Carbon cycling of forest ecosystems in response to global nitrogen deposition: a review

森林土壤和植被储存着全球陆地生态系统大约46%的碳,在全球碳平衡中起着非常重要的作用。过去几十年来,森林生态系统的碳循环和碳吸存受到了全球氮沉降的深刻影响,因为氮沉降改变了陆地生态系统的生产力和生物量积累。以欧洲和北美温带森林区域开展的研究为基础,综述了氮沉降对植物光合作用、土壤呼吸、土壤DOM及林木生长的影响特征和机理,探讨了森林生态系统碳动态对氮沉降响应的不确定性因素。热带森林C、N循环与大部分温带森林不同,人为输入的氮对热带生态系统过程的影响也可能不同,因此指出了在热带地区开展碳氮循环耦合研究的必要性和紧迫性。Forest soils and vegetation store about 46 percent of all carbon in the terrestrial biosphere, which play a critical role in global carbon balance. Increases in atmospheric nitrogen deposition over the last several decades have altered carbon cycling and sequestration of forest ecosystems by affecting productivity and biomass accumulation in terrestrial ecosystems. Based on the studies conducted in temperate forest regions in Europe and North America, the paper reviewed mechanism and characteristics underlying the impacts of nitrogen deposition on plant photosynthesis, soil respiration, soil dissolved organic matter (DOM), and tree growth, and the uncertainties as to the interactions between forest ecosystem carbon dynamics and nitrogen deposition were also analyzed and discussed. Most tropical forests function quite differently from temperate forests with regard to N and C cycling, and that the effects of anthropogenic N inputs on tropical ecosystem processes may also differ, so it is urgent and necessary to initiate studies related to carbon-nitrogen cycle coupling in the tropical regions.国家自然科学基金资助项目(30370259);; 福建省自然科学基金重点资助项目(B0320001)~

Single-crystalline and multiple-twinned gold nanoparticles: an atomistic perspective on structural and thermal stabilities

National Natural Science Foundation of China [51271156, 11204252]; Natural Science Foundation of Fujian Province of China [2013J06002]; Fundamental Research Funds for the Central Universities of China [2012121010]Morphologies of gold nanoparticles play an important role in determining their chemical and physical (catalytic, electronic, optical, etc.) properties. Therefore, a fundamental understanding of the morphological stability is of crucial importance to their applications. In this article, we employed atomistic simulations to systematically investigate the structural and thermal stabilities of gold particles with eight representative nanoshapes, including single-crystalline and multiple-twinned structures. Our investigation has revealed that the truncated octahedron and the octahedron possessed the best structural stability, while the tetrahedron and the icosahedron did the worst. Further analyses have discovered different thermal stabilities and diverse melting behaviors in these particles. Especially, an inhomogeneous melting of the icosahedron was disclosed, and the relevant mechanism was elucidated. This study provides significant insight not only into the experimental preparation of gold nanoparticles but also into the design of gold nanostructures with both high catalytic activity and excellent stability

绝经后子宫出血的病因及诊断方法研究

目的: 研究绝经后子宫出血的原因和最佳诊断方法。方法: 对 1994 年 9 月～ 1999 年 2 月我院收治的 435 例绝经 后子宫出血患者进行 B超检查和宫腔镜检查加刮宫或组织活检。结果: 单纯子宫病变占 97. 2%, 单纯附件肿瘤或附件肿瘤与 宫内病变并存占 2. 8%; 子宫与附件的良性病变占 90. 6%, 恶性肿瘤占 9. 4%; 宫腔镜下诊断宫腔内良性非赘生性病变与病理 的总符合率为 100%, 诊断赘生性病变与病理的总符合率为 96. 8%。结论: 绝经后子宫子宫出血的原因以子宫的良性病变占 绝大多数; 随年龄增长, 恶性肿瘤的发生率有上升趋势; 宫腔镜检查对绝经后子宫出血的诊断具有很高的价值,宫腔镜联合 B 超检查是较完善的病因检查手段

Two-stage melting in core-shell nanoparticles: An atomic-scale perspective

Microscopic understanding of thermodynamic behaviors of metallic nanoparticles is of significance for their applications in nanoscale catalysis and thermal energy storage. In this article, molecular dynamics simulations are used to investigate the thermal stabilities of Pt-Pd core-shell nanoparticles with different core sizes and shell thicknesses. Our study shows that a distinct two-stage melting occurs during the continuous heating of bimetallic nanoparticles. It has experienced a much broader temperature range compared with the melting of monometallic nanoparticles, although they have both developed from surface into interior. The temperature width for the two-stage melting is dependent not only on the bulk melting points of two component metals but also on the ratio of the shell thickness and core size. Furthermore, due to the melting of the Pd shell beforehand, the melting point of the Pt core is lower than that of the same size Pt nanoparticle not encapsulated by the Pd shell. This study provides a fundamental perspective on the melting behavior of bimetallic (even multimetallic) nanoparticles at the atomic level. 漏 2012 American Chemical Society

Pt-Pd bimetallic catalysts: Structural and thermal stabilities of core-shell and alloyed nanoparticles

Atomic-level understanding of structural characteristics and thermal behaviors of nanocatalysts is important for their syntheses and applications. In this article, we present a systematic study on structural and thermal stabilities of Pt-Pd bimetallic nanoparticles with core-shell and alloyed structures by using atomistic simulations. It was revealed that the Pd-core/Pt-shell structures are the least structurally stable, while the inverted Pt-core/Pd-shell nanoparticles are more stable than the alloyed ones when the Pt percentage exceeds 42% or so. The origin for this order was clarified through analysis of atomic energy distribution in these structures. Furthermore, the core-shell structures exhibit enhanced thermal stability as compared to the alloyed ones for Pt composition more than about 30%. The diverse melting behaviors of bimetallic nanoparticles, associating with their thermally driven structural evolutions under the heating process, were characterized by the measurement of the Lindemann index. In addition, the analyses of diffusion behavior and atomic distribution suggest that the minimization of surface energy tends to form Pd surface segregation. This study is of considerable importance not only to experimental preparation of Pt-Pd nanocatalysts but also to design of bimetallic (even multimetallic) nanostructures of high catalytic activity and excellent stability. 漏 2012 American Chemical Society

Prediction of Energy Resolution in the JUNO Experiment

International audienceThis paper presents the energy resolution study in the JUNO experiment, incorporating the latest knowledge acquired during the detector construction phase. The determination of neutrino mass ordering in JUNO requires an exceptional energy resolution better than 3% at 1 MeV. To achieve this ambitious goal, significant efforts have been undertaken in the design and production of the key components of the JUNO detector. Various factors affecting the detection of inverse beta decay signals have an impact on the energy resolution, extending beyond the statistical fluctuations of the detected number of photons, such as the properties of liquid scintillator, performance of photomultiplier tubes, and the energy reconstruction algorithm. To account for these effects, a full JUNO simulation and reconstruction approach is employed. This enables the modeling of all relevant effects and the evaluation of associated inputs to accurately estimate the energy resolution. The study reveals an energy resolution of 2.95% at 1 MeV. Furthermore, the study assesses the contribution of major effects to the overall energy resolution budget. This analysis serves as a reference for interpreting future measurements of energy resolution during JUNO data taking. Moreover, it provides a guideline in comprehending the energy resolution characteristics of liquid scintillator-based detectors