考虑体应变及干湿循环的黑龙江膨胀土土水特征研究

【目的】探讨初始干密度、干湿循环作用及膨胀土体应变对黑龙江引嫩工程渠基膨胀土土水特征的影响,为松嫩平原地区膨胀土土体的渗流研究及其非饱和本构模型的建立提供参考。【方法】以黑龙江膨胀土为研究对象,采用高速恒温冷冻离心机,对4种不同初始干密度（1.45,1.53,1.58和1.63 g/cm³）重塑试样及同一初始干密度下1,3,5次干湿循环试样进行恒温冷冻离心试验,同时平行进行4种不同初始干密度下的收缩试验,并对膨胀土进行体应变修正;基于Gardner模型,建立可以考虑体应变及干湿循环影响的土水特征拟合公式。【结果】体应变修正后的土样体积含水率较修正前提高1.4%~2.8%,且基质吸力越高提高的幅度越大;初始干密度为1.45,1.53,1.58和1.63 g/cm³的4种试样的进气值分别为12.42,38.46,52.21和87.19 kPa,说明初始干密度越大进气值越大,且初始干密度越大试样的土水特征曲线越平缓,持水性越好;随循环次数增加,试样的持水性变差,但会在循环3次后趋于稳定;所建立的土水特征拟合公式能够同时描述基质吸力随初始孔隙比（或干湿循环次数）、体积含水率2个因素的变化规律。【结论】初始干密度及干湿循环作用对黑龙江膨胀土的土水特征曲线有显著影响,同时膨胀土自身性质引起的体应变对土水特征曲线影响较大,在分析膨胀土土水特征时要充分考虑以上因素的影响。     

超声波-反复冻融协同法优化黑木耳菌丝体破壁条件

[目的]研究超声波-反复冻融协同作用对黑木耳菌丝体破壁的影响,并确定最佳破壁组合条件。[方法]利用单因素试验,研究了超声波处理过程中破壁时间、加水量、破壁次数、冷冻时间、冻融次数对多糖得率的影响,并利用正交试验设计确定最佳条件组合。[结果]单因素试验结果表明,破壁时间以20 min为宜,选择15倍为最适加水量,选择2次超声波破壁次数较宜,冷冻时间以30 min为宜,选择3次冻融次数较为合适。正交试验结果表明,各因素的影响效果依次为破壁时间、破壁次数和冻结时间,最佳组合条件为冷冻时间30 min,破壁时间25 min,破壁2次,此时多糖得率可达到57.76 mg/g。[结论]该研究可为指导实际生产提供依据和参考。     

模拟冻融循环对黑土黏化层孔隙结构的影响

以东北典型黑土区耕地土壤为研究对象,采用室内模拟冻融以及CT(Computerized tomography)扫描相结合的方法,通过孔隙数目、平均面积、成圆率3个指标的量化与分析,研究了冻融循环对黏化层土壤孔隙特征的影响规律,以期为探明该区土壤侵蚀机理提供科学依据。研究结果表明,冻融循环不同程度地降低了原状土和填充土的孔隙数目和面积,均在循环3次时达到最低值,冻融循环对≥5 mm孔隙影响较为明显。相对原状土而言,前期含水量对黏化层填充土柱孔隙特征的影响较小。黏化层结构对模拟冻融循环的响应特征印证了季节性冻融循环对黑土区黏化层可蚀性的影响,进而诱发土壤侵蚀、促进沟蚀发展的可能。      

Climate‐strategic agriculture and the water‐soil‐waste nexus

Adoption of input‐responsive varieties enhanced food production during the second half of the 20th century. However, even bigger challenges lie ahead because of the growing societal demands. For example, the global population of 7.2 billion in 2013 is projected to reach 9.2 billion by 2050 and stabilize at 10 billion by 2100. The growing and increasingly affluent population, with preference towards more and more meat‐based diet, is likely to jeopardize the finite, fragile, and dwindling soil and water resources which are already under great stress in densely populated countries in Asia and elsewhere. Economic growth and increase in gross domestic product also lead to generation of waste or by‐products, along with contamination and eutrophication of water resources. International trade in food/feed products also involves transfer of virtual water, which is a serious issue when water‐scarce countries export virtual water to water‐endowed countries. The problem is confounded by the present and future climate change driven by the growing energy demands of the carbon civilization. Thus, adaptation to climate change represents both a threat and an opportunity for sustainable development. Adaptive strategies must be sustainable socially and environmentally and advance the Millennium Development Goals, while buffering agroecosystems against extreme climate events (e.g., pedologic, agronomic, and ecologic drought). Thus, recognizing and addressing the water‐soil‐waste nexus is important to achieving climate‐strategic agriculture. Sustainable intensification of agroecosystems, producing more per unit consumption of essential resources, must consider judicious management of hydrological and biogeochemical cycles (C, N, P, S). The soil C pool must be managed and enhanced to offset anthropogenic emissions, and mitigate/adapt to the climate change. The pace of adoption of recommended land use and soil‐/plant‐/animal‐management practices can be kept at par with advances in scientific knowledge through continuous dialogue between scientists on the one hand and policy makers / land managers on the other to translate research data into policy and action plans.     

冻融循环下冷冻非发酵面团品质的变化及机理

为了探讨储运销售过程引起的冻融循环对冷冻非发酵面团品质的影响,利用低场核磁共振分析仪（LF-NMR）、质构仪与流变仪等对样品面团水分与蛋白质组分、质构与流变特性进行测定,研究冻融循环下冷冻非发酵面团品质变化。结果表明：5次冻融交替中,失水率显著上升,达至3.14%;总水分中半结合水含量在 F1后整体呈下降趋势,表明冻融循环过程中,半结合水不断散失;至第5次冻融时,醇溶蛋白含量显著下降（P＜0.05）,谷蛋白与谷蛋白大分子聚合物（GMP）含量至第4次冻融后均显著下降（P＜0.05）,分别降至2.26%与0.70%;生面坯剪切力显著上升,强韧性则与之相反;熟面坯硬度呈上升再下降趋势,黏性基本呈上升,弹性呈下降趋势;弹性模量G'与黏性模量G'均呈下降趋势,且在第4次时,tanδ（tanδ=G'/G'）至最大,表明G'的变化程度比G'大。由此可见,冻融循环致使冷冻非发酵面团品质有所下降。总而言之,冻融循环对冷冻非发酵面团的品质下降产生一定的负面影响。     

一种特殊情况的焦点量计算问题

为了讨论微分方程系统是否存在极限环，常常归结为讨论系统的细焦点等问题。用极坐标方法，讨论一类特殊系统的焦点量。化简了二阶及三阶焦点量公式：ｒ５（２π）＝∫０＾２π Ｒ５ｄθ；ｒ７（２π）＝∫０＾２πＲ７ｄθ＋２∫０＾２πＲ５ｒ３ｄθ；并且具体计算出这类系统的二阶焦点量。此类系统的二次项中有两个可变参数ｆｙ＾２（０，０），ｇｘ＾２（０，０）可供调解。     

Impact of rewilding,species introductions and climate change on the structure and function of the Yukon boreal forest ecosystem

Community and ecosystem changes are happening in the pristine boreal forest ecosystem of the Yukon for 2 reasons. First, climate change is affecting the abiotic environment (temperature, rainfall and growing season) and driving changes in plant productivity and predator–prey interactions. Second, simultaneously change is occurring because of mammal species reintroductions and rewilding. The key ecological question is the impact these faunal changes will have on trophic dynamics. Primary productivity in the boreal forest is increasing because of climatic warming, but plant species composition is unlikely to change significantly during the next 50–100 years. The 9–10‐year population cycle of snowshoe hares will persist but could be reduced in amplitude if winter weather increases predator hunting efficiency. Small rodents have increased in abundance because of increased vegetation growth. Arctic ground squirrels have disappeared from the forest because of increased predator hunting efficiency associated with shrub growth. Reintroductions have occurred for 2 reasons: human reintroductions of large ungulates and natural recolonization of mammals and birds extending their geographic ranges. The deliberate rewilding of wood bison (Bison bison) and elk (Cervus canadensis) has changed the trophic structure of this boreal ecosystem very little. The natural range expansion of mountain lions (Puma concolor), mule deer (Odocoileus hemionus) and American marten (Martes americana) should have few ecosystem effects. Understanding potential changes will require long‐term monitoring studies and experiments on a scale we rarely deem possible. Ecosystems affected by climate change, species reintroductions and human alteration of habitats cannot remain stable and changes will be critically dependent on food web interactions.     

Voles and weasels in the boreal Fennoscandian small mammal community: what happens if the least weasel disappears due to climate change?

Climate change, habitat loss and fragmentation are major threats for populations and a challenge for individual behavior, interactions and survival. Predator–prey interactions are modified by climate processes. In the northern latitudes, strong seasonality is changing and the main predicted feature is shortening and instability of winter. Vole populations in the boreal Fennoscandia exhibit multiannual cycles. High amplitude peak numbers of voles and dramatic population lows alternate in 3–5‐year cycles shortening from North to South. One key factor, or driver, promoting the population crash and causing extreme extended lows, is suggested to be predation by the least weasel. We review the arms race between prey voles and weasels through the multiannual density fluctuation, affected by climate change, and especially the changes in the duration and stability of snow cover. For ground‐dwelling small mammals, snow provides thermoregulation and shelter for nest sites, and helps them hide from predators. Predicted increases in the instability of winter forms a major challenge for species with coat color change between brown summer camouflage and white winter coat. One of these is the least weasel, Mustela nivalis nivalis. Increased vulnerability of wrong‐colored weasels to predation affects vole populations and may have dramatic effects on vole dynamics. It may have cascading effects on other small rodent–predator interactions and even on plant–animal interactions and forest dynamics.     

Impact of climate change on the small mammal community of the Yukon boreal forest

Long‐term monitoring is critical to determine the stability and sustainability of wildlife populations, and if change has occurred, why. We have followed population density changes in the small mammal community in the boreal forest of the southern Yukon for 46 years with density estimates by live trapping on 3–5 unmanipulated grids in spring and autumn. This community consists of 10 species and was responsible for 9% of the energy flow in the herbivore component of this ecosystem from 1986 to 1996, but this increased to 38% from 2003 to 2014. Small mammals, although small in size, are large in the transfer of energy from plants to predators and decomposers. Four species form the bulk of the biomass. There was a shift in the dominant species from the 1970s to the 2000s, with Myodes rutilus increasing in relative abundance by 22% and Peromyscus maniculatus decreasing by 22%. From 2007 to 2018, Myodes comprised 63% of the catch, Peromyscus 20%, and Microtus species 17%. Possible causes of these changes involve climate change, which is increasing primary production in this boreal forest, and an associated increase in the abundance of 3 rodent predators, marten (Martes americana), ermine (Mustela ermine) and coyotes (Canis latrans). Following and understanding these and potential future changes will require long‐term monitoring studies on a large scale to measure metapopulation dynamics. The small mammal community in northern Canada is being affected by climate change and cannot remain stable. Changes will be critically dependent on food–web interactions that are species‐specific.     

Relationship between rectal findings of corpus luteum and whole milk progesterone levels in postpartum dairy cows

The reliability of clinical ovarian findings was assessed as an indicator of luteal function in primiparous dairy cows. The postpartum period of 103 cows following their first parturition was studied by thrice weekly rectal palpation of ovaries and whole milk progesterone assay from 1 week after parturition to the first insemination. The relationship between milk progesterone levels and 1101 ovarian findings was compared during the follicular phases, short luteal phases and during the early, mid and late thirds of normal luteal phases. The compatibility between elevated progesterone and palpable corpus luteum was 71%, and between low progesterone and lack of corpus luteum 77%. In 10% of all rectal examinations the finding was unspecified; i.e. the clinician could not differentiate between luteal and follicular activity. During the acyclic period prior to the initiation of luteal function, the proportion of false corpus luteum findings was 11%. The corpora lutea of the short oestrous cycles were more difficult to palpate than those of normal cycles. During early dioestrus the corpus luteum was significantly more difficult to palpate than during the rest of dioestrus. The percentage of unspecified findings was highest during early dioestrus.The paper discusses the reliability of rectal examination as a method of diagnosing cyclicity and of evaluating the responsiveness of a cow to prostaglandin treatment.