In this article, we use parcel-based land-use data to analyze 50 years of residential development in the Toronto region. We test two hypotheses: (1) Toronto’s form does not conform to conventional definitions of suburban sprawl and (2) Toronto’s suburban development shows high levels of continuity over time with relatively high densities and mixed housing types. Contrary to recent research suggesting a convergence of urban forms among North American metropolitan regions, Ontario’s robust planning system has created a distinctive, highly consistent pattern of residential development that has, for half a century, achieved many of the core goals of smart growth including relatively compact, contiguous, and concurrent development. This form continues to be automobile dependent, however, and is not producing many of the benefits ascribed to smart growth. Rather than continuing to adopt United States-inspired smart growth policies, a more ambitious set of initiatives will be required to address current regional challenges. 相似文献
There are currently no industry‐wide standards for the calibration and specification of water‐level monitoring pressure transducers. Consequently, specifications from different manufacturers are currently not directly comparable, and different branded sensors may not perform similarly under the same environmental conditions. This has been highlighted by the varied performance of 14 leading brands of pressure transducers under test conditions. In laboratory tests, transducers generally met product accuracy specifications, although temperature compensation was substandard in five absolute sensors. In a 99‐day field test, accuracy was typically within around ±10 mm for lower range pressure sensors, which exceeded some product specifications. Furthermore, there was evidence for linear and curved forms of instrument drift. As a result of the diverse performance of the transducers, it is recommended that an industry‐wide standard for calibration and specification is introduced. This would eliminate any uncertainty surrounding the current procedures and lead to more informed procurement by the user who would have a greater understanding of comparative instrument performance. Any new standard should also address sensor drift which is currently rarely cited in product specifications. 相似文献
Clementine was a technology demonstration mission jointly sponsored by the Department of Defense (DOD) and NASA that was launched
on January 25th, 1994. Its principal objective was to use the Moon, a near-Earth asteroid, and the spacecraft’s Interstage
Adapter as targets to demonstrate lightweight sensor performance and several innovative spacecraft systems and technologies.
The design, development, and operation of the Clementine spacecraft and ground system was performed by the Naval Research
Laboratory. For over two months Clementine mapped the Moon, producing the first multispectral global digital map of the Moon,
the first global topographic map, and contributing several other important scientific discoveries, including the possibility
of ice at the lunar South Pole. New experiments or schedule modifications were made with minimal constraints, maximizing science
return, thus creating a new paradigm for mission operations. Clementine was the first mission known to conduct an in-flight
autonomous operations experiment. After leaving the Moon, Clementine suffered an onboard failure that caused cancellation
of the asteroid rendezvous. Despite this setback, NASA and the DOD applied the lessons learned from the Clementine mission
to later missions. Clementine set the standard against which new small spacecraft missions are commonly measured. More than
any other mission, Clementine has the most influence (scientifically, technically, and operationally) on the lunar missions
being planned for the next decade. 相似文献
The relationships between watershed variables and lakewater chemistry were examined for 53 lakes in the Upper Peninsula of
Michigan to identify factors influencing lake sensitivity to atmospheric inputs. The lakes lie in three distinct geologic/geomorphic
regions. Acid neutralization capacity (ANC), sulfate, and color were correlated with parameters related to atmospheric loading,
watershed area and relief, hydrology, geology, and land use for the entire 53-lake set and for lower alkalinity subsets. Acid-neutralizing
capacity was related to atmospheric acidic inputs and, in the southern portion of the Upper Peninsula, to the presence of
mineralized groundwater inputs. In the north, ANC is correlated with hydrologic lake type and surficial deposits. Results
show the highest density of acidified lakes in the northern region, which is underlain by noncalcareous sedimentary rocks.
Color was related to lake size and the presence of organic soils in the watershed, whereas lake sulfate concentration was
mainly influenced by atmospheric or groundwater inputs, surficial deposits, and soil type. 相似文献
This paper described a technique for obtaining three-dimensional mine design information using a two-dimensional finite element program where the mining geometry consists of an extensive array of underground rooms and pillars. The technique is based upon a simple augmentation of forces in a two-dimensional analysis to produce the same average pillar stress that would occur in a full three dimensional analysis. Detailed comparisons between a three-dimensional analysis, a two-dimensional analysis (plane stress and plane strain) and an augmented two-dimensional analysis (also plane stress and plane strain) of stress about a typical coal mine pillar are presented. A local factor of safety is defined and then mapped over the pillar midplane, the immediate roof and immediate floor using the results from the full three-dimensional analysis. Comparisons of roof and pillar safety factor distributions obtained by the three-dimensional, two-dimensional and augmented two-dimensional analyses show that the minimum safety factors in the pillar (at the pillar sides) are predicted quite closely by the augmented two-dimensional techniqe (plane stress). The same is true of the immediate roof, although the three-dimensional safety factor tends to be higher in the roof (over the room) than that calculated by the augmented twodimensional technique. The augmented loading procedure appears to hold considerable promise as a very efficient and cost reducing techniqe for mine pillar design. 相似文献
There is a scarcity of long-term groundwater hydrographs from sub-Saharan Africa to investigate groundwater sustainability, processes and controls. This paper presents an analysis of 21 hydrographs from semi-arid South Africa. Hydrographs from 1980 to 2000 were converted to standardised groundwater level indices and rationalised into four types (C1–C4) using hierarchical cluster analysis. Mean hydrographs for each type were cross-correlated with standardised precipitation and streamflow indices. Relationships with the El Niño–Southern Oscillation (ENSO) were also investigated. The four hydrograph types show a transition of autocorrelation over increasing timescales and increasingly subdued responses to rainfall. Type C1 strongly relates to rainfall, responding in most years, whereas C4 notably responds to only a single extreme event in 2000 and has limited relationship with rainfall. Types C2, C3 and C4 have stronger statistical relationships with standardised streamflow than standardised rainfall. C3 and C4 changes are significantly (p <?0.05) correlated to the mean wet season ENSO anomaly, indicating a tendency for substantial or minimal recharge to occur during extreme negative and positive ENSO years, respectively. The range of different hydrograph types, sometimes within only a few kilometres of each other, appears to be a result of abstraction interference and cannot be confidently attributed to variations in climate or hydrogeological setting. It is possible that high groundwater abstraction near C3/C4 sites masks frequent small-scale recharge events observed at C1/C2 sites, resulting in extreme events associated with negative ENSO years being more visible in the time series.