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Magnetic Neutral Points and Electric Lines of Force in Strong Gravity of a Rotating Black Hole

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International Journal of Astronomy and Astrophysics 2013年第3期3卷 18-24页

作者： V.Karas o.Kopácek D.Kunneriath Astronomical Institute Academy of SciencesPragueCzech Republic

Magnetic field can be amplified and twisted near a supermassive black hole residing in a galactic nucleus. At the same time magnetic null points develop near the horizon. We examine a large-scale oblique magnetic field near a rotating (Kerr) black hole as an origin of magnetic layers, where the field direction changes abruptly in the ergosphere region. In consequence of this, magnetic null points can develop by purely geometrical effects of the strong gravitational field and the frame-dragging mechanism. We identify magnetic nulls as possible sites of magnetic reconnection and suggest that particles may be accelerated efficiently by the electric component. The situation we discuss is relevant for starving nuclei of some galaxies which exhibit episodic accretion events, namely, Sagittarius A* black hole in our Galaxy.

关键词： Galaxies:Nuclei Galaxy:Center Black Hole Physics Magnetic Fields

Traditional Utilization of Aquatic Resources in Eastern Arc Catchments of Tanzania

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Natural Resources 2019年第5期10卷 153-178页

作者： Agnes G. Kapinga Abimbola Sangodoyin olayinka o. ogunkoya Department of Environmental Management Pan Africa University Life and Earth Sciences Institute (PAULESI) University of Ibadan Ibadan Nigeria Department of Agriculture and Environmental Engineering University of Ibadan Ibadan Nigeria Department of Department of Geography Obafemi Awolowo University Ile Ife Nigeria

Aquatic resources are vital for human well-being particularly to rural communities that largely depend?onthem for livelihood. Currently, it appears that pressure from human activities related to utilization has impacted negatively on catchment management, particularly of the aquatic resources. This study focuses on the aquatic resources found in the Eastern Arc Catchments of Tanzania which include Upper Zigi and Lower Mngeta. The study employs catchment community participatory mapping approach so as to elucidate how man interacts with and modifies the aquatic environment, the impacts of their behavior, and the responses to changes which occur. The aim of the research is to realize a more comprehensive understanding of water resource management from a cultural, social, economic, political, and biological perspective and facilitate sustainable socio-hydrological interaction model. The study found that there are some similarities and differences in aquatic resources management and utilization among communities. Also, it established that there are more aquatic resources in Lower Mngeta catchment than in Upper Zigi catchment. The study found out that the manner of utilization of aquatic resources depends on their availability, levels of skills, knowledge, and beliefs among members of the communities of the catchments. It was also found that the traditional cultural structures that regulated aquatic resource utilization are weakening at an alarming rate due to factors such as modernization and the establishment of?the?formal?institution. Weak traditional structures contribute in many ways to mismanagement and destruction of aquatic resources. The study recommends that ecological database should not only focus on the resources stock, but also on the dynamics of resources utilization. This would lead identification of appropriate local actors with knowledge and skills and cultural advantage who can be involved in planning and management of these important resources. It woul

关键词： Traditional Utilization Aquatic Resources Management

Differential Flatness and Control of Nonlinear Systems

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Differential Flatness and Control of Nonlinear Systems

第三十届中国控制会议

作者： Antoine Drouin Sebastio Simoes Cunha Alexandre C.Brando Ramos Felix Mora-Camino UNIFEI Itajuba 37500-000Brazil LAAS du CNRS Toulouse 31077

＜正＞The purpose of this communication is to investigate the connection between output relative degrees and differential flatness property of non linear *** the relative degrees of the outputs of a non linear system,necessary and sufficient conditions for differential flatness are ***,it is shown that the application of the non linear inverse approach to an output observable and output differential flat system is identical with the differential flat control *** application of the non linear control approach to a four rotor aircraft is considered.A trajectory tracking system based on a two layers non linear inverse control structure is then proposed.

关键词： Differential Flatness Nonlinear Inverse Control Trajectory Tracking

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电子计算机及其应用

电子计算机及其应用

Assessment of Heavy Metal Contaminants Using Pollution Indices in Ankobra River at Prestea Huni-Valley District, Ghana

作者： o.E.·克拉克(o.E. Clark)

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Journal of Geoscience and Environment Protection 2019年第9期7卷 25-35页

作者： Austin Asare Benjamin D. Asamoah Peter o. Sanful Department of Environmental Management University of Energy and Natural Resources Sunyani Ghana Department of Chemical Sciences University of Energy and Natural Resources Sunyani Ghana Department of Fisheries and Water Resources University of Energy and Natural Resources Sunyani Ghana

The reliance of communities on River Ankobra as the source of drinking water makes the assessment of its quality very imperative to human health and environmental management. The objective of this work was to investigate the concentration of heavy metal in the Ankobra River sediments at the Prestea Huni-Valley District using pollution indices. Sediments were collected randomly from the bottom of the Ankobra River at four different communities namely: Awodua, Heman, Ankobra and Tarkwa Breman. The presence of a set of heavy metals Fe, Mn, Cd, Pb, Zn, Cu, and Hg in the sediments was determined using Atomic Absorption Spectroscopy (AAS). The results showed that the concentration of Fe, As, and Hg did not differ significantly (p > 0.05) amongst the four communities but significant variation in the levels of Cu, Mn, Cd, Pb, and Zn was found (p ongst the sampling areas. The geo-accumulation index revealed that the communities were not polluted with Cu, Mn, Fe, Pb and Zn. However, all communities except Tarkwa Breman were found to have exceptionally high levels of Cd. The contamination factor results were consistent with the I-geo results. The pollution load index (PLI) showed that the four communities were not polluted with heavy metals. Strong statistical positive relationship were found between Mn and Cu;Cd and Cu;Pb and Mn;Hg and Mn;Zn and Cu;Zn and Mn;Zn and Pb;Zn and Hg whilst As and Fe showed strong negative correlation.

关键词： Heavy Metal Ankobra River Pollution Index Sediment

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中国黑室--谍海奇遇

中国黑室--谍海奇遇

Effect of Lanthanum Accumulation on Cation Exchange Capacity and Solution Composition of Red Soil

作者： H.o.·亚德利(H.o. Yardley)

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Pedosphere 2000年第2期10卷 171-176页

作者： XIE ZUBIN ZHU JIANGUo CHU HAIYAN CAo ZHIHoNG and DENG XIHAI(Institute of Soil Science, the Chinese Academy of Sciences, P.o. Box 821, Naviing 210008 China) Institute of Soil Science the Chinese Academy of Sciences P.O. Box 821 Nanjing 210008 China

Pot and adsorpt ion- exchange experiments were carried out by collecting the soil samples from the surfacelayer (0~15 cm) of red soil at the Ecological Experiment Station of Red Soil, the Chinese Academy of Sciences,in Jiangxi Province of China. When concentration of the exogenous La3+ exceeded 400 mg kg-1, therewas less non-exchangeable La3+ than exchangeable La3+ in the soil. Cation exchange capacity of the soilchanged slightly with increasing concentration of the exogenous La3+ in both experiments. However, in theadsorption-exchange experiment, when concentration of the exogenous La3+ was higher than 3oo mg kg-1 ,exchangeable basic cations decreased significantly, while exchangeable hydrogen and exchangeable aluminumincreased significantly compared with the control treatments. The amounts of base cations (Ca2+ ) Mg2+, K+and Na+) exchanged by La3+ in the supernatant solution increased with the concentration of the exogenousLa3+, especially when concentration of the exogenous La3+ was higher than 50 mg kg-1.

关键词： CEC exchangeable acidity lanthanum red soil solution composition

Implementation of the Estimating Functions Approach in Asset Returns Volatility Forecasting Using First order Asymmetric GARCH Models

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open Journal of Statistics 2015年第5期5卷 455-464页

作者： Timothy Ndonye Mutunga Ali Salim Islam Luke Akong’o orawo Department of Mathematics Egerton University Egerton Kenya

This paper implements the method of estimating functions (EF) in the modelling and forecasting of financial returns volatility. This estimation approach incorporates higher order moments which are common in most financial time series, into modelling, leading to a substantial gain of information and overall efficiency benefits. The two models considered in this paper provide a better in-sample-fit under the estimating functions approach relative to the traditional maximum likely-hood estimation (MLE) approach when fitted to empirical time series. on this ground, the EF approach is employed in the first order EGARCH and GJR-GARCH models to forecast the volatility of two market indices from the USA and Japanese stock markets. The loss functions, mean square error (MSE) and mean absolute error (MAE), have been utilized in evaluating the predictive ability of the EGARCH vis-à-vis the GJR-GARCH model.

关键词： Estimating Function Asymmetric GARCH Volatility Mean Square Error Mean Absolute Error