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   

Adaptation strategy of bivalve Modiolus modiolus from upwelling regions of the Kuril Islands shelf (Sea of Okhotsk) to heavy metal effects     

Victor Ya. Kavun  Olga V. Podgurskaya 《Continental Shelf Research》2009

Cd, Cu, Fe, Mn, Ni, Pb, Zn concentration in the organs (muscle, gonads, mantle, gills, digestive gland, kidney) of mussel Modiolus modiolus was studied. Mussels were collected from shelf upwelling sites of Kuril Is. Sea of Okhotsk (104 and 85 m) and, for comparison, coastal high contaminated and clean sites (Peter the Great Bay, Sea of Japan). It was found that mussels from shelf upwelling regions accumulated unusually high Cd concentration in studied organs, excepting digestive gland. Shelf mussels have evolved passive adaptation to elevated level of ambient heavy metals (distribution of heavy metal load between all organs, especially, muscle). In contrast, mussels from high contaminated sites have evolved active adaptation (strong regulation of metal concentration in the organs at the maximal permissible concentration due to increased kidney function). We supported that under natural condition, passive adaptation of aquatic organisms to increased ambient metal level have been evolved only under constant low-water temperature.  相似文献   

Does sediment grain size affect diatom grazing by harpacticoid copepods?     

De Troch M  Houthoofd L  Chepurnov V  Vanreusel A 《Marine environmental research》2006,61(3):265-277

Estuarine soft sediments support a diverse group of eukaryotic and prokaryotic organisms though the role of the sediment per se for the functioning of these organisms remains largely unknown. The present study aimed to test the effect of sediment grain size on the grazing activities of harpacticoid copepods. In controlled experiments, two common intertidal harpacticoid species (Paramphiascella fulvofasciata and Nitokra spinipes) were each offered a mix of two benthic diatom species (Navicula phyllepta and Seminavis robusta) in different sedimentary conditions. Several microcosms were created using a variety of sediment types, including fine silt (<63 microm), coarser grained sands (125-250, 250-450, 100-300 microm), artificial 'sediments' of glass beads (250-500, 2000 microm) and even the absence of sediment was tested. The diatoms were enriched in the stable carbon (13)C to facilitate tracing in the harpacticoids. Both copepod species were able to graze on the diatoms with highest uptake when sediment was absent. In contrast, both harpacticoid species showed no uptake in silty conditions. In general, grazing was favoured when mean sediment grain size increased. The strong negative effect of fine grains on the grazer's efficiency can be explained by the resulting differences in the structure (and accessibility) of the diatom biofilm on the one hand and the mobility of the grazer on the other hand. In view of the subtle equilibrium between primary producers and grazers, these results might have important implications for the effect of siltation of tidal flats due to, e.g., human activities.  相似文献   

SINGAPORE LANDSCAPE: A HISTORICAL OVERVIEW OF HOUSING CHANGE     

Teo Siew Eng  B.A.  M.A.  Ph.D.  Victor R. Savage  B.A.  M.A.  Ph.D. 《Singapore journal of tropical geography》1985,6(1):48-63

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Open problems on the eve of the next millennium     

Victor Szebehely 《Celestial Mechanics and Dynamical Astronomy》1996,65(1-2):205-211

To predict the future of Celestial Mechanics and to investigate unsolved problems for the next millennium contradicts the nature of our field of science which is based on non-integrable and transcendental equations with short time predictability. The reliability and predictability in our field depend on several factors, most of them unpredictable. Numerical predictions depend on the development of computer technology, which is itself not predictable. New analytical approaches call for the genius of Newton. We must realize that between Ptolemaeus (100–178) and Copernicus (1473–1543) our field received little attention. Between 1700 and 1800 the explosion occurred (Newton, Euler, Laplace, Lagrange and Gauss) followed by the period of 1800–1900 associated with Hamilton, Hill, Jacobi, Poincaré and Tisserand. Can we expect anyone to make similar contributions in the next 1000 years? The entrance and emphasis of probability in our field certainly will continue. Speaking about bounds of trajectories instead of individual orbits gains significant popularity. Theory of stability and chaos are expected to receive more and more attention together with Poincare's conjectures concerning the denseness of periodic orbits in the set of bounded orbits. Planetary computations for long time have shown considerable advances, partly due to computer advances as well as the selection of the proper formulation of the problems. The preparation of “exact” short time ephemerides and qualitative long time predictions require initial conditions with small observational errors, the use of proper models (including relativity effects and non-conservative forces) and the use of correct values of astronomical constants. The results of such calculations in the future should include approximate estimations of errors in the outcome. The observations and orbital calculations of Earth-crossing asteroids should receive special attention along with development of various techniques of space dynamics to avoid collisions. Interplanetary orbit calculations of space probes with optimizations included, shall receive additional attention since interplanetary flights expect to become regular travels in the next millennium. Here, again, the use of proper models, constants and planetary ephemerides will be essential. This paper was prepared with the help of many of my colleagues whose suggestions and ideas were incorporated with my many thanks.[/p]  相似文献   

Derivative of Kaula's inclination function     

Dmitry V. Brumberg  Victor A. Brumberg 《Celestial Mechanics and Dynamical Astronomy》1995,62(2):183-189

The derivative of Kaula's inclination function is expressed as a linear combination of two inclination functions themselves.On leave from Institute of Applied Astronomy, 197042 St.-Petersburg, Russia.  相似文献   

Next-generation robotic planetary reconnaissance missions: A paradigm shift   总被引：1，自引：1，他引：0  

Wolfgang Fink  James M. Dohm  Mark A. Tarbell  Trent M. Hare  Victor R. Baker 《Planetary and Space Science》2005,53(14-15):1419-1426

A fundamentally new scientific mission concept for remote planetary surface and subsurface reconnaissance will soon replace the engineering and safety constrained mission designs of the past, allowing for optimal acquisition of geologic, paleohydrologic, paleoclimatic, and possible astrobiologic information of Mars and other extraterrestrial targets. Traditional missions have performed local ground-level reconnaissance through rovers and immobile landers, or global mapping performed by an orbiter. The former is safety and engineering constrained, affording limited detailed reconnaissance of a single site at the expense of a regional understanding, while the latter returns immense datasets, often overlooking detailed information of local and regional significance. A “tier-scalable” paradigm integrates multi-tier (orbitatmosphereground) and multi-agent (orbiterblimpsrovers/sensorwebs) hierarchical mission architectures, not only introducing mission redundancy and safety, but enabling and optimizing intelligent, unconstrained, and distributed science-driven exploration of prime locations on Mars and elsewhere, allowing for increased science return, and paving the way towards fully autonomous robotic missions.  相似文献   

A widespread positive δ13Ccarb anomaly at around 2.33–2.06 Ga on the Fennoscandian Shield: a paradox?     

Victor A. Melezhik  Anthony E. Fallick 《地学学报》1996,8(2):141-157

Carbon isotope measurements carried out on 201 carbonate samples from the early Proterozoic of the Kola Peninsula, N. Karelia and Norway yield δ¹³C (PDB) spanning - 20.5% to + 11%. A general δ¹³C secular trend shows that prior to 2.33 Ga values are typically 'normal' marine, averaging around - 3%0. Between 2.33 and 2.06 Ga, in Jatulian time, there follows a rapid excursion to positive δ¹³C of around + 6%. Post-Jatulian time is characterized by δ¹³C of sedimentary carbonates fluctuating between - 5% and +3%; also it is remarkable for the first pronounced development of diagenetic carbonates, which have δ¹³C between - 14 % and - 6% . The c. 6% positive δ¹³C shift with a duration of about 270 Myr coincides with a maximum in the diversity and abundance of stromatolites, and with widespread development of 'red beds', but does not coincide with the maximum of buried C_org mass. The Fennoscandian Shield represents the largest isotoically anomalous carbonate province yet reported, and the positive δ¹³C excursion together with a series of major global palaeoenviromental changes seems to be more intense than the Precambrian/Cambrian transition events. However, it is still not clear what kind of mechanism this phenomenon could be attributed to. An increase of the 'Ronov ratio', and/or 'Broecker ratio' and other possible models are discussed as the target for future investigations.  相似文献   

Climatic constraints for the maize-soybean system in the humid subtropical region of Argentina     

Victor?David?Giménez  José?Roberto?Micheloud  Gustavo?ángel?MaddonniEmail author 《Theoretical and Applied Climatology》2018,134(3-4):753-767

The implementation of two summer crops in the same growing season is a possible alternative for land intensification in areas with a long frost-free period. The aim of this study was to analyse the strategy of land intensification through the implementation of the maize-soybean succession at two locations (Reconquista, 29°09′S 59°40′W and Las Breñas, 27°05′S 61°5′W) of the humid subtropical region of Argentina. CERES-Maize and CROPGRO-Soybean models were used to evaluate the impact of inter-annual variability of climate (36 years) of both locations on rain-fed grain yields of the following productive alternatives: (i) monoculture of maize, (ii) monoculture of soybean and (iii) the succession of a short-cycle maize followed by soybean as the second summer crop (maize-soybean system). The maize-soybean system was evaluated by the method of land equivalent ratio (LER), based on the sum of the relative grain yields of its components. The impact of the inter-annual variability of climate and of “El Niño” or “La Niña” episodes (El Niño Southern Oscillation phenomenon (ENSO)) on LER values was analysed. Simulated yields of maize monoculture (5687 kg ha^?1; CV = 49.7% and 5637 kg ha^?1; CV = 57.6% at Reconquista and Las Breñas, respectively) were higher than those of the short-cycle maize, especially at Las Breñas (5448 kg ha^?1; CV = 49.3% and 2322 kg ha^?1; CV = 33.9% at Reconquista and Las Breñas, respectively). Simulated yields of the soybean monoculture were higher (3588 kg ha^?1; CV = 26.1% and 2883 kg ha^?1; CV = 20.7% at Reconquista and Las Breñas, respectively) that those of the soybean as the second crop (2634 kg ha^?1; CV = 38.1% and 2456 kg ha^?1; CV = 32.9% at Reconquista and Las Breñas, respectively) at both locations. Average LERs were 1.69 (CV = 11.4%) at Reconquista and 1.41 (CV = 26.1%) at Las Breñas, and the inter-annual variability of LER was mainly determined by grain yields of (i) soybean as the second crop at Reconquista and (ii) maize monoculture at Las Breñas. Soil water content after maize harvest and rainfalls during reproductive period of soybean as the second crop conditioned LER values, but they were generally greater than 1. At Reconquista, LER values were not affected by the different episodes of ENSO phenomenon. By contrast, at Las Breñas, LER values were higher during La Niña episodes (1.48; CV = 26.6%) than during El Niño episodes (1.32; CV = 23.7%) mainly by their effects on grain yields of maize monoculture. Therefore, crop simulation models demonstrate the possibility to intensify land use (40–70%) at two locations of the humid subtropical region of Argentina, by the implementation of the maize-soybean system.  相似文献   

On writing good histories of climate change and testing social science theories     

David G. Victor 《Climatic change》1995,29(4):363-369

David G. Victor is co-Leader, project on Implementation and Effectiveness of International Environmental Commitments (IEC), International Institute for Applied Systems Analysis, A-2361 Lazenburg, Austria. The views expressed here are his own.  相似文献