Coordinate gauge conditions in theN-body equations of motion in the first-order post-Newtonian approximation of general relativity     

Rajat Roy  N. C. Rana 《Astrophysics and Space Science》1990,167(1):125-138

The explicit forms of the metric as well as the equations of motion in the first-order post-Newtonian approximation are worked out under several gauge conditions. It is noted that the so-called EIH (Einstein, Infeld, and Hoffman) equation of motion for an assembly ofN finite mass points mutually interacting via gravitation is identically obtained under three different gauge conditions, namely the harmonic gauge, Chandrasekhar gauge and a composite Chandrasekhar gauge used by Misneret al. (1970), even though the solutions for the metric are found to be all different. In one case the metric has a component apparently diverging, but finally generates regular affine connections so that the equations of motions become free from any singularity. By use of the Chandrasekhar gauge and his formulation, the second-order contribution to the acceleration of planets in the limit of test particle motion around the Sun has been calculated, the inclusion of which in the EIH set of the equations of motion would extend the relative accuracy of computing the total acceleration of any planet to better than one part in 10¹⁷.  相似文献   

Socio-economic and Environmental Implications of the Hydroelectric Projects in Uttarakhand Himalaya, India   总被引：1，自引：1，他引：0  

Naresh Rana S.P. Sati Y.P. Sundriyal Madan Mohan Doval Navin Juyal 《山地科学学报》2007,4(4):344-353

This paper deals with detailed analysis of the fiasco created by the Tehri High Dam in Uttarakhand, India, particularly in terms of resettlement and rehabilitation of the local inhabitants. Aspects pertaining to the environmental issues are also discussed. Currently, the river valleys in Uttarakhand state of India are the targets of increasing hydroelectric projects. Virtually all rivers are being exploited for generating environmental friendly power. Having being learned the hard lesson from Tehri Dam, it has been decided to opt for such schemes in which comparatively little submergence and tempering with the fragile eco-systems is involved.However, our observations suggest that even in such schemes if due care is not taken they may turn out to be a failure.  相似文献   

Hydrogeologic assessment of escalating groundwater exploitation in the Indus Basin, Pakistan   总被引：1，自引：1，他引：0  

S. Khan  T. Rana  H. F. Gabriel  Muhammad K. Ullah 《Hydrogeology Journal》2008,16(8):1635-1654

Groundwater development has contributed significantly to food security and reduction in poverty in Pakistan. Due to rapid population growth there has been a dramatic increase in the intensity of groundwater exploitation leading to declining water tables and deteriorating groundwater quality. In such prevailing conditions, the hydrogeological appraisal of escalating groundwater exploitation has become of paramount importance. Keeping this in view, a surface water–groundwater quantity and quality model was developed to assess future groundwater trends in the Rechna Doab (RD), a sub-catchment of the Indus River Basin. Scenario analysis shows that if dry conditions persist, there will be an overall decline in groundwater levels of around 10 m for the whole of RD during the next 25 years. The lower parts of RD with limited surface water supplies will undergo the highest decline in groundwater levels (10 to 20 m), which will make groundwater pumping very expensive for farmers. There is a high risk of groundwater salinization due to vertical upconing and lateral movement of highly saline groundwater into the fresh shallow aquifers in the upper parts of RD. If groundwater pumping is allowed to increase at the current rate, there will be an overall decline in groundwater salinity for the lower and middle parts of RD because of enhanced river leakage.  相似文献   

Limiting the soil degradational impacts of wildfire in pine and eucalyptus forests in Portugal: A comparison of alternative post-fire management practices     

Richard A Shakesby  David J Boakes  Celeste de OA Coelho  AJ Bento Gonçalves  Rory PD Walsh 《Applied geography (Sevenoaks, England)》1996,16(4):337-355

In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.  相似文献   

Spatial,temporal and frequency based climate change assessment in Columbia River Basin using multi downscaled-scenarios   总被引：1，自引：0，他引：1  

Arun Rana  Hamid Moradkhani 《Climate Dynamics》2016,47(1-2):579-600

  相似文献   

Integrated methodology for flood risk assessment and application in urban communities of Pakistan     

Irfan Ahmad Rana  Jayant K. Routray 《Natural Hazards》2018,91(1):239-266

Flood disasters and its consequent damages are on the rise globally. Pakistan has been experiencing an increase in flood frequency and severity along with resultant damages in the past. In addition to the regular practices of loss and damage estimation, current focus is on risk assessment of hazard-prone communities. Risk measurement is complex as scholars engaged in disaster science and management use different quantitative models with diverse interpretations. This study tries to provide clarity in conceptualizing disaster risk and proposes a risk assessment methodology with constituent components such as hazard, vulnerability (exposure and sensitivity) and coping/adaptive capacity. Three communities from different urban centers in Pakistan have been selected based on high flood frequency and intensity. A primary survey was conducted in selected urban communities to capture data on a number of variables relating to flood hazard, vulnerability and capacity to compute flood risk index. Households were categorized into different risk levels, such as can manage risk, can survive and cope, and cannot cope. It was found that risk levels varied significantly across the households of the three communities. Metropolitan city was found to be highly vulnerable as compared to smaller cities due to weak capacity. Households living in medium town had devised coping mechanisms to manage risk. The proposed methodology is tested and found operational for risk assessment of flood-prone areas and communities irrespective of locations and countries.  相似文献   

A simple parameterization of sub-grid scale open water for climate models     

AJ Pitman 《Climate Dynamics》1991,6(2):99-112

The effects of small fractions ( < 30%) of open water covering a grid element are currently neglected even in atmospheric general circulation models (AGCMs) which incorporate complex land surface parameterization schemes. Here, a method for simulating sub-grid scale open water is proposed which permits any existing land surface model to be modified to account for open water. This new parameterization is tested as an addition to an advanced land surface scheme and, as expected, is shown to produce general increases in the surface latent heat flux at the expense of the surface sensible heat flux. Small changes in temperature are associated with this change in the partitioning of available energy which is driven by an increase in the wetness of the grid element. The sensitivity of the land surface to increasing amounts of open water is dependent upon the type of vegetation represented. Dense vegetation (with a high leaf area index) is shown to complicate the apparently simple model sensitivity and indicates that more advanced methods of incorporating open water into AGCMs need to be considered and compared against the parameterization suggested here. However, the sensitivity of one land surface model to incorporating open water is large enough to warrant consideration of its incorporation into climate models.  相似文献   

Evapotranspiration measurement for tall plant canopies: The sweet sorghum case   总被引：3，自引：0，他引：3  

G. Rana  N. Katerji 《Theoretical and Applied Climatology》1996,54(3-4):187-200

Summary A methodological study on a tall canopy in a Mediterranean region was carried out in order to identify the most suitable method for measuring the actual evapotranspiration (ET). ET from a sweet sorghum crop was measured by 4 different methods: (i) energy balance/eddy correlation, (ii) energy balance/Bowen ratio, (iii) energy balance/aerodynamic simplified, and (iv) floating lysimeter (ETmeter). In order to compare a very large range of ET values and to reduce experimental errors due to low gradients of air humidity and temperature, the crop was submitted to two soil drying-wetting cycles. To evaluate the main limitations of each method with respect to crop height, crop ET was monitored during the entire vegetative cycle, from stem elongation (crop height 0.85 m, full canopy) to grain filling (when the crop was 2.5 m high). The comparison between the micrometeorological methods (i, ii, and iii) was made on hourly and daily time steps, while the analysis of ETmeter measurements was made on a daily time step only. On an hourly scale: eddy correlation ET was 106% of Bowen ratio ET and simplified aerodynamic ET was 116%, 125% and 135% of Bowen ratio ET with the first sensors are placed at the top of the canopy and the second sensors at 0.7 m, 1.4 m and 2.8 m from the first sensors, respectively. On a daily scale: eddy correlation ET was 102% of Bowen ratio ET, simplified aerodynamic was 114% of Bowen ratio ET and ETmeter ET was 97% of Bowen ratio ET. In the last case the values are very widely spread and the correlation is really not so good. The results show that the Bowen ratio method and the eddy correlation method are in good agreement on daily scales, however, certain precautions, must be taken concerning the eddy correlation method on an hourly scale. The simplified aerodynamic method failed when crop height was > 1.5 m and the ETmeter failed under windy conditions (wind speed > 2.0 m/s) and limited crop water conditions.With 13 Figures  相似文献   

X-ray absorption effects due to intergalactic abundance of carbon     

N. C. Rana 《Astrophysics and Space Science》1980,67(1):201-204

The absorption effects at the soft X-ray and hard ultraviolet wavelengths due to some model abundance of intergalactic carbon material have been investigated for different cosmologies. Even though the local density, 2 × 10⁹ <ϱ ₀ = 1.0 × 10⁻³⁴ g cm⁻³ of the absorbing component of the intergalactic material in the form of carbon is not adequate for the thermalization of the discrete background radiation, the amount of absorption in the X-rays up to the Hubble radius is not negligible.  相似文献   

List of forthcoming papers     

N. C. Rana 《Astrophysics and Space Science》1990,164(1):172-177

List of forthcoming papers  相似文献