Trojan resonant dynamics,stability, and chaotic diffusion,for parameters relevant to exoplanetary systems     

Rocío Isabel Páez  Christos Efthymiopoulos 《Celestial Mechanics and Dynamical Astronomy》2015,121(2):139-170

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Spatial patterns of biodiversity in the Black Sea: An assessment using benthic polychaetes     

Victor Surugiu  Nikolai Revkov  Valentina Todorova  Nafsika Papageorgiou  Vasilis Valavanis  Christos Arvanitidis 《Estuarine, Coastal and Shelf Science》2010

The current study broadens the biodiversity information available for the Black Sea and neighbouring regions and improves our knowledge about the polychaete biogeographic patterns to be discerned in them. There appears to be a well-defined zoogeocline from the Marmara Sea and Bosphorus Strait to the inner parts of the region (Azov Sea), depicted both as a multivariate pattern and in terms of species (or taxa) numbers. The emergent multivariate pattern complies, to a certain extent, with Jakubova’s (1935) views: three main sectors can be defined in the basin: (a) Prebosphoric, (b) the Black Sea and, (c) the Azov Sea, whereas the Bosphorus Strait and Marmara Sea show less faunal affinities with the afore-mentioned sectors. Patterns derived both from the cosmopolitan and Atlanto-Mediterranean species closely follow the one coming from the polychaete species and genera inventories. As a general trend, species numbers decrease along with the decrease in salinity towards the inner parts of the region. The trend is homologous to that seen in the benthic invertebrate inventories of all the major European semi-enclosed regional seas. Salinity and food availability appear to be the dominant abiotic factors correlated, though weakly, with the various patterns deriving from the taxonomic/zoogeographic categories. With the exception of the Anatolia, polychaete inventories from all sectors appear to be random samples of the total inventory of the region, in terms of taxonomic distinctness values. Therefore, these sectoral inventories can be used for future biodiversity/environmental impact assessment studies. A massive invasion of Mediterranean species after the opening of the Black Sea, in the lower Quaternary period, appears to be the likely biogeographic mechanism through which the old Sarmatic fauna was almost completely replaced by species of marine origin.  相似文献   

Seasonal abundance of non-commercial demersal fish in the eastern Mediterranean Sea in relation to hydrographic and sediment characteristics     

Dimitrios Damalas  Christos D. Maravelias  Stelios Katsanevakis  Aristomenis P. Karageorgis  Costas Papaconstantinou 《Estuarine, Coastal and Shelf Science》2010

Fish-habitat associations were investigated for twenty-five non-commercial demersal species in the Aegean Sea (eastern Mediterranean) using Generalized Additive Modeling techniques. Fishery related abundance indices, derived from experimental bottom trawl surveys, were linked to various habitat variables: substrate characteristics, area, season, depth, temperature and salinity. Depth was the most important factor for all species. Eleven species showed decreasing abundance with depth, while the remaining species were more abundant in specific depth zones either on the continental shelf or in the upper continental slope. Most species were associated with specific substratum characteristics such as the dry weight percentage of sand-gravel and the carbonate content. The dry weight percentage of sand-gravel in the sediments was selected as a predictor of the relative abundance of most (twenty three) species. Seasonal patterns in the relative abundance of species were observed, related in most cases to the seasonal differentiation of temperature. The effect of temperature was more pronounced in summer and autumn, when a marked thermocline is observed, while it was much less intense in winter. For most of the species, the preferable habitat was identified, that contributes valuable information for the successful implementation of an ecosystem approach to fisheries management.  相似文献   

Formal Integrals and Nekhoroshev Stability in a Mapping Model for the Trojan Asteroids     

Christos Efthymiopoulos 《Celestial Mechanics and Dynamical Astronomy》2005,92(1-3):29-52

A symplectic mapping model for the co-orbital motion (Sándor et al., 2002, Cel. Mech. Dyn. Astr. 84, 355) in the circular restricted three body problem is used to derive Nekhoroshev stability estimates for the Sun–Jupiter Trojans. Following a brief review of the analytical part of Nekhoroshev theory, a direct method is developed to construct formal integrals of motion in symplectic mappings without use of a normal form. Precise estimates are given for the region of effective stability based on the optimization of the size of the remainder of the formal series. The stability region found for t=10¹⁰ yrs corresponds to a libration amplitude D_p=10.6°. About 30% of asteroids with accurately known proper elements (Milani, 1993, Cel. Mech. Dyn. Astron. 57, 59), at low eccentricities and inclinations, are included within this region. This represents an improvement with respect to previous estimates given in the literature. The improvement is due partly to the choice of better variables, but also to the use of a mapping model, which is a simplification of the circular restricted three body problem.  相似文献   

The Phase Space Structure Around L4 in the Restricted Three-Body Problem     

Zsolt Sándor  Bálint Érdi  Christos Efthymiopoulos 《Celestial Mechanics and Dynamical Astronomy》2000,78(1-4):113-123

The phase space structure around L ₄ in the restricted three-body problem is investigated. The connection between the long period family emanating from L ₄ and the very complex structure of the stability region is shown by using the method of Poincarés surface of section. The zero initial velocity stability region around L ₄ is determined by using a method based on the calculation of finite-time Lyapunov characteristic numbers. It is shown that the boundary of the stability region in the configuration space is formed by orbits suffering slow chaotic diffusion.  相似文献   

Multivariate analysis of landscape wildfire dynamics in a Mediterranean ecosystem of Greece   总被引：5，自引：0，他引：5  

Kostas D Kalabokidis  Nikos Koutsias  Pavlos Konstantinidis†  Christos Vasilakos‡ 《Area》2007,39(3):392-402

This paper focuses on spatial distribution of long-term fire patterns versus physical and anthropogenic elements of the environment that determine wildfire dynamics in Greece. Logistic regression and correspondence analysis were applied in a spatial database that had been developed and managed within a Geographic Information System. Cartographic fire data were statistically correlated with basic physical and human geography factors (geomorphology, climate, land use and human activities) to estimate the degree of their influence at landscape scale. Land cover types of natural and agricultural vegetation were the most influential factors for explaining landscape wildfire dynamics in conjunction with topography and grazing.  相似文献   

Universal properties of escape in dynamical systems     

Christos Siopis  Henry E. Kandrup  G. Contopoulos  Rudolf Dvorak 《Celestial Mechanics and Dynamical Astronomy》1996,65(1-2):57-68

This paper summarizes a numerical study of the escape properties of three two-dimensional, time-independent potentials possessing different symmetries. It was found, for all three cases, that (i) there is a rather abrupt transition in the behaviour of the late-time probability of escape, when the value of a coupling parameter, , exceeds a critical value, 2. For e > e2, it was found that (ii) the escape probability manifests an initial convergence towards a nearly time-independent value, p _o(), which exhibits a simple scaling that may be universal. However, (iii) at later times the escape probability slowly decays to zero as a power-law function of time. Finally, it was found that (iv) in a statistical sense, orbits that escape from the system at late times tend to have short time Lyapounov exponents which are lower than for orbits that escape at early times.  相似文献   

The summer maximum in total ozone over northwest Europe     

Homer T. Mantis  Christos C. Repapis  Christos S. Zerefos 《Pure and Applied Geophysics》1980,119(2):213-230

Station records of ozone observations have been critically reviewed to investigate the reality of the reported maximum in total ozone over northwest Europe in July. The existence of a longitudinal excess of ozone over the British Isles is confirmed but strong horizontal gradients can be verified only over central Europe and there is no evidence for east-west gradients over the Atlantic. Ozone sounding data as well as total ozone daily variability make it most plausible that the ozone excess over northwest Europe is confined to the lower stratosphere. The isopleths in the region of strong ozone gradients are parallel to the mean flow at 100 mb as required by the calculated constraint on the magnitude of the mean flow advection. It is proposed that analyses of the ozone distribution over oceanic areas could be improved by extending ozone isopleths parallel to the mean lower stratospheric flow from land areas where the pattern is better defined.  相似文献   

Structural identification of Egnatia Odos bridges based on ambient and earthquake induced vibrations     

Evaggelos Ntotsios  Christos Karakostas  Vasilios Lekidis  Panagiotis Panetsos  Ioannis Nikolaou  Costas Papadimitriou  Thomas Salonikos 《Bulletin of Earthquake Engineering》2009,7(2):485-501

The dynamic characteristics of two representative R/C bridges on Egnatia Odos motorway in Greece are estimated based on low amplitude ambient and earthquake-induced vibrations. The present work outlines the instrumentation details, algorithms for computing modal characteristics (modal frequencies, damping ratios and modeshapes), modal-based finite element model (FEM) updating methods for estimating structural parameters, and numerical results for the modal and structural dynamic characteristics of the two bridges based on ambient and earthquake induced vibrations. Transverse, bending and longitudinal modes are reliably identified and stiffness-related properties of the piers, deck and elastomeric bearings of the FEMs of the two bridges are estimated. Results provide qualitative and quantitative information on the dynamic behavior of the bridge systems and their components under low-amplitude vibrations. Modeling assumptions are discussed based on the differences in the characteristics identified from ambient and earthquake vibration measurements. The sources of the differences observed between the identified modal and structural characteristics of the bridges and those predicted by FEMs used for design are investigated and properly justified.  相似文献   

中国鲤科鱼类游泳能力综合分析和应用     

蔡露  Katopodis Christos  金瑶  黄应平  韩德举  胡望斌  陈小娟  陶江平  侯轶群 《湖泊科学》2022,34(6):1788-1801

该研究利用学术论文数据库筛选出中国鲤科鱼类游泳能力相关论文115篇,并用Origin软件进行了数据统计分析,旨在归纳和分析中国鲤科鱼类游泳能力并建立估算方法,可为正处于规划阶段和可行性研究阶段的过鱼设施流速设计提供依据.结果表明：（1）鱼类游泳速度与鱼体长度具有显著的非线性相关关系,据此建立了一系列幂函数经验公式,可为游泳能力和过鱼设施研究及设计提供依据.（2）依据所得到的经验公式和协方差分析可知,喜流水型鲤科鱼类的游泳能力>广适型>喜静水型.根据该研究得到的经验公式并结合行业规范和文献资料,对正处于规划阶段和可行性研究阶段过鱼设施流速设计的建议如下：西南地区以裂腹鱼成鱼为主要过鱼对象的过鱼设施进鱼口吸引流速范围为0.61~0.76 m/s,通道内最高流速阈值为1.28 m/s;长江中下游以四大家鱼成鱼为主要过鱼对象的进鱼口吸引流速范围为0.76~0.93 m/s,通道内最高流速阈值为1.49 m/s,以四大家鱼幼鱼为主要过鱼对象的进鱼口吸引流速范围为0.42~0.62 m/s,通道内最高流速阈值可为0.82 m/s.  相似文献