New perspectives on ethnic segregation over time and space. A domains approach     

Maarten van Ham  Tiit Tammaru 《Urban geography》2016,37(7):953-962

Ethnic segregation has most often been studied at the place of residence, segregation being defined on the basis of the relative presence of different groups within city neighbourhoods. It is increasingly recognized, however, that segregation occurs in different ways in different domains (such as the workplace, leisure, social media, etc.), the residential domain being just one of many in which segregation can occur. In this research note we present the domains approach to segregation and outline some its conceptual, methodological and empirical underpinnings and challenges.  相似文献   

Mesozoic exhumation of the southern Cape, South Africa, quantified using apatite fission track thermochronology   总被引：4，自引：2，他引：2  

Justine Tinker  Maarten de Wit  Roderick Brown   《Tectonophysics》2008,455(1-4):77-93

Southern Africa's topography is distinctive. An inland plateau of low relief and high average elevation is separated from a coastal plane of high relief and low average elevation by a steeply dipping escarpment. The origin and evolution of this topography is poorly understood because, unlike high plateaus elsewhere, its development cannot be easily linked to present day compressional plate boundary processes. Understanding the development of this regional landscape since the break-up of Gondwana is a first order step towards resolving regional epeirogenesis. We present data that quantifies the timing and extent of exhumation across the southern Cape escarpment and coastal plane, using apatite fission track analysis (AFTA) of 25 outcrop samples and 31 samples from three deep boreholes (KW1/67, SA1/66, CR1/68). Outcrop fission track (AFT) ages are Cretaceous and are significantly younger than the stratigraphic ages of their host rocks, indicating that the samples have experienced elevated paleotemperatures. Mean track lengths vary from 11.86 to 14.23 μm. The lack of Cenozoic apatite ages suggests that major cooling was over by the end Cretaceous. The results for three boreholes, situated seaward (south) of the escarpment, indicate an episode of increased denudation in the mid-late Cretaceous (100–80 Ma). An earlier episode of increased denudation (140–120 Ma) is identified from a borehole north of the escarpment. Thermal modelling indicates a history involving 2.5–3.5 km of denudation in the mid-late Cretaceous (100–80 Ma) at a rate of 175 to 125 m/Ma. The AFT data suggest that less than 1 km of overburden has been eroded regionally since the late Cretaceous (< 80 Ma) at a rate of 10 to 15 m/Ma, but do not discount the possibility of minor (in relative amplitude) episodes of uplift and river incision through the Cenozoic. The reasons for rapid denudation in these early and mid-Cretaceous episodes are less clear, but may be related to epeirogenic uplift associated with an increase in mantle buoyancy as reflected in two punctuated episodes of alkaline intrusions (e.g. kimberlites) across southern Africa and contemporaneous formation of two large mafic igneous provinces (~ 130 and 90 Ma) flanking its continental margins. Because Cenozoic denudation rates are relatively minimal, epeirogenic uplift of southern Africa and its distinct topography cannot be primarily related to Cenozoic mantle processes, consistent with the lack of any significant igneous activity across this region during that time.  相似文献   

How climate metrics affect global mitigation strategies and costs: a multi-model study     

Mathijs J. H. M. Harmsen  Maarten van den Berg  Volker Krey  Gunnar Luderer  Adriana Marcucci  Jessica Strefler  Detlef P. Van Vuuren 《Climatic change》2016,135(2):203-209

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Kinematics of elliptical galaxies with a diffuse dust component – III. A Monte Carlo approach to include the effects of scattering     

Maarten Baes †  Herwig Dejonghe 《Monthly notices of the Royal Astronomical Society》2002,335(2):441-458

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Reply to comment by F. A. Dahlen and G. Nolet on 'On sensitivity kernels for 'wave-equation' transmission tomography'     

Maarten V. de Hoop  Robert D. van der Hilst 《Geophysical Journal International》2005,163(3):952-955

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Modulation of near-inertial motions on the Mississippi-Alabama Shelf     

Buijsman  Maarten C.  Earls  Jordan  Weierbach  Helen 《Ocean Dynamics》2021,71(11):1087-1103

Ocean Dynamics - In this study, we diagnose the time variability and vertical structure of the high- and low-frequency motions on the Mississippi-Alabama Shelf as observed with a bottom-mounted...  相似文献   

How important is it to integrate riverine suspended sediment chemical composition with depth? Clues from Amazon River depth-profiles   总被引：1，自引：0，他引：1  

Julien Bouchez  Maarten Lupker  Christian France-Lanord 《Geochimica et cosmochimica acta》2011,75(22):6955-6970

The vertical variability in mineralogical, chemical and isotopic compositions observed in large river suspended sediments calls for a depth-integration of this variability to accurately determine riverine geochemical fluxes. In this paper, we present a method to determine depth-integrated chemical particulate fluxes of large rivers, based on river sampling along depth-profiles, and applied to the Amazon Basin lowland tributaries. The suspended particulate matter (SPM) concentration data from depth-profiles is modeled for a number of individual grain size fractions using the Rouse model, which allows to predict the grain size distribution of suspended sediment throughout the whole river cross-section. Then, using (1) the relationship between grain size distribution and the Al/Si ratio (2) relationships between the Al/Si ratio and the chemical concentrations, the chemical composition of river sediment is predicted throughout the river cross-section, and integrated to yield the depth-integrated chemical particulate flux for a number of chemical elements (e.g. Si, Al, Fe, Na, REEs, …). For elements such as Al, Fe, REEs, Th, the depth-integrated flux is around twice as high as the one calculated from river surface sample characteristics. For Na and Si, the depth-integrated flux is three times higher than the “surface” estimate, due to the enrichment of albite and quartz at the bottom of the river. Depth-integrated ⁸⁷Sr/⁸⁶Sr composition of suspended sediment, also predictable using this method, differs by more than 10⁻³ from the surface sample composition.Finally, potential implications of depth-integrated estimates of Amazon sediment chemistry are explored. Depth-integration of particulate ⁸⁷Sr/⁸⁶Sr isotopic ratios is necessary for a reliable use of Sr isotopes as a provenance tracer. The concept of steady-state weathering of a large river basin is revisited using depth-integrated sediment composition. This analysis shows that, in the Amazon Basin river, the previously observed discrepancy between (1) weathering intensities of channel surface sediment and (2) silicate-derived dissolved fluxes is only slightly accounted for by the vertical variability of suspended sediment weathering intensities. This observation confirms that most large rivers basins are not eroding at steady-state.  相似文献   

Evolution of a bifurcation in a meandering river with adjustable channel widths,Rhine delta apex,The Netherlands     

Maarten G. Kleinhans  Kim M. Cohen  Jantine Hoekstra  Janneke M. IJmker 《地球表面变化过程与地形》2011,36(15):2011-2027

Rivers may dramatically change course on a fluvial plain. Such an avulsion temporarily leads to two active channels connected at a bifurcation. Here we study the effect of dynamic meandering at the bifurcation and the effect of channel width adjustment to changing discharge in both downstream branches on the evolution of a bifurcation and coexisting channels. As an example, we reconstructed the last major avulsion at the Rhine delta apex. We combined historical and geological data to reconstruct a slowly developing avulsion process spanning 2000 years and involving channel width adjustment and meandering at the bifurcation. Based on earlier idealised models, we developed a one‐dimensional model for long‐term morphodynamic prediction of upstream channel and bifurcates connected at the bifurcation node. The model predicts flow and sediment partitioning at the node, including the effect of migrating meanders at the bifurcation and channel width adjustment. Bifurcate channel width adaptation to changing discharge partitioning dramatically slows the pacing of bifurcation evolution because the sediment balance for width adjustment and bed evolution are coupled. The model further shows that meandering at the bifurcation modulates channel abandonment or enlargement periodically. This explains hitherto unrecognised reactivation signals in the sedimentary record of the studied bifurcation meander belts, newly identified in our geological reconstruction. Historical maps show that bifurcation migration due to meander bend dynamics increases the bifurcation angle, which increases the rate of closure of one bifurcate. The combination of model and reconstruction identifies the relevant timescales for bifurcation evolution and avulsion duration. These are the time required to fill one downstream channel over one backwater length, the time to translate one meander wavelength downstream and, for strong river banks, the adaptation timescale to adjust channel width. The findings have relevance for all avulsions where channel width can adjust to changing discharge and where meandering occurs. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The impact of technology availability on the timing and costs of emission reductions for achieving long-term climate targets     

Jasper van Vliet  Andries F. Hof  Angelica Mendoza Beltran  Maarten van den Berg  Sebastiaan Deetman  Michel G. J. den Elzen  Paul L. Lucas  Detlef P. van Vuuren 《Climatic change》2014,123(3-4):559-569

While most long-term mitigation scenario studies build on a broad portfolio of mitigation technologies, there is quite some uncertainty about the availability and reduction potential of these technologies. This study explores the impacts of technology limitations on greenhouse gas emission reductions using the integrated model IMAGE. It shows that the required short-term emission reductions to achieve long-term radiative forcing targets strongly depend on assumptions on the availability and potential of mitigation technologies. Limited availability of mitigation technologies which are relatively important in the long run implies that lower short-term emission levels are required. For instance, limited bio-energy availability reduces the optimal 2020 emission level by more than 4 GtCO₂eq in order to compensate the reduced availability of negative emissions from bioenergy and carbon capture and storage (BECCS) in the long run. On the other hand, reduced mitigation potential of options that are used in 2020 can also lead to a higher optimal level for 2020 emissions. The results also show the critical role of BECCS for achieving low radiative forcing targets in IMAGE. Without these technologies achieving these targets become much more expensive or even infeasible.  相似文献   

Formation of a cohesive floodplain in a dynamic experimental meandering river     

Wout M. van Dijk  Wietse I. van de Lageweg  Maarten G. Kleinhans 《地球表面变化过程与地形》2013,38(13):1550-1565

Field studies suggest that a cohesive floodplain is a necessary condition for meandering in contrast to braided rivers. However, it is only partly understood how the balance between floodplain construction by overbank deposition and removal by bank erosion and chutes leads to meandering. This is needed because only then does a dynamic equilibrium exist and channels maintain meandering with low width–depth ratios. Our objective is to understand how different styles of floodplain formation such as overbank deposition and lateral accretion cause narrower channels and prevent chute cutoffs that lead to meandering. In this study we present two experiments with a self‐forming channel in identical conditions, but to one we added cohesive silt at the upstream boundary. The effect of cohesive silt on bank stability was tested in auxiliary bank erosion experiments and showed that an increase in silt reduced erosion rates by a factor of 2. The experiment without silt developed to a braided river by continuous and extensive shifting of multiple channels. In contrast, in the meandering river silt deposits increased bank stability of the cohesive floodplain and resulted in a reduction of chute cutoffs and increased sinuosity by continuous lateral migration of a single channel. Overbank flow led to deposition of the silt and two styles of cohesive floodplain were observed: first, overbank vertical‐accretion of silt, e.g. levee, overbank sedimentation or splays; and second, lateral point bar accretion with silt on the scrolls and in the swales. The first style led to a reduction in bank erosion, while the second style reduced excavation of chutes. We conclude that sedimentation of fine cohesive material on the floodplain by discharge exceeding bankfull is a necessary condition for meandering. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献