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221.
The Greenland ice core from NorthGRIP (NGRIP) contains a proxy climate record across the Pleistocene-Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision.  相似文献   
222.
The Second World War marked an epochal change in the relation of geographers to war and the military. The military had long utilised the skills of geographers, but from World War II the relation changed at least in the United States, and the military began less drawing upon existing geographical knowledge than directing a new kind that was increasingly formal, instrumental, and model driven. With the growing importance of the computer, this trend continued even more strongly during the early Cold War period, and was further propelled by the interests of a new, collective assemblage, the military-industrial complex. A cyborg entity, the military-industrial complex enfolded diverse performances, ideas, inanimate objects, people and even academic disciplines into a larger composite, one product of which was a new regime for the production of knowledge. The purposes of the paper are to examine the process by which geography within the United Stated joined this cyborg entity, and the character of the disciplinary knowledge regime that eventuated. The argument is pursued by examining three individuals key to the new disciplinary regime: Waldo Tobler a pioneer of analytical cartography and later GIS whose first job was at RAND on a project to develop an early warning system for nuclear attack; William Garrison who spearheaded the use of economic modelling in studies of transportation that he carried out with his students at the University of Washington Seattle; and Arthur Strahler, a geologist at Columbia University, who through his links to the US Office of Naval Research, funded and directed a set of students who later entered physical geography utterly transforming it to meet the dictates of the new regime.  相似文献   
223.
The world is facing a severe water crisis. According to the UN, by 2025 50% of the world’s population will face water scarcity. In India, where 70% of irrigation and 80% of domestic needs are met with groundwater, demand for this resource is expected to exceed supply by 2020. This has led to recent calls for groundwater governance reforms within India, and specifically within the state of Rajasthan, where no regulation exists today. The success of these reforms hinges on the interaction of the state and its agents with local users and managers of groundwater resources. Underpinning these encounters, though, are tensions between local and state forms of groundwater knowledges. The question analyzed here is in what ways do conflicting environmental knowledges adversely affect the management of overexploited groundwater resources in water-scarce India? To address this question, I examine the coevolution of pre-colonial, colonial, and post-independence groundwater and irrigation knowledges and technologies in Rajasthan, India to expose the ways that they are produced, contested, legitimated, and hybridized. The paper argues the following three claims. First, the relationship between the state and local producers of groundwater knowledge practices is non-linear and porous. For instance, the way that state subjects experience the state is uneven because within and in-between historical moments the state may attempt to assimilate, reorganize, plagiarize, or disparage local knowledge. Second, these attempts produce or exacerbate existing historically rooted tensions between farmers and state groundwater engineers. But in response, farmers often seek out non-state avenues of expertise, such as tubewell drilling firms. This results in the further hybridization of knowledge practices and also in the present-day marginalization of the state. Third, the relationship between farmers and the state is further strained because of a current lack of state visibility in the study area and also because the state continues to “see like a state”. These shifting meanings and power relations around groundwater and irrigation knowledges produce tensions that will undoubtedly negatively impact future groundwater governance strategies.  相似文献   
224.
A magnetotelluric study of the Alpine Fault, New Zealand   总被引:1,自引:0,他引:1  
Magnetotelluric soundings have been made at seven locations on a 4  km profile crossing the Alpine Fault in the South Island of New Zealand. The 'distortion' techniques of Groom & Bailey (1989 ) and Lilley (1998a , b ) have been used to derive regional apparent resistivity and phase curves that correspond to electromagnetic induction in orientations parallel and perpendicular to the fault. 2-D inversion of the regional responses reveals that a narrow (<1  km wide) conductive zone is associated with the Alpine Fault. This conductor is most probably related to the heating of deep circulating meteoric water in a region in which enhanced temperatures occur at shallow depth due to the tectonic uplift of the Southern Alps.  相似文献   
225.
Geographic scholarship in critical toponymy has highlighted the importance of place naming as a form of discursive power within processes of urbanization. This paper builds on such literature and advances a novel theory of toponymic assemblage to interpret findings from a participatory research project in the Downtown Eastside of Vancouver, Canada. We foreground neighborhood history in the form of a Japanese Canadian enclave and its wartime uprooting and dispossession, and trace the historical antecedents of a resurrected toponymy of “Japantown” that has appropriated and renarrated Japanese Canadian history to facilitate further rounds of dispossession. Using a genealogical method, we highlight three “moments” of Japanese Canadian uprooting, return, presence, and activism, demonstrating how toponymies are assembled in place in heterogeneous and historically contiguous ways. This approach expands on current research in critical toponymy, offering a novel methodology for exploring the enrolment of toponymy, discourse, and materiality in the formation of place.  相似文献   
226.
We present some numerical methods which simplify the analysis of equipment-structure systems composed of an equipment component which is light with respect to the structure component. We consider completely general forms of equipment-structure interaction. In particular, we consider that an arbitrary number of natural frequencies of the equipment and the structure are nearly equal (or equal) to each other. We show that this coincidence of natural frequencies implies that the equipment-structure system will itself have several closely spaced natural frequencies. The essence of equipment-structure interaction is the formation of beats, with slowly varying amplitude in each degree of freedom, between these natural frequencies-at least in response to a δ-function ground motion. We derive some differential equations, the solutions of which are a slowly varying envelope function (a vector) which yields the above slowly varying amplitudes. It is obtained by numerical integration using some conventional, but modified, methods and using a step size appropriate to capture its slowly varying nature. This envelope function defines the response to a δ-function ground motion. We show how it may be combined with the properties of an arbitrary ground motion (acceleration record or response spectrum) to yield the response to such a ground motion.  相似文献   
227.
228.
A series of geomagnetic induction studies has been undertaken in Scotland since 1973. It includes the operation of two geomagnetic arrays, one over northern Scotland and the other over southern Scotland, subsequent individual station and small-scale geomagnetic array studies, and three sets of magnetotelluric soundings which traverse Scotland from the Lewisian Foreland to the English border. The problems associated with the interpretation of induction data from an island located in the subauroral region are discussed qualitatively and the manner in which both coast and source field effects can be accounted for, is described. The geomagnetic deep sounding data (GDS) from all the observation sites have been collated, and examples of hypothetical event contour maps and traverses across the Great Glen and of individual events from the northern array are presented. They indicate that significant lateral variations in electrical conductivity structure within the crust and upper mantle are associated with the major geological faults in the region. Examples of the results of the magnetotelluric soundings are also presented, together with an outline of the procedure used for one- and two-dimensional modelling. Models of the geo-electric structure in both northern and southern Scotland have been obtained. These show distinctive features which are compatible with the qualitative interpretation of the magnetovariational data. For example, the major granitic blocks are highly resistive while regions of relatively low resistivity exist at upper crustal depths near the Great Glen, Highland boundary and Southern Uplands faults. A zone of low resistivity exists at lower crust-uppermost mantle depths throughout much of the region, the lowest value occurring under the Southern Uplands.  相似文献   
229.
Bedload pulses in gravel-bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology. Bedload transport and channel morphology were measured in a small-scale generic model of braided gravel-bed streams. Two experiments are described in which braided channels developed in a 14 m × 3 m sand tray. Total bedload output from the tray was weighed every 15 minutes. Stream bed geometry was surveyed every four hours. Pulses were observed in the bedload output time series, and were qualitatively related to the channel morphology immediately upstream of the measuring section. The Bagnold (1980) bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading. Underprediction occurred when applied to degrading channels. Aggradation was associated with channel multiplication and bar deposition. Channel pattern simplification occurred when degradation took place, and bars emerged from the water flow. Development of phases of aggradation and degradation is dependent upon the three-dimensional geometry of the stream beds. Spatial and temporal feedback loops can be identified, enabling links between channel morphology and bedload transport rate to be directly identified.  相似文献   
230.
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