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Susan E. Hume 《The Professional geographer》2013,65(4):555-557
Research on small cities has begun to attract the attention of scholars who argue that contemporary urban scholarship, in its preoccupation with the largest and most advanced world-class cities, have largely ignored small to medium-sized cities. In China, although much attention has been paid to economically advanced urban centers, there actually has been a steady stream of work on small cities. This article profiles how a comparatively smaller city in western China attempts to market itself by selectively placing itself within various social–spatial and political–economic realities. Through Jinghong, we illustrate how local officials and planners attempt to center the city as a gateway to Southeast Asia. By activating, often discursively, multiscalar transborder strategies, local officials in Jinghong not only mobilize ethnic imaginaries, but they also adopt forms of entrepreneurial tactics to promote growth. Developmental strategies of Jinghong not only vacillate between (and draw on) both rural and urban resources; they are furthermore expected to alleviate rural poverty. Through highlighting the agency of small cities like Jinghong in China, this article speaks to the broader developmentalist critique of third- and fourth-world cities as an unfortunate footnote in global urban restructuring, often depicted as places of uniform marginalization and structural irrelevance. Indeed, by focusing on the geography of small cities and giving due attention to their size and proximity to rural spaces, case studies like Jinghong might yet point empathetically to different ways and imperatives of “being urban” where the weight that they carry can also be duly recognized. 相似文献
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In 2013, we celebrate the 50th anniversary of the publication of V. B. Sochava’s first paper in which he offered the definition of the term “geosystem”. His paper entitled “The definition of some notions and terms in physical geography” remains one of the most frequently cited articles in the national geographical literature. The concept of the geosystem was included in encyclopedias. The geosystem ideology is used in training of specialists in the field of geography. 相似文献
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Glen M. MacDonald David F. Porinchu Nicolas Rolland Konstantine V. Kremenetsky Darrell S. Kaufman 《Journal of Paleolimnology》2009,41(1):129-141
Instrumental climate records from the central Canadian treeline zone display a pattern of variation similar to general Northern
Hemisphere temperature trends. To examine whether this general correspondence extends back beyond the instrumental record,
we obtained a sediment core from Lake S41, a small lake in the Northwest Territories of Canada at 63°43.11′ N, 109°19.07′ W.
A radiocarbon-based chronology was developed for the core. The sediments were analyzed for organic-matter content by loss-on-ignition
(LOI), biogenic-silica content (BSi), and chironomid community composition to reconstruct July air temperature and summer
water temperature. The paleolimnological records were compared with records of atmospheric CO2 concentration, solar variability, and hemispheric temperature variations over the past 2000 years. The results of the analyses
suggest that widely-documented long-term variations in Northern Hemisphere temperature associated with radiative forcing,
namely the cooling following the medieval period during the Little Ice Age (LIA), and twentieth century warming, are represented
in the central Canadian treeline zone. There is also evidence of a brief episode of warming during the eighteenth century.
As evidenced by LOI and BSi, the twentieth century warming is typified by increased lake productivity relative to the LIA.
Depending upon the measure, the increased productivity of the twentieth century nearly equals or exceeds that of any other
period in the past 2000 years. In contrast, the rate of chironomid head capsule accumulation decreased and remained low during
the twentieth century. Although the chironomid-inferred temperature reconstructions indicate cooling during the LIA, they
present no evidence of greatly increased temperatures during the twentieth century. Warming during the twentieth century might
have enhanced lake stratification, and the response of the chironomid fauna to warming was attenuated by decreased oxygen
and lower temperatures in the hypolimnion of the more stratification-prone lake.
相似文献
Glen M. MacDonaldEmail: |
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The Chilean Lake District (38–42°S) is strongly influenced by Southern westerlies-driven precipitations. At 40°S Lago Puyehue
provides high resolution sedimentation rates (∼1–2 mm/yr) suitable for annual climate reconstruction. Several short and long
sediment cores were collected in this lake. Their analysis aim at a better understanding of climate mechanisms related to
ENSO in this part of the world. The recognition of ENSO related periodicities and their stability is studied through the analysis
of two short varved cores collected from underflow and interflow key sites. According to varve chronology controlled by 137Cs and 210Pb profiles and chronostratigraphical markers, the short core from underflow site (PU-I) spans 294 ± 18 years and the core
in the interflow site (PU-II) covers 592 ± 9 years. Several methods of spectral analysis were applied on the total varve thickness
to identify potential periodicities in the signal. Blackman–Tuckey, Maximum Entropy, Multi-Taper Methods (MTM) and singular
spectrum analysis were applied on the whole record. In addition, evolutive MTM and wavelet analyses allow to identify temporal
influence of some periodicities. In the PU-I studied interval (AD 1700–2000), a period at ∼3.0 years appears in a large part
of the interval, mostly in the recent part. Periods at ∼5.2 and ∼23 years also show up. PU-II record (AD 1400–2000) displays
the most robust periodicities at around 15, 9, 4.4, 3.2 and 2.4 years. These periodicities are in good agreement with the
sub-decadal periods identified by Dean and Kemp (2004) and linked to the El Nino Southern Oscillation and the Pacific Decadal
Oscillation. Differences in the recorded periodicities between PU-I and PU-II sites are consistent with different sedimentation
processes in the lake. According to climate instrumental data for the last 20 years, varves in PU-I site are mostly related
to fluvial dynamics and regional climate factors, i.e., precipitation, temperature and wind. In PU-II site, varves increment
is related to both regional and global climate forcing factors, i.e., El Nino Southern Oscillation. The evolutive MTM analysis
and the wavelet analysis suggest a striking break in the periodicities at around AD 1820. Finally relationships between El
Nino and longer term climate phase like the Little Ice Age (LIA) are also assessed.
This is the seventh in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre
and E. Chapron. 相似文献
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J. T. COPPOCK 《International journal of geographical information science》2013,27(2):191-192
ABSTRACT A wide range of environmental process simulations would benefit from the development of GIS able to cope with the additional dimensions of vertical space and time, and having extended spatial modelling facilities. The results of a project in the first of these areas, namely on the development of techniques for handling four-dimensional (4-D) data, are described. The key topics of data models, visualization and interpolation have been studied. Problems include the large size of some 4-D data sets, the sparseness of sampling in some dimensions compared with others, and the need to combine data sets from different sensors which may be of different dimensionalities and scales. The gridded volume data common to most environmental models are stored in a 4-D bintree form in which all dimensions are treated identically. Simple 4-D objects may also be stored, and links are provided between volume and object databases. The techniques have been implemented within a computational testbed allowing parallel processing to cope with large data sizes. 相似文献
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Variations of monsoonal precipitation over the last 16,000 years in the eastern Nanling Mountains,South China 总被引:1,自引:0,他引:1
Wei Zhong Jibin Xue Yanming Zheng Qiaohong Ma Ying Cai Jun Ouyang Liubin Xu Shangzhe Zhou Xuefeng Yu 《Journal of Paleolimnology》2010,44(1):177-188
A 350-cm-long sediment core was recovered from Dahu Swamp in the eastern Nanling Mountains in south China for paleoclimatic investigation. Twelve 14C dates determined on organic-rich bulk samples establish a chronological sequence for this core and yield a bottom age of ~16,000 cal years BP. Multiproxies including dry bulk density, magnetic susceptibility, organic carbon isotope, median grain size, silt-size fraction and total organic matter content were used to study variations of precipitation in relation to the East Asian monsoon. The core sediments are characterized by shifts between the lacustrine sediments and marshy sediments, implying hydrological variations between expansion and shrinkage of the water body in the swamp, and suggesting relatively wetter and drier conditions, respectively. Two relatively wetter episodes lasting from ~15,000 to 14,000 cal years BP and from ~13,500 to 12,800 cal years BP were revealed, possibly corresponding to the Bølling and the Allerød warming events, and three relatively drier phases occurred between ~16,000 and 15,000 cal years BP, between ~14,000 and 13,500 cal years BP and between ~12,800 and 11,500 cal years BP. The three events synchronize with the Oldest Dryas, the Older Dryas and the Younger Dryas cooling events, respectively. A distinctly humid period lasted from ~10,000 to 6,000 cal years BP in the early- and mid- Holocene was interpreted as the Holocene Optimum period. Several short dry events were revealed, including the most pronounced one at ~8,100 cal years BP that coincides with the “8,200 year” cooling event. Multiproxies indicate an evidently dry climate prevailing in the mid-Holocene (from ~6,000 to 3,000 cal years BP), reflecting a weakening of the East Asian summer monsoon. The general trend of Holocene climate shows agreement with the 25°N summer solar insolation, suggesting that the orbitally induced insolation have played a key role in the Holocene climate in south China. 相似文献
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An outline is given of the career and scientific and teaching activity of the outstanding geomorphologist, professor of Moscow State University S.S. Voskresenskii, who created new scientific directions in the study of topography. He is rightfully given credit for geographical investigations of Siberia and the Far East in the latter half of the 20th century. 相似文献
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Hanna Maoh Kevin Gingerich Rahaf Husein William Anderson 《The Professional geographer》2018,70(3):350-362
Land borders connecting Canada and the United States are vital transportation facilities for the two countries. Truck crossing times at these facilities can have a significant impact on the performance of the economy. To date, knowledge about border crossing times has been limited due to lack of detailed data on the Canadian border. This article explores and models the patterns of crossing times at the three major land crossings connecting Canada to the United States: Ambassador Bridge, Blue Water Bridge, and Peace Bridge. The analysis is based on 387,775 border crossing truck trips that were generated between Canada and the United States over a course of twelve months. Seemingly unrelated regression (SUR) models are estimated to evaluate the seasonal and hourly crossing times of Canada- and U.S.-bound trips on each border crossing, controlling for traffic intensity in the models. The SUR modeling approach is chosen to control for potential cross-model correlations. The results suggest that crossing times at the border vary by season and hour of the day. Crossing times also vary by direction of traffic and by type of day (i.e., weekday vs. weekend). Traffic intensity has a significant influence on crossing times at two of the crossings but not the Blue Water Bridge. Finally, crossing times are more variable during the summer season and tend to be higher during the late evening hours and past midnight. 相似文献
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Variations in the oxygen-isotope composition of paleo-water bodies in the Lake Superior Basin provide information about the
timing and pathways of glacial meltwater inflow into and within the Lake Superior Basin. Here, the oxygen-isotope compositions
of Lake Superior have been determined using ostracodes from four sediment cores from across the Basin (Duluth, Caribou and
Ile Parisienne sub-basins, Thunder Bay trough). The δ18O values indicate that lake water (Lake Minong) at ~10,600–10,400 cal [~9,400–9,250] BP was dominated by glacial meltwater
derived from Lake Agassiz and the Laurentide Ice Sheet (LIS). From that time to ~9,000 cal [~8,100] BP, a period associated
with formation of thick varves across the Lake Superior Basin, the δ18O values of Lake Minong decreased even further (−24 to −28‰), symptomatic of an increasing influx of glacial meltwater. Its
supply was reduced between ~9,000 and ~8,900 cal [~8,100–8,000] BP, and lake water δ18O values grew higher by several per mil during this period. Between ~8,900 and ~8,800 cal [~8,000–7,950] BP, there was a return
to δ18O values as low as −29‰ in some parts of the Lake Superior Basin, indicating a renewed influx of glacial meltwater before
its final termination at ~8,800–8,700 cal [~7,950–7,900] BP. The sub-basins in the Lake Superior Basin generally displayed
very similar patterns of lake water δ18O values, typical of a well-mixed system. The final stage of glacial meltwater input, however, was largely expressed near
its input (Thunder Bay trough) and recognizable in dampened form mainly in the Duluth sub-basin to the west. Water in the
easternmost Ile Parisienne sub-basin was enriched in 18O relative to the rest of the lake, particularly after ~10,000 cal [~8,900] BP, probably because of a strong influence of
local precipitation/runoff, and perhaps also enhanced evaporation. By ~9,200 cal [~8,250] BP, lake water δ18O values in the Ile Parisienne sub-basin were similar to the adjacent Lake Huron Basin, suggesting a strong hydraulic connection
between the two water bodies, and common responses to southern Ontario’s shift to warmer and dry climatic conditions after
~9,000 cal [~8,100] BP. 相似文献
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Anna Augustsson Pasi Peltola Bo Bergbäck Timo Saarinen Eeva Haltia-Hovi 《Journal of Paleolimnology》2010,44(4):1025-1038
A high-resolution geochemical profile from a 5,500-year-old sediment core of Lake Lehmilampi in eastern Finland was analyzed
to study long-term trends and variability in element concentrations and accumulation rates. The accumulation rates of all
studied elements followed the same trend, responding to changes in the total sedimentation rate. Concentration profiles differed
among elements and showed considerable variation over time. Principal components analysis (PCA) was used on the concentration
data to identify groups of elements that have similar geochemical controls. The first principal component was influenced by
changes in mineral matter accumulation, and it incorporated elements that are associated with stable allochthonous minerals
(such as Mg, K, Cs, Rb, Li, Ti and Ga), as well as elements in forms that become diluted when mineral matter increases (e.g.,
S, Fe and Mn). The second and third principal components showed that a large proportion of the variance was accounted for
by elements with continuously increasing or decreasing concentrations related to pedogenetical development of the catchment
soil. In the case of Hg, Pb and Cd, however, accumulation rates increased faster at the surface than is simply accounted for
by changes in total sedimentation rates. For Cu, Cr, Ni and Zn, concentrations increased over the past 150 years, but there
were no indications of a significant addition due to atmospheric deposition. These elements had more variable concentrations
before the mid nineteenth century than after, as did elements that are often used for normalization. These findings suggest
that lake sediments may not properly reflect the history of atmospheric metal deposition in remote areas. 相似文献
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Slavomír Nehyba Daniel Nývlt Uwe Schkade Gerald Kirchner Eva Franců 《Journal of Paleolimnology》2011,45(1):41-55
Facies analysis, magnetic susceptibility, and analysis of grain size, TOC content and isotopes (137Cs, 210Pb, 226Ra, 228Ra, and 238U concentrations) were used to determine the history of the modern deposits of the Brno reservoir. The sedimentary succession
can be subdivided into two main units. The lower unit is formed predominantly by medium- to coarse-grained silty sands and
is interpreted as a fluvial succession deposited before the Svratka River was dammed. The upper unit consists of brownish
planar laminated silts and rarely of clayey or sandy silts and is interpreted as a product of the reservoir deposition. The
concentrations of 238U reflect the history of uranium mining in the upper part of the Svratka River catchment. As a consequence, 210Pb radionuclide concentrations cannot be used for establishing a sediment chronology. Concentrations of 137Cs show two marked peaks, the upper of which is attributed to the Chernobyl reactor accident in 1986, and the lower one is
attributed to the maximum rate of atomic weapons testing in 1963. From these peaks, mean depositional rates of 3.2 cm year−1 for the time period of 1986–2007 and of 3.4 cm year−1 between 1963 and 1986 are calculated. Based on the known age of the reservoir, which was constructed in 1939, we can also
calculate mean depositional rate for the time period of 1939–1963, which is 3.1 cm year−1. 相似文献
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Natural Resources Research - The U.S. Gulf of Mexico is a world-class hydrocarbon basin and industry has an impressive track record of advancing its capabilities in the region. From 1947 to 2017,... 相似文献