一类带有扰动因子的Euler方程的Lax对和等谱理论

二维的带有扰动因子的Euler方程的整体适定性已经被证明,但是三维带有扰动因子的Euler方程的整体适定性尚未被解决,仍然是一个数学难题,给出的定理希望在证明三维带有扰动因子的Euler方程的整体适定性上有所帮助.主要研究一种带有扰动因子a(t)的Euler方程的Lax对,另外,还进一步研究关于带有此类扰动因子的Eul...     

A comparison of the population genetics of Lethrinus miniatus and Lutjanus sebae from the east and west coasts of Australia: Evidence for panmixia and isolation

Lethrinus miniatus and Lutjanus sebae are important commercial and recreational species of reef fish. Within Australian waters the former species is less widespread than the latter and has a discontinuous distribution, whilst the latter is continuously distributed in tropical Australian waters. The demographic attributes of these species (e.g. long life span, low rates of natural mortality) make them vulnerable to over-exploitation. Consequently, conservative harvest strategies including no-take zones for these species have been adopted by fisheries management agencies to control exploitation. Information on the genetic stock structure of these species is important for developing specific management strategies. However, little is known about genetic stock structures within and between east and west Australian populations of these species. The current study used the mitochondrial genome hypervariable region 1 (HVR1) of the control region to examine variation between two sites from both the east and west Australian coasts for each species. HVR1 for L. sebae did not differ genetically either within or between coasts (F_st < 0.018, p > 0.15) at the sites studied, suggesting a panmictic population structure. Similarly, L. miniatus did not differ significantly between sites sampled within coast. However, the west coast HVR1 for L. miniatus east and west coast populations, were discrete (F_st of at least 0.92, p < 0.0001). The degree of genetic sub-division between east and west coast populations indicates that they should be managed as discrete stocks. Further, when considering both species, the lower genetic (both haplotype and nucleotide) diversity in three of the four sites on the west coast of Australia, indicates that this region is genetically impoverished and neutrality tests suggest that selection is responsible. Consequently, west Australian populations will be less resilient to perturbations (e.g. fishing, climate change) than east Australian populations, which have higher genetic diversity.     

Factors of winter wheat yield robustness in France under unfavourable weather conditions

To face increasing uncertainties, future farming systems must be sustainable not only under average conditions but also in extreme climatic and economic situations. Various concepts such as stability, robustness, vulnerability or resilience have been proposed to analyze the ability of agricultural systems to adapt to changing production conditions. The operational effectiveness of these concepts remains nevertheless limited. In this paper, we developed an original analytical framework allowing characterizing and quantifying crop yield robustness, as well as identifying agricultural practices linked to cropping systems differentiated according to their robustness pattern. This framework was applied to 2300 bread wheat plots belonging to 145 cropping systems in various regions of France over the period 2011–2014. The analysis was performed at the scale of the cropping system. In a first step, we defined a regression statistical model allowing us to link wheat yield variability to an index of abiotic perturbations constructed using the STICS agronomic model; the cropping systems were taken into account through the use of dummy variables. In a second step, the different cropping systems were positioned within four quadrants using the regional average wheat yield in conditions of average abiotic perturbations and the regional average estimated robustness to abiotic perturbations as cut-offs for the quadrants. In a third step, the cropping systems of the different spaces defined by the four-quadrant approach were compared on the basis on three types of agronomic practices, i.e., management intensification, rotation and heterogeneity practices. Empirical results show that abiotic perturbations had an impact on wheat yield variability. This impact differed from one system to another which means that there is a ”cropping system effect” of abiotic perturbations on wheat yield robustness. Several agronomic practices allowed differentiating high versus low wheat yield cropping systems. High yield cropping systems relied more intensively on chemical inputs (fertilizers and pesticides) and used more diversified rotations, with more frequently legumes as preceding crops and a lower frequency of cereals. Fewer agronomic practices allowed differentiating robust versus sensitive wheat cropping systems. In addition to the sowing date (later for robust systems) and the sowing density (greater), these practices were essentially linked to spatial adjustments of the sowing date, total pesticide use, variety earliness at heading stage and variety disease resistance.     

Freshwater biodiversity under climate warming pressure: Identifying the winners and losers in temperate standing waterbodies

Climate warming is affecting the biodiversity all around the world, resulting in the expansion or contraction of the geographical range of species, and leading to colonisation (winners) and extinction (losers) events in ecosystems. It is crucial for the conservation of biodiversity to identify these potential winners and losers.We focus here on small standing waterbodies in Switzerland and on five taxonomic groups: vascular plants, snails, beetles, dragonflies and amphibians. We first assessed the sensitivity of each species to climate warming through their thermal preferences, using current altitudinal and latitudinal distribution, as a surrogate for temperature. We then evaluated the resilience of species to perturbations through five ecological and biogeographical criteria applicable to the perturbation “warming”: dispersal ability, degree of habitat specialisation, geographical extent in the study area, future trend in geographical extent, and future trend of habitat availability for species.Potential winners and losers of a warming climate could be quantified through their thermal preferences. The proportion of potential losers ranged from zero species for snails to 33% of the regional species pool for dragonflies. The set of potential winners was much larger, ranging from 53% for amphibians to 61% for dragonflies. A multimetric index combining the five resilience criteria enabled the further prioritisation of the species along a gradient of extinction risk.This potential threat from climate warming is not reflected by the current Red Lists of dragonflies and amphibians, suggesting that conservation management could gain from a complementary label indicating the degree of sensitivity to warming.     

Metabolic response of Medicago sativa to severe nutrient imbalances and disturbances under field conditions

Our experiments were focused on the metabolic footprint of mineral‐nutrient availability under field conditions. While there are multiple factors potentially blurring such footprints, we hypothesized that physiological and metabolic adaptations of established plants are particularly important mechanisms under field conditions. To study respective differences between young and established plants and to study the impact of disturbances on the adaptive capacity of established plants, we analyzed Medicago sativa plants of different age from plots with marked differences in the levels of soil mineral nutrients established in a long‐term fertilization experiment. Gas chromatography–mass spectrometry was used to determine metabolite profiles of sink and source leaves of plants in an early state of development (“young plants”), just before the first harvest (“established plants”), and a short time after the second harvest (“regrowing plants”). Metabolite profiles from young plants were markedly responsive to soil mineral nutrients and resembled respective profiles from controlled conditions, demonstrating that overall variability of growth and sampling conditions had relatively little importance for the metabolite profiles recorded. In the case of established plants, however, we observed only little impact of availability of mineral nutrients on metabolite profiles. This low metabolic responsiveness of plants was partially lost after severe disturbances (removal of the plant shoot). Metabolite profiling, in summary, is able to detect a metabolic footprint of mineral‐nutrient availability in young plants under field conditions and may provide information about the ability of older plants to partially uncouple their metabolism from the environment. In addition, it is also possible to determine the impact of disturbances on this ability of the plant organism.     

Hybrid Power Supply Based on One Cycle Control

A hybrid power supply is composed by both a linear and a switching source connected in parallel and it can improve the dynamic response. But the hybrid power supply cant not effectively reject the perturbations in the power supply. A hybrid power supply based on one cycle control theory is proposed in order to improve the capability and the control precision. A switching source based on one cycle control is adopted in the hybrid power supply. The analysis results indicate that the hybrid power supply can effectively reject the perturbations in the power supply. And the analysis results also show that not only the control precision is improved, but also the control circuit is simple. The simulation resuits given verify the correctness and effectiveness of the proposed method.     

地震扰动区生态修复的概念与四拗

分析提出地震扰动区生态修复的概念,就是在重力侵蚀造成的植被破损处打＂补丁＂。进而分析了植被重建的土、水、树木种苗和当地人四要素的基本特性,分别为土碎、水漫、籽拗、羊狠,均具有执拗特质,合称＂四拗＂,是生态修复的难点所在,均具成败与否的决定性作用。     

Short-term temperature dependence of heterotrophic soil respiration after one-month of pre-incubation at different temperatures

Quantification of microbial activities involved in soil organic carbon (SOC) decomposition is critical for the prediction of the long-term impact of climate change on soil respiration (SR) and SOC stock. Although the temperature sensitivity of SR is especially critical in semi-arid regions, such as North West Tunisia, where the SOC stock is low, little research has been carried out in these environments. More needs to be known about factors, such as SOC availability that influence temperature sensitivity. In this study, soil samples were incubated with and without glucose addition for 28 days after a 28-day pre-incubation period. Pre-incubation and incubation was carried out at 20 °C, 30 °C, 40 °C and 50 °C. Respiration measurements were taken with temperature, glucose addition and incubation time as independent variables. The highest pre-incubation temperature reduced the temperature sensitivity of SR during the subsequent incubation period, both with and without glucose addition. Soil samples pre-incubated at 50 °C had the lowest SR at all subsequent incubation temperatures and the lowest temperature sensitivity of SR, even after glucose addition. However, after glucose addition, the effect of a high pre-incubation temperature on soil respiration lasted only two days. Measuring the water-soluble carbon (WSC) in soil samples suggested that the high pre-incubation temperature may have killed part of the microbial biomass, modified microbial communities or solubilized SOC. For quantifying the possible effect of global warming, in particular heat waves, on soil respiration in the soil studied, the results indicate a moderate response of soil respiration to temperature at high temperatures, as shown by Q₁₀ close to 1.7, even in the range 40-50 °C.     

具有非线性扰动的中立型系统的变结构控制

针对具有非线性扰动的中立型系统,利用交结构控制及时滞系统的一般结论选择切换函数,在非线性扰动的情形下,构造了交结构控制率,通过引进合理的Lyapunov函数证明了滑模渐近稳定,同时验证了满足到达条件.     

Functional diversity amongst soil protozoa

Organismal and functional diversity of soil protozoa are reviewed and the importance of protozoa in soil metabolism is discussed. Existing methods of determining protozoan organismal diversity in soils are briefly listed and some of their shortcomings outlined. Feeding guilds amongst soil protozoa are described and a preliminary classification of feeding habits of soil protozoa based on Pratt and Cairns (1985) system for freshwater protozoa is proposed. Protozoan diversity during the recovery of soil communities from serious environmental disturbance is discussed and some proposals for the direction of future research are made.