bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of wood sawdust content on rheological and structural changes, and thermo‐mechanical properties of PVC/sawdust composites
Authors: Sombatsompop Narongrit , Chaochanchaikul Kantima , Phromchirasuk Chakarin , Thongsang Sirinthorn
Published: December 2003

The use of untreated sawdust as a filler in poly(vinyl chloride) (PVC) was examined—the effects of sawdust content on structural and thermal changes, and rheological and mechanical properties being of main interest. The results revealed that the torque and die entrance pressure drop values during mixing were independent of sawdust particles up to 23.1 wt%. The extrudate swell monotonically decreased up to 33.3 wt% sawdust content. Smooth wood‐like texture with controllable size of the extrudate could be obtained at a sawdust content greater than 33.3 wt%. Tensile, impact, flexural and hardness properties of the PVC/sawdust composites considerably decreased with up to 16.7 wt% sawdust content before leveling off for higher sawdust loadings. The composites having sawdust higher than 16.7 wt% showed a benefit of cost savings. The decreases in the mechanical properties of PVC with sawdust are explained in association with the presence of moisture, interfacial defects between fibre and polymer, and fibre dispersions in the PVC matrix. Thermal degradations of PVC in PVC/sawdust composites were evidenced by a decrease in decomposition temperature and an increase in polyene sequences, which were caused by Cl cleavage due to strong hydrogen bonds of fibre–PVC molecules. The maximum of tanδ transition and the glass transition temperature were found to improve with sawdust content as a result of re‐formation of hydrogen bonds between the macromolecules of the fibre and the polymer. The overall results in this work suggest that the properties of PVC/sawdust composites were strongly influenced by sawdust content up to 16.7 wt%. Beyond this value the effect of sawdust content on the properties was comparatively small. Copyright © 2003 Society of Chemical Industry
Conformational properties of macromolecules of heterocyclic polyester imides in dilute dichloroacetic acid solutions
Authors: Andreeva L. N. , Bushin S. V. , Tsvetkov N. V. , Belyaeva E. V. , Il'In V. V. , Bilibin A. Yu. , Pospiech D. , Friedel P.
Published: December 2003

Several series of polyester imides (PEIs) were prepared by melt polycondensation of trimellitimidobenzoic acid and acetylated, substituted hydroquinones as well as by solution polycondensation of corresponding dichlorides with hydroquinones. The influence of either phenyl‐ or tert‐butyl substituents at the hydroquinone unit on the hydrodynamic (diffusion and viscometry) and optical [flow (FB) and electrical (EB) birefringence] properties of solutions of these PEIs were investigated. Independent methods for quantitative evaluation of the length of the statistical Kuhn segment A gave values of 14.5 nm (translational friction and electrical birefringence) and 12.0 nm (flow birefringence), respectively. The equilibrium rigidity of PEIs with phenyl and tert‐butyl lateral substituents at the para‐aromatic chain fragment was comparable. Conformational properties of the PEIs were analyzed, and the conjugation energies of the ester and amide groups for para‐aromatic polyesters, PEIs, and structurally similar polyamidobenzoxazoles and polyamidobenzimidazoles were compared. The introduction of the phthalimide ring leads to a decrease of conjugation energy and deviation of the ester group from coplanarity. The Kuhn segment values obtained were useful for calculations of phase diagrams of semiflexible segmented block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 12–24, 2004
Effects of the drawing form and draw ratio on the fiber structure and mechanical properties of CO2‐laser‐heated‐drawn poly(ethylene terephthalate) fibers
Authors: Okumura W. , Ohkoshi Y. , Gotoh Y. , Nagura M. , Urakawa H. , Kajiwara K.
Published: December 2003

The structure, mechanical properties, and thermomechanical properties of poly(ethylene terephthalate) (PET) fibers obtained by laser‐heated drawing were investigated in terms of their dependence on the draw ratio and feed speed and the differences between neck‐drawn fibers and flow‐drawn fibers. The long period at a draw ratio of 6.0 reached 19.0 nm, notably larger than at lower ratios, whereas the tilting angle of the laminar structure was constant at about 60°, regardless of the draw ratio. A maximum value of 15.0 GPa was attained for the initial modulus, and 1.07 GPa was attained for the tensile strength. A higher tensile strength orientation‐induced crystallized fiber at the same initial modulus was obtained from higher molecular weight PET. The relationship between the compliance and molecular orientation of the amorphous phase was studied with a series model of crystalline and amorphous phases. The results revealed that, in the high‐draw‐ratio fibers, the compliance of the amorphous phase decreased with the draw ratio at a higher rate than indicated by extrapolation to intrinsic values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 79–90, 2004
Analysis of the 1030‐cm−1 band of poly(ethylene terephthalate) fibers using polarized raman microscopy
Authors: Yang Shuying , Michielsen Stephen
Published: December 2003

Polarized Raman spectroscopy was used to analyze uniaxially oriented fibers of poly(ethylene terephthalate) (PET) fibers. The second‐order and fourth‐order Legendre polynomials of the orientation distribution function of the 1030‐cm−1 vibrational band were determined to be zero for samples of low‐to‐moderate orientation. Because this band was assigned to the gauche conformation of the ethylene glycol unit, the orientation of the gauche configuration of ethylene glycol units in PET for PET of low‐to‐moderate orientation was random. This was consistent with the assumptions used by Ward and coworkers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 47–52, 2004
Nonlinear conduction in nylon‐6/foliated graphite nanocomposites above the percolation threshold
Authors: Chen Guohua , Weng Wengui , Wu Dajun , Wu Cuiling
Published: December 2003

The nonlinear conduction behavior of composite materials of foliated graphite nanosheets and nylon‐6 subjected to a variable direct‐current electric field has been studied. Corresponding to the onset of the nonlinearity, there is a crossover current density/electric field (or current–voltage) couple. The current density or current decreases as the foliated graphite concentration decreases. Through discussions of the nonlinearities within the frameworks of the two theoretical models, the nonlinear random resistor network and the dynamic random resistor network, it is shown that neither of these models can explain fully the results obtained for this system. On the basis of the microscopic structures and conduction processes of the nanocomposites, it is found that a combination of the models can generally account for the nonlinear characteristics. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 155–167, 2004
An integrated model for statistical and vision monitoring in manufacturing transitions
Authors: Nembhard Harriet Black , Ferrier Nicola J. , Osswald Tim A. , Sanz‐Uribe Juan R.
Published: December 2003

Manufacturing transitions have been increasing due to higher pressures for product variety. One dimension of this variety is color. A major quality control challenge is to regulate the color by capturing data on color in real‐time during the operation and to use it to assess the opportunities for good parts. Control charting, when applied to a stable state process, is an effective monitoring tool to continuously check for process shifts or upsets. However, the presence of transition events can impede the normal performance of a traditional control chart. In this paper, we present an integrated model for statistical and vision monitoring using a tracking signal to determine the start of the transition and a confirmation signal to ensure that any process oscillation has concluded. We also developed an automated color analysis and forecasting system (ACAFS) that we can adjust and calibrate to implement this methodology in different production processes. We use a color transition process in plastic extrusion to illustrate a transition event and demonstrate our proposed methodology. Copyright © 2003 John Wiley & Sons, Ltd.
Process monitoring for correlated gamma‐distributed data using generalized‐linear‐model‐based control charts
Authors: Jearkpaporn Duangporn , Montgomery Douglas C. , Runger George C. , Borror Connie M.
Published: December 2003

A model‐based scheme is proposed for monitoring multiple gamma‐distributed variables. The procedure is based on the deviance residual, which is a likelihood ratio statistic for detecting a mean shift when the shape parameter is assumed to be unchanged and the input and output variables are related in a certain manner. We discuss the distribution of this statistic and the proposed monitoring scheme. An example involving the advance rate of a drill is used to illustrate the implementation of the deviance residual monitoring scheme. Finally, a simulation study is performed to compare the average run length (ARL) performance of the proposed method to the standard Shewhart control chart for individuals. Copyright © 2003 John Wiley & Sons, Ltd.
Using Neural Networks to Detect and Classify Out‐of‐control Signals in Autocorrelated Processes
Authors: Noorossana R. , Farrokhi M. , Saghaei A.
Published: December 2003

This paper presents an artificial neural network model for detecting and classifying three types of non‐random disturbances referred to as level shift, additive outlier and innovational outlier which are common in autocorrelated processes. To the best of our knowledge, this is the first time that a neural network has been considered for simultaneous detection and classification of such non‐random disturbances. An AR (1) model is considered to characterize the quality characteristic of interest in a continuous process where autocorrelated observations are generated over time. The performance of the proposed procedure is evaluated through the use of a numerical example. Preliminary results indicate that the procedure can be used effectively to detect and classify unusual shocks in autocorrelated processes. Copyright © 2003 John Wiley & Sons, Ltd.
Quantifying nitrate retention processes in a riparian buffer zone using the natural abundance of 15N in NO3−
Authors: Dhondt Karel , Boeckx Pascal , Van Cleemput Oswald , Hofman Georges
Published: December 2003

Quantifying the relative importance of denitrification and plant uptake to groundwater nitrate retention in riparian zones may lead to methods optimising the construction of riparian zones for water pollution control. The natural abundance of 15N in NO3− has been shown to be an interesting tool for providing insights into the NO3− retention processes occurring in riparian zones. In this study, 15N isotope fractionation (variation in δ15N of the residual NO3−) due to denitrification and due to plant uptake was measured in anaerobic soil slurries at different temperatures (5, 10 and 15°C) and in hydroponic systems with different plant species (Lolium perenne L., Urtica dioica L. and Epilobium hirsutum L.). It was found that temperature had no significant effect on isotope fractionation during denitrification, which resulted in a 15N enrichment factor εD of −22.5 ± 0.6‰. On the other hand, nitrate uptake by plants resulted in 15N isotope fractionation, but was independent of plant species, leading to a 15N enrichment factor εP of −4.4 ± 0.3‰. By relating these two laboratory‐defined enrichment factors to a field enrichment factor for groundwater nitrate retention during the growing season (εR = −15.5 ± 1.0‰), the contribution of denitrification and plant uptake to groundwater nitrate retention could be calculated. The relative importance of denitrification and plant uptake to groundwater nitrate retention in the riparian buffer zone was 49 and 51% during spring, 53 and 47% during summer, and 75 and 25% during autumn. During wintertime, high micropore dissolved organic carbon (DOC) concentrations and low redox potentials due to decomposition of the highly productive riparian vegetation probably resulted in a higher denitrification rate and favoured other nitrate retention processes such as nitrate immobilisation or dissimilatory nitrate reduction to ammonium (DNRA). This could have biased the 15N isotope fractionation and led to a low 15N enrichment factor for groundwater nitrate retention during wintertime (−6.2 ± 0.9‰). In contradiction to what many other studies suggest, it is possible that due to plant decomposition during the winter period other nitrate transformation processes compete with denitrification. Copyright © 2003 John Wiley & Sons, Ltd.
Effect of preparation and preservation procedures on carbon and nitrogen stable isotope determinations from zooplankton
Authors: Feuchtmayr Heidrun , Grey Jonathan
Published: December 2003

A literature survey of zooplankton stable isotope studies revealed inconsistencies between authors concerning (a) fixation and (b) allowance for gut clearance of zooplankton prior to δ13C and δ15N determinations. To address whether commonly used preservation techniques induce changes in stable isotope values, fresh lake zooplankton (control) were compared with preserved (ethanol, methanol, formaldehyde, gluteraldehyde, frozen and shock frozen) material. Differences of up to 1.1‰ for carbon and 1.5‰ for nitrogen isotopic signatures were found. Even freezing, the most frequently used method identified from the literature, caused significant changes compared with the control. We advocate the use of fresh material prepared immediately whenever possible, or complementary testing of the preservative method to be used.

Larger organisms are routinely eviscerated, or specific tissues are dissected, and analysed for stable isotopes to reduce errors introduced via the gut contents. Yet zooplankton gut clearance is rarely performed: the gut content assumed to be negligible relative to organism mass. Experimental determinations of relative gut mass, from both original and compiled data, range from 1–26% for different zooplankton species. Using reported isotopic values of basal resources from natural systems, we calculated that, when analysing bulk zooplankton, inclusion of the gut mass may introduce substantial errors of >3‰. Thus it appears prudent to perform the simple procedure of gut clearance, especially for copepod species. Copyright © 2003 John Wiley & Sons, Ltd.
Simultaneous measurement of drug metabolic stability and identification of metabolites using ion‐trap mass spectrometry
Authors: Kantharaj E. , Tuytelaars An , Proost Pascale E. A. , Ongel Zuleyha , van Assouw Harrie P. , Gilissen Ron A. H. J.
Published: December 2003

The use of in vitro drug metabolism data in the understanding of in vivo pharmacokinetic, safety and toxicity data has become a large area of scientific interest. This has stemmed from a trend in the pharmaceutical industry to use in vitro data generated from human tissue as a criterion to select compounds for further investigation. As well as measuring metabolic stability in vitro using human liver microsomal preparations, the identification of possible metabolite(s) formed may play a vital role in Hit‐to‐Lead and Lead optimisation processes. The data‐dependent scan function mode with the ion‐trap instrumentation provides the ability to measure the metabolic stability and identification of possible metabolites of a compound. A gradient liquid chromatographic method with a run time of 6 min/injection was developed for this purpose. The approach of simultaneous metabolic stability measurements and rapid identification of metabolites of drugs with high (verapamil), medium (propranolol and cisapride) and low (flunarazine) metabolic stabilities using ion‐trap mass spectrometry is described. The metabolites identified after 15 min incubation for verapamil, propranolol and cisapride are in good agreement with those reported as the major metabolites in human in vivo studies. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of ketones by selected ion flow tube mass spectrometry
Authors: Smith David , Wang Tianshu , Španĕl Patrik
Published: December 2003

A selected ion flow tube mass spectrometry (SIFT‐MS) study of the reactions of H3O+, NO+ and O2+. ions with the ketones (M) 2‐heptanone, 2‐octanone, 2‐nonanone, 2‐undecanone and 2‐aminoacetophenone has been conducted in preparation for studies of volatile emissions from bacteria. The H3O+ reactions all proceed rapidly via exothermic proton transfer, producing only MH+ ions that form their monohydrates when water vapour is present in the helium carrier gas. The O2+. reactions proceed rapidly via dissociative charge transfer producing parent cations M+. and some fragment ions. The NO+ reactions form the NO+M adduct ions at rates which are dependent on the pressure of the helium carrier gas. Combining the present NO+ kinetic data with those available from previous SIFT studies, the phenomenon of charge transfer complexing is clearly demonstrated. This results in adduct formation in these NO+/ketone reactions at or near the collisional rate. SIFT‐MS spectra are presented to illustrate the simplicity of SIFT‐MS analysis of ketones using both H3O+ and NO+ precursor ions. Copyright © 2003 John Wiley & Sons, Ltd.
The emergence of a giant component in random subgraphs of pseudo‐random graphs
Authors: Frieze Alan , Krivelevich Michael , Martin Ryan
Published: December 2003

Let G be a d‐regular graph G on n vertices. Suppose that the adjacency matrix of G is such that the eigenvalue λ which is second largest in absolute value satisfies λ = o(d). Let Gp with p = α/d be obtained from G by including each edge of G independently with probability p. We show that if α < 1, then whp the maximum component size of Gp is O(log n) and if α > 1, then Gp contains a unique giant component of size Ω(n), with all other components of size O(log n). © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004
A stochastic model for solitons
Authors: Itoh Yoshiaki , Mahmoud Hosam M. , Takahashi Daisuke
Published: December 2003

The soliton physics for the propagation of waves is represented by a stochastic model in which the particles of the wave can jump ahead according to some probability distribution. We demonstrate the presence of a steady state (stationary distribution) for the wavelength. It is shown that the stationary distribution is a convolution of geometric random variables. Approximations to the stationary distribution are investigated for a large number of particles. The model is rich and includes Gaussian cases as limit distribution for the wavelength (when suitably normalized). A sufficient Lindeberg‐like condition identifies a class of solitons with normal behavior. Our general model includes, among many other reasonable alternatives, an exponential aging soliton, of which the uniform soliton is one special subcase (with Gumbel's stationary distribution). With the proper interpretation, our model also includes the deterministic model proposed in Takahashi and Satsuma [A soliton cellular automaton, J Phys Soc Japan 59 (1990), 3514–3519]. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004
General urn models with several types of balls and Gaussian limiting fields
Authors: Drmota Michael , Gardy Danièle , Gittenberger Bernhard
Published: December 2003

We study a system of m urns, where several types of balls are thrown, and an additive valuation is assigned to each urn depending on its state. Examples are the join models studied in a database context, and some models with two types of balls. The object of our investigation is the evolution of the valuation with time, when a ball is thrown at each time unit. By means of a generating function approach we show the weak convergence of the valuation process to a Gaussian field. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004
Modified methodology for computing interference in LEO satellite environments
Authors: Chávez Santiago Raúl , Kontorovitch Valeri Ya. , Lara Barrón Mauricio
Published: December 2003

Computing interference is very important in satellite networks design in order to assure the electromagnetic compatibility (EMC) with other radiocommunication systems. There are different methods to compute interference in geostationary (GEO) satellite systems including conventional methods using link budget equations and alternate methods such as increase in noise temperature. However, computing interference in low earth orbit (LEO) systems represents a different problem. Due to the special characteristics of this kind of orbits, the elevation angle at any site changes continuously over time, meaning a time dependent change of the propagation path length between an interfering transmitter and an interfered‐with receiver, and of the discrimination provided by the transmitting and/or the receiving antenna. Thus, conventional interference prediction methods developed for fixed links must be adapted to the case of LEO systems. To overcome this problem a mathematical model that characterizes the path length variations by an average value obtained from the probability density function of the varying distance between an interfering transmitter and an interfered‐ with receiver is proposed in this paper. This average path length enables the use of conventional link budget methods to reduce the computation time for the evaluation of interference in LEO satellite environments. Two practical examples show the possible applications of the proposed model. Copyright © 2003 John Wiley & Sons, Ltd.
On the rain attenuation dynamics: spatial‐temporal analysis of rainfall rate and fade duration statistics
Authors: Panagopoulos Athanasios D. , Kanellopoulos John D.
Published: December 2003

Knowledge about the dynamic characteristics of rain attenuation is of utmost importance for many applications in terrestrial and satellite communication systems operating at frequencies above 10 GHz. Long‐term rain rate statistics and rain rate duration statistics are usually available from meteorological data. In this paper, a spatial–temporal analysis is employed in order to evaluate the rain attenuation power spectrum of a terrestrial/satellite path. The predicted power spectrum is compared with experimental data. Based on the spectral analysis of rainfall rate a method for converting rain rate duration statistics to link fade duration statistics is also proposed. Fade duration statistics are presented for terrestrial and satellite links and compared with available experimental data. The agreement between the predicted results and the experimental data has been found to be quite encouraging. Finally, numerical results are presented for various climatic zones, elevation angles and frequencies. Some very useful conclusions concerning the dynamic properties of rain attenuation for a microwave path are deduced. Copyright © 2003 John Wiley & Sons, Ltd.
Freezing height distribution in the tropics
Authors: Thurai Merhala , Deguchi Eri , Iguchi Toshio , Okamoto Ken'ichi
Published: December 2003

The calculation of fade margins required to meet the user‐specified availability criteria needs to take into consideration a number of meteorological factors specific to the earth‐station location. One such factor is the annual average of the freezing level height. Information on this height is available in ITU‐R Recommendation P. 839‐3, which provides contours that are generated on a 1.5° by 1.5° latitude by longitude resolution grid. This paper compares these heights with the bright‐band heights (BBH) obtained from the precipitation radar on‐board the TRMM (Tropical Rainfall Measuring Mission) satellite. Four years of TRMM radar data have been analysed, and their averages are compared within the latitude range covered by the satellite orbit (35°N to 35°S). Comparisons show that the radar bright‐band heights typically occur 300 m below the 0°C isotherm heights. However, results also indicate that this difference may be latitude dependent. Also examined are the year‐to‐year variability and the seasonal variation. In the former case, only 1998 showed BBH values which are somewhat higher in tropical regions, this year having had one of the strongest El Niño events recorded. In the latter case, results show significant seasonal variation, becoming more pronounced at higher latitudes. Copyright © 2003 John Wiley & Sons, Ltd.
A note on non‐parametric ANCOVA for covariate adjustment in randomized clinical trials
Authors: Lesaffre Emmanuel , Senn Stephen
Published: December 2003

Koch et al. recently (1998) proposed two covariate‐adjusted approaches for the comparison of continuous, ordinal and binary responses in a randomized clinical trial (Statist. Med. 1998; 17: 1863–1892). The first is a randomization approach while the second assumes that the study is a sample of a population. Here, we study the second approach and consider the simplest cases of two treatments with a continuous response and with a binary response. Koch's second approach will be compared with the classical ANCOVA for a continuous response. From this relationship we demonstrate that Koch's method cannot preserve the probability of the type I error. Simulations with continuous responses as well as with binary outcomes confirm the aforementioned theoretical result on the performance of Koch's method under the null hypothesis of no treatment effect. However, this poses only a problem for relatively small to moderate sample sizes. Further, as specified in the original paper of Koch et al., the first approach does preserve the type I error for any sample size, as the P‐values can be reported in an exact manner (Statist. Med. 1998; 17: 1863–1892). Finally, we propose a correction factor for Koch's test statistic that better preserves the type I error. Copyright © 2003 John Wiley & Sons, Ltd.
Comparison of multiple regression to two latent variable techniques for estimation and prediction
Authors: Wall Melanie M. , Li Ruifeng
Published: December 2003

In the areas of epidemiology, psychology, sociology, and other social and behavioural sciences, researchers often encounter situations where there are not only many variables contributing to a particular phenomenon, but there are also strong relationships among many of the predictor variables of interest. By using the traditional multiple regression on all the predictor variables, it is possible to have problems with interpretation and multicollinearity. As an alternative to multiple regression, we explore the use of a latent variable model that can address the relationship among the predictor variables. We consider two different methods for estimation and prediction for this model: one that uses multiple regression on factor score estimates and the other that uses structural equation modelling. The first method uses multiple regression but on a set of predicted underlying factors (i.e. factor scores), and the second method is a full‐information maximum‐likelihood technique that incorporates the complete covariance structure of the data. In this tutorial, we will explain the model and each estimation method, including how to carry out prediction. A data example will be used for demonstration, where respiratory disease death rates by county in Minnesota are predicted by five county‐level census variables. A simulation study is performed to evaluate the efficiency of prediction using the two latent variable modelling techniques compared to multiple regression. Copyright © 2003 John Wiley & Sons, Ltd.
A discrete simulation model for assessing software project scheduling policies
Authors: Padberg Frank
Published: December 2003

Good project scheduling is an essential, but extremely hard task in software management practice. In a software project, the time needed to complete some development activity is difficult to estimate. Often, the completion of activities is delayed due to unanticipated rework which is caused by feedback in the process.

In this paper, we show how process simulation can be used to support managers in finding good schedules for their software projects. We present a novel, stochastic simulation model which is tailored to the special dynamics of software projects, and which explicitly takes a scheduling strategy as input. The model represents task assignments, staff skill levels, component coupling, and rework caused by design changes. The simulation model is implemented in theModLlanguage of the general‐purpose graphical simulation toolEXTEND.

As an illustration of our simulation model, we study the performance of various list policies for a small sample project. The simulations quickly show the impact that the choice of the list policy will have on the progress and completion time of the sample project. To explain the performance difference between the list policies, we use the simulation traces to provide a detailed analysis of the task assignments which actually occur in the simulations. Copyright © 2003 John Wiley & Sons, Ltd.
A novel simulation model for the development process of open source software projects
Authors: Antoniades I. P. , Stamelos I. , Angelis L. , Bleris G. L.
Published: December 2003

The present paper presents a first attempt to produce a dynamical simulation model for the development process of open source software projects. First, a general framework for such models is introduced. Then, a specific simulation model is described and demonstrated. The model equations are based on available literature case studies whenever possible or reasonable assumptions when literature data are not adequate. The model is demonstrated against data obtained from a recent case study by A. Mockus, R. Fielding and J. Herbsleb (‘A case study of open source software development: the Apache server’) on the Apache www server software so as to reproduce quantitatively real results as closely as possible. Computer simulation results based on the calibrated model are thus presented and analysed. OSS dynamic simulation models could serve as generic predicting tools of key OSS project factors such as project failure/success as well as time dependent factors such as the evolution of source code, defect density, number of programmers and distribution of work effort to distinct project modules and tasks. Copyright © 2003 John Wiley & Sons, Ltd.
High‐level data races
Authors: Artho Cyrille , Havelund Klaus , Biere Armin
Published: December 2003

Data races are a common problem in concurrent and multi‐threaded programming. Experience shows that the classical notion of a data race is not powerful enough to capture certain types of inconsistencies occurring in practice. This paper investigates data races on a higher abstraction layer. This enables detection of inconsistent uses of shared variables, even if no classical race condition occurs. For example, a data structure representing a coordinate pair may have to be treated atomically. By lifting the meaning of a data race to a higher level, such problems can now be covered. The paper defines the concepts ‘view’ and ‘view consistency’ to give a notation for this novel kind of property. It describes what kinds of errors can be detected with this new definition, and where its limitations are. It also gives a formal guideline for using data structures in a multi‐threaded environment. © US Government copyright
Reformed undergraduate instruction and its subsequent impact on secondary school teaching practice and student achievement
Authors: Adamson Scott L. , Banks Debra , Burtch Mark , Cox Frank , Judson Eugene , Turley Jeffery B. , Benford Russell , Lawson Anton E.
Published: December 2003

The Arizona Collaborative for Excellence in the Preparation of Teachers (ACEPT) Program is one of several reform efforts supported by the National Science Foundation. The primary ACEPT reform mechanism has been month‐long summer workshops in which university and community college science and mathematics faculty learn about instructional reforms and then attempt to apply them in their courses. Previous ACEPT evaluation efforts suggest that, when implemented, the reforms boost undergraduate student achievement. The initial purpose of the present study was to discover whether enrollment of preservice teachers in one or more of these reformed undergraduate courses is linked to the way they teach after they graduate and become in‐service teachers. Assuming that a link is found, a second purpose was to discover whether the presumed positive effect is in turn linked to their students' achievement. In short, the answer appears to be yes, at least among the biology teachers and students surveyed. Compared with controls, the biology teachers who had enrolled in one or more ACEPT reformed course during their teacher preparation program demonstrated significantly higher scores on the measure of reformed instruction and their students demonstrated significantly higher achievement in terms of scientific reasoning, nature of science, and biology concepts. These results support the hypothesis that teachers teach as they have been taught. Furthermore, it appears that instructional reform in teacher preparation programs including both methods and major's courses can improve secondary school student achievement. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 939–957, 2003
Comparison of student performance using web and paper‐based homework in college‐level physics
Authors: Bonham Scott W. , Deardorff Duane L. , Beichner Robert J.
Published: December 2003

Homework gives students an opportunity to practice important college‐level physics skills. A switch to Web‐based homework alters the nature of feedback received, potentially changing the pedagogical benefit. Calculus‐ and algebra‐based introductory physics students enrolled in large paired lecture sections at a public university completed homework of standard end‐of‐the‐chapter exercises using either the Web or paper. Comparison of their performances on regular exams, conceptual exams, quizzes, laboratory, and homework showed no significant differences between groups; other measures were found to be strong predictors of performance. This indicates that the change in medium itself has limited effect on student learning. Ways in which Web‐based homework could enable exercises with greater pedagogical value are discussed. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 1050–1071, 2003
Learning from inquiry‐based laboratories in nonmajor biology: An interpretive study of the relationships among inquiry experience, epistemologies, and conceptual growth
Authors: Wallace Carolyn S. , Tsoi Mai Yin , Calkin Jamie , Darley Marshall
Published: December 2003

The use of inquiry‐based laboratory in college science classes is on the rise. This study investigated how five nonmajor biology students learned from an inquiry‐based laboratory experience. Using interpretive data analysis, the five students' conceptual ecologies, learning beliefs, and science epistemologies were explored. Findings indicated that students with constructivist learning beliefs tended to add more meaningful conceptual understandings during inquiry labs than students with positivist learning beliefs. All students improved their understanding of experiment in biology. Implications for the teaching of biology labs are discussed. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 986–1024, 2003
The AS interactive project: single‐user and collaborative virtual environments for people with high‐functioning autistic spectrum disorders
Authors: Rutten Anja , Cobb Sue , Neale Helen , Kerr Steven , Leonard Anne , Parsons Sarah , Mitchell Peter
Published: December 2003

The AS Interactive Project aimed to assess the potential of single‐user and collaborative virtual environments to support learning and enhancing of social skills in people with autistic disorders on the high‐functioning end of the autistic spectrum. The project had two distinct phases of research: Phase I focused mainly on development and design using user‐centred principles. Phase II was concerned with implementation of design feedback, further improvements and evaluation studies of the virtual environments developed. This paper describes the research process, summarizes results of the project and briefly outlines plans for future research. Copyright © 2003 John Wiley & Sons, Ltd.
Development of a gait rehabilitation system using a locomotion interface
Authors: Yano Hiroaki , Kasai Kaori , Saitou Hideyuki , Iwata Hiroo
Published: December 2003

A locomotion interface (LI) is a piece of equipment that can give a user the sense that he/she is walking while his/her actual position remains localized in the real world. We developed an LI system (GaitMaster2) that has two footpads, which can move to represent a virtual terrain for each user's foot. In this research, we applied our LI to gait rehabilitation. The footpads on our LI follow a pre‐recorded motion sequence to move the user's feet. We conducted evaluation tests with the assistance of hemiplegic patients. The effectiveness of our system was verified through EMG, video analysis and the measurement of physical values such as average velocity. Copyright © 2003 John Wiley & Sons, Ltd.
Energy efficient routing protocols for mobile ad hoc networks
Authors: Yu Chansu , Lee Ben , Yong Youn Hee
Published: December 2003

Although establishing correct and efficient routes is an important design issue in mobile ad hoc networks (MANETs), a more challenging goal is to provide energy efficient routes because mobile nodes' operation time is the most critical limiting factor. This article surveys and classifies the energy‐aware routing protocols proposed for MANETs. They minimize either theactive communication energyrequired to transmit or receive packets or theinactive energyconsumed when a mobile node stays idle but listens to the wireless medium for any possible communication requests from other nodes.Transmission power control approachandload distribution approachbelong to the former category, andsleep/power‐down mode approachbelongs to the latter category. While it is not clear whether any particular algorithm or a class of algorithms is the best for all scenarios, each protocol has definite advantages/disadvantages and is well suited for certain situations. The purpose of this paper is to facilitate the research efforts in combining the existing solutions to offer a more energy efficient routing mechanism. Copyright © 2003 John Wiley & Sons, Ltd.
DSP implementation of successive interference cancellation (SIC) receiver for 3GPP WCDMA uplink transmission
Authors: Chang Yu‐jung , Lin Yu‐Nan , Lin David W.
Published: December 2003

The 3GPP WCDMA is a widely accepted third‐generation cellular system standard. By using nonorthogonal codes for different users, the multiple access interference (MAI) can be a limiting factor for system performance, as for other CDMA systems. Multiuser detection (MUD) is known to reduce MAI and improve CDMA system performance, but many such techniques have high complexity. Successive interference cancellation (SIC) is an effective MUD technique with relatively low complexity. We consider the software implementation of an SIC receiver for WCDMA uplink transmission on a commercially available general‐purpose multi digital signal processor (DSP) platform. This also goes in line with the recent interest in software‐defined radio. Issues addressed in this work include job partitioning and signal routing for multiprocessor implementation, design of SIC components (especially the channel estimator and the signal regenerator), determination of the precision of fixed‐point computations, consideration of the receiver's error performance and analysis of the implementation's complexity and efficiency. These issues are tightly coupled with the 3GPP WCDMA specifications. Because the employed platform only contains four DSPs, the implementation only considers up to three users. But this is sufficient for us to appreciate various DSP implementation issues of an SIC receiver. Moreover, by the nature of SIC, it is easy to extend the implementation to handle more users with an enlarged platform. Our present implementation achieves real‐time speed in the RAKE receiver part of the complete receiver. Due to the complexity in signal regeneration, the overall SIC receiver still falls short of the real‐time requirement when interference cancellation is activated. In fact, the platform employed presently cannot support real‐time processing when the number of multipaths is four or more, unless either the system architecture or the SIC algorithm is redesigned. Such and other ways of improvement are relegated to potential future work. Copyright © 2003 John Wiley & Sons, Ltd.
Dynamic resource allocation for CDMA‐TDD indoor wireless systems
Authors: Lee Chae Y. , Sung Ki Won
Published: December 2003

Future wireless communication systems are expected to provide a broad range of multimedia services that have a significant traffic asymmetry between uplink and downlink. The code division multiple access‐time division duplex (CDMA‐TDD) system is a promising solution to cope with the problem of traffic asymmetry. However, the TDD system is subject to inter‐cell interference compared to frequency division duplex (FDD) system. Since both uplink and downlink share the same frequency in TDD, uplink and downlink may interfere each other especially when neighboring cells require different rates of traffic load. Thus, the resource allocation among cells is an important issue in TDD. In this paper, the resource allocation in the CDMA‐TDD is formulated as a mixed integer programming (MIP) problem. A dynamic resource allocation algorithm (DRAA) is provided that effectively solves the traffic asymmetry problem. The MIP problem is also solved by a well‐known branch and bound procedure. Both the crossed slot and non‐crossed slot allocation are examined and compared to the DRAA. Computational result shows that proposed DRAA gives a good performance as the traffic asymmetry increases between the uplink and downlink. Copyright © 2003 John Wiley & Sons, Ltd.
Viscous and Aeroelastic Effects on Wind Turbine Blades. The VISCEL project. Part I: 3D Navier–Stokes Rotor simulations
Authors: Chaviaropoulos P. K. , Nikolaou I. G. , Aggelis K. A. , Soerensen N. N. , Johansen J. , Hansen M. O. L. , Gaunaa Mac , Hambraus T. , von Geyr Heiko Frhr. , Hirsch Ch. , Shun Kang , Voutsinas S. G. , Tzabiras G. , Perivolaris Y. , Dyrmose S. Z.
Published: December 2003

Aerodynamic modelling of HAWT rotors by means of “engineering methods” has reached a saddle point, where no further development can be expected without a breakthrough in understanding the physics of unsteady, rotating three‐dimensional flows. However, such a breakthrough becomes ever more necessary, as the size of the wind turbines increases. With the experimental work in that direction being mostly limited to observing the phenomena and interpreting the associated mechanisms, and its increased cost, alternatives are being sought. The use of CFD techniques and state‐of‐the‐art Navier–Stokes solvers is considered a very serious contender, a belief shared by the members of the present consortium, which has worked on the VISCEL JOR3‐CT98‐0208 Joule III project. This project's goal was to determine the aerodynamic characteristics as well as the aeroelastic behaviour of wind turbine blades across their broad range of operational conditions, from attached to highly separated flow regimes. The work programme included specific tasks for the validation and assessment of existing 3D solvers, for the parametric study of 3D flow around realistic blades and for the investigation of aeroelastic stability, at the blade section level. Copyright © 2003 John Wiley & Sons, Ltd.
The Use of a Code‐generating System for the Derivation of the Equations for Wind Turbine Dynamics
Authors: Ganander Hans
Published: December 2003

For many reasons the size of wind turbines on the rapidly growing wind energy market is increasing. Relations between aeroelastic properties of these new large turbines change. Modifications of turbine designs and control concepts are also influenced by growing size. All these trends require development of computer codes for design and certification. Moreover, there is a strong desire for design optimization procedures, which require fast codes. General codes, e.g. finite element codes, normally allow such modifications and improvements of existing wind turbine models. This is done relatively easy. However, the calculation times of such codes are unfavourably long, certainly for optimization use. The use of an automatic code generating system is an alternative for relevance of the two key issues, the code and the design optimization. This technique can be used for rapid generation of codes of particular wind turbine simulation models. These ideas have been followed in the development of new versions of the wind turbine simulation code VIDYN. The equations of the simulation model were derived according to the Lagrange equation and using Mathematica®, which was directed to output the results in Fortran code format. In this way the simulation code is automatically adapted to an actual turbine model, in terms of subroutines containing the equations of motion, definitions of parameters and degrees of freedom. Since the start in 1997, these methods, constituting a systematic way of working, have been used to develop specific efficient calculation codes. The experience with this technique has been very encouraging, inspiring the continued development of new versions of the simulation code as the need has arisen, and the interest for design optimization is growing. Copyright © 2003 John Wiley & Sons, Ltd.
Implications of the Regional Haze Rule on Renewable and Wind Energy Development on Native American Lands in the West
Authors: Acker Thomas L. , Auberle William M. , Duque Earl P. N. , Jeffery William D. , LaRoche David R. , Masayesva Virgil , Smith Dean H.
Published: December 2003

A study conducted at Northern Arizona University investigated the barriers and opportunities facing Native American tribes in the West when considering development of their renewable energy resources in order to reduce regional haze. This article summarizes some of the findings of that work with special attention to wind energy. Background information is presented concerning the Regional Haze Rule and the Western Regional Air Partnership, and some of the circumstances surrounding development of tribal energy resources. An assessment of tribal energy issues revealed that many Native American tribes are interested in developing their renewable resources. However, this development should occur within the context of maintaining and strengthening their cultural, social, economic and political integrity. Furthermore, it is shown that Native American lands possess an abundant wind resource. A list of potential actions in which tribes may participate prior to or during development of their wind or renewable resources is provided. Copyright © 2003 John Wiley & Sons, Ltd.
Mercurous Azide, Hg2(N3)2
Authors: Nockemann Peter , Cremer Ulrich , Ruschewitz Uwe , Meyer Gerd
Published: December 2003

White polycrystalline mercurous azide, Hg2(N3)2, is obtained by combining aqueous solutions of NaN3 and Hg2(NO3)2·2H2O (made viscuous by addition of tetramethoxysilane and heating at 65 °C). The crystal structure was solved and refined from X‐ray powder diffraction data (monoclinic, P21/n, a = 596.07(2) pm, b = 1259.07(4) pm, c = 357.95(1) pm, β = 103.253(2)°, Z = 2, RB = 0.0519). Solid Hg2(N3)2 contains, essentially, molecules of that composition with Hg‐Hg distances of 254.4(3) pm, Hg‐N distances of 218(2) pm and Hg‐Hg‐N angles of 178.7(6)°. Weak intermolecular interactions with Hg‐N distances starting at 280(3) pm lead to a three‐dimensional structure.