Weighted-average Model Research Articles

Modeling the Continuum and Line Spectra of the Seyfert 2 Galaxy NGC 5252

The S0 galaxy NGC 5252 is one of the best examples of the anisotropic radiation theories believed to govern the physics of active galactic nuclei. Considerable amounts of observational data, from the radio to the hard X-ray domain, have been accumulated from the central nuclear region of this galaxy. This work makes use of all the available observational information in an attempt to model in a self-consistent manner the continuum and line emission spectra of the nuclear region and the extended emission-line region. It is suggested that both the nuclear continuum and the nuclear line emission originate in gaseous clouds that are exposed to the nuclear ionizing radiation and subjected to shocks. The best fit to the data in the nuclear region is obtained with a weighted-average model that includes radiation-dominated clouds with low velocities (100 km s-1), producing most of the emission lines and the low-frequency continuum, and high-velocity (~400 km s-1) shock-dominated clouds, where the soft X-ray continuum originates. The far-infrared emission is due to dust heated by both the nuclear radiation and shocks. Modeling of the extended emission-line region was performed on the basis of the derived nuclear model. That region was found to be characterized by densities of a few cm-3 and a cloud size of about 100 pc. Excitation via shocks is found negligible, whereas photoionization by the central power source widely accounts for the observed line spectrum.

Distribution of diatoms among intermittent ponds on the Atlantic Coastal Plain: development of a model to preduct drought periodicity from surface-sediment assemblages

Inferences of past climate from the fossil record in lakes rely on the accurate quantification of a relationship of fossilizing organisms to their environment. Whereas the relationship of diatoms to water chemistry parameters has been modeled in many systems, few studies adequately address the relationship of diatoms to physical properties, such as water depth or hydrology, that may be more directly tied to climate. We examined the composition of modern diatoms in surface sediments of 75 isolated ponds (mostly Carolina bays) of the Atlantic Coastal Plain to: (1) assess the influence of physical and chemical variables on the distribution of diatoms among ponds of the region, and (2) develop a model that predicts hydroperiod (a measure of pond permanence) from diatom assemblages. We constructed two hydroperiod calibration models: the first infers hydroperiod from the weighted-average optima and tolerances of taxa along the hydroperiod gradient, the second bases inferences on the hydroperiod estimates of compositionally similar samples. Both approaches incorporate a-priori and post-hoc tests of assumptions often inherent in the construction of transfer functions. Diatom assemblage composition had strong, approximately linear relationships to hydroperiod, water depth, and calcium concentration in non-metric multidimensional ordination space; effects of other variables, including pH, were non-linear or ambiguous. Overall, the assemblages reflected the dilute, acidic chemical characteristics of bays. The assemblages contained differing abundances of euterrestrial, benthic and planktonic taxa, depending on a pond's susceptibility to drying. A weighted-averaging regression model based on taxon-specific hydroperiod optima generated adequate, unbiased hydroperiod inferences from diatom species composition (r2 = 0.81). This model may be used to infer past drought episodes from fossil diatom assemblages at appropriate sites on the Atlantic Coastal Plain.

A weighted-averaging regression and calibration model for inferring lakewater salinity from fossil diatom assemblages in saline lakes of the Vestfold Hills: a new tool for interpreting Holocene lake histories in Antarctica

The relationship between surface sediment diatom assemblages and measured limnological variables in thirty-three coastal Antarctic lakes from the Vestfold Hills was examined by constructing a diatom-water chemistry dataset. Previous analysis of this dataset by canonical correspondence analysis revealed that salinity accounted for a significant amount of the variation in the distribution of the diatom assemblages. Weighted-averaging regression and calibration of this diatom-salinity relationship was used to establish a transfer function for the reconstruction of past lakewater salinity from fossil diatom assemblages. Weighted-averaging regression and calibration with classical deshrinking provided the best model for salinity reconstructions and this was applied to the fossil diatom assemblages from one of the saline lakes in the Vestfold Hills in order to assess its potential for palaeosalinity and palaeoclimate reconstruction.

Macroinvertebrate-inferred stream-water acidity in north eastern finland along a sulphur deposition gradient

Recently developed weighted averaging (WA) models and widely used tolerance-limit approaches for inferring stream minimum pH from macroinvertebrates were tested in northeastern Finnish Lapland. Surface waters there are threatened by large sulphur emissions in the Russian Kola Peninsula. The modelled sulphur deposition increases from west to east approximately parallel to longitude. The effect of deposition on stream minimum pH was assessed by relating the macroinvertebrate-inferred stream minimum pH to longitude. In a test set of 17 streams, the minimum pH inferred from pooled invertebrate samples of three seasons by WA models showed a strong correlation (r = 0.67–0.72) with the minimum pH (range 6.3–7.1) observed during the spring snow-melt period. The relationship was slightly weaker (r = 0.59–0.69) using autumn samples only. The tolerance-limit approaches assigned the streams into the correct acidity class, but the inferred pH was not related to the observed minimum pH. This further demonstrates the superiority of the WA approach, especially in detecting early signs of acidification. The minimum pH inferred by WA from autumn assemblages of 37 streams along the deposition gradient showed a significant negative correlation with longitude, suggesting that the emissions from the Kola region contribute to low pH events in streams of northeastern Finnish Lapland. The results demonstrate the potential of bioassessment and monitoring using invertebrates in detecting impacts and changes that could remain unnoticed by conventional water quality-analyses.

Comparison of diatoms, fossil pigments and historical records as measures of lake eutrophication

1. Analysis of fossil diatoms and pigments was used to examine the effects of land‐management practises on the trophic status of Williams Lake, a eutrophic lake in central British Columbia, Canada. Published weighted‐average (WA) models were used to infer changes in total phosphorus concentration (TP) during the past 200 years.2. Diatom‐inferred TP (DI‐TP) was compared to 20 years of direct chemical TP measurements to determine the accuracy of diatom‐TP models in inferring mean summer TP in Williams Lake. Plant pigments were measured using high performance liquid chromatography (HPLC) to quantify historical changes in gross algal community composition and abundance and to evaluate further diatom‐TP inferences.3. Palaeolimnological analyses showed that Williams Lake has been productive throughout the last 200 years. Diatoms characteristic of alkaline, eutrophic conditions were continuously present c. 1765–1990 AD. Carotenoids from filamentous cyanobacteria (myxoxanthophyll, aphanizophyll) were regularly present in Williams Lake sediments, although cryptophytes (alloxanthin), diatoms (diatoxanthin), chlorophytes (lutein‐zeaxanthin, b‐phorbins), and siliceous algae (diatoms, chrysophytes) or dinoflagellates (fucoxanthin) were also important components of past algal communities. Terrestrial disturbance (railway and road constructions, cattle ranching) increased lake production, but resulted in relatively little permanent environmental change.4. Comparison of DI‐TP with measured TP (1972–91) showed that inferences from simple WA models were similar to average summer TP (39.1 vs. 35.2 μg TP l–1). Inferences resulting from data manipulations that down‐weighted eutrophic lakes (outlier elimination, bootstrapping) or diatom species (square‐root transformation, tolerance‐weighting) were weakly and negatively correlated with measured TP, introduced bias into inference models, or underestimated measured TP. These patterns suggest that, when using diatom‐TP models developed from sparsely populated regions, accurate palaeoecological inferences for TP in eutrophic lakes should avoid data manipulations which down‐weight the most productive sites and taxa.5. Comparison of DI‐TP and fossil‐inferred algal abundance during the past 200 years suggested that changes in nutrient inputs accounted for relatively little variation in past algal abundance. Although past changes in total algal biomass (as β‐carotene) and DI‐TP were broadly similar, the two variables were not significantly correlated (α = 0.05). In contrast, changes in DI‐TP were significantly correlated with mean concentrations of diatom‐specific carotenoids (diatoxanthin), although the explanatory power was low (r2 = 0.16). These patterns suggest that the DI‐TP model reflects more closely environmental conditions in Williams Lake during periods of diatom growth, and not necessarily those when total algal biomass is greatest.

Numerical evaluation of isostrain and weighted-average models for elastic moduli of three-dimensional composites

The isostrain model is being widely used for predicting the elastic properties of three-dimensional composites, i.e. composites in which the reinforcement extends in the general three-dimensional space. Recently, it has been suggested that a weighted average of the isostrain and isostress model predictions yields better results, when compared to the predictions of the isostrain model alone. Critical evaluation of these models through experiments alone is expensive and time consuming owing to the large number of material and geometric variables involved in these models. We have conducted a numerical study to evaluate the accuracies of these simplistic analytical models. A finite element model, based on the commonly used representative volume element of the three-dimensionally braided composite, was developed for this purpose. The variables considered in this study included the type of loading, the braid angle, the fiber volume fraction, and the yarn elastic properties. The study revealed that a suitable weighted average of the isostrain and isostress model predictions is in better agreement with the corresponding finite element model predictions for the elastic moduli of 3-D braided composites. Furthermore, the weighting factor was observed to be fairly insensitive to braid angles, yarn volume fraction, and the type of loading, but strongly influenced by the non-axial elastic properties of the yarn.

Inferring the minimum pH of streams from macroinvertebrates using weighted averaging regression and calibration

1. Data on macroinvertebrates and stream chemistry were collected from sixty‐four streams in Finland. Weighted averaging (WA) regression and calibration models were constructed to infer the minimum pH of streams from their invertebrate assemblages. The purpose was to develop an instrument for biological assessment and monitoring of stream acidification. The WA method was compared with simpler approaches, based on qualitative invertebrate data and pH tolerance limits, that are widely used.2. Performance of the two approaches was assessed in terms of correlation between the inferred and observed minimum pH within the ‘training set’, and in terms of root mean squared differences (predicted – observed) (RMSEP) estimated by cross‐validation or bootstrap resampling techniques. The models were further tested using independent data from the literature representative of a wide geographical range.3. The predictive power of the WA models was reasonable (RMSEP 0.40–0.44 pH units) in the training set and consistently better than that of the tolerance limit method. In contrast to the latter, the WA models were able to infer a minimum pH above 5.5, suggesting they could detect the early stages of acidification.4. The WA models performed better than the tolerance limit method in inferring pH from the independent literature, further demonstrating the superiority and generality of the WA approach.5. The weighted averaging technique could be an effective and widely applicable tool for contemporary biological monitoring and assessment using aquatic invertebrates.

Paleolimnological assessment of long-term water-quality changes in south-central Ontario lakes affected by cottage development and acidification

Sediment diatom assemblages were used to evaluate water-quality changes since preindustrial times in south-central Ontario lakes receiving acidic deposition and moderate shoreline (mainly cottage) development. Canonical correspondence analysis identified significant relationships between surface sediment diatoms and environmental factors. Relationships were sufficiently strong to develop weighted-averaging regression-calibration models for inferring lake water pH and total phosphorus concentration ((TP)) from diatoms. These models were accurate to within ±0.21 pH units and ±4.2 µg TP·L -1 . Postindustrial pH and (TP) changes were inferred from surface and pre-1850 sediment diatom assemblages. Results suggest that presently acid lakes (pH 7) has increased, as observed in other regions receiving elevated acidic deposition. Diatom-inferred (TP) suggests that cultural eutrophication has not been widespread. In almost all lakes, present-day (TP) is not higher than before European settlement. In many mesotrophic lakes, preindustrial (TP) was higher than at present. Several factors could account for declining lake water (TP), including (i) lake and (or) watershed acidification processes that reduce P loading, or increase P loss rates; and (ii) reductions in nutrient loading from watersheds as a result of reforestation. Resume : Nous nous sommes servis des assemblages de diatomees dans les sediments pour evaluer les changements de la qualite de l'eau, depuis la periode preindustrielle, dans des lacs du centre-sud de l'Ontario qui ont connu des depots acides et un developpement du littoral modere (principalement construction de chalets). L'analyse de correspondance canonique a releve des relations significatives entre la presence des diatomees dans les sediments superficiels et les facteurs environnementaux. Les relations etaient suffisamment fortes pour que nous elaborions des modeles de regression-calibration a moyenne ponderee permettant de calculer le pH de l'eau du lac et la concentration de phosphore total ((PT)) a partir des diatomees. Ces modeles etaient exacts jusqu'a ±0,21 unite de pH et ±4,2 µg PT·L -1 . Nous avons

An expanded weighted-averaging model for inferring past total phosphorus concentrations from diatom assemblages in eutrophic British Columbia (Canada) lakes

Eighteen lakes were added to a published training set of 46 British Columbia (BC) lakes in order to expand the original range of total phosphorus (TP) concentrations. Canonical correspondence analysis (CCA) was used to analyze the relationship between diatom assemblages and environmental variables. Specific conductivity and [TP] each explained significant (P≤0.05) directions of variance in the distribution of the diatoms. The relationship between diatom assemblages and [TP] was sufficiently strong to warrant the development of a weighted-averaging (WA) regression and calibration model that can be used to infer past trophic status from fossil diatom assemblages. The relationship between observed and inferred [TP] was not improved by the addition of more eutrophic lakes, however the [TP] range and the number of taxa used in the transfer function are now superior to the original model. Diatom species assemblages changed very little in lakes with TP concentrations greater than 85 µg 1−1, so we document the development of a model containing lakes with TP≤85 µg 1−1. The updated model uses 59 training lakes and covers a range of species optima from 6 to 41.9 µg 1−1 TP, and a total of 150 diatom taxa. The updated inference model provided a more realistic reconstruction of the anthropogenic history of a highly eutrophic BC lake. The model can now be used to infer past nutrient conditions in other BC lakes in order to assess changes in trophic status.

A weighted-averaging regression and calibration model for inferring lakewater salinity using chrysophycean stomatocysts from lakes in western Canada

Chrysophycean stomatocysts were identified and enumerated from the surface sediments of 60 lakes located on the Interior Plateau of British Columbia. The lakes span a salinity gradient from freshwater to hypersaline (0.0–92.4 g L−1), with the majority being fresh to hyposaline. One hundred and ten stomatocyst morphotypes, almost all of which were previously described, were identified from the lake sediments. The first axis of direct gradient analysis, which was highly significant, was essentially a salinity axis (i.e. [Ca], [Mg], [K], [Na], [SO4], [DIC], and [Cl]). Most cysts were found to have fairly broad tolerances, with the narrowest tolerances occurring among morphotypes with the lowest salinity optima. Weighted-averaging regression and calibration techniques were used to develop an inference model to measure the relationship between measured average lakewater salinity and stomatocyst inferred salinity (apparent r2=0.80). Simple weighted-averaging produced a model with a lower bootstrapped RMSE of prediction than weighted-averaging with tolerance downweighting. These data indicate that chrysophyte stomatocysts are useful quantitative indicators of past lakewater salinity (in the freshwater to hyposaline range) in B.C. lakes, and can be used to strengthen the interpretations from diatom-inference models already developed from the same region.

Importance Ratings and Specific Components of Physical Self-Concept: Relevance to Predicting Global Components of Self-Concept and Exercise

Fox (1990) proposed a personalized hierarchical model of physical self-concept that integrated self-concept and perceived importance ratings, and he developed instruments to measure these constructs. Alternative approaches based on his instruments are evaluated with data from Sonstroem, Harlow, and Josephs’ (1994) study of 216 adult female aerobic dancers and their exercise activity. Consistent with previous research, there was little support for importance weighted-average or importance discrepancy models in the prediciton of self-esteem, general physical self-concept, or exercise behavior. However, condition self-concept was more positively related to exercise than other components of physical self-concept, and importance ratings of specific components of physical self-concept were positively related to exercise. These results support the construct validity of multidimensional physical self-concept responses, the value of specific domains of self-concept most relevant to a particular application rather than global measures of self, and the usefulness of importance ratings for predicting exercise activity.

Using the past to predict the future: lake sediments and the modelling of limnological disturbance

Most lakes have been disturbed to varying degrees but for an individual lake the timescale of these disturbances is rarely known. Lake sediments, however, can be used as natural archives of perturbation histories, e.g. acidification and eutrophication. At present the use of simple weighted averaging models permits the reconstruction of a variety of water chemical variables from diatom and other microfossils preserved in lake sediments (pH, total phosphorus, salinity and lakewater temperature). Sediment records can, therefore, provide lake-specific background data for lake management as well as information about their ecological histories. The common models used in palaeolimnology (dating, transfer-functions) are reviewed and their role in environmental monitoring discussed. Predictions of future lake water quality following lake restoration methods tend to be made from dynamic mathematical models, but they are also used for hindcasting (e.g. the MAGIC model of catchment acidification). A problem with using dynamic models is that they are often site-specific and require calibration for a given lake. Combined with reliable dating, chemical reconstructions from microfossil-based transfer functions offer the possibility of testing hindcast predictions derived from dynamic mathematical models, e.g. for salinity, TP and pH. In this way, sediment microfossil-based models can assist with the parameterization of more complex, dynamic models of contemporary processes. In this review, comparisons between the two approaches (sediment-based and dynamic models) are given and possible future interactions outlined. Validation of mathematical models by palaeolimnological data might enhance their predictive ability when used for forecasting lake recovery. There is clearly, however, a need for a more rigorous approach to palaeolimnology, i.e. critical hypothesis generation. Multidisciplinary studies of lake disturbance, that combine palaeolimnology, dynamic modelling and contemporary process studies, would also be beneficial.

A Jamesian model of self-investment and self-esteem: Comment on Pelham (1995).

B. W. Pelham (1995) proposed new perspectives for a weighted-average model of esteem based on W. James (1890) and responded to my (H. W. Marsh, 1993b) critique of B. W. Pelham and W. B. Swann (1989). In this Jamesian perspective, the effect of a specific self-view on global esteem is moderated by the importance an individual places on the self-view. For example, if one judges musical skills to be unimportant, then one's self-evaluation of musical skill should have little effect on one's self-esteem. The intuitive appeal of this Jamesian perspective is so compelling that it has been widely accepted for over 100 years despite a dearth of supportive research. B. W. Pelham and I seem to agree that support is weaker than previously assumed and limited primarily to specific traits and, perhaps, specific subgroups of individuals. This continuing dialogue offers new theoretical insights and methodological advances for this central issue in self-concept research.

A weighted—averaging regression and calibration model for inferring total phosphorus concentration from diatoms in British Columbia (Canada) lakes

SUMMARY1. The relationship between surficial sediment diatom taxa (Bacillariophyceae) and measured limnological variables in forty‐six British Columbia lakes was explored using canonical correspondence analysis (CCA). Lake‐water total phosphorus concentration (TP), maximum lake depth, conductivity, and calcium concentration each accounted for independent and statistically significant directions of variation in the distribution of diatom taxa.2. Weighted‐averaging (WA) models were developed to infer lake‐water TP from the relative abundances of 131 diatom taxa in the surficial sediments of thirty‐seven lakes. WA regression and calibration with classical deshrinking provided the best model for TP reconstructions.3. Our quantitative inference model has two major advantages over existing multiple linear‐regression models: (i) inferences are based on the responses of individual taxa to TP, and do not involve grouping the taxa into a small number of ecological categories; and (ii) the model assumes that diatoms respond to TP in a unimodal, rather than a linear, fashion.4. The WA model can now be used to infer past lake‐water TP, within the range 5–28νgr1−1, from diatoms preserved in the sediments of British Columbia lakes. The model can provide quantitative estimates of the onset, rate, and magnitude of lake eutrophication in response to natural processes and human disturbances.

A weighted-average model of achromatic transparency

A model of achromatic transparency based on the idea that neural representations of transparency are activated by proximal contours is described. It is proposed that the weighted average of the magnitudes of the representations of transparency relative to a perceived continuous transparent surface corresponds to the judgement of the overall degree of transparency of the same surface. Tests of this weighted-average model were carried out with bistable patterns formed by two overlapping surfaces that appeared opaque where they were superimposed on the background and transparent where they were superimposed on each other (partial transparency). In agreement with predictions from the weighted-average model, the rated degrees of transparency of these two surfaces were noncomplementary and independent of background reflectance. Two experiments confirmed the contention of this model that the relevant proximal contours for the judgement of partial transparency of the two overlapping transparent surfaces in a bistable pattern correspond to the part where these surfaces are superimposed.

A general model of consensus and accuracy in interpersonal perception.

Consensus refers to the extent to which 2 judges agree in their ratings of a common target. A general model of interpersonal perception based on Anderson's (1981) weighted-average model is developed. The model shows that increased acquaintance does not always lead to large changes in consensus. Degree of overlap between the target behaviors observed by the judges and similarity of meaning systems are key but neglected parameters. The model can also be used as a basis for determining the accuracy of person perception. In some cases, accuracy can increase with greater acquaintance, whereas consensus may not.

Personal and Indoor/Outdoor Nitrogen Dioxide Exposure Assessments of 23 Homes in Taiwan

Indoor and outdoor nitrogen dioxide (NO2) concentrations of 23 homes from two areas in Taiwan, the city of Taipei and a rural village in central Taiwan, were measured concurrently from December 1987 to January 1988. NO2 measurements were carried out by Palmes tube for one week and filter badges for two days. In Taipei, the mean NO2 concentrations outdoors, in the kitchens, in the livingrooms, and in the bedrooms were 40.1 ppb, 34.4 ppb, 32.1 ppb, and 29.7 ppb for one week, and were 25.7 ppb, 25.6 ppb, 22.6 ppb, and 20.5 ppb for two days. In the village of central Taiwan, the corresponding concentrations were 23.5 ppb, 24.5 ppb, 20.4 ppb, and 17.5 ppb for one week, and 20.3 ppb, 24.7 ppb, 18.8 ppb, and 15.4 ppb for two days. The NO2 concentrations of all microenvironments in Taipei were significantly higher than those in the village of central Taiwan. The outdoor NO2 concentrations were significantly higher than the indoor NO2 concentrations in Taipei. The NO2 measurements in the kitchens were higher than all other measurements indoors and outdoors in the village of central Taiwan. The houses which used natural gas as cooking fuel had slightly higher indoor NO2 concentrations than the houses which used LPG as cooking fuel in Taipei city. Cement houses had slightly higher indoor NO2 concentrations than brick houses. The mean of housewives' exposures was 30.8 ppb in Taipei and 19.9 ppb in the village of central Taiwan. The explanation power of the housewife's exposure to NO2 was 72% by the time weighted-average model and 70% by the simple linear regression model.

The Impact of Evaluative Disposition and Subsequent Information on Clinical Impressions

This experiment assessed the effects of clinicians' initial “evaluative dispositions,” defined as the general tendency to see a patient either positively or negatively, and subsequent information about a patient's progress in therapy on clinical impressions. Clinical trainees (n = 48) reported their first impressions of a videotaped patient and were divided equally into those who expressed positive or negative dispositions. Subjects were then randomly assigned to the experimental conditions, Where they received one of the following sets of subsequent information about the patient: patient improved, patient no change, patient deteriorated. Repeated-measures analysis of variance (ANOVA) showed a main effect for initial evaluative disposition. An interaction between subsequent information and impression change indicated that final impressions differed from first impressions as a function of subsequent information. The results are discussed in terms of a weighted-average model of clinical impressions, where initial evaluative dispositions and subsequent information carry equal weight. Research is needed to determine factors that contribute to initial evaluative dispositions and also to delineate the conditions under which such dispositions are given more or less weight in the process of clinical impression formation.

Multidimensional generality of an integration model for personality impression formation

A primary concern of the present study was a quantitative test of the dimensional generality of the weighted-average model of personality impression formation. Japanese college students were asked to make both likableness and intellectual judgments of stimulus persons described by two or four equal-valued personality adjectives. The two kinds of judgment both showed a strong set-size effect, with larger sets yielding more extreme responses. The results of the set-size analysis indicate that the weight parameters were constant across set sizes within each of the two response dimensions, thereby providing evidence to support the generality of the model on a multidimensional basis. The results also give some support to the cross-cultural generality of the weighted-average model.

Integration Theory and Inoculation Theory as Explanations of the “Paper Tiger” Effect

Summary This experiment compared a weighted-average model from information integration theory with McGuire's inoculation theory as explanations of the “paper tiger” effect. Ss were 24 male and 24 female American college students. Procedure and design were similar to that used by McGuire, and his messages were used verbatim. Each S indicated his attitude on each of four health issues and also made direct estimates of the weight and scale value of each piece of information upon his attitude. An apparent paper tiger effect was observed for some issues, but the opposite effect was observed for other issues. The predictions of the averaging model were quite good in six of eight cases. The two discrepancies seemed to reflect an underestimation of the importance of attacking message. Overall, the results were interpreted as supportive of the informational interpretation. No need was found for the motivational concepts of belief threat and refutational practice used in inoculation theory.