A Configuration Counterpart of the Kepler Problem Hodograph     

Maria Dina Vivarelli 《Celestial Mechanics and Dynamical Astronomy》1997,68(4):305-311

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Disrupting the 'whiteness' of fieldwork in geography     

Dina Abbott 《Singapore journal of tropical geography》2006,27(3):326-341

This paper argues that whilst fieldwork continues to make an important contribution to the learning and teaching of geography, analysis of the present-day practice of UK universities taking students on long-distance overseas trips remains apolitical and, by and large, concerned with practicalities. If this practice is analysed by locating it within a postcolonial theoretical framework of 'whiteness' it is then possible to look at the differing standpoint and positionality of those doing the viewing and those being viewed, and to also see the connections between the imperialist history of geographical exploration and present-day overseas field trips, in particular to developing countries. Using personal experience of taking UK undergraduates to visit historic slave trading sites in The Gambia as an example, the paper argues that the potential of field study to contribute to the critical pedagogy of geographical fieldwork within UK institutions of higher education requires stronger political analysis.  相似文献   

A quasi 3-D model of an outburst pattern that explains the behavior of Comet 17P/Holmes     

Yael Hillman  Dina Prialnik 《Icarus》2012,221(1):147-159

Upon discovery, in November of 1892, Comet 17P/Holmes was experiencing a very strong explosion, which repeated itself on an even greater scale in October of 2007. Using a numerical scheme, based on mass and energy conservation laws, a model is presented simulating the outbursting nature of Comet 17P/Holmes by regarding the comet as a stratified sphere. The model, adopting input parameters for physical and chemical characteristics, produces output for volatile, water and dust production rates and temperature distribution. Providing the model with known properties of Comet 17P/Holmes, and then filling in the blanks based on properties of other short period comets, allowed the derivation of a specific chemical composition and thermal conductivity that produced a recurring outburst pattern every ～30 years, while within these there is a near-perihelion outburst every ～10² years. The specific composition that generated the desired results, consists of an ice-dust ratio of 0.6/0.4, and mass fractions of 0.015, 0.002 and 0.0005 for CO, CO₂ and NH₃ accordingly. The effective dust conductivity accompanying this composition is K_d = 0.7 W/(m K). The results are consistent with observations on multiple levels, including the various production rates during outbursts and the time span between near perihelion outbursts.  相似文献   

Geochemical modeling and low-frequency geoelectrical methods to evaluate the impact of an open dump in arid and deltaic environments     

Francisco?Javier?Gómez-Puentes  Marco?Antonio?Pérez-Flores  Jaime?Alonso?Reyes-LópezEmail author  Dina?L.?Lopez  Fernando?Herrera-Barrientos  Rafael?Onofre?García-Cueto  Socorro?Romero-Hernández  Fernando?Amílcar?Solís-Domínguez  Miguel?Martín-Loeches Garrido 《Environmental Earth Sciences》2016,75(13):1062

In Mexico, open dumps that are maintained by the municipality but provide no covering of waste are not uncommon. Further, disposal at these sites is often performed by burning. The aim of this study was to determine the leachate plume from an open dump located in a depositional deltaic environment, with arid climate, low rainfall and where the water table is about 2 m below the surface. The methodology comprised analysis of groundwater monitoring wells and geophysical and geochemical prospecting techniques. The 3D geoelectric interpretation shows a typical area of these depositional environments with low resistive values (10–20 Ω-m) associated with the presence of sands and clays interbedded. However, there is a very low resistivity zone associated with the dump’s impact which reaches values below 5 Ω-m, and it is located where the disposal and burning of wastes occurred. Another zone with values above 16 Ω-m appears as a limit for the advance of the saline. This is interpreted as a sandy lenses area. These sandy lenses with higher porosity transport aquifer’s water. Thus the dump is in direct contact by this conduct with clean groundwater. Piper diagrams constructed with the chemical data analysis reveal that the groundwater in the area corresponds to the chlorinated and/or sulfated sodium type, showing the impact caused by the dump. The monitoring well (NP8, on-site) with the highest dissolved solids content behaves anomalously and belongs to the more conductive zone according to the geoelectric profiles. The subsoil geochemical behavior is influenced by the seasonal water table variations provoking the dissolution of burned and unburned wastes, but the effects of slow flows in the direction of the regional flow are not discarded. Although the most impacted area within the dump is characterized to a depth of 10 m, there is a slow flow in the direction of the regional flow that has been moving pollutants out of the dumpsite during its almost 20 years of operation. The results of this study provide valuable information for the authorities to carry out an appropriate restoration project.  相似文献