Mandelbrot集与Julia集的图象生成算法

介绍一种在计算机上生成Ｍａｎｄｅｌｂｒｏｔ集和Ｊｕｌｉａ集图象的简易算法。该算法对计算机的软硬件要求均不高，在普通的微机以及工作站上均可实现。

Modelling the long-term sustainability of indigenous hunting in Manu National Park, Peru: landscape-scale management implications for Amazonia

P> Widespread hunting throughout Amazonia threatens the persistence of large primates and other vertebrates. Most studies have used models of limited validity and restricted spatial and temporal scales to assess the sustainability. We use human-demographi

Fish ES cells and applications to biotechnology

ES cells provide a promising tool for the generation of transgenic animals with site-directed mutations. When ES cells colonize germ cells in chimeras, transgenic animals with modified phenotypes are generated and used either for functional genomics studies or for improving productivity in commercial settings. Althought the ES cell approach has been limited to, mice, there is strong interest for developing the technology in fish.. We describe the step-by-step procedure for developing ES cells in fish. Key aspects include avoiding cell differentiation, specific in vitro traits of pluripotency, and, most importantly, testing for production of chimeric animals as the main evidence of pluripotency. The entire process focuses on two model species, zebrafish and medaka, in which most work has been done. The achievements attained in these species, as well as their applicability to other commercial fish, are discussed. Because of the difficulties relating to germ line competence, mostly of long-term fish ES cells, alternative cell-based approaches such as primordial germ cells and nuclear transfer need to be considered. Although progress to date has been slow, there are promising achievements in homologous recombination and alternative avenues yet to be explored that can bring ES technology in fish to fruition.

eta-production on the proton via electromagnetic and hadronic probes

The reactions pi(-)p -> eta n and gamma p -> eta p are investigated within a dynamical coupled-channels model of meson production reactions in the nucleon resonance region The meson-baryon channels included are pi N, pi Delta, sigma N, and rho N The direct eta-photoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU(6)circle times O(3) symmetry In the models search, the following known nucleon resonances are embodied S-11(1535), S-11(1650), P-11(1440), P-11(1710), P-13(1720), D-13(1520), D-13(1700), D-15(1675), and F-15(1680). Data for the pi(-)p -> eta n reaction from threshold up to a total center-of-mass energy of W approximate to 2 GeV are satisfactorily reproduced For the photoproduction channel: two additional higher mass known resonances, P-13(1900) and F-15(2000), are also considered However, reproducing the data for gamma p -> eta p requires, within our approach, two new nucleon resonances, for which we extract, mass and width

Decline in medicinal and forage species with warming is mediated by plant traits on the Tibetan Plateau

Experimental studies of how global changes and human activities affect plant diversity often focus on broad measures of diversity and discuss the implications of these changes for ecosystem function. We examined how experimental warming and grazing affected species within plant groups of direct importance to Tibetan pastoralists: medicinal plants used by humans and palatable plants consumed by livestock. Warming resulted in species losses from both the medicinal and palatable plant groups; however, differential relative vulnerability to warming occurred. With respect to the percent of warming-induced species losses, the overall plant community lost 27%, medicinal plants lost 21%, and non-medicinal plants lost 40% of species. Losses of palatable and non-palatable species were similar to losses in the overall plant community. The deep-rootedness of medicinal plants resulted in lowered sensitivity to warming, whereas the shallow-rootedness of non-medicinal plants resulted in greater sensitivity to warming; the variable rooting depth of palatable and non-palatable plants resulted in an intermediate response to warming. Predicting the vulnerability of plant groups to human activities can be enhanced by knowledge of plant traits, their response to specific drivers, and their distribution within plant groups. Knowledge of the mechanisms through which a driver operates, and the evolutionary interaction of plants with that driver, will aid predictions. Future steps to protect ecosystem services furnished by medicinal and palatable plants will be required under the novel stress of a warmer climate. Grazing may be an important tool in maintaining some of these services under future warming.

Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes

Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide. Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.

Experimental warming, not grazing, decreases rangeland quality on the Tibetan Plateau

We investigated experimental warming and simulated grazing ( clipping) effects on rangeland quality, as indicated by vegetation production and nutritive quality, in winter-grazed meadows and summer- grazed shrublands on the Tibetan Plateau, a rangeland system experiencing climatic and pastoral land use changes. Warming decreased total aboveground net primary productivity ( ANPP) by 40 g . m(-2) . yr(-1) at the meadow habitats and decreased palatable ANPP ( total ANPP minus non- palatable forb ANPP) by 10 g . m(-2) . yr(-1) at both habitats. The decreased production of the medicinal forb Gentiana straminea and the increased production of the non- palatable forb Stellera chamaejasme with warming also reduced rangeland quality. At the shrubland habitats, warming resulted in less digestible shrubs, whose foliage contains 25% digestible dry matter ( DDM), replacing more digestible graminoids, whose foliage contains 60% DDM. This shift from graminoids to shrubs not only results in lower- quality forage, but could also have important consequences for future domestic herd composition. Although warming extended the growing season in non- clipped plots, the reduced rangeland quality due to decreased vegetative production and nutritive quality will likely overwhelm the improved rangeland quality associated with an extended growing season.Grazing maintained or improved rangeland quality by increasing total ANPP by 20 - 40 g . m(-2) . yr(-1) with no effect on palatable ANPP. Grazing effects on forage nutritive quality, as measured by foliar nitrogen and carbon content and by shifts in plant group ANPP, resulted in improved forage quality. Grazing extended the growing season at both habitats, and it advanced the growing season at the meadows. Synergistic interactions between warming and grazing were present, such that grazing mediated the warming- induced declines in vegetation production and nutritive quality. Moreover, combined treatment effects were nonadditive, suggesting that we cannot predict the combined effect of global changes and human activities from single- factor studies.Our findings suggest that the rangelands on the Tibetan Plateau, and the pastoralists who depend on them, may be vulnerable to future climate changes. Grazing can mitigate the negative warming effects on rangeland quality. For example, grazing management may be an important tool to keep warming- induced shrub expansion in check. Moreover, flexible and opportunistic grazing management will be required in a warmer future.

Dynamic and complex microclimate responses to warming and grazing manipulations

Synthesis efforts that identify patterns of ecosystem response to a suite of warming manipulations can make important contributions to climate change science. However, cross-study comparisons are impeded by the paucity of detailed analyses of how passive warming and other manipulations affect microclimate. Here we document the independent and combined effects of a common passive warming manipulation, open-top chambers (OTCs), and a simulated widespread land use, clipping, on microclimate on the Tibetan Plateau. OTCs consistently elevated growing season averaged mean daily air temperature by 1.0-2.0 degrees C, maximum daily air temperature by 2.1-7.3 degrees C and the diurnal air temperature range by 1.9-6.5 degrees C, with mixed effects on minimum daily air temperature, and mean daily soil temperature and moisture. These OTC effects on microclimate differ from reported effects of a common active warming method, infrared heating, which has more consistent effects on soil than on air temperature. There were significant interannual and intragrowing season differences in OTC effects on microclimate. For example, while OTCs had mixed effects on growing season averaged soil temperatures, OTCs consistently elevated soil temperature by approximately 1.0 degrees C early in the growing season. Nonadditive interactions between OTCs and clipping were also present: OTCs in clipped plots generally elevated air and soil temperatures more than OTCs in nonclipped plots. Moreover, site factors dynamically interacted with microclimate and with the efficacy of the OTC manipulations.These findings highlight the need to understand differential microclimate effects between warming methods, within warming method across ecosystem sites, within warming method crossed with other treatments, and within sites over various timescales. Methods, sites and scales are potential explanatory variables and covariables in climate warming experiments. Consideration of this variability among and between experimental warming studies will lead to greater understanding and better prediction of ecosystem response to anthropogenic climate warming.

Local warming about 1.3 degrees C in alpine meadow has no effect on root vole (Microtus oeconomus L.) population during winter

The influence of air and soil warming on root vole (Microtus oeconomus L.) population was studied in winter period in top open chambers (OTC) (0.8-1.8 m(2) warmed by conical fiberglass material and situated in alpine meadow (3250 m) at Qinghai-Tibet Plateau, China. The OTCs were distributed on an area of 30 x 30 m of experimental warming site; another site of the same area was a control one. The root vole population was investigated on two pairs of sites in "low-grazing" and "high-grazing" (by sheep) parts of the meadow; mark-recapture method was used. The winter-season averaged air and soil temperature inside of the chambers were 1.3 degrees C higher than the temperature outside the chambers. The warming in the chambers had no statistically significant effect on root vole numbers, on average body mass of individual, and on average body mass of males and females. In conclusion, as small as 1.3 degrees C warming of soil and air introduced locally and on small (several m(2)) scale, in the alpine meadow habitat in winter period, has possibly no effect on root vole numbers and biomass.

Experimental warming causes large and rapid species loss, dampened by simulated grazing, on the Tibetan Plateau

We investigated the independent and combined effects of experimental warming and grazing on plant species diversity on the north-eastern Tibetan Plateau, a region highly vulnerable to ongoing climate and land use changes. Experimental warming caused a 26-36% decrease in species richness, a response that was generally dampened by experimental grazing. Higher species losses occurred at the drier sites where N was less available. Moreover, we observed an indirect effect of climate change on species richness as mediated by plant-plant interactions. Heat stress and warming-induced litter accumulation are potential explanations for the species' responses to experimental warming. This is the first reported experimental evidence that climate warming could cause dramatic declines in plant species diversity in high elevation ecosystems over short time frames and supports model predictions of species losses with anthropogenic climate change.