排序方式： 共有14条查询结果，搜索用时 15 毫秒
1.
临界转换的早期预警信号 总被引：1，自引：0，他引：1
Marten Scheffer George Sugihara Jordi Bascompte Victor Brovkin Vasilis Dakos Hermann Held Max Rietkerk 李迎春 闫伟 蒋长胜 《国际地震动态》2009,(9):1-14
从生态系统到金融市场和气候在内的很多复杂动力系统,都会有临界点,在这样的点上系统可能会发生突变,从而演变到一个对立的动力模式上。在这样的临界点到达之前对其进行预测极为困难,但是现在,不同科学领域的研究工作表明,普遍性的早期预警信号有迹可循。对一系列不同类型的系统来说,这些信号会指示是否正在趋近一个临界阈值。 相似文献
2.
Antonietta Rosso Rossana Sanfilippo Adriano Guido Vasilis Gerovasileiou Emma Taddei Ruggiero Genuario Belmonte 《Marine Ecology》2021,42(1):e12634
Metazoan/microbial bioconstructions, or biostalactites (BSTs), discovered in submarine caves of Apulia c. 20 years ago—and later found in several shallow‐water Mediterranean caves—are receiving increasing attention in the last years. Examination of a single BST from the “lu Lampiùne” cave (Apulia), at the limit between the Adriatic and the Ionian seas, has been addressed for the first time in this paper. The BST started growing at c. 6,000 years ago with a rapid accretion of large‐sized serpulids (Protula), slowing down since about 3,000–4,000 years ago with a shift in main bioconstructors, probably caused by environmental changes. The present‐day community on the outer BST surface is dominated by skeletonised epibionts, mostly small‐sized serpulids, bryozoans and foraminifers, which contribute carbonate to the BST growth, by encrusting sponges, and by a few endobionts, including boring bivalves and insinuating sponges. New data remarkably increase biodiversity known for the “lu Lampiùne” cave and the cave habitat in the region. Thirty‐five taxa (16 bryozoans, 10 serpulids, 3 brachiopods, 2 foraminifers, 2 sponges, 1 bivalve and 1 cirriped) are recorded for the first time from Apulian marine caves, highlighting the need for further research in the area. In addition, the BST‐associated community seems to differ from those of individual BSTs from other Mediterranean caves, revealing the individuality of these communities. 相似文献
3.
Accurate reproduction of time series with diverse frequency characteristics is a central issue in structural testing. This is true not only for simple experimental tests performed by reaction walls or shaking tables but also for more sophisticated ones, such as hybrid testing. Especially in the latter case, where actual feedback from an ongoing test is used in the calculation of the next excitation value, any possible mismatch may be fatal for both the validity of the test and the safety. The objective of this study is to propose a framework for the adaptive inverse control of shaking tables, which succeeds in this matching to a certain degree. By formulating a critical set of design specifications that correspond to safety, implementation, robustness and ease of use, the conducted research results in a design that is based on a modified version of the filtered‐X algorithm with very competitive features. These are the following: (i) default operation in hard real‐time and acceleration mode; (ii) very low hardware requirements; (iii) effective cancelation of the shaking table's dynamics; and (iv) robustness against specimen dynamics. For its practical evaluation, the method is applied to shaking table waveform replication tests under the installation of an approximately linear specimen of sufficiently high mass and complex geometry. The results are promising and suggest further research toward this field, especially in conjunction with hybrid testing, as the method retains certain global applicability attributes and it can be easily extended to other transfer systems, apart from shaking tables. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
Nikolaos Skliris Sarantis Sofianos Athanasios Gkanasos Anneta Mantziafou Vasilis Vervatis Panagiotis Axaopoulos Alex Lascaratos 《Ocean Dynamics》2012,62(1):13-30
Twenty-four years of AVHRR-derived sea surface temperature (SST) data (1985–2008) and 35 years of NOCS (V.2) in situ-based
SST data (1973–2008) were used to investigate the decadal scale variability of this parameter in the Mediterranean Sea in
relation to local air–sea interaction and large-scale atmospheric variability. Satellite and in situ-derived data indicate
a strong eastward increasing sea surface warming trend from the early 1990s onwards. The satellite-derived mean annual warming
rate is about 0.037°C year–1 for the whole basin, about 0.026°C year–1 for the western sub-basin and about 0.042°C year–1 for the eastern sub-basin over 1985–2008. NOCS-derived data indicate similar variability but with lower warming trends for
both sub-basins over the same period. The long-term Mediterranean SST spatiotemporal variability is mainly associated with
horizontal heat advection variations and an increasing warming of the Atlantic inflow. Analysis of SST and net heat flux inter-annual
variations indicates a negative correlation, with the long-term SST increase, driving a net air–sea heat flux decrease in
the Mediterranean Sea through a large increase in the latent heat loss. Empirical orthogonal function (EOF) analysis of the
monthly average anomaly satellite-derived time series showed that the first EOF mode is associated with a long-term warming
trend throughout the whole Mediterranean surface and it is highly correlated with both the Eastern Atlantic (EA) pattern and
the Atlantic Multidecadal Oscillation (AMO) index. On the other hand, SST basin-average yearly anomaly and NAO variations
show low and not statistically significant correlations of opposite sign for the eastern (negative correlation) and western
(positive correlation) sub-basins. However, there seems to be a link between NAO and SST decadal-scale variations that is
particularly evidenced in the second EOF mode of SST anomalies. NOCS SST time series show a significant SST rise in the western
basin from 1973 to the late 1980s following a large warming of the inflowing surface Atlantic waters and a long-term increase
of the NAO index, whereas SST slowly increased in the eastern basin. In the early 1990s, there is an abrupt change from a
very high positive to a low NAO phase which coincides with a large change in the SST spatiotemporal variability pattern. This
pronounced variability shift is followed by an acceleration of the warming rate in the Mediterranean Sea and a change in the
direction (from westward to eastward) of its spatial increasing tendency. 相似文献
5.
Vasilis P. Tritakis 《Pure and Applied Geophysics》1985,123(3):476-486
A significant tendency is shown for both Etesians and (+, –) sector boundaries of the interplanetary magnetic field (IMF) to occur on the same solar rotation days, during the main period of the Etesians effect (July–August). In addition, the solar activity seems to control the Etesians distribution within the IMF sector structure. In the epoch of maximum there is a significant tendency of Etesians to occur during toward IMF days. In contrast, in the epoch of minimum Etesians occur mainly during away IMF days. Finally, in the epoch of intermediate the Etesians are uniformly distributed in away and toward IMF days. Since these conclusions are statistically significant at high confidence levels, it is fair to assume that IMF and solar activity seem to contribute, to some extent, to the Etesians occurrences, as well as to their distribution within the solar rotation and the IMF sector structure; that is, some solar contribution to the tropospheric circulation is implied. 相似文献
6.
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
7.
Vasilis Gerovasileiou Eleni Voultsiadou Yiannis Issaris Argyro Zenetos 《Marine Ecology》2016,37(2):239-256
The number of alien species in the Mediterranean Sea is increasing rapidly, but few attempts have been made to evaluate impacts on specific habitat types. The present study investigated alien biodiversity in Mediterranean marine caves, both by contributing new records of Eastern Mediterranean cave aliens, and by reviewing the scattered existing literature; the main goals were to highlight potential impacts and investigate the importance of cave environments for the expansion of alien species. Seven new alien species were found in marine caves of the Aegean and Ionian seas, raising the total number of aliens reported from Mediterranean marine caves to 56 species, classified as molluscs, cnidarians, bryozoans, polychaetes, crustaceans, macroalgae, fishes and tunicates. Most cave aliens (66%) were recorded from the Southeastern Levantine coasts, specifically from Lebanese caves. Shipping and Lessepsian migration have been suggested as the main pathways of alien introduction into caves of the Mediterranean Sea. The comparison of alien cave biodiversity with the updated Mediterranean alien inventory (32 species added to the latest inventory) showed similar patterns and trends for species richness, biogeographical origin and major introduction pathways, corroborating previous findings on the high local representativeness of Mediterranean cave biodiversity. Alien species seem to have invaded mostly the entrance and semi‐dark zones of shallow and/or semi‐submerged caves and tunnels, whereas only a few have reached the dark inner sectors or caves of the anchialine type; thus, the unfavourable cave environment seems to be naturally protected from impacts related to opportunistic invasive species, at least to a certain point. Currently there is no research confirming any direct impacts of alien biota on the native cavernicolous one. However, some issues have emerged, implying potential threats that need to be further explored: (i) the presence of a considerable proportion of aliens in most studied marine caves of the Southeastern Mediterranean basin, (ii) the recently observed population explosion of alien cave‐dwelling fishes in the same area, (iii) several indications that alien diversity in marine caves is much higher than we know today. Quantitative surveys and monitoring schemes are needed in order to evaluate potential effects of alien diversity on cave community structure and the role of marine caves as stepping stones for its expansion in the Mediterranean. 相似文献
8.
Evanthia Lekka Ifigenia Kagalou Maria Lazaridou‐Dimitriadou Triantafilos Albanis Vasileios Dakos Dimitra Lambropoulou Vasilis Sakkas 《洁净——土壤、空气、水》2004,32(3):175-188
In the present study, the water quality of Kalamas river (NW Greece) was evaluated using physicochemical and hydromorphological parameters and benthic macroinvertebrates. Statistical analyses (Cluster and FUZZY analyses) were performed and two biotic scores (BMWP' and HS) were used in order to classify the sites according to water quality. Kalamas river appeared to have excellent tomoderate water quality at all sampling sites except one (close to the delta area) which was ”fairly or significantly polluted”. During the low flow season water quality appeared poorer than during the high flow season. The ecological parameters (hydromorphological, chemical, and biological) used for this integrated approach are the ones proposed by the New Water Directive 2000/60 EC for an efficient surveying monitoring of running waters. 相似文献
9.