Excursion to the Mount,Ealing, and Horsington Hill: June 18th, 1887     

J. Allen Brown 《Proceedings of the Geologists' Association. Geologists' Association》1887,10(4):172-181

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Determinants of smallholder farmers’ perceptions of impact of climate change on beef production in Malawi     

Gregory Chingala  Cletos Mapiye  Emiliano Raffrenato  Louw Hoffman  Kennedy Dzama 《Climatic change》2017,142(1-2):129-141

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Urban policy mobilities,argumentation and the case of the model city     

Sean M. Kennedy 《Urban geography》2016,37(1):96-116

In recent years urban geographers have devoted considerable attention to the dynamics of policy mobility. After reviewing the progress achieved in this literature, in this article I offer two distinctive contributions. First, I draw on the “argumentative turn” in policy studies and related fields in order to develop an alternative conceptualization of urban policy mobility that pays greater attention to its discursive and argumentative aspects. I thus reassert the significance of democratic processes in the negotiation of urban policy. Second, I outline an alternative methodology for the study of urban policy mobility, focusing on the analysis of argumentation. I apply this methodology to historical instances of urban policy mobilities arising from a recent research project that aimed to historicize the phenomenon of the “model city,” defined as the local deployment of another city’s experience as an argumentative resource supporting particular policy claims.  相似文献   

Cognitive Abilities in the Service of Wayfinding: A Functional Approach     

Gary L. Allen 《The Professional geographer》1999,51(4):555-561

A functionally oriented framework for examining the cognitive abilities that are involved in human wayfinding is suggested. The framework includes a categorical distinction among types of wayfinding tasks (commutes, explores, and quests) and means used most frequently to accomplish these tasks (piloting, repetition of locomotor pattern, path integration, and navigation by cognitive map). The cognitive abilities contributing to these wayfinding means have been demonstrated by research on spatial cognition and behavior or can be inferred from relevant research and theory.  相似文献   

Sediment type distribution in reservoirs: sediment source versus morphometry     

J. Abraham  P. M. Allen  J. A. Dunbar  S. I. Dworkin 《Environmental Geology》1999,38(2):101-110

 Bottom sediments were collected from seven Texas reservoirs to assess the spatial distribution of sediment types in reservoirs. The sediment samples were analyzed for water content, organic content, and grain-size distributions. The reservoirs are characterized by distinct water content patterns (referred to in this paper as Types I, II, and III) that reflect the lithologic units comprising their drainage area. The water content, organic content, and percent mud decreases from Type I (shale, marl) through Type II (limestone-marl-sandstone) to Type III (granite-gneiss-schist-sandstone) reservoirs. Reported elemental concentrations in the reservoir sediments are consistent with concentrations in the dominant rocks within their drainage area. While water depth accounts for part of the spatial distribution, sediment source explains the overall distribution of sediment types. Coarse-grained source rocks, multiple source rocks, and multiple tributaries which input sediment at different points contribute to an inconsistent sediment type distribution. Depending on the sediment source, sand and gravel-size sediments are present in the deeper regions of some reservoirs. This disrupts the classical morphometry (water depth, slope) controlled sediment distribution pattern (coarser sediments in shallower regions and finer sediments in deeper regions) of natural lakes. Thus, the location of tributaries and the type of sediments they carry are the dominant factors that control the sediment type distribution in reservoirs. Received: 16 June 1998 · Accepted: 24 August 1998  相似文献   

Checking for model consistency in optimal fingerprinting   总被引：3，自引：2，他引：1  

M. R. Allen  S. F. B. Tett 《Climate Dynamics》1999,15(6):419-434

 Current approaches to the detection and attribution of an anthropogenic influence on climate involve quantifying the level of agreement between model-predicted patterns of externally forced change and observed changes in the recent climate record. Analyses of uncertainty rely on simulated variability from a climate model. Any numerical representation of the climate is likely to display too little variance on small spatial scales, leading to a risk of spurious detection results. The risk is particularly severe if the detection strategy involves optimisation of signal-to-noise because unrealistic aspects of model variability may automatically be given high weight through the optimisation. The solution is to confine attention to aspects of the model and of the real climate system in which the model simulation of internal climate variability is adequate, or, more accurately, cannot be shown to be deficient. We propose a simple consistency check based on standard linear regression which can be applied to both the space-time and frequency domain approaches to optimal detection and demonstrate the application of this check to the problem of detection and attribution of anthropogenic signals in the radiosonde-based record of recent trends in atmospheric vertical temperature structure. The influence of anthropogenic greenhouse gases can be detected at a high confidence level in this diagnostic, while the combined influence of anthropogenic sulphates and stratospheric ozone depletion is less clearly evident. Assuming the time-scales of the model response are correct, and neglecting the possibility of non-linear feedbacks, the amplitude of the observed signal suggests a climate sensitivity range of 1.2–3.4 K, although the upper end of this range may be underestimated by up to 25% due to uncertainty in model-predicted response patterns. Received: 9 December 1997 / Accepted: 24 December 1998  相似文献   

Contributing Areas to Domestic Wells in Dipping Sedimentary Rocks under Extreme Recharge Events     

Claire R. Tiedeman  Allen M. Shapiro 《Ground water》2022,60(4):460-476

We use particle tracking to determine contributing areas (CAs) to wells for transient flow models that simulate cyclic domestic pumping and extreme recharge events in a small synthetic watershed underlain by dipping sedimentary rocks. The CAs consist of strike-oriented bands at locations where the water table intersects high-hydraulic conductivity beds, and from which groundwater flows to the pumping well. Factors that affect the size and location of the CAs include topographic flow directions, rock dip direction, cross-bed fracture density, and position of the well relative to streams. For an effective fracture porosity (n_e) of 10⁻⁴, the fastest advective travel times from CAs to wells are only a few hours. These results indicate that wells in this type of geologic setting can be highly vulnerable to contaminants or pathogens flushed into the subsurface during extreme recharge events. Increasing n_e to 10⁻³ results in modestly smaller CAs and delayed well vulnerability due to slower travel times. CAs determined for steady-state models of the same setting, but with long-term average recharge and pumping rates, are smaller than CAs in the models with extreme recharge. Also, the earliest-arriving particles arrive at the wells later in the steady-state models than in the extreme-recharge models. The results highlight the importance of characterizing geologic structure, simulating plausible effective porosities, and simulating pumping and recharge transience when determining CAs in fractured rock aquifers to assess well vulnerability under extreme precipitation events.  相似文献   

Marine algae are ‘taught’ the basics of angular momentum   总被引：1，自引：1，他引：0  

John Taylor Allen 《Ocean Dynamics》2017,67(11):1429-1442

Advanced modelling studies and high-resolution observations have shown that flows related to instability of the mesoscale (~ 1–10 km scale) may provide both the fertilisation mechanism for nutrient-depleted (oligotrophic) surface waters and a subduction mechanism for the rapid export of phytoplankton biomass to the deep ocean. Here, a detailed multidisciplinary analysis of the data from an example high-resolution observational campaign is presented. The data provide direct observations of the transport of phytoplankton through baroclinic instability. Furthermore, the data confirm that this transport is constrained by the requirement to conserve angular momentum, expressed in a stratified water column as the conservation of potential vorticity. This constraint is clearly seen to produce long thin filaments of phytoplankton populations strained out along isopycnal vorticity annuli associated with mesoscale frontal instabilities.  相似文献   

Structure-from-motion photogrammetry analysis of historical aerial photography: Determining beach volumetric change over decadal scales     

Rafael C. Carvalho  David M. Kennedy  Yakufu Niyazi  Chloe Leach  Teresa M. Konlechner  Daniel Ierodiaconou 《地球表面变化过程与地形》2020,45(11):2540-2555

Historical aerial photographs are an invaluable tool in shoreline mapping and change detection in coastal landscapes. We evaluate the extent to which structure-from-motion (SfM) photogrammetric methods can be applied to quantify volumetric changes along sandy beaches, using archival imagery. We demonstrate the application of SfM-derived digital surface models (DSMs) at East Beach and Lady Bay in southwest Victoria, Australia, using photographic datasets taken in 1969, 1977 and 1986, and compare them to LiDAR-derived DSMs acquired at both sites in 2007. The SfM approaches resulted in two entire and two partial suitable DSMs out of six datasets. Good-quality DSMs were spatially continuous with a good spread of ground control points (GCPs) near the beach at Lady Bay, whereas unsuitable DSMs were mostly restricted by poor distribution and number of GCPs in spatially segmented areas of East Beach, due to limited overlapping of images, possible poor quality of GCPs and also the propagation of errors in the derived point clouds. A volume of approximately 223 000 ± 72 000 m³ was deposited at Lady Bay between 1969 and 2007, despite minimal erosion observed near the breakwater. The partially suitable dataset of East Beach indicated that beach erosion of at least 39 m³ m⁻¹ occurred immediately to the east of the seawall after 1977. We also discuss the drawbacks and strengths of SfM approaches as a benchmark of historical erosion assessments along sandy beaches. © 2020 John Wiley & Sons, Ltd.  相似文献   

The Pushtashan juvenile suprasubduction zone assemblage of Kurdistan (northeastern Iraq): A Cretaceous (Cenomanian) Neo-Tethys missing link     

Sabah A. Ismail  Sarmad A. Ali  Allen P. Nutman  Vickie C. Bennett  Brain G. Jones 《地学前缘(英文版)》2017,8(5):1073-1087

The Pushtashan suprasubduction zone assemblage of volcanic rocks, gabbros, norites and peridotites occurs in the Zagros suture zone, Kurdistan region, northeastern Iraq. Volcanic rocks are dominant in the assemblage and consist mainly of basalt and basaltic andesite flows with interlayered red shale and limestone horizons. Earlier lavas tend to be MORB-like, whereas later lavas display island arc tholeiite to boninitic geochemical characteristics. Tholeiitic gabbros intrude the norites and display fractionation trends typical of crystallisation under low-pressure conditions, whereas the norites display calc-alkaline traits, suggesting their source included mantle metasomatised by fluids released from subducted oceanic crust. Enrichment of Rb, Ba, Sr, Th and the presence of negative Nb anomalies indicate generation in a suprasubduction zone setting. Trondhjemite and granodiorite intrusions are present in the volcanic rocks, gabbros and norites. SHRIMP U-Pb dating of magmatic zircons from a granodiorite yields a mean~(206)Pb/~(238)U age of 96.0 ±2.0 Ma(Cenomanian). The initial ε_(Hf) value for the zircons show a narrow range from +12.8 to+15.6, with a weighted mean of + 13.90±0.96. This initial value is within error of model depleted mantle at 96 Ma or slightly below that, in the field of arc rocks with minimal contamination by older continental crust. The compositional bimodality of the Pushtashan suprasubduction sequence suggests seafloor spreading during the initiation of subduction, with a lava stratigraphy from earlyerupted MORB transitioning into calc-alkaline lavas and finally by 96 Ma intrusion of granodioritic and trondhjemitic bodies with juvenile crustal isotopic signatures. The results confirm another Cretaceous arc remnant preserved as an allochthon within the Iraqi segment of the Cenozoic Zagros suture zone. Implications for the closure of Neo-Tethys are discussed.  相似文献