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1.
Energetic particle (0.1 to 100 MeV protons) acceleration is studied by using high resolution interplanetary magnetic field and plasma measurements at 1 AU (HEOS-2) and at 5 AU (Pioneer 10). Energy changes of a particle population are followed by computing test particle trajectories and the energy changes through the particle interaction with the time varying magnetic field. The results show that considerable particle acceleration takes place throughout the interplanetary medium, both in the corotating interaction regions (CIR) (5 AU), and in quiet regions (1 AU). Although shocks may contribute to acceleration we suggest statistical acceleration within the CIRs is sufficient to explain most energetic particle observations (e.g., McDonaldet al., 1975; Barnes and Simpson, 1976).The first and second order statistical acceleration coefficients which include transit time damping and Alfvén resonance interactions, are found to be well represented byD
T
8.5×10–6
T
0.5 MeV s–1 andD
TT
4×10–6
T
1.5 MeV2 s–1 at 5 AU.By comparison, Fisk's estimates (1976), based on quasi-linear theory for transit-time damping, gaveD
TT
5×10–7
T MeV2 s–1 at 1 AU. 相似文献
2.
Leticia Gmez-Mendoza Ernesto Vega-Pea M. Isabel Ramírez Jos Luis Palacio-Prieto Leopoldo Galicia 《Applied geography (Sevenoaks, England)》2006,26(3-4):276-290
The objective of study was to explore short-term trends of processes that determine land-use change in Sierra Norte of Oaxaca (SNO), Mexico. Land use and land cover changes (LULCC) were estimated in a complex mosaic of vegetation in the SNO from 1980 to 2000, and projected them to 2020 through a Markovian model. SNO is highly vulnerable to climatic change according to a 2050 GCM scenario. However, 3% annual rate of tropical and temperate forest deforestation from agriculture and livestock encroachment, suggest the threat from land-use change is higher than that from climatic change for this study site. Productive land-use strategies are needed to reduce such high deforestation rates for tropical regions. Controlling deforestation would also reduce short-term effects of CO2 emissions to the atmosphere. Because of the necessity to evaluate anthropogenic ecosystem changes, it is imperative to separate short-term influences such as deforestation, from long-term influences such as climatic change. 相似文献
3.
J. F. Valdés Galicia X. Moussas J. J. Quenby F. M. Neubauer R. Schwenn 《Solar physics》1984,91(2):399-413
Pitch angle scattering of energetic particles (100 MeV) in the interplanetary medium are studied using Helios 1 and 2 magnetometer and plasma data during 1976 near the minimum of solar activity. An IMF configuration was used in the computer experiments which allowed the pitch angle diffusion coefficient, D
and hence the parallel mean free path,
to be determined. The radial mean free path was found to vary as
r r
-0.9 between 0.4 and 1 AU, but between 0.3 and 0.4 AU it decreases significantly. To reconcile our value of
r at 1 AU, lying between 0.01 and 0.02 AU, with the average prompt solar proton event profile, an increasing value of
r at lower radial distances would be required. 相似文献
4.
安徽巢湖凤凰山剖面石炭系微相和层序地层特征 总被引：9，自引：1，他引：9
应用露头层序地层学基本原理和方法 ,对巢湖凤凰山石炭系剖面进行重新研究。巢湖凤凰山石炭系总厚度为79.0 2 m ,在这个剖面中可以识别出 6种主要岩相、18种微相和 11个三级沉积层序 ,其中六个三级沉积层序属于 I型沉积层序 ,三个属于 II型沉积层序 ,缺失第 9和第 10沉积层序。三级沉积层序在不同的古地理单元和不同的沉积环境中可以进行对比。根据各微相特征和成因 ,揭示了沉积间断面上存在的多期古岩溶现象。阐述了三级层序及其对应的三级海平面升降旋回的特征 相似文献
5.
塔里木盆地库鲁克塔格地区二叠纪末-中三叠世基性岩床的发现及其地质意义 总被引：2，自引：1，他引：1
新疆塔里木盆地东北缘库鲁克塔格地区的中寒武统莫合尔山组沉积地层中发现三条形成于二叠纪末到中三叠世的基性岩床。三条岩床沿沉积岩层面顺层侵入,按照从下到上的顺序,分别为辉绿岩床(厚3m)、辉长岩床(厚20m)和粗玄岩床(厚2.5m)。三条岩床的地球化学特征相似,稀土含量高(∑REE=210×10-6~297×10-6),轻稀土元素富集((La/Yb)N =13.54~17.96),Eu负异常不明显(δEu=0.97~1.21),Ce稍具正异常(δCe=1.11~1.25)。大离子亲石元素(Rb、Ba、Th、Sr)富集,Sr具明显正异常; Ta、Nb和Hf具负异常。低氧化度(0.13~0.40)。三条岩床为同源岩浆活动的产物,岩浆源于上地幔或下地壳,但有下陆壳成分混染。三个样品的MgO含量在4%~6%之间,Mg#值在37.6~55.6之间,固结指数SI值位于18.7~29.3之间,反映原始的岩浆经历了比较明显的分异作用。粗玄岩床K-Ar年龄为255.2±7.3Ma,辉绿岩床K-Ar年龄为242.8±5.7Ma,辉长岩床Ar-Ar年龄为229.7±3.7Ma。本次岩浆侵入事件发生在南天山洋闭合之后,构造背景为造山后碰撞伸展环境。 相似文献
6.
Land use/cover, landforms and fragmentation patterns in a tropical dry forest in the southern Pacific region of Mexico 总被引：1，自引：0，他引：1
Leopoldo Galicia Alba Esmeralda Zarco-Arista Karla Ivette Mendoza-Robles José Luis Palacio-Prieto Arturo García-Romero 《Singapore journal of tropical geography》2008,29(2):137-154
In spite of widely documented studies of deforestation rates and land use/cover changes in tropical dry forests in Mexico, relatively little is known about fragmentation patterns in such forests. This study defines the spatial distribution of landforms and land use/cover types the lower Papagayo River basin and examines their influence on fragmentation patterns and biological diversity in a tropical dry forest in that southern Pacific region. The land use/cover map was constructed from aerial photographs, Landsat TM imagery (2000) and fieldwork. Landform units were defined based on altitude, slope, lithology and morphology. Landscape fragmentation parameters were obtained using FRAGSTATS (version 3.3) considering the numbers of patches, mean, minimum and maximum patch size, edge density, total edge and connectivity. Results show tropical dry forest to be remnant vegetation (~11 per cent), characterized by isolation and low connectivity. Land use/cover types have different effects on fragmentation patterns. Agriculture and cattle raising produce similar numbers of patches, but with a different mean size; and human settlements have a scattered distribution pattern. The abandonment of rural agricultural livelihoods has favoured the expansion of secondary tropical dry forest characterized by continuity and high connectivity, which suggests a high regeneration potential from land abandonment. It can be concluded that tropical dry forest fragmentation and recovery at regional scales depend on such landscape attributes as lithology, slope, geomorphology and management. 相似文献
7.
Residues of UV filters used as ultraviolet absorbers in sunscreens, cosmetics and in light protection have been found in surface water and fish. Recently some of them were shown bearing estrogenic activity, however, very little is known about possible adverse effects to aquatic life. Here we investigate whether two UV filters, 4-methylbenzylidene camphor (4-MBC) and 3-benzylidene camphor (3-BC), interfere with the thyroid and sex hormone system during frog metamorphosis. Xenopus laevis tadpoles were exposed to 1, 5 and 50 μg/L of 4-MBC and 3-BC, respectively, for 35 days (NF stage 52–66). The rate of metamorphosis was not affected, and no obvious differences in body and tail length compared to controls were observed. Neither 4-MBC, nor 3-BC led to effects on the sex ratio or gross gonad morphology of X. laevis at stage 66. Our results indicate that these UV filters do not negatively affect the thyroid system and sex ratio of frogs at environmental concentrations. 相似文献
8.
Melanie Kolb Jean-François Mas Leopoldo Galicia 《International journal of geographical information science》2013,27(9):1804-1827
Understanding and analysis of drivers of land-use and -cover change (LUCC) is a requisite to reduce and manage impacts and consequences of LUCC. The aim of the present study is to analyze drivers of LUCC in Southern Mexico and to see how these are used by different conceptual and methodological approaches for generating transition potential maps and how this influences the effectiveness to produce reliable LUCC models. Spatial factors were tested for their relation to main LUCC processes, and their importance as drivers for the periods 1993–2002 and 2002–2007 was evaluated by hierarchical partitioning analysis and logistic regression models. Tested variables included environmental and biophysical variables, location measures of infrastructure and of existing land use, fragmentation, and demographic and social variables. The most important factors show a marked persistence over time: deforestation is mainly driven by the distance of existing land uses; degradation and regeneration by the distance of existing disturbed forests. Nevertheless, the overall number of important factors decreases slightly for the second period. These drivers were used to produce transition potential maps calibrated with the 1993–2002 data by two different approaches: (1) weights of evidence (WoE) to represent the probabilities of dominant change processes, namely deforestation, forest degradation, and forest regeneration for temperate and tropical forests and (2) logistic RM that show the suitability regarding the different land-use and -cover (LUC) classes. Validation of the transition potential maps with the 2002–2007 data indicates a low precision with large differences between LUCC processes and methods. Areas of change evaluated by difference in potential showed that WoE produce transition potential maps that are more accurate for predicting LUCC than those produced with RM. Relative operating characteristic (ROC) statistics show that transition potential models based on RM do usually better predict areas of no change, but the difference is rather small. The poor performance of maps based on RM could be attributed to their too general representation of suitability for certain LUC classes when the goal is modeling complex LUCC and the LUC classes participate in several transitions. The application of a multimodel approach enables to better understand the relations of drivers to LUCC and the evaluation of model calibration based on spatial explanatory factors. This improved understanding of the capacity of LUCC models to produce accurate predictions is important for making better informed policy assessments and management recommendations to reduce deforestation. 相似文献
9.
Energetic particle (1–100 MeV) pitch angle scattering in the Interplanetary Magnetic Field (IMF) is studied using spacecraft magnetometer data at 1 AU (IMP 7 and HEOS 2) and at 5 AU (Pioneer 10). Particle trajectories are followed by a computer simulation of their movement in a realistic model of the IMF. Determination of the pitch angle diffusion coefficient at 1 AU (D
) leads to a parallel mean free path which is roughly independent of particle energy, 0.03 AU. At the lowest energy our result is at least a factor of 3 larger than the predictions of quasi linear theory. Results at 5 AU lead to a radial mean free path which is between 2 to 6 times smaller than at 1 AU, probably indicating a greater importance for perpendicular diffusion at large heliodistances. In fact a roughly constant radial mean free path (
r
0.01 AU) is obtained when the contribution of perpendicular diffusion at 5 AU is taken into account (Moussaset al., 1981). 相似文献
10.
A coastal state benefits from importing the services of a distant water fishing nation (DWFN) fleet if the DWFN has a comparative advantage in exploiting the fishery, based on factors such as market access, costs or technology. The paper compares the activities of the Australian and Japanese vessels in the east coast tuna longline fishery and finds the Australian vessels receive higher prices, have higher costs and use a different technology from the Japanese fleet. These differences suggest a pattern of comparative advantage which can lead to Australia benefitting from importing the services of the Japanese fleet. 相似文献