成都平原稻田甲烷排放的实验研究

根据1996～1999年四个稻季的观测资料,分析了成都平原单季稻甲烷排放的季节变化和年际变化特征.结果表明:在水稻生长季节甲烷排放通量变化很大,在分蘖期和成熟期一般会出现峰值.年际间的通量变化也很大,其年均排放通量的变化范围在2.35～33.95mg m-2 h-1之间.4年的平均排放通量为12 mg m-2 h-1,与四川乐山的7年平均值30mg m-2 h-1相比,存在着明显的地区差异.同时分析讨论了温度、施肥、水稻品种、土壤氧化还原电位(Eh)以及稻田水位等诸多因素对稻田甲烷排放的影响.结果表明:在成都平原水稻生长季节的平均气温对CH4的平均排放通量影响不大;而气温对CH4排放的日变化有相对重要的影响,但气温对甲烷排放日变化的影响与水稻植物体的生长阶段有关;发现了水稻植物体(根、茎、叶)重量对CH4排放的重要作用.讨论了合理使用肥料和施肥量,控制水位和Eh值对稻田CH4的减排作用,提出优化组合诸影响因子,以充分发挥其减排潜力.     

A regularization of multiple encounters in gravitationalN-body problems

A method is introduced to regularize binary collisions between one of the bodies and any number of other bodies in the three-dimensional problem ofn-bodies. The coordinates are first transformed from an inertial system to a system relative to one of the bodies. The KS dependent variable transformation and a new independent variable transformation are introduced for the regularization.     

Solutions for Exterior Orientation in Photogrammetry: A Review

The determination of the attitude, the position and the intrinsic geometric characteristics of the camera is recognised as the fundamental photogrammetric problem. It can be summarised as the determination of camera interior and exterior orientation parameters, as well as the determination of 3D coordinates of object points. The term "exterior orientation"of an image refers to its position and orientation related to an exterior (object space) coordinate system. Several methods can be applied to determine the parameters of the orientation of one, two or more photos. The orientation can be processed in steps (as relative and absolute orientation) but simultaneous methods (such as bundle adjustments) are now available in many software packages. Several methods have also been developed for the orientation of single images. They are based in general on geometric and topological characteristics of imaged objects.
This paper presents a survey of classical and modern methods for the determination of the exterior parameters in photogrammetry, some of which are available as software packages (with practical examples) on the Internet. The methods presented are classified in three principal groups. In the first, a selection of approximate methods for applications that do not require great accuracy is presented. Such methods are also used to calculate values required for iterative processes. In the second group, standard point–based methods derived from collinearity, coplanarity or coangularity conditions are briefly reviewed, followed by line–based approaches. The third group represents orientation methods based on constraints and on concepts of projective geometry, which are becoming of increasing interest for photogrammetrists. In the last section, the paper gives a summary of existing strategies for automatic exterior orientation in aerial photogrammetry.     

Differences in the concentrations of atmospheric trace gases in and above the tropical boundary layer

Weekly air samples were collected at Cape Kumakahi (0 km) and at nearby Mauna Loa Observatory (3.4 km) which is above the boundary layer. EC/GC and GC/FID techniques were used to measure CH₃I, CHCl₃, CO and CH₄, which are largely natural in origin, and C₂Cl₄, CCl₄, CH₃, CCl₃, CCl₃F (F-11), CCl₂F₂ (F-12), CHClF₂ (F-22) and C₂F₃Cl₃ (F-113), which are due to anthropogenic activities. It was found that all these gases are significantly (0.05) more abundant in the boundary layer than above it.     

Comparison of SEBAL,METRIC, and ALARM algorithms for estimating actual evapotranspiration of wheat crop

Theoretical and Applied Climatology - Evapotranspiration is one of the main components of water balance and its accurate estimation is of great importance in planning and optimizing water...     

Spatial and temporal analysis of the drought vulnerability and risks over eight decades in a semi-arid region (Tensift basin: Morocco)

Theoretical and Applied Climatology - The multiple downscaled scenario products allow us to assess the uncertainty of the variations of precipitation and temperature in the current and future...     

The Western Boundary of the Equatorial Pacific Upwelling: Some Consequences of Climatic Variability on Hydrological and Planktonic Properties

The longitude of the western limit of the equatorial Pacific upwelling is a key parameter for studies of carbon budget and pelagic fisheries variability. Although it is well defined at the surface on the equator by a salinity front and a sharp variation of the partial pressure of CO₂, data from two equatorial cruises make it clear that this hydrological limit does not necessarily coincide with the boundary of the nitrate and chlorophyll enriched area. In January-February 1991 during a non-El Niño period, when trade winds and the South Equatorial current (SEC) were favorable to upwelling, the two limits were at the same longitude. Conversely, in September-October 1994 during El Niño conditions, when the equatorial upwelling had stopped, the nitrate and chlorophyll enriched zone was found a few degrees of longitude east of the hydrological boundary (5.5° at the surface and 2.5° for the 50 m upper layer), whereas no such offset was observed for zooplankton biomass. A simple model, based on the HNLC (High Nutrient - Low Chlorophyll) ecosystem functioning, was initialized with nitrate uptake measurements and estimates of upwelling break duration. The model results support the hypothesis that zonal separation of the limits arises from biological processes (i.e. nitrate uptake and phytoplankton grazing) achieved during that upwelling break.     

Inverse geochemical modeling of groundwater salinization in Azraq Basin,Jordan

The aim is to define the mechanism of chemical reactions that are responsible for the salinization of the Azraq basin along groundwater flow path, using inverse modeling technique by PHREEQC Interactive 2.8 for Windows. The chemical analysis of representative groundwater samples was used to predict the causes of salinization of groundwater. In addition, the saturation indices analysis was used to characterize the geochemical processes that led to the dissolution of mineral constituents within the groundwater aquifer system. According to the modeling results, it was noted that the groundwater at the recharge area was undersaturated with respect to calcite, dolomite, gypsum, anhydrite, and halite. Thus, the water dissolved these minerals during water rock interaction, and therefore, the concentration of Ca, Mg, Na, and SO₄ increased along the groundwater flow path. Furthermore, the groundwater at the discharge area was oversaturated with respect to calcite and dolomite. This meant that the water would precipitate these minerals along the flow path, while the water was undersaturated with respect to gypsum and halite throughout the simulated path; this showed the dissolution processes that take place during water-rock interaction. Therefore, the salinity of the groundwater increased significantly along the groundwater flow paths.