bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparison of three random effects approaches to analyze repeated bounded outcome scores with an application in a stroke revalidation study
Authors: Molas Marek , Lesaffre Emmanuel 
Published: September 2008

AbstractDiscrete bounded outcome scores (BOS), i.e. discrete measurements that are restricted on a finite interval, often occur in practice. Examples are compliance measures, quality of life measures, etc. In this paper we examine three related random effects approaches to analyze longitudinal studies with a BOS as response: (1) a linear mixed effects (LM) model applied to a logistic transformed modified BOS; (2) a model assuming that the discrete BOS is a coarsened version of a latent random variable, which after a logistic‐normal transformation, satisfies an LM model; and (3) a random effects probit model. We consider also the extension whereby the variability of the BOS is allowed to depend on covariates. The methods are contrasted using a simulation study and on a longitudinal project, which documents stroke rehabilitation in four European countries using measures of motor and functional recovery. Copyright © 2008 John Wiley & Sons, Ltd.
Multivariate logit copula model with an application to dental data
Authors: Nikoloulopoulos Aristidis K. , Karlis Dimitris 
Published: September 2008

AbstractApplications of copulas for multivariate continuous data abound but there are only a few that treat multivariate binary data. In the present paper, we model multivariate binary data based on copulas using mixtures of max‐infinitely divisible copulas, introduced by Joe and Hu (J. Multivar. Anal.1996;57(2): 240–265). When applying copulas to binary data the marginal distributions also contribute to the dependence measures. We propose the use of covariate information in the copula parameters to obtain a direct effect of a covariate on dependence. To deal with model uncertainty due to selecting among several candidate models, we use a model averaging technique. We apply the model to data from the Signal‐Tandmobiel©dental study and, in particular, to four binary responses that refer to caries experience in the mandibular and maxillary left and right molars. We aim to model Kendall's tau associations between them, and examine how covariate information affects these associations. We found that there are systematically larger associations between the two mandibular and the two maxillary molars. Using covariates to model these associations more closely, we found that the systematic fluoride and age of the children affect the associations. Note that such relationships could not have been revealed by methods that focus on the marginal models. Copyright © 2008 John Wiley & Sons, Ltd.
Recombinant Glycans on an S‐Layer Self‐Assembly Protein: A New Dimension for Nanopatterned Biomaterials
Authors: Steiner Kerstin , Hanreich Angelika , Kainz Birgit , Hitchen Paul G. , Dell Anne , Messner Paul , Schäffer Christina 
Published: September 2008

AbstractCrucial biological phenomena are mediated through carbohydrates that are displayed in a defined manner and interact with molecular scale precision. We lay the groundwork for the integration of recombinant carbohydrates into a “biomolecular construction kit” for the design of new biomaterials, by utilizing the self‐assembly system of the crystalline cell surface (S)‐layer protein SgsE of Geobacillus stearothermophilus NRS 2004/3a. SgsE is a naturally O‐glycosylated protein, with intrinsic properties that allow it to function as a nanopatterned matrix for the periodic display of glycans. By using a combined carbohydrate/protein engineering approach, two types of S‐layer neoglycoproteins are produced in Escherichia coli. Based on the identification of a suitable periplasmic targeting system for the SgsE self‐assembly protein as a cellular prerequisite for protein glycosylation, and on engineering of one of the natural protein O‐glycosylation sites into a target for N‐glycosylation, the heptasaccharide from the AcrA protein of Campylobacter jejuni and the O7 polysaccharide of E. coli are co‐ or post‐translationally transferred to the S‐layer protein by the action of the oligosaccharyltransferase PglB. The degree of glycosylation of the S‐layer neoglycoproteins after purification from the periplasmic fraction reaches completeness. Electron microscopy reveals that recombinant glycosylation is fully compatible with the S‐layer protein self‐assembly system. Tailor‐made (“functional”) nanopatterned, self‐assembling neoglycoproteins may open up new strategies for influencing and controlling complex biological systems with potential applications in the areas of biomimetics, drug targeting, vaccine design, or diagnostics.
Structural dominance analysis and theory building in system dynamics
Authors: Kampmann Christian Erik , Oliva Rogelio 
Published: September 2008

AbstractWe provide a review of different approaches to linking model structure to observed behaviour with a particular view towards using models for theory building. We argue that theory building cannot be based upon pure simulation and model building alone: the inference from system dynamics models invariably uses concepts and analogies from simple feedback systems and models. Strengthening the analytical foundation for this inference will therefore have a direct impact on the strength of system dynamics as a theory‐building tool. We identify four approaches to establish this link (traditional, pathway participation, eigenvalue and eigenvector), assess the strengths and weaknesses of each approach, and point to challenges and tasks ahead. We find that the eigenvalue and eigenvector approaches carry significant potential but that a more solid theoretical foundation of the method is required. However, since a ‘grand unified theory’ will never be possible, all tools will be based on approximations and it is only in their practical use that we can discover their real value. Copyright © 2008 John Wiley & Sons, Ltd.
Common learning and opportunistic behaviour in learning alliances
Authors: Kapmeier Florian 
Published: September 2008

AbstractIn this paper, we propose a system dynamics model that gives deeper insight into the dynamics involved in opportunistic behaviour in learning alliances. Although current research widely recognizes opportunistic behaviour of alliance partners as a reason for alliance failure, most research in this field focuses on opportunism in the area of private learning and of outlearning the partner. Opportunism is mostly ignored in situations of common learning. In the following, we study opportunism in alliances where there is no intention of learning privately. Moreover, in current studies, feedback perspectives are often neglected. A feedback perspective can be helpful to explain the reasons for certain unanticipated long‐term effects. We transfer findings from recent learning alliance literature and from a case study to a system dynamics simulation model. After describing the model structure, different scenarios offer insights into the dynamics of learning, particularly when the partners have different intentions with regard to common learning. We discuss the model runs and subsequently deduce propositions for future research. Copyright © 2008 John Wiley & Sons, Ltd.
Formal theory building for the avalanche game: explaining counter‐intuitive behaviour of a complex system using geometrical and human behavioural/physiological effects
Authors: Lane David C. 
Published: September 2008

AbstractIn ‘Avalanche’, an object is lowered, players staying in contact throughout. Normally the task is easily accomplished. However, with larger groups counter‐intuitive behaviours appear. The paper proposes a formal theory for the underlying causal mechanisms. The aim is to not only provide an explicit, testable hypothesis for the source of the observed modes of behaviour—but also to exemplify the contribution that formal theory building can make to understanding complex social phenomena. Mapping reveals the importance of geometry to the Avalanche game; each player has a pair of balancing loops, one involved in lowering the object, the other ensuring contact. For more players, sets of balancing loops interact and these can allow dominance by reinforcing loops, causing the system to chase upwards towards an ever‐increasing goal. However, a series of other effects concerning human physiology and behaviour (HPB) is posited as playing a role. The hypothesis is therefore rigorously tested using simulation. For simplicity a ‘One Degree of Freedom’ case is examined, allowing all of the effects to be included whilst rendering the analysis more transparent. Formulation and experimentation with the model gives insight into the behaviours. Multi‐dimensional rate/level analysis indicates that there is only a narrow region in which the system is able to move downwards. Model runs reproduce the single ‘desired’ mode of behaviour and all three of the observed ‘problematic’ ones. Sensitivity analysis gives further insight into the system's modes and their causes. Behaviour is seen to arise only when the geometric effects apply (number of players greater than degrees of freedom of object) in combination with a range of HPB effects. An analogy exists between the co‐operative behaviour required here and various examples: conflicting strategic objectives in organizations; Prisoners' Dilemma and integrated bargaining situations. Additionally, the game may be relatable in more direct algebraic terms to situations involving companies in which the resulting behaviours are mediated by market regulations. Finally, comment is offered on the inadequacy of some forms of theory building and the case is made for formal theory building involving the use of models, analysis and plausible explanations to create deep understanding of social phenomena. Copyright © 2008 John Wiley & Sons, Ltd.
Closing the loop: promoting synergies with other theory building approaches to improve system dynamics practice
Authors: Kopainsky Birgit , Luna‐Reyes Luis F. 
Published: September 2008

AbstractThis paper contributes to the development of better methods for the conceptualization of system dynamics models. It does so by looking at the model building process as a theory building process and by reviewing theory building approaches in other social sciences, such as grounded theory and case study research. Concepts of these modes of qualitative research constitute a tool set to build relevant system dynamics models, grounded in data, and with higher potential to provide rigorous and relevant generic structures. The deductive capability of simulation models, on the other hand, helps to close the loop in the theory building process, putting together the inductive and deductive stages in theory building. Copyright © 2008 John Wiley & Sons, Ltd.
First‐trimester screening in pregnancies conceived by assisted reproductive technology: significance of gestational dating by oocyte retrieval or sonographic measurement of crown–rump length
Authors: Gjerris A. C. , Loft A. , Pinborg A. , Tabor A. , Christiansen M. 
Published: September 2008

AbstractObjectivesTo evaluate, in pregnancies conceived by assisted reproductive technology, whether determination of gestational age (GA) by date of oocyte aspiration (DOA) or crown–rump length (CRL) at first‐trimester screening influences the distribution of serum and sonographic markers or the performance of first‐trimester screening for chromosomal abnormalities.MethodsGA was calculated using either DOA or CRL at blood sampling and nuchal translucency thickness (NT) measurement in 729 singleton pregnancies conceived by in‐vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Weight‐corrected log multiples of the median (MoM) marker distributions specific for IVF pregnancy were established using multiple log regression and compared for DOA‐ and CRL‐based GA calculation.ResultsGA determined by CRL was significantly larger, albeit slightly, than was GA determined by DOA, with a mean difference of 1.50 (SD, 2.4) days (P < 0.001). Log MoM distributions of free beta‐human chorionic gonadotropin and NT showed that GA dating by CRL resulted in significantly higher, albeit slightly, mean log MoM values compared with DOA dating. The reverse was the case for mean log MoM pregnancy‐associated plasma protein‐A. The SDs were similar for CRL and DOA dating. According to Monte Carlo simulation, the use of DOA or CRL for GA dating did not appreciably influence the performance of first‐trimester screening.ConclusionsDOA and CRL are practically equivalent when calculating GA for first‐trimester screening. The correct method of GA dating for other purposes (e.g. estimated time of delivery) in IVF/ICSI pregnancies is still unresolved. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Use of transvaginal ultrasonography to predict preterm birth in women with a history of preterm birth
Authors: Crane J. M. G. , Hutchens D. 
Published: September 2008

AbstractObjectiveTo investigate whether cervical length measured by transvaginal ultrasonography predicts spontaneous preterm birth at < 35 weeks' gestation in women with a history of spontaneous preterm birth, stratified by spontaneous preterm birth history subtype (preterm premature rupture of membranes (PPROM) or preterm labor with intact membranes at onset of labor).MethodsThis retrospective cohort study included women with a history of spontaneous preterm birth that were subsequently pregnant with singleton gestations, compared with a low‐risk control group. Transvaginal ultrasonographic cervical lengths were measured at 24 to 30 weeks of gestation. The primary outcome was spontaneous preterm birth at < 35 weeks. Secondary outcomes included spontaneous preterm birth at < 37 weeks and < 34 weeks, low birth weight, Cesarean delivery and perinatal morbidity and mortality. Multiple logistic regression analysis was used to control for potential confounders and calculate odds ratios and 95% confidence intervals. Receiver–operating characteristics (ROC) curves were used to determine the best cut‐off for transvaginal ultrasound cervical length in predicting spontaneous preterm birth at < 35 weeks.ResultsWomen with a history of spontaneous preterm birth with intact membranes at onset of labor (n = 42) had a shorter cervical length (3.28 cm) than women with a history of spontaneous preterm birth with PPROM at onset of labor (n = 48, cervical length 3.77 cm; P = 0.019), and both subgroups had shorter cervical lengths than the low‐risk control group (n = 103, cervical length 4.30 cm; P < 0.0001). Both subgroups were associated with spontaneous preterm birth at < 35 weeks, < 37 weeks, < 34 weeks and birth weight < 2500 g. ROC curves determined that the best cut‐off for cervical length to predict spontaneous preterm birth at < 35 weeks was 3.0 cm. By multiple logistic regression analysis, the only independent predictors of spontaneous preterm birth at < 35 weeks were cervical length < 3.0 cm, a history of spontaneous preterm birth and antepartum bleeding in the current pregnancy. In women with a history of spontaneous preterm birth, a cervical length as measured by transvaginal ultrasonography of < 3.0 cm had a sensitivity of 63.6%, specificity of 77.2%, positive predictive value of 28.0% and negative predictive value of 93.8%, for preterm birth at < 35 weeks.ConclusionWomen with a history of spontaneous preterm birth with preterm labor and intact membranes at the onset of labor have shorter cervices than women with a history of spontaneous preterm birth and PPROM at the onset of labor, and both groups have shorter cervices than a low‐risk control group. Both groups of women with a history of spontaneous preterm birth have an increased risk of recurrent spontaneous preterm birth at < 35 weeks, and this is predicted by a transvaginal ultrasound cervical length of < 3.0 cm. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Fetal celiac and splenic artery flow velocity and pulsatility index: longitudinal reference ranges and evidence for vasodilation at a low portocaval pressure gradient
Authors: Ebbing C. , Rasmussen S. , Godfrey K. M. , Hanson M. A. , Kiserud T. 
Published: September 2008

AbstractObjectivesTo establish longitudinal reference ranges for the fetal celiac and splenic arteries flow velocity and pulsatility index (PI), and to determine their hemodynamic relationship to venous liver perfusion and distribution and to other essential arteries.MethodsThis was a prospective longitudinal study of 161 low‐risk pregnancies. Doppler recordings of the celiac and splenic arteries were made on three to five occasions at 3–5‐week intervals to establish reference ranges for blood velocity and PI measurements. Peak systolic velocity in the ductus venosus, a shunt between the umbilical and inferior caval veins, was used to represent the umbilicocaval (i.e. portocaval) pressure gradient, and the left portal vein blood velocity represented the umbilical distribution to the right liver lobe. The correlations between the celiac, splenic and hepatic arteries were determined, and their association with the middle cerebral and umbilical artery PIs (MCA‐PI and UA‐PI) was assessed.ResultsLongitudinal reference ranges for the fetal celiac and splenic arteries were established based on 510 and 521 observations, respectively, during gestational weeks 21–39. Terms for calculating conditional reference ranges to be used for repeat observations are provided. Celiac and splenic artery PIs were low when portocaval pressure and umbilical supply to the right lobe were low (P< 0.0001). Their peak systolic velocity and PI were correlated (r= 0.7 (95% CI, 0.6–0.8) andr= 0.5 (95% CI, 0.3–0.6), respectively), while the PI of the hepatic artery correlated weakly with those of the celiac and splenic arteries. They were positively associated with the MCA‐PI and UA‐PI (P< 0.0001).ConclusionWe provide longitudinal reference ranges for the fetal celiac and splenic arteries Doppler measurements and show that they are involved in maintaining portal liver perfusion independently from the hepatic artery. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Efficient call admission control scheme for 4G wireless networks
Authors: Tarek Bejaoui , Nidal Nasser 
Published: September 2008

AbstractNext generation wireless networks (NGWNs) will utilize several different radio access technologies, seamlessly integrated to form one access network. This network has the potential to provide many of the requirements that other previous systems did not achieve such as high data transfer rates, effectives user control, seamless mobility, and others which will potentially change the way users utilize mobile devices. NGWN will integrate a multitude of different heterogeneous networks including (a) cellular networks, passed through multiple generations—1G, 2G, 3G, and 3.5G; (b) wireless LANs, championed by the IEEE 802.11 wireless fidelity (WiFi) networks; and (c) broadband wireless access networks (IEEE 802.16, WiMAX). In this paper, a new adaptive quality of service (QoS) oriented CAC scheme is proposed to limit the occurrence of hard IEEE 802.11 WLAN‐UMTS handovers to mobile users using real time (RT) applications. This scheme is hybrid, based on the service class differentiation, the location in the heterogeneous infrastructure and a vertical handoff decision function as well. Simulation results show that our policy achieves significant performance gains. It maximizes the utilization of the resources available at the WLAN cells, and meets as much as possible the QoS requirement of higher priority users. Copyright © 2008 John Wiley & Sons, Ltd.
Cross‐layer optimization for energy‐efficient wireless communications: a survey
Authors: Miao Guowang , Himayat Nageen , Li Ye (Geoffrey) , Swami Ananthram 
Published: September 2008

AbstractSince battery technology has not progressed as rapidly as semiconductor technology, power efficiency has become increasingly important in wireless networking, in addition to the traditional quality and performance measures, such as bandwidth, throughput, and fairness. Energy‐efficient design requires a cross layer approach as power consumption is affected by all aspects of system design, ranging from silicon to applications. This article presents a comprehensive overview of recent advances in cross‐layer design for energy‐efficient wireless communications. We particularly focus on a system‐based approaches toward energy optimal transmission and resource management across time, frequency, and spatial domains. Details related to energy‐efficient hardware implementations are also covered. Copyright © 2008 John Wiley & Sons, Ltd.
Offshore wind profiling using light detection and ranging measurements
Authors: Peña Alfredo , Hasager Charlotte Bay , Gryning Sven‐Erik , Courtney Michael , Antoniou Ioannis , Mikkelsen Torben 
Published: September 2008

AbstractThe advantages and limitations of the ZephIR®, a continuous‐wave, focused light detection and ranging (LiDAR) wind profiler, to observe offshore winds and turbulence characteristics were tested during a 6 month campaign at the transformer/platform of Horns Rev, the world's largest wind farm. The LiDAR system is a ground‐based sensing technique which avoids the use of high and costly meteorological masts. Three different inflow conditions were selected to perform LiDAR wind profiling. Comparisons of LiDAR mean wind speeds against cup anemometers from different masts showed high correlations for the open sea sectors and good agreement with their longitudinal turbulence characteristics. Cup anemometer mean wind speed profiles were extended with LiDAR profiles up to 161 m on each inflow sector. The extension resulted in a good profile match for the three surrounding masts. These extended profiles, averaged over all observed stabilities and surface roughness lengths, were compared to the logarithmic profile. The observed deviations were relatively small. Offshore wind farm wakes were also observed from LiDAR measurements where the wind speed deficits were detected at all LiDAR heights. Profile‐derived friction velocities and roughness lengths were compared to Charnock's sea roughness model. These average values were found to be close to the model, although the scatter of the individual estimations of sea roughness length was large. Copyright © 2008 John Wiley & Sons, Ltd.
Determination of the composition of Ultra‐thin Ni‐Si films on Si: constrained modeling of electron probe microanalysis and x‐ray reflectivity data
Authors: Phung Tran M. , Jensen Jacob M. , Johnson David C. , Donovan John J. , McBurnett Brian G. 
Published: September 2008

AbstractThe homogeneous bulk assumption used in traditional electron probe microanalysis (EPMA) can be applied for thin‐layered systems with individual layers as thick as 50 nm provided the penetration depth of the lowest accelerating voltage exceeds the total film thickness. Analysis of an NIST Ni‐Cr thin film standard on Si using the homogeneous model yielded certified compositions and application of the same model to ultra‐thin Ni‐Si layers on GaAs yielded their expected compositions. In cases where the same element is present in multiple layers or in the substrate as well as the film, the homogeneous assumption in EPMA alone is not sufficient to determine composition. By combining x‐ray reflectivity (XRR) thickness and critical angle data and using an iterative approach, quantitative compositional data in EPMA can be achieved. This technique was utilized to determine the composition of Ni‐Si ultra‐thin films grown on silicon. The Ni‐Si composition determined using this multi‐instrumental technique matched that of Ni‐Si films simultaneously deposited on GaAs. Copyright © 2008 John Wiley & Sons, Ltd.