Proper orthogonal decomposition reduced model for mass transport in heterogenous media

Numerical models with fine discretization normally demand large computational time and space, which lead to computational burden for state estimations or model parameter inversion calculation. This article presented a reduced implicit finite difference scheme that based on proper orthogonal decomposition (POD) for two-dimensional transient mass transport in heterogeneous media. The reduction of the original full model was achieved by projecting the high-dimension full model to a low-dimension space created by POD bases, and the bases are derived from the snapshots generated from the model solutions of the forward simulations. The POD bases were extracted from the ensemble of snapshots by singular value decomposition. The dimension of the Jacobian matrix was then reduced after Galerkin projection. Thus, the reduced model can accurately reproduce and predict the original model’s transport process with significantly decreased computational time. This scheme is practicable with easy implementation of the partial differential equations. The POD method is illustrated and validated through synthetic cases with various heterogeneous permeability field scenarios. The accuracy and efficiency of the reduced model are determined by the optimal selection of the snapshots and POD bases.     

Placing dots in dot maps

Dot mapping is a cartographic representation method to visualise discrete absolute values and their spatial distribution. To achieve this, dots equal in size and represented value are used. According to the dot value, a certain number of dots are used to depict a data value. These dots usually form dot clusters. The data value needs to be rounded to a multiple of the dot value. It is possible to roughly determine the visualised data value by counting the dots and multiplying this number with the dot value. As there are many parameters – dot size, dot value, map scale – to consider when designing a dot map, the manual way is very complex and time consuming. This paper presents a method to automatically create a dot representation of a dot map from given statistical data that needs no cartographic expertise. The dot representation may be combined with other elements, such as a topographic background, to form a complete map. So the algorithm can easily be integrated into the map design process. The paper refines the basic approach of automated dot mapping published earlier. The dot placement and arrangement have been improved compared to the basic method.     

Isotope methods for management of shared aquifers in northern Africa

Access to fresh water is one of the major issues of northern and sub-Saharan Africa. The majority of the fresh water used for drinking and irrigation is obtained from large ground water basins where there is minor contemporary recharge and the aquifers cross national borders. These aquifers include the Nubian Aquifer System shared by Chad, Egypt, Libya, and Sudan; the Iullemeden Aquifer System, extending over Niger, Nigeria, Mali, Benin, and Algeria; and the Northwest Sahara Aquifer System shared by Algeria, Libya, and Tunisia. These resources are subject to increased exploitation and may be severely stressed if not managed properly as witnessed already by declining water levels. In order to make appropriate decisions for the sustainable management of these shared water resources, planners and managers in different countries need an improved knowledge base of hydrological information. Three technical cooperation projects related to aquifer systems will be implemented by the International Atomic Energy Agency, in collaboration with the United Nations Educational, Scientific and Cultural Organization and United Nations Development Programme/Global Environmental Facility. These projects focus on isotope hydrology studies to better quantify ground water recharge and dynamics. The multiple isotope approach combining commonly used isotopes 18O and 2H together with more recently developed techniques (chlorofluorocarbons, 36Cl, noble gases) will be applied to improve the conceptual model to study stratification and ground water flows. Moreover, the isotopes will be an important indicator of changes in the aquifer due to water abstraction, and therefore they will assist in the effort to establish a sustainable ground water management.     

Color centers,associated rare-earth ions and the origin of coloration in natural fluorites

Natural colored fluorites were studied by means of optical absorption and electron paramagnetic resonance (EPR). Complex centers involving rare-earth ions and/or oxygen give rise to the various colors observed. These include yttrium-associated F centers (blue), coexisting yttrium and cerium-associated F centers (yellowish-green), the (YO₂) center (rose) and the O ₃ ^? molecule ion (yellow). Divalent rare-earth ions also contribute to the colorations, as for instance Sm³⁺ (green fluorites), or they are at the origin of strong fluorescence observed (Eu²⁺). Strong irradiation of the crystals with ionizing radiation leads to coagulation of color centers, and to precipitation of metallic calcium colloids. There is probably no simple relation connecting the coloration and the growth process of the crystal. Thermal stability studies, however, have allowed to partially classify the colors as being of primary or secondary origin.     

Lower tropospheric transport over the Southern Ocean

Radon and particle concentrations obtained at Macquarie Island, halfway between Australia and Antarctica, and on Tasmania's north-west coast at Cape Grim during 1987 are examined. Four-day trajectories based on 12 hourly analyses over the Australian region are used to explore the transport of continental material across the Southern Ocean. This study suggests that at least 25% of the variance of radon concentration at Macquarie Island can be accounted for by transport from the Australian continent. Trajectories at intervals of one hour are used to demonstrate the agreement between episodes of trajectories passing over land and episodes of elevated radon and particle concentration. Wind roses of percentage probability of various levels of radon and particle concentration are compared with back trajectories for their accuracy in depicting episodes of continental air incursion.     

How Much Warming are We Committed to and How Much can be Avoided?

This paper examines different concepts of a ‘warming commitment’ which is often used in various ways to describe or imply that a certain level of warming is irrevocably committed to over time frames such as the next 50 to 100 years, or longer. We review and quantify four different concepts, namely (1) a ‘constant emission warming commitment’, (2) a ‘present forcing warming commitment’, (3) a‘zero emission (geophysical) warming commitment’ and (4) a ‘feasible scenario warming commitment’. While a ‘feasible scenario warming commitment’ is probably the most relevant one for policy making, it depends centrally on key assumptions as to the technical, economic and political feasibility of future greenhouse gas emission reductions. This issue is of direct policy relevance when one considers that the 2002 global mean temperatures were 0.8± 0.2 ^°C above the pre-industrial (1861–1890) mean and the European Union has a stated goal of limiting warming to 2 ^°C above the pre-industrial mean: What is the risk that we are committed to overshoot 2 ^°C? Using a simple climate model (MAGICC) for probabilistic computations based on the conventional IPCC uncertainty range for climate sensitivity (1.5 to 4.5 ^°C), we found that (1) a constant emission scenario is virtually certain to overshoot 2 ^°C with a central estimate of 2.0 ^°C by 2100 (4.2 ^°C by 2400). (2) For the present radiative forcing levels it seems unlikely that 2 ^°C are overshoot. (central warming estimate 1.1 ^°C by 2100 and 1.2 ^°C by 2400 with ～10% probability of overshooting 2 ^°C). However, the risk of overshooting is increasing rapidly if radiative forcing is stabilized much above 400 ppm CO₂ equivalence (1.95 W/m²) in the long-term. (3) From a geophysical point of view, if all human-induced emissions were ceased tomorrow, it seems ‘exceptionally unlikely’ that 2 ^°C will be overshoot (central estimate: 0.7 ^°C by 2100; 0.4 ^°C by 2400). (4) Assuming future emissions according to the lower end of published mitigation scenarios (350 ppm CO₂eq to 450 ppm CO₂eq) provides the central temperature projections are 1.5 to 2.1 ^°C by 2100 (1.5 to 2.0 ^°C by 2400) with a risk of overshooting 2 ^°C between 10 and 50% by 2100 and 1–32% in equilibrium. Furthermore, we quantify the ‘avoidable warming’ to be 0.16–0.26 ^°C for every 100 GtC of avoided CO₂ emissions – based on a range of published mitigation scenarios.     

云南-香港宽视场巡天新发现的一个磁活动双星系统

云南-香港宽视场巡天新发现了一个磁活动双星系统,其轨道周期为0.60286 d.利用云南天文台1 m光学望远镜附加CCD (Charge-Coupled Device)相机,观测得到了这个双星系统的V、Rc双色光变曲线,结果表明该系统食外存在明显的测光畸变.借助云南天文台丽江2.4 m望远镜附加云南暗弱天体光谱成像仪(Yunnan Faint Object Spectrograph and Camera, YFOSC)对该双星系统的分光观测,测定了该双星系统主星的视向速度曲线并发现该系统的主星表面存在着强烈的色球活动,从而证明系统的光变曲线畸变源自主星的黑子活动.使用W-D (Wilson-Devinney)程序分析上述观测得到的光变曲线和视向速度曲线,得到了该双星系统的轨道参数以及黑子参数.最后,对该系统的特性进行了讨论并对未来的工作进行了展望.