Reduced nitrogenase efficiency dominates response of the globally important nitrogen fixer Trichodesmium to ocean acidification

工业革命以来，海洋吸收了约三分之一人为排放的CO2，以迄今3亿年来最快的速度酸化（CO2升高、pH下降），这势必影响海洋生态系统的关键过程和功能。研究团队创新性地从区分海洋酸化过程中CO2上升和pH下降的双重效应入手，揭示了海水CO2升高的正效应小于pH下降的负效应，故酸化的净效应为抑制束毛藻的固氮作用。这是因为酸化引起束毛藻胞质 pH下降，从而降低固氮酶效率、干扰胞内pH稳态、影响细胞产能。在上述研究工作的基础上，进一步系统地测定了固氮和光合系统蛋白的表达量及其含铁量，建立了一个束毛藻的“资源最优化分配”细胞模型。实现了实验数据和数值模型的紧密结合：实验数据是构筑模型的坚实基础，并提高了模型的预测水平；通过模型模拟，加深了对实验发现的认知，并对实验结论进行了时空拓展。 罗亚威博士和史大林博士为论文的共同第一作者和共同通讯作者，史大林课题组的洪海征教授、研究助理沈容和博士生张福婷为共同作者。论文的共同作者还包括美国佛罗里达州立大学助理教授Sven Kranz博士和乔治亚大学副教授Brian Hopkinson博士。【Abstract】The response of the prominent marine dinitrogen (N2)-fixing cyanobacteria Trichodesmium to ocean acidification (OA) is critical to understanding future oceanic biogeochemical cycles. Recent studies have reported conflicting findings on the effect of OA on growth and N2 fixation of Trichodesmium. Here, we quantitatively analyzed experimental data on how Trichodesmium reallocated intracellular iron and energy among key cellular processes in response to OA, and integrated the findings to construct an optimality-based cellular model. The model results indicate that Trichodesmium growth rate decreases under OA primarily due to reduced nitrogenase efficiency. The downregulation of the carbon dioxide (CO2)-concentrating mechanism under OA has little impact on Trichodesmium, and the energy demand of anti-stress responses to OA has a moderate negative effect. We predict that if anthropogenic CO2 emissions continue to rise, OA could reduce global N2 fixation potential of Trichodesmium by 27% in this century, with the largest decrease in iron-limiting regions.This work was funded by the National Key R&D Program of China (2016YFA0601404 and 2016YFA0601203), NSFC (41476093, 41721005, 41890802, 31861143022 and 41376116), and the MEL internal research fund (MELRI1502).本项研究得到了国家重点研发计划（2016YFA0601404 和2016YFA0601203）以及国家自然科学基金系列项目（41476093, 41721005, 41890802, 31861143022 和41376116）的资助

貌合神离：中英文同款广告的符号和眼动分析

通过一系列中英文同款广告，该研究结合符号和眼动技术，指出相似的表象之下，微妙的细节调整如何折射出中西方读者对媒介内容叙述方式的不同偏好，以及处理群己关系的不同价值取向，从而呈现出“貌合神离”的警民、亲子、师生、夫妻、男女等社会关系。本文系国家自然科学基金项目“东西方不同文化思维方式对广告说服的影响：一个自下而上的脉络建构与验证”（项目编号：71372076）的阶段性研究成果

The synergetic effects of shot peening and laser-shot peening on the microstructural evolution and fatigue performance of a medium carbon steel

The synergetic effect of shot peening (SP) and laser shot peening (LSP) on the fatigue behavior of a medium carbon steel was investigated. A fatigue life transition was observed in the S-N curve, where the fatigue per-formance of the SP + LSP specimen was improved only at lower stress levels. This result is consistent with the short crack propagation behavior observed in the near-threshold region. The heterogeneous structures comprised by ultra-fine grains, dislocation tangles, and more high-angle grain boundaries were responsible for this behavior which effectively retard the short crack propagation

Assessment of Social and Economic Effect of Soil and Water Conservation in Loess Plateau

采用灰色关联分析法对黄土高原10条小流域开展水土保持后的社会经济效应做了定量评价,结果表明:水土保持对农村社会经济发展产生了极大的推动作用,农民人均收入水平是反映水土保持的社会经济影响好坏的首要因子,此外,人均粮食占有水平、土地利用率、人均水土保持投资、农业总收入以及基本农田面积也是反映社会经济效应的重要因素。只有当这些单项指标效益均较好时,整体的社会经济效应才会处于良好状态,水土保持要采用系统工程原理,才能保证生态环境与社会经济良性发展

一种新型光码分多址系统平衡检测技术

为了有效抑制多用户干扰,采用改良双重码构建了基于新型平衡检测技术的光码分多址系统。使用归零与非归零脉冲发生器,在不同传输长度和传输比特率下对比系统性能,并对平衡检测和光谱直接检测技术进行了比较。通过系统测试得出:在2.5Gbit/s的传输比特率下,采用改良双重码编码的新型平衡检测技术的性能优于光谱直接检测技术,并且能够有效地消除多址干扰

Numerical simulation of ti-based metallic glasses as whipple shield bumper by smoothed particle hydrodynamics methods

The debris clouds produced by hypervelocity impacts on Ti-based metallic glasses (Ti-MGs) and Al-6061-T6 bumper were studied by smoothed particle hydrodynamics (SPH) methods. The change of the vanguard shape, dispersion and ejection angle were also obtained with the same bumper thickness to the projectile-diameter ratio (h/d). For the same h/d valve, the debris cloud of Ti-MGs bumper had a more widely dispersion and ejection angle than with Al-6061-T6 bumper; the vanguard velocity of Ti-MGs bumper was also lower than Al-6061-T6 bumper. Moreover, for the same bumper areal density, the vanguard of the debris cloud in MGs bumper was plane-shaped. This study demonstrates that Ti-MGs exhibit an excellent bumper protection performance, which asset can pave new paths for their further applications. © 2020 Trans Tech Publications Ltd, Switzerland

OPLC温度分布及光单元传输损耗特性研究分析

针对温度变化对光纤复合低压电缆（OPLC）传输性能的影响,综合考虑电缆温度场分布以及材料膨胀系数不同导致的应力差分布特性,建立了OPLC温度变化与传输损耗的数学模型。在此基础上,设计了基于电力场、光场、温度场和应力场等多物理场耦合的仿真模型,采用有限元分析方法,结合COMSOL Multiphysics仿真软件,分别模拟了OPLC在稳定运行状态和短路故障状态下的温度分布及光单元传输损耗特性。仿真结果表明,OPLC在稳定运行状态和短路故障状态下的温度分布及传输损耗与理论计算基本相符,由短路故障引起的光纤传输损耗呈平稳衰减趋势,在工程上可以忽略不计

陕西蓝田全新世黄土AMS-~(14)C测年与环境变迁

加速器质谱计14C(AMS-14C)测年技术具有精度高、速度快以及样品需求量少的特点,已广泛用于晚第四纪和新石器时期的断代研究。通过对蓝田县新街遗址旁的全新世黄土-古土壤序列进行AMS-14C测年,并利用贝叶斯分析方法,建立了该地层序列的年代学框架。结合新街遗址考察、黄土-古土壤地层划分、磁化率测量和孢粉分析,表明马兰黄土晚期气候偏凉干,进入全新世时期气候转暖,仰韶时期温暖湿润,龙山时期气候暖偏干,新黄土堆积时期气候转干冷。</p

Abnormal softening of Ti-metallic glasses during nanosecond laser shock peening

Nanosecond laser shock peening (NLSP) has been proved to be an effective way to enhance the mechanical properties of metallic components through modifying the surface microstructures. However, the micromechanism of structure and property fluctuations induced by shock wave propagation is still limited due to the intrinsic defects in crystalline materials. Here, NLSP treatment has been performed into the Ti-metallic glasses. Owing to the absence of dislocations, grain boundary and phase segregation, the structural signals caused by the shock wave could come into sight. According to grid nanoindentation results, the shock-affected region can be divided into three sections: (I) the rapid softening region, (II) the recovery region and (III) the matrix region. The fronted first pop-in event and the reduced hardness found in the subsurface region provide clear evidence of the release wave-induced structural rearrangement. The abnormal change of the average volume of the shear transformation zone (STZ) could be explained by a two-step transformation mechanism, due to the fluctuations of the "weak spot" induced by the release stress wave. By means of these results, this work provides an opportunity to shed light on the common laser-solid interaction