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1.
While much of the research on neighborhood crime considers the neighborhood as a whole, this study utilizes spatial analysis techniques to examine how the presence of disorder and collective efficacy create unique pockets of opportunities for criminal behavior within neighborhoods. This spatial perspective reveals how the effect of disorder and efficacy upon crime patterns itself varies across a neighborhood. Physical disorder is measured through systematic social observations and the level of collective efficacy is evaluated through survey responses of neighborhood residents. The indices of disorder and efficacy are compared to crime data from police call logs using geographically weighted regression. Our findings demonstrate a complex spatial relationship between disorder and efficacy. The effects of disorder and efficacy are not consistent across an entire neighborhood, but rather display local variations in small geographical areas within neighborhoods, including some pockets of the neighborhood where the relationships between disorder, efficacy, and crime were contrary to the expected relationships. Based upon these findings, we conclude opportunity is central to understanding crime, and emphasize the role of informal social control in neighborhoods.  相似文献   

2.
Precipitation is a major climatic element with high spatial variations. Temporal and spatial variations may differ in large and small scales. It is, therefore, of utmost importance to study areas with similar gradients in terms of precipitation patterns in order to shed light on the complexities of precipitation variations. In the present study, attempts were made to identify areas with similar gradients experiencing the same precipitation pattern over a 50-year period (1964–2013). To this end, data were collected from synoptic stations in Iran in two phases (i.e., 1434 stations in the first phase and 673 stations in the second one). Alexanderson’s technique was adopted to examine sudden changes in precipitation patterns. The results showed that five regions with similar gradients could be identified in terms of precipitation patterns: negative and high variations, negative and moderate variations, positive and high variations, positive and moderate variations, and little or no variations. The distribution of such regions indicated that the regions with positive trends experienced more annual variations and had further spatial distribution. Furthermore, the findings revealed that the regions with negative precipitation patterns experienced more sudden changes in comparison with those with positive precipitation patterns. Additionally, more variations were observed in the precipitation patterns in recent years.  相似文献   

3.
A large and detailed data set is used to examine the influence of airports and airport light paths on housing prices. The results indicate that individuals consider airport proximity and airport flight patterns in their housing purchases. This shows that there exist two distinct measurable price gradients that distinguish large airports from small airports. In addition, homes located under the flight path of a large airport have a price gradient that is significantly larger than homes located under the flight path of a small airport.  相似文献   

4.
Data from sixteen deep walls drilled for oil exploration purposes in the Anambra Basin of southeastern Nigeria indicate large variations in temperature gradients and heat flow within the basin. Geothermal gradients vary between 25 and 49 ± 1°C km−1, while heat flow estimates are in the range 48 to 76 ± 3 mW m−2. The highest geothermal gradients and heat flow values were computed for the wells located in the southwestern part of the basin north of Onitsha and Asaba. This part of the basin coincides with zones of thick, low conductivity sediments, low ground surface elevation, and hydraulic discharge zones. The general direction of increase in geothermal gradient, originally projected as south to north by earlier workers dealing with the Niger Delta data and the very limited well data from the Anambra Basin, is inconsistent with the results of the present study.The distribution of subsurface temperatures, geothermal gradients and heat flow is found to be directly related to the basin hydrodynamics - higher geothermal gradients and heat flow in areas of low hydraulic head distribution. Hydrocarbon metamorphism and migration appear to have been greatly influenced by the movements of circulating meteoric waters. A higher level of organic maturity of sediments should be expected in the southwestern zone, where the thermal anomaly exists. However, owing to hydrodynamic activities, tertiary migration would have taken place leaving many traces of residual hydrocarbons. The several cases of fluorescence noticed in wells in the southwestern zone of the Anambra Basin are taken as evidence that this process may indeed have taken place in the geological past of the basin.  相似文献   

5.
《Gondwana Research》2014,25(3-4):1091-1107
The eastern Tibetan margin is characterized by a steep topographic gradient and remarkably lateral variations in crustal/lithospheric structure and thermal state. GPS measurements show that the surface convergence rate in this area is strikingly low. How can such a mountain range grow without significant upper crustal shortening? In order to investigate the formation mechanism of the eastern Tibetan-type margins, we conducted 2D numerical simulations based on finite difference and marker-in-cell techniques. The numerical models were constrained with geological and geophysical observations in the eastern Tibetan margin. Several major parameters responsible for topography building, such as the convergence rate, the erosion/sediment rate, and the presence of partially molten crust, were systematically examined. The results indicate that the presence of partially molten material in the middle/lower crust can make a positive contribution to the formation of steep topography, but it is not a necessary factor. A steep topographic gradient may be a characteristic feature when a thin lithosphere with thick crust converges with a thick lithosphere with thin crust. In the context of a high erosion rate, the Longmen Shan range still gains and maintains its steep high topography to the present. This could be explained by exerting a large push force on Tibet side. Our numerical experiments suggest that topographic characteristic across the eastern Tibetan-type margins is mainly derived from isostatic equilibration forces and intensive convergence between two continental lithospheres with totally different rheological properties.  相似文献   

6.
Fractal-dimension analysis is an effective means of quantifying complex map patterns of structures and lithological contacts, which are conduits for hydrothermal fluid flow during the formation of orogenic-gold deposits. In this study, fractal dimensions, calculated on a 10 km grid across a geologic map of the Yilgarn Craton of uniform data quality, highlight relationships between geologic complexity and the location and size of Archaean orogenic-gold deposits. In the Kalgoorlie Terrane and Laverton Tectonic Zone, the largest gold deposits occur along steep gradients defined by fractal-dimension values. These steep gradients in the greenstone belts occur between massive sedimentary rock sequences of low complexity, and volcanic and intrusive rock units with more complex map patterns. The formation of world-class orogenic-gold deposits requires that hydrothermal fluids become focused from a large volume of well-connected rocks at depth, towards narrow, high-permeability zones near the location of deposit formation. Connectivity is indirectly related to permeability, and the degree of connectivity is related to the density and orientation of fluid pathways, which are quantified in map patterns using fractal-dimension analysis. Thus, fractal dimensions are a measure of the potential for increased connectivity and the likelihood of increased permeability. Greater complexity, as measured by larger fractal dimensions, implies that a certain area has the potential to produce more interconnected pathways, or zones of high connectivity. Therefore, the steep complexity gradients defined in the Kalgoorlie Terrane and Laverton Tectonic Zone correspond to areas that focused large volumes of hydrothermal fluid and enhanced the potential for significant gold mineralisation. Fractal-dimension analysis thus provides a link between empirical map features and the processes that have enhanced hydrothermal fluid flow and resulted in the formation of larger orogenic-gold deposits.  相似文献   

7.
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8.
Depending on the orientation of thermal and compositional gradientsat the margins of a cooling intrusion, double-diffusive convectionmay take one of two principal forms. If the body is coolingat a steep wall, so that both gradients are horizontal, theresult can be boundary layer flow up or down the wall and segregationof the fractionated liquid under the roof or on the floor. Ifcooling is through the roof or floor of a broad sheet-like body,the gradients will be vertical and if the physical propertiesof the liquid are appropriate, they could lead to broad horizontallystratified convection. The first case has been analysed by Nilsonet al. (1985) and shown to be a physically plausible explanationfor certain types of zoned magmas, but the second case, in whichboth gradients are vertical, appears to be less likely, especiallyin slowly cooled intrusions in which temperatures are controlledby crystal-liquid equilibrium. Depending on whether the magma is losing heat through its roofor floor and on whether its density increases or decreases withcooling and differentiation, four possible conditions are possible.A linear stability analysis based on the experimental and theoreticalcriteria of Baines & Gill (1969) and Shirtcliffe (1969)indicates that neither calc-alkaline liquids that accumulateunder their roof nor tholeiitic liquids ponded on their floorare likely to convect in stratified layers. Even though thegradients and relative diffusivities of heat and compositionmay be in a direction that tends to destabilize the magma, themagnitude of the compositional effect on density is so greatthat the temperature gradient would have to diverge widely fromthe liquidus, and convection would be possible only with largeamounts of under-cooling or superheat. A similar mechanism, based on opposed gradients of two chemicalcomponents of differing diffusivities, may provide an alternativeexplanation for certain types of stratification, but field relationsin the Skaergaard Intrusion do not support any origin that isprimarily dependent on gravity.  相似文献   

9.
地球化学块体与大型矿集区的关系——以东天山为例   总被引：11，自引：5，他引：11  
通过在东天山15万km2的战略性深穿透地球化学调查共圈出大于1000km2以上的地球化学块体18处,其中铜-铅-锌-银地球化学块体5处,铜地球化学块体3处,铜-镍地球化学块体1处,金的地球化学块体4处,铀的地球化学块体3处,铂-钯地球化学块体1处,钨地球化学块体1处。有6处地球化学块体与已知矿集区相对应,新圈定的地球化学块体12处,其中有3处发现了新的矿床。根据这些块体与矿集区的对比得出如下结论:所有的已知矿集区都位于地球化学块体的范围之内,地球化学块体为矿集区的形成提供了丰富的物质基础;有矿集区的存在一定有地球化学块体的存在,但反过来有地球化学块体的存在不一定有矿集区的存在,地球化学块体是客观存在的,而矿集区是已经发现了一系列矿床并勘探到一定程度才能称作矿集区,因此,地球化学块体内可能会存在潜在的矿集区,这为利用地球化学块体预测新的矿集区提供了依据。  相似文献   

10.
An analysis of Bouguer gravity anomaly data and geothermal gradient data obtained from bottom hole and drill stem tests temperature is used to determine the crustal structure of the Sahel Basin in eastern Tunisia and its role in the maturation and location of the large number of oil and gas fields in the region. The regional Bouguer gravity anomaly field is dominated by gradual increase in values from the northwest to southeast and is may be caused by crustal thinning as revealed by regional seismic studies. In addition, higher geothermal gradients in the same region as the Bouguer gravity anomaly maximum add an additional constraint for the existence of crustal thinning in the region. A detailed analysis of the Bouguer gravity anomaly data was performed by both upward continuation and horizontal gradients. These two techniques were combined to show that the study area consists of two structural regions: (1) the North–South Axis (NOSA)–Zeramedine region which is characterized by northwest-dipping, northeast-striking faults, thicker crust (30–31 km) and low geothermal gradients, and (2) the Mahres–Kerkennah region which is characterized by vertical, northwest-striking faults, thinner crust (28–29 km) and higher geothermal gradients. The correlation of a variety of features includes mapped and geophysically defined faults, volcanic rocks, a thinned crust and high geothermal gradients within the same location as known oil and gas fields indicate that the faults are a major factor in the location of these petroleum accumulations.  相似文献   

11.
Concentrations of Re, Ir and Au are nearly constant within individual masses of the Cape York IIIAB iron meteorite, but differences between masses can be as large as a factor of 2, the extremes being Savik (5.1 μg/g Ir) and Agpalilik (2.7 μg/g Ir). The S concentration shows a still larger range from 13 mg/g in Agpalilik to 1.4 mg/g in Savik. A relatively large compositional hiatus between Dog and Agpalilik probably reflects inadequate sampling of the original material.Concentrations of Ir vary by ~10% and Au by ~3% between the ends of an 85-cm section from the Agpalilik mass of Cape York, but other sections through Agpalilik show smaller variations. These concentration ranges are much larger than expected from radial crystallization of a moderately large (radius 10 s of km) core. These variations in the Agpalilik mass may reflect dendritic crystallization, or they may have resulted from the process that produced the large concentration range among the Cape York masses.Large gradients in Re and Ir and small gradients in Ni and Au were also observed in samples within 2 cm of a large (100 cm3) troilite nodule. These gradients may reflect rapidly changing solid/liquid distribution coefficients during the final crystallization of S-rich liquid.The compositional trends among the various masses can either be explained by mixing of disparate end members followed by diffusive homogenization on a scale of m, or by dendritic crystallization on the ceiling of the IIIAB magma chamber. The mixing of a solid similar in composition to Savik with a liquid in equilibrium with this solid yields a good match to the observed trends, in which case Agpalilik consists of a mixture of 64% liquid and 36% solids. The bulk S content of the IIIAB core is calculated to be 14 mg/g on the basis of this model.  相似文献   

12.
The aim of this paper is to address two critical but largely neglected issues in the spatial analysis of urban crime which are spatial spillover effects of crime penetrating neighborhood boundaries and non-stationarity regarding the relationships between contextual factors and neighborhood crime. We use a GIS-based spatial approach to normalize the estimate of burglary crime at block group level and use the geographically weighted regression (GWR) to investigate the correlates of neighborhood crime. Results suggest that the use of normalized measure of neighborhood crime helps better reveal the spatial patterns of burglary crime and the use of GWR accounts for the spatial variations of relationships between contextual factors and crime. In particular, the normalized measure of crime has implications for improving the measurement accuracy of the risk of crime across urban neighborhoods and can be applied to the spatial analysis of other socioeconomic issues such as housing foreclosures and environmental hazards which are also plagued by the spatial spillover issue when geographically contiguous data are analyzed.  相似文献   

13.
More than half of the US rural population lives inside metro or micropolitan areas and even at more disaggregated scales, such as the census tracts, most spatial units mix rural and urban population. At a national scale, only 30% of the country are inhabited by 100% urban or 100% rural population, implying that more than two third of the US territory are somewhere in between both situations. As the rural/urban dichotomy appears today to be blurred by the emergence of new phenomena like rurbanization or exurbanization, our perception of rural America may be somewhat twisted and the reality of rural areas underplayed. This paper focuses on using finer-grade spatial units such as the census blocks and block groups, in order to provide new elements about the extension, localization and characteristics of rural America as well as about its inner dynamics. To that end, we analyze and process geographical and social data at these two levels of information, and use population density as a main factor of analysis. This allows us not only to propose new measurement of the extent of rural space in the USA but also to propose a new vision of its spatial dynamics by studying how several social indicators such as income, median age or sex ratio reveal regional and micro-regional variations and situations in the rural part of the US.  相似文献   

14.
Takeshi Kudo  Koshun Yamaoka   《Tectonophysics》2003,367(3-4):203-217
The driving force for the basin subsiding against isostatic balance in and around Lake Biwa in the Kinki district, Japan is discussed. The lake region is characterized by strong negative Bouguer anomalies, especially by a steep horizontal gradient zone of gravity anomaly running along the western margin of the lake. The large negative anomaly (>50 mgal) cannot be explained by low-density sediments beneath it. A down-warping structure extending to the Moho depth should be taken into account. This conjecture has been strongly supported by a short-period receiver function imaging, which shows a clear offset of about 8 km for the Moho discontinuity under the steep gravity gradient zone.A question arises as to what is the driving force to create such a large down-warping structure. We consider that the subduction of the shallow-dipping slab under the region (Philippine Sea Slab) may cause crustal deformation by dragging the viscous mantle downward. In order to verify this model, we simulated the induced mantle flow due to the subduction of the Philippine Sea Slab and the pressure distribution on the crust–mantle boundary. This numerical experiment showed that the induced flow makes a strong negative pressure zone under the lake region if the slab has a vertical offset along the direction of subduction. This offset of the slab is consistent with plate models deduced from hypocentral distributions and Sp phases of the deep-focus earthquakes.  相似文献   

15.
Epistemic uncertainties arise during the estimation of hydraulic gradients in unconfined aquifers due to planar approximation of the water table as well as data gaps arising from factors such as instrument failures and site inaccessibility. A multidimensional fuzzy least-squares regression approach is proposed here to estimate hydraulic gradients in situations where epistemic uncertainty is present in the observed water table measurements. The hydraulic head at a well is treated as a normal (Gaussian) fuzzy variable characterized by a most likely value and a spread. This treatment results in hydraulic gradients being characterized as normal fuzzy numbers as well. The multidimensional fuzzy least-squares regression has an exact analytical form and as such can be implemented easily using matrix algebra methods. However, the method was noted to be sensitive to round-off and truncation errors when the epistemic uncertainties are small. A closeness index based on the cardinality of a fuzzy number is used to evaluate how well the regression model fits the fuzzy hydraulic head observations. A fuzzy Euclidian distance measure is used to compare two fuzzy numbers and to evaluate how fuzziness in the observed hydraulic heads affects the fuzziness in the estimated hydraulic gradients. The Euclidian distance measure is also used to ascertain the influence of each well on the fuzzy hydraulic gradient estimation. The fuzzy regression framework is illustrated by applying it to evaluate hydraulic gradients in the unconfined portion of the Gulf Coast aquifer in Goliad County, TX. The results from the case-study indicate that there is greater uncertainty associated with the estimation of the hydraulic gradients in the vertical (Z-axis) direction. The epistemic uncertainties in the hydraulic head data at the wells have a significant impact on the gradient estimates when they are of the same order of magnitude as the most likely values of the observed heads. The influence analysis indicated that 5 of the 13 wells in the network had a critical influence on at least one of the hydraulic gradients. Three wells along the northeastern section of the study area and bordering the Victoria County were noted to have the least influence on the regression estimates. The fuzzy regression framework along with the associated goodness-of-fit and influence measures provides a useful set of tools to characterize the uncertainties in the hydraulic heads and gradients arising from data gaps and planar water table approximation.  相似文献   

16.
Identity theft is among the fastest growing white-collar crimes in the United States, although official recognition of it as a criminal act is a relatively recent development. Utilizing theoretical framework established in crime geography, GIS mapping and spatial statistics are employed to conduct a spatial analysis of identity theft in the U.S. from 2002 to 2006. Distinct regional variations, such as high rates in the western and southwestern states, and low rates in New England and the central plains states, are identified for identity theft. Significant spatial patterns of identity theft victims alongside social demographic variables are also revealed in order to better understand the regional patterns that may suggest underlying social causes contributing to identity theft. Potential social variables, such as race/ethnicity and urban–rural populations, are shown to have similar patterns that may be directly associated with U.S. identity theft victims.  相似文献   

17.
Geothermal gradients and present day heat flow values were evaluated for about seventy one wells in parts of the eastern Niger delta, using reservoir and corrected bottom–hole temperatures data and other data collected from the wells. The results showed that the geothermal gradients in the shallow/continental sections in the Niger delta vary between 10 - 18° C/km onshore, increasing to about 24° C/km seawards, southwards and eastwards. In the deeper (marine/paralic) section, geothermal gradients vary between 18 - 45° C/km. Heat flow values computed using Petromod 1–D modeling software and calibrated against corrected BHT and reservoir temperatures suggests that heat flow variations in this part of the Niger delta range from 29–55 mW/m2 (0.69–1.31 HFU) with an average value of 42.5 mW/m2 (1.00 HFU). Heat flow variations in the eastern Niger delta correspond closely to variations in geothermal gradients. Geothermal gradients increase eastwards, northwards and seawards from the coastal swamp. Vertically, thermal gradients in the Niger delta show a continuous and non-linear relationship with depth, increasing with diminishing sand percentages. As sand percentages decrease eastwards and seawards, thermal gradient increases. Lower heat flow values (< 40 mW/m2) occur in the western and north central parts of the study area. Higher heat flow values (40 - 55 mW/m2) occur in the eastern and northwestern parts of the study area. A significant regional trend of eastward increase in heat flow is observed in the area. Other regional heat flow trends includes; an eastwards and westwards increase in heat flow from the central parts of the central swamp and an increase in heat flow from the western parts of the coastal swamp to the shallow offshore. Vertical and lateral variations in thermal gradients and heat flow values in parts of the eastern Niger delta are influenced by certain mechanisms and geological factors which include lithological variations, variations in basement heat flow, temporal changes in thermal gradients and heat flow, related to thicker sedmentary sequence, prior to erosion and evidenced by unconformities, fluid redistribution by migration of fluids and different scales of fluid migration in the sub-surface and overpressures.  相似文献   

18.
模拟降雨条件下坡面流水动力学特性研究   总被引：10，自引：0，他引：10       下载免费PDF全文
为探明降雨条件下沙黄土坡面水流水动力学特性,以流体力学和泥沙运动力学理论为依据,通过5个坡度和5个雨强组合条件下室内模拟降雨试验,系统研究了坡面水流水力参数的变化规律。结果表明,降雨条件下坡面薄层水流雷诺数均小于580,处于层流失稳区;水流流型随雨强和坡度的变化而发生转捩,当坡度较缓、雨强较小时,床面形态处于低能态区和过渡区,床面出现沙纹现象,水流宏观上呈缓流,反之,坡度较陡、雨强较大时,床面由沙纹和沙垄向动平床过渡,宏观上多呈急流;并根据薄层水流阻力组成特点,推导出沙黄土坡面薄层水流阻力计算公式。验证结果表明,该式误差较小,可为坡面侵蚀预报模型的构建提供参考。  相似文献   

19.
The recharge mechanism of a very large spring area in the town of Zieleniec in the Orlickie Mountains (part of the Sudety mountain chain) in southwestern Poland, was investigated and characterized. The spring area is located on a steep mountain slope at a high elevation, next to the continental water divide. It is estimated that at least 90% of the spring discharge comes from outside its topographic drainage basin. The study area has been strongly affected by tectonic episodes of different ages. Thus, there is a high density of fractures in the crystalline massif, which determines the water content of the area and the occurrence of large springs. The low variability in discharge of the Zieleniec spring area indicates the presence of a strong and stable component source of recharge. It has also been shown that gravitational drainage of solid-rock blocks and small fissures is also an important recharge component. The stable recharge component is associated with deep-water circulation from the B?lá River drainage basin in the Czech Republic, flowing beneath the continental divide. Water flows in conformity with a high hydraulic head gradient through deep, open, NW?CSE-oriented fissures.  相似文献   

20.
王帅  盛谦  朱泽奇  肖培伟 《岩土力学》2012,33(10):2897-2902
目前地下结构地震动力分析主要研究围岩响应特征,对围岩中赋存的岩体结构的动力响应规律、塌落机制还缺乏深入研究。结合大岗山水电站工程地下洞室群,基于块体理论选取3种不利地质结构组合作为地下洞室群动力分析的主要结构形式,接着运用离散元程序UDEC研究两种地震动工况作用下不同不利地质结构组合切割的地下洞室围岩动力响应、变形特征以及节理的张开、滑移特征,分析开挖面附近块体的塌落机制。研究结果表明,陡倾角结构面切割形成不利地质结构对地下洞室围岩变形破坏机制影响较大;在地震荷载作用下,陡倾不利地质结构沿节理面的滑塌具有突发性,并且塌落模式随地震强度增加可能发生变化。  相似文献   

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