Sensitivity to H- and Al ions limiting growth and distribution of the woodland grass Bromus benekenii

One pH experiment and two aluminium experiments were conducted in order to investigate the effects of H- and Al ions on growth of Bromus benekenii. Continuously flowing solution cultures were used with ion concentrations simulating natural soil solutions. In all experiments, treatment effects were more pronounced on root than on shoot growth. In the pH experiment, root growth decreased with decreasing pH within the pH range 4.5 to 3.5. The critical pH for root growth of Bromus benekenii was between 3.8 and 4.0. In the Al experiments, root growth started to decrease at 20 M of quickly reacting Al and almost ceased at 70 M Al. This characterizes Bromus benekenii as an Al sensitive species. In the pH experiment, shoot concentrations of Ca, Mg, K and P decreased with decreasing pH, but root concentrations were not affected. In the Al experiments, the Al concentrations of both shoots and roots increased with Al in the nutrient solution. At treatments of 70 M Al or higher, Ca, Mg, K and P concentrations in the shoots were reduced. The critical concentrations of H- and Al ions in the experiments were similar to the highest concentrations found at field sites of Bromus benekenii, analysed in soil solutions obtained by centrifugation technique. Both Al and H toxicity were considered to be of importance as limiting factors for the distribution of Bromus benekenii in south Sweden. Probably, Al toxicity starts to limit growth when also pH itself influences growth negatively. The importance of simulating natural soil solutions in experiments is emphazised, in order to obtain information on the importance of chemical soil factors to the distribution of plants.     

Asymptotic behaviour of positive solutions of periodic delay logistic equations

The delay logistic equation with periodic coefficients is studied. Under condition (2.1) below the existence and global attractivity of a unique periodic solution is proved by mean of monotonicity methods.Work partially supported by G.N.A.F.A.-C.N.R.     

一类带混合边界条件的比率依赖捕食模型正稳态解的存在性

研究了一个带混合边界条件和扩散作用的比率依赖捕食模型,其中食物带第二类边值,而捕食者带第三类边值．利用指数理论、度理论和逼近方法,我们获得了当a〉m1且b〉d2λ1：或d2λ1-m2〈b〈d2λ1时对应的捕食模型至少存在一个正稳态解．     

A computational study of the effect of Li–K solid solutions on the structures and stabilities of layered silicate materials—an application of the use of Condor pools in molecular simulation

Computer modelling techniques were used to investigate the structures and stabilities of Li–K solid solutions of three different disilicate structures, employing a newly developed program based on symmetry arguments to identify identical configurations and hence eliminate unnecessary duplication of calculations. Even so, the large number of calculations needed to sample the complete set of configurations of a wide range of solid solutions necessitated the use of an extensive Condor pool of PC clusters, which afforded the necessary computing resources for this study.

The results of our calculations show that in the wide range of Li–K solid solutions investigated, the mixed-cationic KLiSi₂O₅ material retains its original structure when the composition was varied, where six-membered rings of silica tetrahedra are linked to form continuous channels throughout the structure. The channel positions are found to be preferentially occupied by the potassium ions rather than by the smaller lithium ions. The original framework of the experimental K₂Si₂O₅ structure, containing 14-membered rings of silica tetrahedra, similarly remains intact with the introduction of smaller lithium atoms into the bigger potassium lattice sites. However, the replacement of potassium ions for lithium ions in the Li₂Si₂O₅ material causes significant distortions of the original structure, which loses its symmetry, although the ring structure remains.     

Cryopreservation of human bone marrow‐derived mesenchymal stem cells with reduced dimethylsulfoxide and well‐defined freezing solutions

The aim of this study is to investigate the feasibility of using well defined, serum‐free freezing solutions with a reduced level of dimethylsulfoxide (DMSO) of 7.5, 5, and 2.5% (v/v) in the combination with polyethylene glycol (PEG) or trehalose to cryopreserve human bone marrow‐derived mesenchymal stem cells (hBMSCs), a main source of stem cells for cell therapy and tissue engineering. The standard laboratory freezing protocol of around 1°C/min was used in the experiments. The efficiency of 1,2‐propandiol on cryopreservation of hBMSCs was explored. We measured the post‐thawing cell viability and early apoptotic behaviors, cell metabolic activities, and growth dynamics. Cell morphology and osteogenic, adipogenic and chondrogenic differentiation capability were also tested after cryopreservation. The results showed that post‐thawing viability of hBMSCs in 7.5% DMSO (v/v), 2.5% PEG (w/v), and 2% bovine serum albumin (BSA) (w/v) was comparable with that obtained in conventional 10% DMSO, that is, 82.9 ± 4.3% and 82.7 ± 3.7%, respectively. In addition, 5% DMSO (v/v) with 5% PEG (w/v) and 7.5% 1,2‐propandiol (v/v) with 2.5% PEG (w/v) can provide good protection to hBMSCs when 2% albumin (w/v) is present. Enhanced cell viability was observed with the addition of albumin to all tested freezing solutions. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

0-1整数规划问题的半自动化DNA计算模型

对一般的0—1整数规划问题提出了一种半自动化的DNA计算模型。首先产生所给定的0—1整数规划问题的所有可能解,然后设置对应于0—1整数规划问题的约束不等式的探针,利用这些探针设计半自动化装置对所有可能解进行自动分离,最终找出0—1整数规划问题的解。该模型的最大优点在于具有自动化的特点;同时,从理论上来讲,该模型适合含有任意变量的任意0—1整数规划问题的求解。     

2020年后生物多样性保护需要建立新的资金机制

《生物多样性公约》第十五次缔约方大会(COP15)将评估全球生物多样性保护已有进展, 审议并通过“2020年后全球生物多样性框架”, 后者是实现2050愿景“与自然和谐相处”的关键, 有助于达成联合国可持续发展的目标。生物多样性资金机制现在是将来也是实施全球生物多样性保护行动计划的重要保证。根据《生物多样性公约》信息交换所的数据, 目前各缔约方每年对本国生物多样性保护的投资额度占其当年国内生产总值(GDP)的比例比较小。中国作为发展中国家, 2015年时生物多样性保护资金投入占GDP比例为0.255%, 在世界各国中处于比较高的水平。近年中国对生物多样性保护的投入连年增加, 2019年时已经达约0.6%。有研究表明, 目前全球每年生物多样性保护资金的缺口至少500亿美元, 未来十年还有更大的资金缺口, 而且当前已有生物多样性资金渠道比较单一, 并存在一些短板, 远远不能满足生物多样性保护行动的要求, 急需建立新的资金机制, 调动更多资源, 推动2030年生物多样性保护任务和目标的实现。《生物多样性公约》的资金机制可以与包括《联合国气候变化框架公约》在内的其他相关环境公约协同增效, 比如基于自然的解决方案将生物多样性保护与气候变化减缓等环境目标联系起来。中国作为COP15的东道国, 有积极协调磋商的责任, 力求在大会上推动形成一个新的资金机制, 即全球生物多样性保护基金, 为“2020年后全球生物多样性框架”的实施保驾护航。新的生物多样性保护资金机制将独立于现有的生物多样性保护资金机制, 具有多样化投资渠道并引入绩效评估机制, 将经费与任务目标关联, 提高资金的使用效率, 支持发展中国家的生物多样性保护行动。     

Effects of macromolecular crowding on intracellular diffusion from a single particle perspective

Compared to biochemical reactions taking place in relatively well-defined aqueous solutions in vitro, the corresponding reactions happening in vivo occur in extremely complex environments containing only 60-70% water by volume, with the remainder consisting of an undefined array of bio-molecules. In a biological setting, such extremely complex and volume-occupied solution environments are termed 'crowded'. Through a range of intermolecular forces and pseudo-forces, this complex background environment may cause biochemical reactions to behave differently to their in vitro counterparts. In this review, we seek to highlight how the complex background environment of the cell can affect the diffusion of substances within it. Engaging the subject from the perspective of a single particle's motion, we place the focus of our review on two areas: (1) experimental procedures for conducting single particle tracking experiments within cells along with methods for extracting information from these experiments; (2) theoretical factors affecting the translational diffusion of single molecules within crowded two-dimensional membrane and three-dimensional solution environments. We conclude by discussing a number of recent publications relating to intracellular diffusion in light of the reviewed material.     

Amylose conformation in aqueous solution: a small-angle X-ray scattering study

An investigation of the small-angle X-ray scattering properties of aqueous solutions of an amylose derivative has been carried out. Experiments have been conducted in stable and fairly concentrated polymer solutions (up to 3.2%) by using a slightly substituted carboxymethylamylose having a degree of substitution of 0.08. Scattering intensities display a maximum in the low angle range which prevents extrapolation of the angular dependence to zero angle. Data obtained in the range of scattering vector 0.01<η<0.1Å^?1 yield 8 Å as the radius of gyration of the chain cross-section and 140 dalton Å^?1 as the mass per unit length. These results are analysed in terms of the current model of amylose solution conformation and compared with the theoretical calculations of the Debye scattering function of the isolated chain.