从流动到可塑状态软黏土的一维固结特性试验研究

软土在固结过程中含水率的减小将导致其物理状态从流动态进入可塑态,为研究物理状态变化对软黏土的压缩性和渗透性的作用影响,采用饱和重塑黏土,配制高于液限含水率和接近液限含水率的试样,分别开展不同压力作用下的一维固结试验,依据位移和孔压测试数据,对比分析了固结过程中的位移发展、孔压消散、压缩系数以及渗透系数的变化特性。结果表明：在流动状态下,位移快速发展,而孔压却存在明显的滞消现象;进入可塑状态后,压缩系数和渗透系数的对数随孔隙比的变化关系均发生明显的转折。这意味着,在软土固结问题的理论分析中,应考虑物理状态的变化对土体压缩性和渗透性参数变化规律的影响。

RARα调控稳态突触可塑性在孤独症谱系障碍发病机制中的研究进展

孤独症谱系障碍是儿童神经精神发育性疾病领域亟需解决的重要疾病,发病率逐年增高,给家庭和社会带来了沉重负担。不同单基因突变模型的功能研究表明稳态突触可塑性受损是导致这些重叠表型的共同机制。视黄酸受体α(retinoic acid receptorα,RARα)通过谷氨酸受体亚基1翻译控制和RARα/mTOR信号传导途径双向调控神经系统稳态突触可塑性,影响感觉信息整合和情境适应能力,同时通过树突棘生长影响学习记忆功能和神经突触信号网络。这些研究进展提示RARα可能作为调节稳态突触可塑性和改善孤独症谱系障碍症状的潜在药物靶点,有助于临床上对孤独症谱系障碍进行临床分子分型和精准诊治工作。

Alarm cue induces an antipredator morphological defense in juvenile Nicaragua cichlids Hypsophrys nicaraguensis

Olfactory cues that indicate predation risk elicit a number of defensive behaviors in fishes, but whether they are sufficient to also induce morphological defenses has received little attention. Cichlids are characterized by a high level of morphological plasticity during development, and the few species that have been tested do exhibit defensive behaviors when exposed to alarm cues released from the damaged skin of conspecifics. We utilized young juvenile Nicaragua cichlids Hypsophrys nicaraguensis to test if the perception of predation risk from alarm cue （conspecific skin extract） alone induces an increased relative body depth which is a defense against gape-limited predators. After two weeks of exposure, siblings that were exposed to conspecific alarm cue increased their relative body depth nearly double the amount of those exposed to distilled water （control） and zebrafish Danio rerio alarm cue. We repeated our measurements over the last two weeks （12 and 14） of cue exposure when the fish were late-stage juveniles to test if the rate of increase was sustained; there were no differences in final dimensions between the three treatments. Our results show that 1） the Nicaragua cichlid has an innate response to conspecific alarm cue which is not a generalized response to an injured fish, and 2） this innate recognition ultimately results in developing a deeper body at a stage of the life history where predation risk is high [Current Zoology 56 （1）： 36-42, 2010].

神经电活动稳态调控抑制性突触传递的分子机制

发育中的神经网络需要兼顾生长与稳定这两种相辅相成的需求。稳态可塑性可通过调节兴奋性或抑制性突触传递从而维持神经网络的稳定。已报道的关于稳态可塑性机制方面的研究主要集中在其对兴奋性突触传递的影响,很少关注其对抑制性突触的调控。运用体外培养的原代海马神经元,本项研究发现了持续增强神经元电活动4小时能够诱导抑制性突触传递的稳态上调,且该过程明显早于兴奋性突触的变化。抑制性突触,即γ-氨基丁酸(GABA)突触的改变表现为微小抑制性突触后电流幅度和频率的增加,及GAD65、vGAT和GABAA受体α1亚基等抑制性突触相关蛋白表达的上调。通过在单个神经元中过表达内向整流型钾离子通道Kir2.1从而降低其电活动,发现电活动诱导的神经元自身放电增强对其抑制性突触传递的调节是必须的。与上述结果相互补,在单个神经元中激活过表达的配体门控TRPV1通道,从而直接增强该神经元的自发放电,导致了其抑制性突触传递的增强,模拟了整体增强神经网络电活动的效果。上述结果说明抑制性突触传递的稳态调控依赖于锥体神经元自身电活动的改变,是一种自治性的调节方式。这种调控通过锥体神经元分泌的脑源性神经营养因子(BDNF)逆突触作用于突触前的抑制性神经元末梢,从而增强其自身的抑制性突触输入。通过对幼年大鼠腹腔注射红藻氨酸在体增强神经网络电活动,在海马CA1区域的锥体神经元中诱导出了这种抑制性突触传递的稳态调控。上述结果提示抑制性突触传递的自治性稳态调控是神经元应对网络电活动增强的一个重要代偿性保护机制。

Hybrid memristor-CMOS neurons for in-situ learning in fully hardware memristive spiking neural networks

Spiking neural network,inspired by the human brain,consisting of spiking neurons and plastic synapses,is a promising solution for highly efficient data processing in neuromorphic computing.Recently,memristor-based neurons and synapses are becoming intriguing candidates to build spiking neural networks in hardware,owing to the close resemblance between their device dynamics and the biological counterparts.However,the functionalities of memristor-based neurons are currently very limited,and a hardware demonstration of fully memristor-based spiking neural networks supporting in-situ learning is very challenging.Here,a hybrid spiking neuron combining a memristor with simple digital circuits is designed and implemented in hardware to enhance neuron functions.The hybrid neuron with memristive dynamics not only realizes the basic leaky integrate-and-fire neuron function but also enables the in-situ tuning of the connected synaptic weights.Finally,a fully hardware spiking neural network with the hybrid neurons and memristive synapses is experimentally demonstrated for the first time,and in-situ Hebbian learning is achieved with this network.This work opens up a way towards the implementation of spiking neurons,supporting in-situ learning for future neuromorphic computing systems.

Influence of structure transition on plastic behaviors of iron based ordered alloys

The influence of ordered structure on the dislocation configuration,structure of anti-phase domain boundary,partial dislocation slips,etc.are analyzed in the background of promoting the plasticity of iron based ordered solid solutions with second-order phase transformation.The principles of deformation softening and annealing hardening in ordered solid solutions are discussed because of deformation induced structure disordering.It is concluded that the independent slip ability of the partial dislocations and the corresponding low temperature plasticity of ordered solid solutions could be promoted obviously by proper alloying effects,which reduces the anti-phase domain boundary energy,or by maintaining the disordering state into the low temperature range.The similar principles could be also used to modify the low temperature plasticity of other metal based ordered solid solutions.

Phenotypic plasticity can explain evolution of sympatric polymorphism in the hairy snail Trochulus hispidus （Linnaeus, 1758）

Morphological variation of snails from the genus Trochulus is so huge that their taxonomy is unclear. The greatest variability concerns forms hispidus and sericeus/plebeius, which are often considered as separate species. To evidence the species barriers, we carried out crossbreeding ex- periments between these two sympatric morphs. Moreover, we compared the shell morphology of laboratory-bred offspring with their wild parents to test if the variation can be explained by the phenotypic plasticity model. We found that the two Trochulus morphs show no reproductive bar- riers. The fecundity rates, the mean clutch size, and F~ viability observed for all crosses were not significantly different. In hybrid crosses （in F2 generation）, we also recorded reproduction compati- bility, similar fecundity, and hatching success as in their parents. Accordingly, phylogenetic ana- lyses revealed the significant grouping of sequences from these different morphs and supported no constrains in reproduction between them. Comparison of shell morphology between wild and laboratory samples showed that various characters appeared highly plastic. The average shell shape of the hispidus morph changed significantly from flat with wide umbilicus to elevated with narrower umbilicus such as in the sericeus/plebeius morph. All these findings indicate that the examined morphs do not represent separate biological species and the evolutionary process is not advanced enough to separate their genetic pool. Therefore, phenotypic plasticity has played a sig- nificant role in the evolution of Trochulus shell polymorphism. The two morphs can evolve inde- pendently in separate phylogenetic lineages under the influence of local environmental conditions.

Lack of functional link in the tadpole morphology induced by predators

Most studies of predator-induced plasticity have focused on documenting how prey species re- spond to predators by modifying phenotypic traits and how traits correlate with fitness. We have previously shown that Pleurodema thaul tadpoles exposed to the dragonfly Rhionaeschna varie- gata responded strongly by showing morphological changes, less activity, and better survival than non-exposed tadpoles. Here, we tested whether there is a functional link between morphological plasticity and increased survival in the presence of predators. Tadpoles that experienced predation risk were smaller, less developed, and much less active than tadpoles without this experience. Burst speed did not correlate significantly with morphological changes and predator-induced deeper tails did not act as a lure to divert predator strikes away from the head. Although we have previously found that tadpoles with predator-induced morphology survive better under a direct predator threat, our results on the functional link between morphology and fitness are not conclu- sive. Our results suggest that in P. thaultadpoles （1） burst speed is not important to evade preda- tors, （2） those exposed to predators reduce their activity, and （3） morphological changes do not divert predator attacks away from areas that compromise tadpole survivalEE. Our results show that morphological changes in P. thaul tadpoles do not explain burst speed or lure attraction, al- though there was a clear reduction of activity, which itself reduces predation. We propose that changes in tadpole activity could be further analyzed from another perspective, with morphological change as an indirect product of behavior mediated by physiological mechanisms.

Model predictions for behaviors of sand-nonplastic-fines mixtures using equivalent-skeleton void-ratio state index

It is a challenge to suggest a constitutive model for describing the stress-strain behavior of sand-fines mixtures due to that these granular mixtures exhibited very complex behaviors at different densities, pressures and fines contents. In this study, an elastoplastic constitutive model within the framework of the bounding surface plasticity and critical state theories was proposed for sand-nonplastic-fines mixtures by using the concept of the equivalent-skeleton void ratio and equivalent-skeleton void-ratio state index. The proposed model with a set of material constants calibrated from a few tests could be used to model the fines-dependent and state-dependent behaviors of the sand-nonplastic-fines mixture including the strain- softening and volumetric-expansion behaviors in the drained triaxial compression tests, and also the effects of fines content on the critical state lines in both the deviatoric stress versus mean effective stress and the void ratio versus mean effective stress planes.

How might epigenetics contribute to ecological speciation？

Speciation research has seen a renewed interest in ecological speciation, which emphasises divergent ecological se- lection leading to the evolution of reproductive isolation. Selection from divergent ecologies means that phenotypic plasticity can play an important role in ecological speciation. Phenotypic plasticity involves the induction of phenotypes over the lifetime of an organism and emerging evidence suggests that epigenetic marks such as cytosine and protein （histone） modifications might regu- late such environmental induction. Epigenetic marks play a wide role in a variety of processes including development, sex dif- ferentiation and allocation, sexual conflict, regulation of transposable elements and phenotypic plasticity. Here we describe recent studies that investigate epigenetic mechanisms in a variety of contexts. There is mounting evidence for environmentally induced epigenetic variation and for the stable inheritance of epigenetic marks between generations. Thus, epigenetically-based pheno- typic plasticity may play a role in adaptation and ecological speciation. However, there is less evidence for the inheritance of in- duced epigenetic variation across multiple generations in animals. Currently few studies of ecological speciation incorporate the potential for the involvement of epigenetically-based induction of phenotypes, and we argue that this is an important omission [Current Zoology 59 （5）： 686-696, 2013 ].

Inducible competitors and adaptive diversification

Identifying the causes of diversification is central to evolutionary biology. The ecological theory of adaptive diversi- fication holds that the evolution of phenotypic differences between populations and species--and the formation of new spe- cies-stems from divergent natural selection, often arising from competitive interactions. Although increasing evidence suggests that phenotypic plasticity can facilitate this process, it is not generally appreciated that competitively mediated selection often also provides ideal conditions for phenotypic plasticity to evolve in the first place. Here, we discuss how competition plays at least two key roles in adaptive diversification depending on its pattern. First, heterogenous competition initially generates heterogeneity in resource use that favors adaptive plasticity in the form of ＂inducible competitors＂. Second, once such competitively induced plas- ticity evolves, its capacity to rapidly generate phenotypic variation and expose phenotypes to alternate selective regimes allows populations to respond readily to selection favoring diversification, as may occur when competition generates steady diversifying selection that permanently drives the evolutionary divergence of populations that use different resources. Thus, competition plays two important roles in adaptive diversification---one well-known and the other only now emerging--mediated through its effect on the evolution ofphenotypic plasticity

EXTERNAL AND INTERNAL CONTROL IN PLANT DEVELOPMENT

Bodies of plants are modularly organized. Development proceeds by adding new modules to open endings with a potential for branching. Each module is autonomous to some extent. Development relies on the self-organized patterns that emerge from the interactions of individual modules. Interactions include both competition and cooperation,and several types of positive and negative feedback loops are involved. Development can be open to external influences, thus enabling the plant to adjust its form to the environment,for example, to the spatial distribution of ecological resources. This paper provides a review on adaptive plasticity in plants.