细水雾中雾滴和高温环境的热质交换研究

由雾滴的表面的组分方程和能量方程入手,探讨雾滴在静止的高温环境中的热质交换及生存时间。应用折算薄膜理论,通过特征时间的比较,提出雾滴与高温环境主要通过沸腾机制实现热质交换;考虑滴径与速度变化的耦合作用,应用数值方法研究雾滴在强迫对流环境中与高温环境的热质交换情况。结果表明:对于滴径较小的雾滴不可能达到火焰区或可燃物表面实施火焰冷却和表面冷却,其灭火作用主要依赖于汽化吸热。     

Seminal fluid enhances sperm viability in the leafcutter ant Atta colombica

The seminal fluid that accompanies sperm in ejaculates has been shown or suggested to affect sperm competition and paternity success of insects by preventing female remating, inducing oviposition, and forming mating plugs. In Atta leafcutter ants, queens have multiple mates but never remate later in life, although they may live and produce fertilized eggs for several decades. The mating biology and life history of these ants therefore suggests that the major function of seminal fluid is to maximize sperm viability during copulation, sperm transfer, and initial sperm storage. We tested this hypothesis by comparing the viability of testis sperm and ejaculated sperm (mixed with seminal fluid) and found a significant positive effect of seminal fluid on sperm viability. We further quantified this positive effect by adding accessory gland secretion (a major component of seminal fluid) in a dilution series, to show that minute quantities of accessory gland secretion achieve significant increases in sperm viability. Sperm stored by queens for 1 year benefited in a similar way from being exposed to accessory gland compounds after dissection in control saline solution. Our results provide the first empirical evidence that seminal fluid is important for the production of viable ejaculates and that the accessory glands of Atta males—despite their small size—are functional and produce a very potent secretion.     

Stochastic Transfer Function Model and Neural Networks to Estimate Soil Moisture1

Abstract: A practical methodology is proposed to estimate the three‐dimensional variability of soil moisture based on a stochastic transfer function model, which is an approximation of the Richard’s equation. Satellite, radar and in situ observations are the major sources of information to develop a model that represents the dynamic water content in the soil. The soil‐moisture observations were collected from 17 stations located in Puerto Rico (PR), and a sequential quadratic programming algorithm was used to estimate the parameters of the transfer function (TF) at each station. Soil texture information, terrain elevation, vegetation index, surface temperature, and accumulated rainfall for every grid cell were input into a self‐organized artificial neural network to identify similarities on terrain spatial variability and to determine the TF that best resembles the properties of a particular grid point. Soil moisture observed at 20 cm depth, soil texture, and cumulative rainfall were also used to train a feedforward artificial neural network to estimate soil moisture at 5, 10, 50, and 100 cm depth. A validation procedure was implemented to measure the horizontal and vertical estimation accuracy of soil moisture. Validation results from spatial and temporal variation of volumetric water content (vwc) showed that the proposed algorithm estimated soil moisture with a root mean squared error (RMSE) of 2.31% vwc, and the vertical profile shows a RMSE of 2.50% vwc. The algorithm estimates soil moisture in an hourly basis at 1 km spatial resolution, and up to 1 m depth, and was successfully applied under PR climate conditions.     

The controlled short circuit GMAW process: A tutorial

The paper reviews the principles, benefits and limitations of the conventional short circuit transfer mode in GMA welding before describing the development and benefits of the controlled short circuit approach. Various options are described and an attempt is made to categorize the current commercial systems.     

污水处理过程水温变化模型构建与验证

污水处理是一个复杂的生物、物理及化学反应过程.污水水温直接影响到污染物生物处理效果,并对污水处理运行能耗产生重要影响.另一方面,污水中也蕴含着相当热能,是潜在可以回收的低品位能源,加以利用则有望实现污水处理碳中和运行.然而,现有研究很少涉及 污水处理厂污水进、出水水温变化及其影响因素;工程中也只强调冬季保温,并无法从微观角度认识处理过程水温变化规律.为此,研究尝试构建污水处理过程水温变化热量衡算模型,涵盖污水生化反应、机械传热、环境热传递和水蒸发热损失等4个主要涉热过程.与此同时,收集北京某污水处理厂实际水温、气温数据,借助热量平衡图来模拟污水处理过程中水温变化,并对理论模型参数进行校验和修正.通过参数敏感性分析,可以评价不同参数对水温热量的影响程度.基于这些工作,一个污水温度变化模型被构建成功,可用于指导实际污水处理厂水温控制或余温热能回收过程,可助力污水处理厂节能降耗、甚至实现碳中和目标.     

非农就业与土地流转对农户耕地撂荒行为的影响——以闽赣湘山区为例

耕地撂荒是世界各国长期普遍存在的一种土地利用变化现象。基于闽赣湘山区640户农户调查数据,运用Tobit和IV-Tobit模型回归分析得出：农户家庭非农就业每提升10%,耕地撂荒占比会增加1.11%;小规模农户土地转入会提升其耕地撂荒规模,此时扩大经营规模对耕地撂荒的减缓作用甚微,而土地转出会降低非农就业对耕地撂荒的正向影响。此外,农户的劳动力、土地与农业机械等要素投入,以及灌溉条件和地块数等均稳健影响其耕地撂荒行为。农业机械化和土地流转是缓解山区耕地撂荒的重要举措,政府在推动经营规模扩大的同时,应着重提高地块规模,鼓励留村务农劳动力换工,并提升农机社会化服务水平,以及拓宽农户家庭多元化的收入机会。     

可见光促有机物诱导铁还原的多相类芬顿体系强化效能与机制

近年来,亚铁离子活化过硫酸盐的类芬顿(Fe²⁺-PMS/PS)高级氧化技术发展日趋成熟,但因Fe³⁺无法还原导致反应停止的问题仍制约其大规模应用.结果发现,当把以双酚A（BPA）为代表的某些有机物与Fe³⁺和TiO₂混合,所形成的某种络合物可以拓宽TiO₂光响应范围捕获可见光,通过TiO₂将光生电子传递给Fe³⁺进行还原,从而实现Fe³⁺/Fe²⁺的无限循环.依据上述原理,构建了可见光下BPA-TiO₂-Fe³⁺-PS复合体系来降解BPA,并对其催化性能、催化机制和影响因素进行探讨.结果表明,该体系具有突出的催化性能,60 min内BPA(50 mg·L^-1)降解率达到93.1%,矿化度达到70%.同时验证该体系可以通过双酚A自生光电子还原Fe³⁺, 60 min还原得到的Fe²⁺稳...     

Developing “precise-acting” strategies for improving anaerobic methanogenesis of organic waste: Insights from the electron transfer system of syntrophic partners

Methanogenesis is the last step in anaerobic digestion, which is usually a rate-limiting step in the biological treatment of organic waste. The low methanogenesis efficiency (low methane production rate, low methane yield, low methane content) substantially limits the development of anaerobic digestion technology. Traditional pretreatment methods and bio-stimulation strategies have impacts on the entire anaerobic system and cannot directly enhance methanogenesis in a targeted manner, which was defined as “broad-acting” strategies in this perspective. Further, we discussed our opinion of methanogenesis process with insights from the electron transfer system of syntrophic partners and provided potential targeted enhancing strategy for high-efficiency electron transfer system. These “precise-acting” strategies are expected to achieve an efficient methanogenesis process and enhance the bio-energy recovery of organic waste.     

高温高湿巷道内不稳定换热系数影响因素分析及模型建立*

为研究高温高湿巷道不稳定换热系数的变化规律,采用Fluent软件对高温高湿巷道内的热湿交换进行数值模拟,通过单因素和正交模拟实验探讨风流温度、风流速度、岩石导热系数、原岩温度以及巷道当量直径对高温高湿巷道不稳定换热系数的影响。研究结果表明:高温高湿巷道不稳定换热系数随时间的变化规律与普通巷道一致,均与通风时间呈负相关,但通风时间为1 a的高温高湿巷道不稳定换热系数较普通巷道增加了12.5%。通过单因素分析得到风流速度、岩石导热系数和当量直径与不稳定换热系数呈正相关。通过极差分析得到各因素对不稳定换热系数的影响程度为:岩石导热系数>当量直径>风流速度>风流温度>原岩温度。利用SPSS软件对正交实验数据进行拟合,建立不稳定换热系数的计算模型,拟为高温高湿巷道内热负荷计算及井下风温预测提供参考。     

我国危险化学品产业转移及安全风险分析*

为深入分析我国国内（不含港澳台,下同）危险化学品产业转移及安全风险,通过调研产业转移现状,统计典型地区产业政策、转移企业数量、转移时间及安全生产形势,分析产业转移带来的安全风险。研究结果表明:危险化学品产业转移呈现明显地域趋势,从以江苏、浙江为主的东部沿海地区向中西部等地区转移;转移时间集中在2个阶段,分别是:2002—2008年、2017—2020年;转移集中在精细化工、炼焦、煤化工等产业,医药等高端产业未发生转移;危险化学品产业转移安全风险主要表现在:“重经济,轻安全”现象突出、转移项目安全风险高、承接地基础薄弱、人才储备不足等方面;针对呈现的产业转移安全风险,提出相关对策措施及建议。研究结果可为我国危险化学品产业转移安全风险管控政策措施制定提供相关数据与理论支撑。