Sensitivity of multifrequency magnetic resonance elastography and diffusion-weighted imaging to cellular and stromal integrity of liver tissue

Microscopic structural alterations of liver tissue induced by freeze-thaw cycles give rise to palpable property changes. However, the underlying damage to tissue architecture is difficult to quantify histologically, and published data on macroscopic changes in biophysical properties are sparse.To better understand the influence of hepatic cells and stroma on global biophysical parameters, we studied rat liver specimens freshly taken (within 30 min after death) and treated by freeze-thaw cycles overnight at either −20 °C or –80 °C using diffusion-weighted imaging (DWI) and multifrequency magnetic resonance elastography (MRE) performed at 0.5 T in a tabletop MRE scanner. Tissue structure was analyzed histologically and rheologic data were analyzed using fractional order derivatives conceptualized by a called spring-pot component that interpolates between pure elastic and viscous responses.Overnight freezing and thawing induced membrane disruptions and cell detachment in the space of Disse, resulting in a markedly lower shear modulus μ and apparent diffusion coefficient (ADC) (μ[−20 °C] = 1.23 ± 0.73 kPa, μ[−80 °C] = 0.66 ± 0.75 kPa; ADC[–20 °C] = 0.649 ± 0.028 μm²/s, ADC[−80 °C] = 0.626 ± 0.025 μm²/s) compared to normal tissue (μ = 9.92 ± 3.30 kPa, ADC = 0.770 ± 0.023 μm²/s, all p < 0.001). Furthermore, we analyzed the springpot-powerlaw coefficient and observed a reduction in −20 °C specimens (0.22 ± 0.14) compared to native tissue (0.40 ± 0.10, p = 0.033) and −80 °C specimens (0.54 ± 0.22, p = 0.002), that correlated with histological observations of sinusoidal dilation and collagen distortion within the space of Disse. Overall, the results suggest that shear modulus and water diffusion in liver tissue markedly decrease due to cell membrane degradation and cell detachment while viscosity-related properties appear to be more sensitive to distorted stromal and microvascular architecture.     

基于长时间序列landsat数据的科尔沁沙地土地利用演变分析

以科尔沁沙地沙丘-草甸过渡带区域主要土地覆被类型为研究对象，以1987-2017年多时相Landsat TM/OLI遥感影像解译分类为基础，参考生态学植被演替研究方法，系统分析研究区30年来的土地利用/覆被动态演变规律，研究结果表明：（1）决策树法在复杂下垫面不同覆被类型的同步识别效果较好，所有影像分类精度均达到88%以上，分类效果较好，其中2017年分类精度最高为95.24%，达到了分类研究的要求；（2）研究区存在着"半灌丛-草甸地-灌丛"的植被结构特征，且整体表现为"南进北退"的变化趋势。结合土地利用动态度分析结果表明人类活动干涉下，研究区整体上遵循了半干旱区植被条件改善的一般规律，侧面反映该研究区域生态环境的持续不稳定性和脆弱性；（3）研究区覆被类型发生变化的总面积达到2623.59 hm²，总变化强度为63.76%。其中正向演替的比例为52.61%，以半灌丛面积的持续减小与沙地草甸面积的持续扩张为主要变化特征。但同时，半灌丛转为沙地的面积为184.95 hm²，表明以放牧为主的研究区同时发生着局部的逆行演变；（4）质心迁移结果反映了1987-2017年间，除人为影响较大的林地、草地以及耕地向北迁移外，其他植被类型的质心都有很明显的南迁，主要植被类型重心迁移距离依次由大到小为耕地 > 半灌丛 > 灌丛 > 沙地草甸 > 湿地草甸 > 林地。研究通过记录科尔沁沙地连续扩展的时空模式，展示了遥感-生态和时间序列影像在30 m分辨率下跟踪土地利用/覆被变化的潜力，为提高干旱半干旱区土地利用情况的动态监测效率，开展土地利用/覆被动态演变研究提供参考。     

A comprehensive analysis of blue water scarcity from the production,consumption, and water transfer perspectives

The issue of growing water scarcity has been increasingly perceived as a global systemic risk. To solve it, an integrated approach considering different perspectives of water scarcity is at a premise. In this study, we developed an approach to calculate the blue water scarcity (BWS) and integrated the production, consumption, and water transfer perspectives into a single framework. The results are as follows: The average BWS in the Hetao irrigation district was 0.491 during the 2001–2010 year period, which was much larger than the threshold of 0.30, indicating a high water stress level. From the production perspective, the agricultural sector was the largest contributor to regional water scarcity and the average BWS was as high as 0.479. From the consumption perspective, BWS related to virtual water export was much larger than that related to water consumption for making products to be consumed locally and the values were 0.422 and 0.069, respectively. Under the influence of physical and virtual water transfer, BWS changed from 0.242 (medium to high water stress level) to 0.491 (high water stress level). Strategies for reducing agricultural water consumption, such as increasing crop water productivity, improving irrigation efficiency, and promoting more reasonable irrigation water price, could be adopted in the Hetao irrigation district to alleviate regional BWS. Compared with physical and virtual water import, the virtual water export played a more important role in influencing the regional water scarcity, and the increase in crop water productivity, decrease in crop export volume, or adjustment of trade pattern from water-intensive crops to water-extensive ones could be feasible measures to decrease virtual water export for lower water stress, while the trade-offs in the product-consuming regions should be considered.     

Can cost–benefit analysis explain fish distribution patterns?

This review describes some recent theoretical and empirical research into the way fish respond to spatial heterogeneity in their environment, and particularly to patchily distributed resources. The ways in which the need to acquire food interacts with other important requirements such as thermoregulation and predator avoidance to determine space use are considered, as are interactions with other members of the same species, viewed both as shoaling companions and as competitors. Recent developments in ideal free theory are discussed and the extent to which this formulation can explain how fish distribute themselves among feeding patches is examined. The implications of overtly aggressive interactions, in the form of dominance hierarchies and territorial systems, for distribution patterns in the laboratory and in the field are also reviewed. Finally the extent to which cost–benefit analysis can help to explain fish distribution patterns and the relative importance of behavioural processes compared to other determinants of the distribution of fish are considered.     

Short-term variability of plant populations within a regularly disturbed habitat

The changing populations of weeds during 13 years of the Broadbalk continuous wheat experiment were analysed to investigate the extent of differences in shortterm variability of cover between species. The data were from two sections of the experiment where winter wheat was grown continuously under herbicide treatment for 13 and 6 years respectively. Logistic regressions were fitted to the data. Equisetum arvense showed significant long-term increases on both sections; long-term trends were also detected in the longer data run for Agrostis stolonifera, Cirsium arvensa, Poa trivialis, Ranunculus arvensis and Vicia sativa, and for Medicago lupulina on the shorter data run. Variation around long-term trends was low in the case of Equisetum, and, in the longer data run, for Cirsium and Tussilago farfara, and high for Poa spp. and Vicia. Cover values on the two sections were positively correlated for Alopecurus myosuroides, Equisetum, Poa annua and Tripleurospermum inodorum. There was a weak correlation between C-S-R strategy and short-term variability; the more competitive species displayed less variability than the ruderal species. Furthermore, species regenerating from persistent seed banks were more variable in the short term than those regenerating from short-lived seed or bud banks. This can be explained by differences in response to year-to-year variation in environmental conditions, those species with persistent seed banks being typically more sensitive to annual fluctuations in the environment than those without.     

Evolutionarily stable seasonal timing for insects with competition for renewable resource

Summary I study the evolutionarily stable seasonal patterns of hatching and pupation for herbivorous insects that engage in exploitative competition for a renewable resource. A longer larval feeding period enhances female fecundity, but also causes a higher mortality by predation and parasitism. Previously, it was shown that the evolutionarily stable population exhibits asynchronous starting and ending of the larval feeding period in a model in which larval growth rate decreases with the total larval biomass in the population due presumably to interference competition. Here I study the case in which resource availability changes not only with environmental seasonality but with the depletion by the feeding of larvae. I find that if the impact of the herbivory is strong, both hatching and pupation should occur asynchronously in the evolutionarily stable population. And if the favourable season for the host plant is short the ESS population may include synchronous timing of pupation. If the timing of hatching and pupation occurs asynchronously, in the first day of each interval some fraction of the population hatch or pupate, respectively and the rest do so gradually over the interval. In addition, if the environmental variable changes as a symmetric function of time, the length of the period in which hatching occurs tends to be much shorter than the period in which pupation occurs.     

Environmental indicators for sustainable production of algal biofuels

For analyzing sustainability of algal biofuels, we identify 16 environmental indicators that fall into six categories: soil quality, water quality and quantity, air quality, greenhouse gas emissions, biodiversity, and productivity. Indicators are selected to be practical, widely applicable, predictable in response, anticipatory of future changes, independent of scale, and responsive to management. Major differences between algae and terrestrial plant feedstocks, as well as their supply chains for biofuel, are highlighted, for they influence the choice of appropriate sustainability indicators. Algae strain selection characteristics do not generally affect which indicators are selected. The use of water instead of soil as the growth medium for algae determines the higher priority of water- over soil-related indicators. The proposed set of environmental indicators provides an initial checklist for measures of algal biofuel sustainability but may need to be modified for particular contexts depending on data availability, goals of stakeholders, and financial constraints. Use of these indicators entails defining sustainability goals and targets in relation to stakeholder values in a particular context and can lead to improved management practices.     

Effect of the non-fertilizer N supply of grassland soils on the response of herbage to N fertilization under mowing conditions

I tested whether the non-fertilizer N supply of grassland soils (NFNS; N uptake on unfertilized plots) affects the relationships between N uptake and dry matter production, N application and N uptake, N application and dry matter production, as well as the optimum fertilizer application rate.At low N uptake rates the amount of dry matter production per kg of N uptake was negatively correlated with NFNS; at higher N uptake levels the correlation was not significant. The apparent nitrogen recovery of fertilizer N was not correlated with NFNS. The optimum fertilizer application rate was correlated positively with the maximum dry matter production (Max DM) and negatively with NFNS. The relationship optimum fertilizer application = –81–0.8 × NFNS + 0.0375 × Max DM accounted for 89% of the variance in optimum fertilizer application rate between soils at a marginal N effect of 7.5 kg dry matter per kg N applied. So an increase in NFNS of 100 kg N resulted in a decrease of the optimum N application rate of 80 kg N.     

Predation risk and feeding patterns of crucian carp

As part of an experimental study of the direct and indirect effects of piscivory on prey fish, the diets of crucian carp Carassius carassius were compared across sections of a divided pond; two sections were stocked with crucian carp alone and two with crucian carp plus perch Perca fluviatilis . Analysis of crucian gut contents indicated that the composition of invertebrate prey did not differ in the presence v . absence of perch. However, crucians, particularly small individuals (<10cm) that were most vulnerable to predation, displayed a lower intake of invertebrate prey in sections with perch. Although diet composition differed between crucians caught in inshore v. offshore habitats (with habitat use being related to crucian size and the presence or absence of perch), no clear pattern existed between habitat and total food intake. Overall, the major effects of predators on the diet of crucian carp appeared to be caused by increased ecological density (resulting from confinement of small crucians inshore) and reduced activity levels, rather than simple shifts to safer habitats.