On flow of a heat conducting fluid through a porous medium

Summary . A two-space singular perturbation technique is employed to derive approximate governing equations for flow of a viscous heat-conducting fluid through a rigid porous solid. It is assumed that buoyancy forces are significant, and it is shown that standard approximations used in the study of flow through a porous medium are valid provided that Gr ≫ 1, where Gr is a Grashof number calculated using a typical pore radius as the length scale. Results previously derived in the literature for flow through an isotropic random array of spherical particles are used to show how the permeability and conductivity tensors can be calculated for a problem of interest in planetary science.     

One year irrigation experiment to assess losses and runoff volume relationships for a residential road in hertfordshire,England

Six sections of a residential road (75 mm bituminous macadam over 200mm lean mix concrete over 100 mm hoggin with a recent surface dressing of 10 mm granite chippings and K1-70 binder) that drain to individual instrumented gully pots were irrigated along the kerb and then over the whole road approximately monthly for a year. The aim was the determination of terminal infiltration losses, initial losses, percentage runoff, and infiltration curves for the kerb and road surface. The results were not as expected from the literature. There is an annual cycle of infiltration losses at the kerb with a winter peak caused by frost action that is 3.2 times greater than the terminal loss rate at kerbs in summer. The terminal loss rate for an ‘average catchment’ was 6.4251 min^?1 from the road surface and 14.251 min^?1 in summer and 46.281 min^?1 in winter at the kerb. Evaporation was usually more than an order of magnitude less significant than infiltration. The wide variation in initial losses before runoff commenced was inexplicable. Two sections of road behaved in the classic manner with initial losses averaging 0.8 mm, two other catchments had highly variable initial losses in the range 1.2 to 8.8mm, and the last two pieces of road were even more erratic. The percentage runoff for those irrigations of over 15 mm of equivalent rainfall was never more than 10 per cent. The maximum per cent runoff was around 50 per cent following 10 mm of equivalent rainfall for kerbside irrigation and only 5 mm of irrigation over the whole road. There were no significant simple or multiple regression relationships between percentage runoff from the kerb or the whole road irrigations and irrigation amount, slope, UCWI, and SMD. Infiltration curves, for kerb and road irrigation, were so diverse that they do not represent the ‘simple impervious surfaces’ envisaged at the start of the experiment and described in the literature. Since the artificial irrigation of kerbs and roads has failed to substantiate existing theory, these experiments should be repeated at a variety of sites with a high rate of irrigation.     

Diagenetic signatures of stratal surfaces in the Upper Jurassic Fulmar Formation, Central North Sea, UKCS

Sedimentation rate and changes in relative sea level affect early diagenetic cementation along key stratal surfaces within the deeply buried Upper Jurassic Fulmar Formation, South Central Graben, UKCS. As a result of the bioturbated nature of the shallow marine strata, variations in ichnofabrics and cross-cutting relationships between trace fossils are important in identifying and correlating stratal surfaces. Two transgressive and two regressive surfaces/sequence boundaries were studied, using petrographical, mineralogical and geochemical techniques. Cements, including early diagenetic pyrite framboids, grain-rimming apatite, microcrystalline dolomite and ankerite, occur at, above and immediately below both transgressive and forced regressive surfaces/sequence boundaries. Breaks or subdued rates of sedimentation associated with both types of surfaces meant that the sediment package resided within early diagenetic zones for prolonged periods of time, enhancing diagenetic reactions at and below the surfaces. The distribution of ankerite, despite being a deep-burial cement, was primarily controlled by concentrations of bioclasts that are particularly abundant at transgressive surfaces. The diagenetic character of the forced regressive surfaces/sequence boundaries is more complex than that of the transgressive surfaces, both in terms of mineralogy and paragenesis. This is attributed to the superimposition of diagenetic assemblages as a result of erosion, re-sedimentation and sediment by-passing. Although the diagenetic signature of the surfaces has been modified by dissolution/replacement reactions during deep burial, early diagenetic signatures can still be distinguished.     

WHCORS的技术拓展与应用现状

介绍了武汉市连续运行卫星定位服务系统(WHCORS)的基本情况和发展现状;对基于WHCORS技术拓展研究的相关情况和WHCORS的应用推广进行了详述,针对具体的关键技术问题提出了较详细的解决方案,对用户有一定的参考和借鉴作用。     

区县级多源异构空间数据共享平台研究及应用

针对区县级空间数据凌乱、共享程度低、应用效率不高等现状,充分考虑区县级政府部门对多源异构地理空间数据资源共建共享的需求,基于Web Service和ArcGIS Server技术,构建了包含数据管理、运维管理、共享交换、公共服务等四大子系统为核心的多源异构空间数据共享服务平台框架,并在佛山市顺德区成功应用,实现了区县级多源异构空间数据的集成与共享。     

Palaeosurfaces and major valleys in the area of the Kjǿlen Mountains,southern Norway - consequences of uplift and climatic change

Protected area management in Norway is undergoing institutional changes with the implementation of management models aimed at increased public participation. At the same time tourism enterprises are increasing in number within the protected areas. Greater levels of interaction with stakeholders place new demands on lead institutions in terms of communication, transparency, involvement, and power sharing. A governance perspective was used to examine some facets of the interaction between a local council managing a national park in Norway and tourism companies using the park for their operations. The main objective was to assess how the tourism sector perceives the cooperation and interface with the management institution. Semi-structured interviews were used, together with a framework of United Nations Development Programme principles of good governance: legitimacy and voice, direction, performance, accountability, and fairness. The results showed rather negative evaluations by the tourism sector, and operators expressed views, implying that the current management model fails to achieve most of the principles of good governance. Although based on a one-sided view by one group of stakeholders, the study suggests that lack of access to important processes and decisions, perceived bias towards traditional conservation, neglect of cultural heritage, and undue restrictions on access could have serious implications for developing an effective management model.     

Analysis and interpretation of Cassini Titan radar altimeter echoes

The Cassini spacecraft has acquired 25 radar altimeter elevation profiles along Titan's surface as of April 2008, and we have analyzed 18 of these for which there are currently reconstructed ephemeris data. Altimeter measurements were collected at spatial footprint sizes from 6-60 km along ground tracks of length 400-3600 km. The elevation profiles yield topographic information at this resolution with a statistical height accuracy of 35-50 m and kilometer-scale errors several times greater. The data exhibit significant variations in terrain, from flat regions with little topographic expression to very rugged Titanscapes. The bandwidth of the transmitted waveform admits vertical resolution of the terrain height to 35 m at each observed location on the surface. Variations in antenna pointing and changes in surface statistics cause the range-compressed radar echoes to exhibit strong systematic and time-variable biases of hundreds of meters in delay. It is necessary to correct the received echoes for these changes, and we have derived correction algorithms such that the derived echo profiles are accurate at the 100 m level for off-nadir pointing errors of 0.3° and 0.6°, for leading edge and echo centroid estimators, respectively. The leading edge of the echo yields the elevation of the highest points on the surface, which we take to be the peaks of any terrain variation. The mean value of the echo delay is more representative of the mean elevation, so that the difference of these values gives an estimate of any local mountain heights. Finding locations where these values diverge indicates higher-relief terrain. Elevation features are readily seen in the height profiles. Several of the passes show mountains of several hundred m altitude, spread over 10's or even 100's of km in spatial extent, so that slopes are very small. Large expanses of sub-100 m topography are commonplace on Titan, so it is rather smooth in many locations. Other areas exhibit more relief, although the overall observed variation in surface height on any pass is less than about 1 km. Some elevation features correspond to observed changes in brightness in Cassini infrared images, but many do not. Correspondence between the imaging SAR ground tracks and the altimeter paths is limited, so that identifying elevation changes with higher resolution SAR features is premature at present.     

Titan's surface at 2.2-cm wavelength imaged by the Cassini RADAR radiometer: Calibration and first results

The first comprehensive calibration and mapping of the thermal microwave emission from Titan's surface is reported based on radiometric data obtained at 2.2-cm wavelength by the passive radiometer included in the Cassini Radar instrument. The data reported were accumulated from 69 separate observational segments in Titan passes from Ta (October 2004) through T30 (May 2007) and include emission from 94% of Titan's surface. They are diverse in the key observing parameters of emission angle, polarization, and spatial resolution, and their reduction into calibrated global mosaic maps involved several steps. Analysis of the polarimetry obtained at low to moderate resolution (50+ km) enabled integration of the radiometry into a single mosaic of the equivalent brightness temperature at normal incidence with a relative precision of about 1 K. The Huygens probe measurement of Titan's surface temperature and radiometry obtained on Titan's dune fields allowed us to infer an absolute calibration estimated to be accurate to a level approaching 1 K. The results provide evidence for a surface that is complex and varied on large scales. The radiometry primarily constrains physical properties of the surface, where we see strong evidence for subsurface (volume) scattering as a dominant mechanism that determines the emissivity, with the possibility of a fluffy or graded-density surface layer in many regions. The results are consistent with, but not necessarily definitive of a surface composition resulting from the slow deposition and processing of organic compounds from the atmosphere.     

Thermal convection in the porous methane-soaked regolith of Titan: Investigation of stability

Titan is the only body, other than the Earth where liquid is present on the surface. In the present work we consider behavior of methane in the pores of Titan's regolith. Using numerical model we investigate quantitative conditions necessary for the onset of convection. We have found that the methane convection in Titan's regolith is possible. It can be expected in regions where the regolith has sufficiently high porosity, independently of the geothermal heat flux.