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Parameter Settings (parameter + setting)
Selected AbstractsMulti-variable parameter estimation to increase confidence in hydrological modellingHYDROLOGICAL PROCESSES, Issue 2 2002Sten Bergström Abstract The expanding use and increased complexity of hydrological runoff models has given rise to a concern about overparameterization and risks for compensating errors. One proposed way out is the calibration and validation against additional observations, such as snow, soil moisture, groundwater or water quality. A general problem, however, when calibrating the model against more than one variable is the strategy for parameter estimation. The most straightforward method is to calibrate the model components sequentially. Recent results show that in this way the model may be locked up in a parameter setting, which is good enough for one variable but excludes proper simulation of other variables. This is particularly the case for water quality modelling, where a small compromise in terms of runoff simulation may lead to dramatically better simulations of water quality. This calls for an integrated model calibration procedure with a criterion that integrates more aspects on model performance than just river runoff. The use of multi-variable parameter estimation and internal control of the HBV hydrological model is discussed and highlighted by two case studies. The first example is from a forested basin in northern Sweden and the second one is from an agricultural basin in the south of the country. A new calibration strategy, which is integrated rather than sequential, is proposed and tested. It is concluded that comparison of model results with more measurements than only runoff can lead to increased confidence in the physical relevance of the model, and that the new calibration strategy can be useful for further model development. Copyright © 2002 John Wiley & Sons, Ltd. [source] Governance in Global Value ChainsIDS BULLETIN, Issue 3 2001John Humphrey Summaries The concept of ,governance' is central to the global value chain approach. This article explains what it means and why it matters for development research and policy. The concept is used to refer to the inter-firm relationships and institutional mechanisms through which non-market co-ordination of activities in the chain takes place. This co-ordination is achieved through the setting and enforcement of product and process parameters to be met by actors in the chain. In global value chains in which developing country producers typically operate, buyers play an important role in setting and enforcing these parameters. They set these parameters because of the (perceived) risk of producer failure. Product and process parameters are also set by government agencies and inter-national organisations concerned with quality standards or labour and environmental standards. To the extent that external parameter setting and enforcement develop and gain credibility, the need for governance by buyers within the chain will decline. [source] IT for niche companies: is an ERP system the solution?INFORMATION SYSTEMS JOURNAL, Issue 1 2007Kai A Olsen Abstract., Niche companies are per definition idiosyncratic. They survive in a competitive world by mastering a small market niche, providing what their customers need. This often requires a flexible organization, and the ability to customize products. To be more efficient, many of these companies rely on extensive use of IT, often by installing general Enterprise Resource Planning (ERP) systems. These systems have grown from isolated systems that handle planning based on incoming orders and the component structure of the various products, to systems with ambitions to embrace the total functioning of the company including vendor and customer relation management. In this paper, we present four case studies. One company is a part of a large enterprise, but performs niche functions within this enterprise. The other three are small- or medium-sized enterprises. Each of these performs in small niche markets. Common to all is the fact that they encounter problems with the utilization of their ERP systems. The major problem seems to be that the ERP system has an inherent business model that may not conform to the needs of the company. Without a good understanding of the underlying models and the constraints under which the fundamental algorithms operate, it is difficult to use these systems correctly. Even excellent systems may give bad results if they are applied to situations where they are not suited. Further, the monolithic structure of an ERP system, with a rather complicated parameter setting, is often insufficient to mould the system to the needs of a niche company. We discuss these problems based on our four case studies, and offer alternative approaches that may be considered. [source] Performance characterization of a non-linear system as both an adaptive notch filter and a phase-locked loopINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 1 2004M. Karimi-Ghartemani Abstract The behaviour of a non-linear dynamical system is described. The system may be characterized as an adaptive notch filter, or alternatively, as a phase-locked loop. Either way, the system has the inherent capability of directly providing estimates of the parameters of the extracted sinusoidal component of its input signal, namely its amplitude, phase and frequency. The structure and mathematical properties of the system are presented for two cases of fixed-frequency and varying-frequency operation. The effects of parameter setting of the system on its performance are studied in detail using computer simulations. Transient and steady-state behaviour of the system are studied in the presence of noise. Simplicity of structure, high noise immunity and robustness and the capability of direct estimation of amplitude, phase and frequency are the salient features of the system when envisaged as an adaptive notch filter or a phase-locked loop. Copyright © 2004 John Wiley & Sons, Ltd. [source] The effect of parameter mismatches on the output waveform of an LC -VCOINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 5 2010Antonio Buonomo Abstract The effect of parameter mismatches on the output waveforms of a popular voltage-controlled oscillator is investigated, schematizing the circuit as a system of two mutually coupled oscillators, whose describing equations are derived in a perturbation form. The circuit is studied using the method of two time-scales showing the existence of synchronization phenomena leading in presence of mismatches to a locking frequency, which significantly differs from the natural frequencies of the tanks, and to an oscillation amplitude different from that of the symmetric case. We also show that in-phase and quadrature oscillations at the drain nodes can be generated with a proper parameter setting. Circuit simulations confirm the presence of a synchronized oscillation, which is consistent with the prediction of the presented analysis. Copyright © 2009 John Wiley & Sons, Ltd. [source] DRED: a random early detection algorithm for TCP/IP networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2002James Aweya Abstract It is now widely accepted that a RED [2] controlled queue certainly performs better than a drop-tail queue. But an inherent weakness of RED is that its equilibrium queue length cannot be maintained at a preset value independent of the number of TCP active connections. In addition, RED's optimal parameter setting is largely correlated with the number of connections, the round-trip time, the buffer space, etc. In light of these observations, we propose DRED, a novel algorithm which uses the basic ideas of feedback control to randomly discard packets with a load-dependent probability when a buffer in a router gets congested. Over a wide range of load levels, DRED is able to stabilize a router queue occupancy at a level independent of the number of active TCP connections. The benefits of stabilized queues in a network are high resources utilization, predictable maximum delays, more certain buffer provisioning, and traffic-load-independent network performance in terms of traffic intensity and number of connections. Copyright © 2002 John Wiley & Sons, Ltd. [source] Morphological alterations of radicular dentine pretreated with different irrigating solutions and irradiated with 980-nm diode laserMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2009Edson Alfredo Abstract Background: The topographical features of intraradicular dentine pretreated with sodium hypochlorite (NaOCl) or ethylenediamine tetraacetic acid (EDTA) followed by diode laser irradiation have not yet been determined. Purpose: To evaluate the alterations of dentine irradiated with 980-nm diode laser at different parameters after the surface treatment with NaOCl and EDTA. Study design: Roots of 60 canines were biomechanically prepared and irrigated with NaOCl or EDTA. Groups were divided according to the laser parameters: 1.5 W/CW; 1.5 W/100 Hz; 3.0 W/CW; 3.0 W/100 Hz and no irradiation (control). The roots were splited longitudinally and analyzed by scanning electron microscopy (SEM) in a quali-quatitative way. The scores were submitted to two-way Kruskal,Wallis and Dunn's tests. Results: The statistical analysis demonstrated that the specimens treated only with NaOCl or EDTA (control groups) were statistically different (P < 0.05) from the laser-irradiated specimens, regardless of the parameter setting. The specimens treated with NaOCl showed a laser-modified surface with smear layer, fissures, and no visible tubules. Those treated with EDTA and irradiated by laser presented absence of smear layer, tubules partially exposed and melting areas. Conclusions: The tested parameters of 980-nm diode laser promoted similar alterations on dentine morphology, dependent to the type of surface pretreatment. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc. [source] ON SOCIAL LEARNING AND ROBUST EVOLUTIONARY ALGORITHM DESIGN IN THE COURNOT OLIGOPOLY GAMECOMPUTATIONAL INTELLIGENCE, Issue 2 2007Floortje Alkemade Agent-based computational economics (ACE) combines elements from economics and computer science. In this article, the focus is on the relation between the evolutionary technique that is used and the economic problem that is modeled. In the field of ACE, economic simulations often derive parameter settings for the genetic algorithm directly from the values of the economic model parameters. This article compares two important approaches that are dominating in ACE and shows that the above practice may hinder the performance of the genetic algorithm and thereby hinder agent learning. More specifically, it is shown that economic model parameters and evolutionary algorithm parameters should be treated separately by comparing the two widely used approaches to social learning with respect to their convergence properties and robustness. This leads to new considerations for the methodological aspects of evolutionary algorithm design within the field of ACE. [source] Improvement of interactions among facts controlsEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2000X. Lei Interaction among the FACTS (flexible AC transmission systems) devices in a multi-machine system can adversely influence the damping properties of individual FACTS devices. In some critical cases, it may even amplify power swings or increase voltage deviations. This paper presents a global tuning method for the FACTS controllers in a multi-machine system. Based on a non-linear optimization algorithm implemented in a simulation program, the parameter settings of the FACTS controllers involved can be simultaneously optimized at transient conditions in coping with the non-linear nature of the power system. By minimizing a non-explicit target function in which swing characteristics between areas are included, interactions among the FACTS controls at transient conditions in the multi-machine system are minimized. Two multi-machine power systems equipped individually with a TCSC (thyristor-controlled series compensator) and a SVC (static Var compensator) are applied to demonstrate the efficiency of the proposed tuning procedure. The results obtained from simulations validate the improvement in damping of overall power oscillations. The simulations also show that the optimized FACTS controllers are robust in providing adequate damping for a range of conditions on the system. [source] Evaluation of a digital camera image applied to PCB inspectionHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 4 2008Bernard C. Jiang Rapid advancement and widespread digital camera applications have made it possible to replace charge-coupled device (CCD) cameras in automatic inspections for industrial applications. However, most digital camera applications using the automatic exposure mode may not be effective in some of the inspection environments. The reflection from a board surface in printed circuit board (PCB) inspections is one such problem area. The objective of this study is to develop a methodology to evaluate the effectiveness of using digital cameras for inspection. The indices used for evaluating digital camera image quality are the perceived image quality, the visual resolution, and the noise. An experiment was designed and conducted to determine the optimal camera parameter combination for attaining the best image quality. The desirability function was used to compare various digital camera parameter settings in considering three image quality indices for selecting the best camera-operating conditions. Based on the developed model and the subjective image quality index, the overall image quality improved 9.4% and 13.86%, respectively. The developed methodology can be used to: (a) determine the digital camera image quality, (b) provide an improved model for determining the automatic exposure setting for digital camera designers, and (c) adjust the digital camera parameters for automatic inspection. © 2008 Wiley Periodicals, Inc. [source] The health and economic effects of HPV DNA screening in The Netherlands,INTERNATIONAL JOURNAL OF CANCER, Issue 9 2010Johannes Berkhof Abstract We studied the health and economic effects of human papillomavirus (HPV) DNA testing in cervical screening using a simulation model. The key data source was a Dutch longitudinal screening trial. We compared cytological testing with repeat cytology (for borderline/mildly abnormal smears) to HPV testing with cytology triage (for HPV-positive smears), combination testing (combined HPV and cytology) and cytological testing with HPV triage (for borderline/mildly abnormal smears). We varied the screening interval from 5 to 10 years. The main outcome measures were the number of cervical cancer cases, the number of quality-adjusted life years (QALYs), and the incremental cost-effectiveness ratio (ICER). The base-case estimates were accompanied with ranges across 118 calibrated parameter settings (calibration criteria: cervical intraepithelial neoplasia 2/3, cancer and mortality rates). In comparison to 5-yearly cytology, 5-yearly HPV testing with cytology triage gave a reduction in the number of cancer cases of 23% (range, 9,27%). The reduction was 26% (range, 10,29%) for combination testing and 3% (range, ,1 to 8%) for cytology with HPV triage. For strategies with primary HPV testing, the model also estimated a reduction in cancer cases when the screening interval was extended to 7.5 years. Five-yearly cytology with HPV triage and 5 to 7.5-yearly HPV testing with cytology triage were cost effective for the base-case settings and the majority of calibrated parameter settings (ICER below Dutch willingness-to-pay threshold of ,20,000/QALY). Our model indicates that HPV testing with cytology triage is likely to be cost effective. An extension of the screening interval may be considered to control costs. [source] Timing of Depolarization and Contraction in the Paced Canine Left Ventricle:JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2003Experiment, Model Introduction: For efficient pump function, contraction of the heart should be as synchronous as possible. Ventricular pacing induces asynchrony of depolarization and contraction. The degree of asynchrony depends on the position of the pacing electrode. The aim of this study was to extend an existing numerical model of electromechanics in the left ventricle (LV) to the application of ventricular pacing. With the model, the relation between pacing site and patterns of depolarization and contraction was investigated. Methods and Results: The LV was approximated by a thick-walled ellipsoid with a realistic myofiber orientation. Propagation of the depolarization wave was described by the eikonal-diffusion equation, in which five parameters play a role: myocardial and subendocardial velocity of wave propagation along the myofiber cm and ce; myocardial and subendocardial anisotropy am and ae; and parameter k, describing the influence of wave curvature on wave velocity. Parameters cm, ae, and k were taken from literature. Parameters am and ce were estimated by fitting the model to experimental data, obtained by pacing the canine left ventricular free wall (LVFW). The best fit was found with cm= 0.75 m/s, ce= 1.3 m/s, am= 2.5, ae= 1.5, and k= 2.1 × 10,4 m2/s. With these parameter settings, for right ventricular apex (RVA) pacing, the depolarization times were realistically simulated as also shown by the wavefronts and the time needed to activate the LVFW. The moment of depolarization was used to initiate myofiber contraction in a model of LV mechanics. For both pacing situations, mid-wall circumferential strains and onset of myofiber shortening were obtained. Conclusion: With a relatively simple model setup, simulated depolarization timing patterns agreed with measurements for pacing at the LVFW and RVA in an LV. Myocardial cross-fiber wave velocity is estimated to be 0.40 times the velocity along the myofiber direction (0.75 m/s). Subendocardial wave velocity is about 1.7 times faster than in the rest of the myocardium, but about 3 times slower than as found in Purkinje fibers. Furthermore, model and experiment agreed in the following respects. (1) Ventricular pacing decreased both systolic pressure and ejection fraction relative to natural sinus rhythm. (2) In early depolarized regions, early shortening was observed in the isovolumic contraction phase; in late depolarized regions, myofibers were stretched in this phase. Maps showing timing of onset of shortening were similar to previously measured maps in which wave velocity of contraction appeared similar to that of depolarization. (J Cardiovasc Electrophysiol, Vol. 14, pp. S188-S195, October 2003, Suppl.) [source] Rapid evolution of social learningJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 9 2009M. FRANZ Abstract Culture is widely thought to be beneficial when social learning is less costly than individual learning and thus may explain the enormous ecological success of humans. Rogers (1988. Does biology constrain culture. Am. Anthropol. 90: 819,831) contradicted this common view by showing that the evolution of social learning does not necessarily increase the net benefits of learned behaviours in a variable environment. Using simulation experiments, we re-analysed extensions of Rogers' model after relaxing the assumption that genetic evolution is much slower than cultural evolution. Our results show that this assumption is crucial for Rogers' finding. For many parameter settings, genetic and cultural evolution occur on the same time scale, and feedback effects between genetic and cultural dynamics increase the net benefits. Thus, by avoiding the costs of individual learning, social learning can increase ecological success. Furthermore, we found that rapid evolution can limit the evolution of complex social learning strategies, which have been proposed to be widespread in animals. [source] Product Yield and Gaping in Cold-smoked Atlantic Salmon (Salmo salar) Fillets as Influenced by Different Injection-salting TechniquesJOURNAL OF FOOD SCIENCE, Issue 5 2003S. Birkeland ABSTRACT Product yield and fillet gaping severity were determined in cold-smoked Atlantic salmon fillets subjected to injection-salting. Effects of process parameter settings (brine injection pressure, number of repeated injections, needle speed, injection of brine in 1 or 2 directions, and chilled fillet resting before smoking) were tested. Repeated injections increased the yield up to 5.3% (wt/wt). Increasing injection pressure significantly increased the severity of fillet gaping in smoked fillets by 18%. Brine injection directions or needle speed did not affect smoking yield. The stability of the injection system was high. The results show that choice of process parameter settings during injection-salting affects product yield after smoking. [source] Phylogenetic signal and the utility of 12S and 16S mtDNA in frog phylogenyJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 1 2004S. Hertwig Abstract Genes selected for a phylogenetic study need to contain conserved information that reflects the phylogenetic history at the specific taxonomic level of interest. Mitochondrial ribosomal genes have been used for a wide range of phylogenetic questions in general and in anuran systematics in particular. We checked the plausibility of phylogenetic reconstructions in anurans that were built from commonly used 12S and 16S rRNA gene sequences. For up to 27 species arranged in taxon sets of graded inclusiveness, we inferred phylogenetic hypotheses based on different a priori decisions, i.e. choice of alignment method and alignment parameters, including/excluding variable sites, choice of reconstruction algorithm and models of evolution. Alignment methods and parameters, as well as taxon sampling all had notable effects on the results leading to a large number of conflicting topologies. Very few nodes were supported in all of the analyses. Data sets in which fast evolving and ambiguously aligned sites had been excluded performed worse than the complete data sets. There was moderate support for the monophyly of the Discoglossidae, Pelobatoidea, Pelobatidae and Pipidae. The clade Neobatrachia was robustly supported and the intrageneric relationships within Bombina and Discoglossus were well resolved indicating the usefulness of the genes for relatively recent phylogenetic events. Although 12S and 16S rRNA genes seem to carry some phylogenetic signal of deep (Mesozoic) splitting events the signal was not strong enough to resolve consistently the inter-relationships of major clades within the Anura under varied methods and parameter settings. Zusammenfassung Zur Anwendung in einer phylogenetische Analyse müssen die ausgewählten Gene konservierte und detektierbare Information zum untersuchten phylogenetischen Niveau enthalten. Ribosomale Gene des Mitochondriums wurden für ein breites Spektrum phylogenetischer Fragestellungen bei verschiedenen Gruppen und insbesondere bei Froschlurchen eingesetzt. Wir untersuchten die Frage, ob Rekonstruktionen der Anuren-Phylogenie, basierend auf 12S und 16S rRNA Gensequenzen, plausibel sind. An einer Auswahl von 27 Arten, arrangiert in Taxa-Gruppen abgestufter Hierarchie, rekonstruierten wir phylogenetische Hypothesen unter verschiedenen, a priori festgelegten Bedingungen. Dazu gehörten die Auswahl verschiedener Alinierungsmethoden und,parameter, der Umgang mit variabel alinierten Positionen, die Auswahl der Algorithmen zur Baumkonstruktion sowie die Auswahl alternativer Modelle der Sequenzevolution. Die Methoden und Parameter der Alinierung und der Rekonstruktion, sowie die Auswahl der Taxa, hatten bedeutenden Einfluss auf die Resultate. Daraus resultierte eine große Anzahl alternativer Topologien, in denen nur sehr wenige Knoten in allen Analysen Unterstützung fanden. Ausschluss variabel alinierter Positionen ergaben Topologien mit niedrigem Grad der Auflösung. Die Sequenzen enthielten ein gewisses Signal für die Monophylie von Discoglossidae, Pelobatoidea, Pelobatidae und Pipidae. Der Knoten Neobatrachia wurde deutlich unterstützt. Die robuste Auflösung intragenerischer Phylogenien von Bombina und Discoglossus weisen auf eine besondere Eignung der Gene für die Untersuchung junger Aufspaltungsereignisse hin. Obwohl 12S und 16S rRNA-Gene eine heterogene Unterstützung für wenige frühe (mesozoische) phylogenetische Ereignisse zeigten, war das Signal nicht geeignet, um die Beziehungen der Taxa höherer Ordnung der Anura unter variierten Parametern und Analysemethoden konsistent aufzulösen. [source] Introduction to the programming of deep brain stimulatorsMOVEMENT DISORDERS, Issue S3 2002Jens Volkmann MD Abstract The clinical success of deep brain stimulation (DBS) for treating Parkinson's disease, tremor, or dystonia critically depends on the quality of postoperative neurologic management. Movement disorder specialists becoming involved with this therapy need to acquire new skills to optimally adapt stimulation parameters and medication after implantation of a DBS system. In clinical practice, the infinite number of possible parameter settings in DBS can be reduced to few relevant combinations. In this article, the authors describe a general scheme of selecting stimulation parameters in DBS and provide clinical and neurophysiological arguments for such a standardized algorithm. They also describe noninvasive technical trouble shooting by using programming features of the commercially available neurostimulation devices. © 2002 Movement Disorder Society [source] Outbound supply chain network design with mode selection and lead time considerationsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 3 2007Erdem Eskigun Abstract We present a large-scale network design model for the outbound supply chain of an automotive company that considers transportation mode selection (road vs. rail) and explicitly models the relationship between lead times and the volume of flow through the nodes of the network. We formulate the problem as a nonlinear zero-one integer program, reformulate it to obtain a linear integer model, and develop a Lagrangian heuristic for its solution that gives near-optimal results in reasonable time. We also present scenario analyses that examine the behavior of the supply chain under different parameter settings and the performance of the solution procedures under different experimental conditions. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2007 [source] EWMA techniques for computer intrusion detection through anomalous changes in event intensityQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 6 2002Nong Ye Abstract Intrusion detection is used to monitor and capture intrusions into computer and network systems, which attempt to compromise the security of computer and network systems. To protect information systems from intrusions and thus assure the reliability and quality of service of information systems, it is highly desirable to develop techniques that detect intrusions into information systems. Many intrusions manifest in dramatic changes in the intensity of events occurring in information systems. Because of the ability of exponentially weighted moving average (EWMA) control charts to monitor the rate of occurrences of events based on the their intensity, we apply three EWMA statistics to detect anomalous changes in the events intensity for intrusion detections. They include the EWMA chart for autocorrelated data, the EWMA chart for uncorrelated data and the EWMA chart for monitoring the process standard deviation. The objectives of this paper are to provide design procedures for realizing these control charts and investigate their performance using different parameter settings based on one large dataset. The early detection capability of these EWMA techniques is also examined to provide the guidance about the design capacity of information systems. Copyright © 2002 John Wiley & Sons, Ltd. [source] Analysis of estrogenic contaminants in river water using liquid chromatography coupled to ion trap based mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2002Tom Benijts A precise and reliable method, using liquid chromatography combined with ion trap based mass spectrometry, for the determination of three endogenous estrogens, namely, estrone, estradiol, and estriol, and two synthetic estrogens, ethinyl estradiol and diethylstilbestrol, in environmental water samples was developed. Optimization of the parameter settings of the ion source and mass analyzer as well as evaluation of solvent composition were carried out by continuous introduction of standards through a syringe pump. In negative ion mode the electrospray ionization source gave acceptable results. The optimum solvent used consisted of water/acetonitrile, with no volatile bases or buffers added. A simple, off-line, manual solid-phase extraction method was developed for sample preparation of environmental water samples. Recoveries were over 86% for all compounds. The method was validated and found to be linear, selective, and robust. For analysis of a 50-mL sample, the limit of detection (LOD) ranged from 3.2 to 10.6,ng/L for all compounds, and the limit of quantitation (LOQ) from 10.6 to 35.0,ng/L. Within-day (n,=,5) and total (n,=,5) reproducibility were investigated at three different concentration levels and ranged from 6.2 to 9.5% and 9.4 to 12.1%, respectively. Finally, the method was applied to real-world samples. Copyright © 2002 John Wiley & Sons, Ltd. [source] Phylogeny of Nerillidae (Polychaeta, Annelida) as inferred from combined 18S rDNA and morphological dataCLADISTICS, Issue 2 2005Katrine Worsaae A phylogeny of the meiofaunal polychaete family Nerillidae based on morphological, molecular and combined data is presented here. The data sets comprise nearly complete sequences of 18S rDNA and 40 morphological characters of 17 taxa. Sequences were analyzed simultaneously with the morphological data by direct optimization in the program POY, with a variety of parameter sets (costs of gaps: transversions: transitions). Three outgroups were selected from the major polychaete group Aciculata and one from Scolecida. The 13 nerillid species from 11 genera were monophyletic in all analyses with very high support, and three new apomorphies for Nerillidae are identified. The topology of the ingroup varied according to the various parameter settings. Reducing the number of outgroups to one decreased the variance among the phylogenetic hypotheses. The congruence among these was tested and a parameter set, with equal weights (222) and extension gap weighted 1, yielded minimum incongruence (ILD). Several terminal clades of the combined analysis were highly supported, as well as the position of Leptonerilla prospera as sister terminal to the other nerillids. The evolution of morphological characters such as segment numbers, chaetae, appendages and ciliation are traced and discussed. A regressive pathway within Nerillidae is indicated for several characters, however, generally implying several convergent losses. Numerous genera are shown to require revision. © The Willi Hennig Society 2005. [source] | |||||||||||||||||||||||||