bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnosis and formulation of heterogeneous background‐error covariances at the mesoscale
Authors: Montmerle Thibaut , Berre Loïk
Published: August 2010

This study focuses on diagnosing variations of background‐error covariances between precipitating and non‐precipitating areas, and on presenting a heterogeneous covariance formulation to represent these variations in a variational framework. The context of this work is the assimilation of observations linked to precipitation (radar data especially) in the AROME model, which has been running operationally at Météo‐France since December 2008 over French territory with a 2.5 km horizontal resolution. This system uses multivariate background‐error covariances deduced from an ensemble‐based method. At first, such statistics have been computed for 17 precipitating cases using an ensemble of AROME forecasts coupled with an ALADIN ensemble assimilation. Results, obtained from 3 h forecast differences performed separately for non‐precipitating and precipitating columns, display large discrepancies in error variances, correlation lengths and the correlations between humidity, temperature and divergence errors.

These results argue in favour of including heterogeneous background‐error covariances in AROME incremental 3D‐Var, allowing different covariances to be used in regions with different meteorological patterns. Such a method enables us to get increments more adequately structured in those regions, and thus potentially to make better use of observations in a data assimilation system. The implementation consists of expressing the analysis increment as the sum of two terms, one for precipitating areas and the other for non‐precipitating areas, making use of a mask that defines rainy regions. This implies a doubling in the size of the control variable and of the gradient of the cost function. The feasibility of this method is shown through experiments with four isolated observations. Copyright © 2010 Royal Meteorological Society
Tooling adjustment strategy for acceptable product quality in assembly processes
Authors: Kantanyarat Anantanat , Jin Jionghua (Judy)
Published: August 2010

This paper develops an approach to minimize the number of process tooling adjustments and deliver an acceptable fraction of non‐conforming products based on given product quality specification limits in assembly processes. A linear model is developed to describe the relationships between product quality and process tooling locating positions. Based on the model, the process mean shifts of tooling locating positions are estimated for both deterministic and stochastic cases by using the least‐square estimation or linear mixed model estimation, respectively. A simultaneous confidence interval is obtained to construct the estimation region of a process mean shift under the given false alarm rate. Furthermore, a tooling adjustment strategy is proposed to determine when the process adjustment is essentially needed in order to ensure an acceptable fraction of non‐conforming units based on the given product quality specification limits. Finally, a case study is conducted to illustrate the developed methodology by using a real‐world autobody assembly process. Copyright © 2010 John Wiley & Sons, Ltd.
Nonparametric multivariate control charts based on a linkage ranking algorithm
Authors: Bush Helen Meyers , Chongfuangprinya Panitarn , Chen Victoria C. P. , Sukchotrat Thuntee , Kim Seoung Bum
Published: August 2010

Control charts have been widely recognized as important and critical tools in system monitoring for detection of abnormal behavior and quality improvement. In particular, multivariate control charts have been effectively used when a process involves a number of correlated quality characteristics. Most existing multivariate control charts were developed using the assumption of normally distributed quality characteristics. However, process data from modern industries often do not follow the normal distribution. Despite the great need for nonparametric control charts that can control the error rate regardless of the underlying distribution, few efforts have been made in this direction. In this paper, we propose a new nonparametric control chart (called the kLINK chart) based on a k‐linkage ranking algorithm that calculates the ranking of a new observation relative to the in‐control training data. A simulation study was performed to demonstrate the effectiveness of our kLINK chart and its superiority over the traditional Hotelling's T2 chart and the ranking depth control chart in nonnormal situations. In addition, to enable increased sensitivity to small shifts, we present an exponentially weighted moving average version of a kLINK chart. Copyright © 2010 John Wiley & Sons, Ltd.
A Bayesian approach for integration of physical and computer experiments for quality improvement in nano‐composite manufacturing
Authors: Vanli O. Arda , Zhang Chuck , Chen Li‐Jen , Wang Kan (Kevin) , Wang Ben
Published: August 2010

This paper presents a new Bayesian predictive approach for quality improvement in nano‐composite manufacturing that aims to improve the accuracy of computer model simulations by combining physical process data and computer model predictions. Such a data augmentation method is of crucial importance for capital‐intensive nano‐composite processes for which large experimental studies are usually very costly or impractical. A simulation example and a case study on a real vacuum‐assisted resin transfer molding (VARTM) composite manufacturing process are used to illustrate the proposed approach. The results of these studies show that the proposed approach can achieve more accurate predictions of the process variability than pure empirically based or pure simulation‐based methods for a given experimental data size. An important practical implication of the results of this work is that, by using the proposed Bayesian method that leverages computational methods with the experimental data, one can accomplish significant reduction in product development costs by reducing the number of physical experiments and improving the prediction accuracy of computer models. Copyright © 2010 John Wiley & Sons, Ltd.
Multiresponse optimization with consideration of probabilistic covariates
Authors: Hejazi T. H. , Bashiri Mahdi , Noghondarian Kazem , Atkinson A. C.
Published: August 2010

In many complex experiments, nuisance factor may have large effects that must be accounted for. Covariates are one of the most important kinds of nuisance factors that can be measured but cannot be controlled within the experimental runs. In this paper a novel approach is proposed, based on goal programming, to find the best combination of factors so as to optimize multiresponse‐multicovariate surfaces with consideration of location and dispersion effects. Furthermore, it is supposed that several covariates considered in the experiment have probability distributions of known form. One objective is to find the most probable values of each covariate. For this purpose, a multiobjective mathematical optimization model is proposed and its efficacy is demonstrated by two numerical examples. Copyright © 2010 John Wiley & Sons, Ltd.
Control charts based on models derived from differential equations
Authors: Weihs Claus , Messaoud Amor , Raabe Nils
Published: August 2010

The development of technical processes over time can often be adequately modelled by means of differential equations. In order to monitor such processes, control charts may be derived from stochastic models based on such differential equations. In this work, this is demonstrated for a deep‐hole drilling process used for producing holes with a high length‐to‐diameter ratio, good surface finish and straightness. The process is subject to dynamic disturbances classified as either chatter vibration or spiraling. For chatter, a differential equation for the drilling torque and a model known to well approximate processes with similar characteristics are used to set up monitoring procedures. For spiraling a control chart can be based on a statistical model for the spectrum of the structure‐born vibrations derived from a differential equation for the deflection of the boring bar. Copyright © 2010 John Wiley & Sons, Ltd.
Statistical monitoring of control loops performance: an improved historical‐data benchmark index
Authors: Rato Tiago J. , Reis Marco S.
Published: August 2010

Control systems are key elements of virtually all industrial processes, whose performance directly impacts aspects as important as: product quality and variability, operations safety, process efficiency/costs and environmental impact. In this paper we address the problem of monitoring the performance of such control systems, and in particular a new historical‐data benchmark index is proposed (IM), which is able to discern between perturbations in the system's core modules, which are under the supervision of process owners, from those originated at the level of disturbances, usually involving other stakeholders. It is a generalization of the current index (Iv) as it can be shown that it reduces to this index for the particular case where the variability of the disturbances is the same as in the reference or benchmark period and in the monitoring period. The results obtained demonstrate that the proposed historical‐data benchmark index is able to maintain the target false alarm rate under situations where the variability of the disturbances increases, a situation where the current index, Iv, fails. When the disturbances variability is maintained, both indices present similar detection capability, as expected. The subsequent identification of the modules in fault was also analysed, and the results show that the proposed methodology is able to identify the general source of the degradation in the controller performance, namely, if it is due to a perturbation within the system's core (and which loop is affected) or at the level of the disturbances (increasing variability of the loads or change in their dynamical behaviour). Copyright © 2010 John Wiley & Sons, Ltd.
A high‐dimensional control chart for profile monitoring
Authors: Chen Shuohui , Nembhard Harriet Black
Published: August 2010

Profile monitoring is an important and rapidly emerging area of statistical process control. In many industries, the quality of processes or products can be characterized by a profile that describes a relationship or a function between a response variable and one or more independent variables. A change in the profile relationship can indicate a change in the quality characteristic of the process or product and, therefore, needs to be monitored for control purposes. We propose a high‐dimensional (HD) control chart approach for profile monitoring that is based on the adaptive Neyman test statistic for the coefficients of discrete Fourier transform of profiles. We investigate both linear and nonlinear profiles, and we study the robustness of the HD control chart for monitoring profiles with stationary noise. We apply our control chart to monitor the process of nonlinear woodboard vertical density profile data of Walker and Wright (J. Qual. Technol. 2002; 34:118–129) and compare the results with those presented in Williams et al. (Qual. Reliab. Eng. Int. 2007; to appear). Copyright © 2010 John Wiley & Sons, Ltd.
Approaches to robust ℋ︁∞static output feedback control of discrete‐time piecewise‐affine systems with norm‐bounded uncertainties
Authors: Qiu Jianbin , Feng Gang , Gao Huijun
Published: August 2010

This paper investigates the problem of robust ℋ︁∞static output feedback controller design for a class of discrete‐time piecewise‐affine systems with norm‐bounded time‐varying parametric uncertainties. The objective is to design a piecewise‐linear static output feedback controller guaranteeing the asymptotic stability of the resulting closed‐loop system with a prescribed ℋ︁∞disturbance attenuation level. Based on a piecewise Lyapunov function combined with S‐procedure, Projection lemma, and some matrix inequality convexifying techniques, several novel approaches to the static output feedback controller analysis and synthesis are developed for the underlying piecewise‐affine systems. It is shown that the controller gains can be obtained by solving a set of strict linear matrix inequalities (LMIs) or a family of LMIs parameterized by one or two scalar variables, which are numerically efficient with commercially available software. Finally, three simulation examples are provided to illustrate the effectiveness of the proposed approaches. Copyright © 2010 John Wiley & Sons, Ltd.
Stabilization for a class of minimum phase hybrid systems under an average dwell‐time constraint
Authors: Teel A. R. , Marconi L.
Published: August 2010

We consider the class of nonlinear systems in normal form with unitary relative degree whose zero and output dynamics are affected by state jumps fulfilling an average dwell‐time constraint. Under a minimum‐phase assumption requiring the existence of a compact set, which is globally pre‐asymptotically stable for the hybrid zero dynamics, we show how to design continuous, global state‐ and semiglobal output‐feedback control laws. The proposed design methodology extends to the considered class of hybrid systems well‐known design techniques for robustly stabilizing the class of continuous‐time minimum‐phase nonlinear systems having unitary relative degree. Examples are given to show the usefulness of the technical result. Copyright © 2010 John Wiley & Sons, Ltd.
Robust generalized asymptotic regulation against non‐stationary sinusoidal disturbances with uncertain frequencies
Authors: Köroğlu Hakan , Scherer Carsten W.
Published: August 2010

Attenuation of sinusoidal disturbances with uncertain and arbitrarily time‐varying frequencies is considered in the form of a generalized asymptotic regulation problem. The disturbances are modeled as the outputs of a parameter‐dependent, unexcited and neutrally stable exogenous system that evolves from nonzero initial conditions. The problem is considered for a plant that depends partially on the uncertain parameters. Moreover, both the plant and the exogenous system are allowed to have dependence on another parameter vector that is measurable during online operation. The problem is then formulated as the synthesis of a controller that is scheduled on the measurable parameter in a way to guarantee robust internal stability and attenuate the disturbance according to a desired profile in steady state. The main result of the paper is a synthesis procedure based on a convex optimization problem, which is identified by a set of parameter‐dependent linear matrix inequalities and can be rendered tractable through standard relaxation schemes. It is also clarified how the transient behavior of the controller can be improved by some additional constraints. The order of the synthesized controller is equal to the order of the plant plus the order of the exogenous system. Copyright © 2010 John Wiley & Sons, Ltd.
On l∞ stability and performance of spatiotemporally varying systems
Authors: Sarwar Azeem , Voulgaris Petros G. , Salapaka Srinivasa M.
Published: August 2010

A characterization of stability for spatiotemporally varying systems based on input–output description of the plant and controller is presented. The overall controller is generated by a collection of controllers indexed in space and time, which are based on frozen spatially and temporally invariant descriptions of the plant. In particular, we consider the case where these frozen controllers are not necessarily adjusted for every instance in space and time, and hence are used for some fixed window in time and space. It is shown that the actual spatiotemporally varying system can be stabilized using frozen in space and time controllers, provided the variations in the spatiotemporal dynamics are small enough. We also show that the l∞ to l∞ performance of such systems cannot be much worse than that of the frozen spatially and temporally invariant systems. Copyright © 2010 John Wiley & Sons, Ltd.
Robust delay‐dependent ℋ︁∞control of time‐delay systems with state and input delays
Authors: Parlakçı M. N. Alpaslan , Küçükdemiral İbrahim B.
Published: August 2010

This paper studies the design problem of robust delay‐dependent ℋ︁∞controller for a class of time‐delay control systems with time‐varying state and input delays, which are assumed to be noncoincident. The system is subject to norm‐bounded uncertainties and ℒ︁2disturbances. Based on the selection of an augmented form of Lyapunov–Krasovskii (L‐K) functional, first a Bounded Real Lemma (BRL) is obtained in terms of linear matrix inequalities (LMIs) such that the nominal, unforced time‐delay system is guaranteed to be globally asymptotically stable with minimum allowable disturbance attenuation level. Extending BRL, sufficient delay‐dependent criteria are developed for a stabilizing ℋ︁∞controller synthesis involving a matrix inequality for which a nonlinear optimization algorithm with LMIs is proposed to get feasible solution to the problem. Moreover, for the case of existence of norm‐bounded uncertainties, both the BRL and ℋ︁∞stabilization criteria are easily extended by employing a well‐known bounding technique. A plenty of numerical examples are given to illustrate the application of the proposed methodology of this note. The achieved numerical results on the maximum allowable delay bound and minimum allowable disturbance attenuation level are exhibited to be less conservative in comparison to those of existing methods in the literature. Copyright © 2010 John Wiley & Sons, Ltd.
Output feedback observation and control for visual servoing of VTOL UAVs
Authors: Le Bras Florent , Hamel Tarek , Mahony Robert , Treil Aurélie
Published: August 2010

This paper considers the question of stabilizing vertical take‐off and landing (VTOL) unmanned aerial vehicles (UAVs) using a minimal and an inexpensive sensor suite. The sensor suite considered consists of rate gyros and a single embedded video camera system. The approach taken is based on the principles of dynamic image‐based visual servo control and extends the authors' earlier work by removing dependence on additional sensors, such as accelerometers and magnetometers. The technique presented has potential for mini‐UAVs evolving in urban areas where global positioning system signals may not be available. The control algorithms and coupled state observers are presented in details. The main result of the paper is synthesized in a theorem along with a rigorous stability analysis of the closed‐loop system. An estimate of the basin of attraction for the closed‐loop system is provided. Simulation results are performed to illustrate the performance of the proposed control. Copyright © 2010 John Wiley & Sons, Ltd.
Constructing consensus controllers for networks with identical general linear agents
Authors: Yang Tao , Roy Sandip , Wan Yan , Saberi Ali
Published: August 2010

We use a high‐gain methodology to construct linear decentralized controllers for consensus, in networks with identical but general multi‐input linear time‐invariant (LTI) agents and quite‐general time‐invariant and time‐varying observation topologies. Copyright © 2010 John Wiley & Sons, Ltd.
Leader‐following control for multiple inertial agents
Authors: Chen Gang , Lewis Frank L.
Published: August 2010

This paper investigates distributed controller design problem for a leader‐follower network in the presence of communication delays. Two main contributions are made in this work. First, the second‐order controlled consensus scheme for the weakly connected communication graph topology is proposed. A necessary and sufficient condition is given under which the exponential consensus is achieved. Meanwhile, the relationship among the agents' inertias, the allowable delay bound, the communication topology, the consensus convergence rate, and the control gains is unveiled. Second, the robustness performances of the distributed control scheme with respect to the communication failures and delays are provided. It is shown that if the communication failure rate and the topology switching frequency, respectively, satisfy the given bounds, the exponential second‐order controlled consensus can be achieved under a bounded delay. Numerical examples are given to illustrate the theoretical results. Copyright © 2010 John Wiley & Sons, Ltd.
Discrete‐time mixed ℋ︁2/ℋ︁∞nonlinear filtering
Authors: Aliyu M. D. S. , Boukas E. K.
Published: August 2010

In this paper, we consider the discrete‐time mixed ℋ︁2/ℋ︁∞filtering problem for affine nonlinear systems. Necessary and sufficient conditions for the solvability of this problem with a finite‐dimensional filter are given in terms of a pair of coupled discrete‐time Hamilton–Jacobi‐Isaac's equations (DHJIE) with some side‐conditions. For linear systems, it is shown that these conditions reduce to a pair of coupled discrete‐time algebraic‐Riccati‐equations (DAREs) or a system of linear matrix inequalities (LMIs) similar to the ones for the control case. Both the finite‐horizon and infinite‐horizon problems are discussed. Moreover, sufficient conditions for approximate solvability of the problem are also derived. These solutions are especially useful for computational purposes, considering the difficulty of solving the coupled DHJIEs. An example is also presented to demonstrate the approach. Copyright © 2010 John Wiley & Sons, Ltd.
RobustH∞output‐feedback control of retarded state‐multiplicative stochastic systems
Authors: Gershon E. , Shaked U.
Published: August 2010

Linear, state‐delayed, continuous‐time systems are considered with both stochastic and norm‐bounded deterministic uncertainties in the state–space model. The problem of robust dynamicH∞output‐feedback control is solved, for the stationary case, via the input–output approach where the system is replaced by a nonretarded system with additional deterministic norm‐bounded uncertainties. A delay‐dependent result is obtained which involves the solution of a simple linear matrix inequality. In this problem, a cost function is defined which is the expected value of the standardH∞performance cost with respect to the stochastic parameters. A practical example taken from the field of guidance control is given that demonstrates the applicability of the theory. Copyright © 2010 John Wiley & Sons, Ltd.
Cooperative adaptive control for synchronization of second‐order systems with unknown nonlinearities
Authors: Das Abhijit , Lewis Frank L.
Published: August 2010

This paper studies synchronization to a desired trajectory for multi‐agent systems with second‐order integrator dynamics and unknown nonlinearities and disturbances. The agents can have different dynamics and the treatment is for directed graphs with fixed communication topologies. The command generator or leader node dynamics is also nonlinear and unknown. Cooperative tracking adaptive controllers are designed based on each node maintaining a neural network parametric approximator and suitably tuning it to guarantee stability and performance. A Lyapunov‐based proof shows the ultimate boundedness of the tracking error. A simulation example with nodes having second‐order Lagrangian dynamics verifies the performance of the cooperative tracking adaptive controller. Copyright © 2010 John Wiley & Sons, Ltd.
A Bayesian approach to simultaneously adjusting for verification and reference standard bias in diagnostic test studies
Authors: Lu Ying , Dendukuri Nandini , Schiller Ian , Joseph Lawrence
Published: August 2010

Verification bias arises in diagnostic test evaluation studies when the results from a first test are verified by a reference test only in a non‐representative subsample of the original study subjects. This occurs, for example, when inclusion probabilities for the subsample depend on first‐stage results and/or on a covariate related to disease status. Reference standard bias arises when the reference test itself has imperfect sensitivity and specificity, but this information is ignored in the analysis. Reference standard bias typically results in underestimation of the sensitivity and specificity of the test under evaluation, since subjects that are correctly diagnosed by the test can be considered as misdiagnosed owing to the imperfections in the reference standard. In this paper, we describe a Bayesian approach for simultaneously addressing both verification and reference standard bias. Our models consider two types of verification bias, first when subjects are selected for verification based on initial test results alone, and then when selection is based on initial test results and a covariate. We also present a model that adjusts for a third potential bias that arises when tests are analyzed assuming conditional independence between tests, but some dependence exists between the initial test and the reference test. We examine the properties of our models using simulated data, and then apply them to a study of a screening test for dementia, providing bias‐adjusted estimates of the sensitivity and specificity. Copyright © 2010 John Wiley & Sons, Ltd.
Consonant closed likelihood ratio test procedures with application to dose–response study
Authors: Wang Bushi , Cui Xinping
Published: August 2010

Coherence and Consonance are two important concepts in multiple testing procedures (MTP). Closed test is a well‐known coherent hypothesis testing procedure, which is not necessarily consonant. In this paper, we propose two consonant closed likelihood ratio tests which are compared with the step‐down Dunnett test (SD) and Dunnett–Tamhane step‐up test (SU) in several aspects. Simulation and dose–response study examples show that the new procedures have certain advantages over the SD and SU test. For example, the rejection region of our new procedures is larger than that of the SD test particularly when most of the null hypotheses are false. The new procedures control the family‐wise error rate (FWER) strongly without the equal correlation assumption, which is a necessary condition for the SU test. In terms of computing effort, the new procedures require similar moderate computation for critical constants as the SU test and they follow the same steps as any closed test procedures. We also provide guideline in applying consonance adjustment in multivariate analysis with mixed model and repeated measurements. Copyright © 2010 John Wiley & Sons, Ltd.
Links between analysis of surrogate endpoints and endogeneity
Authors: Ghosh Debashis , Elliott Michael R. , Taylor Jeremy M. G.
Published: August 2010

There has been substantive interest in the assessment of surrogate endpoints in medical research. These are measures that could potentially replace ‘true’ endpoints in clinical trials and lead to studies that require less follow‐up. Recent research in the area has focused on assessments using causal inference frameworks. Beginning with a simple model for associating the surrogate and true endpoints in the population, we approach the problem as one of endogenous covariates. An instrumental variables estimator and general two‐stage algorithm are proposed. Existing surrogacy frameworks are then evaluated in the context of the model. In addition, we define an extended relative effect estimator as well as a sensitivity analysis for assessing what we term the treatment instrumentality assumption. A numerical example is used to illustrate the methodology. Copyright © 2010 John Wiley & Sons, Ltd.
An easy‐to‐implement approach for analyzing case–control and case‐only studies assuming gene–environment independence and Hardy–Weinberg equilibrium
Authors: Lee Wen‐Chung , Wang Liang‐Yi , Cheng K. F.
Published: August 2010

The case–control study is a simple and an useful method to characterize the effect of a gene, the effect of an exposure, as well as the interaction between the two. The control‐free case‐only study is yet an even simpler design, if interest is centered on gene–environment interaction only. It requires the sometimes plausible assumption that the gene under study is independent of exposures among the non‐diseased in the study populations. The Hardy–Weinberg equilibrium is also sometimes reasonable to assume. This paper presents an easy‐to‐implement approach for analyzing case–control and case‐only studies under the above dual assumptions. The proposed approach, the ‘conditional logistic regression with counterfactuals’, offers the flexibility for complex modeling yet remains well within the reach to the practicing epidemiologists. When the dual assumptions are met, the conditional logistic regression with counterfactuals is unbiased and has the correct type I error rates. It also results in smaller variances and achieves higher powers as compared with using the conventional analysis (unconditional logistic regression). Copyright © 2010 John Wiley & Sons, Ltd.
Sequential generalized likelihood ratio tests for vaccine safety evaluation
Authors: Shih Mei‐Chiung , Lai Tze Leung , Heyse Joseph F. , Chen Jie
Published: August 2010

The evaluation of vaccine safety involves pre‐clinical animal studies, pre‐licensure randomized clinical trials, and post‐licensure safety studies. Sequential design and analysis are of particular interest because they allow early termination of the trial or quick detection that the vaccine exceeds a prescribed bound on the adverse event rate. After a review of the recent developments in this area, we propose a new class of sequential generalized likelihood ratio tests for evaluating adverse event rates in two‐armed pre‐licensure clinical trials and single‐armed post‐licensure studies. The proposed approach is illustrated using data from the Rotavirus Efficacy and Safety Trial. Simulation studies of the performance of the proposed approach and other methods are also given. Copyright © 2010 John Wiley & Sons, Ltd.
Interval estimation of quantile ratios applied to anti‐cancer drug screening by xenograft experiments
Authors: Cheng Cheng , Wu Jianrong
Published: August 2010

The current practice in analyzing data from anti‐cancer drug screening by xenograft experiments lacks statistical consideration to account for experimental noise, and a sound inference procedure is necessary. A novel confidence bound and interval procedure for estimating quantile ratios developed in this paper fills the void. Justified by rigorous large‐sample theory and a simulation study of small‐sample performance, the proposed method performs well in a wide range of scenarios involving right‐skewed distributions. By providing rigorous inference and much more interpretable statistics that account for experimental noise, the proposed method improves the current practice of analyzing drug activity data in xenograft experiments. The proposed method is fully nonparametric, simple to compute, performs equally well or better than known nonparametric methods, and is applicable to any statistical inference of a ‘fold change’ that can be formulated as a quantile ratio. Copyright © 2010 John Wiley & Sons, Ltd.
A Runx1 Intronic Enhancer Marks Hemogenic Endothelial Cells and Hematopoietic Stem Cells
Authors: Ng Cherry Ee Lin , Yokomizo Tomomasa , Yamashita Namiko , Cirovic Branko , Jin Hao , Wen Zilong , Ito Yoshiaki , Osato Motomi
Published: August 2010

Runx1 is essential for the generation of hematopoietic stem cells (HSCs) and is frequently mutated in human leukemias. However, the cis-regulatory mechanisms modulating the Runx1 gene expression remain to be elucidated. Herewith, we report the identification of an intronic Runx1 enhancer, Runx1 +24 mouse conserved noncoding element (mCNE), using a combinatorial in silico approach involving comparative genomics and retroviral integration sites mapping. The Runx1 +24 mCNE was found to possess hematopoietic-specific enhancer activity in both zebrafish and mouse models. Significantly, this enhancer is active specifically in hemogenic endothelial cells (ECs) at sites where the de novo generation of HSCs occurs. The activity of this enhancer is also strictly restricted to HSCs within the hematopoietic compartment of the adult bone marrow. We anticipate that Runx1 +24 mCNE HSC enhancer will serve as a molecular handle for tracing and/or manipulating hemogenic ECs/HSCs behavior in vivo, and consequently become an invaluable tool for research on stem cell and cancer biology.
ETV5 Regulates Sertoli Cell Chemokines Involved in Mouse Stem/Progenitor Spermatogonia Maintenance
Authors: Simon Liz , Ekman Gail C. , Garcia Thomas , Carnes Kay , Zhang Zhen , Murphy Theresa , Murphy Kenneth M. , Hess Rex A. , Cooke Paul S. , Hofmann Marie-Claude
Published: August 2010

Spermatogonial stem cells are the only stem cells in the body that transmit genetic information to offspring. Although growth factors responsible for self-renewal of these cells are known, the factors and mechanisms that attract and physically maintain these cells within their microenvironment are poorly understood. Mice with targeted disruption of Ets variant gene 5 (Etv5) show total loss of stem/progenitor spermatogonia following the first wave of spermatogenesis, resulting in a Sertoli cell-only phenotype and aspermia. Microarray analysis of primary Sertoli cells from Etv5 knockout (Etv5−/−) versus wild-type (WT) mice revealed significant decreases in expression of several chemokines. Chemotaxis assays demonstrated that migration of stem/progenitor spermatogonia toward Etv5−/− Sertoli cells was significantly decreased compared to migration toward WT Sertoli cells. Interestingly, differentiating spermatogonia, spermatocytes, and round spermatids were not chemoattracted by WT Sertoli cells, whereas stem/progenitor spermatogonia showed a high and significant chemotactic index. Rescue assays using recombinant chemokines indicated that C-C-motif ligand 9 (CCL9) facilitates Sertoli cell chemoattraction of stem/progenitor spermatogonia, which express C-C-receptor type 1 (CCR1). In addition, there is protein-DNA interaction between ETV5 and Ccl9, suggesting that ETV5 might be a direct regulator of Ccl9 expression. Taken together, our data show for the first time that Sertoli cells are chemoattractive for stem/progenitor spermatogonia, and that production of specific chemokines is regulated by ETV5. Therefore, changes in chemokine production and consequent decreases in chemoattraction by Etv5−/− Sertoli cells helps to explain stem/progenitor spermatogonia loss in Etv5−/− mice.
Myoblast-Derived Neuronal Cells Form Glutamatergic Neurons in the Mouse Cerebellum
Authors: Gopalakrishnan Vidya , Bie Bihua , Sinnappah-Kang Neeta D. , Adams Henry , Fuller Gregory N. , Pan Zhizhong Z. , Majumder Sadhan
Published: August 2010

Production of neurons from non-neural cells has far-reaching clinical significance. We previously found that myoblasts can be converted to a physiologically active neuronal phenotype by transferring a single recombinant transcription factor, REST-VP16, which directly activates target genes of the transcriptional repressor, REST. However, the neuronal subtype of M-RV cells and whether they can establish synaptic communication in the brain have remained unknown. M-RV cells engineered to express green fluorescent protein (M-RV-GFP) had functional ion channels but did not establish synaptic communication in vitro. However, when transplanted into newborn mice cerebella, a site of extensive postnatal neurogenesis, these cells expressed endogenous cerebellar granule precursors and neuron proteins, such as transient axonal glycoprotein-1, neurofilament, type-III β-tubulin, superior cervical ganglia-clone 10, glutamate receptor-2, and glutamate decarboxylase. Importantly, they exhibited action potentials and were capable of receiving glutamatergic synaptic input, similar to the native cerebellar granule neurons. These results suggest that M-RV-GFP cells differentiate into glutamatergic neurons, an important neuronal subtype, in the postnatal cerebellar milieu. Our findings suggest that although activation of REST-target genes can reprogram myoblasts to assume a general neuronal phenotype, the subtype specificity may then be directed by the brain microenvironment.
Effect of steady deflections on the aeroelastic stability of a turbine blade
Authors: Kallesøe B. S.
Published: August 2010

This paper deals with effects of geometric non‐linearities on the aeroelastic stability of a steady‐state deflected blade. Today, wind turbine blades are long and slender structures that can have a considerable steady‐state deflection which affects the dynamic behaviour of the blade. The flapwise blade deflection causes the edgewise blade motion to couple to torsional blade motion and thereby to the aerodynamics through the angle of attack. The analysis shows that in the worst case for this particular blade, the edgewise damping can be decreased by half. Copyright © 2010 John Wiley & Sons, Ltd.
Evaluation of the effects of turbulence model enhancements on wind turbine wake predictions
Authors: Prospathopoulos J. M. , Politis E. S. , Rados K. G. , Chaviaropoulos P. K.
Published: August 2010

The modelling of wind turbine wakes is investigated in this paper using a Navier–Stokes solver employing the k–ω turbulence model appropriately modified for atmospheric flows. It is common knowledge that even single‐wind turbine wake predictions with computational fluid dynamic methods underestimate the near wake deficit, directly contributing to the overestimation of the power of the downstream turbines. For a single‐wind turbine, alternative modelling enhancements under neutral and stable atmospheric conditions are tested in this paper to account for and eventually correct the turbulence overestimation that is responsible for the faster flow recovery that appears in the numerical predictions. Their effect on the power predictions is evaluated with comparison with existing wake measurements. A second issue addressed in this paper concerns multi‐wake predictions in wind farms, where the estimation of the reference wind speed that is required for the thrust calculation of a turbine located in the wake(s) of other turbines is not obvious. This is overcome by utilizing an induction factor‐based concept: According to it, the definition of the induction factor and its relationship with the thrust coefficient are employed to provide an average wind speed value across the rotor disk for the estimation of the axial force. Application is made on the case of five wind turbines in a row. Copyright © 2010 John Wiley & Sons, Ltd.
Trellis display
Authors: Robbins Naomi B.
Published: August 2010

Displaying data with three or more dimensions effectively on a two‐dimensional paper or screen is not an easy task. Commonly used graphs such as pie charts and bar graphs do not allow for easy comparisons across all variables. This article discusses trellis display, a framework for the visualization of data through multiple panels organized in rows, columns, and pages. Each panel displays some of the variables with the values of the other variables held fixed. We demonstrate the effectiveness of trellis display by comparing identical sets of data first using traditional pie charts or bar graphs and then using trellis display. In all cases, the trellis figures show characteristics of the data more clearly than the more common graphs do. We discuss additional advantages of trellis display such as the ability of trellis figures to distinguish variables without the use of color. Copyright © 2010 John Wiley & Sons, Inc.

This article is categorized under:

Statistical and Graphical Methods of Data Analysis > Statistical Graphics and Visualization
Genome‐wide screen of Saccharomyces cerevisiae for killer toxin HM‐1 resistance
Authors: Miyamoto Masahiko , Furuichi Yasuhiro , Komiyama Tadazumi
Published: August 2010

We screened a set of Saccharomyces cerevisiae deletion mutants for resistance to killer toxin HM‐1, which kills susceptible yeasts through inhibiting 1,3‐beta‐glucan synthase. By using HM‐1 plate assay, we found that eight gene‐deletion mutants had higher HM‐1‐resistance compared with the wild‐type. Among these eight genes, five—ALG3, CAX4, MNS1, OST6 and YBL083C—were associated with N‐glycan formation and maturation. The ALG3 gene has been shown before to be highly resistant to HM‐1. The YBL083C gene may be a dubious open reading frame that overlaps partially the ALG3 gene. The deletion mutant of the MNS1 gene that encodes 1,2‐alpha‐mannosidase showed with a 13‐fold higher HM‐1 resistance compared with the wild‐type. By HM‐1 binding assay, the yeast plasma membrane fraction of alg3 and mns1 cells had less binding ability compared with wild‐type cells. These results indicate that the presence of the terminal 1,3‐alpha‐linked mannose residue of the B‐chain of the N‐glycan structure is essential for interaction with HM‐1. A deletion mutant of aquaglyceroporin Fps1p also showed increased HM‐1 resistance. A deletion mutant of osmoregulatory mitogen‐activated protein kinase Hog1p was more sensitive to HM‐1, suggesting that high‐osmolarity glycerol pathways plays an important role in the compensatory response to HM‐1 action. Copyright © 2010 John Wiley & Sons, Ltd.
Metabolic regulation rather than de novo enzyme synthesis dominates the osmo‐adaptation of yeast
Authors: Bouwman Jildau , Kiewiet José , Lindenbergh Alexander , van Eunen Karen , Siderius Marco , Bakker Barbara M.
Published: August 2010

Intracellular accumulation of glycerol is essential for yeast cells to survive hyperosmotic stress. Upon hyperosmotic stress the gene expression of enzymes in the glycerol pathway is strongly induced. Recently, however, it was shown that this gene‐expression response is not essential for survival of an osmotic shock [Mettetal JT et al. (2008) Science 319: 482–484 and Westfall PJ et al. (2008) Proc Natl Acad Sci 105: 12212–12217]. Instead, pure metabolic adaptation can rescue the yeast. The existence of two alternative mechanisms urged the question which of these mechanisms dominates time‐dependent adaptation of wild‐type yeast to osmotic stress under physiological conditions. The regulation of the glycerol pathway was analysed in aerobic, glucose‐limited cultures upon addition of 1 M of sorbitol, leading to a hyperosmotic shock. In agreement with earlier studies, the mRNA levels of the glycerol‐producing enzymes as well as their catalytic capacities increased. Qualitatively this induction followed a similar time course to the increase of the glycerol flux. However, a quantitative regulation analysis of the data revealed an initial regulation by metabolism alone. After only a few minutes gene expression came into play, but even after an hour, 80% of the increase in the glycerol flux was explained by metabolic changes in the cell, and 20% by induction of gene expression. This demonstrates that the novel metabolic mechanism is not just a secondary rescue mechanism, but the most important mechanism to regulate the glycerol flux under physiological conditions. Copyright © 2010 John Wiley & Sons, Ltd.
Contact problems for several transversely isotropic elastic layers bonded to an elastic half‐space
Authors: Fabrikant V.I.
Published: August 2010

The idea of generalized images, first used by the author for the case of crack problems, is applied here to solve a contact problem forntransversely isotropic elastic layers, bonded to each other and to an elastic half‐space, made of a different transversely isotropic material. A rigid punch of arbitrary shape is pressed against the top layer's free surface. The governing integral equation is derived for the case of two layers; it is mathematically equivalent to that of an electrostatic problem of an infinite row of coaxial charge disks in the shape of the domain of contact. This result is then generalized for an arbitrary number of layers. As a comparison, the method of integral transforms is also used to solve the problem. The main difference of our integral transform approach with the existing ones is in separating of our half‐space solution from the integral transform terms. It is shown that both methods lead to the same results, thus giving a new interpretation to the integral transform as a sum of an infinite series of generalized images.
Colorectal Cancer in Young Patients in Israel: A Distinct Clinicopathological Entity?
Authors: Shemesh‐Bar L. , Kundel Y. , Idelevich E. , Sulkes J. , Sulkes A. , Brenner B.
Published: August 2010

Purpose

This study was designed to characterize the entity of colorectal cancer (CRC) in young patients and to evaluate whether it has any unique epidemiological or clinicopathological features.

Methods

The study population consisted of all consecutive young (≤50 years old at diagnosis) patients with CRC who were diagnosed during the years 1997–2007 and were treated at our institution, and a matching group of patients (>50 years at diagnosis). The medical files of these patients were reviewed, and the epidemiological, clinical, and pathological features of both groups were compared.

Results

There were 406 patients: 203 in each group. The features of the older group were typical for patients with CRC, but the younger group showed female predominance, different ethnic composition, prevalence of family history of cancer and hereditary CRC syndromes, and lower incidence of polyps. The incidence of left‐sided tumors and advanced stages (III–IV) at diagnosis was higher in the younger patients. Mucinous/signet ring histology, grade, stage, lymphatic and vascular invasion were all predictive of survival, whereas age was not.

Conclusions

Colorectal cancer in young patients was found to display a cluster of unique characteristics but fewer than previously reported and young age by itself was not found to impact patient outcome.
Building a 2010 biodiversity conservation data baseline: contributions of the Group on Earth Observations
Authors: Muchoney Douglas M. , Williams Michael
Published: August 2010

Characterizing, modeling, and monitoring the distribution and condition of the Earth's biodiversity and ecosystems has a long history of being aided by Earth Observation data and the models and derivative products that they support. At the global scale, there need to be more coordinated efforts to acquire, process, analyze, and make available these observation data across all disciplines, particularly since many applications use the same primary and derived data. Towards that end, the Group on Earth Observations (GEO) is implementing the Global Earth Observing System of Systems. The purpose of this article is to provide information on GEO's goals and activities relevant to biodiversity and ecosystems. The article also describes the data that would best serve as a year 2010 baseline in order to support the objectives of the Convention on Biological Diversity (CBD) as well as many other international agreements, programs, and activities. Indeed, an assessment of existing biodiversity observations with a concomitant recognition of the remaining gaps will promote the establishment of an integrated framework for biodiversity observations in support of the CBD's efforts.
Design and Fabrication of Fiber-Optic Nanoprobes for Optical Sensing
Authors: Zhang Yan , Dhawan Anuj , Vo-Dinh Tuan
Published: August 2010

This paper describes the design and fabrication of fiber-optic nanoprobes developed for optical detection in single living cells. It is critical to fabricate probes with well-controlled nanoapertures for optimized spatial resolution and optical transmission. The detection sensitivity of fiber-optic nanoprobe depends mainly on the extremely small excitation volume that is determined by the aperture sizes and penetration depths. We investigate the angle dependence of the aperture in shadow evaporation of the metal coating onto the tip wall. It was found that nanoaperture diameters of approximately 50 nm can be achieved using a 25° tilt angle. On the other hand, the aperture size is sensitive to the subtle change of the metal evaporation angle and could be blocked by irregular metal grains. Through focused ion beam (FIB) milling, optical nanoprobes with well-defined aperture size as small as 200 nm can be obtained. Finally, we illustrate the use of the nanoprobes by detecting a fluorescent species, benzo[a]pyrene tetrol (BPT), in single living cells. A quantitative estimation of the numbers of BPT molecules detected using fiber-optic nanoprobes for BPT solutions shows that the limit of detection was approximately 100 molecules.