bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal setpoint chasing in dynamic positioning of deep‐water drilling and intervention vessels
Authors: Sørensen Asgeir J. , Leira Bernt , Peter Strand Jann , Larsen Carl M.
Published: January 2005

Conventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal‐plane about desired position and heading co‐ordinates defined by the operator. A three degrees‐of‐freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi‐submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust‐induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work‐over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co‐ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi‐submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd.
An intelligent control concept for formation flying satellites
Authors: Vadali S. R. , Vaddi S. S. , Alfriend K. T.
Published: January 2005

This paper deals with the determination of initial conditions and the design of fuel‐balancing orbit control laws for a formation of satellites. Hill's equations describe the linearized dynamics of relative motion between two satellites. They admit bounded relative orbit solutions as special cases. Predictably, these bounded solutions break down in the presence of nonlinearities and perturbations. A method for determining the initial conditions that result in quasi‐periodic relative orbits over the short term, in the presence of J2 perturbation, is presented. The control acceleration or equivalently, the fuel required to cancel the perturbation on a satellite depends upon its orbital inclination with respect to that of the reference satellite. An intelligent control concept that exploits the physics of the relative motion dynamics is presented. Analysis shows that this concept minimizes the total fuel consumption of the formation and maintains equal, average fuel consumption for each satellite. The concept is implemented using a novel, disturbance accommodating control design process. Numerical simulations and analytical results are in excellent agreement with each other. Copyright © 2002 John Wiley & Sons, Ltd.
Impact of an urban centre on the nitrogen cycle processes of epilithic biofilms during a summer low‐water period *
Authors: Teissier S. , Garabetian F. , Torre M. , Dalger D. , Labroue L.
Published: January 2005

Nitrogen transformations in epilithic biofilms of a large gravel bed river, the Garonne, France, has been studied upstream (one site) and downstream (four sites) of a large urban centre (Toulouse, 740 000 inhabitants).

High biomass, up to 49 g AFDM m−2 (ashes free dry matter) and 300 mg chlorophyll a m−2 (Chl. a), were recorded at 6 and 12 km downstream from the main wastewater treatment plant outlet. The lowest records upstream and larger downstream (less than 16 g AFDM m−2 or 120 mg Chl. a m−2) could be explained by recent water fall (early summer low‐water period).

Measurements of nitrogen exchange at the biofilm–overlying water interface were performed in incubation chambers under light and dark conditions. The addition of acetylene at the mid‐incubation time allowed evaluation of both nitrification (variation in NH4+ flux after the ammonium monooxygenase inhibition) and denitrification (N2O accumulation related to the inhibition of N2O reduction). Denitrification (Dw) and nitrification rates were maximum at sites close to the city discharges in dark conditions (up to 9.1 and 5.6 mg N m−2 h−1, respectively). Unexpected denitrification activities in light conditions (up to 1.4 mg N m−2 h−1) at these sites provided evidence for enhanced nitrogen self‐purification downstream.

As confirmed by most probable number (MPN) counts, high nitrification rates in biofilm close downstream were related to enhanced (more than almost 3 log) nitrifying bacteria densities (up to 7.6×109 MPN m−2). Downstream of an urban centre, nitrogen transformations in the biofilm appeared to be influenced by the occurrence of an adapted microflora which is inoculated or stimulated by anthropic pollution. Copyright © 2002 John Wiley & Sons, Ltd.
Seasonal changes of fish diversity in the main channel of the large lowland River Oder
Authors: Wolter Christian , Bischoff Antje
Published: January 2005

Between June 1998 and May 2000 an adult fish sampling was carried out in the lowland River Oder using bottom otter trawls in the mid channel and electric fishing at the shorelines. This study focused on the lateral connectivity between mid channel and river margins with the aim to characterize the importance of mid‐channel sections as fish habitat.

Altogether 15 660 fish of 30 species were sampled, 8169 fish of 20 species in the mid‐channel section and 7491 fish of 27 species at the shoreline. At the shoreline we observed significantly higher fish densities (345.4±51.8 fish per 1000 m3 compared to 5.2±1.0, mean±standard error) and numbers of species (11.1±0.5, respectively, 5.2±0.3). However, three species were exclusively in the mid channel and a further six more frequent there. The mid channel was dominated by silver bream (Abramis bjoerkna) representing 75.6% of the total catch. It was generally colonized by bigger fish (22.1±0.12 cm total length compared to 13.0±0.08 cm).

According to the observed significant habitat preferences, we classified a guild of potamal species, which shift during their first year of life to mid‐channel habitats and exhibited the highest relative abundance there. To this guild belong the following species: silver bream, common bream (Abramis brama), blue bream (Abramis ballerus), whitefin gudgeon (Gobio albipinnatus), zander (Sander lucioperca) and wels (Silurus glanis). Copyright © 2001 John Wiley & Sons, Ltd.
Regional‐scale effects of flow regulation on lowland riverine fish communities in New South Wales, Australia
Authors: Gehrke P.C. , Harris J.H.
Published: January 2005

Lowland reaches of 40 rivers in New South Wales, Australia, were designated as ‘regulated’ or ‘unregulated’, depending upon the degree to which flows were modified by the operation of a dam upstream. Five replicate rivers of each type were selected from the North Coast, South Coast, Darling and Murray regions in the State. Fish communities in each river were sampled in summer and winter in two consecutive years. Regulated and unregulated rivers contained significantly different fish communities, although communities in each region retained characteristic features. The proportion of native species in the total catch was greater in unregulated rivers in all regions, ranging from 27% in the Murray region to 100% in South Coast rivers. In regulated rivers, native species made up 20% of the catch in the Murray region compared with a maximum of 99% in the North Coast. Carp, Cyprinus carpio, were the main alien species contributing to changes in the proportional abundance of native fish. Native species most affected by river regulation were western carp gudgeons, Hypseleotris spp., bony herring, Nematalosa erebi, and striped gudgeons, Gobiomorphus australis. Fifteen native species showed some effect of river regulation on their population structures. Individual species showed positive, negative or mixed positive and negative, effects of regulation, at population, species or community levels. Three abundant alien species and seven native species showed only positive or mixed responses, whereas 13 native species exhibited only negative effects. Flow regulation has reduced the resilience of New South Wales rivers and native fish communities to invasion by alien species. New research has commenced to investigate whether recently introduced environmental flow rules are effective in reducing the effects of river flow alteration on fish communities in New South Wales rivers. Copyright © 2001 John Wiley & Sons, Ltd.
Effects of flood interruption on species richness, diversity and floristic composition of woody regeneration in the Upper Rhine alluvial hardwood forest
Authors: Deiller Anne‐Frédérique , Walter Jean‐Michel N. , Trémolières Michèle
Published: January 2005

Regulation works in the Upper Rhine carried out since the 19th century have drastically modified the floodplain forest ecosystem in the Alsace Plain. These works have disconnected the largest part of the riparian forest from the river and interrupted the flooding. This study aims at assessing the effects of the flood interruption on woody regeneration in three hardwood stands: one still liable to flooding, the second one unflooded for 30 years and the third one unflooded for 130 years. Fieldwork was carried out to determine the species richness of seed rain, seed bank and extant vegetation of the regeneration understorey. The potential species richness was calculated using the first‐order jackknife estimator. In addition, floristic composition and diversity indices of extant vegetation were calculated. Results show that species richness of the seed bank is lower than seed rain and extant vegetation. The species richness of the extant vegetation increases with the duration of interruption of the floods in the Rhine forest as a result of introduction of flood‐intolerant species in the unflooded forest. Although species richness of the extant vegetation was the lowest in the flooded site, Shannon–Weaver diversity and equitability were found to be the highest, because the disturbance caused by floods allows a more equal coexistence of several species. Conversely, in the unflooded sites, a small number of species represent most of the woody individuals of the regeneration phase. Implications of flood restoration on species richness and diversity of the regeneration compartment are discussed. Copyright © 2001 John Wiley & Sons, Ltd.
Field experiments on stranding in juvenile atlantic salmon (Salmo salar) and brown trout (Salmo trutta) during rapid flow decreases caused by hydropeaking
Authors: Saltveit S.J. , Halleraker J.H. , Arnekleiv J.V. , Harby A.
Published: January 2005

Field experiments showed that sudden reductions in river flow may cause high mortality of juvenile salmonids through stranding. A 75‐m2 enclosure in the drawdown zone of a regulated river was stocked with a known number of wild 0+ and/or 1+ wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). The number stranded was estimated by counting the surviving fish collected in a bag as they left the enclosure.

In general, a far higher incidence of fish stranding was found during winter conditions (<4.5°C) compared with the higher temperatures during late summer and early autumn. This is probably mainly because of lower fish activity during the cold season and a substrate seeking behaviour especially during daytime. Stranding was lower at night, probably because of a predominant night active behaviour. Hatchery salmon behaved oppositely to wild fish, and studies based on cultivated fish may give wrong conclusions as to the consequences of hydropeaking. Searching for fish in the substrate underestimated the consequences of sudden flow reductions, as fish were difficult to find. Stranding is not equal to mortality, as fish were found to survive for several hours in the substrate after dewatering. Long shut down procedures of the turbines during daytime, decreased stranding of Atlantic salmon (7–9 cm) drastically under spring conditions. Temperature, season and light conditions have the most pronounced effect on stranding of juvenile salmonids. It is possible to reduce stranding by taking into account these ecological considerations during hydropeaking operations. Copyright © 2001 John Wiley & Sons, Ltd.
Bank profile and structure as determinants of macroinvertebrate assemblages—seasonal changes and management
Authors: Armitage P.D. , Lattmann K. , Kneebone N. , Harris I.
Published: January 2005

Management and restoration procedures in rivers frequently have a major influence on the bank and marginal zone, depending on the timing of disturbance and the eventual structure of the bank. This study examines changes in macroinvertebrate communities in four different bank types at 3‐weekly intervals throughout a year. The banks differed in their profile and in their structure: shallow sloping and vegetated, stepped shallow profile, steep profile (eroded soil bank), and iron revetments. Velocity patterns over the year showed much variability, both between and within bank types ranging from standing water in the summer to velocities in excess of 0.9 m s−1 in the winter. The shallow‐sloping vegetated site supported a total of 115 taxa, in contrast to the artificial iron revetment, on which only 32 taxa were recorded. Total abundances were five to six times greater in the shallow vegetated sites compared with the steeply sloped and artificial banks. Highest abundances were recorded in the late spring (May/June) and most taxa were found in August and September. Fluctuations in both abundance and number of taxa were least on the reveted bank. Ordination of the fauna/site matrix revealed a seasonal separation with specific winter and summer communities. The results suggest that the bankside is a dynamic environment where communities change in relation to growth of bankside vegetation and its concomitant effect on flow. The implications of these findings to management activities and restoration procedures are discussed. Copyright © 2001 John Wiley & Sons, Ltd.
Hydromorphological control of phosphorus in a large free‐flowing gravel bed river: the Garonne River (France)
Authors: Bonvallet Garay S. , Sauvage S. , Vervier P.
Published: January 2005

The objective of this paper is to relate phosphorus (P) transport dynamics and hydromorphological characteristics of a large human‐influenced river, the River Garonne within a sector receiving the waste water of a sewage treatment plant for a population of 600 000. Two studies were conducted in 1997 and 1999 during two different hydrological conditions at low‐flow periods. The 1997 study was carried out on an 18‐km stretch with discharges varying between 33 and 53 m3/s and with very small fluctuations. The 1999 study concerned a longer stretch of 47 km, divided into four smaller reaches, and with discharges fluctuating rapidly from 40 to 108 m3/s.

Downstream of the sewage treatment plant, total phosphorus (TP) concentrations ranged from 0.19 to 0.27 mg/L and were mainly in the dissolved form: between 60 and 78% of TP was dissolved reactive phosphorus (DRP). P concentrations were significantly lower upstream of the sewage treatment plant.

By a mass‐balance approach, we estimated that the sewage treatment plant represents more than half the input (between 59 and 67%) of the studied sector. TP dynamic is linked to suspended solids for discharges above 60 m3/s.

During established low‐flow period in the 1997 study (<60 m3/s), 22 and 27% of TP and DRP were retained by the river bed.

In the 1999 study, under different low‐water period hydraulic conditions, we calculate that particulate P retention occurred in two reaches among the four under study and only for discharges below 60 m3/s.

We show that for established discharges below 60 m3/s, there is an active uptake of transported P by functional compartments (i.e. the hyporheic zone and the periphyton). During the low‐water period with relatively high hydraulic fluctuations, and for discharges >60 m3/s, P retention is controlled as expected by suspended matter dynamics.

We conclude that management of the hydrological regime can influence P retention during sensitive low‐water periods. Copyright © 2001 John Wiley & Sons, Ltd.
Reallocation of compensation releases to restore river flows and improve instream habitat availability in the Upper Derwent Catchment, Derbyshire, UK
Authors: Maddock I.P. , Bickerton M.A. , Spence R. , Pickering T.
Published: January 2005

The Upper Derwent catchment is situated in the Peak District National Park in North Derbyshire, England and includes the Derwent Valley Reservoir System. The natural inflows to the reservoir system are boosted by flow diversion schemes from the River Ashop and River Noe, leaving almost dry stretches in these rivers for long periods of time. Compensation releases are made into Jaggers Clough and the River Derwent. This study examined the possibility of altering the operation of the diversion scheme and compensation flow releases, both temporally and spatially to restore flows within these dry reaches. The overall intention was to minimize the ecological impacts of regulation in the four rivers whilst protecting the yield of this critical public water supply.

The study utilized the Physical Habitat Simulation System (PHABSIM) to identify and compare feasible operational changes. This technique enables quantitative comparisons of the suitable habitat available under different flow regime scenarios.

Brown Trout is the most abundant fish species in the Upper Derwent streams, with Grayling, Brook Lamprey and Bullhead also present. The invertebrate fauna is typical of upland streams with neutral to acid waters. The ecological data were assessed to identify suitable target species/life stages for use with PHABSIM. Brown Trout, Grayling and four invertebrate families (Rhyacophilidae, Leuctridae, Chloroperlidae and Heptageniidae) were selected.

Habitat mapping along four stretches of river totalling 10 km was carried out in the summer of 1998, followed by PHABSIM fieldwork on 24 transects in the autumn. This information was utilized to examine the tradeoffs in habitat availability between reinstating flows in the dry stretches of river, and reducing compensation flows elsewhere to minimize the supply impact. Various operating scenarios were examined and two sets of compensation control rules proposed for normal and drought years. Each set included seasonal variability in the rules.

The PHABSIM work described here is the first stage in the process of developing a more ecologically acceptable flow regime in the Upper Derwent catchment. The decision on the final implementation will be subject to further resource modelling and negotiation between the Environment Agency, the water company and local interested stakeholders. Copyright © 2001 John Wiley & Sons, Ltd.
Ecological integrity of river–floodplain systems—assessment by dragonfly surveys (Insecta: Odonata)
Authors: Chovanec Andreas , Waringer Johann
Published: January 2005

Dragonflies are reliable indicators of the ecological quality of land–water ecotones, habitat heterogeneity and the hydrological dynamics of water bodies. In recent years, surveys of dragonfly communities have become a powerful tool for the ecological assessment of floodplain areas. The goal of this paper is to present a new approach towards assessing the ecological integrity of river–floodplain systems by analysing resident breeding dragonfly species. The methodology is based on experiences with existing approaches using macroinvertebrates as bioindicators, in particular, calculations of saprobic indices, longitudinal zonation and functional feeding group patterns. In addition to the total number of species and the number of sensitive species, the ‘Odonate Habitat Index’ (OHI) is a key element of the assessment method. It indicates characteristic features of a river–floodplain system, such as connectivity aspects, flow dynamics and terrestrialization processes. The OHI is calculated from the species‐specific habitat values (expressing habitat preferences), abundances and the species‐specific indication weight, which distinguishes eurytopic from stenotopic species. The comparison of the status quo with a reference condition allows an assessment of individual water bodies and/or of a whole area in a five‐tiered classification scheme. The approach presented may also be used for the evaluation of restoration measures (e.g. reconnection of side arms) and for the definition of management objectives. Apart from the methodological framework, the results of a first application of this approach are presented in the paper as well. The study areas were selected floodplain systems of the Austrian section of the Danube and man‐made inshore structures of the impounded Danube section in Vienna. Copyright © 2001 John Wiley & Sons, Ltd.
Sustainability indicators: the problem of integration
Authors: Morse Stephen , McNamara Nora , Acholo Moses , Okwoli Benjamin
Published: January 2005

Sustainability indicators (SIs) are increasingly seen as important tools in the implementation of sustainable development. Numerous suggested SI lists and matrices exist, but a remaining problem is how these diverse SIs are to be integrated into an answer as to whether something is sustainable or not. In some studies of sustainability workers have adopted a quantitative integration approach whereby SIs are given numerical values and integrated mathematically to produce a value for sustainability. In this paper the authors discuss SI integration by drawing upon the results of a six‐year research project based in a village in Nigeria. They conclude that an element of'qualitative integration' incorporating value judgements and subjectivity is inevitable with a concept such as sustainability, even if one begins with what may seem like sharp and quantitative SIs. It is argued that SIs are primarily a product of development intervention rather than a desire to understand, and as a result carry with them the desired characteristics, from the donor perspective, of efficiency and accountability. Copyright © 2001 John Wiley & Sons, Ltd and ERP Environment
Sustainable development: is it achievable within the existing international political economy context?
Authors: Carvalho Georgia O.
Published: January 2005

The past few years have not been particularly auspicious in environmental terms; there is increasing evidence of a fairly widespread environmental crisis, increasing the pressure to rethink many of the concepts related to environment and development. Among the important concepts that need to be revisited and further explored is ‘sustainable development’. This paper examines the roots of the sustainable development concept and argues that within the current international political economic system it would be nearly impossible to adopt development strategies that are conducive to truly sustainable development. Four hypotheses about international political economic structures and their relationship to sustainable development are examined. The analysis builds on the linkages between historical processes, international political economic structures, international institutions and the development process posited by globalist theories. The paper concludes that profound changes in economic, political and social structure would be necessary to foster sustainable development. Copyright © 2001 John Wiley & Sons, Ltd and ERP Environment
Surface structuring and phase formation in thin metallic layers deposited at various temperatures
Authors: Markwitz A. , Matz W. , Short K. , Waldschmidt M.
Published: January 2005

Scanning electron microscopy, atomic force microscopy and x‐ray diffraction analyses were performed for the study of the influence of substrate temperature during deposition on the surface structuring and phase formation on thin metallic double layers. Thin layers of Au, Al and Cr were deposited at 150 and 300 °C on 30 nm thick Cu layers evaporated on Si (100) wafer substrates. Possible applications of such layers are Raman‐active surfaces and model layers for diffusion experiments. The topographical investigation revealed an increase of surface structuring with temperature that is related to the formation of intermetallic and oxide phases. At 150 °C deposition temperature, the average roughness (Ra) of the films was determined to be 2–3 nm and the surfaces appeared smooth. In agreement with previous ion beam analysis measurements, a significant surface roughness occurred at 300 °C, depending on the type of the metallic films. The lowest average surface roughness value was measured for the Al/Cu/Si system (Ra = 14.1 nm) and, about double the roughness was measured for the Au/Cu/Si and Cr/Cu/Si layer systems. In contrast, for single Cu layers a high value of Ra = 93.0 nm was determined. The combined analyses showed that the formation of intermetallic phases such as AlCu and CuAl2, reduces a surface roughening. However, the formation of oxide phases such as CuO2, increases, the average surface roughness. Copyright © 2002 John Wiley & Sons, Ltd.
Atomic force microscopy study of ultrafiltration membranes: solute interactions and fouling in pulp and paper processing
Authors: Richard Bowen W. , Stoton J. Austin G. , Doneva Teodora A.
Published: January 2005

Atomic force microscopy (AFM) has been used to quantify directly the interaction (adhesion) of cellubiose and cellulose with two polymeric ultrafiltration membranes of similar molecular weight cut‐off (MWCO) but different materials (ES404 and EM006, PCI Membranes, UK). Membrane ES404 is made from polyethersulphone alone and EM006 is made of a polyethersulphone–polyacrylate blend chosen specifically to increase the hydrophilic properties and decrease the fouling properties of the membrane. Cellubiose‐modified silica probes were used to quantify the interaction of cellubiose with the clean membranes. Pure cellulose probes were used to quantify the interaction of cellulose with both clean and cellubiose‐fouled membranes. All measurements were made in 10−2 M NaCl solution. It was found that the cellubiose‐modified probes had three times greater adhesion with the ES404 than with the EM006 membrane. The pure cellulose probe also had greater adhesion with the ES404 membrane. Cellubiose fouling of both membranes gave close to an order of magnitude increase in the adhesion of the cellulose probe. The results show how AFM in conjunction with the colloid probe technique can elucidate surface interactions in solution, in particular how macromolecular adsorption can modify the subsequent adhesion of particulates. Copyright © 2002 John Wiley & Sons, Ltd.
A non‐parametric method for the comparison of partial areas under ROC curves and its application to large health care data sets
Authors: Zhang Dong D. , Zhou Xia‐Hua , Freeman Daniel H. , Freeman Jean L.
Published: January 2005

The receiver operating characteristic (ROC) curve is a statistical tool for evaluating the accuracy of diagnostic tests. Investigators often compare the validity of two tests based on the estimated areas under the respective ROC curves. However, the traditional way of comparing entire areas under two ROC curves is not sensitive when two ROC curves cross each other. Also, there are some cutpoints on the ROC curves that are not considered in practice because their corresponding sensitivities or specificities are unacceptable. For the purpose of comparing the partial area under the curve (AUC) within a specific range of specificity for two correlated ROC curves, a non‐parametric method based on Mann–Whitney U‐statistics has been developed. The estimation of AUC along with its estimated variance and covariance is simplified by a method of grouping the observations according to their cutpoint values. The method is used to evaluate alternative logistic regression models that predict whether a subject has incident breast cancer based on information in Medicare claims data. Copyright © 2002 John Wiley & Sons, Ltd.
A seminar series in applied biostatistics for clinical research fellows, faculty and staff
Authors: Deutsch Reena
Published: January 2005

Familiarity with experimental design and statistical analysis techniques is necessary for investigators to conduct state‐of‐the‐art research in clinical medicine. A wide range of options for biostatistical training is available. These include formal academic courses for credit, one‐on‐one education offered under the guise of consultation, self‐paced textbook or computer learning, intensive short courses, portions of extended courses spanning an assortment of other subjects, and a continuing series of seminars or lectures covering selected topics in statistics. The latter structure is described in this article. We offered an eight‐week lecture series focusing on a new topic in biostatistics each week. The course targeted clinical faculty, postdoctoral fellows, residents, and other interested research staff at a large medical research institution. The series focused on interpretation of medical journal articles with regard to statistical issues. Another objective was to provide information to increase a participant's expertise in the design of research studies. Guidance was offered for effective communication with collaborating biostatisticians. The format and contents of the seminar series are described. Aspects of the course that proved to be successful are discussed. Copyright © 2002 John Wiley & Sons, Ltd.
Statistical approaches to establishing vaccine safety
Authors: Dragalin Vladimir , Fedorov Valerii , Cheuvart Brigitte
Published: January 2005

In a vaccine safety trial, the primary interest is to demonstrate that the vaccine is sufficiently safe, rejecting the null hypothesis that the relative risk of an adverse event attributable to the new vaccine is above a prespecified value, greater than one. We evaluate the exact probability of type I error of the likelihood score test, with sample size determined by normal approximation, by enumeration of the binomial outcomes in the rejection region and show that it exceeds the nominal level. In the case of rare adverse events, we recommend the Poisson approximation as an alternative and develop the corresponding conditional and unconditional tests. We give sample size and power calculations for these tests. We also propose optimal randomization strategies which either (i) minimize the total number of adverse cases or (ii) minimize the expected number of subjects when the vaccine is unsafe. We illustrate the proposed methods using a hypothetical vaccine safety study. Copyright © 2002 John Wiley & Sons, Ltd.
A quasi‐exact method for the confidence intervals of the difference of two independent binomial proportions in small sample cases
Authors: Chen Xun
Published: January 2005

In this paper we propose a quasi‐exact alternative to the exact unconditional method by Chan and Zhang (1999) estimating confidence intervals for the difference of two independent binomial proportions in small sample cases. The quasi‐exact method is an approximation to a modified version of Chan and Zhang's method, where the two‐sided p‐value of an observation is defined by adding to the one‐sided p‐value the sum of all probabilities of more ‘extreme’ events in the unobserved tail. We show that distinctively less conservative interval estimates can be derived following the modified definition of the two‐sided p‐value. The approximations applied in the quasi‐exact method help to simplify the computations greatly, while the resulting infringements to the nominal level are low. Compared with other approximate methods, including the mid‐p quasi‐exact methods and the Miettinen and Nurminen (M&N) asymptotic method, our quasi‐exact method demonstrates much better reliability in small sample cases. Copyright © 2002 John Wiley & Sons, Ltd.
Semi‐parametric models of long‐ and short‐term survival: an application to the analysis of breast cancer survival in Utah by age and stage
Authors: Tsodikov A.
Published: January 2005

A flexible class of semi‐parametric survival models is proposed that takes account of long‐ and short‐term covariate effects in cancer survival. The diversity of responses described by the models include non‐proportional and crossing survival curves as well as a fraction of long‐term survivors. Restricted non‐parametric maximum likelihood estimation procedures (RNPMLE) are developed to provide point estimates, confidence intervals and tests for the models. Numerical algorithms to fit semi‐parametric survival models are emphasized. The methods are applied to analyse post‐treatment survival of breast cancer patients diagnosed in Utah by age and stage. Copyright © 2002 John Wiley & Sons, Ltd.
Some further results on incorporating risk factor information in assessing the dependence between paired failure times arising from case‐control family studies: an application to prostate cancer
Authors: Hsu Li , Prentice Ross L. , Stanford Janet L.
Published: January 2005

In a typical case‐control family study, detailed risk factor information is often collected on cases and controls, but not on their relatives for reasons of cost and logistical difficulty in locating the relatives. The impact of missing risk factor information for relatives on estimation of the strength of dependence between the disease risk of pairs of relatives is largely unknown. In this paper, we extend our earlier work on estimating the dependence of ages at onset between paired relatives from case‐control family data to include covariates on cases and controls, and possibly relatives. Using population‐based case‐control families as our basic data structure, we study the effect of missing covariates for relatives and/or cases and controls on the bias of certain dependence parameter estimators via a simulation study. Finally we illustrate various analyses using a case‐control family study of early onset prostate cancer. Copyright © 2002 John Wiley & Sons, Ltd.
Bayesian estimation of the proportion of treatment effect captured by a surrogate marker
Authors: Cowles Mary Kathryn
Published: January 2005

Surrogate endpoints in clinical trials are biological markers or events observable earlier than the clinical endpoints (such as death) that are actually of primary interest. The ‘proportion of treatment effect captured’ by a surrogate endpoint (PTE) is a frequentist measure intended to address the question of whether trials based on a surrogate endpoint reach the same conclusions as would have been reached using the true endpoint. The question of inferential interest is whether PTE for a given marker exceeds some threshold value, say 0.5. Calculating PTE requires fitting two different models to the same data. We develop a Markov chain Monte Carlo based method for estimating the Bayesian posterior distribution of PTE. The new method conditions on the truth of a single model. Obtaining the full posterior distribution enables direct statements such as ‘the posterior probability that PTE>0.5 is 0.085’. Furthermore, credible sets do not depend on asymptotic approximations and can be computed using data sets for which the frequentist methods may be inaccurate or even impossible to apply. We illustrate with Bayesian proportional hazards models for clinical trial data. As a by‐product of developing the Bayesian method, we show that the frequentist estimate of PTE also may be computed from quantities in a single model and calculate frequentist confidence intervals for PTE that tend to be narrower than those produced by standard methods but that provide equally good coverage. Copyright © 2002 John Wiley & Sons, Ltd.
Sample size calculations for comparative studies of medical tests for detecting presence of disease
Authors: Alonzo Todd A. , Pepe Margaret S. , Moskowitz Chaya S.
Published: January 2005

Technologic advances give rise to new tests for detecting disease in many fields, including cancer and sexually transmitted disease. Before a new disease screening test is approved for public use, its accuracy should be shown to be better than or at least not inferior to an existing test. Standards do not yet exist for designing and analysing studies to address this issue. Established principles for the design of therapeutic studies can be adapted for studies of screening tests. In particular, drawing upon methods for superiority and non‐inferiority studies of therapeutic agents, we propose that confidence intervals for the relative accuracy of dichotomous tests drive the design of comparative studies of disease screening tests. We derive sample size formulae for a variety of designs, including studies where patients undergo several tests and studies where patients receive only one of the tests under evaluation. Both cohort and case‐control study designs are considered. Modifications to the confidence intervals and sample size formulae are discussed to accommodate studies where, because of the invasive nature of definitive testing, true disease status can only be obtained for subjects who are positive on one or more of the screening tests. The methods proposed are applied to a study comparing a modified pap test to the conventional pap for cervical cancer screening. The impact of error in the gold standard reference test on the design and evaluation of comparative screening test studies is also discussed. Copyright © 2002 John Wiley & Sons, Ltd.
Regression‐based variable clustering for data reduction
Authors: McClelland R. L. , Kronmal R. A.
Published: January 2005

In many studies it is of interest to cluster states, counties or other small regions in order to obtain improved estimates of disease rates or other summary measures, and a more parsimonious representation of the country as a whole. This may be the case if there are too many to summarize concisely, and/or many regions with a small number of cases. By merging the regions into larger geographic areas, we obtain more cases within each area (and hence lower standard errors for parameter estimates), as well as fewer areas to summarize in terms of disease rates. The resulting clusters should be such that regions within the same cluster are similar in terms of their disease rates. In this paper we present a clustering algorithm which uses data at the subject‐specific level in order to cluster the original regions into a reduced set of larger areas. The proposed clustering algorithm expresses the clustering goals in terms of a regression framework. This formulation of the problem allows the regions to be clustered in terms of their association with the response, and confounding variables measured at the subject‐specific level may be easily incorporated during the clustering process. Additionally, this framework allows estimation and testing of the association between the areas and the response. The statistical properties and performance of the algorithm were evaluated via simulation studies, and the results are promising. Additional simulations illustrate the importance of controlling for confounding variables during the clustering process, rather than after the clusters are determined. The algorithm is illustrated with data from the Cardiovascular Health Study. Although developed with a specific application in mind, the method is applicable to a wide range of problems. Copyright © 2002 John Wiley & Sons, Ltd.
Analytic methods for comparing two dichotomous screening or diagnostic tests applied to two populations of differing disease prevalence when individuals negative on both tests are unverified
Authors: Berry Geoffrey , Smith Catherine L. , Macaskill Petra , Irwig Les
Published: January 2005

Two dichotomous screening tests may be compared by applying both tests to all members of a sampled population. For individuals with a positive result on either test the disease status may be verified by a reference standard, but for individuals negative on both tests the disease status may be unverified because the probability of disease is so low that further investigation is costly, unacceptable and perhaps unethical. If the tests have been applied to samples from two populations which have different disease prevalences then unbiased estimates of the true positive and false positive rates of each test, the prevalences in the two populations, and two parameters representing dependence between the two tests can be estimated using maximum likelihood methods. The methods are based on the assumption that the sensitivities and specificities of the two tests, and the dependencies between the tests, are independent of prevalence. A test of goodness of fit provides a test of this. Copyright © 2002 John Wiley & Sons, Ltd.
Comparing results of large clinical trials to those of meta‐analyses
Authors: Moses Lincoln E. , Mosteller Frederick , Buehler John H.
Published: January 2005

We consider methods for assessing agreement or disagreement between the results of a meta‐analysis of small studies addressing a clinical question and the result of a large clinical trial (LCT) addressing the same clinical question. We recommend basing conclusions about agreement upon the difference between the two results (relative risk, log‐odds ratio or similar summary statistic), in the light of the estimated standard error of that difference. To estimate the standard error of the meta‐analytic result we recommend a random effects analysis, and where a between‐studies variance component is found, that component of variance should be used twice: once in the estimated standard error for the meta‐analytic result and again in the standard error of the LCT result (augmenting the internal standard error of that statistic). Such broadening of the standard error reduces the appearance of disagreement. We also offer a critique of a different published approach, which is based on consistency of findings of statistical significance, a matter of how the two results regard zero, which is a poor measure of how closely they agree with each other. Copyright © 2002 John Wiley & Sons, Ltd.
Followers' entry timing: evidence from the Spanish banking sector after deregulation
Authors: Fuentelsaz Lucio , Gomez Jaime , Polo Yolanda
Published: January 2005

Much of the literature dedicated to the analysis of entry timing decisions has been devoted to the study of their consequences in terms of performance. However, only a limited amount of effort has been dedicated to analyzing the factors that determine these decisions. In addition, previous papers have centered their efforts on the product dimension, paying no attention to entry into new geographical markets. This paper departs from previous works in this respect and extends the entry timing literature through a consideration of the geographical side of entry. Our analysis shows that organizational size, organizational competence, and organizational experience appear as key factors when explaining the pattern of geographic diversification. Our results also indicate that diversification takes place sequentially, first proceeding to closer locations, then occupying markets further from the origin. Copyright © 2002 John Wiley & Sons, Ltd.
The communication turn in the theory of social systems
Authors: Leydesdorff Loet
Published: January 2005

The theory of social systems has been contested as a part of sociology. Social order can be expected to emerge as an expectation that is communicated. A communication can be provided with meaning and meaning may evolve into codified meaning. The social system can thus be considered as developing in layers of communication among reflexive actors. At the interfaces between systems theory, communication theory and evolution theory puzzles emerge which can also be formulated as analytical and empirical questions. The mathematical theory of communication can be used for the clarification of the relations among these different perspectives, since a message is expected to contain information. Copyright © 2002 John Wiley & Sons, Ltd.
Ambition and ambivalence, or: is there any system in andragology?
Authors: Notten Ton
Published: January 2005

Andragogy and andragology do have something in common. It concerns something systems researchers have tried to deal with as well. Usually, in systems theory the ‘systemic’ aspect is equated, exclusively, with the functional aspects of human action, its ambitions and ambivalence, and the related justifications. According to that view, social (or moral) expressive ambitions are viewed as not being systematic and well organized, and are consequently identified as ‘life‐world related’. This option, however, might be disastrous for scientific progress in andragology. What seems most characteristic is that andragologists at least have learnt to consider this ‘life‐world’ as constitutive also and worthy of scientific study. They actually succeeded in finding a fertile holon, one that allows for the consideration of value descriptions in scientific exploration, thus integrating andragogy and andragology. This even appears to be a distinguishing contribution, brought forth by all those who ‘found themselves together’ in this old and new, strange and familiar area. They did not succumb to the present‐day seductive confusion between what is part of life and of experience (andragogy), and what is part of reflection and resistance to the evils of the day, with sufficient strength (andragology). The former aims to contribute functional, moral and expressive insights as supports to basic daily life; the latter to provide stability and authority against any fundamental, moral and expressive imposition, or colonization beyond such supports. Andragologists research functional, moral and expressive improvement, with the help of and adding to the andragogue's functional, moral and expressive insights. Copyright © 2002 John Wiley & Sons, Ltd.
Gerard de Zeeuw: models, systems, support and research
Authors: Vahl Martha
Published: January 2005

In this bio‐memo an introduction to, and some background of, the life and work of Gerard de Zeeuw is presented. Copyright © 2002 John Wiley & Sons, Ltd.
A rigorous method for test templates generation from object‐oriented specifications
Authors: Periyasamy K. , Alagar V. S.
Published: January 2005

This paper describes a rigorous method that investigates the suitability of formal specifications written in Object‐Z specification language for testing object‐oriented software implementation in a black‐box fashion. The insight gained in the formalization of a model, the inherent abstractions, and formally specified intended behaviours and exceptions lead to the generation of test templates that are free from any implementation bias. The method described in this paper is an extension of the one proposed by Stocks and Carrington. In particular, the focus of the paper is on generating test templates for composite operations in an Object‐Z specification. The method is illustrated using the specification for an electronic mail system. The specification and the test templates generated for the electronic mail system show several interesting properties of the application that require considerable attention during testing. Copyright © 2001 John Wiley & Sons, Ltd.
Investigating the effectiveness of object‐oriented testing strategies using the mutation method
Authors: Kim Sun‐Woo , Clark John A. , McDermid John A.
Published: January 2005

The mutation method assesses test quality by examining the ability of a test set to distinguish syntactic deviations representing specific types of faults from the program under test. This paper describes an empirical study performed to evaluate the effectiveness of object‐oriented (OO) test strategies using the mutation method. The test sets for the experimental system are generated according to three selected OO test strategies and their effectiveness is compared by determining how well the developed test sets kill injected mutants derived from an established mutation system Mothra and the authors' own OO‐specific mutation technique which is termed Class Mutation. Copyright © 2001 John Wiley & Sons, Ltd.