热机碎岩钻进工艺的试验研究

论述了热机碎岩的基本概念、基本原理;阐述了热机碎岩试验的基本方法,试验设备、试验钻头以及试验岩样;对试验数据以及试验工艺参数的关系做了详细的分析;得出了热机碎岩的最佳工艺参数及结论.     

Uncovering the spatio-temporal dynamics of land cover change and fragmentation of mangroves in the Ca Mau peninsula,Vietnam using multi-temporal SPOT satellite imagery (2004–2013)

Mangrove forests provide vital ecosystem services for millions of people living in coastal communities. The expansion of aquaculture production and urbanization have been identified as major causes of mangrove clearance in South-East Asia. The Ca Mau peninsula in Vietnam is leading the country in shrimp aquaculture and at the same time, the region is home to the largest remaining mangrove forests. This study aims to assess the spatial and temporal mangrove forest dynamics in Ngoc Hien district in Ca Mau. Land cover change and fragmentation are quantified using remote sensing imagery consisting of a series of SPOT5 scenes from 2004, 2009 and 2013. The results indicate a high turnover of land cover change, with close to half of the mangrove forests being affected by land cover changes between 2004 and 2014. Net changes in mangrove forest are found to average −0.34% annually, characterized by deforestation between 2004 and 2009 and afforestation of between 2009 and 2013. Fragmentation remains a plausible threat; approximately 35.4% of the mangrove forests in Ngoc Hien are part of interior ‘core’ forests. Forest zones with different regulation regimes play a significant role in shaping the geographic distribution of mangrove forest changes. The insights into recent mangrove forest dynamics facilitate the informed discussion on improving future protection of the mangrove forests abiding anthropogenic pressures.     

Structural attributes of individual trees for identifying homogeneous patches in a tropical rainforest

Mapping and monitoring tropical rainforests and quantifying their carbon stocks are important, both for devising strategies for their conservation and mitigating the effects of climate change. Airborne Laser Scanning (ALS) has advantages over other remote sensing techniques for describing the three-dimensional structure of forests. This study identifies forest patches using ALS-based structural attributes in a tropical rainforest in Sumatra, Indonesia. A method to group trees with similar attributes into forest patches based on Thiessen polygons and k-medoids clustering is developed, combining the advantages of both raster and individual tree–based methods. The structural composition of the patches could be an indicator of habitat type and quality. The patches could also be a basis for developing allometric models for more accurate estimation of carbon stock than is currently possible with generalised models.     

Lateral bedrock erosion and valley formation in a heterogeneously layered landscape,Northeast Kansas

In this study, we present direct field measurements of modern lateral and vertical bedrock erosion during a 2-year study period, and optically stimulated luminescence (OSL) ages of fluvial material capping a flat bedrock surface at Kings Creek located in northeast Kansas, USA. These data provide insight into rates and mechanisms of bedrock erosion and valley-widening in a heterogeneously layered limestone-shale landscape. Lateral bedrock erosion outpaced vertical incision during our 2-year study period. Modern erosion rates, measured at erosion pins in limestone and shale bedrock reveal that shale erosion rate is a function of wetting and drying cycles, while limestone erosion rate is controlled by discharge and fracture spacing. Variability in fracture spacing amongst field sites controls the size of limestone block collapse into the stream, which either allowed continued lateral erosion following rapid detachment and transport of limestone blocks, or inhibited lateral erosion due to limestone blocks that protected the valley wall from further erosion. The OSL ages of fluvial material sourced from the strath terrace were older than any material previously dated at our study site and indicate that Kings Creek was actively aggrading and incising throughout the late Pleistocene. Coupling field measurements and observations with ages of fluvial terraces can be useful to investigate the timing and processes linked to how bedrock rivers erode laterally over time to form wide bedrock valleys.     

Periglacial disruption and subsequent glacitectonic deformation of bedrock: an example from Anglesey,North Wales,UK

The deformed metasedimentary bedrock and overlying diamictons in western Anglesey, NW Wales, record evidence of glacier-permafrost interactions during the Late Devensian (Weichselian). The locally highly brecciated New Harbour Group bedrock is directly overlain by a bedrock-rich diamicton which preserves evidence of having undergone both periglacial (brecciation, hydrofracturing) and glacitectonic deformation (thrusting, folding), and is therefore interpreted as periglacial head deposit. The diamicton locally posses a well-developed clast macrofabric which preserves the orientation of the pre-existing tectonic structures within underlying metasedimentary rocks. Both the diamicton and New Harbour Group were variably reworked during the deposition of the later Irish Sea diamicton, resulting in the detachment of bedrock rafts and formation of a pervasively deformed glacitectonite. These structural and stratigraphic relationships are used to demonstrate that a potentially extensive layer of permafrost developed across the island before it was overridden by the Irish Sea Ice Stream. These findings have important implications for the glacial history of Anglesey, indicating that the island remained relatively ice-free prior to its inundation by ice flowing southwards down the Irish Sea Basin. Palynological data obtained from the diamictons across Anglesey clearly demonstrates that they have an Irish Sea provenance. Importantly no Lower Palaeozoic palynomorphs were identified, indicating that it is unlikely that Anglesey was overridden by ice emanating from the Snowdon ice cap developed on the adjacent Welsh mainland. Permafrost was once again re-established across Anglesey after the Irish Sea Ice Stream had retreated, resulting in the formation of involutions which deform both the lower bedrock-rich and overlying Irish Sea diamictons.     

Particle size distribution and strain rate attenuation in hypervelocity impact and shock recovery experiments

Particle size distribution (PSD) is an often used parameter to describe and quantify fragmentation of deformed rock. Our analyses of shock deformed sandstone show that dynamic fragmentation influences the PSD, expressed as fractal dimension (D-value). Image analysis was used to derive fractal dimensions from a hypervelocity impact cratering experiment (2.5 mm steel sphere, 4.8 km/s) and a planar shock recovery experiment (2.5 GPa). The D-values in the cratering experiment decrease from 1.74 at the crater floor to 0.84 at a distance of 7.2 mm to the crater floor. The D-values found in this experiment are closely related to the microstructural features found at distinct distances from the crater floor. The obtained values are in good agreement with the D-values reported for fault zones, impact sites and deformation experiments. The D-value measured in the shock recovery experiment is 2.42. Such high D-values were usually attributed to abrasive processes related to high strain. Since the strain in our experiment is only ∼23% we suggest that at highly dynamic deformation very high d-values can be reached at small strain. To quantify this, numerical impact modelling has been used to estimate strain rates for the impact experiment. This is related to the activation of more inherent flaws and fracture bifurcation at very high strain rates ∼>10² s⁻¹.     

Activities of American Geographers

Cognitive distance is analyzed in relation to various elements of the built environment. The basis for accepting a power function as the underlying functional relationship between cognitive distance and its objective counterpart is discussed. This counterpart has been assumed to be objective distance. Evidence is presented to indicate that cognition of distance is based upon travel time rather than upon objective distance or upon objective distance modified by other elements of the built environment.     

Comparative tempo‐spatial pattern analysis: CTSPA

A new method is illustrated for describing the characteristics of urban pattern changes over different time periods. This method employs vector geometry, paired centroids, shared boundary lines, and overlain polygons. Three new statistics are proposed for characterizing local polygon feature changes in quantity, shape, and size. These statistics are standardized, based on conventional theories from urban geography such as directional concentric zones and user‐designated corridors to document both regional and global patterns of land‐use change. This method is used to analyse land‐use changes in metropolitan Detroit between 1990 and 2000. The Detroit case study indicates that the CTSPA statistics are effective in describing urban spatial pattern changes and in characterizing the evolution of discrete urban landscapes over selected periods.     

Using kernel density estimation to assess the spatial pattern of road density and its impact on landscape fragmentation

Road density (i.e., km/km²) is a useful broad index of the road network in a landscape and has been linked to several ecological effects of roads. However, previous studies have shown that road density, estimated by grid computing, has weak correlation with landscape fragmentation. In this article, we propose a new measure of road density, namely, kernel density estimation function (KDE) and quantify the relation between road density and landscape fragmentation. The results show that road density estimated by KDE (km/km²) elucidates the spatial pattern of the road network in the region. Areas with higher road density are dominated by a larger proportion of built-up landscape and less possession of forest and vice versa. Road networks segregated the landscape into smaller pieces and a greater number of patches. Furthermore, Spearman rank correlation model indicates that road density (km/km²) is positively related to landscape fragmentation. Our results suggest that road density, estimated by KDE, may be a better correlate with effects of the road on landscape fragmentation. Through KDE, the regional spatial pattern of road density and the prediction of the impact of the road on landscape fragmentation could be effectively acquired.