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1

Generating Dependent Random Variables Over Networks  

CERN Document Server

In this paper we study the problem of generation of dependent random variables, known as the "coordination capacity" [4,5], in multiterminal networks. In this model $m$ nodes of the network are observing i.i.d. repetitions of $X^{(1)}$, $X^{(2)}$,..., $X^{(m)}$ distributed according to $q(x^{(1)},...,x^{(m)})$. Given a joint distribution $q(x^{(1)},...,x^{(m)},y^{(1)},...,y^{(m)})$, the final goal of the $i^{th}$ node is to construct the i.i.d. copies of $Y^{(i)}$ after the communication over the network where $X^{(1)}$, $X^{(2)}$,..., $X^{(m)}, Y^{(1)}$, $Y^{(2)}$,..., $Y^{(m)}$ are jointly distributed according to $q(x^{(1)},...,x^{(m)},y^{(1)},...,y^{(m)})$. To do this, the nodes can exchange messages over the network at rates not exceeding the capacity constraints of the links. This problem is difficult to solve even for the special case of two nodes. In this paper we prove new inner and outer bounds on the achievable rates for networks with two nodes.

Gohari, Amin Aminzadeh

2011-01-01

2

On Strong Law of Large Numbers for Dependent Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available We discuss strong law of large numbers and complete convergence for sums of uniformly bounded negatively associate (NA random variables (RVs. We extend and generalize some recent results. As corollaries, we investigate limit behavior of some other dependent random sequence.

Wang Zhongzhi

2011-01-01

3

Some strong limit theorems for arrays of rowwise negatively orthant-dependent random variables  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract In this article, the strong limit theorems for arrays of rowwise negatively orthant-dependent random variables are studied. Some sufficient conditions for strong law of large numbers for an array of rowwise negatively orthant-dependent random variables without assumptions of identical distribution and stochastic domination are presented. As an application, the Chung-type strong law of large numbers for arrays of rowwise negatively orthant-dependent random variables is obtained. MR(2000 Subject Classification: 60F15

Shen Aiting

2011-01-01

4

Strong Law of Large Numbers for a 2-Dimensional Array of Pairwise Negatively Dependent Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, we obtain the strong law of large numbers for a 2-dimensional array of pairwise negatively dependent random variables which are not required to be identically distributed. We found the sufficient conditions of strong law of large numbers for the difference of random variables which independent and identically distributed conditions are regarded. In this study, we consider the limit as  which is stronger than the limit as m× n? ?  when m, n ? ? are natural numbers.

Kritsana Neammanee

2013-02-01

5

Weak laws of large numbers for arrays of rowwise negatively dependent random variables  

Directory of Open Access Journals (Sweden)

Full Text Available Weak laws of large numbers for arrays of rowwise negatively dependent random variables are obtained in this paper. The more general hypothesis of negative dependence relaxes the usual assumption of independence. The moment conditions are similar to previous results, and the stochastic bounded condition also provides a generalization of the usual distributional assumptions.

R. L. Taylor

2001-01-01

6

Explicit Bounds for the Distribution Function of the Sum of Dependent Normally Distributed Random Variables  

CERN Document Server

In this paper an analytic expression is given for the bounds of the distribution function of the sum of dependent normally distributed random variables. Using the theory of copulas and the important Frechet bounds the dependence structure is not restricted to any specific type. Numerical illustrations are provided to assess the quality of the derived bounds.

Schneider, Walter

2011-01-01

7

Negatively dependent bounded random variable probability inequalities and the strong law of large numbers  

Directory of Open Access Journals (Sweden)

Full Text Available Let X1,…,Xn be negatively dependent uniformly bounded random variables with d.f. F(x. In this paper we obtain bounds for the probabilities P(|?i=1nXi|?nt and P(|?ˆpn??p|>? where ?ˆpn is the sample pth quantile and ?p is the pth quantile of F(x. Moreover, we show that ?ˆpn is a strongly consistent estimator of ?p under mild restrictions on F(x in the neighborhood of ?p. We also show that ?ˆpn converges completely to ?p.

M. Amini

2000-01-01

8

On the characteristic function of a sum of M-dependent random variables  

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Full Text Available Let S=f1+f2+…+fn be a sum of 1-dependent random variables of zero mean. Let σ2=ES2, L=σ−3∑1≦i≦nE|fi|3. There is a universal constant a such that for a|t|L<1, we have|Eexp(itSσ−1|≦(1+a|t|sup{(a|t|L−1/4lnL,   exp(−t2/80}.This bound is a very useful tool in proving Berry-Esseen theorems.

Wansoo T. Rhee

1986-06-01

9

Variable survival exponents in history-dependent random walks: hard movable reflector  

CERN Document Server

We review recent studies demonstrating a nonuniversal (continuously variable) survival exponent for history-dependent random walks, and analyze a new example, the hard movable partial reflector. These processes serve as a simplified models of infection in a medium with a history-dependent susceptibility, and for spreading in systems with an infinite number of absorbing configurations. The memory may take the form of a history-dependent step length, or be the result of a partial reflector whose position marks the maximum distance the walker has ventured from the origin. In each case, a process with memory is rendered Markovian by a suitable expansion of the state space. Asymptotic analysis of the probability generating function shows that, for large t, the survival probability decays as S(t) \\sim t^{-delta}, where \\delta varies with the parameters of the model. We report new results for a hard partial reflector, i.e., one that moves forward only when the walker does. When the walker tries to jump to the site R...

Dickman, R; Dickman, Ronald; Jr, Francisco Fontenele Araujo; ben-Avraham, Daniel

2003-01-01

10

Variable survival exponents in history-dependent random walks: hard movable reflector  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english We review recent studies demonstrating a nonuniversal (continuously variable) survival exponent for history-dependent random walks, and analyze a new example, the hard movable partial reflector. These processes serve as simplified models of infection in a medium with a history-dependent susceptibili [...] ty, and for spreading in systems with an infinite number of absorbing configurations. The memory may take the form of a historydependent step length, or be the result of a partial reflector whose position marks the maximum distance the walker has ventured from the origin. In each case, a process with memory is rendered Markovian by a suitable expansion of the state space. Asymptotic analysis of the probability generating function shows that, for large t, the survival probability decays as S(t) ~ t -d, where d varies with the parameters of the model. We report new results for a hard partial reflector, i.e., one that moves forward only when the walker does. When the walker tries to jump to the site R occupied by the reflector, it is reflected back with probability r, and stays at R with probability 1 - r; only in the latter case does the reflector move (R ® R+1). For this model, d = 1/2(1 - r), and becomes arbitrarily large as r approaches 1. This prediction is confirmed via iteration of the transition matrix, which also reveals slowly-decaying corrections to scaling.

Ronald, Dickman; Francisco Fontenele, Araujo Jr.; Daniel, ben-Avraham.

2003-09-01

11

Variable survival exponents in history-dependent random walks: hard movable reflector  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english We review recent studies demonstrating a nonuniversal (continuously variable) survival exponent for history-dependent random walks, and analyze a new example, the hard movable partial reflector. These processes serve as simplified models of infection in a medium with a history-dependent susceptibili [...] ty, and for spreading in systems with an infinite number of absorbing configurations. The memory may take the form of a historydependent step length, or be the result of a partial reflector whose position marks the maximum distance the walker has ventured from the origin. In each case, a process with memory is rendered Markovian by a suitable expansion of the state space. Asymptotic analysis of the probability generating function shows that, for large t, the survival probability decays as S(t) ~ t -d, where d varies with the parameters of the model. We report new results for a hard partial reflector, i.e., one that moves forward only when the walker does. When the walker tries to jump to the site R occupied by the reflector, it is reflected back with probability r, and stays at R with probability 1 - r; only in the latter case does the reflector move (R ® R+1). For this model, d = 1/2(1 - r), and becomes arbitrarily large as r approaches 1. This prediction is confirmed via iteration of the transition matrix, which also reveals slowly-decaying corrections to scaling.

Ronald, Dickman; Francisco Fontenele, Araujo Jr.; Daniel, ben-Avraham.

12

On Complex Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available Normal 0 false false false EN-US X-NONE X-NONE In this paper, it is shown that a complex multivariate random variable  is a complex multivariate normal random variable of dimensionality if and only if all nondegenerate complex linear combinations of  have a complex univariate normal distribution. The characteristic function of  has been derived, and simpler forms of some theorems have been given using this characterization theorem without assuming that the variance-covariance matrix of the vector  is Hermitian positive definite. Marginal distributions of  have been given. In addition, a complex multivariate t-distribution has been defined and the density derived. A characterization of the complex multivariate t-distribution is given. A few possible uses of this distribution have been suggested.

Anwer Khurshid

2012-07-01

13

Strong invariance principle for dependent random fields  

CERN Document Server

A strong invariance principle is established for random fields which satisfy dependence conditions more general than positive or negative association. We use the approach of Cs\\"{o}rg\\H{o} and R\\'{e}v\\'{e}sz applied recently by Balan to associated random fields. The key step in our proof combines new moment and maximal inequalities, established by the authors for partial sums of multiindexed random variables, with the estimate of the convergence rate in the CLT for random fields under consideration.

Bulinski, A; Bulinski, Alexander; Shashkin, Alexey

2006-01-01

14

Extension of Two-Dimensional Discrete Random Variables Conditional Distribution  

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Full Text Available Conditional distribution reflects the dependency link among random variables, but two-dimensional random variables Conditional Distribution has some limitations.  In order to rich the content of conditional distribution this paper gives the extension of conditional distribution under discrete random variables and some examples. This article obtains the extension strictly in accordance with the definition of two-dimensional random variables. So it can get conditional distributions after changing the condition and get conditional distributions that are extended into n-dimensional random variables, thereby enriching the contents of the conditional distribution.

Feixue Huang

2010-03-01

15

On Sums of Conditionally Independent Subexponential Random Variables  

CERN Document Server

The asymptotic tail-behaviour of sums of independent subexponential random variables is well understood, one of the main characteristics being \\textit{the principle of the single big jump}. We study the case of dependent subexponential random variables, for both deterministic and random sums, using a fresh approach, by considering conditional independence structures on the random variables. We seek sufficient conditions for the results of the theory with independent random variables still to hold. For a subexponential distribution, we introduce the concept of a boundary class of functions, which we hope will be a useful tool in studying many aspects of subexponential random variables. The examples we give in the paper demonstrate a variety of effects owing to the dependence, and are also interesting in their own right.

Foss, Serguei

2008-01-01

16

Nonhermitean Random Matrix Models : a Free Random Variable Approach  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using the standard concepts of free random variables, we show that for a large class of nonhermitean random matrix models, the support of the eigenvalue distribution follows from their hermitean analogs using a conformal transformation. We also extend the concepts of free random variables to the class of nonhermitean matrices, and apply them to the models discussed by Ginibre-Girko (elliptic ensemble) and Mahaux-Weidenm\\"uller (chaotic resonance scattering).

Janik, Romuald A.; Nowak, Maciej A.; Papp, Gabor; Wambach, Jochen; Zahed, Ismail

1996-01-01

17

Independent and dependent variables  

Science.gov (United States)

The National Science Education Standards Science as Inquiry Standard states middle school students should develop general abilities, such as systematic observation, making accurate measurements, and identifying and controlling variables. The Standards acknowledge this can be challenging for students. Resources highlighted here focus on helping learners acquire knowledge of variables in scientific inquiry.

University, Staff A.

2008-03-07

18

A Measure of Monotonicity of two Random Variables  

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Full Text Available Problem statement: When analyzing random variables it was useful to measure the degree of their monotone dependence or compare pairs of random variables with respect to their monotonicity. Existing coefficients measure general or linear dependence of random variables. Developing a measure of monotonicity was useful for practical applications as well as for general theory, since monotonicity was an important type of dependence. Approach: Existing measures of dependence are briefly reviewed. The Reimann coefficient was generalized to arbitrary random variables with finite variances. Results: The article describes criteria for monotone dependence of two random variables and introduces a measure of this dependence-monotonicity coefficient. The advantages of this coefficient are shown in comparison with other global measures of dependence. It was shown that the monotonicity coefficient satisfies natural conditions for a monotonicity measure and that it had properties similar to the properties of the Pearson correlation; in particular, it equals 1 (-1 if and only if the pair X, Y was comonotonic (counter-monotonic. The monotonicity coefficient was calculated for some bivariate distributions and the sample version of the coefficient was defined. Conclusion/Recommendations: The monotonicity coefficient should be used to compare pairs of random variables (such as returns from financial assets with respect to their degree of monotone dependence. In the problems where the monotone relation of two variables has a random noise, the monotonicity coefficient can be used to estimate variance and other central moments of the noise. By calculating the sample version of the coefficient one will quickly find pairs of monotone dependent variables in a big dataset."

Ilias Kachapov

2012-01-01

19

Variability measures of positive random variables.  

Science.gov (United States)

During the stationary part of neuronal spiking response, the stimulus can be encoded in the firing rate, but also in the statistical structure of the interspike intervals. We propose and discuss two information-based measures of statistical dispersion of the interspike interval distribution, the entropy-based dispersion and Fisher information-based dispersion. The measures are compared with the frequently used concept of standard deviation. It is shown, that standard deviation is not well suited to quantify some aspects of dispersion that are often expected intuitively, such as the degree of randomness. The proposed dispersion measures are not entirely independent, although each describes the interspike intervals from a different point of view. The new methods are applied to common models of neuronal firing and to both simulated and experimental data. PMID:21799762

Kostal, Lubomir; Lansky, Petr; Pokora, Ondrej

2011-01-01

20

Extreme value statistics of correlated random variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Extreme value statistics (EVS) concerns the study of the statistics of the maximum or the minimum of a set of random variables. This is an important problem for any time-series and has applications in climate, finance, sports, all the way to physics of disordered systems where one is interested in the statistics of the ground state energy. While the EVS of uncorrelated variables are well understood, little is known for strongly correlated random variables. Only recently this...

Majumdar, Satya N.; Pal, Arnab

2014-01-01

 
 
 
 
21

Distributionally Robust Stochastic Programming with Binary Random Variables  

CERN Document Server

In this paper, we consider stochastic programming with binary random variables, that is, when the random variable represents random subsets of a set. We consider a distributionally robust model, where the only knowledge about the distribution is the marginal probability of each element to appear in the random set. The objective is to minimize expected cost under the worst case distribution with these marginals. We show the problem can be solved efficiently when the cost function is convex in the decision variable and a) supermodular in the random variable, or b) has (or can be approximated by) a weakly "super-monotonic" cost sharing method. We also provide an approximation algorithm for general convex cost functions that depends on an approximate separating oracle.

Agrawal, Shipra; Saberi, Amin; Ye, Yinyu

2009-01-01

22

Unbalanced Bidding Problem with Fuzzy Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available Unbalanced bidding problem with mixed uncertainty of fuzziness and randomness is considered in this paper, where the bidding engineering quantities of each activity are assumed to be fuzzy random variables. Two types of fuzzy random models as expected value maximization model and maximax chance-constrained model are built to satisfy different optimization requirements. Then a hybrid intelligent algorithm integrating fuzzy random simulations, neural network and genetic algorithm is designed to solve these models. Finally, a numerical experiment is given to illustrate its effectiveness of the algorithm. The results show that the algorithm is feasible and effective.

Dongran Zang

2009-02-01

23

Probabilistic graphs using coupled random variables  

Science.gov (United States)

Neural network design has utilized flexible nonlinear processes which can mimic biological systems, but has suffered from a lack of traceability in the resulting network. Graphical probabilistic models ground network design in probabilistic reasoning, but the restrictions reduce the expressive capability of each node making network designs complex. The ability to model coupled random variables using the calculus of nonextensive statistical mechanics provides a neural node design incorporating nonlinear coupling between input states while maintaining the rigor of probabilistic reasoning. A generalization of Bayes rule using the coupled product enables a single node to model correlation between hundreds of random variables. A coupled Markov random field is designed for the inferencing and classification of UCI's MLR `Multiple Features Data Set' such that thousands of linear correlation parameters can be replaced with a single coupling parameter with just a (3%, 4%) reduction in (classification, inference) performance.

Nelson, Kenric P.; Barbu, Madalina; Scannell, Brian J.

2014-05-01

24

Reduction of the Random Variables of the Turbulent Wind Field  

DEFF Research Database (Denmark)

Applicability of the Probability Density Evolution Method (PDEM) for realizing evolution of the probability density for the wind turbines has rather strict bounds on the basic number of the random variables involved in the model. The efficiency of most of the Advanced Monte Carlo (AMC) methods, i.e. Importance Sampling (IS) or Subset Simulation (SS), will be deteriorated on problems with many random variables. The problem with PDEM is that a multidimensional integral has to be carried out over the space defined by the random variables of the system. The numerical procedure requires discretization of the integral domain; this becomes increasingly difficult as the dimensions of the integral domain increase. On the other hand efficiency of the AMC methods is closely dependent on the design points of the problem. Presence of many random variables may increase the number of the design points, hence affects the efficiency of the AMC methods. The idea of the paper is to propose new schemes which allow reduction of the basic random variables of the turbulence such that PDEM and Advanced Monte Carlo (AMC) methods, i.e. subset simulation, are applicable on it.

Sichani, Mahdi Teimouri; Nielsen, SØren R.K.

2012-01-01

25

Random forest automated supervised classification of Hipparcos periodic variable stars  

CERN Document Server

We present an evaluation of the performance of an automated classification of the Hipparcos periodic variable stars into 26 types. The sub-sample with the most reliable variability types available in the literature is used to train supervised algorithms to characterize the type dependencies on a number of attributes. The most useful attributes evaluated with the random forest methodology include, in decreasing order of importance, the period, the amplitude, the V-I colour index, the absolute magnitude, the residual around the folded light-curve model, the magnitude distribution skewness and the amplitude of the second harmonic of the Fourier series model relative to that of the fundamental frequency. Random forests and a multi-stage scheme involving Bayesian network and Gaussian mixture methods lead to statistically equivalent results. In standard 10-fold cross-validation experiments, the rate of correct classification is between 90 and 100%, depending on the variability type. The main mis-classification case...

Dubath, P; Süveges, M; Blomme, J; López, M; Sarro, L M; De Ridder, J; Cuypers, J; Guy, L; Lecoeur, I; Nienartowicz, K; Jan, A; Beck, M; Mowlavi, N; De Cat, P; Lebzelter, T; Eyer, L

2011-01-01

26

Probabilistic norms and statistical convergence of random variables  

Directory of Open Access Journals (Sweden)

Full Text Available The paper extends certain stochastic convergence of sequences of Rk -valued random variables (namely, the convergence in probability, in Lp and almost surely to the context of E-valued random variables.

Mohamad Rafi Segi Rahmat

2009-03-01

27

Random forest automated supervised classification of Hipparcos periodic variable stars  

Science.gov (United States)

We present an evaluation of the performance of an automated classification of the Hipparcos periodic variable stars into 26 types. The sub-sample with the most reliable variability types available in the literature is used to train supervised algorithms to characterize the type dependencies on a number of attributes. The most useful attributes evaluated with the random forest methodology include, in decreasing order of importance, the period, the amplitude, the V-I colour index, the absolute magnitude, the residual around the folded light-curve model, the magnitude distribution skewness and the amplitude of the second harmonic of the Fourier series model relative to that of the fundamental frequency. Random forests and a multi-stage scheme involving Bayesian network and Gaussian mixture methods lead to statistically equivalent results. In standard 10-fold cross-validation (CV) experiments, the rate of correct classification is between 90 and 100 per cent, depending on the variability type. The main mis-classification cases, up to a rate of about 10 per cent, arise due to confusion between SPB and ACV blue variables and between eclipsing binaries, ellipsoidal variables and other variability types. Our training set and the predicted types for the other Hipparcos periodic stars are available online.

Dubath, P.; Rimoldini, L.; Süveges, M.; Blomme, J.; López, M.; Sarro, L. M.; De Ridder, J.; Cuypers, J.; Guy, L.; Lecoeur, I.; Nienartowicz, K.; Jan, A.; Beck, M.; Mowlavi, N.; De Cat, P.; Lebzelter, T.; Eyer, L.

2011-07-01

28

Summability of Double Independent Random Variables  

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Full Text Available We will examine double sequence to double sequence transformation of independent identically distribution random variables with respect to four-dimensional summability matrix methods. The main goal of this paper is the presentation of the following theorem. If max⁡k,l|am,n,k,l|=max⁡k,l|am,kan,l|=O(m−γ1O(n−γ2, γ1,γ2>0, then E|X⌣|1+1/γ1<∞ and E|X⌣⌣|1+1/γ2<∞ imply that Ym,n→μ almost sure P-convergence.

Ekrem Sava?

2008-09-01

29

Fuzzy Random Dependent-Chance Programming Models of Loan Portfolio  

Directory of Open Access Journals (Sweden)

Full Text Available The environment of loan in bank is very complex, there are not only random factors but also fuzzy factors, so the return rates of loan often have fuzzy random characteristic. Mean chance is a measure of fuzzy random variable. This paper proposes two fuzzy random dependent-chance programming models of loan portfolio, one is minimize the mean chance of a bad outcome under the certain expected return rate, one is maximize the mean chance of the prospective return rate under the certain expected return rate. Hybrid intelligent algorithms are employed to solve the models. Finally, two numerical examples are given to show the validity and feasibility of the models and algorithms.

Dongjing Pan

2011-02-01

30

Probability, random variables, and random processes theory and signal processing applications  

CERN Document Server

Probability, Random Variables, and Random Processes is a comprehensive textbook on probability theory for engineers that provides a more rigorous mathematical framework than is usually encountered in undergraduate courses. It is intended for first-year graduate students who have some familiarity with probability and random variables, though not necessarily of random processes and systems that operate on random signals. It is also appropriate for advanced undergraduate students who have a strong mathematical background. The book has the following features: Several app

Shynk, John J

2012-01-01

31

Ordering properties of convolutions of exponential random variables.  

Science.gov (United States)

Convolutions of independent random variables are usually compared. In this paper, after a synthetic comparison with respect to hazard rate ordering between sums of independent exponential random variables, we focus on the special case where one sum is identically distributed. So, for a given sum of n independent exponential random variables, we deduce the "best" Erlang-n bounds, with respect to each of the usual orderings: mean ordering, stochastic ordering, hazard rate ordering and likelihood ratio ordering. PMID:10408184

Bon, J L; P?lt?nea, E

1999-06-01

32

Environment-dependent continuous time random walk  

International Nuclear Information System (INIS)

A generalized continuous time random walk model which is dependent on environmental damping is proposed in which the two key parameters of the usual random walk theory: the jumping distance and the waiting time, are replaced by two new ones: the pulse velocity and the flight time. The anomalous diffusion of a free particle which is characterized by the asymptotical mean square displacement 2(t)> ? t? is realized numerically and analysed theoretically, where the value of the power index ? is in a region of 0 < ? < 2. Particularly, the damping leads to a sub-diffusion when the impact velocities are drawn from a Gaussian density function and the super-diffusive effect is related to statistical extremes, which are called rare-though-dominant events. (general)

33

COVAL - A computer code for random variables - How to use  

International Nuclear Information System (INIS)

COVAL CODE computes the probability distribution of a function of random variables given the probability distribution of these variables. The code is divided in two steps. The first step COVAL 1, computes functions in which each variable is contained only once. The second step COVAL 2, computes functions in which variables can be repeated

34

A note on convergence of weighted sums of random variables  

Directory of Open Access Journals (Sweden)

Full Text Available Under uniform integrability condition, some Weak Laws of large numbers are established for weighted sums of random variables generalizing results of Rohatgi, Pruitt and Khintchine. Some Strong Laws of Large Numbers are proved for weighted sums of pairwise independent random variables generalizing results of Jamison, Orey and Pruitt and Etemadi.

M. Bhaskara Rao

1985-12-01

35

Maximum Entropy Functions of Discrete Fuzzy Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available Due to deficiency of information, the probability distribution and membership functions of a fuzzy random variablecannot be obtained explicitly. It is a challenging work to find an appropriate probability distribution and membershipfunction when certain partial information about a fuzzy random variable is given, such as expected value or moments.This paper solves such problems for the maximum entropy of discrete fuzzy random variables with certain constraints. Agenetic algorithm is designed to solve the general maximum entropy model for discrete fuzzy random variables, which isillustrated by numerical experiment.

Lianlong Gao

2010-07-01

36

Dependent Variable Reliability and Determination of Sample Size.  

Science.gov (United States)

Arguments have recently been put forth that standard textbook procedures for determining the sample size necessary to achieve a certain level of power in a completely randomized design are incorrect when the dependent variable is fallible because they ignore measurement error. In fact, however, there are several correct procedures, one of which is…

Maxwell, Scott E.

37

Mathematical Discussions About Data Oriented Modeling of Uniform Random Variable  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, to show that UDPD is an acceptable and efficient model of uniform random variable, we introduce mathematical and numerical discussions for identification and characterization of it and also we show how to calculate some probabilistic parameters as mean, variance and mathematical expectation by using UDPD. Thus we provide a way to discuss random variables with n digits and make a new theory named numerical probability. This theory is enables us to discuss about random variables with predefined number of digits as required in applied and engineering systems.

Ahmad Habibizad Navin

2008-01-01

38

Approximation and Computation of Random Variables using Finite Elements  

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Full Text Available A method is introduced with which continuous random variables can be represented and linked with one another. The distribution functions of the random variables are approximated using a Finite Element approach in a finite interval [tmin; tmax]. As an example, two stochastically independent random variables are added by numerical computation of the convolution integral of their probability density functions.Es wird ein Verfahren vorgestellt, mit dem stetige Zufallsgrößen rechnerunterstützt dargestellt und miteinander verknüpft werden können. Die Verteilungsfunktionen der Zufallsgrößen werden mit einem Finite-Elemente-Ansatz in einem endlichen Intervall [tmin; tmax] approximiert. Die Addition zweier Zufallsgrößen wird durch numerische Berechnung des Faltungsintegrals durchgeführt.

Dr.-Ing. Helge Plehn

2005-07-01

39

Transcription, intercellular variability and correlated random walk.  

Science.gov (United States)

We develop a simple model for the random distribution of a gene product. It is assumed that the only source of variance is due to switching transcription on and off by a random process. Under the condition that the transition rates between on and off are constant we find that the amount of mRNA follows a scaled Beta distribution. Additionally, a simple positive feedback loop is considered. The simplicity of the model allows for an explicit solution also in this setting. These findings in turn allow, e.g., for easy parameter scans. We find that bistable behavior translates into bimodal distributions. These theoretical findings are in line with experimental results. PMID:18762199

Müller, Johannes; Kuttler, Christina; Hense, Burkhard A; Zeiser, Stefan; Liebscher, Volkmar

2008-11-01

40

Applying Free Random Variables to Random Matrix Analysis of Financial Data. Part I: A Gaussian Case  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We apply the concept of free random variables to doubly correlated (Gaussian) Wishart random matrix models, appearing for example in a multivariate analysis of financial time series, and displaying both inter-asset cross-covariances and temporal auto-covariances. We give a comprehensive introduction to the rich financial reality behind such models. We explain in an elementary way the main techniques of the free random variables calculus, with a view to promote them in the qu...

Burda, Z.; Jarosz, A.; Jurkiewicz, J.; Nowak, M. A.; Papp, G.; Zahed, I.

2006-01-01

 
 
 
 
41

Optical variability of quasars: a damped random walk  

CERN Document Server

A damped random walk is a stochastic process, defined by an exponential covariance matrix that behaves as a random walk for short time scales and asymptotically achieves a finite variability amplitude at long time scales. Over the last few years, it has been demonstrated, mostly but not exclusively using SDSS data, that a damped random walk model provides a satisfactory statistical description of observed quasar variability in the optical wavelength range, for rest-frame timescales from 5 days to 2000 days. The best-fit characteristic timescale and asymptotic variability amplitude scale with the luminosity, black hole mass, and rest wavelength, and appear independent of redshift. In addition to providing insights into the physics of quasar variability, the best-fit model parameters can be used to efficiently separate quasars from stars in imaging surveys with adequate long-term multi-epoch data, such as expected from LSST.

Ivezic, Zeljko

2013-01-01

42

Problems Identifying Independent and Dependent Variables  

Science.gov (United States)

This paper discusses one step from the scientific method--that of identifying independent and dependent variables--from both scientific and mathematical perspectives. It begins by analyzing an episode from a middle school mathematics classroom that illustrates the need for students and teachers alike to develop a robust understanding of…

Leatham, Keith R.

2012-01-01

43

On the freezing of variables in random constraint satisfaction problems  

CERN Document Server

The set of solutions of random constraint satisfaction problems (zero energy groundstates of mean-field diluted spin glasses) undergoes several structural phase transitions as the amount of constraints is increased. This set first breaks down into a large number of well separated clusters. At the freezing transition, which is in general distinct from the clustering one, some variables (spins) take the same value in all solutions of a given cluster. In this paper we study the critical behavior around the freezing transition, which appears in the unfrozen phase as the divergence of the sizes of the rearrangements induced in response to the modification of a variable. The formalism is developed on generic constraint satisfaction problems and applied in particular to the random satisfiability of boolean formulas and to the coloring of random graphs. The computation is first performed in random tree ensembles, for which we underline a connection with percolation models and with the reconstruction problem of inform...

Semerjian, Guilhem

2008-01-01

44

Energy-dependent variability from accretion flows  

CERN Document Server

We develop a formalism to calculate energy-dependent fractional variability (rms) in accretion flows. We consider rms spectra resulting from radial dependencies of the level of local variability (as expected from propagation of disturbances in accretion flows) assuming the constant shape of the spectrum emitted at a given radius. We consider the cases when the variability of the flow is either coherent or incoherent between different radial zones. As example local emission, we consider blackbody, Wien and thermal Comptonization spectra. In addition to numerical results, we present a number of analytical formulae for the resulting rms. We also find an analytical formula for the disc Wien spectrum, which we find to be a very good approximation to the disc blackbody. We compare our results to the rms spectrum observed in an ultrasoft state of GRS 1915+105.

Zdziarski, A A

2005-01-01

45

Accessible versus Holevo Information for a Binary Random Variable  

CERN Document Server

The accessible information I_acc(E) of an ensemble E is the maximum mutual information between a random variable encoded into quantum states, and the probabilistic outcome of a quantum measurement of the encoding. Accessible information is extremely difficult to characterize analytically; even bounds on it are hard to place. The celebrated Holevo bound states that accessible information cannot exceed chi(E), the quantum mutual information between the random variable and its encoding. However, for general ensembles, the gap between the I_acc(E) and chi(E) may be arbitrarily large. We consider the special case of a binary random variable, which often serves as a stepping stone towards other results in information theory and communication complexity. We show that for an ensemble E = {(p, rho_0), (1-p, rho_1)}, I_acc(E) >= H(p)- sqrt{4p(1-p) - chi(E)^2}.

Jain, R; Jain, Rahul; Nayak, Ashwin

2006-01-01

46

Laws of Large Numbers for Asymmetrical Cauchy Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available We generalize the Cauchy distribution so that we can have asymmetrical tails. This allows us to obtain unusual laws of large numbers involving weighted sums of these random variables. Unusual in the sense that even though in every case E|X|=∞, we can still obtain a nonzero limit for these weighted sums.

André Adler

2007-01-01

47

Complete Convergence for Weighted Sums of ??-Mixing Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available We obtain the complete convergence for weighted sums of ??-mixing random variables. Our result extends the result of Peligrad and Gut (1999 on unweighted average to a weighted average under a mild condition of weights. Our result also generalizes and sharpens the result of An and Yuan (2008.

Soo Hak Sung

2010-01-01

48

ADORAVA - A computer code to sum random variables  

International Nuclear Information System (INIS)

The ADORAVA computer code was carried out aiming to determine the moments of random variable sum distribution when moments are known. The ADORAVA computer code was developed to be applied in probabilistic safety analysis, more specifically for uncertainty propagation in fault trees. The description of ADORAVA algorithm, input, examples and the output of compiled code are presented. (M.C.K.)

49

Variability in the pattern of random amplified polymorphic DNA.  

Science.gov (United States)

The random amplified polymorphic DNA (RAPD) technique is a simple method to detect DNA polymorphism. It is sensitive to reaction conditions. Small changes in the reactants' concentration cause variations in amplification products. Using DNA from Asparagus officinalis, Dactylis glomerata, Mercurialis annua and Escherichia coli, we examined variability in the amplification pattern associated with reaction constituents. An increase in the ratio of Taq DNA polymerase to DNA in the reaction increased the number of amplified fragments. Increasing the concentration of primer resulted in the amplification of low molecular weight DNA fragments, while lowering the concentration resulted in high molecular weight fragments. Subsets of amplified fragments required different concentrations of magnesium for their highest intensity. Mechanical shearing of DNA obtained by sonication led to reduction in amplification of a subset of products. Enzymatic fragmentation of DNA by restriction enzymes led to loss or gain of specific fragments, depending on the DNA, primer, and restriction enzyme. RAPD markers of pooled DNA of anonymous pedigree should be critically evaluated for frequent 'false positive' markers. PMID:9504820

Khandka, D K; Tuna, M; Tal, M; Nejidat, A; Golan-Goldhirsh, A

1997-12-01

50

Limit theorems for multi-indexed sums of random variables  

CERN Document Server

Presenting the first unified treatment of limit theorems for multiple sums of independent random variables, this volume fills an important gap in the field. Several new results are introduced, even in the classical setting, as well as some new approaches that are simpler than those already established in the literature. In particular, new proofs of the strong law of large numbers and the Hajek-Renyi inequality are detailed. Applications of the described theory include Gibbs fields, spin glasses, polymer models, image analysis and random shapes. Limit theorems form the backbone of probability theory and statistical theory alike. The theory of multiple sums of random variables is a direct generalization of the classical study of limit theorems, whose importance and wide application in science is unquestionable. However, to date, the subject of multiple sums has only been treated in journals. The results described in this book will be of interest to advanced undergraduates, graduate students and researchers who ...

Klesov, Oleg

2014-01-01

51

Characteristics of quantum open systems: free random variables approach  

International Nuclear Information System (INIS)

Random Matrix Theory provides an interesting tool for modelling a number of phenomena where noises (fluctuations) play a prominent role. Various applications range from the theory of mesoscopic systems in nuclear and atomic physics to biophysical models, like Hopfield-type models of neural networks and protein folding. Random Matrix Theory is also used to study dissipative systems with broken time-reversal invariance providing a setup for analysis of dynamic processes in condensed, disordered media. In the paper we use the Random Matrix Theory (RMT) within the formalism of Free Random Variables (alias Blue's functions), which allows to characterize spectral properties of non-Hermitean ''Hamiltonians''. The relevance of using the Blue's function method is discussed in connection with application of non-Hermitean operators in various problems of physical chemistry. (author)

52

Parameter Learning in PRISM Programs with Continuous Random Variables  

CERN Document Server

Probabilistic Logic Programming (PLP), exemplified by Sato and Kameya's PRISM, Poole's ICL, De Raedt et al's ProbLog and Vennekens et al's LPAD, combines statistical and logical knowledge representation and inference. Inference in these languages is based on enumerative construction of proofs over logic programs. Consequently, these languages permit very limited use of random variables with continuous distributions. In this paper, we extend PRISM with Gaussian random variables and linear equality constraints, and consider the problem of parameter learning in the extended language. Many statistical models such as finite mixture models and Kalman filter can be encoded in extended PRISM. Our EM-based learning algorithm uses a symbolic inference procedure that represents sets of derivations without enumeration. This permits us to learn the distribution parameters of extended PRISM programs with discrete as well as Gaussian variables. The learning algorithm naturally generalizes the ones used for PRISM and Hybrid ...

Islam, Muhammad Asiful; Ramakrishnan, I V

2012-01-01

53

An Exponential Inequality for Negatively Associated Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available An exponential inequality is established for identically distributed negatively associated random variables which have the finite Laplace transforms. The inequality improves the results of Kim and Kim (2007, Nooghabi and Azarnoosh (2009, and Xing et al. (2009. We also obtain the convergence rate for the strong law of large numbers, which improves the corresponding ones of Kim and Kim, Nooghabi and Azarnoosh, and Xing et al.

Sung SooHak

2009-01-01

54

An Exponential Inequality for Negatively Associated Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available An exponential inequality is established for identically distributed negatively associated random variables which have the finite Laplace transforms. The inequality improves the results of Kim and Kim (2007, Nooghabi and Azarnoosh (2009, and Xing et al. (2009. We also obtain the convergence rate O(1n1/2(log?n?1/2 for the strong law of large numbers, which improves the corresponding ones of Kim and Kim, Nooghabi and Azarnoosh, and Xing et al.

Soo Hak Sung

2009-01-01

55

Problems of variance reduction in the simulation of random variables  

International Nuclear Information System (INIS)

The definition of the uniform linear generator is given and some of the mostly used tests to evaluate the uniformity and the independence of the obtained determinations are listed. The problem of calculating, through simulation, some moment W of a random variable function is taken into account. The Monte Carlo method enables the moment W to be estimated and the estimator variance to be obtained. Some techniques for the construction of other estimators of W with a reduced variance are introduced

56

Positive definite functions and multidimensional versions of random variables  

CERN Document Server

We say that a random vector $X=(X_1,...,X_n)$ in $R^n$ is an $n$-dimensional version of a random variable $Y$ if for any $a\\in R^n$ the random variables $\\sum a_iX_i$ and $\\gamma(a) Y$ are identically distributed, where $\\gamma:R^n\\to [0,\\infty)$ is called the standard of $X.$ An old problem is to characterize those functions $\\gamma$ that can appear as the standard of an $n$-dimensional version. In this paper, we prove the conjecture of Lisitsky that every standard must be the norm of a space that embeds in $L_0.$ This result is almost optimal, as the norm of any finite dimensional subspace of $L_p$ with $p\\in (0,2]$ is the standard of an $n$-dimensional version ($p$-stable random vector) by the classical result of P.L\\`evy. An equivalent formulation is that if a function of the form $f(\\|\\cdot\\|_K)$ is positive definite on $R^n,$ where $K$ is an origin symmetric star body in $R^n$ and $f:R\\to R$ is an even continuous function, then either the space $(R^n,\\|\\cdot\\|_K)$ embeds in $L_0$ or $f$ is a constant fu...

Koldobsky, Alexander

2009-01-01

57

A Note on Strong Laws of Large Numbers for Dependent Random Sets and Fuzzy Random Sets  

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Full Text Available This paper deals with a sequence of identically distributed random sets or fuzzy random sets with -mixing dependence in a separable Banach space. The strong laws of large numbers for these two sequences are derived under Kuratowski-Mosco sense.

Fu Ke-Ang

2010-01-01

58

A Note on Strong Laws of Large Numbers for Dependent Random Sets and Fuzzy Random Sets  

Directory of Open Access Journals (Sweden)

Full Text Available This paper deals with a sequence of identically distributed random sets or fuzzy random sets with ?(??-mixing dependence in a separable Banach space. The strong laws of large numbers for these two sequences are derived under Kuratowski-Mosco sense.

Ke-Ang Fu

2010-01-01

59

On inequalities for sums of bounded random variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Let $\\eta_{1},\\eta_2,...$ be independent (not necessarily identically distributed) zero-mean random variables (r.v.'s) such that $|\\eta_i|\\le1$ almost surely for all $i$, and let $Z$ stand for a standard normal r.v. Let $a_1,a_2,...$ be any real numbers such that $a_1^2+a_2^2+...=1.$ It is shown that then $$ \\P(a_1\\eta_1+a_2\\eta_2+...\\ge x) \\le \\P(Z\\ge x-\\la/x) \\forall x>0, $$ where $\\la := \\ln\\frac{2e^3}9=1.495...$. The proof relies on (i) another probability inequality and...

Pinelis, Iosif

2006-01-01

60

Spherically symmetric random walks. II. Dimensionally dependent critical behavior  

International Nuclear Information System (INIS)

A recently developed model of random walks on a D-dimensional hyperspherical lattice, where D is not restricted to integer values, is extended to include the possibility of creating and annihilating random walkers. Steady-state distributions of random walkers are obtained for all dimensions D approx-gt 0 by solving a discrete eigenvalue problem. These distributions exhibit dimensionally dependent critical behavior as a function of the birth rate. This remarkably simple model exhibits a second-order phase transition with a universal, nontrivial critical exponent for all dimensions D approx-gt 0. copyright 1996 The American Physical Society

 
 
 
 
61

Strong Law of Large Numbers for Weighted Sum of Exchangeable Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, the Marcinkiewicz type theorem is extended to the case of exchangeable random variables. As a generalization,we also obtain two strong laws of large numbers on the weighted sum of exchangeable random variables

Zhaoxia Huang

2009-08-01

62

Partial summations of stationary sequences of non-Gaussian random variables  

DEFF Research Database (Denmark)

The distribution of the sum of a finite number of identically distributed random variables is in many cases easily determined given that the variables are independent. The moments of any order of the sum can always be expressed by the moments of the single term without computational problems. However, in the case of dependency between the terms even calculation of a few of the first moments of the sum presents serious computational problems. By use of computerized symbol manipulations it is practicable to obtain exact moments of partial sums of stationary sequences of mutually dependent lognormal variables or polynomials of standard Gaussian variables. The dependency structure is induced by specifying the autocorrelation structure of the sequence of standard Gaussian variables. Particularly useful polynomials are the Winterstein approximations that distributionally fit with non-Gaussian variables up to the moments of the fourth order [Winterstein, S. R. Nonlinear vibration models for extremes and fatigue. J. Engng Mech. ASCE 114 (1988) 1772-1790](1). A method to obtain the Winterstein approximation to a partial sum of a sequence of Winterstein approximations is explained and results are given for different autocorrelation functions of the generic Gaussian sequence. The primary purpose of the investigation is to provide a tool for judging the validity of the central limit theorem argument in specific applicational situations occurring in stochastic mechanics, that is, to judge the speed of convergence of the distribution of a sum (or an integral) of mutually dependent random variables to the Gaussian distribution. The paper is closely related to the work in Ditlevsen el al. [Ditlevsen, O., Mohr, G. & Hoffmeyer, P. Integration of non-Gaussian fields. Prob. Engng Mech 11 (1996) 15-23](2).

Mohr, Gunnar; Ditlevsen, Ove Dalager

1996-01-01

63

Nonuniversal dependence of spatiotemporal regularity on randomness in coupling connections.  

Science.gov (United States)

We investigate the spatiotemporal dynamics of a network of coupled nonlinear oscillators, modeled by sine-circle maps, with varying degrees of randomness in coupling connections. We show that the change in the basin of attraction of the spatiotemporal fixed point due to varying fraction of random links, p , is crucially related to the nature of the local dynamics. Even the qualitative dependence of the spatiotemporal regularity on p changes drastically as the angular frequency of the oscillators changes, ranging from a monotonic increase or monotonic decrease to nonmonotonic variation. Thus it is evident here that the influence of random coupling connections on spatiotemporal order is highly nonuniversal and depends very strongly on the nodal dynamics. PMID:19256918

Jabeen, Zahera; Sinha, Sudeshna

2008-12-01

64

Automatic Probabilistic Program Verification through Random Variable Abstraction  

CERN Document Server

The weakest pre-expectation calculus has been proved to be a mature theory to analyze quantitative properties of probabilistic and nondeterministic programs. We present an automatic method for proving quantitative linear properties on any denumerable state space using iterative backwards fixed point calculation in the general framework of abstract interpretation. In order to accomplish this task we present the technique of random variable abstraction (RVA) and we also postulate a sufficient condition to achieve exact fixed point computation in the abstract domain. The feasibility of our approach is shown with two examples, one obtaining the expected running time of a probabilistic program, and the other the expected gain of a gambling strategy. Our method works on general guarded probabilistic and nondeterministic transition systems instead of plain pGCL programs, allowing us to easily model a wide range of systems including distributed ones and unstructured programs. We present the operational and weakest pr...

Barsotti, Damián; 10.4204/EPTCS.28.3

2010-01-01

65

Inference in Probabilistic Logic Programs with Continuous Random Variables  

CERN Document Server

Probabilistic Logic Programming (PLP), exemplified by Sato and Kameya's PRISM, Poole's ICL, Raedt et al's ProbLog and Vennekens et al's LPAD, is aimed at combining statistical and logical knowledge representation and inference. A key characteristic of PLP frameworks is that they are conservative extensions to non-probabilistic logic programs which have been widely used for knowledge representation. PLP frameworks extend traditional logic programming semantics to a distribution semantics, where the semantics of a probabilistic logic program is given in terms of a distribution over possible models of the program. However, the inference techniques used in these works rely on enumerating sets of explanations for a query answer. Consequently, these languages permit very limited use of random variables with continuous distributions. In this paper, we present a symbolic inference procedure that uses constraints and represents sets of explanations without enumeration. This permits us to reason over PLPs with Gaussian...

Islam, Muhammad Asiful; Ramakrishnan, I V

2011-01-01

66

A Strong Limit Theorem for Functions of Continuous Random Variables and an Extension of the Shannon-McMillan Theorem  

Directory of Open Access Journals (Sweden)

Full Text Available By means of the notion of likelihood ratio, the limit properties of the sequences of arbitrary-dependent continuous random variables are studied, and a kind of strong limit theorems represented by inequalities with random bounds for functions of continuous random variables is established. The Shannon-McMillan theorem is extended to the case of arbitrary continuous information sources. In the proof, an analytic technique, the tools of Laplace transform, and moment generating functions to study the strong limit theorems are applied.

Gaorong Li

2008-05-01

67

Radio Variability and Random Walk Noise Properties of Four Blazars  

CERN Document Server

We present the results of a time series analysis of the long-term radio lightcurves of four blazars: 3C 279, 3C 345, 3C 446, and BL Lacertae. We exploit the data base of the University of Michigan Radio Astronomy Observatory (UMRAO) monitoring program which provides densely sampled lightcurves spanning 32 years in time in three frequency bands located at 4.8, 8, and 14.5 GHz. Our sources show mostly flat or inverted (spectral indices -0.5 < alpha < 0) spectra, in agreement with optically thick emission. All lightcurves show strong variability on all time scales. Analyzing the time lags between the lightcurves from different frequency bands, we find that we can distinguish high-peaking flares and low-peaking flares in accord with the classification of Valtaoja et al. (1992). The periodograms (temporal power spectra) of the observed lightcurves are consistent with random-walk powerlaw noise without any indication of (quasi-)periodic variability. The fact that all four sources studied are in agreement with...

Park, Jong-Ho

2014-01-01

68

Analysis of discrete dependent variable models with spatial correlation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we consider ML estimation for a broad class of parameter-driven models for discrete dependent variables with spatial correlation. Under this class of models, which includes spatial discrete choice models, spatial Tobit models and spatial count data models, the dependent variable is driven by a latent stochastic state variable which is specified as a linear spatial regression model. The likelihood is a high-dimensional integral whose dimension depends on the sample size. For its ...

Liesenfeld, Roman; Richard, Jean-franc?ois; Vogler, Jan

2013-01-01

69

On the Spatial Dependence Structure of Isotropic Pairwise Gaussian-Markov Random Field Models  

CERN Document Server

Markov Random Field (MRF) models are powerful tools for contextual modeling. However, little is known about how the spatial dependence between its elements is encoded in terms of statistical information, more precisely, information-theoretic measures. In this paper, we enlight the connection between Fisher information, Shannon entropy and spatial properties of the random field in the case of Gaussian variables (a Gaussian Markov random field), by defining analytical expressions to compute the local and global versions of these measures using Besag's pseudo-likelihood function (conditional independence assumption). Besides, we use the derived expressions to define an exact expression for the asymptotic variance of the maximum pseudo-likelihood estimator of the spatial dependence parameter, showing that it does not reach the Cramer-R\\'ao lower bound, since information equality fails. The obtained results provide a rich framework for extraction of relevant statistical information in a variety of MRF applications...

Levada, Alexandre L M

2011-01-01

70

A queueing system with a fixed accumulation level, random server capacity and capacity dependent service time  

Directory of Open Access Journals (Sweden)

Full Text Available This paper introduces a bulk queueing system with a single server processing groups of customers of a variable size. If upon completion of service the queueing level is at least r the server takes a batch of size r and processes it a random time arbitrarily distributed. If the queueing level is less than r the server idles until the queue accumulates r customers in total. Then the server capacity is generated by a random number equals the batch size taken for service which lasts an arbitrarily distributed time dependent on the batch size.

Lotfi Tadj

1992-03-01

71

Phase Dependent Spectroscopy of Mira Variable Stars  

CERN Document Server

Spectroscopic measurements of Mira variable stars, as a function of phase, probe the stellar atmospheres and underlying pulsation mechanisms. For example, measuring variations in TiO, VO, and ZrO with phase can be used to help determine whether these molecular species are produced in an extended region above the layers where Balmer line emission occurs or below this shocked region. Using the same methods, the Balmer-line increment, where the strongest Balmer line at phase zero is H-delta and not H-alpha can be measured and explanations tested, along with another peculiarity, the absence of the H-epsilon line in the spectra of Miras when other Balmer lines are strong. We present new spectra covering the spectral range from 6200 Angstroms to 9000 Angstroms of 20 Mira variables. A relationship between variations in the CaII IR triplet and H-alpha as a function of phase support the hypothesis that H-epsilon's observational characteristics result from an interaction of H-epsilon photons with the CaII H line. New p...

Castelaz, M W; Caton, D B; Piontek, R A; Castelaz, Michael W.; Luttermoser, Donald G.; Caton, Daniel B.; Piontek, Robert A.

2000-01-01

72

Maximum Entropy Functions of Discrete Random Fuzzy Variables and Genetic Algorithm  

Directory of Open Access Journals (Sweden)

Full Text Available Due to deficiency of information, the membership functions and probability distribution of a random fuzzy variable cannot be obtainedexplicitly. It is a challenging work to find an appropriate membership function and an appropriate probability distribution when certain partial information about a random fuzzy variable is given, such as expected value or moments. This paper solves such problems for the maximum entropy of discrete random fuzzy variables with certain constraints. A genetic algorithm is designed to solve the general maximum entropy model for discrete random fuzzy variables, which is illustrated by some numerical experiments.

Lianlong Gao

2010-10-01

73

The impact of random frequency-dependent mutations on the average population fitness  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background In addition to selection, the process of evolution is accompanied by stochastic effects, such as changing environmental conditions, genetic drift and mutations. Commonly it is believed that without genetic drift, advantageous mutations quickly fixate in a halpoid population due to strong selection and lead to a continuous increase of the average fitness. This conclusion is based on the assumption of constant fitness. However, for frequency dependent fitness, where the fitness of an individual depends on the interactions with other individuals in the population, this does not hold. Results We propose a mathematical model that allows to understand the consequences of random frequency dependent mutations on the dynamics of an infinite large population. The frequencies of different types change according to the replicator equations and the fitness of a mutant is random and frequency dependent. To capture the interactions of different types, we employ a payoff matrix of variable size and thus are able to accommodate an arbitrary number of mutations. We assume that at most one mutant type arises at a time. The payoff entries to describe the mutant type are random variables obeying a probability distribution which is related to the fitness of the parent type. Conclusions We show that a random mutant can decrease the average fitness under frequency dependent selection, based on analytical results for two types and simulations for n types. Interestingly, in the case of at most two types the probabilities to increase or decrease the average fitness are independent of the concrete probability density function. Instead, they only depend on the probability that the payoff entries of the mutant are larger than the payoff entries of the parent type.

Huang Weini

2012-08-01

74

Variable Voltage Source Inverter with controlled frequency spectrum based on Random Pulse Width Modulation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper presents a new method for single phase variable voltage inverter based on Random Pulse Width Modulation. In Random Pulse Width Modulation based inverter, the frequency spectrum of the output current and voltage waveforms becomes continuous because of the randomization of the switching function of the devices controlling the output voltages. This paper establishes a theory that if the distributions of the random numbers generated by the random source are kept within certain limi...

Muhammad Farrukh Yaqub; Tahir Izhar; Muhammad Safian Adeel

2012-01-01

75

Development of a localized probabilistic sensitivity method to determine random variable regional importance  

International Nuclear Information System (INIS)

There are many methods to identify the important variable out of a set of random variables, i.e., “inter-variable” importance; however, to date there are no comparable methods to identify the “region” of importance within a random variable, i.e., “intra-variable” importance. Knowledge of the critical region of an input random variable (tail, near-tail, and central region) can provide valuable information towards characterizing, understanding, and improving a model through additional modeling or testing. As a result, an intra-variable probabilistic sensitivity method was developed and demonstrated for independent random variables that computes the partial derivative of a probabilistic response with respect to a localized perturbation in the CDF values of each random variable. These sensitivities are then normalized in absolute value with respect to the largest sensitivity within a distribution to indicate the region of importance. The methodology is implemented using the Score Function kernel-based method such that existing samples can be used to compute sensitivities for negligible cost. Numerical examples demonstrate the accuracy of the method through comparisons with finite difference and numerical integration quadrature estimates. - Highlights: ? Probabilistic sensitivity methodology. ? Determines the “region” of importance within random variables such as left tail, near tail, center, right tail, etc. ? Uses the Score Function approach to reuse the samples, hence, negligible cost. ? No restrictions on the random variable types or limit states.

76

Bias in random forest variable importance measures: Illustrations, sources and a solution  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract Background Variable importance measures for random forests have been receiving increased attention as a means of variable selection in many classification tasks in bioinformatics and related scientific fields, for instance to select a subset of genetic markers relevant for the prediction of a certain disease. We show that random forest variable importance measures are a sensible means for variable selection in many applications, but are not reliable in situations whe...

Hothorn Torsten; Zeileis Achim; Boulesteix Anne-Laure; Strobl Carolin

2007-01-01

77

Explaining the Dark Energy, Baryon and Dark Matter Coincidence via Domain-Dependent Random Densities  

CERN Document Server

The dark energy, dark matter and baryon densities in the Universe are observed to be similar, with a factor of no more than 20 between the largest and smallest densities. We show that this coincidence can be understood via superhorizon domains of randomly varying densities when the baryon density at initial collapse of galaxy-forming perturbations is determined by anthropic selection. The baryon and dark matter densities are assumed to be dependent on random variables \\theta_{d} and \\theta_{b} according to \\rho_{dm} ~ \\theta_{d}^{\\alpha} and \\rho_{b} ~ \\theta_{b}^{\\beta}, while the effectively constant dark energy density is dependent upon a random variable \\phi_{Q} according to \\rho_{Q} ~ \\phi_{Q}^{n}. The ratio of the baryon density to the dark energy density at initial collapse, r_{Q}, and the baryon-to-dark matter ratio, r, are then determined purely statistically, with no dependence on the anthropically-preferred baryon density. We compute the probability distribution for r_{Q} and r and show that the ob...

McDonald, John

2013-01-01

78

Explaining the dark energy, baryon and dark matter coincidence via domain-dependent random densities  

International Nuclear Information System (INIS)

The dark energy, dark matter and baryon densities in the Universe are observed to be similar, with a factor of no more than 20 between the largest and smallest densities. We show that this coincidence can be understood via superhorizon domains of randomly varying densities when the baryon density at initial collapse of galaxy-forming perturbations is determined by anthropic selection. The baryon and dark matter densities are assumed to be dependent on random variables ?d and ?b according to ?dm??d? and ?b??b?, while the effectively constant dark energy density is dependent upon a random variable ?Q according to ?Q??Qn. The ratio of the baryon density to the dark energy density at initial collapse, rQ, and the baryon-to-dark matter ratio, r, are then determined purely statistically, with no dependence on the anthropically-preferred baryon density. We compute the probability distribution for rQ and r and show that the observed values of rQ and r can be naturally understood within this framework. In particular, for the case ? = 2, ? = 1 and n = 4, which can be physically realized via a combination of axion dark matter, Affleck-Dine baryogenesis and frozen quintessence with a ?Q4 potential, the range of rQ and r which corresponds to the observed Universe is a quite natural, with a probability which is broadly similar to other ranges of rQ and r

79

Inter- and intra-specific patterns of density dependence and population size variability in Salmoniformes.  

Science.gov (United States)

Population dynamics are typically affected by a combination of density-independent and density-dependent factors, the latter of which have been conceptually and theoretically linked with how variable population sizes are over time-which in turn has been tied to how prone populations are to extinction. To address evidence for the occurrence of density dependence and its relationship with population size variability (pv), we quantified each of these for 126 populations of 8 species of Salmoniformes. Using random-effects models, we partitioned variation in the strength of density dependence and the magnitude of pv between and within species and estimated the correlation of density dependence and population size variability at both the between- and within-species levels. We found that variation in the strength of density dependence was predominately within species (I(2) = 0.12 [corrected] variation in population size variability was distributed both between and within species (I(2) = 0.40). Contrary to theoretical and conceptual expectations, the strength of density dependence and the magnitude of population size variability were positively correlated at the between species level (r = 0.90), although this estimate had 95 % credibility intervals (Bayesian analogues to confidence intervals) that overlapped zero. The within-species correlation between density dependence and population size variability was not distinguishable from zero. Given that density dependence for Salmoniformes was highly variable within species, we next determined the joint effects of intrinsic (density-dependent) and extrinsic (density-independent) factors on the population dynamics of a threatened salmonid, the Lahontan cutthroat trout (Oncorhynchus clarkii henshawi). We found that density-dependent and -independent factors additively contributed to population dynamics. This finding suggests that the observed within-species variability in density dependence might be attributable to local differences in the strength of density-independent factors. PMID:22776906

Dochtermann, Ned A; Peacock, Mary M

2013-01-01

80

Hajek-Renyi-type inequality for some nonmonotonic functions of associated random variables  

Directory of Open Access Journals (Sweden)

Full Text Available Let be a sequence of nonmonotonic functions of associated random variables. We derive a Newman and Wright (1981 type of inequality for the maximum of partial sums of the sequence and a Hajek-Renyi-type inequality for nonmonotonic functions of associated random variables under some conditions. As an application, a strong law of large numbers is obtained for nonmonotonic functions of associated random varaibles.

Rao BLS Prakasa

2006-01-01

 
 
 
 
81

Stable limits for sums of dependent infinite variance random variables.  

DEFF Research Database (Denmark)

The aim of this paper is to provide conditions which ensure that the affinely transformed partial sums of a strictly stationary process converge in distribution to an infinite variance stable distribution. Conditions for this convergence to hold are known in the literature. However, most of these results are qualitative in the sense that the parameters of the limit distribution are expressed in terms of some limiting point process. In this paper we will be able to determine the parameters of the limiting stable distribution in terms of some tail characteristics of the underlying stationary sequence.We will apply our results to some standard time seriesmodels, including the GARCH(1, 1) process and its squares, the stochastic volatility models and solutions to stochastic recurrence equations.

Bartkiewicz, Katarszyna; Jakubowski, Adam

2011-01-01

82

Stable limits for sums of dependent infinite variance random variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The aim of this paper is to provide conditions which ensure that the affinely transformed partial sums of a strictly stationary process converge in distribution to an infinite variance stable distribution. Conditions for this convergence to hold are known in the literature. However, most of these results are qualitative in the sense that the parameters of the limit distribution are expressed in terms of some limiting point process. In this paper we will be able to determine ...

Bartkiewicz, Katarzyna; Jakubowski, Adam; Mikosch, Thomas; Wintenberger, Olivier

2009-01-01

83

Infinite variance stable limits for sums of dependent random variables  

CERN Document Server

The aim of this paper is to provide conditions which ensure that the affinely transformed partial sums of a strictly stationary process converge in distribution to an in?nite variance stable distribution. Conditions for this convergence to hold are known in the literature. However, most of these results are qualitative in the sense that the parameters of the limit distribution are expressed in terms of some limiting point process. In this paper we will be able to determine the parameters of the limiting stable distribution in terms of some tail characteristics of the underlying stationary sequence. We will apply our results to some standard time series models, including the GARCH(1, 1) process and its squares, the stochastic volatility models and solutions to stochastic recurrence equations.

Bartkiewicz, Katarzyna; Mikosch, Thomas; Wintenberger, Olivier

2009-01-01

84

A preliminary, randomized trial of aerobic exercise for alcohol dependence.  

Science.gov (United States)

Interventions targeting physical activity may be valuable as an adjunct to alcohol treatment, but have been relatively untested. In the current study, alcohol dependent, physically sedentary patients were randomized to: a 12-week moderate-intensity, group aerobic exercise intervention (AE; n=25) or a brief advice to exercise intervention (BA-E; n=23). Results showed that individuals in AE reported significantly fewer drinking and heavy drinking days, relative to BA-E during treatment. Furthermore adherence to AE strengthened the beneficial effect of intervention on alcohol use outcomes. While high levels of moderate-intensity exercise appeared to facilitate alcohol recovery regardless of intervention arm, attending the group-based AE intervention seemed to further enhance the positive effects of exercise on alcohol use. Study findings indicate that a moderate intensity, group aerobic exercise intervention is an efficacious adjunct to alcohol treatment. Improving adherence to the intervention may enhance its beneficial effects on alcohol use. PMID:24666811

Brown, Richard A; Abrantes, Ana M; Minami, Haruka; Read, Jennifer P; Marcus, Bess H; Jakicic, John M; Strong, David R; Dubreuil, Mary Ella; Gordon, Alan A; Ramsey, Susan E; Kahler, Christopher W; Stuart, Gregory L

2014-07-01

85

Conditional expectation and Bayes' rule for quantum random variables and positive operator valued measures  

CERN Document Server

A quantum probability measure is a function on a sigma-algebra of subsets of a (locally compact and Hausdorff) sample space that satisfies the formal requirements for a measure, but whose values are positive operators acting on a complex Hilbert space, and a quantum random variable is a measurable operator-valued function. Although quantum probability measures and random variables are used extensively in quantum mechanics, some of the fundamental probabilistic features of these structures remain to be determined. In this paper we take a step toward a better mathematical understanding of quantum random variables and quantum probability measures by introducing a quantum analogue for the expected value of a quantum random variable relative to a quantum probability measure. In so doing we are led to theorems for a change of quantum measurement and a change of quantum variables. We also introduce a quantum conditional expectation which results in quantum versions of some standard identities for Radon-Nikodym deriv...

Farenick, Douglas

2011-01-01

86

Variable Voltage Source Inverter with controlled frequency spectrum based on Random Pulse Width Modulation  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents a new method for single phase variable voltage inverter based on Random Pulse Width Modulation. In Random Pulse Width Modulation based inverter, the frequency spectrum of the output current and voltage waveforms becomes continuous because of the randomization of the switching function of the devices controlling the output voltages. This paper establishes a theory that if the distributions of the random numbers generated by the random source are kept within certain limit with respect to the peak value of reference sinusoidal waveform, the frequency spectrum can be controlled. On the basis of the results, a novel drive using variable tap changing transformer (optional and adaptive random number generator, to control the ratio between the numbers generated by the random source and the reference waveform has been suggested that will guarantee a better power quality profile for a broad range of output voltages.

Muhammad Farrukh Yaqub

2012-01-01

87

Multivariate non-normally distributed random variables in climate research – introduction to the copula approach  

Directory of Open Access Journals (Sweden)

Full Text Available Probability distributions of multivariate random variables are generally more complex compared to their univariate counterparts which is due to a possible nonlinear dependence between the random variables. One approach to this problem is the use of copulas, which have become popular over recent years, especially in fields like econometrics, finance, risk management, or insurance. Since this newly emerging field includes various practices, a controversial discussion, and vast field of literature, it is difficult to get an overview. The aim of this paper is therefore to provide an brief overview of copulas for application in meteorology and climate research. We examine the advantages and disadvantages compared to alternative approaches like e.g. mixture models, summarize the current problem of goodness-of-fit (GOF tests for copulas, and discuss the connection with multivariate extremes. An application to station data shows the simplicity and the capabilities as well as the limitations of this approach. Observations of daily precipitation and temperature are fitted to a bivariate model and demonstrate, that copulas are valuable complement to the commonly used methods.

P. Friederichs

2008-10-01

88

On the supremum of the tails of normalized sums of independent Rademacher random variables  

CERN Document Server

A well-known longstanding conjecture on the supremum of the tails of normalized sums of independent Rademacher random variables is disproved. A related conjecture, also recently disproved, is discussed.

Pinelis, Iosif

2012-01-01

89

Extremal distributions for tail probabilities of sums of iid random variables on [0,1  

CERN Document Server

Two old conjectures from problem sections, one of which from SIAM Review, concern the question of finding distributions that maximize P(Sn <= t), where Sn is the sum of i.i.d. random variables X1, ..., Xn on the interval [0,1], satisfying E[X1]=m. In this paper a Lagrange multiplier technique is applied to this problem, yielding necessary conditions for distributions to be extremal, for arbitrary n. For n=2, a complete solution is derived from them: extremal distributions are discrete and have one of the following supports, depending on m and t: {0,t}, {t-1,1}, {t/2,1}, or {0,t,1}. These results suffice to refute both conjectures. However, acquired insight naturally leads to a revised conjecture: that extremal distributions always have at most three support points and belong to a (for each n, specified) finite collection of two and three point distributions.

Meester, Ludolf E

2008-01-01

90

Random variables as pathwise integrals with respect to fractional Brownian motion  

CERN Document Server

We show that a pathwise stochastic integral with respect to fractional Brownian motion with an adapted integrand $g$ can have any prescribed distribution, moreover, we give both necessary and sufficient conditions when random variables can be represented in this form. We also prove that any random variable is a value of such integral in some improper sense. We discuss some applications of these results, in particular, to fractional Black--Scholes model of financial market.

Mishura, Yuliya; Valkeila, Esko

2011-01-01

91

Moderate deviations for stationary sequences of Hilbert valued bounded random variables  

CERN Document Server

In this paper, we derive the moderate deviation principle for stationary sequences of bounded random variables with values in a Hilbert space. The conditions obtained are expressed in terms of martingale-type conditions. The main tools are martingale approximations and a new Hoeffding inequality for non adpated sequences of Hilbert-valued random variables. Applications to Cramer-Von Mises statistics, functions of linear processes and stable Markov chains are given.

Dede, Sophie

2008-01-01

92

The rates of convergence for generalized entropy of the normalized sums of IID random variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider the generalized differential entropy of normalized sums of independent and identically distributed (IID) continuous random variables. We prove that the R\\'{e}nyi entropy and Tsallis entropy of order $\\alpha\\ (\\alpha>0)$ of the normalized sum of IID continuous random variables with bounded moments are convergent to the corresponding R\\'{e}nyi entropy and Tsallis entropy of the Gaussian limit, and obtain sharp rates of convergence.

Cui, Hongfei; Sun, Jianqiang; Ding, Yiming

2011-01-01

93

On the use of fractional calculus for the probabilistic characterization of random variables  

CERN Document Server

In this paper, the classical problem of the probabilistic characterization of a random variable is re-examined. A random variable is usually described by the probability density function (PDF) or by its Fourier transform, namely the characteristic function (CF). The CF can be further expressed by a Taylor series involving the moments of the random variable. However, in some circumstances, the moments do not exist and the Taylor expansion of the CF is useless. This happens for example in the case of $\\alpha$--stable random variables. Here, the problem of representing the CF or the PDF of random variables (r.vs) is examined by introducing fractional calculus. Two very remarkable results are obtained. Firstly, it is shown that the fractional derivatives of the CF in zero coincide with fractional moments. This is true also in case of CF not derivable in zero (like the CF of $\\alpha$--stable r.vs). Moreover, it is shown that the CF may be represented by a generalized Taylor expansion involving fractional moments. ...

Cottone, Giulio; 10.1016/j.probengmech.2008.08.002

2013-01-01

94

The dependence of crack closure on fatigue loading variables  

Science.gov (United States)

Optical and electron microscopy and stereoimaging techniques are used to determine crack opening loads local to the crack tip in aluminum alloy 7091 and 304 stainless steel. It is found that the crack peels open nonlinearly such that significant load increases are necessary to open the crack the last few microns from the tip. The stress intensity range ratio is shown to depend on fatigue loading variables according to a given relationship.

Hudak, Stephen J., Jr.; Davidson, David L.

1988-01-01

95

Nonlinear scale dependence and spatiotemporal variability in planktonic food webs  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Zooplankton food webs of Lake Okeechobee, Florida, were analyzed in order to examine spatiotemporal variability and test for scale dependence of major food web properties. 46 webs were constructed from data collected during several years (1988-92) at six locations. For all these webs, the following food web properties were calculated: number of species, total links, links per species, connectance, percentage of top and intermediate species, and food chain length. We did not find any statistic...

Carney Heath J.; Havens Karl E.; Bersier, Louis-fe?lix

2009-01-01

96

Bayesian Approaches for Limited Dependent Variable Change Point Problems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Limited dependent variable (LDV) data are common in political science, and political methodologists have given much good advice on dealing with them. We review some methods for LDV "change point problems" and demonstrate the use of Bayesian approaches for count, binary, and duration-type data. Our applications are drawn from American politics, Comparative politics, and International Political Economy. We discuss the tradeoffs both philosophically and computationally. We conclude with possibil...

Spirling, Arthur P.

2007-01-01

97

Epoch-dependent absorption line profile variability in lambda Cep  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6Ief star lambda Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star. Our data reveal a much more complex situation. The frequency content of the power spectrum considerably changes from one epoch to the other. We find no stable frequency that can unambiguously be attributed to pulsations. The epoch-dependence of the frequencies and variability ...

Uuh-sonda, J. M.; Rauw, Gre?gor; Eenens, P.; Mahy, L.; Palate, Matthieu; Gosset, Eric; Flores, C. A.

2014-01-01

98

Numerical simulation of random paths with a curvature dependent action  

CERN Document Server

We have performed a numerical simulation of an ensemble of fixed length closed random paths, embedded in R^3, weighted with an action proportional to both, the length of the path and the curvature. This model can be considered as an one dimensional analog of the theory of crystaline random surfaces. Two different regimes have been identified, namely Brownian paths (small curvature coupling) and rigid paths (large curvature coupling). The transition between this two regimes seems to be rather smooth, but, nevertheless, a continuous phase transition cannot be excluded. This transition would be the analogous of the crumpling transition.

Baig, M; Jaramillo, A

1996-01-01

99

Ultraviolet variability of quasars: dependence on the accretion rate  

Science.gov (United States)

Aims: Although the variability in the ultraviolet and optical domain is one of the major characteristics of quasars, the dominant underlying mechanisms are still poorly understood. There is a broad consensus on the relationship between the strength of the variability and such quantities as time-lag, wavelength, luminosity, and redshift. However, evidence on a dependence on the fundamental parameters of the accretion process is still inconclusive. This paper is focused on the correlation between the ultraviolet quasar long-term variability and the accretion rate. Methods: We compiled a catalogue of about 4000 quasars including individual estimators for the variability strength derived from the multi-epoch photometry in the SDSS Stripe 82, virial black hole masses M derived from the Mg ii line, and mass accretion rates ? from the Davis-Laor scaling relation. Several statistical tests were applied to evaluate the correlations of the variability with luminosity, mass, Eddington ratio, and accretion rate. Results: We confirm the existence of significant anti-correlations between the variability estimator V and the accretion rate ?, the Eddington ratio ?, and the bolometric luminosity Lbol, respectively. The Eddington ratio is tightly correlated with ?. A weak, statistically not significant positive trend is indicated for the dependence of V on M. As a side product, we find a strong correlation of the radiative efficiency ? with M in our sample. We show via numerical simulations that this trend is most likely produced by selection effects in combination with the mass errors and the use of the scaling relation for ?. The anti-correlations of V with ?, ?, and Lbol cannot be explained in such a way. The strongest anti-correlation is found between V and ?. However, it is difficult to decide which of the quantities L,?, and ? is intrinsically correlated with V and which of the observed correlations of V are produced by the L - ? - ? relation. A V - ? anti-correlation is qualitatively expected for the strongly inhomogeneous accretion disks. We argue that the observed amplitudes of the variability at far-UV wavelengths, the stochastic nature of variability, and the variability time-scales are not adequately explained by the simple multi-temperature black-body model of a standard disk and suggest to check whether the strongly inhomogeneous disk model is capable of reproducing these observations better. The catalogue of quasars is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A104

Meusinger, H.; Weiss, V.

2013-12-01

100

MODELING THE TIME VARIABILITY OF SDSS STRIPE 82 QUASARS AS A DAMPED RANDOM WALK  

International Nuclear Information System (INIS)

We model the time variability of ?9000 spectroscopically confirmed quasars in SDSS Stripe 82 as a damped random walk (DRW). Using 2.7 million photometric measurements collected over 10 yr, we confirm the results of Kelly et al. and Kozlowski et al. that this model can explain quasar light curves at an impressive fidelity level (0.01-0.02 mag). The DRW model provides a simple, fast (O(N) for N data points), and powerful statistical description of quasar light curves by a characteristic timescale (?) and an asymptotic rms variability on long timescales (SF?). We searched for correlations between these two variability parameters and physical parameters such as luminosity and black hole mass, and rest-frame wavelength. Our analysis shows SF? to increase with decreasing luminosity and rest-frame wavelength as observed previously, and without a correlation with redshift. We find a correlation between SF? and black hole mass with a power-law index of 0.18 ± 0.03, independent of the anti-correlation with luminosity. We find that ? increases with increasing wavelength with a power-law index of 0.17, remains nearly constant with redshift and luminosity, and increases with increasing black hole mass with a power-law index of 0.21 ± 0.07. The amplitude of variability is anti-correlated with the Eddington ratio, which suggests a scenario where optical fluctuations are tied to variations in the accretion rate. However, we find an additional dependence on luminosity and/or black hole mass that cannot be explained by the trend with Eddington ratio. The radio-loudest quasars have systematically larger variability amplitudes by about 30%, when corrected for the other observed trends, while the distribution of their characteristic timescale is indistinguishable from that of the full sample. We do not detect any statistically robust differences in the characteristic timescale and variability amplitude between the full sample and the small subsample of quasars detected by ROSAT. Our results provide a simple quantitative framework for generating mock quasar light curves, such as currently used in LSST image simulations.

 
 
 
 
101

Randomness and variability of the neuronal activity described by the Ornstein-Uhlenbeck model  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Normalized entropy as a measure of randomness is explored. It is employed to characterize those properties of neuronal firing that cannot be described by the first two statistical moments. We analyze randomness of firing of the Ornstein-Uhlenbeck (OU) neuronal model with respect either to the variability of interspike intervals (coefficient of variation) or the model parameters. A new form of the Siegert's equation for first-passage time of the OU process is given. The parametric space of the...

Zucca, Cristina

2007-01-01

102

An AUC-based Permutation Variable Importance Measure for Random Forests  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The random forest (RF) method is a commonly used tool for classification with high dimensional data as well as for ranking candidate predictors based on the so-called random forest variable importance measures (VIMs). However the classification performance of RF is known to be suboptimal in case of strongly unbalanced data, i.e. data where response class sizes differ considerably. Suggestions were made to obtain better classification performance based either on sampling procedures or on cost ...

Janitza, Silke; Strobl, Carolin; Boulesteix, Anne-laure

2012-01-01

103

Modelado con variables aleatorias en simulink utilizando simulación montercarlo / Modeling with random variables in simulink using montecarlo simulations  

Scientific Electronic Library Online (English)

Full Text Available SciELO Venezuela | Language: Spanish Abstract in spanish Este artículo presenta el Modelado Con Variables Aleatorias En Simulink Utilizando Simulación Montecarlo, muchos modelos de sistemas reales contienen elementos que precisan o admiten un modelado estadístico, Sistemas de comunicaciones, Sistemas de conmutación, Sistemas sensores, Modelado toma forma [...] definiendo, Variables aleatorias que rigen ciertos comportamientos del sistema Procesos estocásticos para modelar variación de entradas en el tiempo, como lo son las fluctuaciones en la bolsa de valores e ciertos productos. Se deben definir métodos para generar muestras de variables aleatorias y muestras de procesos estocásticos. Entre ellos está el método de Montecarlo, el modelo implementado mostro la capacidad proponer precios optativos al precio de mercado ante cambios en el precio de un producto. Las simulaciones permitieron conocer con mayor exactitud la versatilidad del Método ante otros Métodos usados, prediciendo con gran exactitud las fluctuaciones de precios ocurridas en el producto de prueba. Abstract in english This article presents the model with random variables in Monte CarloSimulation Using Simulink, many models of real systems contain elements that require or permit a statistical modeling, communication systems,switching systems, sensor systems, modeling takes definite shape, random variables governin [...] g certain stochastic processes system behavior modelinginputs change over time, as are the fluctiaciones in the stock market andsome products. You must define methods to generate samples of random variables and stochastic samples. Among them is the Monte Carlo method, the implemented model showed the ability to propose optional pricing to the market price to changes in the price of a product. The simulations allowed to know more precisely the versatility of the method to other methods used, predicting with great accuracy the price fluctuations that occurred in the trial product.

Sergio, Velásquez; Ronny, Velásquez.

2012-09-01

104

Modelado con variables aleatorias en simulink utilizando simulación montercarlo / Modeling with random variables in simulink using montecarlo simulations  

Scientific Electronic Library Online (English)

Full Text Available SciELO Venezuela | Language: Spanish Abstract in spanish Este artículo presenta el Modelado Con Variables Aleatorias En Simulink Utilizando Simulación Montecarlo, muchos modelos de sistemas reales contienen elementos que precisan o admiten un modelado estadístico, Sistemas de comunicaciones, Sistemas de conmutación, Sistemas sensores, Modelado toma forma [...] definiendo, Variables aleatorias que rigen ciertos comportamientos del sistema Procesos estocásticos para modelar variación de entradas en el tiempo, como lo son las fluctuaciones en la bolsa de valores e ciertos productos. Se deben definir métodos para generar muestras de variables aleatorias y muestras de procesos estocásticos. Entre ellos está el método de Montecarlo, el modelo implementado mostro la capacidad proponer precios optativos al precio de mercado ante cambios en el precio de un producto. Las simulaciones permitieron conocer con mayor exactitud la versatilidad del Método ante otros Métodos usados, prediciendo con gran exactitud las fluctuaciones de precios ocurridas en el producto de prueba. Abstract in english This article presents the model with random variables in Monte CarloSimulation Using Simulink, many models of real systems contain elements that require or permit a statistical modeling, communication systems,switching systems, sensor systems, modeling takes definite shape, random variables governin [...] g certain stochastic processes system behavior modelinginputs change over time, as are the fluctiaciones in the stock market andsome products. You must define methods to generate samples of random variables and stochastic samples. Among them is the Monte Carlo method, the implemented model showed the ability to propose optional pricing to the market price to changes in the price of a product. The simulations allowed to know more precisely the versatility of the method to other methods used, predicting with great accuracy the price fluctuations that occurred in the trial product.

Sergio, Velásquez; Ronny, Velásquez.

105

Exact Distribution of the Ratio of Gamma and Rayleigh Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available The distributions of the ratio of two independent random variables arise in many applied problems and have been extensively studied by many researchers. This article derives the distributions of the ratio Z=|x/y| , when x and y are gamma and Rayleigh random variables respectively and are distributed independently of each other. The associated pdf, cdf, and moments have been given in terms of different special functions, for examples, confluent hypergeometric function, parabolic-cylinder function and beta functions. Some plots for the cdf and pdf associated with the distribution of the ratio have been provided.

M. Shakil

2006-07-01

106

On the Distribution of the Minimum or Maximum of a Random Number of i.i.d. Lifetime Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available Statisticians are usually concerned with the proposition of new distributions. In this paper we point out that a unified and concise derivation procedure of the distribution of the minimum or maximum of a random number N of indepen-dent and identically distributed continuous random variables Yi,{i = 1,2,…,N} is obtained if one compounds the probability generating function of N with the survival or the distribution func-tion of Yi. Expressions are then derived in closed form for the density, hazard and quantile func-tions of the minimum or maximum. The methodology is illustrated with examples of the distributions proposed by Adamidis and Loukas (1998, Kus (2007, Tahmasbi and Rezaei (2008, Barreto-Souza and Cribari-Neto (2009, Cancho, Louzada, and Barriga (2011 and Louzada, Roman and Cancho (2011.

Maria A. P. Franco

2012-04-01

107

Strain-Dependent Creep Damage in Random Inhomogeneous Materials.  

Science.gov (United States)

Employing a recent homogeneous strain-dependent creep damage theory, the propagation of a failure front in a beam under pure bending is studied. A local inhomogeneous strain-dependent creep damage theory is then postulated, based on creep damage data obta...

C. Lee, F. A. Cozzarelli

1980-01-01

108

From Moment Explosion to the Asymptotic Behavior of the Cumulative Distribution for a Random Variable  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the Tauberian relations between the moment generating function (MGF) and the complementary cumulative distribution function of a variable whose MGF is finite only on part of the real line. We relate the right tail behavior of the cumulative distribution function of such a random variable to the behavior of its MGF near the critical moment. We apply our results to an arbitrary superposition of a CIR process and the time-integral of this process.

Ould Aly, Sidi Mohamed

2013-01-01

109

Approximation to Distribution of Product of Random Variables Using Orthogonal Polynomials for Lognormal Density  

CERN Document Server

We derive a closed-form expression for the orthogonal polynomials associated with the general lognormal density. The result can be utilized to construct easily computable approximations for probability density function of a product of random variables. As an example, we have calculated the approximative distribution for the product of correlated Nakagami-m variables. Simulations indicate that accuracy of the proposed approximation is good.

Zheng, Zhong; Hämäläinen, Jyri; Tirkkonen, Olav

2012-01-01

110

Event-controlled constructions of random fields of maxima with non-max-stable dependence  

CERN Document Server

Max-stable random fields can be constructed according to Schlather (2002) with a random function or a stationary process and a kind of random event magnitude. These are applied for the modelling of natural hazards. We simply extend these event-controlled constructions to random fields of maxima with non-max-stable dependence structure (copula). The theory for the variant with a stationary process is obvious; the parameter(s) of its correlation function is/are determined by the event magnitude. The introduced variant with random functions can only be researched numerically. The scaling of the random function is exponentially determined by the event magnitude. The location parameter of the Gumbel margins depends only on this exponential function in the researched examples; the scale parameter of the margins is normalized. In addition, we propose a method for the parameter estimation for such constructions by using Kendall's tau. The spatial dependence in relation to the block size is considered therein. Finally...

Raschke, Mathias

2014-01-01

111

Epoch-dependent absorption line profile variability in lambda Cep  

CERN Document Server

We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6Ief star lambda Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star. Our data reveal a much more complex situation. The frequency content of the power spectrum considerably changes from one epoch to the other. We find no stable frequency that can unambiguously be attributed to pulsations. The epoch-dependence of the frequencies and variability patterns are similar to what is seen in the wind emission lines of this and other Oef stars, suggesting that both phenomena likely have the same, currently still unknown, origin.

Uuh-Sonda, J M; Eenens, P; Mahy, L; Palate, M; Gosset, E; Flores, C A

2014-01-01

112

The generation of dependent input variables to a performance assessment simulation code  

International Nuclear Information System (INIS)

Mathematical models are being developed in many countries to aid in the assessment of risks associated with the deep geologic disposal of high-level nuclear wastes. The models are designed to simulate one or more steps in the following scenario: waste containment is lost, and the radionuclides are released from the repository, are transported to the biosphere, and become accessible to man. The models typically involve a large number of variables that may be highly dependent. When the models are implemented in computer simulation codes, it becomes necessary to generate input values for these variables. Widely used methods for generating input values, such as simple random sampling (SRS) and Latin hypercube sampling (LHS), do not necessarily produce samples that are consistent with the known dependence structure of the input variables. Moreover, it is procedurally impracticable to generate realizations of correlated input variables from many multivariate probability distributions of interest. Two important cases in which it is feasible to generate multivariate realizations are those in which all input variables are either normally distributed or mutually independent. Neither case is adequate for large-scale performance assessment codes with many input variables. Iman and Conover (1982) have developed a practical method for generating nonzero pairwise rank correlations among the components of an input vector that overcomes some of these difficulties. The method requires f these difficulties. The method requires samples of specified size from the marginal (univariate) distributions of the input variables. The method further requires a target matrix of desired pairwise correlations among the input variables. The Cholesky decomposition of the target matrix is used to transform the rank matrix of the input sample

113

The behaviour of random forest permutation-based variable importance measures under predictor correlation  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Random forests (RF have been increasingly used in applications such as genome-wide association and microarray studies where predictor correlation is frequently observed. Recent works on permutation-based variable importance measures (VIMs used in RF have come to apparently contradictory conclusions. We present an extended simulation study to synthesize results. Results In the case when both predictor correlation was present and predictors were associated with the outcome (HA, the unconditional RF VIM attributed a higher share of importance to correlated predictors, while under the null hypothesis that no predictors are associated with the outcome (H0 the unconditional RF VIM was unbiased. Conditional VIMs showed a decrease in VIM values for correlated predictors versus the unconditional VIMs under HA and was unbiased under H0. Scaled VIMs were clearly biased under HA and H0. Conclusions Unconditional unscaled VIMs are a computationally tractable choice for large datasets and are unbiased under the null hypothesis. Whether the observed increased VIMs for correlated predictors may be considered a "bias" - because they do not directly reflect the coefficients in the generating model - or if it is a beneficial attribute of these VIMs is dependent on the application. For example, in genetic association studies, where correlation between markers may help to localize the functionally relevant variant, the increased importance of correlated predictors may be an advantage. On the other hand, we show examples where this increased importance may result in spurious signals.

Malley James D

2010-02-01

114

Asynchronous Random Boolean Network Model with Variable Number of Parents Based on Elementary Cellular Automata Rule 126  

Science.gov (United States)

A Boolean network with N nodes, each node's state at time t being determined by a certain number of parent nodes, which can vary from one node to another, is considered. This is a generalization of previous results obtained for a constant number of parent nodes, by Matache and Heidel in "Asynchronous Random Boolean Network Model Based on Elementary Cellular Automata Rule 126", Phys. Rev. E 71, 026 232, 2005. The nodes, with randomly assigned neighborhoods, are updated based on various asynchronous schemes. The Boolean rule is a generalization of rule 126 of elementary cellular automata, and is assumed to be the same for all the nodes. We provide a model for the probability of finding a node in state 1 at a time t for the class of generalized asynchronous random Boolean networks (GARBN) in which a random number of nodes can be updated at each time point. We generate consecutive states of the network for both the real system and the models under the various schemes, and use simulation algorithms to show that the results match well. We use the model to study the dynamics of the system through sensitivity of the orbits to initial values, bifurcation diagrams, and fixed point analysis. We show that the GARBN's dynamics range from order to chaos, depending on the type of random variable generating the asynchrony and the parameter combinations.

Matache, Mihaela T.

115

Structural Fatigue Reliability Based on Extension of Random Loads into Interval Variables  

Directory of Open Access Journals (Sweden)

Full Text Available According to the problem that for a structure under random loads, the structural fatigue life cant be directly calculated out by S-N curves and linear Miner cumulative damage rule. Owing to the uncertainty of loads, and the problem of the inaccuracy of calculated structural reliability index for the existence of deviation between measured data in projects and real data, the research method for structural fatigue reliability based on extension of random loads into interval variables is proposed. The innovation is that we can accurately calculate out the interval of the structural fatigue life and reliability index of a structure according to the probability density function of stress level of random loads and the coefficient of variation of measured loads. By practical calculation example, it is proved that this method is more suitable to practical engineering comparing to traditional methods. It will provide a perfect research approach for reliability analysis of the structure under random loads.

Qiangfeng Wang

2013-01-01

116

Analytical study on analysis methods of several random variables for seismic nonlinear responses of reactor buildings  

International Nuclear Information System (INIS)

In the case wherein nonlinear seismic response analyses are carried out, the response values vary due to the variations in materials and modeling. In this paper, nonlinear analyses of several random variables are carried out using: i. a conventional method; ii. a two-point estimation method (i. and ii. are simplified methods); and iii. Monte Carlo simulation (detailed method) to examine the variability of the response in the excessive nonlinear range for seismic responses of shear walls. The analyses are performed to a PWR-3 loop type reactor building which is one of the most typical reactor buildings in Japan. The variations are considered in specified compressive strength of concrete, concrete damping factor, shear wave velocity of soil and shapes of shear stress-strain relation curves of shear walls. As the results by the two simplified methods closely matched the Monte Carlo simulation results, the appropriateness for applying the simplified methods to nonlinear analyses of several random variables was ascertained. (author)

117

Statistics of rogue waves in random sea states and their dependence on inverse scattering data.  

Science.gov (United States)

Extreme waves are frequently modeled using the nonlinear Schrodinger (NLS) equation and it's higher order extensions (HONLS). In earlier work we introduced ?, the 'splitting distance' between two consecutive simple points in the Floquet spectrum of the associated Zakharov-Shabaat problem of the NLS equation, as a measure of proximity to instabilities in the wavefield. As and alternative to the Benjamin-Feir index, the splitting distance can be seen as a measure of the localization of the energy in the wave field. In [1] we correlated the development of localized rogue waves in random sea states characterized by JONSWAP spectra with the splitting distance ?. In [2] Sura shows that the kurtosis (?) and skewness (s) of deep ocean field data obey the relationship ? = 3/2s2 + c which is not satisfied by Gaussian or double exponential noise. Here we show that sea states modeled using the HONLS equation and random phase JONSWAP initial data exhibit a significant deviation from Gaussianity and satisfy Sura's relation between the skewness and kurtosis. For the HONLS equation, ? is not invariant in time. We determine both the initial splitting distance ?0 and the time averaged splitting distance ?avg. We find that the maximum strength, skewness, and kurtosis of the sea state are strongly dependent on ?avg. Using the Mori-Janssen relationship between kurtosis and P, the probability a wave height exceeds a given quantity, we determine P(?avg). References 1 A.L. Islas and C.M. Schober, Predicting rogue waves in random oceanic sea states, Phys. Fluids 17 (2005) 2 P. Sura and S.T. Gille, Stochastic dynamics of sea surface height variability, J. Phys. Oceanogr. 40 (2010).

Schober, Constance

2014-05-01

118

Exploring Local Item Dependence Using a Random-Effects Facet Model  

Science.gov (United States)

The random-effects facet model that deals with local item dependence in many-facet contexts is presented. It can be viewed as a special case of the multidimensional random coefficients multinomial logit model (MRCMLM) so that the estimation procedures for the MRCMLM can be directly applied. Simulations were conducted to examine parameter recovery…

Wang, Wen-Chung; Wilson, Mark

2005-01-01

119

SOERP, Statistics and 2. Order Error Propagation for Function of Random Variables  

International Nuclear Information System (INIS)

1 - Description of problem or function: SOERP computes second-order error propagation equations for the first four moments of a function of independently distributed random variables. SOERP was written for a rigorous second-order error propagation of any function which may be expanded in a multivariable Taylor series, the input variables being independently distributed. The required input consists of numbers directly related to the partial derivatives of the function, evaluated at the nominal values of the input variables and the central moments of the input variables from the second through the eighth. 2 - Method of solution: The development of equations for computing the propagation of errors begins by expressing the function of random variables in a multivariable Taylor series expansion. The Taylor series expansion is then truncated, and statistical operations are applied to the series in order to obtain equations for the moments (about the origin) of the distribution of the computed value. If the Taylor series is truncated after powers of two, the procedure produces second-order error propagation equations. 3 - Restrictions on the complexity of the problem: The maximum number of component variables allowed is 30. The IBM version will only process one set of input data per run

120

Efficient Estimation of Mutual Information for Strongly Dependent Variables  

CERN Document Server

We demonstrate that a popular class of nonparametric mutual information (MI) estimators based on k-nearest-neighbor graphs requires number of samples that scales exponentially with the true MI. Consequently, accurate estimation of MI between two strongly dependent variables is possible only for prohibitively large sample size. This important yet overlooked shortcoming of the existing estimators is due to their implicit reliance on local uniformity of the underlying joint distribution. We introduce a new estimator that is robust to local non-uniformity, works well with limited data, and is able to capture relationship strengths over many orders of magnitude. We demonstrate the superior performance of the proposed estimator on both synthetic and real-world data.

Gao, Shuyang; Galstyan, Aram

2014-01-01

 
 
 
 
121

Modeling dependence induced by a common random effect and risk measures with insurance applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Random effects models are of particular importance in modeling heterogeneity. A commonly used random effects model for multivariate survival analysis is the frailty model. In this thesis, a special frailty model with an Archimedean dependence structure is used to model dependent risks. This modeling approach allows the construction of multivariate distributions through a copula with univariate marginal distributions as parameters. Copulas are constructed by modeling distribution functions and...

Liu, Junjie

2012-01-01

122

Delay-distribution-dependent state estimation for discrete-time stochastic neural networks with random delay.  

Science.gov (United States)

This paper is concerned with the state estimation problem for a class of discrete-time stochastic neural networks (DSNNs) with random delays. The effect of both variation range and distribution probability of the time delay are taken into account in the proposed approach. The stochastic disturbances are described in terms of a Brownian motion and the time-varying delay is characterized by introducing a Bernoulli stochastic variable. By employing a Lyapunov-Krasovskii functional, sufficient delay-distribution-dependent conditions are established in terms of linear matrix inequalities (LMIs) that guarantee the existence of the state estimator which can be checked readily by the Matlab toolbox. The main feature of the results obtained in this paper is that they are dependent on not only the bound but also the distribution probability of the time delay, and we obtain a larger allowance variation range of the delay, hence our results are less conservative than the traditional delay-independent ones. One example is given to illustrate the effectiveness of the proposed result. PMID:20950998

Bao, Haibo; Cao, Jinde

2011-01-01

123

Discovery of Fourier-dependent time lags in cataclysmic variables  

CERN Document Server

We report the first study of Fourier-frequency-dependent coherence and phase/time lags at optical wavelengths of cataclysmic variables (MV Lyr and LU Cam) displaying typical flickering variability in white light. Observations were performed on the William Herschel Telescope using ULTRACAM. Lightcurves for both systems have been obtained with the SDSS filters $u'$, $g'$ and $r'$ simultaneously with cadences between $\\approx0.5-2$ seconds, and allow us to probe temporal frequencies between ~10^{-3} Hz and ~1 Hz. We find high levels of coherence between the u', g' and r' lightcurves up to at least ~10^{-2} Hz. Furthermore we detect red/negative lags where the redder bands lag the bluer ones at the lowest observed frequencies. For MV Lyr time lags up to ~3 seconds are observed, whilst LU Cam displays larger time lags of ~10 seconds. Mechanisms which seek to explain red/negative lags observed in X-ray binaries and Active Galactic Nuclei involve reflection of photons generated close to the compact object onto the s...

Scaringi, S; Groot, P J; Uttley, P; Marsh, T; Knigge, C; Maccarone, T; Dhillon, V S

2013-01-01

124

Strong Laws of Large Numbers for Arrays of Rowwise ρ∗-Mixing Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available Some strong laws of large numbers for arrays of rowwise ρ∗-mixing random variables are obtained. The result obtainted not only generalizes the result of Hu and Taylor (1997 to ρ∗-mixing random variables, but also improves it.

Meng-Hu Zhu

2007-01-01

125

General Limit Distributions for Sums of Random Variables with a Matrix Product Representation  

Science.gov (United States)

The general limit distributions of the sum of random variables described by a finite matrix product ansatz are characterized. Using a mapping to a Hidden Markov Chain formalism, non-standard limit distributions are obtained, and related to a form of ergodicity breaking in the underlying non-homogeneous Hidden Markov Chain. The link between ergodicity and limit distributions is detailed and used to provide a full algorithmic characterization of the general limit distributions.

Angeletti, Florian; Bertin, Eric; Abry, Patrice

2014-09-01

126

Uniform error bounds for a continuous approximation of non-negative random variables  

CERN Document Server

In this work, we deal with approximations for distribution functions of non-negative random variables. More specifically, we construct continuous approximants using an acceleration technique over a well-know inversion formula for Laplace transforms. We give uniform error bounds using a representation of these approximations in terms of gamma-type operators. We apply our results to certain mixtures of Erlang distributions which contain the class of continuous phase-type distributions.

Sangüesa, Carmen

2010-01-01

127

Constraints on belief functions imposed by fuzzy random variables: Some technical remarks on Romer-Kandel.  

Science.gov (United States)

C. Romer and A. Kandel (1995) investigated a new approach of fuzzy data analysis combining Dempster-Shafer theory and fuzzy set theory. Especially, belief measures are derived from fuzzy random variables but proved incompletely. This paper offers a completion using topological properties induced by the Hausdorff metric which is defined on the space of closed intervals of the real numbers. Moreover little corrections of some other assertions in the paper of Romer-Kandel are presented. PMID:18256008

Kratschmer, V

1998-01-01

128

How to Convince a Student that an Estimator is a Random Variable  

Science.gov (United States)

This classroom example illustrates the concept that estimators are random variables. The example makes use of the classic problem of estimating the size of a population by observing serial numbers, specifically estimating the number of taxis in a city. In this article from the Journal "Teaching Statistics," The author explains how to encourage a discussion among students about the best estimator for a population size. The author then uses a simulation to determine which of a group of candidate estimates should be used.

Vannman, Kerstin

2009-08-11

129

Exact lower bounds on the exponential moments of Winsorized and truncated random variables  

CERN Document Server

Exact lower bounds on the exponential moments of min(y,X) and XI{Xrandom variable X. These bounds are useful in work on large deviations probabilities and nonuniform Berry-Esseen bounds, when the Cram\\'er tilt transform may be employed. Asymptotic properties of these lower bounds are presented. Comparative advantages of the Winsorization min(y,X) over the truncation XI{X

Pinelis, Iosif

2010-01-01

130

Convergence Rates for Probabilities of Moderate Deviations for Multidimensionally Indexed Random Variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Let {X,Xn¯;n¯?Z+d} be a sequence of i.i.d. real-valued random variables, and Sn¯=?k¯?n¯Xk¯, n¯?Z+d. Convergence rates of moderate deviations are derived; that is, the rates of convergence to zero of certain tail probabilities of the partial sums are determined. For example, we obtain equivalent conditions for the convergence of the series ?n¯b(n¯)?2(a(n¯))P{|Sn¯|?a(n&#...

Dianliang Deng

2009-01-01

131

Generalized madogram and pairwise dependence of maxima over two disjoint regions of a random field  

CERN Document Server

Quantifying dependence between extreme events occurring at several locations of a random field is a fundamental issue in applied spatial extreme value analysis. For max-stable processes, an important measure of pairwise dependence is the $\\lambda$-madogram. In this paper we propose a generalization of this coefficient that enables the analysis of dependence between maxima over two disjoint regions of locations and present some of its properties. Two estimatores of this function are given. Finally, we define a multivariate maxima of moving maxima random field, compute its generalized madogram for some choices of regions of locations and analyze the performance of the proposed estimators through a simulation study.

Fonseca, Cecília; Ferreira, Helena; Martins, Ana Paula

2011-01-01

132

Epoch-dependent absorption line profile variability in ? Cep  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Reportamos el análisis de una campaña de monitoreo espectroscópico multiépoca de la estrella O6 Ief ? Cep. Observaciones previas habían reportado la existencia de dos modos de pulsaciones no-radiales en esta estrella. Nuestros datos revelan una situación considerablemente más compleja. Las frequenci [...] as contenidas en el espectro de potencia cambian considerablemente de una época a otra. No encontramos ninguna frecuencia estable que pueda ser atribuida inequívocamente a pulsaciones. La dependencia temporal de las frequencias y los patrones devariabilidad son similares a los observados en las líneas de emisión del viento en esta y otras estrellas Oef, lo cual sugiere que ambos fenómenos tienen probablemente el mismo origen, aunque éste siga todavía sin conocerse. Abstract in english We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6Iefstar ? Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star. Our data reveal a much more complex situation. The frequency content of the power spectrum considerably [...] changes from one epoch to the other. We find no stable frequency that can unambiguously be attributed to pulsations. The epoch-dependence of the frequencies and variability patterns are similar to what is seen in the wind emission lines of this and other Oef stars, suggesting that both phenomena likely have the same, currently still unknown, origin.

J.M., Uuh-Sonda; G., Rauw; P., Eenens; L., Mahy; M., Palate; E., Gosset; C.A., Flores.

133

Epoch-dependent absorption line profile variability in ? Cep  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Reportamos el análisis de una campaña de monitoreo espectroscópico multiépoca de la estrella O6 Ief ? Cep. Observaciones previas habían reportado la existencia de dos modos de pulsaciones no-radiales en esta estrella. Nuestros datos revelan una situación considerablemente más compleja. Las frequenci [...] as contenidas en el espectro de potencia cambian considerablemente de una época a otra. No encontramos ninguna frecuencia estable que pueda ser atribuida inequívocamente a pulsaciones. La dependencia temporal de las frequencias y los patrones devariabilidad son similares a los observados en las líneas de emisión del viento en esta y otras estrellas Oef, lo cual sugiere que ambos fenómenos tienen probablemente el mismo origen, aunque éste siga todavía sin conocerse. Abstract in english We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6Iefstar ? Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star. Our data reveal a much more complex situation. The frequency content of the power spectrum considerably [...] changes from one epoch to the other. We find no stable frequency that can unambiguously be attributed to pulsations. The epoch-dependence of the frequencies and variability patterns are similar to what is seen in the wind emission lines of this and other Oef stars, suggesting that both phenomena likely have the same, currently still unknown, origin.

J.M., Uuh-Sonda; G., Rauw; P., Eenens; L., Mahy; M., Palate; E., Gosset; C.A., Flores.

2014-04-01

134

Spontaneous temporal changes and variability of peripheral nerve conduction analyzed using a random effects model  

DEFF Research Database (Denmark)

SUMMARY: The reproducibility of variables commonly included in studies of peripheral nerve conduction in healthy individuals has not previously been analyzed using a random effects regression model. We examined the temporal changes and variability of standard nerve conduction measures in the leg. Peroneal nerve distal motor latency, motor conduction velocity, and compound motor action potential amplitude; sural nerve sensory action potential amplitude and sensory conduction velocity; and tibial nerve minimal F-wave latency were examined in 51 healthy subjects, aged 40 to 67 years. They were reexamined after 2 and 26 weeks. There was no change in the variables except for a minor decrease in sural nerve sensory action potential amplitude and a minor increase in tibial nerve minimal F-wave latency. Reproducibility was best for peroneal nerve distal motor latency and motor conduction velocity, sural nerve sensory conduction velocity, and tibial nerve minimal F-wave latency. Between-subject variability was greaterthan within-subject variability. Sample sizes ranging from 21 to 128 would be required to show changes twice the magnitude of the spontaneous changes observed in this study. Nerve conduction studies have a high reproducibility, and variables are mainly unaltered during 6 months. This study provides a solid basis for the planning of future clinical trials assessing changes in nerve conduction.

KrØigård, Thomas; Gaist, David

2014-01-01

135

COGNITIVE-BEHAVIORAL THERAPY FOR INSOMNIA IN ALCOHOL DEPENDENT PATIENTS: A RANDOMIZED CONTROLLED PILOT TRIAL  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In a randomized controlled trial, we evaluated the efficacy of cognitive-behavioral treatment for insomnia to improve sleep and daytime symptoms, and to reduce relapse in recovering alcohol dependent (AD) participants. Seventeen abstinent AD patients with insomnia (6 women, mean age 46.2 ± 10.1 years) were randomized to 8 sessions of cognitive behavioral treatment for insomnia for AD (CBTI-AD, n=9) or to a behavioral placebo treatment (BPT, n=8). Subjective measures of sleep, daytime consequ...

Arnedt, J. Todd; Conroy, Deirdre A.; Armitage, Roseanne; Brower, Kirk J.

2011-01-01

136

Computerized Behavior Therapy for Opioid-Dependent Outpatients: A Randomized Controlled Trial  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We evaluated the efficacy of an interactive, computer-based behavioral therapy intervention, grounded in the community reinforcement approach (CRA) plus voucher-based contingency management model of behavior therapy. Our randomized, controlled trial was conducted at a university-based research clinic. Participants comprised 135 volunteer adult outpatients who met DSM-IV criteria for opioid dependence. All participants received maintenance treatment with buprenorphine and were randomly assigne...

Bickel, Warren K.; Marsch, Lisa A.; Buchhalter, August R.; Badger, Gary J.

2008-01-01

137

Continuous-variable phase estimation with unitary and random linear disturbance  

Science.gov (United States)

We address the problem of continuous-variable quantum phase estimation in the presence of linear disturbance at the Hamiltonian level by means of Gaussian probe states. In particular we discuss both unitary and random disturbance by considering the parameter which characterizes the unwanted linear term present in the Hamiltonian as fixed (unitary disturbance) or random with a given probability distribution (random disturbance). We derive the optimal input Gaussian states at fixed energy, maximizing the quantum Fisher information over the squeezing angle and the squeezing energy fraction, and we discuss the scaling of the quantum Fisher information in terms of the output number of photons, nout. We observe that, in the case of unitary disturbance, the optimal state is a squeezed vacuum state and the quadratic scaling is conserved. As regards the random disturbance, we observe that the optimal squeezing fraction may not be equal to one and, for any nonzero value of the noise parameter, the quantum Fisher information scales linearly with the average number of photons. Finally, we discuss the performance of homodyne measurement by comparing the achievable precision with the ultimate limit imposed by the quantum Cramér-Rao bound.

Delgado de Souza, Douglas; Genoni, Marco G.; Kim, M. S.

2014-10-01

138

Blind estimation of statistical properties of non-stationary random variables  

Science.gov (United States)

To identify or equalize wireless transmission channels, or alternatively to evaluate the performance of many wireless communication algorithms, coefficients or statistical properties of the used transmission channels are often assumed to be known or can be estimated at the receiver end. For most of the proposed algorithms, the knowledge of transmission channel statistical properties is essential to detect signals and retrieve data. To the best of our knowledge, most proposed approaches assume that transmission channels are static and can be modeled by stationary random variables (uniform, Gaussian, exponential, Weilbul, Rayleigh, etc.). In the majority of sensor networks or cellular systems applications, transmitters and/or receivers are in motion. Therefore, the validity of static transmission channels and the underlying assumptions may not be valid. In this case, coefficients and statistical properties change and therefore the stationary model falls short of making an accurate representation. In order to estimate the statistical properties (represented by the high-order statistics and probability density function, PDF) of dynamic channels, we firstly assume that the dynamic channels can be modeled by short-term stationary but long-term non-stationary random variable (RV), i.e., the RVs are stationary within unknown successive periods but they may suddenly change their statistical properties between two successive periods. Therefore, this manuscript proposes an algorithm to detect the transition phases of non-stationary random variables and introduces an indicator based on high-order statistics for non-stationary transmission which can be used to alter channel properties and initiate the estimation process. Additionally, PDF estimators based on kernel functions are also developed. The first part of the manuscript provides a brief introduction for unbiased estimators of the second and fourth-order cumulants. Then, the non-stationary indicators are formulated. Finally, simulation results are presented and conclusions are derived.

Mansour, Ali; Mesleh, Raed; Aggoune, el-Hadi M.

2014-12-01

139

Aleatoriedade e variabilidade produtiva de feijão-de-vagem / Randomness and variability productive of bean pod  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese Com o objetivo de estudar a aleatoriedade e a variabilidade produtiva de feijão-de-vagem, foram realizados os seguintes experimentos em branco: 1) em estufa no outono-inverno; 2) em túnel no outono-inverno; 3) em ambiente não protegido no outono-inverno; 4) em túnel na primavera-verão; e 5) em ambie [...] nte não protegido na primavera-verão. A variável mensurada foi a fitomassa fresca de vagens. Foram realizados estudos por colheita e por agrupamentos de colheitas. Foram planejados diferentes tamanhos de parcela e, para cada um, foram realizados testes de homogeneidade de variâncias entre as fileiras de cultivo e entre as colheitas, e testes de aleatoriedade em cada fileira de cultivo. A não aleatoriedade e a variabilidade da produção de fitomassa fresca de vagens são maiores em condições meteorológicas adversas a cultura do feijão-de-vagem e diminuem com o aumento do tamanho de parcela. O uso de parcelas constituídas por seis unidades básicas (12 plantas), em ambiente protegido ou não protegido, torna a produção de fitomassa fresca de vagens aleatória e proporciona menor variabilidade entre fileiras de cultivo e entre colheitas. Abstract in english With the aim of studying the randomness and variability of productive bean pod, the following experiments were performed on white: 1) in greenhouse in autumn-winter, 2) in tunnel in autumn-winter, 3) in unprotected environment in autumn-winter, 4) in tunnel in spring-summer and 5) in unprotected env [...] ironment in spring-summer. The variable measured was the fresh weight of pods. Studies were conducted by harvest and harvest groupings. Were planned different plot sizes, and for each, were conducted tests of homogeneity of variances between crop row and between harvests, and tests of randomness in each crop row. The non-randomness and variability in production of fresh pods are larger in adverse weather conditions the culture of the bean pod and decrease with increasing plot size. The use of plots consisting of six basic units (12 plants) in protected or unprotected makes the production of fresh pods random and provides lower variability between rows and between harvests.

Daniel, Santos; Fernando Machado, Haesbaert; Alessandro Dal' Col, Lúcio; Sidinei José, Lopes; Alberto, Cargnelutti Filho; Vilson, Benz.

140

Some One Parameter Models for Continuous Random Variables Defined on the Interval [0, 1  

Directory of Open Access Journals (Sweden)

Full Text Available The Beta Distribution is almost exclusively used for situations, after range normalization, wherein a continuous random variable is defined on the closed range [0, 1]. Since the beta distribution is intrinsically a two parameter distribution, this creates problems in some applications where specification of more than one parameter is difficult. In this note, two new classes of single parameter continuous probability distributions on a closed interval are introduced. These distributions remove some of the theoretical and practical problems of using the Beta Distribution for applications. The Burr Type XI Distribution has desirable characteristics for many applications especially when there is ambiguity in the definition of the specified parameter.

John J. Wiorkowski

2013-04-01

 
 
 
 
141

Rearrangement Invariant Norms of Symmetric Sequence Norms of Independent Sequences of Random Variables  

CERN Document Server

Let X_1, X_2,..., X_n be a sequence of independent random variables, let M be a rearrangement invariant space on the underlying probability space, and let N be a symmetric sequence space. This paper gives an approximate formula for the quantity || ||(X_i)||_N ||_M whenever L_q embeds into M for some 1 le q < infty. This extends work of Johnson and Schechtman who tackled the cases when N = l_1 or N = l_2, and recent work of Gordon, Litvak, Schuett and Werner who obtained similar results for Orlicz spaces.

Montgomery-Smith, S J

2001-01-01

142

Random Variables and Positive Definite Kernels Associated with the Schroedinger Algebra  

International Nuclear Information System (INIS)

We show that the Feinsilver-Kocik-Schott (FKS) kernel for the Schroedinger algebra is not positive definite. We show how the FKS Schroedinger kernel can be reduced to a positive definite one through a restriction of the defining parameters of the exponential vectors. We define the Fock space associated with the reduced FKS Schroedinger kernel. We compute the characteristic functions of quantum random variables naturally associated with the FKS Schroedinger kernel and expressed in terms of the renormalized higher powers of white noise (or RHPWN) Lie algebra generators.

143

Wavelength-dependent absorption in structurally tailored randomly branched vertical arrays of InSb nanowires.  

Science.gov (United States)

Arrays of semiconductor nanowires are of potential interest for applications including photovoltaic devices and IR detectors/imagers. While nominally uniform arrays have typically been studied, arrays containing nanowires with multiple diameters and/or random distributions of diameters could allow tailoring of the photonic properties of the arrays. In this Letter, we demonstrate the growth and optical properties of randomly branched InSb nanowire arrays. The structure mentioned can be approximated as three vertically stacked regions, with average diameters of 20, 100, and 150 nm within the respective layers. Reflectance and transmittance measurements on structures with different average nanowire lengths have been performed over the wavelength range of 300-2000 nm, and absorbance has been calculated from these measurements. The structures show low reflectance over the visible and IR regions and wavelength-dependent absorbance in the IR region. A model considering the diameter-dependent photonic coupling (at a given wavelength) and random distribution of nanowire diameters within the regions has been developed. The diameter-dependent photonic coupling results in a roll-off in the absorbance spectra at wavelengths well below the bulk cutoff of ?7 ?m, and randomness is observed to broaden the absorbance response. Varying the average diameters would allow tailoring of the wavelength dependent absorption within various layers, which could be employed in photovoltaic devices or wavelength-dependent IR imagers. PMID:23131195

Mohammad, Asaduzzaman; Das, Suprem R; Khan, M Ryyan; Alam, Muhammad A; Janes, David B

2012-12-12

144

Gametocytes infectiousness to mosquitoes: variable selection using random forests, and zero inflated models  

CERN Document Server

Malaria control strategies aiming at reducing disease transmission intensity may impact both oocyst intensity and infection prevalence in the mosquito vector. Thus far, mathematical models failed to identify a clear relationship between Plasmodium falciparum gametocytes and their infectiousness to mosquitoes. Natural isolates of gametocytes are genetically diverse and biologically complex. Infectiousness to mosquitoes relies on multiple parameters such as density, sex-ratio, maturity, parasite genotypes and host immune factors. In this article, we investigated how density and genetic diversity of gametocytes impact on the success of transmission in the mosquito vector. We analyzed data for which the number of covariates plus attendant interactions is at least of order of the sample size, precluding usage of classical models such as general linear models. We then considered the variable importance from random forests to address the problem of selecting the most influent variables. The selected covariates were ...

Genuer, Robin; Toussile, Wilson

2011-01-01

145

An uncertainty conserving probability/possibility transformation for the combined treatment of random and fuzzy variables  

Energy Technology Data Exchange (ETDEWEB)

Different formalisms can be applied to decision-making problems with uncertain quantities. If the information is given by a large number of statistical data, the corresponding parameters can be interpreted as random variables and the results can be calculated by the rules of the probability theory. If the information consists however of subjective expert knowledge, the parameters can be interpreted as fuzzy variables and the results can be calculated by the rules of possibility theory. If both kinds of information appear in a problem with several parameters, transformations between probability and possibility distributions are necessary to make the problem treatable within one formalism. A probability/possibility transformation that fulfills simultaneously the consistency principle and conserves uncertainty is presented. For the implementation of expert knowledge into a probablistic framework, it is an alternative to the method of unbiased guess.

Wonneberger, S. [Brenk Systemplanung Ingenieurbuero fuer Wissenschaftlich-Technischen Umweltschutz, Aachen (Germany)

1994-12-31

146

On the nonexistence of a law of the iterated logarithm for weighted sums of identically distributed random variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

For weighted sums of independent and identically distributed random variables, conditions are placed under which a generalized law of the iterated logarithm cannot hold, thereby extending the usual nonweighted situation.

André Adler

1990-01-01

147

On the nonexistence of a law of the iterated logarithm for weighted sums of identically distributed random variables  

Directory of Open Access Journals (Sweden)

Full Text Available For weighted sums of independent and identically distributed random variables, conditions are placed under which a generalized law of the iterated logarithm cannot hold, thereby extending the usual nonweighted situation.

André Adler

1990-01-01

148

EM-random forest and new measures of variable importance for multi-locus quantitative trait linkage analysis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Motivation: We developed an EM-random forest (EMRF) for Haseman–Elston quantitative trait linkage analysis that accounts for marker ambiguity and weighs each sib-pair according to the posterior identical by descent (IBD) distribution. The usual random forest (RF) variable importance (VI) index used to rank markers for variable selection is not optimal when applied to linkage data because of correlation between markers. We define new VI indices that borrow information from linked markers usi...

Lee, Sophia S. F.; Sun, Lei; Kustra, Rafal; Bull, Shelley B.

2008-01-01

149

Metamagnetic transitions in a random anisotropy model with mixed temperature dependent exchange coupling  

International Nuclear Information System (INIS)

The random magnetic anisotropy model with mixed temperature dependent exchange coupling is used to describe metamagnetic transitions in certain amorphous rare earth alloys. The Hamiltonian for these amorphous magnetic systems is derived. In order to see the antiferromagnetic to ferromagnetic metamagnetic transition the free energy in absence of an external magnetic field is calculated in dependence on absolute temperature. The critical temperature of the metamagnetic transition is the same for both the crystalline and the amorphous phases

150

Brief Treatments for Cannabis Dependence: Findings From a Randomized Multisite Trial  

Science.gov (United States)

This study evaluated the efficacy of 2 brief interventions for cannabis-dependent adults. A multisite randomized controlled trial compared cannabis use outcomes across 3 study conditions: (a) 2 sessions of motivational enhancement therapy (MET); (b) 9 sessions of multicomponent therapy that included MET, cognitive-behavioral therapy, and case…

Babor, Thomas F.

2004-01-01

151

On homogenization of space-time dependent and degenerate random flows II  

CERN Document Server

We study the long time behavior (homogenization) of a diffusion in random medium with time and space dependent coefficients. The diffusion coefficient may degenerate. In Stochastic Process. Appl. (2007) (to appear), an invariance principle is proved for the critical rescaling of the diffusion. Here, we generalize this approach to diffusions whose space-time scaling differs from the critical one.

Rhodes, Rémi

2008-01-01

152

Nuclear partition functions in the random phase approximation and the temperature dependence of collective states  

International Nuclear Information System (INIS)

Green functions techniques at finite temperature are used to calculate nuclear partition functions in the random phase approximation. The theory is shown to yield corrections to the results of functional methods neglecting exchange terms. We discuss the special case of a schematic model for which the level density and the temperature dependence of collective states can be worked out explicitly. (orig.)

153

The covariation of independent and dependant variables in neurofeedback: a proposal framework to identify cognitive processes and brain activity variables.  

Science.gov (United States)

This methodological article proposes a framework for analysing the relationship between cognitive processes and brain activity using variables measured by neurofeedback (NF) carried out by functional Magnetic Resonance Imagery (fMRI NF). Cognitive processes and brain activity variables can be analysed as either the dependant variable or the independent variable. Firstly, we propose two traditional approaches, defined in the article as the "neuropsychological" approach (NP) and the "psychophysiology" approach (PP), to extract dependent and independent variables in NF protocols. Secondly, we suggest that NF can be inspired by the style of inquiry used in neurophenomenology. fMRI NF allows participants to experiment with his or her own cognitive processes and their effects on brain region of interest (ROI) activations simultaneously. Thus, we suggest that fMRI NF could be improved by implementing "the elicitation interview method", which allows the investigator to gather relevant verbatim from participants' introspection on subjective experiences. PMID:24755406

Micoulaud-Franchi, Jean-Arthur; Quiles, Clélia; Fond, Guillaume; Cermolacce, Michel; Vion-Dury, Jean

2014-05-01

154

Measuring spatiotemporal dependencies in bivariate temporal random sets with applications to cell biology.  

Science.gov (United States)

Analyzing spatio-temporal dependencies between different types of events is highly relevant to numerous biological phenomena (e.g. signalling and trafficking) especially as advances in probes and microscopy have facilitated imaging of dynamic processes in living cells. For many types of events, the segmented areas can overlap spatially and temporally forming random clumps. In this paper, we model binary image sequences of two different event types as a realization of a bivariate temporal random set and propose a non-parametric approach to quantify spatial and spatio-temporal interrelations using the pair-correlation, cross-covariance and the Ripley IK functions. Based on these summary statistics we propose a randomization procedure to test independence between event types by applying random toroidal shifts and Monte Carlo tests. A simulation study assessed the performance of the proposed estimators and showed that these statistics capture the spatio-temporal dependencies accurately. The estimation of the spatio-temporal interval of interactions was also obtained. The method was successfully applied to analyze the interdependencies of several endocytic proteins using image sequences of living cells and validated the procedure as a new way to automatically quantify dependencies between proteins in a formal and robust manner. PMID:18617722

Díaz, Ester; Sebastian, Rafael; Ayala, Guillermo; Díaz, María Elena; Zoncu, Roberto; Toomre, Derek; Gasman, Stéphane

2008-09-01

155

Estimation of a System Performance in Pareto Distribution with Two Independent Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available This study relied on applications of statistical methods used in the field of physics, specifically study the relationship between the strength and stress of a component in the mechanical system and so the performance of the mechanical system can be estimated. The study dealt with the estimation of the system performance R where R is equal to P[Yrandom variables represent the strength of a component in the system and stress, respectively belonging to Pareto distributions with three parameters. The maximum likelihood was implemented to estimate the values of the parameters. On the other hand, simulation study was applied to investigate the measure of the system performance R and a numerical application was presented to illustrate the implementation of mathematical procedures, moreover the steps method used in this study enables the researchers to apply it in their fields.

Medhat Ahmed El Damsesy

2014-01-01

156

On Direction of Dependence in Latent Variable Contexts  

Science.gov (United States)

Approaches to determining direction of dependence in nonexperimental data are based on the relation between higher-than second-order moments on one side and correlation and regression models on the other. These approaches have experienced rapid development and are being applied in contexts such as research on partner violence, attention deficit…

von Eye, Alexander; Wiedermann, Wolfgang

2014-01-01

157

Testing serial dependence by Random-shuffle surrogates and the Wayland method  

International Nuclear Information System (INIS)

Given time series, a primary concern is existence of serial dependence and determinism. They are often tested with Random-shuffle surrogates, which totally break serial dependence, and the Wayland method. Since the statistic of the Wayland method fundamentally shows a smaller value for a more deterministic time series, for real-world data, we usually expect that the statistic for the original data is smaller than or equal to those of Random-shuffle surrogates. However, we show herewith an opposite result with wind data in high time resolution. We argue that this puzzling phenomenon can be produced by observational or dynamical noise, both of which may be produced by a low-dimensional deterministic system. Thus the one-sided test is dangerous

158

Advantages of joint modeling of component HIV risk behaviors and non-response: application to randomized trials in cocaine-dependent and methamphetamine-dependent populations  

Directory of Open Access Journals (Sweden)

Full Text Available The HIV risk-taking behavior scale (HRBS is an 11-item instrument designed to assess the risks of HIV infection due self-reported injection drug use and sexual behavior. A retrospective analysis was performed on HRBS data collected from approximately 1,000 participants pooled across seven clinical trials of pharmacotherapies for either the treatment of cocaine-dependence or methamphetamine-dependence. Analysis faced three important challenges. The sample contained a high proportion of missing assessments after randomization. Also, the HRBS scale consists of two distinct behavioral components which may or may not coincide in response patterns. In addition, distributions of responses on the subscales were highly concentrated at just a few values (e.g., 0, 6. To address these challenges, a single probit regression model was fit to three outcomes variables simultaneously—the two subscale totals plus an indicator variable for assessments not obtained (non-response. This joint-outcome regression model was able to identify that those who left assessment early had higher self-reported risk of injection-drug use and lower self-reported risky sexual behavior because the model was able to draw on information on associations among the three outcomes collectively. These findings were not identified in analyses performed on each outcome separately. No evidence for an effect of pharmacotherapies was observed, except to reduce missing assessments. Univariate-outcome modeling is not recommended for the HRBS.

TysonHHolmes

2011-07-01

159

On Rates of Convergence for Markov Chins under Random Time State Dependent Drift Criteria  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Many applications in networked control require intermittent access of a controller to a system, as in event-triggered systems or information constrained control applications. Motivated by such applications and extending the literature on Lyapunov-theoretic drift criteria, we establish both subgeometric and geometric rates rates of convergence for Markov chains under state dependent random time drift criteria. We quantify how the rate of ergodicity, nature of Lyapunov functio...

Zurkowski, Ramiro; Yu?ksel, Serdar; Linder, Tama?s

2013-01-01

160

The limit distribution of the maximum increment of a random walk with dependent regularly varying jump sizes  

DEFF Research Database (Denmark)

We investigate the maximum increment of a random walk with heavy-tailed jump size distribution. Here heavy-tailedness is understood as regular variation of the finite-dimensional distributions. The jump sizes constitute a strictly stationary sequence. Using a continuous mapping argument acting on the point processes of the normalized jump sizes, we prove that the maximum increment of the random walk converges in distribution to a Fréchet distributed random variable.

Mikosch, Thomas Valentin; Moser, Martin

2013-01-01

 
 
 
 
161

Electrochemical variable dependence of zinc electrodeposited onto electropolished steel substrate  

International Nuclear Information System (INIS)

The texture and morphology of zinc coatings obtained onto a low carbon electropolished steel substrate in an acid sulfate bath have been compared. Morphology of zinc deposit on electropolished surfaces consisted of layered thin hexagonal crystals, which were laid on each other and aligned, in a specific variant on each grain surface. Variants observed on various grain surfaces were different. Partial textures evaluated by means of In-Sheet-Plane Percentage method revealed that electropolished surface promoted strong basal plane component along with weaker low angle pyramidal planes. Increasing current density up to 200 mA.cm-2 or decreasing temperature increased the intensity of basal plane and decreased the intensity of low angle pyramidal ones. Potentiostatic current-time plots and AC Impedance were used to observe effects of electrochemical variables on nucleation and growth. The results showed that nucleation process was instantaneous, and growth process was charge transfer controlled, influenced effectively with overvoltage. It can be concluded that increasing the current density and/or decreasing the temperature would increase the overvoltage, and thus increase the basal planes parallel to steel surface. (author)

162

The Distribution of Minimum of Ratios of Two Random Variables and Its Application in Analysis of Multi-hop Systems  

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Full Text Available The distributions of random variables are of interest in many areas of science. In this paper, ascertaining on the importance of multi-hop transmission in contemporary wireless communications systems operating over fading channels in the presence of cochannel interference, the probability density functions (PDFs of minimum of arbitrary number of ratios of Rayleigh, Rician, Nakagami-m, Weibull and ?-µ random variables are derived. These expressions can be used to study the outage probability as an important multi-hop system performance measure. Various numerical results complement the proposed mathematical analysis.

A. Stankovic

2012-12-01

163

Statistical analysis of mesoscale rainfall: Dependence of a random cascade generator on large-scale forcing  

Science.gov (United States)

Under the theory of independent and identically distributed random cascades, the probability distribution of the cascade generator determines the spatial and the ensemble properties of spatial rainfall. Three sets of radar-derived rainfall data in space and time are analyzed to estimate the probability distribution of the generator. A detailed comparison between instantaneous scans of spatial rainfall and simulated cascades using the scaling properties of the marginal moments is carried out. This comparison highlights important similarities and differences between the data and the random cascade theory. Differences are quantified and measured for the three datasets. Evidence is presented to show that the scaling properties of the rainfall can be captured to the first order by a random cascade with a single parameter. The dependence of this parameter on forcing by the large-scale meteorological conditions, as measured by the large-scale spatial average rain rate, is investigated for these three datasets. The data show that this dependence can be captured by a one-to-one function. Since the large-scale average rain rate can be diagnosed from the large-scale dynamics, this relationship demonstrates an important linkage between the large-scale atmospheric dynamics and the statistical cascade theory of mesoscale rainfall. Potential application of this research to parameterization of runoff from the land surface and regional flood frequency analysis is briefly discussed, and open problems for further research are presented.

Over, Thomas, M.; Gupta, Vijay K.

1994-01-01

164

Marcinkiewicz-type strong law of large numbers for double arrays of pairwise independent random variables  

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Full Text Available Let {Xij} be a double sequence of pairwise independent random variables. If P{|Xmn|≥t}≤P{|X|≥t} for all nonnegative real numbers t and E|X|p(log+|X|3<∞, for 1random variables under the conditions E|X|p(log+|X|r+1<∞,E|X|p(log+|X|r−1<∞, respectively, thus, extending Choi and Sung's result [1] of the one-dimensional case.

Seok Yoon Hwang

1999-03-01

165

Numerical Simulation of Blinking Quantum dot Based on Temperature Dependence 3-Dimensional Levy Random Walk  

Directory of Open Access Journals (Sweden)

Full Text Available Blinking statistics of quantum dot has attracted much attraction in recent years. Various experiments were conducted and various theories have been given to explain this phenomenon. However, the problem is not yet resolved. The weak temperature dependence of the power law parameters have complicated the phenomena. We have simulated the blinking statistics of quantum dot based on the random walk model. We have shown that three-dimensional biased Levy random walk of electrons, the bias being the Columbic interaction between electrons and ionized atoms can explain the observed experimental results. We have simulated the blinking properties of quantum dots in a broad temperature range (10-300 K. The distributions exhibit power law behavior for a wide range of temperature, but the power law parameter increases marginally with temperature. The trend of change is independent of the size of the quantum dots as confirmed from the simulation.

Anita Sharma

2011-01-01

166

Data analysis with ordinal and interval dependent variables: examples from a study of real estate salespeople  

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Full Text Available This paper re-examines the problems of estimating the parameters of an underlying linear model using survey response data in which the dependent variables are in discrete categories of ascending order (ordinal, as distinct from numerical or, where they are observed to fall into certain groups on a continuous scale (interval, where the actual values remain unobserved. An ordered probit model is discussed as an appropriate framework for statistical analysis for ordinal dependent variables. Next, a maximum likelihood estimator (MLE derived from grouped data regression for interval dependent variable is discussed. Using LIMDEP, a packaged statistical program, survey data from an earlier manuscript are analyzed and the findings presented.

G. Martin Izzo

2008-05-01

167

The use of random amplified polymorphic DNA to evaluate the genetic variability of Ponkan mandarin (Citrus reticulata Blanco accessions  

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Full Text Available RAPD analysis of 19 Ponkan mandarin accessions was performed using 25 random primers. Of 112 amplification products selected, only 32 were polymorphic across five accessions. The absence of genetic variability among the other 14 accessions suggested that they were either clonal propagations with different local names, or that they had undetectable genetic variability, such as point mutations which cannot be detected by RAPD.

Coletta Filho Helvécio Della

2000-01-01

168

Towards Swarm Diversity: Random Sampling in Variable Neighborhoods Procedure Using a Lévy Distribution  

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Full Text Available Particle Swarm Optimization (PSO es un método de búsqueda no directo para la optimización numérica. Las principales ventajas de esta meta-heurística están relacionadas principalmente con su simplicidad, pocos parámetros y alta tasa de convergencia. En el PSO canónico usando una topología totalmente conectada, una partícula ajusta su posición usando dos atractores: el mejor registro almacenado por el individuo y el mejor punto descubierto por la bandada completa. Este esquema conduce a un alto factor de convergencia, pero también deteriora la diversidad de la población progresivamente. Como resultado la bandada de partículas frecuentemente es atraída por puntos sub-óptimos. Una vez que las partículas han sido atraídas hacia un óptimo local, ellas continúan el proceso de búsqueda dentro de una región muy pequeña del espacio de soluciones, reduciendo las capacidades de exploración del algoritmo. Para tratar esta situación este artículo presenta una variante del procedimiento Random Sampling in Variable Neighborhoods (RSVN usando una distribución de Lévy. Este algoritmo es capaz de mejorar notablemente la capacidad de búsqueda de los algoritmos PSO en problemas multimodales de optimización.

Gonzalo N\\u00E1poles

2014-01-01

169

Optimal two-value zero-mean disintegration of zero-mean random variables  

CERN Document Server

For any continuous zero-mean random variable (r.v.) X, a reciprocating function r is constructed, based only on the distribution of X, such that the conditional distribution of X given the (at-most-)two-point set {X,r(X)} is the zero-mean distribution on this set; in fact, a more general construction without the continuity assumption is given in this paper, as well as a large variety of other related results, including characterizations of the reciprocating function and modeling distribution asymmetry patterns. The mentioned disintegration of zero-mean r.v.'s implies, in particular, that an arbitrary zero-mean distribution is represented as the mixture of two-point zero-mean distributions; moreover, this mixture representation is most symmetric in a variety of senses. Somewhat similar representations -- of any probability distribution as the mixture of two-point distributions with the same skewness coefficient (but possibly with different means) -- go back to Kolmogorov; very recently, Aizenman et al. further...

Pinelis, Iosif

2008-01-01

170

Credible Mendelian Randomization Studies: Approaches for Evaluating the Instrumental Variable Assumptions  

Science.gov (United States)

As with other instrumental variable (IV) analyses, Mendelian randomization (MR) studies rest on strong assumptions. These assumptions are not routinely systematically evaluated in MR applications, although such evaluation could add to the credibility of MR analyses. In this article, the authors present several methods that are useful for evaluating the validity of an MR study. They apply these methods to a recent MR study that used fat mass and obesity-associated (FTO) genotype as an IV to estimate the effect of obesity on mental disorder. These approaches to evaluating assumptions for valid IV analyses are not fail-safe, in that there are situations where the approaches might either fail to identify a biased IV or inappropriately suggest that a valid IV is biased. Therefore, the authors describe the assumptions upon which the IV assessments rely. The methods they describe are relevant to any IV analysis, regardless of whether it is based on a genetic IV or other possible sources of exogenous variation. Methods that assess the IV assumptions are generally not conclusive, but routinely applying such methods is nonetheless likely to improve the scientific contributions of MR studies. PMID:22247045

Glymour, M. Maria; Tchetgen Tchetgen, Eric J.; Robins, James M.

2012-01-01

171

Bell-Boole Inequality: Nonlocality or Probabilistic Incompatibility of Random Variables?  

Directory of Open Access Journals (Sweden)

Full Text Available The main aim of this report is to inform the quantum information community about investigations on the problem of probabilistic compatibility of a family of random variables: a possibility to realize such a family on the basis of a single probability measure (to construct a single Kolmogorov probability space. These investigations were started hundred of years ago by J. Boole (who invented Boolean algebras. The complete solution of the problem was obtained by Soviet mathematician Vorobjev in 60th. Surprisingly probabilists and statisticians obtained inequalities for probabilities and correlations among which one can find the famous Bell’s inequality and its generalizations. Such inequalities appeared simply as constraints for probabilistic compatibility. In this framework one can not see a priori any link to such problems as nonlocality and “death of reality” which are typically linked to Bell’s type inequalities in physical literature. We analyze the difference between positions of mathematicians and quantum physicists. In particular, we found that one of the most reasonable explanations of probabilistic incompatibility is mixing in Bell’s type inequalities statistical data from a number of experiments performed under different experimental contexts.

Andrei Khrennikov

2008-03-01

172

Double-blind, randomized placebo-controlled clinical trial of benfotiamine for severe alcohol dependence.  

Science.gov (United States)

Alcohol dependence is associated with severe nutritional and vitamin deficiency. Vitamin B1 (thiamine) deficiency erodes neurological pathways that may influence the ability to drink in moderation. The present study examines tolerability of supplementation using the high-potency thiamine analog, benfotiamine (BF), and BF's effects on alcohol consumption in severely affected, self-identified, alcohol dependent subjects. A randomized, double-blind, placebo-controlled trial was conducted on 120 non-treatment seeking, actively drinking, alcohol dependent men and women volunteers (mean age=47 years) from the Kansas City area who met DSM-IV-TR criteria for current alcohol dependence. Subjects were randomized to receive 600 mg benfotiamine or placebo (PL) once daily by mouth for 24 weeks with 6 follow-up assessments scheduled at 4 week intervals. Side effects and daily alcohol consumption were recorded. Seventy (58%) subjects completed 24 weeks of study (N=21 women; N=49 men) with overall completion rates of 55% (N=33) for PL and 63% (N=37) for BF groups. No significant adverse events were noted and alcohol consumption decreased significantly for both treatment groups. Alcohol consumption decreased from baseline levels for 9 of 10 BF treated women after 1 month of treatment compared with 2 of 11 on PL. Reductions in total alcohol consumption over 6 months were significantly greater for BF treated women (BF: N=10, -611 ± 380 standard drinks; PL: N=11, -159 ± 562 standard drinks, p-value=0.02). BF supplementation of actively drinking alcohol dependent men and women was well-tolerated and may discourage alcohol consumption among women. The results do support expanded studies of BF treatment in alcoholism. PMID:23992649

Manzardo, Ann M; He, Jianghua; Poje, Albert; Penick, Elizabeth C; Campbell, Jan; Butler, Merlin G

2013-12-01

173

Continuum quasiparticle random phase approximation and the time dependent Hartree-Fock-Bogoliubov approach  

CERN Document Server

Quadrupole excitations of neutron-rich nuclei are analyzed by using the linear response method in the Quasiparticle Random Phase Approximation (QRPA). The QRPA response is derived starting from the time-dependent Hartree-Fock-Bogoliubov (HFB) equations. The residual interaction between the quasiparticles is determined consistently from the two-body force used in the HFB equations, and the continuum coupling is treated exactly. Calculations are done for the neutron-rich oxygen isotopes. It is found that pairing correlations affect the low-lying states, and that a full treatment of the continuum can change the structure of the states in the giant resonance region.

Khan, E; Grasso, M; Nguyen Van Giai; Giai, Nguyen Van

2002-01-01

174

Continuum quasiparticle random phase approximation and the time dependent Hartree-Fock-Bogoliubov approach  

Energy Technology Data Exchange (ETDEWEB)

Quadrupole excitations of neutron-rich nuclei are analyzed by using the linear response method in the Quasiparticle Random Phase Approximation (QRPA). The QRPA response is derived starting from the time-dependent Hartree-Fock-Bogoliubov (HFB) equations. The residual interaction between the quasiparticles is determined consistently from the two-body force used in the HFB equations, while the continuum coupling is treated exactly. Calculations are done for the neutron-rich oxygen isotopes. It is found that pairing correlations affect the low-lying states, and that a full treatment of the continuum can change the structure of the states in the giant resonance region. (authors)

Khan, E.; Grasso, M; Van Giai, Nguyen [Institut de Physique Nucleaire, IN2P3-CNRS, F-91406 Orsay (France); Sandulescu, N. [Horia Hulubei National Institute for Physics and Nuclear Engineering, PO Box MG-6, RO-76900 Bucharest - Magurele (Romania)]|[Research Center for Nuclear Physics, Osaka University, 567-0047 Osaka (Japan)

2002-07-01

175

Some inequalities for random variables whose probability density functions are absolutely continuous using a pre-Chebychev inequality  

Directory of Open Access Journals (Sweden)

Full Text Available Using the pre-Chebychev inequality considered by Matic, Pecaric and Ujevic in [2], some inequalities are obtained for random variables whose p.d.f.s are absolutely continuous and whose derivatives are in $ L_{\\infty} [a,b] $.

N. S. Barnett

2001-03-01

176

Secure Mobile Banking Application Using Elliptic Curve Cryptography & RGB Intensity Based Randomized Pixels With Variable Bits Image Steganography  

Directory of Open Access Journals (Sweden)

Full Text Available The Wide-expansion of mobile telecommunication technology mobile banking emerged as a new type of financial services and can provide efficient and effective financial services for clients. Mobile banking is a way for the customer to perform banking actions on his or her cell phone or other mobile device. It is a quite popular method of banking that fits in well with a busy, technologically oriented lifestyle. Framework conditions for mobile banking services differ from country to country but one thing is certain: the future of mobile banking depends on getting the security right. In this paper, we present a new way of securing mobile banking. We introduce a system which makes use of Elliptic curve cryptography and RGB Intensity Based Randomized pixels with variable Bits image Steganography [5]. Elliptic Curve Cryptography suites well for resources constraint devices like mobile phones and PDA, because of its less computation time, short key’s length, fast digital signature, flexibility and less resource consumption

K.Manikandan

2011-02-01

177

Complete Convergence and Weak Law of Large Numbers for ?-Mixing Sequences of Random Variables  

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Full Text Available In this paper, the complete convergence and weak law of large numbers are established for ?-mixing sequences of random variables. Our results extend and improve the Baum and Katz complete convergence theorem and the classical weak law of large numbers, etc. from independent sequences of random variables to ?-mixing sequences of random variables without necessarily adding any extra conditions.

Qunying Wu

2012-12-01

178

Detection of Genetic Variability using Random Amplified Polymorphic DNA Markers in Some Accessions of Moringa oleifera Lam. from Northern Nigeria  

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Full Text Available To investigate genetic variability in Moringa oleifera Lam., 75 accessions from the Sudan and Guinea savanna zones in Nigeria were taxonomically analysed using Random Amplified polymorphic DNA (RAPD markers. The electrophoresis bands were analysed using NTSYSpc software and the result of their matrices indicated different variability in the accessions. High degrees of polymorphism (74% among the accessions were observed in terms of genetic relationship and were grouped into five clusters. This high variability can be utilised for mapping out breeding strategies in the production of cultivars with better yield of M. oleifera to meet the pressing needs of these multi-purpose crop to our growing populations.

A.U. Khan

2011-01-01

179

Cryptography based on chaotic random maps with position dependent weighting probabilities  

International Nuclear Information System (INIS)

Chaotic cryptology has been widely investigated recently. A common feature in the most recent developments of chaotic cryptosystems is the use of a single dynamical rule in the encoding-decoding process. The main objective of this paper is to provide a set of chaotic systems instead of a single one for cryptography. In this paper, we introduce a chaotic cryptosystem based on the symbolic dynamics of random maps with position dependent weighting probabilities. The random maps model is a deterministic dynamical system in a finite phase space with n points. The maps that establish the dynamics of the system are chosen randomly for every point. The essential idea of this paper is that, given two dynamical systems that behave in a certain way, it is possible to combine them (by composing) into a new dynamical system. This dynamically composed system behaves in a completely different way compared to the constituent systems. The proposed scheme exploits the symbolic dynamics of a set of chaotic maps in order to encode the binary information. The performance of the new cryptosystem based on chaotic dynamical systems properties is examined. Both theoretical and experimental results demonstrate that the proposed algorithm using symbolic dynamics achieves the optimal security criteria.

180

Analysis, quantification, and mitigation of electrical variability due to layout dependent effects in SOC designs  

Science.gov (United States)

Variability in performance and power of 40nm and 28nm CMOS cells is highly dependent on the context in which the cells are used. In this study, the effects of context on a number of clock tree cells from standard cell libraries have been investigated. The study also demonstrated how the Litho Electrical Analyzer (LEA) tool from Cadence® is used to analyze the context-dependent variability. During the study, it was observed that the device characteristics including Vth, Idsat, and Ioff are significantly affected by Layout Dependent Effects (LDE), resulting in variability of performance and power of standard cells. Moreover, the dummy diffusions acting as mitigation process offered limited improvement for the effects of context. On the other hand, the cell level variability due to stress was analyzed. So, it is suggested that the relative variability of a cell is determined by its size and structure, and the variability can be improved to some extent by editing the cells' structure. Based on the analysis of the physical sources and properties of LDE, this paper presents a set of layout guidelines for mitigating layout dependent variability of 40 and 28nm CMOS cells.

Wang, Yangang; Zwolinski, Mark; Appleby, Andrew; Scoones, Mark; Caldwell, Sonia; Azam, Touqeer; Hurat, Philippe; Pitchford, Chris

2012-03-01

 
 
 
 
181

Auricular acupuncture for chemically dependent pregnant women: a randomized controlled trial of the NADA protocol  

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Full Text Available Abstract Background The prevalence of maternal drug use during pregnancy in North America has been estimated to be as high as 6-10%. The consequences for the newborn include increased risk for perinatal mortality and ongoing physical, neurobehavioral, and psychosocial problems. Methadone is frequently used to wean women off street drugs but is implicated as a cause of adverse fetal/neonatal outcomes itself. The purpose of our study was to test the ability of maternal acupuncture treatment among mothers who use illicit drugs to reduce the frequency and severity of withdrawal symptoms among their newborns. Methods We randomly assigned chemically dependent pregnant women at BC Women’s Hospital in Vancouver, British Columbia to daily acupuncture treatments versus usual care. By necessity, neither our participants nor acupuncturists were blinded as to treatment allocation. Our primary outcome was days of neonatal morphine treatment for symptoms of neonatal withdrawal. Secondary neonatal outcomes included admission to a neonatal ICU and transfer to foster care. Results We randomized 50 women to acupuncture and 39 to standard care. When analyzed by randomized groups, we did not find benefit of acupuncture; the average length of treatment with morphine for newborns in the acupuncture group was 2.7 (6.3 compared to 2.8 (7.0 in the control group. Among newborns of women who were compliant with the acupuncture regime, we observed a reduction of 2.1 and 1.5 days in length of treatment for neonatal abstinence syndrome compared to the non-compliant and control groups, respectively. These differences were not statistically significant. Conclusions Acupuncture may be a safe and feasible treatment to assist mothers to reduce their dosage of methadone. Our results should encourage ongoing studies to test the ability of acupuncture to mitigate the severity of neonatal abstinence syndrome among their newborns. Clinical Trial Registration http://www.clinicaltrials.gov registry: W05-0041

Janssen Patricia A

2012-12-01

182

Dimension-Dependent behavior in the satisfability of random k-Horn formulae  

CERN Document Server

We determine the asymptotical satisfiability probability of a random at-most-k-Horn formula, via a probabilistic analysis of a simple version, called PUR, of positive unit resolution. We show that for k=k(n)->oo the problem can be ``reduced'' to the case k(n)=n, that was solved in cs.DS/9912001. On the other hand, in the case k= a constant the behavior of PUR is modeled by a simple queuing chain, leading to a closed-form solution when k=2. Our analysis predicts an ``easy-hard-easy'' pattern in this latter case. Under a rescaled parameter, the graphs of satisfaction probability corresponding to finite values of k converge to the one for the uniform case, a ``dimension-dependent behavior'' similar to the one found experimentally by Kirkpatrick and Selman (Science'94) for k-SAT. The phenomenon is qualitatively explained by a threshold property for the number of iterations of PUR makes on random satisfiable Horn formulas.

Istrate, Gabriel

2000-01-01

183

Advancing density waves and phase transitions in a velocity dependent randomization traffic cellular automaton  

CERN Document Server

Within the class of stochastic cellular automata models of traffic flows, we look at the velocity dependent randomization variant (VDR-TCA) whose parameters take on a specific set of extreme values. These initial conditions lead us to the discovery of the emergence of four distinct phases. Studying the transitions between these phases, allows us to establish a rigorous classification based on their tempo-spatial behavioral characteristics. As a result from the system's complex dynamics, its flow-density relation exhibits a non-concave region in which forward propagating density waves are encountered. All four phases furthermore share the common property that moving vehicles can never increase their speed once the system has settled into an equilibrium.

Maerivoet, S; Maerivoet, Sven; Moor, Bart De

2004-01-01

184

Spatial variability and its scale dependency of observed and modeled soil moisture over different climate regions  

Directory of Open Access Journals (Sweden)

Full Text Available Past studies on soil moisture spatial variability have been mainly conducted at catchment scales where soil moisture is often sampled over a short time period; as a result, the observed soil moisture often exhibited smaller dynamic ranges, which prevented the complete revelation of soil moisture spatial variability as a function of mean soil moisture. In this study, spatial statistics (mean, spatial variability and skewness of in situ soil moisture, modeled and satellite-retrieved soil moisture obtained in a warm season (198 days were examined over three large climate regions in the US. The study found that spatial moments of in situ measurements strongly depend on climates, with distinct mean, spatial variability and skewness observed in each climate zone. In addition, an upward convex shape, which was revealed in several smaller scale studies, was observed for the relationship between spatial variability of in situ soil moisture and its spatial mean when statistics from dry, intermediate, and wet climates were combined. This upward convex shape was vaguely or partially observable in modeled and satellite-retrieved soil moisture estimates due to their smaller dynamic ranges. Despite different environmental controls on large-scale soil moisture spatial variability, the correlation between spatial variability and mean soil moisture remained similar to that observed at small scales, which is attributed to the boundedness of soil moisture. From the smaller support (effective area or volume represented by a measurement or estimate to larger ones, soil moisture spatial variability decreased in each climate region. The scale dependency of spatial variability all followed the power law, but data with large supports showed stronger scale dependency than those with smaller supports. The scale dependency of soil moisture variability also varied with climates, which may be linked to the scale dependency of precipitation spatial variability. Influences of environmental controls on soil moisture spatial variability at large scales are discussed. The results of this study should be useful for diagnosing large scale soil moisture estimates and for improving the estimation of land surface processes.

B. Li

2013-03-01

185

Simple, Efficient Estimators of Treatment Effects in Randomized Trials Using Generalized Linear Models to Leverage Baseline Variables  

Science.gov (United States)

Models, such as logistic regression and Poisson regression models, are often used to estimate treatment effects in randomized trials. These models leverage information in variables collected before randomization, in order to obtain more precise estimates of treatment effects. However, there is the danger that model misspecification will lead to bias. We show that certain easy to compute, model-based estimators are asymptotically unbiased even when the working model used is arbitrarily misspecified. Furthermore, these estimators are locally efficient. As a special case of our main result, we consider a simple Poisson working model containing only main terms; in this case, we prove the maximum likelihood estimate of the coefficient corresponding to the treatment variable is an asymptotically unbiased estimator of the marginal log rate ratio, even when the working model is arbitrarily misspecified. This is the log-linear analog of ANCOVA for linear models. Our results demonstrate one application of targeted maximum likelihood estimation. PMID:20628636

Rosenblum, Michael; van der Laan, Mark J.

2010-01-01

186

RELIABILITY MEASURES OF A SINGLE-UNIT SYSTEM UNDER PREVENTIVE MAINTENANCE AND DEGRADATION WITH ARBITRARY DISTRIBUTIONS OF RANDOM VARIABLES  

Directory of Open Access Journals (Sweden)

Full Text Available The main objective of this paper is to analyze a si ngle-unit system with arbitrary distributions for all random variables associated w ith failure time, preventive maintenance (PM, maximum operation time (MOT, inspection and repair times. There is a single server who visits the system immediately whenever needed. The partial ly failed unit undergoes for PM after a MOT. The unit is considered as degraded after repai r while preventive maintenance is perfect. Server inspects the degraded unit at its failure to see the feasibility of repair. If repair of the degraded unit is not feasible, it is replaced immed iately by new one. The expressions for some reliability measures are obtained in steady state u sing regenerative point technique. Giving particular values to various parameters and costs, the numerical results for mean time to system failure (MTSF, availability and profit function ar e obtained considering exponential and Rayleigh distributions for all random variables .

Jitender Kumar

2014-04-01

187

Limiting behavior of the perturbed empirical distribution functions evaluated at U-statistics for strongly mixing sequences of random variables  

Directory of Open Access Journals (Sweden)

Full Text Available We prove the almost sure representation, a law of the iterated logarithm and an invariance principle for the statistic Fˆn(Un for a class of strongly mixing sequences of random variables {Xi,i?1}. Stationarity is not assumed. Here Fˆn is the perturbed empirical distribution function and Un is a U-statistic based on X1,…,Xn.

Shan Sun

1997-01-01

188

On angular momentum and parity dependence of nuclear level densities in a simple random sampling approach  

International Nuclear Information System (INIS)

Based on simple random sampling (SRS), we propose a Monte Carlo method for the faster computation of the smoothed part of the density of nuclear states. To test the applicability of the SRS approach we study in this framework the excitation energy (E), angular momentum (J) and parity dependence of nuclear level densities for an independent particle system. As an illustrative example, we consider a pf-shell nucleus, 48Cr. It is found that the values of a few lower order moments for the state density I(E) calculated using SRS and combinatorial (or direct counting) methods are almost the same and a locally smoothed part of the state density can be constructed using these moments in a univariate Edgeworth expansion. We calculate the energy dependent spin-cutoff factor and parity asymmetry and find that for both cases the SRS approach works quite well. We use the SRS moments to construct different forms of the bivariate distribution for I(E,M) (M is the z-component of J) namely (a) a bivariate Edgeworth expansion, (b) a product of the univariate Edgeworth expansion (I(E)) and a Gaussian form for conditional M distribution I(M vertical stroke E) and (c) a product of the univariate Edgeworth expansions for both I(E) and I(M vertical stroke E) and compare the resulting fixed-J level density Il(E,J) with the corresponding combinatorial results. (orig.)

189

Spatial variability and its scale dependency of observed and modeled soil moisture under different climate conditions  

Directory of Open Access Journals (Sweden)

Full Text Available Past studies on soil moisture spatial variability have been mainly conducted in catchment scales where soil moisture is often sampled over a short time period. Because of limited climate and weather conditions, the observed soil moisture often exhibited smaller dynamic ranges which prevented the complete revelation of soil moisture spatial variability as a function of mean soil moisture. In this study, spatial statistics (mean, spatial variability and skewness of in situ soil moisture measurements (from a continuously monitored network across the US, modeled and satellite retrieved soil moisture obtained in a warm season (198 days were examined at large extent scales (>100 km over three different climate regions. The investigation on in situ measurements revealed that their spatial moments strongly depend on climates, with distinct mean, spatial variability and skewness observed in each climate zone. In addition, an upward convex shape, which was revealed in several smaller scale studies, was observed for the relationship between spatial variability of in situ soil moisture and its spatial mean across dry, intermediate, and wet climates. These climate specific features were vaguely or partially observable in modeled and satellite retrieved soil moisture estimates, which is attributed to the fact that these two data sets do not have climate specific and seasonal sensitive mean soil moisture values, in addition to lack of dynamic ranges. From the point measurements to satellite retrievals, soil moisture spatial variability decreased in each climate region. The three data sources all followed the power law in the scale dependency of spatial variability, with coarser resolution data showing stronger scale dependency than finer ones. The main findings from this study are: (1 the statistical distribution of soil moisture depends on spatial mean soil moisture values and thus need to be derived locally within any given area; (2 the boundedness of soil moisture plays a pivoting role in the dependency of soil moisture spatial variability/skewness on its mean (and thus climate conditions; (3 the scale dependency of soil moisture spatial variability changes with climate conditions.

B. Li

2012-09-01

190

Evaluation of sampling techniques to characterize topographically-dependent variability for soil moisture downscaling  

Science.gov (United States)

Downscaling methods have been proposed to estimate catchment-scale soil moisture patterns from coarser resolution patterns. These methods usually infer the fine-scale variability in soil moisture using variations in ancillary variables like topographic attributes that have relationships to soil moisture. Previously, such relationships have been observed in catchments using soil moisture observations taken on uniform grids at hundreds of locations on multiple dates, but collecting data in this manner limits the applicability of this approach. The objective of this paper is to evaluate the effectiveness of two strategic sampling techniques for characterizing the relationships between topographic attributes and soil moisture for the purpose of constraining downscaling methods. The strategic sampling methods are conditioned Latin hypercube sampling (cLHS) and stratified random sampling (SRS). Each sampling method is used to select a limited number of locations or dates for soil moisture monitoring at three catchments with detailed soil moisture datasets. These samples are then used to calibrate two available downscaling methods, and the effectiveness of the sampling methods is evaluated by the ability of the downscaling methods to reproduce the known soil moisture patterns. cLHS outperforms random sampling in almost every case considered. SRS usually performs better than cLHS when very few locations are sampled, but it can perform worse than random sampling for intermediate and large numbers of locations.

Werbylo, Kevin L.; Niemann, Jeffrey D.

2014-08-01

191

A randomized, controlled study of treatment for alcohol dependence in patients awaiting liver transplantation.  

Science.gov (United States)

Alcohol is the second most common cause of cirrhosis necessitating liver transplantation in the United States, yet rates of posttransplant drinking approach 50% and no controlled clinical trials of alcoholism treatment exist in this population. Eligible patients were randomly assigned to receive Motivational Enhancement Therapy (MET), or referral to local treatment sources ("treatment as usual" [TAU]). Addictive behavior, mood states, and general health were compared. Candor concerning alcohol use was encouraged by keeping drinking questionnaires in confidence, except in medical emergencies. Ninety-one subjects were studied; 46 received MET, 45 received TAU, 29 proceeded to transplantation (MET, n = 13; TAU, n = 16). A total of 69 subjects completed 24 weeks of observation, and 25 subjects were assessed at 96 weeks. No difference in study attendance was observed, but significantly more MET subjects attended 1 or more treatment sessions. Twenty-three subjects (25% of sample) drank after randomization but before transplant. Excluding an extreme outlier, MET drinkers had significantly fewer drinks per drinking days than TAU drinkers. Neither treatment plan resulted in significant variances in measures of psychosocial health. In conclusion, although MET afforded no significant benefit over TAU for mood or general health outcomes, this study provides some degree of support for MET to limit the quantity and frequency of pretransplant alcohol consumption among liver transplant candidates with alcohol dependence. However, because of the limited number of study subjects, these data must be interpreted cautiously. Further research to validate our findings or to identify better methods to identify and intervene with patients at risk of pretransplant and posttransplant drinking should continue. PMID:21506242

Weinrieb, Robert M; Van Horn, Deborah H A; Lynch, Kevin G; Lucey, Michael R

2011-05-01

192

Variability of stream flow discharge in response to self-similar random fields of temporal fluctuations in lateral inflow rate  

Science.gov (United States)

This article presents the use of stochastic methodology for quantitative analysis of variability in stream flow discharge in response to fluctuations in lateral inflow rate, where the lateral inflow rate is considered to be the difference between rainfall and infiltration rates. In this work, we focus on the case where the temporal correlation structure of the fluctuations in the lateral inflow rate can be characterized by the statistics of random fractals. A closed-form expression quantifying the stream flow variability is therefore developed to investigate the influence of the fractal dimension of lateral inflow process and the size of time domain. It is found that the stream flow discharge variability increases with the time domain size, while the fractal dimension of lateral inflow process plays a role in the smoothness of fluctuations in stream flow discharge around the mean.

Chang, Ching-Min; Yeh, Hund-Der

2014-09-01

193

Computational studies of history dependence in nematic liquid crystals in random environments  

Science.gov (United States)

Glassy liquid crystalline systems are expected to show significant history-dependent effects. Two model glassy systems are the RAN and SSS (sprinkled silica spin) lattice models. The RAN model is a Lebwohl-Lasher lattice model with locally coupled nematic spins, together with uncorrelated random anisotropy fields at each site, while the SSS model has a finite concentration of impurity spins frozen in random directions. Here Brownian simulation is used to study the effect of different sample histories in the low temperature regime in a three-dimensional (d =3) model intermediate between SSS and RAN, in which a finite concentration p Simulations were performed at temperature T ˜TNI/2 (TNI the bulk nematic-isotropic transition temperature) for temperature-quenched and field-quenched histories (TQH and FQH, respectively), as well as for temperature-annealed histories (AH). The first two of these limits represent extreme histories encountered in typical experimental studies. Using long-time averages for equilibrated systems, we calculate orientational order parameters and two-point correlation functions. Finite-size scaling was used to determine the range of the orientational ordering, as a function of coupling strength W ,p and sample history. Sample history plays a significant role; for given concentration p, as disorder strength W is increased, TQH systems sustain quasi-long-range order (QLRO) and short-range order (SRO). The data are also consistent with a long-range order (LRO) phase at very low disorder strength. By contrast, for FQH and p ?0.1, only LRO and QLRO occur within the range of parameters investigated. The crossover between regimes depends on history, but in general, the FQH phase is more ordered than the AH phase, which is more ordered than the TQH phase. However, at temperatures close to the isotropic-nematic phase transition of pure samples we observe SRO for p =0.1 even for FQH. We detect also in the QLRO phase a domain-type structural pattern, consistent with ideas introduced by Giamarchi and Doussal [Phys. Rev. B 52, 1242 (1995), 10.1103/PhysRevB.52.1242] on superconducting flux lattices. In the weak-disorder limit the orientational correlation length obeys the Larkin-Imry-Ma scaling ? ˜D-2/(4-d).

Ranjkesh, Amid; Ambroži?, Milan; Kralj, Samo; Sluckin, Timothy J.

2014-02-01

194

Methadone Induction in Primary Care for Opioid Dependence: A Pragmatic Randomized Trial (ANRS Methaville)  

Science.gov (United States)

Objective Methadone coverage is poor in many countries due in part to methadone induction being possible only in specialized care (SC). This multicenter pragmatic trial compared the effectiveness of methadone treatment between two induction models: primary care (PC) and SC. Methods In this study, registered at ClinicalTrials.Gov (NCT00657397), opioid-dependent individuals not on methadone treatment for at least one month or receiving buprenorphine but needing to switch were randomly assigned to start methadone in PC (N?=?155) or in SC (N?=?66) in 10 sites in France. Visits were scheduled at months M0, M3, M6 and M12. The primary outcome was self-reported abstinence from street-opioids at 12 months (M12) (with an underlying 15% non-inferiority hypothesis for PC). Secondary outcomes were abstinence during follow-up, engagement in treatment (i.e. completing the induction period), retention and satisfaction with the explanations provided by the physician. Primary analysis used intention to treat (ITT). Mixed models and the log-rank test were used to assess the arm effect (PC vs. SC) on the course of abstinence and retention, respectively. Results In the ITT analysis (n?=?155 in PC, 66 in SC), which compared the proportions of street-opioid abstinent participants, 85/155 (55%) and 22/66 (33%) of the participants were classified as street-opioid abstinent at M12 in PC and SC, respectively. This ITT analysis showed the non-inferiority of PC (21.5 [7.7; 35.3]). Engagement in treatment and satisfaction with the explanations provided by the physician were significantly higher in PC than SC. Retention in methadone and abstinence during follow-up were comparable in both arms (p?=?0.47, p?=?0.39, respectively). Conclusions Under appropriate conditions, methadone induction in primary care is feasible and acceptable to both physicians and patients. It is as effective as induction in specialized care in reducing street-opioid use and ensuring engagement and retention in treatment for opioid dependence. Trial registration Number Eudract 2008-001338-28; ClinicalTrials.gov: NCT00657397; International Standard Randomized Controlled Trial Number Register ISRCTN31125511 PMID:25393311

Carrieri, Patrizia Maria; Michel, Laurent; Lions, Caroline; Cohen, Julien; Vray, Muriel; Mora, Marion; Marcellin, Fabienne; Spire, Bruno; Morel, Alain; Roux, Perrine

2014-01-01

195

Relationship Between Field Dependence - Field Independence, Piaget Conservation Tasks and School Variables.  

Science.gov (United States)

This study investigates relationships among conservation, field dependence/independence, school variables, achievement, screening measures, sex and race. A total of 124 first, second and third graders in a Southern rural school were administered 8 typical Piagetian conservation tasks (PCT), Children's Embedded Figures Test (CEFT), Comprehensive…

Wicker, Tommie E.; O'Tuel, Frances S.

196

Maximal averages along a planar vector field depending on one variable  

CERN Document Server

We prove (essentially) sharp $L^2$ estimates for a restricted maximal operator associated to a planar vector field that depends only on the horizontal variable. The proof combines an understanding of such vector fields from earlier work of the author with a result of Nets Katz on directional maximal operators.

Bateman, Michael

2011-01-01

197

Episodic Severity: An Overlooked Dependent Variable in the Application of Behavior Analysis to Challenging Behavior  

Science.gov (United States)

Although applied behavior analysis has made a significant contribution in the area of challenging behavior, to date, researchers have not systematically investigated the episodic severity of behavior as a dependent variable. "Episodic severity" is defined as the measure of intensity or gravity of a behavioral incident. Research up to now has…

LaVigna, Gary W.; Willis, Thomas J.; Koegel, Robert L.

2005-01-01

198

A Maximum Likelihood Method for Latent Class Regression Involving a Censored Dependent Variable.  

Science.gov (United States)

A method is proposed to simultaneously estimate regression functions and subject membership in "k" latent classes or groups given a censored dependent variable for a cross-section of subjects. Maximum likelihood estimates are obtained using an EM algorithm. The method is illustrated through a consumer psychology application. (SLD)

Jedidi, Kamel; And Others

1993-01-01

199

On the moments of random variables uniformly distributed over a polytope  

Directory of Open Access Journals (Sweden)

Full Text Available Suppose X=(X1,X2,…,Xn is a random vector uniformly distributed over a polytope. In this note, the author derives a formula for E(XirXjs…, (the expected value of XirXjs…, in terms of the extreme points of the polytope.

S. Paramasamy

1997-03-01

200

COMPARISON OF VARIANCE ESTIMATORS OF THE HORVITZ-THOMPSON ESTIMATOR FOR RANDOMIZED VARIABLE PROBABILITY SYSTEMATIC SAMPLING  

Science.gov (United States)

Two large-scale environmental surveys, the National Stream Survey (NSS) and the Environmental Protection Agency's proposed Environmental Monitoring and Assessment Program (EMAP), motivated investigation of estimators of the variance of the Horvitz-Thompson estimator under variabl...

 
 
 
 
201

Reduced plasma aldosterone concentrations in randomly selected patients with insulin-dependent diabetes mellitus.  

LENUS (Irish Health Repository)

Abnormalities of the renin-angiotensin system have been reported in patients with diabetes mellitus and with diabetic complications. In this study, plasma concentrations of prorenin, renin, and aldosterone were measured in a stratified random sample of 110 insulin-dependent (Type 1) diabetic patients attending our outpatient clinic. Fifty-four age- and sex-matched control subjects were also examined. Plasma prorenin concentration was higher in patients without complications than in control subjects when upright (geometric mean (95% confidence intervals (CI): 75.9 (55.0-105.6) vs 45.1 (31.6-64.3) mU I-1, p < 0.05). There was no difference in plasma prorenin concentration between patients without and with microalbuminuria and between patients without and with background retinopathy. Plasma renin concentration, both when supine and upright, was similar in control subjects, in patients without complications, and in patients with varying degrees of diabetic microangiopathy. Plasma aldosterone was suppressed in patients without complications in comparison to control subjects (74 (58-95) vs 167 (140-199) ng I-1, p < 0.001) and was also suppressed in patients with microvascular disease. Plasma potassium was significantly higher in patients than in control subjects (mean +\\/- standard deviation: 4.10 +\\/- 0.36 vs 3.89 +\\/- 0.26 mmol I-1; p < 0.001) and plasma sodium was significantly lower (138 +\\/- 4 vs 140 +\\/- 2 mmol I-1; p < 0.001). We conclude that plasma prorenin is not a useful early marker for diabetic microvascular disease. Despite apparently normal plasma renin concentrations, plasma aldosterone is suppressed in insulin-dependent diabetic patients.

Cronin, C C

2012-02-03

202

Importance analysis for models with correlated input variables using state dependent parameters approach  

Science.gov (United States)

For clearly exploring the origin of the variance of the output response in case the correlated input variables involved and establishing efficient method to calculate the importance measures of correlated input variables, a novel method on the state dependent parameters (SDPs) approach is proposed to decompose the contribution by correlated input variables to the output variance into two parts: the uncorrelated contribution due to the unique variations of a variable and the correlated one due to the variations of a variable correlated with other variables. In the proposed method, the transformation of the correlated inputs into independent and orthogonal ones and the calculation of the importance measures of the transformed independent ones are obtained by the SDP method simultaneously, thus it can improve the computational efficiency considerably in case of acceptable accuracy. In addition, the relationship between the existing independent orthogonalisation-based and the regression-based importance measures of the correlated input variables is revealed in the paper, which is then demonstrated by the numerical examples. The proposed method not only possesses higher computational efficiency in case of acceptable precision, but also has wider applicability compared with the polynomial chaos expansion (PCE) based method. Several numerical and engineering examples are used to demonstrate the advantages of the proposed method.

Li, Luyi; Lu, Zhenzhou; Hao, Wenrui

2013-12-01

203

Temperature dependence of resistive switching behaviors in resistive random access memory based on graphene oxide film  

Science.gov (United States)

We reported resistive switching behaviors in the resistive random access memory (RRAM) devices based on the different annealing temperatures of graphene oxide (GO) film as active layers. It was found that the resistive switching characteristics of an indium tin oxide (ITO)/GO/Ag structure have a strong dependence on the annealing temperature of GO film. When the annealing temperature of the GO film was 20 °C, the devices showed typical write-once-read-many-times (WORM) type memory behaviors, which have good memory performance with a higher ON/OFF current ratio (˜104), the higher the high resistance state (HRS)/low resistance state (LRS) ratio (˜105) and stable retention characteristics (>103 s) under lower programming voltage (-1 V and -0.5 V). With the increasing annealing temperature of GO film, the resistive switching behavior of RRAM devices gradually weakened and eventually disappeared. This phenomenon could be understood by the different energy level distributions of the charge traps in GO film, and the different charge injection ability from the Ag electrode to GO film, which is caused by the different annealing temperatures of the GO film.

Yi, Mingdong; Cao, Yong; Ling, Haifeng; Du, Zhuzhu; Wang, Laiyuan; Yang, Tao; Fan, Quli; Xie, Linghai; Huang, Wei

2014-05-01

204

Contribution to the application of the random vibration theory to the seismic analysis of structures via state variables  

International Nuclear Information System (INIS)

Several problems related to the application of the theory of random by means of state variables are studied. The well-known equations that define the propagation of the mean and the variance for linear and non-linear systems are first presented. The Monte Carlo method is next resorted to in order to determine the applicability of the hypothesis of a normally distributed output in case of linear systems subjected to non-Gaussian excitations. Finally, attention is focused on the properties of linear filters and modulation functions proposed to simulate seismic excitations as non stationary random processes. Acceleration spectra obtained by multiplying rms spectra by a constant factor are compared with design spectra suggested by several authors for various soil conditions. In every case, filter properties are given. (Author)

205

Continuously-variable survival exponent for random walks with movable partial reflectors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study a one-dimensional lattice random walk with an absorbing boundary at the origin and a movable partial reflector. On encountering the reflector, at site x, the walker is reflected (with probability r) to x-1 and the reflector is simultaneously pushed to x+1. Iteration of the transition matrix, and asymptotic analysis of the probability generating function show that the critical exponent delta governing the survival probability varies continuously between 1/2 and 1 as ...

Dickman, Ronald; Ben-avraham, Daniel

2001-01-01

206

The effect of misspecification of random effects distributions in clustered data settings with outcome-dependent sampling.  

Science.gov (United States)

Genetic epidemiologists often gather outcome-dependent samples of family data to measure within-family associations of genetic factors with disease outcomes. Generalized linear mixed models provide effective methods to estimate within-family associations but typically require parametric specification of the random effects distribution. Although misspecification of the random effects distribution often leads to little bias in estimated regression coefficients in standard, prospective clustered data settings, some recent studies suggest that such misspecification will impact parameter estimates from outcome-dependent cluster sampling designs. Using analytic results, simulation studies and fits to example data, this study examines the effect of misspecification of random effects distributions on parameter estimates in clustered data settings with outcome-dependent sampling. We show that the effects are consistent with results from prospective cluster sampling settings. In particular, ascertainment corrected mixed model methods that assume normally distributed random intercepts and conditional likelihood approaches provide accurate estimates of within-family covariate effects even under a misspecified random effects distribution. PMID:23204632

Neuhaus, John M; McCulloch, Charles E

2011-09-01

207

Critical moment definition and estimation, for finite size observation of log-exponential-power law random variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This contribution aims at studying the behaviour of the classical sample moment estimator, $S(n,q)= \\sum_{k=1}^n X_k^{q}/n $, as a function of the number of available samples $n$, in the case where the random variables $X$ are positive, have finite moments at all orders and are naturally of the form $X= \\exp Y$ with the tail of $Y$ behaving like $e^{-y^\\rho}$. This class of laws encompasses and generalizes the classical example of the log-normal law. This form is motivated b...

Angeletti, Florian; Bertin, Eric; Abry, Patrice

2011-01-01

208

On construction of random variables with prescribed marginal distributions and correlation coefficients  

CERN Document Server

In this paper we propose a generalized extension of the trivariate reduction method for exact generation of variables with prespecified marginal distributions and the correlation coefficient (positive or negative). We compare the new algorithm to several common approaches, with a particular emphasis on the copula-based ones, and discuss its benefits and limitations.

Dukic, Vanja

2010-01-01

209

Existence and Uniqueness Conditions for the Maximum Likelihood Solution In Regression Models For Correlated Bernoulli Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available We give sufficient and necessary conditions for the existence of the maximum likelihood estimate in a class of multivariate regression models for correlated Bernoulli random variables. The models use the concept of threshold crossing technique of an underlying multivariate latent variable with univariate components formulated as a linear regression model. However, in place of their Gaussian assumptions, any specified distribution with a strictly increasing cumulative distribution function is allowed for error terms. A well known member of this class of models is the multivariate probit model. We show that our results are a generalization of the concepts of separation and overlap of Albert and Anderson for the study of the existence of maximum likelihood estimate in generalized linear models. Implications of our findings are illustrated through some hypothetical examples.

David Todem

2007-01-01

210

A Randomized Trial of Extended Telephone-Based Continuing Care for Alcohol Dependence: Within-Treatment Substance Use Outcomes  

Science.gov (United States)

Objective: The study tested whether adding up to 18 months of telephone continuing care, either as monitoring and feedback (TM) or longer contacts that included counseling (TMC), to intensive outpatient programs (IOPs) improved outcomes for alcohol-dependent patients. Method: Participants (N = 252) who completed 3 weeks of IOP were randomized to…

McKay, James R.; Van Horn, Deborah H. A.; Oslin, David W.; Lynch, Kevin G.; Ivey, Megan; Ward, Kathleen; Drapkin, Michelle L.; Becher, Julie R.; Coviello, Donna M.

2010-01-01

211

Estimation and Computer Simulation of the Effective Doses in the Dose-Effect Dependence Over Random Experiment Plans  

Directory of Open Access Journals (Sweden)

Full Text Available In this article for the model of dose-effect dependence we propose estimators of the effective dose level based on a random experiment plans which are consistency and asymptotic normality. We also compare the proposed estimators with an DNP-estimate by means of computer simulation.

Mikhail S. Tikhov

2012-05-01

212

Some Data Reduction Methods to Analyze the Dependence with Highly Collinear Variables: A Simulation Study  

Directory of Open Access Journals (Sweden)

Full Text Available The dependence relationship between two sets of variables is a subject of interest in statistical field. A frequent obstacle is that several of the explanatory variables will vary in rather similar ways. As a result, their collective power of explanation is considerably less than the sum of their individual powers. This phenomenon, called multicollinearity, is a common problem in regression analysis. The major problem with multicollinearity is that the ordinary least squares coefficients estimators involved in the linear dependencies have large variances. All additional adverse effects are a consequence of them. In statistical literature several methods have been proposed to counter with multicollinearity problem. By a simulation study and considering different case of collinearity among the regressors, in this paper we have compared, using RV coefficient, five statistical methods, alternative to the ordinary least square regression.

A. D`Ambra

2010-01-01

213

Simultaneous extraction of charge density dependent mobility and variable contact resistance from thin film transistors  

Science.gov (United States)

A model for the extraction of the charge density dependent mobility and variable contact resistance in thin film transistors is proposed by performing a full derivation of the current-voltage characteristics both in the linear and saturation regime of operation. The calculated values are validated against the ones obtained from direct experimental methods. This approach allows unambiguous determination of gate voltage dependent contact and channel resistance from the analysis of a single device. It solves the inconsistencies in the commonly accepted mobility extraction methods and provides additional possibilities for the analysis of the injection and transport processes in semiconducting materials.

Di Pietro, Riccardo; Venkateshvaran, Deepak; Klug, Andreas; List-Kratochvil, Emil J. W.; Facchetti, Antonio; Sirringhaus, Henning; Neher, Dieter

2014-05-01

214

Nonlocal problem with dependent coefficients in conditions for the second-order equation in time variable  

Directory of Open Access Journals (Sweden)

Full Text Available In the Cartesian product of a time segment and a spatial multidimensional torus, we investigate nonlocal two-point problem with dependent coefficients on a smooth curve in conditions for typeless partial differential equation of the second order in time variable. Conditions for the one-valued solvability of the problem are established. Metric theorem on lower bound of small denominators on smooth curve are proved.

Savka I.Ya.

2010-12-01

215

Variability of motor potentials evoked by transcranial magnetic stimulation depends on muscle activation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The purpose of this research was to determine whether motor cortex excitability assessed using transcranial magnetic stimulation (TMS) is less variable when subjects maintain a visually controlled low-level contraction of the muscle of interest. We also examined the dependence of single motor evoked potential (MEP) amplitude on stimulation intensity and pre-stimulus muscle activation level using linear and non-linear multiple regression analysis. Eight healthy adult subjects received single p...

Darling, Warren G.; Wolf, Steven L.; Butler, Andrew J.

2006-01-01

216

Nonparametric changepoint analysis for bernoulli random variables based on neural networks  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In many medical, financial, industrial, e.t.c. applications of statistics, the model parameters may undergo changes at unknown moment of time. In this thesis, we consider change point analysis in a regression setting for dichotomous responses, i.e. they can be modeled as Bernoulli or 0-1 variables. Applications are widespread including credit scoring in financial statistics and dose-response relations in biometry. The model parameters are estimated using neural network method. We show that th...

Gichuhi, Anthony Waititu

2008-01-01

217

On the weak law of large numbers for normed weighted sums of I.I.D. random variables  

Directory of Open Access Journals (Sweden)

Full Text Available For weighted sums ∑j=1najYj of independent and identically distributed random variables {Yn,n≥1}, a general weak law of large numbers of the form (∑j=1najYj−νn/bn→P0 is established where {νn,n≥1} and {bn,n≥1} are statable constants. The hypotheses involve both the behavior of the tail of the distribution of |Y1| and the growth behaviors of the constants {an,n≥1} and {bn,n≥1}. Moreover, a weak law is proved for weighted sums ∑j=1najYj indexed by random variables {Tn,n≥1}. An example is presented wherein the weak law holds but the strong law fails thereby generalizing a classical example.

Andrew Rosalsky

1991-03-01

218

Spatiotemporal dependency of age-related changes in brain signal variability.  

Science.gov (United States)

Recent theoretical and empirical work has focused on the variability of network dynamics in maturation. Such variability seems to reflect the spontaneous formation and dissolution of different functional networks. We sought to extend these observations into healthy aging. Two different data sets, one EEG (total n = 48, ages 18-72) and one magnetoencephalography (n = 31, ages 20-75) were analyzed for such spatiotemporal dependency using multiscale entropy (MSE) from regional brain sources. In both data sets, the changes in MSE were timescale dependent, with higher entropy at fine scales and lower at more coarse scales with greater age. The signals were parsed further into local entropy, related to information processed within a regional source, and distributed entropy (information shared between two sources, i.e., functional connectivity). Local entropy increased for most regions, whereas the dominant change in distributed entropy was age-related reductions across hemispheres. These data further the understanding of changes in brain signal variability across the lifespan, suggesting an inverted U-shaped curve, but with an important qualifier. Unlike earlier in maturation, where the changes are more widespread, changes in adulthood show strong spatiotemporal dependence. PMID:23395850

McIntosh, A R; Vakorin, V; Kovacevic, N; Wang, H; Diaconescu, A; Protzner, A B

2014-07-01

219

Random variables in forest policy: A systematic sensitivity analysis using CGE models  

Energy Technology Data Exchange (ETDEWEB)

Computable general equilibrium (CGE) models are extensively used to simulate economic impacts of forest policies. Parameter values used in these models often play a central role in their outcome. Since econometric studies and best guesses are the main sources of these parameters, some randomness exists about the 'true' values of these parameters. Failure to incorporate this randomness into these models may limit the degree of confidence in the validity of the results. In this study, we conduct a systematic sensitivity analysis (SSA) to assess the economic impacts of: 1) a 1 % increase in tax on Canadian lumber and wood products exports to the United States (US), and 2) a 1% decrease in technical change in the lumber and wood products and pulp and paper sectors of the US and Canada. We achieve this task by using an aggregated version of global trade model developed by Hertel (1997) and the automated SSA procedure developed by Arndt and Pearson (1996).The estimated means and standard deviations suggest that certain impacts are more likely than others. For example, an increase in export tax is likely to cause a decrease in Canadian income, while an increase in US income is unlikely. On the other hand, a decrease in US welfare is likely, while an increase in Canadian welfare is unlikely, in response to an increase in tax. It is likely that income and welfare both fall in Canada and the US in response to a decrease in the technical change in lumber and wood products and pulp and paper sectors 21 refs, 1 fig, 5 tabs.

Alavalapati, J.R.R. [Florida Univ., Gainesville, FL (United States). School of Forest Resources and Conservation; Adamowicz, W.L. [Alberta Univ., Edmonton, AB (Canada). Dept. of Rural Economy; White, W.A. [Canadian Forest Service, Edmonton (Canada)

1999-07-01

220

Random variables in forest policy: A systematic sensitivity analysis using CGE models  

Energy Technology Data Exchange (ETDEWEB)

Computable general equilibrium (CGE) models are extensively used to simulate economic impacts of forest policies. Parameter values used in these models often play a central role in their outcome. Since econometric studies and best guesses are the main sources of these parameters, some randomness exists about the `true` values of these parameters. Failure to incorporate this randomness into these models may limit the degree of confidence in the validity of the results. In this study, we conduct a systematic sensitivity analysis (SSA) to assess the economic impacts of: 1) a 1 % increase in tax on Canadian lumber and wood products exports to the United States (US), and 2) a 1% decrease in technical change in the lumber and wood products and pulp and paper sectors of the US and Canada. We achieve this task by using an aggregated version of global trade model developed by Hertel (1997) and the automated SSA procedure developed by Arndt and Pearson (1996). The estimated means and standard deviations suggest that certain impacts are more likely than others. For example, an increase in export tax is likely to cause a decrease in Canadian income, while an increase in US income is unlikely. On the other hand, a decrease in US welfare is likely, while an increase in Canadian welfare is unlikely, in response to an increase in tax. It is likely that income and welfare both fall in Canada and the US in response to a decrease in the technical change in lumber and wood products and pulp and paper sectors 21 refs, 1 fig, 5 tabs

Alavalapati, J.R.R. [Florida Univ., Gainesville, FL (United States). School of Forest Resources and Conservation; Adamowicz, W.L. [Alberta Univ., Edmonton, AB (Canada). Dept. of Rural Economy; White, W.A. [Canadian Forest Service, Edmonton (Canada)

1999-11-01

 
 
 
 
221

Random variables in forest policy: A systematic sensitivity analysis using CGE models  

International Nuclear Information System (INIS)

Computable general equilibrium (CGE) models are extensively used to simulate economic impacts of forest policies. Parameter values used in these models often play a central role in their outcome. Since econometric studies and best guesses are the main sources of these parameters, some randomness exists about the 'true' values of these parameters. Failure to incorporate this randomness into these models may limit the degree of confidence in the validity of the results. In this study, we conduct a systematic sensitivity analysis (SSA) to assess the economic impacts of: 1) a 1 % increase in tax on Canadian lumber and wood products exports to the United States (US), and 2) a 1% decrease in technical change in the lumber and wood products and pulp and paper sectors of the US and Canada. We achieve this task by using an aggregated version of global trade model developed by Hertel (1997) and the automated SSA procedure developed by Arndt and Pearson (1996). The estimated means and standard deviations suggest that certain impacts are more likely than others. For example, an increase in export tax is likely to cause a decrease in Canadian income, while an increase in US income is unlikely. On the other hand, a decrease in US welfare is likely, while an increase in Canadian welfare is unlikely, in response to an increase in tax. It is likely that income and welfare both fall in Canada and the US in response to a decrease in the technical change in lumber and wood products and pulp and paper sectors 21 refs, 1 fig, 5 tabs

222

Multidimensional time-dependent discrete variable representations in multiconfiguration Hartree calculations  

Science.gov (United States)

In the multiconfiguration time-dependent Hartree (MCTDH) approach, the wave function is expanded in time-dependent basis functions, called single-particle functions, to increase the efficiency of the wave-packet propagation. The correlation discrete variable representation (CDVR) approach, which is based on a time-dependent discrete variable representation (DVR), can be employed to evaluate matrix elements of the potential energy. The efficiency of the MCTDH method can be further enhanced by using multidimensional single-particle functions. However, up to now the CDVR approach could not be used in MCTDH calculations employing multidimensional single-particle functions, since this would require a general multidimensional non-direct-product DVR scheme. Recently, Dawes and Carrington presented a practical scheme to implement general non-direct-product multidimensional DVRs [R. Dawes and T. Carrington, Jr., J. Chem. Phys. 121, 726 (2004)]. The present work utilizes their scheme in the MCTDH/CDVR approach. The accuracy is tested using the photodissociation of NOCl as example. The results show that the CDVR scheme based on multidimensional time-dependent DVRs allows for an accurate evaluation of the potential in MCTDH calculations with multidimensional single-particle functions.

van Harrevelt, Rob; Manthe, Uwe

2005-08-01

223

Multidimensional time-dependent discrete variable representations in multiconfiguration Hartree calculations  

International Nuclear Information System (INIS)

In the multiconfiguration time-dependent Hartree (MCTDH) approach, the wave function is expanded in time-dependent basis functions, called single-particle functions, to increase the efficiency of the wave-packet propagation. The correlation discrete variable representation (CDVR) approach, which is based on a time-dependent discrete variable representation (DVR), can be employed to evaluate matrix elements of the potential energy. The efficiency of the MCTDH method can be further enhanced by using multidimensional single-particle functions. However, up to now the CDVR approach could not be used in MCTDH calculations employing multidimensional single-particle functions, since this would require a general multidimensional non-direct-product DVR scheme. Recently, Dawes and Carrington presented a practical scheme to implement general non-direct-product multidimensional DVRs [R. Dawes and T. Carrington, Jr., J. Chem. Phys. 121, 726 (2004)]. The present work utilizes their scheme in the MCTDH/CDVR approach. The accuracy is tested using the photodissociation of NOCl as example. The results show that the CDVR scheme based on multidimensional time-dependent DVRs allows for an accurate evaluation of the potential in MCTDH calculations with multidimensional single-particle functions

224

Variable length and context-dependent HMM letter form models for Arabic handwritten word recognition  

Science.gov (United States)

We present in this paper an HMM-based recognizer for the recognition of unconstrained Arabic handwritten words. The recognizer is a context-dependent HMM which considers variable topology and contextual information for a better modeling of writing units. We propose an algorithm to adapt the topology of each HMM to the character to be modeled. For modeling the contextual units, a state-tying process based on decision tree clustering is introduced which significantly reduces the number of parameters. Decision trees are built according to a set of expert-based questions on how characters are written. Questions are divided into global questions yielding larger clusters and precise questions yielding smaller ones. We apply this modeling to the recognition of Arabic handwritten words. Experiments conducted on the OpenHaRT2010 database show that variable length topology and contextual information significantly improves the recognition rate.

Bianne-Bernard, Anne-Laure; Menasri, Fares; Likforman-Sulem, Laurence; Mokbel, Chafic; Kermorvant, Christopher

2012-01-01

225

The dependence of J/?-nucleon inelastic cross section on the Feynman variable  

International Nuclear Information System (INIS)

By means of two typical sets of nuclear parton distribution functions, meanwhile taking account of the energy loss of the beam proton and the nuclear absorption of the charmonium states traversing the nuclear matter in the uniform framework of the Glauber model, a leading order phenomenological analysis is given in the color evaporation model of the E866 experimental data on J/? production differential cross section ratios RFe/Be(xF). It is shown that the energy loss effect of beam proton on RFe/Be(xF) is more important than the nuclear effects on parton distribution functions in the high Feynman variable xF region. It is found that the J/?-nucleon inelastic cross section depends on the Feynman variable xF and increases linearly with xF in the region xF > 0.2. (authors)

226

Stochasticity and determinism: how density-independent and density-dependent processes affect population variability.  

Science.gov (United States)

A persistent debate in population ecology concerns the relative importance of environmental stochasticity and density dependence in determining variability in adult year-class strength, which contributes to future reproduction as well as potential yield in exploited populations. Apart from the strength of the processes, the timing of density regulation may affect how stochastic variation, for instance through climate, translates into changes in adult abundance. In this study, we develop a life-cycle model for the population dynamics of a large marine fish population, Northeast Arctic cod, to disentangle the effects of density-independent and density-dependent processes on early life-stages, and to quantify the strength of compensatory density dependence in the population. The model incorporates information from scientific surveys and commercial harvest, and dynamically links multiple effects of intrinsic and extrinsic factors on all life-stages, from eggs to spawners. Using a state-space approach we account for observation error and stochasticity in the population dynamics. Our findings highlight the importance of density-dependent survival in juveniles, indicating that this period of the life cycle largely determines the compensatory capacity of the population. Density regulation at the juvenile life-stage dampens the impact of stochastic processes operating earlier in life such as environmental impacts on the production of eggs and climate-dependent survival of larvae. The timing of stochastic versus regulatory processes thus plays a crucial role in determining variability in adult abundance. Quantifying the contribution of environmental stochasticity and compensatory mechanisms in determining population abundance is essential for assessing population responses to climate change and exploitation by humans. PMID:24893001

Ohlberger, Jan; Rogers, Lauren A; Stenseth, Nils Chr

2014-01-01

227

Lower limits for distributions of randomly stopped sums  

CERN Document Server

We study lower limits for the ratio $\\frac{\\bar{F^{*\\tau}}(x)}{\\bar F(x)}$ of tail distributions where $ F^{*\\tau}$ is a distribution of a sum of a random size $\\tau$ of i.i.d. random variables having a common distribution $F$, and a random variable $\\tau$ does not depend on summands.

Denisov, Denis; Korshunov, Dmitry

2007-01-01

228

Time-dependent tree-structured survival analysis with unbiased variable selection through permutation tests.  

Science.gov (United States)

Incorporating time-dependent covariates into tree-structured survival analysis (TSSA) may result in more accurate prognostic models than if only baseline values are used. Available time-dependent TSSA methods exhaustively test every binary split on every covariate; however, this approach may result in selection bias toward covariates with more observed values. We present a method that uses unbiased significance levels from newly proposed permutation tests to select the time-dependent or baseline covariate with the strongest relationship with the survival outcome. The specific splitting value is identified using only the selected covariate. Simulation results show that the proposed time-dependent TSSA method produces tree models of equal or greater accuracy as compared to baseline TSSA models, even with high censoring rates and large within-subject variability in the time-dependent covariate. To illustrate, the proposed method is applied to data from a cohort of bipolar youths to identify subgroups at risk for self-injurious behavior. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25043382

Wallace, M L

2014-11-30

229

An MGF-based Unified Framework to Determine the Joint Statistics of Partial Sums of Ordered Random Variables  

CERN Document Server

Order statistics find applications in various areas of communications and signal processing. In this paper, we introduce an unified analytical framework to determine the joint statistics of partial sums of ordered random variables (RVs). With the proposed approach, we can systematically derive the joint statistics of any partial sums of ordered statistics, in terms of the moment generating function (MGF) and the probability density function (PDF). Our MGF-based approach applies not only when all the K ordered RVs are involved but also when only the Ks (Ks < K) best RVs are considered. In addition, we present the closed-form expressions for the exponential RV special case. These results apply to the performance analysis of various wireless communication systems over fading channels.

Nam, Sung Sik; Yang, Hong-Chuan

2010-01-01

230

Use of the Fieller-Hinkley distribution of the ratio of random variables in testing for noninferiority.  

Science.gov (United States)

We address the noninferiority assessment problem defined in terms of the ratio of population means in a parallel group design analysis of variance setting. The sample ratio as a point estimate of the corresponding population ratio has been considered. It has been shown that the Fieller-Hinkley distribution of the ratio of two correlated normally distributed random variables readily provide a technique for constructing confidence intervals comparable to the bootstrap percentile and Fieller's confidence intervals. A finite parameter space based level alpha test of an inferiority hypothesis formulated in terms of a fixed margin has been derived. We illustrate our approach using the forced vital capacity (FVC) data. We claim that it is easy to construct and straight forward to interpret our bootstrap equivalent confidence intervals that are used to assess noninferiority. We discuss appropriate methods for calculation of sample sizes. PMID:17365219

Koti, Kallappa M

2007-01-01

231

The turbulent mean-flow, Reynolds-stress, and heat flux equations in mass-averaged dependent variables  

Science.gov (United States)

The time-dependent, turbulent mean-flow, Reynolds stress, and heat flux equations in mass-averaged dependent variables are presented. These equations are given in conservative form for both generalized orthogonal and axisymmetric coordinates. For the case of small viscosity and thermal conductivity fluctuations, these equations are considerably simpler than the general Reynolds system of dependent variables for a compressible fluid and permit a more direct extension of low speed turbulence modeling to computer codes describing high speed turbulence fields.

Rubesin, M. W.; Rose, W. C.

1973-01-01

232

Flow-Dependent Topographic and Hydrodynamic Variability Control Channel Change in Mountain Rivers  

Science.gov (United States)

An emerging view in fluvial geomorphology is that rivers are systems with multiple scales of variability. This is especially true in mountain rivers that have spatially variable alluvial-bedrock boundaries as multiple scales of topography, from individual boulders to valley scale deposits, can steer flow paths affecting the erosion and deposition patterns of transported sediments. We hypothesize that depending on flow discharge and stage, different scales of channel topography can become dominant in routing sediment such that the resulting topography is a layered sequence of past flows. Here we evaluate gravel and cobble channel change associated with hydraulic unit to reach scale (e.g. 10-1-102 channel widths) changes in topographic and stage-dependent hydrodynamic variability in a mixed alluvial-bedrock river canyon. This study takes advantage of a unique opportunity where 4,535 metric tons of gravel ranging from 6-128 mm was augmented directly below a dam for spawning habitat rehabilitation in a 1,200 m long mountain river reach with no other sources of gravel sediment supply and an existing substrate of bedrock, large cobbles (>250mm), angular shot rock (>0.5m) and boulders (>1m). While the study site is a regulated river flows above 117 m3/s, just below the bankfull discharge, still overtop the dam so natural aspects of the hydrograph are still retained such that the reach still experiences large floods capable of considerable topographic change. We utilize kite-blimp aerial photography, kayak-based surveying, topographic change detection, and 2D modeling to understand how flow discharge can activate topographic features that ultimately control channel change following a controlled gravel injection upstream of a mountain river with no other gravel or cobble sediment inputs. The spatial covariance of flow width and bed elevation are strongly associated with the volume of gravel deposition and erosion, but this also changes depending on flow discharge as different topographic elements become more effective in controlling hydrodynamics. Similarly, analyzing changes in 2D model derived flow directions shows that different flows can effectively push gravel and cobble into bedrock protrusions that at higher flows, become disconnected from the main flow routing in the river canyon. Results from this study suggest that both existing channel boundary variability and input hydrologic variability work together to create hydrodynamics spatial patterns that control the fate and transport of sediments in mountain rivers and ultimately their spatial structure.

Brown, R. A.; Pasternack, G. B.

2013-12-01

233

The effects of frequency-dependent quasar variability on the celestial reference frame  

Science.gov (United States)

We examine the relationship between source position stability and astrophysical properties of radio-loud quasars making up the International Celestial Reference Frame (ICRF2). Understanding this relationship is important for improving quasar selection and analysis strategies, and therefore reference frame stability. We construct flux density time series, known as light curves, for 95 of the most frequently observed ICRF2 quasars at both the 2.3 and 8.4 GHz geodetic very long baseline interferometry (VLBI) observing bands. Because the appearance of new quasar components corresponds to an increase in quasar flux density, these light curves alert us about potential changes in source structure before they appear in VLBI images. We test how source position stability depends on three astrophysical parameters: (1) flux density variability at X band; (2) time lag between flares in S and X bands; (3) spectral index root-mean-square (rms), defined as the variability in the ratio between S and X band flux densities. We find that the time lag between S and X band light curves provides a good indicator of position stability: sources with time lags 0.06 years are significantly more stable (20 % improvement in weighted rms) than sources with larger time lags. A similar improvement is obtained by observing sources with low 0.12) spectral index variability. On the other hand, there is no strong dependence of source position stability on flux density variability in a single frequency band. These findings can be understood by interpreting the time lag between S and X band light curves as a measure of the size of the source structure. Monitoring of source flux density at multiple frequencies therefore appears to provide a useful probe of quasar structure on scales important to geodesy. The observed astrometric position of the brightest quasar component (the core) is known to depend on observing frequency. We show how multi-frequency flux density monitoring may allow the dependence on frequency of the relative core positions along the jet to be elucidated. Knowledge of the position-frequency relation has important implications for current and future geodetic VLBI programs, as well as the alignment between the radio and optical celestial reference frames.

Shabala, Stanislav S.; Rogers, Jonathan G.; McCallum, Jamie N.; Titov, Oleg A.; Blanchard, Jay; Lovell, James E. J.; Watson, Christopher S.

2014-06-01

234

Hot-spot model for accretion disc variability as random process - II. Mathematics of the power-spectrum break frequency  

CERN Document Server

We study some general properties of accretion disc variability in the context of stationary random processes. In particular, we are interested in mathematical constraints that can be imposed on the functional form of the Fourier power-spectrum density (PSD) that exhibits a multiply broken shape and several local maxima. We develop a methodology for determining the regions of the model parameter space that can in principle reproduce a PSD shape with a given number and position of local peaks and breaks of the PSD slope. Given the vast space of possible parameters, it is an important requirement that the method is fast in estimating the PSD shape for a given parameter set of the model. We generated and discuss the theoretical PSD profiles of a shot-noise-type random process with exponentially decaying flares. Then we determined conditions under which one, two, or more breaks or local maxima occur in the PSD. We calculated positions of these features and determined the changing slope of the model PSD. Furthermor...

Pechacek, Tomas; Karas, Vladimir; Czerny, Bozena; Dovciak, Michal

2013-01-01

235

Critical moment definition and estimation, for finite size observation of log-exponential-power law random variables  

CERN Document Server

This contribution aims at studying the behaviour of the classical sample moment estimator, $S(n,q)= \\sum_{k=1}^n X_k^{q}/n $, as a function of the number of available samples $n$, in the case where the random variables $X$ are positive, have finite moments at all orders and are naturally of the form $X= \\exp Y$ with the tail of $Y$ behaving like $e^{-y^\\rho}$. This class of laws encompasses and generalizes the classical example of the log-normal law. This form is motivated by a number of applications stemming from modern statistical physics or multifractal analysis. Borrowing heuristic and analytical results from the analysis of the Random Energy Model in statistical physics, a critical moment $q_c(n)$ is defined as the largest statistical order $q$ up to which the sample mean estimator $S(n,q)$ correctly accounts for the ensemble average $\\E X^q$, for a given $n$. A practical estimator for the critical moment $q_c(n)$ is then proposed. Its statistical performance are studied analytically and illustrated nume...

Angeletti, Florian; Abry, Patrice

2011-01-01

236

Concurrence of Quantum States: Algebraic Dynamical Method Study XXX Models in a Time-Depending Random External Field  

International Nuclear Information System (INIS)

Based on algebraic dynamics and the concept of the concurrence of the entanglement, we investigate the evolutive properties of the two-qubit entanglement that formed by Heisenberg XXX models under a time-depending external held. For this system, the property of the concurrence that is only dependent on the coupling constant J and total values of the external field is proved. Furthermore, we found that the thermal concurrence of the system under a static random external field is a function of the coupling constant J, temperature T, and the magnitude of external held. (general)

237

Shape dependency of the extinction and absorption cross sections of dust aerosols modeled as randomly oriented spheroids  

Directory of Open Access Journals (Sweden)

Full Text Available We present computational results on the shape dependency of the extinction and absorption cross sections of dustlike aerosol particles that were modeled as randomly oriented spheroids. Shape dependent variations in the extinction cross sections are largest in the size regime that is governed by the interference structure. Elongated spheroids best fitted measured extinction spectra of re-dispersed Saharan dust samples. For dust particles smaller than 1.5 ?m in diameter and low absorption potential, shape effects on the absorption cross sections are very small.

R. Wagner

2011-09-01

238

Building the nodal nuclear data dependences in a many-dimensional state-variable space  

Energy Technology Data Exchange (ETDEWEB)

Highlights: > The Abstract and Introduction are revised to reflect reviewers' comments. > Section is revised and simplified. > The third paragraph in Section is revised. > All typos are fixed. - Abstract: We present new methods for building the polynomial-regression based nodal nuclear data models. The data models can reflect dependences on a large number of state variables, and they can consider various history effects. Suitable multivariate polynomials that approximate the nodal data dependences are identified efficiently in an iterative manner. The history effects are analysed using a new sampling scheme for lattice calculations where the traditional base burnup and branch calculations are replaced by a large number of diverse burnup histories. The total number of lattice calculations is controlled so that the data models are built to a required accuracy.

Dufek, Jan, E-mail: jan@nephy.chalmers.se [Nuclear Engineering Division, Department of Applied Physics, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden)

2011-07-15

239

Solution of the energy-dependent neutron transport equation in plane geometry by separation of variables  

International Nuclear Information System (INIS)

The authors give a new method for solving the energy-dependent transport equation in plane geometry by separating the space, lethargy, and angle variables. The method reduces the solution of the transport equation to the solution of a coupled pair of one-speed and slowing down equations. As these two equations have been studied in detail, their solution procedures are utilized to solve the more complicated energy-dependent equation. The method of this paper is thus basically promising, though it is not clear at the present how it can be implemented for general scattering anisotropy. The fundamental separation constant of the method is a continuous parameter, and the solution is in the form of an integral over this parameter. Suitable discretization of this separation constant reduces the solution to an infinite sum. The authors compare their solution to the exact, though formal, singular eigenfunction-Laplace transform technique and establish a correspondence between the two approaches

240

Variable-range hopping transport: crossovers from temperature dependence to electric field dependence in disordered carbon materials  

Science.gov (United States)

Variable-range hopping (VRH) is an important conduction mechanism in disordered conductors. One example of such a disordered conductor is reduced graphene oxide in which VRH dominates the temperature dependence of electronic conduction. Electronic transport is generally by electric field-assisted, thermally-driven VRH, following the theory of Mott, and Pollak and Riess. However, with the increase of electric field and decrease of temperature, we identify a surprisingly smooth crossover to solely field-driven VRH described by the theory of Shklovskii. We give the analytic expression for the crossover field E_C as a function of temperature and coefficients from thermally-driven and field-driven VRH. Besides reduced graphene oxide, we show in this work that our crossover scenario can also account for the experimentally measured conductivity data of three-dimensional (3D) carbon networks as well as that of quasi-1D highly-doped conducting polymers, illustrating the wide validity of our proposed physical scenario. Our crossover scenario has the advantage of combining two distinct regimes of VRH conduction yet remaining within the currently established theoretical framework.

Cheah, Chun Y.; Kaiser, Alan B.

2014-04-01

 
 
 
 
241

The use of random amplified polymorphic DNA to evaluate the genetic variability of Ponkan mandarin (Citrus reticulata Blanco) accessions  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Amplificações RAPD foram desenvolvidas utilizando-se 25 "primers" de seqüência aleatória e 19 acessos de tangerinas pertencentes ao grupo das Ponkan. Dos 112 produtos de amplificação selecionados somente 32 foram polimórficos, sendo este polimorfismo restrito somente a 5 acessos. Nos 14 acessos rest [...] antes não pôde ser detectada qualquer variabilidade genética, sugerindo que estes podem ser propagação clonal da tangerina `Ponkan', tendo os mesmos adquirido diferentes nomes regionais ao longo do tempo. Ou, por outro lado, a técnica RAPD utilizada pode não ter detectado qualquer mutação de ponto que tenha ocorrido nestes materiais ao longo do tempo. Abstract in english RAPD analysis of 19 Ponkan mandarin accessions was performed using 25 random primers. Of 112 amplification products selected, only 32 were polymorphic across five accessions. The absence of genetic variability among the other 14 accessions suggested that they were either clonal propagations with dif [...] ferent local names, or that they had undetectable genetic variability, such as point mutations which cannot be detected by RAPD.

Helvécio Della, Coletta Filho; Marcos Antonio, Machado; M. Luiza P.N., Targon; Jorgino, Pompeu Jr..

242

Genetic variability in geographical populations of Culex quinquefasciatus Say (Diptera: Culicidae) from India based on random amplified polymorphic DNA analysis.  

Science.gov (United States)

Genetic variability and environmental factors may influence the refractiveness, propagation of pathogen and transmission of disease. Random amplified polymorphic DNA (RAPD) is one of the widely used molecular markers for population genetic diversity studies. In present study, RAPD is used to ascertain the genetic variability in Culex quinquefasciatus populations collected from various Indian geographical locations. Out of 50 RAPD primers screened, 14 primers exhibited clear, concrete and distinct banding pattern showing up to 100% polymorphism. Primer OPBD3 was tested with DNA of 14 geographical populations from India (including one laboratory population) showed 21 loci representing 14 populations with 100% polymorphism. The genetic diversity among the populations indicated the Shannon index (I) and gene diversity index (H(ST)), 0.48 and 0.31, respectively among the population, displaying rich genetic variation among the Cx. quinquefasciatus populations. Consensus tree showed two clusters indicating the genetic variation among the various geographical populations. The findings of this study may be useful to understand the population variation under different ecological conditions and development of effective vector management strategies. PMID:19577531

Sharma, A K; Mendki, M J; Tikar, S N; Chandel, K; Sukumaran, D; Parashar, B D; Veer, Vijay; Agarwal, O P; Prakash, Shri

2009-10-01

243

Layered discrete variable representations and their application within the multiconfigurational time-dependent Hartree approach  

Science.gov (United States)

The multiconfigurational time-dependent Hartree (MCTDH) approach facilitates multidimensional quantum dynamics calculations by employing a layered representation: in the upper layer of the representation the multidimensional wave function is expanded in a basis of time-dependent single-particle functions, in the lower layer then these single-particle functions are represented in a larger time-independent basis. This two layer approach can be generalized to a multilayer MCTDH representation to further increase the numerical efficiency. In recent work [U. Manthe, J. Chem. Phys. 128, 164116 (2008)], a quadrature scheme has been introduced which facilitates multilayer MCTDH calculations for Hamiltonians with general potential energy functions. Based on time-dependent discrete variable representation (DVR) grids corresponding to the single-particle function bases the scheme employs the correlation DVR (CDVR) approach. The present work shows that serious problems arise when this original multilayer CDVR approach is applied for accurate calculations of vibrational states. A solution to these problems is presented which uses a revised scheme to define the time-dependent DVR grids entering into the CDVR scheme. Applications studying the vibrational states of CH3 demonstrate that the resulting revised multilayer MCTDH/CDVR approach yields smoothly convergent and accurate results.

Manthe, Uwe

2009-02-01

244

Central limit theorems for the excursion sets volumes of weakly dependent random fields  

CERN Document Server

The multivariate central limit theorems (CLT) for the volumes of excursion sets of stationary quasi-associated random fields on $\\mathbb{R}^d$ are proved. Special attention is paid to Gaussian and shot noise fields. Formulae for the covariance matrix of the limiting distribution are provided. Statistical versions of the CLT are considered as well. They employ three different estimators of the asymptotic covariance matrix. Some numerical results are also discussed.

Bulinski, Alexander; Timmermann, Florian

2010-01-01

245

A Randomized Trial of Contingency Management for Adolescent Marijuana Abuse and Dependence  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An initial efficacy test of an innovative behavioral outpatient treatment model for adolescents with problematic use of marijuana enrolled 69 adolescents, aged 14–18, and randomly assigned them to one of two treatment conditions. Both conditions received individualized Motivational Enhancement and Cognitive Behavioral Therapy (MET/CBT) and a twice-weekly drug-testing program. The experimental contingency management condition involved a clinic delivered, abstinence-based incentive program, a...

Stanger, Catherine; Budney, Alan J.; Kamon, Jody L.; Thostensen, Jeff

2009-01-01

246

The dependence of damage on internal variables and its incorporation into constitutive equations  

International Nuclear Information System (INIS)

A model is presented for the prediction of the lifetime of metals in the high-temperature range under arbitrary variable uniaxial load. The influence of deformation on damage is discussed. The definition of damage in continuum damage mechanics, which allows indirect measurement of damage via the deformation behaviour, is adopted. To collect some knowledge about the damage evolution, damage is in two ways measured during the strain controlled LCF tests: change of the modulus of elasticity and decrease of the peak stress. Surprisingly, both methods lead to results which are in good agreement. The damage law is then developed by reference to known models and lifetime rules. The damage model is a modification of the creep damage law by Rabotnov. It is extended by a dependence on the inelastic strain rate used instead of the dependence on internal variables describing the internal state. The parameters of the damage model are determined with a view to apply them to AISI 316 L(N) austenitic steel. Some of the parameters are derived from standard creep experiments. To determine further parameters, the damage model is applied to the LCF tests. Both, failure behaviour and damage evolution are described well. (author)

247

Spectral variability of deciduous leaves depending on the developmental stages and tree condition  

Science.gov (United States)

Foliar spectral characteristics could be the key information in modeling forest ecosystem and the remote sensing of vegetation identification. But it is not easy to determine a typical leaf spectrum of a species in a standardized state. That is because of variables critically influencing on the spectral property of leaves, such as inter- and intra-species features, phenological phase, or biotic and abiotic stress. In this study, we attempted to quantify the spectral variability of leaves depending on species, developmental stages, and the condition of trees. The contribution of these factors to the spectral variation was analyzed at the single leaf level, with a large number of samples from deciduous plants in the urban forested area. First, we collected tens of leaf-samples at every biweekly fieldwork in the growing season, for the selected 5 tree species popular in urban parks; Acer palmatum, Carpinus laxiflora, Prunus yedoensis, Quercus acutissima, and Zelkova serrata. And absorbance, reflectance and transmittance spectra of the leaves were acquired at the short-visible (400-700 nm) to infrared (700-2500 nm) spectral region with 1 nm interval. Seasonality in these leaf-spectra was used to understand the inter-species variation depending on developmental stages. Second, as a benchmark for testing intra-species variability and differences by tree condition, we additionally analyzed the spectral reflectance of 504 ripe leaves from 56 cherry trees (Cerasus × yedoensis) collected in the middle of summer. Last, using ANOVA (analysis of variance) and general linear model, we assessed the influence of our tested variables (i.e., species, developmental stage, and tree condition) on the spectral characteristics and their vegetation indices. As a result, we clarified that the changes in leaf-spectra was apparent across all the tested species during the growing season from May to June, indicating the increasing trend of absorbance in photosynthetically active radiation region (400 to 700 nm; PAR) and reflectance in the near infrared region (700 to 1300 nm; NIR). Inter-species variability still appeared substantial and those inherit spectral characteristics was difficult to be described in a single universal vegetation index. The reflectance values of leaves were significantly differed in good and poor tree condition, which could be the other important consideration in the representative scheme of leaf sampling. More discussions will be present about the effect of species, developmental stage, and tree condition to the leaf-spectra and the published vegetation indices.

Song, Y.; Ryu, Y.

2013-12-01

248

Variability for Categorical Variables  

Science.gov (United States)

Introductory statistics textbooks rarely discuss the concept of variability for a categorical variable and thus, in this case, do not provide a measure of variability. The impression is thus given that there is no measurement of variability for a categorical variable. A measure of variability depends on the concept of variability. Research has…

Kader, Gary D.; Perry, Mike

2007-01-01

249

Testing for Cross-Sectional Dependence in a RandomEffects Model  

Directory of Open Access Journals (Sweden)

Full Text Available This paper extends and generalizes the works of [1,2] to allow for cross-sectional dependence in the context of a two-way error components model and consequently develops LM test. The cross-sectional dependence follows the first order spatial autoregressive error (SAE process and is imposed on the remainder disturbances. It is important to note that this paper does not consider alternative forms of spatial lag dependence other than SAE. It also does not allow for endogeneity of the regressors and requires the normality assumption to derive the LM test.

Eugene Kouassi

2012-01-01

250

A versatile variable field module for field and angular dependent scanning probe microscopy measurements  

CERN Document Server

We demonstrate a versatile variable field module (VFM) with capability of both field and angular dependent measurements up to 1800 Oe for scanning probe system. The magnetic field strength is changed by adjusting the distance between a rare earth magnet and the probe tip and is monitored in-situ by a built-in Hall sensor. Rotating the magnet allows the field vector to change from the horizontal to vertical direction and makes it possible to do angular dependent measurements. The capability of the VFM system is demonstrated by degaussing a floppy disk media with increasing magnetic field. Angular dependent measurements clearly show the evolution of magnetic domain structures, with a completely reversible magnetic force microscopy phase contrast observed when the magnetic field is rotated by 180{\\deg}. A further demonstration of out-of-plane and in-plane magnetic switching of CoFe2O4 pillars in CoFe2O4-BiFeO3 nanocomposites was presented and discussed.

Liu, Hongxue; Lu, Jiwei; Wolf, Stuart; Hodgson, Jim; Rutgers, Maarten

2013-01-01

251

Monte Carlo simulation of size, random field and temperature dependences of exchange bias in a core/shell magnetic nanoparticle  

Energy Technology Data Exchange (ETDEWEB)

By using Monte Carlo simulation on a ferromagnetic core/antiferromagnetic shell nanoparticle, we investigate in detail the exchange bias of the magnetic hysteresis as a function of both core radius and shell thickness, at low temperature. It is found that the exchange bias is very sensitive to the core radius and a small variation of the radius may lead to a big fluctuation of the bias. In a general tendency the exchange bias is enhanced by increasing shell thickness and decreasing core radius. The intrinsic correlation between the exchange bias and the spin configuration on the core-shell interface is demonstrated. We further investigate the dependence of the exchange bias on temperature and random field inside the nanoparticle, indicating a monotonic decreasing of the bias with the magnitude of random field and temperature, respectively.

Wu, M H; Li, Q C; Liu, J-M [Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); International Center for Materials Physics, Chinese Academy of Sciences, Shenyang (China)

2007-05-08

252

Loneliness, self-efficacy and stereotypes as predictor variables of the variation of informal caregiver burden for dependent elderly  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In order to examine what is the best set of predictive variables of overall change in caregiver burden, along with 232 informal caregivers of dependent elderly people residing in the district of Braganc;a in Portugal, were selected as independent variables to loneliness, stereotypes about people elderly and caregiver self-efficacy, and appealed to the multiple linear regression analysis by Backward method. It was found that when loneliness as the variable that best pre...

Mata, Maria Augusta; Pimentel, Maria Helena; Pereira, Fernando

2012-01-01

253

Ecological drivers of guanaco recruitment: variable carrying capacity and density dependence.  

Science.gov (United States)

Ungulates living in predator-free reserves offer the opportunity to study the influence of food limitation on population dynamics without the potentially confounding effects of top-down regulation or livestock competition. We assessed the influence of relative forage availability and population density on guanaco recruitment in two predator-free reserves in eastern Patagonia, with contrasting scenarios of population density. We also explored the relative contribution of the observed recruitment to population growth using a deterministic linear model to test the assumption that the studied populations were closed units. The observed densities increased twice as fast as our theoretical populations, indicating that marked immigration has taken place during the recovery phase experienced by both populations, thus we rejected the closed-population assumption. Regarding the factors driving variation in recruitment, in the low- to medium-density setting, we found a positive linear relationship between recruitment and surrogates of annual primary production, whereas no density dependence was detected. In contrast, in the high-density scenario, both annual primary production and population density showed marked effects, indicating a positive relationship between recruitment and per capita food availability above a food-limitation threshold. Our results support the idea that environmental carrying capacity fluctuates in response to climatic variation, and that these fluctuations have relevant consequences for herbivore dynamics, such as amplifying density dependence in drier years. We conclude that including the coupling between environmental variability in resources and density dependence is crucial to model ungulate population dynamics; to overlook temporal changes in carrying capacity may even mask density dependence as well as other important processes. PMID:24899131

Marino, Andrea; Pascual, Miguel; Baldi, Ricardo

2014-08-01

254

Variability in interval production is due to timing-dependent deficits in Huntington's disease.  

Science.gov (United States)

In Huntington's disease (HD), increased variability is seen in performance of motor tasks that require implicit control of timing. We examined whether timing variability was also evident in an explicit interval-timing task. Sixty subjects (21 controls, 19 manifest HD, and 20 pre-manifest HD) performed a single-interval production task with three target intervals (1.1 s, 2.2 s, 3.3 s). We analyzed accuracy (proportional error) and precision (standard deviation) across groups and intervals. No differences were seen in accuracy across groups or intervals. Precision was significantly lower in manifest (P?=?0.0001) and pre-manifest HD (P?=?0.04) compared with controls. This was particularly true for pre-manifest subjects close to diagnosis (based on probability of diagnosis in 5 years). Precision was correlated with proximity to diagnosis (r2 ?=?0.3, P?linear regression of standard deviation with interval duration. Slope of the regression was significantly higher in manifest HD (P?=?0.02) and in pre-manifest HD close to diagnosis (P?=?0.04) compared with controls and pre-manifest participants far from diagnosis. Timing precision is impaired before clinical diagnosis in Huntington's disease. Slope analysis suggests that timing variability (decreased precision) was attributable to deficits in timing-dependent processes. Our results provide additional support for the proposal that the basal ganglia are implicated in central timekeeping functions. Because the single interval production task was sensitive to deficits in pre-manifest HD, temporal precision may be a useful outcome measure in future clinical trials. PMID:25154339

Rao, Ashwini K; Marder, Karen S; Uddin, Jasim; Rakitin, Brian C

2014-10-01

255

Cast microstructure of Inconel 713C and its dependence on solidification variables  

Energy Technology Data Exchange (ETDEWEB)

The dependence of cast microstructure of Inconel 713C on solidification variables was investigated over a wide range of local cooling rates, epsilon, and thermal gradients in the liquid at the solid-liquid interface, G. The shape of MC carbide particles was found to depend greatly on: 1) the G/R ratio at the solid-liquid interface, where R is growth rate, through the effect of this ratio on the solid phase, ..gamma../sub g/, growth morphology. Under planar front growth conditions the carbide particles were octahedral, under cellular growth conditions they were plate-like, elongated along the cellular growth direction, and under dendritic growth conditions they were irregularly shaped; 2) the local cooling rate, epsilon, when ..gamma.. was dendritic, with a transition from octahedral to dendritic with increasing epsilon. The size of MC carbide particles was found to be controlled by coarsening and to become finer with increasing epsilon. In this alloy the composition of the MC carbide was established as (Nb/sub 0/./sub 63/Ti/sub 0/./sub 31/M0/sub 0/./sub 06/)C and was practically independent of local cooling rate. Other observations were that the precipitation of ..gamma.., d the formation of nonequilibrium eutectics, such as MC-..gamma.., ..gamma..-..gamma..' or MC-..gamma..-..gamma..' were suppressed at splat-cooling rates. Also, microsegregation of all alloying elements with the exception of aluminum was normal, with concentration increasing from the dendrite center-line to the dendrite arm boundary. Aluminum behaved in the opposite manner. Within the cooling rate range used herein, this variable had only a slight effect on microsegregation.

Bhambri, A.K.; Kattamis, T.Z.; Morral, J.E.

1975-03-01

256

Cast microstructure of Inconel 713C and its dependence on solidification variables  

International Nuclear Information System (INIS)

The dependence of cast microstructure of Inconel 713C on solidification variables was investigated over a wide range of local cooling rates, epsilon, and thermal gradients in the liquid at the solid-liquid interface, G. The shape of MC carbide particles was found to depend greatly on: 1) the G/R ratio at the solid-liquid interface, where R is growth rate, through the effect of this ratio on the solid phase, ?/sub g/, growth morphology. Under planar front growth conditions the carbide particles were octahedral, under cellular growth conditions they were plate-like, elongated along the cellular growth direction, and under dendritic growth conditions they were irregularly shaped; 2) the local cooling rate, epsilon, when ? was dendritic, with a transition from octahedral to dendritic with increasing epsilon. The size of MC carbide particles was found to be controlled by coarsening and to become finer with increasing epsilon. In this alloy the composition of the MC carbide was established as (Nb0.63Ti0.31M00.06)C and was practically independent of local cooling rate. Other observations were that the precipitation of ?, d the formation of nonequilibrium eutectics, such as MC-?, ?-?' or MC-?-?' were suppressed at splat-cooling rates. Also, microsegregation of all alloying elements with the exception of aluminum was normal, with concentration increasing from the dendrite center-line to the dendrite arm boundary. Aluminum behaved in the opposite manner. Within the cooling rate range used herein, this variable had only a slight effect on microsegregation

257

Low-loss and low-polarization-dependent fiber variable optical attenuators  

Science.gov (United States)

We present the optical performance of a compact variable optical attenuator (VOA) developed at Photintech. The presented VOA"s operation principle is based on the guided wave evanescent field manipulation. Access to the evanescent portion of the guided radiation is achieved by replacing the original waveguide"s cladding with a thermo-optic composite polymer (TOP) material. By changing the temperature of the thermo-optic (TO) material we create guided radiation partial leakage attenuating thus the light. Nevertheless, using polymer materials usually creates significant birefringence due to shrinkage during polymerization or thermal stresses during operation and the polarization dependence of such devices is relatively high. We apply a specific cladding geometry and heating electrode (pending patent of Photintech Inc.), which ensures axial compensation of the birefringence, providing thus very small polarization dependence. In-fiber design provides also low insertion loss (IL) and high dynamic range operation. Control electronics allow the VOA to operate with a precision better than 0.1dB. The developed VOA can be used in agile optical networks, for applications such as dynamic gain equalisation, dynamic channel equalisation, optical transmitter power control and receivers protection in telecommunication systems.

Galstian, Tigran; Zohrabyan, Armen; Tork, Amir; Birabassov, Rouslan; Jewell, Richard; Dumont, Dany; Gagnon, Bertrand

2004-12-01

258

Statistics of finite-time Lyapunov exponents in a random time-dependent potential.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The sensitivity of trajectories over finite time intervals t to perturbations of the initial conditions can be associated with a finite-time Lyapunov exponent lambda, obtained from the elements M_{ij} of the stability matrix M. For globally chaotic dynamics lambda tends to a unique value (the usual Lyapunov exponent lambda_infty) as t is sent to infinity, but for finite t it depends on the initial conditions of the trajectory and can be considered as a statistical quantity. ...

Schomerus, H.; Titov, M.

2002-01-01

259

The Fundamental Manifold of spiral galaxies: ordered versus random motions and the morphology dependence of the Tully-Fisher relation  

CERN Document Server

(Abridged) We investigate the morphology dependence of the Tully-Fisher relation, and the expansion of the relation into a three-dimensional manifold defined by luminosity, total circular velocity and a third dynamical parameter, to fully characterise spiral galaxies across all morphological types. We use a semi-analytic hierarchical model of galaxy evolution to build the theoretical TF relation. With this tool, we analyse a unique dataset of galaxies for which we cross-match luminosity with total circular velocity and central velocity dispersion. We provide a theoretical framework to calculate such measurable quantities from semi-analytic models. We establish the morphology dependence of the TF relation in both model and data. We analyse the dynamical properties of the model galaxies and determine that the parameter 'sigma/Vc', i.e. the ratio between random and total motions defined by velocity dispersion and circular velocity, accurately characterises the varying slope of the TF relation for different model...

Tonini, Chiara; Mould, Jeremy; Webster, Rachel; Danilovich, Taissa; Ozbilgen, Sinem

2013-01-01

260

Dose dependency and individual variability of the lipopolysaccharide-induced bovine acute phase protein response  

DEFF Research Database (Denmark)

In order to investigate the dose dependency and the individual variability of the lipopolysaccharide (LPS)-induced acute phase protein response in cattle, 8 nonlactating, nonpregnant Danish Holstein cows were challenged 3 times each by intravenous injection of increasing doses (10, 100, and 1000 ng/kg, consecutively) of Escherichia coli LPS with 3-wk intervals. All 3 LPS doses resulted in a rapid increase in serum concentrations of haptoglobin and serum amyloid A (SAA) and a decrease in serum concentrations of albumin in all 8 cows. Serum concentrations of acute phase proteins (APP) remained altered for several days after each LPS injection, and their increase or decrease was significantly related to LPS dose. In addition to dose dependency, the response was also dependent on the individual, as APP concentrations differed significantly among cows. To compare APP production in 2 consecutive challenges, individual APP levels after the challenge with 100 ng LPS/kg were correlated to levels attained after the challenge with 1000 ng LPS/kg. Serum amyloid A concentrations correlated between the 2 challenges, whereas haptoglobin concentrations tended to correlate; no correlation could be demonstrated between SAA and haptoglobin concentrations in either of the challenges, which suggests that the synthesis of haptoglobin and SAA are regulated in different ways. In conclusion, cattle are highly susceptible to LPS, as very low doses of LPS elicited acute phase albumin, SAA, and haptoglobin responses. Concentrations of APP not only reflect the magnitude of LPS exposure but are also influenced by the ability of the individual cow to mount an acute phase response. The ability to produce SAA and haptoglobin may be an innate characteristic of the individual, as responses in consecutive challenges were quantitatively similar.

TØlbØll, T.; Heegaard, Peter M. H.

2004-01-01

 
 
 
 
261

Calculation of the Effect of Random Superfluid Density on the Temperature Dependence of the Penetration Depth  

Energy Technology Data Exchange (ETDEWEB)

Microscopic variations in composition or structure can lead to nanoscale inhomogeneity in superconducting properties such as the magnetic penetration depth, but measurements of these properties are usually made on longer length scales. We solve a generalized London equation with a non-uniform penetration depth {lambda}(r), obtaining an approximate solution for the disorder-averaged Meissner screening. We find that the effective penetration depth is different from the average penetration depth and is sensitive to the details of the disorder. These results indicate the need for caution when interpreting measurements of the penetration depth and its temperature dependence in systems which may be inhomogeneous.

Lippman, Thomas; Moler, Kathryn A.

2012-07-20

262

Baclofen for maintenance treatment of opioid dependence: A randomized double-blind placebo-controlled clinical trial [ISRCTN32121581  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Results of preclinical studies suggest that the GABAB receptor agonist baclofen may be useful in treatment of opioid dependence. This study was aimed at assessing the possible efficacy of baclofen for maintenance treatment of opioid dependence. Methods A total of 40 opioid-dependent patients were detoxified and randomly assigned to receive baclofen (60 mg/day or placebo in a 12-week, double blind, parallel-group trial. Primary outcome measure was retention in treatment. Secondary outcome measures included opioids and alcohol use according to urinalysis and self-report ratings, intensity of opioid craving assessed with a visual analogue scale, opioid withdrawal symptoms as measured by the Short Opiate Withdrawal Scale and depression scores on the Hamilton inventory. Results Treatment retention was significantly higher in the baclofen group. Baclofen also showed a significant superiority over placebo in terms of opiate withdrawal syndrome and depressive symptoms. Non-significant, but generally favorable responses were seen in the baclofen group with other outcome measures including intensity of opioid craving and self-reported opioid and alcohol use. However, no significant difference was seen in the rates of opioid-positive urine tests. Additionally, the drug side effects of the two groups were not significantly different. Conclusion The results support further study of baclofen in the maintenance treatment of opioid dependence.

Ahmadi-Abhari Seyed Ali

2003-11-01

263

Dose-Dependent Effects of the Cimicifuga racemosa Extract Ze 450 in the Treatment of Climacteric Complaints: A Randomized, Placebo-Controlled Study.  

Science.gov (United States)

Extracts from Cimicifuga racemosa (CR, synonym Actaea racemosa) have shown efficacy in trials in women with menopausal symptoms. Yet, dose dependency remains unclear. Therefore, 180 female outpatients with climacteric complaints were treated for 12 weeks in a randomized, double-blind, placebo-controlled, 3-armed trial (CR extract Ze 450 in 6.5?mg or 13.0?mg, or placebo). Primary outcome was the difference in menopausal symptoms (vasomotor, psychological, and somatic), assessed by the Kupperman Menopausal Index between baseline and week 12. Secondary efficacy variables were patients' self-assessments of general quality of life (QoL), responder rates, and safety. Compared to placebo, patients receiving Ze 450 showed a significant reduction in the severity of menopausal symptoms in a dose-dependent manner from baseline to endpoint (mean absolute differences 17.0 (95% CI 14.65-19.35) score points, P menopausal symptoms and QoL were inversely correlated. Reported adverse events and clinical laboratory testing did not raise safety concerns. The CR extract Ze 450 is an effective and well-tolerated nonhormonal alternative to hormone treatment for symptom relief in menopausal women. PMID:23346194

Schellenberg, Ruediger; Saller, Reinhard; Hess, Lorenzo; Melzer, Jörg; Zimmermann, Christian; Drewe, Juergen; Zahner, Catherine

2012-01-01

264

Time-dependence in relativistic collisionless shocks: theory of the variable  

International Nuclear Information System (INIS)

We describe results from time-dependent numerical modeling of the collisionless reverse shock terminating the pulsar wind in the Crab Nebula. We treat the upstream relativistic wind as composed of ions and electron-positron plasma embedded in a toroidal magnetic field, flowing radially outward from the pulsar in a sector around the rotational equator. The relativistic cyclotron instability of the ion gyrational orbit downstream of the leading shock in the electron-positron pairs launches outward propagating magnetosonic waves. Because of the fresh supply of ions crossing the shock, this time-dependent process achieves a limit-cycle, in which the waves are launched with periodicity on the order of the ion Larmor time. Compressions in the magnetic field and pair density associated with these waves, as well as their propagation speed, semi-quantitatively reproduce the behavior of the wisp and ring features described in recent observations obtained using the Hubble Space Telescope and the Chandra X-Ray Observatory. By selecting the parameters of the ion orbits to fit the spatial separation of the wisps, we predict the period of time variability of the wisps that is consistent with the data. When coupled with a mechanism for non-thermal acceleration of the pairs, the compressions in the magnetic field and plasma density associated with the optical wisp structure naturally account for the location of X-ray features in the Crab. We also discuss the origin of the high energy lso discuss the origin of the high energy ions and their acceleration in the equatorial current sheet of the pulsar wind

265

[Relationship between psychopathological comorbidity and outcomes variables in-treatment cocaine dependent subject in therapeutic community].  

Science.gov (United States)

Over the last years, the therapeutic community treatment with people who have cocaine problems and psychopathological comorbidity has been increasing and it is important to know more about the success of these treatments. The aim of this paper is to study the psychopathological profile of cocaine-dependent patients and its association with outcome variables. It is interviewed by the Psychiatric Research Interview for Substance and Mental Disorders (PRISM-IV) and the Conners' Adult ADHD Diagnostic Interview for DSM-IV (CAADID) a total sample of 218 patients who sought treatment at any of the six public therapeutics community of Andalusia (Spain). The results show that the retention rate after three months of 68.3% (149), 43.5% that leaves the resource with a therapeutic discharge and 52.8% with clinically significant changes. Besides, the 57.8% have psychopathological comorbidity. Finally, there is a higher treatment success (measured by days of stay, type of discharge and therapeutic community outcome clinical impression) among people without psychopathological comorbidity. These data show the need to adapt the therapeutic communities to treat people with comorbid psychopathology and, thus, improve therapeutic success. PMID:23748941

Vergara-Moragues, Esperanza; González-Saiz, Francisco; Lozano-Rojas, Oscar; Fernández Calderón, Fermín; Verdejo García, Antonio; Betanzos Espinosa, Patricia; Bilbao Acedos, Izaskun; Pérez García, Miguel

2013-01-01

266

Thermal radiation effects on the time-dependent MHD permeable flow having variable viscosity  

International Nuclear Information System (INIS)

The present work is devoted to the impacts of thermal radiation on the unsteady laminar convective MHD flow of a viscous electrically conducting fluid having a temperature-dependent viscosity over a rotating porous disk of infinite extend impulsively set into motion. The fluid is subjected to an external uniform magnetic field perpendicular to the plane of the disk. The governing Navier-Stokes and Maxwell equations of the hydromagnetic fluid, together with the energy equation, are reduced into a system of nonlinear ordinary differential equations via the Von Karman similarity transformations. Due to the radiation effect and variable viscosity property the equations are highly coupled. These equations are then solved numerically by using a technique based on the spectral Chebyshev collocation in the direction normal to the disk and forward marching in time. Transient effects are discussed first. Later a parametric study of all parameters involved is performed and a representative set of results incorporating the effects of Prandtl number, the viscosity variation parameter, the magnetic interaction parameter, the radiation parameter, the uniform suction/blowing parameter, the relative temperature difference parameter and the Eckert number on physically meaningful quantities such as the radial and tangential skin friction coefficients, the torque, the vertical wall suction and the rate of heat transfer from the disk surface are illustrated graphically and discussed. (autllustrated graphically and discussed. (author)

267

From an unstable periodic orbit to the Lyapunov exponent and a macroscopic variable in a Hamiltonian lattice: periodic orbit dependencies  

International Nuclear Information System (INIS)

We study the problem of determining which periodic orbits in phase space can predict the largest Lyapunov exponent and the expectation values of macroscopic variables in a Hamiltonian system with many degrees of freedom. We also attempt to elucidate the manner in which these orbits yield such predictions. The model which we use in this paper is a discrete nonlinear Schroedinger equation. Using a method based on the modulational estimate of a periodic orbit, we predict the largest Lyapunov exponent and the expectation value of a macroscopic variable. We show that (1) the predicted largest Lyapunov exponent generally depends on the periodic orbit which we employ, and (2) the predicted expectation value of the macroscopic variable does not depend on the periodic orbit, at least in a high energy regime. In addition, the physical meanings of these dependencies are considered. (author)

268

A randomized controlled trial of targeted prefrontal cortex modulation with tDCS in patients with alcohol dependence.  

Science.gov (United States)

Preliminary small studies have shown that transcranial direct current stimulation (tDCS) reduces craving in alcoholic subjects. It is unclear whether tDCS also leads to changes in clinically meaningful outcomes for alcohol dependence in a properly powered phase II randomized clinical trial. We aimed to investigate whether repetitive tDCS changes the risk of alcohol use relapse in severe alcoholics from outpatient services. Thirty-five subjects were randomized to receive active bilateral [left cathodal/right anodal over the dorsolateral prefrontal cortex (dlPFC)] repetitive (five consecutive days) tDCS (2 mA, 35 cm2, two times daily stimulation for 13 min with a 20-min interval) or sham-tDCS. There were two dropouts before treatment. From 33 alcoholic subjects, 17 (mean age 45.5 ± 8.9 s.d., 16 males) were randomized to sham and 16 (44 ± 7.8 s.d., 16 males) to real tDCS treatment. By the end of the six months of follow-up, two subjects treated with sham (11.8%) and eight treated with real tDCS (50%) were still alcohol-abstinent [p = 0.02, Long-rank (Mantel-Cox) Test, HR = 0.35 (95% CI, 0.14-0.85)]. No differences with regard to changes on scores of craving, frontal function, global mental status, depressive or anxiety symptoms were observed between groups. However, subjects from the tDCS group improved with regard to their overall perception of quality of life (p = 0.02), and increased their scores in the environment domain (p = 0.04) after treatment. Bilateral tDCS over dlPFC reduces relapse probability in severe alcoholic subjects and results in improved perception of quality of life. PMID:25008145

Klauss, Jaisa; Penido Pinheiro, Leon Cleres; Silva Merlo, Bruna Lima; Correia Santos, Gerson de Almeida; Fregni, Felipe; Nitsche, Michael A; Miyuki Nakamura-Palacios, Ester

2014-11-01

269

Radial dependence of line profile variability in seven O9--B0.5 stars  

CERN Document Server

Massive stars show a variety of spectral variability: presence of discrete absorption components in UV P-Cygni profiles, optical line profile variability, X-ray variability, radial velocity modulations. Our goal is to study the spectral variability of single OB stars to better understand the relation between photospheric and wind variability. For that, we rely on high spectral resolution, high signal-to-noise ratio optical spectra collected with the spectrograph NARVAL on the Telescope Bernard Lyot at Pic du Midi. We investigate the variability of twelve spectral lines by means of the Temporal Variance Spectrum (TVS). The selected lines probe the radial structure of the atmosphere, from the photosphere to the outer wind. We also perform a spectroscopic analysis with atmosphere models to derive the stellar and wind properties, and to constrain the formation region of the selected lines. We show that variability is observed in the wind lines of all bright giants and supergiants, on a daily timescale. Lines form...

Martins, F; Hillier, D J; Donati, J -F; Bouret, J -C

2014-01-01

270

Field and temperature dependent electron transport properties of random network single walled and multi walled carbon nanotubes  

Science.gov (United States)

Field and temperature dependent electron transport properties of random network single walled carbon nanotubes (SWCNTs) and multi walled carbon nanotubes (MWCNTs) were investigated and compared. The electrical characterizations of drop casted CNT samples were done by two probe measurements by varying temperatures from 80 K to 300 K in the field region 1-400 V cm-1. The charge transport mechanisms at low (3.5 V) fields were analyzed from measured I-V characteristic curves at various temperatures (<300 K) with respect to applied field. At low field, the ohmic behavior was observed and at high field the charge transport appears to be Poole-Frenkel type in both types of CNTs network. Electron-electron and electron-phonon scatterings in the localized defect states dominate in SWCNTs, whereas in MWCNTs the delocalization of charge carriers as well as the scattering centers is responsible due to the presence of inner shells. Because of the different nature of chirality in random network, the SWCNTs displayed lower conduction when compared to MWCNTs. The variation in Poole-Frenkel co-efficient (?) (SWCNTs-0.193 × 10-22 MWCNTs-0.089 07 × 10-22 J V1/2 cm-1/2), activation energy (SWCNTs-90 meV; MWCNTs-60 meV for field of 7\\;{{V}^{1/2}}\\;c{{m}^{-1/2}}) and trap energy levels (SWCNTs-109 meV; MWCNTs-37 meV) are discussed for both SWCNTs and MWCNTs.

Rajavel, K.; Verma, S.; Asokan, K.; Rajendra Kumar, R. T.

2014-09-01

271

variables  

Directory of Open Access Journals (Sweden)

Full Text Available Este trabajo analiza, mediante regresiones lineales, el vínculo entre el uso de ingeniería concurrente (IC y el éxito en el proceso de desarrollo de nuevos productos (DNP bajo condiciones de incertidumbre variables. Los resultados obtenidos indican que, en entornos de reducida o moderada incertidumbre, el solapamiento de actividades, la integración interfuncional y el trabajo en equipo afectan positivamente al rendimiento del DNP en términos de tiempo de desarrollo, calidad y éxito en el lanzamiento de nuevos productos. Por el contrario, tales efectos no se observan en situaciones de elevada incertidumbre. Por todo ello, se concluye que el empleo de IC debe ser contingente a las condiciones particulares del entorno

Daniel V\\u00E1zquez-Bustelo

2008-01-01

272

Relative thermoluminescent efficiency of LiF detectors for proton radiation: Batch variability and energy dependence  

International Nuclear Information System (INIS)

The available experimental data on the relative thermoluminescent efficiency of the LiF:Mg,Ti dosimetric peaks for protons are contradictory. There are several reports showing that the efficiency exceeds unity by even more than 30%, however, many others show the efficiency close to unity or even lower. These contradictory data might be a result of the real variability of TLD properties or of not perfectly reproduced experimental conditions. In an attempt to resolve this issue, the efficiency of 16 batches of LiF:Mg,Ti (MTS) detectors for 60 MeV protons produced at the IFJ Kraków over the last 20 years was measured. All values of the relative TL efficiency were found to exceed unity significantly, with an average of 1.09. Dispersion between different batches was very low, all data were within 4% of the mean value. In second part of experiment the dependence of the relative efficiency of LiF:Mg,Ti and LiF:Mg,Cu,P detectors on proton energy was determined. The efficiency for LiF:Mg,Ti dosimetric peaks was found to have a maximum of 1.20 at about 20 MeV. For LiF:Mg,Cu,P the relative efficiency decreases systematically with decreasing proton energy, from 0.96 at 56 MeV, to 0.61 at 11 MeV. -- Highlights: ? We compared the relative TL efficiency to protons of 16 different LiF:Mg,Ti batches. ? Efficiency values are larger than 1 and show only minimal scatter between batches. ? LiF:Mg,Ti efficiency shows a maximum of 1.2 for about 20 MeV protons. ? LiF:Mg,Cu,P efficiency decreases with decreasing proton energy

273

Effect of an office worksite-based yoga program on heart rate variability: A randomized controlled trial  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Chronic work-related stress is a significant and independent risk factor for cardiovascular and metabolic diseases and associated mortality, particularly when compounded by a sedentary work environment. Heart rate variability (HRV provides an estimate of parasympathetic and sympathetic autonomic control, and can serve as a marker of physiological stress. Hatha yoga is a physically demanding practice that can help to reduce stress; however, time constraints incurred by work and family life may limit participation. The purpose of the present study is to determine if a 10-week, worksite-based yoga program delivered during lunch hour can improve resting HRV and related physical and psychological parameters in sedentary office workers. Methods and design This is a parallel-arm RCT that will compare the outcomes of participants assigned to the experimental treatment group (yoga to those assigned to a no-treatment control group. Participants randomized to the experimental condition will engage in a 10-week yoga program delivered at their place of work. The yoga sessions will be group-based, prescribed three times per week during lunch hour, and will be led by an experienced yoga instructor. The program will involve teaching beginner students safely and progressively over 10 weeks a yoga sequence that incorporates asanas (poses and postures, vinyasa (exercises, pranayama (breathing control and meditation. The primary outcome of this study is the high frequency (HF spectral power component of HRV (measured in absolute units; i.e. ms2, a measure of parasympathetic autonomic control. Secondary outcomes include additional frequency and time domains of HRV, and measures of physical functioning and psychological health status. Measures will be collected prior to and following the intervention period, and at 6 months follow-up to determine the effect of intervention withdrawal. Discussion This study will determine the effect of worksite-based yoga practice on HRV and physical and psychological health status. The findings may assist in implementing practical interventions, such as yoga, into the workplace to mitigate stress, enhance health status and reduce the risk of cardiovascular and metabolic diseases. Trial Registration ACTRN12611000536965 URL: http://www.anzctr.org.au/ACTRN12611000536965.aspx

Chang Dennis

2011-07-01

274

Learning dependence from samples.  

Science.gov (United States)

Mutual information, conditional mutual information and interaction information have been widely used in scientific literature as measures of dependence, conditional dependence and mutual dependence. However, these concepts suffer from several computational issues; they are difficult to estimate in continuous domain, the existing regularised estimators are almost always defined only for real or vector-valued random variables, and these measures address what dependence, conditional dependence and mutual dependence imply in terms of the random variables but not finite realisations. In this paper, we address the issue that given a set of realisations in an arbitrary metric space, what characteristic makes them dependent, conditionally dependent or mutually dependent. With this novel understanding, we develop new estimators of association, conditional association and interaction association. Some attractive properties of these estimators are that they do not require choosing free parameter(s), they are computationally simpler, and they can be applied to arbitrary metric spaces. PMID:24449692

Seth, Sohan; Príncipe, José C

2014-01-01

275

Angular dependence of multiple-bit upset response in static random access memories under heavy ion irradiation  

International Nuclear Information System (INIS)

Experimental evidence is presented relevant to the angular dependences of multiple-bit upset (MBU) rates and patterns in static random access memories (SRAMs) under heavy ion irradiation. The single event upset (SEU) cross sections under tilted ion strikes are overestimated by 23.9%–84.6%, compared with under normally incident ion with the equivalent linear energy transfer (LET) value of ? 41 MeV/(mg/cm2), which can be partially explained by the fact that the MBU rate for tilted ions of 30° is 8.5%–9.8% higher than for normally incident ions. While at a lower LET of ? 9.5 MeV/(mg/cm2), no clear discrepancy is observed. Moreover, since the ion trajectories at normal and tilted incidences are different, the predominant double-bit upset (DBU) patterns measured are different in both conditions. Those differences depend on the LET values of heavy ions and devices under test. Thus, effective LET method should be used carefully in ground-based testing of single event effects (SEE) sensitivity, especially in MBU-sensitive devices. (condensed matter: structural, mechanical, and thermal properties)

276

Conductance of partially disordered graphene: crossover from temperature-dependent to field-dependent variable-range hopping  

International Nuclear Information System (INIS)

We report an analysis of low-temperature measurements of the conductance of partially disordered reduced graphene oxide, finding that the data follow a simple crossover scenario. At room temperature, the conductance is dominated by two-dimensional (2D) electric field-assisted, thermally driven (Pollak–Riess) variable-range hopping (VRH) through highly disordered regions. However, at lower temperatures T, we find a smooth crossover to follow the exp(?E0/E)1/3 field-driven (Shklovskii) 2D VRH conductance behaviour when the electric field E exceeds a specific crossover value EC(T)2D=(EaE01/3/3)3/4 determined by the scale factors E0 and Ea for the high-field and intermediate-field regimes respectively. Our crossover scenario also accounts well for experimental data reported by other authors for three-dimensional disordered carbon networks, suggesting wide applicability. (paper)

277

An Analysis of a Demand for Roundwood in South Korea on a Basis of the Lagged Dependent Variable  

Energy Technology Data Exchange (ETDEWEB)

The object of this paper is to forecast the change of wood demand in the long run through the demand analysis of wood using a time differential dependent variable. The wood demand was analyzed assuming a derived demand using wood demand data for 27 years from 1970 to 1996. The wood demand in 1980s shows a continuos and slow increase and then after 1991 it shows a downward stability. An adaptive expectation model and a partial adjustment model were used in the analysis. To explain a steep increase of wood demand from 1977 and 1979, a pile variable in the model was used. An explanatory variable used the wood price, the pile variable, the price of derived goods (lumber and wood products), and a time differential dependent variable. As a result, the result of adaptive expectation model was insignificant, but the estimated value of each variable in the partial adjustment model was generally significant. Particularly, an estimated value of time differential dependent variable, t, was significant with the value of 2.07. The correction coefficient of the partial adjustment model was 0.74. Under the partial adjustment model, the wood demand was forecasted by using two methods. One is assuming the increase rate of wood price indicator 6.7% and domestic wood product price indicator 5.8% every year up to 2010, and another is assuming wood price indicator 6.8% and wood product price indicator 5.6%. As a result, the wood demand showed a continuous increase. The amount of forecasted demand with uniform price increase rate showed higher than with uniform increase of price indicator. (author). 17 refs., 4 figs., 4 tabs.

Kim, Joon Soon [Korea University, Seoul (Korea)

1998-09-01

278

Methylphenidate for treating tobacco dependence in non-attention deficit hyperactivity disorder smokers: A pilot randomized placebo-controlled trial  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Methylphenidate blocks the re-uptake of dopamine by binding to the dopamine transporter in the presynaptic cell membrane and increases extracellular dopamine levels. Similarities in neuropsychologic effects between nicotine and methylphenidate make it an intriguing potential therapeutic option. Previous research of methylphenidate in smokers has suggested a possible beneficial effect for the relief of nicotine withdrawal symptoms, but showed no efficacy in helping smokers with attention deficit hyperactivity disorder (ADHD to stop smoking. Methods To investigate potential efficacy for relieving nicotine withdrawal symptoms and promoting smoking abstinence, we conducted a randomized, double-blind, placebo-controlled, phase II study of once-a-day osmotic-release oral system methylphenidate (OROS-MPH, Concerta® at a target dose of 54-mg/day for 8 weeks compared with placebo in 80 adult cigarette smokers. Results Of the 80 randomized subjects and median smoking rate was 20 cigarettes per day. At the end of the medication phase, the biochemically confirmed 7-day point prevalence smoking abstinence was 10% (4/40 for the placebo group and 2.5% (1/40 for the OROS-MPH group. Nicotine withdrawal was not found to differ significantly between treatment groups during the first 14 days following the start of medication prior to the target quit date (p = 0.464 or during the first 14 days following the target quit date (p = 0.786. Conclusion We observed no evidence of efficacy of OROS-MPH to aid smokers to stop smoking. Although there are biologically plausible hypotheses that support the use of OROS-MPH for treating tobacco dependence, we found no evidence to support such hypotheses. In addition to no increase in smoking abstinence, we saw no effect of OROS-MPH for tobacco withdrawal symptom relief and no change in smoking rates was observed in the OROS-MPH group compared to the placebo group.

Croghan Ivana T

2011-01-01

279

Methylphenidate for treating tobacco dependence in non-attention deficit hyperactivity disorder smokers: A pilot randomized placebo-controlled trial  

Science.gov (United States)

Background Methylphenidate blocks the re-uptake of dopamine by binding to the dopamine transporter in the presynaptic cell membrane and increases extracellular dopamine levels. Similarities in neuropsychologic effects between nicotine and methylphenidate make it an intriguing potential therapeutic option. Previous research of methylphenidate in smokers has suggested a possible beneficial effect for the relief of nicotine withdrawal symptoms, but showed no efficacy in helping smokers with attention deficit hyperactivity disorder (ADHD) to stop smoking. Methods To investigate potential efficacy for relieving nicotine withdrawal symptoms and promoting smoking abstinence, we conducted a randomized, double-blind, placebo-controlled, phase II study of once-a-day osmotic-release oral system methylphenidate (OROS-MPH, Concerta®) at a target dose of 54-mg/day for 8 weeks compared with placebo in 80 adult cigarette smokers. Results Of the 80 randomized subjects and median smoking rate was 20 cigarettes per day. At the end of the medication phase, the biochemically confirmed 7-day point prevalence smoking abstinence was 10% (4/40) for the placebo group and 2.5% (1/40) for the OROS-MPH group. Nicotine withdrawal was not found to differ significantly between treatment groups during the first 14 days following the start of medication prior to the target quit date (p = 0.464) or during the first 14 days following the target quit date (p = 0.786). Conclusion We observed no evidence of efficacy of OROS-MPH to aid smokers to stop smoking. Although there are biologically plausible hypotheses that support the use of OROS-MPH for treating tobacco dependence, we found no evidence to support such hypotheses. In addition to no increase in smoking abstinence, we saw no effect of OROS-MPH for tobacco withdrawal symptom relief and no change in smoking rates was observed in the OROS-MPH group compared to the placebo group. PMID:21276244

2011-01-01

280

Variable screening and ranking using sampling-based sensitivity measures  

International Nuclear Information System (INIS)

This paper presents a methodology for screening insignificant random variables and ranking significant important random variables using sensitivity measures including two cumulative distribution function (CDF)-based and two mean-response based measures. The methodology features (1) using random samples to compute sensitivities and (2) using acceptance limits, derived from the test-of-hypothesis, to classify significant and insignificant random variables. Because no approximation is needed in either the form of the performance functions or the type of continuous distribution functions representing input variables, the sampling-based approach can handle highly nonlinear functions with non-normal variables. The main characteristics and effectiveness of the sampling-based sensitivity measures are investigated using both simple and complex examples. Because the number of samples needed does not depend on the number of variables, the methodology appears to be particularly suitable for problems with large, complex models that have large numbers of random variables but relatively few numbers of significant random variables

 
 
 
 
281

A spectral semi-implicit method for a convection problem with viscosity dependent on temperature in primitive variables formulation  

CERN Document Server

This article discusses the performance of several spectral numerical methods to solve the time evolution of a convection problem with viscosity strongly dependent on temperature. The setup is a 2D domain with periodic boundary conditions along the horizontal coordinate. The numerical schemes are based on a primitive variable formulation and we compare the efficiency of several boundary conditions for pressure. Various numerical examples are presented to illustrate the performance of the different methods. As a result we find that time transients are best resolved by a semi-implicit method with variable time step and improved boundary conditions for pressure.

Curbelo, Jezabel

2014-01-01

282

The fundamental manifold of spiral galaxies: ordered versus random motions and the morphology dependence of the Tully-Fisher relation  

Science.gov (United States)

We investigate the morphology dependence of the Tully-Fisher (TF) relation, and the expansion of the relation into a three-dimensional manifold defined by luminosity, total circular velocity and a third dynamical parameter, to fully characterize spiral galaxies across all morphological types. We use a full semi-analytic hierarchical model (based on Croton et al.), built on cosmological simulations of structure formation, to model galaxy evolution and build the theoretical TF relation. With this tool, we analyse a unique data set of galaxies for which we cross-match luminosity with total circular velocity and central velocity dispersion. We provide a theoretical framework to calculate such measurable quantities from hierarchical semi-analytic models. We establish the morphology dependence of the TF relation in both model and data. We analyse the dynamical properties of the model galaxies and determine that the parameter ?/VC, i.e. the ratio between random and total motions defined by velocity dispersion and circular velocity, accurately characterizes the varying slope of the TF relation for different model galaxy types. We apply these dynamical cuts to the observed galaxies and find indeed that such selection produces a differential slope of the TF relation. The TF slope in different ranges of ?/VC is consistent with that for the traditional photometric classification in Sa, Sb and Sc. We conclude that ?/VC is a good parameter to classify galaxy type, and we argue that such classification based on dynamics more closely mirrors the physical properties of the observed galaxies, compared to visual (photometric) classification. We also argue that dynamical classification is useful for samples where eye inspection is not reliable or impractical. We conclude that ?/VC is a suitable parameter to characterize the hierarchical assembly history that determines the disc-to-bulge ratio, and to expand the TF relation into a three-dimensional manifold, defined by luminosity, circular velocity and ?/VC.

Tonini, C.; Jones, D. H.; Mould, J.; Webster, R. L.; Danilovich, T.; Ozbilgen, S.

2014-03-01

283

Examination of nicotine pharmacokinetics dependent on biological and anamnestic smoking-related variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Tobacco dependence is still the single most important risk to health and remains the leading preventable cause of premature death (WHO-Kollaborationszentrum für Tabakkontrolle im Deutschen Krebsforschungszentrum 2006). In order to be able to improve the treatment of tobacco dependency it is of great importance to obtain thorough knowledge about the causes of tobacco dependency and about nicotine pharmacokinetics. Objective: The objective of this study was to examine possible influences of...

Bannier, Oliver

2008-01-01

284

A Large Cohort Study Concerning Age-Dependent Impacts of Anthropometric Variables on Spirometric Parameters in Nonsmoking Healthy Adults  

Science.gov (United States)

Backgrounds Although height (H) has been considered the principal anthropometric variable governing lung function, the age-dependent differences in its influences on determining spirometric parameters (SPs) have not been conclusively investigated. Moreover, there has been no study centered on age-dependent effects of other anthropometric variables, including body weight (BW) and body fat mass (BFM) on SPs. In addition, the age-dependent influences of these anthropometric variables are anticipated to differ quantitatively between male and female participants. Methods A total of 16,919 nonsmoking healthy Japanese adults (men: 6,116, women: 10,803) were partitioned into six groups stratified by gender and age at intervals of 20-years: young-, middle-, and advanced-age groups of either gender. Using a model in which a SP was described by a logarithmic additive function of age, H, BW, and BFM, we determined the partial regression coefficients of the respective anthropometric variables to predict the reference means of SPs, including FVC, FEV1, FEV1/FVC, PEF, FEF50, and FEF75, in the six groups. Results/Discussion Although the impact of H on FVC and FEV1 was relatively homogeneous irrespective of gender and age, its homogeneity faded for flow parameters, particularly in the female middle- and advanced-age groups, indicating that the age-dependent contribution of H to SPs was enhanced more in women. The impact of BW on SPs differed depending on age, and this effect was also more conspicuous for female participants. H and BW generally exerted positive effects on SPs, whereas BFM had negative effects. Opposite effects of BW and BFM were observed in the female middle-age group in particular. Conclusions The effects of anthropometric variables on spirometric parameters are highly age-dependent, particularly in women, leading to the conclusion that the assumption of age-independent, constant partial regression coefficients of anthropometric variables while predicting the reference mean of a certain spirometric parameter may result in substantial errors. PMID:24955585

Omori, Hisamitsu; Onoue, Ayumi; Katoh, Takahiko; Ogata, Yasuhiro; Kawashima, Hidetoshi; Miyao, Naoki; Tsuji, Takao; Aoshiba, Kazutetsu; Nagai, Atsushi; Yamaguchi, Kazuhiro

2014-01-01

285

Physically-based internal variable model for rate-dependent plasticity  

International Nuclear Information System (INIS)

A unified model is developed for creep and plasticity in metals, using internal state variables to reflect the current microstructure. The inelastic flow rule is taken to be a power function incorporating a kinematic and an isotropic internal variable, where the microstructural origins of these properties are dislocation pileups and dislocation obstacle interaction, respectively. The model is generalized for three-dimensional deformation and evolutionary functions are developed for the internal variables to account for strain hardening and thermal recovery. An experimental test and data reduction procedure is presented which allows all the material constants to be determined for materials which exhibit secondary creep. The procedure is applied to pure aluminum. This generalized model provides a physical basis for predicting mechanical response along arbitrary deformation paths

286

Stimulus-dependent variability and noise correlations in cortical MT neurons.  

Science.gov (United States)

Population codes assume that neural systems represent sensory inputs through the firing rates of populations of differently tuned neurons. However, trial-by-trial variability and noise correlations are known to affect the information capacity of neural codes. Although recent studies have shown that stimulus presentation reduces both variability and rate correlations with respect to their spontaneous level, possibly improving the encoding accuracy, whether these second order statistics are tuned is unknown. If so, second-order statistics could themselves carry information, rather than being invariably detrimental. Here we show that rate variability and noise correlation vary systematically with stimulus direction in directionally selective middle temporal (MT) neurons, leading to characteristic tuning curves. We show that such tuning emerges in a stochastic recurrent network, for a set of connectivity parameters that overlaps with a single-state scenario and multistability. Information theoretic analysis shows that second-order statistics carry information that can improve the accuracy of the population code. PMID:23878209

Ponce-Alvarez, Adrián; Thiele, Alexander; Albright, Thomas D; Stoner, Gene R; Deco, Gustavo

2013-08-01

287

On history dependence of stress-strain diagrams and creep curves under variable repeated loading  

International Nuclear Information System (INIS)

The ability of structural alloys to 'keep in memory' the loading prehistory becomes of special importance when inelastic variable repeated loading is considered. There are two main approaches to the development of the mathematical description of this phenomenon: the inclusion of hidden state variables in the incremental theory constitutive equations (a) and construction of proper hereditary functionals (b). In this respect the assumption that the 'memory' regarding the previous deformation history is due to structural nonhomogeneity of actual materials proves to be fruitful. (orig.)

288

On Integrating Variables and Separating Facts in the Complex Relationship between Dependency and Domestic Violence  

Science.gov (United States)

Presents a reply by Robert Bornstein to comments from Chronister and regarding his article, "The complex relationship between dependency and domestic violence: Converging psychological factors and social forces." In addition to raising some important issues regarding the link between dependency and domestic violence, the comments by Chronister and…

Bornstein, Robert F.

2007-01-01

289

The effect of antihypertensive treatment on headache and blood pressure variability in randomized controlled trials: a systematic review.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Antihypertensive drugs reduce headache but it is unclear whether there are differences between drug classes. Calcium channel blockers (CCBs) decrease variability in systolic blood pressure (SBPV) and stroke risk more than other classes, possibly due to decreased vascular tone. If so, there might be a correlation between drug-class effects on variability in SBP and on headache. We determined antihypertensive class effects on SBPV and headache during follow-up in a systematic review of randomiz...

Webb, Aj; Rothwell, Pm

2012-01-01

290

Morphology dependence of TiO{sub 2} nanotube arrays on anodization variables and buffer medium  

Energy Technology Data Exchange (ETDEWEB)

Vertically oriented TiO{sub 2} nanotube arrays were prepared by potentiostatic anodization of Ti foils in HF/acetic acid (HAC) aqueous solution. Anodization variables including anodization electrolyte concentration, anodization voltage, anodization time and buffer medium can be chosen and adjusted to manipulate the nanotube arrays to give the required length and morphology. (semiconductor materials)

Wen Xin; Cao Meng; Wu Jie; Tao Junchao; Sun Yan; Dai Ning, E-mail: wx0373@mail.sitp.ac.c, E-mail: ndai@mail.sitp.ac.c [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China)

2010-06-15

291

Age Dependent Variability in Gene Expression in Fischer 344 Rat Retina.  

Science.gov (United States)

Recent evidence suggests older adults may be a sensitive population with regard to environmental exposure to toxic compounds. One source of this sensitivity could be an enhanced variability in response. Studies on phenotypic differences have suggested that variation in response d...

292

Application of Differential Transform Method to Thermoelastic Problem for Annular Disks of Variable Thickness with Temperature-Dependent Parameters  

Science.gov (United States)

This article analyzes the one-dimensional steady temperature field and related thermal stresses in an annular disk of variable thickness that has a temperature-dependent heat transfer coefficient and is capable of temperature-dependent internal heat generation. The temperature dependencies of the thermal conductivity, Young's modulus, and the coefficient of linear thermal expansion of the disk are considered, whereas Poisson's ratio is assumed to be constant. The differential transform method (DTM) is employed to analyze not only the nonlinear heat conduction but also the resulting thermal stresses. Analytical solutions are developed for the temperature and thermal stresses in the form of simple power series. Numerical calculations are performed for an annular cooling/heating fin of variable thickness. Numerical results show that the sufficiently converged analytical solutions are in good agreement with the solutions obtained by the Adomian decomposition method and give the effects of the temperature-dependent parameters on the temperature and thermal stress profiles in the disk. The DTM is useful as a new analytical method for solving thermoelastic problems for a body with temperature-dependent parameters including material properties.

Chiba, Ryoichi

2012-02-01

293

Strictly and asymptotically scale invariant probabilistic models of N correlated binary random variables having q-Gaussians as N ? ? limiting distributions  

International Nuclear Information System (INIS)

The celebrated Leibnitz triangle has a remarkable property, namely that each of its elements equals the sum of its south-west and south-east neighbors. In probabilistic terms, this corresponds to a specific form of correlation of N equally probable binary variables which satisfy scale invariance. Indeed, the marginal probabilities of the N-system precisely coincide with the joint probabilities of the (N?1)-system. On the other hand, the non-additive entropy which grounds non-extensive statistical mechanics, is, under appropriate constraints, extremized by the (q-Gaussian) distribution. These distributions also result, as attractors, from a generalized central limit theorem for random variables which have a finite generalized variance, and are correlated in a specific way called q-independence. In order to provide physical enlightenment as regards this concept, we introduce here three types of asymptotically scale invariant probabilistic models with binary random variables, namely (i) a family, characterized by an index ? = 1,2,3,..., unifying the Leibnitz triangle (? = 1) and the case of independent variables (???); (ii) two slightly different discretizations of q-Gaussians; (iii) a special family, characterized by the parameter ?, which generalizes the usual case of independent variables (recovered for ? = 1/2). Models (i) and (iii) are in fact strictly scale invariant. For models (i), we analytically show that the N ? ? probability distribution is a qability distribution is a q-Gaussian with q = (??2)/(??1). Models (ii) approach q-Gaussians by construction, and we numerically show that they do so with asymptotic scale invariance. Models (iii), like two other strictly scale invariant models recently discussed by Hilhorst and Schehr, approach instead limiting distributions which are not q-Gaussians. The scenario which emerges is that asymptotic (or even strict) scale invariance is not sufficient but it might be necessary for having strict (or asymptotic) q-independence, which, in turn, mandates q-Gaussian attractors

294

Cross-comparison of the performance of discrete, phase and functional data analysis to describe a dependent variable  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The aim of this study was to assess and contrast the ability of discrete point, functional principal component analysis (fPCA) and analysis of characterizing phases (ACP) to describe a dependent variable (jump height) from vertical ground reaction force curves captured during the propulsion phase of a countermovement jump. A stepwise multiple regression analysis was used to assess the ability of each data analysis technique. The order of effectiveness (high to low) was ACP, fPCA and discrete ...

Richter, Chris; Gualano, Leonardo; O Connor, Noel; Moran, Kieran

2013-01-01

295

On the frequency-dependent specific heat and TMDSC: Constitutive modelling based on thermodynamics with internal state variables  

International Nuclear Information System (INIS)

To develop constitutive models to represent the thermomechanically chemically coupled behaviour of curing resins, vulcanizing elastomers or melting and crystallizing polymers the technique of DSC is extremely helpful. In the present study, the method of TMDSC is interpreted and evaluated in the context of thermodynamics with internal state variables. The balance equation of energy and the dissipation principle in the form of the Clausius-Duhem inequality form the theoretical basis of our study. Since the pressure and the temperature are the external variables in DSC, the specific Gibbs free energy is used as thermodynamic potential. It depends on temperature, stress and a set of internal state variables to represent the microstructure of the material on a phenomenological basis. The temperature- and internal variable-induced changes in the Gibbs free energy are approximated by a Taylor series up to second order terms. As a substantial result of this work, closed-form expressions for the dynamic calorimetric response due to harmonic temperature perturbations and the frequency-dependent complex heat capacity are derived. The theory allows a physical interpretation of the complex heat capacity and its underlying phenomena and is in accordance with experimental observations from literature.

296

Nonlinear thermal buckling and postbuckling analyses of imperfect variable thickness temperature-dependent bidirectional functionally graded cylindrical shells  

International Nuclear Information System (INIS)

Influences of the thickness variability and bidirectional material heterogeneity on the thermal buckling of the cylindrical shells have not been investigated so far. In the present paper, nonlinear thermal buckling and postbuckling analyses of imperfect, variable thickness cylindrical shells made of bidirectional functionally graded materials undergoing uniform temperature rises are accomplished for the first time, employing a third-order shear-deformation theory, von Karman-type kinematic nonlinearity, and a nonlinear finite element method. Material properties may vary in both radial and axial directions and can be temperature-dependent. Buckling temperature is detected by a modified Budiansky's criterion. The results reveal that temperature-dependency of the material properties reduces the buckling temperature. Moreover, effects of the volume fraction index on decreasing the buckling temperature are more remarkable for higher radius to thickness ratios. Furthermore, effects of reduction of the thickness in the axial direction may be compensated by an appropriate distribution of the material properties. -- Highlights: • Nonlinear thermal postbuckling of imperfect FGM cylindrical shells is investigated. • Material properties of the shell may vary in both radial and axial directions. • Geometric imperfections and thickness variability are also taken into account. • Material properties are considered to be temperature-dependent. • The nonlinear governing equations are solved by an updating finite element scheme

297

Scale-dependent spatial variability in peatland lead pollution in the southern Pennines, UK  

International Nuclear Information System (INIS)

Increasingly, within-site and regional comparisons of peatland lead pollution have been undertaken using the inventory approach. The peatlands of the Peak District, southern Pennines, UK, have received significant atmospheric inputs of lead over the last few hundred years. A multi-core study at three peatland sites in the Peak District demonstrates significant within-site spatial variability in industrial lead pollution. Stochastic simulations reveal that 15 peat cores are required to calculate reliable lead inventories at the within-site and within-region scale for this highly polluted area of the southern Pennines. Within-site variability in lead pollution is dominant at the within-region scale. The study demonstrates that significant errors may be associated with peatland lead inventories at sites where only a single peat core has been used to calculate an inventory. Meaningful comparisons of lead inventories at the regional or global scale can only be made if the within-site variability of lead pollution has been quantified reliably. - Multiple peat cores are required for accurate peatland Pb inventories

298

Vitamin D production depends on ultraviolet-B dose but not on dose rate: a randomized controlled trial  

DEFF Research Database (Denmark)

Ultraviolet-B (UV-B) radiation increases serum vitamin D level expressed as 25-hydroxyvitamin D(3) (25(OH)D), but the dose-response relationship and the importance of dose rate is unclear. Of 172 fair-skinned persons screened for 25(OH)D, 55 with insufficient baseline 25(OH)D?50 nm (mean 31.2 nm) were selected and randomized to one of 11 groups of five participants. Each group was exposed to one of four different UV-B doses: 0.375, 0.75, 1.5 or 3.0 standard erythema dose (SED) for 1, 5, 10 or 20 min. All participants had four UV-B sessions with 2- to 3-day interval with 24% of their skin exposed. Skin pigmentation and 25(OH)D were measured before and after the irradiations. The increase in 25(OH)D after UV-B exposure (adjusted for baseline 25(OH)D) was positively correlated with the UV-B dose (P=0.001; R(2) =0.176) but not to dose rate (1-20 min). 25(OH)D increased in response to four UV-B treatments of 3 SED with 24.8 nm on average and 14.2 nm after four UV-B treatments of just 0.375 SED. In conclusion, the increase in 25(OH)D after UV-B exposure depends on the dose but not on the dose rate (1-20 min). Further, a significant increase in 25(OH)D was achieved with a very low UV-B dose.

Bogh, Morten K B; Schmedes, Anne V

2011-01-01

299

Compact radio sources: The dependence of variability and polarization on spectral shape  

International Nuclear Information System (INIS)

VLA observations have been made at 20, 6, and 2 cm of an unbiased sample of 40 flat-spectrum (?>-0.5;Sproportionalv/sup ?/) radio sources selected from the S4 (6 cm strong source) survey. We have explored the polarization properties of these sources and examined their variability over a 6--8 year baseline at 6 cm by comparing our flux density values with the original S4 measurements. Most of the flux density in these sources is from regions unresolved (< or approx. =0.2) on the VLA. We find that the source properties divide fairly clearly when one classifies the sources according to simple spectral shape categories; viz, straight, simple-convex (''humped''), and complex. The complex sources are significantly more variable and reach higher polarizations. The straight sources are relatively quiescent and show signs of substantial Faraday depolarization. The simple-convex sources are also relatively quiescent and show none of the high polarizations seen amonng the complex sources. The complex sources exhibit, on average, about the same degree of polarization at all three wavelengths, but, for a given source, the degree of polarization shows little correlation from one wavelength to another. The VLBI structures may also be related to these spectral shape categories. Possible interpretations of these relations are discussed. We also argue that if the complex, variable sources are relativistically ''beamed'' toward us, then their unbeamed counterparts have not been found,beamed counterparts have not been found, at least in this subset of the S4 survey

300

The Relationships between Cognitive Style of Field Dependence and Learner Variables in E-Learning Instruction  

Science.gov (United States)

This study examines the relationships between cognitive styles of field dependent learners with their attitudes towards e-learning (distance education) and instructional behavior in e-learning instruction. The Group Embedded Figures Test (GEFT) and the attitude survey (for students' preferences) towards e-learning instruction as distance…

Sozcu, Omer Faruk

2014-01-01

 
 
 
 
301

Re-examining the ontogeny of the context preexposure facilitation effect in the rat through multiple dependent variables.  

Science.gov (United States)

The capability to acquire context conditioning does not emerge until weaning, at least when the defining features of the context lack explicit and salient olfactory cues. Contextual learning deficits in preweanling rats have been associated with functional immaturity of the dorsal hippocampus. According to recent studies, the so-called context preexposure facilitation effect (CPFE) - a hippocampus-dependent effect - is not observed until postnatal day 23 (PD23). In these studies the footshock intensity employed was higher (1.5 mA) than in adult studies, and context conditioning was inferred from a single behavioral measure (percentage of freezing). The present study examined the CPFE on PD17 and PD23 by analyzing multiple dependent variables, including fecal boli and an ethogram covering the complete behavioral repertoire of the rat. A non-shocked control group was included in the design and two footshock intensities were employed (0.5 and 1.5 mA). Results showed clear evidence of contextual fear conditioning in preweanling and weanling rats, as well as evidence of conditioned fear in non-preexposed rats from both age groups. In some cases, some dependent variables, such as grooming or vertical exploration, were more sensitive than freezing for detecting evidence of memory. Strong fear responses were detected in weanling (but not preweanling) rats, when rats were evaluated in a different context from the one employed at conditioning. These results indicate that preweanling rats are capable of acquiring contextual conditioning, even in a context lacking explicit odor cues, and highlight the importance of multiple dependent variables for analyzing the ontogeny of memory. PMID:22561035

Pisano, M V; Ferreras, S; Krapacher, F A; Paglini, G; Arias, C

2012-07-15

302

Social communication intervention effects vary by dependent variable type in preschoolers with autism spectrum disorders  

Science.gov (United States)

Individuals with autism spectrum disorders (ASDs) have difficulty communicating in ways that are primarily for initiating and maintaining social relatedness (i.e., social communication). We hypothesized that the way researchers measured social communication would affect whether treatment effects were found. Using a best evidence review method, we found that treatments were shown to improve social communication outcomes approximately 54% of the time. The probability that a treatment affected social communication varied greatly depending on whether social communication was directly targeted (63%) or not (39%). Finally, the probability that a treatment affected social communication also varied greatly depending on whether social communication as measured in (a) contexts very similar to treatment sessions (82%) or (b) contexts that differed from treatment on at least setting, materials, and communication partner (33%). This paper also provides several methodological contributions.

Yoder, Paul J.; Bottema-Beutel, Kristen; Woynaroski, Tiffany; Chandrasekhar, Rameela; Sandbank, Michael

2014-01-01

303

Saddlepoint expansions for sums of Markov dependent variables on a continuous state space  

DEFF Research Database (Denmark)

Based on the conjugate kernel studied in Iscoe et al. (1985) we derive saddlepoint expansions for either the density or distribution function of a sum f(X1)+...+f(Xn), where the Xi's constitute a Markov chain. The chain is assumed to satisfy a strong recurrence condition which makes the results here very similar to the classical results for i.i.d. variables. In particular we establish also conditions under which the expansions hold uniformly over the range of the saddlepoint. Expansions are also derived for sums of the form f(X1, X0)+f(X2, X1)+...+f(Xn, Xn-1) although the uniformity result just mentioned does not generalize. © 1991 Springer-Verlag.

Jensen, J.L.

1991-01-01

304

The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength  

Directory of Open Access Journals (Sweden)

Full Text Available There is ample evidence that the state of the northern polar stratospheric vortex in boreal winter influences tropospheric variability. Therefore, the main teleconnection patterns over the North Atlantic are defined separately for winter episodes in which the zonal mean wind at 50 hPa and 65° N is above or below the critical Rossby velocity for zonal planetary wave one. It turns out that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the "polar vortex is strong", there exists "one" meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the "polar vortex is weak", there exist "two" such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results show that it is essential to include the state of the upper dynamic boundary conditions (the polar vortex strength in any study of the variability over the North Atlantic. Climate forecast based solely on the forecast of a "classic NAO" and further statistical downscaling may lead to the wrong conclusions if the state of the polar vortex is not considered as well.

K. Walter

2004-10-01

305

Sensitivity of firing rate to input fluctuations depends on time scale separation between fast and slow variables in single neurons.  

Science.gov (United States)

Neuronal responses are often characterized by the firing rate as a function of the stimulus mean, or the f-I curve. We introduce a novel classification of neurons into Types A, B-, and B+ according to how f-I curves are modulated by input fluctuations. In Type A neurons, the f-I curves display little sensitivity to input fluctuations when the mean current is large. In contrast, Type B neurons display sensitivity to fluctuations throughout the entire range of input means. Type B- neurons do not fire repetitively for any constant input, whereas Type B+ neurons do. We show that Type B+ behavior results from a separation of time scales between a slow and fast variable. A voltage-dependent time constant for the recovery variable can facilitate sensitivity to input fluctuations. Type B+ firing rates can be approximated using a simple "energy barrier" model. PMID:19353260

Lundstrom, Brian Nils; Famulare, Michael; Sorensen, Larry B; Spain, William J; Fairhall, Adrienne L

2009-10-01

306

Randomized random walk on a random walk  

International Nuclear Information System (INIS)

This paper discusses generalizations of the model introduced by Kehr and Kunter of the random walk of a particle on a one-dimensional chain which in turn has been constructed by a random walk procedure. The superimposed random walk is randomised in time according to the occurrences of a stochastic point process. The probability of finding the particle in a particular position at a certain instant is obtained explicitly in the transform domain. It is found that the asymptotic behaviour for large time of the mean-square displacement of the particle depends critically on the assumed structure of the basic random walk, giving a diffusion-like term for an asymmetric walk or a square root law if the walk is symmetric. Many results are obtained in closed form for the Poisson process case, and these agree with those given previously by Kehr and Kunter. (author)

307

Time-dependent excitation and ionization modelling of absorption-line variability due to GRB080310  

DEFF Research Database (Denmark)

We model the time-variable absorption of Feii, Feiii, Siii, Cii and Crii detected in Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of gamma-ray burst (GRB) 080310, with the afterglow radiation exciting and ionizing the interstellar medium in the host galaxy at a redshift of z = 2.42743. To estimate the rest-frame afterglow brightness as a function of time, we use a combination of the optical VRI photometry obtained by the RAPTOR-T telescope array, which is presented in this paper, and Swift's X-Ray Telescope (XRT) observations. Excitation alone, which has been successfully applied for a handful of other GRBs, fails to describe the observed column density evolution in the case of GRB080310. Inclusion of ionization is required to explain the column density decrease of all observed Feii levels (including the ground state D) and increase of the Feiii S level. The large population of ions in this latter level (up to 10% of all Feiii) can only be explained through ionization of Feii, as a large fraction of the ionized Feii ions (we calculate 31% using the Flexible Atomic and Cowan codes) initially populate the S level of Feiii rather than the ground state. This channel for producing a significant Feiii S level population may be relevant for other objects in which absorption lines from this level, the UV34 triplet, are observed, such as broad absorption line (BAL) quasars and ¿ Carinae. This provides conclusive evidence for time-variable ionization in the circumburst medium, which to date has not been convincingly detected. However, the best-fit distance of the neutral absorbing cloud to the GRB is 200-400 pc, i.e. similar to GRB-absorber distance estimates for GRBs without any evidence for ionization. We find that the presence of time-varying ionization in GRB080310 is likely due to a combination of the super-solar iron abundance ([Fe/H] = +0.2) and the low Hi column density (log N(Hi) = 18.7) in the host of GRB080310. Finally, the modelling provides indications for the presence of an additional cloud at 10 50 pc from the GRB with log N(Hi) ~ 19 20 before the burst, which became fully ionized by the radiation released during the first few tens of minutes after the GRB. © 2012 ESO.

Vreeswijk, P.M.; De Cia, A.

2013-01-01

308

Bucket-by-bucket on-axis/off-axis injection by fast kicker with variable position dependence of kick  

International Nuclear Information System (INIS)

The bucket-by-bucket on-axis/off-axis injection system is proposed with new stripline fast kicker with variable position dependence of kick, from dipole to quadrupole, controlled by the drive voltage and its polarity. Applying the injection system to on-axis injection necessary for ultimate storage rings with narrow dynamic aperture, every bucket can be stored to achieve high average current with top-up operation. Also the minimum perturbation for stored beam can be achieved with the system by limiting the perturbations to injected bucket. Also the impurity electrons are prevented from injection with this system. (author)

309

Studies of Hot Photoluminescence in Plasmonically Coupled Silicon via Variable Energy Excitation and Temperature-Dependent Spectroscopy.  

Science.gov (United States)

By integrating silicon nanowires (?150 nm diameter, 20 ?m length) with an ?-shaped plasmonic nanocavity, we are able to generate broadband visible luminescence, which is induced by high order hybrid nanocavity-surface plasmon modes. The nature of this super bandgap emission is explored via photoluminescence spectroscopy studies performed with variable laser excitation energies (1.959 to 2.708 eV) and finite difference time domain simulations. Furthermore, temperature-dependent photoluminescence spectroscopy shows that the observed emission corresponds to radiative recombination of unthermalized (hot) carriers as opposed to a resonant Raman process. PMID:25120156

Aspetti, Carlos O; Cho, Chang-Hee; Agarwal, Rahul; Agarwal, Ritesh

2014-09-10

310

Spreading under variable viscosity and time-dependent boundary conditions: estimate of viscosity from spreading experiments  

International Nuclear Information System (INIS)

One of the cooling concepts of the high-temperature corium melt which may form in a core meltdown accident relies on sufficiently homogeneous spreading. The conditions under which complete spreading can be expected are the objects of current theoretical and experimental studies. The lubrication approximation for low Reynolds number flows leads to an equation for which self-similar solutions for various conditions have been found by many authors. This paper offers self-similar solutions for the spreading of a volume of liquid which increases as a power law of time. The effect of cooling on the viscosity is represented by the time-dependent viscosity. A variety of spreading experiments have been performed within many international programs. The initial conditions and boundary conditions used are more complex than those for which self-similar solutions are known explicitly. Based on the asymptotic behavior, as t??, of solutions of the Cauchy problem for a quite general class of initial data, approximate solutions are given describing the spreading of finite volume with a time dependent flux release, and some of the high-temperature experiments are analyzed. The effect of bubbles on rheology in spreading experiments with water and shear-thinning fluids is investigated

311

Time-dependent excitation and ionization modelling of absorption-line variability due to GRB 080310  

CERN Document Server

We model the time-variable absorption of FeII, FeIII, SiII, CII and CrII detected in UVES spectra of GRB 080310, with the afterglow radiation exciting and ionizing the interstellar medium in the host galaxy at a redshift of z=2.42743. To estimate the rest-frame afterglow brightness as a function of time, we use a combination of the optical VRI photometry obtained by the RAPTOR-T telescope array -- which are presented in this paper -- and Swift's X-Ray Telescope observations. Excitation alone, which has been successfully applied for a handful of other GRBs, fails to describe the observed column-density evolution in the case of GRB 080310. Inclusion of ionization is required to explain the column-density decrease of all observed FeII levels (including the ground state 6D9/2) and increase of the FeIII 7S3 level. The large population of ions in this latter level (up to 10% of all FeIII) can only be explained through ionization of FeII, whereby a large fraction of the ionized FeII ions -- we calculate 31% using th...

Vreeswijk, P M; Raassen, A J J; Smette, A; De Cia, A; Wo?niak, P R; Fox, A J; Vestrand, W T; Jakobsson, P

2012-01-01

312

A Comparison of the Prognostic Value of Early PSA Test-Based Variables Following External Beam Radiotherapy, With or Without Preceding Androgen Deprivation: Analysis of Data From the TROG 96.01 Randomized Trial  

International Nuclear Information System (INIS)

e postradiation nPSA value is the strongest prognostic indicator of all early PSA-based variables. However, its use as a surrogate endpoint needs to take into account its dependence on pretreatment variables and treatment method.

313

ALDH5A1 variability in opioid dependent patients could influence response to methadone treatment.  

Science.gov (United States)

Methadone maintenance treatment is the most widely-used therapy in opioid dependence, but some patients relapse or drop out from treatment. We genotyped a genetic variant in the succinic semialdehyde dehydrogenase enzyme gene, ALDH5A1, and found that subjects carrying the T variant allele have a higher risk to be nonresponders to methadone treatment (OR=3.16; 95% CI [1.48-6.73], P=0.0024). This could be due to a reduction in the ALDH5A1 enzyme activity, that would increase endogenous gamma-hydroxbutyric acid (GHB) and gamma-aminobutyric acid (GABA) levels and therefore, inducing symptoms such as sedation and impaired pschomotor performance. These neuropsychological effects related with the reduction in enzyme activity could be responsible for a higher propensity to relapse in these genetically predisposed patients. PMID:24230997

Fonseca, Francina; Gratacòs, Mònica; Escaramís, Geòrgia; De Cid, Rafael; Martín-Santos, Rocío; Farré, Magi; Estivill, Xavier; Torrens, Marta

2014-03-01

314

ENERGY-DEPENDENT POWER SPECTRAL STATES AND ORIGIN OF APERIODIC VARIABILITY IN BLACK HOLE BINARIES  

Energy Technology Data Exchange (ETDEWEB)

We found that the black hole candidate MAXI J1659-152 showed distinct power spectra, i.e., power-law noise (PLN) versus band-limited noise (BLN) plus quasi-periodic oscillations (QPOs) below and above about 2 keV, respectively, in observations with Swift and the Rossi X-ray Timing Explorer during the 2010 outburst, indicating a high energy cutoff of the PLN and a low energy cutoff of the BLN and QPOs around 2 keV. The emergence of the PLN and the fading of the BLN and QPOs initially took place below 2 keV when the source entered the hard intermediate state and settled in the soft state three weeks later. The evolution was accompanied by the emergence of the disk spectral component and decreases in the amplitudes of variability in the soft and hard X-ray bands. Our results indicate that the PLN is associated with an optically thick disk in both hard and intermediate states, and the power spectral state is independent of the X-ray energy spectral state in a broadband view. We suggest that in the hard or intermediate state, the BLN and QPOs emerge from the innermost hot flow subjected to Comptonization, while the PLN originates from the optically thick disk farther out. The energy cutoffs of the PLN and the BLN or QPOs then follow the temperature of the seed photons from the inner edge of the optically thick disk, while the high frequency cutoff of the PLN follows the orbital frequency of the inner edge of the optically thick disk as well.

Yu Wenfei; Zhang Wenda, E-mail: wenfei@shao.ac.cn [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China)

2013-06-20

315

Population Synthesis Studies of Close Binary Systems Using a Variable Common Envelope Efficiency Parameter: I. Dependence upon Secondary Mass  

CERN Document Server

We perform population synthesis calculations of present-day post common envelope binaries (PCEBs) and zero-age cataclysmic variables (ZACVs) using a common envelope efficiency parameter, alphaCE, that is a function of secondary mass, Ms. We investigate three basic possibilities: (1) a standard constant alphaCE prescription, with alphaCE = 1.0, 0.6, 0.3, 0.2, 0.1 and 0.05, to provide a baseline for comparison, (2) a power law dependence, alphaCE = (Ms)^n, with n = 0.5, 1.0 and 2.0, and (3) a dependence in which ?CE approaches 1 for large secondary masses and alphaCE = 0 below some assumed cutoff mass, alphaCE = 1?Mcut/Ms, where Mcut is the cutoff mass and is equal to 0.0375, 0.075 and 0.15 solar mass. For each population, we compute orbital period, orbital separation, white dwarf mass and secondary mass distributions. We find that if alphaCE < 0.2 in our constant ?CE sequence, the predicted present-day ZACV population is significantly modified compared with our standard model (alphaCE = 1.0). In our variabl...

Politano, M; Politano, Michael; Weiler, Kevin P.

2007-01-01

316

Time dependent simulations of multiwavelength variability of the blazar Mrk 421 with a Monte Carlo multi-zone code  

CERN Document Server

(abridged) We present a new time-dependent multi-zone radiative transfer code and its application to study the SSC emission of Mrk 421. The code couples Fokker-Planck and Monte Carlo methods, in a 2D geometry. For the first time all the light travel time effects (LCTE) are fully considered, along with a proper treatment of Compton cooling, which depends on them. We study a set of simple scenarios where the variability is produced by injection of relativistic electrons as a `shock front' crosses the emission region. We consider emission from two components, with the second one either being pre-existing and co-spatial and participating in the evolution of the active region, or spatially separated and independent, only diluting the observed variability. Temporal and spectral results of the simulation are compared to the multiwavelength observations of Mrk 421 in March 2001. We find parameters that can adequately fit the observed SEDs and multiwavelength light curves and correlations. There remain however a few o...

Chen, Xuhui; Liang, Edison; Boettcher, Markus

2011-01-01

317

Do drug treatment variables predict cognitive performance in multidrug-treated opioid-dependent patients? A regression analysis study  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Cognitive deficits and multiple psychoactive drug regimens are both common in patients treated for opioid-dependence. Therefore, we examined whether the cognitive performance of patients in opioid-substitution treatment (OST is associated with their drug treatment variables. Methods Opioid-dependent patients (N = 104 who were treated either with buprenorphine or methadone (n = 52 in both groups were given attention, working memory, verbal, and visual memory tests after they had been a minimum of six months in treatment. Group-wise results were analysed by analysis of variance. Predictors of cognitive performance were examined by hierarchical regression analysis. Results Buprenorphine-treated patients performed statistically significantly better in a simple reaction time test than methadone-treated ones. No other significant differences between groups in cognitive performance were found. In each OST drug group, approximately 10% of the attention performance could be predicted by drug treatment variables. Use of benzodiazepine medication predicted about 10% of performance variance in working memory. Treatment with more than one other psychoactive drug (than opioid or BZD and frequent substance abuse during the past month predicted about 20% of verbal memory performance. Conclusions Although this study does not prove a causal relationship between multiple prescription drug use and poor cognitive functioning, the results are relevant for psychosocial recovery, vocational rehabilitation, and psychological treatment of OST patients. Especially for patients with BZD treatment, other treatment options should be actively sought.

Rapeli Pekka

2012-11-01

318

A prospective randomized study comparing perioperative outcome variables after epidural or general anesthesia for lumbar disc surgery.  

Science.gov (United States)

General and regional anesthesia (spinal and epidural) can be performed successfully for lumbar disc surgery. The aim of this study was to assess the superiority of general anesthesia or epidural anesthesia techniques in lumbar laminectomy and discectomy. Sixty patients undergoing lumbar partial hemilaminectomy and discectomy were randomly divided into two groups receiving standardized general anesthesia (GA) or epidural anesthesia (EA). Demographically, both groups were similar. Surgical onset time (36.72 +/- 5.47 vs. 25.40 +/- 7.83 minutes) was longer in the EA group, but total anesthesia time (154.32 +/- 35.73 vs. 162.40 +/- 26.79 minutes) did not differ between the two groups. Surgical time (118.80 +/- 35.42 vs. 139.60 +/- 26.80 minutes) was longer in the GA group. The heart rate and mean arterial pressure values of the EA group measured 15, 20, and 25 minutes after local anesthetic administration to the epidural catheter were found to be lower than in the GA group measured after induction of general anesthesia. The frequency of bradycardia (EA vs. GA, 3 vs. 2), tachycardia (3 vs. 7), and hypotension (6 vs. 4) during anesthesia did not differ between the groups, but the occurrence of hypertension (1 vs. 7) was higher in the GA group. Blood loss was less in the EA group than in the GA group (180.40 +/- 70.38 vs. 288.60 +/- 112.51 mL). Postanesthesia care unit (PACU) heart rate and mean arterial pressure were higher in the GA group. Peak pain scores in PACU and postoperative 24 hours were higher in the GA group when compared with the EA group. Nausea was more common in the GA group both in PACU and 24 hours after surgery. There was no difference between the hospitalization duration of the groups. In conclusion, this study suggests that EA is an important alternative to GA during lumbar disc surgery. PMID:12826965

Demirel, Cengiz Bekir; Kalayci, Murat; Ozkocak, Isil; Altunkaya, Hanife; Ozer, Yetkin; Acikgoz, Bektas

2003-07-01

319

Dose-Dependent Effects of the Cimicifuga racemosa Extract Ze 450 in the Treatment of Climacteric Complaints: A Randomized, Placebo-Controlled Study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Extracts from Cimicifuga racemosa (CR, synonym Actaea racemosa) have shown efficacy in trials in women with menopausal symptoms. Yet, dose dependency remains unclear. Therefore, 180 female outpatients with climacteric complaints were treated for 12 weeks in a randomized, double-blind, placebo-controlled, 3-armed trial (CR extract Ze 450 in 6.5?mg or 13.0?mg, or placebo). Primary outcome was the difference in menopausal symptoms (vasomotor, psychological, and somatic), assessed by the Kupp...

Ruediger Schellenberg; Reinhard Saller; Lorenzo Hess; Amp Xf Rg Melzer, J.; Christian Zimmermann; Juergen Drewe; Catherine Zahner

2012-01-01

320

Nightside electron precipitation at Mars: Geographic variability and dependence on solar wind conditions  

Science.gov (United States)

Electron precipitation is usually the dominant source of energy input to the nightside Martian atmosphere, with consequences for ionospheric densities, chemistry, electrodynamics, communications, and navigation. We examine downward-traveling superthermal electron flux on the Martian nightside from May 1999 to November 2006 at 400 km altitude and 2 A.M. local time. Electron precipitation is geographically organized by crustal magnetic field strength and elevation angle, with higher fluxes occurring in regions of weak and/or primarily vertical crustal fields, while stronger and more horizontal fields retard electron access to the atmosphere. We investigate how these crustal field-organized precipitation patterns vary with proxies for solar wind (SW) pressure and interplanetary magnetic field (IMF) direction. Generally, higher precipitating fluxes accompany higher SW pressures. Specifically, we identify four characteristic spectral behaviors: (1) "stable" regions where fluxes increase mildly with SW pressure, (2) "high-flux" regions where accelerated (peaked) spectra are more common and where fluxes below ~500 eV are largely independent of SW pressure, (3) permanent plasma voids, and (4) intermittent plasma voids where fluxes depend strongly on SW pressure. The locations, sizes, shapes, and absence/existence of these plasma voids vary significantly with solar wind pressure proxy and moderately with IMF proxy direction; average precipitating fluxes are 40% lower in strong crustal field regions and 15% lower globally for approximately southwest proxy directions compared with approximately northeast directions. This variation of the strength and geographic pattern of the shielding effect of Mars' crustal fields exemplifies the complex interaction between those fields and the solar wind.

Lillis, Robert J.; Brain, David A.

2013-06-01

 
 
 
 
321

Is there an absolutely continuous random variable with equal probability density and cumulative distribution functions in its support? Is it unique? What about in the discrete case?  

Directory of Open Access Journals (Sweden)

Full Text Available This paper inquires about the existence and uniqueness of a univariate continuous random variable for which both cumulative distribution and density functions are equal and asks about the conditions under which a possible extrapolation of the solution to the discrete case is possible. The issue is presented and solved as a problem and allows to obtain a new family of probability distributions. The different approaches followed to reach the solution could also serve to warn about some properties of density and cumulative functions that usually go unnoticed, helping to deepen the understanding of some of the weapons of the mathematical statistician’s arsenal. Keywords: Cumulative Distribution Function; Density Function; Elasticity; Mathematical Statistics; Reversed Hazard Rate.

Ernesto Veres-Ferrer

2014-06-01

322

Random frog: an efficient reversible jump Markov Chain Monte Carlo-like approach for variable selection with applications to gene selection and disease classification.  

Science.gov (United States)

The identification of disease-relevant genes represents a challenge in microarray-based disease diagnosis where the sample size is often limited. Among established methods, reversible jump Markov Chain Monte Carlo (RJMCMC) methods have proven to be quite promising for variable selection. However, the design and application of an RJMCMC algorithm requires, for example, special criteria for prior distributions. Also, the simulation from joint posterior distributions of models is computationally extensive, and may even be mathematically intractable. These disadvantages may limit the applications of RJMCMC algorithms. Therefore, the development of algorithms that possess the advantages of RJMCMC methods and are also efficient and easy to follow for selecting disease-associated genes is required. Here we report a RJMCMC-like method, called random frog that possesses the advantages of RJMCMC methods and is much easier to implement. Using the colon and the estrogen gene expression datasets, we show that random frog is effective in identifying discriminating genes. The top 2 ranked genes for colon and estrogen are Z50753, U00968, and Y10871_at, Z22536_at, respectively. (The source codes with GNU General Public License Version 2.0 are freely available to non-commercial users at: http://code.google.com/p/randomfrog/.). PMID:22840646

Li, Hong-Dong; Xu, Qing-Song; Liang, Yi-Zeng

2012-08-31

323

Hybrid model of light propagation in random media based on the time-dependent radiative transfer and diffusion equations  

Science.gov (United States)

Numerical modeling of light propagation in random media has been an important issue for biomedical imaging, including diffuse optical tomography (DOT). For high resolution DOT, accurate and fast computation of light propagation in biological tissue is desirable. This paper proposes a space-time hybrid model for numerical modeling based on the radiative transfer and diffusion equations (RTE and DE, respectively) in random media under refractive-index mismatching. In the proposed model, the RTE and DE regions are separated into space and time by using a crossover length and the time from the ballistic regime to the diffusive regime, ?DA~10/?t? and tDA~20/v?t? where ?t? and v represent a reduced transport coefficient and light velocity, respectively. The present model succeeds in describing light propagation accurately and reduces computational load by a quarter compared with full computation of the RTE.

Fujii, Hiroyuki; Okawa, Shinpei; Yamada, Yukio; Hoshi, Yoko

2014-11-01

324

Variability Measures of Positive Random Variables  

Digital Repository Infrastructure Vision for European Research (DRIVER)

During the stationary part of neuronal spiking response, the stimulus can be encoded in the firing rate, but also in the statistical structure of the interspike intervals. We propose and discuss two information-based measures of statistical dispersion of the interspike interval distribution, the entropy-based dispersion and Fisher information-based dispersion. The measures are compared with the frequently used concept of standard deviation. It is shown, that standard deviation is not well sui...

Kostal, Lubomir; Lansky, Petr; Pokora, Ondrej

2011-01-01

325

Random series of functions and applications  

CERN Document Server

We study the continuity properties of trajectories for some random series of functions $\\sum a\\_kf(\\alpha X\\_k(\\omega))$ where $a\\_k$ is a complex sequence, $X\\_k$ a sequence of real independent random variables, $f$ is a real valued function with period one and summable Fourier coefficients. We obtain almost sure continuity results for these periodic or almost periodic series for a large class of functions, where the "almost sure" does not depend on the function.

Paccaut, F; Paccaut, Fr\\'{e}d\\'{e}ric; Schneider, Dominique

2006-01-01

326

Influence of Some Formulation Variables on the Optimization of pH-dependent, Colon-targeted, Sustained-release Mesalamine Microspheres  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The aim of this work was to understand the influence of different formulation variables on the optimization of pH-dependent, colon-targeted, sustained-release mesalamine microspheres prepared by O/O emulsion solvent evaporation method, employing pH-dependent Eudragit S and hydrophobic pH-independent ethylcellulose polymers. Formulation variables studied included concentration of Eudragit S in the internal phase and the ratios between; internal to external phase, drug to Eudragit S and Eudragi...

El-bary, Ahmed Abd; Aboelwafa, Ahmed A.; Al Sharabi, Ibrahim M.

2012-01-01

327

Gender-dependent effects of metformin on vaspin and adiponectin in type 2 diabetes patients: a randomized clinical trial.  

Science.gov (United States)

The aim of the study was to assess the effects of metformin on serum concentrations of vaspin and adiponectin in diabetes. Randomized clinical trial of 99 newly diagnosed, medication-naïve, type 2 diabetes patients (NCT01521624) was carried out. Patients were randomly assigned to either metformin 1 000 mg daily plus advice for exercise and lifestyle modification (n=50) or modification alone (n=49). A third group of 50 normoglycemic subjects were also enrolled to compare adipokine concentrations between healthy and diabetes subjects. Serum concentrations of adipokines were measured at baseline and after 12 weeks using ELISA method. Healthy subjects had significantly higher adiponectin levels, but lower concentrations of serum vaspin (plifestyle modification in the final multivariate model after controlling for potential confounders only in women (p=0.002) but not men (p=0.896). Conversely, adiponectin levels increased more significantly in the control group, again only in women (p=0.012 and 0.579 for women and men, respectively). Our findings suggest that metformin therapy reduces vaspin concentration in a gender-specific manner. Metformin exerts little benefit in increasing adiponectin levels in diabetes patients. PMID:23225237

Esteghamati, A; Mousavizadeh, M; Noshad, S; Zandieh, A; Zarei, H; Nakhjavani, M

2013-04-01

328

How the Landscape of Random Job Shop Scheduling Instances Depends on the Ratio of Jobs to Machines  

CERN Document Server

We characterize the search landscape of random instances of the job shop scheduling problem (JSP). Specifically, we investigate how the expected values of (1) backbone size, (2) distance between near-optimal schedules, and (3) makespan of random schedules vary as a function of the job to machine ratio (N/M). For the limiting cases N/M approaches 0 and N/M approaches infinity we provide analytical results, while for intermediate values of N/M we perform experiments. We prove that as N/M approaches 0, backbone size approaches 100%, while as N/M approaches infinity the backbone vanishes. In the process we show that as N/M approaches 0 (resp. N/M approaches infinity), simple priority rules almost surely generate an optimal schedule, providing theoretical evidence of an "easy-hard-easy" pattern of typical-case instance difficulty in job shop scheduling. We also draw connections between our theoretical results and the "big valley" picture of JSP landscapes.

Smith, S F; 10.1613/jair.2013

2011-01-01

329

Large strain rate-dependent response of elastomers at different strain rates: convolution integral vs. internal variable formulations  

Science.gov (United States)

Two different viscoelastic frameworks adapted to large strain rate-dependent response of elastomers are compared; for each approach, a simple model is derived. Within the Finite Linear Viscoelasticity theory, a time convolution integral model based on an extension to solid of the K-BKZ model is proposed. Considering the multiplicative split of the deformation gradient into elastic and inelastic parts, an internal variable model based on a large strain version of the Standard Linear Solid model is considered. In both cases, the strain energy functions involved are chosen neo-Hookean, and then each model possesses three material parameters: two stiffnesses and a viscosity parameter. These parameters are set to ensure the equivalence of the model responses for uniaxial large strain quasi-static and infinitely fast loading conditions, and for uniaxial rate-dependent small strain loading conditions. Considering their responses for different Eulerian strain rates, their differences are investigated with respect to the strain rate; more specifically, both stiffness and dissipative properties are studied. The comparison reveals that these two models differ significantly for intermediate strain rates, and a closing discussion highlights some issues about their foundations and numerical considerations.

Petiteau, J.-C.; Verron, E.; Othman, R.; Le Sourne, H.; Sigrist, J.-F.; Barras, G.

2013-08-01

330

The supply voltage scaled dependency of the recovery of single event upset in advanced complementary metal—oxide—semiconductor static random-access memory cells  

Science.gov (United States)

Using computer-aided design three-dimensional simulation technology, the supply voltage scaled dependency of the recovery of single event upset and charge collection in static random-access memory cells are investigated. It reveals that the recovery linear energy transfer threshold decreases with the supply voltage reducing, which is quite attractive for dynamic voltage scaling and subthreshold circuit radiation-hardened design. Additionally, the effect of supply voltage on charge collection is also investigated. It is concluded that the supply voltage mainly affects the bipolar gain of the parasitical bipolar junction transistor (BJT) and the existence of the source plays an important role in supply voltage variation.

Li, Da-Wei; Qin, Jun-Rui; Chen, Shu-Ming

2013-02-01

331

Towards Swarm Diversity: Random Sampling in Variable Neighborhoods Procedure Using a Lévy Distribution / Hacia la diversidad de la bandada: procedimiento RSVN usando una distribución de Lévy  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Particle Swarm Optimization (PSO) es un método de búsqueda no directo para la optimización numérica. Las principales ventajas de esta meta-heurística están relacionadas principalmente con su simplicidad, pocos parámetros y alta tasa de convergencia. En el PSO canónico usando una topología totalmente [...] conectada, una partícula ajusta su posición usando dos atractores: el mejor registro almacenado por el individuo y el mejor punto descubierto por la bandada completa. Este esquema conduce a un alto factor de convergencia, pero también deteriora la diversidad de la población progresivamente. Como resultado la bandada de partículas frecuentemente es atraída por puntos sub-óptimos. Una vez que las partículas han sido atraídas hacia un óptimo local, ellas continúan el proceso de búsqueda dentro de una región muy pequeña del espacio de soluciones, reduciendo las capacidades de exploración del algoritmo. Para tratar esta situación este artículo presenta una variante del procedimiento Random Sampling in Variable Neighborhoods (RSVN) usando una distribución de Lévy. Este algoritmo es capaz de mejorar notablemente la capacidad de búsqueda de los algoritmos PSO en problemas multimodales de optimización. Abstract in english Particle Swarm Optimization (PSO) is a non-direct search method for numerical optimization. The key advantages of this metaheuristic are principally associated to its simplicity, few parameters and high convergence rate. In the canonical PSO using a fully connected topology, a particle adjusts its p [...] osition by using two attractors: the best record stored for the current agent, and the best point discovered for the entire swarm. It leads to a high convergence rate, but also progressively deteriorates the swarm diversity. As a result, the particle swarm frequently gets attracted by sub-optimal points. Once the particles have been attracted to a local optimum, they continue the search process within a small region of the solution space, thus reducing the algorithm exploration. To deal with this issue, this paper presents a variant of the Random Sampling in Variable Neighborhoods (RSVN) procedure using a Lévy distribution, which is able to notably improve the PSO search ability in multimodal problems.

Gonzalo, Nápoles; Isel, Grau; Marilyn, Bello; Rafael, Bello.

2014-03-01

332

Effects of additional repeated sprint training during preseason on performance, heart rate variability, and stress symptoms in futsal players: a randomized controlled trial.  

Science.gov (United States)

Soares-Caldeira, LF, de Souza, EA, de Freitas, VH, de Moraes, SMF, Leicht, AS, and Nakamura, FY. Effects of additional repeated sprint training during preseason on performance, heart rate variability, and stress symptoms in futsal players: A randomized controlled trial. J Strength Cond Res 28(10): 2815-2826, 2014-The aim of this study was to investigate whether supplementing regular preseason futsal training with weekly sessions of repeated sprints (RS) training would have positive effects on repeated sprint ability (RSA) and field test performance. Thirteen players from a professional futsal team (22.6 ± 6.7 years, 72.8 ± 8.7 kg, 173.2 ± 6.2 cm) were divided randomly into 2 groups (AddT: n = 6 and normal training group: n = 7). Both groups performed a RSA test, Yo-Yo intermittent recovery test level 1 (YoYo IR1), squat (SJ) and countermovement jumps (CMJ), body composition, and heart rate variability (HRV) measures at rest before and after 4 weeks of preseason training. Athletes weekly stress symptoms were recorded by psychometric responses using the Daily Analysis of Life Demands for Athletes questionnaire and subjective ratings of well-being scale, respectively. The daily training load (arbitrary units) was assessed using the session of rating perceived exertion method. After the preseason training, there were no significant changes for body composition, SJ, CMJ, and RSAbest. The YoYo IR1, RSAmean, RSAworst, and RSAdecreament were significantly improved for both groups (p ? 0.05). The HRV parameters improved significantly within both groups (p ? 0.05) except for high frequency (HF, absolute and normalized units, [n.u.]), low frequency (LF) (n.u.), and the LF/HF ratio. A moderate effect size for the AddT group was observed for resting heart rate and several HRV measures. Training load and psychometric responses were similar between both groups. Additional RS training resulted in slightly greater positive changes for vagal-related HRV with similar improvements in performance and training stress during the preseason training in futsal players. PMID:24662230

Soares-Caldeira, Lúcio F; de Souza, Eberton A; de Freitas, Victor H; de Moraes, Solange M F; Leicht, Anthony S; Nakamura, Fábio Y

2014-10-01

333

Effect of variability in the 7-day baseline pain diary on the assay sensitivity of neuropathic pain randomized clinical trials: an ACTTION study.  

Science.gov (United States)

The degree of variability in the patient baseline 7-day diary of pain ratings has been hypothesized to have a potential effect on the assay sensitivity of randomized clinical trials of pain therapies. To address this issue, we obtained clinical trial data from the Food and Drug Administration (FDA) through the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership, and harmonized patient level data from 12 clinical trials (4 gabapentin and 8 pregabalin) in postherpetic neuralgia (PHN) and painful diabetic peripheral neuropathy (DPN). Models were developed using exploratory logistic regression to examine the interaction between available baseline factors and treatment (placebo vs active medication) in predicting patient response to therapy (ie, >30% improvement). Our analysis demonstrated an increased likelihood of response in the placebo-treated group for patients with a higher standard deviation in the baseline 7-day diary without affecting the likelihood of a response in the active medication-treated group, confirming our hypothesis. In addition, there was a small but significant age-by-treatment interaction in the PHN model, and small weight-by-treatment interaction in the DPN model. The patient's sex, baseline pain level, and the study protocol had an effect only on the likelihood of response overall. Our results suggest the possibility that, at least in some disease processes, excluding patients with a highly variable baseline 7-day diary has the potential to improve the assay sensitivity of these analgesic clinical trials, although reductions of external validity must be considered when increasing the homogeneity of the investigated sample. PMID:24831421

Farrar, John T; Troxel, Andrea B; Haynes, Kevin; Gilron, Ian; Kerns, Robert D; Katz, Nathaniel P; Rappaport, Bob A; Rowbotham, Michael C; Tierney, Ann M; Turk, Dennis C; Dworkin, Robert H

2014-08-01

334

Analysis of the genetic variability and structure of Ochlerotatus taeniorhynchus (Diptera: Culicidae) populations from the Colombian Atlantic coast on the basis of random amplified polymorphic DNA markers.  

Science.gov (United States)

Ochlerotatus taeniorhynchus (Diptera: Culicidae) is a mosquito, which is an efficient vector of the virus causing epidemic-epizootic Venezuelan equine encephalitis in Colombia. This study used 9 random amplified polymorphic DNA (RAPD) markers to analyze the mosquito's genetic variability and genetic structure of 122 specimens in 7 populations from the Colombian Atlantic coast. Assuming that all loci were in Hardy-Weinberg equilibrium, diversity statistics and analyses were performed. The average number of amplified fragments for each primer was 8.3, and the size of these fragments ranged from 350 to 3600 bp. The expected average heterozygosity was 0.358 ± 0.103. The genetic heterogeneity among the populations studied was small (GST = 0.05 ± 0.01); meanwhile, the gene flow estimates (Nm = 7.32 ± 1.35) were high. In an identical way, the Nei's genetic distances obtained yielded very small values amongst the populations that were studied in this Colombian region. Furthermore, a spatial autocorrelation analysis with Moran's I index revealed a very weak, or inexistent, spatial genetic structure among these populations. The comparison of these results with those performed for other markers (isoenzymes and microsatellites) in populations of this same mosquito from the Colombian Atlantic coast was discussed. The results of our RAPD analysis showed scarce genetic differentiation among the mosquito populations on the Colombian Atlantic coast, which was probably determined by high gene flow levels. PMID:24938703

Bello, F J; Segura, N A; Ruiz-Garcia, M

2014-01-01

335

Investigation of time-dependent reactions of H+ ions with variable and constant charge soils: a comparative study  

International Nuclear Information System (INIS)

A sampling-separation method and a dynamic monitoring method were used to investigate the time-dependent reactions of H+ ions with two contrasting types of soil, variable charge soils (VCS) and constant charge soils (CCS), by directly evaluating H+ ion consumption and other relevant consequences. The results for both CCS and VCS show that H+ ion consumption, increase in positive surface charge and increase in soluble Al are all characterized by a rapid step followed by a slow one. The higher the content of free Fe oxides in the soil, the larger the increase in positive surface charge and in H+ ion consumption in the initial rapid step. This is due mainly to protonation on external surfaces. The gradual increase in positive surface charge in the slow step for the 3 VCSs is a result of H+ ion diffusion to the reactive sites of ?Fe-OH on internal surfaces. The very low content of free Fe oxides on internal surfaces of the 2 CCSs render a negligible increase in positive surface charge in the slow step. For the 3 VCSs, the gradual consumption of H+ ions in the slow process is the result of protonation, Al dissolution and/or transformation into exchangeable acidity. For the 2 CCSs, however, the gradual consumption is mainly the result of Al dissolution and/or transformation into exchangeable acidity. The time-dependent Al dissolution from both VCS and CCS is influenced by several factors such as mineral comd by several factors such as mineral components, solubility and dissolution rates of the soils, and H+ ion concentration in soil suspensions

336

Nonequilibrium phase transitions and stationary-state solutions of a three-dimensional random-field Ising model under a time-dependent periodic external field.  

Science.gov (United States)

Nonequilibrium behavior and dynamic phase-transition properties of a kinetic Ising model under the influence of periodically oscillating random fields have been analyzed within the framework of effective-field theory based on a decoupling approximation. A dynamic equation of motion has been solved for a simple-cubic lattice (q=6) by utilizing a Glauber-type stochastic process. Amplitude of the sinusoidally oscillating magnetic field is randomly distributed on the lattice sites according to bimodal and trimodal distribution functions. For a bimodal type of amplitude distribution, it is found in the high-frequency regime that the dynamic phase diagrams of the system in the temperature versus field amplitude plane resemble the corresponding phase diagrams of the pure kinetic Ising model. Our numerical results indicate that for a bimodal distribution, both in the low- and high-frequency regimes, the dynamic phase diagrams always exhibit a coexistence region in which the stationary state (ferro or para) of the system is completely dependent on the initial conditions, whereas for a trimodal distribution, the coexistence region disappears depending on the values of the system parameters. PMID:23004719

Yüksel, Yusuf; Vatansever, Erol; Ak?nc?, Umit; Polat, Hamza

2012-05-01

337

A numerical model for density-and-viscosity-dependent flows in two-dimensional variably saturated porous media  

Science.gov (United States)

We present a formulation for water flow and solute transport in two-dimensional variably saturated media that accounts for the effects of the solute on water density and viscosity. The governing equations are cast in a dimensionless form that depends on six dimensionless groups of parameters. These equations are discretized in space using the Galerkin finite element formulation and integrated in time using the backward Euler scheme with mass lumping. The modified Picard method is used to linearize the water flow equation. The resulting numerical model, the MARUN model, is verified by comparison to published numerical results. It is then used to investigate beach hydraulics at seawater concentration (about 30 g l -1) in the context of nutrients delivery for bioremediation of oil spills on beaches. Numerical simulations that we conducted in a rectangular section of a hypothetical beach revealed that buoyancy in the unsaturated zone is significant in soils that are fine textured, with low anisotropy ratio, and/or exhibiting low physical dispersion. In such situations, application of dissolved nutrients to a contaminated beach in a freshwater solution is superior to their application in a seawater solution. Concentration-engendered viscosity effects were negligible with respect to concentration-engendered density effects for the cases that we considered.

Boufadel, Michel C.; Suidan, Makram T.; Venosa, Albert D.

1999-04-01

338

Radiocaesium contamination of meadow vegetation--time-dependent variability and influence of soil characteristics at grassland sites in Austria  

International Nuclear Information System (INIS)

Long-term trends of 137Cs and 40K concentrations in meadow grass and soil-plant transfer data at eight different sites in Upper Austria are presented. Geometric means of 137Cs TF-data and Tagg values vary between 0.03-1.06 and 0.0005-0.0184 depending on site, respectively. 40K results are less variable with TF values covering a range of 0.31-2.01. Only at one site was a significant decrease of 137Cs concentration (decay-corrected) in meadow vegetation observed during the observation period 1992-1999. Seasonal trends of 40K and 137Cs were investigated at one site in 1996. Both elements show decreasing concentrations in plants from beginning of May-July, followed by a peak in September. Although this pattern was not very pronounced, there are some hints that it may explain deviations of long-term trends in 137Cs levels in grass caused by unusual weather conditions as indicated by phenological climate data (beginning of sweet cherry and black elder blossoming). Finally, TF values were correlated with soil characteristics, revealing a negative correlation of radiocaesium soil-plant transfer with soil pH, exchangeable and extractable fractions of Mg, Ca and Na as well as a positive correlation with exchangeable Al

339

Role of functional genetic variation in the dopamine D2 receptor (DRD2) in response to bupropion and nicotine replacement therapy for tobacco dependence: results of two randomized clinical trials.  

Science.gov (United States)

Although bupropion and nicotine replacement therapy (NRT) are efficacious tobacco dependence treatments, there is substantial interindividual variability in therapeutic response and most smokers relapse. Pharmacogenetics research may improve treatment outcomes by identifying genetic variants predictive of therapeutic response. We investigated the roles of two functional genetic variants in the dopamine D2 receptor (DRD2) gene in response to pharmacotherapy for tobacco dependence among participants in two randomized clinical trials with a 6-month follow-up period: a double-blind placebo-controlled trial of bupropion (n=414) and an open label trial of transdermal nicotine vs nicotine nasal spray (n=368). At the end of the treatment phase, a statistically significant (p=0.01) interaction between the DRD2 - 141C Ins/Del genotype and treatment indicated a more favorable response to bupropion among smokers homozygous for the Ins C allele compared to those carrying a Del C allele. By contrast, smokers carrying the Del C allele had statistically significantly (p=0.006) higher quit rates on NRT compared to those homozygous for the Ins C allele, independent of NRT type. The C957T variant was also associated (p=0.03) with abstinence following NRT. These results suggest that bupropion may be the preferred pharmacologic treatment for smokers homozygous for the DRD2 - 141 Ins C allele, while NRT may be more beneficial for those who carry the Del C allele. Study findings require confirmation in additional larger samples before they are applied in practice. PMID:16123753

Lerman, Caryn; Jepson, Christopher; Wileyto, E Paul; Epstein, Leonard H; Rukstalis, Margaret; Patterson, Freda; Kaufmann, Vyga; Restine, Stephanie; Hawk, Larry; Niaura, Ray; Berrettini, Wade

2006-01-01

340

A proof-of-concept randomized controlled study of gabapentin: effects on cannabis use, withdrawal and executive function deficits in cannabis-dependent adults.  

Science.gov (United States)

There are no FDA-approved pharmacotherapies for cannabis dependence. Cannabis is the most widely used illicit drug in the world, and patients seeking treatment for primary cannabis dependence represent 25% of all substance use admissions. We conducted a phase IIa proof-of-concept pilot study to examine the safety and efficacy of a calcium channel/GABA modulating drug, gabapentin, for the treatment of cannabis dependence. A 12-week, randomized, double-blind, placebo-controlled clinical trial was conducted in 50 unpaid treatment-seeking male and female outpatients, aged 18-65 years, diagnosed with current cannabis dependence. Subjects received either gabapentin (1200?mg/day) or matched placebo. Manual-guided, abstinence-oriented individual counseling was provided weekly to all participants. Cannabis use was measured by weekly urine toxicology and by self-report using the Timeline Followback Interview. Cannabis withdrawal symptoms were assessed using the Marijuana Withdrawal Checklist. Executive function was measured using subtests from the Delis-Kaplan Executive Function System. Relative to placebo, gabapentin significantly reduced cannabis use as measured both by urine toxicology (p=0.001) and by the Timeline Followback Interview (p=0.004), and significantly decreased withdrawal symptoms as measured by the Marijuana Withdrawal Checklist (ptests of executive function (p=0.029). This POC pilot study provides preliminary support for the safety and efficacy of gabapentin for treatment of cannabis dependence that merits further study, and provides an alternative conceptual framework for treatment of addiction aimed at restoring homeostasis in brain stress systems that are dysregulated in drug dependence and withdrawal. PMID:22373942

Mason, Barbara J; Crean, Rebecca; Goodell, Vivian; Light, John M; Quello, Susan; Shadan, Farhad; Buffkins, Kimberly; Kyle, Mark; Adusumalli, Murali; Begovic, Adnan; Rao, Santosh

2012-06-01

 
 
 
 
341

An efficient algorithm to generate large random uncorrelated Euclidean distances: the random link model  

CERN Document Server

A disordered medium is often constructed by $N$ points independently and identically distributed in a $d$-dimensional hyperspace. Characteristics related to the statistics of this system is known as the random point problem. As $d \\to \\infty$, the distances between two points become independent random variables, leading to its mean field description: the random link model. While the numerical treatment of large random point problems pose no major difficulty, the same is not true for large random link systems due to Euclidean restrictions. Exploring the deterministic nature of the congruential pseudo-random number generators, we present techniques which allow the consideration of models with memory consumption of order O(N), instead of $O(N^2)$ in a naive implementation but with the same time dependence $O(N^2)$.

Tercariol, C A S; Tercariol, Cesar Augusto Sangaletti; Martinez, Alexandre Souto

2005-01-01

342

Harris-Luck criterion for random lattices  

Science.gov (United States)

The Harris-Luck criterion judges the relevance of (potentially) spatially correlated, quenched disorder induced by, e.g., random bonds, randomly diluted sites, or a quasiperiodicity of the lattice, for altering the critical behavior of a coupled matter system. We investigate the applicability of this type of criterion to the case of spin variables coupled to random lattices. Their aptitude to alter critical behavior depends on the degree of spatial correlations present, which is quantified by a wandering exponent. We consider the cases of Poissonian random graphs resulting from the Voronoï-Delaunay construction and of planar, “fat” ?3 Feynman diagrams and precisely determine their wandering exponents. The resulting predictions are compared to various exact and numerical results for the Potts model coupled to these quenched ensembles of random graphs.

Janke, Wolfhard; Weigel, Martin

2004-04-01

343

Sequential Cross-Validated Bandwidth Selection Under Dependence and Anscombe-Type Extensions to Random Time Horizons  

CERN Document Server

To detect changes in the mean of a time series, one may use previsible detection procedures based on nonparametric kernel prediction smoothers which cover various classic detection statistics as special cases. Bandwidth selection, particularly in a data-adaptive way, is a serious issue and not well studied for detection problems. To ensure data adaptation, we select the bandwidth by cross-validation, but in a sequential way leading to a functional estimation approach. This article provides the asymptotic theory for the method under fairly weak assumptions on the dependence structure of the error terms, which cover, e.g., GARCH($p,q$) processes, by establishing (sequential) functional central limit theorems for the cross-validation objective function and the associated bandwidth selector. It turns out that the proof can be based in a neat way on \\cite{KurtzProtter1996}'s results on the weak convergence of \\ito integrals and a diagonal argument. Our gradual change-point model covers multiple change-points in th...

Steland, Ansgar

2012-01-01

344

Chronic kidney disease in the type 2 diabetic patients: prevalence and associated variables in a random sample of 2642 patients of a Mediterranean area  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Kidney disease is associated with an increased total mortality and cardiovascular morbimortality in the general population and in patients with Type 2 diabetes. The aim of this study is to determine the prevalence of kidney disease and different types of renal disease in patients with type 2 diabetes (T2DM. Methods Cross-sectional study in a random sample of 2,642 T2DM patients cared for in primary care during 2007. Studied variables: demographic and clinical characteristics, pharmacological treatments and T2DM complications (diabetic foot, retinopathy, coronary heart disease and stroke. Variables of renal function were defined as follows: 1 Microalbuminuria: albumin excretion rate & 30 mg/g or 3.5 mg/mmol, 2 Macroalbuminuria: albumin excretion rate & 300 mg/g or 35 mg/mmol, 3 Kidney disease (KD: glomerular filtration rate according to Modification of Diet in Renal Disease 2 and/or the presence of albuminuria, 4 Renal impairment (RI: glomerular filtration rate 2, 5 Nonalbuminuric RI: glomerular filtration rate 2 without albuminuria and, 5 Diabetic nephropathy (DN: macroalbuminuria or microalbuminuria plus diabetic retinopathy. Results The prevalence of different types of renal disease in patients was: 34.1% KD, 22.9% RI, 19.5% albuminuria and 16.4% diabetic nephropathy (DN. The prevalence of albuminuria without RI (13.5% and nonalbuminuric RI (14.7% was similar. After adjusting per age, BMI, cholesterol, blood pressure and macrovascular disease, RI was significantly associated with the female gender (OR 2.20; CI 95% 1.86–2.59, microvascular disease (OR 2.14; CI 95% 1.8–2.54 and insulin treatment (OR 1.82; CI 95% 1.39–2.38, and inversely associated with HbA1c (OR 0.85 for every 1% increase; CI 95% 0.80–0.91. Albuminuria without RI was inversely associated with the female gender (OR 0.27; CI 95% 0.21–0.35, duration of diabetes (OR 0.94 per year; CI 95% 0.91–0.97 and directly associated with HbA1c (OR 1.19 for every 1% increase; CI 95% 1.09–1.3. Conclusions One-third of the sample population in this study has KD. The presence or absence of albuminuria identifies two subgroups with different characteristics related to gender, the duration of diabetes and metabolic status of the patient. It is important to determine both albuminuria and GFR estimation to diagnose KD.

Coll-de-Tuero Gabriel

2012-08-01

345

Stochastic domination and weak convergence of conditioned Bernoulli random vectors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

For n>=1 let X_n be a vector of n independent Bernoulli random variables. We assume that X_n consists of M "blocks" such that the Bernoulli random variables in block i have success probability p_i. Here M does not depend on n and the size of each block is essentially linear in n. Let X'_n be a random vector having the conditional distribution of X_n, conditioned on the total number of successes being at least k_n, where k_n is also essentially linear in n. Define Y'_n simila...

Broman, Erik; Brug, Tim; Kager, Wouter; Meester, Ronald

2011-01-01

346

A Randomized, Controlled Trial of the Efficacy of an Interoceptive Exposure-Based CBT for Treatment-Refractory Outpatients with Opioid Dependence.  

Science.gov (United States)

Abstract Many patients diagnosed with opioid dependence do not adequately respond to pharmacologic, psychosocial, or combination treatment, highlighting the importance of novel treatment strategies for this population. The current study examined the efficacy of a novel behavioral treatment focusing on internal cues for drug use (Cognitive Behavioral Therapy for Interoceptive Cues; CBT-IC) relative to an active comparison condition, Individual Drug Counseling (IDC), when added to methadone maintenance treatment (MMT) among those who had not responded to MMT. Participants (N=78) were randomly assigned to receive 15 sessions of CBT-IC or IDC as an adjunct to ongoing MMT and counseling. Oral toxicology screens were the primary outcome. Results indicated no treatment differences between CBT-IC and IDC and a small, significant reduction of self-reported drug use, but no change on toxicology screens. Tests of potential moderators, including sex, anxiety sensitivity, and coping motives for drug use, did not yield significant interactions. Among opioid-dependent outpatients who have not responded to MMT and counseling, the addition of IDC or CBT-IC did not result in additive outcome benefits. These results highlight the need for more potent treatment strategies for opioid dependence, particularly among those who do not fully respond to frontline treatment. PMID:25364993

Otto, Michael W; Hearon, Bridget A; McHugh, R Kathryn; Calkins, Amanda W; Pratt, Elizabeth; Murray, Heather W; Safren, Steven A; Pollack, Mark H

2014-01-01

347

Strength training versus robot-assisted gait training after incomplete spinal cord injury: a randomized pilot study in patients depending on walking assistance  

Science.gov (United States)

Background Task-specific locomotor training has been promoted to improve walking-related outcome after incomplete spinal cord injury (iSCI). However, there is also evidence that lower extremity strength training might lead to such improvements. The aim of this randomized cross-over pilot study was to compare changes in a broad spectrum of walking-related outcome measures and pain between robot-assisted gait training (RAGT) and strength training in patients with chronic iSCI, who depended on walking assistance. We hypothesized that task-specific locomotor training would result in better improvements compared to strength training. Methods Nine participants with a chronic iSCI were randomized to group 1 or 2. Group 1 received 16 sessions of RAGT (45 min each) within 4 weeks followed by 16 sessions of strength training (45 min each) within 4 weeks. Group 2 received the same interventions in reversed order. Main outcome measures were the 10 m Walk Test (10MWT) at preferred and maximal speed. Furthermore, we assessed several measures such as walking speed under different conditions, balance, strength, and 2 questionnaires that evaluate risk of falling and pain. Data were collected at baseline, between interventions after 4 weeks, directly after the interventions and at follow-up 6 months after the interventions. Pain was assessed repeatedly throughout the study. Results There were no significant differences in changes in scores between the 2 interventions, except for maximal walking speed (10MWT), which improved significantly more after strength training than after RAGT. Pain reduced after both interventions. Conclusion In patients with chronic iSCI dependent on walking assistance, RAGT was not more effective in improving walking-related outcome compared to lower extremity strength training. However, the low sample size limits generalizability and precision of data interpretation. Trial registration This study was registered at Clinicaltrials.gov (NCT01087918). PMID:24401143

2014-01-01

348

Study of the low-frequency variability of the atmospheric general circulation with the use of time-dependent empirical orthogonal functions  

Science.gov (United States)

The theory of both time-and space-dependent empirical orthogonal functions (EOFs) is outlined from a common point of view as a discrete version of the Karhunen-Loeve expansion. EOF techniques are used to process the results of a 1300-day-long numerical experiment in the mode of perpetual January with a daily step. As a result, the component determined by internal hydrothermodynamic processes was isolated from the general variability of the atmospheric circulation. To isolate intraseasonal variability (a winter season), the principal components of the 500-hPa height field were processed with a filter close to a ?-shaped filter isolating the frequency band 0.1 0.01 day-1. The spatial principal components were analyzed via the method of time-dependent EOFs. The spectral characteristics obtained can characterize the intraseasonal low-frequency variability and agree partially with empirical data.

Galin, M. B.

2007-02-01

349

An Analysis of Some Variables Affecting the Internet Dependency Level of Turkish Adolescents by Using Decision Tree Methods  

Science.gov (United States)

Internet dependency is going to expand into social life in wide area whereas it has been accepted as a pathological and psychological disease. Knowing the basic effects of internet dependency is an inevitable approach to use the internet technology healthy. In this study, internet dependency levels of 754 students were examined with the Internet…

Kayri, Murat; Gunuc, Selim

2010-01-01

350

Thermal dependence of brine salinity in the surface layer of snow-covered sea ice under the variable conditions  

Science.gov (United States)

We observed snow covered sea ice in Barrow, Alaska in February 2004 to investigate thermal dependence of brine salinity in the surface layer. The observed data was compared with simulated data, which was estimated by existing thermal models (Nakawo and Sinha, 1981; Ono, 1968). The brine salinity of the surface layer is very important to analyze microwave images, because its dielectric properties determine emissivity and penetration depth. In combination with the observation, we took some sea ice cores, measuring their length, temperature and salinity. After the observation, we obtained vertical temperature and salinity profiles. We also measured air temperature, snow surface temperature, snow/ice interface temperature, water temperature and snow depth and density. These data were used for the simulations. Regarding the simulation, at first, we estimated snow/ice interface temperature using the equation of Nakawo and Sinha (1981). This equation is formed by 6 parameters, which are the thermal conductivity of snow and sea ice, snow depth, sea ice thickness, air temperature and melting point of sea ice. And then, we estimated brine salinity using the results of Nakawo and Sinha and the equation of Ono (1968). This equation for obtaining brine salinity is calculated as a function of sea ice temperature. When we simulate brine salinity, only four data points are needed, because melting point and thermal conductivity of sea ice can be assumed as -1.8° C and 2 W m-1 K-1, respectively. As for the thermal conductivity of snow, we can obtain from the equation of Devaux (1933). This equation requires information on snow density. Namely, we need air temperature, snow depth, snow density and thickness of sea ice when we simulate brine salinity. This means that field work and calculation relevant to simulation becomes more easily. Comparisons between observation and simulation have indicated good correlation. This result suggests the applicability of the simple simulation method. Based on these positive results, we calculated the relation between snow/ice interface temperature and snow depth as a function of air temperature. Specifically, we varied air temperature between -10° C, -20° C and -30° C. For a sea ice thickness of 1.25m and 2m, and an air temperature of -10° C, snow/ice interface temperature is almost same. On the other hand, when sea ice thickness was 30cm, snow/ice interface temperature became almost same at each air temperature if snow depth was over 50cm. And also, mean snow/ice interface temperature was higher than for the other two cases. We also calculated brine salinity in the surface layer of snow covered sea ice as a function of air temperature using the simulated results of snow/ice interface temperature. The variable range of air temperature is same as case of simulation for the snow/ice interface temperature. There was proportionality relation between sea ice thickness and brine salinity in the surface of sea ice, but relation between snow/ice interface temperature and brine salinity indicated inverse proportion. As indicated above, we compared observed data with simulated results to investigate the thermal dependence of brine salinity in the surface layer of snow covered sea ice. As a result, observed data and simulated results have indicated good correlation. We can estimate the dielectric constant of snow covered sea ice in the surface layer by simulating brine salinity under the various conditions. Hereby, we can expect an improvement of the accuracy of observation by satellite microwave remote sensing.

Kojima, S.; Saito, Y.; Enomoto, H.

2004-12-01

351

Static correlation beyond the random phase approximation: Dissociating H2 with the Bethe-Salpeter equation and time-dependent GW  

Science.gov (United States)

We investigate various approximations to the correlation energy of a H2 molecule in the dissociation limit, where the ground state is poorly described by a single Slater determinant. The correlation energies are derived from the density response function and it is shown that response functions derived from Hedin's equations (Random Phase Approximation (RPA), Time-dependent Hartree-Fock (TDHF), Bethe-Salpeter equation (BSE), and Time-Dependent GW) all reproduce the correct dissociation limit. We also show that the BSE improves the correlation energies obtained within RPA and TDHF significantly for intermediate binding distances. A Hubbard model for the dimer allows us to obtain exact analytical results for the various approximations, which is readily compared with the exact diagonalization of the model. Moreover, the model is shown to reproduce all the qualitative results from the ab initio calculations and confirms that BSE greatly improves the RPA and TDHF results despite the fact that the BSE excitation spectrum breaks down in the dissociation limit. In contrast, second order screened exchange gives a poor description of the dissociation limit, which can be attributed to the fact that it cannot be derived from an irreducible response function.

Olsen, Thomas; Thygesen, Kristian S.

2014-04-01

352

Static correlation beyond the random phase approximation : Dissociating H2 with the Bethe-Salpeter equation and time-dependent GW  

DEFF Research Database (Denmark)

We investigate various approximations to the correlation energy of a H2 molecule in the dissociation limit, where the ground state is poorly described by a single Slater determinant. The correlation energies are derived from the density response function and it is shown that response functions derived from Hedin's equations (Random Phase Approximation (RPA), Time-dependent Hartree-Fock (TDHF), Bethe-Salpeter equation (BSE), and Time-Dependent GW) all reproduce the correct dissociation limit. We also show that the BSE improves the correlation energies obtained within RPA and TDHF significantly for intermediate binding distances. A Hubbard model for the dimer allows us to obtain exact analytical results for the various approximations, which is readily compared with the exact diagonalization of the model. Moreover, the model is shown to reproduce all the qualitative results from the ab initio calculations and confirms that BSE greatly improves the RPA and TDHF results despite the fact that the BSE excitation spectrum breaks down in the dissociation limit. In contrast, second order screened exchange gives a poor description of the dissociation limit, which can be attributed to the fact that it cannot be derived from an irreducible response function. (C) 2014 AIP Publishing LLC.

Olsen, Thomas; Thygesen, Kristian Sommer

2014-01-01

353

Static correlation beyond the random phase approximation: dissociating H2 with the Bethe-Salpeter equation and time-dependent GW.  

Science.gov (United States)

We investigate various approximations to the correlation energy of a H2 molecule in the dissociation limit, where the ground state is poorly described by a single Slater determinant. The correlation energies are derived from the density response function and it is shown that response functions derived from Hedin's equations (Random Phase Approximation (RPA), Time-dependent Hartree-Fock (TDHF), Bethe-Salpeter equation (BSE), and Time-Dependent GW) all reproduce the correct dissociation limit. We also show that the BSE improves the correlation energies obtained within RPA and TDHF significantly for intermediate binding distances. A Hubbard model for the dimer allows us to obtain exact analytical results for the various approximations, which is readily compared with the exact diagonalization of the model. Moreover, the model is shown to reproduce all the qualitative results from the ab initio calculations and confirms that BSE greatly improves the RPA and TDHF results despite the fact that the BSE excitation spectrum breaks down in the dissociation limit. In contrast, second order screened exchange gives a poor description of the dissociation limit, which can be attributed to the fact that it cannot be derived from an irreducible response function. PMID:24784262

Olsen, Thomas; Thygesen, Kristian S

2014-04-28

354

Common Variable Immune Deficiency in Children—Clinical Characteristics Varies Depending on Defect in Peripheral B Cell Maturation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Common variable immune deficiency (CVID) is a heterogeneous disease associated with ineffective production of antibodies. It is usually diagnosed in adulthood, but a variable proportion of children develop CVID. Early identification of patients with potentially worse prognosis may help to avoid serious complications. The goal of this study was to associate the clinical phenotype of patients with early onset CVID with peripheral B-cell maturation profile. Four color flow cytometry was used to ...

Pia?tosa, Barbara; Pac, Ma?gorzata; Siewiera, Katarzyna; Pietrucha, Barbara; Klaudel-dreszler, Maja; Heropolitan?ska-pliszka, Edyta; Wolska-kus?nierz, Beata; Dmen?ska, Hanna; Gregorek, Hanna; Sokolnicka, Irena; Re?kawek, Aneta; Tkaczyk, Katarzyna; Bernatowska, Ewa

2013-01-01

355

The Energy Dependence of the Aperiodic Variability for Cygnus X-1, GX 339-4, GRS 1758-258, & 1E 1740.7-2942  

CERN Document Server

Using the data from the Rossi X-ray Timing Explorer (RXTE), we report the different energy dependence of the variability of the four persistent hard X-ray sources in the low-hard state: Cygnus X-1, GX 339-4, GRS 1758-258 and 1E 1740.7-2942. Cygnus X-1 is found to have a flatter power density spectrum (PDS) shape at higher energies. The other three sources have energy independent PDS shapes. The energy dependence of the overall variability (the integrated rms amplitude) varies from source to source and from observation to observation. 1E~1740.7-2942, for example, has a variability generally increasing with energy while GX 339-4 has a decreasing variability. A general trend is found in the four sources that the integrated rms amplitude anti-correlates with the X-ray flux. We compare these distinct energy dependent behaviors with several emission models. None of the models can fully explain all the features that we have found.

Lin, D; Böttcher, M; Liang, E P

1999-01-01

356

Determinants of the Levels of Development Based on the Human Development Index: A Comparison of Regression Models for Limited Dependent Variables  

Directory of Open Access Journals (Sweden)

Full Text Available This paper aims to examine the factors affecting the level of development of countries using various regression models for limited dependent variables including binary logit, probit and Tobit analyses. In this manner, the paper may suggest a road map for high developed countries to achieve very high developed levels. For this purpose, Human Development Indices of 84 countries were involved in the analysis with respect to nine independent variables. The results of the all regression models indicates that determinants including life expectancy at birth, expected years of schooling, labour force participation rate (female-male ratio, and GDP per capita have statistically significant effects on the level of development.

Mirac Eren

2014-01-01

357

Predictors of Outcome for Short-Term Medically Supervised Opioid Withdrawal during a Randomized, Multi Center Trial of Buprenorphine-Naloxone and Clonidine in the NIDA Clinical Trials Network Drug and Alcohol Dependence  

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Few studies in community settings have evaluated predictors, mediators, and moderators of treatment success for medically supervised opioid withdrawal treatment. This report presents new findings about these factors from a study of 344 opioid dependent men and women prospectively randomized to either buprenorphine-naloxone or clonidine in an open-label 13-day medically-supervised withdrawal study. Subjects were either inpatient or outpatient in community treatment settings; however not random...

Ziedonis, Douglas M.; Amass, Leslie; Steinberg, Marc; Woody, George; Krejci, Jonathan; Annon, Jeffrey J.; Cohen, Allan J.; Waite-o’brien, Nancy; Stine, Susan M.; Mccarty, Dennis; Reid, Malcolm S.; Brown, Lawrence S.; Maslansky, Robert; Winhusen, Theresa; Babcock, Dean

2009-01-01

358

Free Random Levy Matrices  

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Using the theory of free random variables (FRV) and the Coulomb gas analogy, we construct stable random matrix ensembles that are random matrix generalizations of the classical one-dimensional stable L\\'{e}vy distributions. We show that the resolvents for the corresponding matrices obey transcendental equations in the large size limit. We solve these equations in a number of cases, and show that the eigenvalue distributions exhibit L\\'{e}vy tails. For the analytically known ...

Burda, Z.; Janik, R. A.; Jurkiewicz, J.; Nowak, M. A.; Papp, G.; Zahed, I.

2000-01-01

359

Time dependence of the UV resonance lines in the cataclysmic variables SU UMa, RX And and 0623+71  

International Nuclear Information System (INIS)

We present IUE observations of the dwarf novae SU UMa and RX And, and of the nova-like variable 0623 + 71. At the time of observation, SU UMa and RX And were in outburst. All three systems show variability in the wind-formed UV resonance lines of N v ? 1240, Si IV ? 1397 and C IV ? 1549 on timescale of hours. The amplitude of variation is smallest in RX And and largest in 0623 + 71. There is evidence that the variations observed in SU UMa's UV spectrum repeat on the orbital period. Our observations of SU UMa also reveal variability in the continuum flux during the decline from outburst maximum that is much more marked in the UV than at optical wavelengths. (author)

360

Scaling in the mean of the p+p??0+X inclusive reaction data and the energy dependence of Feynman variable  

International Nuclear Information System (INIS)

The p+p??0+X inclusive reaction data of Carey et al. were studied in the framework of the ''scaling in the mean'' hypothesis first proposed by Dao et al. These data were used to obtain the gamma ray spectrum in terms of the average value of the Feynman variable . A comparison with the observed gamma ray spectrum at Mt. Chacaltaya by the Japanese and Brazilian Group gives the energy dependence of at very high energy. (author)

 
 
 
 
361

Distance measurements across randomly distributed nitroxide probes from the temperature dependence of the electron spin phase memory time at 240 GHz  

Science.gov (United States)

At 8.5 T, the polarization of an ensemble of electron spins is essentially 100% at 2 K, and decreases to 30% at 20 K. The strong temperature dependence of the electron spin polarization between 2 and 20 K leads to the phenomenon of spin bath quenching: temporal fluctuations of the dipolar magnetic fields associated with the energy-conserving spin "flip-flop" process are quenched as the temperature of the spin bath is lowered to the point of nearly complete spin polarization. This work uses pulsed electron paramagnetic resonance (EPR) at 240 GHz to investigate the effects of spin bath quenching on the phase memory times (TM) of randomly-distributed ensembles of nitroxide molecules below 20 K at 8.5 T. For a given electron spin concentration, a characteristic, dipolar flip-flop rate (W) is extracted by fitting the temperature dependence of TM to a simple model of decoherence driven by the spin flip-flop process. In frozen solutions of 4-Amino-TEMPO, a stable nitroxide radical in a deuterated water-glass, a calibration is used to quantify average spin-spin distances as large as r¯=6.6 nm from the dipolar flip-flop rate. For longer distances, nuclear spin fluctuations, which are not frozen out, begin to dominate over the electron spin flip-flop processes, placing an effective ceiling on this method for nitroxide molecules. For a bulk solution with a three-dimensional distribution of nitroxide molecules at concentration n, we find W?n?1/r, which is consistent with magnetic dipolar spin interactions. Alternatively, we observe W?n for nitroxides tethered to a quasi two-dimensional surface of large (Ø ˜ 200 nm), unilamellar, lipid vesicles, demonstrating that the quantification of spin bath quenching can also be used to discern the geometry of molecular assembly or organization.

Edwards, Devin T.; Takahashi, Susumu; Sherwin, Mark S.; Han, Songi

2012-10-01

362

Selection of Common Items as an Unrecognized Source of Variability in Test Equating: A Bootstrap Approximation Assuming Random Sampling of Common Items  

Science.gov (United States)

The standard error of equating quantifies the variability in the estimation of an equating function. Because common items for deriving equated scores are treated as fixed, the only source of variability typically considered arises from the estimation of common-item parameters from responses of samples of examinees. Use of alternative, equally…

Michaelides, Michalis P.; Haertel, Edward H.

2014-01-01

363

THE IMPACT OF CLINICAL AND DEMOGRAPHIC VARIABLES ON COGNITIVE PERFORMANCE IN METHAMPHETAMINE-DEPENDENT INDIVIDUALS IN RURAL SOUTH CAROLINA  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Inconsistencies in reports on methamphetamine (METH) associated cognitive dysfunction may be attributed, at least in part, to the diversity of study sample features (egg, clinical and demographic characteristics). The current study assessed cognitive function in a METH-dependent population from rural South Carolina, and the impact of demographic and clinical characteristics on performance. Seventy-one male (28.2%) and female (71.8%) METH-dependent subjects were administered a battery of neuro...

Price, Kl; Desantis, Sm; Simpson, An; Tolliver, Bk; Mcrae-clark, Al; Saladin, Me; Baker, Nl; Wagner, Mt; Brady, Kt

2011-01-01

364

Small-scale spatial variability in phylogenetic community structure during early plant succession depends on soil properties.  

Science.gov (United States)

During early plant succession, the phylogenetic structure of a community changes in response to important environmental filters and emerging species interactions. We traced the development of temperate-zone plant communities during the first 7 years of primary succession on catchment soils to explore patterns of initial species assembly. We found pronounced small-scale differences in the phylogenetic composition of neighbouring plant assemblages and a large-scale trend towards phylogenetic evenness. This small-scale variability appears to be mediated by soil properties, particularly carbonate content. Therefore, abiotic environmental conditions might counteract or even supersede the effects of interspecific competition among closely related species, which are usually predicted to exhibit patterns of phylogenetic evenness. We conclude that theories on phylogenetic community composition need to incorporate effects of small-scale variability of environmental factors. PMID:24810325

Ulrich, Werner; Piwczy?ski, Marcin; Zaplata, Markus Klemens; Winter, Susanne; Schaaf, Wolfgang; Fischer, Anton

2014-07-01

365

Thin Film Flow of a Second Grade Fluid over a Stretching/Shrinking Sheet with Variable Temperature-Dependent Viscosity  

International Nuclear Information System (INIS)

Effects of variable viscosity on the flow and heat transfer in a thin film on a horizontal porous stretching sheet are analyzed. The steady boundary layer equations for momentum and thermal energy are simplified by using similarity transformations. The resulted and coupled nonlinear differential equations are solved by Homotopy analysis method. The results are presented graphically to interpret various physical parameters appearing in the problem. (fundamental areas of phenomenology (including applications))

366

Relationships among selected physical science misconceptions held by preservice elementary teachers and four variables: Formal reasoning ability, working memory capacity, verbal intelligence, and field dependence/independence  

Science.gov (United States)

The purpose of this study was to determine the relationship of selected cognitive abilities and physical science misconceptions held by preservice elementary teachers. The cognitive abilities under investigation were: formal reasoning ability as measured by the Lawson Classroom Test of Formal Reasoning (Lawson, 1978); working memory capacity as measured by the Figural Intersection Test (Burtis & Pascual-Leone, 1974); verbal intelligence as measured by the Acorn National Academic Aptitude Test: Verbal Intelligence (Kobal, Wrightstone, & Kunze, 1944); and field dependence/independence as measured by the Group Embedded Figures Test (Witkin, Oltman, & Raskin, 1971). The number of physical science misconceptions held by preservice elementary teachers was measured by the Misconceptions in Science Questionnaire (Franklin, 1992). The data utilized in this investigation were obtained from 36 preservice elementary teachers enrolled in two sections of a science methods course at a small regional university in the southeastern United States. Multiple regression techniques were used to analyze the collected data. The following conclusions were reached following an analysis of the data. The variables of formal reasoning ability and verbal intelligence were identified as having significant relationships, both individually and in combination, to the dependent variable of selected physical science misconceptions. Though the correlations were not high enough to yield strong predictors of physical science misconceptions or strong relationships, they were of sufficient magnitude to warrant further investigation. It is recommended that further investigation be conducted replicating this study with a larger sample size. In addition, experimental research should be implemented to explore the relationships suggested in this study between the cognitive variables of formal reasoning ability and verbal intelligence and the dependent variable of selected physical science misconceptions. Further research should also focus on the detection of a broad range of science misconceptions among preservice elementary teachers.

Griffin, Leslie Little

367

The Satisfiability Threshold of Random 3-SAT Is at Least 3.52  

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We prove that a random 3-SAT instance with clause-to-variable density less than 3.52 is satisfiable with high probability. The proof comes through an algorithm which selects (and sets) a variable depending on its degree and that of its complement.

Hajiaghayi, Mohammadtaghi; Sorkin, Gregory B.

2003-01-01

368

Method-Dependent Variability in Determination of Prevalence of Campylobacter jejuni and Campylobacter coli in Canadian Retail Poultry.  

Science.gov (United States)

Campylobacter is the most frequent cause of bacterial gastroenteritis in Canada, and the illness is commonly associated with poultry consumption. Whereas Canadian retail poultry is often contaminated with campylobacters, studies on the prevalence of this organism are inconsistent due to variability in sampling and microbiological methodology. To determine the current microbiological status of Canadian poultry, and to evaluate two commonly used microbiological methods, 348 raw poultry samples were collected at retail across Canada over a period of 3 years (2007 to 2010) and were analyzed for the presence of thermophilic Campylobacter species. The overall prevalence of Campylobacter spp. was found to be 42.8% by a combination of the two testing methods, with 33.9% of the samples positive for C. jejuni, 3.7% of the samples positive for C. coli, and 5.2% of the samples positive for both. Variability in Campylobacter spp. prevalence was observed in samples obtained from different regions across Canada and from poultry with or without skin, but this was not statistically significant. In co-contaminated samples, C. jejuni was preferentially recovered from Preston agar compared with mCCDA and Campy-Cefex agar, with an increase in recovery of C. coli on all selective media after 48 h of enrichment. A subset of 214 of the poultry rinses were analyzed by both Health Canada's standard method, MFLP-46 (enrichment in Park and Sanders broth), and a second method requiring enrichment in Bolton broth. Significantly more positive samples were obtained with the MFLP-46 method (40.6%) than with the alternate method (35.0%). This improved recovery with MFLP-46 may be due to the omission of cycloheximide from this method. These results demonstrate that determination of prevalence of Campylobacter spp. on poultry products may be significantly impacted by the choice of microbiological methods used. Canadian poultry continues to be a source of exposure to Campylobacter spp. PMID:25285484

Carrillo, Catherine D; Plante, Daniel; Iugovaz, Irène; Kenwell, Robyn; Bélanger, Ghislaine; Boucher, Francine; Poulin, Nathalie; Trottier, Yvon-Louis

2014-10-01

369

Comparing the effects of distilled Rehmannia glutinosa, Wild Ginseng and Astragali Radix pharmacopuncture with heart rate variability (HRV): a randomized, sham-controlled and double-blind clinical trial.  

Science.gov (United States)

This study compared the effects of distilled Rehmannia glutinosa, Wild Ginseng and Astragali Radix pharmacopuncture on the autonomic nervous system and heart rate variability. The purpose of the trial was to observe the influence distilled Astragali Radix, Wild Ginseng and Rehmannia glutinosa pharmacopuncture have on the autonomic nervous system. 120 healthy male volunteers were divided into four groups, which consisted of three experimental groups and a control group. This study was a randomized, placebo-controlled, double-blind clinical trial. Volunteers in experimental groups were underwent pharmacopuncture at GB21 (Kyonjong), and volunteers in the control group were injected with normal saline at GB21 (Kyonjong). Heart rate variability was measured seven times: before and after injection, every 5 minutes for 30 minutes. The result was distilled Rehmannia glutinosa, Wild Ginseng and Astragali Radix pharmacopuncture in healthy adult males tended to activate the autonomic nervous system, particularly the sympathetic nervous system. PMID:20633498

Yook, Taehan; Yu, Jungsuk; Lee, Hwiyong; Song, Beomyong; Kim, Lakhyung; Roh, Jungdu; Shin, Jinchul; Lim, Sungtaek

2009-09-01

370

Adeno-associated virus vectors show variable dependence on divalent cations for thermostability: implications for purification and handling.  

Science.gov (United States)

Recombinant adeno-associated virus (rAAV) shows significant promise as a vector for gene transfer in pre-clinical models of human disease, and is currently being evaluated in human clinical trials. As a consequence, increasing attention is being turned to the important tasks of optimizing rAAV titer, purity, and stability. We have observed dramatic variation in divalent cation dependence for thermostability of different rAAV vectors. To further investigate this observation, the thermostability of eight different vector constructs ranging in size from 73 to 107% of wild-type genome size (4.68 kilobases) was determined in the presence and absence of divalent cations. Virions containing smaller genomes (i.e., 95% wild type) were dependent on divalent cations for thermostability. Genome sequence also appeared to be a factor in the thermostability of the larger rAAV vectors. These observations are of both practical and theoretical significance. Divalent cations should be included in all buffer solutions used during rAAV purification and storage, and unnecessary heat exposure avoided. These data also demonstrate that different recombinants of a particular virus should not be assumed to possess the same thermostability profile. PMID:10724041

Turnbull, A E; Skulimowski, A; Smythe, J A; Alexander, I E

2000-03-01

371

Wearable monitoring for mood recognition in bipolar disorder based on history-dependent long-term heart rate variability analysis.  

Science.gov (United States)

Current clinical practice in diagnosing patients affected by psychiatric disorders such as bipolar disorder is based only on verbal interviews and scores from specific questionnaires, and no reliable and objective psycho-physiological markers are taken into account. In this paper, we propose to use a wearable system based on a comfortable t-shirt with integrated fabric electrodes and sensors able to acquire electrocardiogram, respirogram, and body posture information in order to detect a pattern of objective physiological parameters to support diagnosis. Moreover, we implemented a novel ad hoc methodology of advanced biosignal processing able to effectively recognize four possible clinical mood states in bipolar patients (i.e., depression, mixed state, hypomania, and euthymia) continuously monitored up to 18 h, using heart rate variability information exclusively. Mood assessment is intended as an intrasubject evaluation in which the patient's states are modeled as a Markov chain, i.e., in the time domain, each mood state refers to the previous one. As validation, eight bipolar patients were monitored collecting and analyzing more than 400 h of autonomic and cardiovascular activity. Experimental results demonstrate that our novel concept of personalized and pervasive monitoring constitutes a viable and robust clinical decision support system for bipolar disorders recognizing mood states with a total classification accuracy up to 95.81%. PMID:24240031

Valenza, Gaetano; Nardelli, Mimma; Lanatà, Antonio; Gentili, Claudio; Bertschy, Gilles; Paradiso, Rita; Scilingo, Enzo Pasquale

2014-09-01

372

VARIABILITY OF ANTHOCYANIN CONTENT AND DRY MATTER AMOUNT IN FRUITS OF SOME LONICERA CAERULEA SELECTIONS DEPENDING ON STORAGE CONDITIONS  

Directory of Open Access Journals (Sweden)

Full Text Available Lonicera caerulea var. kamtschatica is a species with multiple uses mainly due to the valuable biologicallyactive substances with high antioxidative potential. The anthocianins occupy an important place in inducing the health-protective benefits of the berries of this species. The aim of our work was to determine the total anthocyanin and drymatter amounts in the fruits collected from Romanian selections of blue honeysuckle, preserved by freezing (three monthsin refrigerator and drying at 60°C (to constant weight. The obtained results showed that the storage conditions havegenerally influenced the anthocyanin content. Thus, in freezing storage conditions, the anthocyanin amount eitherdecreased (C, SL6, SL8, SL15 or increased (SL17, SL57, depending on the biological material, whereas the dryingpreservation declined the anthocyanin level with ~ 80%, also varying with the selections of blue honeysuckle.

Zenovia Olteanu

2013-12-01

373

Variable angle XAFS study of multilayer nanostructure: Determination of selective concentration profile and depth-dependent partial atomic distributions  

Energy Technology Data Exchange (ETDEWEB)

We propose a new method for studying multilayer structure using angle resolved extended x-ray absorption fine structure (EXAFS) measurements. The linear integral equation describing a connection between the fluorescence intensity for spectrum of element C, the incident beam energy E, the incident angle {phi} and the concentration profile p(z,C) has been derived. It is a Fredholm integral equation of the first kind, it belongs to the class of ill-posed problems and for solution it needs special methods. We use the regularization method. For determining the depth-dependent partial interatomic distances we use angle resolved EXAFS data. The effectiveness of the method has been tested during numerical simulation on the model crystalline three-layer with BCC structure: Cr/Fe/Cr.

Babanov, Yuri; Salamatov, Yuri [Institute of Metal Physics Russian Academy of Sciences, 18 S. Kovalevskaya str., 620041 Ekaterinburg (Russian Federation); Mukhamedzhanov, Enver, E-mail: babanov@imp.uran.r [Russian Research Centre ' Kurchatov Institute' , 1 Kurchatov Sq., 123182 Moscow (Russian Federation)

2009-11-15

374

Once daily versus conventional dosing of pH-dependent mesalamine long-term to maintain quiescent ulcerative colitis: Preliminary results from a randomized trial  

Directory of Open Access Journals (Sweden)

Full Text Available Sunanda Kane1, William Holderman2, Peter Jacques2, Todd Miodek31Mayo Clinic College of Medicine, Rochester, MN, USA; 2Digestive Health Specialists, Tacoma, WA, USA; 3University of Chicago, Chicago, IL, USABackground and Aims: Multiple studies have demonstrated the efficacy of aminosalicylates in maintaining remission in ulcerative colitis (UC. A newer formulation of mesalamine can be administered once daily. We aimed to examine the efficacy and tolerability of pH-dependent mesalamine for long-term maintenance, and compare the rates of medication consumption between groups over a prolonged period.Methods: Subjects whose UC had been quiescent for at least 4 months, and who had been receiving mesalamine for maintenance only, were randomized to once daily or conventional dosing for 12 months. Disease activity and medication consumption was assessed every 3 months. The primary endpoint was the percentage of those with quiescent disease at 12 months.Results: We enrolled 20 patients, 12 to once daily and 8 to conventional dosing. Six of the 12 patients (50% in the once daily group compared with 5 of the 8 patients (62.5% in the conventional group experienced a flare (p = 0.31. Only 5 of the 12 (42% patients in the once daily group were adherent compared with 3 of 8 patients (37.5% in the conventional dosing group (p = NS. Median amount consumed in the once daily group was 63% (range 0%–100% and in the conventional group 55% (range 0%–100%, (p > 0.5. None of the adherent subjects in the once daily group experienced a flare, while 6 out of 7 (86% who were non-adherent experienced a flare (p < 0.01. In the conventional dosing group, 1 in 3 adherent patients (33% experienced a fl are compared with 4 out of 5 (80% in the non-adherent group (p < 0.01.Conclusion: Adherence, rather than medication regimen, appeared to be important in disease outcome at 12 months.Keywords: ulcerative colitis, mesalamine, aminosalicylates, remission

Sunanda Kane

2008-09-01

375

High-Rate Pacing Reduces Variability of Repolarization and Prevents Repolarization-Dependent Arrhythmias in Dogs With Chronic AV Block  

DEFF Research Database (Denmark)

High-rate pacing may have an inhibitory effect on the initiation of Torsade de Pointes arrhythmias (TdP). However, permanent pacing is only indicated in high-risk patients. We performed a proof of concept study into automatic overdrive pacing for prevention of drug-induced TdP, using short-term variability of repolarization (STV) as a feedback parameter of arrhythmic risk. Methods and Results: The minimal signal sampling frequency required for measuring STV was determined through computer simulation. Arrhythmogenic response to dofetilide (25 µg/kg/5minutes) was tested at two different paced heart rates (60–65 bpm vs 100–110 bpm) in 7 dogs with chronic atrioventricular block, while recording right and left ventricular (LV) monophasic action potential (MAP) and LV electrogram (EGM). Simulations showed a sampling frequency of 500 Hz is sufficient to capture relevant STV values. High-rate pacing prevented dofetilide-induced TdP seen at the low rate (low: 6/7 vs high: 1/7). At the low rate, STV from LV MAP duration increased before occurrence of spontaneous, ectopic activity and TdP (1.7 ± 0.6–3.0 ± 1.8 ms, P < 0.05), but at the high-rate STV did not change significantly (0.9 ± 0.2–1.5 ± 1.4 ms, NS). Regression analysis showed a close relation between STV calculated from LV MAP and from LV EGM (R2= 0.71). Conclusions: High-rate pacing increases repolarization reserve in dogs with chronic atrioventricular block, preventing dofetilide-induced TdP. Changes in repolarization reserve are reflected in values of STV.

Oosterhoff, Peter; Thomsen, Morten Bækgaard

2010-01-01

376

Performance of Empirical Bayes Estimators of Level-2 Random Parameters in Multilevel Analysis: A Monte Carlo Study for Longitudinal Designs  

Science.gov (United States)

Multilevel analysis is a useful technique for analyzing longitudinal data. To describe a person's development across time, the quality of the estimates of the random coefficients, which relate time to individual changes in a relevant dependent variable, is of importance. The present study compares three estimators of the random coefficients: the…

Candel, Math J. J. M.; Winkens, Bjorn

2003-01-01

377

Zeros of Random Analytic Functions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dominant theme of this thesis is that random matrix valued analytic functions, generalizing both random matrices and random analytic functions, for many purposes can (and perhaps should) be effectively studied in that level of generality. We study zeros of random analytic functions in one complex variable. It is known that there is a one parameter family of Gaussian analytic functions with zero sets that are stationary in each of the three symmetric spaces, namely the pl...

Krishnapur, Manjunath

2006-01-01

378

Strictly and asymptotically scale invariant probabilistic models of N correlated binary random variables having q-Gaussians as N ? ? limiting distributions  

Science.gov (United States)

The celebrated Leibnitz triangle has a remarkable property, namely that each of its elements equals the sum of its south-west and south-east neighbors. In probabilistic terms, this corresponds to a specific form of correlation of N equally probable binary variables which satisfy scale invariance. Indeed, the marginal probabilities of the N-system precisely coincide with the joint probabilities of the (N-1)-system. On the other hand, the non-additive entropy S_q\\equiv ({1-\\int_{-\\infty }^{\\infty } [p(x)]^q})/({q-1})\\ (q \\in {\\mathbb R}; S_1=-\\int_{-\\infty }^\\infty p(x) \\ln p(x)) , which grounds non-extensive statistical mechanics, is, under appropriate constraints, extremized by the (q-Gaussian) distribution p_q(x) \\propto [1-(1-q) \\, \\beta \\, x^2]^{1/(1-q)} (qLeibnitz triangle (? = 1) and the case of independent variables (\

Rodríguez, A.; Schwämmle, V.; Tsallis, C.

2008-09-01

379

No effect of short-term amino acid supplementation on variables related to skeletal muscle damage in 100 km ultra-runners - a randomized controlled trial  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background The purpose of this study was to investigate the effect of short-term supplementation of amino acids before and during a 100 km ultra-marathon on variables of skeletal muscle damage and muscle soreness. We hypothesized that the supplementation of amino acids before and during an ultra-marathon would lead to a reduction in the variables of skeletal muscle damage, a decrease in muscle soreness and an improved performance. Methods Twenty-eight experienced male ultra-runners were divided into two groups, one with amino acid supplementation and the other as a control group. The amino acid group was supplemented a total of 52.5 g of an amino acid concentrate before and during the 100 km ultra-marathon. Pre- and post-race, creatine kinase, urea and myoglobin were determined. At the same time, the athletes were asked for subjective feelings of muscle soreness. Results Race time was not different between the groups when controlled for personal best time in a 100 km ultra-marathon. The increases in creatine kinase, urea and myoglobin were not different in both groups. Subjective feelings of skeletal muscle soreness were not different between the groups. Conclusions We concluded that short-term supplementation of amino acids before and during a 100 km ultra-marathon had no effect on variables of skeletal muscle damage and muscle soreness.

Rosemann Thomas

2011-04-01

380

A variable-order time-dependent neutron transport method for nuclear reactor kinetics using analytically-integrated space-time characteristics  

International Nuclear Information System (INIS)

A new time-dependent neutron transport method based on the method of characteristics (MOC) has been developed. Whereas most spatial kinetics methods treat time dependence through temporal discretization, this new method treats time dependence by defining the characteristics to span space and time. In this implementation regions are defined in space-time where the thickness of the region in time fulfills an analogous role to the time step in discretized methods. The time dependence of the local source is approximated using a truncated Taylor series expansion with high order derivatives approximated using backward differences, permitting the solution of the resulting space-time characteristic equation. To avoid a drastic increase in computational expense and memory requirements due to solving many discrete characteristics in the space-time planes, the temporal variation of the boundary source is similarly approximated. This allows the characteristics in the space-time plane to be represented analytically rather than discretely, resulting in an algorithm comparable in implementation and expense to one that arises from conventional time integration techniques. Furthermore, by defining the boundary flux time derivative in terms of the preceding local source time derivative and boundary flux time derivative, the need to store angularly-dependent data is avoided without approximating the angular dependence of the angular flux time derivative. The accuracy of this method is assessed through implementation in the neutron transport code DeCART. The method is employed with variable-order local source representation to model a TWIGL transient. The results demonstrate that this method is accurate and more efficient than the discretized method. (authors)

 
 
 
 
381

Comparing the Variances of Dependent Groups.  

Science.gov (United States)

Recent attempts have been made to find a robust method for comparing the variances of "J" dependent random variables. However, these procedures can give unsatisfactory results. Several new procedures that are derived heuristically are examined. The most effective method is based on the statistic derived by D. Quade. (TJH)

Wilcox, Rand R.

1989-01-01

382

Variable effects of parabrachial nucleus lesions on salt appetite in rats depending upon experimental paradigm and saline concentration.  

Science.gov (United States)

Previous studies have demonstrated that bilateral lesions of the gustatory (medial) zone of the parabrachial nucleus (PBN) in the pons eliminate the salt (sodium chloride; NaCl) appetite induced in rats by treatment with the diuretic drug, furosemide. The present studies reexamined NaCl intake of rats with PBN lesions induced by ibotenic acid, using multiple models of salt appetite. The impairment of a conditioned taste aversion, an established consequence of PBN damage, was used as an initial screen with which to assess the effectiveness of the lesions. Rats with PBN lesions did not drink either 0.3 of a molar (M) solution of NaCl or 0.5 M NaCl in response to daily treatment with desoxycorticosterone acetate. These findings suggest that the excitatory stimulus of salt appetite mediated by mineralocorticoids is abolished by PBN lesions. In contrast, rats with PBN lesions drank some 0.5 M NaCl and more 0.3 M NaCl, in addition to water, in response to hypovolemia induced by subcutaneous injection of 30% polyethylene glycol solution. Those findings suggest that an excitatory stimulus of salt appetite, presumably mediated by Angiotensin II, is not abolished by PBN lesions. These and other observations indicate that lesions of the gustatory PBN in rats may or may not eliminate salt appetite, depending on which model is used and which concentration of NaCl solution is available. PMID:23398436

Stricker, Edward M; Grigson, Patricia S; Norgren, Ralph

2013-04-01

383

Dose dependency and individual variability in selected clinical, haematological and blood biochemical responses after systemic lipopolysaccharide challenge in cattle.  

Science.gov (United States)

Previous studies have noted that susceptibility to systemic lipopolysaccharide (LPS) exposure seems to differ between individual cows. However, to date inter-individual variation in the response to intravenous injection of LPS has been reported only as an empirical finding, and its existence or extent has never been backed up by statistical analyses. The aim of the present study was therefore to investigate the dose-dependency of clinical, haematological and blood biochemical responses to intravenous LPS injection in dairy cattle and to determine the extent to which these responses differed between individual cows. Eight dairy cows each received three intravenous injections of Escherichia coli LPS (10, 100, and 1000 ng/kg, consecutively) at three-week intervals. All three LPS doses induced clinical, haematological, and blood biochemical responses lasting up to several days. The strength of all of the responses increased significantly with an increasing LPS dose. A statistically significant inter-individual variation was demonstrated for all clinical, haematological, and blood biochemical responses except for serum calcium concentrations. More than half of the statistical variation in white blood cell and thrombocyte counts could be attributed to the individual. The results of this study show that despite the existence of a dose-response relationship between LPS and ensuing clinical, haematological, and blood biochemical responses, the majority of responses to LPS differ significantly in strength and duration from cow to cow. PMID:15720970

Jacobsen, Stine; Toelboell, Trine; Andersen, Pia H

2005-01-01

384

Randomized benchmarking with confidence  

Science.gov (United States)

Randomized benchmarking is a promising tool for characterizing the noise in experimental implementations of quantum systems. In this paper, we prove that the estimates produced by randomized benchmarking (both standard and interleaved) for arbitrary Markovian noise sources are remarkably precise by showing that the variance due to sampling random gate sequences is small. We discuss how to choose experimental parameters, in particular the number and lengths of random sequences, in order to characterize average gate errors with rigorous confidence bounds. We also show that randomized benchmarking can be used to reliably characterize time-dependent Markovian noise (e.g., when noise is due to a magnetic field with fluctuating strength). Moreover, we identify a necessary property for time-dependent noise that is violated by some sources of non-Markovian noise, which provides a test for non-Markovianity.

Wallman, Joel J.; Flammia, Steven T.

2014-10-01

385

A-Collapsibility of Distribution Dependence and Quantile Regression Coefficients  

CERN Document Server

The Yule-Simpson paradox notes that an association between random variables can be reversed when averaged over a background variable. Cox and Wermuth (2003) introduced the concept of distribution dependence between two random variables X and Y , and developed two dependence conditions, each of which guarantees that reversal cannot occur. Ma, Xie and Geng (2006) studied the collapsibility of distribution dependence over a background variable W, under a rather strong homogeneity condition. Collapsibility ensures the association remains the same for conditional and marginal models, so that Yule-Simpson reversal cannot occur. In this paper, we investigate a more general condition for avoiding e?ect reversal: A-collapsibility. The conditions of Cox and Wermuth imply A-collapsibility, without assuming homogeneity. In fact, we show that, when W is a binary variable, collapsibility is equivalent to A-collapsibility plus homogeneity, and A-collapsibility is equivalent to the conditions of Cox and Wermuth. Recently, Co...

Meerschaert, Mark M

2010-01-01

386

The Harris-Luck criterion for random lattices  

CERN Document Server

The Harris-Luck criterion judges the relevance of (potentially) spatially correlated, quenched disorder induced by, e.g., random bonds, randomly diluted sites or a quasi-periodicity of the lattice, for altering the critical behavior of a coupled matter system. We investigate the applicability of this type of criterion to the case of spin variables coupled to random lattices. Their aptitude to alter critical behavior depends on the degree of spatial correlations present, which is quantified by a wandering exponent. We consider the cases of Poissonian random graphs resulting from the Voronoi-Delaunay construction and of planar, ``fat'' $\\phi^3$ Feynman diagrams and precisely determine their wandering exponents. The resulting predictions are compared to various exact and numerical results for the Potts model coupled to these quenched ensembles of random graphs.

Janke, W; Janke, Wolfhard; Weigel, Martin

2004-01-01

387

Estimations of the Central Tendency Measures of the Random-sum Poisson-Weibull Distribution using Saddlepoint Approximation  

Directory of Open Access Journals (Sweden)

Full Text Available The random-sum Poisson-Weibull variable is the sum of a random sample from a Weibull distribution with a sample size that is an independent Poisson random variable. It has a wide range of applications. This random sum is complex and difficult to analyze. Saddlepoint approximations are powerful tools for obtaining accurate expressions for closed-form distribution functions for these complex distributions. The use of saddlepoint approximations almost outperforms other methods with respect to computational costs, though not necessarily with respect to accuracy. This study introduces saddlepoint approximations to the cumulative distribution function for the Poisson-Weibull model, from which we can obtain some important statistical measures of the central tendency of a cumulative distribution. We discuss approximations of a random-sum variable using dependent components, assuming the existence of a moment-generating function. Numerical examples of Poisson-Weibull random sums are presented.

O. Al Mutairi Alya

2014-01-01

388

Modeling Randomness in Judging Rating Scales with a Random-Effects Rating Scale Model  

Science.gov (United States)

This study presents the random-effects rating scale model (RE-RSM) which takes into account randomness in the thresholds over persons by treating them as random-effects and adding a random variable for each threshold in the rating scale model (RSM) (Andrich, 1978). The RE-RSM turns out to be a special case of the multidimensional random…

Wang, Wen-Chung; Wilson, Mark; Shih, Ching-Lin

2006-01-01

389

Spontaneous breathing with airway pressure release ventilation favors ventilation in dependent lung regions and counters cyclic alveolar collapse in oleic-acid-induced lung injury: a randomized controlled computed tomography trial  

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Introduction: Experimental and clinical studies have shown a reduction in intrapulmonary shunt with spontaneous breathing during airway pressure release ventilation (APRV) in acute lung injury. This reduction was related to reduced atelectasis and increased aeration. We hypothesized that spontaneous breathing will result in better ventilation and aeration of dependent lung areas and in less cyclic collapse during the tidal breath.Methods: In this randomized controlled experimental trial, 22 p...

Wrigge, Hermann; Zinserling, Jo?rg; Neumann, Peter; Muders, Thomas; Magnusson, Anders; Putensen, Christian; Hedenstierna, Go?ran

2005-01-01

390

Genetic variability in Gibberella fujikuroi and some related species of the genus Fusarium based on random amplification of polymorphic DNA (RAPD).  

Science.gov (United States)

One of the most important rice pathogens is Fusarium moniliforme (perfect stage: Gibberella fujikuroi), the causal agent of the super-elongation ("bakanae") disease. Thirty-seven strains of this species from different geographical regions were analyzed for their ability to produce gibberellins (GA) and for genetic relatedness by random amplified polymorphic DNA (RAPD). All GA-producing isolates showed nearly identical RAPD patterns using 51 oligonucleotide nona- and deca-mers as arbitrary primers. On the other hand, large differences between GA-nonproducing isolates were obtained. Comparison of the RAPD patterns with those of the tester strains of the six known mating populations (A, B, C, D, E, F) of G. fujikuroi showed that all producer strains belong to mating population C and all nonproducer isolates to other mating populations. Evidence for the usefulness of the RAPD technique to distinguish between mating populations was provided by sexual crossings. Consensus phylogenetic trees based on RAPDs were constructed by the Phylogenetic Analysis Using Parsimony (PAUP) system. In combination with morphological analysis, RAPD can distinguish between different species of the genus Fusarium. These investigations may find an application in the diagnosis of unknown Fusarium spp. and in distinguishing isolates of G. fujikuroi within the section Liseola. PMID:7553937

Voigt, K; Schleier, S; Brückner, B

1995-05-01

391

Detection of genetic variability in Basmati and non-Basmati rice varieties and their radiation induced mutants through random amplified polymorphic DNA (RAPD)  

International Nuclear Information System (INIS)

Random Amplified Polymorphic DNA (RAPDs) markers were utilized to detect polymorphism between pure lines and commercially available Basmati rice varieties to assess variation which may be helpful in quality control and varietal identification (Basmati-370 and derived radiation induced mutants), differentiation of mutants and parents, and identification of RAPD markers co-segregating with important agronomic traits including plant height, days to flower and grain quality. Basmati varieties were distinguished from non-Basmati varieties with the help of five diagnostic markers which will be useful for detecting mixing of non-Basmati and Basmati rices, currently a serious marketing problem. Different Basmati cultivars were identified with the help of diagnostic RAPD markers which can be used in quality control as well as for ''fingerprinting'' of cultivars. Different radiation induced mutants were also successfully distinguished from the parents on the basis of variety specific and mutant specific markers which will be useful for varietal identification. In addition to this, other markers were also identified which can differentiate mutants from each other and are being, used for the fingerprinting of different mutants, particularly the dwarf mutants having similar appearance but different parentage. For identification of RAPD markers co-segregating with plant height and days to flower, 50 F2 plants and four F3 families were studied from a reciprocal cross made between Kashmir Basmati (tall and early) and Basmati-198 (dwarf and late). Segregating bands were observed within these populations, and indicating the possible use of RAPD markers for tagging gene(s) of agronomic importance in rice. (author)

392

An inventory model of two-warehouse system with variable demand dependent on instantaneous displayed stock and marketing decisions via hybrid RCGA  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, a single item deterministic inventory model with two separate warehouses called owned warehouse/show-room (OW and rented warehouse (RW is developed. The proposed model of this paper also considers a realistic assumption regarding the storage capacity of the rented warehouse. Demand is a function of selling price, advertisement of an item and displayed inventory level in OW. The stocks of RW are shipped to OW under bulk release pattern where shortages are not allowed. We discuss different scenarios of the proposed model to address relative size of stock dependency parameters and the capacity of owned warehouse. For each scenario, the corresponding problem is formulated as a constrained mixed integer nonlinear programming problem with three integer and two non-integer variables and a real coded genetic algorithm (RCGA is developed to solve the resulted problem. The proposed model of the paper is also examined using some numerical examples and sensitivity analysis is performed.

A. K. Bhunia

2011-04-01

393

A Composite Likelihood Inference in Latent Variable Models for Ordinal Longitudinal Responses  

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The paper proposes a composite likelihood estimation approach that uses bivariate instead of multivariate marginal probabilities for ordinal longitudinal responses using a latent variable model. The model considers time-dependent latent variables and item-specific random effects to be accountable for the interdependencies of the multivariate…

Vasdekis, Vassilis G. S.; Cagnone, Silvia; Moustaki, Irini

2012-01-01

394

Dynamic Quantum Allocation and Swap-Time Variability in Time-Sharing Operating Systems.  

Science.gov (United States)

The effects of dynamic quantum allocation and swap-time variability on central processing unit (CPU) behavior are investigated using a model that allows both quantum length and swap-time to be state-dependent random variables. Effective CPU utilization is defined to be the proportion of a CPU busy period that is devoted to program processing, i.e.…

Bhat, U. Narayan; Nance, Richard E.

395

Effects of amlodipine and other classes of antihypertensive drugs on long-term blood pressure variability: evidence from randomized controlled trials.  

Science.gov (United States)

Blood pressure (BP) is monitored and managed to prevent cardiovascular complications of hypertension, but BP variability (BPV) has not been sufficiently studied. This analysis assessed whether patients receiving amlodipine vs other antihypertensive agents had lower BPV after ?12 weeks of treatment. Studies were included if individual subject data were available, had ?1 active comparator, and treatment duration was ?12 weeks. BPV was assessed using standard deviation (SD) and coefficient of variation (CV) of systolic BP across visits from 12 weeks. Individual trial and meta-analyses were performed for SD- and CV-based methodology. Five studies (47,558 BPV-evaluable patients) were included. Patient characteristics were largely consistent across the studies, but BP measurements varied from ?4 months to ?6 years. BPV with amlodipine was significantly (P enalapril in one study and numerically, but not significantly lower in another; and similar to chlorthalidone and losartan. Meta-analysis revealed a treatment difference (standard error) for amlodipine vs all active comparators of -1.23 (0.46; P = .008) mm Hg using SD and -0.86 (0.31; P = .005) using CV. These findings suggest that amlodipine is effective for minimizing BPV. Future studies need to confirm a causal link between BPV and cerebrovascular/cardiovascular outcomes. PMID:24685006

Wang, Ji-Guang; Yan, Ping; Jeffers, Barrett W

2014-05-01

396

Random lattice superstrings  

International Nuclear Information System (INIS)

We propose some new simplifying ingredients for Feynman diagrams that seem necessary for random lattice formulations of superstrings. In particular, half the fermionic variables appear only in particle loops (similarly to loop momenta), reducing the supersymmetry of the constituents of the type IIB superstring to N=1, as expected from their interpretation in the 1/N expansion as super Yang-Mills

397

MC Estimator Variance Reduction with Antithetic and Common Random Fields  

Science.gov (United States)

Monte Carlo methods are widely used to estimate the outcome of complex physical models. For physical models with spatial parameter uncertainty, it is common to apply spatial random functions to the uncertain variables, which can then be used to interpolate between known values or to simulate a number of equally likely realizations .The price, that has to be paid for such a stochastic approach, are many simulations of the physical model instead of just running one model with one 'best' input parameter set. The number of simulations is often limited because of computational constraints, so that a modeller has to make a compromise between the benefit in terms of an increased accuracy of the results and the effort in terms of a massively increased computational time. Our objective is, to reduce the estimator variance of dependent variables in Monte Carlo frameworks. Therefore, we adapt two variance reduction techniques (antithetic variates and common random numbers) to a sequential random field simulation scheme that uses copulas as spatial dependence functions. The proposed methodology leads to pairs of spatial random fields with special structural properties, that are advantageous in MC frameworks. Antithetic Random fields (ARF) exhibit a reversed structure on the large scale, while the dependence on the local scale is preserved. Common random fields (CRF) show the same large scale structures, but different spatial dependence on the local scale. The performances of the proposed methods are examined with two typical applications of stochastic hydrogeology. It is shown, that ARF have the property to massively reduce the number of simulation runs required for convergence in Monte Carlo frameworks while keeping the same accuracy in terms of estimator variance. Furthermore, in multi-model frameworks like in sensitivity analysis of the spatial structure, where more than one spatial dependence model is used, the influence of different dependence structures becomes obvious significantly faster using CRF.

Guthke, P.; Bardossy, A.

2011-12-01

398

Identifying Independent and Dependent Variables  

Science.gov (United States)

This activity is used in an Introductory to Sociology class for undergraduate students. This activity teaches students about research method elements. This activity teaches basic research method skills.

Hilal, Susan

399

Randomized recruitment in case-control studies.  

Science.gov (United States)

A new sampling approach for case-control studies offers a flexible alternative to frequency matching. In the "randomized recruitment" method, subjects are individually randomized to be recruited or not on the basis of investigator-imposed recruitment probabilities that can depend on both disease status and values of covariates already available or ascertained in a screening interview. When there is prior information about the odds ratios associated with the screening variables, such a design can achieve "probability matching," without the well-known disadvantages that encumber traditional matching. The method can also be used to enlarge the relative size of subsamples of interest. Following randomized recruitment, a modified logistic regression analysis allows unbiased estimation of effects associated with all variables studied, including the "matching" variables. One can also readily fit an additive model. The method is illustrated by developing the recruitment probabilities required for probability matching on age, sex, and cigarette smoking status in an ongoing study of lung cancer and exposure to radon progeny in which smoking cases are undersampled. PMID:1877602

Weinberg, C R; Sandler, D P

1991-08-15

400

Random Block Operators  

CERN Document Server

We study fundamental spectral properties of random block operators that are common in the physical modelling of mesoscopic disordered systems such as dirty superconductors. Our results include ergodic properties, the location of the spectrum, existence and regularity of the integrated density of states, as well as Lifshits tails. Special attention is paid to the peculiarities arising from the block structure such as the occurrence of a robust gap in the middle of the spectrum. Without randomness in the off-diagonal blocks the density of states typically exhibits an inverse square-root singularity at the edges of the gap. In the presence of randomness we establish a Wegner estimate that is valid at all energies. It implies that the singularities are smeared out by randomness, and the density of states is bounded. We also show Lifshits tails at these band edges. Technically, one has to cope with a non-monotone dependence on the random couplings.

Kirsch, Werner; Müller, Peter

2010-01-01

 
 
 
 
401

Dependence of P-wave dispersion on mean arterial pressure as an independent hemodynamic variable in school children / Dependencia de la dispersión de la onda P en la presión arterial media como variable hemodinámica independiente en niños en edad escolar  

Scientific Electronic Library Online (English)

Full Text Available SciELO Colombia | Language: English Abstract in spanish Resumen Introducción: La relación entre la disfunción diastólica y la dispersión de la onda P (PWD) en el electrocardiograma se ha estudiado durante algún tiempo. En este sentido, la ecocardiografía se está convirtiendo en una herramienta de diagnóstico para mejorar la estratificación de riesgo en l [...] a hipertensión leve. Objetivo: Determinar la dependencia de las PWD en el electrocardiograma de las variables ecocardiográficas en una población pediátrica. Métodos: De un total de 565 niños de tres escuelas primarias, fueron estudiados 515 niños. Fueron excluidos del estudio, aquellos niños cuyos padres se negaron a participar, y los niños con enfermedades congénitas conocidas. Se les realizó electrocardiograma de superficie de 12 derivaciones y se realizaron 4 tomas de presión arterial. Fueron medidas las ondas P del electrocardiograma y calculada su dispersión. Se realizó ecocardiografía para medidas estructurales y Doppler pulsado del flujo mitral. Resultados Se demuestra correlación significativa entre la PWD y la tensión arterial media para prehipertensos e hipertensos r= 0.32, p Abstract in english Abstract Introduction: The relationship between diastolic dysfunction and P-wave dispersion (PWD) in the electrocardiogram has been studied for some time. In this regard, echocardiography is emerging as a diagnostic tool to improve risk stratification for mild hypertension. Objective: To determine t [...] he dependence of PWD on the electrocardiogram and on echocardiographic variables in a pediatric population. Methods: Five hundred and fifteen children from three elementary schools were studiedfrom a total of 565 children. Those whose parents did not want them to take part in the study, as well as those with known congenital diseases, were excluded. Tests including 12-lead surface ECGs and 4 blood pressure (BP) measurements were performed. Maximum and minimum P-values were measured, and the PWD on the electrocardiogram was calculated. Echocardiography for structural measurements and the pulsed Doppler of mitral flow were also performed. Results: A significant correlation in statistical variables was found between PWD and mean BP for pre-hypertensive and hypertensive children, i.e., r= 0.32, p

Elibet, Chávez; Emilio F, González; María del Carmen, Llanes; Merlin, Garí Llanes; Yosvany, Garc.

2013-09-01

402

Dependence of P-wave dispersion on mean arterial pressure as an independent hemodynamic variable in school children / Dependencia de la dispersión de la onda P en la presión arterial media como variable hemodinámica independiente en niños en edad escolar  

Scientific Electronic Library Online (English)

Full Text Available SciELO Colombia | Language: English Abstract in spanish Resumen Introducción: La relación entre la disfunción diastólica y la dispersión de la onda P (PWD) en el electrocardiograma se ha estudiado durante algún tiempo. En este sentido, la ecocardiografía se está convirtiendo en una herramienta de diagnóstico para mejorar la estratificación de riesgo en l [...] a hipertensión leve. Objetivo: Determinar la dependencia de las PWD en el electrocardiograma de las variables ecocardiográficas en una población pediátrica. Métodos: De un total de 565 niños de tres escuelas primarias, fueron estudiados 515 niños. Fueron excluidos del estudio, aquellos niños cuyos padres se negaron a participar, y los niños con enfermedades congénitas conocidas. Se les realizó electrocardiograma de superficie de 12 derivaciones y se realizaron 4 tomas de presión arterial. Fueron medidas las ondas P del electrocardiograma y calculada su dispersión. Se realizó ecocardiografía para medidas estructurales y Doppler pulsado del flujo mitral. Resultados Se demuestra correlación significativa entre la PWD y la tensión arterial media para prehipertensos e hipertensos r= 0.32, p Abstract in english Abstract Introduction: The relationship between diastolic dysfunction and P-wave dispersion (PWD) in the electrocardiogram has been studied for some time. In this regard, echocardiography is emerging as a diagnostic tool to improve risk stratification for mild hypertension. Objective: To determine t [...] he dependence of PWD on the electrocardiogram and on echocardiographic variables in a pediatric population. Methods: Five hundred and fifteen children from three elementary schools were studiedfrom a total of 565 children. Those whose parents did not want them to take part in the study, as well as those with known congenital diseases, were excluded. Tests including 12-lead surface ECGs and 4 blood pressure (BP) measurements were performed. Maximum and minimum P-values were measured, and the PWD on the electrocardiogram was calculated. Echocardiography for structural measurements and the pulsed Doppler of mitral flow were also performed. Results: A significant correlation in statistical variables was found between PWD and mean BP for pre-hypertensive and hypertensive children, i.e., r= 0.32, p

Elibet, Chávez; Emilio F, González; María del Carmen, Llanes; Merlin, Garí Llanes; Yosvany, Garc.

403

Threshold-dependent variability of coronary artery calcification measurements - implications for contrast-enhanced multi-detector row-computed tomography  

International Nuclear Information System (INIS)

Introduction: The present study investigated the threshold-dependent variability of coronary artery calcification (CAC) measurements and the potential to quantify CAC in contrast-enhanced