Temperature Sensitivity of Soil Respiration Probed by Numerical Analysis of Field-Observed Data Sets

Temperature sensitivity of soil respiration is essential to predict possible changes in terrestrial carbon budget on various scenarios about atmospheric and soil climates. Although it is often evaluated by using respiratory quotient “Q10”, Q10 values of soil respiration seem to vary depending on methods or scales of evaluation. Aiming at probing how Q10 values of soil respiration are evaluated differently for a field, this study used a model of soil respiration rate, and numerically evaluated soil respiration rates along depth by fitting the model to depth distributions of CO2 concentration measured in a field. And temperature sensitivity of soil respiration rate was evaluated by comparing the determined soil respiration rates with atmospheric and soil temperatures measured in the field. The results showed that the relation between surface CO2 emission rates and atmospheric temperatures was represented by lower Q10 values than that between soil respiration rates and soil temperatures, presumably because the top soil layers had acclimatized in more extent to the existing thermal regime than the underlying deeper layers. Thus, for evaluating effects of long-term rise in atmospheric temperature on soil respiration, it is necessary to precisely predict the long-term change in depth distribution of soil temperature as well as to quantify temperature sensitivity of soil respiration along depth. The evaluated sensitivity of surface CO2 emission rate to atmospheric temperature showed hysteresis, implying the needs for more knowledge about temperature sensitivity of soil respiration evaluated in both warming and cooling processes for better understandings and predictions about terrestrial carbon cycling.

Degradation products of different water content sevoflurane in carbon dioxide absorbents by gas chromatography-mass spectrometry analysis

Background Sevoflurane is currently used as a volatile inhalation anesthetic with many clinical advantages. A representative degradation product, compound A, was quantitatively measured to investigate whether there are different reactions between two kinds of water content sevoflurane formulations with different carbon dioxide （CO2） absorbents.

高电流密度下薄膜PEMFC自润湿特性研究

为研究薄膜质子交换膜燃料电池在高电流密度下的自润湿特性,使用FLUENT建立三维多物理场稳态模型,并用实验结果验证模型的可靠性。研究发现:随着电流密度的增加,水分布均匀性会提高,1200 mA/cm^(2)为薄膜可实现自润湿的电流密度临界点,高于此电流密度时薄膜中可实现良好的自润湿。在高电流密度下,阴极的加湿会加剧局部水淹现象并导致电池性能下降。降低温度、增加背压及减小膜厚会提升膜的自润湿特性,且膜厚对薄膜的自润湿特性影响最为显著。

Seasonal Change in CO2 Production Rate along Depth in a Grassland Field

Soil is a large terrestrial carbon pool so that the evaluation and prediction of soil respiration is important for understanding and managing carbon cycling between the pedosphere and the atmosphere. For better understanding about characteristics and mechanisms of soil respiration, this study monitored seasonal behaviors of soil gaseous CO2 concentration profile with relevant soil physical conditions in a meadow field, and numerically analyzed the monitored data sets to inversely determine time-series of depth distributions of CO2 production rate in the field by assuming optimum ranges of depth and moisture condition for aerobic respiration of soil fauna and flora. The results of the inverse analyses showed that the depth range of intense CO2 production resided in top soil layers during summer and moved down into subsoil layers in winter, implying that the depth range of main CO2 sources can change dynamically with seasons. The surface CO2 emission rates derived from the inverse analyses fell in the range typically found in the same kind of land use. The evaluated mean residence time of gaseous CO2 in the study field was around half a day. These findings suggested that the modelling assumptions about soil respiration in this study are effective to probe spatial and temporal behavior of respiratory activity in a soil layer, and it is still important to integrate facts about in-situ CO2 concentration profiles with soil physical parameters for quantitatively predicting possible behaviors of soil respiration in response to hypothetical changes in atmospheric and soil climates.

两种工况下进气相对湿度对燃料电池性能影响的研究

为研究进气相对湿度对燃料电池在不同工况(工作温度为70℃,进气相对湿度为40%和100%)下的影响,提出了进气加湿效率(Inlet Humidification Efficiency,IHE)模型。该模型将燃料电池总的水含量分为两部分:外部进气加湿携带的水和内部电化学反应生成的水,由此推导出进气加湿效率公式。建立几何模型并划分计算网格,将进气加湿效率模型导入计算流体动力学软件(Fluent)中进行计算。建立燃料电池测试系统,对工作温度为70℃,进气相对湿度分别为40%和100%的工况进行了试验。对IHE模型、Fluent模型和试验值进行比较分析,结果表明:当电池工作温度为70℃,电流密度为350 m A/cm2,进气相对湿度为100%时,IHE模型精确度比Fluent模型提高了37.4%;当进气相对湿度为40%时,进气加湿效率为34%。

不同进气相对湿度下PEMFC进气加湿效率分析

为研究不同进气相对湿度下PEMFC的加湿效率,提出了进气加湿效率(IHE)模型。该模型认为燃料电池中的水由两部分组成,并推导出进气加湿效率计算公式。建立几何模型并划分计算网格,将IHE模型导入Fluent中进行计算。建立燃料电池测试系统,对工作温度为70℃,进气相对湿度分别为55%和85%的工况进行了实验。并比较分析了Fluent模型、IHE模型和实验值,结果表明:工作温度为70℃,进气相对湿度为55%,电流密度为350 mA/cm2时,IHE模型精确度比Fluent模型提高15%;在进气相对湿度为55%时,电池进气加湿效率达到52%。

湿陷性黄土地基处理中新增湿技术的应用

西北地区常年干旱少雨,地基土的天然含水率较低,一般在3.3%-10%之间,在现行地基处理施工中,地基土含水率偏低将直接影响地基处理效果,需对地基土进行增湿处理。目前,西北湿陷性黄土地基处理中增湿案例较少,本文以甘肃靖远净化站工程为依托,采用深层和浅层联合法对地基土进行增湿处理,施工设计成功解决了注水孔塌孔问题,增湿不均匀性问题,提出了增湿设计过程中影响注水孔间距的因素,注水孔间距与增湿时间之间的关系,长短注水孔的设计取值,为黄土场地增湿处理提供了借鉴。