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21.
Despite the fact that virtual environments are increasingly deployed to study the relation between urban planning, physical and social disorder, and fear of crime, their ecological validity for this type of research has not been established. This study compares the effects of similar signs of public disorder (litter, warning signs, cameras, signs of vandalism and car burglary) in an urban neighborhood and in its virtual counterpart on the subjective perception of safety and livability of the neighborhood. Participants made a walking tour through either the real or the virtual neighborhood, which was either in an orderly (baseline) state or adorned with numerous signs of public disorder. During their tour they reported the signs of disorder they noticed and the degree to which each of these affected their emotional state and feelings of personal safety. After finishing their tour they appraised the perceived safety and livability of the environment. Both in the real and in the simulated urban neighborhood, signs of disorder evoked associations with social disorder. In all conditions, neglected greenery was spontaneously reported as a sign of disorder. Disorder did not inspire concern for personal safety in reality and in the virtual environment with a realistic soundscape. However, in the absence of sound disorder compromised perceived personal safety in the virtual environment. Signs of disorder were associated with negative emotions more frequently in the virtual environment than in its real-world counterpart, particularly in the absence of sound. Also, signs of disorder degraded the perceived livability of the virtual, but not of the real neighborhood. Hence, it appears that people focus more on details in a virtual environment than in reality. We conclude that both a correction for this focusing effect and realistic soundscapes are required to make virtual environments an appropriate medium for both etiological (e.g. the effects of signs of disorder on fear of crime) and intervention (e.g. CPTED) research. 相似文献
22.
Mathieu Fortin Steve Bdard Josianne DeBlois Sbastien Meunier 《Ecological modelling》2009,220(20):2770-2781
Estimating prediction uncertainty for a single tree-based model is hindered by the complex structure of these models. In this paper, we addressed this issue with a case study applied to northern hardwood stands in Québec, Canada. SaMARE is a stochastic single tree-based model that was designed for these types of stands. Using a Monte Carlo approach, the model can provide a mean predicted value and its confidence limits for some plot-level attributes.The mean predicted values were compared to observed values in terms of bias and accuracy. In addition to these common statistics, we compared nominal coverage of Monte Carlo-simulated confidence intervals with real (observed) coverage to verify the adequacy of the simulated uncertainty. A comparison was made using several plot-level attributes, which exhibited an increasing discriminative complexity. This complexity ranges from coarse attributes, such as all-species basal area, up to more complex ones, such as basal area for stems of a particular species and with sawlog potential.The results showed that in terms of absolute value, biases were small, but could be relatively high with respect to the average observed value when the discriminative complexity of the attribute increased. The comparison between nominal and real coverage of confidence intervals gave satisfactory results for all-species plot-level attributes. However, for some species-specific attributes, the Monte Carlo-simulated confidence intervals overestimated the real coverage. 相似文献
23.
Natural circulation driven boiling systems are extensively used for passive heat removal, such as in nuclear power plants. The flashing phenomenon and the associated flow instabilities in a natural circulation loop are reported here. An experimental facility is constructed with a heater, an adiabatic riser, a condenser and an adiabatic down comer to study the instability regions. The experimental geometry is modeled using RELAP5. At high power (i.e., at 6 kW) flashing instability is observed when the inlet sub cooling is within the range of 7° C to 12° C. It is also found that the presence of an inlet restriction does not help to suppress the flashing induced flow oscillation. A good comparison between the experimental and numerical results is observed and this loop can be used for validation exercises of commercial codes. 相似文献
24.
A hierarchical approach to fisheries planning and modeling in the Columbia River Basin 总被引:1,自引:0,他引:1
The Columbia River Basin is the scene of a massive effort to restore populations of Pacific salmon (Oncorhynchus spp.) and steelhead (O. mykiss). Efficient restoration is confounded by a high level of complexity, competing sociopolitical goals and values, and uncertainty
about key system properties. Simulation models and other tools of systems analysis are important to development of a comprehensive,
regionally acceptable strategy. Hierarchy theory provides a useful paradigm for organized complexity within the Columbia Basin
and the basis for a trilevel hierarchical structure for organizing and integrating models. Life-stage models compose the most
basic simulation units at the lowest level in the proposed hierarchical modeling structure. Each life-stage model simulates
a distinct period in the life cycle of anadromous salmonids. Population models at the intermediate level simulate the complete
life cycles of salmon and steelhead populations. At the highest level in the hierarchy, interpopulation models simulate extensive,
long-term processes that affect multiple species and stocks. A hierarchical system of models is preferable to a single model
or to a group of models lacking formal structure. A principal advantage is that models have the correct spatial and temporal
resolution for analyzing questions at different scales. A hierarchical structure also facilitates the flow of information
among models, and aids in understanding the impacts of uncertainty. Constructing a hierarchy of models should involve both
bottom-up and top-down perspectives that maintain logical consistency among models, while allowing unique model structures
appropriate for each level in the hierarchy. 相似文献
25.
高层建筑火灾人员疏散和人员伤亡的模拟 总被引:4,自引:0,他引:4
基于建筑火灾全风网网络模型的基础上 ,结合紧急疏散模型 ,模拟火灾时期疏散时间和建筑物内人员滞留的情况 ,同时也可以模拟可能出现的伤亡情况 ,有助于高层建筑的疏散系统设计 ,为火灾的再现提供了一个有效的分析工具 ,也为高层建筑火灾的风险评价提供了理论数据 相似文献
26.
27.
Forest growth models are useful tools for investigating the long-term impacts of logging. In this paper, the results of the rain forest growth model FORMIND were assessed by a multicriteria decision analysis. The main processes covered by FORMIND include tree growth, mortality, regeneration and competition. Tree growth is calculated based on a carbon balance approach. Trees compete for light and space; dying large trees fall down and create gaps in the forest. Sixty-four different logging scenarios for an initially undisturbed forest stand at Deramakot (Malaysia) were simulated. The scenarios differ regarding the logging cycle, logging method, cutting limit and logging intensity. We characterise the impacts with four criteria describing the yield, canopy opening and changes in species composition. Multicriteria decision analysis was used for the first time to evaluate the scenarios and identify the efficient ones. Our results plainly show that reduced-impact logging scenarios are more 'efficient' than the others, since in these scenarios forest damage is minimised without significantly reducing yield. Nevertheless, there is a trade-off between yield and achieving a desired ecological state of logged forest; the ecological state of the logged forests can only be improved by reducing yields and enlarging the logging cycles. Our study also demonstrates that high cutting limits or low logging intensities cannot compensate for the high level of damage caused by conventional logging techniques. 相似文献
28.
29.
A GIS/Simulation Framework for Assessing Change in Water Yield over Large Spatial Scales 总被引:1,自引:0,他引:1
Recent legislation to initiate vegetation management in the Central Sierra hydrologic region of California includes a focus
on corresponding changes in water yield. This served as the impetus for developing a combined geographic information system
(GIS) and simulation assessment framework. Using the existing vegetation density condition, together with proposed rules for
thinning to reduce fire risk, a set of simulation model inputs were generated for examining the impact of the thinning scenario
on water yield. The approach allows results to be expressed as the mean and standard deviation of change in water yield for
each 1-km2 map cell that is thinned. Values for groups of cells are aggregated for typical watershed units using area-weighted averaging.
Wet, dry, and average precipitation years were simulated over a large region. Where snow plays an important role in hydrologic
processes, the simulated change in water yield was less than 0.5% of expected annual runoff for a typical watershed. Such
small changes would be undetectable in the field using conventional stream flow analysis. These results suggest that use of
water yield increases to help justify forest-thinning activities or offset their cost will be difficult. 相似文献
30.
S. Taku Ide Kristian Jessen Franklin M. Orr Jr. 《International Journal of Greenhouse Gas Control》2007,1(4):481-491
CO2 can be effectively immobilized during CO2 injection into saline aquifers by residual trapping – also known as capillary trapping – a process resulting from capillary snap-off of isolated CO2 bubbles. Simulations of CO2 injection were performed to investigate the interplay of viscous and gravity forces and capillary trapping of CO2. Results of those simulations show that gas injection processes in which gravitational forces are weak compared to viscous forces (low gravity number Ngv) trap significantly more CO2 than do flows with strong gravitational forces relative to the viscous forces (high Ngv). The results also indicate that over a wide range of gravity numbers (Ngv), significant fractions of the trapping of CO2 can occur relatively quickly. The amount of CO2 that is trapped after injection ceases is demonstrated to correlate with Ngv. For some simulated displacements, effects of capillary pressure and aquifer dip angle on the amount and the rate of trapping are reported. Trapping increases when effects of capillary pressure and aquifer inclination are included in the model. Finally we show that injection schemes such as alternating injection of brine and CO2 or brine injection after CO2 injection can also enhance the trapping behavior. 相似文献