353 research outputs found
Efficient Processing of Spatial Joins Using R-Trees
Abstract: In this paper, we show that spatial joins are very suitable to be processed on a parallel hardware platform. The parallel system is equipped with a so-called shared virtual memory which is well-suited for the design and implementation of parallel spatial join algorithms. We start with an algorithm that consists of three phases: task creation, task assignment and parallel task execu-tion. In order to reduce CPU- and I/O-cost, the three phases are processed in a fashion that pre-serves spatial locality. Dynamic load balancing is achieved by splitting tasks into smaller ones and reassigning some of the smaller tasks to idle processors. In an experimental performance compar-ison, we identify the advantages and disadvantages of several variants of our algorithm. The most efficient one shows an almost optimal speed-up under the assumption that the number of disks is sufficiently large. Topics: spatial database systems, parallel database systems
The impact of climate change and urban growth on urban climate and heat stress in a subtropical city
Urban residents face increasing risk of heat stress due to the combined impact of climate change and intensification of the urban heat island (UHI) associated with urban growth. Considering the combined effect of urban growth and climate change is vital to understanding how temperatures in urban areas will change in the future. This study investigated the impact of urban growth and climate change on the UHI and heat stress in a subtropical city (Brisbane, Australia) in the present day (1991â2000) and medium term (2041â2050; RCP8.5) during summer. A control and urban growth scenario was used to compare the temperature increase from climate change alone with the temperature increase from climate change and urban growth. Average and minimum temperatures increased more with climate change and urban growth combined than with climate change alone, indicating that if urban growth is ignored, future urban temperatures could be underestimated. Under climate change alone, rural temperatures increased more than urban temperatures, decreasing the effect of the UHI by 0.4 °C at night and increasing the urban cool island by 0.8 °C during the day. With climate change, the number of hot days and nights doubled in urban and rural areas in 2041â2050 as compared to 1991â2000. The number of hot nights was higher in urban areas and with urban growth. Dangerous heat stress, defined as apparent temperature above 40â°C, increased with climate change and occurred on average 1â2 days every summer during 2041â2050, even in shaded conditions. There was higher temperature increases with urban growth and climate change than with climate change alone, indicating that reducing the effect of the UHI is vital to ensuring urban growth does not increase the heat stress risks that urban residents will face in the future
Status of the Resource Room Model in Local Education Agencies: A Descriptive Study
Although resource room programs are widely used, only limited information is available on implementation of this model. The purpose of the present investigation was to survey a nationwide sample of local education agencies (LEAs) to determine the status of this model at the local level and to identify the characteristics of resource programs as they are currently implemented. A questionnaire was sent to a 5% stratified random sample of LEAs with a 53.4% response rate. Results indicated that most local education agencies use resource room programs, and have done so for at least three years. Most programs are multicategorical. The majority of respondents indicated that they believed the programs were effective, and that they would continue to be used. A major conclusion from this study relates to the need for descriptions of model resource room programs and practices.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Recommended from our members
Summertime surface energy balance fluxes at two Beijing sites
Summertime (June to August 2015) radiative and turbulent heat fluxes were measured concurrently at two sites (urban and suburban) in Beijing. The urban site has slightly lower incoming and outgoing shortwave radiation, lower atmospheric transmissivity and a lower surface albedo compared to the suburban site. Both sites receive similar incoming longwave radiation. Although the suburban site had larger daytime outgoing longwave radiation (L_â), differences in the daily mean L_â values are small, as the urban site has higher nocturnal L_â. Overall, both the midday and daily mean net all-wave radiation (Q^*) for the two sites are nearly equal. However, there are significant differences between the sites in the surface energy partitioning. The urban site has smaller turbulent sensible heat (Q_H) (21-25% of Q^* (midday â daily)) and latent heat (Q_E) fluxes (21-45% of Q^*). Whereas, the suburban proportions of Q^* are Q_H 32-32% and Q_E 39-66%. The daily (midday) mean Bowen ratio (Q_HâQ_E ) was 0.56 and 0.49 (0.98 and 0.83) for the urban and suburban sites, respectively. These values are low compared to other urban and suburban areas with similar or larger fractions of vegetated cover. Likely these are caused by the widespread external water use for road cleaning/wetting, greenbelts, and air conditioners. Our suburban site has quite different land cover to most previous suburban studies as crop irrigation supplements rainfall. These results are important in enhancing our understanding of surfaceâatmosphere energy exchanges in Chinese cities, and can aid the development and evaluation of urban climate models and inform urban planning strategies in the context of rapid global urbanization and climate change
Prioritizing Stream Barrier Removal to Maximize Connected Aquatic Habitat and Minimize Water Scarcity
Instream barriers, such as dams, culverts, and diversions, alter hydrologic processes and aquatic habitat. Removing uneconomical and aging instream barriers is increasingly used for river restoration. Historically, selection of barrier removal projects used scoreâandârank techniques, ignoring cumulative change and the spatial structure of stream networks. Likewise, most water supply models prioritize either human water uses or aquatic habitat, failing to incorporate both human and environmental water use benefits. Here, a dualâobjective optimization model identifies barriers to remove that maximize connected aquatic habitat and minimize water scarcity. Aquatic habitat is measured using monthly average streamflow, temperature, channel gradient, and geomorphic condition as indicators of aquatic habitat suitability. Water scarcity costs are minimized using economic penalty functions while a budget constraint specifies the money available to remove barriers. We demonstrate the approach using a case study in Utah\u27s Weber Basin to prioritize removal of instream barriers for Bonneville cutthroat trout, while maintaining human water uses. Removing 54 instream barriers reconnects about 160 km of qualityâweighted habitat and costs approximately US$10 M. After this point, the costâeffectiveness of removing barriers to connect river habitat decreases. The modeling approach expands barrier removal optimization methods by explicitly including both economic and environmental water uses
Agro-materials : a bibliographic review
Facing the problems of plastic recycling and fossil resources exhaustion, the use of biomass to conceive new materials appears like a reasonable solution. Two axes of research are nowadays developed : on the one hand the synthesis of biodegradable plastics, whichever the methods may be, on the other hand the utilization of raw biopolymers, which is the object of this paper. From this perspective, the âplasticâ properties of natural polymers, the caracteristics of the different classes of polymers, the use of charge in vegetable matrix and the possible means of improving the durability of these agro-materials are reviewed
The Milky Way Bulge: Observed properties and a comparison to external galaxies
The Milky Way bulge offers a unique opportunity to investigate in detail the
role that different processes such as dynamical instabilities, hierarchical
merging, and dissipational collapse may have played in the history of the
Galaxy formation and evolution based on its resolved stellar population
properties. Large observation programmes and surveys of the bulge are providing
for the first time a look into the global view of the Milky Way bulge that can
be compared with the bulges of other galaxies, and be used as a template for
detailed comparison with models. The Milky Way has been shown to have a
box/peanut (B/P) bulge and recent evidence seems to suggest the presence of an
additional spheroidal component. In this review we summarise the global
chemical abundances, kinematics and structural properties that allow us to
disentangle these multiple components and provide constraints to understand
their origin. The investigation of both detailed and global properties of the
bulge now provide us with the opportunity to characterise the bulge as observed
in models, and to place the mixed component bulge scenario in the general
context of external galaxies. When writing this review, we considered the
perspectives of researchers working with the Milky Way and researchers working
with external galaxies. It is an attempt to approach both communities for a
fruitful exchange of ideas.Comment: Review article to appear in "Galactic Bulges", Editors: Laurikainen
E., Peletier R., Gadotti D., Springer Publishing. 36 pages, 10 figure
Ambivalence towards discourse of disaster resilience
This paper investigates empirically how the international aid community (IAC)âdonors and practitionersâconsiders and implements disaster resilience in a specific country setting, Nepal, and throughout the rest of the world. A key finding is that there is ambivalence about a concept that has become a discourse. On a global level, the IAC utilises the discourse of resilience in a cautiously positive manner as a bridging concept. On a national level, it is being used to influence the Government of Nepal, as well as serving as an operational tool of donors. The mythical resilient urban community is fashioned in the IAC's imaginary; understanding how people create communities and what type of linkages with government urban residents desire to develop their resilience strategies is missing, though, from the discussion. Disaster resilience can be viewed as another grand plan to enhance the lives of people. Yet, regrettably, an explicit focus on individuals and their communities is lost in the process
Multicenter prospective validation of the Baveno IV and Baveno II/III criteria in cirrhosis patients with variceal bleeding
UNLABELLED: The criteria for defining failure to control bleeding in cirrhosis patients were introduced at the Baveno II/III meetings and were widely used as endpoints in clinical trials. Because they lacked specificity, the Baveno IV criteria were proposed in 2005 and slightly modified in 2010 (Baveno V). These criteria included a new index for patients undergoing transfusion, called adjusted-blood-requirement-index (ABRI=number of blood units/(final-initial hematocrit+0.01)), with a cutoff value of 0.75. In this multicenter prospective study, we sought to 1) validate the Baveno IV/V criteria; 2) compare them to the Baveno II/III criteria; 3) assess ABRI performance using a standardized calculation. The key inclusion criteria were: 1) variceal bleeding; 2) cirrhosis; 3) no need to modify the transfusion policy. The patients were classified according to the Baveno IV, V, and II/III criteria. The gold standard for failure during a 5-day period was the clinical judgment of three independent experts, blinded to the Baveno assessments. A total of 249 patients were included. The experts\u27 agreement in clinical judgment of the failure was 80%. Failure occurred in 20.5% of patients; the c-statistics were 0.72 versus 0.64 and 0.65 for Baveno IV versus Baveno II/III and Baveno V criteria (P=0.001 for both). ABRI did not improve the diagnostic performance of the Baveno IV criteria. The Baveno IV, but not Baveno II/III, criteria independently predicted survival.
CONCLUSION: The Baveno IV criteria demonstrated a higher accuracy than the Baveno II/III and Baveno V criteria for assessing failure to control bleeding and predicted survival independently. Together, our results show that ABRI is not a useful metric, and the Baveno IV criteria should replace the Baveno II/III criteria
- âŠ