Are migrants exceptional resource degraders? A study of agricultural households in Ghana     

Samuel Nii Ardey Codjoe  Richard E. Bilsborrow 《GeoJournal》2012,77(5):681-694

Although some scholars describe migrant farmers as ‘exceptional resource degraders’ others do not. This paper uses evidence from the transitional agro-ecological zone of Ghana, to examine whether there are substantial differences between households of migrants and the host population regarding agricultural land use. The aim is to determine whether migrants are more destructive of the land (and hence the environment) than the host population. This will be examined using a standard model of the determinants of agricultural land use, to which we add variables representing demographic impacts, including in-migration. The data used are from a household survey undertaken in 2002 among 110 migrant and 142 host population farming households in central Ghana. Results are mixed. We find no support for the hypothesis that households with migrants are less likely to consider the long-term effects of land use by increasing the land area in cultivation, but at the same time there is evidence of use of more land-intensive agricultural practices which tend to degrade farm land over time.  相似文献   

Scenes from Avellaneda, Argentina     

Samuel R. Friedman 《GeoJournal》2012,77(4):451-451

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SPECTRAL SIGNATURE OF COUPLED FLOW IN THE REFREEZING ACTIVE LAYER,NORTHERN ALASKA     

Samuel I. Outcalt  Kenneth M. Hinkel  Frederick E. Nelson 《自然地理学》2013,34(3):273-284

Soil temperature records obtained from the active layer above permafrost at a site in northern Alaska during autumn and winter have variance spectra inconsistent with a purely conductive heat-transfer system. Although conductive heat-transfer theory predicts that temperature fluctuations are attenuated with depth, sub-diurnal thermal variance at the 50-cm level, near the base of the active layer, exceeded that at the 10-cm level. Short segments of the temperature record were drawn from three distinct periods of soil-frost conditions: (1) at the maximum vertical development of the active layer in early autumn; (2) during frost penetration and the formation of a zero curtain in early winter; and (3) after freezeback of the active layer. The variance spectra of these time series show systematic seasonal transitions that reflect changing mechanisms of heat transfer. During the first and second periods, heat transfer by internal evaporation and condensation dominates at wavelengths in the diurnal range. The spectral traces are not strongly self-similar and the fractal dimensions indicate extreme space-filling, especially at deeper levels. Once the active layer is frozen, conductive heat transfer dominates, producing a trend toward self-similarity. Both the thermal variance and the fractal dimension decrease with depth in the frozen regime. [Key words: Alaska, active layer, coupled flow, fractal dimension, frozen ground, heat transfer, permafrost, soil freezing, spectral analysis, zero curtain.]  相似文献   

A method for discovery and analysis of temporal patterns in complex event data     

Donna J. Peuquet  Anthony C. Robinson  Samuel Stehle  Franklin A. Hardisty  Wei Luo 《International journal of geographical information science》2013,27(9):1588-1611

Pattern analysis techniques currently common within geography tend to focus either on characterizing patterns of spatial and/or temporal recurrence of a single event type (e.g., incidence of flu cases) or on comparing sequences of a limited number of event types where relationships between events are already represented in the data (e.g., movement patterns). The availability of large amounts of multivariate spatiotemporal data, however, requires new methods for pattern analysis. Here, we present a technique for finding associations among many different event types where the associations among these varying event types are not explicitly represented in the data or known in advance. This pattern discovery method, known as T-pattern analysis, was first developed within the field of psychology for the purpose of finding patterns in personal interactions. We have adapted and extended the T-pattern method to take the unique characteristics of geographic data into account and implemented it within a geovisualization toolkit for an integrated computational-geovisual environment we call STempo. To demonstrate how T-pattern analysis can be employed in geographic research for discovering patterns in complex spatiotemporal data, we describe a case study featuring events from news reports about Yemen during the Arab Spring of 2011–2012. Using supplementary data from the Global Database of Events, Language, and Tone, we briefly summarize and reference a separate validation study, then evaluate the scalability of the T-pattern approach. We conclude with ideas for further extensions of the T-pattern technique to increase its utility for spatiotemporal analysis.  相似文献   

Damped Lyman α systems and disc galaxies: number density, column density distribution and gas density     

Samuel Boissier  Céline Péroux  Max Pettini 《Monthly notices of the Royal Astronomical Society》2003,338(1):131-140

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Shear and vorticity in inflationary Brans–Dicke cosmology with lambda-term     

Marcelo Samuel Berman 《Astrophysics and Space Science》2007,310(3-4):205-207

We find a solution for exponential inflation in Brans–Dicke cosmology endowed with a cosmological term, which includes time-varying shear and vorticity. We find that the scalar field and the scale factor increase exponentialy while shear, vorticity, energy density, cosmic pressure and the cosmological term decay exponentialy for negative beta, where beta is defined in the text.  相似文献   

Erratum to: Combined effect of pulse density and grid cell size on predicting and mapping aboveground carbon in fast-growing Eucalyptus forest plantation using airborne LiDAR data     

Carlos Alberto Silva  Andrew Thomas Hudak  Carine Klauberg  Lee Alexandre Vierling  Carlos Gonzalez-Benecke  Samuel de Padua Chaves Carvalho  Luiz Carlos Estraviz Rodriguez  Adrián Cardil 《Carbon balance and management》2017,12(1):14

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Supra-subduction and abyssal mantle peridotites of the Coast Range ophiolite,California   总被引：6，自引：0，他引：6  

Sung Hi Choi  John W. Shervais  Samuel B. Mukasa 《Contributions to Mineralogy and Petrology》2008,156(5):551-576

The Coast Range ophiolite (CRO) of California is one of the most extensive tracts of oceanic crust preserved in the North American Cordillera, but its origin has long remained controversial. We present here new data on mineral compositions in mantle peridotites that underlie crustal sections of the ophiolite, and show that these are dominantly refractory harzburgites related to high apparent melting in a supra-subduction zone (SSZ) setting. Abyssal peridotite (characterized by high-Al spinels and relatively high Ti, Na, Nd, Sm, Lu, and Hf in pyroxene) occurs at one location where it is associated with SSZ mantle peridotite and volcanic rocks with both oceanic and arc-like geochemistry. SSZ mantle peridotites (characterized by intermediate-Cr/Al or high-Cr spinels, and by extremely low Ti, Na, Nd, Sm, Lu, and Hf in pyroxenes) are associated with crustal sections containing arc-related volcanic rocks, including boninites. This convergence between conclusions based on crustal lithologies and their underlying mantle sections confirms previous proposals that link the CRO to SSZ processes, and seriously undermines hypotheses that invoke formation of the ophiolite at a mid-ocean ridge spreading center.  相似文献   

Geography and paratactical interdisciplinarity: Views from the ESRC-NERC PhD studentship programme     

James Evans  Samuel Randalls 《Geoforum》2008,39(2):581-592

Interdisciplinarity is a notoriously difficult concept to define, and even harder to achieve in practice. All too often social approaches reduce science to an object of study, or conversely physical science approaches are invoked as a source of ‘higher’ truth. Drawing upon our experiences as ESRC-NERC PhD students within geography, we outline a paratactical approach that links disciplines by adjacency rather than hierarchy. Toppling the disciplinary hierarchy creates the potential for non-reductionistic dialogue between science and social science, but it also raises a series of practical difficulties. These are considered around the themes of polyvocality, breadth over depth and (im)permanence. We suggest that while this kind of approach is increasingly encouraged by research funding bodies, it is less easily sustained within the everyday mechanics of the academic world.  相似文献   

Stratigraphy and geochemical characterization of the Oligocene–Miocene Maikop series: Implications for the paleogeography of Eastern Azerbaijan     

Samuel M. Hudson  Cari L. Johnson  Malakhat A. Efendiyeva  Harold D. Rowe  Akper A. Feyzullayev  Chingiz S. Aliyev 《Tectonophysics》2008,451(1-4):40-55

The Oligocene–Miocene Maikop Series is a world-class source rock responsible for much of the oil and gas found in the South Caspian Basin. It is composed of up to 3 km of marine mudstone, and contains a nearly continuous record of deposition during progressive tectonic closure of the basin as the Arabian Peninsula converged northward into Eurasia. Historically, the stratigraphy of this interval has been difficult to define due to the homogenous nature of the fine-grained, clay-dominated strata. Outcrop exposures in eastern Azerbaijan allow direct observation and detailed sampling of the interval, yielding a more comprehensive stratigraphic context and a more advanced understanding of syndepositional conditions in the eastern Paratethys Sea. Specifically, the present investigation reveals that coupling field-based stratigraphic characterization with geochemical analyses (e.g., bulk elemental geochemistry, Rock-Eval pyrolysis, bulk stable isotope geochemistry) yields a more robust understanding of internal variations within the Maikop Series. Samples from seven sections located within the Shemakha–Gobustan oil province reveal consistent stratigraphic and spatial geochemical trends. It is proposed that the Maikop Series be divided into three members based on these data along with lithostratigraphic and biostratigraphic data reported herein. When comparing Rupelian (Early Oligocene) and Chattian (Late Oligocene) strata, the Rupelian-age strata commonly possess higher TOC values, more negative δ¹⁵N_tot values, more positive δ¹³C_org values, and higher radioactivity relative to Chattian-age rocks. The trace metals Mo and V (normalized to Al) are positively correlated with TOC, with maximum values occurring at the Rupelian–Chattian boundary and overall higher average values in the Rupelian. Across the Oligocene–Miocene boundary, a slight drop in V/Al, Mo/Al ratios is observed, along with drops in %S and TOC. These results indicate that geochemical signatures of the Maikop Series are regional in nature, and furthermore that analogous fine-grained sections may be better characterized and subdivided using similar techniques. In general, geochemical indicators suggest that the basin was in limited communication with the Tethys Sea throughout the Oligocene–Early Miocene, with suboxic to anoxic conditions present during the Oligocene and to a lesser extent in the Miocene. This increased isolation was likely due to tectonic uplift to both the south and north of the study area, and greatly enhanced by global sea-level fluctuations. These data serve as the basis for a more detailed understanding of the tectonic evolution of the region, and support a standardized chemostratigraphic division of the important petroleum source interval.  相似文献