bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Repeated Count Data: Some Extensions of the Rasch Poisson Counts Model
Authors: van Duijn Marijtje A. J. , Jansen Margo G. H.
Published: March 2008

We consider data that can be summarized as an N × K table of counts—for example, test data obtained by administering K tests to N subjects. The cell entries yij are assumed to be conditionally independent Poisson-distributed random variables, given the NK Poisson intensity parameters μij. The Rasch Poisson Counts Model (RPCM) postulates that the intensity parameters are products of test difficulty and subject ability parameters. We expand the RPCM by assuming that the subject parameters are random variables having a common gamma distribution with fixed unknown parameters and that the vectors of test difficulty parameters per subject follow a common Dirichlet distribution with fixed unknown parameters. Further, we show how additional structures can be imposed on the test parameters, modeling a within-subjects design. Methods for testing the fit and estimating the parameters of these models are presented and illustrated with the analysis of two empirical data sets.
Standard Error of Linear Equating for the Counterbalanced Design
Authors: Zeng Lingjia , Cope Ronald T.
Published: March 2008

Large-sample standard errors of linear equating for the counterbalanced design are derived using the general delta method. Computer simulations were conducted to compare the standard errors derived by Lord under the normality assumption with those derived in this article without such an assumption. The standard errors derived without the normality assumption were found to be more accurate than those derived with the normality assumption in an example using large sample size and moderately skewed score distributions. In an example using nearly symmetric distributions, the standard errors computed with the normality assumption were found to be at least as accurate as those derived without the normality assumption.
A Look at the Literature (and Other Resources) on Teaching Statistics
Authors: Becker Betsy Jane
Published: March 2008

Statistics instructors and others interested in the teaching of statistics will find many print and nonprint resources on this topic. The print literature on the teaching of statistics is largely anecdotal and comprises mainly recommendations for instruction based on the experiences and intuitions of individual instructors. Less than 30% of the print literature reports the results of empirical studies, but these cover a broad range of topics, including the use of computers in statistics instruction, teaching materials, and teaching strategies. A large portion of the nonempirical literature is devoted to descriptions of statistics courses and specific lessons that, though untested, still provide a resource for instruction. Recently numerous nonprint (electronic) resources for instruction, problem solving, and discussions about statistics instruction have also become available. These include many data sets and other instructional resources, statistics discussion groups, and the electronic Journal of Statistics Education.
Modeling Structure and Chance in Transitions: Mixed Latent Partial Markov-Chain Models
Authors: Meiser Thorsten , Ohrt Barbara
Published: March 2008

A family of finite mixture distribution models is presented which allows specification of basically different developmental processes in distinct latent subpopulations. In particular, random fluctuation between states for one latent subpopulation can be modeled together with stability or coherent developmental trajectories for others. Formally, these models are introduced within the framework of mixed latent Markov chains with multiple indicators per occasion. Identifiability conditions which become necessary because of the random fluctuation assumption for a part of the population are discussed. Model specification and interpretation are illustrated by an application to empirical data on therapeutic interventions in infancy and early childhood.
Using a Measure of Variable Importance to Investigate the Standardization of Discriminant Coefficients
Authors: Thomas D. Roland , Zumbo Bruno D.
Published: March 2008

This article addresses the issue of standardization of discriminant functions, which has recently been debated in the literature by Mueller & Cozad (1988 , 1993) and Nordlund & Nagel (1991) . It is argued that instead of using the standardized discriminant coefficients (DCs) to assess variable importance, the parallel and total discriminant ratio coefficients (DRCs) proposed by Thomas (1992) should be used. Furthermore, it is argued that the parallel DRCs should be adopted as the actual importance measures. The issue of standardization is then investigated by considering the effect of different definitions of discriminant coefficients and structure coefficients on the parallel DRCs. The main finding is that either of the two competing standardizations (within or total) can be used provided that the normalization and standardization of the discriminant coefficients is consistent, and consistent also with the definition of the structure coefficients. However, consistent total standardization is shown to lead to particularly convenient definitions of the total DRCs. It is also shown that standardized DCs based on total quantities are numerically closer to parallel DRCs than are standardized DCs based on within-group quantities.
Evaluating the Magnitude of Differential Item Functioning in Polytomous Items
Authors: Zwick Rebecca , Thayer Dorothy T.
Published: March 2008

Several recent studies have investigated the application of statistical inference procedures to the analysis of differential item functioning (DIF) in polytomous test items that are scored on an ordinal scale. Mantel’s extension of the Mantel-Haenszel test is one of several hypothesis-testing methods for this purpose. The development of descriptive statistics for characterizing DIF in polytomous test items has received less attention. As a step in this direction, two possible standard error formulas for the polytomous DIF index proposed by Dorans and Schmitt were derived. These standard errors, as well as associated hypothesis-testing procedures, were evaluated though application to simulated data. The standard error that performed better is based on Mantel’s hypergeometric model. The alternative standard error, based on a multinomial model, tended to yield values that were too small.
Sample Size Determination in a Chi-Squared Test Given Information From an Earlier Study
Authors: Gillett Raphael
Published: March 2008

When an effect size estimate from an earlier study is available, it is common practice to calculate a sample size for a future study by postulating that the true effect size equals the point estimate from the previous study. Such an approach is methodologically flawed because it ignores the presence of uncertainty in the point estimate. In view of the fact that the sample size needed for a specified power does not vary linearly with effect size, the traditional approach typically leads to less power than is desired for the specified effect. A rigorous method of utilizing information from a previous study when determining the sample size for a chi-squared test is outlined. The approach is able to guarantee that the average power of all experiments in a discipline attains the desired level.
Comments on Huberty’s Test of the Squared Multiple Correlation Coefficient
Authors: Yung Yiu-Fai
Published: March 2008

It is argued that Huberty’s (1994) test for inferring a better-than-“chance” performance of the observed R2 value is inconsistent. Because there is a hidden change of the null distribution of R2, the “chance” value and the observed R2 value are not comparable in Huberty’s test. A new test is proposed for resolving these difficulties. It is shown that the new test is equivalent to an adjustment of the α-level of the classical test of the squared multiple correlation coefficient.
Comparison of SPRT and Sequential Bayes Procedures for Classifying Examinees Into Two Categories Using a Computerized Test
Authors: Spray Judith A. , Reckase Mark D.
Published: March 2008

Many testing applications focus on classifying examinees into one of two categories (e.g., pass/fail) rather than on obtaining an accurate estimate of level of ability. Examples of such applications include licensure and certification, college selection, and placement into entry-level or developmental college courses. With the increased availability of computers for the administration and scoring of tests, computerized testing procedures have been developed for efficiently making these classification decisions. The purpose of the research reported in this article was to compare two such procedures, one based on the sequential probability ratio test and the other on sequential Bayes methodology, to determine which required fewer items for classification when the procedures were matched on classification error rates. The results showed that under the conditions studied, the SPRT procedure required fewer test items than the sequential Bayes procedure to achieve the same level of classification accuracy.
Hierarchical Linear Models for Multivariate Outcomes
Authors: Thum Yeow Meng
Published: March 2008

In this article, we develop a class of two-stage models to accommodate three common characteristics of behavioral data. First, behavior is invariably multivariate in its conceptualization and communication. Separate univariate analyses of related outcome variables are fraught with potential interpretive blind spots for the researcher. This practice also suffers, from an inferential standpoint, because it fails to take advantage of any redundant information in the outcomes. Second, studies of behavior, especially in experimental research, employ smaller samples. This situation raises issues of robustness of inference with respect to outlying individuals. Third, the outcome variable may have observations missing because of accidents or by design. The model permits the estimation of the full spectrum of plausible measurement error structures while using all the available information. Maximum likelihood estimates are obtained for various members of a multivariate hierarchical linear model (MHLM), and, in the context of several illustrative examples, these estimates match closely the results from a Bayesian approach to the normal-normal MHLM and to the normal- t MHLM.
Some New Item Selection Criteria for Adaptive Testing
Authors: Veerkamp Wim J. J. , Berger Martijn P. F.
Published: March 2008

In this study some alternative item selection criteria for adaptive testing are proposed. These criteria take into account the uncertainty of the ability estimates. A general weighted information criterion of which the usual maximum information criterion and the proposed alternative criteria are special cases is suggested. A small simulation study was conducted to compare the different criteria. The results showed that the likelihood weighted information criterion is a good alternative to the maximum information criterion. Another good alternative is a maximum information criterion with the maximum likelihood estimator of ability replaced by the Bayesian expected a posteriori estimator.
Teacher’s Corner: Using Exams for Teaching Concepts in Probability and Statistics
Authors: Gelman Andrew
Published: March 2008

We present several classroom demonstrations that have sparked student involvement in our introductory undergraduate courses in probability and statistics. The demonstrations involve both experimentation using exams and statistical analysis and adjustment of exam scores.
Local Dependence Indexes for Item Pairs Using Item Response Theory
Authors: Chen Wen-Hung , Thissen David
Published: March 2008

Four statistics are proposed for the detection of local dependence (LD) among items analyzed using item response theory. Among them, the X2 and G2 LD indexes are of special interest. Simulated data are used to study the distribution and sensitivity of these statistics under the null condition, as well as under conditions in which LD is introduced. The results show that under the null condition of local independence, both the X2 and G2 LD indexes have distributions very similar to the X2 distribution with 1 degree of freedom. Under the locally dependent conditions, both indexes appear to be sensitive in detecting LD or multidimensionality among items. When compared to Q3, another statistic often used to detect LD, these new statistics are somewhat less powerful for underlying LD, equally powerful for surface LD, and better behaved in the null case.
Finite Intersection Tests: A Paradigm for Optimizing Simultaneous and Sequential Inference
Authors: Hancock Gregory R. , Klockars Alan J.
Published: March 2008

When testing a family of comparisons or contrasts across k treatment groups, researchers are often encouraged to maintain control over the familywise Type I error rate. For common families such as comparisons against a reference group, sets of orthogonal and/or nonorthogonal contrasts, and all possible pairwise comparisons, numerous simultaneous (and more recently sequential) testing methods have been proposed. Many of the simultaneous methods can be shown to be a form of Krishnaiah’s (e.g., 1979) finite intersection test (FIT) for simultaneous multiple comparisons, which controls the familywise error rate to precisely a under conditions assumed in standard ANOVA scenarios. Other methods, however, merely represent conservative approximations to a FIT procedure, yielding suboptimal power for conducting simultaneous testing. The purpose of the current article is threefold. First, we discuss how FIT methodology represents a paradigm that unifies many existing methods for simultaneous inference, as well as how it suggests an improved method for testing nonorthogonal contrasts. Second, we illustrate more powerful multiple comparison procedures that combine FIT methodology with sequential hypothesis testing strategies. Third, we present a simple simulation strategy for generating critical values necessary to conduct these more powerful FIT-based methods. Examples of these methods are given.
A Model-Based Approach to Validating Education Indicators Using Multilevel Structural Equation Modeling
Authors: Kaplan David , Elliott Pamela R.
Published: March 2008

This article considers an approach to validating the selection of education indicators by incorporating them into a multilevel structural model and using the estimates from that model to engage in policy-relevant simulations. Multilevel structural equation modeling was applied to a subsample of the first follow-up of the National Education Longitudinal Study of 1988 ( National Center for Education Statistics, 1988 ) to demonstrate the potential of this approach. Focus of attention was on science education indicators. A within-school model of science achievement was linked to a between-school model of the academic press of the school. Separate estimation of these models revealed adequate fit to the data after minor modifications. The multilevel model also showed adequate fit to the data. Utilizing the reduced form of the full multilevel model, predictive validity of the model was studied by gauging movements in various outcome indicators as a function of changes in policy-relevant input indicators. The article closes with a discussion of the limitations of the proposed modeling approach, the potential for future model development, and the implications of this approach for quantitative modeling within the domain of education policy.
Interval Estimation of Bivariate Correlations With Missing Data on Both Variables: A Bayesian Approach
Authors: Gross Alan L.
Published: March 2008

The posterior distribution of the bivariate correlation ( ρxy) is analytically derived given a data set consisting N1 cases measured on both x and y, N2 cases measured only on x, and N3 cases measured only on y. The posterior distribution is shown to be a function of the subsample sizes, the sample correlation ( rxy) computed from the N1 complete cases, a set of four statistics which measure the extent to which the missing data are not missing completely at random, and the specified prior distribution for ρxy. A sampling study suggests that in small ( N = 20) and moderate ( N = 50) sized samples, posterior Bayesian interval estimates will dominate maximum likelihood based estimates in terms of coverage probability and expected interval widths when the prior distribution for ρxy is simply uniform on (0, 1). The advantage of the Bayesian method when more informative priors based on beta densities are employed is not as consistent.
Multiple Correspondence Analysis as a Tool for Quantification or Classification of Career Data
Authors: van der Heijden Peter G. M. , Teunissen Joop , van Orlé Charles
Published: March 2008

Career data of an individual are defined by counts that describe the amount of time an individual has spent in each of a number of mutually exclusive states. It is argued that correspondence analysis is particularly suited to such data, and this is illustrated by an example from educational careers. Furthermore it is shown that correspondence analysis can be used for a quantification of individual careers into one or more scores, or a classification, that can then be used in further analyses.
Teacher’s Corner: Toward a Coherent View of Reliability in Test Theory
Authors: Li Heng , Wainer Howard
Published: March 2008

Reliability of test scores, as estimated through measures of internal consistency, has been characterized mathematically in many ways that appear, on the surface at least, to be very dissimilar to one another. In this essay we provide a general mathematical framework that specializes to four different reliability coefficients. Through consideration of this general framework it becomes easier to convey to students both the individual character of the different formulations of reliability and the extent of their underlying similarity. In addition to providing a coherent view of reliability, the unified formula is also found to be a convenient vehicle for introducing more specialized topics, such as the Kaiser-Guttman rule.
Optimization of Classical Reliability in Test Construction
Authors: Armstrong Ronald D. , Jones Douglas H. , Wang Zhaobo
Published: March 2008

This article considers the problem of generating a test from an item bank using a criterion based on classical test theory parameters. A mathematical programming model is formulated that maximizes the reliability coefficient α, subject to logical constraints on the choice of items. The special structure of the problem is exploited with network theory and Lagrangian relaxation techniques. An empirical study shows that the method produces tests with high coefficient a subject to various practicable item constraints.
On Score Locations of Binary and Partial Credit Items and Their Applications to Item Mapping and Criterion-Referenced Interpretation
Authors: Huynh Huynh
Published: March 2008

A procedure is presented for locating on the latent trait scale the scores (or responses) of items that follow the three-parameter logistic (3PL) and monotone partial credit (MPC) models. The procedure is based on a Bayesian updating of the item information and is identical to locating the score at the latent trait value that maximizes the Bock score information. Applications are provided in terms of selecting items or score categories for criterion-referenced interpretation and mapping and analyzing score categories.
Measuring Variability and Change With an Item Response Model for Polytomous Variables
Authors: Eid Michael , Hoffmann Lore
Published: March 2008

An extension of the graded response model of Samejima (1969) for the measurement of variability and change is presented. In this model it is assumed that an occasion-specific latent variable is decomposed into (a) a person-specific variable (a trait variable) and (b) an occasion-specific deviation variable measuring the variability caused by situational and/or interactional effects. Furthermore, it is assumed that interindividual differences in intraindividual trait change occur between a priori specified periods of time. The correlations of the latent trait variables between periods of time indicate the degree of (trait) change. It is shown how the parameters of the model can be estimated and some implications of the model can be tested with structural equation models for ordered variables. Finally, the model is illustrated by an application to the measurement of students’ interest in the topic of radioactivity. Based on the results of a longitudinal study of students over 4’years, it is shown that a model considering two periods of time—one before and one after the incident in Chernobyl—fits well. According to the accepted model, it can be concluded that 30% to 60% of the variance of interest in radioactivity on an occasion of measurement are due to situational and/or interactional effects. The autocorrelations of the latent trait variables between both periods of time (r = .72 and r = .76, respectively) indicate that there are interindividual differences in intraindividual changes on the level of the latent trait variables.
Evaluating Latent Variable Growth Models Through Ex Post Simulation
Authors: Kaplan David , George Rani
Published: March 2008

This article considers the use of ex post (historical) simulation statistics as a means of evaluating latent variable growth models. Ex post simulation involves using the estimated parameters of a latent variable growth model to track the known historical values of an outcome of interest. Such methods of evaluating temporal models were developed primarily in applied economic forecasting and have been known for some time. This paper applies a variety of simulation quality statistics to latent variable growth models. In particular, Theil’s (1966) inequality coefficient, bias proportion, variance proportion, and covariance proportion are used to gauge the simulation adequacy of growth models. An application to the study of change in science achievement using data from the Longitudinal Study of American Youth is provided to illustrate the methodology. The results illustrate the importance of using these measures as adjuncts to more traditional forms of model evaluation, especially if one is considering the use of these models for subsequent forecasting or other policy purposes.
Uniform DIF and DIF Defined by Differences in Item Response Functions
Authors: Hanson Bradley A.
Published: March 2008

Uniform differential item functioning (DIF) exists when the statistical relationship between item response and group is constant for all levels of a matching variable. Two other types of DIF are defined based on differences in item response functions (IRFs) among the groups of examinees: unidirectional DIF (the IRFs do not cross) and parallel DIF (the IRFs are the same shape but shifted from one another by a constant, i.e., the IRFs differ only in location). It is shown that these three types of DIF are not equivalent and the relationships among them are examined in this paper for two item response categories, two groups, and an ideal continuous univariate matching variable. The results imply that unidirectional and parallel DIF which have been considered uniform DIF by several authors are not uniform DIF. For example, it is shown in this paper that parallel three-parameter logistic IRFs do not result in uniform DIF. It is suggested that the term “uniform DIF” be reserved for the condition in which the association between the item response and group is constant for all values of the matching variable, as distinguished from parallel and unidirectional DIF.
A More Powerful Post Hoc Multiple Comparison Procedure in Analysis of Variance
Authors: Klockars Alan J. , Hancock Gregory R.
Published: March 2008

Scheffé’s test ( Scheffé, 1953 ), which is commonly used to conduct post hoc contrasts among k group means, is unnecessarily conservative because it guards against an infinite number of potential post hoc contrasts when only a small set would ever be of interest to a researcher. This paper identifies a set of post hoc contrasts based on subsets of the treatment groups and simulates critical values from the appropriate multivariate F-distribution to be used in place of those associated with Scheffé’s test. The proposed method and its critical values provide a uniformly more powerful post hoc procedure.
On the Behrens-Fisher Problem: A Review
Authors: Kim Seock-Ho , Cohen Allan S.
Published: March 2008

The Behrens-Fisher problem arises when one seeks to make inferences about the means of two normal populations without assuming the variances are equal. This paper presents a review of fundamental concepts and applications used to address the Behrens-Fisher problem under fiducial, Bayesian, and frequentist approaches. Methods of approximations to the Behrens-Fisher distribution and a simple Bayesian framework for hypothesis testing are also discussed. Finally, a discussion is provided for the use of generalized p values in significance testing of hypotheses in the presence of nuisance parameters. It is shown that the generalized p values based on a frequentist probability for the Behrens-Fisher problem are numerically the same as those from the fiducial and Bayesian solutions. A table for tests of significance is also included.
Catalyst Forming
Authors: Schüth Ferdi , Hesse Michael
Published: March 2008

The sections in this article are

Introduction

The Physico‐Chemical Background of Forming Processes

Spray Drying

The Spray‐Drying Process

Atomizers

A
Rotary Atomizers

B
Hydraulic Nozzles

C
Two‐fluid Atomizers

Dryer Configuration

Extrusion

Basic Considerations

Equipment

Paste Composition and Additives

A
Water Content

B
Peptization Agents

C
Binders

D
Plasticizers

E
Lubricants

F
Porogens

Drying and Calcination

Tableting

Basic Considerations

Equipment

Formulation of the Feed

Granulation

Basic Considerations

Equipment

A
The Granulation Pan

B
The Granulation Drum

Miscellaneous Techniques

Oil Drop Coagulation

Pastillation

Coating of Preshaped Bodies

Perspectives
Neutron Scattering
Authors: Jobic Hervé
Published: March 2008

The sections in this article are

Introduction

Interaction of Neutrons with Matter

Experimental

Structure

Dynamics

Conclusions
Simultaneous Heat and Mass Transfer and Chemical Reaction
Authors: Dittmeyer Roland , Emig Gerhard
Published: March 2008

The sections in this article are

Introduction

Mathematical Description

Single Reactions (Conversion Problem)

Pore Diffusion in an Isothermal Pellet

Film and Pore Diffusion in an Isothermal Pellet

Film and Pore Diffusion Together with Interphase Heat Transfer

Film and Pore Diffusion Together with Interphase and Intraparticle Heat Transfer

External Heat and Mass Transfer

Use of Complex Rate Expressions

Simple Reversible Reactions

Simple Irreversible Reactions withLangmuir–Hinshelwood‐Type Kinetics

Simple Reversible Reactions withLangmuir–Hinshelwood‐Type Kinetics

Temperature Dependence and Reaction Order of Transport‐Limited Reactions

Intraparticle Diffusion

Interphase Mass Transfer

Diagnostic Criteria and Experimental Methods for Estimating the Influence of Heat and Mass Transfer on the Effective Reaction Rate

Experimental Criteria

Theoretical Criteria

Experimental Methods for Estimating the Influence of Heat and Mass Transfer Effects

Multiple Reactions (Selectivity Problem)

TypeISelectivity

TypeIISelectivity

TypeIIISelectivity

Mathematical Description of the Diffusional Transport

Fick's Law with Constant Effective Diffusivities

Bulk Diffusion andKnudsen Diffusion

Pressure‐Driven Viscous Flow and Surface Diffusion

Maxwell–Stefan Equations and Related Models

Bulk Diffusion,Knudsen Diffusion and Pressure‐Driven Viscous Flow

Surface Diffusion

Control of Selectivity in the Disproportionation of Ethylbenzene to Benzene and Diethylbenzenes on anHZSM‐5 Catalyst by Utilizing Diffusion Effects

Shape‐Selective Catalysis

Microkinetics

Macrokinetics

Modeling of Shape Selectivity Effects

Simplifying Assumptions

Model Equations

Simulation Results

AProduct Shape Selectivity (Unaffected by Other Factors)

BProduct Shape Selectivity and Reactant Diffusion Limitation (Combined Effect)

CProduct Shape Selectivity and Selective Adsorption (Combined Effect)

DProduct Shape Selectivity and Restricted Transition State Shape Selectivity (Combined Effect)

Controlled Modification of the Pore Structure

Concluding Remarks
Adaptive identification of linear time‐delay systems: From theory toward application to engine transient fuel identification
Authors: Orlov Y. , Kolmanovsky I. V. , Gomez O.
Published: March 2008

The paper is of tutorial value. A theoretical treatment of adaptive (online) identification issues is reviewed side by side for linear time‐delay systems (LTDSs) with state measurements and for single‐input single‐output (SISO) LTDS with output measurements. A class of parameter identification algorithms is then presented for SISO LTDS with known and unknown delays. An application of the proposed algorithms to transient fuel identification in a port‐fuel‐injected internal combustion engine is illustrated in an experimental study. Copyright © 2008 John Wiley & Sons, Ltd.
Electrically Directed On‐Chip Reversible Patterning of Two‐Dimensional Tunable Colloidal Structures
Authors: Xie Rongguo , Liu Xiang‐Yang
Published: March 2008

In this work, we report a versatile approach to two‐dimensional colloidal patterning based on the lateral assembly of colloidal particles by an alternating electric field (AEF). Under the AEF, the lithographically templated electrodes provide an effective way to reversibly and rapidly assemble colloidal particles into some desirable patterns. By controlling the AEF and the electrode pattern geometry, various colloidal patterns with tunable lattice spacing and even with binary lattice spacing have been formed. Particularly, we demonstrate that well‐defined linear defects can be embedded inside the colloidal crystals, whereas the unwanted existing defects can be controllably relaxed by this patterning process. This novel patterning technique is amenable to both large scale on‐chip patterning and micro‐structural control with single‐particle resolution on a time scale of seconds. Furthermore, it introduces a new class of colloidal structures with the properties that can be finely tuned, reversibly switched, or permanently fixed, opening a new way for the engineering of novel materials and devices at micro levels.
The clinical spectrum associated with a chromosome 17 short arm proximal duplication (dup 17p11.2) in three patients
Authors: Doco‐Fenzy Martine , Holder‐Espinasse Muriel , Bieth Eric , Magdelaine Corinne , Vincent Marie‐Claire , Khoury Maroun , Andrieux Joris , Zhang Feng , Lupski James R. , Klink Rabih , Schneider Anouck , Goze‐Martineau Odile , Cuisset Jean‐Marie , Vallee Louis , Manouvrier‐Hanu Sylvie , Gaillard Dominique , de Martinville Bérengère
Published: March 2008

The p11.2‐p12 region of human chromosome 17 is gene rich and composed of at least two genomically unstable domains: the Smith–Magenis syndrome region (17p11.2) and the Charcot‐Marie‐Tooth region (17p12), both of which are flanked by several low‐copy repeat sequences. Homologous recombination between these flanking repeats results in either deletion‐ or duplication‐associated phenotypes caused by a gene dosage effect. We report on the clinical phenotype of three patients presenting with either a 17p11.2 or 17p11.2p12 duplication, revealed by chromosome analysis and confirmed by fluorescent in situ hybridization analysis, high resolution genomic analysis of the 17p region using oligonucleotide array comparative genomic hybridization, and molecular studies with microsatellite markers. Two patients carry the 17p11.2 duplication, while the third one shows a larger duplication including the 17p12 region. The facial features observed in our patients include triangular face, full cheeks, smooth philtrum, thin upper lip, dental malocclusion, irregular eyebrows, and sparse hair, all of which are consistent with the pure proximal dup 17p phenotype. The patients' other clinical features are compared with previously published cases. © 2008 Wiley‐Liss, Inc.
Senescence of reproduction may explain adaptive menopause in humans: A test of the “mother” hypothesis
Authors: Pavard Samuel , E. Metcalf C. Jessica , Heyer Evelyne
Published: March 2008

The “mother” hypothesis is one of the main adaptive explanations of human menopause. It postulates that reproductive cessation constitutes a strategy that has been selected for during human evolution because mothers at older ages might maximize their fitness by investing resources in the survival and reproduction of their living children rather than by continuing to reproduce. This study provides a test of this hypothesis. Fertility functions that maximize fitness are built into a model incorporating the fact that the survival of females during the rearing period is a major determinant of their children's survival. Results are given according to different scenarios of increase with mothers' age of maternal mortality risk and risk of stillbirth and birth defects (on the assumption that these females do not experience menopause). Different estimates of the effect of a mother's death on her child's survival were also incorporated. Finally, a population genetics framework allows us to estimate selection on these optimal fertility functions. To determine whether or not these fertility functions show a menopause, three criteria are discussed: the rapidity of fertility decline, if any; the magnitude of selection on menopause compared with a nonmenopausal strategy; and the selection on survival during post‐reproductive life. Our results show that menopause and subsequent post‐reproductive life are significantly advantageous when two conditions are satisfied: a marked increase in stillbirth and risk of birth defects as well as in maternal mortality with mother's age. Am J Phys Anthropol, 2008. © 2008 Wiley‐Liss, Inc.
Weld line characteristics of PC/ABS blend. II. Effect of reactive compatibilizer
Authors: Lim Jong Cheol , Cho Kuk Young , Park Jung‐Ki
Published: March 2008

The effects of reactive compatibilizer and processing temperature on the morphology and the mechanical properties at the weld line of 60/40 (wt/wt) poly‐ carbonate (PC) and acrylonitrile‐butadiene‐styrene (ABS) copolymer blends were investigated. Amine functionalized styrene/n‐phenyl maleimide/maleic anhydride terpolymer (amine‐SPMIMA) was used as the in‐situ reactive compatibilizer for PC/ABS blend. Weld tensile strength increased as the content of amine‐SPMIMA was increased. Weld impact strength showed maximum value for the blend containing about 3% amine‐SPMIMA. The variation in the mechanical property at the weld line was correlated with the change in the morphology of the blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Hyaluronic acid–polyethyleneimine conjugate for target specific intracellular delivery of siRNA
Authors: Jiang Ge , Park Kitae , Kim Jiseok , Kim Ki Su , Oh Eun Ju , Kang Hyungu , Han Su‐Eun , Oh Yu‐Kyoung , Park Tae Gwan , Kwang Hahn Sei
Published: March 2008

A novel target specific small interfering RNA (siRNA) delivery system was successfully developed using polyethyleneimine (PEI)–hyaluronic acid (HA) conjugate. Anti‐PGL3‐Luc siRNA was used as a model system suppressing the PGL3‐Luc gene expression. The siRNA/PEI‐HA complex with an average size of ca. 21 nm appeared to be formed by electrostatic interaction between the negatively charged siRNA and the positively charged PEI of PEI‐HA conjugate. The cytotoxicity of siRNA/PEI‐HA complex to B16F1 cells was lower than that of siRNA/PEI complex according to the MTT assay. When B16F1 and HEK‐293 cells were treated with fluorescein isothiocyanate (FITC) labeled siRNA/PEI‐HA complex, B16F1 cells, with a lymphatic vessel endothelial hyaluronan receptor‐1 (LYVE‐1), showed higher green fluorescent intensity than HEK‐293 cells because of the HA receptor mediated endocytosis of the complex. Accordingly, the PGL3‐Luc gene silencing of anti‐PGL3‐Luc siRNA/PEI‐HA complex was more efficient in B16F1 cells than in HEK‐293 cells. In addition, the inhibited PGL3‐Luc gene silencing effect in the presence of free HA in the transfection medium revealed that siRNA/HA‐PEI complex was selectively taken up to B16F1 cells via HA receptor mediated endocytosis. All these results demonstrated that the intracellular delivery of anti‐PGL3‐Luc siRNA/PEI‐HA complex could be facilitated by the HA receptor mediated endocytosis. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 635–642, 2008.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Intestinal regeneration by a novel surgical procedure
Authors: Jwo S-C , Chiu J-H , Ng K-K , Chen H-Y
Published: March 2008

Background

Treatment of short bowel syndrome is problematical. Small bowel tissue engineering has achieved modest results in animal studies. The aim of this study was to investigate intestinal regeneration in a novel surgical model.

Methods

Roux-en-Y bypass procedures were performed on 40 Wistar rats weighing 250–350 g. Animals were killed at 1, 2, 3, 4, 8, 12 and 24 weeks after implantation with a 3-cm silicone tube. The spatio temporal relationship of intestinal regeneration was analysed using three-dimensional multislice computed tomography, and examination of sequential morphological changes on gross or histological findings and measurement of missing intestinal tissue (growth defects).

Results

Progressive intestinal regeneration on a silicone tube was identifiable in 35 animals. Most adhesions were initially localized on the tube but spread to a distal site 4 weeks after implantation. Growth defects decreased with time, with a marked reduction in the first 4 weeks and a gradual reduction to week 24 after implantation. Luminal patency shown radiologically as well as sequential histological findings, such as mucosal lining, matrix remodelling and muscular regeneration, suggested that regeneration of intestinal tissue took place, not merely scar contraction.

Conclusion

Non-invasive as well as histomorphological assessment followed intestinal regeneration over time in this model, which provides scope for further studies.
An efficient dynamic point algorithm for line‐based collision detection in real time virtual environments involving haptics
Authors: Maciel Anderson , De Suvranu
Published: March 2008

In real time computer graphics, “interactivity” is limited to a display rate of 30 frames per second. However, in multimodal virtual environments involving haptic interactions, a much higher update rate of about 1 kHz is necessary to ensure continuous interactions and smooth transitions. The simplest and most efficient interaction paradigm in such environments is to represent the haptic cursor as a point. However, in many situations, such as those in the development of real time medical simulations involving the interactions of long slender surgical tools with soft deformable organs, such a paradigm is nonrealistic and at least a line‐based interaction is desirable. While such paradigms exist, the main impediment to their widespread use is the associated computational complexity. In this paper, we introduce, for the first time, an efficient algorithm for computing the interaction of a line‐shaped haptic cursor and polygonal surface models which has a near constant complexity. The algorithm relies on space‐time coherence, topological information, and the properties of lines in 3D space to maintain proximity information between a line segment and triangle meshes. For interaction with convex objects, the line is represented by its end points and a dynamic point, which is the closest point on the line to any potentially colliding triangle. To deal with multiple contacts and non‐convexities, the line is decomposed into segments and a dynamic point is used for each segment. The algorithm may be used to compute collision detection and response with rigid as well as deformable objects with no performance penalty. Realistic examples are presented to demonstrate the effectiveness of our approach. Copyright © 2008 John Wiley & Sons, Ltd.
IR Spectroscopic Properties of H(MeOH)n+ Clusters in the Liquid Phase: Evidence for a Proton Wire
Authors: Stoyanov Evgenii S. , Stoyanova Irina V. , Reed Christopher A.
Published: March 2008

The long‐standing problem of understanding the nature of the “excess proton” in acidified water is simplified by studying the proton in methanol. The 3D network of hydrogen bonds in H(aq)+ is reduced to a 1D problem. Infrared spectroscopic characterization of linear chain methanol proton solvates in H(CH3OH)n+ for n=2–8 provides insight into some of the puzzling IR spectral features associated with O‐H‐O vibrations. These include the virtual disappearance of otherwise strong bands from H‐bonded methanol molecules adjacent to symmetrical O‐H+‐O groups. The data indicate that a chain of up to four OH⋅⋅⋅O bonds either side of this group can act as an electrical wire to separate positive charge. This suggests a refinement of the Grotthuss proton‐hopping mechanism for explaining the anomalously high mobility of H+ in H‐bonded media.
ChemInform Abstract: Structural Phase Transition of Gd3RuO7.
Authors: Ishizawa Nobuo , Tateishi Kenji , Kondo Saki , Suwa Tsuyoshi
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Experimental Investigation and Thermodynamic Description of the In—Sb—Sn Ternary System.
Authors: Manasijevic Dragan , Vrest'al Jan , Minic Dusko , Kroupa Ales , Zivkovic Dragana , Zivkovic Zivan
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Self‐Templated Synthesis of Nanoporous CdS Nanostructures for Highly Efficient Photocatalytic Hydrogen Production under Visible Light.
Authors: Bao Ningzhong , Shen Liming , Takata Tsuyoshi , Domen Kazunari
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Facile Synthesis of Troilite.
Authors: Pedoussaut Nathalie M. , Lind Cora
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Construction of Three Contiguous Tertiary Stereocenters from Aziridines in One Step.
Authors: Blyumin Evgeniy V. , Gallon Helen J. , Yudin Andrei K.
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: N‐Heterocyclic Carbene‐Catalyzed Redox Amidations of α‐Functionalized Aldehydes with Amines.
Authors: Bode Jeffrey W. , Sohn Stephanie S.
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Rh‐Catalyzed Highly Enantioselective Formation of Functionalized Cyclopentanes and Cyclopentanones
Authors: Liu Fei , Liu Qiang , He Minsheng , Zhang Xumu , Lei Aiwen
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Functional Group‐Selective Poisoning of Molecular Catalysts: A Ruthenium Cluster‐Catalyzed Highly Amide‐Selective Silane Reduction that Does Not Affect Ketones or Esters.
Authors: Sasakuma Hidehiro , Motoyama Yukihiro , Nagashima Hideo
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Catalytic Oxidation of Hydrazo Derivatives Promoted by a TiCl3/HBr System.
Authors: Drug Eyal , Gozin Michael
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Ruthenium Janus—Head Complexes with a Triazolediylidene Ligand. Structural Features and Catalytic Applications.
Authors: Viciano Monica , Sanau Mercedes , Peris Eduardo
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: One‐Step Synthesis of SBA‐15 Containing Tungsten Oxide Nanoclusters: A Chemoselective Catalyst for Oxidation of Sulfides to Sulfoxides under Ambient Conditions.
Authors: Bordoloi Ankur , Vinu Ajayan , Halligudi S. B.
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Solvent Effect on Sulfur Ylide Mediated Epoxidation Reaction.
Authors: Lee Hee‐Yoon , Bae Imhyuck , Min Kyung‐Hyun
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Oxidation of 3,4‐Diaryl‐2,5‐dihydrothiophenes to 3,4‐Diarylthiophenes Using CuBr2: Simple and Efficient Preparation of 3,4‐Diarylthiophenes.
Authors: Dang Yizhe , Chen Yi
Published: March 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.