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Model Helps (model + help)
Selected AbstractsA new cost-distance model for human accessibility and an evaluation of accessibility bias in permanent vegetation plots in Great Smoky Mountains National Park, USAJOURNAL OF VEGETATION SCIENCE, Issue 6 2009R. Todd Jobe Abstract Question: Can a new cost-distance model help us to evaluate the potential for accessibility bias in ecological observations? How much accessibility bias is present in the vegetation monitoring plots accumulated over the last three decades in Great Smoky Mountains National Park? Location: Great Smoky Mountains National Park, North Carolina and Tennessee, USA. Methods: Distance, slope, stream crossings, and vegetation density were incorporated into a least-cost model of energetic expenditure for human access to locations. Results: Estimated round-trip energy costs for the park ranged from 0 to 1.62 × 105 J kg,1. The estimated round-trip energetic expenditure for the surveys ranged from 53 to 1.51 × 105 J kg,1. Their distribution was more accessible than the random expectation. Ten (17%) of the vegetation types in the park are significantly under-sampled relative to their area, and 16 (29%) are over-sampled. Plots in 18 of the 40 vegetation types exhibited a significant positive correlation with accessibility. Conclusions: The least-cost model is an improvement over previous attempts to quantify accessibility. The bias in plot locations suggests using a least-cost model to test for bias in cases in which human accessibility is confounded with other sources of ecosystem variation. [source] CONSTANCY OF THE G MATRIX IN ECOLOGICAL TIMEEVOLUTION, Issue 6 2004Mats BjÖrklund Abstract The constancy of the genetic variance-covariance matrix (G matrix) across environments and populations has been discussed and tested empirically over the years but no consensus has so far been reached. In this paper, I present a model in which morphological traits develop hierarchically, and individuals differ in their resource allocation and acquisition patterns. If the variance in resource acquisition is many times larger than the variance in resource allocation then strong genetic correlations are expected, and with almost isometric relations among traits. As the variation in resource acquisition decreases below a certain threshold, the correlations decrease overall and the relations among traits become a function of the allocation patterns, and in particular reflecting the basal division of allocation. A strong bottleneck can break a pattern of strong genetic correlation, but this effect diminishes rapidly with increasing bottleneck size. This model helps to understand why some populations change their genetic correlations in different environments, whereas others do not, since the key factor is the relation between the variances in resource acquisition and allocation. If a change in environment does not lead to a change in this ratio, no change can be expected, whereas if the ratio is changed substantially then major changes can be expected. This model can also help to understand the constancy of morphological patterns within larger taxa as a function of constancy in resource acquisition patterns over time and environments. When this pattern breaks, for example on islands, larger changes can be expected. [source] The application of an empowerment modelHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 4 2001Eric Molleman In this study we applied an empowerment model that focuses on (a) the need for empowerment in light of organizational strategy, (b) job design issues such as job enlargement and job enrichment that facilitate empowerment, and (c) the abilities, and (d) the attitudes of workers that make empowerment work. We applied the model in the manufacturing department of a firm that produces catheters for medical use and interviewed managers and supporting staff and surveyed 231 operators. The leading performance indicators in this firm are efficiency and quality. The reassignment of 12 out of 33 tasks was believed to contribute to these organizational objectives. For most workers, their abilities and their attitudes toward empowerment proved to be no major barrier to the reallocation of these tasks. However, for temporary workers, mainly working in a "short shift," the leeway to learn skills is limited, which probably impedes empowerment. The study shows that our model helps to diagnose the need for empowerment, to design work structures that facilitate empowerment, and to select appropriate human resource management practices. Further validation in other organizational settings is desirable. © 2001 John Wiley & Sons, Inc. [source] Induction of early murine cytomegalovirus infection by different reporter gene-associated recombinant virusesJOURNAL OF VIRAL HEPATITIS, Issue 6 2006U. Drebber Summary., Murine cytomegalovirus (MCMV) has provided useful models for acute, chronic and latent CMV infection because of its similarities in structure and biology with human CMV. We report the induction of acute MCMV hepatitis with different bacterial artificial chromosome (BAC)-cloned virus constructs [MCMV-SEAP which includes the gene for secreted alkaline phosphatase (SEAP) under Rous sarcoma virus (RSV)-promoter control, MCMV-GFP which includes the gene for enhanced green fluorescent protein (eGFP) under HCMV-ie promoter control, MCMV-HBs includes the gene for hepatitis B surface antigen (HBsAg) under simian virus (SV)40-promoter control and the DeltaMC95.21 virus in which the m152 gene was deleted and substituted by the reporter gene lacZ] in order to elucidate the histopathological changes together with different reporter-gene products in the liver tissue and the effect of the deletion of a certain gene. All the virus constructs induced a similar mild acute hepatitis which had its climax from days 3 to 5 post-infection in immunocompetent mice. In situ, the reporter-gene products beta-galactosidase and secreted alkaline phosphatase could be visualized in relation to the inflammatory changes. The composition of the invading cell populations did not change even in the absence of the m152 gene. Additionally discrete inflammatory changes were seen in kidney and serosa while the other organs were not involved. This model helps us understand the immunological and histopathological mechanisms of the CMV-induced hepatitis, which plays an important role especially in the immunocompromised patient. The morphological changes can be analysed while the respective reporter gene product is expressed by the virus construct. [source] The New Keynesian Model and the Euro Area Business Cycle,OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 2 2007Miguel Casares Abstract This paper describes a New Keynesian model incorporating transactions-facilitating money and a time-to-build constraint into endogenous capital accumulation. The calibrated New Keynesian model performs almost as well as the estimated vector autoregressive model in replicating Euro area cyclical correlations between key variables such as output and inflation, although it fares less well in predicting the procyclical dynamics of nominal interest rates. The presence of a time-to-build requirement in the model helps to improve its fit to Euro area data, whereas the role of transactions-facilitating money is much less important. Impulse,response functions and a decomposition of variance complete the analysis. [source] Modeling above-ground litterfall in eastern Mediterranean conifer forests using fractional tree cover, and remotely sensed and ground dataAPPLIED VEGETATION SCIENCE, Issue 4 2010Sibel Taskinsu-Meydan Abstract Question: How can we model above-ground litterfall in Mediterranean conifer forests using remotely sensed and ground data, and geographic information systems (GIS)? Location: Eastern Mediterranean conifer forest of Turkey. Methods: Above-ground litterfall from Mediterranean forest stands of Pinus nigra, Cedrus libani, Pinus brutia and Juniperus excelsa and mixed Abies cilicica, C. libani and P. nigra was modeled as a function of fractional tree cover using a regression tree algorithm, based on IKONOS and Landsat TM/ETM+data. Landsat TM/ETM+images for the study area were used to map actual stand patterns, based on a land-cover map of species stands using a supervised classification. Results: Total amount of annual above-ground litterfall for the entire study area (12 260 km2) was estimated at 417.2 Mg ha,1 for P. brutia, 291.1 Mg ha,1 for the mixed stand, 115.5 Mg ha,1 for P. nigra, 54.6 Mg ha,1 for J. excelsa and 45.9 Mg ha,1 for C. libani. The maps generated indicate the distribution of the seasonal amount of total above-ground litterfall for different species and the distribution of species stands in the study area. There was an increase in the amount of above-ground litterfall for P. brutia stand in summer, for J. excelsa in autumn and for C. libani, P. nigra and the mixed stand of A. cilicica, P. nigra and C. libani in winter. Conclusion: Application of this model helps to improve the accuracy of estimated litterfall input to soil organic carbon pools in the Mediterranean conifer forests. [source] Inhibition of allergen-induced wheal and flare reactions by levocetirizine and desloratadineBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 2 2008Nelly Frossard What is already known about this subject ,,The reproducible and standardized histamine-induced wheal and flare model helps identify the objective effectiveness of antihistamines in humans, as well as their differences in onset and duration of action. ,,Some of the newest antihistamines have already been compared in a head-to-head setting using this model. However, their objective action at inhibiting the allergen-induced wheal and flare response has not been reported yet. What this study adds ,,The time,response study presented here shows the objective activity of two of the newest generation of antihistamines, levocetirizine and desloratadine, at inhibiting the allergen-induced wheal and flare response in a randomized, cross over, placebo-controlled trial. ,,This model is interesting to the clinical setting since allergic subjects are recruited, and the response to allergen involves mast cell degranulation and release of numerous vasoactive and pro-inflammatory mediators additionally to histamine. ,,In addition, this study reports receptor occupancy for both antihistamines at therapeutic dosage, leading to analysis of potential differences in activity. ,,This study clearly shows the potential anti-inflammatory properties of desloratadine and levocetirizine in their skin activity when allergen is the challenging agent as occurs in the clinical situation. Aims To evaluate the inhibitory activity of the new-generation antihistamines levocetirizine and desloratadine at their therapeutic doses on the allergen-induced wheal and flare reaction at 1.5 h, 4 h, 7 h, 12 h and 24 h postdose, and to measure their plasma and skin concentrations. Methods A double-blind, randomized, cross-over, placebo-controlled study in 18 allergic subjects was carried out. The time,response of the wheal and flare reaction areas under the curve (AUC) were compared by anova. Results Both antihistamines significantly (P < 0.001) inhibited the allergen-induced wheal and flare reactions compared with placebo. Levocetirizine was significantly more potent than desloratadine. Mean ± SEM wheal AUC(0,24 h) was 506.4 ± 81.0 with levocetirizine and 995.5 ± 81.0 mm2 h with desloratadine as compared with placebo (1318.5 ± 361.0 mm2 h). Flare AUC(0,24 h) was 5927.3 ± 1686.5 and 15838.2 ± 1686.5 mm2 h, respectively [P < 0.001 for both compared with placebo (22508.2 ± 7437.1 mm2 h)]. Levocetirizine showed significant inhibition of wheal and flare already at 1.5 h postdose compared with placebo (P , 0.001); desloratadine achieved a significant effect only after 4 h. The mean total plasma concentration at 12 h and 24 h after intake was higher for levocetirizine (58.1 ± 13.4 and 20.0 ± 8.1 ng ml,1, respectively) as compared with desloratadine (0.82 ± 0.24 and 0.45 ± 0.16 ng ml,1). Similarly, higher mean unbound skin concentrations were observed for levocetirizine 24 h after intake (1.80 ng g,1) than for desloratadine (0.07 ng g,1). This was associated with greater receptor occupancy for levocetirizine (54%) than desloratadine (34%) at 24 h. Conclusions Levocetirizine suppressed the cutaneous allergic reactions with a higher potency than desloratadine, which correlated with its high receptor occupancy. Receptor occupancy rather than drug affinity or plasma half-life is more representative of antihistamine potency. [source] | |||||||||||||