, uniqueness, and global asymptotical stability of the equilibrium point is obtained for both continuous-time QVNNs and their discrete-time version. Finally, two numerical examples are provided to substantiate the effectiveness of the proposed results.
Selected determinants may account for dropout risks among medical students.
Mørcke, Anne Mette; O'Neill, Lotte; Kjeldsen, Inge Trads; Eika, Berit
2012-09-01
The dropout level from the Danish medical schools is high, but we have only little insight into this problem. The purpose of this study was to qualify the ongoing discussions concerning dropout. In this retrospective cohort study, relevant variables were extracted from the established database of Aarhus University for the 639 students initiating medicine studies between 1 January 1999 and 31 December 2000. A multivariate pre-admission and post-admission model was examined. Of the 639 medical students, 20% dropped out. Most students dropped out during their first year. The type of admission exam was a strong predictor of dropout in the pre-admission model, whereas previous higher education protected against dropout. Obtaining leave was a very strong predictor of dropout in the post-admission model, whereas high grades protected against dropout. The dropout rate has been decreasing during the past decade. Young people considering studying medicine could be advised to choose natural science subjects in high school, and a number of research questions concerning preparedness for medical school are worth pursuing. Leave or very low grades during the first and second study years might serve as red flags to supervisors. Study research was funded by Aarhus University. Not relevant, register-based research with no biological human material cannot be notified to the Danish Committee System. The Danish Data Protection Agency allows schools to conduct anonymized, non-sensitive, educational analyses without notification.
Lost without trace: oximetry signal dropout in preterm infants.
Lim, Kathleen; Wheeler, Kevin I; Jackson, Hamish D; Sadeghi Fathabadi, Omid; Gale, Timothy J; Dargaville, Peter A
2015-09-01
Oxygen saturation (SpO2) signal dropout leaves caregivers without a reliable measure to guide oxygen therapy. We studied SpO2 dropout in preterm infants on continuous positive airway pressure, noting the SpO2 values at signal loss and recovery and thus the resultant change in SpO2, and the factors influencing this parameter. In 32 infants of median gestation 26 weeks, a total of 3932 SpO2 dropout episodes were identified (1.1 episodes/h). In the episodes overall, SpO2 decreased by 1.1%, with the SpO2 change influenced by starting SpO2 (negative correlation), but not dropout duration. For episodes starting in hypoxia (SpO2 dropout, with a downward trajectory in a quarter of cases. We conclude that after signal dropout SpO2 generally recovers in a relative normoxic range. Blind FiO2 adjustments are thus unlikely to be of benefit during most SpO2 dropout episodes. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
Patterns and Factors of High School Dropout Risks of Racial and Linguistic Groups
Kim, Sunha; Chang, Mido; Singh, Kusum; Allen, Katherine R.
2015-01-01
This study examined the dropout trajectories of racial and linguistic minority students and explored the effects of students' contextual factors on their high school dropout risks. Our motivation was to identify the dropout patterns of Black, Hispanic, and Hispanic English language learner (ELL) students, who have comparatively high dropout rates,…
Service-Learning. National Dropout Prevention Center/Network Newsletter. Volume 22, Number 4
Duckenfield, Marty, Ed.
2011-01-01
The "National Dropout Prevention Newsletter" is published quarterly by the National Dropout Prevention Center/Network. This issue contains the following articles: (1) Dropouts and Democracy (Robert Shumer); (2) 2011 NDPN Crystal Star Winners; (3) Service-Learning as Dropout Intervention and More (Michael VanKeulen); and (4) Teacher…
Model-Free Adaptive Control Algorithm with Data Dropout Compensation
Directory of Open Access Journals (Sweden)
Xuhui Bu
2012-01-01
Full Text Available The convergence of model-free adaptive control (MFAC algorithm can be guaranteed when the system is subject to measurement data dropout. The system output convergent speed gets slower as dropout rate increases. This paper proposes a MFAC algorithm with data compensation. The missing data is first estimated using the dynamical linearization method, and then the estimated value is introduced to update control input. The convergence analysis of the proposed MFAC algorithm is given, and the effectiveness is also validated by simulations. It is shown that the proposed algorithm can compensate the effect of the data dropout, and the better output performance can be obtained.
How can we strengthen students’ social relations in order to reduce school dropout?
DEFF Research Database (Denmark)
Ingholt, Liselotte; Sørensen, Betina Bang; Andersen, Susan
2015-01-01
on ethnographic methods, including 22 qualitative interviews with students 17-19 years old and fieldwork with participant observations at four vocational schools over 40 days, including informal interviews and discussion meetings with managers, teachers, counselors and students. As part of the fieldwork, four......BACKGROUND: This article describes the rationale and contents of an intervention program aimed at strengthening students' social relations in order to reduce dropout from vocational schools in Denmark. Taking its theoretical cue from the concept of 'social participation', a qualitative study...... was performed to investigate the specific relationships between the social environment within the schools and the institutional structures in order to analyse reasons for school dropout and their relation to well-being, cigarette smoking and substance use. METHODS: The development study was based...
Immunization dropout rate and data quality among children 12-23 months of age in Ghana.
Baguune, Benjamin; Ndago, Joyce Aputere; Adokiya, Martin Nyaaba
2017-01-01
Immunization against diseases is one of the most important public health interventions with cost effective means to preventing childhood morbidity, mortality and disability. However, a proportion of children particularly in Africa are not fully immunized with the recommended vaccines. Thus, many children are still susceptible to the Expanded Program on Immunization (EPI) targeted diseases. The objective of this study was to determine the immunization dropout rate and data quality among children aged 12-23 months in Techiman Municipality, Ghana. A cross-sectional cluster survey was conducted among 600 children. Data was collected using semi-structured questionnaire through face-to-face interviews. Before the main data collection, the tools were pre-tested in three different communities in the Municipality. The mothers/caregivers were interviewed, extracted information from the child immunization cards and observation employed to confirm the presence of Bacillus Calmette-Guerin (BCG) scar on each child. Routine immunization data was also extracted from immunization registers and annual reports in the Municipality. I mmunization coverage for each of the fifteen vaccines doses is above 90.0% while full childhood immunized status is 89.5%. Immunization dropout rate was 5.6% (using BCG and Measles as proxy vaccines). This is lower than the 10.0% cutoff point by World Health Organization. However, routine administrative data was characterized by some discrepancies (e.g. > 100.0% immunization coverage for each of the vaccines) and high dropout rate (BCG - Measles = 31.5%). Binary regression was performed to determine predictors of dropout rate. The following were statistically significant: married (OR = 0.31; 95% = CI 0.15-0.62; and p = 0.001), Christianity (OR = 0.27; 95% CI = 0.13-0.91; and p dropout. Childhood full immunized status (89.5%) and immunization coverages (>90%) are high while dropout rate is lower than the recommended cutoff point by WHO
Vibration analysis diagnostics by continuous-time models: A case study
International Nuclear Information System (INIS)
Pedregal, Diego J.; Carmen Carnero, Ma.
2009-01-01
In this paper a forecasting system in condition monitoring is developed based on vibration signals in order to improve the diagnosis of a certain critical equipment at an industrial plant. The system is based on statistical models capable of forecasting the state of the equipment combined with a cost model consisting of defining the time of preventive replacement when the minimum of the expected cost per unit of time is reached in the future. The most relevant features of the system are that (i) it is developed for bivariate signals; (ii) the statistical models are set up in a continuous-time framework, due to the specific nature of the data; and (iii) it has been developed from scratch for a real case study and may be generalised to other pieces of equipment. The system is thoroughly tested on the equipment available, showing its correctness with the data in a statistical sense and its capability of producing sensible results for the condition monitoring programme
Vibration analysis diagnostics by continuous-time models: A case study
Energy Technology Data Exchange (ETDEWEB)
Pedregal, Diego J. [Escuela Tecnica Superior de Ingenieros Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)], E-mail: Diego.Pedregal@uclm.es; Carmen Carnero, Ma. [Escuela Tecnica Superior de Ingenieros Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)], E-mail: Carmen.Carnero@uclm.es
2009-02-15
In this paper a forecasting system in condition monitoring is developed based on vibration signals in order to improve the diagnosis of a certain critical equipment at an industrial plant. The system is based on statistical models capable of forecasting the state of the equipment combined with a cost model consisting of defining the time of preventive replacement when the minimum of the expected cost per unit of time is reached in the future. The most relevant features of the system are that (i) it is developed for bivariate signals; (ii) the statistical models are set up in a continuous-time framework, due to the specific nature of the data; and (iii) it has been developed from scratch for a real case study and may be generalised to other pieces of equipment. The system is thoroughly tested on the equipment available, showing its correctness with the data in a statistical sense and its capability of producing sensible results for the condition monitoring programme.
Lee, Jae Young; Park, Jin Bae; Choi, Yoon Ho
2015-05-01
This paper focuses on a class of reinforcement learning (RL) algorithms, named integral RL (I-RL), that solve continuous-time (CT) nonlinear optimal control problems with input-affine system dynamics. First, we extend the concepts of exploration, integral temporal difference, and invariant admissibility to the target CT nonlinear system that is governed by a control policy plus a probing signal called an exploration. Then, we show input-to-state stability (ISS) and invariant admissibility of the closed-loop systems with the policies generated by integral policy iteration (I-PI) or invariantly admissible PI (IA-PI) method. Based on these, three online I-RL algorithms named explorized I-PI and integral Q -learning I, II are proposed, all of which generate the same convergent sequences as I-PI and IA-PI under the required excitation condition on the exploration. All the proposed methods are partially or completely model free, and can simultaneously explore the state space in a stable manner during the online learning processes. ISS, invariant admissibility, and convergence properties of the proposed methods are also investigated, and related with these, we show the design principles of the exploration for safe learning. Neural-network-based implementation methods for the proposed schemes are also presented in this paper. Finally, several numerical simulations are carried out to verify the effectiveness of the proposed methods.
Well-posedness and accuracy of the ensemble Kalman filter in discrete and continuous time
Kelly, D. T B
2014-09-22
The ensemble Kalman filter (EnKF) is a method for combining a dynamical model with data in a sequential fashion. Despite its widespread use, there has been little analysis of its theoretical properties. Many of the algorithmic innovations associated with the filter, which are required to make a useable algorithm in practice, are derived in an ad hoc fashion. The aim of this paper is to initiate the development of a systematic analysis of the EnKF, in particular to do so for small ensemble size. The perspective is to view the method as a state estimator, and not as an algorithm which approximates the true filtering distribution. The perturbed observation version of the algorithm is studied, without and with variance inflation. Without variance inflation well-posedness of the filter is established; with variance inflation accuracy of the filter, with respect to the true signal underlying the data, is established. The algorithm is considered in discrete time, and also for a continuous time limit arising when observations are frequent and subject to large noise. The underlying dynamical model, and assumptions about it, is sufficiently general to include the Lorenz \\'63 and \\'96 models, together with the incompressible Navier-Stokes equation on a two-dimensional torus. The analysis is limited to the case of complete observation of the signal with additive white noise. Numerical results are presented for the Navier-Stokes equation on a two-dimensional torus for both complete and partial observations of the signal with additive white noise.
Continuous-Time Public Good Contribution Under Uncertainty: A Stochastic Control Approach
International Nuclear Information System (INIS)
Ferrari, Giorgio; Riedel, Frank; Steg, Jan-Henrik
2017-01-01
In this paper we study continuous-time stochastic control problems with both monotone and classical controls motivated by the so-called public good contribution problem. That is the problem of n economic agents aiming to maximize their expected utility allocating initial wealth over a given time period between private consumption and irreversible contributions to increase the level of some public good. We investigate the corresponding social planner problem and the case of strategic interaction between the agents, i.e. the public good contribution game. We show existence and uniqueness of the social planner’s optimal policy, we characterize it by necessary and sufficient stochastic Kuhn–Tucker conditions and we provide its expression in terms of the unique optional solution of a stochastic backward equation. Similar stochastic first order conditions prove to be very useful for studying any Nash equilibria of the public good contribution game. In the symmetric case they allow us to prove (qualitative) uniqueness of the Nash equilibrium, which we again construct as the unique optional solution of a stochastic backward equation. We finally also provide a detailed analysis of the so-called free rider effect.
Continuous-time interval model identification of blood glucose dynamics for type 1 diabetes
Kirchsteiger, Harald; Johansson, Rolf; Renard, Eric; del Re, Luigi
2014-07-01
While good physiological models of the glucose metabolism in type 1 diabetic patients are well known, their parameterisation is difficult. The high intra-patient variability observed is a further major obstacle. This holds for data-based models too, so that no good patient-specific models are available. Against this background, this paper proposes the use of interval models to cover the different metabolic conditions. The control-oriented models contain a carbohydrate and insulin sensitivity factor to be used for insulin bolus calculators directly. Available clinical measurements were sampled on an irregular schedule which prompts the use of continuous-time identification, also for the direct estimation of the clinically interpretable factors mentioned above. An identification method is derived and applied to real data from 28 diabetic patients. Model estimation was done on a clinical data-set, whereas validation results shown were done on an out-of-clinic, everyday life data-set. The results show that the interval model approach allows a much more regular estimation of the parameters and avoids physiologically incompatible parameter estimates.
Occupation times and ergodicity breaking in biased continuous time random walks
International Nuclear Information System (INIS)
Bel, Golan; Barkai, Eli
2005-01-01
Continuous time random walk (CTRW) models are widely used to model diffusion in condensed matter. There are two classes of such models, distinguished by the convergence or divergence of the mean waiting time. Systems with finite average sojourn time are ergodic and thus Boltzmann-Gibbs statistics can be applied. We investigate the statistical properties of CTRW models with infinite average sojourn time; in particular, the occupation time probability density function is obtained. It is shown that in the non-ergodic phase the distribution of the occupation time of the particle on a given lattice point exhibits bimodal U or trimodal W shape, related to the arcsine law. The key points are as follows. (a) In a CTRW with finite or infinite mean waiting time, the distribution of the number of visits on a lattice point is determined by the probability that a member of an ensemble of particles in equilibrium occupies the lattice point. (b) The asymmetry parameter of the probability distribution function of occupation times is related to the Boltzmann probability and to the partition function. (c) The ensemble average is given by Boltzmann-Gibbs statistics for either finite or infinite mean sojourn time, when detailed balance conditions hold. (d) A non-ergodic generalization of the Boltzmann-Gibbs statistical mechanics for systems with infinite mean sojourn time is found
Continuous-Time Public Good Contribution Under Uncertainty: A Stochastic Control Approach
Energy Technology Data Exchange (ETDEWEB)
Ferrari, Giorgio, E-mail: giorgio.ferrari@uni-bielefeld.de; Riedel, Frank, E-mail: frank.riedel@uni-bielefeld.de; Steg, Jan-Henrik, E-mail: jsteg@uni-bielefeld.de [Bielefeld University, Center for Mathematical Economics (Germany)
2017-06-15
In this paper we study continuous-time stochastic control problems with both monotone and classical controls motivated by the so-called public good contribution problem. That is the problem of n economic agents aiming to maximize their expected utility allocating initial wealth over a given time period between private consumption and irreversible contributions to increase the level of some public good. We investigate the corresponding social planner problem and the case of strategic interaction between the agents, i.e. the public good contribution game. We show existence and uniqueness of the social planner’s optimal policy, we characterize it by necessary and sufficient stochastic Kuhn–Tucker conditions and we provide its expression in terms of the unique optional solution of a stochastic backward equation. Similar stochastic first order conditions prove to be very useful for studying any Nash equilibria of the public good contribution game. In the symmetric case they allow us to prove (qualitative) uniqueness of the Nash equilibrium, which we again construct as the unique optional solution of a stochastic backward equation. We finally also provide a detailed analysis of the so-called free rider effect.
EVALUATING CONTINUOUS-TIME SLAM USING A PREDEFINED TRAJECTORY PROVIDED BY A ROBOTIC ARM
Directory of Open Access Journals (Sweden)
B. Koch
2017-09-01
Full Text Available Recently published approaches to SLAM algorithms process laser sensor measurements and output a map as a point cloud of the environment. Often the actual precision of the map remains unclear, since SLAMalgorithms apply local improvements to the resulting map. Unfortunately, it is not trivial to compare the performance of SLAMalgorithms objectively, especially without an accurate ground truth. This paper presents a novel benchmarking technique that allows to compare a precise map generated with an accurate ground truth trajectory to a map with a manipulated trajectory which was distorted by different forms of noise. The accurate ground truth is acquired by mounting a laser scanner on an industrial robotic arm. The robotic arm is moved on a predefined path while the position and orientation of the end-effector tool are monitored. During this process the 2D profile measurements of the laser scanner are recorded in six degrees of freedom and afterwards used to generate a precise point cloud of the test environment. For benchmarking, an offline continuous-time SLAM algorithm is subsequently applied to remove the inserted distortions. Finally, it is shown that the manipulated point cloud is reversible to its previous state and is slightly improved compared to the original version, since small errors that came into account by imprecise assumptions, sensor noise and calibration errors are removed as well.
Backward jump continuous-time random walk: An application to market trading
Gubiec, Tomasz; Kutner, Ryszard
2010-10-01
The backward jump modification of the continuous-time random walk model or the version of the model driven by the negative feedback was herein derived for spatiotemporal continuum in the context of a share price evolution on a stock exchange. In the frame of the model, we described stochastic evolution of a typical share price on a stock exchange with a moderate liquidity within a high-frequency time scale. The model was validated by satisfactory agreement of the theoretical velocity autocorrelation function with its empirical counterpart obtained for the continuous quotation. This agreement is mainly a result of a sharp backward correlation found and considered in this article. This correlation is a reminiscence of such a bid-ask bounce phenomenon where backward price jump has the same or almost the same length as preceding jump. We suggested that this correlation dominated the dynamics of the stock market with moderate liquidity. Although assumptions of the model were inspired by the market high-frequency empirical data, its potential applications extend beyond the financial market, for instance, to the field covered by the Le Chatelier-Braun principle of contrariness.
Continuous-time modeling of cell fate determination in Arabidopsis flowers
Directory of Open Access Journals (Sweden)
Angenent Gerco C
2010-07-01
Full Text Available Abstract Background The genetic control of floral organ specification is currently being investigated by various approaches, both experimentally and through modeling. Models and simulations have mostly involved boolean or related methods, and so far a quantitative, continuous-time approach has not been explored. Results We propose an ordinary differential equation (ODE model that describes the gene expression dynamics of a gene regulatory network that controls floral organ formation in the model plant Arabidopsis thaliana. In this model, the dimerization of MADS-box transcription factors is incorporated explicitly. The unknown parameters are estimated from (known experimental expression data. The model is validated by simulation studies of known mutant plants. Conclusions The proposed model gives realistic predictions with respect to independent mutation data. A simulation study is carried out to predict the effects of a new type of mutation that has so far not been made in Arabidopsis, but that could be used as a severe test of the validity of the model. According to our predictions, the role of dimers is surprisingly important. Moreover, the functional loss of any dimer leads to one or more phenotypic alterations.
Learning a Continuous-Time Streaming Video QoE Model.
Ghadiyaram, Deepti; Pan, Janice; Bovik, Alan C
2018-05-01
Over-the-top adaptive video streaming services are frequently impacted by fluctuating network conditions that can lead to rebuffering events (stalling events) and sudden bitrate changes. These events visually impact video consumers' quality of experience (QoE) and can lead to consumer churn. The development of models that can accurately predict viewers' instantaneous subjective QoE under such volatile network conditions could potentially enable the more efficient design of quality-control protocols for media-driven services, such as YouTube, Amazon, Netflix, and so on. However, most existing models only predict a single overall QoE score on a given video and are based on simple global video features, without accounting for relevant aspects of human perception and behavior. We have created a QoE evaluator, called the time-varying QoE Indexer, that accounts for interactions between stalling events, analyzes the spatial and temporal content of a video, predicts the perceptual video quality, models the state of the client-side data buffer, and consequently predicts continuous-time quality scores that agree quite well with human opinion scores. The new QoE predictor also embeds the impact of relevant human cognitive factors, such as memory and recency, and their complex interactions with the video content being viewed. We evaluated the proposed model on three different video databases and attained standout QoE prediction performance.
A lattice-model representation of continuous-time random walks
International Nuclear Information System (INIS)
Campos, Daniel; Mendez, Vicenc
2008-01-01
We report some ideas for constructing lattice models (LMs) as a discrete approach to the reaction-dispersal (RD) or reaction-random walks (RRW) models. The analysis of a rather general class of Markovian and non-Markovian processes, from the point of view of their wavefront solutions, let us show that in some regimes their macroscopic dynamics (front speed) turns out to be different from that by classical reaction-diffusion equations, which are often used as a mean-field approximation to the problem. So, the convenience of a more general framework as that given by the continuous-time random walks (CTRW) is claimed. Here we use LMs as a numerical approach in order to support that idea, while in previous works our discussion was restricted to analytical models. For the two specific cases studied here, we derive and analyze the mean-field expressions for our LMs. As a result, we are able to provide some links between the numerical and analytical approaches studied
Low Power Continuous-Time Delta-Sigma ADC with Current Output DAC
DEFF Research Database (Denmark)
Marker-Villumsen, Niels; Jørgensen, Ivan Harald Holger; Bruun, Erik
2015-01-01
The paper presents a continuous-time (CT) DeltaSigma (∆Σ) analog-to-digital converter (ADC) using a current output digital-to-analog converter (DAC) for the feedback. From circuit analysis it is shown that using a current output DAC makes it possible to relax the noise requirements of the 1st...... integrator of the loopfilter, and thereby reduce the current consumption. Furthermore, the noise of the current output DAC being dependent on the ADC input signal level, enabling a dynamic range that is larger than the peak signal-to-noise ratio (SNR). The current output DAC is used in a 3rd order multibit...... CT ∆Σ ADC for audio applications, designed in a 0.18 µm CMOS process, with active-RC integrators, a 7-level Flash ADC quantizer and current output DAC for the feedback. From simulations the ADC achieves a dynamic range of 95.0 dB in the audio band, with a current consumption of 284 µA for a 1.7 V...
Fluctuations around equilibrium laws in ergodic continuous-time random walks.
Schulz, Johannes H P; Barkai, Eli
2015-06-01
We study occupation time statistics in ergodic continuous-time random walks. Under thermal detailed balance conditions, the average occupation time is given by the Boltzmann-Gibbs canonical law. But close to the nonergodic phase, the finite-time fluctuations around this mean are large and nontrivial. They exhibit dual time scaling and distribution laws: the infinite density of large fluctuations complements the Lévy-stable density of bulk fluctuations. Neither of the two should be interpreted as a stand-alone limiting law, as each has its own deficiency: the infinite density has an infinite norm (despite particle conservation), while the stable distribution has an infinite variance (although occupation times are bounded). These unphysical divergences are remedied by consistent use and interpretation of both formulas. Interestingly, while the system's canonical equilibrium laws naturally determine the mean occupation time of the ergodic motion, they also control the infinite and Lévy-stable densities of fluctuations. The duality of stable and infinite densities is in fact ubiquitous for these dynamics, as it concerns the time averages of general physical observables.
Continuous time random walk analysis of solute transport in fractured porous media
Energy Technology Data Exchange (ETDEWEB)
Cortis, Andrea; Cortis, Andrea; Birkholzer, Jens
2008-06-01
The objective of this work is to discuss solute transport phenomena in fractured porous media, where the macroscopic transport of contaminants in the highly permeable interconnected fractures can be strongly affected by solute exchange with the porous rock matrix. We are interested in a wide range of rock types, with matrix hydraulic conductivities varying from almost impermeable (e.g., granites) to somewhat permeable (e.g., porous sandstones). In the first case, molecular diffusion is the only transport process causing the transfer of contaminants between the fractures and the matrix blocks. In the second case, additional solute transfer occurs as a result of a combination of advective and dispersive transport mechanisms, with considerable impact on the macroscopic transport behavior. We start our study by conducting numerical tracer experiments employing a discrete (microscopic) representation of fractures and matrix. Using the discrete simulations as a surrogate for the 'correct' transport behavior, we then evaluate the accuracy of macroscopic (continuum) approaches in comparison with the discrete results. However, instead of using dual-continuum models, which are quite often used to account for this type of heterogeneity, we develop a macroscopic model based on the Continuous Time Random Walk (CTRW) framework, which characterizes the interaction between the fractured and porous rock domains by using a probability distribution function of residence times. A parametric study of how CTRW parameters evolve is presented, describing transport as a function of the hydraulic conductivity ratio between fractured and porous domains.
Energy Technology Data Exchange (ETDEWEB)
Geiger, S.; Cortis, A.; Birkholzer, J.T.
2010-04-01
Solute transport in fractured porous media is typically 'non-Fickian'; that is, it is characterized by early breakthrough and long tailing and by nonlinear growth of the Green function-centered second moment. This behavior is due to the effects of (1) multirate diffusion occurring between the highly permeable fracture network and the low-permeability rock matrix, (2) a wide range of advection rates in the fractures and, possibly, the matrix as well, and (3) a range of path lengths. As a consequence, prediction of solute transport processes at the macroscale represents a formidable challenge. Classical dual-porosity (or mobile-immobile) approaches in conjunction with an advection-dispersion equation and macroscopic dispersivity commonly fail to predict breakthrough of fractured porous media accurately. It was recently demonstrated that the continuous time random walk (CTRW) method can be used as a generalized upscaling approach. Here we extend this work and use results from high-resolution finite element-finite volume-based simulations of solute transport in an outcrop analogue of a naturally fractured reservoir to calibrate the CTRW method by extracting a distribution of retention times. This procedure allows us to predict breakthrough at other model locations accurately and to gain significant insight into the nature of the fracture-matrix interaction in naturally fractured porous reservoirs with geologically realistic fracture geometries.
A lattice-model representation of continuous-time random walks
Energy Technology Data Exchange (ETDEWEB)
Campos, Daniel [School of Mathematics, Department of Applied Mathematics, University of Manchester, Manchester M60 1QD (United Kingdom); Mendez, Vicenc [Grup de Fisica Estadistica, Departament de Fisica, Universitat Autonoma de Barcelona, 08193 Bellaterra (Barcelona) (Spain)], E-mail: daniel.campos@uab.es, E-mail: vicenc.mendez@uab.es
2008-02-29
We report some ideas for constructing lattice models (LMs) as a discrete approach to the reaction-dispersal (RD) or reaction-random walks (RRW) models. The analysis of a rather general class of Markovian and non-Markovian processes, from the point of view of their wavefront solutions, let us show that in some regimes their macroscopic dynamics (front speed) turns out to be different from that by classical reaction-diffusion equations, which are often used as a mean-field approximation to the problem. So, the convenience of a more general framework as that given by the continuous-time random walks (CTRW) is claimed. Here we use LMs as a numerical approach in order to support that idea, while in previous works our discussion was restricted to analytical models. For the two specific cases studied here, we derive and analyze the mean-field expressions for our LMs. As a result, we are able to provide some links between the numerical and analytical approaches studied.
Continuous-time random walks on networks with vertex- and time-dependent forcing.
Angstmann, C N; Donnelly, I C; Henry, B I; Langlands, T A M
2013-08-01
We have investigated the transport of particles moving as random walks on the vertices of a network, subject to vertex- and time-dependent forcing. We have derived the generalized master equations for this transport using continuous time random walks, characterized by jump and waiting time densities, as the underlying stochastic process. The forcing is incorporated through a vertex- and time-dependent bias in the jump densities governing the random walking particles. As a particular case, we consider particle forcing proportional to the concentration of particles on adjacent vertices, analogous to self-chemotactic attraction in a spatial continuum. Our algebraic and numerical studies of this system reveal an interesting pair-aggregation pattern formation in which the steady state is composed of a high concentration of particles on a small number of isolated pairs of adjacent vertices. The steady states do not exhibit this pair aggregation if the transport is random on the vertices, i.e., without forcing. The manifestation of pair aggregation on a transport network may thus be a signature of self-chemotactic-like forcing.
Tataru, Paula; Hobolth, Asger
2011-12-05
Continuous time Markov chains (CTMCs) is a widely used model for describing the evolution of DNA sequences on the nucleotide, amino acid or codon level. The sufficient statistics for CTMCs are the time spent in a state and the number of changes between any two states. In applications past evolutionary events (exact times and types of changes) are unaccessible and the past must be inferred from DNA sequence data observed in the present. We describe and implement three algorithms for computing linear combinations of expected values of the sufficient statistics, conditioned on the end-points of the chain, and compare their performance with respect to accuracy and running time. The first algorithm is based on an eigenvalue decomposition of the rate matrix (EVD), the second on uniformization (UNI), and the third on integrals of matrix exponentials (EXPM). The implementation in R of the algorithms is available at http://www.birc.au.dk/~paula/. We use two different models to analyze the accuracy and eight experiments to investigate the speed of the three algorithms. We find that they have similar accuracy and that EXPM is the slowest method. Furthermore we find that UNI is usually faster than EVD.
Directory of Open Access Journals (Sweden)
Tataru Paula
2011-12-01
Full Text Available Abstract Background Continuous time Markov chains (CTMCs is a widely used model for describing the evolution of DNA sequences on the nucleotide, amino acid or codon level. The sufficient statistics for CTMCs are the time spent in a state and the number of changes between any two states. In applications past evolutionary events (exact times and types of changes are unaccessible and the past must be inferred from DNA sequence data observed in the present. Results We describe and implement three algorithms for computing linear combinations of expected values of the sufficient statistics, conditioned on the end-points of the chain, and compare their performance with respect to accuracy and running time. The first algorithm is based on an eigenvalue decomposition of the rate matrix (EVD, the second on uniformization (UNI, and the third on integrals of matrix exponentials (EXPM. The implementation in R of the algorithms is available at http://www.birc.au.dk/~paula/. Conclusions We use two different models to analyze the accuracy and eight experiments to investigate the speed of the three algorithms. We find that they have similar accuracy and that EXPM is the slowest method. Furthermore we find that UNI is usually faster than EVD.
Coherent exciton transport in dendrimers and continuous-time quantum walks
Mülken, Oliver; Bierbaum, Veronika; Blumen, Alexander
2006-03-01
We model coherent exciton transport in dendrimers by continuous-time quantum walks. For dendrimers up to the second generation the coherent transport shows perfect recurrences when the initial excitation starts at the central node. For larger dendrimers, the recurrence ceases to be perfect, a fact which resembles results for discrete quantum carpets. Moreover, depending on the initial excitation site, we find that the coherent transport to certain nodes of the dendrimer has a very low probability. When the initial excitation starts from the central node, the problem can be mapped onto a line which simplifies the computational effort. Furthermore, the long time average of the quantum mechanical transition probabilities between pairs of nodes shows characteristic patterns and allows us to classify the nodes into clusters with identical limiting probabilities. For the (space) average of the quantum mechanical probability to be still or to be again at the initial site, we obtain, based on the Cauchy-Schwarz inequality, a simple lower bound which depends only on the eigenvalue spectrum of the Hamiltonian.
A Continuous-Time Delta-Sigma ADC for Portable Ultrasound Scanners
DEFF Research Database (Denmark)
Llimos Muntal, Pere; Jørgensen, Ivan Harald Holger; Bruun, Erik
2017-01-01
A fully diﬀerential fourth-order 1-bit continuous-time delta-sigma ADC designed in a 65nm process for portable ultrasound scanners is presented in this paper. The circuit design, implementation and measurements on the fabricated die are shown. The loop ﬁlter consists of RC-integrators, programmable...... capacitor arrays, resistors and voltage feedback DACs. The quantizer contains a pulse generator, a high-speed clocked comparator and a pull-down clocked latch to ensure constant delay in the feedback loop. Using this implementation, a small and low-power solution required for portable ultrasound scanner...... applications is achieved. The converter has a supply voltage of 1.2V, a bandwidth of 10MHz and an oversampling ratio of 16 leading to an operating frequency of 320MHz. The design occupies a die area of 0.0175mm2. Simulations with extracted parasitics show a SNR of 45.2dB and a current consumption of 489 µ...
A low power CMOS 3.3 Gbps continuous-time adaptive equalizer for serial link
International Nuclear Information System (INIS)
Ju Hao; Zhou Yumei; Zhao Jianzhong
2011-01-01
This paper describes using a high-speed continuous-time analog adaptive equalizer as the front-end of a receiver for a high-speed serial interface, which is compliant with many serial communication specifications such as USB2.0, PCI-E2.0 and Rapid IO. The low and high frequency loops are merged to decrease the effect of delay between the two paths, in addition, the infinite input impedance facilitates the cascade stages in order to improve the high frequency boosting gain. The implemented circuit architecture could facilitate the wide frequency range from 1 to 3.3 Gbps with different length FR4-PCB traces, which brings as much as 25 dB loss. The replica control circuits are injected to provide a convenient way to regulate common-mode voltage for full differential operation. In addition, AC coupling is adopted to suppress the common input from the forward stage. A prototype chip was fabricated in 0.18-μm 1P6M mixed-signal CMOS technology. The actual area is 0.6 x 0.57 mm 2 and the analog equalizer operates up to 3.3 Gbps over FR4-PCB trace with 25 dB loss. The overall power dissipation is approximately 23.4 mW. (semiconductor integrated circuits)
A low power CMOS 3.3 Gbps continuous-time adaptive equalizer for serial link
Hao, Ju; Yumei, Zhou; Jianzhong, Zhao
2011-09-01
This paper describes using a high-speed continuous-time analog adaptive equalizer as the front-end of a receiver for a high-speed serial interface, which is compliant with many serial communication specifications such as USB2.0, PCI-E2.0 and Rapid IO. The low and high frequency loops are merged to decrease the effect of delay between the two paths, in addition, the infinite input impedance facilitates the cascade stages in order to improve the high frequency boosting gain. The implemented circuit architecture could facilitate the wide frequency range from 1 to 3.3 Gbps with different length FR4-PCB traces, which brings as much as 25 dB loss. The replica control circuits are injected to provide a convenient way to regulate common-mode voltage for full differential operation. In addition, AC coupling is adopted to suppress the common input from the forward stage. A prototype chip was fabricated in 0.18-μm 1P6M mixed-signal CMOS technology. The actual area is 0.6 × 0.57 mm2 and the analog equalizer operates up to 3.3 Gbps over FR4-PCB trace with 25 dB loss. The overall power dissipation is approximately 23.4 mW.
Optimal Compensation with Hidden Action and Lump-Sum Payment in a Continuous-Time Model
International Nuclear Information System (INIS)
Cvitanic, Jaksa; Wan, Xuhu; Zhang Jianfeng
2009-01-01
We consider a problem of finding optimal contracts in continuous time, when the agent's actions are unobservable by the principal, who pays the agent with a one-time payoff at the end of the contract. We fully solve the case of quadratic cost and separable utility, for general utility functions. The optimal contract is, in general, a nonlinear function of the final outcome only, while in the previously solved cases, for exponential and linear utility functions, the optimal contract is linear in the final output value. In a specific example we compute, the first-best principal's utility is infinite, while it becomes finite with hidden action, which is increasing in value of the output. In the second part of the paper we formulate a general mathematical theory for the problem. We apply the stochastic maximum principle to give necessary conditions for optimal contracts. Sufficient conditions are hard to establish, but we suggest a way to check sufficiency using non-convex optimization
Evaluating Continuous-Time Slam Using a Predefined Trajectory Provided by a Robotic Arm
Koch, B.; Leblebici, R.; Martell, A.; Jörissen, S.; Schilling, K.; Nüchter, A.
2017-09-01
Recently published approaches to SLAM algorithms process laser sensor measurements and output a map as a point cloud of the environment. Often the actual precision of the map remains unclear, since SLAMalgorithms apply local improvements to the resulting map. Unfortunately, it is not trivial to compare the performance of SLAMalgorithms objectively, especially without an accurate ground truth. This paper presents a novel benchmarking technique that allows to compare a precise map generated with an accurate ground truth trajectory to a map with a manipulated trajectory which was distorted by different forms of noise. The accurate ground truth is acquired by mounting a laser scanner on an industrial robotic arm. The robotic arm is moved on a predefined path while the position and orientation of the end-effector tool are monitored. During this process the 2D profile measurements of the laser scanner are recorded in six degrees of freedom and afterwards used to generate a precise point cloud of the test environment. For benchmarking, an offline continuous-time SLAM algorithm is subsequently applied to remove the inserted distortions. Finally, it is shown that the manipulated point cloud is reversible to its previous state and is slightly improved compared to the original version, since small errors that came into account by imprecise assumptions, sensor noise and calibration errors are removed as well.
Giver, Hanne; Faber, Anne; Strøyer, Jesper; Hannerz, Harald; Albertsen, Karen
2011-05-01
The eldercare sector in Denmark as in many industrialised countries is characterised by difficulties in retaining labour. Research suggests a possible imbalance between lifestyle and health among eldercare trainees and the demanding work encountered as eldercare employees. The aim of the present study was to determine the predictive effect of lifestyle and self-rated health on dropout from the Danish eldercare sector two years after qualification. We included 4,526 female eldercare trainees in the analyses of lifestyle parameters and 5,023 in the analyses of self-rated health. The participants in this prospective study were recruited from 27 of the 28 Danish colleges for eldercare. We linked survey data with national register data to obtain information about labour market attachment two years after qualification. The results of the present study showed that the poorer self-rated health, the higher the risk for dropout from the labour market (p lifestyle. We found that overweight/obesity (p = 0.0021 and p = 0.0012) as well as smoking (p = 0.0017) decreased the risk of dropout from eldercare into education. We found no support for increased likelihood of dropout among physically inactive. The results of the present study show that a poorer self-rated health is a predictor for dropout, not only from the eldercare two years after qualification, but from the labour market as a whole. However, the results were less consistent regarding the predictive effect of a detrimental lifestyle on dropout.
Karyotaki, E; Kleiboer, A; Smit, F; Turner, D T; Pastor, A M; Andersson, G; Berger, T; Botella, C; Breton, J M; Carlbring, P; Christensen, H; de Graaf, E; Griffiths, K; Donker, T; Farrer, L; Huibers, M J H; Lenndin, J; Mackinnon, A; Meyer, B; Moritz, S; Riper, H; Spek, V; Vernmark, K; Cuijpers, P
2015-10-01
It is well known that web-based interventions can be effective treatments for depression. However, dropout rates in web-based interventions are typically high, especially in self-guided web-based interventions. Rigorous empirical evidence regarding factors influencing dropout in self-guided web-based interventions is lacking due to small study sample sizes. In this paper we examined predictors of dropout in an individual patient data meta-analysis to gain a better understanding of who may benefit from these interventions. A comprehensive literature search for all randomized controlled trials (RCTs) of psychotherapy for adults with depression from 2006 to January 2013 was conducted. Next, we approached authors to collect the primary data of the selected studies. Predictors of dropout, such as socio-demographic, clinical, and intervention characteristics were examined. Data from 2705 participants across ten RCTs of self-guided web-based interventions for depression were analysed. The multivariate analysis indicated that male gender [relative risk (RR) 1.08], lower educational level (primary education, RR 1.26) and co-morbid anxiety symptoms (RR 1.18) significantly increased the risk of dropping out, while for every additional 4 years of age, the risk of dropping out significantly decreased (RR 0.94). Dropout can be predicted by several variables and is not randomly distributed. This knowledge may inform tailoring of online self-help interventions to prevent dropout in identified groups at risk.
Immunization Dropout Rates in Ihe, Awgu Local Government Area ...
African Journals Online (AJOL)
vaccine. Subjects and Methods: This is a cross sectional study where immunization dropout rate of ... especially with the addition of other vaccines such as yellow fever in endemic areas and tetanus toxoid (injections for the pregnant women.
Unconditionally Stable Low Dropout Regulators for Extreme Environments, Phase II
National Aeronautics and Space Administration — We have developed a low dropout (LDO) regulator using a patented MESFET transistor technology that can be manufactured in commercial CMOS foundries with no changes...
Dropout in VET – institutional selection and social exclusion
DEFF Research Database (Denmark)
Jørgensen, Christian Helms
Dropout – institutional selection and social exclusion For the last ten years dropout of vocational education has increased strongly in Denmark. The questions addressed in this paper are why and how dropout in VET takes place. The objective is to provide more detailed and qualified knowledge...... of the complex processes of dropping out. The present study is part of a large national research project on retention in VET. The paper aims to understand dropout as a result of the interplay of students’ agentic actions and social interactions and the opportunities for participation afforded by the colleges...... area, sub-cultural style, etc. It is shown how the students, through the interplay of institutional selection and social in- and exclusion, pass through different trajectories of participation in the programmes....
Brown, Halley J; Andreason, Hope; Melling, Amy K; Imel, Zac E; Simon, Gregory E
2015-08-01
Retention, or its opposite, dropout, is a common metric of psychotherapy quality, but using it to assess provider performance can be problematic. Differences among providers in numbers of general dropouts, "good" dropouts (patients report positive treatment experiences and outcome), and "bad" dropouts (patients report negative treatment experiences and outcome) were evaluated. Patient records were paired with satisfaction surveys (N=3,054). Binomial mixed-effects models were used to examine differences among providers by dropout type. Thirty-four percent of treatment episodes resulted in dropout. Of these, 14% were bad dropouts and 27% were good dropouts. Providers accounted for approximately 17% of the variance in general dropout and 10% of the variance in both bad dropout and good dropout. The ranking of providers fluctuated by type of dropout. Provider assessments based on patient retention should offer a way to isolate dropout type, given that nonspecific metrics may lead to biased estimates of performance.
Discrete- vs. Continuous-Time Modeling of Unequally Spaced Experience Sampling Method Data
Directory of Open Access Journals (Sweden)
Silvia de Haan-Rietdijk
2017-10-01
Full Text Available The Experience Sampling Method is a common approach in psychological research for collecting intensive longitudinal data with high ecological validity. One characteristic of ESM data is that it is often unequally spaced, because the measurement intervals within a day are deliberately varied, and measurement continues over several days. This poses a problem for discrete-time (DT modeling approaches, which are based on the assumption that all measurements are equally spaced. Nevertheless, DT approaches such as (vector autoregressive modeling are often used to analyze ESM data, for instance in the context of affective dynamics research. There are equivalent continuous-time (CT models, but they are more difficult to implement. In this paper we take a pragmatic approach and evaluate the practical relevance of the violated model assumption in DT AR(1 and VAR(1 models, for the N = 1 case. We use simulated data under an ESM measurement design to investigate the bias in the parameters of interest under four different model implementations, ranging from the true CT model that accounts for all the exact measurement times, to the crudest possible DT model implementation, where even the nighttime is treated as a regular interval. An analysis of empirical affect data illustrates how the differences between DT and CT modeling can play out in practice. We find that the size and the direction of the bias in DT (VAR models for unequally spaced ESM data depend quite strongly on the true parameter in addition to data characteristics. Our recommendation is to use CT modeling whenever possible, especially now that new software implementations have become available.
Well-posedness and accuracy of the ensemble Kalman filter in discrete and continuous time
International Nuclear Information System (INIS)
Kelly, D T B; Stuart, A M; Law, K J H
2014-01-01
The ensemble Kalman filter (EnKF) is a method for combining a dynamical model with data in a sequential fashion. Despite its widespread use, there has been little analysis of its theoretical properties. Many of the algorithmic innovations associated with the filter, which are required to make a useable algorithm in practice, are derived in an ad hoc fashion. The aim of this paper is to initiate the development of a systematic analysis of the EnKF, in particular to do so for small ensemble size. The perspective is to view the method as a state estimator, and not as an algorithm which approximates the true filtering distribution. The perturbed observation version of the algorithm is studied, without and with variance inflation. Without variance inflation well-posedness of the filter is established; with variance inflation accuracy of the filter, with respect to the true signal underlying the data, is established. The algorithm is considered in discrete time, and also for a continuous time limit arising when observations are frequent and subject to large noise. The underlying dynamical model, and assumptions about it, is sufficiently general to include the Lorenz '63 and '96 models, together with the incompressible Navier–Stokes equation on a two-dimensional torus. The analysis is limited to the case of complete observation of the signal with additive white noise. Numerical results are presented for the Navier–Stokes equation on a two-dimensional torus for both complete and partial observations of the signal with additive white noise. (paper)
Directory of Open Access Journals (Sweden)
François Niragire
2017-05-01
Full Text Available Child survival programmes are efficient when they target the most significant and area-specific factors. This study aimed to assess the key determinants and spatial variation of child mortality at the district level in Rwanda. Data from the 2010 Rwanda Demographic and Health Survey were analysed for 8817 live births that occurred during five years preceding the survey. Out of the children born, 433 had died before survey interviews were carried out. A full Bayesian geo-additive continuous-time hazard model enabled us to maximise data utilisation and hence improve the accuracy of our estimates. The results showed substantial district- level spatial variation in childhood mortality in Rwanda. District-specific spatial characteristics were particularly associated with higher death hazards in two districts: Musanze and Nyabihu. The model estimates showed that there were lower death rates among children from households of medium and high economic status compared to those from low-economic status households. Factors, such as four antenatal care visits, delivery at a health facility, prolonged breastfeeding and mothers younger than 31 years were associated with lower child death rates. Long preceding birth intervals were also associated with fewer hazards. For these reasons, programmes aimed at reducing child mortality gaps between districts in Rwanda should target maternal factors and take into consideration district-specific spatial characteristics. Further, child survival gains require strengthening or scaling-up of existing programmes pertaining to access to, and utilisation of maternal and child health care services as well as reduction of the household gap in the economic status.
Niragire, François; Achia, Thomas N O; Lyambabaje, Alexandre; Ntaganira, Joseph
2017-05-11
Child survival programmes are efficient when they target the most significant and area-specific factors. This study aimed to assess the key determinants and spatial variation of child mortality at the district level in Rwanda. Data from the 2010 Rwanda Demographic and Health Survey were analysed for 8817 live births that occurred during five years preceding the survey. Out of the children born, 433 had died before survey interviews were carried out. A full Bayesian geo-additive continuous-time hazard model enabled us to maximise data utilisation and hence improve the accuracy of our estimates. The results showed substantial district- level spatial variation in childhood mortality in Rwanda. District-specific spatial characteristics were particularly associated with higher death hazards in two districts: Musanze and Nyabihu. The model estimates showed that there were lower death rates among children from households of medium and high economic status compared to those from low-economic status households. Factors, such as four antenatal care visits, delivery at a health facility, prolonged breastfeeding and mothers younger than 31 years were associated with lower child death rates. Long preceding birth intervals were also associated with fewer hazards. For these reasons, programmes aimed at reducing child mortality gaps between districts in Rwanda should target maternal factors and take into consideration district-specific spatial characteristics. Further, child survival gains require strengthening or scaling-up of existing programmes pertaining to access to, and utilisation of maternal and child health care services as well as reduction of the household gap in the economic status.
Fitting and interpreting continuous-time latent Markov models for panel data.
Lange, Jane M; Minin, Vladimir N
2013-11-20
Multistate models characterize disease processes within an individual. Clinical studies often observe the disease status of individuals at discrete time points, making exact times of transitions between disease states unknown. Such panel data pose considerable modeling challenges. Assuming the disease process progresses accordingly, a standard continuous-time Markov chain (CTMC) yields tractable likelihoods, but the assumption of exponential sojourn time distributions is typically unrealistic. More flexible semi-Markov models permit generic sojourn distributions yet yield intractable likelihoods for panel data in the presence of reversible transitions. One attractive alternative is to assume that the disease process is characterized by an underlying latent CTMC, with multiple latent states mapping to each disease state. These models retain analytic tractability due to the CTMC framework but allow for flexible, duration-dependent disease state sojourn distributions. We have developed a robust and efficient expectation-maximization algorithm in this context. Our complete data state space consists of the observed data and the underlying latent trajectory, yielding computationally efficient expectation and maximization steps. Our algorithm outperforms alternative methods measured in terms of time to convergence and robustness. We also examine the frequentist performance of latent CTMC point and interval estimates of disease process functionals based on simulated data. The performance of estimates depends on time, functional, and data-generating scenario. Finally, we illustrate the interpretive power of latent CTMC models for describing disease processes on a dataset of lung transplant patients. We hope our work will encourage wider use of these models in the biomedical setting. Copyright © 2013 John Wiley & Sons, Ltd.
Directory of Open Access Journals (Sweden)
Botond Molnár
Full Text Available There has been a long history of using neural networks for combinatorial optimization and constraint satisfaction problems. Symmetric Hopfield networks and similar approaches use steepest descent dynamics, and they always converge to the closest local minimum of the energy landscape. For finding global minima additional parameter-sensitive techniques are used, such as classical simulated annealing or the so-called chaotic simulated annealing, which induces chaotic dynamics by addition of extra terms to the energy landscape. Here we show that asymmetric continuous-time neural networks can solve constraint satisfaction problems without getting trapped in non-solution attractors. We concentrate on a model solving Boolean satisfiability (k-SAT, which is a quintessential NP-complete problem. There is a one-to-one correspondence between the stable fixed points of the neural network and the k-SAT solutions and we present numerical evidence that limit cycles may also be avoided by appropriately choosing the parameters of the model. This optimal parameter region is fairly independent of the size and hardness of instances, this way parameters can be chosen independently of the properties of problems and no tuning is required during the dynamical process. The model is similar to cellular neural networks already used in CNN computers. On an analog device solving a SAT problem would take a single operation: the connection weights are determined by the k-SAT instance and starting from any initial condition the system searches until finding a solution. In this new approach transient chaotic behavior appears as a natural consequence of optimization hardness and not as an externally induced effect.
Astrand, Elaine
2018-06-01
Working memory (WM), crucial for successful behavioral performance in most of our everyday activities, holds a central role in goal-directed behavior. As task demands increase, inducing higher WM load, maintaining successful behavioral performance requires the brain to work at the higher end of its capacity. Because it is depending on both external and internal factors, individual WM load likely varies in a continuous fashion. The feasibility to extract such a continuous measure in time that correlates to behavioral performance during a working memory task remains unsolved. Multivariate pattern decoding was used to test whether a decoder constructed from two discrete levels of WM load can generalize to produce a continuous measure that predicts task performance. Specifically, a linear regression with L2-regularization was chosen with input features from EEG oscillatory activity recorded from healthy participants while performing the n-back task, [Formula: see text]. The feasibility to extract a continuous time-resolved measure that correlates positively to trial-by-trial working memory task performance is demonstrated (r = 0.47, p performance before action (r = 0.49, p < 0.05). We show that the extracted continuous measure enables to study the temporal dynamics of the complex activation pattern of WM encoding during the n-back task. Specifically, temporally precise contributions of different spectral features are observed which extends previous findings of traditional univariate approaches. These results constitute an important contribution towards a wide range of applications in the field of cognitive brain-machine interfaces. Monitoring mental processes related to attention and WM load to reduce the risk of committing errors in high-risk environments could potentially prevent many devastating consequences or using the continuous measure as neurofeedback opens up new possibilities to develop novel rehabilitation techniques for
GPU-accelerated algorithms for many-particle continuous-time quantum walks
Piccinini, Enrico; Benedetti, Claudia; Siloi, Ilaria; Paris, Matteo G. A.; Bordone, Paolo
2017-06-01
Many-particle continuous-time quantum walks (CTQWs) represent a resource for several tasks in quantum technology, including quantum search algorithms and universal quantum computation. In order to design and implement CTQWs in a realistic scenario, one needs effective simulation tools for Hamiltonians that take into account static noise and fluctuations in the lattice, i.e. Hamiltonians containing stochastic terms. To this aim, we suggest a parallel algorithm based on the Taylor series expansion of the evolution operator, and compare its performances with those of algorithms based on the exact diagonalization of the Hamiltonian or a 4th order Runge-Kutta integration. We prove that both Taylor-series expansion and Runge-Kutta algorithms are reliable and have a low computational cost, the Taylor-series expansion showing the additional advantage of a memory allocation not depending on the precision of calculation. Both algorithms are also highly parallelizable within the SIMT paradigm, and are thus suitable for GPGPU computing. In turn, we have benchmarked 4 NVIDIA GPUs and 3 quad-core Intel CPUs for a 2-particle system over lattices of increasing dimension, showing that the speedup provided by GPU computing, with respect to the OPENMP parallelization, lies in the range between 8x and (more than) 20x, depending on the frequency of post-processing. GPU-accelerated codes thus allow one to overcome concerns about the execution time, and make it possible simulations with many interacting particles on large lattices, with the only limit of the memory available on the device.
Influence of mental disorders on school dropout in Mexico.
Borges, Guilherme; Medina Mora-Icaza, María Elena; Benjet, Corina; Lee, Sing; Lane, Michael; Breslau, Joshua
2011-11-01
To study the impact of mental disorders on failure in educational attainment in Mexico. Diagnoses and age of onset for each of 16 DSM-IV disorders were assessed through retrospective self-reports with the Composite International Diagnostic Instrument (CIDI) during fieldwork in 2001-2002. Survival analysis was used to examine associations between early onset DSM-IV/CIDI disorders and subsequent school dropout or failure to reach educational milestones. More than one of two Mexicans did not complete secondary education. More than one-third of those who finished secondary education did not enter college, and one of four students who entered college did not graduate. Impulse control disorders and substance use disorders were associated with higher risk for school dropout, secondary school dropout and to a lesser degree failure to enter college. Anxiety disorders were associated with lower risk for school dropout, especially secondary school dropout and, to a lesser degree, primary school dropout. The heterogeneity of results found in Mexico may be due to the effect of mental disorders being diminished or masked by the much greater effect of economic hardship and low cultural expectations for educational achievement. Future research should inquire deeper into possible reasons for the better performance of students with anxiety disorders in developing countries.
Relativistic electron dropout echoes induced by interplanetary shocks
Schiller, Q.; Kanekal, S. G.; Boyd, A. J.; Baker, D. N.; Blake, J. B.; Spence, H. E.
2017-12-01
Interplanetary shocks that impact Earth's magnetosphere can produce immediate and dramatic responses in the trapped relativistic electron population. One well-studied response is a prompt injection capable of transporting relativistic electrons deep into the magnetosphere and accelerating them to multi-MeV energies. The converse effect, electron dropout echoes, are observations of a sudden dropout of electron fluxes observed after the interplanetary shock arrival. Like the injection echo signatures, dropout echoes can also show clear energy dispersion signals. They are of particular interest because they have only recently been observed and their causal mechanism is not well understood. In the analysis presented here, we show observations of electron drift echo signatures from the Relativistic Electron-Proton Telescope (REPT) and Magnetic Electron and Ion Sensors (MagEIS) onboard NASA's Van Allen Probes mission, which show simultaneous prompt enhancements and dropouts within minutes of the associated with shock impact. We show that the observations associated with both enhancements and dropouts are explained by the inward motion caused by the electric field impulse induced by the interplanetary shock, and either energization to cause the enhancement, or lack of a seed population to cause the dropout.
Giver, Hanne; Faber, Anne; Hannerz, Harald; Strøyer, Jesper; Rugulies, Reiner
2010-05-01
The eldercare sector is characterized by a shortage of labour and a high turnover rate, which constitutes a major challenge for the ageing societies of western Europe. The aim of the present study was to investigate if a low level of psychological well-being at the time of graduation predicts dropout among eldercare workers two years later. We included 4,968 female eldercare trainees in this prospective study, recruited from 27 of the 28 Danish colleges for eldercare. Psychological well-being in 2004 was measured with the five-item Mental Health Inventory (MHI-5) of the 36-item Short-Form Health Survey (SF-36). We linked the survey data with national register data to obtain information about labour market attachment two years after qualification. In 2006, 37% of all participants had left the eldercare sector. Compared to participants with high psychological well-being at baseline, participants with medium and low psychological well-being were more likely to dropout to sectors unrelated to health and welfare (odds ratio (OR) 1.40 (95% confidence interval (95% CI) = 1.06-1.85) and 1.66 (95% CI = 1.27-2.19), respectively). They were also more likely to drop out of the labour market (OR 1.48 (95% CI = 1.08-2.04) and 1.60 (95% CI = 1.12-2.20), respectively). Psychological well-being was not related to dropout to other health- and welfare sectors or dropout to further education. The fact that more than one third of all participants had left the eldercare sector two years after qualification demonstrates the importance of retention initiatives early in working life. In addition a focus on psychological well-being among eldercare workers should be considered.
International Nuclear Information System (INIS)
Helmstetter, A.; Sornette, D.
2002-01-01
The epidemic-type aftershock sequence (ETAS) model is a simple stochastic process modeling seismicity, based on the two best-established empirical laws, the Omori law (power-law decay ∼1/t 1+θ of seismicity after an earthquake) and Gutenberg-Richter law (power-law distribution of earthquake energies). In order to describe also the space distribution of seismicity, we use in addition a power-law distribution ∼1/r 1+μ of distances between triggered and triggering earthquakes. The ETAS model has been studied for the last two decades to model real seismicity catalogs and to obtain short-term probabilistic forecasts. Here, we present a mapping between the ETAS model and a class of CTRW (continuous time random walk) models, based on the identification of their corresponding master equations. This mapping allows us to use the wealth of results previously obtained on anomalous diffusion of CTRW. After translating into the relevant variable for the ETAS model, we provide a classification of the different regimes of diffusion of seismic activity triggered by a mainshock. Specifically, we derive the relation between the average distance between aftershocks and the mainshock as a function of the time from the mainshock and of the joint probability distribution of the times and locations of the aftershocks. The different regimes are fully characterized by the two exponents θ and μ. Our predictions are checked by careful numerical simulations. We stress the distinction between the 'bare' Omori law describing the seismic rate activated directly by a mainshock and the 'renormalized' Omori law taking into account all possible cascades from mainshocks to aftershocks of aftershock of aftershock, and so on. In particular, we predict that seismic diffusion or subdiffusion occurs and should be observable only when the observed Omori exponent is less than 1, because this signals the operation of the renormalization of the bare Omori law, also at the origin of seismic diffusion in
Continuous-time random-walk model for anomalous diffusion in expanding media
Le Vot, F.; Abad, E.; Yuste, S. B.
2017-09-01
Expanding media are typical in many different fields, e.g., in biology and cosmology. In general, a medium expansion (contraction) brings about dramatic changes in the behavior of diffusive transport properties such as the set of positional moments and the Green's function. Here, we focus on the characterization of such effects when the diffusion process is described by the continuous-time random-walk (CTRW) model. As is well known, when the medium is static this model yields anomalous diffusion for a proper choice of the probability density function (pdf) for the jump length and the waiting time, but the behavior may change drastically if a medium expansion is superimposed on the intrinsic random motion of the diffusing particle. For the case where the jump length and the waiting time pdfs are long-tailed, we derive a general bifractional diffusion equation which reduces to a normal diffusion equation in the appropriate limit. We then study some particular cases of interest, including Lévy flights and subdiffusive CTRWs. In the former case, we find an analytical exact solution for the Green's function (propagator). When the expansion is sufficiently fast, the contribution of the diffusive transport becomes irrelevant at long times and the propagator tends to a stationary profile in the comoving reference frame. In contrast, for a contracting medium a competition between the spreading effect of diffusion and the concentrating effect of contraction arises. In the specific case of a subdiffusive CTRW in an exponentially contracting medium, the latter effect prevails for sufficiently long times, and all the particles are eventually localized at a single point in physical space. This "big crunch" effect, totally absent in the case of normal diffusion, stems from inefficient particle spreading due to subdiffusion. We also derive a hierarchy of differential equations for the moments of the transport process described by the subdiffusive CTRW model in an expanding medium
Continuous-time random-walk model for anomalous diffusion in expanding media.
Le Vot, F; Abad, E; Yuste, S B
2017-09-01
Expanding media are typical in many different fields, e.g., in biology and cosmology. In general, a medium expansion (contraction) brings about dramatic changes in the behavior of diffusive transport properties such as the set of positional moments and the Green's function. Here, we focus on the characterization of such effects when the diffusion process is described by the continuous-time random-walk (CTRW) model. As is well known, when the medium is static this model yields anomalous diffusion for a proper choice of the probability density function (pdf) for the jump length and the waiting time, but the behavior may change drastically if a medium expansion is superimposed on the intrinsic random motion of the diffusing particle. For the case where the jump length and the waiting time pdfs are long-tailed, we derive a general bifractional diffusion equation which reduces to a normal diffusion equation in the appropriate limit. We then study some particular cases of interest, including Lévy flights and subdiffusive CTRWs. In the former case, we find an analytical exact solution for the Green's function (propagator). When the expansion is sufficiently fast, the contribution of the diffusive transport becomes irrelevant at long times and the propagator tends to a stationary profile in the comoving reference frame. In contrast, for a contracting medium a competition between the spreading effect of diffusion and the concentrating effect of contraction arises. In the specific case of a subdiffusive CTRW in an exponentially contracting medium, the latter effect prevails for sufficiently long times, and all the particles are eventually localized at a single point in physical space. This "big crunch" effect, totally absent in the case of normal diffusion, stems from inefficient particle spreading due to subdiffusion. We also derive a hierarchy of differential equations for the moments of the transport process described by the subdiffusive CTRW model in an expanding medium
Astrand, Elaine
2018-06-01
Objective. Working memory (WM), crucial for successful behavioral performance in most of our everyday activities, holds a central role in goal-directed behavior. As task demands increase, inducing higher WM load, maintaining successful behavioral performance requires the brain to work at the higher end of its capacity. Because it is depending on both external and internal factors, individual WM load likely varies in a continuous fashion. The feasibility to extract such a continuous measure in time that correlates to behavioral performance during a working memory task remains unsolved. Approach. Multivariate pattern decoding was used to test whether a decoder constructed from two discrete levels of WM load can generalize to produce a continuous measure that predicts task performance. Specifically, a linear regression with L2-regularization was chosen with input features from EEG oscillatory activity recorded from healthy participants while performing the n-back task, n\\in [1,2] . Main results. The feasibility to extract a continuous time-resolved measure that correlates positively to trial-by-trial working memory task performance is demonstrated (r = 0.47, p < 0.05). It is furthermore shown that this measure allows to predict task performance before action (r = 0.49, p < 0.05). We show that the extracted continuous measure enables to study the temporal dynamics of the complex activation pattern of WM encoding during the n-back task. Specifically, temporally precise contributions of different spectral features are observed which extends previous findings of traditional univariate approaches. Significance. These results constitute an important contribution towards a wide range of applications in the field of cognitive brain–machine interfaces. Monitoring mental processes related to attention and WM load to reduce the risk of committing errors in high-risk environments could potentially prevent many devastating consequences or
Factors associated with dropout in medical education: a literature review.
O'Neill, Lotte Dyhrberg; Wallstedt, Birgitta; Eika, Berit; Hartvigsen, Jan
2011-05-01
Medical school dropout may have negative consequences for society, patients, the profession, schools and dropouts. To our knowledge, the literature dealing with dropout from medical school has never been systematically and critically appraised. This review aimed to systematically and critically review studies dealing with factors found to be associated with dropping out of medical school. A systematic critical literature review of the international peer-reviewed research literature on medical education was performed. A primary search was conducted and subsequently supplemented with ancestry and descendancy searches. The population of interest was medical students and the outcome was dropout. Abstract/title screening and quality assessment were performed by two independent researchers. Studies were assessed on six domains of quality: study participation; study attrition; predictor measurement; measurement of and accounting for confounders; outcome measurement, and analysis. Only studies that accounted for confounding were included in the final analysis. Of 625 studies found, 48 were quality-assessed and 13 of these were eventually included based on their fulfilment of our quality-related criteria. A range of entry qualifications seemed to be associated with greater chances of a student dropping out (odds ratio [OR] = 1.65-4.00). Struggling academically in medical school may be strongly associated with dropout. By contrast, no specific pattern of demographic variables was particularly important in relation to dropout. The effects of socio-economic, psychological and educational variables on dropout were not well investigated. More research into causal models and theory testing, which considers the effects of education, organisation and institution, is necessary if we are to learn more about how we can actively prevent medical student withdrawal. © Blackwell Publishing Ltd 2011.
Fall, Anna-Mária; Roberts, Greg
2012-08-01
Research suggests that contextual, self-system, and school engagement variables influence dropping out from school. However, it is not clear how different types of contextual and self-system variables interact to affect students' engagement or contribute to decisions to dropout from high school. The self-system model of motivational development represents a promising theory for understanding this complex phenomenon. The self-system model acknowledges the interactive and iterative roles of social context, self-perceptions, school engagement, and academic achievement as antecedents to the decision to dropout of school. We analyzed data from the Education Longitudinal Study of 2002-2004 in the context of the self-system model, finding that perception of social context (teacher support and parent support) predicts students' self-perceptions (perception of control and identification with school), which in turn predict students' academic and behavioral engagement, and academic achievement. Further, students' academic and behavioral engagement and achievement in 10th grade were associated with decreased likelihood of dropping out of school in 12th grade. Published by Elsevier Ltd.
2013-06-04
... the National Dropout Prevention Center for Students With Disabilities [Catalog of Federal Domestic... period enables the currently funded National Dropout Prevention Center for Students with Disabilities... Dropout Prevention Center for Students with Disabilities. The Center was funded under the Technical...
Directory of Open Access Journals (Sweden)
Wendy Manona
2015-12-01
Full Text Available This study investigated and analysed factors responsible for high dropout rate of learners at selected high schools in King William’s Town District, Province of the Eastern Cape. The aim of the study is provide an understanding into inherent problems of early exit of learners in the education sector, which impede the long-term production of professionals with bright future. The main findings of this study revealed that multiple motives, associated with individual characteristics of dropouts and social problems emanating from their family background and influence of the community, prompted learners to dropout. Moreover, learner dropout is inter alia caused by social factors such as lack of resources, the effect of poverty, orphans at school, the distance between the school and the community, drug abuse, pregnancy and HIV and AIDS prevalence in schools, gangsterism and learning barriers. The results of this research suggest that the government should make resources available with regard to scholar transport, school nurses to provide education awareness programmes in relation to early pregnancies, HIV and AIDS infection to improve attendance rate. The Department of Social Development should provide information with regard to benefits available to orphaned learners. The government should ensure sustainable provision of the school nutrition programme to alleviate hunger and poverty. School management should effectively regulate the behaviour of learners to promote discipline in schools so that substance abuse is eliminated.
Directory of Open Access Journals (Sweden)
George A. Kelley
2013-01-01
Full Text Available Background. Dropouts and compliance to exercise interventions targeting bone mineral density (BMD in adults are not well established. The purpose of this study was to address that gap. Methods. Meta-analysis of randomized controlled exercise intervention trials in adults ≥18 years of age. The primary outcomes were dropouts in the exercise and control groups as well as compliance to the exercise interventions. A random-effects model was used to pool results. Moderator analyses were conducted using mixed-effects ANOVA-like models and metaregression. Statistical significance was set at . Results. Thirty-six studies representing 3,297 participants (1,855 exercise, 1,442 control were included. Dropout rates in the exercise and control groups averaged 20.9% (95% CI 16.7%–25.9% and 15.9% (11.8%–21.1% while compliance to exercise was 76.3% (71.7%–80.3%. For both exercise and control groups, greater dropout rates were associated with studies conducted in the USA versus other countries, females versus males, premenopausal versus postmenopausal women, younger versus older participants, longer studies (controls only, and high- versus moderate-intensity training (exercisers only. Greater compliance to exercise was associated with being female, home- or facility-based exercise versus both, and shorter studies. Conclusion. These findings provide important information for researchers and practitioners with respect to exercise programs targeting BMD in adults.
Yin, Yue; Gong, Lan
2015-10-01
To evaluate the distribution of meibomian gland dropout and analyze the correlation between dropout and meibomian gland dysfunction (MGD). A total of 161 eyes of 85 patients with MGD were recruited as the MGD group; 88 eyes of 46 health volunteers were enrolled as the control group (2:1 matched for age and sex). Examinations included the Schirmer I test, breakup time, symptom questionnaire, corneal fluorescein staining, meibum quality, meibomian gland expressibility, and meibomian gland dropout. (1) The incidences of chalazion and eyelid surgery were significantly higher in patients with MGD. (2) All clinical indexes were better in healthy volunteers (all P dropout in the upper eyelid was statistically lower (P dropout than did the middle part, except in the lower eyelid of the control group. (4) The entire or partial dropout was positively related to MGD occurrence. Both additive dropout of the entire 2 eyelids and that of the 2 nasal parts had the strongest correlation (r = 0.792, P dropout (r = -0.229, P dropout of additive (r = 0.185, P dropouts exist in different or single eyelids. (2) Dropout evaluation is better when covering the entire area of both upper and lower meibomians. (3) Nasal part dropout plays a more essential role than the other dropouts in MGD occurrence.
Electron dropout echoes induced by interplanetary shock: Van Allen Probes observations
International Nuclear Information System (INIS)
Hao, Y. X.; Zong, Q.-G.; Zhou, X.-Z.; Fu, S. Y.; Rankin, R.
2016-01-01
On 23 November 2012, a sudden dropout of the relativistic electron flux was observed after an interplanetary shock arrival. The dropout peaks at ~1 MeV and more than 80% of the electrons disappeared from the drift shell. Van Allen twin Probes observed a sharp electron flux dropout with clear energy dispersion signals. The repeating flux dropout and recovery signatures, or “dropout echoes”, constitute a new phenomenon referred to as a “drifting electron dropout” with a limited initial spatial range. The azimuthal range of the dropout is estimated to be on the duskside, from ~1300 to 0100 LT. We then conclude that the shock-induced electron dropout is not caused by the magnetopause shadowing. Furthermore, the dropout and consequent echoes suggest that the radial migration of relativistic electrons is induced by the strong dusk-dawn asymmetric interplanetary shock compression on the magnetosphere.
Directory of Open Access Journals (Sweden)
Kathryn Ann Kaiser
2014-12-01
Full Text Available Introduction: Understanding participant demographic characteristics that inform the optimal design of obesity RCTs have been examined in few studies. The objective of this study was to investigate the association of individual participant characteristics and dropout rates (DORs in obesity randomized controlled trials (RCT by pooling data from several publicly available datasets for analyses. We comprehensively characterize DORs and patterns in obesity RCTs at the individual study level, and describe how such rates and patterns vary as a function of individual-level characteristics. Methods: We obtained and analyzed nine publicly-available, obesity RCT datasets that examined weight loss or weight gain prevention as a primary or secondary endpoint. Four risk factors for dropout were examined by Cox proportional hazards including sex, age, baseline BMI, and race/ethnicity. The individual study data were pooled in the final analyses with a random effect for study, and HR and 95% CIs were computed. Results: Results of the multivariate analysis indicated that the risk of dropout was significantly higher for females compared to males (HR= 1.24, 95% CI = 1.05, 1.46. Hispanics and Non-Hispanic blacks had a significantly higher dropout rate compared to non-Hispanic whites (HR= 1.62, 95% CI = 1.37, 1.91; HR= 1.22, 95% CI = 1.11, 1.35, respectively. There was a significantly increased risk of dropout associated with advancing age (HR= 1.02, 95% CI = 1.01, 1.02 and increasing BMI (HR= 1.03, 95% CI = 1.03, 1.04. Conclusion/Significance: As more studies may focus on special populations, researchers designing obesity RCTs may wish to oversample in certain demographic groups if attempting to match comparison groups based on generalized estimates of expected dropout rates, or otherwise adjust a priori power estimates. Understanding true reasons for dropout may require additional methods of data gathering not generally employed in obesity RCTs, e.g. time on
Dropout policies and trends for students with and without disabilities.
Kemp, Suzanne E
2006-01-01
Students with and without disabilities are dropping out of school at an alarming rate. However, the precise extent of the problem remains elusive because individual schools, school districts, and state departments of education often use different definitional criteria and calculation methods. In addition, specific reasons why students drop out continues to be speculative and minimal research exists validating current dropout prevention programs for students with and without disabilities. This study examined methods secondary school principals used to calculate dropout rates, reasons they believed students dropped out of school, and what prevention programs were being used for students with and without disabilities. Results indicated that school districts used calculation methods that minimized dropout rates, students with and without disabilities dropped out for similar reasons, and few empirically validated prevention programs were being implemented. Implications for practice and directions for future research are discussed.
Authoritative school climate and high school dropout rates.
Jia, Yuane; Konold, Timothy R; Cornell, Dewey
2016-06-01
This study tested the association between school-wide measures of an authoritative school climate and high school dropout rates in a statewide sample of 315 high schools. Regression models at the school level of analysis used teacher and student measures of disciplinary structure, student support, and academic expectations to predict overall high school dropout rates. Analyses controlled for school demographics of school enrollment size, percentage of low-income students, percentage of minority students, and urbanicity. Consistent with authoritative school climate theory, moderation analyses found that when students perceive their teachers as supportive, high academic expectations are associated with lower dropout rates. (PsycINFO Database Record (c) 2016 APA, all rights reserved).
Energy Technology Data Exchange (ETDEWEB)
Dmitriev, Alexander S.; Yemelyanov, Ruslan Yu. [V.A. Kotelnikov Institute of Radio Engineering and Electronics of the RAS Mokhovaya 11-7, Moscow, 125009 (Russian Federation); Moscow Institute of Physics and Technology (State University) 9 Institutskiy per., Dolgoprudny, Moscow, 141700 (Russian Federation); Gerasimov, Mark Yu. [V.A. Kotelnikov Institute of Radio Engineering and Electronics of the RAS Mokhovaya 11-7, Moscow, 125009 (Russian Federation); Itskov, Vadim V. [Moscow Institute of Physics and Technology (State University) 9 Institutskiy per., Dolgoprudny, Moscow, 141700 (Russian Federation)
2016-06-08
The paper deals with a new multi-element processor platform assigned for modelling the behaviour of interacting dynamical systems, i.e., active wireless network. Experimentally, this ensemble is implemented in an active network, the active nodes of which include direct chaotic transceivers and special actuator boards containing microcontrollers for modelling the dynamical systems and an information display unit (colored LEDs). The modelling technique and experimental results are described and analyzed.
Structure and Randomness of Continuous-Time, Discrete-Event Processes
Marzen, Sarah E.; Crutchfield, James P.
2017-10-01
Loosely speaking, the Shannon entropy rate is used to gauge a stochastic process' intrinsic randomness; the statistical complexity gives the cost of predicting the process. We calculate, for the first time, the entropy rate and statistical complexity of stochastic processes generated by finite unifilar hidden semi-Markov models—memoryful, state-dependent versions of renewal processes. Calculating these quantities requires introducing novel mathematical objects (ɛ -machines of hidden semi-Markov processes) and new information-theoretic methods to stochastic processes.
A continuous-time random-walk approach to the Cole-Davidson dielectric response of dipolar liquids
DEFF Research Database (Denmark)
Szabat, B.; Langner, K. M.; Klösgen-Buchkremer, Beate Maria
2004-01-01
We show how the Cole-Davidson relaxation response, characteristic of alcoholic systems, can be derived within the framework of the continuous-time random walk (CTRW). Using the random-variable formalism, we indicate that the high-frequency power law of dielectric spectra is determined by the heavy...
Cao, Qi; Buskens, Erik; Feenstra, Talitha; Jaarsma, Tiny; Hillege, Hans; Postmus, Douwe
Continuous-time state transition models may end up having large unwieldy structures when trying to represent all relevant stages of clinical disease processes by means of a standard Markov model. In such situations, a more parsimonious, and therefore easier-to-grasp, model of a patient's disease
Hofstede, ter F.; Wedel, M.
1998-01-01
This study investigates the effects of time aggregation in discrete and continuous-time hazard models. A Monte Carlo study is conducted in which data are generated according to various continuous and discrete-time processes, and aggregated into daily, weekly and monthly intervals. These data are
Time-aggregation effects on the baseline of continuous-time and discrete-time hazard models
ter Hofstede, F.; Wedel, M.
In this study we reinvestigate the effect of time-aggregation for discrete- and continuous-time hazard models. We reanalyze the results of a previous Monte Carlo study by ter Hofstede and Wedel (1998), in which the effects of time-aggregation on the parameter estimates of hazard models were
A continuous-time random-walk approach to the Cole-Davidson dielectric response of dipolar liquids
DEFF Research Database (Denmark)
Szabat, Bozena; Langner, Karol M.; Klösgen, Beate Maria
2005-01-01
We show how the Cole-Davidson relaxation response, characteristic of alcoholic systems, can be derived within the framework of the continuous-time random walk 4CTRW). Using the random-variable formalism, we indicate that the high-frequency power law of dielectric spectra is determined by the heav...
Pharmacogenetic analysis of opioid dependence treatment dose and dropout rate.
Crist, Richard C; Li, James; Doyle, Glenn A; Gilbert, Alex; Dechairo, Bryan M; Berrettini, Wade H
2018-01-01
Currently, no pharmacogenetic tests for selecting an opioid-dependence pharmacotherapy have been approved by the US Food and Drug Administration. Determine the effects of variants in 11 genes on dropout rate and dose in patients receiving methadone or buprenorphine/naloxone (ClinicalTrials.gov Identifier: NCT00315341). Variants in six pharmacokinetic genes (CYP1A2, CYP2B6, CYP2C19, CYP2C9, CYP2D6, CYP3A4) and five pharmacodynamic genes (HTR2A, OPRM1, ADRA2A, COMT, SLC6A4) were genotyped in samples from a 24-week, randomized, open-label trial of methadone and buprenorphine/naloxone for the treatment of opioid dependence (n = 764; 68.7% male). Genotypes were then used to determine the metabolism phenotype for each pharmacokinetic gene. Phenotypes or genotypes for each gene were analyzed for association with dropout rate and mean dose. Genotype for 5-HTTLPR in the SLC6A4 gene was nominally associated with dropout rate when the methadone and buprenorphine/naloxone groups were combined. When the most significant variants associated with dropout rate were analyzed using pairwise analyses, SLC6A4 (5-HTTLPR) and COMT (Val158Met; rs4860) had nominally significant associations with dropout rate in methadone patients. None of the genes analyzed in the study was associated with mean dose of methadone or buprenorphine/naloxone. This study suggests that functional polymorphisms related to synaptic dopamine or serotonin levels may predict dropout rates during methadone treatment. Patients with the S/S genotype at 5-HTTLPR in SLC6A4 or the Val/Val genotype at Val158Met in COMT may require additional treatment to improve their chances of completing addiction treatment. Replication in other methadone patient populations will be necessary to ensure the validity of these findings.
Student Drop-Out Trends at Sultan Qaboos University and Kuwait University: 2000-2011
Al Ghanboosi, Salim Saleem; Alqahtani, Abdulmuhsen Ayedh
2013-01-01
The current study aims to explore the drop-out trends at Sultan Qaboos. University and Kuwait University. Archival data of the period 2000-2011 were used to achieve this goal. Main findings showed that (a) male drop-out rates are higher than female drop-out rates; (b) drop- out rates at scientific colleges are higher; (c) drop-out rates of…
Tenth Grade Dropout Rates by Native Language, Race/Ethnicity, and Socioeconomic Status
Rumberger, Russell W.
2006-01-01
One of the most important indicators of educational performance is the high school dropout rate. Reducing dropout rates and improving high school graduation rates are important goals for both educators and policymakers. Yet there is a great deal of controversy about how best to measure dropout and graduation rates. This issue of EL Facts provides estimates of dropout rates for language minority students, racial and ethnic groups, and socioeconomic groups.
Tanggaard, Lene
2013-01-01
The present paper addresses the phenomenon of student dropout from vocational education in Denmark. It does so by addressing the need to critically discuss the term "drop-out" taking the perspective of students' own reflections on the topic. The empirical findings indicate that dropout is considered in terms of two very different, but…
Meta-Analysis of Dropout in Treatments for Posttraumatic Stress Disorder
Imel, Zac E.; Laska, Kevin; Jakupcak, Matthew; Simpson, Tracy L.
2013-01-01
Objective: Many patients drop out of treatments for posttraumatic stress disorder (PTSD); some clinicians believe that trauma-focused treatments increase dropout. Method: We conducted a meta-analysis of dropout among active treatments in clinical trials for PTSD (42 studies; 17 direct comparisons). Results: The average dropout rate was 18%, but it…
Tracking Drop-out Students in Palestinian Refugee Camps in Lebanon
Al-Hroub, Anies
2015-01-01
This research paper examines the perceptions of students on the school drop-out problem in Palestinian refugee camps in Lebanon regarding (a) the social and economic causes associated with the phenomenon of school drop-out; (b) the educational policies and practices used in UNRWA schools and their relationship to student drop-out; and (c) the role…
The reasons of dropout of sport in Hong Kong school athletes
Hassan, Abdul-Rahman; Lam, Michael Huen Sum; Ku, Susanna; Li, William Ho Cheung; Lee, Ka Yiu; Ho, Eva; Flint, Stuart W.; Wong, Anthony Siu Wo
2017-01-01
Dropout of sport is an issue in sport and public health domains. The aim of this study was to identify the potential dropout reasons of school athletes and to examine if their perception of dropout was affected by the previous dropout experience. There were 50 subjects who were divided into two groups based on their previous dropout experience (Dropout Group=22, No Dropout Group=28). They filled a questionnaire about potential dropout reasons of the current sport. Coach and teammates were two predominated reasons of dropout; Influence of parent and training seemed to affect the termination of the sport to a lesser extent. Moreover, the perception of social value and lost focus were significantly different between two groups. Character of coach and teammates affect the engagement of training in school athletes. However, the parental influence had less influence than expected. Training intensity played little role as the dropout reason. Previous experience of dropout had an impact of potential dropout reasons on their current sport training. PMID:28959788
Is Drop-Out from University Dependent on National Culture and Policy? The Case of Denmark
Troelsen, Rie; Laursen, Per F.
2014-01-01
National cultures are known to influence educational institutions and practices in many ways. It therefore seems reasonable to assume that drop-out from university is also influenced by differences in national cultures. In this article, we compare drop-out from Danish universities with drop-out from European universities. Based on Danish national…
Dropout and Federal Graduation Rates 2013-2014. Research Brief. Volume 1407
Froman, Terry
2015-01-01
The District conducts two kinds of dropout analyses every year in Miami-Dade County Public Schools. The "cross-sectional" analysis of student dropouts examines dropout rates among students enrolled in various grades at one point in time. A "longitudinal" analysis, also conducted annually, tracks a group of students in the same…
The impact of community schools on student dropout in pre-vocational education
Heers, Marieke; Van Klaveren, Chris; Groot, Wim; van den Brink, Henriëtte Maassen
2014-01-01
Dropout prevention is highly ranked on the political agenda in many countries. It remains unclear, however, how dropout can be effectively reduced, as many different factors determine student dropout. Community schools recognize this and aim to modernize education such that it better accommodates
Hidden School Dropout among Immigrant Students: A Cross-Sectional Study
Makarova, Elena; Herzog, Walter
2013-01-01
Actual school dropout among immigrant youth has been addressed in a number of studies, but research on hidden school dropout among immigrant students is rare. Thus, the objective of this paper is to analyze hidden school dropout among primary school students with an immigrant background. The analyses were performed using survey data of 1186…
The impact of community schools on student dropout in pre-vocational education
Heers, M.; van Klaveren, C.; Groot, W.; Maassen van den Brink, H.
2012-01-01
Dropout prevention is highly ranked on the political agenda in many countries. It remains unclear, however, how dropout can be effectively reduced, as many different factors are determining student dropout. Community schools recognize this and modernize education such that it better accommodates
Reducing Dropouts in Online Education-Group Tutoring in Virtual Seminars and Support Structures
Holmgren, Robert; Johansson, Sigurd
2012-01-01
This paper describes a development project aimed at reducing the large number of dropouts in online degree project courses. The idea was that the introduction of group tutorials in virtual seminars, combined with extensive support materials, would reduce dropout rates. Among the students who participated, the dropout rate was reduced by 50%…
The reasons of dropout of sport in Hong Kong school athletes.
Hassan, Abdul-Rahman; Lam, Michael Huen Sum; Ku, Susanna; Li, William Ho Cheung; Lee, Ka Yiu; Ho, Eva; Flint, Stuart W; Wong, Anthony Siu Wo
2017-05-16
Dropout of sport is an issue in sport and public health domains. The aim of this study was to identify the potential dropout reasons of school athletes and to examine if their perception of dropout was affected by the previous dropout experience. There were 50 subjects who were divided into two groups based on their previous dropout experience (Dropout Group=22, No Dropout Group=28). They filled a questionnaire about potential dropout reasons of the current sport. Coach and teammates were two predominated reasons of dropout; Influence of parent and training seemed to affect the termination of the sport to a lesser extent. Moreover, the perception of social value and lost focus were significantly different between two groups. Character of coach and teammates affect the engagement of training in school athletes. However, the parental influence had less influence than expected. Training intensity played little role as the dropout reason. Previous experience of dropout had an impact of potential dropout reasons on their current sport training.
2010-04-01
... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false When is dropout status determined... INVESTMENT ACT Out-of-School Youth § 664.310 When is dropout status determined, particularly for youth attending alternative schools? A school dropout is defined as an individual who is no longer attending any...
Celebrating 25 Years. National Dropout Prevention Center/Network Newsletter. Volume 22, Number 3
Duckenfield, Marty, Ed.
2011-01-01
The "National Dropout Prevention Newsletter" is published quarterly by the National Dropout Prevention Center/Network. This issue contains the following articles: (1) Leading the Way in Dropout Prevention; (2) The 15 Effective Strategies in Action; (3) Technology Changes 1986-2011 (Marty Duckenfield); (4) 25 Years of Research and Support…
Denial-of-Service Security Attack in the Continuous-Time World
DEFF Research Database (Denmark)
Wang, Shuling; Nielson, Flemming; Nielson, Hanne Riis
2014-01-01
-of-service security attack, the expected information from the controllers is not received and as a consequence the physical systems may fail to behave as expected. This paper proposes a formal framework for expressing denial-of-service security attack in hybrid systems. As a virtue, a physical system is able to plan......Hybrid systems are integrations of discrete computation and continuous physical evolution. The physical components of such systems introduce safety requirements, the achievement of which asks for the correct monitoring and control from the discrete controllers. However, due to denial...... for reasonable behavior in case the ideal control fails due to unreliable communication, in such a way that the safety of the system upon denial-of-service is still guaranteed. In the context of the modeling language, we develop an inference system for verifying safety of hybrid systems, without putting any...
Enoksen, Eystein
2011-01-01
© Eystein Enoksen, 2011 The aim of the present study was to identify the total drop-out rate and drop-out reasons for a group of promising track and field athletes. 202 males and 98 females, aged 16 ±2 years, took part in this study. Questionnaires were administrated in 1975, 1983, and 1989. In-depth interviews were conducted in 1989 and in 2000. A chi-square test was administrated to test the difference between males and females dropping out and to test the most significant reasons influe...
Larsen, Michael Søgaard; Kornbeck, Kasper Pihl; Kristensen, Rune; Larsen, Malene Rode; Sommersel, Hanna Bjørnøy
2013-01-01
Dropout from university studies comprises a number of complex phenomena with serious complex consequences and profound political attention. Further analysis of the field is, therefore, warranted. Such an analysis is offered here as a systematic review which gives answers based on the best possible evidence found in the research field comprised by the three review questions to be addressed.The aims of this systematic review can, thus, be summarized like this:Which answers can be offered from r...
Predicting Drop-Out from Social Behaviour of Students
Bayer, Jaroslav; Bydzovska, Hana; Geryk, Jan; Obsivac, Tomas; Popelinsky, Lubomir
2012-01-01
This paper focuses on predicting drop-outs and school failures when student data has been enriched with data derived from students social behaviour. These data describe social dependencies gathered from e-mail and discussion board conversations, among other sources. We describe an extraction of new features from both student data and behaviour…
Factors that Influence Students' Decision to Dropout of Online Courses
Willging, Pedro A.; Johnson, Scott D.
2009-01-01
Although there are many reasons why students dropout of college courses, those reasons may be unique for students who are enrolled in an online program. Issues of isolation, disconnectedness, and technological problems may be factors that influence a student to leave a course. To understand these factors, an online survey was developed to collect…
Theoretical and methodological considerations to investigate school dropout
Directory of Open Access Journals (Sweden)
Román Hernández –Dávila
2017-07-01
Full Text Available This work offers an exhaustive analysis of different authors and studies– falling under general and methodological criteria – of the reasons responsible for school dropouts, predominantly in vulnerable areas. To do so it is necessary to reflect on the problem with the intention of identifying the contributing factors. In these situations, various elements come into play, ranging from the organization of education systems, application of public policies, social conditions, the individual’s situation, health, the psychological and emotional impact, as well as the cultural patterns that may in compass the minor’s family, student-teacher relationship and school management. As an addition, a series of useful proposals is offered in bringing about change in the educational sector, focused on the reducing of school dropouts. It is assumed that research about dropouts should be undertaken from a qualitative concept, with hermeneutical characteristics, that allow the phenomenon under study to be interpreted reliably. This methodological basis has ethnographic foundations since it requires the reviewing of specific aspects of the socio cultural context present in the factors subject to investigation. Works of this nature should identify the determinants of school dropouts in a specific line of inquiry, describe them, and generate a database that displays the indicators of the causes that create this phenomenon.
The Hegemonic Curriculum and School Dropout: The Newfoundland Case.
Gedge, Joseph L.
1991-01-01
Confronted by a disturbing dropout rate and low student achievement, the Newfoundland (Canada) government is attempting to rationalize organizational restructuring and curriculum reform based on a centralized core academic curriculum aimed at college entrance. This article argues for an expanded, hegemonic curriculum that is organic to the…
Understanding the Mechanism behind Maternal Imprisonment and Adolescent School Dropout
Cho, Rosa M.
2011-01-01
This study empirically tested 3 mechanisms commonly suggested to disadvantage youths whose mothers are incarcerated in prison. An event history analysis of school dropout was conducted on a sample of 6,008 adolescents in a large city created by merging several Illinois state administrative data. Findings revealed that adolescents are indeed at…
Predictors of lifestyle intervention outcome and dropout: the SLIM study
Roumen, C.; Feskens, E.J.M.; Corpeleijn, E.; Mensink, M.R.; Saris, W.H.M.; Blaak, E.E.
2011-01-01
Original Article European Journal of Clinical Nutrition (2011) 65, 1141–1147; doi:10.1038/ejcn.2011.74; published online 18 May 2011 Predictors of lifestyle intervention outcome and dropout: the SLIM study C Roumen1, E J M Feskens2, E Corpeleijn1, M Mensink2, W H M Saris1 and E E Blaak1 1Department
A comparison of outer electron radiation belt dropouts during solar ...
Indian Academy of Sciences (India)
Utilizing multiple data sources from the year 1997–2007, this study identifies radiation belt electron dropouts which are ultimately triggered when solar wind stream interfaces (SI) arrived at ... Center for Space Research, School for Physical and Chemical Sciences, North–West University, Potchefstroom 2520, South Africa.
So Close, yet So Far Away: Early vs. Late Dropouts
Ma, Yanli; Cragg, Kristina M.
2013-01-01
While some students drop out early in their academic career, others drop out close to completion. What similarities and differences exist between these early and late dropouts? Using a sample 3,520 first-time, full-time (FTFT) students seeking a bachelor's degree at a state university, this study employs multinomial logistic regression to model…
Predicting Dropouts of University Freshmen: A Logit Regression Analysis.
Lam, Y. L. Jack
1984-01-01
Stepwise discriminant analysis coupled with logit regression analysis of freshmen data from Brandon University (Manitoba) indicated that six tested variables drawn from research on university dropouts were useful in predicting attrition: student status, residence, financial sources, distance from home town, goal fulfillment, and satisfaction with…
Dropout from Secondary Education: All's Well That Begins Well
De Witte, Kristof; Rogge, Nicky
2013-01-01
Despite the increased attention to students leaving secondary education without a diploma numerous students still dropout yearly. This paper makes a distinction between the "individual perspective" and the "institutional perspective" of dropping out. The former is explored by multinominal logit models. We observe that…
Emotional Competence and Drop-Out Rates in Higher Education
Kingston, Emma
2008-01-01
Purpose: The purpose of this paper is to compare the emotional competence of first year undergraduates enrolled on a high or low drop-out rate (HDR and LDR, respectively) course, at a newly established university within the UK. Design/methodology/approach: A mixed methods approach using both quantitative and qualitative data collection methods was…
Project SAIL: An Evaluation of a Dropout Prevention Program.
Thompson, John L.; And Others
Project SAIL (Student Advocates Inspire Learning) is a Title IV-C Project located in Hopkins, Minnesota, designed to prevent students from dropping out of school by keeping them successfully involved in the mainstream environment. This study presents a review of other dropout prevention approaches, describes the intervention strategies involved in…
Reasons for Dropout for Vocational High School Students
Tas, Ali; Selvitopu, Abdullah; Bora, Veysel; Demirkaya, Yusuf
2013-01-01
This study aimed to determine the reasons for dropout for persons who have not completed vocational education programme and left school without a diploma. By using snowball sampling method, 19 persons, willing to participate in the study, were reached. Data were obtained by semi structured interview forms. In data analysis process, inductive…
Immunization Dropout Rates in Ihe, Awgu Local Government Area ...
African Journals Online (AJOL)
Background: Immunization against childhood diseases is one of the most important ways of preventing childhood morbidity and mortality. Aims: The objective of this study is to review the dropout rates of immunization of children in a health center using a single dose of diphtheria‑pertussis‑tetanus (DPT1) and three doses of ...
Analyzing the Discourse of Dropouts and Resilient Students
Lessard, Anne; Butler-Kisber, Lynn; Fortin, Laurier; Marcotte, Diane
2014-01-01
The authors focused on high school students who were at risk of dropping out and examined why some of these students persevered and graduated while others ended up dropping out of school. Sixty resilient students and 80 dropouts participated in the study. Our results indicate that although learning difficulties were shared by participants, 4 types…
Emotional variables, dropout and academic performance in Spanish nursing students.
Roso-Bas, Fátima; Pades Jiménez, Antonia; García-Buades, Esther
2016-02-01
The dropout of university studies is a main concern in many countries, also for Health Sciences degrees. The reviews on dropout in all university degrees as well as nursing generally show multidimensional causes with factors related both to institutional and students' characteristics. Regarding the personal variables of students, researchers have focused on financial, family and personality features. Far less attention has been devoted to emotional variables. This study aims to explore whether individual variables of the emotional domain such as perceived emotional intelligence, dispositional optimism/pessimism and depressive rumination are related and/or can predict students' intention to dropout and academic performance. Using a cross-correlational approach, data were obtained from a sample of 144 nursing students. Students with a pessimistic disposition revealed a greater tendency to drop out. The remaining variables correlated significantly with pessimism but had no predictive value on dropout. Our results suggest that students with low levels of emotional clarity and repair and high depressive rumination have pessimistic expectations, so they are more likely to leave studies. No significant results were found in relation to academic performance. We conclude with an identification of strategies to increase retention and academic success. Copyright © 2015 Elsevier Ltd. All rights reserved.
Re-Engaging School Dropouts with Emotional and Behavioral Disorders
Wilkins, Julia; Bost, Loujeania Williams
2015-01-01
Students with emotional and behavioral disorders have the highest dropout rates of any student group--about 40%. The outcomes for students who drop out of school are dire but are particularly bleak for students with poor academic, interpersonal, and decision-making skills. Helping students earn a high school diploma and gain the skills needed to…
The Societal Benefits and Costs of School Dropout Recovery
Directory of Open Access Journals (Sweden)
James S. Catterall
2011-01-01
Full Text Available This article reports an analysis of the societal benefits and costs of recovering school dropouts. Successful recovery is defined by subsequent graduation from high school. The analysis is based on established estimates of the societal costs of dropping out including reduced government tax collections and higher social costs of welfare, healthcare, and crime. These potential costs are cast as benefits when a dropout is recovered. A large dropout recovery program provides the setting for the analysis. Rigorous attention is given to accurate estimation of the number of students who would not have graduated without the program in the year assessed and to the induced public costs of their continued education. Estimated benefits are weighed against the total annual public costs of the program, which operates in 65 school centers and commands an annual budget of about $70 million. The estimated benefit-cost ratio for this program is 3 to 1, a figure comparable to benefit-cost ratio estimates reported in studies of dropout prevention. The sensitivity of this conclusion to specific assumptions within the analysis is discussed.
Dropout from secondary education: All's well that begins well
de Witte, K.
2010-01-01
Despite the increased attention to students leaving secondary education without a diploma, numerous students dropout yearly. This paper makes a distinction between the individual perspective and the institutional perspective of dropping out. The former is explored by multinominal logit models, with
Dropout prevention measures in the Netherlands, an evaluation
de Witte, K.; Cabus, S.J.
2010-01-01
In line with the Lisbon Agenda, set by the European Council in the year 2000, European governments formulated ambitious plans to half the level of early school leavers by 2012. This paper outlines the dropout prevention measures in the Netherlands and analyzes their effect at both the individual
Dropout Prevention Measures in the Netherlands, an Explorative Evaluation
De Witte, Kristof; Cabus, Sofie J.
2013-01-01
In line with the Lisbon Agenda, set by the European Council in the year 2000, European governments formulated ambitious plans to halve the level of early school-leavers by 2012. This paper outlines the dropout prevention measures in the Netherlands and analyzes their influence at both the individual and school level. While most policy measures…
Grade Repetition and Primary School Dropout in Uganda
Kabay, Sarah
2016-01-01
Research on education in low-income countries rarely focuses on grade repetition. When addressed, repetition is typically presented along with early school dropout as the "wasting" of educational resources. Simplifying grade repetition in this way often fails to recognize significant methodological concerns and also overlooks the unique…
Drop-out from parenting training programmes: a retrospective study ...
African Journals Online (AJOL)
Objective:Parent training programmes are a well-established treatment approach for children and adolescents with disruptive behaviour disorders. However, dropout from treatment is a common problem that confounds research on the efficacy of this approach, and wastes important mental health resources. This study ...
The High School Dropout Problem: Perspectives of Teachers and Principals
Bridgeland, John M.; Dilulio, John J., Jr.; Balfanz, Robert
2009-01-01
To better understand the views of teachers and administrators on the high school dropout problem, focus groups and nationally representative surveys were conducted of high school teachers and principals. A focus group of superintendents and school board members was also included. To help interpret the results, the authors convened a colloquium…
Causes of customer dropouts in fitness and wellness centres: A ...
African Journals Online (AJOL)
The aim of this study was to identify which factors have an influence on customer dropouts in fitness and wellness centres in Spain based on the opinion of the agents involved in their management (managers, employees and customers). For that purpose, an interview was designed for each of the key agents to analyse ...
Authoritative School Climate and High School Dropout Rates
Jia, Yuane; Konold, Timothy R.; Cornell, Dewey
2016-01-01
This study tested the association between school-wide measures of an authoritative school climate and high school dropout rates in a statewide sample of 315 high schools. Regression models at the school level of analysis used teacher and student measures of disciplinary structure, student support, and academic expectations to predict overall high…
Degree Flexibility and University Drop-out: The Italian Experience
Di Pietro, Giorgio; Cutillo, Andrea
2008-01-01
How to reduce university drop-out is a topic of increasing concern. Although several measures have been the subject of numerous debates, little attention has been given to those impacting on the duration, structure and content of the supply of university education. This paper looks at the Italian experience to see what can be learnt about the…
Teachers Make the Critical Difference in Dropout Prevention.
Bucci, John A.; Reitzammer, Ann F.
1992-01-01
Teachers' daily interaction is a powerful influence on at-risk students. Effective dropout prevention components include positive instructional environment, enhancement of self-esteem, alternative education, absence monitoring, mentoring, parent involvement, social and health services, teen parent programs, and transition strategies. (SK)
International Nuclear Information System (INIS)
Younmyoung Lee; Kunjai Lee
1995-01-01
A model using continuous time Markov process for nuclide transport of decay chain of arbitrary length in the fractured rock medium has been developed. Considering the fracture in the rock matrix as a finite number of compartments, the transition probability for nuclide from the transition intensity between and out of the compartments is represented utilizing Chapman-Kolmogorov equation, with which the expectation and the variance of nuclide distribution for the fractured rock medium could be obtained. A comparison between continuous time Markov process model and available analytical solutions for the nuclide transport of three decay chains without rock matrix diffusion has been made showing comparatively good agreement. Fittings with experimental breakthrough curves obtained with nonsorbing materials such as NaLS and uranine in the artificial fractured rock are also made. (author)
Capasso, Vincenzo
2015-01-01
This textbook, now in its third edition, offers a rigorous and self-contained introduction to the theory of continuous-time stochastic processes, stochastic integrals, and stochastic differential equations. Expertly balancing theory and applications, the work features concrete examples of modeling real-world problems from biology, medicine, industrial applications, finance, and insurance using stochastic methods. No previous knowledge of stochastic processes is required. Key topics include: * Markov processes * Stochastic differential equations * Arbitrage-free markets and financial derivatives * Insurance risk * Population dynamics, and epidemics * Agent-based models New to the Third Edition: * Infinitely divisible distributions * Random measures * Levy processes * Fractional Brownian motion * Ergodic theory * Karhunen-Loeve expansion * Additional applications * Additional exercises * Smoluchowski approximation of Langevin systems An Introduction to Continuous-Time Stochastic Processes, Third Editio...
A Design Methodology for Power-efficient Continuous-time Sigma-Delta A/D Converters
DEFF Research Database (Denmark)
Nielsen, Jannik Hammel; Bruun, Erik
2003-01-01
In this paper we present a design methodology for optimizing the power consumption of continuous-time (CT) ΣΔ A/D converters. A method for performance prediction for ΣΔ A/D converters is presented. Estimation of analog and digital power consumption is derived and employed to predict the most power...... bits performance. Expected power consumption for the prototype is approx. 170 μW....
Directory of Open Access Journals (Sweden)
Haroldo Valetin Ribeiro
2012-03-01
Full Text Available We investigate how it is possible to obtain different diffusive regimes from the Continuous Time Random Walk (CTRW approach performing suitable changes for the waiting time and jumping distributions in order to get two or more regimes for the same diffusive process. We also obtain diffusion-like equations related to these processes and investigate the connection of the results with anomalous diffusion.
Directory of Open Access Journals (Sweden)
Mokaedi V. Lekgari
2014-01-01
Full Text Available We investigate random-time state-dependent Foster-Lyapunov analysis on subgeometric rate ergodicity of continuous-time Markov chains (CTMCs. We are mainly concerned with making use of the available results on deterministic state-dependent drift conditions for CTMCs and on random-time state-dependent drift conditions for discrete-time Markov chains and transferring them to CTMCs.
Directory of Open Access Journals (Sweden)
J. F. Opadiji
2010-06-01
Full Text Available We present the development and deployment process of a computer-aided learning tool which serves as a training aid for undergraduate control engineering courses. We show the process of algorithm construction and implementation of the software which is also aimed at teaching software development at undergraduate level. The scope of this project is limited to graphical analysis of continuous-time control systems.
International Nuclear Information System (INIS)
Benth, Fred Espen; Taib, Che Mohd Imran Che
2013-01-01
We extend the concept of half life of an Ornstein–Uhlenbeck process to Lévy-driven continuous-time autoregressive moving average processes with stochastic volatility. The half life becomes state dependent, and we analyze its properties in terms of the characteristics of the process. An empirical example based on daily temperatures observed in Petaling Jaya, Malaysia, is presented, where the proposed model is estimated and the distribution of the half life is simulated. The stationarity of the dynamics yield futures prices which asymptotically tend to constant at an exponential rate when time to maturity goes to infinity. The rate is characterized by the eigenvalues of the dynamics. An alternative description of this convergence can be given in terms of our concept of half life. - Highlights: • The concept of half life is extended to Levy-driven continuous time autoregressive moving average processes • The dynamics of Malaysian temperatures are modeled using a continuous time autoregressive model with stochastic volatility • Forward prices on temperature become constant when time to maturity tends to infinity • Convergence in time to maturity is at an exponential rate given by the eigenvalues of the model temperature model
Treatment dropout in web-based cognitive behavioral therapy for patients with eating disorders.
Ter Huurne, Elke D; Postel, Marloes G; de Haan, Hein A; van der Palen, Job; DeJong, Cor A J
2017-01-01
Treatment dropout is an important concern in eating disorder treatments as it has negative implications for patients' outcome, clinicians' motivation, and research studies. Our main objective was to conduct an exploratory study on treatment dropout in a two-part web-based cognitive behavioral therapy with asynchronous therapeutic support. The analysis included 205 female patients with eating disorders. Reasons for dropout, treatment experiences, and predictors of dropout were analyzed. Overall treatment dropout was 37.6%, with 18.5% early dropout (before or during treatment part 1) and 19.0% late dropout (after part 1 or during part 2). Almost half of the participants identified personal circumstances as reason for dropout. The other participants mostly reported reasons related to the online delivery or treatment protocol. Predictors of early dropout included reporting less vigor and smoking at baseline and a longer average duration per completed treatment module of part 1. Late dropout was predicted by reporting less vigor at baseline and uncertainty about recommendation of the treatment to others after completion of treatment part 1. Generally, the web-based treatment and online therapeutic support were evaluated positively, although dropouts rated the treatment as significantly less helpful and effective than completers did. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.
Landes, Sara J; Chalker, Samantha A; Comtois, Katherine Anne
2016-01-01
Rates of treatment dropout in outpatient Dialectical Behavior Therapy (DBT) in the community can be as high as 24 % to 58 %, making dropout a great concern. The primary purpose of this article was to examine predictors of dropout from DBT in a community mental health setting. Participants were 56 consumers with borderline personality disorder (BPD) who were psychiatrically disabled participating in a larger feasibility trial of Dialectical Behavior Therapy- Accepting the Challenges of Exiting the System. The following variables were examined to see whether they predicted dropout in DBT: age, education level, baseline level of distress, baseline level of non-acceptance of emotional responses, and skills module in which a consumer started DBT skills group. These variables were chosen based on known predictors of dropout in consumers with BPD and in DBT, as well as an interest in what naturally occurring variables might impact dropout. The dropout rate in this sample was 51.8 %. Results of the logistic regression show that younger age, higher levels of baseline distress, and a higher level of baseline non-acceptance of emotional responses were significantly associated with dropout. The DBT skills module in which an individual started group did not predict dropout. The implications of these findings are that knowledge of consumer age and pretreatment levels of distress and non-acceptance of emotional responses can impact providers' choice of commitment and treatment strategies to reduce dropout. Future research should examine these strategies, as well as the impact of predictor variables on outcome and reasons for dropout.
Kelly, Michael; Rae, Glen; Partington, Sarah; Dodd-Reynolds, Caroline; Caplan, Nick
2016-01-01
Background: Exercise Referral Schemes (ERS) are a prevalent method of increasing physical activity levels. However, they suffer from participant dropout and research predicting dropout or barriers to adherence is limited. This study aimed to focus upon the effect of referral characteristics on dropout, dropout predictors and whether self-reported barriers to exercise predict dropout.\\ud \\ud Methods: ERS data from 2009-2014 were retrieved for analysis. Chi squared and t-tests were used to inve...
Directory of Open Access Journals (Sweden)
Deslandes Emmanuelle
2010-07-01
Full Text Available Abstract Background Joint modeling of longitudinal and survival data has been increasingly considered in clinical trials, notably in cancer and AIDS. In critically ill patients admitted to an intensive care unit (ICU, such models also appear to be of interest in the investigation of the effect of treatment on severity scores due to the likely association between the longitudinal score and the dropout process, either caused by deaths or live discharges from the ICU. However, in this competing risk setting, only cause-specific hazard sub-models for the multiple failure types data have been used. Methods We propose a joint model that consists of a linear mixed effects submodel for the longitudinal outcome, and a proportional subdistribution hazards submodel for the competing risks survival data, linked together by latent random effects. We use Markov chain Monte Carlo technique of Gibbs sampling to estimate the joint posterior distribution of the unknown parameters of the model. The proposed method is studied and compared to joint model with cause-specific hazards submodel in simulations and applied to a data set that consisted of repeated measurements of severity score and time of discharge and death for 1,401 ICU patients. Results Time by treatment interaction was observed on the evolution of the mean SOFA score when ignoring potentially informative dropouts due to ICU deaths and live discharges from the ICU. In contrast, this was no longer significant when modeling the cause-specific hazards of informative dropouts. Such a time by treatment interaction persisted together with an evidence of treatment effect on the hazard of death when modeling dropout processes through the use of the Fine and Gray model for sub-distribution hazards. Conclusions In the joint modeling of competing risks with longitudinal response, differences in the handling of competing risk outcomes appear to translate into the estimated difference in treatment effect on the
Steuwe, Carolin; Berg, Michaela; Driessen, Martin; Beblo, Thomas
2017-01-01
This study focused on the predictors of therapy dropout in a naturalistic sample of patients with borderline pathology receiving dialectical behavior therapy (DBT) in an inpatient setting. We assumed that the change of the therapist between DBT-briefing and start of DBT-treatment as well as comorbid posttraumatic stress disorder (PTSD) and childhood trauma history were associated with elevated dropout. Eighty-nine participants with borderline pathology (≥ 3 borderline personality disorder criteria) receiving an inpatient DBT program completed a quality assurance questionnaire set assessing demographic information and pretreatment psychopathology during the days of their inpatient stay. Beyond that, changes of therapists were documented. The predictor analyses were investigated with generalized estimating equations. The dropout rate was 24.7%. A change of therapist between DBT-briefing and treatment as well as high childhood emotional abuse was associated with premature termination of treatment. Higher values of physical neglect during childhood were associated with a protective effect on treatment dropout. Surprisingly, this was also true for comorbid PTSD. This study supports the importance of therapy process variables as predictors of therapy dropout in borderline pathology. A change of therapist between DBT-briefing and treatment was associated with an increased vulnerability for dropping out of treatment and should therefore be avoided if possible. Against our hypotheses, a comorbid PTSD was even protective with regard to DBT dropout. Therefore, this severely suffering patient group should not be rejected from treatment assuming them to be too unstable for psychotherapy. However, results need to be replicated. ClinicalTrials.gov Identifier: NCT03018639, retrospectively registered on January 9, 2017.
Predictive factors of dropout from inpatient treatment for anorexia nervosa.
Roux, H; Ali, A; Lambert, S; Radon, L; Huas, C; Curt, F; Berthoz, S; Godart, Nathalie
2016-09-30
Patients with severe Anorexia Nervosa (AN) whose condition is life-threatening or who are not receiving adequate ambulatory care are hospitalized. However, 40 % of these patients leave the hospital prematurely, without reaching the target weight set in the treatment plan, and this can compromise outcome. This study set out to explore factors predictive of dropout from hospital treatment among patients with AN, in the hope of identifying relevant therapeutic targets. From 2009 to 2011, 180 women hospitalized for AN (DSM-IV diagnosis) in 10 centres across France were divided into two groups: those under 18 years (when the decision to discharge belongs to the parents) and those aged 18 years and over (when the patient can legally decide to leave the hospital). Both groups underwent clinical assessment using the Morgan & Russell Global Outcome State questionnaire and the Eating Disorders Examination Questionnaire (EDE-Q) for assessment of eating disorder symptoms and outcome. Psychological aspects were assessed via the evaluation of anxiety and depression using the Hospital Anxiety and Depression Scale (HADS). Socio-demographic data were also collected. A number of factors identified in previous research as predictive of dropout from hospital treatment were tested using stepwise descending Cox regressions. We found that factors predictive of dropout varied according to age groups (being under 18 as opposed to 18 and over). For participants under 18, predictive factors were living in a single-parent family, severe intake restriction as measured on the "dietary restriction" subscale of the Morgan & Russell scale, and a low patient-reported score on the EDE-Q "restraint concerns" subscale. For those over 18, dropout was predicted from a low depression score on the HADS, low level of concern about weight on the EDE-Q subscale, and lower educational status. To prevent dropout from hospitalization for AN, the appropriate therapeutic measures vary according to whether
Lam, H K; Leung, Frank H F
2007-10-01
This correspondence presents the stability analysis and performance design of the continuous-time fuzzy-model-based control systems. The idea of the nonparallel-distributed-compensation (non-PDC) control laws is extended to the continuous-time fuzzy-model-based control systems. A nonlinear controller with non-PDC control laws is proposed to stabilize the continuous-time nonlinear systems in Takagi-Sugeno's form. To produce the stability-analysis result, a parameter-dependent Lyapunov function (PDLF) is employed. However, two difficulties are usually encountered: 1) the time-derivative terms produced by the PDLF will complicate the stability analysis and 2) the stability conditions are not in the form of linear-matrix inequalities (LMIs) that aid the design of feedback gains. To tackle the first difficulty, the time-derivative terms are represented by some weighted-sum terms in some existing approaches, which will increase the number of stability conditions significantly. In view of the second difficulty, some positive-definitive terms are added in order to cast the stability conditions into LMIs. In this correspondence, the favorable properties of the membership functions and nonlinear control laws, which allow the introduction of some free matrices, are employed to alleviate the two difficulties while retaining the favorable properties of PDLF-based approach. LMI-based stability conditions are derived to ensure the system stability. Furthermore, based on a common scalar performance index, LMI-based performance conditions are derived to guarantee the system performance. Simulation examples are given to illustrate the effectiveness of the proposed approach.
A low-power 10-bit continuous-time CMOS ΣΔ A/D converter
DEFF Research Database (Denmark)
Nielsen, Jannik Hammel; Bruun, Erik
2004-01-01
This paper presents the design of a third-order low-pass ΣΔ analog-to-digital converter (ADC) employing a continuous-time (CT) loop filter. The loop filter is implemented using Gm - C integrators, where the transconductors are implemented using CMOS transistors only. System level as well...... as transistor level design issues for power efficiency is discussed. A prototype ΣΔ ADC intended for weak biological signals restricted to bandwidths below 4 kHz has been manufactured in a standard 0.35 μm CMOS technology. The ADC has a measured resolution of 10 bits and a dynamic range (DR) of 67 d...
Robust Adaptive Dynamic Programming of Two-Player Zero-Sum Games for Continuous-Time Linear Systems.
Fu, Yue; Fu, Jun; Chai, Tianyou
2015-12-01
In this brief, an online robust adaptive dynamic programming algorithm is proposed for two-player zero-sum games of continuous-time unknown linear systems with matched uncertainties, which are functions of system outputs and states of a completely unknown exosystem. The online algorithm is developed using the policy iteration (PI) scheme with only one iteration loop. A new analytical method is proposed for convergence proof of the PI scheme. The sufficient conditions are given to guarantee globally asymptotic stability and suboptimal property of the closed-loop system. Simulation studies are conducted to illustrate the effectiveness of the proposed method.
A New Approach to Rational Discrete-Time Approximations to Continuous-Time Fractional-Order Systems
Matos , Carlos; Ortigueira , Manuel ,
2012-01-01
Part 10: Signal Processing; International audience; In this paper a new approach to rational discrete-time approximations to continuous fractional-order systems of the form 1/(sα+p) is proposed. We will show that such fractional-order LTI system can be decomposed into sub-systems. One has the classic behavior and the other is similar to a Finite Impulse Response (FIR) system. The conversion from continuous-time to discrete-time systems will be done using the Laplace transform inversion integr...
A meta-analysis of dropout rates in acceptance and commitment therapy.
Ong, Clarissa W; Lee, Eric B; Twohig, Michael P
2018-05-01
Many psychotherapies, including cognitive behavioral therapy and acceptance and commitment therapy (ACT), have been found to be effective interventions for a range of psychological and behavioral health concerns. Another aspect of treatment utility to consider is dropout, as interventions only work if clients are engaged in them. To date, no research has used meta-analytic methods to examine dropout in ACT. Thus, the objectives of the present meta-analysis were to (1) determine the aggregate dropout rate for ACT in randomized controlled trials, (2) compare dropout rates in ACT to those in other psychotherapies, and (3) identify potential moderators of dropout in ACT. Our literature search yielded 68 studies, representing 4,729 participants. The weighted mean dropout rates in ACT exclusive conditions and ACT inclusive conditions (i.e., those that included an ACT intervention) were 15.8% (95% CI: 11.9%, 20.1%) and 16.0% (95% CI: 12.5%, 19.8%), respectively. ACT dropout rates were not significantly different from those of established psychological treatments. In addition, dropout rates did not vary by client characteristics or study methodological quality. However, master's-level clinicians/therapists (weighted mean = 29.9%, CI: 17.6%, 43.8%) were associated with higher dropout than psychologists (weighted mean = 12.4%, 95% CI: 6.7%, 19.4%). More research on manipulable, process variables that influence dropout is needed. Copyright © 2018 Elsevier Ltd. All rights reserved.
Meta-analysis of Dropout in Treatments for Post-traumatic Stress Disorder
Imel, Zac E.; Laska, Kevin; Jakcupcak, Matthew; Simpson, Tracy L.
2013-01-01
Objective Many patients dropout of treatments for Post-traumatic stress disorder (PTSD) and some clinicians believe that ‘trauma focused’ treatments increase dropout. Method We conducted a meta-analysis of dropout among active treatments in clinical trials for PTSD (42 studies; 17 direct comparisons). Results The average dropout rate was 18%, but it varied significantly across studies. Group modality and greater number of sessions, but not trauma focus, predicted increased dropout. When the meta-analysis was restricted to direct comparisons of active treatments, there were no differences in dropout. Differences in trauma focus between treatments in the same study did not predict dropout. However, trauma focused treatments resulted in higher dropout as compared to Present Centered Therapy (PCT) – a treatment originally designed as a control, but now listed as a research supported intervention for PTSD. Conclusion Dropout varies between active interventions for PTSD across studies, but differences are primarily driven by differences between studies. There do not appear to be systematic differences across active interventions when they are directly compared in the same study. The degree of clinical attention placed on the traumatic event does not appear to be a primary cause of dropout from active treatments. However comparisons of PCT may be an exception to this general pattern, perhaps due to a restriction of variability in trauma focus among comparisons of active treatments. More research is needed comparing trauma focused interventions to trauma avoidant treatments such as PCT. PMID:23339535
Enjoyment and Behavioral Intention Predict Organized Youth Sport Participation and Dropout.
Gardner, Lauren A; Magee, Christopher A; Vella, Stewart A
2017-11-01
Dropout from organized youth sport has significant adverse health implications. Enjoyment and behavioral intentions have consistently been linked with participation and dropout; however, few studies have investigated these links using a prospective design. This study explored whether enjoyment and intentions to continue predicted dropout behavior at 1-year follow-up. Questionnaires were completed by 327 regular sport participants (mean age = 13.01 y at baseline). After 1 year, 247 individuals (75.5%) continued participating in their main sport and 26 individuals (8%) dropped out. A hierarchical logistic regression model estimated the probability of dropout. In step 1, the following covariates were included: age, sex, competition level, perceived competence, parental support, coach-athlete relationship, friendship quality, and peer acceptance. In step 2, enjoyment and intentions to continue were included. Step 1 indicated that age, parental support, coach-athlete relationship quality, and peer acceptance were significantly associated with dropout. Step 2 explained further variance in dropout, with both enjoyment and intentions inversely associated with dropout. Peer acceptance was the only covariate to remain significantly associated with dropout in step 2. Findings support the use of enjoyment and behavioral intentions as indicators of sport participation/dropout behavior and may aid the development of interventions aimed at preventing future dropout.
Physical exercise in treatment of AUDs – a dropout study
DEFF Research Database (Denmark)
Sari, Sengül; Roessler, Kirsten Kaya
Background: The Healthy Lifestyle Study is one out of five alcohol research studies in the RESCueH research project. It is a randomized controlled study which aims to understand the effect of physical exercise on alcohol, fitness and wellness outcomes for outpatients in treatment of alcohol use...... disorders. Relapse rates in treatment of AUD ranges between 60 and 90 % in the first year after treatment. The Healthy Lifestyle Study offers physical exercise as add on treatment to better maintenance. However intervention studies with physical exercise can suffer from high dropout rates. To gain a better...... understanding of lived lives of dropouts from The Healthy Lifestyle Study, a qualitative interview study was conducted. Objective: This interview study aims to gain better understanding of and more in depth knowledge about how alcohol patients experience, think and feel about physical exercise when...
New Approach to reduce High School Dropout Rates
Directory of Open Access Journals (Sweden)
Mauricio Cristhian Portillo-Torres
2015-05-01
Full Text Available From 2006 to 2014, the Ministry of Public Education of Costa Rica implemented four strategic actions to reduce high school dropout rates. The main purpose of these actions was to promote student participation and student identification with their school. Studies prepared by the Ministry of Education and the Comptroller of the Republic were revised to assess the impact of these actions. The result of these actions does not show an actual decrease in the number of students who leave high school. Therefore, a more holistic view is necessary to ensure the students’ stay. This review suggests using use the concept of student engagement and applying a three tier system-wide dropout preventive actions: universal, targeted and intensive.
GENDER STEREOTYPES IN THE SCHOOL DROPOUT: CASE EL FUERTE, SINALOA
Directory of Open Access Journals (Sweden)
Rosalva Ruíz-Ramírez
2014-07-01
Full Text Available Gender stereotypes are accepted preconceptions of what should be a man and a woman. Affect all areas of life, in the relationships that stablished in the family and the school. Within education, these stereotypes are reflected in the access, retention and completion of education degrees, as well as the area of study that preferred the women and men. They also have different effects on the causes of dropout depending on the gender to which they belong. This article aims to show the influence of gender stereotypes on dropout students and high school students in rural areas, specifically in three schools located in the municipality of El Fuerte, Sinaloa, the academic unit (AU San Blas and its extensions La Constancia and Las Higueras of Los Natoches. The results were obtained through a wider investigation in 2013.
Teacher professionalisation and dropout rates in adult education
DEFF Research Database (Denmark)
Wahlgren, Bjarne; Mariager-Anderson, Kristina
2015-01-01
in by the teachers, interviews with the teachers, and by the teachers’ written logbooks. The preliminary conclusion is that it is the general attitude in the teacher groups towards the importance of improving retention that is of significance for the documented effects on the drop-out rates.......This article reports findings from a research project titled New roles for the teacher - Increased completion through social responsibility. This research, designed as an intervention project, has an overall aim of reducing absence and drop-out rates in the Danish vocational and general adult...... educational system by developing and improving the teachers’ competences. This has been pursued in the research project through engaging teachers in training aimed at improving their socio-pedagogical competences. The effect of this training has been measured by electronic questionnaires filled...
Wang, Licheng; Wang, Zidong; Han, Qing-Long; Wei, Guoliang
2017-09-06
The synchronization control problem is investigated for a class of discrete-time dynamical networks with packet dropouts via a coding-decoding-based approach. The data is transmitted through digital communication channels and only the sequence of finite coded signals is sent to the controller. A series of mutually independent Bernoulli distributed random variables is utilized to model the packet dropout phenomenon occurring in the transmissions of coded signals. The purpose of the addressed synchronization control problem is to design a suitable coding-decoding procedure for each node, based on which an efficient decoder-based control protocol is developed to guarantee that the closed-loop network achieves the desired synchronization performance. By applying a modified uniform quantization approach and the Kronecker product technique, criteria for ensuring the detectability of the dynamical network are established by means of the size of the coding alphabet, the coding period and the probability information of packet dropouts. Subsequently, by resorting to the input-to-state stability theory, the desired controller parameter is obtained in terms of the solutions to a certain set of inequality constraints which can be solved effectively via available software packages. Finally, two simulation examples are provided to demonstrate the effectiveness of the obtained results.
Directory of Open Access Journals (Sweden)
Samuel de Oliveira Durso
2018-05-01
Full Text Available ABSTRACT: The purpose of this article was to identify explanatory factors for undergraduate student’s dropout from the Accounting program of a Brazilian public university. The theoretical platform that guided the study was formulated using three evasion models related to higher education. The survey database consisted of socioeconomic and demographic information of 371 students. The research used quantitative and qualitative methodologies to reach the proposed goal. Quantitative data analysis was performed through logistic regression. The model proposed by the study was able to accurately predict 77% of the cases of dropout/completion from the sample. The qualitative step was based on five semi-structured interviews with those in the sample who dropped out of their studies. The findings of the research have helped understand the phenomenon of undergraduate student dropout from the Accounting program and stresses the importance of rethinking public policies for the retention of talent and, especially, of those students who depend on their work to maintain their studies.
Influence analysis to assess sensitivity of the dropout process
Molenberghs, Geert; Verbeke, Geert; Thijs, Herbert; Lesaffre, Emmanuel; Kenward, Michael
2001-01-01
Diggle and Kenward (Appl. Statist. 43 (1994) 49) proposed a selection model for continuous longitudinal data subject to possible non-random dropout. It has provoked a large debate about the role for such models. The original enthusiasm was followed by skepticism about the strong but untestable assumption upon which this type of models invariably rests. Since then, the view has emerged that these models should ideally be made part of a sensitivity analysis. One of their examples is a set of da...
DATA MINING IN HIGHER EDUCATION : UNIVERSITY STUDENT DROPOUT CASE STUDY
Ghadeer S. Abu-Oda; Alaa M. El-Halees
2015-01-01
In this paper, we apply different data mining approaches for the purpose of examining and predicting students’ dropouts through their university programs. For the subject of the study we select a total of 1290 records of computer science students Graduated from ALAQSA University between 2005 and 2011. The collected data included student study history and transcript for courses taught in the first two years of computer science major in addition to student GPA , high school average ...
Marijuana Use and High School Dropout: The Influence of Unobservables
Daniel F. McCaffrey; Rosalie Liccardo Pacula; Bing Han; Phyllis Ellickson
2008-01-01
In this study we reconsider the relationship between heavy and persistent marijuana use and high school dropout status using a unique prospective panel study of over 4500 7th grade students from South Dakota who are followed up through high school. Propensity score weighting is used to adjust for baseline differences that are found to exist before marijuana initiation occurs (7th grade). Weighted logistic regression incorporating these propensity score weights is then used to examine the exte...
Hobolth, Asger; Stone, Eric A
2009-09-01
Analyses of serially-sampled data often begin with the assumption that the observations represent discrete samples from a latent continuous-time stochastic process. The continuous-time Markov chain (CTMC) is one such generative model whose popularity extends to a variety of disciplines ranging from computational finance to human genetics and genomics. A common theme among these diverse applications is the need to simulate sample paths of a CTMC conditional on realized data that is discretely observed. Here we present a general solution to this sampling problem when the CTMC is defined on a discrete and finite state space. Specifically, we consider the generation of sample paths, including intermediate states and times of transition, from a CTMC whose beginning and ending states are known across a time interval of length T. We first unify the literature through a discussion of the three predominant approaches: (1) modified rejection sampling, (2) direct sampling, and (3) uniformization. We then give analytical results for the complexity and efficiency of each method in terms of the instantaneous transition rate matrix Q of the CTMC, its beginning and ending states, and the length of sampling time T. In doing so, we show that no method dominates the others across all model specifications, and we give explicit proof of which method prevails for any given Q, T, and endpoints. Finally, we introduce and compare three applications of CTMCs to demonstrate the pitfalls of choosing an inefficient sampler.
International Nuclear Information System (INIS)
Ko, Hyoungho; Park, Sangjun; Paik, Seung-Joon; Choi, Byoung-doo; Park, Yonghwa; Lee, Sangmin; Kim, Sungwook; Lee, Sang Chul; Lee, Ahra; Yoo, Kwangho; Lim, Jaesang; Cho, Dong-il
2006-01-01
A microaccelerometer with highly reliable, wafer-level packaged MEMS sensing element and fully differential, continuous time, low noise, BiCMOS interface circuit is fabricated. The MEMS sensing element is fabricated on a (111)-oriented SOI wafer by using the SBM (Sacrificial/Bulk Micromachining) process. To protect the silicon structure of the sensing element and enhance the reliability, a wafer level hermetic packaging process is performed by using a silicon-glass anodic bonding process. The interface circuit is fabricated using 0.8 μm BiCMOS process. The capacitance change of the MEMS sensing element is amplified by the continuous-time, fully-differential transconductance input amplifier. A chopper-stabilization architecture is adopted to reduce low-frequency noise including 1/f noise. The fabricated microaccelerometer has the total noise equivalent acceleration of 0.89 μg/√Hz, the bias instability of 490 μg, the input range of ±10 g, and the output nonlinearity of ±0.5 %FSO
Dropout of a multidisciplinary treatment program for women with fibromyalgia
Directory of Open Access Journals (Sweden)
Tatiana Rehder Gonçalves
2010-03-01
Full Text Available Objective: To evaluate the dropout of a multidisciplinary treatment program in fibromyalgia (FM. Methods: An observational study conducted during the period of April 2000 to December 2005, including 133 women with fibromyalgia, participating in a multidisciplinary treatment program. Those who had left the treatment for two weeks or more were classified as inactive and contacted by telephone to record the reasons for their noncompliance, which were divided into four groups: 1 Family; 2 Occupations; 3 Medical; 4 Other Reasons. Results: When collecting data, 92 (69.4% women were considered inactive. There was no significant difference between noncompliance before and after six months of treatment. Of the total number of inactive women, 54 (40.8% participants left for medical reasons, 30 (22.6% for other reasons, 26 (19.4% for family reasons and 23 (17.2% due to occupation. There was no statistical difference between the motives of dropout according to the length of stay in the program (p> 0.05. Conclusion: We conclude that the multidisciplinary program for women with fibromyalgia had high levels of noncompliance, half of them occurred in the first six months. Among the main reasons reported for dropout, the medical reasons were more frequent.
The impact of community schools on student dropout in pre-vocational education
Heers, M.; van Klaveren, C.; Groot, W.; Maassen van den Brink, H.
2012-01-01
Dropout prevention is highly ranked on the political agenda in many countries. It remains unclear, however, how dropout can be effectively reduced, as many different factors are determining student dropout. Community schools recognize this and modernize education such that it better accommodates students' personal needs. As a result these schools cooperate more with external organizations, stimulate parental involvement in the educational process and organize more extracurricular activities. ...
Prediction of Student Dropout in E-Learning Program Through the Use of Machine Learning Method
Mingjie Tan; Peiji Shao
2015-01-01
The high rate of dropout is a serious problem in E-learning program. Thus it has received extensive concern from the education administrators and researchers. Predicting the potential dropout students is a workable solution to prevent dropout. Based on the analysis of related literature, this study selected student’s personal characteristic and academic performance as input attributions. Prediction models were developed using Artificial Neural Network (ANN), Decision Tree (DT) and Bayesian Ne...
Factors associated with dropout in a group weight-loss programme: a longitudinal investigation.
Yackobovitch-Gavan, M; Steinberg, D M; Endevelt, R; Benyamini, Y
2015-02-01
Attrition is a major limitation of most weight management intervention programmes. The present study aimed to conduct an extensive investigation of personal, sociodemographic and treatment-related factors associated with attrition at different stages of a 10-week group weight-loss programme. The present study is part of a longitudinal, clinical intervention study comparing three conditions in a 10-week group programme: Control, Behavioural Intentions and Implementation Intentions. The study included 587 participants with a mean (SD) age of 46 (11) years (range 18-78 years) and a mean (SD) body mass index (BMI) of 31.9 (5.5) kg m(-2), with 90% being female. To characterise dropout in each week separately, as well as overall dropout (dropout until week 9, the median time of dropout), we tested several logistic regression models, including multiple imputations to cope with missing data. The results of the different dropout models consistently showed that a smaller reduction in BMI in the first 2 weeks of the programme was the strongest predictor of dropout. Dropout in the tenth and last week differed from the earlier weeks both in the relatively high dropout rate (56% of total dropout) and in that, in contrast to earlier weeks, the week 10 model included the reduction in BMI during the last 2 weeks before dropout but did not include the reduction in BMI at the initiation of the intervention. Weight-loss in the beginning of the programme is a crucial independent determinant of dropout in each week except the last one. This finding is important because it suggests a simple assessment for a major dropout risk factor in adult weight-loss intervention programmes. © 2014 The British Dietetic Association Ltd.
Risk Factors for School Dropout in a Sample of Juvenile Offenders
Fernández-Suárez, Asunción; Herrero, Juan; Pérez, Beatriz; Juarros-Basterretxea, Joel; Rodríguez-Díaz, Francisco J.
2016-01-01
Backgrounds: The high rates of school dropout worldwide and their relevance highlight the need for a close study of its causes and consequences. Literature has suggested that school dropout might be explained by multiple causes at different levels (individual, family, school, and neighborhood). The aim of the current study is to examine the relation between individual (defiant attitude, irresponsibility, alcohol abuse, and illegal drugs use), family (educational figure absent and parental monitoring), school factors (truancy and school conflict) and school dropout. Method: Judicial files of all juvenile offenders (218 males and 46 females) with a judicial penal measure in Asturias (Spain) in the year 2012 were examined. Multivariate logistic regression analyses were performed to estimate the relationships between school dropout and individual, family and school variables. Results: As for the individual characteristics, results showed that school dropouts were more irresponsible than non-dropouts. Also they had higher rates of illegal drug use and alcohol abuse. Moreover, lack of parental monitoring emerged as a key predictive factor of school dropout, beyond the type of family structure in terms of the presence of both or only one educational figure. Finally, school factors did not show a significant relationship to school dropout. Conclusions: These findings indicate that school dropout is a multidimensional process. School and family policies that emphasize the role of parental monitoring and prevent alcohol and substance abuse are recommended. PMID:28082934
Risk Factors for School Dropout in a Sample of Juvenile Offenders.
Fernández-Suárez, Asunción; Herrero, Juan; Pérez, Beatriz; Juarros-Basterretxea, Joel; Rodríguez-Díaz, Francisco J
2016-01-01
Backgrounds: The high rates of school dropout worldwide and their relevance highlight the need for a close study of its causes and consequences. Literature has suggested that school dropout might be explained by multiple causes at different levels (individual, family, school, and neighborhood). The aim of the current study is to examine the relation between individual (defiant attitude, irresponsibility, alcohol abuse, and illegal drugs use), family (educational figure absent and parental monitoring), school factors (truancy and school conflict) and school dropout. Method: Judicial files of all juvenile offenders (218 males and 46 females) with a judicial penal measure in Asturias (Spain) in the year 2012 were examined. Multivariate logistic regression analyses were performed to estimate the relationships between school dropout and individual, family and school variables. Results: As for the individual characteristics, results showed that school dropouts were more irresponsible than non-dropouts. Also they had higher rates of illegal drug use and alcohol abuse. Moreover, lack of parental monitoring emerged as a key predictive factor of school dropout, beyond the type of family structure in terms of the presence of both or only one educational figure. Finally, school factors did not show a significant relationship to school dropout. Conclusions : These findings indicate that school dropout is a multidimensional process. School and family policies that emphasize the role of parental monitoring and prevent alcohol and substance abuse are recommended.
International Nuclear Information System (INIS)
Ticos, Catalin M; Andrei, Ionut R; Pascu, Mihail L; Bulinski, Mircea
2011-01-01
The injection current of an external-cavity semiconductor laser working in a regime of low-frequency fluctuations (LFFs) is modulated at several MHz. The rate of power dropouts in the laser emission is correlated with the amplitude and frequency of the modulating signal. The occurrence of dropouts becomes more regular when the laser is driven at 7 MHz, which is close to the dominant frequency of dropouts in the solitary laser. Driving the laser at 10 MHz also induces dropouts with a periodicity of 0.1 μs, resulting in LFFs with two dominant frequencies.
DEFF Research Database (Denmark)
Tvedebrink, Torben; Eriksen, Poul Svante; Asplund, Maria
2012-01-01
We discuss the model for estimating drop-out probabilities presented by Tvedebrink et al. [7] and the concerns, that have been raised. The criticism of the model has demonstrated that the model is not perfect. However, the model is very useful for advanced forensic genetic work, where allelic drop-out...... is occurring. With this discussion, we hope to improve the drop-out model, so that it can be used for practical forensic genetics and stimulate further discussions. We discuss how to estimate drop-out probabilities when using a varying number of PCR cycles and other experimental conditions....
Directory of Open Access Journals (Sweden)
Mindaugas Snipas
2015-01-01
Full Text Available The primary goal of this work was to study advantages of numerical methods used for the creation of continuous time Markov chain models (CTMC of voltage gating of gap junction (GJ channels composed of connexin protein. This task was accomplished by describing gating of GJs using the formalism of the stochastic automata networks (SANs, which allowed for very efficient building and storing of infinitesimal generator of the CTMC that allowed to produce matrices of the models containing a distinct block structure. All of that allowed us to develop efficient numerical methods for a steady-state solution of CTMC models. This allowed us to accelerate CPU time, which is necessary to solve CTMC models, ∼20 times.
Energy Technology Data Exchange (ETDEWEB)
Salimi, S; Radgohar, R, E-mail: shsalimi@uok.ac.i, E-mail: r.radgohar@uok.ac.i [Faculty of Science, Department of Physics, University of Kurdistan, Pasdaran Ave, Sanandaj (Iran, Islamic Republic of)
2010-01-28
In this paper, we consider decoherence in continuous-time quantum walks on long-range interacting cycles (LRICs), which are the extensions of the cycle graphs. For this purpose, we use Gurvitz's model and assume that every node is monitored by the corresponding point-contact induced by the decoherence process. Then, we focus on large rates of decoherence and calculate the probability distribution analytically and obtain the lower and upper bounds of the mixing time. Our results prove that the mixing time is proportional to the rate of decoherence and the inverse of the square of the distance parameter (m). This shows that the mixing time decreases with increasing range of interaction. Also, what we obtain for m = 0 is in agreement with Fedichkin, Solenov and Tamon's results [48] for cycle, and we see that the mixing time of CTQWs on cycle improves with adding interacting edges.
Zhu, Wei; Wang, Dandan; Liu, Lu; Feng, Gang
2017-08-18
This paper investigates exponential stabilization of continuous-time dynamic systems (CDSs) via event-based impulsive control (EIC) approaches, where the impulsive instants are determined by certain state-dependent triggering condition. The global exponential stability criteria via EIC are derived for nonlinear and linear CDSs, respectively. It is also shown that there is no Zeno-behavior for the concerned closed loop control system. In addition, the developed event-based impulsive scheme is applied to the synchronization problem of master and slave memristive neural networks. Furthermore, a self-triggered impulsive control scheme is developed to avoid continuous communication between the master system and slave system. Finally, two numerical simulation examples are presented to illustrate the effectiveness of the proposed event-based impulsive controllers.
DEFF Research Database (Denmark)
Jimenez, M.J.; Madsen, Henrik; Bloem, J.J.
2008-01-01
This paper focuses on a method for linear or non-linear continuous time modelling of physical systems using discrete time data. This approach facilitates a more appropriate modelling of more realistic non-linear systems. Particularly concerning advanced building components, convective and radiati...... that a description of the non-linear heat transfer is essential. The resulting model is a non-linear first order stochastic differential equation for the heat transfer of the PV component....... heat interchanges are non-linear effects and represent significant contributions in a variety of components such as photovoltaic integrated facades or roofs and those using these effects as passive cooling strategies, etc. Since models are approximations of the physical system and data is encumbered...
Belkhatir, Zehor; Laleg-Kirati, Taous-Meriem
2017-01-01
This paper proposes a two-stage estimation algorithm to solve the problem of joint estimation of the parameters and the fractional differentiation orders of a linear continuous-time fractional system with non-commensurate orders. The proposed algorithm combines the modulating functions and the first-order Newton methods. Sufficient conditions ensuring the convergence of the method are provided. An error analysis in the discrete case is performed. Moreover, the method is extended to the joint estimation of smooth unknown input and fractional differentiation orders. The performance of the proposed approach is illustrated with different numerical examples. Furthermore, a potential application of the algorithm is proposed which consists in the estimation of the differentiation orders of a fractional neurovascular model along with the neural activity considered as input for this model.
Angraini, Yenni; Toharudin, Toni; Folmer, Henk; Oud, Johan H L
2014-01-01
This article analyzes the relationships among nationalism (N), individualism (I), ethnocentrism (E), and authoritarianism (A) in continuous time (CT), estimated as a structural equation model. The analysis is based on the General Election Study for Flanders, Belgium, for 1991, 1995, and 1999. We find reciprocal effects between A and E and between E and I as well as a unidirectional effect from A on I. We furthermore find relatively small, but significant, effects from both I and E on N but no effect from A on N or from N on any of the other variables. Because of its central role in the N-I-E-A complex, mitigation of authoritarianism has the largest potential to reduce the spread of nationalism, ethnocentrism, and racism in Flanders.
Energy Technology Data Exchange (ETDEWEB)
Chen Yong; Chen Xi; Qian Minping [School of Mathematical Sciences, Peking University, Beijing 100871 (China)
2006-03-17
A general form of the Green-Kubo formula, which describes the fluctuations pertaining to all the steady states whether equilibrium or non-equilibrium, for a system driven by a finite Markov chain with continuous time (briefly, MC) {l_brace}{xi}{sub t}{r_brace}, is shown. The equivalence of different forms of the Green-Kubo formula is exploited. We also look at the differences in terms of the autocorrelation function and the fluctuation spectrum between the equilibrium state and the non-equilibrium steady state. Also, if the MC is in the non-equilibrium steady state, we can always find a complex function {psi}, such that the fluctuation spectrum of {l_brace}{phi}({xi}{sub t}){r_brace} is non-monotonous in [0, + {infinity})
Directory of Open Access Journals (Sweden)
Songlin Wo
2018-01-01
Full Text Available Singular systems arise in a great deal of domains of engineering and can be used to solve problems which are more difficult and more extensive than regular systems to solve. Therefore, in this paper, the definition of finite-time robust H∞ control for uncertain linear continuous-time singular systems is presented. The problem we address is to design a robust state feedback controller which can deal with the singular system with time-varying norm-bounded exogenous disturbance, such that the singular system is finite-time robust bounded (FTRB with disturbance attenuation γ. Sufficient conditions for the existence of solutions to this problem are obtained in terms of linear matrix equalities (LMIs. When these LMIs are feasible, the desired robust controller is given. A detailed solving method is proposed for the restricted linear matrix inequalities. Finally, examples are given to show the validity of the methodology.
Pranevicius, Henrikas; Pranevicius, Mindaugas; Pranevicius, Osvaldas; Bukauskas, Feliksas F.
2015-01-01
The primary goal of this work was to study advantages of numerical methods used for the creation of continuous time Markov chain models (CTMC) of voltage gating of gap junction (GJ) channels composed of connexin protein. This task was accomplished by describing gating of GJs using the formalism of the stochastic automata networks (SANs), which allowed for very efficient building and storing of infinitesimal generator of the CTMC that allowed to produce matrices of the models containing a distinct block structure. All of that allowed us to develop efficient numerical methods for a steady-state solution of CTMC models. This allowed us to accelerate CPU time, which is necessary to solve CTMC models, ∼20 times. PMID:25705700
Belkhatir, Zehor
2017-05-31
This paper proposes a two-stage estimation algorithm to solve the problem of joint estimation of the parameters and the fractional differentiation orders of a linear continuous-time fractional system with non-commensurate orders. The proposed algorithm combines the modulating functions and the first-order Newton methods. Sufficient conditions ensuring the convergence of the method are provided. An error analysis in the discrete case is performed. Moreover, the method is extended to the joint estimation of smooth unknown input and fractional differentiation orders. The performance of the proposed approach is illustrated with different numerical examples. Furthermore, a potential application of the algorithm is proposed which consists in the estimation of the differentiation orders of a fractional neurovascular model along with the neural activity considered as input for this model.
Transport properties of the continuous-time random walk with a long-tailed waiting-time density
International Nuclear Information System (INIS)
Weissman, H.; Havlin, S.; Weiss, G.H.
1989-01-01
The authors derive asymptotic properties of the propagator p(r, t) of a continuous-time random walk (CTRW) in which the waiting time density has the asymptotic form ψ(t) ∼ T α /t α+1 when t >> T and 0 = ∫ 0 ∞ τψ(τ)dτ is finite. One is that the asymptotic behavior of p(0, t) is demonstrated by the waiting time at the origin rather than by the dimension. The second difference is that in the presence of a field p(r, t) no longer remains symmetric around a moving peak. Rather, it is shown that the peak of this probability always occurs at r = 0, and the effect of the field is to break the symmetry that occurs when < ∞. Finally, they calculate similar properties, although in not such great detail, for the case in which the single-step jump probabilities themselves have an infinite mean
International Nuclear Information System (INIS)
Chen Yong; Chen Xi; Qian Minping
2006-01-01
A general form of the Green-Kubo formula, which describes the fluctuations pertaining to all the steady states whether equilibrium or non-equilibrium, for a system driven by a finite Markov chain with continuous time (briefly, MC) {ξ t }, is shown. The equivalence of different forms of the Green-Kubo formula is exploited. We also look at the differences in terms of the autocorrelation function and the fluctuation spectrum between the equilibrium state and the non-equilibrium steady state. Also, if the MC is in the non-equilibrium steady state, we can always find a complex function ψ, such that the fluctuation spectrum of {φ(ξ t )} is non-monotonous in [0, + ∞)
Behzadi, Kobra; Baghelani, Masoud
2014-05-01
This paper presents a third order continuous time current mode ΣΔ modulator for WLAN 802.11b standard applications. The proposed circuit utilized feedback architecture with scaled and optimized DAC coefficients. At circuit level, we propose a modified cascade current mirror integrator with reduced input impedance which results in more bandwidth and linearity and hence improves the dynamic range. Also, a very fast and precise novel dynamic latch based current comparator is introduced with low power consumption. This ultra fast comparator facilitates increasing the sampling rate toward GHz frequencies. The modulator exhibits dynamic range of more than 60 dB for 20 MHz signal bandwidth and OSR of 10 while consuming only 914 μW from 1.8 V power supply. The FoM of the modulator is calculated from two different methods, and excellent performance is achieved for proposed modulator.
Song, Rui-Zhuo; Xiao, Wen-Dong; Wei, Qing-Lai
2014-05-01
We develop an online adaptive dynamic programming (ADP) based optimal control scheme for continuous-time chaotic systems. The idea is to use the ADP algorithm to obtain the optimal control input that makes the performance index function reach an optimum. The expression of the performance index function for the chaotic system is first presented. The online ADP algorithm is presented to achieve optimal control. In the ADP structure, neural networks are used to construct a critic network and an action network, which can obtain an approximate performance index function and the control input, respectively. It is proven that the critic parameter error dynamics and the closed-loop chaotic systems are uniformly ultimately bounded exponentially. Our simulation results illustrate the performance of the established optimal control method.
Schilkowsky, Louise Bastos; Portela, Margareth Crisóstomo; Sá, Marilene de Castilho
2011-06-01
This study aimed to identify factors associated with the health care of patients with HIV/AIDS who drop out. The study was developed in a specialized health care unit of a University hospital in Rio de Janeiro, Brazil, considering a stratified sample of adult patients including all dropout cases (155) and 44.0% of 790 cases under regular follow-up. Bivariate analyses were used to identify associations between health care dropout and demographic, socioeconomic and clinical variables. Logistic and Cox regression models were used to identify the independent effects of the explanatory variables on risk for dropout, in the latter by incorporating information on the outcome over time. Patients were, on average, 35 years old, predominantly males (66.4%) and of a low socioeconomic level (45.0%). In both models, health care dropout was consistently associated with being unemployed or having an unstable job, using illicit drugs and having psychiatric background--positive association; and with age, having AIDS, and having used multiple antiretroviral regimens--negative association. In the logistic regression, dropping out was also positively associated with time between diagnosis and the first outpatient visit, while in the Cox model, the hazard for dropping out was positively associated with being single, and negatively associated with a higher educational level. The results of this work allow for the identification of HIV/AIDS patients more likely to drop out from health care.
Psychological well-being as a predictor of dropout among recently qualified Danish eldercare workers
DEFF Research Database (Denmark)
Giver, Hanne; Faber, Anne; Hannerz, Harald
2010-01-01
BACKGROUND: The eldercare sector is characterized by a shortage of labour and a high turnover rate, which constitutes a major challenge for the ageing societies of western Europe. The aim of the present study was to investigate if a low level of psychological well-being at the time of graduation...... predicts dropout among eldercare workers two years later. METHODS: We included 4,968 female eldercare trainees in this prospective study, recruited from 27 of the 28 Danish colleges for eldercare. Psychological well-being in 2004 was measured with the five-item Mental Health Inventory (MHI-5) of the 36......-item Short-Form Health Survey (SF-36). We linked the survey data with national register data to obtain information about labour market attachment two years after qualification. RESULTS: In 2006, 37% of all participants had left the eldercare sector. Compared to participants with high psychological well...
Alternative education programmes and middle school dropout in Honduras
Marshall, Jeffery H.; Aguilar, Claudia R.; Alas, Mario; Castellanos, Renán Rápalo; Castro, Levi; Enamorado, Ramón; Fonseca, Esther
2014-05-01
Honduras has made steady progress in expanding post-primary school coverage in recent years, but many rural communities still do not provide a middle (lower secondary) school. As a result, Honduras has implemented a number of middle school alternative programmes designed to meet the needs of at-risk populations throughout the country. This article analyses dropout in three of the four main alternative lower secondary school programmes in Honduras over a three-year period for a cohort of roughly 5,500 students. The results show that these programmes are indeed reaching a vulnerable population in the country, but dropout rates are generally very high - upwards of 50 per cent in some cases - between Grades 7 and 9. Furthermore, even in the control school comparison samples made up of formal lower secondary schools, about 25 per cent of children leave school between Grades 7 and 9. The authors' analysis includes propensity score matching (PSM) methods that make more focused comparisons between students in alternative programmes and control samples. These results show that dropout rates in alternative programmes are not much different than in control schools, and only significant in one programme comparison, when taking into account family background characteristics like socioeconomic status (SES). Multivariate analysis within alternative programme samples finds that attrition is lower in those learning centres which have adopted key features of formal schools, such as university-educated teachers. The results highlight the tremendous variation in the alternative middle school sector in terms of programme features, school quality and student outcomes, as well as the challenges of expanding this sector to meet the growing demand for lower secondary schooling in Honduras.
International Nuclear Information System (INIS)
Lee, Youn Myoung
1995-02-01
As a newly approaching model, a stochastic model using continuous time Markov process for nuclide decay chain transport of arbitrary length in the fractured porous rock medium has been proposed, by which the need for solving a set of partial differential equations corresponding to various sets of side conditions can be avoided. Once the single planar fracture in the rock matrix is represented by a series of finite number of compartments having region wise constant parameter values in them, the medium is continuous in view of various processes associated with nuclide transport but discrete in medium space and such geologic system is assumed to have Markov property, since the Markov process requires that only the present value of the time dependent random variable be known to determine the future value of random variable, nuclide transport in the medium can then be modeled as a continuous time Markov process. Processes that are involved in nuclide transport are advective transport due to groundwater flow, diffusion into the rock matrix, adsorption onto the wall of the fracture and within the pores in the rock matrix, and radioactive decay chain. The transition probabilities for nuclide from the transition intensities between and out of the compartments are represented utilizing Chapman-Kolmogorov equation, through which the expectation and the variance of nuclide distribution for each compartment or the fractured rock medium can be obtained. Some comparisons between Markov process model developed in this work and available analytical solutions for one-dimensional layered porous medium, fractured medium with rock matrix diffusion, and porous medium considering three member nuclide decay chain without rock matrix diffusion have been made showing comparatively good agreement for all cases. To verify the model developed in this work another comparative study was also made by fitting the experimental data obtained with NaLS and uranine running in the artificial fractured
Finishing high school: alternative pathways and dropout recovery.
Tyler, John H; Lofstrom, Magnus
2009-01-01
John Tyler and Magnus Lofstrom take a close look at the problems posed when students do not complete high school. The authors begin by discussing the ongoing, sometimes heated, debate over how prevalent the dropout problem is. They note that one important reason for discrepancies in reported dropout rates is whether holders of the General Educational Development (GED) credential are counted as high school graduates. The authors also consider the availability of appropriate student data. The overall national dropout rate appears to be between 22 and 25 percent, but the rate is higher among black and Hispanic students, and it has not changed much in recent decades. Tyler and Lofstrom conclude that schools are apparently doing about as well now as they were forty years ago in terms of graduating students. But the increasingly competitive pressures associated with a global economy make education ever more important in determining personal and national well-being. A student's decision to drop out of school, say the authors, is affected by a number of complex factors and is often the culmination of a long process of disengagement from school. That decision, not surprisingly, carries great cost to both the student and society. Individual costs include lower earnings, higher likelihood of unemployment, and greater likelihood of health problems. Because minority and low-income students are significantly more likely than well-to-do white students to drop out of school, the individual costs fall unevenly across groups. Societal costs include loss of tax revenue, higher spending on public assistance, and higher crime rates. Tyler and Lofstrom go on to survey research on programs designed to reduce the chances of students' dropping out. Although the research base on this question is not strong, they say, close mentoring and monitoring of students appear to be critical components of successful programs. Other dropout-prevention approaches associated with success are family
Dropout prediction in a public mental health intervention for sub-threshold and mild panic disorder
Meulenbeek, Petrus Antonius Maria; Seeger, Kristin; ten Klooster, Peter M.
2015-01-01
Dropout is a common and serious problem in psychological research and practice. When participants terminate treatment prematurely, this may have methodological and clinical consequences. The aim of this study was to identify predictors of dropout in a sample of patients (N = 217) with sub-threshold
Schneider, Brian W.; Gerdes, Alyson C.; Haack, Lauren M.; Lawton, Katie E.
2013-01-01
Premature treatment dropout is a problem for many families seeking mental health services for their children. Research is currently limited in identifying factors that increase the likelihood of dropout in families of school-aged children with Attention-Deficit/Hyperactivity Disorder (ADHD). Thus, the goal of the current study was to examine…
The Meaning of School from Dropout's View Point (A Phenomenological Study)
Habibi; Setiawan, Cally
2017-01-01
Student dropouts are complex problems in Indonesia. Some of the dropouts living in rural areas have migrated to the large cities. It contributes to the child labor growth which is already one the major problems in Indonesia. Knowledge about the meaning of school from their perspective could be helpful for policy and programs related to dropout…
Exploring the Effects of Financial Aid on the Gap in Student Dropout Risks by Income Level
Chen, Rong; DesJardins, Stephen L.
2008-01-01
Using national survey data and discrete-time logit modeling, this research seeks to understand whether student aid mediates the relationship between parental income and student dropout behavior. Our analysis confirms that there is a gap in dropout rates for low-income students compared with their upper income peers, and suggests that some types of…
Dropout and Graduation Rates 2007-2008. Research Brief. Volume 0804
Research Services, Miami-Dade County Public Schools, 2009
2009-01-01
The District conducts a "cross-sectional" analysis of student dropouts annually; it examines dropout rates among students enrolled in various grades at one point in time. A "longitudinal" analysis, also conducted annually, tracks a group of students in the same grade or cohort over a period of several years. Each method…
Student Enrollment and Dropout: An Evaluation Study of DCSA Program at Bangladesh Open University
Rashid, Mohammad Mamunur; Jahan, Monira; Islam, Md. Anwarul; Ratna, Meherin Munjarin
2015-01-01
The aim of this study is to investigate the present status of DCSA program focusing on student enrollment, dropout, and completion trends. The study tries to explore the factors that attract or pull students to enroll in the program and push them to dropout from the program. Secondary data analysis and interview are used to generate data of the…
Dimensions Of Basic School Dropouts In Rural Ghana: The Case Of ...
African Journals Online (AJOL)
The objective of this paper was to investigate the various dimensions of basic school dropouts in rural Ghana using the Asutifi district as a case study. The analysis of data (both quantitative and qualitative) gathered from several stakeholders of basic education in the district, revealed that the causes of school dropout were ...
Dropout Prevention: A Study of Prevention Programs Used by High Schools to Increase Graduation Rate
Simmons, Christopher L.
2013-01-01
This mixed methods study focused on the relationship between dropout prevention programs and graduation rates in one school district in Florida during the 2010-2011 school year. The dropout prevention program data analyzed included high school principals' perceptions in regard to perceived effectiveness, fidelity of implementation, cost efficacy,…
Basic school dropout in Ghana: a case study of the Amansie West ...
African Journals Online (AJOL)
In view of the increasing cost of education the persistent phenomenon of school dropout has become a constant worry to all stakeholders. The focus of this paper was to assess the trend of basic school dropout in Amansie West, a predominantly rural district in Ghana and to further determine the main causes and policy ...
A Systematic Review of Dropout from Organized Sport among Children and Youth
Crane, Jeff; Temple, Viviene
2015-01-01
Leisure constraints theory was used as a framework to systematically review factors associated with dropout of organized sport among children and adolescents. Keyword searches for the population, context and construct of interest (i.e. dropout) identified articles from the entire contents of the following databases: Academic Search Complete, ERIC,…
The Determinants of University Dropouts: A Bivariate Probability Model with Sample Selection.
Montmarquette, Claude; Mahseredjian, Sophie; Houle, Rachel
2001-01-01
Studies determinants of university dropouts, using a longitudinal data set on student enrollments at the University of Montreal. Variables explaining persistence and dropouts are related to a nontraditional class-size effect in first-year required courses and to type of university program. Strong academic performance influences student…
How Do Tertiary Dropouts Fare in the Labour Market? A Comparison between EU Countries
Schnepf, Sylke V.
2017-01-01
Dropping out of university is regularly discussed as a negative indicator. However, research on actual career trajectories of dropouts is virtually non-existent. This study estimates the association between tertiary dropouts and career chances in 15 European countries. Using data from the 2011 Programme for the International Assessment of Adult…
Jung, Jisun; Kim, Yangson
2018-01-01
With an increasing number of international students in South Korea, the issue of retaining these students and reducing their dropout rates has become important. This study explores the multilevel factors that affect the institutional dropout rate among international students in Korea. The research questions are as follows: (a) to what extent do…
Dropout and Graduation Rates 2008-2009. Research Brief. Volume 0902
Research Services, Miami-Dade County Public Schools, 2010
2010-01-01
The District conducts a "cross-sectional" analysis of student dropouts annually; it examines dropout rates among students enrolled in various grades at one point in time. A "longitudinal" analysis, also conducted annually, tracks a group of students in the same grade or cohort over a period of several years. Each method…
An Examination of Dropout Rates for Hispanic or Latino Students Enrolled in Online K-12 Schools
Corry, Michael; Dardick, William; Stella, Julie
2017-01-01
As the number of online K-12 educational offerings continues to grow it is important to better understand key indicators of success for students enrolled in these classes. One of those indicators is student dropout rates. This is particularly important for Hispanic or Latino students who traditionally have high dropout rates. The purpose of this…
Working While Studying: The Impact of Term-Time Employment on Dropout Rates
Hovdhaugen, Elisabeth
2015-01-01
There are many possible reasons why students leave university prior to degree completion, and one of the more commonly cited is being employed while studying. This paper analyses the impact of employment status on dropout rates using survival analysis. It finds that employment status does have an impact on dropout rates; students who work full…
Of Needles and Haystacks: Building an Accurate Statewide Dropout Early Warning System in Wisconsin
Knowles, Jared E.
2015-01-01
The state of Wisconsin has one of the highest four year graduation rates in the nation, but deep disparities among student subgroups remain. To address this the state has created the Wisconsin Dropout Early Warning System (DEWS), a predictive model of student dropout risk for students in grades six through nine. The Wisconsin DEWS is in use…
Student Dropout from the Perspectives of Junior High Counselors in Northeast Mississippi
Bennett, Kelly Ann
2013-01-01
I investigated fifteen junior high counselors' understandings about student dropout, particularly about identification of and interventions for students at risk for dropping out of school. As an educator, I desired to research the phenomenon of student dropout to understand how to better reach these types of students. Research is available…
Dropout and Graduation Rates 2009-2010. Research Brief. Volume 1101
Research Services, Miami-Dade County Public Schools, 2011
2011-01-01
The District conducts a "cross-sectional" analysis of student dropouts annually; it examines dropout rates among students enrolled in various grades at one point in time. A "longitudinal" analysis, also conducted annually, tracks a group of students in the same grade or cohort over a period of several years. Each method…
Investigating the Impact of Financial Aid on Student Dropout Risks: Racial and Ethnic Differences
Chen, Rong; DesJardins, Stephen L.
2010-01-01
This study focuses on the differences in college student dropout behavior among racial/ethnic groups. We employ event history methods and data from the Beginning Postsecondary Students (BPS) and National Postsecondary Student Aid Study (NPSAS) surveys to investigate how financial aid may differentially influence dropout risks among these student…
Reducing School Factors That Lead to Student Dropout at Sussex Central High School
Jerns, Pamela Renee
2012-01-01
The focus of this Executive Position Paper (EPP) is to address the dropout rate at Sussex Central High School (SCHS) in the Indian River School District (IRSD). Studies conducted for this EPP align with current research--student dropout is a result of culminating school-based factors that include poor attendance and lack of exposure to rigorous…
Predicting Dropout Using Student- and School-Level Factors: An Ecological Perspective
Wood, Laura; Kiperman, Sarah; Esch, Rachel C.; Leroux, Audrey J.; Truscott, Stephen D.
2017-01-01
High school dropout has been associated with negative outcomes, including increased rates of unemployment, incarceration, and mortality. Dropout rates vary significantly depending on individual and environmental factors. The purpose of our study was to use an ecological perspective to concurrently explore student- and school-level predictors…
Ecker-Lyster, Meghan; Niileksela, Christopher
2016-01-01
This article reviews the literature on dropout trends, prevention, and intervention initiatives for school-aged children. Theoretical and consequential trends are highlighted to offer educators a perspective in which to view the dropout problem. This article also examines current trends in prevention and intervention initiatives aimed at reducing…
Reexamining Gifted Underachievement and Dropout through the Lens of Student Engagement
Landis, Rebecca N.; Reschly, Amy L.
2013-01-01
The issue of high school dropout has long concerned policy makers, educational professionals, and the general public. In the gifted literature, this concern is no less pressing. Student engagement is becoming an increasingly discussed construct for conceptualizing the dropout phenomenon and designing appropriate interventions to prevent this…
Dropout and Graduation Rates 2010-2011. Research Brief. Volume 1107
Research Services, Miami-Dade County Public Schools, 2012
2012-01-01
The District conducts a "cross-sectional" analysis of student dropouts annually; it examines dropout rates among students enrolled in various grades at one point in time. A "longitudinal" analysis, also conducted annually, tracks a group of students in the same grade or cohort over a period of several years. Each method…
Teachers' Opinions of Student Dropout from Formal Music Education Centres of the Canary Islands
Lorenzo Socorro, Sonia; Escandell Bermúdez, María Olga; Castro Sánchez, José Juan
2016-01-01
One hundred and eighty-five teachers were surveyed to determine their opinion of student dropout from formal music centres in the Canary Islands. The goal of the study was to investigate the causes of dropout and strategies to prevent it. Teachers' opinions were collected by means of a questionnaire. The influence of the environment on the…
Luyten, H; Bosker, R.J.; Dekkers, H; Derks, A
2003-01-01
This study analyses the data from a large-scale longitudinal investigation into the effect of both school and student characteristics on the dropout rate for students in lower secondary education in The Netherlands. Dropout rates were found to vary significantly between schools, but only a single
Predictors of dropout from community clinic child CBT for anxiety disorders.
Wergeland, Gro Janne H; Fjermestad, Krister W; Marin, Carla E; Haugland, Bente Storm-Mowatt; Silverman, Wendy K; Öst, Lars-Göran; Havik, Odd E; Heiervang, Einar R
2015-04-01
The aim was to investigate predictors of treatment dropout among 182 children (aged 8-15 years) participating in an effectiveness trial of manual-based 10-session individual and group cognitive behavior therapy (CBT) for anxiety disorders in community clinics. The dropout rate was 14.4%, with no significant difference between the two treatment conditions. We examined predictors for overall dropout (n=26), early (≤session 4, n=15), and late dropout (≥session 5, n=11). Overall dropout was predicted by low child and parent rated treatment credibility, and high parent self-rated internalizing symptoms. Low child rated treatment credibility predicted both early and late dropout. High parent self-rated internalizing symptoms predicted early dropout, whereas low parent rated treatment credibility predicted late dropout. These results highlight the importance of addressing treatment credibility, and to offer support for parents with internalizing symptoms, to help children and families remain in treatment. Copyright © 2015 Elsevier Ltd. All rights reserved.
Illness perception of dropout patients followed up at bipolar outpatient clinic, Turkey.
Oflaz, Serap; Guveli, Hulya; Kalelioglu, Tevfik; Akyazı, Senem; Yıldızhan, Eren; Kılıc, Kasım Candas; Basyigit, Sehnaz; Ozdemiroglu, Filiz; Akyuz, Fatma; Gokce, Esra; Bag, Sevda; Kurt, Erhan; Oral, Esat Timucin
2015-06-01
Dropout is a common problem in the treatment of psychiatric illnesses including bipolar disorders (BD). The aim of the present study is to investigate illness perceptions of dropout patients with BD. A cross sectional study was done on the participants who attended the Mood Disorder Outpatient Clinic at least 3 times from January 2003 through June 2008, and then failed to attend clinic till to the last one year, 2009, determined as dropout. Thirty-nine dropout patients and 39 attendent patients with BD were recruited for this study. A sociodemographic form and brief illness perception questionnaire were used to capture data. The main reasons of patients with BD for dropout were difficulties of transport (31%), to visit another doctor (26%), giving up drugs (13%) and low education level (59%) is significant for dropout patients. The dropout patients reported that their illness did not critically influence their lives, their treatment had failed to control their illnesses, they had no symptoms, and that their illness did not emotionally affect them. In conclusion, the nonattendance of patients with serious mental illness can result in non-compliance of therapeutic drug regimens, and a recurrence of the appearance symptoms. The perception of illness in dropout patients with BD may be important for understanding and preventing nonattendance. Copyright © 2015 Elsevier B.V. All rights reserved.
Forster, Jeri E.; MaWhinney, Samantha; Ball, Erika L.; Fairclough, Diane
2011-01-01
Dropout is common in longitudinal clinical trials and when the probability of dropout depends on unobserved outcomes even after conditioning on available data, it is considered missing not at random and therefore nonignorable. To address this problem, mixture models can be used to account for the relationship between a longitudinal outcome and dropout. We propose a Natural Spline Varying-coefficient mixture model (NSV), which is a straightforward extension of the parametric Conditional Linear Model (CLM). We assume that the outcome follows a varying-coefficient model conditional on a continuous dropout distribution. Natural cubic B-splines are used to allow the regression coefficients to semiparametrically depend on dropout and inference is therefore more robust. Additionally, this method is computationally stable and relatively simple to implement. We conduct simulation studies to evaluate performance and compare methodologies in settings where the longitudinal trajectories are linear and dropout time is observed for all individuals. Performance is assessed under conditions where model assumptions are both met and violated. In addition, we compare the NSV to the CLM and a standard random-effects model using an HIV/AIDS clinical trial with probable nonignorable dropout. The simulation studies suggest that the NSV is an improvement over the CLM when dropout has a nonlinear dependence on the outcome. PMID:22101223
Cooper, Andrew A; Conklin, Laren R
2015-08-01
Dropout from mental health treatment poses a substantial problem, but rates vary substantially across studies and diagnoses. Focused reviews are needed to provide more detailed estimates for specific areas of research. Randomized clinical trials involving individual psychotherapy for unipolar depression are ubiquitous and important, but empirical data on average dropout rates from these studies is lacking. We conducted a random-effects meta-analysis of 54 such studies (N=5852) including 80 psychotherapy conditions, and evaluated a number of predictors of treatment- and study-level dropout rates. Our overall weighted dropout estimates were 19.9% at the study level, and 17.5% for psychotherapy conditions specifically. Therapy orientation did not significantly account for variance in dropout estimates, but estimates were significantly higher in psychotherapy conditions with more patients of minority racial status or with comorbid personality disorders. Treatment duration was also positively associated with dropout rates at trend level. Studies with an inactive control comparison had higher dropout rates than those without such a condition. Limitations include the inability to test certain potential predictors (e.g., socioeconomic status) due to infrequent reporting. Overall, our findings suggest the need to consider how specific patient and study characteristics may influence dropout rates in clinical research on individual therapy for depression. Copyright © 2015 Elsevier Ltd. All rights reserved.
A review of mental health treatment dropout by ethnic minority youth.
de Haan, Anna M; Boon, Albert E; de Jong, Joop T V M; Vermeiren, Robert R J M
2018-02-01
A large proportion of treatments in youth mental health care are prematurely terminated by the patient. Treatment dropout can have severe consequences. Since ethnic minority youth are treated less often for mental disorders than other youth, it is important to analyse their risk for dropout and to determine if there are ethnicity-specific determinants. This review aimed to provide an overview of the findings from empirical studies on child and adolescent therapy dropout by ethnic minority and to determine if there were ethnicity-specific dropout determinants. An extensive literature search was performed to locate relevant journal articles. Identified articles were inspected for relevant references and these articles were then included in the meta-analysis. A total of 27 studies were accepted for analysis. The results showed that ethnic minority patients have a higher risk of treatment dropout than ethnic majority patients and that dropout rates are ethnically specific. Several differences in dropout predictors among the ethnic groups were found. In spite of diverse results, review limitations, and the lack of several key variables in the available research, some clinical recommendations are made. The review indicates that to prevent dropout, therapists should pay attention to variables such as ethnic background, therapist-patient ethnic match, and the quality of the therapeutic relationship.
Electron–Ion Intensity Dropouts in Gradual Solar Energetic Particle Events during Solar Cycle 23
International Nuclear Information System (INIS)
Tan, Lun C.
2017-01-01
Since the field-line mixing model of Giacalone et al. suggests that ion dropouts cannot happen in the “gradual” solar energetic particle (SEP) event because of the large size of the particle source region in the event, the observational evidence of ion dropouts in the gradual SEP event should challenge the model. We have searched for the presence of ion dropouts in the gradual SEP event during solar cycle 23. From 10 SEP events the synchronized occurrence of ion and electron dropouts is identified in 12 periods. Our main observational facts, including the mean width of electron–ion dropout periods being consistent with the solar wind correlation scale, during the dropout period the dominance of the slab turbulence component and the enhanced turbulence power parallel to the mean magnetic field, and the ion gyroradius dependence of the edge steepness in dropout periods, are all in support of the solar wind turbulence origin of dropout events. Also, our observation indicates that a wide longitude distribution of SEP events could be due to the increase of slab turbulence fraction with the increased longitude distance from the flare-associated active region.
Gambling Disorder: Exploring Pre-treatment and In-treatment Dropout Predictors. A UK Study.
Ronzitti, Silvia; Soldini, Emiliano; Smith, Neil; Clerici, Massimo; Bowden-Jones, Henrietta
2017-12-01
The aim of this study was to identify predictors of treatment dropout in a sample of gamblers attending a specialist clinic for gambling disorder. We analysed data on 846 treatment-seeking pathological gamblers. Firstly, we investigated differences in socio-demographic and clinical variables between treatment completers and pre-treatment dropouts, as well as between treatment completers and during-treatment dropouts. Subsequently, variables were entered into a multinomial logistic regression model to identify significant predictors of pre-treatment and in-treatment dropout. Overall, 44.8% of clients did not complete the treatment: 27.4% dropped out before starting it, while 17.4% dropped out during the treatment. Younger age and use of drugs were associated with pre-treatment dropout, while family history of gambling disorder, a lower PGSI score, and being a smoker were related with in-treatment dropout. Our findings suggest that pre-treatment dropouts differ from in-treatment dropouts, and, thus, further research will benefit from considering these groups separately. In addition, this newly gained knowledge will also be helpful in increasing treatment retention in specific subgroups of problem gamblers.
de Haan, Anna M.; Boon, Albert E.; Vermeiren, Robert R. J. M.; Hoeve, Machteld; de Jong, Joop T. V. M.
2015-01-01
Background: Dropout from child and adolescent psychotherapy is a common phenomenon which can have negative consequences for the individual later in life. It is therefore important to gain insight on dropout risk factors. Objective: Several potential risk factors [ethnic minority status, a lower socioeconomic status (SES), and higher problem…
A meta-analytic review on treatment dropout in child and adolescent outpatient mental health care
de Haan, A.M.; Boon, A.E.; de Jong, J.T.V.M.; Hoeve, M.; Vermeiren, R.R.J.M.
2013-01-01
A large proportion (28% up to 75%) of the treatments in youth mental health care results in premature termination (dropout). It is important to gain knowledge of the determinants of dropout because it can have very severe consequences. The aim of our meta-analytic review was to provide an overview
Electron-Ion Intensity Dropouts in Gradual Solar Energetic Particle Events during Solar Cycle 23
Tan, Lun C.
2017-09-01
Since the field-line mixing model of Giacalone et al. suggests that ion dropouts cannot happen in the “gradual” solar energetic particle (SEP) event because of the large size of the particle source region in the event, the observational evidence of ion dropouts in the gradual SEP event should challenge the model. We have searched for the presence of ion dropouts in the gradual SEP event during solar cycle 23. From 10 SEP events the synchronized occurrence of ion and electron dropouts is identified in 12 periods. Our main observational facts, including the mean width of electron-ion dropout periods being consistent with the solar wind correlation scale, during the dropout period the dominance of the slab turbulence component and the enhanced turbulence power parallel to the mean magnetic field, and the ion gyroradius dependence of the edge steepness in dropout periods, are all in support of the solar wind turbulence origin of dropout events. Also, our observation indicates that a wide longitude distribution of SEP events could be due to the increase of slab turbulence fraction with the increased longitude distance from the flare-associated active region.
Stressors and Turning Points in High School and Dropout: A Stress Process, Life Course Framework
Dupéré, Véronique; Leventhal, Tama; Dion, Eric; Crosnoe, Robert; Archambault, Isabelle; Janosz, Michel
2015-01-01
High school dropout is commonly seen as the result of a long-term process of failure and disengagement. As useful as it is, this view has obscured the heterogeneity of pathways leading to dropout. Research suggests, for instance, that some students leave school not as a result of protracted difficulties but in response to situations that emerge…
Klein-Radukic, Sarah; Zmyj, Norbert
2015-11-01
Dropout of infants in looking time studies sometimes occurs at high rates, raising concerns that the representativeness of the final sample might be reduced in comparison to the originally obtained sample. The current study investigated which infant characteristics play a role in dropout. Infants were presented with a preferential looking task at 6 and 9 months of age. At 9 months of age, an additional habituation task and a subsequent novelty preference task were conducted. In addition, temperament was assessed via the Infant Behavior Questionnaire - Revised (IBQ-R, Gartstein & Rothbart, 2003), and cognitive developmental status was assessed via the Cognitive Scale of the Bayley Scale of Infant and Toddler Development (BSID-III, Bayley, 2006). Dropout was positively related to the IBQ-R temperament scales Distress to Limitations and Approach, and negatively related to the scales Falling Reactivity and Cuddliness. The representativeness of the final sample regarding situation-specific temperament dimensions is affected by dropout. Dropout was not related to cognitive developmental status as measured via the BSID-III, habituation speed and novelty preference. Dropout at 6 months of age was associated with dropout at 9 months of age. We concluded that in looking time studies, the representativeness of the final sample regarding performance-relevant temperament dimensions or cognitive developmental status is not affected by dropout. Copyright © 2015 Elsevier Inc. All rights reserved.
Evaluation of a Public Awareness Campaign to Prevent High School Dropout.
Babinski, Leslie M; Corra, Ashley J; Gifford, Elizabeth J
2016-08-01
Many advocacy organizations devote time and resources to increasing community awareness and educating the public in an effort to gain support for their issue. One such effort, the Dropout Prevention Campaign by America's Promise Alliance, aimed to increase the visibility of the high school dropout problem and mobilize the community to take action. The objective of this paper is to evaluate the framing of the Dropout Prevention Campaign in television news media. To evaluate this campaign, television news coverage about high school dropout in 12 U.S. communities (N = 982) was examined. A content analysis of news transcripts was conducted and coded to determine the definition of the problem, the reasons for dropout and the possible solutions. Findings indicated that the high school dropout problem was most often framed (30 % of news segments) in terms of the economic and societal implications for the community. Individual student factors as well as broader societal influences were frequently discussed as possible reasons for dropout. The most commonly mentioned solutions were school-based interventions. News segments that mentioned America's Promise Alliance were more likely to frame the issue as a crisis and to use statistics to illustrate that point. Solutions that were more likely to appear in America's Promise segments promoted community and cross-sector involvement, consistent with the messages promoted by the Dropout Prevention Campaign. The findings suggest that a media content analysis can be an effective framework for analyzing a prevention campaign.
Treatment Dropout in Web-Based Cognitive Behavioral Therapy for Patients with Eating Disorders
ter Huurne, E.D.; Postel, Marloes Gerda; de Haan, H.A.; van der Palen, Jacobus Adrianus Maria; de Jong, C.A.
2017-01-01
Treatment dropout is an important concern in eating disorder treatments as it has negative implications for patients’ outcome, clinicians’ motivation, and research studies. Our main objective was to conduct an exploratory study on treatment dropout in a two-part web-based cognitive behavioral
Adelman, Melissa A.; Székely, Miguel
2017-01-01
School dropout is a growing concern in Central America, and in Latin America as a whole, because of its consequences for economic productivity, the inclusiveness of growth, social cohesion, and increasing youth risks. This paper utilizes more than two decades of household survey data to construct a systematic overview of school dropout at the…
Bridgeland, John M.; Balfanz, Robert; Moore, Laura A.; Friant, Rebecca S.
2010-01-01
High dropout rates continue to be a silent epidemic afflicting the nation's schools. Although some measurable progress is being made in some school districts and states to raise high school graduation rates, and federal, state, and local policies and practices are changing to meet the dropout challenge, the nation's progress is too slow and the…
Directory of Open Access Journals (Sweden)
Tomba Elena
2009-10-01
Full Text Available Abstract Background Dropout (DO is common in the treatment of eating disorders (EDs, but the reasons for this phenomenon remain unclear. This study is an extensive review of the literature regarding DO predictors in EDs. Methods All papers in PubMed, PsycINFO and Cochrane Library (1980-2009 were considered. Methodological issues and detailed results were analysed for each paper. After selection according to inclusion criteria, 26 studies were reviewed. Results The dropout rates ranged from 20.2% to 51% (inpatient and from 29% to 73% (outpatient. Predictors of dropout were inconsistent due to methodological flaws and limited sample sizes. There is no evidence that baseline ED clinical severity, psychiatric comorbidity or treatment issues affect dropout. The most consistent predictor is the binge-purging subtype of anorexia nervosa. Good evidence exists that two psychological traits (high maturity fear and impulsivity and two personality dimensions (low self-directedness, low cooperativeness are related to dropout. Conclusion Implications for clinical practice and areas for further research are discussed. Particularly, these results highlight the need for a shared definition of dropout in the treatment of eating disorders for both inpatient and outpatient settings. Moreover, the assessment of personality dimensions (impulse control, self-efficacy, maturity fear and others as liability factors for dropout seems an important issue for creating specific strategies to reduce the dropout phenomenon in eating disorders.
Electron–Ion Intensity Dropouts in Gradual Solar Energetic Particle Events during Solar Cycle 23
Energy Technology Data Exchange (ETDEWEB)
Tan, Lun C., E-mail: ltan@umd.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
2017-09-01
Since the field-line mixing model of Giacalone et al. suggests that ion dropouts cannot happen in the “gradual” solar energetic particle (SEP) event because of the large size of the particle source region in the event, the observational evidence of ion dropouts in the gradual SEP event should challenge the model. We have searched for the presence of ion dropouts in the gradual SEP event during solar cycle 23. From 10 SEP events the synchronized occurrence of ion and electron dropouts is identified in 12 periods. Our main observational facts, including the mean width of electron–ion dropout periods being consistent with the solar wind correlation scale, during the dropout period the dominance of the slab turbulence component and the enhanced turbulence power parallel to the mean magnetic field, and the ion gyroradius dependence of the edge steepness in dropout periods, are all in support of the solar wind turbulence origin of dropout events. Also, our observation indicates that a wide longitude distribution of SEP events could be due to the increase of slab turbulence fraction with the increased longitude distance from the flare-associated active region.