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Experimental Comparison (experimental + comparison)
Selected AbstractsEffect of isometric exercise and body scanning on cigarette cravings and withdrawal symptomsADDICTION, Issue 7 2009Michael Ussher ABSTRACT Aims To examine the acute effects of a guided relaxation routine (body scan) and isometric exercise on desire to smoke and tobacco withdrawal symptoms. Design Experimental comparison of three conditions. Participants Forty-eight individuals reporting smoking ,10 cigarettes daily. Intervention Random assignment to one of three interventions delivered via a 10-minute audio: isometric exercise (IE, n = 14), body scanning (BS, n = 18) or a reading about natural history (control group, n = 16). Interventions were delivered twice on the same day: in the laboratory, then in their ,normal' environment. Measurements Desire to smoke (primary outcome) and withdrawal symptoms were rated at pre-intervention and up to 30 minutes post-intervention. Findings Controlling for baseline scores, post-intervention desire to smoke and withdrawal symptoms were significantly lower for IE and BS groups, compared with the controls, in both environments. There were no significant differences for IE versus BS. For desire to smoke, controlling for baseline values, ratings in the laboratory were significantly lower for IE and BS versus the control up to 30 minutes post-intervention. In the normal environment, these ratings were significantly lower only up to 5 minutes post-intervention. Conclusions Brief IE and BS interventions are effective for reducing desire to smoke and withdrawal symptoms in temporarily abstaining smokers. These interventions were found to be more effective in the laboratory than in the smoker's normal environment, but this may be an artefact of there not being a sufficient ,wash-out' period between interventions. These techniques may be beneficial for managing desire to smoke and tobacco withdrawal. [source] Rule Quality Measures for Rule Induction Systems: Description and EvaluationCOMPUTATIONAL INTELLIGENCE, Issue 3 2001Aijun An A rule quality measure is important to a rule induction system for determining when to stop generalization or specialization. Such measures are also important to a rule-based classification procedure for resolving conflicts among rules. We describe a number of statistical and empirical rule quality formulas and present an experimental comparison of these formulas on a number of standard machine learning datasets. We also present a meta-learning method for generating a set of formula-behavior rules from the experimental results which show the relationships between a formula's performance and the characteristics of a dataset. These formula-behavior rules are combined into formula-selection rules that can be used in a rule induction system to select a rule quality formula before rule induction. We will report the experimental results showing the effects of formula-selection on the predictive performance of a rule induction system. [source] Theoretical and experimental comparison of the performance of a single-stage heat transformer operating with water/lithium bromide and water/CarrolÔINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2002W. Rivera This paper compares under the same operating conditions, the theoretical and experimental performance of a single-stage heat transformer operating with the water/lithium bromide and the water/CarrolÔ mixtures, where CarrolÔ is a mixture of lithium bromide and ethylene glycol [(CH2OH)2] in the ratio 1:4.5 by weight patented by Carrier Corp. Flow ratios, gross temperature lifts, useful heat, and coefficients of performance are plotted for the heat transformer against temperatures and solution concentrations. Because the water/CarrolÔ mixture has higher solubility than water/lithium bromide and high experimental values were obtained for the gross temperature lift, it seems to be a better alternative mixture to be used in absorption heat transformers. Copyright © 2002 John Wiley & Sons, Ltd. [source] An analytical and experimental analysis of a very fast thermal transientINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2001C. Aprea Abstract According to some international standards, some products, developed for use under heavy thermal conditions, have to be tested by subjecting them for a short time to a particular heating and cooling thermal stress to allow them an acceptable future operative life. It is possible to obtain these fast thermal gradients in confined environments, called climatic chambers where the air is heated by an electrical resistance and is cooled with a finned evaporator which is linked to a vapour compression system subjected to a particular control system of the refrigerating power. In particular, in this paper the air and object tested thermal transients are studied from an analytical and experimental point of view. The study of the mathematical model is realized assuming simplified hypotheses about the air, the object and the air cooled evaporator temperature. The most complex circumstances are related to a very fast temperature decrease because under this working condition the mathematical model is characterized by a nonlinear differential system. The nonlinear term is represented by the refrigerating power that varies in a definite range with the evaporator temperature according to a sinusoid trend. For this power a suitable analytical expression, derived by the control system performance and by the compressor characteristic, has been found. The analytical,experimental comparison during a cooling thermal stress of typical products subjected to international standard tests as the electronic boards, has been carried out showing acceptable results. The model presented is useful to foresee the climatic chamber performances in the presence of a specific refrigerating power trend; this is the start-point for the design of the vapour compression plant and its control system. Copyright © 2001 John Wiley & Sons, Ltd. [source] Fire and species range in Mediterranean landscapes: an experimental comparison of seed and seedling performance among Centaurea taxaJOURNAL OF BIOGEOGRAPHY, Issue 1 2002Miquel Riba Aim Fire is a major disturbance event in Mediterranean landscapes. In this paper, we experimentally assess the effects of fire and post-fire conditions on seed germination and establishment of twenty Centaurea taxa to test whether differences among taxa are associated with range size. Methods The taxa (species and subspecies) considered were classified as rare and widespread according to their `area of occupancy' in the Mediterranean coast of Spain and France. In a first experiment, we analyse the effects of heat-shock (particularly, room temperature, 70 and 110 °C) on percentage germination and speed of germination (T50). In a second experiment, we analyse the effects of post-fire conditions (shading and soil type: burned/unburned) on seed germination and establishment ability. Results Temperatures over 120 °C resulted in 100% mortality, while temperatures in the range of those expected to be found in the first centimetres down the soil profile during a wildfire (70,110 °C) had no effect on seed germination. Differences in germination percentage and T50 among taxa were not related to rarity. In the post-fire conditions experiment, decreased radiation (shading) increased percentage germination and T50 in most taxa, while burned soil decreased germination in some of them. The effects of post-fire conditions on seedling growth (number of leaves and leaf size) were also different among taxa, but such differences were not related to rarity. However, rarity was associated with low establishment ability, as rare taxa tended to show smaller seedling size and higher mortality rates under the whole range of conditions tested. Main conclusions The results obtained indicate that fire has a negative effect upon the survival of populations in all the taxa considered, and that rare-common differences in germination and seedling establishment are not directly related to disturbance by fire. As far as interspecific differences in range size are concerned, other factors, either alone or in combination with a low regeneration ability after fire, need to be explored further. [source] Experimental study of reactive chaotic flows in tubular reactorsAICHE JOURNAL, Issue 8 2005C. Boesinger For many reactive processes, fluid mixing has a significant effect on the rate of a chemical reaction and on the quality of the product. Mixing in a chaotic flow reactor is a promising phenomenon to control and optimize chemical processes. The effect of three-dimensional (3-D) chaotic flow advection on mixing efficiency and on chemical reaction advancement is examined. An experimental comparison is made, for low Reynolds number flows, between two tubular reactors made of successive bends, with the same number of bends (equal to 80) mounted in different configurations : a helical configuration (for regular flow) and a chaotic flow configuration with bends in perpendicular planes. We show that the mixing and the chemical reaction (for an instantaneous bimolecular chemical reaction) are more efficient in the chaotic flow reactor than in the helical reactor. The different effects of chaotic advection, molecular diffusion and reaction are discussed in view of laboratory findings. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] On the multilevel preconditioning of Crouzeix,Raviart elliptic problemsNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 5 2008J. Kraus Abstract We consider robust hierarchical splittings of finite element spaces related to non-conforming discretizations using Crouzeix,Raviart type elements. As is well known, this is the key to the construction of efficient two- and multilevel preconditioners. The main contribution of this paper is a theoretical and an experimental comparison of three such splittings. Our starting point is the standard method based on differences and aggregates (DA) as introduced in Blaheta et al. (Numer. Linear Algebra Appl. 2004; 11:309,326). On this basis we propose a more general (GDA) splitting, which can be viewed as the solution of a constraint optimization problem (based on certain symmetry assumptions). We further consider the locally optimal (ODA) splitting, which is shown to be equivalent to the first reduce (FR) method from Blaheta et al. (Numer. Linear Algebra Appl. 2004; 11:309,326). This means that both, the ODA and the FR splitting, generate the same subspaces, and thus the local constant in the strengthened Cauchy,Bunyakowski,Schwarz inequality is minimal for the FR (respectively ODA) splitting. Moreover, since the DA splitting corresponds to a particular choice in the parameter space of the GDA splitting, which itself is an element in the set of all splittings for which the ODA (or equivalently FR) splitting yields the optimum, we conclude that the chain of inequalities ,,,,,,3/4 holds independently of mesh and/or coefficient anisotropy. Apart from the theoretical considerations, the presented numerical results provide a basis for a comparison of these three approaches from a practical point of view. Copyright © 2007 John Wiley & Sons, Ltd. [source] Data clustering as an optimum-path forest problem with applications in image analysisINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2009Leonardo Marques Rocha Abstract We propose an approach for data clustering based on optimum-path forest. The samples are taken as nodes of a graph, whose arcs are defined by an adjacency relation. The nodes are weighted by their probability density values (pdf) and a connectivity function is maximized, such that each maximum of the pdf becomes root of an optimum-path tree (cluster), composed by samples "more strongly connected" to that maximum than to any other root. We discuss the advantages over other pdf-based approaches and present extensions to large datasets with results for interactive image segmentation and for fast, accurate, and automatic brain tissue classification in magnetic resonance (MR) images. We also include experimental comparisons with other clustering approaches. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 50,68, 2009. [source] Application of an adjusted ,2 statistic to site-specific data in observational dental studiesJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 1 2002Chul Ahn Abstract Background: When a binary response is observed on teeth from each subject belonging to 2 or more exposure groups, application of the usual Pearson ,2 tests is invalid, since such responses within the same subject are not independent. Consequently, special statistical methods are needed to control for the correlation among teeth (sites) within the same subject. A simple adjustment to the Pearson ,2 statistic has been proposed for comparing proportions in site-specific data. However, the required assumptions for this statistic have not yet been thoroughly addressed. These assumptions are guaranteed to hold in experimental comparisons, but may be violated in some observational studies. Method: We investigate the conditions under which the adjusted ,2 statistic is valid and examine the performance of the adjusted ,2 statistic when these conditions are violated. Results: Our simulation study shows that the adjusted ,2 statistic generally produces good empirical type I errors under the assumption of a common intracluster correlation coefficient. Even if the intracluster correlations are different, the adjusted statistic performs well when the groups have equal numbers of clusters (subjects). Conclusion: The discussion is illustrated using an observational study of caries on the roots of teeth. Zusammenfassung Hintergründe: Wenn eine binäre Antwort auf Zähne von jedem Subjekt, das zu 2 oder mehreren experimentellen Gruppen gehört, benutzt wird, ist die Anwendung des gewöhnlich genutzten Pearson ,2 Testes nicht zulässig, da solche Antworten innerhalb des selben Subjektes nicht unabhängig sind. In der Konsequent werden spezielle statistische Methoden gebraucht, um die Korrelation unter den Zähnen (Flächen) innerhalb desgleichen Subjektes zu kontrollieren. Eine simple Adjustierung zu der Pearson ,2 Statistik wurde vorgeschlagen, um die Verhältnisse der flächenspezifischen Daten zu vergleichen. Jedoch wurde sich der notwendigen Anwendung für diese Statistik noch nicht ausführlich gewidmet. Diese Anwendungen sind garantiert bei experimentellen Vergleichen anzuwenden, aber mögen in einigen beobachteten Studien verletzt werden. Methoden: Wir untersuchten die Bedingungen unter welchen der adjustierte ,2 Test richtig ist und prüften die Leistung des adjustierten ,2 Testes, wenn diese Bedingungen verletzt werden. Ergebnisse: Unsere Simulationsstudie zeigt, dass die adjustierte ,2 Statistik im Allgemeinen gute empirische Irrtümer vom Typ I erbringt unter der Anwendung eines gewöhnlichen Intracluster Korrelationskoeffizienten. Auche wenn die Intracluster-Korrelationen unterschiedlich sind, ist die adjustierte Statistik gut zu nutzen, wenn die Gruppen gleiche Nummern von Clustern haben (Subjekte). Schlußfolgerungen: Die Diskussion wird illustriert unter Nutzung einer beobachteten Studie von Wurzelkaries. Résumé Origine: Lorsqu'une réponse binaire est observée sur les dents de chaque sujet appartenant à 2 groupes ou plus, l'application du test habituel ,2 de Pearson n'est pas valable puisque de telles réponses pour le même sujet sont indépendante. En conséquence, des méthodes statistiques spéciales sont nécessaires pour contrôler les corrélation entre les dents (sites) pour le même sujet. Un simple ajustement de la statistique ,2 de Pearson a été proposée pour comparer les proportions pour les données spécifiques de sites. Cependant, les hypothèses requises pour cette statistique n'ont pas encore été consciencieusement émises. Ces hypothèses sont certifiées être valable pour les comparaisons experimentales, mais peuvent ne pas être respectées dans quelques études observationnelles. Méthode: Nous recherchons les conditions pour lesquelles la statistique ,2 ajustée est valable et examinons sa performance lorsque ces conditions ne sont pas respectées. Résultats: Notre étude simulée montre que la statistique ,2 ajustée produit généralement de bonnes érreurs empiriques de type 1 dans l'hypothèse d'un coéfficient de corrélation commun intra-groupe. Même si les corrélations intragroupes sont différentes, la statistique ,2 ajustée s'exécute bien quand les ensembles ont des nombres égaux de groupes (sujets). Conclusion: La discussion est illustrée par une étude observationnelle des caries radiculaires. [source] | ||||||||||