WorldWideScience
1

Benford's Law and Continuous Dependent Random Variables  

CERN Document Server

Many systems exhibit a digit bias. For example, the first digit base 10 of the Fibonacci numbers, or of $2^n$, equals 1 not 10% or 11% of the time, as one would expect if all digits were equally likely, but about 30% of the time. This phenomenon, known as Benford's Law, has many applications, ranging from detecting tax fraud for the IRS to analyzing round-off errors in computer science. The central question is determining which data sets follow Benford's law. Inspired by natural processes such as particle decay, our work examines models for the decomposition of conserved quantities. We prove that in many instances the distribution of lengths of the resulting pieces converges to Benford behavior as the number of divisions grow. The main difficulty is that the resulting random variables are dependent, which we handle by a careful analysis of the dependencies and tools from Fourier analysis to obtain quantified convergence rates.

Becker, Thealexa; Miller, Steven J; Ronan, Ryan; Strauch, Frederick W

2011-01-01

2

Central Limit Theorem for the Sum of a Random Number of Dependent Random Variables  

OpenAIRE

In this study, the central limit theorem for certain classes of dependent random variables is explored. The dependency structure, as defined in the class of random variables can be reflected in some physical phenomena. Sufficient conditions for the sum of a random number of dependent random variables tending to normality are provided.

Yilun Shang

2011-01-01

3

Benford's Law and Continuous Dependent Random Variables  

OpenAIRE

Many mathematical, man-made and natural systems exhibit a leading-digit bias, where a first digit (base 10) of 1 occurs not 11% of the time, as one would expect if all digits were equally likely, but rather 30%. This phenomenon is known as Benford's Law. Analyzing which datasets adhere to Benford's Law and how quickly Benford behavior sets in are the two most important problems in the field. Most previous work studied systems of independent random variables, and relied on th...

Becker, Thealexa; Greaves-tunnell, Alec; Miller, Steven J.; Ronan, Ryan; Strauch, Frederick W.

2011-01-01

4

Central limit theorem for sampled sums of dependent random variables  

CERN Document Server

We prove a central limit theorem for linear triangular arrays under weak dependence conditions. Our result is then applied to the study of dependent random variables sampled by a $\\bbZ$-valued transient random walk. This extends the results obtained by Guillotin-Plantard & Schneider (2003). An application to parametric estimation by random sampling is also provided.

Guillotin-Plantard, Nadine

2007-01-01

5

Discrete approximations for sums of m-dependent random variables  

OpenAIRE

Sums of of 1-dependent integer-valued random variables are approximated by compound Poisson, negative binomial and Binomial distributions and signed compound Poisson measures. Estimates are obtained for total variation and local metrics. The results are then applied to statistics of $m$-dependent $(k_1,k_2)$ events and 2-runs. Heinrich's method and smoothing properties of convolutions are used for the proofs.

C?ekanavic?ius, V.; Vellaisamy, P.

2013-01-01

6

Stein's method for dependent random variables occurring in Statistical Mechanics  

CERN Document Server

We obtain rates of convergence in limit theorems of partial sums $S_n$ for certain sequences of dependent, identically distributed random variables, which arise naturally in statistical mechanics, in particular, in the context of the Curie-Weiss models. Under appropriate assumptions there exists a real number $\\alpha$, a positive real number $\\mu$, and a positive integer $k$ such that $(S_n- n \\alpha)/n^{1 - 1/2k}$ converges weakly to a random variable with density proportional to $\\exp(-\\mu |x|^{2k} /(2k)!)$. We develop Stein's method for exchangeable pairs for a rich class of distributional approximations including the Gaussian distributions as well as the non-Gaussian limit distributions with density proportional to $\\exp(-\\mu |x|^{2k} /(2k)!)$. Our results include the optimal Berry-Esseen rate in the Central Limit Theorem for the total magnetization in the classical Curie-Weiss model, for high temperatures as well as at the critical temperature $\\beta_c=1$, where the Central Limit Theorem fails. Moreover,...

Eichelsbacher, Peter

2009-01-01

7

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

8

Non-uniform approximations for sums of discrete m-dependent random variables  

OpenAIRE

Non-uniform estimates are obtained for Poisson, compound Poisson, translated Poisson, negative binomial and binomial approximations to sums of of m-dependent integer-valued random variables. Estimates for Wasserstein metric also follow easily from our results. The results are then exemplified by the approximation of Poisson binomial distribution, 2-runs and $m$-dependent $(k_1,k_2)$-events.

Vellaisamy, P.; Cekanavicius, V.

2013-01-01

9

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

10

Asymptotic Normality of Random Sums of m-dependent Random Variables  

OpenAIRE

We prove a central limit theorem for random sums of the form $\\sum_{i=1}^{N_n} X_i$, where $\\{X_i\\}_{i \\geq 1}$ is a stationary $m-$dependent process and $N_n$ is a random index independent of $\\{X_i\\}_{i\\geq 1}$. Our proof is a generalization of Chen and Shao's result for i.i.d. case and consequently we recover their result. Also a variation of a recent result of Shang on $m-$dependent sequences is obtained as a corollary. Examples on moving averages and descent processes a...

Islak, Umit

2013-01-01

11

Symmetric and centered binomial approximation of sums of locally dependent random variables  

OpenAIRE

Stein's method is used to approximate sums of discrete and locally dependent random variables by a centered and symmetric Binomial distribution. Under appropriate smoothness properties of the summands, the same order of accuracy as in the Berry-Essen Theorem is achieved. The approximation of the total number of points of a point processes is also considered. The results are applied to the exceedances of the $r$-scans process and to the Mat\\'ern hardcore point process type I.

Ro?llin, Adrian

2006-01-01

12

Large deviation asymptotics for the left tail of the sum of dependent positive random variables  

OpenAIRE

We study the left tail behavior of the logarithm of the distribution function of a sum of dependent positive random variables. Asymptotics are computed under the assumption that the marginal distribution functions decay slowly at zero, meaning that the their logarithms are slowly varying functions. This includes parametric families such as log-normal, gamma, Weibull and many distributions from the financial mathematics literature. We show that the logarithmic asymptotics of ...

Tankov, Peter

2014-01-01

13

An edgeworth expansion for a sum of M-Dependent random variables  

Directory of Open Access Journals (Sweden)

Full Text Available Given a sequence X1,X2,…,Xn of m-dependent random variables with moments of order 3+α (0<α≦1, we give an Edgeworth expansion of the distribution of Sσ−1(S=X1+X2+…+Xn, σ2=ES2 under the assumption that E[exp(it Sσ1] is small away from the origin. The result is of the best possible order.

Wan Soo Rhee

1985-09-01

14

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

OpenAIRE

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.

Rhee, Wansoo T.

1986-01-01

15

A local limit theorem for strongly dependent random variables and its application to a chaotic configuration of atoms  

Science.gov (United States)

We investigate one-dimensional chaotic configurations of atoms, which are generated by the Baker transformation or, equivalently, by the Bernoulli shift. The problem of calculating the distribution of the jth nearest-neighbor distances of these configurations is shown to be equivalent to the task of finding the limit distribution of the sum of the strongly dependent random variables Xl:([0,1),?L)?[0,1), x?(2lx)mod 1 (l?N0, ?L is the Lebesgue measure). We prove the validity of a local limit theorem for this sequence of random variables and conclude, therefore, that the distribution density Gj of the jth nearest-neighbor distances is asymptotically (as j??) a Gaussian distribution, the width of which grows as (j)1/2. With the aid of this result, we prove that the pair distribution function G of our configurations, which is the sum of the Gj's, tends to unity in the limit of large distances.

Reichert, P.; Schilling, R.

1985-06-01

16

Students' Misconceptions about Random Variables  

Science.gov (United States)

This article describes some misconceptions about random variables and related counter-examples, and makes suggestions about teaching initial topics on random variables in general form instead of doing it separately for discrete and continuous cases. The focus is on post-calculus probability courses. (Contains 2 figures.)

Kachapova, Farida; Kachapov, Ilias

2012-01-01

17

On Inverse Moments for a Class of Nonnegative Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available Using exponential inequalities, Wu et al. (2009 and Wang et al. (2010 obtained asymptotic approximations of inverse moments for nonnegative independent random variables and nonnegative negatively orthant dependent random variables, respectively. In this paper, we improve and extend their results to nonnegative random variables satisfying a Rosenthal-type inequality.

Sung SooHak

2010-01-01

18

Complete convergence for randomly indexed sums of random variables  

Energy Technology Data Exchange (ETDEWEB)

The complete convergence of normed sums of independent identically distributed random variables with random indices is studied. Some applications for subsequences and sequences with multidimensional indices are given.

Klesov, O.I. [Kiev Polytechnic Inst. (Ukraine)

1995-08-25

19

Limit theorem for random walk in weakly dependent random scenery  

CERN Document Server

Let $S=(S_k)_{k\\geq 0}$ be a random walk on $\\mathbb{Z}$ and $\\xi=(\\xi_{i})_{i\\in\\mathbb{Z}}$ a stationary random sequence of centered random variables, independent of $S$. We consider a random walk in random scenery that is the sequence of random variables $(\\Sigma_n)_{n\\geq 0}$ where

Guillotin-Plantard, Nadine

2008-01-01

20

Randomness and Earth climate variability  

CERN Document Server

Paleo-Sciences including palaeoclimatology and palaeoecology have accumulated numerous records related to climatic changes. The researchers have usually tried to identify periodic and quasi-periodic processes in these paleoscientific records. In this paper, we show that this analysis is incomplete. As follows from our results, random processes, namely processes with a single-time-constant (noise with a Lorentzian noise spectrum), play a very important and, perhaps, a decisive role in numerous natural phenomena. For several of very important natural phenomena the characteristic time constants are very similar and equal to (5-8)x10^3 years. However, this value is not universal. For example, the spectral density fluctuations of the atmospheric radiocarbon 14C are characterized by a Lorentzian with time constant 300 years. The frequency dependence of spectral density fluctuations for benthic 18O records contains two Lorentzians with time constans 8000 years and > 105 years.

Levinshtein, Michael E; Dmitriev, Alexander P; Shmakov, Pavel M

2015-01-01

21

Random Effect and Latent Variable Model Selection  

CERN Document Server

Presents various methods for accommodating model uncertainty in random effects and latent variable models. This book focuses on frequentist likelihood ratio and score tests for zero variance components. It also focuses on Bayesian methods for random effects selection in linear mixed effects and generalized linear mixed models

Dunson, David B

2008-01-01

22

Strong Decomposition of Random Variables  

DEFF Research Database (Denmark)

En stokastisk variabel X er strkt dekombinerbar hvis X=Y+Z, hvor Y=?(X) og Z=X-?(X) er uafhngige og ikke-degenerede stokastiske variable (kaldet komponenterne). Det vises at mindst en af komponenterne ndvendigvis m vre singulr, og der gives en ndvendig og tilstrkkelig betingelse for at en diskret stokastisk er strkt dekombinerbar.

Hoffmann-Jrgensen, Jrgen; Kagan, Abram M.

2007-01-01

23

Interpersonal variability in dependent personality.  

Science.gov (United States)

The interpersonal circumplex (IPC) was recommended as a personality trait dimensional model with good potential to identify the phenomenological scope of personality disorders whose core dysfunction involves maladaptive expression of interpersonal traits. The IPC was then applied to the reconceptualization of dependent personality and dependent personality disorder. In Study 1, Pincus and Gurtman's (1995) three interpersonal vectors of dependency were validated via factor analyses conducted on two large samples (N = 921; N = 472) and a reliable self-report measure, the 3 Vector Dependency Inventory (3VDI) was constructed. In Study 2, two samples (N = 103; N = 122) of individuals identified as predominantly endorsing submissive dependence, exploitable dependence, or love dependence, or who were low in aspects of dependency were compared via ANOVA and chi-square analyses on parental representations, adult attachment styles, loneliness, and pathological attachment. Submissive dependence was associated with higher scores on maladaptive constructs (fearful attachment, pathological attachment, and loneliness) and was also associated with lower parental affiliation and higher maternal control. Love dependence was associated with lower scores on maladaptive constructs and higher scores on secure attachment and parental affiliation. Variability in dependent phenomenology was related to its three component traits. Multiple perspectives on integrating love dependence, exploitable dependence, and submissive dependence into a reconceptualization of dependent personality disorder were articulated. PMID:11339797

Pincus, A L; Wilson, K R

2001-04-01

24

Asymptotics for Associated Random Variables  

CERN Document Server

The book concerns the notion of association in probability and statistics. Association and some other positive dependence notions were introduced in 1966 and 1967 but received little attention from the probabilistic and statistics community. The interest in these dependence notions increased in the last 15 to 20 years, and many asymptotic results were proved and improved. Despite this increased interest, characterizations and results remained essentially scattered in the literature published in different journals. The goal of this book is to bring together the bulk of these results, presenting

Oliveira, Paulo Eduardo

2012-01-01

25

Delocalization for Random Landau Hamiltonians with Unbounded Random Variables  

CERN Document Server

In this note we prove the existence of a localization/delocalization transition for Landau Hamiltonians randomly perturbed by an electric potential with unbounded amplitude. In particular, with probability one, no Landau gaps survive as the random potential is turned on, the gaps close, filling up partly with localized states. A minimal rate of transport is exhibited in the region of delocalization. To do so, we exploit the a priori quantization of the Hall conductance and extend recent Wegner estimates to the case of unbounded random variables.

Germinet, Franois; Mandy, Benot

2009-01-01

26

Distributions of Ratios: From Random Variables to Random Matrices  

Directory of Open Access Journals (Sweden)

Full Text Available The ratio R of two random quantities is frequently encountered in probability and statistics. But while for unidimensional statistical variables the distribution of R can be computed relatively easily, for symmetric positive definite random matrices, this ratio can take various forms and its distribution, and even its definition, can offer many challenges. However, for the distribution of its determinant, Meijer G-function often provides an effective analytic and computational tool, applicable at any division level, because of its reproductive property.

Thu Pham-Gia

2011-07-01

27

The random-variable canonical distribution  

International Nuclear Information System (INIS)

An alternative interpretation to Gibbs' concept of the canonical distribution for an ensemble of systems in statistical equilibrium is proposed. Whereas Gibbs' theory is based upon a consideration of systems subject to dynamical law, the present analysis relies neither on the classical equations of motion nor makes use of any a priori probability of a complexion; rather, it makes avail of the basic algebra of random variables and, specifically, invokes the law of large numbers. Thereby, a canonical distribution is derived which describes a macrosystem in probabilistic, rather than deterministic, terms, and facilitates the understanding of energy fluctuations which occur in macrosystems at an overall constant ensemble temperature. A discussion is given of a modified form of the Gibbs canonical distribution which takes full account of the effects of random energy fluctuations. It is demonstrated that the results from this modified analysis are entirely consonant with those derived from the random-variable approach. (author)

28

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; Sveges, M; Blomme, J; Lpez, 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

29

Nilpotent adjacency matrices, random graphs and quantum random variables  

International Nuclear Information System (INIS)

While a number of researchers have previously investigated the relationship between graph theory and quantum probability, the current work explores a new perspective. The approach of this paper is to begin with an arbitrary graph having no previously established relationship to quantum probability and to use that graph to construct a quantum probability space in which moments of quantum random variables reveal information about the graph's structure. Given an arbitrary finite graph and arbitrary odd integer m ? 3, fermion annihilation operators are used to construct a family of quantum random variables whose mth moments correspond to the graph's m-cycles. The approach is then generalized to recover a graph's m-cycles for any integer m ? 3 by defining nilpotent adjacency operators in terms of null-square generators of an infinite-dimensional Abelian algebra. It is shown that ordering the vertices of a simple graph induces a canonical decomposition ? = ?+ + ?- on any nilpotent adjacency operator ?. The work concludes with applications to Markov chains and random graphs

30

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.; Sveges, M.; Blomme, J.; Lpez, 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

31

Message Based Random Variable Length Key Encryption Algorithm  

Directory of Open Access Journals (Sweden)

Full Text Available Problem statement: A block ciphers provides confidentiality in cryptography but cryptanalysis of the classical block ciphers demonstrated some old weaknesses grabbing a partial key in any stage of encryption procedure leads to reconstructing the whole key. Exhaustive key search shows that key generation should be indeterminist and random for each round. Matching cipher-text attack shows that larger size of block is more secure. In order to overcome analysis mentioned above a new algorithm is designed that is based on random numbers and also can defeat time and memory constraints. Approach: Dynamic and message dependent key generator was created by producing a random number and it was selected as the size of first chunk. Residual value of second chunk divided by first chunk concatenating with first chunk forms the first cipher as an input for SP-boxes. These processes repeated until whole mesaage get involved into the last cipher. Encrypted messages are not equal under different run. Value of random number should be greater than 35 bits and plaintext must be at least 7 bits. A padding algorithm was used for small size messages or big random numbers. Results: Attack on the key generation process was prevented because of random key generation and its dependency to input message. Encryption and decryption times measured between 5 and 27 m sec in 2 GHz Pentium and java platform so time variant and fast enough key generation had been kept collision and timing attacks away due to small seized storage. Long and variable key length made key exhaustive search and differential attack impossible. None fixed size key caused avoidance of replaying and other attacks that can happen on fixed sized key algorithms. Conclusion: Random process employed in this block cipher increased confidentiality of the message and dynamic length substitution in proposed algorithm may lead to maximum cryptographic confusion and consequently makes it difficult for cryptanalysis.

Hamid Mirvaziri

2009-01-01

32

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

33

Energy-dependent variability from accretion flows  

OpenAIRE

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, ...

Zdziarski, Andrzej A.

2005-01-01

34

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

35

An Inequality for the Sum of Independent Bounded Random Variables  

OpenAIRE

We give a simple inequality for the sum of independent bounded random variables. This inequality improves on the celebrated result of Hoeffding in a special case. It is optimal in the limit where the sum tends to a Poisson random variable.

Dance, Christopher R.

2012-01-01

36

A Note on the Sum of Uniform Random Variables  

OpenAIRE

Abstract An inductive procedure is used to obtain distributions and probability densities for the sum Sn of independent, non equally uniform random variables. Some known results are then shown to follow immediately as special cases. Under the assumption of equally uniform random variables some new formulas are obtained for probabilities and means related to Sn. Finally, some new recursive formulas involving distributions are derived.

Buonocore, Aniello; Pirozzi, Enrica; Caputo, Luigia

2009-01-01

37

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

38

Sparsity considerations for dependent variables  

OpenAIRE

The aim of this paper is to provide a comprehensive introduction for the study of L1-penalized estimators in the context of dependent observations. We define a general $\\ell_{1}$-penalized estimator for solving problems of stochastic optimization. This estimator turns out to be the LASSO in the regression estimation setting. Powerful theoretical guarantees on the statistical performances of the LASSO were provided in recent papers, however, they usually only deal with the iid case. Here, we s...

Alquier, Pierre; Doukhan, Paul

2011-01-01

39

Continuum random combs and scale-dependent spectral dimension  

Energy Technology Data Exchange (ETDEWEB)

Numerical computations have suggested that in causal dynamical triangulation models of quantum gravity (CDT) the effective dimension of spacetime in the ultraviolet (UV) is lower than in the infrared (IR). In this paper we develop a simple model based on the previous work on random combs, which share some of the properties of CDT, in which this effect can be shown to occur analytically. We construct a definition for short- and long-distance spectral dimensions and show that the random comb models exhibit scale-dependent spectral dimension defined in this way. We also observe that a hierarchy of apparent spectral dimensions may be obtained in the cross-over region between UV and IR regimes for suitable choices of the continuum variables. Our main result is valid for a wide class of tooth length distributions thereby extending previous work on random combs by Durhuus et al.

Atkin, Max R; Giasemidis, Georgios; Wheater, John F, E-mail: m.atkin1@physics.ox.ac.uk, E-mail: g.giasemidis1@physics.ox.ac.uk, E-mail: j.wheater1@physics.ox.ac.uk [Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP (United Kingdom)

2011-07-01

40

Continuum Random Combs and Scale Dependent Spectral Dimension  

CERN Document Server

Numerical computations have suggested that in causal dynamical triangulation models of quantum gravity the effective dimension of spacetime in the UV is lower than in the IR. In this paper we develop a simple model based on previous work on random combs, which share some of the properties of CDT, in which this effect can be shown to occur analytically. We construct a definition for short and long distance spectral dimensions and show that the random comb models exhibit scale dependent spectral dimension defined in this way. We also observe that a hierarchy of apparent spectral dimensions may be obtained in the cross-over region between UV and IR regimes for suitable choices of the continuum variables. Our main result is valid for a wide class of tooth length distributions thereby extending previous work on random combs by Durhuus et al.

Atkin, Max R; Wheater, John F

2011-01-01

41

Continuum random combs and scale-dependent spectral dimension  

International Nuclear Information System (INIS)

Numerical computations have suggested that in causal dynamical triangulation models of quantum gravity (CDT) the effective dimension of spacetime in the ultraviolet (UV) is lower than in the infrared (IR). In this paper we develop a simple model based on the previous work on random combs, which share some of the properties of CDT, in which this effect can be shown to occur analytically. We construct a definition for short- and long-distance spectral dimensions and show that the random comb models exhibit scale-dependent spectral dimension defined in this way. We also observe that a hierarchy of apparent spectral dimensions may be obtained in the cross-over region between UV and IR regimes for suitable choices of the continuum variables. Our main result is valid for a wide class of tooth length distributions thereby extending previous work on random combs by Durhuus et al.

42

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)

43

Lower bounds for tails of sums of independent symmetric random variables  

CERN Document Server

The approach of Kleitman (1970) and Kanter (1976) to multivariate concentration function inequalities is generalized in order to obtain for deviation probabilities of sums of independent symmetric random variables a lower bound depending only on deviation probabilities of the terms of the sum. This bound is optimal up to discretization effects, improves on a result of Nagaev (2001), and complements the comparison theorems of Birnbaum (1948) and Pruss (1997). Birnbaum's theorem for unimodal random variables is extended to the lattice case.

Mattner, L

2006-01-01

44

Exponential Inequalities for Positively Associated Random Variables and Applications  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract We establish some exponential inequalities for positively associated random variables without the boundedness assumption. These inequalities improve the corresponding results obtained by Oliveira (2005. By one of the inequalities, we obtain the convergence rate for the case of geometrically decreasing covariances, which closes to the optimal achievable convergence rate for independent random variables under the Hartman-Wintner law of the iterated logarithm and improves the convergence rate derived by Oliveira (2005 for the above case.

Yang Shanchao

2008-01-01

45

Parameter Learning in PRISM Programs with Continuous Random Variables  

OpenAIRE

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 variabl...

Islam, Muhammad Asiful; Ramakrishnan, C. R.; Ramakrishnan, I. V.

2012-01-01

46

Inequality for Variance of Weighted Sum of Correlated Random Variables  

OpenAIRE

The upper bound inequality for variance of weighted sum of correlated random variables is derived according to Cauchy-Schwarz's inequality, while the weights are non-negative with sum of 1. We also give a novel proof with positive semidefinite matrix method. And the variance inequality of sum of correlated random variable with general weights is also obtained.Then,the variance inequalities are applied to the Chebychev's inequality and law of large numbers for sum of correlat...

Liu, Jingwei

2012-01-01

47

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

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

2008-11-01

48

A Note on the Sum of Correlated Gamma Random Variables  

OpenAIRE

The sum of correlated gamma random variables appears in the analysis of many wireless communications systems, e.g. in systems under Nakagami-m fading. In this Letter we obtain exact expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the sum of arbitrarily correlated gamma variables in terms of certain Lauricella functions.

Paris, Jose F.

2011-01-01

49

Exact value for subgaussian norm of centered indicator random variable  

OpenAIRE

We calculate the exact subgaussian norm of a centered (shifted) indicator (Bernoulli's) random variable. Using this result we derive very simple tail estimates for sums of these variables, not necessary to be identical distributed, and give some examples to show the exactness of our estimates.

Ostrovsky, Eugene; Sirota, Leonid

2014-01-01

50

Instrumental Variable Analyses. Exploiting Natural Randomness to Understand Causal Mechanisms  

OpenAIRE

Instrumental variable analysis is a technique commonly used in the social sciences to provide evidence that a treatment causes an outcome, as contrasted with evidence that a treatment is merely associated with differences in an outcome. To extract such strong evidence from observational data, instrumental variable analysis exploits situations where some degree of randomness affects how patients are selected for a treatment. An instrumental variable is a characteristic of the world that leads ...

Iwashyna, Theodore J.; Kennedy, Edward H.

2013-01-01

51

Non-Shannon Information Inequalities in Four Random Variables  

OpenAIRE

Any unconstrained information inequality in three or fewer random variables can be written as a linear combination of instances of Shannon's inequality I(A;B|C) >= 0 . Such inequalities are sometimes referred to as "Shannon" inequalities. In 1998, Zhang and Yeung gave the first example of a "non-Shannon" information inequality in four variables. Their technique was to add two auxiliary variables with special properties and then apply Shannon inequalities to the enlarged list...

Dougherty, Randall; Freiling, Chris; Zeger, Kenneth

2011-01-01

52

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

53

IS QUASAR OPTICAL VARIABILITY A DAMPED RANDOM WALK?  

International Nuclear Information System (INIS)

The damped random walk (DRW) model is increasingly used to model the variability in quasar optical light curves, but it is still uncertain whether the DRW model provides an adequate description of quasar optical variability across all timescales. Using a sample of OGLE quasar light curves, we consider four modifications to the DRW model by introducing additional parameters into the covariance function to search for deviations from the DRW model on both short and long timescales. We find good agreement with the DRW model on timescales that are well sampled by the data (from a month to a few years), possibly with some intrinsic scatter in the additional parameters, but this conclusion depends on the statistical test employed and is sensitive to whether the estimates of the photometric errors are correct to within ?10%. On very short timescales (below a few months), we see some evidence of the existence of a cutoff below which the correlation is stronger than the DRW model, echoing the recent finding of Mushotzky et al. using quasar light curves from Kepler. On very long timescales (>a few years), the light curves do not constrain models well, but are consistent with the DRW model.

54

Applying Free Random Variables to Random Matrix Analysis of Financial Data  

CERN Document Server

We apply the concept of free random variables to correlated Wishart random matrix models. We give a comprehensive rederivation of various spectral densities for a number of financial covariance matrices involving stocks returns without and with exponentially weighted moving averages. We show through simple models how to identify the pertinent underlying correlations. We extend our results to Levy-Wishart random matrix models whereby the risk factors are heavy tailed.

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

2006-01-01

55

Distribution and moments of radial error. [Rayleigh distribution - random variables  

Science.gov (United States)

An investigation of the moments and probability distribution of the resultant of two normally distributed random variables is presented. This is the so-called generalized Rayleigh distribution which has many applications in the study of wind shear, random noise, and radar. The most general formula was derived, and two special cases were considered for which tables of the moments and probability distribution functions are included as an appendix. One of the special cases was generalized to n-dimensions.

White, R. G.

1975-01-01

56

Mendelian randomization equals instrumental variable analysis with genetic instruments  

OpenAIRE

Interest in instrumental variable (IV) analyses using genetic instruments has been growing over the past 4 years. The background, strength and weaknesses of this approach, which in the epidemiology literature has been referred to as Mendelian randomization, has been recently reviewed by Lawlor et al. (Statist. Med. 2007. DOI: 10.1002/sim.3034). We suggest a change in the nomenclature of Mendelian randomization and discuss issues relevant to IV analysis including instrument validat...

Wehby, George L.; Ohsfeldt, Robert L.; Murray, Jeffrey C.

2008-01-01

57

Casual Stability of Some Systems of Random Variables  

OpenAIRE

Self-similarity of systems is very popular and intensively developing field during last decades. To this field belong so-called stable distributions and their generalization. In Klebanov and Sl\\'amov\\'a (2014) there was given an approach to define additive systems with the property of random self-similarity - casual stability (c.s.). Here we continue study the notion of casual stability for additive systems of random variables (r.v.). We also give a modification of this defi...

Klebanov, Lev B.; Sla?mova?, Lenka; Kakosyan, Ashot; Temnov, Gregory

2014-01-01

58

Class of correlated random networks with hidden variables  

OpenAIRE

We study a class models of correlated random networks in which vertices are characterized by \\textit{hidden variables} controlling the establishment of edges between pairs of vertices. We find analytical expressions for the main topological properties of these models as a function of the distribution of hidden variables and the probability of connecting vertices. The expressions obtained are checked by means of numerical simulations in a particular example. The general model...

Bogun?a?, Maria?n; Pastor-satorras, R.

2003-01-01

59

Estimation of Probability Density Function of a Random Variable for Small Samples  

Directory of Open Access Journals (Sweden)

Full Text Available A theoretical method of estimating the most general form of probability density functions of random variables has been described. The estimated probability density function depends on themean value of exponential dimrbut~ono f the lnlt~arla ndom variable. By the most general form of the probability density function, it is meant that the survivor functions are of exp (-A P or exp (-y P or combinations of these functions for different values of h and y.

V.S. Srinivasan

2004-01-01

60

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.)

61

Distribution of Geometrically Weighted Sum of Bernoulli Random Variables  

OpenAIRE

A new class of distributions over (0,1) is obtained by considering geometrically weighted sum of independent identically distributed (i.i.d.) Bernoulli random variables. An expression for the distribution function (d.f.) is derived and some properties are established. This class of distributions includes U(0,1) distribution.

Deepesh Bhati; Phazamile Kgosi; Ranganath Narayanacharya Rattihalli

2011-01-01

62

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

63

Shape and distribution of Jones and Faddy's skew t random variable  

Directory of Open Access Journals (Sweden)

Full Text Available The purpose of this research is to find another way to generate Jones and Faddy's skew t random variable and to construct quantile table, coefficient of skewness, coefficient of kurtosis and coefficient of variation tables of Jones and Faddy's skew t distribution. Graphs of its probability density function and graphs of its distribution function are also presented. The results of this study show that Jones and Faddy's skew t random variable can be generated from a beta random variable on (-1,1. The coefficients of skewness and kurtosis of the distribution depend on parameters a and b. The coefficient of variation of Jones and Faddy's skew t distribution can be calculated.

Saipornchai, N.

2005-09-01

64

'Mendelian randomization' equals instrumental variable analysis with genetic instruments.  

Science.gov (United States)

Interest in instrumental variable (IV) analyses using genetic instruments has been growing over the past 4 years. The background, strength and weaknesses of this approach, which in the epidemiology literature has been referred to as 'Mendelian randomization', has been recently reviewed by Lawlor et al. (Statist. Med. 2007. DOI: 10.1002/sim.3034). We suggest a change in the nomenclature of 'Mendelian randomization' and discuss issues relevant to IV analysis including instrument validation, motivation of IV analysis and interpretation of IV estimates in order to motivate a more consistent and standard use of IV analysis across applications using genetic instruments. PMID:18344186

Wehby, George L; Ohsfeldt, Robert L; Murray, Jeffrey C

2008-07-10

65

Mendelian randomization equals instrumental variable analysis with genetic instruments  

Science.gov (United States)

SUMMARY Interest in instrumental variable (IV) analyses using genetic instruments has been growing over the past 4 years. The background, strength and weaknesses of this approach, which in the epidemiology literature has been referred to as Mendelian randomization, has been recently reviewed by Lawlor et al. (Statist. Med. 2007. DOI: 10.1002/sim.3034). We suggest a change in the nomenclature of Mendelian randomization and discuss issues relevant to IV analysis including instrument validation, motivation of IV analysis and interpretation of IV estimates in order to motivate a more consistent and standard use of IV analysis across applications using genetic instruments. PMID:18344186

Wehby, George L.; Ohsfeldt, Robert L.; Murray, Jeffrey C.

2009-01-01

66

Separation of the maxima in samples of geometric random variables  

Directory of Open Access Journals (Sweden)

Full Text Available We consider samples of $n$ geometric random variables $omega_1, omega_2 cdotsomega_n$ where $P{omega_j=i}=pq^{i-1}$, for $1leq j leq n$, with $p+q=1$. For each fixed integer $d>0$, we study the probability that the distance between the consecutive maxima in these samples is at least $d$. We derive a probability generating function for such samples and from it we obtain an exact formula for the probability as a double sum. Using Rice's method we obtain asymptotic estimates for these probabilities. As a consequence of these results, we determine the average minimum separation of the maxima, in a sample of $n$ geometric random variables with at least two maxima.

Arnold Knopfmacher

2011-10-01

67

Random Variables in Graph W*-Probability Spaces  

OpenAIRE

In [16], we observed the graph W*-probability theory. In this paper, we will review [16] and introduce special amalgamated random variables in this amalgamated W*-probability space. In particular, we will observe the amalgamated semicircularity, amalgamated evenness and amalgamated R-diagonality. As an example, we will compute the trivial moments and trivial cumulants of the generating operator of the graph W*-algebra.

Cho, Ilwoo

2004-01-01

68

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

69

On the Linear Combination of Exponential and Gamma Random Variables  

Science.gov (United States)

The exact distribution of the linear combination ? X + ? Y is derived when X and Y are exponential and gamma random variables distributed independently of each other. A measure of entropy of the linear combination is investigated. We also provide computer programs for generating tabulations of the percentage points associated with the linear combination. The work is motivated by examples in automation, control, fuzzy sets, neurocomputing and other areas of computer science.

Nadarajah, Saralees; Kotz, Samuel

2005-06-01

70

Random variables : a CAI tutorial in statistics for distance education  

OpenAIRE

Available in Afrikaans only Die navorsingsverslag dokumenteer die instruksionele ontwerpproses van 'n rekenaar gesteunde tutoriaal (RGT), "Random Variables", een van 'n reeks van nege soortgelyke tutoriale wat as aanvulling tot die geskrewe studiegids vir 'n eerstejaar kursus in Statistiek by die Universiteit van Suid?Afrika (Unisa) gebruik word. Die instruksionele benadering wat in die RGT gebruik is, probeer om kognitiewe ondersteuning te verskaf en om 'n intuitiewe begrip van a...

Fresen, Jill Winifred

2001-01-01

71

Designing neural networks that process mean values of random variables  

Science.gov (United States)

We develop a class of neural networks derived from probabilistic models posed in the form of Bayesian networks. Making biologically and technically plausible assumptions about the nature of the probabilistic models to be represented in the networks, we derive neural networks exhibiting standard dynamics that require no training to determine the synaptic weights, that perform accurate calculation of the mean values of the relevant random variables, that can pool multiple sources of evidence, and that deal appropriately with ambivalent, inconsistent, or contradictory evidence.

Barber, Michael J.; Clark, John W.

2014-06-01

72

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

73

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

74

Transport in time-dependent random potentials  

CERN Document Server

The classical dynamics in stationary potentials that are random both in space and time is studied. It can be intuitively understood with the help of Chirikov resonances that are central in the theory of Chaos, and explored quantitatively in the framework of the Fokker-Planck equation. In particular, a simple expression for the diffusion coefficient was obtained in terms of the average power density of the potential. The resulting anomalous diffusion in velocity is classified into universality classes. The general theory was applied and numerically tested for specific examples relevant for optics and atom optics.

Krivolapov, Yevgeny

2012-01-01

75

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

76

Oracle Efficient Variable Selection in Random and Fixed Effects Panel Data Models  

DEFF Research Database (Denmark)

This paper generalizes the results for the Bridge estimator of Huang et al. (2008) to linear random and fixed effects panel data models which are allowed to grow in both dimensions. In particular we show that the Bridge estimator is oracle efficient. It can correctly distinguish between relevant and irrelevant variables and the asymptotic distribution of the estimators of the coefficients of the relevant variables is the same as if only these had been included in the model, i.e. as if an oracle had revealed the true model prior to estimation. In the case of more explanatory variables than observations, we prove that the Marginal Bridge estimator can asymptotically correctly distinguish between relevant and irrelevant explanatory variables. We do this without restricting the dependence between covariates and without assuming sub Gaussianity of the error terms thereby generalizing the results of Huang et al. (2008). Furthermore, the number of relevant variables is allowed to be larger than the sample size.

Kock, Anders Bredahl

2010-01-01

77

Conditional Distribution of Heavy Tailed Random Variables on Large Deviations of their Sum  

OpenAIRE

It is known that large deviations of sums of subexponential random variables are most likely realised by deviations of a single random variable. In this article we give a detailed picture of how subexponential random variables are distributed when a large deviation of their sum is observed.

Armenda?riz, Ine?s; Loulakis, Michail

2009-01-01

78

Variance on the Leaves of a Tree Markov Random Field: Detecting Character Dependencies in Phylogenies  

CERN Document Server

Stochastic models of evolution (Markov random fields on trivalent trees) generally assume that different characters (different runs of the stochastic process) are independent and identically distributed. In this paper we take the first steps towards addressing dependent characters. Specifically we show that, under certain technical assumptions regarding the evolution of individual characters, we can detect any significant, history independent, correlation between any pair of multistate characters. For the special case of the Cavender-Farris-Neyman (CFN) model on two states with symmetric transition matrices, our analysis needs milder assumptions. To perform the analysis, we need to prove a new concentration result for multistate random variables of a Markov random field on arbitrary trivalent trees: we show that the random variable counting the number of leaves in any particular subset of states has variance that is subquadratic in the number of leaves.

Chakrabarty, Deeparnab

2011-01-01

79

Products of free random variables and k-divisible partitions  

CERN Document Server

We derive a formula for the moments and the free cumulants of the multiplication of $k$ free random variables in terms of $k$-equal and $k$-divisible non-crossing partitions. This leads to a new simple proof for the bounds of the right-edge of the support of the free multiplicative convolution $\\mu^{\\boxtimes k}$, given by Kargin which show that the support grows at most linearly with $k$. Moreover, this combinatorial approach generalize the results of Kargin since we do not require the convolved measures to be identical. We also give further applications, such as a new proof of the limit theorem of Sakuma and Yoshida.

Arizmendi, Octavio

2012-01-01

80

k-Divisible random variables in free probability  

OpenAIRE

We introduce and study the notion of k-divisible elements in a non-commutative probability space. A k-divisible element is a (non-commutative) random variable whose n-th moment vanishes whenever n is not a multiple of k. First, we consider the combinatorial convolution \\ast in the lattices NC of non-crossing partitions and NC^k of k-divisible non-crossing partitions and show that convolving k times with the zeta-function in NC is equivalent to convolving once with the zeta-f...

Arizmendi, Octavio

2012-01-01

81

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

82

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, Damin; 10.4204/EPTCS.28.3

2010-01-01

83

Generating Correlated QPSK Waveforms By Exploiting Real Gaussian Random Variables  

KAUST Repository

The design of waveforms with specified auto- and cross-correlation properties has a number of applications in multiple-input multiple-output (MIMO) radar, one of them is the desired transmit beampattern design. In this work, an algorithm is proposed to generate quadrature phase shift- keying (QPSK) waveforms with required cross-correlation properties using real Gaussian random-variables (RVs). This work can be considered as the extension of what was presented in [1] to generate BPSK waveforms. This work will be extended for the generation of correlated higher-order phase shift-keying (PSK) and quadrature amplitude modulation (QAM) schemes that can better approximate the desired beampattern.

Jardak, Seifallah

2012-11-01

84

RETRACTED: The transformation of Random Variables under symmetry  

Directory of Open Access Journals (Sweden)

Full Text Available Reason(s: The authors have plagiarized a scientific research report entitled On the symmetrizing transformation of random variables. The corresponding author Mr. M.T. Uddin was a former student of Professor Chaubeys but that Mr. Uddins studies at Concordia ended on or about 2002. One of the conditions for submission of a paper is that authors declare explicity that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on the matter and we apologize to reader of the journal that this was not detected during the submission process. We thank Professor Yogendra Chaubey and Concordial University for bringing this plagiarism to our attention.

M.T. Uddin

2006-01-01

85

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

86

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

87

A Model for the Estimation of Global Solar Radiation Using Fuzzy Random Variables.  

Science.gov (United States)

In this paper, the concept of fuzzy random variables is applied for the estimation of global solar radiation on a surface at ground level. The cloudiness index is defined as the fraction of extraterrestrial radiation that reaches the earth's surface when the sky above the location of interest is obscured by the cloud cover. The cloud cover at the location of interest during the jth time interval of a day is assumed to follow the fuzzy random phenomenon. The cloudiness index, therefore, is considered as a fuzzy random variable that accounts for the cloud cover at the location of interest during the jth time interval of a day. This variable is assumed to depend on four other fuzzy random variables that, respectively, account for the cloud cover corresponding to the 1) type of cloud group, 2) climatic region, 3) season with most of the precipitation, and 4) type of precipitation at the location of interest during the jth time interval. The method is applied to estimate the monthly mean daily global solar irradiation for four different locations corresponding to four different climatic regions in India. The mean hourly global solar irradiation for the months of January and July and the global solar irradiance on a horizontal surface at Delhi for two typical days are also estimated. The deviations of simulated values with respect to the corresponding observed values are calculated using the mean biased error and root-mean-square error statistical parameters characteristic of long-term and short-term predictive values of the deviations, respectively. For the short-term and long-term performances, the simulated values exhibit maximum deviations of 0.532% and 1.86%, respectively, from the corresponding observed values of monthly mean daily global irradiation at Calcutta. The maximum deviations are 3.204% and 5.845%, respectively, for monthly mean hourly global irradiation at Delhi in January.

Gautam, Nalin K.; Kaushika, N. D.

2002-12-01

88

Some Strong Limit Theorems for Weighted Product Sums of -Mixing Sequences of Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available We study almost sure convergence for -mixing sequences of random variables. Many of the previous results are our special cases. For example, the authors extend and improve the corresponding results of Chen et al. (1996 and Wu and Jiang (2008. We extend the classical Jamison convergence theorem and the Marcinkiewicz strong law of large numbers for independent sequences of random variables to -mixing sequences of random variables without necessarily adding any extra conditions.

Wu Qunying

2009-01-01

89

On the distribution of sums of independent exponential random variables via Wilks' integral representation  

OpenAIRE

In this note we consider an alternative approach to compute the distribution of the sum of independent exponential random variables. In particular, by considering the logarithmic relation between exponential and beta distribution functions and by considering the Wilks integral representation for the product of independent beta random variables, we provide a closed-form expression for the distribution of the sum of independent exponential random variables. The expression we obtain is simple...

Favaro, Stefano

2010-01-01

90

Mass fluctuations and diffusion in time-dependent random environments  

OpenAIRE

A mass ejection model in a time-dependent random environment with both temporal and spatial correlations is introduced. When the environment has a finite correlation length, individual particle trajectories are found to diffuse at large times with a displacement distribution that approaches a Gaussian. The collective dynamics of diffusing particles reaches a statistically stationary state, which is characterized in terms of a fluctuating mass density field. The probability d...

Krstulovic, Giorgio; Bitane, Rehab; Bec, Jeremie

2012-01-01

91

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 reusion approach to reuse the samples, hence, negligible cost. ? No restrictions on the random variable types or limit states.

92

k-Divisible random variables in free probability  

CERN Document Server

We introduce and study the notion of k-divisible elements in a non-commutative probability space. A k-divisible element is a (non-commutative) random variable whose n-th moment vanishes whenever n is not a multiple of k. First, we consider the combinatorial convolution \\ast in the lattices NC of non-crossing partitions and NC^k of k-divisible non-crossing partitions and show that convolving k times with the zeta-function in NC is equivalent to convolving once with the zeta-function in NC^k. Furthermore, when x is k-divisible, we derive a formula for the free cumulants of x^k in terms of the free cumulants of x, involving k-divisible non-crossing partitions. Second, we prove that if a and s are free and s is k-divisible then sps and a are free, whenever p is any polynomial (on a and s) of degree k - 2 on s. Moreover, we define a notion of R-diagonal k-tuples and prove similar results. Next, we show that free multiplicative convolution between a measure concentrated in the positive real line and a probability m...

Arizmendi, Octavio

2012-01-01

93

Automatic Probabilistic Program Verification through Random Variable Abstraction  

Directory of Open Access Journals (Sweden)

Full Text Available 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 precondition semantics for this programs and prove its equivalence.

Damin Barsotti

2010-06-01

94

Confidence intervals for negative binomial random variables of high dispersion.  

Science.gov (United States)

We consider the problem of constructing confidence intervals for the mean of a Negative Binomial random variable based upon sampled data. When the sample size is large, it is a common practice to rely upon a Normal distribution approximation to construct these intervals. However, we demonstrate that the sample mean of highly dispersed Negative Binomials exhibits a slow convergence in distribution to the Normal as a function of the sample size. As a result, standard techniques (such as the Normal approximation and bootstrap) will construct confidence intervals for the mean that are typically too narrow and significantly undercover at small sample sizes or high dispersions. To address this problem, we propose techniques based upon Bernstein's inequality or the Gamma and Chi Square distributions as alternatives to the standard methods. We investigate the impact of imposing a heuristic assumption of boundedness on the data as a means of improving the Bernstein method. Furthermore, we propose a ratio statistic relating the Negative Binomial's parameters that can be used to ascertain the applicability of the Chi Square method and to provide guidelines on evaluating the length of all proposed methods. We compare the proposed methods to the standard techniques in a variety of simulation experiments and consider data arising in the serial analysis of gene expression and traffic flow in a communications network. PMID:21969971

Shilane, David; Evans, Steven N; Hubbard, Alan E

2010-01-01

95

Stimulus variability and processing dependencies in speech perception  

OpenAIRE

Processing dependencies in speech perception between voice and phoneme were investigated using the Garner (1974) speeded classification procedure. Variability in the voice of the talker and in the cues to word-initial consonants were manipulated. The results showed that the processing of a talkers voice and the perception of voicing are asymmetrically dependent. In addition, when stimulus variability was increased in each dimension, the amount of orthogonal interference obtained for each d...

Mullennix, John W.; Pisoni, David B.

1990-01-01

96

The dependence of quasar variability on black hole mass  

CERN Document Server

In order to investigate the dependence of quasar variability on fundamental physical parameters like black hole mass, we have matched quasars from the QUEST1 Variability Survey with broad-lined objects from the Sloan Digital Sky Survey. The matched sample contains approximately 100 quasars, and the Sloan spectra are used to estimate black hole masses and bolometric luminosities. Variability amplitudes are measured from the QUEST1 light curves. We find that black hole mass correlates with several measures of the variability amplitude at the 99% significance level or better. The correlation does not appear to be caused by obvious selection effects inherent to flux-limited quasar samples, host galaxy contamination or other well-known correlations between quasar variability and luminosity/redshift. We evaluate variability as a function of rest-frame time lag using structure functions, and find further support for the variability--black hole mass correlation. The correlation is strongest for time lags of the order...

Wold, M; Shang, Z

2006-01-01

97

CONVERGENCE OF THE FRACTIONAL PARTS OF THE RANDOM VARIABLES TO THE TRUNCATED EXPONENTIAL DISTRIBUTION  

Directory of Open Access Journals (Sweden)

Full Text Available Using the stochastic approximations, in this paper it was studiedthe convergence in distribution of the fractional parts of the sum of random variables to the truncated exponential distribution with parameter lambda. This fact is feasible by means of the Fourier-Stieltjes sequence (FSS of the random variable.

Bogdan Gheorghe Munteanu

2013-01-01

98

The Energy of Convolution of 2-Dimension Exponential Random Variables Base on HaarWavelet  

OpenAIRE

In this paper, through wavelet methods, we obtain the energy of convolution of two-dimension exponential random variables and analyze its some properties of wavelet alternation, and we obtain some new results.

Key words:Exponential random variables; Wavelet alternation; Convolution; Energy

Xia, Xuewen; Dai, Ting

2012-01-01

99

ESEARCH OF THE LAW OF DISTRIBUTION OF THE RANDOM VARIABLE OF THE COMPRESSION  

Directory of Open Access Journals (Sweden)

Full Text Available At research of diagnosing the process of modern automobile engines by means of methods of mathematical statistics the experimental data of the random variable of compression are analysed and it is proved that the random variable of compression has the form of the normal law of distribution.

I. Sarayeva

2011-01-01

100

How fast increasing powers of a continuous random variable converge to Benford's law  

OpenAIRE

It is known that increasing powers of a continuous random variable converge in distribution to Benford's law as the exponent approaches infinity. The rate of convergence has been estimated using Fourier analysis, but we present an elementary method, which is easier to apply and provides a better estimation in the widely studied case of a uniformly distributed random variable.

Wo?jcik, Micha? Ryszard

2013-01-01

101

Array Variate Elliptical Random Variables with Multiway Kronecker Delta Covariance Matrix Structure  

CERN Document Server

Standard statistical methods applied to matrix random variables often fail to describe the underlying structure in multiway data sets. In this paper we will discuss the concept of an array variate random variable and introduce a class of elliptical array densities which have elliptical contours.

Akdemir, Deniz

2011-01-01

102

An Inversion Formula for Orlicz Norms and Sequences of Random Variables  

CERN Document Server

Given an Orlicz function $M$, we show which random variables $\\xi_i$, $i=1,...,n$ generate the associated Orlicz norm, i.e., which random variables yield $\\mathbb{E} \\max\\limits_{1\\leq i \\leq n}|x_i\\xi_i| \\sim \

Christensen, Soeren; Riemer, Stiene

2012-01-01

103

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

104

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 where potential predictor variables vary in their scale of measurement or their number of categories. This is particularly important in genomics and computational biology, where predictors often include variables of different types, for example when predictors include both sequence data and continuous variables such as folding energy, or when amino acid sequence data show different numbers of categories. Results Simulation studies are presented illustrating that, when random forest variable importance measures are used with data of varying types, the results are misleading because suboptimal predictor variables may be artificially preferred in variable selection. The two mechanisms underlying this deficiency are biased variable selection in the individual classification trees used to build the random forest on one hand, and effects induced by bootstrap sampling with replacement on the other hand. Conclusion We propose to employ an alternative implementation of random forests, that provides unbiased variable selection in the individual classification trees. When this method is applied using subsampling without replacement, the resulting variable importance measures can be used reliably for variable selection even in situations where the potential predictor variables vary in their scale of measurement or their number of categories. The usage of both random forest algorithms and their variable importance measures in the R system for statistical computing is illustrated and documented thoroughly in an application re-analyzing data from a study on RNA editing. Therefore the suggested method can be applied straightforwardly by scientists in bioinformatics research.

Hothorn Torsten

2007-01-01

105

Local search methods based on variable focusing for random K -satisfiability  

Science.gov (United States)

We introduce variable focused local search algorithms for satisfiabiliity problems. Usual approaches focus uniformly on unsatisfied clauses. The methods described here work by focusing on random variables in unsatisfied clauses. Variants are considered where variables are selected uniformly and randomly or by introducing a bias towards picking variables participating in several unsatistified clauses. These are studied in the case of the random 3-SAT problem, together with an alternative energy definition, the number of variables in unsatisfied constraints. The variable-based focused Metropolis search (V-FMS) is found to be quite close in performance to the standard clause-based FMS at optimal noise. At infinite noise, instead, the threshold for the linearity of solution times with instance size is improved by picking preferably variables in several UNSAT clauses. Consequences for algorithmic design are discussed.

Lemoy, Rmi; Alava, Mikko; Aurell, Erik

2015-01-01

106

Regression analysis of compositional data when both the dependent variable and independent variable are components  

OpenAIRE

It is well known that regression analyses involving compositional data need special attention because the data are not of full rank. For a regression analysis where both the dependent and independent variable are components we propose a transformation of the components emphasizing their role as dependent and independent variables. A simple linear regression can be performed on the transformed components. The regression line can be depicted in a ternary diagram facilitating the interpretation ...

Ark, L. Andries

2005-01-01

107

Model Building with Multiple Dependent Variables and Constraints  

OpenAIRE

The most widely used method for finding relationships between several quantities is multiple regression. This however is restricted to a single dependent variable. We present a more general method which allows models to be constructed with multiple variables on both sides of an equation and which can be computed easily using a spreadsheet program. The underlying principle (originating from canonical correlation analysis) is that of maximising the correlation between the two ...

Tofallis, Chris

2011-01-01

108

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

109

Nonlinear random wave field in shallow water: variable Korteweg-de Vries framework  

Directory of Open Access Journals (Sweden)

Full Text Available The transformation of a random wave field in shallow water of variable depth is analyzed within the framework of the variable-coefficient Korteweg-de Vries equation. The characteristic wave height varies with depth according to Green's law, and this follows rigorously from the theoretical model. The skewness and kurtosis are computed, and it is shown that they increase when the depth decreases, and simultaneously the wave state deviates from the Gaussian. The probability of large-amplitude (rogue waves increases within the transition zone. The characteristics of this process depend on the wave steepness, which is characterized in terms of the Ursell parameter. The results obtained show that the number of rogue waves may deviate significantly from the value expected for a flat bottom of a given depth. If the random wave field is represented as a soliton gas, the probabilities of soliton amplitudes increase to a high-amplitude range and the number of large-amplitude (rogue solitons increases when the water shallows.

A. Sergeeva

2011-02-01

110

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

Science.gov (United States)

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.

Schlzel, C.; Friederichs, P.

2008-10-01

111

On mean square displacement behaviors of anomalous diffusions with variable and random orders  

International Nuclear Information System (INIS)

Mean square displacement (MSD) is used to characterize anomalous diffusion. Recently, models of anomalous diffusion with variable-order and random-order were proposed, but no MSD analysis has been given so far. The purpose of this Letter is to offer a concise derivation of MSD functions for the variable-order model and the random-order model. Numerical results are presented to illustrate the analytical results. In addition, we show how to establish a variable-random-order model for a given MSD function which has clear application potentials.

112

Bayesian variable selection for spatially dependent generalized linear models  

OpenAIRE

Despite the abundance of methods for variable selection and accommodating spatial structure in regression models, there is little precedent for incorporating spatial dependence in covariate inclusion probabilities for regionally varying regression models. The lone existing approach is limited by difficult computation and the requirement that the spatial dependence be represented on a lattice, making this method inappropriate for areal models with irregular structures that of...

Lum, Kristian

2012-01-01

113

Detection probabilities for random inspection in variable flow situations  

International Nuclear Information System (INIS)

Improvements in the efficiency and effectiveness of inventory-change verification are necessary at certain nuclear facilities, of which one example is low-enriched uranium fuel fabrication facilities. The Safeguards Criteria suggested carrying out interim inventory-change verifications with randomized inspections. This paper describes randomized inspection schemes for inventory change verifications and evaluates the achievable detection probabilities for realistic plant receipt and shipment schedules and stratum residence times as a. function of the inspection frequency and effort and compares these with the existing inspection strategies

114

Conditional large and moderate deviations for sums of discrete random variables. Combinatoric applications  

CERN Document Server

We prove large and moderate deviation principles for the distribution of an empirical mean conditioned by the value of the sum of discrete i.i.d. random variables. Some applications for combinatoric problems are discussed.

Gamboa, Fabrice; Prieur, Clmentine

2007-01-01

115

A New Proof for Monotone Likelihood for the Sum of Independent Bernoulli Random Variables.  

Science.gov (United States)

A new direct and short proof is offered for the monotone likelihood ratio for the sum of independent Bernoulli random variables through use of an inequality by Marcus and Lopes (1957) on elementary symmetric functions. (SLD)

Huynh, Huynh

1994-01-01

116

Correlations between record events in sequences of random variables with a linear trend  

CERN Document Server

The statistics of records in sequences of independent, identically distributed random variables is a classic subject of study. One of the earliest results concerns the stochastic independence of record events. Recently, records statistics beyond the case of i.i.d. random variables have received much attention, but the question of independence of record events has not been addressed systematically. In this paper, we study this question in detail for the case of independent, non-identically distributed random variables, specifically, for random variables with a linearly moving mean. We find a rich pattern of positive and negative correlations, and show how their asymptotics is determined by the universality classes of extreme value statistics.

Wergen, Gregor; Krug, Joachim

2011-01-01

117

Correlations Between Record Events in Sequences of Random Variables with a Linear Trend  

Science.gov (United States)

The statistics of records in sequences of independent, identically distributed random variables is a classic subject of study. One of the earliest results concerns the stochastic independence of record events. Recently, records statistics beyond the case of i.i.d. random variables have received much attention, but the question of independence of record events has not been addressed systematically. In this paper, we study this question in detail for the case of independent, non-identically distributed random variables, specifically, for random variables with a linearly moving mean. We find a rich pattern of positive and negative correlations, and show how their asymptotics is determined by the universality classes of extreme value statistics.

Wergen, Gregor; Franke, Jasper; Krug, Joachim

2011-09-01

118

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

119

Conditional Value-at-Risk for Random Immediate Reward Variables in Markov Decision Processes  

Directory of Open Access Journals (Sweden)

Full Text Available We consider risk minimization problems for Markov decision processes. From a standpoint of making the risk of random reward variable at each time as small as possible, a risk measure is introduced using conditional value-at-risk for random immediate reward variables in Markov decision processes, under whose risk measure criteria the risk-optimal policies are characterized by the optimality equations for the discounted or average case. As an application, the inventory models are considered.

Masayuki Kageyama

2011-09-01

120

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

121

On the Distribution of the Sum of n Non-Identically Distributed Uniform Random Variables  

OpenAIRE

The distribution of the sum of independent identically distributed uniform random variables is well-known. However, it is sometimes necessary to analyze data which have been drawn from different uniform distributions. By inverting the characteristic function, we derive explicit formulae for the distribution of the sum of n non-identically distributed uniform random variables in both the continuous and the discrete case. The results, though involved, have a certain elegance. ...

Bradley, David M.; Gupta, Ramesh C.

2004-01-01

122

Gabapentin Treatment for Alcohol Dependence: A Randomized Controlled Trial  

Science.gov (United States)

Importance Approved medications for alcohol dependence are prescribed for fewer than 9% of US alcoholics. Objective To determine if gabapentin, a widely-prescribed generic calcium channel/GABA modulating medication, increases rates of sustained abstinence and no heavy drinking, and decreases alcohol-related insomnia, dysphoria and craving, in a dose-dependent manner. Design, Participants and Setting A 12-week, double-blind, placebo-controlled, randomized dose-ranging trial of 150 men and women over 18 years of age with current alcohol dependence, conducted 20042010 at a single-site outpatient clinical research facility adjoining a general medical hospital. Interventions Oral gabapentin (0, 900, 1800 mg/d) and concomitant manual-guided counseling. Main Outcome Measures Rates of complete abstinence and no heavy drinking (co-primary) and changes in mood, sleep and craving (secondary) over the 12-week study. Results Gabapentin significantly improved the rates of abstinence and no heavy drinking. The abstinence rate was 4.1% (95% CI, 1.1 to 13.7) in the placebo group, 11.1% (95% CI, 5.2 to 22.2) in the 900 mg group, and 17.0% (95% CI, 8.9 to 30.1) in the 1800 mg group (p = 0.04 for linear dose effect, NNT = 8 for 1800 mg). The no heavy drinking rate was 22.5% (95% CI, 13.6 to 37.2) in the placebo group, 29.6% (95% CI, 19.1 to 42.8) in the 900 mg group, and 44.7% (95% CI, 31.4 to 58.8) in the 1800 mg group (p = 0.02 for linear dose effect, NNT = 5 for 1800 mg). Similar linear dose effects were obtained with measures of mood (F=7.37, df=2, p=0.001), sleep (F=136, df=2, p<0.001), and craving (F=3.56, df=2, p=0.029). There were no serious drug-related adverse events, and terminations from adverse-events (9 of 150 participants), time on study (9.1 [3.8] weeks) and rate of study completion (85 of 150 participants) did not differ between groups. Conclusions and Relevance Gabapentin (particularly the 1800 mg dosage) was effective in treating alcohol dependence and relapse-related symptoms of insomnia, dysphoria and craving, with a favorable safety profile. Increased implementation of pharmacological treatment of alcohol dependence in primary care may be a major benefit of gabapentin as a treatment option for alcohol dependence. PMID:24190578

Mason, Barbara J.; Quello, Susan; Goodell, Vivian; Shadan, Farhad; Kyle, Mark; Begovic, Adnan

2013-01-01

123

The transformed rejection method for generating Poisson random variables  

OpenAIRE

The transformed rejection method, a combination of the inversion and the rejection method, which is used to generate non-uniform random numbers from a variety of continuous distributions can be applied to discrete distributions as well. For the Poisson distribution a short and simple algorithm is obtained which is well suited for large values of the Poisson parameter $\\mu$, even when $\\mu$ may vary from call to call. The average number of uniform deviates required is lower than for any of the...

Ho?rmann, Wolfgang

1992-01-01

124

The Discovery of Timescale-Dependent Color Variability of Quasars  

CERN Document Server

Quasars are variable on timescales from days to years in UV/optical, and generally appear bluer while they brighten. The physics behind the variations in fluxes and colors remains unclear. Using SDSS g and r band photometric monitoring data of quasars in Stripe 82, we find that although the flux variation amplitude increases with timescale, the color variability exhibits opposite behavior. The color variability of quasars is prominent at timescales as short as ~ 10 days, but gradually reduces toward timescales up to years. In other words, the variable emission at shorter timescales is bluer than that at longer timescales. This timescale dependence is clearly and consistently detected at all redshifts from z = 0 to 3.5, thus can not be due to contaminations to broadband photometry from emission lines which do not respond to fast continuum variations. The discovery directly rules out the possibility that simply attributes the color variability to contamination from a non-variable redder component, such as the h...

Sun, Yu-Han; Chen, Xiao-Yang; Zheng, Zhen-Ya

2014-01-01

125

The Discovery of Timescale-dependent Color Variability of Quasars  

Science.gov (United States)

Quasars are variable on timescales from days to years in UV/optical and generally appear bluer while they brighten. The physics behind the variations in fluxes and colors remains unclear. Using Sloan Digital Sky Survey g- and r-band photometric monitoring data for quasars in Stripe 82, we find that although the flux variation amplitude increases with timescale, the color variability exhibits the opposite behavior. The color variability of quasars is prominent at timescales as short as ~10 days, but gradually reduces toward timescales up to years. In other words, the variable emission at shorter timescales is bluer than that at longer timescales. This timescale dependence is clearly and consistently detected at all redshifts from z = 0 to 3.5; thus, it cannot be due to contamination to broadband photometry from emission lines that do not respond to fast continuum variations. The discovery directly rules out the possibility that simply attributes the color variability to contamination from a non-variable redder component such as the host galaxy. It cannot be interpreted as changes in global accretion rate either. The thermal accretion disk fluctuation model is favored in the sense that fluctuations in the inner, hotter region of the disk are responsible for short-term variations, while longer-term and stronger variations are expected from the larger and cooler disk region. An interesting implication is that one can use quasar variations at different timescales to probe disk emission at different radii.

Sun, Yu-Han; Wang, Jun-Xian; Chen, Xiao-Yang; Zheng, Zhen-Ya

2014-09-01

126

Random sets and random fuzzy sets as ill-perceived random variables an introduction for Ph.D. students and practitioners  

CERN Document Server

This short book provides a unified view of the history and theory of random sets and fuzzy random variables, with special emphasis on its use for representing higher-order non-statistical uncertainty about statistical experiments. The authors lay bare the existence of two streams of works using the same mathematical ground, but differing form their use of sets, according to whether they represent objects of interest naturally taking the form of sets, or imprecise knowledge about such objects. Random (fuzzy) sets can be used in many fields ranging from mathematical morphology, economics, artificial intelligence, information processing and statistics per se, especially in areas where the outcomes of random experiments cannot be observed with full precision.This book also emphasizes the link between random sets and fuzzy sets with some techniques related to the theory of imprecise probabilities. This small book is intended for graduate and doctoral students in mathematics or engineering, but also provides an i...

Couso, Ins; Snchez, Luciano

2014-01-01

127

Generating Variable and Random Schedules of Reinforcement Using Microsoft Excel Macros  

Science.gov (United States)

Variable reinforcement schedules are used to arrange the availability of reinforcement following varying response ratios or intervals of time. Random reinforcement schedules are subtypes of variable reinforcement schedules that can be used to arrange the availability of reinforcement at a constant probability across number of responses or time.

Bancroft, Stacie L.; Bourret, Jason C.

2008-01-01

128

Modelling the statistical dependence of rainfall event variables by a trivariate copula function  

Directory of Open Access Journals (Sweden)

Full Text Available In many hydrological models, such as those derived by analytical probabilistic methods, the precipitation stochastic process is represented by means of individual storm random variables which are supposed to be independent of each other. However, several proposals were advanced to develop joint probability distributions able to account for the observed statistical dependence. The traditional technique of the multivariate statistics is nevertheless affected by several drawbacks, whose most evident issue is the unavoidable subordination of the dependence structure assessment to the marginal distribution fitting. Conversely, the copula approach can overcome this limitation, by splitting the problem in two distinct items. Furthermore, goodness-of-fit tests were recently made available and a significant improvement in the function selection reliability has been achieved. Herein a trivariate probability distribution of the rainfall event volume, the wet weather duration and the interevent time is proposed and verified by test statistics with regard to three long time series recorded in different Italian climates. The function was developed by applying a mixing technique to bivariate copulas, which were formerly obtained by analyzing the random variables in pairs. A unique probabilistic model seems to be suitable for representing the dependence structure, despite the sensitivity shown by the dependence parameters towards the threshold utilized in the procedure for extracting the independent events. The joint probability function was finally developed by adopting a Weibull model for the marginal distributions.

M. Balistrocchi

2011-01-01

129

Asymptotics for weakly dependent errors-in-variables  

OpenAIRE

Linear relations, containing measurement errors in input and output data, are taken into account in this paper. Parameters of these so-called errors-in-variables (EIV) models can be estimated by minimizing the total least squares (TLS) of the input-output disturbances. Such an estimate is highly non-linear. Moreover in some realistic situations, the errors cannot be considered as independent by nature. Weakly dependent (\\alpha- and \\phi-mixing) disturbances, which are not ne...

Pes?ta, Michal

2013-01-01

130

Epoch-dependent absorption line profile variability in lambda Cep  

OpenAIRE

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

131

Bayesian Approaches for Limited Dependent Variable Change Point Problems  

OpenAIRE

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

132

Danger: High Power! Exploring the Statistical Properties of a Test for Random Forest Variable Importance  

OpenAIRE

Random forests have become a widely-used predictive model in many scientific disciplines within the past few years. Additionally, they are increasingly popular for assessing variable importance, e.g., in genetics and bioinformatics. We highlight both advantages and limitations of different variable importance scores and associated testing procedures, especially in the context of correlated predictor variables. For the test of Breiman and Cutler (2008), we investigate the statistical propertie...

Strobl, Carolin; Zeileis, Achim

2008-01-01

133

The logistic regression model with response variables subject to randomized response  

OpenAIRE

The univariate and multivariate logistic regression model is discussed where response variables are subject to randomized response (RR). RR is an interviewtechnique that can be used when sensitive questions have to be asked and respondents are reluctant to answer directly. RR variables may be described as misclassified categorical variables where conditional misclassification probabilities are known. The univariate model is revisited and is presented as a generalized linear model. St...

Hout, A. D. L. Den; Heijden, P. G. M.; Gilchrist, Robert

2007-01-01

134

Kernel-Type estimation of bivariate distribution for associated random variables  

OpenAIRE

Let a stationary sequence of associated random variables with uniform distribution on [0,1] and F the distribution function of the random pair (X_1,X_{k+1}), for fixed k. We introduce a kernel estimator for F and study its asymptotic properties and moments, characterizing their convergence rates. From these we derive the optimal rate for the bandwidth, which is of order n up -1. Conditions are also given to ensure that the finite dimensional distributions are asymptotically gaussian.

Azevedo, Ceci?lia Maria; Oliveira, Paulo

2000-01-01

135

Variability for agronomic traits in two random-mating sunflower populations: Means, variance components and heritabilities  

OpenAIRE

Genetic variability of two random-mating sunflower (Helianthus annuus L) populations, Local Open and UAF, was evaluated in two seasons (spring and fall). One hundred S: families selected randomly each population were included in the experiment conducted at Faisalabad (Pakistan). Genotype x environment variances for all traits, especially seed yield, oil yield and the number of achenes per head, were larger in Local Open than in UAF.

Syed Waseem Hassan; Syed Sadaqat Mehdi; Shahida Hasnain

2004-01-01

136

A De Finetti-type theorem for nonexchangeable finite-valued random variables  

Science.gov (United States)

We introduce the concept of a random assignment process (roughly speaking, such a process assigns, according to some weight function, labels to the points of an arbitrary set), and we impose conditions on the weight function ensuring that a De Finetti-type theorem is satisfied. In particular, this provides a wide class of finite-valued random variables which, despite they are neither exchangeable nor identically distributed, verify a De Finetti-type theorem (i.e., they are conditionally independent).

Vlez Ibarrola, Ricardo; Prieto-Rumeau, Toms

2008-11-01

137

Mediation Analysis Without Sequential Ignorability: Using Baseline Covariates Interacted with Random Assignment as Instrumental Variables  

OpenAIRE

In randomized trials, researchers are often interested in mediation analysis to understand how a treatment works, in particular how much of a treatment's effect is mediated by an intermediated variable and how much the treatment directly affects the outcome not through the mediator. The standard regression approach to mediation analysis assumes sequential ignorability of the mediator, that is that the mediator is effectively randomly assigned given baseline covariates and th...

Small, Dylan S.

2011-01-01

138

On a conjecture concerning the sum of independent Rademacher random variables  

OpenAIRE

It is shown that at least 50% of the probability mass of a sum of independent Rademacher random variables is within one standard deviation from its mean. This lower bound is sharp, it is much better than for instance the bound that can be obtained from application of the Chebishev inequality and the bound will have nice applications in finite sampling theory and in random walk theory. This old conjecture is of interest in itself, but has also an appealing reformulation in pr...

Zuijlen, Martien C. A.

2011-01-01

139

Summation of random harmonic vectors in presence of statistic dependencies  

Energy Technology Data Exchange (ETDEWEB)

A method for representing harmonic currents as random vectors, injected into the transmission system from disturbing loads, was discussed. It was shown that optimal rotations of the Cartesian axes in which the random vectors are represented, provide favorable results, reducing to zero the correlation between the vector-resolved components. The rotation effects are also extended to deal with the summation of random vectors with low correlation among them. The method of bivariate joint density is reformulated to simplify solution of integral forms. Results of a variety of numerical experiments on the rotation of Cartesian axes are also discussed. 10 refs., 5 figs.

Marino, P.; Testa, A. [Universita degli Studi di Napoli, Aversa (Italy)

1997-12-31

140

A Fully Polynomial-Time Approximation Scheme for Approximating a Sum of Random Variables  

OpenAIRE

Given $n$ independent random variables $X_1, X_2, ..., X_n$ and an integer $C$, we study the fundamental problem of computing the probability that the sum $X=X_1+X_2+...+X_n$ is at most $C$. We assume that each random variable $X_i$ is implicitly given by an oracle which, given an input value $k$, returns the probability $X_i\\leq k$. We give the first deterministic fully polynomial-time approximation scheme (FPTAS) to estimate the probability up to a relative error of $1\\pm ...

Li, Jian; Shi, Tianlin

2013-01-01

141

Random walk approximation for the radial dose dependence  

International Nuclear Information System (INIS)

We investigate the properties of the radial distribution of energy deposited by ions, calculated using a random walk approach, which is an important analytical tool for solving transport problems. This investigation is motivated by the desire to understand the range of applicability of the random walk approximation for problems related to radiation damage assessment. We study the radial dose at small and moderate distances and compare our results to the results of Monte Carlo simulations. (authors)

142

Nonlinear random wave field in shallow water: variable Korteweg-de Vries framework  

OpenAIRE

The transformation of a random wave field in shallow water of variable depth is analyzed within the framework of the variable-coefficient Korteweg-de Vries equation. The characteristic wave height varies with depth according to Green's law, and this follows rigorously from the theoretical model. The skewness and kurtosis are computed, and it is shown that they increase when the depth decreases, and simultaneously the wave state deviates from the Gaussian. The probability of large-amplitude (r...

Sergeeva, A.; Pelinovsky, E.; Talipova, T.

2011-01-01

143

Model selection and randomization for weakly dependent time series forecasting  

CERN Document Server

Observing a stationary time series, we propose in this pape new procedures in two steps for the prediction of the next value of the time series. Following machine learning theory paradigm, the first step consists in determining randomized estimators, or "experts", in (possibly numerous) different predictive models. In the second step estimators are obtained by model selection or randomization associated with exponential weights of these experts. We prove Oracle inequalities for both estimators and provide some applications for linear, artificial Neural Networks and additive non-parametric predictors.

Alquier, Pierre

2009-01-01

144

Array Variate Skew Normal Random Variables with Multiway Kronecker Delta Covariance Matrix Structure  

CERN Document Server

In this paper, we will discuss the concept of an array variate random variable and introduce a class of skew normal array densities that are obtained through a selection model that uses the array variate normal density as the kernel and the cumulative distribution of the univariate normal distribution as the selection function.

Akdemir, Deniz

2011-01-01

145

Sums and Products of Jointly Distributed Random Variables: A Simplified Approach  

Science.gov (United States)

Three basic theorems concerning expected values and variances of sums and products of random variables play an important role in mathematical statistics and its applications in education, business, the social sciences, and the natural sciences. A solid understanding of these theorems requires that students be familiar with the proofs of these

Stein, Sheldon H.

2005-01-01

146

Probability Inequalities for the Sum of Random Variables When Sampling Without Replacement  

Directory of Open Access Journals (Sweden)

Full Text Available Exponential-type upper bounds are formulated for the probability that the maximum of the partial sample sums of discrete random variables having finite equispaced support exceeds or differs from the population mean by a specified positive constant. The new inequalities extend the work of Serfling (1974. An example of the results are given to demonstrate their efficacy.

Kent Riggs

2013-08-01

147

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

148

New alphabet-dependent morphological transition in random RNA alignment.  

Science.gov (United States)

We study the fraction f of nucleotides involved in the formation of a cactuslike secondary structure of random heteropolymer RNA-like molecules. In the low-temperature limit, we study this fraction as a function of the number c of different nucleotide species. We show, that with changing c, the secondary structures of random RNAs undergo a morphological transition: f(c)?1 for c?c(cr) as the chain length n goes to infinity, signaling the formation of a virtually perfect gapless secondary structure; while f(c)c(cr), which means that a nonperfect structure with gaps is formed. The strict upper and lower bounds 2?c(cr)?4 are proven, and the numerical evidence for c(cr) is presented. The relevance of the transition from the evolutional point of view is discussed. PMID:23031133

Valba, O V; Tamm, M V; Nechaev, S K

2012-07-01

149

Is transport in time-dependent random potentials universal ?  

OpenAIRE

The growth of the average kinetic energy of classical particles is studied for potentials that are random both in space and time. Such potentials are relevant for recent experiments in optics and in atom optics. It is found that for small velocities uniform acceleration takes place, and at a later stage fluctuations of the potential are encountered, resulting in a regime of anomalous diffusion. This regime was studied in the framework of the Fokker-Planck approximation. The ...

Krivolapov, Yevgeny; Fishman, Shmuel

2012-01-01

150

Maximum likelihood algorithm for PET image reconstruction based on fuzzy random variable.  

Science.gov (United States)

This work presents a new iterative method for reconstructing positron emission tomography (PET) images. Unlike conventional maximum likelihood-expectation maximization (MLEM), this method intends to introduce the fuzzy set principle to MLEM algorithm. In this work, the noncognitive uncertainty of the observed projection data are described by their probability density function; whereas the cognitive uncertainty of a random variable can be described by the membership function for its fuzziness. The mean of the observed projection data are regard as fuzzy random variables because of the complexity of system. The fuzzy random variable can be represented by a triangular membership function. We establish a joint probability density function that includes the effects of both fuzziness and randomness. The maximum likelihood approach is used to estimate the image vector. The order subset (OS), rescaled block-iterative (RBI), and row-action (RA) techniques are applied to our PET reconstructed method to speed up the convergence rate and to decrease the iteration numbers. PMID:17271945

Zhu, H Q; Shu, H Z; Zhou, J; Luo, L M

2004-01-01

151

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

152

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

153

Band-phase-randomized surrogate data reveal high-frequency chaos in heart rate variability  

OpenAIRE

We propose a new band-phase-randomized surrogate data method to evaluate the chaotic dynamics in the high (HF) and low frequency (LF) bands of heart rate variability (HRV) in healthy subjects. The chaotic strength of normal HRV as assessed by a noise titration assay completely vanished when its power spectrum was phase-randomized over the entire frequency band or the HF band alone, but not the LF band alone. This finding confirms recent evidence that chaotic dynamics in normal HRV is ascribab...

Li, Cheng; Ding, Guang-hong; Wu, Guo-qiang; Poon, Chi-sang

2009-01-01

154

Universality classes of transport in time-dependent random potentials  

Science.gov (United States)

The growth of the average kinetic energy of classical particles is studied for potentials that are random both in space and time. Such potentials are relevant for recent experiments in optics and in atom optics. It is found that for small velocities uniform acceleration takes place, and at a later stage fluctuations of the potential are encountered, resulting in a regime of anomalous diffusion. This regime was studied in the framework of the Fokker-Planck approximation. The diffusion coefficient in velocity was expressed in terms of the average power spectral density, which is the Fourier transform of the potential correlation function. This enabled to establish a scaling form for the Fokker-Planck equation and to compute the large and small velocity limits of the diffusion coefficient. A classification of the random potentials into universality classes, characterized by the form of the diffusion coefficient in the limit of large and small velocity, was performed. It was shown that one-dimensional systems exhibit a large variety of universality classes, contrary to systems in higher dimensions, where only one universality class is possible. The relation to Chirikov resonances, which are central in the theory of chaos, was demonstrated. The general theory was applied and numerically tested for specific physically relevant examples.

Krivolapov, Yevgeny; Fishman, Shmuel

2012-09-01

155

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

156

Cluster-size dependent randomization traffic flow model  

Science.gov (United States)

In order to exhibit the meta-stable states, several slow-to-start rules have been investigated as modification to Nagel-Schreckenberg (NS) model. These models can reproduce some realistic phenomena which are absent in the original NS model. But in these models, the size of cluster is still not considered as a useful parameter. In real traffic, the slow-to-start motion of a standing vehicle often depends on the degree of congestion which can be measured by the clusters' size. According to this idea, we propose a cluster-size dependent slow-to-start model based on the speed-dependent slow-to-start rule (VDR) model. It gives expected results through simulations. Comparing with the VDR model, our new model has a better traffic efficiency and shows richer complex characters.

Gao, Kun; Wang, Bing-Hong; Fu, Chuan-Ji; Lu, Yu-Feng

2007-11-01

157

Random Forests for Metric Learning with Implicit Pairwise Position Dependence  

CERN Document Server

Metric learning makes it plausible to learn distances for complex distributions of data from labeled data. However, to date, most metric learning methods are based on a single Mahalanobis metric, which cannot handle heterogeneous data well. Those that learn multiple metrics throughout the space have demonstrated superior accuracy, but at the cost of computational efficiency. Here, we take a new angle to the metric learning problem and learn a single metric that is able to implicitly adapt its distance function throughout the feature space. This metric adaptation is accomplished by using a random forest-based classifier to underpin the distance function and incorporate both absolute pairwise position and standard relative position into the representation. We have implemented and tested our method against state of the art global and multi-metric methods on a variety of data sets. Overall, the proposed method outperforms both types of methods in terms of accuracy (consistently ranked first) and is an order of ma...

Xiong, Caiming; Xu, Ran; Corso, Jason J

2012-01-01

158

Optimization of Reorder Point Strategy of Assembly Manufacturer with Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available For assembly system, randomness and variableness make it impossible to control the inventory accuratelyspecially. Because the negative effect of them have ripple effects. So we investigate reorder point optimizationstrategy of assembly manufacturing system with random demand and random lead time. We seek themanufacturers order strategy for the minimum integration of the supply chain inventory cost. And we use scalebenefits parameters of suppliers in this system to reflect actual influence of the lots scale. Numerical example oftwo components assembly system is given to illustrate the effectiveness of the reorder point strategy. From thenumerical simulation, it is can be seen backorder rate and order scale effect will impact the total supply chaincost dramatically.

Shuangyan Li

2013-02-01

159

Ultraviolet variability of quasars: dependence on the accretion rate  

CERN Document Server

We compiled a catalogue of about 4000 SDSS quasars including individual estimators V for the variability strength, virial black hole masses M, and mass accretion rates dM/dt from the Davis-Laor scaling relation. We confirm significant anti-correlations between V and dM/dt, the Eddington ratio, and the bolometric luminosity L, respectively. 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 and show that this trend is most likely produced by selection effects in combination with the mass errors and the use of the scaling relation for dM/dt. The anti-correlations found for V cannot be explained in such a way. The strongest anti-correlation is found with dM/dt. However, it is difficult to decide which of the quantities (L, Eddington ratio, dM/dt) is intrinsically correlated with V and which of the observed correlations are produced by the relations between these quantities. A V-dM/dt an...

Meusinger, H

2013-01-01

160

A Classification Study of Respiratory Syncytial Virus (RSV) Inhibitors by Variable Selection with Random Forest  

OpenAIRE

Experimental pEC50s for 216 selective respiratory syncytial virus (RSV) inhibitors are used to develop classification models as a potential screening tool for a large library of target compounds. Variable selection algorithm coupled with random forests (VS-RF) is used to extract the physicochemical features most relevant to the RSV inhibition. Based on the selected small set of descriptors, four other widely used approaches, i.e., support vector machine (SVM), Gaussian process (GP), linear di...

Shuwei Zhang; Yonghua Wang; Yan Li; Ming Hao

2011-01-01

161

Intraspecific Variability within Globodera tabacum solanacearum Using Random Amplified Polymorphic DNA  

OpenAIRE

Random amplified polymorphic DNA (RAPDs) were used to investigate the intraspecific variability among 19 geographic isolates of Globodera tabacum solanacearum from eight counties in Virginia and one county in North Carolina. Globodera tabacum tabacum, G. t. virginiae, and the Mexican cyst nematode (MCN) were included as outgroups. Six primers were used and 119 amplification products were observed. Each primer yielded reproducible differences in fragment patterns that differentiated the isolat...

Syracuse, A. J.; Johnson, C. S.; Eisenback, J. D.; Nessler, C. L.; Smith, E. P.

2004-01-01

162

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

OpenAIRE

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 w...

Malley James D; Nicodemus Kristin K; Strobl Carolin; Ziegler Andreas

2010-01-01

163

Parameter estimation for sums of correlated gamma random variables. Application to anomaly detection in Internet Traffic  

OpenAIRE

A new family of distributions, constructed by summing correlated gamma random variables, is studied. First, a simple closed-form expression for their density is derived. Second, the three parameters characterizing such a density are estimated by using the maximum likelihood (ML) principle. Numerical simulation are conducted to compare the performance of the ML estimator against those of the conventional estimator of moments. Finally, a multiresolution multivariate gamma based modeling of Inte...

Florent, Chatelain; Borgnat, Pierre; Tourneret, Jean-yves; Abry, Patrice

2008-01-01

164

On exchangeable random variables and the statistics of large graphs and hypergraphs  

OpenAIRE

De Finetti's classical result of [18] identifying the law of an exchangeable family of random variables as a mixture of i.i.d. laws was extended to structure theorems for more complex notions of exchangeability by Aldous [1,2,3], Hoover [41,42], Kallenberg [44] and Kingman [47]. On the other hand, such exchangeable laws were first related to questions from combinatorics in an independent analysis by Fremlin and Talagrand [29], and again more recently in Tao [62], where they ...

Austin, Tim

2008-01-01

165

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

2014-12-01

166

Notes on the sum and maximum of independent exponentially distributed random variables with different scale parameters  

OpenAIRE

We consider the distribution of the sum and the maximum of a collection of independent exponentially distributed random variables. The focus is laid on the explicit form of the density functions (pdf) of non-i.i.d. sequences. Those are recovered in a simple and direct way based on conditioning. A connection between the pdf and a representation of the convolution characteristic function as a linear combination of the single characteristic functions is drawn. It is demonstrate...

Bibinger, Markus

2013-01-01

167

On schur-convexity of expectation of weighted sum of random variables with applications  

OpenAIRE

We show that the expectation of a class of functions of the sum of weighted identically independent distributed positive random variables is Schur-concave with respect to the weights. Furthermore, we optimise the expectation by choosing extra-weights with a sum constraint. We show that under this optimisation the expectation becomes Schur-convex with respect to the weights. Finally, we explain the connection to the ergodic capacity of some multiple-antenna wireless communication systems with ...

Boche, H.; Jorswieck, Eduard A.

2004-01-01

168

On the ratio of Pearson type VII and Bessel random variables  

Directory of Open Access Journals (Sweden)

Full Text Available The exact distribution of the ratio |X/Y| is derived when X and Y are, respectively, Pearson type VII and Bessel function random variables distributed independently of each other. The work is motivated by previously published approximate relationships between these two distributions. An application of the result is provided by computing “correction factors” for some of these approximations.

Saralees Nadarajah

2005-01-01

169

On the dimensions of conformal repellers. Randomness and parameter dependency  

OpenAIRE

Bowen's formula relates the Hausdorff dimension of a conformal repeller to the zero of a `pressure' function. We present an elementary, self-contained proof which bypasses measure theory and the Thermodynamic Formalism to show that Bowen's formula holds for $C^1$ conformal repellers. We consider time-dependent conformal repellers obtained as invariant subsets for sequences of conformally expanding maps within a suitable class. We show that Bowen's formula generalizes to such...

Rugh, Hans Henrik

2004-01-01

170

Seasonal Dependency of Bi-Decadal Precipitation Variability  

Science.gov (United States)

Seasonal dependency of precipitation variability on a bi-decadal timescale and associated atmospheric circulation anomalies over the Pacific Ocean are investigated using NCEP/NCAR reanalysis data for a period from 1949-2001. We estimated bi-decadal variability of precipitation by calculating regression coefficients between the bidecadal filtered (pass-band of 10-30-year periods) reanalysis data and a representative time series of the Bi-Decadal Oscillation (BDO). As the representative BDO time series, we use wintertime North Pacific Index (NPI), which is a sea level pressure time series, averaged over the Aleutian Lows. The regression map reveals a precipitation band with positive regressions across the Tropical Pacific (EQ-20N) from autumn to spring. The tropical precipitation band is consistent with gauge data and satellite estimates. In winter, more energetic precipitation changes also occur in the mid-latitude North Pacific with the positive regressions over the northern (50-70N) North Pacific and negative regressions in the central North Pacific (30-50N) as shown by Minobe and Nakanowari (2002, GRL) in addition to the equatorial precipitation change. In order to know the mechanisms of the bi-decadal precipitation changes, we perform a humidity-flux analysis using the reanalysis data. On the bi-decadal time scale, the precipitation anomalies can be approximately explained by the sum of horizontal humidity flux convergence and evaporation anomalies. For the tropical band, the humidity flux convergence has similar amplitudes to the evaporation in autumn and spring seasons, but dominate in winter season. In mid-latitudes, the wintertime precipitation anomalies are well explained by the humidity convergence. The humidity-flux convergences in mid-latitudes are due to anomalous geostrophic winds over climatological humidity gradients, and wind anomalies are essentially non-divergent. On the other hand, humidity-flux convergences in the tropics are resulted from surface wind convergence due to ageostrophic wind components. The difference of the convergence mechanism between mid-latitude and tropics results in that relatively small sea-level pressure anomalies in the tropics yield large humidity-flux convergences. The tropical pressure fluctuations are much smaller than those in mid-latitudes, but cannot be ignored for the bi-decadal precipitation changes.

Nakanowatari, T.; Minobe, S.

2002-12-01

171

Random and systematic spatial variability of 137Cs inventories at reference sites in South-Central Brazil  

Directory of Open Access Journals (Sweden)

Full Text Available The precision of the 137Cs fallout redistribution technique for the evaluation of soil erosion rates is strongly dependent on the quality of an average inventory taken at a representative reference site. The knowledge of the sources and of the degree of variation of the 137Cs fallout spatial distribution plays an important role on its use. Four reference sites were selected in the South-Central region of Brazil which were characterized in terms of soil chemical, physical and mineralogical aspects as well as the spatial variability of 137Cs inventories. Some important differences in the patterns of 137Cs depth distribution in the soil profiles of the different sites were found. They are probably associated to chemical, physical, mineralogical and biological differences of the soils but many questions still remain open for future investigation, mainly those regarding the adsorption and dynamics of the 137Cs ions in soil profiles under tropical conditions. The random spatial variability (inside each reference site was higher than the systematic spatial variability (between reference sites but their causes were not clearly identified as possible consequences of chemical, physical, mineralogical variability, and/or precipitation.

Correchel Vladia

2005-01-01

172

Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk  

CERN Document Server

We model the time variability of ~9,000 spectroscopically confirmed quasars in SDSS Stripe 82 as a damped random walk. Using 2.7 million photometric measurements collected over 10 years, we confirm the results of Kelly et al. (2009) and Koz{\\l}owski et al. (2010) that this model can explain quasar light curves at an impressive fidelity level (0.01-0.02 mag). The damped random walk model provides a simple, fast [O(N) for N data points], and powerful statistical description of quasar light curves by a characteristic time scale (tau) and an asymptotic rms variability on long time scales (SF_inf). We searched for correlations between these two variability parameters and physical parameters such as luminosity and black hole mass, and rest-frame wavelength. We find that tau 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 power law index of 0.21+/-0.07. The amplitude of variability is anti-co...

MacLeod, C L; Kochanek, C S; Koz?owski, S; Kelly, B; Bullock, E; Kimball, A; Sesar, B; Westman, D; Brooks, K; Gibson, R; Becker, A; de Vries, W H

2010-01-01

173

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.

Krigrd, Thomas; Gaist, David

2014-01-01

174

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 Cramr-Rao bound.

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

2014-10-01

175

Marcinkiewicz strong laws for linear statistics of rho*-mixing sequences of random variables  

Directory of Open Access Journals (Sweden)

Full Text Available Strong laws are established for linear statistics that are weighted sums of a random sample. We show extensions of the Marcinkiewicz-Zygmund strong laws under certain moment conditions on both the weights and the distribution. These not only generalize the result of Bai and Cheng (2000, Statist Probab Lett 46: 105-112 to rho*-mixing sequences of random variables, but also improve them.Leis fortes so estabelecidas para estatsticas lineares que so somas ponderadas de uma amostra aleatria. Mostramos extenses das leis fortes de Marcinkiewicz-Zygmund sob certas condies tanto nos pesos quanto na distribuio. Estas ltimas no s generalizam o resultado de Bai e Cheng (2000, Statist Probab Lett 46: 105-112 para sequncias aleatrias "ro*-mixing" como tambm o melhoram.

Guang-Hui Cai

2006-12-01

176

Marcinkiewicz strong laws for linear statistics of rho*-mixing sequences of random variables  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Leis fortes so estabelecidas para estatsticas lineares que so somas ponderadas de uma amostra aleatria. Mostramos extenses das leis fortes de Marcinkiewicz-Zygmund sob certas condies tanto nos pesos quanto na distribuio. Estas ltimas no s generalizam o resultado de Bai e Cheng (2000, Sta [...] tist Probab Lett 46: 105-112) para sequncias aleatrias "ro*-mixing" como tambm o melhoram. Abstract in english Strong laws are established for linear statistics that are weighted sums of a random sample. We show extensions of the Marcinkiewicz-Zygmund strong laws under certain moment conditions on both the weights and the distribution. These not only generalize the result of Bai and Cheng (2000, Statist Prob [...] ab Lett 46: 105-112) to rho*-mixing sequences of random variables, but also improve them.

Guang-Hui, Cai.

2006-12-01

177

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.

Andr Adler

1990-01-01

178

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

OpenAIRE

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.

Andr Adler

1990-01-01

179

Logarithmic Lambert $\\mathrm{W}\\times {\\cal F}$ random variables for the family of chi-squared distributions and their applications  

OpenAIRE

We introduce a class of logarithmic Lambert W random variables for a specific family of distributions. In particular, we characterize the log-Lambert W random variables for chi-squared distributions which naturally appear in the likelihood based inference of normal random variables.

Witkovsky?, Viktor; Wimmer, Gejza; Duby, Tomy

2014-01-01

180

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

181

Heart rate variability during sleep in detoxified alcohol-dependent males: A comparison with healthy controls  

Science.gov (United States)

Context: Alcohol dependence can lead to autonomic neuropathy resulting in increased cardiac morbidity and mortality. This has previously been evaluated using heart-rate variability. Aims: We compared sleep heart-rate variability of alcohol-dependent patients with that of healthy controls in this study. Settings and Design: This study was conducted at NIMHANS, Bangalore. A case control study design was adopted. Materials and Methods: Sleep heart-rate variability of 20 male alcohol-dependent inpatients was recorded on the 5th day after detoxification. Sleep heart-rate variability was also recorded in 18 age- and gender-matched healthy controls. Statistical Analysis: The groups were compared using t-test for continuous variables and Chi-squared test for discrete variables. Results: Both time and frequency domain measures were significantly lower in the patients as compared to the controls, indicating decreased HRV in alcohol-dependent individuals. Conclusions: Decreased HRV in alcohol dependence indicates potential autonomic neuropathy. PMID:23825854

Ganesha, Suhas; Thirthalli, Jagadisha; Muralidharan, Kesavan; Benegal, Vivek; Gangadhar, Bangalore N.

2013-01-01

182

Records and sequences of records from random variables with a linear trend  

International Nuclear Information System (INIS)

We consider records and sequences of records drawn from discrete time series of the form Xn = Yn + cn, where the Yn are independent and identically distributed random variables and c is a constant drift. For very small and very large drift velocities, we investigate the asymptotic behavior of the probability pn(c) of a record occurring in the nth step and the probability PN(c) that all N entries are records, i.e. that X12N. Our work is motivated by the analysis of temperature time series in climatology, and by the study of mutational pathways in evolutionary biology

183

On the LP-convergence for multidimensional arrays of random variables  

Directory of Open Access Journals (Sweden)

Full Text Available For a d-dimensional array of random variables {Xn,n∈ℤ+d} such that {|Xn|p,n∈ℤ+d} is uniformly integrable for some 0

Le Van Thanh

2005-06-01

184

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

185

Aleatoriedade e variabilidade produtiva de feijo-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 feijo-de-vagem, foram realizados os seguintes experimentos em branco: 1) em estufa no outono-inverno; 2) em tnel no outono-inverno; 3) em ambiente no protegido no outono-inverno; 4) em tnel na primavera-vero; e 5) em ambie [...] nte no protegido na primavera-vero. A varivel 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 varincias entre as fileiras de cultivo e entre as colheitas, e testes de aleatoriedade em cada fileira de cultivo. A no aleatoriedade e a variabilidade da produo de fitomassa fresca de vagens so maiores em condies meteorolgicas adversas a cultura do feijo-de-vagem e diminuem com o aumento do tamanho de parcela. O uso de parcelas constitudas por seis unidades bsicas (12 plantas), em ambiente protegido ou no protegido, torna a produo de fitomassa fresca de vagens aleatria 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, Lcio; Sidinei Jos, Lopes; Alberto, Cargnelutti Filho; Vilson, Benz.

1147-11-01

186

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

187

Quantum chaotic scattering in time-dependent external fields: random matrix approach  

CERN Document Server

We review the random matrix description of electron transport through open quantum dots, subject to time-dependent perturbations. All characteristics of the current linear in the bias can be expressed in terms of the scattering matrix, calculated for a time-dependent Hamiltonian. Assuming that the Hamiltonian belongs to a Gaussian ensemble of random matrices, we investigate various statistical properties of the direct current in the ensemble. Particularly, even at zero bias the time-dependent perturbation induces current, called photovoltaic current. We discuss dependence of the photovoltaic current and its noise on the frequency and the strength of the perturbation. We also describe the effect of time-dependent perturbation on the weak localization correction to the conductance and on conductance fluctuations.

Vavilov, M G

2005-01-01

188

Statistical characterization of the random errors in the radioimmunoassay dose--response variable.  

Science.gov (United States)

We have developed practical methods for evaluating the magnitude of the random errors in radioimmunoassay dose--response variables, and the relationship between this error and position on the dose--response curve. This is important: to obtain appropriate weights for each point on the dose--response curve when utilizing least-squares curve-fitting methods; to evaluate whether the standards and the unknowns are subject to error of the same magnitude; for quality-control purposes; and to study the sources of errors in radioimmunoassay. Both standards and unknowns in radioimmunoassays for cAMP and cGMP were analyzed in triplicate. The same mean (Y), sample standard deviation, sy, and variance (2-y) of the response variable were calculated for each dose level. The relationship between s 2-y and y was calculated utilizing several models. Results for standards and unknowns from several assays were pooled, and a curve smoothing procedure was used to minimize random sampling errors. This pooling increased the reliability of the analysis, and confirmed the presence of the theoretically predicted nonuniformity of variance. Thus, the calculation of results from these radioimmunoassays should utilize a weighted least-squares curve-fitting program. These analyses have been computerized, and can be used as a "pre-processor" for programs for routine analysis of results of radioimmunoassay. PMID:175978

Rodbard, D; Lenox, R H; Wray, H L; Ramseth, D

1976-03-01

189

The Energy-Dependence of GRB Minimum Variability Timescales  

CERN Document Server

We constrain the minimum variability timescales for 938 GRBs observed by the Fermi/GBM instrument prior to July 11, 2012. The tightest constraints on progenitor radii derived from these timescales are obtained from light curves in the hardest energy channel. In the softer bands -- or from measurements of the same GRBs in the hard X-rays from Swift -- we show that variability timescales tend to be a factor 2--3 longer. Applying a survival analysis to account for detections and upper limits, we find median minimum timescale in the rest frame for long-duration and short-duration GRBs of 45 ms and 10 ms, respectively. Fewer than 10% of GRBs show evidence for variability on timescales below 2 ms. These shortest timescales require Lorentz factors $\\gtrsim 400$ and imply typical emission radii $R \\approx 1 {\\times} 10^{14}$ cm for long-duration GRBs and $R \\approx 3 {\\times} 10^{13}$ cm for short-duration GRBs. We discuss implications for the GRB fireball model and investigate whether GRB minimum timescales evolve w...

Golkhou, V Zach; Littlejohns, Owen M

2015-01-01

190

Operator dependent variability in quantitative analysis of myocardial perfusion images.  

Science.gov (United States)

The purpose of this study was to evaluate variability in the quantification of myocardial perfusion images obtained by a group of experienced operators using two widely used programs. The Cedars Emory quantitative analysis program (CEqual) was used to quantify the size of perfusion defects and the Cedars-Sinai quantitative gated single-photon emission tomography program was used to quantify left ventricular function. Five patients with reversible apical defects, five with fixed apical defects and three patients with normal perfusion were selected. Eight experienced medical laboratory technologists processed the studies from raw projection data. The manual steps consisted of defining two alignment axes parallel to the long axis of the left ventricle, and for the CEqual program selecting apex and base in the short axis slices in the rest and stress studies. Wide variability between the operators in the quantification of reversibility could be seen in all three vascular territories. A range >10% was found in at least one vascular territory for nine of the 13 patients. The differences in left ventricular ejection fraction (LVEF) between operators were perfusion defects may influence the clinical interpretation and cause false conclusions. In contrast, inter-operator variability for the quantification of the LVEF was low. PMID:15522047

Akesson, L; Svensson, A; Edenbrandt, L

2004-11-01

191

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.)

192

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

193

Blobs in Wolf-Rayet Winds Random Photometric and Polarimetric Variability  

CERN Document Server

Some isolated Wolf-Rayet stars present random variability in their optical flux and polarization. We make the assumption that such variability is caused by the presence of regions of enhanced density, i.e. blobs, in their envelopes. In order to find the physical characteristics of such regions we have modeled the stellar emission using a Monte Carlo code to treat the radiative transfer in an inhomogeneous electron scattering envelope. We are able to treat multiple scattering in the regions of enhanced density as well as in the envelope itself. The finite sizes of the source and structures in the wind are also taken into account. Most of the results presented here are based on a parameter study of models with a single blob. The effects due to multiple blobs in the envelope are considered to a more limited extent. Our simulations indicate that the density enhancements must have a large geometric cross section in order to produce the observed photopolarimetric variability. The sizes must be of the order of one s...

Rodrigues, C V; Rodrigues, Claudia V.

2000-01-01

194

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

195

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

OpenAIRE

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 1

Seok Yoon Hwang; Dug Hun Hong

1999-01-01

196

A Methodological Note on the Convergence of Sequences of Random Variables  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this note is to present a new point of view for introducing all well-known modes of convergence of sequences of random variables. In the one hand, we start from two noteworthy sets in convergence viz $T_{j,\\epsilon}$ and $S_{j,\\epsilon}$. The consideration of certain progressive assumptions on both $T_{j,\\epsilon}$ and $S_{j,\\epsilon}$ gives rise to a part of convergence concepts going from uniform convergence to convergence in probability. On the other hand, some key inequalities implies the rest of convergence concepts whose link with the former scheme lies in uniform and in probability convergence which end the circle of convergence modes. Moreover, all these steps are illustrated with their respective methodological charts.

Salvador Cruz Rambaud

2012-10-01

197

Similarity of Fuzzy Sets and Dominance of Random Variables: a Quest for Transitivity  

Science.gov (United States)

We present several relational frameworks for expressing similarities and preferences in a quantitative way. The main focus is on the occurrence of various types of transitivity in these frameworks. The first framework is that of fuzzy relations; the corresponding notion of transitivity is C-transitivity, with C a conjunctor. We discuss two approaches to the measurement of similarity of fuzzy sets: a logical approach based on biresidual operators and a cardinal approach based on fuzzy set cardinalities. The second framework is that of reciprocal relations; the corresponding notion of transitivity is cycle-transitivity. It plays a crucial role in the description of different types of transitivity arising in the comparison of random variables in terms of winning probabilities.

de Baets, Bernard

198

Records and sequences of records from random variables with a linear trend  

CERN Document Server

We consider records and sequences of records drawn from discrete time series of the form $X_{n}=Y_{n}+cn$, where the $Y_{n}$ are independent and identically distributed random variables and $c$ is a constant drift. For very small and very large drift velocities, we investigate the asymptotic behavior of the probability $p_n(c)$ of a record occurring in the $n$th step and the probability $P_N(c)$ that all $N$ entries are records, i.e. that $X_1 < X_2 < ... < X_N$. Our work is motivated by the analysis of temperature time series in climatology, and by the study of mutational pathways in evolutionary biology.

Franke, Jasper; Krug, Joachim

2010-01-01

199

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 simultaneouslythe 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

200

Dopant size dependent variable range hopping conduction in polyaniline nanorods  

Science.gov (United States)

The present work investigates the electrical transport and dielectric relaxation of polyaniline (PAni) nanorods doped with organic camphorsulfonic acid (CSA) and inorganic hydrochloric acid (HCl) synthesized by interfacial polymerization technique. High resolution transmission electron micrographs (HRTEM) depict that initially spherical nuclei directionally grow into nanorods and CSA doped PAni produces more uniform and aligned structures. The electrical transport studies reveal that the CSA doped nanorods follow 1D Mott variable-range hopping (VRH), whereas the HCl doped nanorods exhibit 2D VRH conduction mechanism. The value of interchain charge transfer integral is found to be higher for smaller size HCl doped PAni than that for larger size CSA doped PAni. The resistivity measurements exhibit semiconducting behavior for both organic and inorganic dopants and the resistivity of the CSA doped nanorods is found to be smaller than that of the HCl doped nanorods. The dielectric relaxation studies suggest Debye type relaxation with a single relaxation peak for both the dopants and the relaxation time of the carriers of the CSA doped PAni nanorods is smaller than that of the HCl doped nanorods.

Chutia, P.; Nath, Chandrani; Kumar, A.

2014-06-01

201

Generalized Hoeffding-Sobol Decomposition for Dependent Variables -Application to Sensitivity Analysis  

CERN Document Server

In this paper, we consider a regression model built on dependent variables. This regression modelizes an input output relationship. Under boundedness assumptions on the joint distribution function of the input variables, we show that a generalized Hoeffding-Sobol decomposition is available. This leads to new indices measuring the sensitivity of the output with respect to the input variables. We also study and discuss the estimation of these new indices.

Chastaing, Galle; Prieur, Clmentine

2011-01-01

202

Generalized Hoeffding-Sobol Decomposition for Dependent Variables - Application to Sensitivity Analysis  

OpenAIRE

In this paper, we consider a regression model built on dependent variables. This regression modelizes an input output relationship. Under boundedness assumptions on the joint distribution function of the input variables, we show that a generalized Hoeffding-Sobol decomposition is available. This leads to new indices measuring the sensitivity of the output with respect to the input variables. We also study and discuss the estimation of these new indices.

Chastaing, Gae?lle; Gamboa, Fabrice; Prieur, Cle?mentine

2012-01-01

203

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 Frchet distributed random variable.

Mikosch, Thomas Valentin; Moser, Martin

2013-01-01

204

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

OpenAIRE

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.Amplificaes RAPD foram desenvolvidas utilizando-se 25 "primer...

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

2000-01-01

205

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

Directory of Open Access Journals (Sweden)

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

206

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

Directory of Open Access Journals (Sweden)

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

207

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 keys length, fast digital signature, flexibility and less resource consumption

K.Manikandan

2011-02-01

208

Reliability estimation of buried gas pipelines in terms of various types of random variable distribution  

International Nuclear Information System (INIS)

This paper presents the effects of corrosion environments of failure pressure model for buried pipelines on failure prediction by using a failure probability. The FORM(First Order Reliability Method) is used in order to estimate the failure probability in the buried pipelines with corrosion defects. The effects of varying distribution types of random variables such as normal, longnormal and Weibull distributions on the failure probability of buried pipelines are systematically investigated. It is found that the failure probability for the MB31G model is larger than that for the B31G model. And the failure probability is estimated as the largest for the Weibull distribution and the smallest for the normal distribution. The effect of data scattering in corrosion environments on failure probability is also investigated and it is recognized that the scattering of wall thickness and yield strength of pipeline affects the failure probability significantly. The normalized margin is defined and estimated. Furthermore, the normalized margin is used to predict the failure probability using the fitting lines between failure probability and normalized margin

209

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

Directory of Open Access Journals (Sweden)

Full Text Available Particle Swarm Optimization (PSO es un mtodo de bsqueda no directo para la optimizacin numrica. Las principales ventajas de esta meta-heurstica estn relacionadas principalmente con su simplicidad, pocos parmetros y alta tasa de convergencia. En el PSO cannico usando una topologa totalmente conectada, una partcula ajusta su posicin 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 tambin deteriora la diversidad de la poblacin progresivamente. Como resultado la bandada de partculas frecuentemente es atrada por puntos sub-ptimos. Una vez que las partculas han sido atradas hacia un ptimo local, ellas continan el proceso de bsqueda dentro de una regin muy pequea del espacio de soluciones, reduciendo las capacidades de exploracin del algoritmo. Para tratar esta situacin este artculo presenta una variante del procedimiento Random Sampling in Variable Neighborhoods (RSVN usando una distribucin de Lvy. Este algoritmo es capaz de mejorar notablemente la capacidad de bsqueda de los algoritmos PSO en problemas multimodales de optimizacin.

Gonzalo N\\u00E1poles

2014-01-01

210

A Classification Study of Respiratory Syncytial Virus (RSV Inhibitors by Variable Selection with Random Forest  

Directory of Open Access Journals (Sweden)

Full Text Available Experimental pEC50s for 216 selective respiratory syncytial virus (RSV inhibitors are used to develop classification models as a potential screening tool for a large library of target compounds. Variable selection algorithm coupled with random forests (VS-RF is used to extract the physicochemical features most relevant to the RSV inhibition. Based on the selected small set of descriptors, four other widely used approaches, i.e., support vector machine (SVM, Gaussian process (GP, linear discriminant analysis (LDA and k nearest neighbors (kNN routines are also employed and compared with the VS-RF method in terms of several of rigorous evaluation criteria. The obtained results indicate that the VS-RF model is a powerful tool for classification of RSV inhibitors, producing the highest overall accuracy of 94.34% for the external prediction set, which significantly outperforms the other four methods with the average accuracy of 80.66%. The proposed model with excellent prediction capacity from internal to external quality should be important for screening and optimization of potential RSV inhibitors prior to chemical synthesis in drug development.

Shuwei Zhang

2011-02-01

211

Baseline-Dependent Effect of Noise-Enhanced Insoles on Gait Variability in Healthy Elderly Walkers  

OpenAIRE

The purpose of this study was to determine whether providing subsensory stochastic-resonance mechanical vibration to the foot soles of elderly walkers could decrease gait variability. In a randomized double-blind controlled trial, twenty nine (29) subjects engaged in treadmill walking while wearing sandals customized with three (3) actuators capable of producing stochastic-resonance mechanical vibration embedded in each sole. For each subject, we determined a subsensory level of vibration sti...

Stephen, Damian G.; Wilcox, Bethany; Niemi, James B.; Franz, Jason; Kerrigan, D. Casey; Dandrea, Susan E.

2012-01-01

212

Lead-position dependent regular oscillations and random fluctuations of conductance in graphene quantum dots  

International Nuclear Information System (INIS)

Quantum interference causes a wavefunction to have sensitive spatial dependence, and this has a significant effect on quantum transport. For example, in a quantum-dot system, the conductance can depend on the lead positions. We investigate, for graphene quantum dots, the conductance variations with the lead positions. Since for graphene the types of boundaries, e.g., zigzag and armchair, can fundamentally affect the quantum transport characteristics, we focus on rectangular graphene quantum dots, for which the effects of boundaries can be systematically studied. For both zigzag and armchair horizontal boundaries, we find that changing the positions of the leads can induce significant conductance variations. Depending on the Fermi energy, the variations can be either regular oscillations or random conductance fluctuations. We develop a physical theory to elucidate the origin of the conductance oscillation/fluctuation patterns. In particular, quantum interference leads to standing-wave-like-patterns in the quantum dot which, in the absence of leads, are regulated by the energy-band structure of the corresponding vertical graphene ribbon. The observed coexistence of regular oscillations and random fluctuations in the conductance can be exploited for the development of graphene-based nanodevices. (paper)

213

Scale-dependent measurement and analysis of ground surface temperature variability in alpine terrain  

OpenAIRE

Measurements of environmental variables are often used to validate and calibrate physically-based models. Depending on their application, the models are used at different scales, ranging from few meters to tens of kilometers. Environmental variables can vary strongly within the grid cells of these models. Validating a model with a single measurement is therefore delicate and susceptible to induce bias in further model applications.

To address the question of uncert...

Gubler, S.; Fiddes, J.; Keller, M.; Gruber, S.

2011-01-01

214

Dependence of vestibular reactions on frequency of action of sign-variable accelerations  

Science.gov (United States)

It was revealed that during the tests with continuous action of sign variable Coriolis acceleration the development of kinetosis was proportionate to the time of head inclinations in the range of 1 to 4 seconds while illusions of rocking in sagittal plane was more expressed in fast inclinations. The obtained data provided the evidence of sufficient dependence of vestibulovegetative and vestibulosensory reactions on the period of repetition of sign variable Coriolis acceleration.

Lapayev, E. V.; Vorobyev, O. A.; Ivanov, V. V.

1980-01-01

215

A normal distribution for tensor-valued random variables: applications to diffusion tensor MRI.  

Science.gov (United States)

Diffusion tensor magnetic resonance imaging (DT-MRI) provides a statistical estimate of a symmetric, second-order diffusion tensor of water, D, in each voxel within an imaging volume. We propose a new normal distribution, p(D) alpha exp(-1/2 D: A: D), which describes the variability of D in an ideal DT-MRI experiment. The scalar invariant, D : A : D, is the contraction of a positive definite symmetric, fourth-order precision tensor, A, and D. A correspondence is established between D: A: D and the elastic strain energy density function in continuum mechanics--specifically between D and the second-order infinitesimal strain tensor, and between A and the fourth-order tensor of elastic coefficients. We show that A can be further classified according to different classical elastic symmetries (i.e., isotropy, transverse isotropy, orthotropy, planar symmetry, and anisotropy). When A is an isotropic fourth-order tensor, we derive an explicit analytic expression for p(D), and for the distribution of the three eigenvalues of D, p(gamma1, gamma2, gamma3), which are confirmed by Monte Carlo simulations. We show how A can be estimated from either real or synthetic DT-MRI data for any given experimental design. Here we propose a new criterion for an optimal experimental design: that A be an isotropic fourth-order tensor. This condition ensures that the statistical properties of D (and quantities derived from it) are rotationally invariant. We also investigate the degree of isotropy of several DT-MRI experimental designs. Finally, we show that the univariate and multivariate distributions are special cases of the more general tensor-variate normal distribution, and suggest how to generalize p(D) to treat normal random tensor variables that are of third- (or higher) order. We expect that this new distribution, p(D), should be useful in feature extraction; in developing a hypothesis testing framework for segmenting and classifying noisy, discrete tensor data; and in designing experiments to measure tensor quantities. PMID:12906233

Basser, Peter J; Pajevic, Sinisa

2003-07-01

216

A hidden variables model for interference phenomena based on $p$-adic random dynamical systems  

CERN Document Server

We propose a model based on random dynamical systems (RDS) in information spaces (realized as rings of $p$-adic integers) which supports Buonomano's non-ergodic interpretation of quantum mechanics. In this model the memory system of an equipment works as a dynamical system perturbed by noise. Interference patterns correspond to attractors of RDS. There exists a large class of $p$-adic RDS for which interference patterns cannot be disturbed by noise. Therefore, if the equipment is described by such a RDS then the result of statistical experiment does not depend on noise in the equipment. On the one hand, we support the corpuscular model, because a quantum particle can be described as a corpuscular object. On the other hand, our model does not differ strongly from the wave model, because a quantum particle interacts with the whole equipment. Hence the interaction has nonlocal character. For example, in the two slit experiment a quantum particle interacts with both slits (but it passes only one of them).

Dubischar, Daniel; Steinkamp, Oliver; Khrennikov, Andrei

2009-01-01

217

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.

218

Propagation of radiation in time-dependent three-dimensional random media  

Science.gov (United States)

In Ref. [1] (Appendix A) we derived equations governing the frequency and spatial spectrum of radiation propagating in three-dimensional time-dependent random media with randomly varying sound speed c (x, t). From the spectral equations we determine equations for the energy flux in both the forward and backward directions. We consider media that are spatially homogeneous and isotropic and stationary in time. In order to allow an independence assumption the analysis is restricted to fluctuations that satisfy the conditions ?? ? Lz/c0 and ?? ? LFS/c0 where ?? is the characteristic time of the fluctuations, k0 is the mean radiation wavenumber, Lz is the characteristic correlation length of the random fluctuations in the mean propagation direction and LFS is a mean scattering length. We consider various values of ? = (k0 Lz)2/2. When ? ? 1 we find the usual radiation transfer equations. When ? ? 1, but back-scattering can be neglected, we find the forward-scattering equations. We also consider ? ? 1, when back-scattering cannot be neglected. We consider as initial boundary conditions a plane wave and an infinite incoherent source. We present numerical solutions for ? ? 1, ? = O (1) and ? ? 1 using a simple Gaussian form for the fluctuation correlation function.

Beran, Mark J.; Frankenthal, Shimshon; Deshmukh, Venkatesh; Whitman, Alan M.

219

Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors  

International Nuclear Information System (INIS)

This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the 'hard gap' energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained

220

A note on the Marchenko-Pastur law for a class of random matrices with dependent entries  

CERN Document Server

We consider a class of real random matrices with dependent entries and show that the limiting empirical spectral distribution is given by the Marchenko-Pastur law. Additionally, we establish a rate of convergence of the expected empirical spectral distribution.

O'Rourke, Sean

2012-01-01

221

Detection and measurement of spin-dependent dynamics in random telegraph signals.  

Science.gov (United States)

A quantum point contact was used to observe single-electron fluctuations of a quantum dot in a GaAs heterostructure. The resulting random telegraph signals (RTS) contain statistical information about the electron spin state if the tunneling dynamics are spin dependent. We develop a statistical method to extract information about spin-dependent dynamics from RTS and use it to demonstrate that these dynamics can be studied in the thermal energy regime. The tunneling rates of each spin state are independently measured in a finite external magnetic field. We confirm previous findings of a decrease in overall tunneling rates for the spin excited state compared to the ground state as an external magnetic field is increased. PMID:24093289

House, M G; Xiao, Ming; Guo, Guoping; Li, Haiou; Cao, Gang; Rosenthal, M M; Jiang, Hongwen

2013-09-20

222

Temperature dependence of collective states in the random-phase approximation  

International Nuclear Information System (INIS)

We investigate the temperature dependence of collective states in the framework of the random-phase approximation at finite temperature. We show that sum rules can be extended to collective energies at finite temperature. Numerical methods are developed to solve the RPA equations at finite temperature. Results are presented and discussed in the case of 40Ca for isovector dipole and isoscalar octupole vibrations, using oscillator wave functions and a zero-range force. We show that the broadening of giant dipole resonances observed experimentally, appears as a natural consequence of the structure of the RPA equations. Comparison is made with the schematic model for which the temperature dependence of collective states can be worked out analytically. (orig.)

223

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

224

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

225

The relative dependence of Spanish landscape pattern on environmental and geographical variables over time  

OpenAIRE

The analysis of the dependence of landscape patterns on environment was carried out in order to investigate the landscape structure evolution of Spain. The underlying concept was that the dependence between landscape spatial structure and environmental factors could be gradually decreasing over time. Land cover data were recorded from aerial photo interpretation of 206 4 x 4 km(2) samples from three different years: 1956, 1984 and 1998. Geographical variables were taken into consideration tog...

Ortega, M.; Bunce, R. G. H.; Barrio, J. M. G.; Elena-rossello, R.

2008-01-01

226

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

227

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 Fn(Un for a class of strongly mixing sequences of random variables {Xi,i?1}. Stationarity is not assumed. Here Fn is the perturbed empirical distribution function and Un is a U-statistic based on X1,,Xn.

Shan Sun

1997-01-01

228

Letter to the Editor: On the stability and ranking of predictors from random forest variable importance measures  

OpenAIRE

A recent study examined the stability of rankings from random forests using two variable importance measures (mean decrease accuracy (MDA) and mean decrease Gini (MDG)) and concluded that rankings based on the MDG were more robust than MDA. However, studies examining data-specific characteristics on ranking stability have been few. Rankings based on the MDG measure showed sensitivity to within-predictor correlation and differences in category frequencies, even when the number of categories wa...

Nicodemus, Kristin K.

2011-01-01

229

A ratio-cum-product estimator of population mean in stratified random sampling using two auxiliary variables  

Directory of Open Access Journals (Sweden)

Full Text Available This paper proposes a ratio-cum-product estimator of finite population mean in stratified random sampling using information on population means of two auxiliary variables. The bias and mean squared error expressions are derived under large sample approximations. Proposed estimator has been compared with usual unbiased estimator in stratified sampling, combined ratio estimator and combined product estimator theoretically as well as empirically.

Rajesh Tailor

2013-05-01

230

Tail Asymptotic of Sum and Product of Random Variables with Applications in the Theory of Extremes of Conditionally Gaussian Processes  

OpenAIRE

We consider two independent random variables with the given tail asymptotic (e.g. power or exponential). We find tail asymptotic for their sum and product. This is done by some cumbersome but purely technical computations and requires the use of the Laplace method for asymptotic of integrals. We also recall the results for asymptotic of a self-similar locally stationary centered Gaussian process plus a deterministic drift; and we find the asymptotic for the same probability ...

Sarantsev, Andrey

2011-01-01

231

On the Sum of Correlated Squared $\\kappa-\\mu$ Shadowed Random Variables and its Application to Performance Analysis of MRC  

OpenAIRE

In this paper, we study the statistical characterization of the sum of the squared $\\kappa-\\mu$ shadowed random variables with correlated shadowing components. The probability density function (PDF) of this sum is obtained in the form of a power series. The derived PDF is utilized for obtaining the performance results of the maximal ratio combining (MRC) scheme over correlated $\\kappa-\\mu$ shadowed fading channels. First, we derive the moment generating function (MGF) of the...

Bhatnagar, Manav R.

2014-01-01

232

The distribution of the square sum of Dirichlet random variables and a table with quantiles of Greenwood's statistic  

OpenAIRE

The exact distribution of the square sum of Dirichlet random variables is given by two different univariate integral representations. Alternatively, three representations by orthogonal series with Jacobi or Legendre polynomials are derived. As a special case the distribution of the square sum of spacings - also called Greenwood's statistic - is obtained. Nine quantiles of this statistic are tabulated with eight digits where the number of squares ranges from 10 to 100.

Royen, Thomas

2010-01-01

233

Field Dependency, n Power and Locus of Control Variables in Alcohol Aversion.  

Science.gov (United States)

Compared individual differences and treatment effectiveness in male volunteer alcoholics (N=47) in a 10-day electroconditioning aversion program. Follow-up showed combination therapy was more successful. Internals and hard liquor drinkers tended to be abstinent as predicted. Field dependency was a more unstable variable for outcome. (Author/JAC)

Query, William T.

1983-01-01

234

Dependence of Technological Routinization on Structural Variables in Human Service Organizations  

Science.gov (United States)

A path analysis of data from 30 human service organizations supports the specification of technological routinization in a dependent relationship with the structural variables of participation in decision-making, hierarchy of authority, division of labor, and procedural specifications. (Author/IRT)

Glisson Charles A.

1978-01-01

235

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

Directory of Open Access Journals (Sweden)

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 Womens 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

236

Delay-dependent robust exponential state estimation of Markovian jumping fuzzy Hopfield neural networks with mixed random time-varying delays  

Science.gov (United States)

This paper investigates delay-dependent robust exponential state estimation of Markovian jumping fuzzy neural networks with mixed random time-varying delay. In this paper, the Takagi-Sugeno (T-S) fuzzy model representation is extended to the robust exponential state estimation of Markovian jumping Hopfield neural networks with mixed random time-varying delays. Moreover probabilistic delay satisfies a certain probability-distribution. By introducing a stochastic variable with a Bernoulli distribution, the neural networks with random time delays is transformed into one with deterministic delays and stochastic parameters. The main purpose is to estimate the neuron states, through available output measurements such that for all admissible time delays, the dynamics of the estimation error is globally exponentially stable in the mean square. Based on the Lyapunov-Krasovskii functional and stochastic analysis approach, several delay-dependent robust state estimators for such T-S fuzzy Markovian jumping Hopfield neural networks can be achieved by solving a linear matrix inequality (LMI), which can be easily facilitated by using some standard numerical packages. The unknown gain matrix is determined by solving a delay-dependent LMI. Finally some numerical examples are provided to demonstrate the effectiveness of the proposed method.

Balasubramaniam, P.; Vembarasan, V.; Rakkiyappan, R.

2011-04-01

237

A modified NaSch model with density-dependent randomization for traffic flow  

Science.gov (United States)

Based on the Nagel-Schreckenberg (NaSch) model of traffic flow, a modified cellular automaton (CA) traffic model with the density-dependent randomization (abbreviated as the DDR model) is proposed to simulate traffic flow. The fundamental diagram obtained by simulation shows the ability of this modified NaSch model to capture the essential features of traffic flow, e.g., synchronized flow, metastable state, hysteresis and phase separation at higher densities. Comparisons are made between this DDR model and the NaSch model, also between this DDR model and the VDR model. And the underlying mechanism is analyzed. All these results indicate that the presented model is reasonable and more realistic.

Zhu, H. B.; Ge, H. X.; Dong, L. Y.; Dai, S. Q.

2007-05-01

238

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

239

On a phase diagram for random neural networks with embedded spike timing dependent plasticity.  

Science.gov (United States)

This paper presents an original mathematical framework based on graph theory which is a first attempt to investigate the dynamics of a model of neural networks with embedded spike timing dependent plasticity. The neurons correspond to integrate-and-fire units located at the vertices of a finite subset of 2D lattice. There are two types of vertices, corresponding to the inhibitory and the excitatory neurons. The edges are directed and labelled by the discrete values of the synaptic strength. We assume that there is an initial firing pattern corresponding to a subset of units that generate a spike. The number of activated externally vertices is a small fraction of the entire network. The model presented here describes how such pattern propagates throughout the network as a random walk on graph. Several results are compared with computational simulations and new data are presented for identifying critical parameters of the model. PMID:17292539

Turova, Tatyana S; Villa, Alessandro E P

2007-01-01

240

Magnetic-field-dependent small-angle neutron scattering on random anisotropy ferromagnets  

International Nuclear Information System (INIS)

We report on the recently developed technique of magnetic-field-dependent small-angle neutron scattering (SANS), with attention to bulk ferromagnets exhibiting random magnetic anisotropy. In these materials, the various magnetic anisotropy fields (magnetocrystalline, magnetoelastic, and/or magnetostatic in origin) perturb the perfectly parallel spin alignment of the idealized ferromagnetic state. By varying the applied magnetic field, one can control one of the ordering terms which competes with the above-mentioned perturbing fields. Experiments which explore the ensuing reaction of the magnetization will therefore provide information not only on the field-dependent spin structure but, importantly, on the underlying magnetic interaction terms. This strategy, which underlies conventional studies of hysteresis loops in magnetometry, is here combined with magnetic SANS. While magnetometry generally records only a single scalar quantity, the integral magnetization, SANS provides access to a vastly richer data set, the Fourier spectrum of the response of the spin system as a function of the magnitude and orientation of the wave vector. The required data-analysis procedures have recently been established, and experiments on a number of magnetic materials, mostly nanocrystalline or nanocomposite metals, have been reported. Here, we summarize the theory of magnetic-field-dependent SANS along with the underlying description of random anisotropy magnets by micromagnetic theory.nisotropy magnets by micromagnetic theory. We review experiments which have explored the magnetic interaction parameters, the value of the exchange-stiffness constant as well as the Fourier components of the magnetic anisotropy field and of the magnetostatic stray field. A model-independent approach, based on the experimental autocorrelation function of the spin misalignment, provides access to the characteristic length of the spin misalignment. The field dependence of this quantity is in quantitative agreement with the predictions of micromagnetic theory. Experiments on nanocomposite ferromagnets reveal that the jump of the magnetization at internal phase boundaries leads to a significant magnetostatic perturbing field, with an unusual 'clover-leaf' SANS pattern as the experimental signature. Furthermore, SANS experiments have been used to monitor the orientation of magnetic domains as well as the length scale of intradomain spin misalignment

241

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

OpenAIRE

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 out...

Ahmadi-Abhari Seyed Ali; Radgoodarzi Reza; Assadi Seyed Mohammad

2003-01-01

242

On a Camassa-Holm type equation with two dependent variables  

International Nuclear Information System (INIS)

We consider a generalization of the Camassa-Holm (CH) equation with two dependent variables, called CH2, introduced in a paper by Liu and Zhang (Liu S-Q and Zhang Y 2005 J. Geom. Phys. 54 427-53). We briefly provide an alternative derivation of it based on the theory of Hamiltonian structures on (the dual of) a Lie algebra. The Lie algebra involved here is the same algebra as underlies the NLS hierarchy. We study the structural properties of the hierarchy defined by the CH2 equation within the bi-Hamiltonian theory of integrable PDEs, and provide its Lax representation. Then we explicitly discuss how to construct classes of solutions, both of peakon and of algebro-geometrical type. Finally we sketch the construction of a class of singular solutions, defined by setting to zero one of the two dependent variables

243

On a Camassa-Holm type equation with two dependent variables  

CERN Document Server

We consider a generalization of the Camassa Holm (CH) equation with two dependent variables, called CH2, introduced by Liu and Zhang. We briefly provide an alternative derivation of it based on the theory of Hamiltonian structures on (the dual of) a Lie Algebra. The Lie Algebra here involved is the same algebra underlying the NLS hierarchy. We study the structural properties of the CH2 hierarchy within the bihamiltonian theory of integrable PDEs, and provide its Lax representation. Then we explicitly discuss how to construct classes of solutions, both of peakon and of algebro-geometrical type. We finally sketch the construction of a class of singular solutions, defined by setting to zero one of the two dependent variables.

Falqui, G

2005-01-01

244

On the approximation of an integral by a sum of random variables  

OpenAIRE

We approximate the integral of a smooth function on [0,1], where values are only known at n random points (i.e., a random sample from the uniform-(0,1) distribution), and at 0 and 1. Our approximations are based on the trapezoidal rule and Simpson's rule (generalized to the non-equidistant case), respectively. In the first case, we obtain an n2-rate of convergence with a degenerate limiting distribution; in the second case, the rate of con-vergence is as fast as n3, whereas the limiting...

Einmahl, John H. J.; Zuijlen, Martien C. A.

1998-01-01

245

Inclination and orbital-phase-dependent resonance line-profile calculations applied to cataclysmic variable winds  

International Nuclear Information System (INIS)

The observed properties of wind-formed resonance lines in the spectra of nova-like variables and dwarf novae in outburst, are discussed. A method is then presented of calculating inclination-and orbital-phase-dependent resonance line profiles formed in a constant-ionization wind flowing from an accretion disc centre. The particular case of the C IV lambda 1549 line is considered. (author)

246

Variability of postsynaptic responses depends non-linearly on the number of synaptic inputs  

OpenAIRE

A conductance-based model for synaptic transmission and postsynaptic integration reveals how postsynaptic responses and their variability depend on the number of synaptic inputs. With increasing number of balanced stochastic excitatory and inhibitory inputs, the postsynaptic responses and their variance first increase and then decrease again. This non-linearity can be attributed to an anti-correlation between the total excitatory and inhibitory currents. The anti-correlation, which occurs eve...

Kretzberg, Jutta; Sejnowski, Terrence; Warzecha, Anne-kathrin; Egelhaaf, Martin

2003-01-01

247

Random functions and turbulence  

CERN Document Server

International Series of Monographs in Natural Philosophy, Volume 32: Random Functions and Turbulence focuses on the use of random functions as mathematical methods. The manuscript first offers information on the elements of the theory of random functions. Topics include determination of statistical moments by characteristic functions; functional transformations of random variables; multidimensional random variables with spherical symmetry; and random variables and distribution functions. The book then discusses random processes and random fields, including stationarity and ergodicity of random

Panchev, S

1971-01-01

248

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)

249

A functional limit theorem for a 2D-random walk with dependent marginals  

OpenAIRE

We prove a non-standard functional limit theorem for a two dimensional simple random walk on some randomly oriented lattices. This random walk, already known to be transient, has different horizontal and vertical fluctuations leading to different normalizations in the functional limit theorem, with a non-Gaussian horizontal behavior. We also prove that the horizontal and vertical components are not asymptotically independent.

Guillotin-plantard, Nadine; Le Ny, Arnaud

2007-01-01

250

Berry-Esseen and Edgeworth approximations for the tail of an infinite sum of weighted gamma random variables  

OpenAIRE

Consider the sum $Z = \\sum_{n=1}^\\infty \\lambda_n (\\eta_n - \\mathbb{E}\\eta_n)$, where $\\eta_n$ are i.i.d.~gamma random variables with shape parameter $r > 0$, and the $\\lambda_n$'s are predetermined weights. We study the asymptotic behavior of the tail $\\sum_{n=M}^\\infty \\lambda_n (\\eta_n - \\mathbb{E}\\eta_n)$ which is asymptotically normal under certain conditions. We derive a Berry-Essen bound and Edgeworth expansions for its distribution function. We illustrate the effecti...

Veillette, Mark S.; Taqqu, Murad S.

2010-01-01

251

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

252

An Investigation of Quasar Variability as a Damped Random Walk in the PanSTARRS-1 Medium Deep Fields  

Science.gov (United States)

We model the lightcurves of 755 optically varying quasars from the Pan-STARRS Medium Deep Field 7 r band using a Damped Random Walk (DRW) model. The DRW describes quasar variability by its characteristic timescale, ?, and its variability at infinite time, V?. We use Monte Carlo techniques to fit our data as a DRW. The model parameters are compared to physical properties of the quasars such as black hole mass, Eddington ratio, and bolometric luminosity. We find that bolometric luminosity, Eddington ratio, and black hole mass are positively correlated with V? and negatively correlated with ?. Quasars of greater luminosity, black hole mass, or Eddington ratio generally display smaller variations, and on longer timescales as estimated in the DRW model framework. This work was supported in part by the NSF REU and DoD ASSURE programs under NSF grant no. 1262851 and by the Smithsonian Institution.

Cunningham, Virginia; Green, Paul J.; Morganson, Eric; Shen, Yue

2015-01-01

253

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

254

The time-dependent relativistic mean-field theory and the random phase approximation  

CERN Document Server

The Relativistic Random Phase Approximation (RRPA) is derived from the Time-dependent Relativistic Mean Field (TD RMF) theory in the limit of small amplitude oscillations. In the no-sea approximation of the RMF theory, the RRPA configuration space includes not only the usual particle-hole states, but also a-h configurations, i.e. pairs formed from occupied states in the Fermi sea and empty negative-energy states in the Dirac sea. The contribution of the negative energy states to the RRPA matrices is examined in a schematic model, and the large effect of Dirac sea states on isoscalar strength distributions is illustrated for the giant monopole resonance in 116Sn. It is shown that, because the matrix elements of the time-like component of the vector meson fields which couple the a-h configurations with the ph-configurations are strongly reduced with respect to the corresponding matrix elements of the isoscalar scalar meson field, the inclusion of states with unperturbed energies more than 1.2 GeV below the Ferm...

Ring, P; Nguyen Van Giai; Vretenar, D; Wandelt, A; Cao, L; Ma, Zhong-yu; Giai, Nguyen Van; Cao, Li-gang

2001-01-01

255

The time-dependent relativistic mean-field theory and the random phase approximation  

Science.gov (United States)

The Relativistic Random Phase Approximation (RRPA) is derived from the Time-Dependent Relativistic Mean-Field (TD RMF) theory in the limit of small amplitude oscillations. In the no-sea approximation of the RMF theory, the RRPA configuration space includes not only the usual particle-hole ph-states, but also ?h-configurations, i.e. pairs formed from occupied states in the Fermi sea and empty negative-energy states in the Dirac sea. The contribution of the negative-energy states to the RRPA matrices is examined in a schematic model, and the large effect of Dirac-sea states on isoscalar strength distributions is illustrated for the giant monopole resonance in 116Sn. It is shown that, because the matrix elements of the time-like component of the vector-meson fields which couple the ?h-configurations with the ph-configurations are strongly reduced with respect to the corresponding matrix elements of the isoscalar scalar meson field, the inclusion of states with unperturbed energies more than 1.2 GeV below the Fermi energy has a pronounced effect on giant resonances with excitation energies in the MeV region. The influence of nuclear magnetism, i.e. the effect of the spatial components of the vector fields is examined, and the difference between the nonrelativistic and relativistic RPA predictions for the nuclear matter compression modulus is explained.

Ring, P.; Ma, Zhong-yu; Van Giai, Nguyen; Vretenar, D.; Wandelt, A.; Cao, Li-gang

2001-11-01

256

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 (?10(4)), the higher the high resistance state (HRS)/low resistance state (LRS) ratio (?10(5)) and stable retention characteristics (>10(3) 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. PMID:24739543

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

2014-05-01

257

Variation among Species in the Temperature Dependence of the Reappearance of Variable Fluorescence following Illumination.  

Science.gov (United States)

The relationship between the thermal dependence of the reappearance of chlorophyll variable fluorescence following illumination and temperature dependence of the apparent Michaelis constant (K(m)) of NADH hydroxypyruvate reductase for NADH was investigated in cool and warm season plant species. Brancker SF-20 and SF-30 fluorometers were used to evaluate induced fluorescence transients from detached leaves of wheat (Triticum aestivum L. cv TAM-101), cotton (Gossypium hirsutum L. cv Paymaster 145), tomato (Lycopersicon esculentum cv Del Oro), bell pepper (Capsicum annuum L. cv California Wonder), and petunia (Petunia hybrida cv. Red Sail). Following an illumination period at 25 degrees C, the reappearance of variable fluorescence during a dark incubation was determined at 5 degrees C intervals from 15 degrees C to 45 degrees C. Variable fluorescence recovery was normally distributed with the maximum recovery observed at 20 degrees C in wheat, 30 degrees C in cotton, 20 degrees C to 25 degrees C in tomato, 30 to 35 degrees C in bell pepper and 25 degrees C in petunia. Comparison of the thermal response of fluorescence recovery with the temperature sensitivity of the apparent K(m) of hydroxypyruvate reductase for NADH showed that the range of temperatures providing fluorescence recovery corresponded with those temperatures providing the minimum apparent K(m) values (viz. the thermal kinetic window). PMID:16667518

Burke, J J

1990-06-01

258

Computation of the temperature dependence of the heat capacity of complex molecular systems using random color noise  

OpenAIRE

We propose a new method for computing the temperature dependence of the heat capacity in complex molecular systems. The proposed scheme is based on the use of the Langevin equation with low frequency color noise. We obtain the temperature dependence of the correlation time of random noises, which enables to model the partial thermalization of high-frequency vibrations, which is a pure quantum effect. By applying the method to carbon nanotubes, we show that the consideration ...

Buyukdagli, Sahin; Savin, Alexander V.; Hu, Bambi

2008-01-01

259

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

260

Vertical random variability of the distribution coefficient in the soil and its effect on the migration of fallout radionuclides  

International Nuclear Information System (INIS)

In the field, the distribution coefficient, Kd, for the sorption of a radionuclide by the soil cannot be expected to be constant. Even in a well defined soil horizon, Kd will vary stochastically in horizontal as well as in vertical direction around a mean value. The horizontal random variability of Kd produce a pronounced tailing effect in the concentration depth profile of a fallout radionuclide, much less is known on the corresponding effect of the vertical random variability. To analyze this effect theoretically, the classical convection-dispersion model in combination with the random-walk particle method was applied. The concentration depth profile of a radionuclide was calculated one year after deposition assuming constant values of the pore water velocity, the diffusion/dispersion coefficient, and the distribution coefficient (Kd = 100 cm3 x g-1) and exhibiting a vertical variability for Kd according to a log-normal distribution with a geometric mean of 100 cm3 x g-1 and a coefficient of variation of CV 0.53. The results show that these two concentration depth profiles are only slightly different, the location of the peak is shifted somewhat upwards, and the dispersion of the concentration depth profile is slightly larger. A substantial tailing effect of the concentration depth profile is not perceivable. Especially with respect to the location of the peak, a very spect to the location of the peak, a very good approximation of the concentration depth profile is obtained if the arithmetic mean of the Kd-values (Kd = 113 cm3 x g-1) and a slightly increased dispersion coefficient are used in the analytical solution of the classical convection-dispersion equation with constant Kd. The evaluation of the observed concentration depth profile with the analytical solution of the classical convection-dispersion equation with constant parameters will, within the usual experimental limits, hardly reveal the presence of a log-normal random distribution of Kd in the vertical direction in contrast to the horizontal direction. (author)

261

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)

262

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

263

On Chung-Teicher type strong law for arrays of vector-valued random variables  

Directory of Open Access Journals (Sweden)

Full Text Available We study the equivalence between the weak and strong laws of large numbers for arrays of row-wise independent random elements with values in a Banach space ℬ. The conditions under which this equivalence holds are of the Chung or Chung-Teicher types. These conditions are expressed in terms of convergence of specific series and o(1 requirements on specific weighted row-wise sums. Moreover, there are not any conditions assumed on the geometry of the underlying Banach space.

Anna Kuczmaszewska

2004-03-01

264

GRS 1915+105: the distance, radiative processes and energy-dependent variability  

Science.gov (United States)

We present an exhaustive analysis of five broad-band observations of GRS 1915+105 in two variability states, ? and ?, observed simultaneously by the Proportional Counter Array (PCA) and High-Energy X-ray Timing Experiment (HEXTE) detectors aboard the Rossi X-ray Timing Explorer, and the Oriented Scintillation Spectrometer Experiment (OSSE) detector aboard the Compton Gamma-ray Observatory. We find all the spectra well fitted by Comptonization of disc blackbody photons, with very strong evidence for the presence of a non-thermal electron component in the Comptonizing plasma. Both the energy and the power spectra in the ? state are typical of the very high/intermediate state of black hole binaries. The spectrum of the ? state is characterized by a strong blackbody component Comptonized by thermal electrons and a weak non-thermal tail. We then calculate rms spectra (fractional variability as functions of energy) for the PCA data. We accurately model the rms spectra by coherent superposition of variability in the components implied by the spectral fits, namely a less variable blackbody and more variable Comptonization. The latter dominates at high energies, resulting in a flattening of the rms at high energies in most of the data. This is also the case for the spectra of the quasi-periodic oscillations present in the ? state. Then, some of our data require a radial dependence of the rms of the disc blackbody. We also study the distance to the source, and find d~= 11 kpc as the most likely value, contrary to a recent claim of a much lower value.

Zdziarski, Andrzej A.; Gierli?ski, Marek; Rao, A. R.; Vadawale, S. V.; Miko?ajewska, Joanna

2005-07-01

265

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

266

Nonparametric changepoint analysis for bernoulli random variables based on neural networks  

OpenAIRE

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

267

Bayesian methods for instrumental variable analysis with genetic instruments (Mendelian randomization): example with urate transporter SLC2A9 as an instrumental variable for effect of urate levels on metabolic syndrome  

OpenAIRE

The Mendelian randomization approach uses genotype as an instrumental variable to distinguish between causal and non-causal explanations of biomarkerdisease associations. Classical methods for instrumental variable analysis are limited to linear or probit models without latent variables or missing data, rely on asymptotic approximations that are not valid for weak instruments and focus on estimation rather than hypothesis testing. We describe a Bayesian approach that overcomes these ...

Mckeigue, Paul M.; Campbell, Harry; Wild, Sarah; Vitart, Veronique; Hayward, Caroline; Rudan, Igor; Wright, Alan F.; Wilson, James F.

2010-01-01

268

Temperature dependence of the positron diffusion length in metallic glasses as studied by variable-energy positrons  

International Nuclear Information System (INIS)

Results are reported on the temperature dependence of the positron diffusion length Lsub(+) in metallic glasses Cu50Zr50 and Fe82B12Si6 utilizing a variable-energy positron beam. A short diffusion length of the order of 10 A is observed in the as-received state indicating a high positron trapping probability into structural defects. Evidenced by positron thermal detrapping these defects seem to be shallow, as e.g., Bernal holes of the dense random packing of hard spheres model. A lower limit for their concentration is estimated to be 0.1-1.0%. Irreversible changes in Lsub(+) occur in the vicinity of the crystallization temperature Tsub(c) associated with a partial removal of the positron trapping sites. However, anneals several hundred degrees above Tsub(c) are required to obtain a level of Lsub(+) approximately 500 A approaching that of a defect-free metal. This is interpreted as evidence that the crystallized samples still have a large concentration of positron traps, possibly dislocations, precipitates, or grain boundaries. (Auth.)

269

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

270

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)

271

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

272

Time-dependent reliability of corrosion-affected RC beams. Part 3: Effect of corrosion initiation time and its variability on time-dependent failure probability  

International Nuclear Information System (INIS)

This paper forms the third part of a study which addresses time-dependent reliability analyses of reinforced concrete (RC) beams affected by reinforcement corrosion. Parts 1 and 2 of the reliability study are presented in companion papers. Part 1 of the reliability study presents evaluation of probabilistic descriptions for time-dependent strengths of a typical simply supported corrosion-affected RC beam. These probabilistic descriptions, i.e., mean and coefficient of variation (c.o.v.) for the time-dependent strengths are presented for two limit states: (a) flexural failure; and (b) shear failure. Part 2 of the reliability study presents evaluation of time-dependent failure probability for the considered RC beam by utilizing the information on probabilistic descriptions for time-dependent strengths available in Part 1. Evaluation of time-dependent failure probability considering the variability in time-dependent strengths and/or time-dependent degradation functions is also presented. This paper investigates the effects of time to corrosion initiation and its variability on failure probability of the same RC beam presented in companion papers. By considering variability in the identified variables that could affect the expected time of first corrosion, simple estimations are presented for mean time to corrosion initiation and variability associated with time to corrosion initiation. Evaluation of time-dependent failure probability for the beam is presented by considerlity for the beam is presented by considering estimated probabilistic descriptions, i.e., mean and c.o.v. for time to corrosion initiation. Parametric analyses show that failure probability for the beam is sensitive to the mode of strength degradation and time to corrosion initiation.

273

Time-dependent reliability of corrosion-affected RC beams. Part 3: Effect of corrosion initiation time and its variability on time-dependent failure probability  

Energy Technology Data Exchange (ETDEWEB)

This paper forms the third part of a study which addresses time-dependent reliability analyses of reinforced concrete (RC) beams affected by reinforcement corrosion. Parts 1 and 2 of the reliability study are presented in companion papers. Part 1 of the reliability study presents evaluation of probabilistic descriptions for time-dependent strengths of a typical simply supported corrosion-affected RC beam. These probabilistic descriptions, i.e., mean and coefficient of variation (c.o.v.) for the time-dependent strengths are presented for two limit states: (a) flexural failure; and (b) shear failure. Part 2 of the reliability study presents evaluation of time-dependent failure probability for the considered RC beam by utilizing the information on probabilistic descriptions for time-dependent strengths available in Part 1. Evaluation of time-dependent failure probability considering the variability in time-dependent strengths and/or time-dependent degradation functions is also presented. This paper investigates the effects of time to corrosion initiation and its variability on failure probability of the same RC beam presented in companion papers. By considering variability in the identified variables that could affect the expected time of first corrosion, simple estimations are presented for mean time to corrosion initiation and variability associated with time to corrosion initiation. Evaluation of time-dependent failure probability for the beam is presented by considering estimated probabilistic descriptions, i.e., mean and c.o.v. for time to corrosion initiation. Parametric analyses show that failure probability for the beam is sensitive to the mode of strength degradation and time to corrosion initiation.

Bhargava, Kapilesh, E-mail: kapil_66@barc.gov.i [Architecture and Civil Engineering Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India); Mori, Yasuhiro [Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8603 (Japan); Ghosh, A.K. [Reactor Safety Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India)

2011-05-15

274

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

Directory of Open Access Journals (Sweden)

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.Amplificaes RAPD foram desenvolvidas utilizando-se 25 "primers" de seqncia aleatria e 19 acessos de tangerinas pertencentes ao grupo das Ponkan. Dos 112 produtos de amplificao selecionados somente 32 foram polimrficos, sendo este polimorfismo restrito somente a 5 acessos. Nos 14 acessos restantes no pde ser detectada qualquer variabilidade gentica, sugerindo que estes podem ser propagao clonal da tangerina `Ponkan', tendo os mesmos adquirido diferentes nomes regionais ao longo do tempo. Ou, por outro lado, a tcnica RAPD utilizada pode no ter detectado qualquer mutao de ponto que tenha ocorrido nestes materiais ao longo do tempo.

Helvcio Della Coletta Filho

2000-03-01

275

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 Amplificaes RAPD foram desenvolvidas utilizando-se 25 "primers" de seqncia aleatria e 19 acessos de tangerinas pertencentes ao grupo das Ponkan. Dos 112 produtos de amplificao selecionados somente 32 foram polimrficos, sendo este polimorfismo restrito somente a 5 acessos. Nos 14 acessos rest [...] antes no pde ser detectada qualquer variabilidade gentica, sugerindo que estes podem ser propagao clonal da tangerina `Ponkan', tendo os mesmos adquirido diferentes nomes regionais ao longo do tempo. Ou, por outro lado, a tcnica RAPD utilizada pode no ter detectado qualquer mutao 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.

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

2000-03-01

276

Random fields on model sets with localized dependency and their diffraction  

CERN Document Server

For a random field on a general discrete set, we introduce a condition that the range of the correlation from each site is within a predefined compact set D. For such a random field {\\omega} defined on the model set Lambda that satisfies a natural geometric condition, we develop a method to calculate the diffraction measure of the random field. The method partitions the random field into a finite number of random fields, each being independent and admitting the law of large numbers. The diffraction measure of {\\omega} consists almost surely of a pure point component and an absolutely continuous component. The former is the diffraction measure of the expectation, while the inverse Fourier transform of the absolutely continuous component of {\\omega} turns out to be a weighted Dirac comb which satisfies a simple formula. Moreover, the pure-point component will be understood quantitatively in a simple exact formula if the weights are continuous over the internal space of Lambda. Then we provide a sufficient condi...

Akama, Yohji

2011-01-01

277

A multivariate logistic regression model for randomized response data.  

OpenAIRE

A multivariate logistic regression model is discussed given that the dependent variables are subject to randomized response. Randomized response is an interview technique that can be used when sensitive questions have to be asked and respondents are reluctant to answer directly. The multivariate model is an adaption of a model without randomized response variables and a Fisher scoring algorithm is used to maximize the likelihood. Randomized response data taken from a study i...

Hout, A. D. L. Den; Heijden, P. G. M.; Gilchrist, B.

2007-01-01

278

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?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

279

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

280

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

281

New alphabet-dependent morphological transition in a random RNA alignment  

OpenAIRE

We study the fraction $f$ of nucleotides involved in the formation of a cactus--like secondary structure of random heteropolymer RNA--like molecules. In the low--temperature limit we study this fraction as a function of the number $c$ of different nucleotide species. We show, that with changing $c$, the secondary structures of random RNAs undergo a morphological transition: $f(c)\\to 1$ for $c \\le c_{\\rm cr}$ as the chain length $n$ goes to infinity, signaling the formation o...

Valba, O. V.; Tamm, M. V.; Nechaev, S. K.

2011-01-01

282

A multivariate CBM model with a random and time-dependent failure threshold  

International Nuclear Information System (INIS)

In a condition-based maintenance setting, the degradation of an item is usually represented by several condition variables, and they can be combined into a composite condition variable. In this case, the functional failure threshold associated with the composite condition variable is usually not a fixed and known constant. It is an open issue to model the failure threshold and accordingly determine a threshold of preventive maintenance (PM). This paper addresses this issue. The condition variables are combined using a weighted power model, the failure threshold is represented by the Gaussian process model, and the PM threshold is determined by two approaches. Based on the gamma process and stressstrength interference models, the distributions of time to failure and to the PM threshold are derived, respectively. The appropriateness of the approach is illustrated by a real-world example

283

Elevated intraindividual variability in methamphetamine dependence is associated with poorer everyday functioning.  

Science.gov (United States)

Methamphetamine (MA) dependence is associated with executive dysfunction, but no studies have evaluated MA-related elevations in neurocognitive intraindividual variability (IIV), an expression of cognitive dyscontrol linked to poor daily functioning in populations with frontal systems injury. We examined IIV during a vigilance task in a well-characterized sample of 35 MA-dependent (MA+) and 55 non-MA using comparison participants (MA-) as part of a larger neuropsychological battery that included self-report and performance-based measures of everyday functioning. A mixed model ANOVA was conducted while controlling for covariates, including factors that differed between the groups (e.g., education) and those with conceptual relevance to IIV: mean reaction time, global cognitive performance, and HIV-infection (which was comparable across groups; p=0.32). This analysis revealed significantly elevated IIV among MA+ relative to MA- individuals that was comparable in magnitude across all trial blocks of the vigilance task. Within the MA group, elevated IIV was associated with executive dysfunction, psychomotor slowing, and recency of MA use, as well as poorer automobile driving simulator performance, worse laboratory-based functional skills, and more cognitive complaints. MA-users are vulnerable to IIV elevation, likely due to cognitive dyscontrol, which may increase their risk of real-world problems. PMID:25081313

Morgan, Erin E; Doyle, Katie L; Minassian, Arpi; Henry, Brook L; Perry, William; Marcotte, Thomas D; Paul Woods, Steven; Grant, Igor

2014-12-15

284

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

OpenAIRE

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 clus...

Khan, A. U.; Mua Zu, S.; Wusirika, R.; Abubakar, B. Y.; Adamu, A. K.

2011-01-01

285

An Objective Method to derive the variable height-dependence of precipitation  

Science.gov (United States)

Most mountain ranges of the world show a significant vertical gradient of precipitation. Besides the general problem of precipitation measurement in mountainous terrain, the basic problem in deriving the height dependence is the fact, that observing stations never are strictly vertically collocated. Hence we can only derive gradients along slopes, which consist of the (wanted) vertical but also of a horizontal gradient component. With the aid of the VERA (Vienna Enhanced Resolution Analysis) system, both components may be separated objectively. The key of this procedure is the splitting of the known precipitation at observing stations into a field distribution of a predescribed vertical and a horizontal function and a residual. A variational procedure allows to derive the strength (weight) of the vertical as well as of the horizontal component of the gradient and the residual part. The mathematical constraint is the smoothness condition of the residual, which is that part of the precipitation field, unexplained by the predescribed vertical and horizontal function. One can think of the latter as being the hypothetic precipitation field, which would exist, if no mountains were in that region. The analysis system can be run with different assumptions of the vertical as well as horizontal gradient function to test, which response is strongest. The determination of the height dependence of precipitation in the larger Alpine area has been carried out in six-hourly intervals for one calendar year, to learn about its short term and spatial variability . The results clearly show, that in general there is a significant increase of precipitation with height. The increase, however is different between the Southern and Northern edges of the Alps and the inner Alpine region. The results furthermore show a seasonal dependence of the gradient and a variability with regard to the flow regime. Knowing such relations, one can also use the vertical functions to downscale precipitation fields from numerical weather prediction models. The basic setup of the system, the results of the statistical evaluation of the one-year test phase and possible applications in a climatological, diagnostic real time as well as prediction mode is being discussed.

Steinacker, R.; Mayer, D.

2012-04-01

286

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.

Jacobsen, S.; Andersen, P.H.

2004-01-01

287

Characterization of randomly amplified polymorphic DNA (RAPD fragments revealing clonal variability in cercariae of avian schistosome Trichobilharzia szidati (Trematoda: Schistosomatidae  

Directory of Open Access Journals (Sweden)

Full Text Available Recently we applied randomly amplified polymorphic DNA (RAPD fingerprinting to detect clonal variability among individual cercariae within daughter sporocysts and rediae of 10 digenean trematodes (Platyhelminthes: Trematoda. The most variable RAPD patterns were obtained for Schistosomatidae representative-avian schistosome Trichobilharzia szidati. In this work, 50 polymorphic DNA fragments of approximately 300-1500 bp from RAPD patterns of individual T. szidati cercariae were cloned and sequenced. As a result genomic DNA sequences (total length of approximately 41,000 bp revealing clonal variability in T. szidati cercariae were obtained and analyzed. The analysis indicated that these sequences contained tandem, inverted and dispersed repeats as well as regions homological to retroelements of two human parasites, Schistosoma mansoni and S. japonicum. Tandem and inverted repeats constituted 8.9% and 22.1% respectively, while the percentage of dispersed repeats was 21.0%. The average content of these components was 41.7% with the average AT content being 59.0%. About 40% of sequences included regions ranging in length from 96 to 1005 bp which displayed amino acid homology with open reading frame pol products of S. mansoni and S. japonicum retroelements: non-long terminal repeat retrotransposons (nLTRs, 76%, long terminal repeat retrotransposons (LTRs, 14%, and Penelope-like elements (PLEs, 10%. Most of these regions (86.4% contained frameshifts, gaps, and stop-codons. The largest portion of them was homological to nLTRs of the RTE clade (67%. The number of sequences homologous to the members of CR1 lineage was 7 times smaller (9%. Homology with LTRs of Gypsy/Ty3 and BEL clades was revealed in 5% and 9% of cases respectively. We assume that the repetitive elements including retroelement-like sequences described in the current study may serve as the source of clonal variability detected previously in T. szidati and other digenean trematodes. Such genome regions rapidly accumulate mutations and thus may play an important functional role in the life history of the species.

Anna Korsunenko

2013-08-01

288

Polarity- and valence-dependent effects of prefrontal transcranial direct current stimulation on heart rate variability and salivary cortisol.  

Science.gov (United States)

Recent evidence has supported the notion that the hypothalamic-pituitary-adrenal (HPA) and the sympatho-adreno-medullary (SAM) systems are modulated by cortical structures such as the prefrontal cortex. This top-down modulation may play a major role in the neuroendocrine changes associated with stressful events. We aimed to investigate further this hypothesis by modulating directly prefrontal cortex excitability using transcranial direct current stimulation (tDCS) - a non-invasive, neuromodulatory tool that induces polarity-dependent changes in cortical excitability - and measuring effects on salivary cortisol and heart rate variability as proxies of the HPA and SAM systems. Twenty healthy participants with no clinical and neuropsychiatric conditions were randomized to receive bifrontal tDCS (left anodal/right cathodal or left cathodal/right anodal) or sham stimulation, in a within-subject design. During each stimulation session, after a resting period, subjects were shown images with neutral or negative valence. Our findings showed that excitability enhancing left anodal tDCS induced a decrease in cortisol levels. This effect is more pronounced during emotional negative stimuli. Moreover, vagal activity was higher during left anodal tDCS and emotional negative stimuli, as compared to sham stimulation and neutral images. We also observed an association between higher mood scores, higher vagal activation and lower cortisol levels for anodal stimulation. Subjective mood and anxiety evaluation revealed no specific changes after stimulation. Our findings suggest that tDCS induced transient, polarity specific modulatory top-down effects with anodal tDCS leading to a down-regulation of HPA and SAM systems. Further research using tDCS and neuroendocrine markers should explore the mechanisms of stress regulation in healthy and clinical samples. PMID:22626867

Brunoni, Andre R; Vanderhasselt, Marie-Anne; Boggio, Paulo S; Fregni, Felipe; Dantas, Eduardo Miranda; Mill, Jos G; Lotufo, Paulo A; Benseor, Isabela M

2013-01-01

289

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

OpenAIRE

An initial efficacy test of an innovative behavioral outpatient treatment model for adolescents with problematic use of marijuana enrolled 69 adolescents, aged 1418, 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

290

Wigner theorems for random matrices with dependent entries: Ensembles associated to symmetric spaces and sample covariance matrices  

CERN Document Server

It is a classical result of Wigner that for an hermitian matrix with independent entries on and above the diagonal, the mean empirical eigenvalue distribution converges weakly to the semicircle law as matrix size tends to infinity. In this paper, we prove analogs of Wigner's theorem for random matrices taken from all infinitesimal versions of classical symmetric spaces. This is a class of models which contains those studied by Wigner and Dyson, along with seven others arising in condensed matter physics. Like Wigner's, our results are universal in that they only depend on certain assumptions about the moments of the matrix entries, but not on the specifics of their distributions. What is more, we allow for a certain amount of dependence among the matrix entries, in the spirit of a recent generalization of Wigner's theorem, due to Schenker and Schulz-Baldes. As a byproduct, we obtain a universality result for sample covariance matrices with dependent entries.

Hofmann-Credner, Katrin

2007-01-01

291

The Wick theorem for non-Gaussian distributions and its application for noise filtering of correlated q-Exponentialy distributed random variables  

CERN Document Server

We derive the Wick theorem for the q-Exponential distribution. We use the theorem to derive an algorithm for finding parameters of the correlation matrix of q-Exponentialy distributed random variables given empirical spectral moments of the time series.

Repetowicz, P; Repetowicz, Przemyslaw; Richmond, Peter

2004-01-01

292

Pure-Triplet Scattering for Radiative Transfer in Semi-infinite Random Media with Refractive-Index Dependent Boundary  

International Nuclear Information System (INIS)

Radiative transfer problem for pure-triplet scattering, in participating half-space random medium is proposed. The medium is assumed to be random with binary Markovian mixtures (e.g. radiation transfer in astrophysical contexts where the clouds and clear sky play and two-phase medium) described by Markovian statistics. The specular reflectivity of the boundary is angular-dependent described by the Fresnel's reflection probability function. The problem is solved at first in the deterministic case, and then the solution is averaged using the formalism developed by Levermore and Pomraning, to treat particles transport problems in statistical mixtures. Some physical quantities of interest such as the reflectivity of the boundary, average radiant energy, and average net flux are computed for various values of refractive index of the boundary

293

Post traumatic stress symptoms and heart rate variability in Bihar flood survivors following yoga: a randomized controlled study  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background An earlier study showed that a week of yoga practice was useful in stress management after a natural calamity. Due to heavy rain and a rift on the banks of the Kosi river, in the state of Bihar in north India, there were floods with loss of life and property. A week of yoga practice was given to the survivors a month after the event and the effect was assessed. Methods Twenty-two volunteers (group average age S.D, 31.5 7.5 years; all of them were males were randomly assigned to two groups, yoga and a non-yoga wait-list control group. The yoga group practiced yoga for an hour daily while the control group continued with their routine activities. Both groups' heart rate variability, breath rate, and four symptoms of emotional distress using visual analog scales, were assessed on the first and eighth day of the program. Results There was a significant decrease in sadness in the yoga group (p Conclusions A week of yoga can reduce feelings of sadness and possibly prevent an increase in anxiety in flood survivors a month after the calamity. Trial Registration Clinical Trials Registry of India: CTRI/2009/091/000285

Joshi Meesha

2010-03-01

294

The Dependence of Cloud Particle Size on Non-Aerosol-Loading Related Variables  

Energy Technology Data Exchange (ETDEWEB)

An enhanced concentration of aerosol may increase the number of cloud drops by providing more cloud condensation nuclei (CCN), which in turn results in a higher cloud albedo at a constant cloud liquid water path. This process is often referred to as the aerosol indirect effect (AIE). Many in situ and remote sensing observations support this hypothesis (Ramanathan et al. 2001). However, satellite observed relations between aerosol concentration and cloud drop size are not always in agreement with the AIE. Based on global analysis of cloud effective radius (r{sub e}) and aerosol number concentration (N{sub a}) derived from satellite data, Sekiguchi et al. (2003) found that the correlations between the two variables can be either negative, or positive, or none, depending on the location of the clouds. They discovered that significantly negative r{sub e} - N{sub a} correlation can only be identified along coastal regions of the continents where abundant continental aerosols inflow from land, whereas Feingold et al. (2001) found that the response of r{sub e} to aerosol loading is the greatest in the region where aerosol optical depth ({tau}{sub a}) is the smallest. The reason for the discrepancy is likely due to the variations in cloud macroscopic properties such as geometrical thickness (Brenguier et al. 2003). Since r{sub e} is modified not only by aerosol but also by cloud geometrical thickness (H), the correlation between re and {tau}{sub a} actually reflects both the aerosol indirect effect and dependence of H. Therefore, discussing AIE based on the r{sub e}-{tau}{sub a} correlation without taking into account variations in cloud geometrical thickness may be misleading. This paper is motivated to extract aerosols' effect from overall effects using the independent measurements of cloud geometrical thickness, {tau}{sub a} and r{sub e}.

Shao, H.; Liu, G.

2005-03-18

295

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

Science.gov (United States)

Context. Massive stars show a variety of spectral variabilities: discrete absorption components in UV P-Cygni profiles, optical line profile variability, X-ray variability, and radial velocity modulations. Aims: 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 and on high signal-to-noise ratio optical spectra collected with the spectrograph NARVAL on the Tlescope Bernard Lyot at Pic du Midi. Methods: We investigated the variability of twelve spectral lines by means of the temporal variance spectrum. The selected lines probe the radial structure of the atmosphere from the photosphere to the outer wind. We also performed a spectroscopic analysis with atmosphere models to derive the stellar and wind properties and to constrain the formation region of the selected lines. Results: We show that variability is observed in the wind lines of all bright giants and supergiants on a daily timescale. Lines formed in the photosphere are sometimes variable, sometimes not. The dwarf stars do not show any sign of variability. If variability is observed on a daily timescale, it can also (but not always) be observed on hourly timescales, albeit with lower amplitude. There is a very clear correlation between amplitude of the variability and fraction of the line formed in the wind. Strong anti-correlations between the different parts of the temporal variance spectrum are observed. Conclusions: Our results indicate that variability is stronger in lines formed in the wind. A link between photospheric and wind variability is not obvious from our study, since wind variability is observed regardless of the level of photospheric variability. Different photospheric lines also show different degrees of variability. Appendices are available in electronic form at http://www.aanda.org

Martins, F.; Marcolino, W.; Hillier, D. J.; Donati, J.-F.; Bouret, J.-C.

2015-02-01

296

Alcohol-related brief intervention in patients treated for opiate or cocaine dependence: a randomized controlled study  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Despite the importance of heavy drinking and alcohol dependence among patients with opiate and cocaine dependence, few studies have evaluated specific interventions within this group. The aim of the present study was to evaluate the impact of screening with the Alcohol Use Disorders Identification Test (AUDIT and of brief intervention (BI on alcohol use in a sample of patients treated for opioid or cocaine dependence in a specialized outpatient clinic. Methods Adult outpatients treated for opioid or cocaine dependence in Switzerland were screened for excessive alcohol drinking and dependence with the AUDIT. Patients with AUDIT scores that indicated excessive drinking or dependence were randomized into two groups--treatment as usual or treatment as usual together with BI--and assessed at 3 months and 9 months. Results Findings revealed a high rate (44% of problematic alcohol use (excessive drinking and dependence among patients with opiate and cocaine dependence. The number of drinks per week decreased significantly between T0 (inclusion and T3 (month 3. A decrease in average AUDIT scores was observed between T0 and T3 and between T0 and T9 (month 9. No statistically significant difference between treatment groups was observed. Conclusions In a substance abuse specialized setting, screening for alcohol use with the AUDIT, followed by feedback on the score, and use of alcohol BI are both possibly useful strategies to induce changes in problematic alcohol use. Definitive conclusions cannot, however, be drawn from the study because of limitations such as lack of a naturalistic group. An important result of the study is the excellent internal consistency of AUDIT in a population treated for opiate or cocaine dependence.

Khan Riaz

2011-08-01

297

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

Energy Technology Data Exchange (ETDEWEB)

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. (author)

Turkyilmazoglu, M. [Mathematics Department, University of Hacettepe, Ankara (Turkey)

2011-01-15

298

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)

299

Range-dependent random graphs and their application to modeling large small-world Proteome datasets  

OpenAIRE

In this paper we consider the problem of characterizing and modeling large-scale networks using classes of range-dependent graphs which possess appropriate small-world properties. The application we have in mind is to bioinformatics, where methods of rapid protein identification mean that such proteome datasets, listing various observed protein-protein associations, will become more and more prevalent. We introduce a class of range-dependent graphs, governed by a power law relating interverte...

Grindrod, P.

2002-01-01

300

Characterizations of joint distributions, copulas, information, dependence and decoupling, with applications to time series  

CERN Document Server

In this paper, we obtain general representations for the joint distributions and copulas of arbitrary dependent random variables absolutely continuous with respect to the product of given one-dimensional marginal distributions. The characterizations obtained in the paper represent joint distributions of dependent random variables and their copulas as sums of $U$-statistics in independent random variables. We show that similar results also hold for expectations of arbitrary statistics in dependent random variables. As a corollary of the results, we obtain new representations for multivariate divergence measures as well as complete characterizations of important classes of dependent random variables that give, in particular, methods for constructing new copulas and modeling different dependence structures. The results obtained in the paper provide a device for reducing the analysis of convergence in distribution of a sum of a double array of dependent random variables to the study of weak convergence for a doub...

De la Pena, V H; Sharakhmetov, S; de la Pea, Victor H; Ibragimov, Rustam; Sharakhmetov, Shaturgun

2006-01-01

301

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

302

Alaskan soil carbon stocks: spatial variability and dependence on environmental factors  

Directory of Open Access Journals (Sweden)

Full Text Available The direction and magnitude of soil organic carbon (SOC changes in response to climate change depend on the spatial and vertical distributions of SOC. We estimated spatially resolved SOC stocks from surface to C horizon, distinguishing active-layer and permafrost-layer stocks, based on geospatial analysis of 472 soil profiles and spatially referenced environmental variables for Alaska. Total Alaska state-wide SOC stock was estimated to be 77 Pg, with 61% in the active-layer, 27% in permafrost, and 12% in non-permafrost soils. Prediction accuracy was highest for the active-layer as demonstrated by highest ratio of performance to deviation (1.5. Large spatial variability was predicted, with whole-profile, active-layer, and permafrost-layer stocks ranging from 1296 kg C m?2, 2166 kg m?2, and 0232 kg m?2, respectively. Temperature and soil wetness were found to be primary controllers of whole-profile, active-layer, and permafrost-layer SOC stocks. Secondary controllers, in order of importance, were found to be land cover type, topographic attributes, and bedrock geology. The observed importance of soil wetness rather than precipitation on SOC stocks implies that the poor representation of high-latitude soil wetness in Earth system models may lead to large uncertainty in predicted SOC stocks under future climate change scenarios. Under strict caveats described in the text and assuming temperature changes from the A1B Intergovernmental Panel on Climate Change emissions scenario, our geospatial model indicates that the equilibrium average 2100 Alaska active-layer depth could deepen by 11 cm, resulting in a thawing of 13 Pg C currently in permafrost. The equilibrium SOC loss associated with this warming would be highest under continuous permafrost (31%, followed by discontinuous (28%, isolated (24.3%, and sporadic (23.6% permafrost areas. Our high-resolution mapping of soil carbon stock reveals the potential vulnerability of high-latitude soil carbon and can be used as a basis for future studies of anthropogenic and climatic perturbations.

U. Mishra

2012-09-01

303

Alaskan soil carbon stocks: spatial variability and dependence on environmental factors  

Directory of Open Access Journals (Sweden)

Full Text Available The direction and magnitude of soil organic carbon (SOC changes in response to climate change depend on the spatial and vertical distributions of SOC. We estimated spatially-resolved SOC stocks from surface to C horizon, distinguishing active-layer and permafrost-layer stocks, based on geospatial analysis of 472 soil profiles and spatially referenced environmental variables for Alaska. Total Alaska state-wide SOC stock was estimated to be 77 Pg, with 61% in the active-layer, 27% in permafrost, and 12% in non-permafrost soils. Prediction accuracy was highest for the active-layer as demonstrated by highest ratio of performance to deviation (1.5. Large spatial variability was predicted, with whole-profile, active-layer, and permafrost-layer stocks ranging from 1296 kg C m?2, 2166 kg m?2, and 0232 kg m?2, respectively. Temperature and soil wetness were found to be primary controllers of whole-profile, active-layer, and permafrost-layer SOC stocks. Secondary controllers, in order of importance, were: land cover type, topographic attributes, and bedrock geology. The observed importance of soil wetness rather than precipitation on SOC stocks implies that the poor representation of high-latitude soil wetness in Earth System Models may lead to large uncertainty in predicted SOC stocks under future climate change scenarios. Under strict caveats described in the text and assuming temperature changes from the A1B Intergovernmental Panel on Climate Change emissions scenario, our geospatial model indicates that the equilibrium average 2100 Alaska active-layer depth could deepen by 11 cm, resulting in a thawing of 13 Pg C currently in permafrost. The equilibrium SOC loss associated with this warming would be highest under continuous permafrost (31%, followed by discontinuous (28%, isolated (24.3%, and sporadic (23.6% permafrost areas. Our high resolution mapping of soil carbon stock reveals the potential vulnerability of high-latitude soil carbon and can be used as a basis for future studies of anthropogenic and climatic perturbations.

U. Mishra

2012-05-01

304

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

305

Switching field dependence on heating pulse duration in thermally assisted magnetic random access memories  

Energy Technology Data Exchange (ETDEWEB)

The minimum applied field H{sub SW} required to reverse the magnetic moment of the ferromagnetic/antiferromagnetic storage layer of a thermally assisted magnetic random access memory (TA-MRAM) device during the application of a heating electric pulse is investigated as a function of pulse power P{sub HP} and duration {delta}. For the same power of the heating pulse P{sub HP} (or, equivalently, for the same temperature of the storage layer), H{sub SW} increases with decreasing heating time {delta}. This behavior is consistently interpreted by a thermally activated propagating domain-wall switching model, corroborated by a real-time study of switching. The increase of H{sub SW} with decreasing pulse width introduces a constraint for the minimum power consumption of a TA-MRAM where writing combines heating and magnetic field application.

Papusoi, C. [Spintec, URA 2512 CEA/CNRS, 17 rue des Martyrs, 38054 Grenoble (France)], E-mail: cristian_papusoi@yahoo.com; Conraux, Y.; Prejbeanu, I.L. [Crocus Technology, 5 Robert Schumann, BP 1510, 38025 Grenoble (France); Sousa, R.; Dieny, B. [Spintec, URA 2512 CEA/CNRS, 17 rue des Martyrs, 38054 Grenoble (France)

2009-08-15

306

Switching field dependence on heating pulse duration in thermally assisted magnetic random access memories  

International Nuclear Information System (INIS)

The minimum applied field HSW required to reverse the magnetic moment of the ferromagnetic/antiferromagnetic storage layer of a thermally assisted magnetic random access memory (TA-MRAM) device during the application of a heating electric pulse is investigated as a function of pulse power PHP and duration ?. For the same power of the heating pulse PHP (or, equivalently, for the same temperature of the storage layer), HSW increases with decreasing heating time ?. This behavior is consistently interpreted by a thermally activated propagating domain-wall switching model, corroborated by a real-time study of switching. The increase of HSW with decreasing pulse width introduces a constraint for the minimum power consumption of a TA-MRAM where writing combines heating and magnetic field application.

307

Moderate deviations for random walk in random scenery  

OpenAIRE

We investigate random walks in independent, identically distributed random sceneries under the assumption that the scenery variables satisfy Cramer's condition. We prove moderate deviation principles in dimensions two and larger, covering all those regimes where rate and speed do not depend on the actual distribution of the scenery. In the case of dimension four and larger we even obtain precise asymptotics for the annealed probability of a moderate deviation, extending a cl...

Fleischmann, Klaus; Morters, Peter; Wachtel, Vitali

2006-01-01

308

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

OpenAIRE

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 moist...

Li, B.; Rodell, M.

2013-01-01

309

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

OpenAIRE

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...

Li, B.; Rodell, M.

2012-01-01

310

Contractile Strength during Variable Heart Duration Is Species and Preload Dependent  

OpenAIRE

We investigate the effect of beat-to-beat variability on cardiac contractility. Cardiac trabeculae were isolated from the right ventricle of rabbits and beagle dogs and stimulated to isometrically contract, alternating between fixed steady state versus variable interbeat intervals. Trabeculae were stimulated at physiologically relevant frequencies for each species (dog 1 and 4?Hz; rabbit 2 and 4?Hz) intercalating fixed periods with 40% variability. A subset of the trabeculae (at 90% of op...

Torres, Carlos A. A.; Janssen, Paul M. L.

2011-01-01

311

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 Krakw 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

312

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

Science.gov (United States)

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. PMID:14624703

Assadi, Seyed Mohammad; Radgoodarzi, Reza; Ahmadi-Abhari, Seyed Ali

2003-01-01

313

Homogenization for Rigid Suspensions with Random Velocity-Dependent Interfacial Forces  

OpenAIRE

We study suspensions of solid particles in a viscous incompressible fluid in the presence of highly oscillatory velocity-dependent surface forces. The flow at a small Reynolds number is modeled by the Stokes equations coupled with the motion of rigid particles arranged in a periodic array. The objective is to perform homogenization for the given suspension and obtain an equivalent description of a homogeneous (effective) medium, the macroscopic effect of the interfacial forc...

Gorb, Yuliya; Maris, Florian; Vernescu, Bogdan

2013-01-01

314

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

OpenAIRE

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

315

A randomized trial of two behavioral interventions to improve outcomes following inpatient detoxification for alcohol dependence.  

Science.gov (United States)

Participants (n=150), undergoing inpatient alcohol detoxification, were randomized into 3 groups: treatment as usual (TAU), motivation enhancement therapy (MET), or peer-delivered 12-step facilitation (P-TSF). The main outcome was the initiation of any type of subsequent rehabilitation service (i.e., professional treatment or self-help) within 30 and 90 days of discharge. At the 30-day follow-up interview, there was no significant difference among the groups in the rate of initiation of any type of subsequent care (82%, 74%, and 82%, respectively, p=0.617); however, the MET group had significantly more patients initiate subsequent inpatient treatment by the 90-day follow-up interview compared to the P-TSF group (31% and 61%, respectively, p=0.007) and a greater proportion of MET participants completed subsequent inpatient treatment compared to both the TAU and P-TSF groups. There were no differences in drinking-related outcomes. MET during inpatient detoxification may help patients initiate subsequent inpatient rehabilitation treatment. PMID:21491295

Blondell, Richard D; Frydrych, Lynne M; Jaanimagi, Urmo; Ashrafioun, Lisham; Homish, Gregory G; Foschio, Elisa M; Bashaw, Heather L

2011-04-01

316

Time-dependent reliability of corrosion-affected RC beams-Part 1: Estimation of time-dependent strengths and associated variability  

International Nuclear Information System (INIS)

Research highlights: ? Predictive models for corrosion-induced damages in RC structures. ? Formulations for time-dependent flexural and shear strengths of corroded RC beams. ? Methodology for mean and c.o.v. for time-dependent strengths of corroded RC beams. ? Simple estimation of mean and c.o.v. for flexural strength with loss of bond. - Abstract: The structural deterioration of reinforced concrete (RC) structures due to reinforcement corrosion is a major worldwide problem. Damages to RC structures due to reinforcement corrosion manifest in the form of expansion, cracking and eventual spalling of the cover concrete; thereby resulting in serviceability and durability degradation of such structures. In addition to loss of cover, RC structure may suffer structural damages due to loss of reinforcement cross-sectional area, and loss of bond between corroded reinforcement and surrounding cracked concrete, sometimes to the extent that the structural failure becomes inevitable. This paper forms the first part of a study which addresses time-dependent reliability analyses of RC beams affected by reinforcement corrosion. In this paper initially the predictive models are presented for the quantitative assessment of time-dependent damages in RC beams, recognized as loss of mass and cross-sectional area of reinforcing bar, loss of concrete section owing to the peeling of cover concrete, and loss of bond between corroded reinforcement and surrounding cracked concrete. Thensurrounding cracked concrete. Then these models have been used to present analytical formulations for evaluating time-dependent flexural and shear strengths of corroded RC beams, based on the standard composite mechanics expressions for RC sections. Further by considering variability in the identified basic variables that could affect the time-dependent strengths of corrosion-affected RC beams, the estimation of statistical descriptions for the time-dependent strengths is presented for a typical simply supported RC beam. The statistical descriptions, i.e., mean and coefficient of variation (c.o.v.) for the time-dependent strengths are presented for two limit states: (a) flexural failure, and (b) shear failure. The other two parts of the reliability study present the estimation of time-dependent failure probability for the considered RC beam by utilizing the information provided on probabilistic descriptions of time-dependent strengths in this paper. The effects of time to corrosion initiation and its variability on the failure probability of the considered RC beam have also been discussed.

317

Time-dependent reliability of corrosion-affected RC beams-Part 1: Estimation of time-dependent strengths and associated variability  

Energy Technology Data Exchange (ETDEWEB)

Research highlights: Predictive models for corrosion-induced damages in RC structures. Formulations for time-dependent flexural and shear strengths of corroded RC beams. Methodology for mean and c.o.v. for time-dependent strengths of corroded RC beams. Simple estimation of mean and c.o.v. for flexural strength with loss of bond. - Abstract: The structural deterioration of reinforced concrete (RC) structures due to reinforcement corrosion is a major worldwide problem. Damages to RC structures due to reinforcement corrosion manifest in the form of expansion, cracking and eventual spalling of the cover concrete; thereby resulting in serviceability and durability degradation of such structures. In addition to loss of cover, RC structure may suffer structural damages due to loss of reinforcement cross-sectional area, and loss of bond between corroded reinforcement and surrounding cracked concrete, sometimes to the extent that the structural failure becomes inevitable. This paper forms the first part of a study which addresses time-dependent reliability analyses of RC beams affected by reinforcement corrosion. In this paper initially the predictive models are presented for the quantitative assessment of time-dependent damages in RC beams, recognized as loss of mass and cross-sectional area of reinforcing bar, loss of concrete section owing to the peeling of cover concrete, and loss of bond between corroded reinforcement and surrounding cracked concrete. Then these models have been used to present analytical formulations for evaluating time-dependent flexural and shear strengths of corroded RC beams, based on the standard composite mechanics expressions for RC sections. Further by considering variability in the identified basic variables that could affect the time-dependent strengths of corrosion-affected RC beams, the estimation of statistical descriptions for the time-dependent strengths is presented for a typical simply supported RC beam. The statistical descriptions, i.e., mean and coefficient of variation (c.o.v.) for the time-dependent strengths are presented for two limit states: (a) flexural failure, and (b) shear failure. The other two parts of the reliability study present the estimation of time-dependent failure probability for the considered RC beam by utilizing the information provided on probabilistic descriptions of time-dependent strengths in this paper. The effects of time to corrosion initiation and its variability on the failure probability of the considered RC beam have also been discussed.

Bhargava, Kapilesh, E-mail: kapilesh_66@yahoo.co.u [Architecture and Civil Engineering Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India); Mori, Yasuhiro [Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8603 (Japan); Ghosh, A.K. [Reactor Safety Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India)

2011-05-15

318

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

319

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 (PollakRiess) 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)

320

Process for the measurement of a random pulsed (or which can be transformed in pulses) physical variable and application to gamma spectrometry  

International Nuclear Information System (INIS)

On a measurement system giving a result relative to the said variable an iterative simulation is performed taking into account the randomness of the measured phenomenon, distinguishing the evolution of simple, double, triple... in the electronic processing. An approximative result is determined and compared to the result obtained by simulation. Application is made to the measurement of activity level of radionuclides present in a circulating fluid, for instance in a PWR

321

Effect of a sugar-free chewing gum containing magnolia bark extract on different variables related to caries and gingivitis: a randomized controlled intervention trial  

OpenAIRE

The effect of magnolia bark extract (MBE) on different variables related to caries and gingivitis administered daily through a sugar-free chewing gum was evaluated. The study was performed with healthy adult volunteers at high risk for caries as a randomized double-blind interventional study. 120 subjects with a salivary mutans streptococci (MS) concentration ?105 CFU/ml and presence of bleeding on probing <25% were enrolled and divided into three groups: magnolia, xylitol and...

Campus, Guglielmo Giuseppe; Cagetti, Maria Grazia; Cocco, Fabio; Sale, Silvana; Sacco, G.; Strohmenger, Laura; Lingstro?m, Peter

2011-01-01

322

Limit distributions of scale-invariant probabilistic models of correlated random variables with the q-Gaussian as an explicit example  

Science.gov (United States)

Extremization of the Boltzmann-Gibbs (BG) entropy S_{BG}=-kint dx p(x) ln p(x) under appropriate norm and width constraints yields the Gaussian distribution pG(x) ?e-?x. Also, the basic solutions of the standard Fokker-Planck (FP) equation (related to the Langevin equation with additive noise), as well as the Central Limit Theorem attractors, are Gaussians. The simplest stochastic model with such features is N ?? independent binary random variables, as first proved by de Moivre and Laplace. What happens for strongly correlated random variables? Such correlations are often present in physical situations as e.g. systems with long range interactions or memory. Frequently q-Gaussians, pq(x) ?[1-(1-q)?x2]1/(1-q) [p1(x)=pG(x)] become observed. This is typically so if the Langevin equation includes multiplicative noise, or the FP equation to be nonlinear. Scale-invariance, e.g. exchangeable binary stochastic processes, allow a systematical analysis of the relation between correlations and non-Gaussian distributions. In particular, a generalized stochastic model yielding q-Gaussians for all (q ? 1) was missing. This is achieved here by using the Laplace-de Finetti representation theorem, which embodies strict scale-invariance of interchangeable random variables. We demonstrate that strict scale invariance together with q-Gaussianity mandates the associated extensive entropy to be BG.

Hanel, R.; Thurner, S.; Tsallis, C.

2009-11-01

323

An MGF-Based Unified Framework to Determine the Joint Statistics of Partial Sums of Ordered i.n.d. Random Variables  

Science.gov (United States)

The joint statistics of partial sums of ordered random variables (RVs) are often needed for the accurate performance characterization of a wide variety of wireless communication systems. A unified analytical framework to determine the joint statistics of partial sums of ordered independent and identically distributed (i.i.d.) random variables was recently presented. However, the identical distribution assumption may not be valid in several real-world applications. With this motivation in mind, we consider in this paper the more general case in which the random variables are independent but not necessarily identically distributed (i.n.d.). More specifically, we extend the previous analysis and introduce a new more general unified analytical framework to determine the joint statistics of partial sums of ordered i.n.d. RVs. Our mathematical formalism is illustrated with an application on the exact performance analysis of the capture probability of generalized selection combining (GSC)-based RAKE receivers operating over frequency-selective fading channels with a non-uniform power delay profile. We also discussed a couple of other sample applications of the generic results presented in this work.

Nam, Sung Sik; Yang, Hong-Chuan; Alouini, Mohamed-Slim; Kim, Dong In

2014-08-01

324

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

325

Calculations on the giant-dipole resonance in the continuum random-phase approximation with a momentum-dependent interaction  

International Nuclear Information System (INIS)

A formulation of the continuum random-phase approximation (CRPA) nuclear response with a velocity-dependent residual interaction of the Skyrme type is presented. The inhomogeneous coupled-channel integro-differential equations obtained are modified so as to use the Lanczos method, by means of which they can be solved relatively easy. The CRPA method here presented can give information on the direct and statistical decay as well as their partial ph components. We apply the method to a detailed analysis of photonuclear reactions in 4He, 16O and 40Ca in the giant-dipole-resonance region. Total cross sections, contributions from direct emission and spreading as well as partial ?p and ?n emission ph components are calculated and compared to experimental data. (orig.)

326

Lactase persistence and bitter taste response: instrumental variables and mendelian randomization in epidemiologic studies of dietary factors and cancer risk  

OpenAIRE

Consumption of dairy products seems to increase the risk of cancer at several sites, while intake of cruciferous vegetables could have protective effects. However, these dietary intakes are subject to measurement error, and associations with cancer could be due to confounders. Mendelian randomization has been suggested as a way to overcome confounding by exploiting the random allocation of alleles from parents to offspring. In mid-2006, the authors conducted a study of allele frequencies for ...

Matullo, Giuseppe; Vineis, Paolo; Guarrera, Simonetta; Sacerdote, Carlotta

2007-01-01

327

Outer Membrane Targeting of Pseudomonas aeruginosa Proteins Shows Variable Dependence on the Components of Bam and Lol Machineries  

OpenAIRE

In Gram-negative bacteria, the Lol and Bam machineries direct the targeting of lipidated and nonlipidated proteins, respectively, to the outer membrane (OM). Using Pseudomonas aeruginosa strains with depleted levels of specific Bam and Lol proteins, we demonstrated a variable dependence of different OM proteins on these targeting pathways. Reduction in the level of BamA significantly affected the ability of the ?-barrel membrane protein OprF to localize to the OM, while the targeting of thre...

Hoang, Hanh H.; Nickerson, Nicholas N.; Lee, Vincent T.; Kazimirova, Anastasia; Chami, Mohamed; Pugsley, Anthony P.; Lory, Stephen

2011-01-01

328

Individual wage and reservation wage: efficient estimation of a simultaneous equation model with endogenous limited dependent variables  

OpenAIRE

We consider a simultaneous equation model with two endogenous limited dependent variables (individual wage and reservation wage) characterized by a selection mechanism determining a two-regimes endogenous-switching. We extend the FIML procedure proposed by Poirier-Ruud (1981) for a single equation switching model providing a stochastic specification for both equations and for the selection criterion. An accurate Monte Carlo experiment shows that the relative efficiency of the FIML estimator o...

Calzolari, Giorgio; Di Pino, Antonino

2009-01-01

329

A Proof-of-Concept Randomized Controlled Study of Gabapentin: Effects on Cannabis Use, Withdrawal and Executive Function Deficits in Cannabis-Dependent Adults  

OpenAIRE

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 w...

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

2012-01-01

330

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

331

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

332

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)

333

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

Science.gov (United States)

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.

Zhang, Zhan-Gang; Liu, Jie; Hou, Ming-Dong; Sun, You-Mei; Su, Hong; Duan, Jing-Lai; Mo, Dan; Yao, Hui-Jun; Luo, Jie; Gu, Song; Geng, Chao; Xi, Kai

2013-08-01

334

Frequency-dependent hopping conductivity in a static electric field in a random one-dimensional lattice  

International Nuclear Information System (INIS)

The frequency-dependent electrical conductivity is studied in a nearest-neighbor-hopping linear lattice with disordered site energies and barrier heights in the presence of a uniform static electric field, allowing for detailed balance between random rates. Exact expressions are obtained for the conductivity for both high and low frequencies. The results reduce to those obtained by previous authors in the absence of site-energy disorder. However, the latter is found to alter the character of the frequency dependence of the conductivity significantly at low frequencies. In this case the conductivity is expanded as sigma(?) = sigma0+isigma1?-sigma2?2 -isigma3?3+.... We find that sigma1 is nonvanishing only if both site energies and barrier heights are disordered and that sigma2 is positive when the fluctuations in site energies are small compared with the thermal energy but becomes negative in the opposite regime. The ac response is found to vanish [i.e., sigma(?) = 0 for ?not =0] in the absence of disorder in barrier heights

335

Experiment and theory of Pb(In1/2Nb1/2)O3. Antiferroelectric, ferroelectric, or relaxor state depending on perovskite B-site randomness  

International Nuclear Information System (INIS)

We review the recent progress in our understanding of the effect of B-site randomness on Pb(In1/2Nb1/2)O3 (PIN) from the experimental and theoretical viewpoints. PIN is one of the ideal systems for investigating the effect of perovskite B-site randomness on relaxor formation, because it can be in the antiferroelectric (AFE), ferroelectric (FE), or relaxor state depending on B-site randomness. Lattice dynamics measured in ordered and disordered PINs indicates the existence of FE instability regardless of the B-site randomness of PIN. AFE is stabilized when the B-site is spatially ordered, overwhelming FE instability. The hidden FE state starts to appear as B-site randomness becomes stronger and suppresses AFE instability. Ultimately, the randomness competes with the development of FE regions and blocks long-range FE ordering, which yields polar nanoregions (PNRs) resulting in relaxor behavior. In order to investigate the interesting behavior of PIN, we constructed a minimal model that includes dipolar interaction and easy-axis anisotropy which depends on B-site randomness. The results from Monte Carlo simulations show that the model well reproduces the phase diagram and dielectric constant of PIN qualitatively. (author)

336

On The Spectral Energy Dependence of Gamma-Ray Burst Variability  

CERN Document Server

The variable activity of a gamma-ray burst (GRB) source is thought to be correlated with its absolute peak luminosity - a relation that, if confirmed, can be used to derive an independent estimate of the redshift of a GRB. We find that bursts with highly variable light curves have greater nu-F_nu spectral peak energies, when we transform these energies to the cosmological rest frame using the redshift estimates derived either from optical spectral features or from the luminosity-variability distance indicator itself. This positive correlation between peak energy and variability spans ~ 2 orders of magnitude and appears to accommodate GRB 980425, lending credibility to the association of this burst with SN 1998bw. The existence of such a correlation not only provides an interesting clue to the nature of this luminosity indicator but potentially reinforces the validity of the redshift estimates derived from this method. It also implies that the rest frame GRB peak energy is correlated with the intrinsic luminos...

Lloyd-Ronning, N M; Lloyd-Ronning, Nicole M.; Ramirez-Ruiz, Enrico

2002-01-01

337

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

338

Highly variable gastric emptying in patients with insulin dependent diabetes mellitus.  

OpenAIRE

Some diabetic patients--particularly those with nausea and vomiting--frequently have evidence of delayed gastric emptying while other diabetic patients may in fact exhibit accelerated gastric emptying. Whether the presence or absence of symptoms of upper gastrointestinal dysfunction correlated with objective measures of gastric emptying in insulin dependent diabetic subjects was investigated. Twenty one insulin dependent diabetic patients underwent a solid phase gastric emptying scintiscan us...

Nowak, T. V.; Johnson, C. P.; Kalbfleisch, J. H.; Roza, A. M.; Wood, C. M.; Weisbruch, J. P.; Soergel, K. H.

1995-01-01

339

Contact-dependent performance variability of monolayer MoS2 field-effect transistors  

Science.gov (United States)

Using self-consistent quantum transport simulations, we investigate the performance variability of monolayer molybdenum disulfide (MoS2) field-effect transistors (FETs) with various contact properties. Varying the Schottky barrier in MoS2 FETs affects the output characteristics more significantly than the transfer characteristics. If doped contacts are realized, the performance variation due to non-ideal contacts becomes negligible; otherwise, channel doping can effectively suppress the performance variability in metal-contact devices. Our scaling study also reveals that for sub-10-nm channels, doped-contact devices can be more robust in terms of switching, while metal-contact MoS2 FETs can undergo the smaller penalty in output conductance.

Han, Gyuchull; Yoon, Youngki

2014-11-01

340

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

Energy Technology Data Exchange (ETDEWEB)

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.

Rothwell, James J. [Upland Environments Research Group, School of Environment and Development, niversity of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)]. E-mail: james.rothwell@manchester.ac.uk; Evans, Martin G. [Upland Environments Research Group, School of Environment and Development, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Lindsay, John B. [Upland Environments Research Group, School of Environment and Development, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Allott, Timothy E.H. [Upland Environments Research Group, School of Environment and Development, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)

2007-01-15

341

Generalised extreme value statistics and sum of correlated variables  

OpenAIRE

We show that generalised extreme value statistics -the statistics of the k-th largest value among a large set of random variables- can be mapped onto a problem of random sums. This allows us to identify classes of non-identical and (generally) correlated random variables with a sum distributed according to one of the three (k-dependent) asymptotic distributions of extreme value statistics, namely the Gumbel, Frechet and Weibull distributions. These classes, as well as the li...

Bertin, Eric; Clusel, Maxime

2006-01-01

342

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

OpenAIRE

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

343

The flux-dependent rms variability of X-ray binaries in the optical  

OpenAIRE

A linear relation between absolute rms variability and flux in X-ray observations of compact accreting sources has recently been identified. Such a relation suggests that X-ray lightcurves are non-linear and composed of a lognormal distribution of fluxes. Here, a first investigation of the optical rms vs. flux behavior in X-ray binaries is presented. Fast timing data on three binaries in the X-ray low/hard state are examined. These are XTE J1118+480, GX 339-4 and SWIFT J1753...

Gandhi, Poshak

2009-01-01

344

Method of nuclear reactor control using a variable temperature load dependent set point  

International Nuclear Information System (INIS)

This invention provides a method and apparatus for nuclear reactor control using a variable reactor coolant temperature set point which is a function of power load demand. The set point has a constant temperature at the mid range of power load and a decreasing temperature at the higher range. A manual control is provided which is based exclusively on feedwater flow and allows power changes of up to 5 percent full power a minute with less boron concentration change than would otherwise be required

345

Effects of Moxa (Folium Artemisiae argyi) Smoke Exposure on Heart Rate and Heart Rate Variability in Healthy Young Adults: A Randomized, Controlled Human Study  

OpenAIRE

Objective. To determine the effects of the moxa smoke on human heart rate (HR) and heart rate variability (HRV). Methods. Fifty-five healthy young adults were randomly divided into experimental (n = 28) and control (n = 27) groups. Experimental subjects were exposed to moxa smoke (2.5 0.5?mg/m3) twice for 25 minutes in one week. ECG monitoring was performed before, during, and after exposure. Control subjects were exposed to normal indoor air in a similar environment and similarly monito...

Yingxue Cui; Baixiao Zhao; Yuhai Huang; Zhanghuang Chen; Ping Liu,; Jian Huang; Lixing Lao

2013-01-01

346

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

347

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

348

The relations of go and stop wave to car accidents in a cellular automaton with velocity-dependent randomization  

Science.gov (United States)

In this paper we numerically study the probability Pac of the occurrence of traffic accidents in the Nagel-Schreckenberg (NS) model with velocity-dependent randomization (VDR). Numerical results show that there is a critical density over which car accidents occur, but below which no car accidents happen. Different from the accident probability in the NS model, the accident probability in the VDR model monotonously decreases with increase of car density above the critical density. The value of the accident probability is only determined by the stochastic noise and the number of cars on road. In the stochastic VDR model with the speed limit vmax=1, no critical density exists and car accidents happen in the whole density region. The braking probabilities of standing cars and moving cars have different influences on the accident probability. A mean-field theory reveals that the accident probability is proportional to the mean density of go and stop wave per time step. Theoretical analyses give excellent agreement with numerical results in the VDR model.

Yang, Xian-Qing; Zhang, Wei; Qiu, Kang; Xu, Wen-tao; Tang, Gang; Ren, Lin

2007-10-01

349

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

350

Study of temperature-dependent ultrathin oxide growth on Si(111) using variable-angle spectroscopic ellipsometry  

Science.gov (United States)

The monolayer-sensitive variable-angle spectroscopic ellipsometry technique was used to study the temperature-dependent growth mechanisms of an ultrathin oxide layer on top of silicon. The oxidation was done in atomic oxygen produced in a pure oxygen plasma and driven by an RF power source. The results have been compared with the recently proposed model of Murali and Murarka for ultrathin oxide growth on top of silicon. The activation energies of different growth parameters associated with the oxide growth have also been determined.

De, Bhola N.; Woollam, John A.

1990-01-01

351

Numerical solution of the time-dependent Ginzburg-Landau equation for a superconducting mesoscopic disk: Link variable method  

International Nuclear Information System (INIS)

The time dependent GinzburgLandau equations (TDGLE) are used to study the superconducting properties of a disk by taking into account the influence of internal defects. The Link variable algorithm is applied to a circular geometry surrounded by an insulator and immersed in an external magnetic field applied perpendicular to its plane. The TDGLE are used upon taking the magnetic field and the order parameter invariant along z-direction. We show that the magnetic response is substantially modified by the competition between the confinement geometry and the geometric position of the defects leads to vortex configurations which are not compatible with the symmetry of the sample geometry.

352

Transient thermal stresses in a perforated plate of variable thickness exhibiting temperature-dependent material properties  

International Nuclear Information System (INIS)

Serious interest has been shown to the problem of plane thermal stress in a multiple connection region having many circular holes, in connection with the high temperature strength design of heat exchangers, nuclear reactor cores, chemical plants and so on. In spite of the relatively large temperature gradient in such problems, the temperature dependence of material properties has not been taken in consideration. Also the problem when the thickness of plates changes such as fins, cylinder heads and rotary disks has not been analyzed. In this study, attention was paid to the fact that the change of plate thickness largely affects the temperature distribution, and the temperature distribution affects the values of material constants, and the problem of unsteady plane thermal stress considering the temperature dependence of the properties of a perforated plate with varying thickness was formulated by stress function method. The obtained equations were expressed in finite difference form, and the numerical analysis was carried out to examine the effects of the change of thickness and the temperature dependence of material properties on the temperature distribution and thermal stress. (Kako, I.)

353

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

354

Adaptive cancellation of variable feedback path for hearing aid using misalignment-dependent step size values.  

Science.gov (United States)

Various methods have been proposed to overcome the problem of compensating the acoustic feedback path that negatively impacts the performance of hearing aid devices. However, in most of them feedback path model is assumed to be fixed which is not quite realistic. In this paper, we consider fixed and variable feedback paths and analyze for each case the performance of one of the robust Adaptive Feedback Cancellation (AFC) schemes, i.e. the Prediction Error Method AFC which uses Partitioned Block Frequency-Domain Normalized Least Mean Square (PBFD-NLMS) algorithm. Based on the analysis results we propose varying the step size values for the same adaptive algorithm on the fly by monitoring the misalignment criteria. The experimental results using the proposed method show improvement made on the system performance. PMID:22256175

Khoubrouy, Soudeh A; Panahi, Issa M S

2011-01-01

355

Lactase persistence and bitter taste response: instrumental variables and mendelian randomization in epidemiologic studies of dietary factors and cancer risk.  

Science.gov (United States)

Consumption of dairy products seems to increase the risk of cancer at several sites, while intake of cruciferous vegetables could have protective effects. However, these dietary intakes are subject to measurement error, and associations with cancer could be due to confounders. Mendelian randomization has been suggested as a way to overcome confounding by exploiting the random allocation of alleles from parents to offspring. In mid-2006, the authors conducted a study of allele frequencies for the lactase (LCT) and taste receptor, type 2, member 38 (TAS2R38) genes, including 634 volunteers recruited (1992-1998) from the Italian branch of the European Prospective Investigation into Cancer and Nutrition. The authors hypothesized that there would be a lower milk intake among carriers of the LCT CC genotype and a different intake of cruciferous vegetables among carriers of the TAS2R38 variant. Overall, the frequency of the LCT T allele was higher in northern Italy than in southern Italy. Food intake was associated with gene variants. An association was evident for ice cream and LCT variants (p = 0.004); less so for milk intake. In addition, the TAS2R38 variant showed a geographic gradient and an association with cruciferous vegetable intake. These results suggest that the LCT and TAS2R38 variants are good candidates for Mendelian randomization studies of cancer and other health outcomes. PMID:17596267

Sacerdote, Carlotta; Guarrera, Simonetta; Smith, George Davey; Grioni, Sara; Krogh, Vittorio; Masala, Giovanna; Mattiello, Amalia; Palli, Domenico; Panico, Salvatore; Tumino, Rosario; Veglia, Fabrizio; Matullo, Giuseppe; Vineis, Paolo

2007-09-01

356

Updating random hydraulic conductivity fields: A two-step procedure  

Science.gov (United States)

Predictions of groundwater travel times at field sites are generally uncertain because of uncertainty and variability in hydrogeological parameters, especially the hydraulic conductivity, K. Uncertainty is a subjective value that depends upon the person performing the analysis. Variability is an objective, though likely unknown, value that depends upon geology and depositional environment. Uncertainty and variability can be combined by treating hydraulic conductivity as a random field in a Bayesian framework [Hachich and Vanmarcke, 1983; Massmann and Freeze, 1987].

Massmann, Joel W.; Freeze, R. Allan

1989-07-01

357

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

358

Energy dependent power spectral states and origin of aperiodic variability in black hole binaries  

CERN Document Server

We found the black hole candidate MAXI J1659-152 showed distinct power spectra, i.e., a power-law noise (PLN) vs. band-limited noise (BLN) plus quasi-periodic oscillations (QPOs), below and above about 2 keV respectively, in the observations with the Swift and the RXTE during the 2010 outburst, indicating a high energy cut-off of the PLN and a low energy cut-off of the BLN and the QPOs around 2 keV. The emergence of the PLN and the fading of the BLN and the QPOs initially took place from below 2 keV when the source entered the hard intermediate state and finally 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 X-ray and the hard X-ray bands. Our results indicate that the PLN is associated with the optically thick disk in both hard and intermediate states, and power spectral state is independent of the X-ray energy spectral state in a broadband view. We suggest that in the hard a...

Yu, Wenfei

2013-01-01

359

The spatial scale dependence of water vapor variability inferred from observations from a very tall tower  

Science.gov (United States)

Recent studies have established that atmospheric water vapor fields exhibit spatial spectra that take the form of power laws and hence can be compactly characterized by scaling exponents. The power law scaling exponents have been shown to exhibit substantial vertical variability. In this work, Taylor's frozen turbulence hypothesis is used to infer the first-order spatial structure function and generalized detrended fluctuation function scaling exponents for scales between 1 km and 100 km. Both methods are used to estimate the Hurst exponent (H) using 10 Hz time series of water vapor measured at 396 m altitude from an Ameriflux tower in Wisconsin. Due to the diurnal cycle in the boundary layer height at the 396 m observational level, H may be estimated for both the daytime convective mixed layer and the nocturnal residual layer. Values of H?1/3 are obtained for the convective mixed layer, while values of H>1/2 apply in the nocturnal residual layer. The results are shown to be remarkably consistent with a similar analysis from satellite-based observations as reported in Pressel and Collins (2012).

Pressel, Kyle G.; Collins, William D.; Desai, Ankur R.

2014-08-01

360

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

361

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

International Nuclear Information System (INIS)

We found that the black hole candidate MAXI J1659152 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.k as well.

362

The Dependencies of Ecosystem Pattern, Structure, and Dynamics on Climate, Climate Variability, and Climate Change  

Science.gov (United States)

A robust understanding of the sensitivity of the pattern, structure, and dynamics of ecosystems to climate, climate variability, and climate change is needed to predict ecosystem responses to current and projected climate change. We present results of a study designed to first quantify the sensitivity of ecosystems to climate through the use of climate and ecosystem data, and then use the results to test the sensitivity of the climate data in a state-of the art ecosystem model. A database of available ecosystem characteristics such as mean canopy height, above ground biomass, and basal area was constructed from sources like the National Biomass and Carbon Dataset (NBCD). The ecosystem characteristics were then paired by latitude and longitude with the corresponding climate characteristics temperature, precipitation, photosynthetically active radiation (PAR) and dew point that were retrieved from the North American Regional Reanalysis (NARR). The average yearly and seasonal means of the climate data, and their associated maximum and minimum values, over the 1979-2010 time frame provided by NARR were constructed and paired with the ecosystem data. The compiled results provide natural patterns of vegetation structure and distribution with regard to climate data. An advanced ecosystem model, the Ecosystem Demography model (ED), was then modified to allow yearly alterations to its mechanistic climate lookup table and used to predict the sensitivities of ecosystem pattern, structure, and dynamics to climate data. The combined ecosystem structure and climate data results were compared to ED's output to check the validity of the model. After verification, climate change scenarios such as those used in the last IPCC were run and future forest structure changes due to climate sensitivities were identified. The results of this study can be used to both quantify and test key relationships for next generation models. The sensitivity of ecosystem characteristics to climate data shown in the database construction and by the model reinforces the need for high-resolution datasets and stresses the importance of understanding and incorporating climate change scenarios into earth system models.

Flanagan, S.; Hurtt, G. C.; Fisk, J. P.; Rourke, O.

2012-12-01

363

Variable loop glycan dependency of the broad and potent HIV-1-neutralizing antibodies PG9 and PG16.  

Science.gov (United States)

The HIV-1-specific antibodies PG9 and PG16 show marked cross-isolate neutralization breadth and potency. Antibody neutralization has been shown to be dependent on the presence of N-linked glycosylation at position 160 in gp120. We show here that (i) the loss of several key glycosylation sites in the V1, V2, and V3 loops; (ii) the generation of pseudoviruses in the presence of various glycosidase inhibitors; and (iii) the growth of pseudoviruses in a mutant cell line (GnT1(-/-)) that alters envelope glycosylation patterns all have significant effects on the sensitivity of virus to neutralization by PG9 and PG16. However, the interaction of antibody is not inhibited by sugar monosaccharides corresponding to those found in glycans on the HIV surface. We show that some of the glycosylation effects described are isolate dependent and others are universal and can be used as diagnostic for the presence of PG9 and PG16-like antibodies in the sera of HIV-1-infected patients. The results suggest that PG9 and PG16 recognize a conformational epitope that is dependent on glycosylation at specific variable loop N-linked sites. This information may be valuable for the design of immunogens to elicit PG9 and PG16-like antibodies, as well as constructs for cocrystallization studies. PMID:20686044

Doores, Katie J; Burton, Dennis R

2010-10-01

364

Predictive modeling of groundwater nitrate pollution using Random Forest and multisource variables related to intrinsic and specific vulnerability: a case study in an agricultural setting (Southern Spain).  

Science.gov (United States)

Watershed management decisions need robust methods, which allow an accurate predictive modeling of pollutant occurrences. Random Forest (RF) is a powerful machine learning data driven method that is rarely used in water resources studies, and thus has not been evaluated thoroughly in this field, when compared to more conventional pattern recognition techniques key advantages of RF include: its non-parametric nature; high predictive accuracy; and capability to determine variable importance. This last characteristic can be used to better understand the individual role and the combined effect of explanatory variables in both protecting and exposing groundwater from and to a pollutant. In this paper, the performance of the RF regression for predictive modeling of nitrate pollution is explored, based on intrinsic and specific vulnerability assessment of the Vega de Granada aquifer. The applicability of this new machine learning technique is demonstrated in an agriculture-dominated area where nitrate concentrations in groundwater can exceed the trigger value of 50 mg/L, at many locations. A comprehensive GIS database of twenty-four parameters related to intrinsic hydrogeologic proprieties, driving forces, remotely sensed variables and physical-chemical variables measured in "situ", were used as inputs to build different predictive models of nitrate pollution. RF measures of importance were also used to define the most significant predictors of nitrate pollution in groundwater, allowing the establishment of the pollution sources (pressures). The potential of RF for generating a vulnerability map to nitrate pollution is assessed considering multiple criteria related to variations in the algorithm parameters and the accuracy of the maps. The performance of the RF is also evaluated in comparison to the logistic regression (LR) method using different efficiency measures to ensure their generalization ability. Prediction results show the ability of RF to build accurate models with strong predictive capabilities. PMID:24463255

Rodriguez-Galiano, Victor; Mendes, Maria Paula; Garcia-Soldado, Maria Jose; Chica-Olmo, Mario; Ribeiro, Luis

2014-04-01

365

Simulation of temperature history-dependent phenomena of glass-forming materials based on thermodynamics with internal state variables  

International Nuclear Information System (INIS)

In ref. , a profound ansatz for modelling the various phenomena associated with the glass-transition was presented. It extends classical theories, such as the concept of fictive temperature or order parameters, for example, in two ways. Firstly, temperature excitations as well as mechanical loadings are accounted for in a single consistent approach. Secondly, it is not formulated in the ?-p-V space, but rather in the ?-T-E space, taking the tensor character of stress T and strain E into account. Hence, it is a three-dimensional theory where the basic thermodynamic potential, the Gibbs free energy, depends on the stress tensor, the temperature and a set of internal variables. In the current article, expressions for the enthalpy, the entropy, the thermal expansion and the specific heat are derived. The specific heat and the thermal expansion behaviour are looked at for various temperature excitations. It is shown, that the results are in accord with experimental observations in literature.

366

Nonvolatile Static Random Access Memory Using Resistive Switching Devices: Variable-Transconductance Metal-Oxide-Semiconductor Field-Effect-Transistor Approach  

Science.gov (United States)

In this paper, we present a variable-transconductance (gm) metal-oxide-semiconductor field-effect-transistor (VGm-MOSFET) architecture using a nonpolar resistive switching device (RSD) for nonvolatile bistable circuit applications. The architecture can be achieved by connecting an RSD to the source terminal of an ordinary MOSFET. The current drive capability of the VGm-MOSFET can be modified by resistance states of the connected RSD, which is a very useful function for nonvolatile bistable circuits, such as nonvolatile static random access memory (NV-SRAM) and nonvolatile flip-flop (NV-FF). NV-SRAM can be easily configured by connecting two additional VGm-MOSFETs to the storage nodes of a standard SRAM cell. Using our developed SPICE macromodel for nonpolar RSDs, successful circuit operations of the proposed NV-SRAM cell were confirmed.

Yamamoto, Shuu'ichirou; Shuto, Yusuke; Sugahara, Satoshi

2010-04-01

367

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)

368

Time-dependent simulations of emission from FSRQ PKS1510-089: multiwavelength variability of external Compton and SSC models  

CERN Document Server

[abridged] We present results of modeling the SED and multiwavelength variability of the bright FSRQ PKS1510-089 with our time-dependent multizone Monte Carlo/Fokker-Planck code (Chen et al. 2001). As primary source of seed photons for inverse Compton scattering, we consider radiation from the broad line region (BLR), from the molecular torus, and the local synchrotron radiation (SSC). Different scenarios are assessed by comparing simulated light curves and SEDs with one of the best flares by PKS1510-089, in March 2009. The time-dependence of our code and its correct handling of light travel time effects allow us to fully take into account the effect of the finite size of the active region, and in turn to fully exploit the information carried by time resolved observed SEDs, increasingly available since the launch of Fermi. We confirm that the spectrum adopted for the external radiation has an important impact on the modeling of the SED, in particular for the lower energy end of the Compton component, observed...

Chen, Xuhui; Liang, Edison; Boettcher, Markus

2012-01-01

369

Do variable compensatory mechanisms explain the polymorphism of the dependence phenotype in the Asobara tabida-wolbachia association?  

Science.gov (United States)

Wolbachia are symbiotic intracellular bacteria, which are classified as reproductive parasites. Although generally facultative, Wolbachia is necessary for Asobara tabida (Hymenoptera), because aposymbiotic females do not produce any offspring. Interestingly, the ovarian phenotype of aposymbiotic females is variable: some females do not produce any eggs, whereas others do produce some eggs, but these are aborted. Here, we show that the ovarian phenotype of aposymbiotic females is highly polymorphic within populations, although dependence remains complete in both cases. We also identified some lines in which aposymbiotic females were able to produce a very few viable offspring, further extending the range of variation observed. These results suggest that various factors actively maintain polymorphism. We demonstrated that Wolbachia is necessary to trigger oogenetic processes, but that the ovarian phenotype was determined by the host only. Phenotypic variation was also correlated with the differential expression of genes controlling iron homeostasis and oxidative stress, which are potentially involved in the evolution of dependence. This suggests that variation in the ovarian phenotype could reflect selection for different levels of compensatory mechanisms in response to Wolbachia infection, and that polymorphism is maintained through selection on different antagonist traits influenced by oxidative stress. PMID:20482609

Kremer, Natacha; Dedeine, Franck; Charif, Delphine; Finet, Cdric; Allemand, Roland; Vavre, Fabrice

2010-10-01

370

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

OpenAIRE

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 ...

Smith, S. F.; Streeter, M. J.

2011-01-01

371

Universality for Random Tensors  

OpenAIRE

We prove two universality results for random tensors of arbitrary rank D. We first prove that a random tensor whose entries are N^D independent, identically distributed, complex random variables converges in distribution in the large N limit to the same limit as the distributional limit of a Gaussian tensor model. This generalizes the universality of random matrices to random tensors. We then prove a second, stronger, universality result. Under the weaker assumption that t...

Gurau, Razvan

2011-01-01

372

Systematic Spatial Bias in DNA Microarray Hybridization Is Caused by Probe Spot Position-Dependent Variability in Lateral Diffusion  

Science.gov (United States)

Background The hybridization of nucleic acid targets with surface-immobilized probes is a widely used assay for the parallel detection of multiple targets in medical and biological research. Despite its widespread application, DNA microarray technology still suffers from several biases and lack of reproducibility, stemming in part from an incomplete understanding of the processes governing surface hybridization. In particular, non-random spatial variations within individual microarray hybridizations are often observed, but the mechanisms underpinning this positional bias remain incompletely explained. Methodology/Principal Findings This study identifies and rationalizes a systematic spatial bias in the intensity of surface hybridization, characterized by markedly increased signal intensity of spots located at the boundaries of the spotted areas of the microarray slide. Combining observations from a simplified single-probe block array format with predictions from a mathematical model, the mechanism responsible for this bias is found to be a position-dependent variation in lateral diffusion of target molecules. Numerical simulations reveal a strong influence of microarray well geometry on the spatial bias. Conclusions Reciprocal adjustment of the size of the microarray hybridization chamber to the area of surface-bound probes is a simple and effective measure to minimize or eliminate the diffusion-based bias, resulting in increased uniformity and accuracy of quantitative DNA microarray hybridization. PMID:21858215

Haider, Susanne; Horn, Matthias; Wagner, Michael; Stocker, Roman; Loy, Alexander

2011-01-01

373

A randomized, double-blind comparison of 10 and 20 mg lercanidipine in patients with stable effort angina: effects on myocardial ischemia and heart rate variability.  

Science.gov (United States)

We evaluated the anti-ischemic action and the effects on autonomic function of lercanidipine, a long-acting dihydropyridine calcium antagonist, in 25 patients with stable effort angina in a randomized, double-blind, parallel trial. After a 2-week placebo run-in period, patients entered a 2-week treatment period with 10 or 20 mg of lercanidipine once daily. During the placebo run-in period and at the study end, the patients underwent clinical examination, electrocardiography, exercise tests, 24-hour Holter electrocardiography for long-term heart rate variability evaluation, and short-term spectral analysis of heart rate and systolic blood pressure variability and plasma epinephrine and norepinephrine levels at rest and during tilting. Results showed that time to onset of ST segment depression > or =1 mm was significantly increased by both drug doses. No significant change was recorded in the average hourly heart rate after treatment with both 10 and 20 mg of lercanidipine. During the 24-hour recordings, no significant change was observed in low-frequency power, high-frequency power, or low frequency/high frequency. In the standing position, there was a significant increase in plasma norepinephrine and epinephrine concentration in both groups, and no change in the supine position after 10 and 20 mg of lercanidipine. When considering short-term heart rate variability, no significant difference was observed in either treatment group in low frequency, high frequency, or their ratio on electrocardiographic R-R spectra. The blood pressure spectral component was also unchanged. In conclusion, lercanidipine is effective in reducing ischemia in patients with stable effort angina. Moreover, lercanidipine does not cause adrenergic activation, which is the main mechanism hypothesized to explain the negative effect on cardiovascular mortality assigned to short-acting dihydropyridine calcium antagonists. PMID:12237738

Acanfora, Domenico; Trojano, Luigi; Gheorghiade, Mihai; Picone, Costantino; Papa, Antimo; Furgi, Giuseppe; Giuliano, Franca; Maestri, Roberto; Rengo, Franco

2002-01-01

374

Free energy of activation. Definition, properties, and dependent variables with special reference to linear free energy relations  

International Nuclear Information System (INIS)

The reaction rate constant is expressed as Z exp(-G/sub a//RT). Z is the binary collision frequency. G/sub a/, the free energy of activation, is shown to be the difference between the free energy of the reactive reactants and the free energy of all reactants. The results are derived from both a statistical mechanical and a collision theoretic point of view. While the later is more suitable for an ab-initio computation of the reaction rate, it is the former that lends itself to the search of systematics and of correlations and to compaction of data. Different thermodynamic-like routes to the characterization of G/sub a/ are thus explored. The two most promising ones appear to be the use of thermodynamic type cycles and the changes of dependent variables using the Legendre transform technique. The dependence of G/sub a/ on ?G0, the standard free energy change in the reaction, is examined from the later point of view. It is shown that one can rigorously express this dependence as G/sub a/ = ??G0 + G/sub a/0M(?). Here ? is the Bronsted slope, ? = -par. delta ln k(T)/par. delta(?G0/RT), G/sub a/0 is independent of ?G0 and M(?), the Legendre transform of G/sub a/, is a function only of ?. For small changes in ?G0, the general result reduces to the familiar ''linear'' free energy relation delta G/sub a/ = ? delta ?G0. It is concluded from general considerations that M(?) is considerations that M(?) is a symmetric, convex function of ? and hence that ? is a monotonically increasing function of ?G0. Experimental data appear to conform well to the form ? = 1/[1 + exp(-?G0/G/sub s/0)]. A simple interpretation of the ?G0 dependence of G/sub a/, based on an interpolation of the free energy from that of the reagents to that of the products, is offered. 4 figures, 69 references

375

Correction of chromosomal mutation and random integration in embryonic stem cells with helper-dependent adenoviral vectors  

OpenAIRE

For gene therapy of inherited diseases, targeted integration/gene repair through homologous recombination (HR) between exogenous and chromosomal DNA would be an ideal strategy to avoid potentially serious problems of random integration such as cellular transformation and gene silencing. Efficient sequence-specific modification of chromosomes by HR would also advance both biological studies and therapeutic applications of a variety of stem cells. Toward these goals, we developed an improved st...

Ohbayashi, Fumi; Balamotis, Michael A.; Kishimoto, Atsuhiro; Aizawa, Emi; Diaz, Arturo; Hasty, Paul; Graham, Frank L.; Caskey, C. Thomas; Mitani, Kohnosuke

2005-01-01

376

Observation of a shape-dependent density maximum in random packings and glasses of colloidal silica ellipsoids  

International Nuclear Information System (INIS)

We have measured the random packing density of monodisperse colloidal silica ellipsoids with a well-defined shape, gradually deviating from a sphere shape up to prolates with aspect ratios of about 5, to find for a colloidal system the first experimental observation for the density maximum (at an aspect ratio near 1.6) previously found only in computer simulations of granular packings. Confocal microscopy of ellipsoid packings, prepared by rapidly quenching ellipsoid fluids via ultra-centrifugation, demonstrates the absence of orientational order and yields pair correlation functions very much like those for random sphere packings. The density maximum, about 12% above the Bernal random sphere packing density, also manifests itself as a maximum in the hydrodynamic friction that resists the swelling osmotic pressure of the ellipsoid packings. The existence of the density maximum is also predicted to strongly effect the dynamics of colloidal non-sphere glasses: slightly perturbing the sphere shape in a sphere glass will cause it to melt

377

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

378

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Particle Swarm Optimization (PSO) es un mtodo de bsqueda no directo para la optimizacin numrica. Las principales ventajas de esta meta-heurstica estn relacionadas principalmente con su simplicidad, pocos parmetros y alta tasa de convergencia. En el PSO cannico usando una topologa totalmente [...] conectada, una partcula ajusta su posicin 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 tambin deteriora la diversidad de la poblacin progresivamente. Como resultado la bandada de partculas frecuentemente es atrada por puntos sub-ptimos. Una vez que las partculas han sido atradas hacia un ptimo local, ellas continan el proceso de bsqueda dentro de una regin muy pequea del espacio de soluciones, reduciendo las capacidades de exploracin del algoritmo. Para tratar esta situacin este artculo presenta una variante del procedimiento Random Sampling in Variable Neighborhoods (RSVN) usando una distribucin de Lvy. Este algoritmo es capaz de mejorar notablemente la capacidad de bsqueda de los algoritmos PSO en problemas multimodales de optimizacin. 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 Lvy distribution, which is able to notably improve the PSO search ability in multimodal problems.

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

2014-03-01

379

Random lsc functions  

OpenAIRE

Random lsc (lower semicontinuous) functions can be indentified with a vector-valued random variable by means of an appropriate scalarization. It is shown that stationarity, ergodicity and independence properties are preserved by this scalarization. The scalarization is exploited to obtain an lsc version of the conditional expectation of a random lsc function.

Korf, Lisa A.; Wets, Roger J. -b

2000-01-01

380

Spanning avalanches in the three-dimensional Gaussian Random Field Ising Model with metastable dynamics: field dependence and geometrical properties  

CERN Document Server

Spanning avalanches in the 3D Gaussian Random Field Ising Model (3D-GRFIM) with metastable dynamics at T=0 have been studied. Statistical analysis of the field values for which avalanches occur has enabled a Finite-Size Scaling (FSS) study of the avalanche density to be performed. Furthermore, direct measurement of the geometrical properties of the avalanches has confirmed an earlier hypothesis that several kinds of spanning avalanches with two different fractal dimensions coexist at the critical point. We finally compare the phase diagram of the 3D-GRFIM with metastable dynamics with the same model in equilibrium at T=0.

Prez-Reche, F J; Perez-Reche, Francisco-Jose; Vives, Eduard

2004-01-01

381

Random and systematic spatial variability of 137Cs inventories at reference sites in South-Central Brazil / Variabilidade espacial randmica e sistemtica dos inventrios de 137Cs de reas de referncia no Sudeste do Brasil  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese A preciso da tcnica de anlise da redistribuio do "fallout" do 137Cs nas avaliaes das taxas de eroso so fortemente dependentes da qualidade de um inventrio mdio tomado em uma rea de referncia representativa. O conhecimento das fontes e do grau de variao da distribuio do "fallout" do [...] 137Cs desempenham um importante papel na aplicao desta tcnica. Quatro reas de referncia foram selecionadas na regio Sudeste do Brasil, sendo estas caracterizadas quanto aos aspectos fsicos, qumicos, mineralgicos do solo, assim como a variabilidade espacial dos inventrios de 137Cs. Houve algumas diferenas importantes no padro da distribuio do 137Cs em profundidade nos perfis de solo dos diferentes locais que, provavelmente, esto associadas s diferenas qumicas, fsicas, mineralgicas e biolgicas dos solos estudados. Mas muitas questes ainda permanecem abertas para futuras investigaes, principalmente em relao adsoro e dinmica do 137Cs no perfil dos solos tropicais. A variabilidade espacial randmica (dentro de cada local de referncia) foi maior do que a variabilidade espacial sistemtica (entre reas de referncia), porm as causas disto no foram claramente identificadas, talvez em conseqncia da variabilidade qumica, fsica e/ou mineralgica bem como da precipitao. Abstract in english The precision of the 137Cs fallout redistribution technique for the evaluation of soil erosion rates is strongly dependent on the quality of an average inventory taken at a representative reference site. The knowledge of the sources and of the degree of variation of the 137Cs fallout spatial distrib [...] ution plays an important role on its use. Four reference sites were selected in the South-Central region of Brazil which were characterized in terms of soil chemical, physical and mineralogical aspects as well as the spatial variability of 137Cs inventories. Some important differences in the patterns of 137Cs depth distribution in the soil profiles of the different sites were found. They are probably associated to chemical, physical, mineralogical and biological differences of the soils but many questions still remain open for future investigation, mainly those regarding the adsorption and dynamics of the 137Cs ions in soil profiles under tropical conditions. The random spatial variability (inside each reference site) was higher than the systematic spatial variability (between reference sites) but their causes were not clearly identified as possible consequences of chemical, physical, mineralogical variability, and/or precipitation.

Vladia, Correchel; Osny Oliveira Santos, Bacchi; Klaus, Reichardt; Isabella Clerici, De Maria.

2005-04-01

382

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

International Nuclear Information System (INIS)

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. (geophysics, astronomy, and astrophysics)

383

An alternative approach to exact wave functions for time-dependent coupled oscillator model of charged particle in variable magnetic field  

CERN Document Server

A general treatment of the quantal time-dependent coupled oscillators in presence of the variable magnetic field is presented. The treatment is based on the use of an alternative canonical transformations, time-dependent unitary transformations and the invariant methods. Exact wave functions for Schr\\"{o}dinger equations of this system are constructed.We applied our theory to a particular case and, co,sequently, showed that our results recovers to the perviously known one.

Menouar, Salah; Choi, Jeong Ryeol

2010-01-01

384

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

385

Effect of a sugar-free chewing gum containing magnolia bark extract on different variables related to caries and gingivitis: a randomized controlled intervention trial.  

Science.gov (United States)

The effect of magnolia bark extract (MBE) on different variables related to caries and gingivitis administered daily through a sugar-free chewing gum was evaluated. The study was performed with healthy adult volunteers at high risk for caries as a randomized double-blind interventional study. 120 subjects with a salivary mutans streptococci (MS) concentration ?10(5) CFU/ml and presence of bleeding on probing >25% were enrolled and divided into three groups: magnolia, xylitol and control. The study design included examinations at baseline, after 7 days, after 30 days of gum use and 7 days after the end of gum use. Plaque pH was assessed using the strip method following a sucrose challenge. Area under the curve (AUC(5.7) and AUC(6.2)) was recorded. Whole saliva was collected and the number of salivary MS (CFU/ml) was counted. Bleeding on probing was recorded as a proxy of dental plaque. Data were analyzed using ANOVA repeated measures. Magnolia gum significantly reduced plaque acidogenicity, MS salivary concentration and gingival bleeding compared to xylitol and control gums. Subjects from the magnolia and xylitol groups showed both MS concentration (p = 0.01 and 0.06, respectively) and AUC(5.7) (p = 0.01 and 0.04, respectively) to be significantly lower compared to baseline. Thirty-day use of a chewing gum containing MBE showed beneficial effects on oral health, including reduction of salivary MS, plaque acidogenicity and bleeding on probing. PMID:21822018

Campus, G; Cagetti, M G; Cocco, F; Sale, S; Sacco, G; Strohmenger, L; Lingstrm, P

2011-01-01

386

Nonlinear Schroedinger equations under random nonlinearity management  

International Nuclear Information System (INIS)

We consider effects of random time modulation of the nonlinearity coefficient on the dynamics of one- and two-dimensional (1D and 2D) solitary waves in the nonlinear Schroedinger equation (NLSE). In particular, the cases of a single Gaussian random variable, and a temporally correlated Gaussian process are considered. In the 1D case, we demonstrate the robustness of solitons against the random nonlinearity management. In the 2D case, the share (percentage) of realizations that lead to collapse of a localized pulse is computed, in order to quantify the effect of the randomness in preventing the collapse. Dependences of this share on the mean value, standard deviation, and correlation length of the random process are obtained, and, whenever possible, compared to analytical predictions

387

Random Simplicial Complexes  

OpenAIRE

In this paper we introduce a new model of random simplicial complexes depending on multiple probability parameters. This model includes the well-known Linial - Meshulam random simplicial complexes and random clique complexes as special cases. Topological and geometric properties of a multi-parameter random simplicial complex depend on the whole combination of the probability parameters and the thresholds for topological properties are convex sets rather than numbers (as in a...

Costa, A.; Farber, M.

2014-01-01

388

Resource variability, aggregation and direct density dependence in an open context: the local regulation of an African elephant population.  

Science.gov (United States)

1. An emerging perspective in the study of density dependence is the importance of the spatial and temporal heterogeneity of resources. Although this is well understood in temperate ungulates, few studies have been conducted in tropical environments where both food and water are limiting resources. 2. We studied the regulation of one of the world's largest elephant populations in Hwange National Park, Zimbabwe. The study period started in 1986 when the population was released from culling. Using census data we investigated changes in elephant abundance with respect to rainfall and density across the entire park and across waterholes. 3. The population more than doubled since culling stopped. The population increased continuously during the first 6 years, and then fluctuated widely at about 30,000 individuals. Immigration processes must have been involved in the increase of the population size. 4. Population growth rates were negatively related to previous population density by a convex relationship, and negatively related to the ratio of previous population density on annual rainfall by a linear relationship. However, only this latter model (i.e. assuming a fluctuating carrying capacity related to annual rainfall) produced realistic dynamics. Overall, population decreased during dry years when the elephant density was high. 5. During dry years there were fewer waterholes retaining water during the dry season and consequently elephant numbers at waterholes increased, while their aggregation level across waterholes decreased. On the long-run elephant numbers increased only at the less crowded waterholes. 6. We suggest that the interaction between population size and the available foraging range determined by the number of active waterholes during the dry season controls the park population. 7. Our results emphasize the need to understand how key-resource areas cause resource-based aggregation, which ultimately influences the strength of density dependence. More specifically, this study suggests that climate variability strongly affects local elephant population dynamics through changes in surface-water availability. Finally, as dispersal is likely to be an important driver of the dynamics of this population, our results support views that a metapopulation framework should be endorsed for elephant management in open contexts. PMID:17986249

Chamaill-Jammes, Simon; Fritz, Herv; Valeix, Marion; Murindagomo, Felix; Clobert, Jean

2008-01-01

389

Italian randomized trial among women with hysterectomy: tamoxifen and hormone-dependent breast cancer in high-risk women.  

Science.gov (United States)

Tamoxifen improves outcome in women with breast cancer and reduces the incidence of estrogen receptor-positive (ER+) breast tumors in prevention trials. Tamoxifen use is associated with an increased risk of potentially serious adverse events, principally endometrial cancer and venous thromboembolic events and, therefore, detailed knowledge of the effects of tamoxifen is important. With more cases of breast cancer being found as the follow-up time increases, it is now possible to perform more detailed analysis of the Italian Randomized Trial of Tamoxifen. Women with hysterectomy (N = 5408) were randomly assigned to receive 20 mg tamoxifen per day (N = 2700) or placebo (N = 2708). After a median of 81.2 months of follow-up, 79 case subjects (34 in the tamoxifen arm and 45 in the placebo arm) were diagnosed with breast cancer. We were able to identify a group of women at increased risk of ER+ breast cancers (high-risk group) on the basis of baseline as well as reproductive and hormonal characteristics (height, age at menarche, parity, age at first birth, and oophorectomy). Tamoxifen administered to women in the high-risk group showed statistically significantly reduced incidence of breast cancer (tamoxifen, 3 and placebo, 15; P =.003), but no such effect was seen in the low-risk group (tamoxifen, 31 and placebo, 30; P =.89). The positive effect of tamoxifen on breast cancer among high-risk women is most marked for ER+ tumors (tamoxifen, 1 and placebo, 11; P =.002). Chemoprevention of breast cancer with tamoxifen appears to be effective in women at high risk of ER+ tumors but not among women at low risk, who may well be protected naturally by late age at menarche or early first pregnancy, or artificially by removal of the ovaries. Tamoxifen could be offered as a preventive agent to women identified at high-risk of breast cancer because of hormone-related risk factors. Such a strategy would greatly reduce the numbers of women who would need to take tamoxifen to obtain the same absolute reduction in breast cancer. These findings are exploratory and need to be confirmed in other randomized trials. PMID:12529349

Veronesi, Umberto; Maisonneuve, Patrick; Rotmensz, Nicole; Costa, Alberto; Sacchini, Virgilio; Travaglini, Roberto; D'Aiuto, Giuseppe; Lovison, Francesco; Gucciardo, Giacomo; Muraca, Maria Grazia; Pizzichetta, Maria Antonietta; Conforti, Serafino; Decensi, Andrea; Robertson, Chris; Boyle, Peter

2003-01-15

390

Modeling scale-dependent bias on the baryonic acoustic scale with the statistics of peaks of Gaussian random fields  

International Nuclear Information System (INIS)

Models of galaxy and halo clustering commonly assume that the tracers can be treated as a continuous field locally biased with respect to the underlying mass distribution. In the peak model pioneered by Bardeen et al.[Astrophys. J. 304, 15 (1986)], one considers instead density maxima of the initial, Gaussian mass density field as an approximation to the formation site of virialized objects. In this paper, the peak model is extended in two ways to improve its predictive accuracy. First, we derive the two-point correlation function of initial density peaks up to second order and demonstrate that a peak-background split approach can be applied to obtain the k-independent and k-dependent peak bias factors at all orders. Second, we explore the gravitational evolution of the peak correlation function within the Zel'dovich approximation. We show that the local (Lagrangian) bias approach emerges as a special case of the peak model, in which all bias parameters are scale independent and there is no statistical velocity bias. We apply our formulas to study how the Lagrangian peak biasing, the diffusion due to large scale flows, and the mode coupling due to nonlocal interactions affect the scale dependence of bias from small separations up to the baryon acoustic oscillation (BAO) scale. For 2? density peaks collapsing at z=0.3, our model predicts a ?5% residual scale-dependent bias around the acoustic scale that arises mostly from first order Lagrangian peak biasing (as oppo order Lagrangian peak biasing (as opposed to second order gravity mode coupling). We also search for a scale dependence of bias in the large scale autocorrelation of massive halos extracted from a very large N-body simulation provided by the MICE Collaboration. For halos with mass M > or approx. 1014M/h, our measurements demonstrate a scale-dependent bias across the BAO feature which is very well reproduced by a prediction based on the peak model.

391

Nonparametric identification with discrete endogenous variables  

OpenAIRE

This paper studies the nonparametric identification of partial differences of a nonseparable structural function that determines the value of a discrete or continuous random variable when the function depends on endogenous variates which have discrete probability distributions. Weak conditions are developed under which a partial difference of a structural function with respect to a discrete endogenous variable is nonparametrically identified up to an interval. The interval is short when there...

Chesher, Andrew

2003-01-01

392

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% 1.862.59, microvascular disease (OR 2.14; CI 95% 1.82.54 and insulin treatment (OR 1.82; CI 95% 1.392.38, and inversely associated with HbA1c (OR 0.85 for every 1% increase; CI 95% 0.800.91. Albuminuria without RI was inversely associated with the female gender (OR 0.27; CI 95% 0.210.35, duration of diabetes (OR 0.94 per year; CI 95% 0.910.97 and directly associated with HbA1c (OR 1.19 for every 1% increase; CI 95% 1.091.3. 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

393

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)

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, Lcio F; de Souza, Eberton A; de Freitas, Victor H; de Moraes, Solange M F; Leicht, Anthony S; Nakamura, Fbio Y

2014-10-01

394

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 (p<0.001). Gabapentin was also associated with significantly greater improvement in overall performance on tests 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

395

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

396

Randomized, Double Blind, Placebo-Controlled Trial of Disulfiram for the Treatment of Cocaine Dependence in Methadone-Stabilized Patients1  

Science.gov (United States)

This study examined the dose-related efficacy of disulfiram for treating cocaine dependence in methadone-stabilized cocaine dependent participants. Design One hundred sixty-one cocaine-and opioid-dependent volunteers were entered into a 14-week, double blind, randomized, placebo-controlled clinical trial at two sites. Methods Participants were stabilized on methadone during weeks 12 and received disulfiram at 0, 62.5, 125 or 250 mg/day during weeks 314. All participants also received weekly cognitive behavioral therapy. Thrice-weekly urine samples and weekly self-reported drug use assessments were obtained. Results Baseline subject characteristics, retention and drug use did not differ across groups. Outcome analyses were performed on those who participated beyond week 2. Opioid positive urine samples and self-reported opioid use did not differ by treatment group. The prevalence of alcohol use was low prior to and during the trial and did not differ by treatment group. Cocaine-positive urines increased over time in the 62.5 and 125 mg disulfiram groups and decreased over time in the 250 mg disulfiram and placebo groups (p<0.0001). Self-reported cocaine use increased in the 125 mg disulfiram group relative to the other three treatment groups (p=0.04). Conclusions Disulfiram may be contraindicated for cocaine dependence at doses less than 250 mg/day. Whether disulfiram at higher doses is efficacious in reducing cocaine use in dually cocaine and opioid dependent individuals needs to be determined. PMID:20828943

Oliveto, Alison; Poling, James; Mancino, Michael J.; Feldman, Zachary; Cubells, Joseph F.; Pruzinsky, Rhonda; Gonsai, Kishorchandra; Cargile, Christopher; Sofuoglu, Mehmet; Chopra, Mohit P.; Gonzalez-Haddad, Gerardo; Carroll, Kathleen M.; Kosten, Thomas R.

2010-01-01

397

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)

398

Analysis of a Random Forests Model  

CERN Document Server

Random forests are a scheme proposed by Leo Breiman in the 00's for building a predictor ensemble with a set of decision trees that grow in randomly selected subspaces of data. Despite growing interest and practical use, there has been little exploration of the statistical properties of random forests, and little is known about the mathematical forces driving the algorithm. In this paper, we offer an in-depth analysis of a random forests model suggested by Breiman in 2004, which is very close to the original algorithm. We show in particular that the procedure is consistent and adapts to sparsity, in the sense that its rate of convergence depends only on the number of strong features and not on how many noise variables are present.

Biau, Grard

2010-01-01

399

Dimensions of random affine code tree fractals  

CERN Document Server

We calculate the almost sure Hausdorff dimension for a general class of random affine planar code tree fractals. The set of probability measures describing the randomness includes natural measures in random $V$-variable and homogeneous Markov constructions.

Jrvenp, Esa; Kenmki, Antti; Koivusalo, Henna; Stenflo, rjan; Suomala, Ville

2012-01-01

400

Sensitivity of the erythrocyte micronucleus assay: dependence on number of cells scored and inter-animal variability.  

Science.gov (United States)

Until recently, the in vivo erythrocyte micronucleus assay has been scored using microscopy. Because the frequency of micronucleated cells is typically low, cell counts are subject to substantial binomial counting error. Counting error, along with inter-animal variability, limit the sensitivity of this assay. Recently, flow cytometric methods have been developed for scoring micronucleated erythrocytes and these methods enable many more cells to be evaluated than is possible with microscopic scoring. Using typical spontaneous micronucleus frequencies reported in mice, rats, and dogs we calculate the counting error associated with the frequency of micronucleated reticulocytes as a function of the number of reticulocytes scored. We compare this counting error with the inter-animal variability determined by flow cytometric scoring of sufficient numbers of cells to assure that the counting error is less than the inter-animal variability, and calculate the minimum increases in micronucleus frequency that can be detected as a function of the number of cells scored. The data show that current regulatory guidelines allow low power of the test when spontaneous frequencies are low (e.g., counting error to less than the inter-animal variability, thereby maintaining a more uniform power of detection of increased micronucleus frequencies across laboratories and species. PMID:17851117

Kissling, Grace E; Dertinger, Stephen D; Hayashi, Makoto; MacGregor, James T

2007-12-01

401

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  

OpenAIRE

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-obrien, Nancy; Stine, Susan M.; Mccarty, Dennis; Reid, Malcolm S.; Brown, Lawrence S.; Maslansky, Robert; Winhusen, Theresa; Babcock, Dean

2008-01-01

402

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

403

Temperature dependence of an estuarine harmful algal bloom: Resolving interannual variability in bloom dynamics using a degree day approach  

Science.gov (United States)

Observations of harmful algal blooms (HABs) of the dinoflagellate Alexandrium fundyense in an estuary over multiple years were used to assess drivers of their spatial and temporal variability. Nauset Estuary on Cape Cod, Massachusetts has a recurrent, self-seeding A. fundyense population that produces paralytic shellfish poisoning toxins and leads to nearly annual closure to shellfishing. Weekly surveys of the entire estuary were made in 3 of 4 consecutive years, with surveys of a subembayment during the intervening year. Major A. fundyense blooms were observed all 4 years, with maximum concentrations >106 cells L?1. Concentrations were greatest in three salt ponds at the distal edges of the estuary. The bloom timing varied among the salt ponds and among years, although the blooms had similar durations and maximum cell concentrations. Nutrient concentrations did not correlate with the growth of the bloom, but differences in water temperature among years and ponds were significant. Net growth rates inferred from the surveys were similar to those from laboratory experiments, and increased linearly with temperature. A growing degree day calculation was used to account for effects of interannual variability and spatial gradients in water temperature on population development. The approach collapsed variability in the timing of bloom onset, development, and termination across years and among ponds, suggesting that this relatively simple metric could be used as an early-warning indicator for HABs in Nauset and similar areas with localized, self-seeding blooms. PMID:25419003

Ralston, David K.; Keafer, Bruce A.; Brosnahan, Michael L.; Anderson, Donald M.

2014-01-01

404

Bounds on the Poincare constant under negative dependence  

OpenAIRE

We give bounds on the Poincare (inverse spectral gap) constant of a non-negative, integer-valued random variable W, under negative dependence assumptions such as ultra log-concavity and total negative dependence. We show that the bounds obtained compare well to others in the literature. Examples treated include some occupancy and urn models, a random graph model and small spacings on the circumference of a circle. Applications to Poisson convergence theorems are considered.

Daly, Fraser; Johnson, Oliver

2008-01-01

405

DIFFERENTIAL VARIABILITY OF TEST SCORES AMONG SCHOOLS: A MULTILEVEL ANALYSIS OF THE FIFTH-GRADE INVALSI TEST USING HETEROSCEDASTIC RANDOM EFFECTS  

OpenAIRE

The performance of a school system can be evaluated through the learning levels of the pupils, usually summarized by school mean scores. The variability of the mean scores among schools is rarely studied in detail, though it is a crucial issue especially in primary schools: in fact, a high variability among schools raises doubts on the capacity of the system to guarantee equal educational opportunities. To investigate the patterns of variability in Italy, we analyse data from INVALSI, the Ita...

Sani, Claudia; Grilli, Leonardo

2011-01-01

406

Self-Intersection Times for Random Walk, and Random Walk in Random Scenery  

OpenAIRE

We consider Random Walk in Random Scenery , denoted $X_n$, where the random walk is symmetric on $Z^d$, with $d>4$, and the random field is made up of i.i.d random variables with a stretched exponential tail decay, with exponent $\\alpha$ with $1n^{\\beta}\\}$ for $1/2<\\beta<1$. To obtain such asymptotics, we establish large deviations estimates for the the self-intersection local times process.

Asselah, Amine; Castell, Fabienne

2005-01-01

407

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

408

The Association of Selected Conative Variables to Field-Dependence with Inferences for Reasoning Characteristics in Marketing Education.  

Science.gov (United States)

A study examined the association between field-dependence and its related information processing characteristics, and educational cognitive style as a model of conative influence. Data were collected from 145 secondary marketing education students in nothern Georgia during spring 1991. Descriptive statistics, Pearson product moment correlations,

Fritz, Robert L.

409

Coupling effects in dynamic calorimetry: Frequency-dependent relations for specific heat and thermomechanical responses - A one-dimensional approach based on thermodynamics with internal state variables  

International Nuclear Information System (INIS)

As shown by Christensen et al. , temperature-induced stresses or strains can have a strong influence on the frequency-dependent specific heat, especially of thin layers of viscoelastic materials near the glass transition. Thus, both the mathematical representation and the physical understanding of these couplings are essential for the interpretation of temperature-modulated DSC data. The approach provided in this paper is based on thermodynamics with internal state variables. It thus differs from the transfer-matrix method which has been applied in Refs. and constitutes a thermodynamic basis from a different point of view for the interpretation of the results obtained in Refs. . Furthermore, although not the object of this paper, time-domain simulations can also be done with the model presented thus allowing for the calculation of temperature-ramping experiments and effects observed therein . The approach in this paper is restricted to one-dimensional states of stress and strain to focus on the main idea and keep the mathematical formalism to a minimum. The Gibbs free energy is chosen as thermodynamic potential and the primary variables - the stress and the temperature - are supplemented by a set of internal state variables which is introduced to include history-dependent and hence viscoelastic effects. The Gibbs free energy is approximated up to second order terms in the vicinity of a reference state. Employing the Legendre transform, a corresponding expression for transform, a corresponding expression for the Helmhotz free energy is obtained. Evaluating the laws of thermodynamics, explicit frequency-dependent expressions for the specific heat under constant stress or strain, the thermal expansion behaviour as well as the mechanical response functions are obtained. Recently published formulations of the Prigogine-Defay ratio can also be derived from the proposed constitutive model.

410

Variable Requirements for DNA-Binding Proteins at Polycomb-Dependent Repressive Regions in Human HOX Clusters  

OpenAIRE

Polycomb group (PcG)-mediated repression is an evolutionarily conserved process critical for cell fate determination and maintenance of gene expression during embryonic development. However, the mechanisms underlying PcG recruitment in mammals remain unclear since few regulatory sites have been identified. We report two novel prospective PcG-dependent regulatory elements within the human HOXB and HOXC clusters and compare their repressive activities to a previously identified element in the H...

Woo, Caroline J.; Kharchenko, Peter V.; Daheron, Laurence; Park, Peter J.; Kingston, Robert E.

2013-01-01

411

Free Randomness Amplification  

CERN Document Server

In many fundamental results in quantum physics (for example, Bell's theorem), it is assumed that measurement settings can be chosen freely. Here we consider a scenario in which this assumption is weakened and show that partially free bits (i.e. bits which cannot be chosen with complete freedom) can be amplified to make arbitrarily free ones. More precisely, given a source of random bits whose correlation with other variables is below a certain threshold, our amplification procedure generates fresh random bits that are virtually uncorrelated with these variables. We also conjecture that free randomness amplification procedures exist for any non-trivial threshold. Our result uses correlations from quantum theory but we do not assume that the theory is complete. One corollary of our result is that, for a generic class of randomness sources, there exist schemes for extracting uniform randomness without a trusted seed, which is provably impossible using classical protocols.

Colbeck, Roger

2011-01-01

412

Mott law as lower bound for a random walk in a random environment  

CERN Document Server

We consider a random walk on the support of a stationary simple point process on $R^d$, $d\\geq 2$ which satisfies a mixing condition w.r.t.the translations or has a strictly positive density uniformly on large enough cubes. Furthermore the point process is furnished with independent random bounded energy marks. The transition rates of the random walk decay exponentially in the jump distances and depend on the energies through a factor of the Boltzmann-type. This is an effective model for the phonon-induced hopping of electrons in disordered solids within the regime of strong Anderson localization. We show that the rescaled random walk converges to a Brownian motion whose diffusion coefficient is bounded below by Mott's law for the variable range hopping conductivity at zero frequency. The proof of the lower bound involves estimates for the supercritical regime of an associated site percolation problem.

Faggionato, A; Spehner, D

2004-01-01

413

Time-dependent diffusion in skeletal muscle with the random permeable barrier model (RPBM): application to normal controls and chronic exertional compartment syndrome patients.  

Science.gov (United States)

The purpose of this work was to carry out diffusion tensor imaging (DTI) at multiple diffusion times Td in skeletal muscle in normal subjects and chronic exertional compartment syndrome (CECS) patients and analyze the data with the random permeable barrier model (RPBM) for biophysical specificity. Using an institutional review board approved HIPAA-compliant protocol, seven patients with clinical suspicion of CECS and eight healthy volunteers underwent DTI of the calf muscle in a Siemens MAGNETOM Verio 3?T scanner at rest and after treadmill exertion at four different T(d) values. Radial diffusion values ?(rad) were computed for each of seven different muscle compartments and analyzed with RPBM to produce estimates of free diffusivity D(0), fiber diameter a, and permeability ?. Fiber diameter estimates were compared with measurements from literature autopsy reference for several compartments. Response factors (post/pre-exercise ratios) were computed and compared between normal controls and CECS patients using a mixed-model two-way analysis of variance. All subjects and muscle compartments showed nearly time-independent diffusion along and strongly time-dependent diffusion transverse to the muscle fibers. RPBM estimates of fiber diameter correlated well with corresponding autopsy reference. D(0) showed significant (p?CECS patients, with patients showing smaller diameter changes (p?=?0.07), and larger permeability increases (p?=?0.07) than controls. Time-dependent diffusion measurements combined with appropriate tissue modeling can provide enhanced microstructural specificity for in vivo tissue characterization. In CECS patients, our results suggest that high-pressure interfiber edema elevates free diffusion and restricts exercise-induced fiber dilation. Such specificity may be useful in differentiating CECS from other disorders or in predicting its response to either physical therapy or fasciotomy. PMID:24610770

Sigmund, Eric E; Novikov, Dmitry S; Sui, Dabang; Ukpebor, Obehi; Baete, Steven; Babb, James S; Liu, Kecheng; Feiweier, Thorsten; Kwon, Jane; McGorty, Kellyanne; Bencardino, Jenny; Fieremans, Els

2014-05-01

414

Preliminary Safety and Efficacy of L-carnitine Infusion for the Treatment of Vasopressor-Dependent Septic Shock: A Randomized Control Trial.  

Science.gov (United States)

Background: Sepsis is characterized by metabolic disturbances, and previous data suggest a relative carnitine deficiency may contribute to metabolic dysfunction. Studies regarding safety and patient-centered efficacy of carnitine during septic shock are lacking. Methods: This was a double-blind randomized control trial of levocarnitine (L-carnitine) infusion vs normal saline for the treatment of vasopressor-dependent septic shock. Patients meeting consensus definition for septic shock with a cumulative vasopressor index ?3 and sequential organ failure assessment (SOFA) score ?5 enrolled within 16 hours of the recognition of septic shock were eligible. The primary safety outcome was difference in serious adverse events (SAEs) per patient between groups. Efficacy outcomes included proportion of patients demonstrating a decrease in SOFA score of 2 or more points at 24 hours and short- and long-term survival. Results: Of the 31 patients enrolled, 16 were in the L-carnitine and 15 were in the placebo arm. There was no difference in SAEs between placebo and intervention (2.1 vs 1.8 SAEs per patient, P = .44). There was no difference in the proportion of patients achieving a decrease in SOFA score of 2 or more points at 24 hours between placebo and treatment (53% vs 44%, P = .59). Mortality was significantly lower at 28 days in the L-carnitine group (4/16 vs 9/15, P = .048), with a nonsignificant improved survival at 1 year (P = .06). Conclusion: L-carnitine infusion appears safe in vasopressor-dependent septic shock. Preliminary efficacy data suggest potential benefit of L-carnitine treatment, and further testing is indicated. PMID:23851424

Puskarich, Michael A; Kline, Jeffrey A; Krabill, Virginia; Claremont, Heather; Jones, Alan E

2013-07-12

415

A Composite Likelihood Inference in Latent Variable Models for Ordinal Longitudinal Responses  

Science.gov (United States)

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

416

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

417

Variable Loop Glycan Dependency of the Broad and Potent HIV-1-Neutralizing Antibodies PG9 and PG16?  

OpenAIRE

The HIV-1-specific antibodies PG9 and PG16 show marked cross-isolate neutralization breadth and potency. Antibody neutralization has been shown to be dependent on the presence of N-linked glycosylation at position 160 in gp120. We show here that (i) the loss of several key glycosylation sites in the V1, V2, and V3 loops; (ii) the generation of pseudoviruses in the presence of various glycosidase inhibitors; and (iii) the growth of pseudoviruses in a mutant cell line (GnT1?/?) that alters ...

Doores, Katie J.; Burton, Dennis R.

2010-01-01

418

Limit theorems for Markov random fields  

International Nuclear Information System (INIS)

Markov Random Fields (MRF's) have been extensively applied in Statistical Mechanics as well as in Bayesian Image Analysis. MRF's are a special class of dependent random variables located at the vertices of a graph whose joint distribution includes a parameter called the temperature. When the number of vertices of the graph tends to infinity, the normalized distribution of statistics based on these random variables converge in distribution. It can happen that for certain values of the temperature, that the rate of growth of these normalizing constants change drastically. This feature is generally used to explain the phenomenon of phase transition as understood by physicist. In this dissertation the author will show that this drastic change in normalizing constants occurs even in the relatively smooth case when all the random variables are Gaussian. Hence any image analytic MRF ought to be checked for such discontinuous behavior before any analysis is performed. Mixed limit theorems in Bayesian Image Analysis seek to replace intensive simulations of MRF's with limit theorems that approximate the distribution of the MRF's as the number of sites increases. The problem of deriving mixed limit theorems for MRF's on a one dimensional lattice graph with an acceptor function that has a second moment has been studied by Chow. A mixed limit theorem for the integer lattice graph is derived when the acceptor function does not have a second moment as for instance when the acceptor moment as for instance when the acceptor function is a symmetric stable density of index 0 < ? < 2

419

The spatial random effects and the spatial fixed effects model: The Hausman test in a Cliff and Ord panel model  

OpenAIRE

This paper studies the spatial random effects and spatial fixed effects model. The model includes a Cliff and Ord type spatial lag of the dependent variable as well as a spatially lagged one-way error component structure, accounting for both heterogeneity and spatial correlation across units. We discuss instrumental variable estimation under both the fixed and the random effects specification and propose a spatial Hausman test which compares these two models accounting for spatial autocorrela...

Mutl, Jan; Pfaffermayr, Michael

2008-01-01

420

Limit laws for sums of independent random products: the lattice case  

OpenAIRE

Let $\\{V_{i,j}; (i,j)\\in\\N^2\\}$ be a two-dimensional array of i.i.d.\\ random variables. The limit laws of the sum of independent random products $$ Z_n=\\sum_{i=1}^{N_n} \\prod_{j=1}^{n} e^{V_{i,j}} $$ as $n,N_n\\to\\infty$ have been investigated by a number of authors. Depending on the growth rate of $N_n$, the random variable $Z_n$ obeys a central limit theorem, or has limiting $\\alpha$-stable distribution. The latter result is true for non-lattice $V_{i,j}$ only. Our aim is t...

Kabluchko, Zakhar

2010-01-01

421

Variable requirements for DNA-binding proteins at polycomb-dependent repressive regions in human HOX clusters.  

Science.gov (United States)

Polycomb group (PcG)-mediated repression is an evolutionarily conserved process critical for cell fate determination and maintenance of gene expression during embryonic development. However, the mechanisms underlying PcG recruitment in mammals remain unclear since few regulatory sites have been identified. We report two novel prospective PcG-dependent regulatory elements within the human HOXB and HOXC clusters and compare their repressive activities to a previously identified element in the HOXD cluster. These regions recruited the PcG proteins BMI1 and SUZ12 to a reporter construct in mesenchymal stem cells and conferred repression that was dependent upon PcG expression. Furthermore, we examined the potential of two DNA-binding proteins, JARID2 and YY1, to regulate PcG activity at these three elements. JARID2 has differential requirements, whereas YY1 appears to be required for repressive activity at all 3 sites. We conclude that distinct elements of the mammalian HOX clusters can recruit components of the PcG complexes and confer repression, similar to what has been seen in Drosophila. These elements, however, have diverse requirements for binding factors, which, combined with previous data on other loci, speaks to the complexity of PcG targeting in mammals. PMID:23775117

Woo, Caroline J; Kharchenko, Peter V; Daheron, Laurence; Park, Peter J; Kingston, Robert E

2013-08-01

422

Meteorological variables affect fertility rate after intrauterine artificial insemination in sheep in a seasonal-dependent manner: a 7-year study  

Science.gov (United States)

A total number of 48,088 artificial inseminations (AIs) have been controlled during seven consecutive years in 79 dairy sheep Spanish farms (41 N). Mean, maximum and minimum ambient temperatures (Ts), temperature amplitude (TA), mean relative humidity (RH), mean solar radiation (SR) and total rainfall of each insemination day and 15 days later were recorded. Temperature-humidity index (THI) and effective temperature (ET) have been calculated. A binary logistic regression model to estimate the risk of not getting pregnant compared to getting pregnant, through the odds ratio (OR), was performed. Successful winter inseminations were carried out under higher SR (P 1 (maximum T, ET and rainfall on AI day, and ET and rainfall on day 15), and two variables presented OR <1 (SR on AI day and maximum T on day 15). However, the effect of meteorological factors affected fertility in opposite ways, so T becomes a protective or risk factor on fertility depending on season. In conclusion, the percentage of pregnancy after AI in sheep is significantly affected by meteorological variables in a seasonal-dependent manner, so the parameters such as temperature reverse their effects in the hot or cold seasons. A forecast of the meteorological conditions could be a useful tool when AI dates are being scheduled.

Palacios, C.; Abecia, J. A.

2014-07-01

423

Dose dependent expression of HDAC4 causes variable expressivity in a novel inherited case of brachydactyly mental retardation syndrome.  

Science.gov (United States)

Histone deacetylase 4 (HDAC4) serves important roles in multiple human systems, including neurological, cardiac, and skeletal functions. Mutation or deletion of HDAC4 causes brachydactyly mental retardation syndrome (BDMR), a disorder that includes intellectual disability, behavioral abnormalities, autism spectrum disorder, and craniofacial and skeletal anomalies, including brachydactyly type E. We present a case of familial BDMR, including a parent with mild symptoms of the disorder and a child exhibiting a more severe phenotype. Cytogenetic testing showed a cryptic balanced translocation in the mother that resulted in a 2q37.1 monosomy and a 10q26.1 trisomy in the son. Gene expression analyses demonstrated 67% HDAC4 expression in the mother and 23% HDAC4 expression in the son relative to normal controls, lending evidence to the hypothesis that HDAC4 modulates severity of this disorder in a dosage-dependent manner. PMID:22753018

Morris, Benjamin; Etoubleau, Ccile; Bourthoumieu, Sylvie; Reynaud-Perrine, Sandrine; Laroche, Ccile; Lebbar, Aziza; Yardin, Catherine; Elsea, Sarah H

2012-08-01

424

Quenched Central Limit Theorems for Random Walks in Random Scenery  

OpenAIRE

Random walks in random scenery are processes defined by $$Z_n:=\\sum_{k=1}^n\\omega_{S_k}$$ where $S:=(S_k,k\\ge 0)$ is a random walk evolving in $\\mathbb{Z}^d$ and $\\omega:=(\\omega_x, x\\in{\\mathbb Z}^d)$ is a sequence of i.i.d. real random variables. Under suitable assumptions on the random walk $S$ and the random scenery $\\omega$, almost surely with respect to $\\omega$, the correctly renormalized sequence $(Z_n)_{n\\geq 1}$ is proved to converge in distribution to a centered G...

Guillotin-plantard, Nadine; Poisat, Julien

2013-01-01

425

A factorial randomized controlled trial to evaluate the effect of micronutrients supplementation and regular aerobic exercise on maternal endothelium-dependent vasodilatation and oxidative stress of the newborn  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Many studies have suggested a relationship between metabolic abnormalities and impaired fetal growth with the development of non-transmissible chronic diseases in the adulthood. Moreover, it has been proposed that maternal factors such as endothelial function and oxidative stress are key mechanisms of both fetal metabolic alterations and subsequent development of non-transmissible chronic diseases. The objective of this project is to evaluate the effect of micronutrient supplementation and regular aerobic exercise on endothelium-dependent vasodilation maternal and stress oxidative of the newborn. Methods and design 320 pregnant women attending to usual prenatal care in Cali, Colombia will be included in a factorial randomized controlled trial. Women will be assigned to the following intervention groups: 1. Control group: usual prenatal care (PC and placebo (maltodextrine. 2. Exercise group: PC, placebo and aerobic physical exercise. 3. Micronutrients group: PC and a micronutrients capsule consisting of zinc (30 mg, selenium (70 ?g, vitamin A (400 ?g, alphatocopherol (30 mg, vitamin C (200 mg, and niacin (100 mg. 4. Combined interventions Group: PC, supplementation of micronutrients, and aerobic physical exercise. Anthropometric measures will be taken at the start and at the end of the interventions. Discussion Since in previous studies has been showed that the maternal endothelial function and oxidative stress are related to oxidative stress of the newborn, this study proposes that complementation with micronutrients during pregnancy and/or regular physical exercise can be an early and innovative alternative to strengthen the prevention of chronic diseases in the population. Trial registration NCT00872365.

Girn Sandra

2011-02-01

426

Introduction to Randomness and Statistics  

OpenAIRE

This text provides a practical introduction to randomness and data analysis, in particular in the context of computer simulations. At the beginning, the most basics concepts of probability are given, in particular discrete and continuous random variables. Next, generation of pseudo random numbers is covered, such as uniform generators, discrete random numbers, the inversion method, the rejection method and the Box-Mueller Method. In the third section, estimators, confidenc...

Hartmann, Alexander K.

2009-01-01

427

Lifted Variable Elimination for Probabilistic Logic Programming  

OpenAIRE

Lifted inference has been proposed for various probabilistic logical frameworks in order to compute the probability of queries in a time that depends on the size of the domains of the random variables rather than the number of instances. Even if various authors have underlined its importance for probabilistic logic programming (PLP), lifted inference has been applied up to now only to relational languages outside of logic programming. In this paper we adapt Generalized Count...

Bellodi, Elena; Lamma, Evelina; Riguzzi, Fabrizio; Costa, Vitor Santos; Zese, Riccardo

2014-01-01

428

How Random is Random?  

Science.gov (United States)

Created by Annenberg Media, this site is a tutorial that takes students through a mayoral election process while discussing the concept of randomness. Topics include margin of error and confidence levels. This is a fairly basic lesson, but it does provide a good example of applied statistical theory. Aside from simply addressing the statistics behind the process, the resource also discusses the actual physical process of taking political polls.

2009-03-02

429

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

430

Effect of a single session of transcranial direct-current stimulation on balance and spatiotemporal gait variables in children with cerebral palsy: A randomized sham-controlled study  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Background: Transcranial direct-current stimulation (tDCS) has been widely studied with the aim of enhancing local synaptic efficacy and modulating the electrical activity of the cortex in patients with neurological disorders. Objective: The purpose of the present study was to determine the ef [...] fect of a single session of tDCS regarding immediate changes in spatiotemporal gait and oscillations of the center of pressure (30 seconds) in children with cerebral palsy (CP). Method: A randomized controlled trial with a blinded evaluator was conducted involving 20 children with CP between six and ten years of age. Gait and balance were evaluated three times: Evaluation 1 (before the stimulation), Evaluation 2 (immediately after stimulation), and Evaluation 3 (20 minutes after the stimulation). The protocol consisted of a 20-minute session of tDCS applied to the primary motor cortex at an intensity of 1 mA. The participants were randomly allocated to two groups: experimental group - anodal stimulation of the primary motor cortex; and control group - placebo transcranial stimulation. Results: Significant reductions were found in the experimental group regarding oscillations during standing in the anteroposterior and mediolateral directions with eyes open and eyes closed in comparison with the control group (p

Luanda A. C., Grecco; Natlia A. C., Duarte; Nelci, Zanon; Manuela, Galli; Felipe, Fregni; Claudia S., Oliveira.

2014-10-01

431

Heart Rate Variability and Hemodynamic Change in the Superior Mesenteric Artery by Acupuncture Stimulation of Lower Limb Points: A Randomized Crossover Trial  

OpenAIRE

Objective. We investigated the relationship between superior mesenteric artery blood flow volume (SMA BFV) and autonomic nerve activity in acupuncture stimulation of lower limb points through heart rate variability (HRV) evaluations. Methods. Twenty-six healthy volunteers underwent crossover applications of bilateral manual acupuncture stimulation at ST36 or LR3 or no stimulation. Heart rate, blood pressure, cardiac index, systemic vascular resistance index, SMA BFV, and HRV at rest and 30?...

Soichiro Kaneko; Masashi Watanabe; Shin Takayama; Takehiro Numata; Takashi Seki; Junichi Tanaka; Seiki Kanemura; Yutaka Kagaya; Tadashi Ishii; Yoshitaka Kimura; Nobuo Yaegashi

2013-01-01

432

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

433

Unit-specific calibration of Actigraph accelerometers in a mechanical setup - is it worth the effort? The effect on random output variation caused by technical inter-instrument variability in the laboratory and in the field  

DEFF Research Database (Denmark)

BACKGROUND: Potentially, unit-specific in-vitro calibration of accelerometers could increase field data quality and study power. However, reduced inter-unit variability would only be important if random instrument variability contributes considerably to the total variation in field data. Therefore, the primary aim of this study was to calculate and apply unit-specific calibration factors in multiple accelerometers in order to examine the impact on random output variation caused by inter-instrument variability. METHODS: Instrument-specific calibration factors were estimated in 25 MTI- and 53 CSA accelerometers in a mechanical setup using four different settings varying in frequencies and/or amplitudes. Calibration effect was analysed by comparing raw and calibrated data after applying unit-specific calibration factors to data obtained during quality checks in a mechanical setup and to data collected during free living conditions. RESULTS: Calibration reduced inter-instrument variability considerably in the mechanical setup, both in the MTI instruments (raw SDbetween units = 195 counts*min-1 vs. calibrated SDbetween units = 65 counts*min-1) and in the CSA instruments (raw SDbetween units = 343 counts*min-1 vs. calibrated SDbetween units = 67 counts*min-1). However, the effect of applying the derived calibration to children's and adolescents' free living physical activity data did not alter the coefficient of variation (CV) (children: CVraw = 30.2% vs. CVcalibrated = 30.4%, adolescents: CVraw = 36.3% vs. CVcalibrated = 35.7%). High correlations (r = 0.99 & r = 0.98, respectively) were observed between raw and calibrated field data, and the proportion of the total variation caused by the MTI- and CSA monitor was estimated to be only 1.1% and 4.2%, respectively. Compared to the CSA instruments, a significantly increased (9.95%) mean acceleration response was observed post hoc in the batch of MTI instruments, in which a significantly reduced inter-instrumental reliability was observed over time. CONCLUSION: The application of unit-specific calibration factors to data collected during free living conditions had no apparent effect on inter-instrument variability. In all probability, the effect of technical calibration was primarily attenuated in the field by other more dominant sources of variation. However, routine technical assessments are still very important for determining the acceleration responses in the batch of instruments being used and, if performed after every field use, for preventing decidedly broken instruments from being returned into the field repeatedly.

Moeller, Niels C; Korsholm, Lars

2008-01-01

434

Reading Dependencies from Covariance Graphs  

CERN Document Server

The covariance graph (aka bi-directed graph) of a probability distribution $p$ is the undirected graph $G$ where two nodes are adjacent iff their corresponding random variables are marginally dependent in $p$. In this paper, we present a graphical criterion for reading dependencies from $G$, under the assumption that $p$ satisfies the graphoid properties as well as weak transitivity and composition. We prove that the graphical criterion is sound and complete in certain sense. We argue that our assumptions are not too restrictive. For instance, all the regular Gaussian probability distributions satisfy them.

Pea, Jose M

2010-01-01

435

Heavy-tailed random matrices  

CERN Document Server

We discuss non-Gaussian random matrices whose elements are random variables with heavy-tailed probability distributions. In probability theory heavy tails of the distributions describe rare but violent events which usually have dominant influence on the statistics. They also completely change universal properties of eigenvalues and eigenvectors of random matrices. We concentrate here on the universal macroscopic properties of (1) Wigner matrices belonging to the Levy basin of attraction, (2) matrices representing stable free random variables and (3) a class of heavy-tailed matrices obtained by parametric deformations of standard ensembles.

Burda, Z

2009-01-01

436

Effect of a single session of transcranial direct-current stimulation on balance and spatiotemporal gait variables in children with cerebral palsy: A randomized sham-controlled study.  

Science.gov (United States)

Background: Transcranial direct-current stimulation (tDCS) has been widely studied with the aim of enhancing local synaptic efficacy and modulating the electrical activity of the cortex in patients with neurological disorders. Objective: The purpose of the present study was to determine the effect of a single session of tDCS regarding immediate changes in spatiotemporal gait and oscillations of the center of pressure (30 seconds) in children with cerebral palsy (CP). Method: A randomized controlled trial with a blinded evaluator was conducted involving 20 children with CP between six and ten years of age. Gait and balance were evaluated three times: Evaluation 1 (before the stimulation), Evaluation 2 (immediately after stimulation), and Evaluation 3 (20 minutes after the stimulation). The protocol consisted of a 20-minute session of tDCS applied to the primary motor cortex at an intensity of 1 mA. The participants were randomly allocated to two groups: experimental group - anodal stimulation of the primary motor cortex; and control group - placebo transcranial stimulation. Results: Significant reductions were found in the experimental group regarding oscillations during standing in the anteroposterior and mediolateral directions with eyes open and eyes closed in comparison with the control group (p<0.05). In the intra-group analysis, the experimental group exhibited significant improvements in gait velocity, cadence, and oscillation in the center of pressure during standing (p<0.05). No significant differences were found in the control group among the different evaluations. Conclusion: A single session of tDCS applied to the primary motor cortex promotes positive changes in static balance and gait velocity in children with cerebral palsy. PMID:25317766

Grecco, Luanda A C; Duarte, Natlia A C; Zanon, Nelci; Galli, Manuela; Fregni, Felipe; Oliveira, Claudia S

2014-10-10

437

Effect of a single session of transcranial direct-current stimulation on balance and spatiotemporal gait variables in children with cerebral palsy: A randomized sham-controlled study  

Science.gov (United States)

Background: Transcranial direct-current stimulation (tDCS) has been widely studied with the aim of enhancing local synaptic efficacy and modulating the electrical activity of the cortex in patients with neurological disorders. Objective: The purpose of the present study was to determine the effect of a single session of tDCS regarding immediate changes in spatiotemporal gait and oscillations of the center of pressure (30 seconds) in children with cerebral palsy (CP). Method: A randomized controlled trial with a blinded evaluator was conducted involving 20 children with CP between six and ten years of age. Gait and balance were evaluated three times: Evaluation 1 (before the stimulation), Evaluation 2 (immediately after stimulation), and Evaluation 3 (20 minutes after the stimulation). The protocol consisted of a 20-minute session of tDCS applied to the primary motor cortex at an intensity of 1 mA. The participants were randomly allocated to two groups: experimental group - anodal stimulation of the primary motor cortex; and control group - placebo transcranial stimulation. Results: Significant reductions were found in the experimental group regarding oscillations during standing in the anteroposterior and mediolateral directions with eyes open and eyes closed in comparison with the control group (p<0.05). In the intra-group analysis, the experimental group exhibited significant improvements in gait velocity, cadence, and oscillation in the center of pressure during standing (p<0.05). No significant differences were found in the control group among the different evaluations. Conclusion: A single session of tDCS applied to the primary motor cortex promotes positive changes in static balance and gait velocity in children with cerebral palsy. PMID:25372004

Grecco, Luanda A. C.; Duarte, Natlia A. C.; Zanon, Nelci; Galli, Manuela; Fregni, Felipe; Oliveira, Claudia S.

2014-01-01

438

Dependence of P-wave dispersion on mean arterial pressure as an independent hemodynamic variable in school children / Dependencia de la dispersin de la onda P en la presin arterial media como variable hemodinmica independiente en nios en edad escolar  

Scientific Electronic Library Online (English)

Full Text Available SciELO Colombia | Language: English Abstract in spanish Resumen Introduccin: La relacin entre la disfuncin diastlica y la dispersin de la onda P (PWD) en el electrocardiograma se ha estudiado durante algn tiempo. En este sentido, la ecocardiografa se est convirtiendo en una herramienta de diagnstico para mejorar la estratificacin de riesgo en l [...] a hipertensin leve. Objetivo: Determinar la dependencia de las PWD en el electrocardiograma de las variables ecocardiogrficas en una poblacin peditrica. Mtodos: De un total de 565 nios de tres escuelas primarias, fueron estudiados 515 nios. Fueron excluidos del estudio, aquellos nios cuyos padres se negaron a participar, y los nios con enfermedades congnitas conocidas. Se les realiz electrocardiograma de superficie de 12 derivaciones y se realizaron 4 tomas de presin arterial. Fueron medidas las ondas P del electrocardiograma y calculada su dispersin. Se realiz ecocardiografa para medidas estructurales y Doppler pulsado del flujo mitral. Resultados Se demuestra correlacin significativa entre la PWD y la tensin 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, Chvez; Emilio F, Gonzlez; Mara del Carmen, Llanes; Merlin, Gar Llanes; Yosvany, Garc.

2013-09-01

439

Multisurface multimode molecular dynamical simulation of naphthalene and anthracene radical cations by using nearly linear scalable time-dependent discrete variable representation method.  

Science.gov (United States)

The major portion of the algorithm of the time-dependent discrete variable representation (TDDVR) method is recently parallelized using the shared-memory parallelization scheme with the aim of performing dynamics on relatively large molecular systems. Because of the astronomical importance of naphthalene and anthracene, we have investigated their radical cations as models for theoretical simulation of complex photoelectron spectra and nonradiative decay process using the newly implemented parallel TDDVR code. The strong vibronic coupling among the six lowest doublet electronic states makes these polynuclear hydrocarbons dynamically important. The aim of the present investigation is to show the efficiency of our current TDDVR algorithm to perform dynamics on large dimensional quantum systems in vibronically coupled electronic manifold. Both the sequential and the parallelized TDDVR algorithms are almost linear scalable for an increase in number of processors. Because a significant speed-up is achieved by cycling in the correct way over arrays, all of the simulations are performed within a reasonable wall clock time. Our theoretical spectra well reproduce the features of the corresponding experimental analog. The dynamical outcomes, for example, population, photoelectron spectra, and diffused interstellar bands, etc., of our quantum-classical approach show good agreement with the findings of the well-established quantum dynamical method, that is, multi configuration time-dependent Hartree (MCTDH) approach. PMID:25426887

Khan, Basir Ahamed; Sardar, Subhankar; Sarkar, Pranab; Adhikari, Satrajit

2014-12-11

440

Vaccine Induced Antibodies to the First Variable Loop of Human Immunodeficiency Virus Type 1 gp120, Mediate Antibody-Dependent Virus Inhibition in Macaques  

Science.gov (United States)

The role of antibodies directed against the hyper variable envelope region V1 of human immunodeficiency virus type 1 (HIV-1), has not been thoroughly studied. We show that a vaccine able to elicit strain-specific non-neutralizing antibodies to this region of gp120 is associated with control of highly pathogenic chimeric SHIV89.6P replication in rhesus macaques. The vaccinated animal that had the highest titers of antibodies to the amino terminus portion of V1, prior to challenge, had secondary antibody responses that mediated cell killing by antibody-dependent cellular cytotoxicity (ADCC), as early as two weeks after infection and inhibited viral replication by antibody-dependent cell-mediated virus inhibition (ADCVI), by four weeks after infection. There was a significant inverse correlation between virus level and binding antibody titers to the envelope protein, (R = -0.83, p 0.015), and ADCVI (R = -0.84 p=0.044). Genotyping of plasma virus demonstrated in vivo selection of three SHIV89.6P variants with changes in potential N-linked glycosylation sites in V1. We found a significant inverse correlation between virus levels and titers of antibodies that mediated ADCVI against all the identified V1 virus variants. A significant inverse correlation was also found between neutralizing antibody titers to SHIV89.6 and virus levels (R = -0.72 p =0.0050). However, passive inoculation of purified immunoglobulin from animal M316, the macaque that best controlled virus, to a nave macaque, resulted in a low serum neutralizing antibodies and low ADCVI activity that failed to protect from SHIV89.6P challenge. Collectively, while our data suggest that anti-envelope antibodies with neutralizing and non-neutralizing Fc?R-dependent activities may be important in the control of SHIV replication, they also demonstrate that low levels of these antibodies alone are not sufficient to protect from infection. PMID:22037204

Bialuk, Izabela; Whitney, Stephen; Andresen, Vibeke; Florese, Ruth H.; Nacsa, Janos; Cecchinato, Valentina; Valeri, Valerio W.; Heraud, Jean-Michel; Gordon, Shari; Parks, Robyn Washington; Montefiori, David C.; Venzon, David; Demberg, Thorsten; Guroff, Marjorie Robert; Landucci, Gary; Forthal, Donald N.; Franchini, Genoveffa

2011-01-01

441

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 multi-detector row-computed tomography (MDCT). Methods: We compared the mean CT attenuation of CAC to luminal contrast enhancement of the coronary arteries in 30 patients (n = 30) undergoing standard coronary contrast-enhanced spiral MDCT. The modified Agatston score [AS], calcified plaque volume [CV], and mineral mass [MM]) at four different thresholds (130, 200, 300, and 400 HU) were measured in 50 patients who underwent non-contrast-enhanced MDCT. Results: Mean CT attenuation of CAC was similar to the attenuation of the contrast-enhanced coronary lumen (CAC 297.1 68.7 HU versus 295 65 HU (p < 0.0001), respectively). Above a threshold of 300 HU CAC measurements significantly varied to standard measurements obtained at a threshold of 130 HU (p < 0.0001). The threshold-dependent variation of MM measurements was significantly smaller than for AS and CV (130 HU versus 400 HU: 63, 75, and 81, respectively; p < 0.001). These differences resulted in a change of age and gender based percentile category for AS in 78% of subjects. Discussion: We demonstrated that CAC measurements are threshold dependent with MM measurements having significantly less variation than AS or CV. Due to the similarity of mean CT attenuation of CAC and the contrast-enhanced coronary lumen accurate quantificatnced coronary lumen accurate quantification of CAC may be difficult in standard coronary contrast-enhanced spiral MDCT

442

Efron-Stein Inequalities for Random Matrices  

OpenAIRE

This paper establishes new concentration inequalities for random matrices constructed from independent random variables. These results are analogous with the generalized Efron-Stein inequalities developed by Boucheron et al. The proofs rely on the method of exchangeable pairs.

Paulin, Daniel; Mackey, Lester; Tropp, Joel A.

2014-01-01

443

Genetic Variability Among Isolates and Sexual Offspring of the Plant Pathogenic Fungus Calonectria morganii on the Basis of Random Amplification of Polymorphic DNA (RAPD) and Restriction Fragment Length Polymorphism (RFLP)  

Science.gov (United States)

Thirty-two strains of the phytopathogenic mold Cylindrocladium scoparium (perfect state Calonectria morganii) isolated from ericaceous hosts and two specimens from the ATCC were examined by random amplification of polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP). Five oligonucleotides were chosen as primers for differentiation of the isolates. RAPD patterns of the ATCC strains differed significantly from those of the field isolates. Diversity among field isolates was low. Results obtained in RFLP analysis, with telomere repeats of Neurospora crassa as a probe, were highly consistent with the RAPD data. Isolates were paired in all possible combinations; fertile perithecia occurred in only one combination, from which ascospores were analyzed by formal genetics and RAPD. A bipolar mechanism of homogenic incompatibility was found. Ascospore-derived strains were much more variable than field isolates. Phylogenetic trees suggested a correlation to the host plants from which the strains were isolated. PMID:8824171

Overmeyer; Lunnemann; von Wallbrunn C; Meinhardt

1996-10-01

444

Goodness-of-fit tests with dependent observations  

International Nuclear Information System (INIS)

We revisit the KolmogorovSmirnov and Cramrvon Mises goodness-of-fit (GoF) tests and propose a generalization to identically distributed, but dependent univariate random variables. We show that the dependence leads to a reduction of the 'effective' number of independent observations. The generalized GoF tests are not distribution-free but rather depend on all the lagged bivariate copulas. These objects, that we call 'self-copulas', encode all the non-linear temporal dependences. We introduce a specific, log-normal model for these self-copulas, for which a number of analytical results are derived. An application to financial time series is provided. As is well known, the dependence is to be long-ranged in this case, a finding that we confirm using self-copulas. As a consequence, the acceptance rates for GoF tests are substantially higher than if the returns were iid random variables

445

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)

446

Limit theorems for associated random fields and related systems  

CERN Document Server

This volume is devoted to the study of asymptotic properties of wide classes of stochastic systems arising in mathematical statistics, percolation theory, statistical physi