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381.
Susanne Burri Patrick Sturm Thomas Baur Matti Barthel Alexander Knohl Nina Buchmann 《Isotopes in environmental and health studies》2014,50(4):497-513
Pulse labelling experiments provide a common tool to study short-term processes in the plant–soil system and investigate below-ground carbon allocation as well as the coupling of soil CO2 efflux to photosynthesis. During the first hours after pulse labelling, the measured isotopic signal of soil CO2 efflux is a combination of both physical tracer diffusion into and out of the soil as well as biological tracer release via root and microbial respiration. Neglecting physical back-diffusion can lead to misinterpretation regarding time lags between photosynthesis and soil CO2 efflux in grassland or any ecosystem type where the above-ground plant parts cannot be labelled in gas-tight chambers separated from the soil. We studied the effects of physical 13CO2 tracer back-diffusion in pulse labelling experiments in grassland, focusing on the isotopic signature of soil CO2 efflux. Having accounted for back-diffusion, the estimated time lag for first tracer appearance in soil CO2 efflux changed from 0 to 1.81±0.56 h (mean±SD) and the time lag for maximum tracer appearance from 2.67±0.39 to 9.63±3.32 h (mean±SD). Thus, time lags were considerably longer when physical tracer diffusion was considered. Using these time lags after accounting for physical back-diffusion, high nocturnal soil CO2 efflux rates could be related to daytime rates of gross primary productivity (R2=0.84). Moreover, pronounced diurnal patterns in the δ13C of soil CO2 efflux were found during the decline of the tracer over 3 weeks. Possible mechanisms include diurnal changes in the relative contributions of autotrophic and heterotrophic soil respiration as well as their respective δ13C values. Thus, after accounting for physical back-diffusion, we were able to quantify biological time lags in the coupling of photosynthesis and soil CO2 efflux in grassland at the diurnal time scale. 相似文献
382.
383.
Previously, we have proposed to analyse the hydrodynamic interactions in a suspension of swimmers with respect to an effective hydrodynamic diffusion coefficient, which only considers the fluctuating motion caused by the stirring of the fluid. In this work, we study the diffusion of colloidal particles immersed in a bath of swimmers. To accurately resolve the many-body hydrodynamic interactions responsible for this diffusion, we use a direct numerical simulation scheme based on the smooth profile method. We consider a squirmer model for the self-propelled swimmers, as it accurately reproduces the flow field generated by real microorganisms, such as bacteria or spermatozoa. We show that the diffusion coefficients of the colloids are comparable with the effective diffusion coefficients of the swimmers, provided that the concentration of swimmers is high enough. At low concentrations, the difference in the way colloids and swimmers react to the flow leads to a reduction in the diffusion coefficient of the colloids. This is clearly seen in the appearance of a negative-correlation region for the velocity-correlation function of the colloids, which does not exist for the swimmers. 相似文献
384.
激光聚变内爆实验中,在燃料中掺杂少量比例的中高Z材料,用X光光谱和X光成像测量掺杂元素的发射信息,诊断燃料的温度、密度和压缩形状。用辐射流体力学数值计算和X光成像后处理程序综合分析方法,给出了内爆靶丸优化设计,并讨论示踪材料在X光诊断中的作用。结果表明:在靶丸燃料D2中掺原子分数约1.0%的氩,内爆压缩中子产额下降约15%。由于氩线发射使整个燃料区X光发射强度提高约50倍,X光成像区域增大约30%,有利于实验诊断测量燃料芯部。为了测量燃料区的边界,在CH内壳层涂厚度0.05 μm的硫,分析表明硫Ly-α单能成像大小与流体力学计算的燃料区大小一致,可用于诊断燃料最终压缩界面。数值分析结果得到了神光Ⅱ间接驱动内爆物理相关实验的验证。 相似文献
385.
We design a nunchakus-like tracer and investigate its self-adaptive behavior in an active Brownian particle (ABP) bath via systematically tuning the self-propelled capability and density of ABPs. Specifically, the nunchakus-like tracer will have a stable wedge-like shape in the ABP bath when the self-propelled force is high enough. We analyze the angle between the two arms of the tracer and the velocity of the joint point of the tracer. The angle exhibits a non-monotonic phenomenon as a function of active force. However, it increases with density of ABPs increasing monotonically. A simple linear relationship between the velocity and the self-propelled force is found under the highly active force. In other words, the joint points of the tracer diffuse and the super-diffusive behavior can make the relation between the self-propelled force and the density of ABPs persist longer. In addition, we find that the tracer can flip at high density of ABPs. Our results also suggest the new self-adaptive model research of the transport properties in a non-equilibrium medium. 相似文献
386.
Dr. Kévin Renault Romain Horion Xavier Maes Maha Rzeigui Dr. Yoann Joyard Dr. Nicolas Maindron Dr. Vincent Tadino Prof. Stéphane Vincent 《European journal of organic chemistry》2023,26(26):e202300307
2-Nitroimidazole based PET tracers are widely used for non-invasive hypoxic tumor diagnosis. In this context, we report here a general method based on a central Mitsunobu reaction to easily access 2-nitroimidazole precursors. Optimization of fluorination conditions is described and successfully applied to the radiofluorination of the 2-nitroimidazole precursors. Moreover, the radiosynthesis of a new potential hypoxia PET tracer is also described. Finally, this article presents a SFC analytical method allowing both an easy monitoring of the fluorination reactions and the measurement of partition coefficients (logP). 相似文献