bluuebunny/crossref_metadata_2025 huggingface dataset:
Phylogeography and cryptic variation within the Lacerta viridis complex (Lacertidae, Reptilia)
Authors: Böhme Manja U. , Fritz Uwe , Kotenko Tatiana ,   Georg Džukić, Ljubisavljević Katarina , Tzankov Nikolay , Berendonk Thomas U.
Published: October 2006

It is well known that the current genetic pattern of many European species has been highly influenced by climatic changes during the Pleistocene. While there are many well known vertebrate examples, knowledge about squamate reptiles is sparse. To obtain more data, a range‐wide sampling of Lacerta viridis was conducted and phylogenetic relations within the L. viridis complex were analysed using an mtDNA fragment encompassing part of cytochrome b, the adjacent tRNA genes and the noncoding control region. Most genetic divergence was found in the south of the distribution range. The Carpathian Basin and the regions north of the Carpathians and Alps are inhabited by the same mitochondrial lineage, corresponding to Lacerta viridis viridis. Three distinct lineages occurred in the south‐eastern Balkans — corresponding to L. v. viridis, L. v. meridionalis, L. v. guentherpetersi— as well as a fourth lineage for which no subspecies name is available. This distribution pattern suggests a rapid range expansion of L. v. viridis after the Holocene warming, leading to a colonization of the northern part of the species range. An unexpected finding was that a highly distinct genetic lineage occurs along the western Balkan coast. Phylogenetic analyses (Bayesian, maximum likelihood, maximum parsimony) suggested that this west Balkan lineage could represent the sister taxon of Lacerta bilineata. Due to the morphological similarity of taxa within the L. viridis complex this cryptic taxon was previously assigned to L. v. viridis. The distribution pattern of several parapatric, in part highly, distinct genetic lineages suggested the existence of several refuges in close proximity on the southern Balkans. Within L. bilineata sensu stricto a generally similar pattern emerged, with a high genetic diversity on the Apennine peninsula, arguing for two distinct refuges there, and a low genetic diversity in the northern part of the range. Close to the south‐eastern Alps, three distinct lineages (L. b. bilineata, L. v. viridis, west Balkan taxon) occurred within close proximity. We suggest that the west Balkan lineage represents an early offshoot of L. bilineata that was isolated during a previous Pleistocene glacial from the more western L. bilineata populations, which survived in refuges on the Apennine peninsula.
Investigation of the Multidimensional Model of Job Insecurity in China and the USA
Authors: Lee Cynthia , Bobko Philip , Chen Zhen Xiong
Published: October 2006

Il y a plus d’une décennie, Ashford, Lee, and Bobko (1989) ont développé un outil de mesure standard permettant évaluer des niveaux individuels d’insécurité au travail. Les années suivantes, des chercheurs se sont demandé si la totalité des mesures composant cet instrument était nécessaire. Nous avons donc examiné l’utilité des différentes dimensions du test multidimensionnel de l’Insécurité au travail de Ashford et al. (1989) aux Etats Unis et en Chine, en éprouvant et élargissant les conclusions antérieures. Nos résultats suggèrent qu’éliminer les dimensions “caractéristiques du travail” et “impuissance” de l’instrument multidimensionnel initial est prématuré dans les deux cultures. D’autres recherches s’avèrent donc nécessaires pour déterminer l’utilité de cet outil dans sa version complète. Les implications de nos résultats sont discutées.

Over a decade ago, Ashford, Lee, and Bobko (1989) developed a standard measure for those interested in assessing levels of individual job insecurity. In ensuing years, some researchers have questioned whether the entire measure is necessary. We examined the usefulness of the components of Ashford et al.'s (1989) multidimensional measure of job insecurity in both the United States and China, as well as replicating and extending prior findings regarding antecedents and consequences. Our results suggest that the call to eliminate job features or powerlessness from the fully composite measure of job insecurity is premature in both cultures. We call for more research on the utility of the fully operationalised measure. Implications of our findings are discussed.
Who Cares about Justice? The Moderating Effect of Values on the Link between Organisational Justice and Work Behaviour
Authors: Fischer Ronald , Smith Peter B.
Published: October 2006

On s’est demandé, dans cette recherche, si les valeurs modérent la relation entre les perceptions de la justice procédurale et les variables d’intervention au travail. Selon le modèle relationnel d’autorité (Tyler et Lind 1992), l’effet de la justice procédurale sur l’engagement dans l’organisation, sur les aspects facilitants et dynamiques du comportement extra‐rôle dépendraient des orientations axiologiques des individus. Les résultats montrent que les employés de structures britanniques et germaniques qui font montre d’ouverture au changement (Schwartz 1992) sont plus influencés dans leur engagement dans leur entreprise et le comportement extra‐rôle par l’absence de justice perçue que ceux qui n’endossent pas les valeurs d’ouverture au changement. Les effets du comportement extra‐rôle étaient plus forts parmi les sujets britanniques. Les valeurs de conservation atténuent la relation entre la justice et l’engagement dans l’organisation uniquement chez les Allemands. Ces résultats permettent de mieux comprendre la façon dont la mesure des valeurs peut expliquer des différences culturelles dans les effets de la perception de la justice.

This study examined whether values moderate the relationship between procedural justice perceptions and work outcome variables. Based on the relational model of authorities (Tyler & Lind, 1992), it was predicted that the effect of procedural justice on organisational commitment and on self‐reported compliant and proactive aspects of extra‐role behaviour would depend on the value orientations of individuals. It was found that employees from British and German organisations who endorsed Schwartz's (1992) openness to change values were more influenced in their organisational commitment and compliant extra‐role behaviour by the absence of perceived justice than those who do not endorse openness values. The effects found for extra‐role behaviour were stronger among UK respondents. Conservation values moderated the relation between justice and organisational commitment only among Germans. These moderation findings extend our understanding of the way that value measures can explain cultural differences in the effects of perceived organisational justice.
State–society relations in contemporary Vietnam: An examination of the arena of youth
Authors: Nguyen Phuong An
Published: October 2006

Abstract:  This paper offers an analysis of the relations between youth and the socialist state in contemporary Vietnam, which sheds light on the wider state–society relations. Amid rapid social changes brought about by economic liberalisation, the Vietnamese Communist Party and socialist state may no longer be the sole driving force that motivates young people. As they seek to be both in control of and in touch with youth, the leaders of the Party and state find themselves negotiating between maintaining their ideological integrity and accommodating the changing needs and desires of youth. An analysis of recent events demonstrates that youth are no longer merely a subject of political propaganda and mass mobilisation, but instead they have evolved to become an important social actor urging the leadership to further reform itself. As young people express a desire to embrace socioeconomic and cultural changes wrought by processes of marketisation and globalisation, the Party and state are actively reforming themselves not only to respond to young people’s desires and aspirations, but also to strengthen their political authority and leadership, and to consolidate their control and management of youth amid the new conditions of a market‐oriented society. Overall, this paper sheds light on the changes in what is considered to be the ‘strategic’ relationship between the state and youth, and the wider process of sociopolitical transformation in present‐day Vietnam.
Corporate Governance and Information Efficiency in Security Markets
Authors: Cai Charlie X. , Keasey Kevin , Short Helen
Published: October 2006

This paper investigates a neglected topic in corporate governance research; namely, do governance characteristics affect the market reaction to news? The topic is important given the emphasis by governance regulations and codes of best practice on the need for greater transparency of corporate activities. For the first time in the corporate governance literature, we show that corporate governance characteristics (particularly the presence of founding family directors and gender diverse boards) affect the market reaction to company specific news. The results of the paper point to the analysis of the impact of governance characteristics on the market reaction to news being a new and complementary research agenda within corporate governance.
New advances in fluorochrome sequential labelling of teeth using seven different fluorochromes and spectral image analysis
Authors: Pautke Christoph , Tischer Thomas , Vogt Stephan , Haczek Cornelia , Deppe Herbert , Neff Andreas , Horch Hans‐Henning , Schieker Matthias , Kolk Andreas
Published: October 2006

Fluorochrome sequential labelling of mineralizing tissues is commonly used in different fields of clinical and basic research. Recently we improved polychrome fluorescent sequential labelling of bone by applying spectral image analysis to discriminate seven different fluorochromes. Although basic mineralization processes of bone and teeth follow comparable principles, the respective tissues differ in terms of matrix composition and mineral assembly. The aim of this study therefore was to investigate the feasibility of this new technique for polychrome sequential labelling of teeth and to demonstrate the advantages in the field of dentistry. Furthermore, the exact labelled area of each fluorochrome could be measured, even in regions of overlapping fluorochromes. The technique presented may provide a basis for further investigations of mineralization processes of different anatomical dental structures.
Evaluating the Contributions of State‐of‐the‐Art Assessment Techniques to Predicting Memory Outcome after Unilateral Anterior Temporal Lobectomy
Authors: Lineweaver Tara T. , Morris Harold H. , Naugle Richard I. , Najm Imad M. , Diehl Beate , Bingaman William
Published: October 2006

Summary:  Purpose: Although anterior temporal lobectomy (ATL) is an effective treatment for many patients with medically refractory temporal lobe epilepsy (TLE), one risk associated with this procedure is postsurgical decline in memory. A substantial number of past studies examined factors that predict memory decline after surgery, but few have investigated multiple predictors simultaneously or considered measures that are currently in use.

Methods: This study compared the relative contributions made by presurgical neuropsychological test scores, MRI‐based hippocampal volumetric analysis, and Wada test results to predicting memory outcome after ATL in a group of 87 patients.

Results: Logistic regression analyses indicated that noninvasive procedures (neuropsychological testing and MRI) made significant contributions to improving the prediction of memory outcome in this sample. The results from the Wada procedure did not significantly improve prediction once these other factors were considered. The only exception was in predicting memory for visual information after a delay, in which Wada results improved prediction accuracy from 78% to 81%.

Conclusions: Current neuropsychological tests and MRI volumetric measures predict changes in verbal and visual memory after ATL. The relatively small change in correct classification rates when Wada memory scores are considered calls into question the benefits of using Wada test results to predict memory outcome when the results of noninvasive procedures are available.
Transfusion‐associated transmission of West Nile virus, United States 2003 through 2005
Authors: Montgomery Susan P. , Brown Jennifer A. , Kuehnert Matthew , Smith Theresa L. , Crall Nicholas , Lanciotti Robert S. , Macedo de Oliveira Alexandre , Boo Thomas , Marfin Anthony A. ,   the 2003 West Nile Virus Transfusion‐Associated Transmission Investigation Team
Published: October 2006

BACKGROUND: National blood donation screening for West Nile virus (WNV) started in June 2003, after the documentation of WNV transfusion‐associated transmission (TAT) in 2002.

STUDY DESIGN AND METHODS: Blood donations were screened with investigational nucleic acid amplification assays in minipool formats. Blood collection agencies (BCAs) reported screening results to state and local public health authorities. Donor test results and demographic information were forwarded to CDC via ArboNET, the national electronic arbovirus surveillance system. State health departments and BCAs also reported suspect WNV TATs to CDC, which investigated these reports to confirm WNV infection in blood transfusion recipients in the absence of likely mosquito exposure.

RESULTS: During 2003 to 2005, a total of 1,425 presumptive viremic donors were reported to CDC from 41 states. Of 36 investigations of suspected WNV TAT in 2003, 6 cases were documented. Estimated viremia levels were available for donations implicated in four TAT cases; the median estimated viremia was 0.1 plaque‐forming units (PFUs) per mL (range, 0.06‐0.50 PFU/mL; 1 PFU equals approximately 400 copies/mL).

CONCLUSIONS: National blood screening for WNV identified and removed more than 1,400 potentially infectious blood donations in 2003 through 2005. Despite the success of screening in 2003, some residual WNV TAT risk remained due to donations containing very low levels of virus. Screening algorithms employing selected individual‐donation testing were designed to address this residual risk and were fully implemented in 2004 and 2005. Continued vigilance for TAT will evaluate the effectiveness of these strategies.
Integrating Cross‐Border Knowledge for Transnational New Product Development
Authors: Subramaniam Mohan
Published: October 2006

Multi‐source knowledge integration, though widely regarded as fundamental for developing new products, remains obscurely understood and a significant challenge for organizations to accomplish. Prior research provides many insights on the approaches by which organizations transfer knowledge; however, how such transferred knowledge gets effectively embodied in products remains uncertain. Also unclear is whether different approaches for knowledge transfer differ in their effectiveness at realizing integration. This study analytically separates the transfer of cross‐border knowledge from its embodiment into products. It examines cross‐border knowledge transfer based on three different approaches: namely, the use of cross‐national teams, cross‐national communication, and cross‐national collaboration in the development of new transnational products. It examines cross‐border knowledge embodiment based on the extent to which new transnational products developed balance standardization with adaptation. The study uses a cross‐sectional survey administered to key members of transnational new product development teams in leading multinational companies across the world. The survey focuses on manufactured products that were developed across several industries: consumer products, consumer durables, and industrial products. Results from 90 new transnational product introductions surveyed reveal that knowledge integration is effective only when knowledge is transferred through cross‐national collaboration, and not when transferred through cross‐national teams and cross‐national communication. As integrating cross‐border knowledge in the development of transnational products involves making difficult trade‐offs for balancing standardization with adaptation, transferring knowledge through cross‐national collaboration stands out as being critical for successful outcomes. Although cross‐national teams and cross‐national communication enhance knowledge flows, they do not result in effective knowledge integration when developing new transnational products. These findings highlight an important point: All knowledge transfer approaches may not necessarily achieve knowledge integration. Hence, it is essential to systematically probe into the interrelationships between knowledge transfer and its effective integration and to identify an underlying set of contingencies that provide insights into when and why some knowledge transfer approaches are better than others at integrating knowledge.
Early patterned stimulation leads to changes in adult behavior and gene expression in C. elegans
Authors: Ebrahimi C. M. , Rankin C. H.
Published: October 2006

Across phylogeny, early experience plays a critical role in nervous system development. In these experiments, we investigated the long‐term effects that specific patterns of sensory experience during development had on the biology and function of the Caenorhabditis elegans nervous system. The delivery of a specific pattern of mechanosensory stimulation in the first larval stage (L1) produced significant enhancement in the tap withdrawal behavioral response, expression patterns of an ionotropic glutamate receptor (iGluR) subunit and mRNA levels for that receptor in 3‐day‐old adult worms and a depression of these same three measures in 5‐day‐old adult worms. A critical period for the 3‐day enhanced behavior and GLR distribution was observed in L1, whereas there was no critical period for the depressed effects observed in 5‐day‐old worms. The spaced pattern of stimulation was essential for expression of this effect: Various forms of massed training produced neither the enhancement at 3 days nor the depression at 5 days. The 5‐day depressed behavioral response had many features in common with long‐term memory, including sensitivity to disruption following retrieval. The different behavioral and molecular effects that early patterned mechanosensory stimulation produced in 3 and 5‐day‐old worms led us to hypothesize that separate cellular phenomena produced the enhanced 3‐day and depressed 5‐day behaviors and molecular effects.
The Norm of Reciprocity: Scale Development and Validation in the Chinese Context
Authors: Wu Joshua B. , Hom Peter W. , Tetrick Lois E. , Shore Lynn M. , Jia Liangding , Li Chaoping , Song Lynda Jiwen
Published: October 2006

To add greater theoretical precision to a fundamental construct in social exchange theory - namely, Gouldner's ‘norm of reciprocity’, this study developed a measure of Sahlins' generalized, balanced, and negative reciprocity types and validated its psychometric quality in China. For a comprehensive construct validation of the new scale, we carried out three studies. After generating a pool of items, we used a panel of experts to classify items according to conceptual definitions of the three reciprocity types. Using factor analysis, the first study revealed a factor structure consistent with Sahlins' reciprocity typology. In the second study, confirmatory factor analysis replicated this factor structure as well as demonstrated that the reciprocity factors are distinct from each other and other social-exchange constructs. In line with extant theories, the third study corroborated a nomological network relating reciprocity types to external constructs. Given this broad array of evidence for its construct validity, future researchers can employ this validated scale to investigate various forms of social exchange in Chinese work settings.
Formulation of the DETECT Population Parameter and Evaluation of DETECT Estimator Bias
Authors: Roussos Louis A. , Ozbek Ozlem Yesim
Published: October 2006

The development of the DETECT procedure marked an important advancement in nonparametric dimensionality analysis. DETECT is the first nonparametric technique to estimate the number of dimensions in a data set, estimate an effect size for multidimensionality, and identify which dimension is predominantly measured by each item. The efficacy of DETECT critically depends on accurate, minimally biased estimation of the expected conditional covariances of all the item pairs. However, the amount of bias in the DETECT estimator has been studied only in a few simulated unidimensional data sets. This is because the value of the DETECT population parameter is known to be zero for this case and has been unknown for cases when multidimensionality is present. In this article, integral formulas for the DETECT population parameter are derived for the most commonly used parametric multidimensional item response theory model, the Reckase and McKinley model. These formulas are then used to evaluate the bias in DETECT by positing a multidimensional model, simulating data from the model using a very large sample size (to eliminate random error), calculating the large‐sample DETECT statistic, and finally calculating the DETECT population parameter to compare with the large‐sample statistic. A wide variety of two‐ and three‐dimensional models, including both simple structure and approximate simple structure, were investigated. The results indicated that DETECT does exhibit statistical bias in the large‐sample estimation of the item‐pair conditional covariances; but, for the simulated tests that had 20 or more items, the bias was small enough to result in the large‐sample DETECT almost always correctly partitioning the items and the DETECT effect size estimator exhibiting negligible bias.
Taking the Time to Improve the Validity of Low‐Stakes Tests: The Effort‐Monitoring CBT
Authors: Wise Steven L. , Bhola Dennison S. , Yang Sheng‐Ta
Published: October 2006

The attractiveness of computer‐based tests (CBTs) is due largely to their capability to expand the ways we conduct testing. A relatively unexplored application, however, is actively using the computer to reduce construct‐irrelevant variance while a test is being administered. This investigation introduces the effort‐monitoring CBT, in which the computer monitors examinee effort (based on item response time) in a low‐stakes test and displays warning messages to those exhibiting rapid‐guessing behavior. The results of an experimental study are presented, which showed that an effort‐monitoring CBT increased examinee effort and yielded more valid test scores than a conventional CBT. Thus, unlike previous research that has focused on identifying rapid‐guessing behavior after it has occurred, the effort‐monitoring CBT proactively attempts to suppress rapid‐guessing behavior. This innovative testing procedure extends the capabilities of measurement practitioners to manage the psychometric challenges posed by unmotivated examinees.
Water industry asset management: a proposed service‐performance model for investment
Authors: Heather A. I. J. , Bridgeman J.
Published: October 2006

The water industry in England and Wales has developed over the last century, from small organisations serving local communities to large integrated companies in private ownership, overseen by a government regulator. Asset management practice has developed greatly in the 17 years since privatisation, with companies able to plan their operations and investment as they believe appropriate for the provision of customer services, subject to justifying their plans to the economic, quality and environmental regulators. Investment has flowed into the industry to replace deteriorated assets and to improve the quality of drinking water and rivers. The asset base is complex and, with a replacement value of approximately £231 billion at the 2002–2003 price base index suitable approaches are required to ensure that both the water service and the sewerage service are delivered at the most appropriate long‐term cost. The 2004 UK water industry price review was supported by the introduction of a Capital Maintenance Planning Common Framework to help companies understand and explain their maintenance investment requirement. In this paper, a service‐performance model is proposed to improve managers' understanding of the way in which businesses and the environment change over time, taking account of maintenance and other strategic requirements. Although developed with the water industry in mind, the model is equally applicable to other asset‐intensive industries.
Theoretical Investigation in Thermoelastohydrodynamic Lubrication With Non-Newtonian Lubricants Under Sudden Load Change
Authors: Mongkolwongrojn M. , Aiumpornsin C. , Thammakosol K.
Published: October 2006

The time-dependent thermal compressible elastohydrodynamic lubrication of a sliding line contact has been developed to investigate the effect of a sudden load change. The time-dependent modified Reynolds equation with non-Newtonian fluids has been formulated using a power law model. Properties of non-Newtonian dilatant fluids for solid-liquid lubricants have been studied experimentally using two common solid particles; namely, molybdenum disulfide and polytetrafluoroethylene. The simultaneous systems of modified Reynolds, elasticity, and energy equations with initial conditions were solved numerically using a multigrid multilevel technique. The performance characteristics of the thermoelastohydrodynamic line contact were presented with varying dimensionless time for the pressure distribution, temperature distribution, and oil film thickness. The transient response of the line contact between two infinitely long cylindrical surfaces was simulated under a heavy step load function. The coefficients of friction were also presented in this work at steady condition with varying particle concentration. This simulation showed a significant effect of solid particles on thermoelastohydrodynamic lubrication under heavy load conditions.
Validation of the Stress Predictions in Rolling EHL Contacts Having In-Line Roughness Using the Inverse Method
Authors: Hooke C. J. , Li K. Y.
Published: October 2006

Using modern EHL programs it is relatively simple to determine the pressures and clearances in rough EHL contacts. The pressures may then be used to calculate the subsurface stresses in the two contacting components. However, the results depend on the assumptions made about the fluid’s rheology. While it is possible to measure the clearances using interferometric techniques, measurement of either the pressures or stresses is extremely difficult. However it is these, rather than the clearances, that determine the life of the contact. In previous papers the authors have described how the inverse method may be used to validate the stress predictions for contacts with transverse roughness. This type of contact has fluid flow in only one plane and it remained necessary to check the results for more general rough surfaces where the flow is three-dimensional. Accordingly, the inverse method is extended, in this paper, to a situation where out-of-plane flow is significant. The paper describes the approach and presents some preliminary results for rolling contacts.
Modeling of Elastic/Plastic Contact Between Nominally Flat Rough Surfaces Using an n-Point Asperity Model
Authors: Hariri A. , Zu J. W. , Ben Mrad R.
Published: October 2006

The asperities of rough surfaces have long been considered to be points higher than their immediate neighbors. Based on this concept, theories were developed for quantitatively understanding the elastic and plastic nature of contact between rough surfaces. Recently it has been recognized that the above model for asperities is inadequate. Consequently, all the models that have been constructed based on that model are inadequate too. In this paper, based on a newly developed multiple-point asperity model, the elastic and plastic contact problem between nominally flat surfaces is reformulated. This leads to finding the deformed area, and load produced by the contact. The model is developed for the general form of isotropic rough surfaces with arbitrary height distribution and autocorrelation function (ACF). The microcontact areas generated by each asperity contact are considered to be circles. The Gaussian distribution of heights and exponential ACF are considered as a benchmark to compare the results of the new model with the existing models. Using results from numerical models developed by other groups, the new model is validated.
Finite Element Analysis of Thermoelastodynamic Instability Involving Frictional Heating
Authors: Yi Yun-Bo
Published: October 2006

A finite element method is used to solve the problem involving thermoelastodynamic instability (TEDI) in frictional sliding systems. The resulting matrix equation contains a complex eigenvalue that represents the exponential growth rate of temperature, displacement, and velocity fields. Compared to the thermoelastic instability (TEI) in which eigenmodes always decay with time when the sliding speed is below a critical value, numerical results from TEDI have shown that some of the modes always grow in the time domain at any sliding speed. As a result, when the inertial effect is considered, the phenomenon of hot spotting can actually occur at a sliding speed below the critical TEI threshold. The finite element method presented here has obvious advantages over analytical approaches and transient simulations of the problem in that the stabilities of the system can be determined for an arbitrary geometry without extensive computations associated with analytical expressions of the contact condition or numerical iterations in the time domain.
Contact of Coated Systems Under Sliding Conditions
Authors: Ma Lifeng , Korsunsky Alexander M. , Sun Kun
Published: October 2006

The contact of coated systems under sliding conditions is considered within the framework of elasticity theory with the assumption of perfect bond between coating and substrate. Formulation is introduced in the form of a system of coupled singular integral equations of the second kind with Cauchy kernels that describe contact problems for coated bodies under complete, semi-complete and incomplete contact conditions. Accurate and efficient numerical method for the solution of sliding contact problems is described. Explicit results are presented for the interpolative Gauss-Jacobi numerical integration scheme for singular integral equations of the second kind with Cauchy kernels. The method captures correctly both regular and singular behavior of the traction distribution near the edges of contact. Several cases of sliding contact are considered to demonstrate the validity of the method.
Local Convective Heat Transfer From a Constant Heat Flux Flat Plate Cooled by Synthetic Air Jets
Authors: Gillespie M. B. , Black W. Z. , Rinehart C. , Glezer A.
Published: October 2006

The effects of a small-scale, rectangular synthetic air jet on the local convective heat transfer from a flat, heated surface were measured experimentally. The synthetic jet impinges normal to the surface and induces small-scale motions by zero-net mass flux, time-periodic entrainment, and ejection of ambient air at frequencies whose periods are far higher than the characteristic thermal time scale. The velocity field between the jet orifice and the target plate is measured in planar cross sections using particle image velocimetry and is related to the local heat transfer from the plate. The present work suggests that synthetic jets can lead to substantial enhancement of the local heat transfer from heated surfaces by strong mixing that disrupts the surface thermal boundary layer. The dependence of the local heat transfer coefficient on the primary parameters of jet motion is characterized over a range of operating conditions.
The Effect of Internal Temperature Gradients on Regenerator Matrix Performance
Authors: Engelbrecht K. L. , Nellis G. F. , Klein S. A.
Published: October 2006

Background. One-dimensional regenerator models treat the solid material as a lumped capacitance with negligible temperature gradients. Advanced regenerator geometries operating at low temperatures or active magnetic regenerators which use a liquid heat transfer fluid may have temperature gradients in the solid regenerator that significantly affect performance. It is advantageous to utilize a one-dimensional, or lumped, model of the regenerator that is coupled with a correction factor in order to account for the impact of the internal temperature gradients. Previous work relative to developing such a correction factor is shown here to be inadequate or only valid over a limited range of dimensionless conditions. Method of Approach. This paper describes a numerical model of a sphere subjected to a time varying fluid temperature (representing a passive process) or time varying internal heat generation induced by a magnetic field (representing an active magnetic process). The governing equations are nondimensionalized and the efficiency of the sphere is presented as a function of the Fourier number and Biot number. Results. An approximate correction (or degradation) factor is obtained based on these results that is valid over a wide range of dimensionless conditions and therefore useful to regenerator designers. The degradation factor correlation was developed for a sinusoidal variation in the fluid temperature, however, the same results can be applied to different functional forms of the time variation using the concept of an effective cycle time that is weighted by the magnitude of the driving temperature difference. Conclusions. The heat transfer degradation factor presented here can be applied to one-dimensional regenerator models in order to accurately account for the transient performance of a matrix with finite thermal conductivity. This degradation factor allows regenerator models to approximately account for internal temperature gradients without explicitly modeling them and therefore remain computationally efficient while improving the range of applicability and accuracy.
Similarity Solution of Laminar Axisymmetric Jets With Effect of
Viscous Dissipation
Authors: Kalteh A. M. , Abbassi A.
Published: October 2006

In this work the similarity solution of the thermal boundary layer for a laminar axisymmetric jet with viscous dissipation is derived and solved numerically, using a fourth-order Runge-Kutta method. The results are compared with the existing solutions, in which viscous dissipation is neglected. After that the effects of Reynolds and Prandtl numbers of the incoming hot jet on the temperature profile of the jet is investigated. It is seen that inclusion of viscous dissipation term results in a more rapid heat exchange between the incoming jet and quiescent fluid than the case where the viscous dissipation term is neglected. Also, it is observed that by increasing the Reynolds and Prandtl numbers of the jet, the heat penetrates better in locations near the symmetry line, whereas in locations farther from the symmetry axis the penetration is less.
Modeling the Influence of Drying Conditions on the Stress Buildup
During Drying of Paperboard
Authors: Östlund Magnus
Published: October 2006

This paper concerns the drying process in the manufacturing of paperboard. Of particular interest are the effects of through-thickness property variation in paperboard during drying. In addition, resulting average properties from different drying histories are discussed. A mathematical model of the drying process is presented. It allows the moisture and temperature histories, the stress and strain histories, and the buildup of mechanical properties to be simulated. The temperature of the heating medium, the humidity and pressure of the ambient air, and either applied loads or prescribed strains are required input data. For symmetric convective drying, the ambient temperature, the humidity, and the thickness of the board were varied. For drying on a heated plate, the temperature of the plate and the thickness of the board were varied. Results regarding the moisture history, the stiffness development, and the buildup of residual stresses are presented and compared to literature experimental data. Also, sheets with a varying fiber base through the thickness, which affects both the moisture history and the influence of moisture on shrinkage, were studied. The model was shown to yield predictions qualitatively inline with empirical knowledge.
Relaxation of Proton Conductivity and Stress in Proton Exchange Membranes Under Strain
Authors: Liu Dan , Hickner Michael A. , Case Scott W. , Lesko John J.
Published: October 2006

The stress relaxation and proton conductivity of Nafion 117 membrane (N117-H) and sulfonated poly(arylene ether sulfone) copolymer membrane with 35% sulfonation (BPSH35) in acid forms were investigated under uniaxial loading conditions. The results showed that when the membranes were stretched, their proton conductivities in the direction of the strain initially increased compared to the unstretched films. The absolute increases in proton conductivities were larger at higher temperatures. It was also observed that proton conductivities relaxed exponentially with time at 30°C. In addition, the stress relaxation of N117-H and BPSH35 films under both atmospheric and an immersed (in deionized water) condition was measured. The stresses were found to relax more rapidly than the proton conductivity at the same strains. An explanation for the above phenomena is developed based on speculated changes in the channel connectivity and length of proton conduction pathway in the hydrophilic channels, accompanied by the rotation, reorientation, and disentanglements of the polymer chains in the hydrophobic domains.
Fluid-Structure Interaction Analysis of Flow-Induced Deformation in a Two-Phase, Neo-Hookean Marine Egg
Authors: Kim T. , Wang C W. , Thomas F. I. M. , Sastry A. M.
Published: October 2006

Coupled computational fluid dynamics and finite element analyses were used to determine the material properties of the egg and jelly layer of the sea urchin Arbacia punctulata. Prior experimental shear flow results were used to provide material parameters for these simulations. A Neo-Hookean model was used to model the hyperelastic behaviors of the jelly layer and egg. A simple compressive simulation was then performed, to compare the maximum von Mises stresses within eggs, with and without jelly layers. Results of this study showed that (1) shear moduli range from ∼100to160Pa, and ∼40to140Pa for an egg without a jelly layer, and jelly layer itself, respectively; and (2) the presence of the jelly layer significantly reduces maximum von Mises stress in an egg undergoing compression.
Nonlinear Viscoelasticity and Viscoplasticity of Flax/Polypropylene Composites
Authors: Marklund Erik , Varna Janis , Wallström Lennart
Published: October 2006

In tensile tests the flax/polypropylene composites clearly show nonlinear behavior in loading and hysteresis loops in unloading. In creep tests performed at different load levels the response was nonlinear viscoelastic, and after recovery, viscoplastic strains were detected. No degradation in stiffness could be seen and thus nonlinear viscoelasticity and viscoplasticity were assumed to be the main cause for the observed behavior. The fracture surface of a specimen that experienced creep rupture at 24 MPa was investigated using a scanning electron microscope. The viscoplastic response was studied experimentally and described by a power law with respect to time and stress level in the creep test. The nonlinear viscoelasticity was described using Schapery’s model. The application of Prony series and a power law to approximate the viscoelastic compliance was investigated. Both descriptions have accuracy sufficient for practical applications. However, at high stresses the attempts to describe the viscoelastic compliance by a power law with a stress-independent exponent failed and therefore stress dependence of this exponent was included in the data analysis. The accuracy within the considered stress range is good, but the thermodynamic consistency of this procedure has to be proven.
Experimentally Evaluating the Equilibrium Stress in Shear of Glassy Polycarbonate
Authors: Negahban Mehrdad , Goel Ashwani , Delabarre Pierre , Feng Ruqiang , Dimick Amy
Published: October 2006

One group of models proposed for characterizing the mechanical response of glassy polymers is based on a structure that resembles finite plasticity. In most cases, a constitutive equation for stress is proposed, which depends on the elastic deformation gradient, supplemented by a flow rule for the plastic deformation, which depends on the “over stress.” The over stress is a properly invariant difference between the stress and the back stress (equilibrium stress). The back stress represents conditions under which relaxation events should stop and the material should be able to carry an applied load indefinitely without a need to change the strain. Questions that arise in using these models are whether such equilibrium stresses exist, how can they be evaluated, and what experiments can be used to characterize the flow rule. One challenge in accurately evaluating the locus of equilibrium conditions is the fact that the relaxation process substantially slow down around these points, and, therefore, a method that does not directly require being at the equilibrium is desirable. Focusing on shear, a thermodynamic theory for characterizing the response of glassy polymers, similar to models currently used for this purpose, is developed, and using this model it is shown that one can set up a method to calculate the plastic strain rate. This method is based on evaluating the slope of stress-strain response under conditions of similar elastic and plastic strain, but different strain rates. Since the equilibrium stress occurs when the plastic strain rate goes to zero, the evaluated plastic strain rates allow evaluation of the needed information for developing the flow rule and obtaining the back stress. This method is used to evaluate the plastic strain rate and back stress at room temperature for polycarbonate. The evaluated results match well with results obtained by direct probing of the equilibrium stress, in which one searches for points at which the stress remains constant at a constant strain over long durations. The method proposed looks promising in evaluating the back stress of glassy polymers. The added advantage of this method is that it also provides a map of plastic strain rate and tangent modulus over a large range of loading conditions.
Localization, Delocalization, and Compression Fracture in Moderately Thick Transversely Isotropic Bilinear Rings Under External Pressure
Authors: Chaudhuri Reaz A.
Published: October 2006

A fully nonlinear finite element analysis for prediction of localization∕delocalization and compression fracture of moderately thick imperfect transversely isotropic rings, under applied hydrostatic pressure, is presented. The combined effects of modal imperfections, transverse shear∕normal deformation, geometric nonlinearity, and bilinear elastic (a special case of hypoelastic) material property on the emergence of interlaminar shear crippling type instability modes are investigated in detail. An analogy to a soliton (slightly disturbed integrable Hamiltonian system) helps understanding the localization (onset of deformation softening) and delocalization (onset of deformation hardening) phenomena leading to the compression damage∕fracture at the propagation pressure. The primary accomplishment is the (hitherto unavailable) computation of the mode II fracture toughness (stress intensity factor∕energy release rate) and shear damage∕crack bandwidth, under compression, from a nonlinear finite element analysis, using Maxwell’s construction and Griffith’s energy balance approach. Additionally, the shear crippling angle is determined using an analysis, pertaining to the elastic plane strain inextensional deformation of the compressed ring. Finally, the present investigation bridges a gap of three or more orders of magnitude between the macro-mechanics (in the scale of mms and up) and micro-mechanics (in the scale of microns) by taking into account the effects of material and geometric nonlinearities and combining them with the concepts of phase transition via Maxwell construction and Griffith-Irwin fracture mechanics.
Design Loads for Wind Turbines Using the Environmental Contour Method
Authors: Saranyasoontorn Korn , Manuel Lance
Published: October 2006

When interest is in establishing ultimate design loads for wind turbines such that a service life of, say, 20 years is assured, alternative procedures are available. One class of methods works by employing statistical loads extrapolation techniques following development first of 10-minute load maxima distributions (conditional on inflow parameters such as mean wind speed and turbulence intensity). The parametric conditional load distributions require extensive turbine response simulations over the entire inflow parameter range. We will refer to this first class of methods as the “parametric method.” An alternative method is based on traditional structural reliability concepts and isolates only a subset of interesting inflow parameter combinations that are easily first found by working backward from the target return period of interest. This so-called inverse reliability method can take on various forms depending on the number of variables that are modeled as random. An especially attractive form that separates inflow (environmental) variables from turbine load∕response variables and further neglects variability in the load variables given inflow is referred to as the environmental contour (EC) method. We shall show that the EC method requires considerably smaller amounts of computation than the parametric method. We compare accuracy and efficiency of the two methods in 1- and 20-year design out-of-plane blade bending loads at the root of two 1.5 MW turbines. Simulation models for these two turbines with contrasting features, in that one is stall-regulated and the other pitch-regulated, are used here. Refinements to the EC method that account for the effects of the neglected response variability are proposed to improve the turbine design load estimates.
Wind Tunnel Hotwire Measurements, Flow Visualization and Thrust Measurement of a VAWT in Skew
Authors: Simão Ferreira Carlos J. , van Bussel Gerard J. W. , van Kuik Gijs A. M.
Published: October 2006

The results of experimental research on the wake and induced flow around a vertical axis wind turbine (VAWT) in skew are presented. The previous research on VAWTs in skew is limited because this operation mode has only recently been found to be significant in the operation of VAWTs in the built environment. These results contain hotwire measurements of the incoming flow and wake of a VAWT in nonskewed and skewed flow. The high sampling rate of the hotwire data allows the effects of blade passing to be identified. Flow visualization of the tip vortices is also presented. Thrust measurements of the rotor were performed to understand the effect of skew on thrust variation and to compare with analytical predictions.