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Variability Increase (variability + increase)

Distribution by Scientific Domains

Engineering	50%
Earth and Environmental Science	50%

Selected Abstracts

Seismic design of bridges accounting for spatial variability of ground motion

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4-5 2005
A. Lupoi
Abstract The effects of the spatial variability of the ground motion on the response of bridge structures are investigated in this study. Following a well-established convention, the phenomenon is represented as the combined effect of three causes: the loss of coherence of the motion with distance, the wave-passage, and the local site conditions. Since the nature and amount of non-synchronism vary within ample limits a statistical approach is adopted. A parametric study is carried out on a representative set of bridges subjected to carefully selected combinations of the factors inducing spatial variability. The investigation has shown that the phenomenon affects the response considerably and, hence, the level of protection of these structures. It is observed that for all bridge types considered, the ductility demands at the base of the piers in the presence of spatial variability increase in the majority of cases. Further, for a given bridge type, the probabilities of failure vary by more than one order of magnitude depending on the combination of the parameters. Attention has been focused on a parameter representing the ratio between the maximum curvature ductility demand and the same quantity for the case of fully synchronous motion. This parameter has been used to correct the conventional synchronous design procedure by increasing the available ductility. The re-analysis of all the cases with a modified ductility capacity shows that the procedure is effective in reducing the fragilities to the values corresponding to synchronous input. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Understory vegetation response to thinning disturbance of varying complexity in coniferous stands

APPLIED VEGETATION SCIENCE, Issue 4 2009
Adrian Ares
Abstract Question: Can augmented forest stand complexity increase understory vegetation richness and cover and accelerate the development of late-successional features? Does within-stand understory vegetation variability increase after imposing treatments that increase stand structural complexity of the overstory? What is the relative contribution of individual stand structural components (i.e. forest matrix, gaps, and leave island reserves) to changes in understory vegetation richness? Location: Seven study sites in the Coastal Range and Cascades regions of Oregon, USA. Methods: We examined the effects of thinning six years after harvest on understory plant vascular richness and cover in 40- to 60-year-old forest stands dominated by Douglas-fir (Pseudotsuga menziesii). At each site, one unthinned control was preserved and three thinning treatments were implemented: low complexity (LC, 300 trees ha,1), moderate complexity (MC, 200 trees ha,1), and high complexity (HC, variable densities from 100 to 300 trees ha,1). Gaps openings and leave island reserves were established in MC and HC. Results: Richness of all herbs, forest herbs, early seral herbs and shrubs, and introduced species increased in all thinning treatments, although early seral herbs and introduced species remained a small component. Only cover of early seral herbs and shrubs increased in all thinning treatments whereas forest shrub cover increased in MC and HC. In the understory, we found 284 vascular plant species. After accounting for site-level differences, the richness of understory communities in thinned stands differed from those in control stands. Within-treatment variability of herb and shrub richness was reduced by thinning. Matrix areas and gap openings in thinned treatments appeared to contribute to the recruitment of early seral herbs and shrubs. Conclusions: Understory vegetation richness increased 6 years after imposing treatments, with increasing stand complexity mainly because of the recruitment of early seral and forest herbs, and both low and tall shrubs. Changes in stand density did not likely lead to competitive species exclusion. The abundance of potentially invasive introduced species was much lower compared to other plant groups. Post-thinning reductions in within-treatment variability was caused by greater abundance of early seral herbs and shrubs in thinned stands compared with the control. Gaps and low-density forest matrix areas created as part of spatially variably thinning had greater overall species richness. Increased overstory variability encouraged development of multiple layers of understory vegetation. [source]

An assessment of temperature and precipitation change projections over Italy from recent global and regional climate model simulations

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2010
Erika Coppola
Abstract We present an assessment of climate change projections over the Italian peninsula for the 21st century from the CMIP3 global and PRUDENCE regional model experiments. We consider the A2, A1B, B2 and B1 emission scenarios. The climate change signal over Italy varies seasonally, with maximum warming in summer (up to several °C) and minimum in winter, decreased precipitation over the entire peninsula in summer (locally up to ,40%) and a dipolar precipitation change pattern in winter (increase to the north and decrease to the south). Inter-annual variability increases in all seasons for precipitation and in summer for temperature, while it decreases for winter temperature. The seasonal temperature anomaly probability density functions (PDFs) show a shift as well as a broadening and flattening in future climate conditions, especially in summer. This implies larger increases for extreme hot seasons than mean summer temperatures. The seasonal precipitation anomaly PDFs are greatly affected in summer, with a strong increase of very dry seasons. Moreover, seasons with large precipitation amounts tend to increase in future climate conditions, i.e. we find an increase of very dry (drought prone) and very wet (flood prone) seasons. The magnitude of future climate change depends on the emission scenario and the temperature and precipitation change signals show substantial fine-scale structure in response to the topographical forcing of the Italian major mountain systems. In addition, the change signal is greater than the inter-model standard deviation for temperature in all seasons and for precipitation in the summer. Finally, the CMIP3 ensemble captures the observed 20th century trends of temperature and precipitation change over northern Italy. A broad agreement between the projections obtained with the CMIP3 and PRUDENCE ensembles is found, which adds robustness to the findings. Copyright © 2009 Royal Meteorological Society [source]

An Analytical Investigation of the Bullwhip Effect

PRODUCTION AND OPERATIONS MANAGEMENT, Issue 2 2004
Roger D. H. Warburton
The Bullwhip Effect is problematic: order variability increases as orders propagate along the supply chain. The fundamental differential delay equations for a retailer's inventory reacting to a surge in demand are solved exactly. Much of the rich and complex inventory behavior is determined by the replenishment delay. The analytical solutions agree with numerical integrations and previous control theory results. Managerially useful ordering strategies are proposed. Exact expressions are derived for the retailer's orders to the manufacturer, and the Bullwhip Effect arises naturally. The approach is quite general and applicable to a wide variety of supply chain problems. [source]