Rugged Mountain Areas Research Articles

DEM DEVELOPMENT AND PRECISION ANALYSIS FOR ANTARCTIC ICE SHEET USING CRYOSAT‐2 ALTIMETRY DATA

AbstractDigital elevation models (DEMs) are of fundamental importance to many geoscientific and environmental studies in Antarctic and due to relatively poor coverage by ground based surveys, the main data source for constructing an Antarctic DEM is satellite altimetry. The newest operating satellite‐borne altimeter with ice applications is the ESA satellite CryoSat‐2, which was launched in April 2010. CryoSat‐2 provides altimetry data up to a latitude of 88°S/N, which is a significant improvement to previous satellite‐borne altimeters. Based on two full cycles of CryoSat‐2 observations acquired between December 2012 and January 2015, we derived a new DEM for the Antarctic Ice Sheet. The accuracy of generated DEM depends largely on the interpolation method adopted and five widely used interpolation methods were compared using the Cross Validation method. The Kriging method yielded better estimates for the Antarctic Ice Sheet and was adopted when constructing the final DEM. For the CryoSat‐2 LRM data we followed an iterative approach to correct for the surface slope, and the slope correction was applied to each data point using the relocation method. Data gap beyond the latitudinal limit of the CryoSat‐2 mission (88°S) was filled by contour data from Antarctic Digital Database (ADD). Finally, we present a new Antarctic DEM with a pixel size of 1 km×1 km. The accuracy of the final DEM was assessed by ICESat, IceBridge and GPS data and compared with four widely used Antarctic DEMs namely Bamber 1 km DEM, ICESat DEM, RAMPv2 DEM and JLB97 DEM. The results show that the CryoSat‐2 DEM has an uncertainty of 0.73±8.398 m. The vertical accuracy of the DEM is better than 1 m at domes, better than 4 m for the ice shelves, better than 10 m for the interior ice sheet and over 150 m for the rugged mountainous and coastal areas.

Tree species composition, biodiversity and regeneration in response to catena shape and position in a mountain forest

ABSTRACTWe examined the variation in woody plant species composition, regeneration and biodiversity in relation to topographic heterogeneity, specifically catena shape (V and Λ) and slope position (summit, shoulder, back slope, foot slope and toe slope). All research took place at the TMU Experimental Forest Station, located in northern Iran. Two sets of replicated quadrats were established along transects that encompassed the different catena shapes and positions. We recorded the density, height, and canopy cover of all trees ≥12 cm diameter at breast height within 30 quadrats (400m2), as well as the density of all tree regenerations within 120 quadrats (4m2). In addition, three measurements of biodiversity were calculated for both mature trees and regenerations. Mature tree species composition varied greatly with catena shape and slope position, as did that of regenerating trees. Despite differences in species composition, the various measurements of biodiversity were consistent across the landscape for mature trees, whereas significant variation in evenness was detected for regenerating trees. We concluded that the broad matrix of environmental conditions occurring within this rugged mountainous area generates a variety of microhabitats, which in turn contributes to both the variation in species composition and the consistent biodiversity of these forests.

Estimates of land surface heat fluxes of the Mt. Everest region over the Tibetan Plateau utilizing ASTER data

Regional land surface albedo, land surface temperature, net radiation flux, ground heat flux, sensible heat flux, and latent heat flux were derived in the Mt. Everest area utilizing topographical enhanced surface energy balance system (TESEBS) model and nine scenes of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) data under clear-sky and in-situ measurements at the QOMS station (the Qomolangma Station for Atmospheric Environmental Observation and Research, Chinese Academy of Sciences). The parameterization schemes for diffused and reflected downward shortwave radiation flux of the TESEBS model were improved by introducing the parameters sky-view factor (SVF) and terrain configuration factor (Ct). Then, a so-called C-correction method for land surface albedo was coupled into the TESEBS model to reduce the influences of topography. After topographical correction, the albedo of the dark tilted surface facing away from the Sun was compensated and albedo of the brightness surface facing the Sun was restrained. The downward shortwave radiation flux was broken down into three components including solar direct radiation flux, solar diffused radiation flux, and reflected solar radiation flux by surrounding terrain. The solar diffused radiation flux ranges from about 30 to 60W/m2 at the satellite passing time on 6 January 2008. The reflected solar radiation flux changes from 0 to more than 100W/m2 in the area covered by glaciers and snows. Thus, it is important to take the topographical effects into account in estimation of surface radiation balance in the mountainous area, especially in the glacier area. The retrieved land surface parameters, land surface radiation balance components, and the land surface energy balance components were evaluated by the field measurements in the QOMS station. The estimated results were very close to the in-situ observations with low mean bias errors, low root mean square errors and high correlation coefficients. Although the proposed schemes are rested on a number of hypotheses and the validation is on the relative flat surface, the topographical correction schemes are very effective and can be widely used in the rugged mountainous areas.

Typical Portal Structure for Single Track High Speed Railway Tunnel in Rugged Mountainous Area with High and Abrupt Slope

On the basis of different landform and multifarious topography in rugged mountainous area in southwest China, typical tunnel portals for single track tunnels in a new high speed railway line have been presented in the paper. The portal comprises headwall, shed tunnel, bridge abutment and its support. Portal with headwall is suitable for tunnel to resist front earth pressure on high and abrupt slope. Shed tunnel is placed in front of headwall so as to prevent rockfall; its outward part is built into a flared one. Meanwhile, the installation of bridge and its abutment are also included in the portal according to landform in the paper.

Spatial Distribution and Breeding Performance of Golden EaglesAquila chrysaetosin Sicily: Implications for Conservation

Understanding ecological requirements of animals is essential to improve habitat management and conservation strategies for endangered species. However, as most studies on Golden Eagle's habitat preferences and breeding ecology have been conducted in northern latitudes (e.g. USA, Scotland, Scandinavia and the European Alpine region), our knowledge of the species ecology in the Mediterranean basin is more limited. Currently, only 16 pairs still remain in Sicily (southern Italy) and in spite of this delicate status of conservation, there were no previous attempts to analyse ecological requirements of the species in the island. Therefore, we monitored Golden Eagles from 1990 to 2012, analyzed habitat characteristics of breeding territories and quantified habitat relationships with breeding performance. We used a case-control design through Generalized Linear Models to examine ecological descriptors at two different spatial scales: (i) “territory” defined as a plot of 4 km radius centered in the nesting area; and (ii) “landscape” by means of the 10 × 10 km Universal Transversal Mercator (UTM) cells where the species was present or absent. At the territory scale, the presence of Golden Eagle was positively related to the ruggedness of the terrain and to the extension of arable land, and negatively to the extension of forests. At the landscape scale the presence of the species was positively correlated with the range of slope and negatively to the aridity of the surrounding landscape and the extension of forest areas. The Golden Eagle has experienced a strong decline in breeding performance during the last two decades in Sicily, which negatively impacted population dynamics. The best model at the territory scale included the surface of sparsely vegetated areas (i.e. a surrogate of prey availability) as the best predictor of breeding output (i.e. number of young fledged). At the landscape scale, the best predictor of breeding output was the average annual temperature (positive effect) and surface of artificial lands (negative effect). Significant differences in environmental characteristics were found between occupied and unoccupied sampling units and between territories of high and low breeding performance. Our results highlight the importance of maintaining the structure of landscape arising from traditional forms of extensive agriculture in the Mediterranean basin, thereby favouring prey availability, and the importance of limiting human activities and changes in land use in rugged mountainous areas.

Grounded electrical-source airborne transient electromagnetics (GREATEM) survey of Aso Volcano, Japan

Grounded electrical-source airborne transient electromagnetics (GREATEM), a type of semi-airborne electromagnetics, was used to examine Aso Volcano in south-west Japan, to verify its applicability to surveying deep subsurface resistivity structures. Comparison of the GREATEM resistivity values with those of ground-based transient electromagnetics (TEM) data, repeated GREATEM survey results at the same and different flight heights, and lithologic descriptions indicated that GREATEM can successfully identify underground structures as deep as ~800 m in rugged mountainous areas. An active volcanic region (Naka-Dake crater) was mapped as a low-resistivity zone from the surface to a depth of 100 m. This low-resistivity zone extended to the west-north-west, implying future volcanic activity in this area. Therefore, the GREATEM method is useful for surveying deep structures in large, inaccessible areas, such as volcanic provinces, in a quick, cost-effective way.

Applications of geographical information systems and remote sensing in natural disaster hazard assessment and mitigation in Taiwan

Geographic Information Systems (GISs) provide a powerful tool in managing and analysing spatial data. Geographic Information System has been applied successfully to large variety of fields, one field of particular interest is the field of disaster mitigation. The island of Taiwan is well known for the typhoons and earthquakes which in recent past has claimed lives and caused significant damage. It is well understood that hazard identification and land management play a major part in the reducing the impact of natural disasters. This is a role GIS is well suited to especially when combined with remote sensing data. This concept has been used throughout the world for purposes including identification of risk areas, real-time modelling of events and scenario modelling. Where this has the greatest potential in Taiwan is in the steep and rugged mountain areas of the Central Mountain Range which are sparsely populated and often difficult to access making conventional ground-based investigations impractical over large areas. Geographic Information System combined with remote sensing data provides the ability to effectively analyse various risk factors over large areas or inaccessible areas to identify localities which have the potential to be at higher risk from the impact of natural disasters.

Mountain glacier displacement estimation using a DEM-assisted offset tracking method with ALOS/PALSAR data

Mountain glaciers, as a sensitive indicator of climate change, are often monitored with all-weather synthetic aperture radar (SAR) technology. In contrast to the differential interferometric SAR approach, which is affected by decorrelation, the offset tracking method is a promising alternative that produces glacier displacement fields directly. The method, however, is often influenced by additional offsets associated with topographic effects in rugged mountain areas. For removing these topographic-related offsets, we present a digital elevation model-(DEM-) assisted offset tracking procedure and employ it with the Advanced Land Observing Satellite (ALOS) Phased Array type L-band SAR (PALSAR) data of Mt. Muztagh Ata. The results demonstrate the advantages of this method by reducing the topographical effects and increasing the accuracy (0.98 m). The approach proposed in this study can increase the accuracy of the results for estimated mountain glacier displacement and also extend the applicable range of the offset tracking method.

No Country for Middlemen: Three Sketches of Conflict on the Xiao Liangshan Frontier

No Country for Middlemen: Three Sketches of Conflict on the Xiao Liangshan Frontier Ann Maxwell Hill (bio) As a result of fieldwork in the Yunnan-Burma border area in July and August 2003, Kris Lehman wrote a paper based on his findings on the cross-border trade, which was published in Chinese under the title “Ethnicity, Politics, and the Structure of Interactions in the China-Burma Cross-Border Trade — A Cognitive Anthropological Approach” (2003). The article focuses on middlemen in the gem trade on China’s border with Burma, and their literally pivotal role in enabling communication and trade across different ethnic traditions and expectations. Current anthropological thinking about border zones and new work by historians on China’s frontiers have emphasized the agency of local people, countering the earlier view of border society as dominated by state actors (e.g., Bragge et al. 2006; Giersch 2006). Lehman’s work is a contribution to this more recent approach in the burgeoning field of border studies. Lehman’s paper prompted me to look at my own work in Xiao Liangshan, a frontier area in southwest China, with an eye toward identifying and analyzing cultural and political mediators. I conclude that inter-ethnic mediation between the Nuosu, the area’s dominant ethnic group, and the Han in the late Qing and first half of the twentieth century in Xiao Liangshan was seldom successful, if what we mean by success was the avoidance of violence and reprisals.1 I also [End Page 7] use ethnography to point out some of the reasons for the lack of success of inter-ethnic mediation and the dearth of mediators. Xiao Liangshan, or the Lesser Cold Mountains, is on the periphery of the rugged mountainous area known as Da Liangshan (Great Cold Mountains), often considered the heartland of the Nuosu who have likely inhabited this daunting upland terrain since the fourteenth century. A Chinese term, Xiao Liangshan originally denoted the frontier east of Da Liangshan along the Jin Sha Jiang (Golden Sands) River. Then in the latter half of the twentieth century, local people on another frontier, this one south and west of Da Liangshan, began to use the term for areas settled by Nuosu migrants over the past two hundred-fifty years. The two areas have in common a history of contact between the Nuosu and other ethnic groups to a degree that Nuosu in the heartland did not experience. Here, I use “Xiao Liangshan” to generalize about both areas when not identifying specific locales on this frontier. On the one hand, I am aware from fieldwork with the Nuosu in Xiao Liangshan, mostly those in what is now Yunnan’s Ninglang Yi Autonomous County, that they thought of themselves as a tightly self-contained, primordial people. On the other hand, I know that historically they sometimes lived in close proximity to other peoples in Xiao Liangshan, including Han populations. A few Nuosu participated in [End Page 8] markets, a very few were Nuosu officials appointed by the Chinese court or lived near to these officials, and some took captives from neighboring ethnic groups—all good evidence that the Nuosu were not isolated from other peoples, contrary to their own self-perception and that of nineteenth-century Western travelers to the area (see Li Lie 2006, 61 for a discussion of these travelers’ tales). Yet instances of successful cultural or political mediation between the Nuosu and other ethnic groups in this frontier area were hard to find in the hundred years before the mid-twentieth century, at which point the mountain-dwelling Nuosu were nominally incorporated into the new Chinese state. Middlemen, their absence or presence, success or failure, are a gauge of the strength and efficacy of interethnic networks. A tautology perhaps, but I mean to say that focusing on middlemen provides insight into frontier social integration, often fragile and temporary, and the sources of violence where local people confront complex forces engendered by state agents, as well as those reflecting particular ethnic political traditions (see Ferguson and Whitehead 1992). As an example of the latter, Nuosu societies in Xiao Liangshan had their own dynamic primarily emanating from clans with their ideology of loyalty and...

GEOBIA Vegetation Mapping in Great Smoky Mountains National Park with Spectral and Non-spectral Ancillary Information

Vegetation mapping was performed using geographic object-based image analysis (GEOS1A) and very high spatial resolution (VHR) imagery for two study areas in Great Smoky Mountains National Park. This study investigated how accurately GEOB1A with ancillary data emulates manual interpretation in rugged mountain areas for multi-level vegetation classes of the National Vegetation Classification System (NVCS). It was discovered that the incorporation of texture and topographic variables with spectral data from scanned color infrared aerial photographs increased the overall accuracy of GEOBIA vegetation classification by 2.8 percent and 5.0 percent Kappa. In a separate study using multispectral Ikonos imagery, the use of elevation, aspect, slope and proximity to streams produced NVCS macro-group vegetation segmentations that resembled manual interpretation and significantly improved the overall accuracy to 76.6 percent, Kappa 0.57. Ancillary information may thus aid in GEOBIA vegetation mapping for updating vegetation inventories in rugged mountain areas.

The estimation of errors in calculated terrain corrections in the Tatra Mountains

The estimation of errors in calculated terrain corrections in the Tatra Mountains In general, calculation of terrain corrections can be a substantial source of errors in evaluating Bouguer anomalies, especially in rugged mountainous areas like the Tatra Mountains where we also get the largest values of the terrain corrections as such. It is then natural that analysis of their calculations in this area can shed light on the magnitude of correction-related errors within the whole Slovak territory. In the framework of our analysis we have estimated the effect of different computing approaches as well as the influence of accuracy of the inputs, i.e. the heights and positions of the measuring points, together with the used digital terrain models. For the sake of testing the computer programs which are currently in use, we have also substituted the real terrain by synthetic topography. We found that among the concerned constituents the most important factor is the used digital terrain model and its accuracy. The possible model-caused errors can exceed 10 mGal in the Tatra Mountains (for the density of 2.67 g.cm-3).

A landscape-scale assessment of the long-term integrated control of an invasive shrub in South Africa

The control of invasive alien plants often involves the integration two or more approaches, including mechanical clearing, the application of herbicides, burning, and biological control. More than one species of invasive plant can threaten the same area, which necessitates prioritization in the allocation of scarce resources to support the control of different species. This paper describes the integrated control of the invasive shrub Hakea sericea over four decades in South Africa. The species is widespread across an area of approximately 800 × 200 km, and occurs mainly in rugged, inaccessible and fire-prone mountain areas. The species is serotinous, and produces copious amounts of seed that are wind dispersed after fires. We present a brief history of the control measures which included a combination of felling and burning, augmented by biological control. We used data from two surveys, 22 years apart, to assess changes in distribution and density of the species. The assessment suggested that the overall distribution of the species was reduced by 64%, from ~530,000 to ~190,000 ha between 1979 and 2001. The species either decreased in density, or was eliminated from 492,113 ha, while it increased in density, or colonised 107,192 ha. We conclude that initial programs of mechanical clearing were responsible for reducing the density and extent of infestations, and biological control was largely responsible for the failure of the species to re-colonize cleared sites, or to spread to new areas following unplanned wildfires. We propose that a significant portion of the resources used for clearing Hakea in the past can be reallocated to mechanical control efforts against other invasive species (such as alien pines) for which effective biological control options are not available, provided that sufficient resources are allocated to ensure the widespread and effective implementation of all biological control agents to maintain the advances reported on here.

Habitat selection by an Alpine ungulate: the significance of forage characteristics varies with scale and season

Habitat selection in ungulates should ensure access to abundant forage of sufficiently high quality. Species living in rugged mountain areas have to face nutritional bottlenecks regularly and should show particularly sophisticated habitat selection behaviour. However, patterns and mechanisms of such adaptations remain little studied. We analysed habitat selection and its seasonal variability of 10 GPS‐collared red deerCervus elaphusliving in a topographically challenging landscape of the Swiss Alps. We hypothesised that resource selection by red deer was scale‐dependent and predicted that scale‐dependence would vary among seasons in relation to seasonal changes of available forage biomass and quality, which we sampled across the entire study area of 250 km2. The studied population of Alpine red deer undertook altitudinal migrations and showed scale‐dependent habitat selection that was strongest in winter and declined through spring and summer. Selection occurred mostly at the larger (landscape/home‐range location) scale and less so at the smaller (within home‐range) scale. Topographic parameters were selected mainly at the landscape scale and mostly in winter. About 70% of all instances of preference for habitat parameters were associated with above‐average forage characteristics, represented mostly by higher crude protein content, in a few cases also by higher biomass or both. The overall pattern of space use by red deer characterised by migration and seasonal habitat selection was therefore closely linked to the quality of food resources, although some trade‐offs with avoiding human disturbance may also have been involved.

Application of TELUM by the Pikes Peak, Colorado, Area Council of Governments

For U.S. metropolitan planning organizations (MPOs), obtaining, preparing, and validating socioeconomic forecasts are fundamental tasks to ensure that logical, consistent, and approved population and employment data are provided to the travel demand models. This process is enhanced if the MPO includes both transportation and land use inputs into the forecast process. To fulfill these desires, the Pikes Peak Area Council of Governments (the MPO in Colorado Springs, Colorado) decided to use TELUM–-transportation, economic, and land use model software–-to conduct the land use forecasting task. TELUM was developed by Stephen Putman and the New Jersey Institute of Technology (NJIT) as part of the transportation, economic, and land use system sponsored by FHWA. With assistance from NJIT, MPO staff serving this 500,000-plus person region calibrated the land use model for the 2000 to 2005 period and then used TELUM to produce land use forecasts for six 5-year increments between 2005 and 2035. The Colorado Springs region has a unique character, including a workforce that is 11% active military personnel, a diverse employment profile including high-tech manufacturing and a large recreation-based workforce, and a growing retiree population. Additionally, the MPO area includes a dense urban area, large exurban developments, rugged mountain areas, and frontier grasslands, all of which challenged the technical staff that worked on model development. The technical and policy insights and lessons learned from the TELUM application in Colorado Springs have transferable value for all sizes of MPOs faced with forecasting development and transportation.

Remote sensing for environmental protection of the eastern Mediterranean rugged mountainous areas, Lebanon

Lying along the eastern Mediterranean coast with elevated mountain chains higher than 2500 m straddling its terrain, Lebanon is a country of natural beauty and is thus attracting tourism. However, with a population density exceeding 800/km 2 and a rugged steep sloping land, problems abound in the country calling for holistic-approach studies. Only remote sensing, whose use is new in Lebanon can secure such needed studies within a scientific and pragmatic framework. The paper demonstrates for the concerned themes, the innovative use of remote sensing in such a difficult terrain, giving three examples of major environmental problems in the coastal mountains. Only few studies have so far focused on those mountains, notably application of remote sensing. The rugged mountainous terrain receives considerable rain, but the water is quickly lost running on the steep slopes, or infiltrating through fractures and the karstic conduits into the subsurface. Field investigations are difficult to achieve, therefore, remote sensing helps reveal various surface land features important in reflecting water feeding into the subsurface. Optical, radar and thermal infrared remotely sensed data cover a wide spectrum serving that purpose. A map of preferential groundwater accumulation potential is produced. It can serve for better water exploitation as well as protection. Because the terrain is karstic and rugged, the subsurface water flow is difficult to discern. Any pollution at a certain spot would certainly spread around. This constitutes the second example of environmental problems facing the mountainous areas in Lebanon. An integrated approach using remote sensing and geographic information systems (GIS) gives good results in finding out the likelihood of how pollution, or contaminants, can selectively move in the subsurface. A diagnostic analysis with a GIS-type software acts as a guide producing indicative maps for the above purpose. The third example given deals with the problem of losing soil, which is a very vital source in such mountainous land. With steep slopes, torrential rain and improper human interference, run-off is high and water–soil erosion is continuously deteriorating the land cover. Remote sensing can facilitate studying the factors enhancing the process, such as soil type, slope gradient, drainage, geology and land cover. Digital elevation models created from SAR imagery contribute significantly to assessing vulnerability of hydric-soil erosion over such a difficult terrain. GIS layers of the above factors are integrated with erosional criteria to produce a risk map of soil erosion. Results indicate that 36% of the Lebanese terrain is under threat of high-level erosion, and 52% of that is concentrated in the rugged mountainous regions.

Development of an Antarctic digital elevation model by integrating cartographic and remotely sensed data: A geographic information system based approach

We present a high‐resolution digital elevation model (DEM) of the Antarctic. It was created in a geographic information system (GIS) environment by integrating the best available topographic data from a variety of sources. Extensive GIS‐based error detection and correction operations ensured that our DEM is free of gross errors. The carefully designed interpolation algorithms for different types of source data and incorporation of surface morphologic information preserved and enhanced the fine surface structures present in the source data. The effective control of adverse edge effects and the use of the Hermite blending weight function in data merging minimized the discontinuities between different types of data, leading to a seamless and topographically consistent DEM throughout the Antarctic. This new DEM provides exceptional topographical details and represents a substantial improvement in horizontal resolution and vertical accuracy over the earlier, continental‐scale renditions, particularly in mountainous and coastal regions. It has a horizontal resolution of 200 m over the rugged mountains, 400 m in the coastal regions, and approximately 5 km in the interior. The vertical accuracy of the DEM is estimated at about 100–130 m over the rugged mountainous area, better than 2 m for the ice shelves, better than 15 m for the interior ice sheet, and about 35 m for the steeper ice sheet perimeter. The Antarctic DEM can be obtained from the authors.

Surveying and Hydraulic Engineering of the Pre-Columbian Chimú State: ad 900–1450

The Chimú state of northern coastal Peru (ad 900–1480) developed massive irrigation-based agricultural systems supplied by intricate networks of canals drawing water from river sources in coastal valleys under their political control. Further intervalley canal systems, some up to 50 miles in length, were constructed to shunt water between river valleys to augment intravalley supplies. A high degree of civil engineering skill was necessary to construct and maintain such complex systems; knowledge of surveying and of open channel flow hydraulics was paramount. Some of the technology used by the Chimú has been investigated: surveying instruments and calculating tools have been unearthed and analyzed to provide some understanding of the technical base used for canal design. Details of the hydraulics knowledge-base have been extracted from computer simulation of the functioning of ancient Chimú canal designs. This article assembles known pieces of information related to Chimú civil engineering practice and attempts to provide a plausible methodology that could have been implemented by the Chimú to survey the precise canal bed slopes necessary for proper hydraulic functioning of large canal systems through rugged Andean foothill and mountain areas.

Rediscovery of Lygodium palmatum in Georgia

On Sunday, January 16, 1955, I had made an appointment with my friend, Mrs. Sammy Ledbetter, to help relocate a colony of Gaultheria procumbens L., a plant nearing its southern limit in northeastern Georgia, and extremely rare in this area. Two weeks previously I had searched for it and became lost in this rugged mountainous area. On our return from a successful collecting trip, Mrs. Ledbetter asked me to look at a plant growing on the road-bank in front of their summer cottage. You can imagine my delight and surprise to see greatly indebted to Mr D J. Hagenah for supi g information about specime s in the herbaria of ranbr ok Ins i ute and of the University of Michi. The field work and phyto eographic research ich ade thi study possible have been supported by ts from the R search Council of Ontario and from niversity of T ronto. 104